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THESIS

3 I!”UNI!H!I”!HINIUIIUIHIHHIIHIUllllfllllllllflfll

301421 6513

This is to certify that the

dissertation entitled

PEDOLOGY AND DATING OF COLLUVIAL DEPOSITS IN THE
BLUE RIDGE MOUNTAINS, NORTH CAROLINA

presented by
Johan Liebens

has been accepted towards fulfillment
of the requirements for

Ph . D . degree in Geography

W/W

Major pro

Date January 22, 1996

 

MS U is an Affirmative Action/Equal Opportunity Institution 0-12771

 

LiaR‘ARY
Michigan State
University

 

 

 

PLACE N RETURN BOX to move thie checked from your record.
TO AVOID FINES return on or bdore dete due.

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II I |

MSU Ie An Aflimetive Action/Ewe! Opportunity Inetltution
W

 

 

”3-9.1

PEDOLOGY AND DATING OF COLLUVIAL DEPOSITS IN THE
BLUE RIDGE MOUNTAINS, NORTH CAROLINA.

By

Johan Liebens

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

DOCTOR OF PHILOSOPHY

Department of Geography

1 996

ABSTRACT

PEDOLOGY AND DATING OF COLLUVIAL DEPOSITS IN THE
BLUE RIDGE MOUNTAINS, NORTH CAROLINA.

By

Johan Liebens

Colluvium and soils in areas of warm, humid climates and metamorphic bedrock
have not been studied in detail. The study area for this research, the Little Tennessee River
basin in the Southern Blue Ridge of North Carolina, exhibits these characteristics. This
research examines debris flow deposits of this basin, and their associated soil, and places
their evolution in a temporal framework. The results of this study provide characterization
data and help identify any possible temporal synchroneity of past periods of increased
landscape stability/instability in the region.

The sedimentology and geomorphology of three sequences of multiple colluvial
deposits were studied. Pedons on each deposit of each sequence were described and
analyzed semi-quantitatively. A relative chronostratigraphy of the deposits was determined
with established techniques based on weathering data, soil morphology and iron species
ratios.

The sediments of the debris flow deposits typically consist of massive, clast

supported diamicts. Flow viscosities appear to have been widely variable and may have

been related to the texture of the source material. Shear zones in the debris flows rendered
the sediments heterogeneous and are reflected in the irregular depth trends of many
pedological properties. Depth to maximum clay accumulation in the soils systematically
occurs at greater depths at higher elevations. Clay mineral assemblages vary little within
sites; between site differences may be linked to the age of the deposits (timespan of
subaerial weathering).

Consistent results from qualitative and statistical evaluation of the relative-age
indicators of the deposits point to the effectiveness of the relative-age proxies used in this
study. These proxies indicate that colluvial deposits at higher elevations are usually older.
The apparent isochronous occurrence of debris flow activity at the three sites suggests that
external factors such as climate variations influence the timing of debris flow activity in the
region. Differences in age between sites suggest that intrinsic factors co-determine the

instability of the basin.

ACKNOWLEDGMENTS

My foremost appreciation is due to my advisor, Dr. R]. Schaetzl, for his
invaluable advice, support, encouragement, and skillful editing. I am also grateful for the
interest and advice of the other members of my committee, Dr. D.G. Brown, Dr. G.
Larson, Dr. D.P. Lusch, and Dr. M.A. Velbel. My sincere thanks go to Dr. F.W.
Cambray for his assistance with fabric analysis. Field and laboratory equipment of the
Department of Geography of Michigan State University was used extensively. Laboratory
facilities were also provided by the Department of Crop and Soil Sciences of Michigan
State University.

This research could not have been carried out without the support of the landowners
who allowed me to dig soil pits on their property. My sincere thanks are due to the Fortner,
Bradley, J acobstein, Ramsey and Hanson families. Several graduate students of the
Department of Geography helped with parts of this research. Dave Nolan was an invaluable
help during the surveying of the sites and often put geography in perspective. Linda Barrett
was the ideal company, and a good sounding board, during the writing stage of the project.

Finally, three people were instrumental in the successful completion of this work
and provided all the understanding and mental support one needs in an endeavor like this.
My parents always have supported and encouraged my educational aspirations and did not
fail to do so now. My wife, Hilde, inspired me by being the perfect example of dedication
and perseverance.

This research was supported by NSF grant SBR-9405198 made to R. Schaetzl and
J. Liebens, and by GSA grant 5404-94 and a grant from Harvard Travelers Club

Permanent Fund made to J. Liebens.

iv

TABLE OF CONTENTS

List of tables ...................................................................................... xiii
List of figures ..................................................................................... xiv
Part I: Introduction .................................... . ............................................. 1
1 Introduction ..................................................................................... 2
1.1 Background ......................................................................... 2

1.2 Social and economic impact of debris flows .................................... 3

1.3 Research objectives ................................................................. 5

1.4 Relevance of the study ............................................................. 7

2 Literature review ............................................................................... 8
2.1 Terminology of mass flows .......... . ............................................. 8

2.2 Localizing factors of debris flows .............................................. 11

2.2.1 Precipitation amount .................................................. 1 1

2.2.2 Precipitation intensity ................................................. 12

2.2.3 Local factors ........................................................... 14

2.2.3.1 Precipitation distribution .................................. 14

2.2.3.2 Slope ......................................................... 14

2.2.3.3 Hillslope form and aspect ................................. 15

2.2.3.4 Geology ..................................................... 15

2.2.3.5 Regolith thickness and texture ............................ 16

2.2.3.6 Vegetation ................................................... 17

3 Studyarea .................................................................................... 19
3.1 Introduction ....................................................................... 19
3.2 Study areadescription ............................................................ 22
3.2.1 Climate .................................................................. 22
3.2.2 Geology ................................................................ 23

3.2.3 Geomorphology ....................................................... 27
3.2.4 Soils ..................................................................... 32

3.2.5 Colluvium .............................................................. 33
3.2.5.1 Geomorphology and sedimentology ..................... 33

3.2.5.2 Elevations ................................................... 35

3.2.5.3 Coarse fragments ........................................... 35

3.2.5.4 Ages ......................................................... 36

3.2.6 Vegetation .............................................................. 38

3.3 Site selection ...................................................................... 39
3.3.1 Reconnaissance survey ............................................... 39
3.3.1.1 Methods ..................................................... 39

3.3.1.1.1 General ........................................... 39

3.3.1.1.2 Specific methods ................................ 39

3.3.1.2 Results ....................................................... 41

3.3.2 Selection criteria ....................................................... 42

3.3.3 Site description and location ......................................... 44
3.3.3.1 Alarkasite ................................................... 44

3.3.3.2 Hidden Valley site .......................................... 48

vi

3.3.3.3 Bradley site ................................................. 52

Part II: Characterization of sediments and soils ............................................... 56
4 Introduction ................................................................................... 57
5 Sediments ..................................................................................... 59
5.1 Literature review .................................................................. 59

5.1.1 Sorting .................................................................. 59

5.1.2 Bed geometry .......................................................... 60

5.1.3 Stratification ............................................................ 60

5. 1 .4 Grading ................................................................. 60

5.1.5 Conglomerate framework ............................................ 61

5.1.6 Fabric shape ............................................................ 62

5.1.7 Fabric strength ......................................................... 64

5.2 Methods ............................................................................ 65

5 .2. 1 Data collection ......................................................... 65

5.2.2 Data analysis ........................................................... 68

5.3 Results ............................................................................. 70

5 .3 . 1 Sediment description .................................................. 70

5.3.1.1 General ...................................................... 70

5.3.1.2 Alarkasite ................................................... 72

5.3.1.3 Hidden Valley site .......................................... 82

5.3.1.4 Bradley site ................................................. 89

5.3.2 Fabric ................................................................... 92

5.3.2.1 A-axis ........................................................ 92

5.3.2.2 A-bplane .................................................... 97

vii

5.4 Discussion ......................................................................... 97

5.4.1 General ................................................................. 97
5.4.2 Alarkasite .............................................................. 99

5.4.3 Hidden Valley site .................................................... 100
5.4.4 Bradley site ............................................................ 101
5.4.5 Fabric .................................................................. 102

5.5 Conclusions ...................................................................... 105
6 Soils .......................................................................................... 108
6.1 Literature review ................................................................. 108
6.1.1 Morphology ........................................................... 108
6.1.2 Physical and chemical properties ................................... 109
6.1.2.1 Clay content ................................................ 109

6.1.2.2 Bulk density ............................................... 109

6.1.2.3 Basesaturation ............................................ 110

6.1.2.4 Free iron content .......................................... 110

6.1.3 Clay mineralogy and weathering ................................... 111
6.1.3.1 Biotite ....................................................... 111

6.1.3.2 Chlorite ..................................................... 111

6.1.3.3 VermiculiteandHIV ...................................... 111

6.1.3.4 Kaolinite .................................................... 112

6.1.3.5 Gibbsite .................................................... 113

6.1.3.6 Ironoxides ................................................. 114

6.1.4 Genesis ................................................................ 115

6.1.5 Classification .......................................................... 117

6.2 Methods ........................................................................... 118
6.2.1 Datacollection ........................................................ 118

viii

6.2.2 Data analysis .......................................................... 1 18

6.3 Results ............................................................................ 120
6.3.1 Soil morphology and classification ................................. 120

6.3.1.1 Alarkasite .................................................. 120

6.3.1.2 Hidden Valley site ......................................... 121

6.3.1.3 Bradley site ................................................ 122

6.3.2 Physical and chemical properties ................................... 122

6.3.2.1 Alarkasite .................................................. 122

6.3.2.2 Hidden Valley site ......................................... 126

6.3.2.3 Bradley site ................................................ 129

6.3.3 Clay mineralogy ...................................................... 133

6.3.3.1 General ..................................................... 133

6.3.3.2 Alarkasite .................................................. 135

6.3.3.3 Hidden Valley site ......................................... 135

6.3.3.4 Bradley site ................................................ 135

6.4 Discussion ........................................................................ 136
6.4.1 Saprolite ............................................................... 136

6.4.2 Lithologic discontinuities ............................................ 137

6.4.3 Clay content ........................................................... 141

6.4.4 Clay mineralogy ...................................................... 142

6.5 Conclusions ...................................................................... 144

Part III: Relative age dating .................................................................... 146
7 Introduction .................................................................................. 147
8 Clast weathering ............................................................................ 150

ix

8. 1 Literature review ................................................................. 150

8.1.1 General ................................................................ 150

8.1.2 Weathering rind thickness .......................................... 150

8.1.3 Percent weathered clasts ............................................. 152

8.2 Methods ........................................................................... 152
8.3 Results and discussion .......................................................... 157
8.4 Conclusions ...................................................................... 156
9 Soil development ............................................................................ 158
9.1 Literature review ................................................................. 158
9.2 Methods ........................................................................... 160
9.2.1 Selection of relative-age indicators ................................. 160

9.2.2 Data collection and analysis ......................................... 161

9.3 Results and discussion .......................................................... 162
9.3.1 Rubification ........................................................... 162

9.3.2 Clay content ........................................................... 164

9.4 Conclusions ...................................................................... 166
10 Iron species .................................................................................. 168
10.1 Literature review ................................................................. 168
10.1.1 General ............................................................... 168

10.1.2 Fed and Feo .......................................................... 169

10.1.3 Fed/Pet, (Fed-Feo)/Fet and Feo/Fed .............................. 170

10.2 Methods ........................................................................... 171
10.2.1 Selection of relative-age indicators ................................ 171

10.2.2 Data collection and analysis ........................................ 173

10.3 Results and discussion .......................................................... 174

10.4 Conclusions ...................................................................... 177

11 Discriminant analyses ...................................................................... 178

11.1 Literature review ................................................................. 178

11.2 Methods ........................................................................... 179

11.2.1 Construction of relative-age groups ............................... 179

11.2.2 Data analysis ......................................................... 181

11.3 Results and discussion ................ i .......................................... 182

1 1.4 Estimation of absolute ages ..................................................... 184

l 1.5 Conclusions ...................................................................... 185

12 Conclusions ................................................................................. 186

Part IV: Conclusions ............................................................................ 188
Part V: Appendixes

Appendix 1: Generalized description of selected pedons of reconnaissance survey ..... 193

Appendix 2: Longitudinal profiles, Alarka and Bradley sites .............................. 198

Appendix 3: Particle size fractionation data .................................................. 201

Appendix 4: Sorting and bulk density data ................................................... 210

Appendix 5: Stereograms for clast a-axis ..................................................... 214

Appendix 6: Stereograms for clast a-b plane ................................................. 221

Appendix 7: Clay mineralogy data ............................................................. 225

Appendix 8: Iron species data .................................................................. 229

Part VI: List of references

List of references ................................................................................ 233

Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.

Table 10.
Table 11.
Table 12.
Table 13.
Table 14.
Table 15.
Table 16.
Table 17.
Table 18.
Table 19.
Table 20.

LIST OF TABLES

Clast fabric data for debris flow-like deposits ................................... 65
Geomorphic position of soil pits .................................................. 66
Soil horizons sampled for clast characterization and fabric .................... 67
Pedon descriptions .................................................................. 73
Clast sizes, all sites ................................................................. 83
Clast sphericities, all sites......... ................................................. 84
Clast lithologies, all sites ........................................................... 85
Orientation of clast a-axes, total population ...................................... 93
Orientation of clast a-axes, subpopulations ...................................... 95
Orientation of clast a-b planes ..................................................... 98
Clay mineralogy by pedon, all sites ............................................. 136
Clast weathering data, all sites ................................................... 155
Cluster analysis of Clast weathering data ........................................ 157
Field description of selected pedons of reconnaissance survey .............. 195
Particle size analyses of selected pedons of reconnaissance survey ......... 197
Particle size data, all sites ......................................................... 203
Clayfree particle size data, all sites ............................................... 208
Sorting and bulk density data, all sites .......................................... 212
Clay mineralogy data, all sites .................................................... 227
Iron species data, all sites ......................................................... 231

xiii

Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.

Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.

Figure 20.

Figure 21.

LIST OF FIGURES

Physiographic provinces of the Southern Appalachians ...................... 20
Location of study area ............................................................. 21
Precipitation frequency diagram for Coweeta Hydrological Laboratory .... 24
Regional geology of southwest North Carolina ................................ 25
Relief map of the Blue Ridge and Piedmont physiographic provinces ...... 28
Location of study sites ............................................................ 45
Basin shapes, all sites ............................................................. 46
Contour map of Alarka site ....................................................... 47
Cross section, Alarka site ......................................................... 49
Contour map of Hidden Valley site .............................................. 50
Cross section, Hidden Valley site ................................................ 51
Cross section, Bradley site ............ i ........................................... 54
Contour map ofBradley site ....................................................... 55
Fabric shape and strength as a function of S 1/S2 and 82/S3 ................. 71
Percent coarse fragments as a function of depth, all sites ..................... 79
Percent fine gravel as a function of depth, Alarka site ......................... 80
Percent clay free sand as a function of depth, Alarka site ..................... 81
Roundness of clasts, all sites ..................................................... 86
Interpretive log column of lithofacies units, lowest deposit at

Hidden Valley site ................................................................. 87
Interpretive log column of lithofacies 'units, highest deposit at

Hidden Valley site ................................................................. 88
Interpretive log column of lithofacies units, Bradley site ..................... 90

xiv

Figure 22.
Figure 23.
Figure 24.
Figure 25.
Figure 26.
Figure 27.
Figure 28.
Figure 29.
Figure 30.
Figure 31.
Figure 32.
Figure 33.
Figure 34.
Figure 35.
Figure 36.
Figure 37.
Figure 38.
Figure 39.
Figure 40.
Figure 41.
Figure 42.
Figure 43.
Figure 44.
Figure 45.
Figure 46.
Figure 47.
Figure 48.

Logarithmic ratio plot of eigenvalues, selected sites ........................... 96

Logarithmic ratio plots, this study and other depositional environments... 106

Clay mass as a function of depth, Alarka site ................................. 123
Bulk density as a function of depth, Alarka site ............................... 124
Clayfree silt as a function of depth, selected pedons ......................... 125
Free iron content as a function of depth, Alarka site .......................... 127
Clay mass as a function of depth, Hidden Valley site ........................ 128
Bulk density as a function of depth, Hidden Valley site ..................... 130
Free iron content as a function of depth, Hidden Valley site ................ 131
Clay mass as a function of depth, Bradley site ................................ 132
Free iron content as a function of depth, Bradley site ........................ 134
Depth of maximum clay content, all sites ...................................... 141
Rubification indices, all sites .................................................... 163
Clay content, all sites ................... . .......................................... 165
Fed/Fet as a function of depth, selected pedons .............................. 175
Mean profile weighted Fed/Fet, all sites ....................................... 176
Discriminant scores, all sites .................................................... 183
Longitudinal profile, Alarka site ................................................ 200
Longitudinal profile, Bradley site ............................................... 201
Stereograms of long axis of clasts, lower deposits at Alarka site ........... 216
Stereograms of long axis of clasts, upper deposit at Alarka site ............ 217
Stereogram of long axis of clasts, Hidden Valley site ........................ 218
Stereograms of long axis of clasts, Bradley site .............................. 219
Stereograms of long axis of clasts, subpopl .................................. 220
Stereograms of long axis of clasts, subpop2 .................................. 221
Stereograms of poles of a—b planes of clasts, lower deposits at Alarka site 223

Stereograms of poles of a-b planes of clasts, upper deposit at Alarka site 224

XV

Figure 49. Stereograms of poles of a-b plane of clasts, Bradley site .................... 225

xvi

PART I: INTRODUCTION

1. INTRODUCTION

1.1 Background

The geomorphology of the Southern Blue Ridge has yet to be studied in detail.
Pen'glacial phenomena of the region have been studied to some extent (e. g., Michalek,
1968; Raymond, 1976; Mills, 1981; Daniels et al., 1987) but work on alluvial and colluvial
deposits from zones that were not affected by periglacial conditions is still in its infancy.
One prevalent geomorphological aspect of these other morpho-climatic zones are debris
flow deposits, the most common and spectacular form of mass wasting in the region
(Scott, 1972; Mills, 1987). According to Scott (1972) and Schneider (1973) these types of
mass movements occur more frequently in the Southern Blue Ridge of North Carolina than
in any other part of the Appalachians. Mills (1987) provided a number of reasons for their
high incidence in the Southern Blue Ridge: i) high permeability of regolith derived from
crystalline rocks relative to that of regolith derived from shales on the Appalachian plateau,
ii) more intense rainfall, and iii) high susceptibility of crystalline rocks to saprolitization.

In spite of their frequent occurrence, many questions about the origin and
distinctive characteristics of debris flows in the Southern Blue Ridge, and humid-temperate
regions in general, remain to be answered. The sedimentology and geomorphology of
debris flows have been studied extensively on alluvial fans in arid and glacial
environments, but little attention has been given to debris flow deposits in humid-temperate
areas (Kochel and Johnson, 1984). This is also true of studies of soil development on
debris flow deposits (Kesel and Spicer, 1985; Norfleet and Smith, 1989). Particularly
lacking are studies of rates of soil formation on this type of colluvial deposit in humid-
temperate areas (Kesel and Spicer, 1985).

Another question that needs further examination deals with the origin(s) of debris

flows. It has been suggested that debris flows in the Southern Blue Ridge are associated

3
with climate change, in particular post-glacial climate change (Mills, 1981; 1982a; 1983;

Kochel and Johnson, 1984). However, it also has been recognized that intrinsic factors,
unrelated to climate, may control the formation of debris flows (Mills, 1983; Wells and
Harvey, 1987). Mills ( 1982a) voiced that an obvious approach to verify the influence of
climatic controls on the formation of colluvial deposits would be to see if the deposits date
to times of glacial climates. In addition to providing information on the effects of intrinsic
and external controls, absolute ages could also serve to identify periods of increased
landscape instability, during which debris flow incidence was higher. Absolute dates on
debris flow deposits in the Southern Blue Ridge have only recently become available
(Kochel and Johnson, 1984; Kochel, 1990), providing only preliminary data. The primary
reason for the scarcity of absolute dates, according to Clark (1979), is that sites where
datable, essentially-continuous sedimentary records have been preserved are scarce and

widely separated.

1.2 ' onomici ac fdebris flows

Mass movements occur in every state of the USA and in virtually every country in
the world. More than 20 million mass movement deposits exist in the USA alone (Brabb,
1989). In the USA, annual economic losses from mass movements, subsidence and
ground failures exceed those from all other natural hazards combined (National Research
Council, 1985). In Japan, more than half of all deaths due to natural hazards are caused by
slope failures (Schuster, 1978).

Debris flows are among the most destructive mass movements. In Canada they
formed 61% of known, damaging mass movements from 1855 to 1983 (Cruden et al.,
1989). Thirty percent of the fatalities during heavy rainstorrns in Japan are caused by debris
flows and about 90 lives are lost annually from this phenomenon (Takahashi, 1981).

4
Because of their viscosity, debris flows can travel large distances and often affect

floodplains, which are usually centers of economic activity.

Estimates of the annual cost of damage to private dwellings by mass movements
range from $44 million (Brabb, 1984) to $400 million (Krohn and Slosson, 1976). Indirect
economic losses to forestry, fisheries, agriculture and infrastructure are difficult to evaluate
but may be larger than direct costs. Chassie and Goughnour (1976) believe that $100
million is a conservative estimate of the annual cost of mass movement damage to
highways and roads in the USA. Total annual losses in the USA have been estimated to be
as high as $1 billion (Schuster, 1978; Fleming and Taylor, 1980) to $1.5 billion (Jahns,
1978; Schuster and Fleming, 1986). Annual damage estimates fluctuate considerably
because of the infrequent, irregular occurrence of large, catastrophic events. One such
event, Hurricane Camille, triggered debris flows in western Virginia in 1969. More than
150 people perished due to this storm, which damaged and destroyed property worth $420
million (Williams and Guy, 1973)

In countries other than the USA the death toll from debris flow events has been
much higher. The principal reason for this is the lack of resources for adequate awareness
campaigns and mitigation in Third World countries. The Andean countries are among the
hardest hit. In 1962 and 1970 debris avalanches on Mt. Huascaran in Peru killed 5000 and
18000 people, respectively, and destroyed several towns (Schuster, 1978). In 1985, a
volcanic debris flow, or lahar, completely destroyed the town of Armero, Colombia, and
killed 20,000 people. In 1987 a landslide in Ecuador resulted in 1000 deaths and ruptured
the trans-Ecuadorian oil pipeline, resulting in an approximate $1.5 billion loss.

Despite a growing understanding of the factors and processes involved in slope
failures, economic and social losses from them continue to increase. This is largely a
consequence of land development that expands onto steeply sloping terrain, where mass

movements occur frequently.

5
A considerable amount of experience with control of mass movements has been

gathered in the last decades. Active and passive mitigation measures have reduced damage
by mass movements but require financial efforts. Passive measures such as hazard
mapping and warning systems are relatively inexpensive and have some merit. Active
intervention usually involves engineering structures, such as retaining walls, dams, channel
linings and deposition basins, and are more costly. The most economical and expeditious
means of supporting unstable slopes is the reinforcement of potential source areas with
rock "rip rap".

Near Port Alice, in the Canadian Cordillera, debris flows at the beginning of the
1970's caused $700,000 damage (Cruden et al., 1989). Protective dikes built in the
following years cost $250,000. In the same general area, debris flow defense measures
worth $1.1 million were put in place after debris flows destroyed $2.5 million in property.
In Howe Sound, Canada, debris flow mitigation structures costing $20 million were built
after storm-induced debris flows caused $1 million in damage (Cruden et al., 1989). In
Washington, avoidance and correction of damage due to landslides that occurred around the

middle of the century behind the Grand Coulee dam cost $20 million (Schuster, 1978).

1.3 Objectives

The rationale for this research centered on the lack of a thorough understanding of
sedirnentological, pedological and age characteristics of debris flow deposits in the
Southern Blue Ridge, in spite of the obvious importance of the phenomenon to the
landscape evolution of the region. A better comprehension of these characteristics can
possibly lead to insights in the timing and evolution of these prevalent colluvial deposits.

Because this research is designed to help elucidate the geomorphic and pedogenic

history of the Southern Blue Ridge as recorded in the Little Tennessee River basin in North

6
Carolina, the findings should help to identify periods of stability/instability in the region.

To achieve this general objective, three specific goals were incorporated in this study.

1. The first specific goal was to locate sites in the Little Tennessee River basin that
have a sequence of debris flow deposits. To optimize the applicability of methods used for
the following goals, deposits that showed little signs of erosion, had soils with contrasting
development and occurred in basins with a uniform lithology, were chosen. This goal was
achieved by studying aerial photographs, soil surveys, geologic and topographic maps, and
by field reconnaissance.

2. The second part of the study had a dual purpose: to characterize the
sedimentologic facies of the debris flow deposits and to elucidate pedogenetic imprinting on
the deposits. These goals were achieved by describing sedimentologic attributes,
geomorphologic features, and soil properties on the debris flow deposits, and by laboratory
analyses of sedimentary fabric, texture, bulk density and clay mineralogy.

3. The third specific goal was to determine the relative ages of the deposits in each
sequence. This goal represented an initial step in the identification of periods of increased
landscape stability/instability in the Southern Blue Ridge. It was accomplished using data

on clast weathering, soil morphology and ratios of iron species.

1,4 Relevance

One of the goals of this research is to provide insight into the facies characteristics
of debris flow deposits of the Southern Blue Ridge. As mentioned above (section 1.1), few
studies on the sedimentology of colluvial deposits are available. This study will, therefore,
produce characterization data that were previously not widely accessible. Additionally,
sedimentary facies characteristics, and fabric characteristics in particular, are related to flow
regimes. A better understanding of these characteristics can, therefore, lead to a more
complete knowledge of the processes involved in the movement of debris flows. This may,
in turn, lead to better mitigation and abatement measures.

This research will also shed light on how the soils associated with the debris flow
deposits have evolved in this warm to temperate humid environment. It will provide data on
soil-geomorphic relationships and spatial variability of soils on previously poorly
documented colluvial deposits. Although the relative-age indicators used here have been
tested extensively, they have not often been used in warm areas where annual precipitation
exceeds 100 cm (Birkeland, 1990). Their application in the present research will, therefore,
be an evaluation of the consistency of the method.

The results of this research may help advance the construction of a Blue Ridge and
Appalachian morpho-stratigraphic framework. Such an advance will further the
understanding of future climatic and other environmental changes in the region (Clark,
1979). It can therefore be anticipated that the results, through their implications for climate
change and carbon cycling by pedologic processes in regolith, may ultimately make a

contribution to the Global Change effort.

2. LITERATURE REVIEW

Wm

Mass wasting is a general term for the downslope movement of regolith or rock
material under the influence of gravity without the direct aid of water, air or ice. These
media are, however, frequently involved in mass wasting by reducing the shear strength of
slope materials. The term landslide is sometimes used as a synonym for rapid mass wasting
events (Cruden et al., 1989) although it usually is employed for mass wasting with the
exclusion of creep and frozen ground phenomena (Hutchinson, 1968; Selby, 1982). In a
stricter sense, landslide is used for a group of mass movements wherein shear failure
occurs along a specific surface or combination of surfaces (Schuster, 1978; Zéruba, 1982).

Many criteria are available for classifying mass wasting events but in practice, the
following criteria are used most often for distinguishing between the types of mass
movement: (i) type of material, (ii) mechanism of movement, (iii) velocity of movement,
(iv) geometry of failure surface and, (v) water content. In most classification systems,
flowage is recognized as one of the mechanisms. Vames (1978) defined flow as a:

"... movement within displaced mass such that the form taken by moving
material or the apparent distribution of velocities and displacements
resemble those of viscous fluids. Slip surfaces within moving material are
usually not visible or are short lived. The boundary between moving mass
and material in place may be a sharp surface of differential movement or a
zone of distributed shear. Movement ranges from extremely rapid to
extremely slow".

Originally, the term debris avalanche was defined by Sharpe (1938) and was used
to describe a rapid and relatively wet flowage. According to the definition, a debris

avalanche has a long and relatively narrow track, occurs on a steep mountain slope or

9
hillside in a humid climate, and is almost invariably preceded by heavy rains. Vames

(1958) used debris avalanche for a flow of relatively dry unconsolidated material and debris
flow for a similar but wetter mass movement. In 1975 Vames did not distinguish between
wet and dry flows anymore and used debris flow to describe all flows of coarse soil
materials. In 1978, Vames used the term debris avalanche again and defined it as a very
rapid to extremely rapid debris flow. In the classification system of Vames (1958; 1978),
the term mudflow is a subcategory of debris flow with less than 50 percent gravel. Lowe
(1979) divided debris flows into non-cohesive types in which dispersive pressure is the
dominant sediment support mechanism, and cohesive types, to which he applies the term
"mudflow", in which matrix strength and buoyancy serve as the dominant support
mechanisms. Pomeroy (1982) defined debris flow as a rapid downward movement of
largely saturated material. He distinguished between debris avalanches and debris flows on
the basis of velocity, debris avalanches being faster (Pomeroy, 1982; 1985; 1986). The
material comprising debris avalanches usually is more heterogeneous than that of debris
flows. Debris flows commonly follow narrow preexisting drainage paths and largely
consist, in contrast to mudflows, of coarse rock fragments. VanDine (1985) used debris
torrent for the kind of debris flow that follows narrow preexisting drainage channels. He
defines it as a:

"... mass movement that involves water-charged, predominantly coarse

grained inorganic and organic material flowing rapidly down a steep,

confined preexisting channel".

In the 19803 several rheologic sub—classifications of mass flows appeared in the
literature (Pierson, 1984; Savage, 1984; Iverson, 1985; Pierson and Costa, 1987). Pierson
and Costa (1987) defined mass flow as ..."the continuous, irreversible deformation of a
geologic material that occurs in response to applied stress". The applied stress in most
geomorphic situations is gravity. Their classification scheme can accommodate the above,

more traditional, nomenclature and is based on the rheologic response of a sediment-water

10
mixture. This response is governed by velocity, a surrogate for shear, and sediment

concentration. The earlier definitions of debris flow correspond, in this new classification,
with a viscous slurry flow of water and fines that behaves as a plastic fluid and moves at
speeds of between 10‘8 and 40 m S‘l. Their lower velocity limit (10'8 m 8‘1 or 0.3 m yr'l)
is in contradiction with most previous nomenclatures that described debris flows as being
rapid. Debris avalanches correspond, in the new classification, with inertial granular flows
of water, air and fines that behave as plastic fluids and travel at speeds of 5 to 40 m 3'1.

Innes (1983) revised an existing sub-classification of debris flows and divided them
in catastrophic debris flows, lahars, hillslope flows and valley confined flows. The author
recognized that catastrophic may not be an appropriate term since all types of debris flow
are initiated by extreme events. The term "debris slide" has been employed to describe
movements similar to debris flows. Although debris slides often develop into flows by
liquefaction and internal deformation of the material (Selby, 1982; Clark, 1987; Ellen and
Fleming, 1987; Mills et al., 1987), the term debris slide should be reserved for mass
movements that are commonly rapid but have a relatively low water content and involve
translational or planar movement (Pomeroy, 1984).

Debris flow is sometimes confused with earth flow (Keefer and Johnson, 1983). A
debris flow differs from an earth flow in several respects. In a debris flow, granular
material admixed with water is mobilized into materials that move more rapidly than earth
flows. Debris flows are not bounded by discrete shear surfaces, and most movement takes
place by distributed internal shear. Debris flow material is coarser-grained than earth flow
material (Vames, 1978). In addition, debris flow deposits generally form during a single
episode of activity, so that, within a few minutes or hours, a typical debris flow mobilizes,
flows through a channel, forms a deposit, and dries. These deposits are rarely remobilized
(Keefer and Johnson, 1983).

By analogy with the definition of Vames (1958; 1978), the term debris flow will be

employed in this study for rapid and wet mass movements of coarse earthy materials in

11

which flowage is the most common form of movement. Some deposits in the study area
may have resulted from debris avalanches sensu Vames (1958) or may have been initiated
as debris slides. Since distinguishing the different kinds of deposits is difficult unless
observations can be made during or immediately after the event, and because this
distinction is not necessary for this research, all will be referred to as debris flow deposits.
In the study area of this research the individual deposits have a lobate shape in plan and
occur, together with other debris flow deposits, in elongated depositional areas. Therefore,
the generic term "deposit" will be used throughout this study, rather than the often used

term "fan".

2.2 alizin fact rs

2.2.1 Precipitation amount

Excessive moisture is generally considered to be the main factor affecting the
occurrence of debris flows (Wolman and Gerson, 1978; Innes, 1983; Pomeroy, 1984;
Mills, 1987). The majority of authors attribute the moisture that produces debris flows to
rainfall, but rapid snow melt (Morton and Campbell, 1974; Owens, 1974) and rapid
drainage of lakes (Costa, 1984) have also been suggested as a trigger.

High rainfall appears to have been the dominant triggering process in historical
Appalachian debris flows (Kochel, 1987). In the southern Appalachians, synoptic weather
patterns indicate that most debris flows can be linked to the incursion of warm, moist
tropical air masses between May and November (Kochel, 1990). Other rains that produced
debris flows in the region have resulted from convective storms along a front separating
extratropical air masses from tropical air.

The amounts of precipitation associated with flows, however, vary greatly.

Hurricane Camille brought 710 mm of rain (in 8 hours) to certain parts of Virginia and

12
produced numerous flows (Williams and Guy, 1973; Kochel and Johnson, 1984), but as

little as 100 mm has caused slopes to fail in Tennessee and Vermont (Bogucki, 1976; Ratte
and Rhodes, 1977; Kochel, 1990). Neary et al. (1986) recorded a total of 164 mm (in 12
hours) near a flow in North Carolina. Eschner and Patric (1982) concluded that 125 mm of
rainfall (in 24 hours) triggers debris flows at most Appalachian sites, in spite of the high
porosity of these forested soils. They estimate a general return period of 100 years for this
kind of storm. In some parts of the study area of the present research the return period for

storms that size is 4 years (see section 3.2).

2.2.2 Precipitation intensity

Rainfall intensity, in relation to infiltration rates of the soils and antecedent
moisture, is also an important factor controlling the occurrence of debris flows (Pomeroy,
1984; Jacobson, et al. 1989; Kochel, 1990). Neary et al. (1986) postulate that, for the Blue
Ridge, intensities of 90 to 100 mm hr] cause debris sliding. This intensity has a return
period of less than 200 years in the study area of the present research. Nearly 40% of the
maximum one hour rainfall intensities recorded by Neary and Swift (1987) in a debris flow
generating storm in western North Carolina were in excess of 76 mm. In the study area of
the present research, that intensity has a return period of about 50 years (see section 3.2).

It also has been argued that the rainfall intensity required to trigger flows may be
very small. In northwest England, Wells and Harvey (1987) found that intensities as low
as 50 mm hrl could trigger debris flows while Kadomura et al. (1980) suggest that 9 mm
hr'1 is sufficient to produce mudflows on volcanic cones. Campbell (1975) determined that
a rainfall intensity as low as 6.4 mm hr'l can be a threshold condition to initiate slope
failure in areas of southern California where the total seasonal antecedent rainfall had

reached 254 mm.

l3
Intensity-duration graphs show that the combined effect of intensity and duration,

i. e. total precipitation, is more important than either of the two factors separately (Caine,
1980; Wieczorek, 1987; Kochel, 1990). According to Kochel's data for the Appalachians,
a total of 100 mm constitutes a threshold of minimum rainfall necessary to trigger debris
flows. Pomeroy (1984) disagreed with this kind of generalization and believes that
antecedent moisture is the determinant factor concerning how much rainfall is required to
initiate slope failure. Cannon and Ellen's (1985) findings in the San Francisco Bay region
corroborate this idea. For storms exceeding a certain total rainfall threshold they found a
strong correlation with periods of continuous high-intensity rainfall and the timing of debris
flows. In the same region, Wieczorek (1987) noted that 7 to 30 day antecedent rainfall
values for debris flow triggering storms were about twice those of storms that did not
trigger flows. Storms with less than 280 mm of seasonal antecedent rainfall did not
produce debris flows. In the southern Appalachians, on the other hand, mass flows can
occur during intense rainfall events irrespective of the preceding moisture conditions
(Clark, 1987).

Regolith texture is also an important factor affecting the duration and intensity of
rainfall required to trigger debris flows (Sidle and Swanston, 1982; Jacobson et al., 1989).
Presumably, long-duration/low-intensity rainfall is needed to fill soil moisture reservoirs in
fine -grained regolith, whereas short-duration/high-intensity rainfall is required to fill soil

moisture reservoirs in coarse regolith where infiltration rates are high.

2.2.3 Local factors

Average rainfall amounts and intensities cannot explain why debris flows occur on
one slope and the adjacent slope remains stable. Thus, various reasons for local variations

in slope failure have been identified.

14
2.2.3.1 Precipitation distribution

Large differences in precipitation amounts on adjacent slopes can occur (Williams
and Guy, 1973; Mills, 1987). The differences may be due to a highly cellular precipitation
pattern or to the orientation (aspect) of the slopes with respect to the predominant direction
of the rainfall.

2.2.3.2 Slope

Slope angle considerably affects slope stability. Most failing slopes have an angle
that is higher than the angle of repose (Scott, 1972; Koch, 1974; Bogucki, 1976; Escher
and Patric, 1982; Pomeroy, 1984; Neary et al., 1986). Williams and Guy (1973) found
slopes of less than 30° that failed and the authors explain their observation by the unusually
high precipitation intensity causing the flows (710 mm in 8 hours). They also note,
however, that flows usually originate on the steepest part of the slope and that average
slope angle may therefore not be a good proxy for slope instability. After hurricane
Camille, flow head scars could be observed on slopes as low as 15% but the average slope
was 35% (Schneider, 1973). In northern Pennsylvania, in an area of sedimentary rocks,
debris flows occurred on slopes between 10 and 25% (Pomeroy, 1982).

In some areas susceptible to debris flow formation, flows were absent on slopes of
more than 45%, probably because the regolith is very thin or absent on those very steep
slopes (Pomeroy, 1984; Innes, 1983). Neary and Swift (1987), however, observed that
the largest debris flows of their study region had initiated on slopes of more than 70%.
2.2.3.3 Hillslope form and aspect

Although some have argued that hillslope form and aspect have little effect on the
formation of debris flows (Schneider, 1973; Mills, 1987) cross-slope profile has been
identified as an important factor. In some areas, the majority of debris flows occurred along
previously existing depressions in hillslopes (Hack and Goodlet, 1960; Williams and Guy,
1973; Bogucki, 1976; Pomeroy, 1984; Clark, 1987; Kochel, 1987). Subsurface flow

15
convergence in such hollows made these sites the most probable locations for failure

(Dietrich and Dom, 1984; Reneau et al., 1984). Peatross (1986) used 23 geomorphic
variables in a discriminant analysis to identify sites that had been stable and unstable during
Hurricane Camille. Variables most successful in producing the two groups included slope
angle, slope aspect and hillslope form.

Most debris flows caused by Hurricane Camille (Williams and Guy, 1973) and a
majority of debris flows in northern and western Pennsylvania (Pomeroy, 1980; 1982;
1984; 1986) were found to occur on northward- or eastward-facing slopes. The regolith on
these slopes was probably more moist (prior to the debris flow triggering storm) than
regolith on other slopes due to a lowered incidence of direct sunshine. In areas with well
developed geologic structures there was a stronger relationship between aspect and flow
initiation than in structureless areas (Schneider, 1973; Bogucki, 1976). This influence of
structure is an alternative for the presumed influence of moisture and lack of sunshine

(Kochel, 1987).

2.2.3.4 Geology

Structural and lithologic factors influence the location of debris flows. Lithology
has an indirect influence because it is partially responsible for the characteristics of the
overlying soil. Debris flows are more common on highly weatherable bedrock (Schneider,
1973; Bogucki, 1976; Pomeroy, 1980) and on cyclic sedimentary rocks with incompetent
layers (Pomeroy, 1982). Slopes in northwestern Pennsylvania were particularly unstable
when the susceptible incompetent layer occurred near the bottom of the slope (Pomeroy,
1982).

Structure has a more direct influence on the origin of flows, especially when the dip
is steep (Bogucki, 1976). When the dip angle is low, bedrock orientation does not appear
to be a significant factor (Schneider, 1973). Most debris flows in the area studied by

Pomeroy (1982) were associated with nearly vertical stress relief joints. The joints increase

16
the secondary permeability of the bedrock and together with other structures they influence

the localization of debris flows by creating preferential paths for groundwater flow and
seepage (Pomeroy, 1984). The influence of bedrock orientation is not equally important
throughout the Southern Blue Ridge, but seems more significant in its western portion
(Scott, 1972). In the west, the relatively low metamorphic grade of the rocks (see below)
has left them more diverse in their susceptibility to weathering. As a consequence, layers
weather differentially and offer more potential planes of failure than might a more
homogeneous regolith.

Schneider (1973) noted that more debris flows occurred on soils with lower stone
content than soils with a greater stone content. The author interpreted this to mean that the
stone content reflects bedrock characteristics which have an impact on flow localization,
rather than the stone content within the soil affecting its potential to fail. The soils with
higher stone content, in this case, generally were derived from rocks with higher quartz

sandstone content.

2.2.3.5 Regolith thickness and texture

A thin soil mantle is generally thought to favor the formation of flows, presumably
because it will accelerate saturation of the regolith during heavy rainfall events (Scott, 1972;
Escher and Patric, 1982; Neary et al., 1986; Neary and Swift, 1987). Pomeroy (1984)
believed, however, that an extremely thin regolith mantle prevents debris flows from
forming. In areas where the regolith was thin, slope failure took place at the colluvial-
bedrock interface but where the regolith was thick (>5 m) failures happened within the
colluvial cover (Pomeroy, 1982; 1984). Working on the Cumberland Plateau in northern
Alabama, Pomeroy (1985) concluded that a supply of regolith downslope from the head
area is needed for debris avalanches to occur because he observed an avalanche that

terminated as soon as it encountered rock ledges. Others (Schneider, 1973; Mills, 1987)

17
have argued that the thickness of the regolith has little effect on the formation of debris

flows.

The effect of regolith texture is hard to determine because the original composition
of the failed mass cannot be determined exactly. It is thought that at least a small amount of
clay is needed to sustain the flow (Pierson, 1981) but a high amount of clay aggravates the
saturation and loss of cohesion in the regolith (Neary and Swift, 1987). In the San
Francisco Bay region regoliths with a broad range of textures are susceptible to debris flow

formation but 98% of the flows have more than 8% clay (Ellen and Fleming, 1987).

2.2.3.6 Vegetation

Ascertaining the effect of vegetation and land use on debris flow formation is
difficult in the Blue Ridge because most steep slopes, where flows occur, are forested
(Mills, 1987). Nevertheless, Scott (1972) reported that clear cutting in the Blue Ridge was
not a major factor contributing to debris sliding, and Eschner and Patric (1982) reported
that flows in forested areas of the eastern United States occurred irrespective of vegetative
cover. Schneider (1973) observed fewer debris flows in forested areas than in cleared land
but those under forest tended to be deeper. Daniels et al. (1987) stated that the importance
of vegetation in protecting s10pes against mass wasting was demonstrated by the numerous
reports of slope failure after logging in the southern Appalachians and reference Hursh
(1941). Hursh did not mention, however, any influence of logging on mass movements.

In the western United States most workers (O'Loughlin, 1974; Greswell et al.,
1979; Swanston, 1979; Swanson et al., 1981) agree that road construction and logging can
aggravate flow incidence. Also well known are the effects of the destruction of vegetation
by fires on the generation of debris flows in southern California In British Columbia,
control of timber harvesting methods and reforestation are employed as primary mitigation

measures for debris flow hazards (Hungr et al., 1987). The inconsistent results from the

18
Appalachian hardwood forests can be explained by the rapid sprouting of the root system

that is left in place after clearcutting (Neary et al., 1986; Escher and Patric, 1982).

19
3 STUDY AREA

3.1 Introduction

The Blue Ridge Mountains run as a long band, in the center of the Appalachian
system, from Pennsylvania to Georgia. The Blue Ridge is narrow at its northeastern end in
Pennsylvania but widens southwestward into Tennessee and North Carolina, where it is a
massive highland 120 km in width (Figure 1). The Blue Ridge Physiographic Province has
two subdivisions, the Northern Blue Ridge and the Southern Blue Ridge. The Southern
Blue Ridge extends from the Roanoke River in Virginia southwestward to Cartersville, Ga
(Hack, 1982). The study area initially considered for this research is located in the
Southern Blue Ridge. It coincides with the basin of the Little Tennessee River south of its
confluence with the Tuckasegee River (Figure 2).

The drainage basin of the Little Tennessee River lies almost completely within
Macon County, North Carolina. Franklin, the main urban center of the study area and
county seat of Macon County, is situated in the center of the basin. It provided a centralized
base of operations for this study. Small parts of the basin extend northwards into Swain
County, NC, and southward into Rabun County, GA.

The Coweeta Hydrologic Laboratory of the US. Forest Service is located in the
study area. The Laboratory is an extremely well studied, outdoor, forest ecology and
hydrology research site. More than half a century of climatologic, hydrologic and
vegetation data have been recorded at Coweeta. The Laboratory lies about 10 km south of
Franklin just west of highway 441. Several of the following paragraphs draw heavily on
research carried out at Coweeta.

In section 3.2 the physical characteristics of the Little Tennessee River basin are

placed in a regional context. The section describes the natural environment of the Southern

 

 

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22

Blue Ridge while focusing on local features. The following section (3.3) explains how the

specific sites for this research were selected, and provides descriptions of those sites.

3.2 tu are escri tion

3.2.1 Climate.

The general climate of the Little Tennessee River basin is humid temperate. The
average annual precipitation just southeast of the basin is the highest in the eastern United
States (>200 cm annually) and keeps soils in protected areas moist year around. In the
study area local precipitation and temperature vary as a function of elevation and aspect.

Franklin, located at 650 m elevation, receives 130 cm of precipitation annually,
50 % of which falls in April through September. The average annual snowfall is 20 cm.
Thunderstorms occur on about 46 days each year. The heaviest l-day rainfall recorded at
Franklin was 15 cm. At higher elevations, just north of the study area, intense rainstorms
associated with hurricanes have dumped as much as 30 cm in one event (Neary et al.,
1986). Rainfall increases to the south of Franklin and/or at higher elevations. The average
temperature for the year is 14 ° C; the summer average is 22° C, while in winter it is 4° C
(Thomas, 1993). During 5 years in 10 the last spring frost occurs before May 4. The first
frost in fall usually occurs earlier than October 11.

At the Coweeta Hydrologic Laboratory, 10 km south of Franklin, precipitation
ranges from 170 cm at 750 In elevation to 250 cm at elevations around 1500 m (Douglas
and Swank, 1975). Annual evapotranspiration at lower elevations approximates 90 cm.
The mean annual temperature for that area is 13° C. The climate of the Laboratory is
classified, under Koppen's system, as marine humid temperate (Cfb) (Swift et al., 1988).
The lower elevations of the Laboratory, and of the main valley of the study area, have a

humid subtropical (Cfa) climate. Of the 133 storms that occur in the Laboratory annually,

23

50% exceed 0.5 cm and 6% exceed 5 cm. Storms exceeding 5 cm of rainfall deliver 34% of
the total annual precipitation. Most of the storms have low intensities because rates surpass
1 cm hr'1 only 4% of the time (Swift et al., 1988). Seventy percent of the precipitation at
the Laboratory falls with intensities of <2 mm hr'l. Nevertheless, storms with intensities
that potentially could cause debris flow have relatively short return periods. Intensities as

high as 7.5 cm hr'1 have return periods of only 50 years (Figure 3).

3.2.2 Geology

The Blue Ridge Mountains coincide with the crest of an anticlinorium. This
structural trend leads to the emergence of Middle and Upper Precambrian and Lower
Cambrian rocks in the Southern Blue Ridge. The Little Tennessee River basin is crossed by
the Hayesville fault which separates the western from the eastern Southern Blue Ridge
(Figure 4) (Hatcher, 1988).

The western part of the Southern Blue Ridge consists of sequences of
metasedimentary rocks and schists. These rocks were derived from and deposited on the
Precambrian Grenville basement of eastern North America. They date from the Upper
Precambrian (Hadley and Nelson, 1971; Hatcher, 1988). In the Little Tennessee basin they
belong to the Great Smoky group and consist of feldspatic metasandstone with interbeds of
quartz-mica schist, phyllite and slate. Beds of conglomerate are also present.

The Grenville basement is almost completely absent from the eastern Southern Blue
Ridge. This region contains an assemblage of Upper Precambrian rocks which are in many
ways different from those to the west of the Hayesville fault (Hadley and Nelson, 1971).
Most of the mafic and ultramafic rocks of the Southern Blue Ridge are found in this eastern
part. Lithologically the region is characterized by biotite and muscovite schist and gneiss.
South of Franklin, in the only part of the study area mapped in detail, rocks of the Coweeta

Group and Tallulah Falls Formation can be found (Hatcher, 1980). The Coweeta Group

24

 

 

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26
dates to the Upper Precambrian or Lower Cambrian. It comprises coarse biotite-garnet

schist, metasandstone, quartz-feldspar gneiss, quartz-diorite gneiss and interlayers of
pelitic schist. The Tallulah Falls Formation, which occupies a significant portion of the
eastern Southern Blue Ridge, is of Upper Precambrian age and consists of coarse grained
biotite gneiss and schist.

The metamorphic grade of the rocks is lower in the western than in the eastern Blue
Ridge (Hadley and Nelson, 1971; Hatcher, 1988). There is a rapid increase, in an easterly
direction, from a greenschist facies to an upper amphibolite or granulite facies. Hadley and
Nelson (1971) and Hatcher (1988) differ in their location of metamorphic zones and facies.
According to Hadley and Nelson (1971) the staurolite and kyanite zones of the amphibolite
facies are reached west of the Hayesville fault while Hatcher (1988) situates those zones
east of the fault. Hadley and Nelson (1971) locate the sillimanite zone of maximum
metamorphic grade in a NE - SW trending zone from Asheville through Franklin into
Georgia, but Hatcher (1988) postulates that the sillimanite zone only occurs in NE Georgia.
Toward the eastern limit of the Blue Ridge, marked by the Blue Ridge Escarpment and the
Brevard fault zone, the metamorphic grade drops off strongly.

The Hayesville fault is the major fault in the study area. It is a pre- to
synmetamorphic thrust fault that was emplaced prior to the thermal peak which affected the
rocks of the Southern Blue Ridge (Hatcher, 1988). It was deformed by later folds that
imparted a very sinuous outcrop to it. The Brevard fault zone, to the SE of the study area,
roughly follows the Blue Ridge escarpment in North Carolina. It is probably the youngest
major fault zone in the region, and is believed to be Paleozoic and may have been active up
to the Triassic Period. Other kinds of tectonism may have been active in the region as late
as the middle Mesozoic (Hack, 1982).

The abrupt difference in relief between the Southern Blue Ridge and the Piedmont
cannot be the result of lithologic differences between the two regions because the

topographic boundary between the two regions does not correspond to the boundary

27
between Piedmont rocks and Blue Ridge rocks (Hack, 1982). Therefore some kind of

tectonism must have influenced the spectacular topographic difference. White (1950)
thought that the escarpment was essentially a fault scarp. The Brevard fault zone can not
have played a major role because the Southern Blue Ridge has high relief. It must owe its
present topography to vertical uplift younger than the middle Mesozoic. Hack (1982)
therefore believed that it probably belongs to the same erosional and tectonic block as the
Valley and Ridge province. According to Battiau-Queney (1989) the Blue Ridge, Valley
and Ridge and Piedmont all are allochtonous terranes above a major detachment, and the
terranes were thrust westward by horizontal creep of a ductile crust over Grenville
basement rocks. The Blue Ridge escarpment reaches its highest relief where discontinuities
in the deeper crust interfere with surficial geological features such as the Brevard fault
zone. However, as pointed out by Hack (1982) the escarpment cannot be completely the
result of surficial tectonics because of their timing. The crustal creep process proposed by
Battiau-Queney (1989) could explain the sustained uplift of the Appalachian highlands and
the relatively stable position of the Blue Ridge escarpment. Hatcher's ( 1988) observations
seem to indicate that he considers the Hayesville fault to be another boundary between

allochtonous terranes, i.e. the western and eastern Southern Blue Ridge.

3.2.3 Geomorphology

The Southern Blue Ridge is an area of steep relief (Figure 5) that is bounded on its
southeast margin by a bold escarpment. The Blue Ridge Escarpment forms the boundary
between the Blue Ridge and the much flatter Piedmont. Rivers on the escarpment drain
southeastward to the Piedmont and the Coastal Plain. From the Georgia - South Carolina
border northward, the crest of the escarpment cuts diagonally across the entire Blue Ridge
anticlinorium. The northwest border of the Southern Blue Ridge province follows the

outcrop of quartzite beds.

28

 

Relief map of the Blue Ridge and Piedmont

physiographic provinces

 
 
 

\~ .3
s‘r‘“

5W8:

v,

In

 

 

\

 

, ‘ 'Z'
.s“\ :-
K . ‘,\Z .
\

\

 

\
\

‘51-.“
.s“\\\\\‘~\
' Z

..-\<\\‘

 

 

 

 

 

 

 

 

 

 

 

I Steep hills and mountains Moderate relief

Low relief 1:] Very low relief

After Hack (1987)

 

 

 

Figure 5

 

 

29 .
The Southern Blue Ridge province can be divided into several areas on the basis of

topography. Although some of these areas correspond to distinctive geologic areas, some
do not and rock control is responsible for many landscape features (Hack 1982).

The largest part of the Southern Blue Ridge consists of the ranges of high
mountains, many of which exceed 1500 m in altitude. Local relief in the highlands
generally exceeds 900 m. Some rock control and structural influence on topography is
evident. For example, the highest part of the Great Smoky Mountains is underlain by
massive conglomerate and sandstone; here, deep trench-like valleys follow weak rock
outcrop areas like carbonate belts. In one case differential weathering and erosion has led to
the formation of a 150 km long trench that extends from Georgia into North Carolina. The
trench culminates in the Nantahala Gorge just west of the study area of this dissertation.
The Asheville basin may be partly controlled by the outcrop of weak rocks but also by
intersecting shear zones. Along the northwest and southeast borders of the highlands the
ranges tend to be roughly parallel to the northeast regional strike of the rocks. Many valleys
have distinct linear trends and some parallel the strike of the rocks or the trends of the thrust
faults. Other valleys clearly crosscut the structural grain, as do major basins such as the
Little Tennessee River (Clark, 1989). Still others are controlled by joint systems at right
angles to the dominant structures (Acker and Hatcher, 1970)

One aspect of the geomorphology of the southern Blue Ridge that has received
much attention are debris flows. They are considered to be the major transporters of
unconsolidated material down the flanks of the mountains and into the channels (Scott,
1972). Colluvial fans in general and debris flows in particular have been attributed to
periglacial conditions during the last glaciation (King, 1964; Michalek, 1968). This
interpretation needs confirmation (Shafer, 1984; Mills, 1987) because it is probable that
drier air associated with Arctic airrnasses may have made intense rainstorms somewhat less

common during the pleniglacials than at present (Delcourt and Delcourt, 1984) and because

30
episodes of alluviation/colluviation in the Southern Appalachians seem to have been

confined to late glacial/interglacial transitions (Delcourt, 1980).

Appalachian debris flow deposits usually do not display fan morphology but are
elongated and irregular, because they are often constricted between narrow basin
interfluves (Kochel and Johnson, 1984). In the Blue Ridge of Virginia, fans that formed
down-basin in expanded valley reaches are free from lateral confinement so that true fan
forms are found (Kochel and Johnson, 1984). Variations in debris fan shape appear to be
controlled by bedrock resistance, bedrock structure and grain size of the debris (Kochel,
1990). Deposits developed in areas of unifomrly resistant rocks tend to be smaller and have
the most irregular shape because they form in confined, narrow valleys.

Most Blue Ridge debris flow deposits are less than 20 m thick and occur on slopes
between 4 and 10%. They have a hummocky lobate topography even if the overall shape of
the deposit is fan-like (Kochel and Johnson, 1983; Kochel, 1990). Many recent deposits
are bordered by boulder levees (Hack and Goodlett, 1960). Kochel and Johnson (1984)
did not observe levees or terminal lobes on fans in Virginia after the passage of Hunicane
Camille, but contend that much of the morphological evidence may have been destroyed by
storm runoff and human intervention.

Because of the predominance of steep slopes in a humid climate, saprolite rarely
extends completely to the surface in the Southern Blue Ridge. Most slopes are covered with
a thin layer of creep colluvium. Level landforms are usually the site of deposition of more
catastrophic colluvial processes or of alluvial processes. Most studies dealing with
pedology and geomorphology have encountered colluvial materials at the surface. Only
near Linville Falls, 175 km northeast of the study area of this dissertation, has saprolite
been reported to extend to the surface (Reed, 1964).

In the Joyce Kilmer Memorial Forest, 60 km northwest of the study area, transect
studies indicated that more than one third of the landscape was underlain by deep saprolite

(Daniels et al., 1987). Evidence of local colluvial activity in the upper soil horizons was

3 1
almost always present. In the Blue Ridge Front, saprolite was only present on the ridges

and footslopes but colluvium occurred on all parts of the landscape (Graham et al., 1990).
According to the authors, the absence of saprolite on the steep backslopes is due to mass
wasting and throughflow that removes water that would otherwise promote weathering.

A mass balance study in the study area indicates that the short-term rate of
saprolitization is about 38 m Ma'l (Velbel, 1985). In other regions of the Appalachian
system, i. e. the Piedmont, saprolitization rates have been found to be much smaller (i 4 m
Ma'l) (Pavich, 1986; Cleaves et al., 1970). However, the average erosion rate for the
eastern US (40 m Ma'l), estimated by Hack (1970), is similar to the saprolitization rate of
Velbel (1985). Taking changes in climate and soil C02 levels into account, Cleaves (1989)
argued that saprolitization rates on the Maryland Piedmont must have been between 15 m
Ma'1 and 48 m Ma'l since the Late Miocene. In the absence of erosion, this translates into
the production of a saprolite between 80 and 255 m thick (Cleaves, 1989). Considering that
the thickness of the present day saprolite is about an order of magnitude smaller, this
suggests that, since the Late Miocene, significant erosion took place on Piedmont uplands.
Pavich (1989) concluded that erosion and saprolitization on the Piedmont of Virginia were
between 4 and 20 m Ma‘l. Pavich reached his conclusion after determining saprolitization
rates on the basis of soil erosion, sediment flux and 10Be inventory studies. Although the
results of Cleaves (1989) and Pavich (1989) cannot be extended to the study area of the
present research without careful examination of underlying assumptions, they do indicate

that the Southern Blue Ridge may have undergone considerable erosion during the

Quaternary.

32
3.2.4 Soils

The following section contains a general description of the soils in the study area.
For a more thorough discussion of the soils on a regional scale and of soils on colluvium
the reader is referred to section 5.2.

The soils of the study area have formed predominantly in regolith weathered from
metamorphic and metasedimentary rocks under hardwood (mainly oak-hickory) forest
vegetation. Most of the regolith underwent transportation and the only landscape positions
where truly residual, saprolitic soils can be found are thought to be the ridgetops and
shoulder SIOpes (Thomas, in press). The dominant soil temperature regime is mesic; soils
above 1460 m have a frigid temperature regime. The soil moisture regime is udic. Most
soils, with the exception of three series on floodplains, are well to excessively drained.
They usually are moderately deep to very deep, although shallow soils occur on steep
slopes in the high mountains. Soils on floodplains and river terraces have a neutral soil
reaction but all other soils are acid to extremely acid (3.5<pH<6.0). Generally the soils
have a loamy texture but clayey soils can be observed on low rolling hills close to the Little
Tennessee River and, occasionally, on other stable landforms. Colluvial soils are present in
many footslope settings and typically have high amounts of coarse fragments. Pedon
thickness is maximal on colluvial landscape positions (Thomas, in press). According to
Thomas, soils in Macon County vary considerably in age, and the length of time that these
soils have been developing is reflected in their morphology. Old soils generally have more
clay accumulation in the Bt horizon than do young soils. Some soils appear young because
they are poorly developed due to erosion of steep s10pes or deposition at the base of these.

Taxonomically, the area is dominated by Inceptisols and Ultisols (Thomas, in
press). Small areas of Entisols (Typic Udipsamments) can be found on the floodplain along
rivers while Alfisols (T ypic Umbraqualfs) occasionally occupy low terraces. In colluvium

Typic Haplumbrepts or Humic Haplaquepts and Aquic or Humic Hapludults usually

33
developed. On the low mountains close to the Little Tennessee River Typic Hapludults

developed while on the higher and steeper mountains Typic Dystrochrepts and Typic

Haplumbrepts originated.

3.2.5 Colluvium

3.2.5.1 Geomorphology and sedimentology

Colluvium has been observed to be a nearly ubiquitous feature in the Southern Blue
Ridge (Mills, 1981). Deposits associated with debris flows usually occur in concave
landscape positions. Many such deposits are small, irregularly-shaped landforms that
developed predominantly in first or second order basins (Kochel, 1990). Similar deposits
in the region occur as fan shaped features that grade into alluvium at their distal ends (King
1964, Michalek 1968, Gryta and Bartholomew 1977, Mills 1981). The fans are sometimes
believed to be relict features inherited from periglacial conditions that may have existed in
the Pleistocene, but some have observed signs of recent activity (Kochel and Johnson,
1984).

The best descriptions of debris flows in the region have been provided by
researchers studying the events produced by hurricane Camille in 1969 (Scott, 1972;
Schneider, 1973; Williams and Guy, 1973; Kochel and Johnson, 1984). The thickness of
the material removed from the slope due to this storm was usually less than 1 m (Mills,
1987) but reached 6 m (Williams and Guy, 1973). The area of debris flow scar heads
varied from 1 m2 to 20,000 m2 (Schneider, 1973). Chutes were generally much longer
than they were wide with lengths ranging from 6 m (Williams and Guy, 1973) to greater
than 800 m (Neary et al., 1986). Typical values ranged from 50 to 300 m (Mills, 1987).
Widths ranged from 3 m (Koch, 1974) to 60 m (Williams and Guy, 1973) with 8 to 24 m
being typical (Mills, 1987). The depth of chutes of debris flows usually depends on the

depth to bedrock. The flows can cut deep paths in regolith but don't scour the top of the

34
bedrock (Neary et al., 1986). When the flows reach low gradient coves or when a stream is

far from the base of the slope of origin the material is often deposited on the hillside. When
the slope remains steep or a stream is close to the base, the greater part of the material is
carried down the valley by the debris flow and is left behind as a fan or lobe shaped deposit
(Mills, 1987). Below a gradient of about 25 % the materials often block or partially block
the channels (Neary et al., 1986). Size and viscosity of the debris flow also determine
where the material is deposited. Large and viscous flows will tend to remain at the foot of
the slope. Complex deposition patterns are evident on many fans. Incised drainageways
usually occur laterally on each margin of a deposit. The thickness of individual deposits
ranges from a few tens of cm to 2 m (Kochel, 1990).

Most of the Blue Ridge debris flow deposits are more constrained by pre-existing
topography than the alluvial/colluvial fans in the semi-arid southwest of the United States
(Mills, 1987). Fans with little constriction, as evidenced by correlations between fan area
and drainage basin area, were found on the west slope of the Blue Ridge in Virginia
(Kochel and Johnson, 1984). They cover areas of more than 10 km7- and their sediments
reach thicknesses of up to 130 m. They are composed of clast supported gravels that appear
to be braided stream deposits, and thus they can be considered to be fans of the fluvial
type. The most topographically constrained deposits, with little correlation between deposit
area and basin area, were described on the eastern slope of the Blue Ridge in Virginia
(Kochel and Johnson, 1984). They are completely constricted within narrow valleys on
steep slopes and do not show a fan-shape. They consist chiefly of diamicts deposited by
debris flows. The deposits therefore represent the .mass flow type of fan-like deposit. Their
gradient is similar to those reported by Bull (1962) for alluvial fans in the southwestern US
(40 to 100 m/km). Considerably steeper gradients can be found in the Southern Blue Ridge
of North Carolina (Mills, 1982; 1983). Paucity of water-laid sediment on the deposits and a

coarse bouldery texture of the debris are possible reasons for these steep gradients.

35
Extensive blankets of colluvium exist on convex sideslopes between 730 and 1220

min the Joyce Kilmer Memorial Forest, 60 km northwest of the study area of this
dissertation (Daniels et al., 1987). The origin of the colluvium has been attributed to
solifluction under a periglacial climate. One site contained high amounts of angular coarse

fragments, reflecting short range colluvial movement or windthrows (Daniels et al., 1987).

3.2.5.2 Elevations

The elevations of the source areas for seven major debris avalanches in western
North Carolina range from 945 m to 1100 m (Neary et al., 1986). Other flow scar heads in
the area are located between 655 m and 1207 m. In the same general area, colluvial deposits
which can be attributed to periglacial activity are present at around 1500 m (Shafer, 1988).
Numerous chutes and debris avalanche deposits can be observed between 600 and 800 m

in northwestern North Carolina (Graham et al., 1990).

3.2.5.3 Coarse fragments

Almost all colluvium in the Southern Blue Ridge is described as being bouldery
(Mills, 1981; Mills, 1982; Shafer, 1984; Daniels et al., 1987; Mills et al., 1987). Large
quantities of boulders were deposited in low gradient coves on the slopes by storm-
generated debris slides in 1977 (Neary et al., 1986). Other boulders were transported
further downslope by debris flows. Small levees consisting of boulders formed alongside
areas of main flow. Below a gradient of 25% the flow spread out and material, including
boulders was deposited. In some areas, elliptical deposits of rock fragments were formed
in eddies downslope of obstructions. Only occasionally, in pools behind obstructions, did
deposits relatively free of boulders form (Neary et al., 1986). Blocks up to 200 tons were
floated into level valleys by "mudflows" in Macon County in 1940 (Hursh, 1941). In the
bottoms of drainage ways in other parts of the Southern Blue Ridge extremely coarse

boulder trains (Daniels et al., 1987) and very poorly sorted debris and angular boulders can

36
be observed. On the bottoms of chutes, boulders and gravelly sediments are common

(Graham et al., 1990a).

On Grandfather Mountain, NC, extensive sheets of bouldery colluvium cover the
slopes (Mills, 1981). Boulder deposits on the lower slopes are confined mainly to the
surface of younger deposits which often coincide with drainageways. The roundness of the
clasts in colluvium was between 1.3 and 2.0 on the visual comparison chart of Krumbein
(1941). Stream gravel that had traveled a comparable distance had a roundness of about

3.1. This supports the opinion that colluvium contains numerous angular clasts.

3.2.5.4 Ages

Early research used relative means of age dating for colluvium in the Southern Blue
Ridge. Hue and percent weathered clasts were used as weathering indices for sheet like
bouldery colluvium in the Grandfather Mountain area, 175 km northeast of the study area
of this dissertation (Mills, 1981). The two indices allowed Mills to distinguish deposits of
two different ages. The younger colluvium could have been Holocene or Late Wisconsinan
while the older deposits could range in age from mid-Wisconsinan to pre—Illinoisan.

In a similar approach, percent clay, hue, percent weathered clasts and mean
weathering rind thickness were employed as relative age indicators for colluvium in three
areas in western North Carolina (Mills, 1982). The deposits could be classified in two to
three distinct age groups representing repeated episodes of rapid colluviation. By linking
colluviation to alluviation that, according to Delcourt (1980), occurred at late
glacial/interglacial times, Mills (1982) concluded that the youngest age group must have
been Late Wisconsinan to Holocene. The older deposits were hypothesized to be mid-
Wisconsinan or older. Based on a visual estimation of soil development, debris flow
deposits in northern Pennsylvania appeared to be Wisconsinan in age (Pomeroy, 1986).

Shafer (1984, 1988) was the first to provide absolute ages for surficial deposits in

the Blue Ridge. His study area was located 70 km northeast of my study area, at an

37
elevation of 1500 m. The dates are based on therrnoluminiscence (TL) dating of the matrix

of a colluvial fan and a blockstream in a small bog. The colluvial fan, at the head of the
bog, was dated 10.1 ka. The blockstream was dated 7.4 ka. These results may only reflect
the age of the last reworking event. Since that reworking event may not have been of the
same process that produced the main deposit, his method does not provide a reliable date
for the age of the formation of colluvial fans and is biased towards lower ages. Conversely,
there may also be a bias toward results that are too old. The matrix of a colluvial deposit or
block stream is not necessarily exposed at the surface for a time long enough to reset the TL
clock to zero (i.e. to annihilate the structural damage measured by TL). Thus, the dates of
Shafer (1984; 1988) are only to be considered a first approximation. In any case, the author
concludes that the deposits did not form during Pleniglacial times, as thought previously
(King, 1964; Clark, 1968), but rather toward the end of the last glaciation.

Paleosols in two debris flow deposits in Central Virginia were dated by 14C at
approximately 10.7 ka (Kochel and Johnson, 1984). The stratigraphy of the two deposits
suggested that at least three events of a magnitude similar to hurricane Camille of 1969
occurred during the past 10.7 ka. However, the recurrence intervals of major sediment
producing events like these are hard to estimate because the number of deposits present in
any one section may not represent the total number of events that occurred in the basin
(Kochel and Johnson, 1984). Another problem is that once a slope has failed even the
heaviest rainfalls may be unable to produce a new failure until a new regolith has formed.
In the Smoky Mountains radiocarbon dating points to a recurrence interval of 400 to 1600
years for major debris flows (Kochel, 1990).

Kochel (1990) reported 14C ages for organic materials at the base of debris fans in
the Dellwood and Smoky Mountains areas of North Carolina. The basal units in Dellwood
generally dated between 16 ka and 18 ka, although ages as old as 25 ka were obtained for

some deposits. Historical debris flows have not been observed in the Dellwood area.

38
In the Valley and Ridge of West Virginia, thick debris flow deposits were dated by

14C at 13.2 to 10.7 ka (Jacobson et al., 1989). In the same area older debris flow terraces
ascended in steps to the tops of spur ridges. The highest terraces may be as old as Middle
Pleistocene as evidenced by their elevation above the river and by their weathering. The
lowest unit was thought to be Holocene in age. The large apparent time intervals between
periods of debris flow terrace aggradation suggests episodicity with a frequency

comparable to Pleistocene climate change (Jacobson et al., 1989).

3.2.6 Vegetation

The natural vegetation in the region is a mixed deciduous forest. Present day
community composition has been affected by human disturbances. The area was occupied
by Cherokee Indians prior to 1842. During the second half of the 19th century the main
disturbances were light burning and grazing. After 1900, logging operations started.
Although logging occurred over the whole region, cutting was heaviest on the lower
slopes, valleys and accessible coves.

At the Coweeta Hydrological Laboratory the forest has traditionally been included
in the oak—chestnut association (Braun, 1972). However, since chestnut has been lost as a
dominant species due to disease, the area is now probably more correctly classified as
belonging to the oak-hickory association (Day et al., 1988). The predominant species
composition is a mix of deciduous oaks with commonly abundant evergreen undergrowth
of rhododendron (Rhododendron maximum) and mountain laurel (Kalmia latifolia).

Forest composition varies with changes in elevation and topographic position (Day
et al., 1988). Northern hardwoods dominate at elevations above 1200 m on slopes and in
coves. Species that occur most frequently include yellow birch (Betula lutea), basswood
(Tilia heterophylla), northern red oak (Quercus rubra) and black cherry (Prunus serotina).

In mesic coves just below the northern hardwoods zone, yellow poplar (Liriodendron

39
tulipefera) and hemlock (T suga canadensis) dominate heterogeneous stands of cove

hardwoods. At middle elevations oaks, and formerly chestnut, are widely distributed.
Chestnut oak (Quercus prinus) is most the widespread species but scarlet oak (Quercus
coccinea) increases in importance on drier slopes and on ridges. At low elevations, on
ridges and drier slopes, oak-pine communities are found. Pitch pine (Pinus rigida) and

scarlet oak (Quercus coccinea) predominate here. -

3.3 Site selection

3.3.1 Reconnaissance survey

3.3.1.1 Methods

3.3. 1.1.1 General

A reconnaissance survey was carried out to evaluate the suitability of the area for
the proposed research and to locate potential sites of colluvial deposition. The survey
involved preparatory work in the office and at the Soil Conservation Service (now the
Natural Resources Conservation Service) office in Franklin, North Carolina, prior to
reconnaissance field work.

Colluvial deposits were identified from aerial photographs, topographic and
geologic maps, the preliminary soil survey of Macon County as well as a "windshield
survey". A large number of potential sites were then subsequently evaluated in the field,

and in 24 cases, sampled for the characterization of the soils and sediments.

3.3.1.1.2 Specific methods

Aerial photographs of Macon County at a scale of l:40,000 and 1:18,000 were

available for study at the Natural Resources Conservation Service office. Colluvial and

40
mixed alluvial/colluvial deposits were identified on the basis of their topographic

expressions and vegetative cover. They usually occurred at the base of slopes or on the
alluvial plains. At the base of the slopes they were present as localized fan shaped deposits
or as more extensive sheets with a smooth topography that masked the contact between the
floodplain and upper slope. On the alluvial plains they occurred as lobes that imparted an
hummocky topography to the area. Because of the dense vegetation and the scale of the
photographs individual, small deposits could not always be delimited, nor was it possible
to positively identify the source areas of individual mass movements. Nevertheless, many
areas in which a number of colluvial deposits seemed to occur were identified. Since this
was the first step in the identification process an "inclusive" approach was used so that no
potential site was excluded.

Topographic maps were used in the same way as were the aerial photographs.
Breaks in slope, especially those at the toe of a long, steep slope, fan shaped landforms and
irregularities on the alluvial plains were considered to be indicators of potential colluvial
materials. The scale, 1:24,000, and the contour interval, 40 ft, of the maps only allowed a
very tentative identification of sites of interest.

Most geologic maps of the area were of too small a scale to be useful. Only one
7.5' map sheet in the Little Tennessee basin has been mapped (Hatcher, 1980). Four
Quaternary units are distinguished on this map, alluvium, colluvium, terrace deposits and
undifferentiated deposits. The colluvium unit occurs as a veneer on slopes and as valley
fill. Only larger bodies were mapped, which made the map of limited use.

The soils of Macon County have been mapped recently (Thomas, in press). Several
of the mapping units of the advance copy of the soil survey occur exclusively on colluvium
in one particular geomorphic setting. These allowed me to distinguish between colluvium at
the base of vertical rock cliffs (Cullasaja map unitl), colluvium on toe slopes in low

mountains (Saunook map unitl), colluvium in coves and drainageways in intermediate

41
mountains (Sylva—Whiteside complexl) and colluvium on toe lepes in intermediate

mountains (Cullasaja-Tuckasegee complexl, Spivey-Santeetlah complex1 and Tuckasegee-
Whiteside complexl). This information was used to corroborate or reject the preliminary
identification of potential sites obtained from the above mentioned sources.

The initial identification of colluvial deposits resulted in approximately 125 potential
sites. An attempt was made to visit all sites but some were inaccessible due to their
remoteness, or access was denied by the owner. The remaining sites were visually
inspected and the likelihood that their geomorphological characteristics reflected a debris
flow-like deposit was evaluated. Twenty four sites, either difficult to assess visually or
considered to be of great potential, were retained for further study. These locations were
sampled with a soil auger up to 2 m deep and in exposures up to 7 m high. The soils and
sediments were described in the field and textures were analyzed in the laboratory

(Appendix 1).

3.3.1.2 Results

These various sources of information revealed that colluvium is prevalent in many
landscape positions in the Little Tennessee River basin. Visual inspection in the field did
not permit a conclusive interpretation of the mode of formation of all deposits. The
nomenclature used in the following paragraphs is therefore tentative. The field check did
however indicate that a wide variety of deposits is present. Colluvium types represented
include coarse blocky scree, blockStreams, slope wash colluvium on toe slopes, sheet-like
creep colluvium, alluvial/colluvial fans, alluvial/colluvial terraces, and deposits of slides
and flows. Several of these types of colluvium are not suited to this study and were
excluded from further consideration. Only the latter four (terraces and fans of mixed origin,

deposits of slides and flows) were examined further.

 

1 The subgroup classification for these units is: Typic Haplumbrept for Cullasaja, Spivey, Santeetlah, and '
Tuckasegee, Humic Hapludult for Saunook, Aquic Hapludult for Whiteside and Humic Haplaquepts for
Sylva. .

42
Some of the deposits had to be excluded from further study because they had been

modified extensively by human intervention and by natural erosion. In some cases the
topography was clearly erosional and prevented the implementation of a meaningful
sampling scheme. Other potential sites had to be rejected because of landuse (i.e. lawns) or
the presence of structures (i.e. homes).

A majority of the terraces of colluvial/alluvial origin had a high degree of
weathering, as evidenced by their reddish color and the brittle nature of quartzite clasts.
These deposits are exposed mainly along highway 441 south of Franklin, close to the Little
Tennessee River and in the lower part of major tributary valleys. In most cases very little of
the terrace is left and the remaining material only represents the outermost part of the terrace
where it rests on saprolite.

Most of the fan-shaped deposits are isolated in separate drainage basins. They occur
throughout the Little Tennessee River basin. Few valleys contain more than two or three
fans. Their sediments are very gravelly and do not show clear evidence for a polygenetic
origin. Correlation of their characteristics seemed difficult.

Flow deposits were observed in low order stream valleys. Some occupied the steep
(>20 %) valley floors of lst order streams but a majority occur in 2nd and 3rd order
valleys. Their surfaces display an irregular topography and are characterized by the
presence of large boulders that often are more than a meter in diameter. In some wide
valleys, usually at elevations around or above 1000 m, extensive areas with a lobate

topography occur.
3.3.2 Selection criteria

Of all the potential debris flow study sites that had been visited, the 10 best sites

met the following criteria:

43
- potential to encounter a sequence of deposits in the same local area,

- perceived likelihood that the deposits were produced by a debris flow like event,

0 absence of accelerated surficial erosion as evidenced by the microtopography and
completeness of the soil profiles,

0 differences in degree of soil development on the deposits of a sequence,

- uniformity of the local bedrock,

° accessibility of the site to a backhoe

This selection procedure resulted in a list of potential sites that spanned the basin of
the Little Tennessee River. All sites had a steplike topography with two or three lobate
deposits. Some sites had an additional fan shaped deposit in the lowest position of the
sequence. Although surficial erosion was probably not absent from any of the sites, it was
judged to be acceptable because of the absence of extensive gullying or slumping and
because of the completeness of soil profiles. The local lithology was uniform in all cases
and usually was comprised of quartz-rich gneiss and metasandstone. Slopes at two of the
sites were steep (>30 %) and obviously near the limit of accessibility.

The 10 sites were then revisited and ranked, based on a reevaluation of the above
six criteria. Subsequently, the landowners of the sites were contacted, starting from the top
of the list. The three highest ranked sites for which permission was obtained became the
subject of this research.

To obtain an accurate representation of the topography of the three sites, they were
surveyed with a total station. At each site, a reference point with X, Y, Z coordinates of
(0,0,0) was established arbitrarily. The deposits and the lower part of the surrounding
slopes were then surveyed on a 20 m grid. At sharp changes in slope a finer grid
(approximately 10 m) was used. Because all deposits of a site were not completely visible
from the original reference point the total station had to be moved to secondary reference

points. To control for inaccuracies in instrument set up, an already surveyed grid node and

44
the previous instrument position were surveyed again from each new instrument position.

The measurements were automatically stored in an electronic field book and subsequently
downloaded to a PC for processing. The contour maps, cross sections and longitudinal

profiles referred to in section 3.3.3 are based on this survey.

3.3.3 Site location and description

3.3.3.1 Alarka site

The Alarka site is located in East Alarka, 5 km south of Bryson City (Figure 6).
The deposits occupy the valley floor of the Little Alarka Creek, about 1.7 km NW of its
confluence with Alarka Creek. At the study site the Little Alarka Creek is a small third order
stream. Its drainage area above the site is 1.7 km2 and has a circular shape (Figure 7). The
valley bottom is at "755 m amsl, more than 300 m lower than the tops of the surrounding
mountains. The average slope of the valley walls is about 35 %. The lithology of the
adjacent mountain sides is relatively uniform. The rocks belong to the Upper Precambrian
Great Smoky Group (Hadley and Nelson, 1971) and comprise feldspathic metasandstone,
gneiss and interbeds of quartz-mica schist. No soil survey for the area is available but
general field observations on lower slope positions indicate that those soils developed in
boulder rich colluvium of metamorphic rocks.

The valley floor has a well pronounced hummocky topography. A number of lobate
rrricrolandforms cover the valley floor over its entire width. They extend along the valley
axis over a distance of approximately 500 m and probably reflect the deposits of individual
debris flow events. The lobate topography is best expressed in the middle of the colluvial
stretch. That central part, 275 m long and 150 m wide, is the focus of the study. To the eye
it appears that there are three deposits. They can be observed between +2 and -4 m, 2 and
12 m and 9 and 18 m, respectively on Figure 8. The deposits are approximately 50 m wide

at their base and slightly longer than 60 m. Along their long axis they have an average slope

45

 

 

 

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48
of about 16 %, with short reaches that are slightly steeper and which presumably represent

the fronts of the different deposits (Appendix 2). The deposits have a relative height of
about 3 m and, in cross section, present a convex shape (Figure 9). The valley has only
one major drainage channel, the Little Alarka Creek, which flows at the side of the
deposits. This imparts an asymmetric cross section to the lower part of the valley (Figure

9). The soils on the deposits are mostly Eutric Dystrochrepts (see section 6.3).

3.3.3.2 Hidden Valley site

This site is located in the town of Bumingtown, 8 km NW from Franklin, in an
area known locally as Hidden Valley (Figure 6). The valley is part of the headwaters of the
Iotla Branch of Iotla Creek. It has a wide, flat floodplain and contains two unnamed,
second order streams that drain 0.5 km2. The floodplain is at an elevation of 640 m amsl,
the crests of the surrounding ridges are at approximately 900 m. The slopes have a gradient
of between 24 % and 38 %. The rocks in Hidden valley are of Middle and Upper
Precambrian age (Hadley and Nelson, 1971) and consist mainly of biotite schist and
gneiss. The northernmost crests of the surrounding ridges contain migmatitic gneisses, in
addition to the above two rock types. Some of the gneiss is very quartz-rich and
approximates quartzite. In the saprolite, highly weathered, well-drained soils have
developed. In most parts the soils are very deep but on the steepest gradients and on slope
breaks only moderately deep soils exist. In undisturbed settings a 20-25 cm thick A horizon
overlays a reddish Bt horizon. Below the Bt horizon the amount of coarse fragments
increases with depth and gradually becomes a Cr horizon (Thomas, in press).

Between the two streams of Hidden Valley there are three clearly separated
topographic levels (Figure 10). The levels are separated by short steep slopes between 14
and 24 m, and 36 and 44 m. The lowest level coincides with the floodplain and is about
200 m wide (Figure 11). The middle bench is about 75 m wide and has a sharp contact
with the floodplain. Its front is steep (i 40 %) and about 10 m high. The top of the second

49

 

 

 

 

 

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52
bench is relatively flat (10 %) and gradually slopes up toward the front of the highest level.

The highest level has a relatively steep front (i 30 %) about 10 m high, but its top is nearly
horizontal in some parts. It grades into the mountain side with a well defined break of
slope. The sequence of the three topographic levels is 540 m long and covers a total
difference in elevation of 80 m.

The soils on the floodplain are mapped as very deep, well-drained Hurrric
Hapludults (Thomas, in press). The soils that were excavated for this study are Typic
Hapludults (see section 6.3). Pedologically the two highest levels are not distinguishable
from the hillsides (Thomas, in press) and their soils can be categorized as Typic

Hapludults.

3.3.3.3 Bradley Site

The Bradley site is located in the Oak Grove community, 12 km NW of Franklin,
just off state highway 28 (Figure 6). It is 7 km north of the Hidden Valley site and
approximately halfway between the Alarka and Hidden Valley sites. The deposits occur in a
small, unnamed, tributary valley of Bradley Creek. Further north other tributaries of
Bradley Creek have produced various small alluvial/colluvial fans. The unnamed valley
studied holds two second order streams that drain 0.2 km2 (Figure 7). The basin has a
relative relief of 350 m, between 650 m and 1000 m amsl, and slopes with an average
gradient of 36 %. This site has a more elongated shape than the basins of the two other
sites (Figure 7). The basin is crossed by the Hayesville fault which separates the Great
Smoky Group from Middle Precambrian rocks (Hadley and Nelson, 1971). Gneisses,
usually rich in quartz, dominate the lithology, but quartzites, metasandstone and migmatites
are also present. The soils on the slopes are very similar to those at Hidden Valley, being
well-drained and moderately to very deep. Their profiles usually are characterized by
reddish horizons and by coarse fragments that, with depth, gradually grade into a Cr

horizon.

53
This site is also similar to Hidden Valley in that two creeks border the colluvial

deposits. In their middle reaches the creeks are deeply incised in separate V-shaped ravines.
Near their confluence with Bradley Creek the ravines unite and become one wide valley
with a relatively smooth valley floor. The creeks occupy the two sides of the valley floor,
rather than an intermediate position, and are barely incised at all at this point (Figure 12).
Distinct deposits or topographic levels are not as readily identifiable here as at the two other
sites. Only slight topographic undulations, l to 2 m in height, hint at the possible presence
of different deposits (Appendix 2). The colluvial material on the valley floor has a drawn
out shape and is 330 m long and 150 m wide. At the confluence with Bradley Creek the
deposit is no longer confined by valley walls and becomes fan shaped (Figure 13). The
slope of the valley floor increases from about 12 % to more than 20 % on the fan-like front.
As in Hidden Valley, the soils of the deposits are mapped as well-drained Humic
Hapludults (Thomas, in press). The present research shows that they are Typic and Umbric

Dystrochrepts.

54

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PART II: CHARACTERIZATION OF SEDIMENTS AND SOILS

56

57
4 INTRODUCTION

The sedimentology of debris flow deposits has been studied extensively (Shultz,
1984; Rust and Koster, 1984; Wells, 1984; Wells and Harvey, 1987; Walton and Palmer,
1988; Ono, 1990; Whipple and Dunne, 1992). Many studies of debris flows have been
carried out in the Appalachians (Williams and Guy, 1973; Mills, 1983; 1988; Kochel and
Johnson, 1984; Pomeroy, 1986; Kochel, 1987; 1990; Whittecar and Ryter, 1992). The
knowledge acquired in these studies will be applied in this part to examine if deposits at the
three sites may have formed by debris flow activity. The characterization of the sediments
will also provide a better comprehension of the nature of the parent material in which the
soils have developed. Relatively little information is available about the strength and
variability of the fabric of debris flow deposits (Lawson,l979; Mills, 1984; Innes, 1984;
Mills, 1988). This part will, therefore, not only use existing information but may also
provide new data on the sedimentology, i.e. fabric, of debris flows. This kind of data may
be important to better understand the origin, and possibly the mitigation, of debris flows.

Few studies have been conducted on the soils of the Southern Appalachians
(Norfleet and Smith, 1989). Recent papers include those by Daniels et al. (1987a; b),
Norfleet and Smith (1989), Graham et al. (1989a; b; 1990), Graham and Buol (1990) and
Feldman et al. (1991a; b). Although most of these studies involved some aspect of colluvial
soils, none of them explicitly dealt with the pedogenetic imprinting on debris flow deposits.
Chapter 6 will generate characterization data for soils that have developed on debris flow
deposits and will relate them to the origin of the parent material. In later chapters these
characterization data will be compared with relative-age estimates for the deposits.

To maintain consistency throughout the text, "coarse fragments" will be used to
designate particles >2 nun. It is equivalent to the sedimentological term " gravel". In

accordance with Soil Survey Division Staff (1993) guidelines, "gravel" was reserved in

58
this research for equiaxial particles of between 2 and 75 mm. "Fine gravel" refers to

particles of between 2 and 8 mm.

59
5 SEDIMENT S

5.1 Literamre review

5.1.1 Sorting

By definition, debris flows consist of a mixture of clasts and a matrix material. The
clasts present in debris flows typically are angular to sub-angular (Williams and Guy,
1973; Nemec and Steel, 1984; Wells and Harvey, 1987). Most studies describe debris flow
deposits as a diamict in which both the matrix and the clasts are poorly sorted (Innes, 1983;
Kochel and Johnson, 1984; Rust and Koster, 1984; Wells, 1984; Pomeroy, 1986; Wells
and Harvey, 1987; Walton and Palmer, 1988; Kochel, 1990; Ono, 1990; Whipple and
Dunne, 1992). Wells and Harvey (1987) studied viscous and fluid flows but did not find a
difference in sorting or mean particle size of the matrix or the clasts. Average sorting
coefficients reported in the literature range from 3.6 to 12.3. Maximum clast size can range
to more than 8 m (Walton and Palmer, 1988; Shultz, 1984). No textural variation was
found in the downslope direction by Williams and Guy (1973), probably because the
deposits were too short (<1 km) for sorting to occur. Other Appalachian debris flow
deposits also show very little change in their sediments from proximal to distal reaches
although they are generally thicker and coarser at the apex (Pomeroy, 1986; Kochel, 1990)
The lack of change can be explained because many debris flows retain their competence
throughout their travel (Kochel, 1990).

Mills (1988) studied various sedimentological parameters of colluvium in the Valley
and Ridge province of Virginia but did not distinguish between debris flow deposits and
other types of colluvium. His general comments suggested that the colluvium he studied

was poorly sorted. The clasts in the colluvium were more angular (2.65 on the visual

60
comparison chart of Krumbein, 1941) and changed less in angularity with distance from

the source than pebbles that had traveled a comparable distance in nearby creeks.

5.1.2 Bed geometry

Beds in debris flow deposits are usually described as tabular or sheet-like (Bull,
1972; Rust and Koster, 1984; Shultz, 1984; Wells, 1984). Nemec and Steel (1984) noted
that beds showed limited basal erosion but often had a highly lenticular overall geometry.
Other authors also recorded that beds of debris flow origin have non-erosional, though
sometimes clear, boundaries (Gloppen and Steel, 1981; Costa ,1984; Nemec and Steel,

1984; Wells, 1984; Velbel, 1987; Kochel, 1990).

5.1.3 Stratification

Beds in debris flow deposits usually show no obvious stratification (Nemec and
Steel, 1984; Rust and Koster, 1984; Smith, 1986; Wells and Harvey, 1987; Mills, 1988;
Kochel, 1990). Some debris flow deposits have a crude layering resulting from an upward-
coarsening sequence (Wells and Harvey, 1987). A succession of deposits may exhibit
pronounced bedded due to distinct bed boundaries (Nemec and Steel, 1984). A tendency
for channeling and some faint stratification were associated with dilute flows by Nemec and

Steel (1984) but Wells and Harvey (1987) did not find stratification in fluid flow deposits.

5.1.4 Grading

Grading in debris flow deposits has been found to be absent (Nemec and Steel,
1984; Shultz, 1984; Smith, 1986; Walton and Palmer, 1988), inverse (Williams and Guy,
1973; Rust and Koster, 1984; Kochel and Johnson, 1984; Walton and Palmer, 1988;

61
Kochel, 1990; Ono, 1990), normal (Nemec and Steel, 1984; Shultz, 1984; Walton and

Palmer, 1988) and reverse-to—normal (Rust and Koster, 1984; Smith, 1986). Nemec and
Steel (1984) called upon turbulence to explain normal grading but it is usually thought to be
the result of differential settling of the clasts in a low yield strength material (Scott, 1986;
Smith, 1986) that moves as a pseudoplastic flow (Shultz, 1984). Inverse grading has been
interpreted as being the result of dispersive pressure (Nemec and Steel, 1984; Walton and
Palmer, 1988). The dispersive pressure develops from shearing, usually near the bottom of
the flow and is restricted to deposits with low original clay content (Smith, 1986). The
grading of the basal few cm of a deposit can change downslope from ungraded to inversely
graded (Nemec and Steel, 1984). This can be related to a change in the flow regime, i.e.
development of shear, downstream (Shultz, 1984).

Bipartite layered beds with the coarser one near the bottom of the deposit may
originate from the settling of coarse material during the deposition of a fully turbulent flow.
A stratified sandy capping with an erosional base or a stratified Clast-rich cap with a sharp

lower contact can represent interflow fluvial activity (Nemec and Steel, 1984).
5.1.5 Conglomerate framework

Rust and Koster (1984) stated that matrix supported diarrricts in which the matrix
consists of unstratified muddy sand, mainly form by debris flow deposition. Matrix
supported diarrricts of debris flow origin were also observed by Gloppen and Steel (1981),
Shultz (1984), Watson and Palmer (1984), Wells (1984), Whipple and Dunne (1992) and
Whittecar and Ryter (1992). Clast supported facies are often produced by fluvial processes
(Miall, 1977; Rust and Koster, 1984; Smith, 1986; Kochel, 1990) but have been observed
in debris flows as well (Gloppen and Steel, 1981; Nemec and Steel, 1984; Shultz, 1984;
Wells, 1984; Walton and Palmer, 1988). Wells and Harvey (1987) distinguished two types

of debris flow, viscous and fluid. In the viscous debris flow deposits they noted a

62
predominance of matrix-supported clasts, except in pressure ridge areas. The pressure

ridges probably represent pulses or surges commonly observed in debris flows. The fluid
flow deposits were characterized by a mud-rich matrix, supporting the clasts.

Fan deposits studied by Kochel (1990) in central Virginia were matrix supported
while others from western Virginia were clast supported. The author argues that the
difference depends upon the amount of water that was involved in the flows that produced
the fans. Flows in central Virginia were associated with less runoff because they formed in
basins that were smaller and of a lower order than-those in western Virginia (Kochel,

1990). Consequently, they might have been flows with low amounts of water.

5.1.6 Fabric shape

Debris flow deposits often present an isotropic fabric (Lawson, 1979; Innes, 1983;
Nemec and Steel, 1984; Wells, 1984; Wells and Harvey, 1984). The disorganized Clast
fabric may reflect short travel distance but often suggests plug flow or weakly sheared,
high viscosity flow (Nemec and Steel, 1984) or, according to Lindsay (1968) and Owens
(1973), turbulent flow. When there is a preferred clast orientation, the clast long (a-) axis is
often subhorizontal and parallel to the flow direction (Nemec and Steel, 1984; Wells, 1984;
Mills, 1988; Kochel, 1990). This fabric may originate from strongly sheared laminar flow,
most likely due to clast interactions and dispersive pressure (Lindsay, 1968; Nemec and
Steel, 1984).

Traverse alignment of clasts can be expected to develop from more fluidal flows
(Mills, 1984; Nemec and Steel, 1984; Smith, 1986; Kohlbeck et al., 1994) but Wells and
Harvey (1987) did not find any preferred clast fabric in fluid flows. The latter authors did
observe, however, that the long axes of clasts were typically oriented perpendicular to the

flow direction in streamflow deposits. Shultz (1984) found a-axis orientations to be

63
clustered in two modes, parallel and perpendicular to the flow direction. It is not clear

whether the samples came from viscous, fluid or both types of debris flow deposits.

The viscosity of the flow also influences the dip of the a-axis. More fluid debris
flows show subhorizontal orientation of clasts (Rust and Koster, 1984) whereas more
viscous flows tend to have larger clasts in predominantly vertical orientations (Bull, 1963;
Lawson, 1979; Nemec and Steel, 1984; Rust and Koster, 1984). The vertical orientation
can only develop in matrix supported units that are viscous enough to support the upright
position of the clasts (Bull, 1963; Reineck and Singh, 1986) or in clast supported units
(Lawson, 1979). An alternative, but less likely, explanation offered by Lawson (1979) is
that the vertical positions develop prior to flow and are preserved within parts of the flow
that do not undergo shear.

Most authors found a weak imbrication in debris flows, but found various
directions of imbrication. Nemec and Steel (1984) state that clast upflow imbrication of the
a- or b—axis is common in debris flow deposits. It is not clear whether they are referring to
subaerial or subaqueous flows. Lahar deposits, especially matrix supported facies, also
showed an upslope dip (Mills, 1984). The debris slope deposits studied by Williams and
Guy (1973) and Kochel and Johnson (1984) exhibited poorly developed imbrication of the
coarse clasts in the downslope direction. Yeend (1969) recorded an apparent downslope
preferred orientation in two debris flow lobes. In one of these a secondary mode dipping
upslope was identified. In small glacial debris flows, slightly more than half of the sampled
sites had an upslope dip, and consequently, less than half had a downslope dip (Lawson,
1979). All of these sites were characterized by a very gentle dip of the a-axis of the clasts.

In measurements of clast orientations in debris flow levees, Innes (1983) noted a
preferred upslope orientation of the clasts that was intermediate between the flow direction
and the local slope of the levee surface. The author speculated that the orientation was the
result of an initial orientation parallel to the flow and a subsequent settling parallel to the

direction of maximum slope. Mills (1988) noted that in the colluvium he studied, preferred

64
dip angles tended to be lower than the slope angle. However, the fabrics generally had an

upslope imbrication with respect to the surface. In the debris flow pressure ridges which
Williams and Harvey (1987) observed, clasts were oriented with their a-b planes dipping

away from lobate boundaries and into the deposit.

5.1.7 Fabric strength

Study of the orientation of clasts in different types of debris flows is critical to the
evaluation of the classification of debris flows (Schultz, 1984). Nevertheless, very few
studies on the fabric strength of debris flow deposits have been carried out and quantitative
studies are almost completely lacking.

Lawson (1979) studied debris flows that formed at the temrinus of a glacier. Visual
observation of contoured Schmidt nets led him to conclude that in general the strength of
the fabric in these deposits is weak but that the strength increases with increasing water
content. According to Lawson (1979), shear, and thus clast alignment, occur only in a thin
basal zone when the flow is relatively dry but as water content of the flow increases the
shear zone thickness and clast alignment increase. Mills (1984) studied lahar facies in
Mount St. Helens debris flows and examined clast supported and matrix supported units
separately. The first and third eigenvalue was larger for the matrix supported units than for
the clast supported units (Table 1). This means that although the matrix supported units
have a somewhat stronger tendency to cluster around the mean direction, the fabric strength
of the two facies is comparable. Their strength is also comparable to that of the small,
glacial debris flows studied by Lawson (1979).

In creep colluvium the a-axis of clasts was also parallel to the slope and imbricated
upslope (Mills, 1983). In that environment the fabric strength was directly related to the
gradient of the slope. Elevation, aspect, and soil texture appeared to have little effect on

fabric strength (Mills, 1983). The strength of the fabric varied between different local

65
environments (Mills, 1988). The conclusions of Mills (1983) and Innes (1984) imply that

fabric is not only a reflection of the genesis of the sediments, but also of local slope

gradient and direction.

Table 1: Clast fabric data for debris flow-like deposits.

 

 

 

 

 

 

 

 

 

 

Author Deposit Deviation of mean a—axis S 1* 83* H
from direction of flow

Mills St. Helens lahar 50° 0.564 0.140 ll
( 1984) (all samples)

Mills St. Helens lahar 65° 0.555 0.133 ll
(1984) (clast supported)

Mills St. Helens lahar 37° 0.572 0.147
(1984) (matrix supported)
Lawson Glacial debris flow 28° 0.567 0.128
(1979)

 

 

* S1=first eigenvalue, S3=third eigenvalue, see section 5.2.2 for explanation

5.2 Methods

5.2.1 .Data collection

As mentioned in section 3.3 (site selection), a number of possible deposits were
identified at each of the three sites. Because different microsites on colluvial deposits often
possess different pedologic characteristics (Daniels et al., 1987; Graham et al., 1990) an
attempt was made to open two backhoe pits on each deposit, one on the apex and one on
the foot. To create optimal conditions to study lateral variations in sedimentary facies the
pits were dug with their longest side (3 to 5 m) perpendicular to the central axis of the

deposits. Pits were excavated to a depth of approximately 2 m.

66
The soil pits, and the pedons described in them, were assigned a three letter code

(Table 2). The first letter stands for the site (A - Alarka, H - Hidden Valley, B - Bradley),
the second letter stands for the position of the deposit in the sequence of each site (L -
lower, M — middle (if more than 2 deposits), U - upper), and the third letter represents the
position of the soil pit on the deposit (f - foot, a - apex). Because no soil pit could be
opened on the apex of the lowest deposit in Alarka, a pit on the foot of another low deposit
was opened. To distinguish between these two localities, a fourth digit ("1 " or "2") was

added to the code of the pedons on the lower Alarka deposits.

Table 2: Geomorphic position of soil pits.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Site/Soil pit Deposit Slope Slope Aspect Depth of soil
number position % pit, cm
Alarka
ALfl 1 foot 15 W 187
ALf2 2 foot ’ 16 w 193 ‘
AUf 3 foot 16 W 195
AUa 3 apex 16 W 213
Hidden
Valley
HLf 1 foot 5 SE 200
HLa 1 apex 11 SE 187
HMf 2 foot 15 S 223
HMa 2 apex 15 S 248
HUf 3 foot 13 S 227
HUa 3 apex 23 S 211
Bradley
BLf 1 foot 12 W 125
BLa 1 apex 16 SW 187
BUa 2 apex 19 W 208

 

 

 

 

 

 

67

At each location sediments were described according to guidelines reported in Miall

(1977; 1978; 1985), Schultz (1984) and Eyles et al. (1983). Properties recorded include

nature of bounding surfaces, internal geometry, external geometry, and scale of beds. With

regard to internal geometry, special attention was paid to grading, sorting and framework

support. To characterize clast properties, 50 clasts (a-axis 2 2 cm) were selected at random

and their size (length of a-axis), sphericity, roundness, lithology and relative weathering

determined (Table 3).

Table 3: Soil horizons sam led for clast characterization and fabric.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizons sampled for clast Horizons sampled for clast
characterization * fabric *
ALf 1 all all
ALf2 all all
AUf all all
AUa all all
HLf 2Cg none u
HMf Btl, Bt2 none
HUf 2Bt2 2Bt2, 3Bt3
3Bt3 none
HUa all none
BLf 2Cg2 none
BLa 2Bw2 4Bw4
4Bw4 none
BUa 3Bw3 5Bw5
5Bw5 none

* For corresponding sedimentary units, see Figures 19 and 20

Sphericity and roundness of the clasts were estimated by visual comparison with a chart

from Powers (1982). For 30 other elongated clasts the azimuth and plunge of the long (a-)

68
axis and the dip and strike of the a-b plane were determined (Table 3). This field procedure

consisted of carefully excavating clasts with an estimated a-b axial ratio greater than two,
and measuring the dip and strike of the a-b plane. The clasts were then removed, an
aluminum rod was inserted in the position of the long axis and the orientation of the rod

determined with a Brunton compass.
5.2.2 Data analysis

The coefficient of sorting for the matrix (grains < 2 mm) of the sediments was
calculated with the formula So=\/Q3/Q1 in which Q1 and Q3 are the first and third quartile
of the cumulative particle size distribution. The quartiles were graphically determined from
graphs of the particle size data from soil horizons. Sorting is therefore reported for soil
horizons rather than sedimentary units (Appendix 2).

Facies codes are based on Miall (1977; 1978), Eyles et al. (1983) and Shultz
(1984). The codes consist of two to three letters. The system of Eyles et al. (1983) was
specifically designed for diamicts and uses a "D" as the first letter of the code. The second
letter, "m" or "c", identifies either matrix support or clast support. The third letter refers to
internal structure and separates massive unstructured organization (m) from stratified (s)
and graded (g) units. Shultz (1984) used "g" for normally graded units and added "i" to
represent reverse grading. The system of Miall (1977; 1978) was designed for use in
fluvial environments. His code consists of two parts. The first part is a capital letter G, S or
F, which represent diarrrict, sand and fines respectively. The second part describes the most
characteristic internal feature of the lithofacies. The only code of Miall used in this study is
F1, which stands for fines (sand, silt, clay) that are laminated.

The orientations of the a-axis and the poles of the a-b planes were plotted on
Schmidt nets with an equal area, lower hemisphere projection. To allow for comparisons

between samples, the local slope was also plotted (Appendix 4, 5). Clasts that were

69
oriented traversely to the axis of the deposit (and presumably traversely to the direction of

flow) were defined as those that had a long axis azimuth that was within any of two 45°
sectors centered on the orthogonal on the axis of the deposit.

Although quantitative methods to describe particle orientations have existed for a
long time, relatively little effort has been invested in statistical analysis of fabric. For this
study, the fabric of the diamict layers was analyzed with the eigenvalue method developed
by Mark (1973) and Woodcock (1977). Successful applications of this method have been
achieved for solifluction lobes (Nelson, 1985), till (Lawson, 1979; May et al., 1980),
creep (Mills, 1983b) and debris flows (Mills, 1984). Woodcock (1977) contended that the
use of eigenvalue plots may reveal fabric shape variation, possibly with genetic
significance. Mills (1984) suggested that Clast fabric may be a useful property for the
characterization of debris flow sedimentology, and that its measurement should be included
in future studies. Lawson (1979) and Nelson (1985), however, cautioned that additional
information beyond that of clast fabric is needed to positively identify the origin of a
deposit.

The eigenvalue method is based on the principle that eigenvectors represent the
common variance in a data set and that all directional data can be completely described with
respect to three orthogonal axes. Since eigenvectors are perpendicular to each other, three
eigenvectors will completely describe the common variance in a directional data set. The
first eigenvector may be considered as the direction around which the data are most
concentrated. Conversely, the third eigenvector is associated with the direction that least
coincides with the directional communality of the data. It is orthogonal to the best plane
through the data. The second eigenvector is normal to eigenvectors 1 and 3.

The first eigenvalue is a measure for the common variance in the data. If eigenvalue
1 (81) is high, the data are highly clustered. The third eigenvalue (S3) describes the
remaining variance that can not be described by eigenvalues 1 (S l) and 2 (S2) and thus is a

measure of scatter. The eigenvalues reported in this study are standardized eigenvalues,

70
also called significance values, that range from 0 to 1. More important than the magnitude

of the eigenvalues, however, are their ratios which represent fabric strength (Figure 14).
The ratio of S 1/S2 represents the goodness of fit of the data distribution to a uniaxial
bundle while S2/S3 represents how well the data conform to a uniaxial girdle. The ratio K
(K=(S1/82)/(S2/S3)) represents the fabric shape. Distributions with K=1 have equal girdle
and cluster tendencies. Low values for K (K<1) define girdles, higher values define
clusters (Figure 14).

The deviation of the azimuths of the mean a-axis from the direction of the slope of
the surface is reported in absolute and relative values. The absolute deviation is the
mathematical subtraction of the azimuth of the mean a-axis from the azimuth of the slope.
The supplement of the absolute deviation is provided as the relative deviation when the
absolute deviation is more than 90°. The relative deviation is provided because the absolute
deviation turned out to be large in most cases and large angles are harder to visualize than
small angles. Moreover, there is no need for the absolute deviation because the direction of
the orientations is shown by the plunge. The deviation from the general orientation rather

than from the direction of the slope also furnishes additional information.

5.3 Results

5.3.1 Sediment description

5.3.1.1 General

The boundaries between sedimentary units, as determined in the field, were rarely
clearly distinguishable. This was at least in part due to the pedogenic alteration of the
deposits, but may also reflect gradual boundaries between the units. Virtually all
sedimentary units were classified as diamicts. They appeared to have a tabular geometry
that blankets the deposits. This finding may be an artifact of the small size of the soil pits

which did not allow the lateral extension of the sediments to be verified. No natural

 

 

Fabric shape and strength as a function of 81/82 and 82/83

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72
exposures were available to substantiate the tabular geometry. The bottom of the deposits

was not encountered in any of the pits. Therefore, the sediments must have a thickness of 2
2 m in most cases.

Interpretative sketches of lithofacies units are provided for the Hidden Valley and
Bradley sites but not for the Alarka site, because no sedimentary boundaries were observed

at the latter.

5.3.1.2 Alarka site.

The sediments at the Alarka site are very poorly sorted (Appendix 4). Some contain
more than 50 % coarse fragments (Table 4). In all four Alarka soil pits, the amount of
coarse fragments decreases near the surface (Figure 15). This is, at least in part, due to
human influence. The area near the Alarka site has been farmed extensively and large rocks
near the surface have been systematically removed by the farmer. They were used to build a
rock wall around one of the fields. It is virtually impossible to verify directly if the trend is
also a natural one because most debris flow deposits in the area have been farmed, since
they constitute the most level part of the landscape. However, in ALfl and ALf2 the fine
gravel and sand fractions follow the same general trend as the coarse fragments (Figures
16, 17). Although increasing amounts of sand with depth may be due to decreasing
weathering intensity with depth, the accordance of the trends of the three different fractions
suggests that the trend is also in part natural because fine gravel and sand were not removed
by the farmer. Consequently, the sediments at these two locations are normally graded.
Their lithofacies code is therefore coded Dmg.

Pedons AUf and AUa are located on a higher deposit. The fine gravel and sand
fractions of these two pedons do not have a uniform trend with depth (Figure 16, 17). This
indicates that the trend of the coarse fragments at AUf and AUa is mainly artificial. The

lithofacies of the sediments at these two soil pits is therefore coded Dmm.

73

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Apart from the grading in ALfl and ALf2, the sediments show no internal

structure. The deposits at Alarka have a matrix supported fabric, in spite of the very high
amount of coarse fragments. The coarse fragments are poorly sorted and contain pebbles,
cobbles and boulders. The maximum clast size (a-axis) observed at the Alarka locations
was more than one meter and the average clast size is about 13 cm (Table 5). The coarse
fragments have a variety of shapes but a relatively large percentage (about 50 %) have disk
or sub-disk shapes (Table 6). This dominance of flattened fragments probably relates to the
metamorphic nature of the bedrock (Table 7). The foliation and fissility planes are loci of
weakness which predispose the rocks to break up into diskoid fragments. Most of the

coarse fragments (>70 %) are sub-angular or sub-rounded (Figure 18).

5.3.1.3 Hidden Valley site.

As compared to the Alarka site, coarse fragments at the Hidden Valley site are less
abundant and smaller (Tables 4 and 5). The average size is 6 to 8 cm and the maximum
clast size sampled was in the cobble grade. Most clasts are sub-angular or sub—rounded;
there are slightly more angular than rounded clasts (Figure 19). All Sphericity classes are
represented (Table 6). The sediments of the Hidden Valley site are poorly sorted and matrix
supported. The clasts are widely dispersed in the matrix and no grading was discernible.

The lowest pit (HLf) is the only one at this site that shows clear stratification
(Figure 19). It contains a 25 cm thick, clast supported, diamict. The coarse fragments“ in the
diamict consist of about 80 % pebbles and 10 % cobbles (Dcm). The sand fraction of this
unit has a grainsize distribution that is clearly different from that of the over and underlying
units (Appendix 3). The overlying unit also has a Dmm facies but has a very low
concentration of coarse fragments.

Sediments at HLa and HUa consist of a material that is similar to the topmost unit
of HLf (33% coarse fragments) but has a finer matrix (Dmm). Soil pit HUf has a zone rich

in coarse fragments at 72 to 183 cm that coincides with soil horizons ZBtZ and 3Bt3

Table 5: Clast sizes, all sites

83

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

  

 

  

 

 

 

 

Soil pit Average a-axis Maximum
cm observed, cm
15 105
13 1 15
AUf 14 140
E AUa 11 110
HLf unit 2 6 2]
HLa 6 10
HMf 6 16
HUf unit 2 7 17
(upper part)
HUf unit 2 6 16
(lower part)
HUa 8 21
BLf 10 95 It
BLa unit 3 95
BLa unit 1 105 II
BUa unit 3 120 ll
BUa unit 1 11 125

   

   

Table 6: Clast s hericities, all sites

84

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

* For definition see section 5.2.1

 

 

 

 

 

 

Soil pit Disk* Sub-disk* Spherical* Sub-prism* Prism*
% % % % %
AU] 29 21 13 13 23 ll
ALf2 31 18 16 12 22
AUf 24 38 14 10 14 II
AUa 24 29 10 20 16 “
HLf unit 2 14 25 24 17 20 II
HMf 14 18 37 25 6 ll
HUf unit 2 34 20 23 11 1 1 ll
(upper part)
HUf unit 2 16 22 18 34 10 fl
(lower part)
HUa 17 33 31 14 4
BLf 53 22 8 10
BLa unit 3 53 16 6 18 8
BLa unit 1 39 22 18 18 4
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(Figure 20). The coarse fragments consist mainly of pebbles and cobbles while relatively

few boulders are present. At the bottom of horizon 2Bt2 the coarse fragments are
dominated by pebbles. The most appropriate facies code is Dmm.

In Hle and HMa there is a gradual transition from highly weathered material at the
top of the profile to saprolite, and (locally) hard rock, at the bottom of the pit. The saprolite
consists of relatively fresh, brownish yellow gneiss in which the shape of crystals is still
recognizable, and reddish, highly weathered, clay rich seams that cross the fresher
material. Soil data presented in sections 6.3 and 6.4 confirm that the pedons at these two
locations are developed entirely in saprolite. Consequently, no colluvial sediments are
present at these locations and they will be excluded from further consideration in the

discussion of sediments.

5.3.1.4 Bradley site.

Sediments show more evidence for stratification at the Bradley site than at the other
two sites. All contacts between the various sedimentary units are planar, horizontal and lack
evidence of erosion.

As in Hidden Valley, the lowest pit (BLf) contains a diamict layer that is clearly
coarser than the overlying units (Figure 21). Unit 1 is matrix supported and poorly sorted
(Dmm). The clasts are of pebble and cobble grade and most tend to be disk or sub-disk
shaped (Tables 4 and 6). As in the other deposits that were studied, sub-rounded and sub—
angular clasts dominate over other roundness classes (Figure 18). By analogy with the Clast
poor units in Hidden Valley, unit 2 was also classified as Dmm. It contains only about 2 %
coarse fragments.

The unit at the bottom of pit BLa is >70 cm thick. It is a clast supported, poorly
sorted diamict (Dcm) (Figure 21, Table 4, Appendix 2). The clasts have predominantly a
disk and sub-disk shape and are sub rounded or sub angular (Table 6 and Figure 18). The

contact with unit 2 is horizontal and appears to be planar. That overlying layer is almost

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91
completely devoid of coarse fragments. It contains only 5 % pebbles and has a loam

texture. The sand subfractions are dominated by fine and very fine sand. The unit is 32 cm
thick and extends horizontally over the entire wall of the pit. The layer is homogeneous
without internal structure. Assuming that pedogenesis and bioturbation have destroyed
small sedimentary structures, this bed can be classified as F]. Considering that its sorting is
no better than that of the other units, it could also be classified as Dmm. The top 79 cm of
BLa consist of matrix supported coarse fragments (Dmm). Both the matrix and clasts are
poorly sorted (Appendix 4). The majority of the clasts are diskoid and have a subrounded
or sub angular shape (Table 6 and Figure 18). The lower contact is relatively sharp and
horizontal over the length of the soil pit. There is no visible internal fabric or grading.

The sediments at BUa are the most heterogeneous at the Bradley site (Figure 21).
At the bottom of soil pit BUa, a >71 cm thick matrix supported diamict was observed. Both
the matrix and clasts are poorly sorted. Several clasts in this soil pit were in an upright
position; imbrication was lacking. Most of the clasts are disk or sub-disk shaped and are
sub-rounded to sub-angular (Table 6 and Figure 18). No internal structure was discernible.
The contact with the suprajacent loam unit is horizontal and relatively clear. The 27 cm
thick loam unit is completely free of coarse fragments. The sand subfractions are dominated
by fine and very fine sand. There is no noticeable internal structure or grading and the
contact with the overlying diamict was relatively sharp, planar and horizontal. This unit is
analogous to unit 2 of BLa, but because no clasts are present it is assigned a Fl facies. The
composition of the suprajacent diamict (unit 3) ranged from a relatively high amount (i 25
%) of diskoid pebbles and cobbles near the bottom to a few small, dispersed, more
spherical, pebbles near the top (Dmg). The matrix of this unit is sandier and better sorted
than the other units in the profile. The shape of the clasts tends to be more spherical and
more rounded than in most other units (Table 6 and Figure 18). At one side of the soil pit a
small lens of massive, clast supported coarse fragments replaced this unit (Dcm).

Pedogenesis and bioturbation have masked the upper and lower contacts of the lens. Unit 4

92
is a matrix supported, reversely graded diamict (Dmi). Near the bottom of the unit the

coarse fragments consist of about 10 % pebbles but near the top there are 12 - 20 %
pebbles, cobbles and boulders. The unit is poorly sorted and does not possess any internal
structure. It is 31 cm thick and extends over the entire length of the pit. Its boundary with
the topmost unit is horizontal and appears to be planar. The top 49 cm of the profile consist
of loam sediments with 2 - 3 % disk and spherical shaped pebbles. It is poorly sorted,

homogeneous and lacks any sedimentary structures (Dmm).
5.3.2. Fabric

5.3.2.1 A-axis

Schmidt nets of clast orientations (Appendixes 5 and 6) indicate that scatter exists in
the orientation of the clast a-axes. However, the distribution is not uniform (test of
uniformity, or = 1 %) and consistent trends exist in the clast orientation.

The mean plunge of the a-axis is very gentle (< 23°) at the Alarka and Bradley sites
(Table 8). The direction of the azimuth of the a-axis at these sites is approximately opposite
to that of the slope (about 180° offset). The deviation from the opposite direction is small
(<21°) for all Alarka and Bradley pits except for AUa where it is 45° (Table 8). The
deviation is in an easterly direction, except for AUf where it is very small and to the west.
This means that, in general, there is a weak, gentle upslope imbrication of the clasts. Only a
minority (<23 % in Alarka, 10 % in Bradley) of clast long axes are oriented traversely to
the slope of the surface.

More detailed analyses of the fabric shape of the distributions (Appendix 5) reveals
that the deposits at Alarka and Bradley have two subpopulations. All samples have one
subpopulation that is concentrated around the mean a-axis. It is called hereafter "subpopl
The second subpopulation ("subpop2") is scattered in AUa, BLa and BUa but appears to
fall on a great circle in AU 1, ALf2 and AUf (Appendix 5). The absolute deviation of the

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94
azimuth of the mean a—axis of subpopl, from the azimuth of the slope, is roughly 180° but

it is consistently greater than the deViation of the mean of the whole population (Tables 9
and 10). The best fit great circle of subpop2 is oriented parallel to the slope in AU] but
occupies an intermediate orientation, with respect to the slope of the surface, in ALf2 and
AUf (Table 9). At the latter two locations the dip of the great circle is downslope.

For ALfl and ALf2 it was determined whether clast size could have affected the
orientation of the clasts, and thus to which subpopulation a clast belongs. In ALfl the
difference in average clast size for the two subpopulations was only about 3 mm (2 %) and
not statistically significant (two tailed t-test with on = 10 %). In ALf2 the difference was 1.8
cm, and although this difference was not statistically significant (two tailed t-test with or =
10 %), it does represent a difference of >11 %.

Clast orientations at the Hidden Valley site (HUf) are very different from all other
distributions. HUf does not have 2 subpopulations, and the a—axes are more concentrated
(lower spherical variance) than in any other sample (Appendix 5). The plunge of the mean
a-axis is steep (47°) and in the general direction of the slope. The plunge is larger than the
gradient of the slope and thus effectively represents a downSIOpe dip. Therefore, there is a
weak downslope imbrication at HUf. Clasts dipping upslope are conspicuously absent
(Appendix 5). The deviation from the azimuth of the surface slope is relatively large (42°)
and to the west. More clasts (27 %) were oriented traversely to the axis of the slope at this
location than at any of the other two sites.

In a relative sense, the first eigenvalue is small (O.467<S 1<O.606) and the third
eigenvalue is large (0.119<S3<O.239) for all samples (Table 8). This results in very small
values for S 1/82 and 82/83. Therefore, the fabric of the samples is very weak (Figure 22).
Sediments of AUa, and to some extent ALfl , have large K values (K>2) indicating a
clustered fabric (Table 8, Figure 22). At the Hidden Valley and Bradley sites K values are
small (K<1), which indicates that the fabric is girdle shaped. The extreme weakness of the

fabric, however, makes these shapes less meaningful.

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97
The eigenvector analysis of the two subpopulations of AMI , ALf2 and AUf

indicate that their separation on the basis of apparent fabric shape is justifiable. The fabric
of the subpopulations is stronger (S 1/S2 or S2/S3 are larger) than the fabric of the total
populations (Tables 9 and 10). The K value for subpopl is systematically higher than the K
value of the total population, indicating that subpopl is more clustered. The K value for
subpop2 is uniformly smaller than that of the whole population and thus points to a better

defined girdle for that subpopulation.

5.3.2.2 A-b plane

The orientation of the a-b planes of individual clasts is very irregular (Appendix 6).
Only in BLa can a clear girdle fabric shape be observed. The orientation of the mean a-b
plane, expressed as a best fit great circle, however, is remarkably consistent among the
various deposits (Table 10). The plunge is always nearly horizontal, the largest divergence

from the horizontal (observed in HUf) being 16°.

Emma

5.4.1 General

One of the most common features of the sediments is the predominance of diamicts.
The shape of the clasts indicates that they were transported by colluvial rather than fluvial
processes. The diamicts are interpreted as various types of debris flow deposits. The
apparent tabular geometry of the beds of this study conforms to descriptions of many
debris flow deposits (Bull, 1972; Nemec and Steel, 1984; Rust and Koster, 1984; Shultz,
1984; Wells, 1984). The weak tendency of the clast long axis to be oriented parallel to the

flow and an otherwise disorganized clast fabric are also characteristic for debris flows

98

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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99
(Lawson, 1979;1nnes, 1983; Mills, 1984; Nemec and Steel, 1984; Shultz, 1984; Wells,

1984; Wells and Harvey, 1987; Kochel, 1990).
5.4.2 Alarka site

Deposits that have a Dmm lithofacies type (Gms sensu Miall, 1977), such as AUf
and AUa, have generally been interpreted as being of debris flow origin (Williams and
Guy, 1973; Miall, 1977; 1978; Kochel and Johnson, 1984; Rust and Koster, 1984; Shultz,
1984; Kochel, 1990). Lack of stratification, characteristic of the Alarka site, is often
mentioned as a typical feature of debris flow deposits (Nemec and Steel, 1984; Rust and
Koster, 1984; Kochel, 1990). It implies that the flows at ALfl and ALf2 arrived in one
surge and not as a succession of pulses. Disorganized clast fabric has been noted in highly
viscous flows (Nemec and Steel, 1984) and in fluid debris flows (Wells and Harvey,
1987). The lack of many traversely oriented clasts (Nemec and Steel, 1984) and the
presence of large matrix supported clasts (Shultz, 1984) supports a plastic, viscous flow
origin for the deposits of AUf and AUa. The upslope imbrication observed in a
subpopulation of clasts in Alarka also is not uncommon for debris flows (Nemec and Steel,
1984).

Normally graded diamicts, such as those of AU] and ALf2, have also been
attributed to debris flow activity (Nemec and Steel, 1984; Shultz, 1984; Walton and
Palmer, 1988). Shultz (1984) found that beds with a Dmg facies are thinner, finer grained
and better organized than Dmm beds. In this study there was no difference in organization
or grain size of the Dmg and Dmm facies. Because the bottom of the deposits was not
reached, no conclusion can be drawn about a difference in thickness. The deposits are,
however, at least twice as thick (>2 m vs. <1 m) as those studied by Shultz (1984). This
suggests that the yield strength of the flows was low enough to allow settling of the clasts

but it must have been sufficiently high to sustain the deposition of a thick deposit.

100

5.4.3 Hidden Valley site

Most sediments at this site have a Dmm facies. As explained above, Dmm facies
with disorganized fabric are generally attributed to plastic, viscous debris flows. The low
amount and small size of the clasts may relate to the composition of the source material. It
has been argued (Velbel, 1987) that the high weathering intensity of the Southern Blue
Ridge produces source materials that do not contain sufficient coarse clasts to produce
Clast-rich debris flow deposits. The predominance of this finer textured facies at the Hidden
Valley site, and not at the other sites, may be due to the presence of less steep, and
therefore more stable, slopes in Hidden Valley. Slope failures on stable slopes may be
widely separated in time and hence, more time for weathering and breakdown of particles
into smaller fragments would be available. This facies is similar to "facies 2" of Walton and
Palmer (1988) and to "mud flows" described by Wells (1984). Considering that the
grainsize of the transported material is the main difference between mud flows and debris
flows, "mud flow" may be the most appropriate term for the Dmm facies at Hidden Valley.

Only two beds at Hidden Valley have high amounts of clasts (Figures 19 and 20).
One of them, in HLf, has a Dcm facies (Gm, sensu Miall, 1977). Clast supported fabrics
are generally associated with fluvial activity or highly mobile, low strength debris flows
(see section 5.2). According to Shultz (1984) this facies may comprise the basal sediment
or bed load of a mass flow. Walton and Palmer (1988), however, argued that clast
supported facies represent low strength flow. Its sharp upper boundary and the textural
differences from the suprajacent unit show that this bed is not the basal part of a thicker
deposit but a separate bed. Additionally, Nemec and Steel (1984) noted that sharp contacts
mark intersurge stream flow or thin fluidal debris flow. This unit, therefore, is likely to be

the deposit of a very fluidal debris flow surge or intersurge stream flow.

101
The other coarse fragment rich zone at Hidden Valley, in HUf, has a Dmm facies

(Figure 20). The smaller clast size at the bottom of soil horizon 2Bt2 suggests that there
could be a sedimentary boundary (lithologic discontinuity) between soil horizon 2Bt2 and
3Bt3. Other characteristics, especially the Sphericity and lithology of the clasts (Tables 7
and 8), seem to support this suggestion but do not allow a final conclusion to be made. If
the apparent gradual nature of the change in Clast size is real, the smaller clasts could

represent a minor debris flow surge between two larger ones.
5.4.4 Bradley site

The relatively clear, non-erosional boundaries such as those observed at the Bradley
site have often been attributed to debris flow origins (Gloppen and Steel, 1981; Nemec and
Steel, 1984; Wells, 1984; Velbel, 1987; Kochel, 1990). Unit 1 in BLf is similar, though
thinner, than the sediments in AUf and AUa (Figure 21). As argued above, the Dmm facies
of unit I typically represents plastic, viscous debris flows. Unit 2 contains only about 2 %
clasts and can be considered to be a mud flow deposit. The facies of this unit is similar to
"facies 1B" of Walton and Palmer (1988). These authors attributed the nongraded nature of
the facies to transformation of a turbulent flow into a plug flow and subsequent "freezing"
of the material. Schultz (1984) interpreted this facies type as being the product of a plastic,
laminar flow.

As noted above, Dcm facies such as that of the bottom unit in BLa (Figure 21),
have been associated with fluidal and high strength debris flows and streamflood. The poor
sorting of the clasts suggests that, in this case, a streamflood origin is not likely. The sharp
contact of the next unit, unit 2, with the overlying unit and its red hue (redder than adjacent
units) could indicate that it was exposed at the surface for some time. Therefore it could

represent fluvial or mud flow activity during the waning stage of a debris flow. Unit 3 has

102
a Dmm facies with few clasts, not unlike "facies 1B" described as lahars by Walton and

Palmer (1988) (see above).

The bottom unit in BUa has a Dmm facies. The relatively high number of large
clasts in a vertical position indicate that this unit was deposited by a high strength flow. The
facies of the overlying unit, on the other hand, suggests that it was deposited by a very
fluidal mud flow or hyperconcentrated streamflow. Its resemblance to unit 2 in BLa
indicates that is probably was deposited during the waning stage of a debris flow. Unit 3
has a Dmg facies. Its well sorted matrix and rounding of the clasts could indicate that some
fluvial reworking took place. Fluvial activity is also implied by the presence of a lens
shaped body of clast supported coarse fragments. Its lenticular shape and composition
indicate that it is a channel fill. Inverse grading, such as in unit 4, has been interpreted as
being the result of dispersive pressure (Nemec and Steel, 1984; Walton and Palmer, 1988).
As in "facies 1A" of Walton and Palmer (1988), the inverse grading does not occur in the
basal zone only but extends over the whole bed. This implies that the flow was sheared
over its whole thickness shortly before deposition (Walton and Palmer, 1988) and that it
had a relatively high clay content. The topmost unit is similar to the topmost unit in BLf and
presents a Dmm facies. A poorly sorted matrix and some dispersed clasts make a debris
flow origin, similar to that of unit 2 in BLf, the most plausible mode of formation for this

unit.

5.4.5 Fabric

The overall isotropic nature of the fabric of the deposits seems to indicate that the
flows were highly viscous (Nemec and Steel, 1984) or turbulent (Lindsay, 1968; Owens,
1973). The existence of two possible subpopulations in the Alarka and Bradley sites,
however, shows that other interpretations are possible. The two suprpulations could

point to the presence of more than one deposit in the zones that were sampled. Although the

103
thicknesses of the described units were not unusual for debris flow deposits and although

an effort was made during the fieldwork to identify lithologic discontinuities, the possibility
that sedimentary boundaries were either too gradual to detect or masked by pedogenesis
cannot be excluded. An alternative, and more likely, explanation is that subpopl (oriented
parallel to the flow) represents the clasts that were located closest to the bottom of the flow,
and thus closest to the zone of maximum shear, and that clasts of subpop2 were collected
elsewhere (higher) in the deposit. This explanation is compatible with the viscous nature of
the flows in which the clast orientations originated. Viscous flows are known to possess a
basal shear zone that promotes alignment of clasts and an overriding zone of turbulence in
which clast alignment is absent (Nemec and Steel, 1984; Shultz, 1984; Watson and Palmer,
1988).

The orientation of subpop2 seems to support this alternative explanation. In the pits
that are located on the apex of a deposit (AUa, BUa) and at an intermediate slope position
(BLa) the a—axes of subpop2 are scattered. This suggests that the clasts were deposited by
"freezing" of the flow. In foot positions (ALfl , ALf2, AUf) the clasts of subpop2 lay on a
great circle and gently dip downslope. Following the reasoning of Innes (1983) (see
section 5.1.6), settling near the foot of a deposit of clasts that initially do not have a
preferred orientation, could lead to the positioning of the a-axis of the clasts on a great
circle (when projected on a Schmidt net). If the samples were taken on the axis of the
deposit the great circles would be perpendicular to the axis. However, the great circles are
clearly not perpendicular to the central axis of the deposit (Table 9). The oblique orientation
of the great circles with respect to the axis of the deposit can be due to the location of the
soil pits on the side, and not the axis, of the deposits. This explanation has to be considered
as an hypothesis and cannot be verified until more systematic measurements of debris flow
fabric in different topographic positions are available. Because larger clasts tend to settle

faster than small clasts, subpop2 should have larger clasts than subpopl if the above

104
hypothesis is correct. The comparison of clast sizes in the two subpopulations of ALfl and

ALf2 is, however, inconclusive and does not permit me to reject or accept the hypothesis.

The deviation of the mean azimuth of the clasts from the direction of flow is smaller
in the debris flow deposits studied in this research than in some lahar facies (Mills,l984)
and small glacial debris flows (Lawson, 1979; Dowdeswell and Sharp, 1986; Visser,
1989) (Tables 1 and 9). The deviation is largest in the clast supported facies studied by
Mills (1984) but in the clast supported unit of this study the deviation is very small (6°).
Mills does not explain his observation but considering that clast alignment is attributed to
shear, which may be produced by Clast-Clast interactions (Lindsay, 1968; Nemec and Steel,
1984), it is not surprising that the clast supported unit of this study is closely aligned with
the direction of flow.

The deviation of the direction of the mean a-axis from the upslope direction is to the
east (except in AUf). A similar deviation, consistently to the right of the downslope
direction, was also observed by Mills (1983). Mills could not explain this observation but
excluded bias in measurement. The reasoning of Innes (1983) could again provide an
explanation. If the soil pits in Alarka and Bradley were not located on the longitudinal axis
of the deposit but to one side, i.e. the east side, and settling occurs, one would expect to
find a systematic deviation to the east. It would be coincidental, however, that all but one of
the soil pits in Alarka and Bradley were located to‘the east of the axis of the deposit,
especially when location on the central axis was sought during sampling.

The dip of the clasts at HUf is downslope and much steeper than at the other
locations (Table 8). The dip is more than two times as steep as the dips found in other
debris flow deposits (Lawson, 1979; Mills, 1984). The absence of two subpopulations at
HUf is compatible with the fluid nature of the flow that presumably deposited the clasts.
Fluidal flows usually are turbulent and lack shear zones that produce clast alignment near

the bottom (Nemec and Steel, 1984; Shultz, 1984; Watson and Palmer, 1988). Traversely

105
oriented clasts, present in relatively high amounts in this unit, are thought to move by

rolling along the bed in fluid flows (Nemec and Steel, 1984; Kohlbeck et al., 1994).

The strength of the fabric of the debris flows in this study is comparable to the
strength of the fabric of lahars and small glacial debris flows (Lawson, 1979; Mills, 1984).
These three types of deposits originate from very similar processes and all have very weak
fabrics (Figure 23). Fabric strength, however, is not a foolproof method for the
identification of debris-flow-like deposits because other processes, e. g. creep, can produce

weak fabrics as well (Figure 23).

5.5 Qonclusions

The sedimentary characteristics of the deposits show that they were most probably
formed by debris flows and mud-flow-like processes. They consist of massive, unstratified
and disorganized diamicts. The debris flow deposits, mainly located at the Alarka and
Bradley sites, have high amounts of clasts (generally >50 %) while the mud-flow—like
deposits at the Hidden Valley site contain very low amounts of clasts (<3 %). Matrix and
clast supported facies were identified, indicating that framework support is not a diagnostic
property of the studied deposits.

The deposits at Alarka are the most homogeneous and have characteristics of highly
viscous to intermediate strength debris flows. A relatively high yield strength for these
deposits is consistent with the observation of a lobate topography in the Alarka site. In this
respect these deposits resemble debris flow deposits emplaced on arid alluvial fans. At
Hidden Valley, mud flow facies predominate but deposits of fluidal debris flows are also
present. The paucity of clasts in the mud flows may reflect the composition of the source
material and the relative geomorphic stability of the basin. At the Bradley site, deposits are
more heterogeneous than elsewhere. Evidence for the stacking of materials from different

events is most clearly expressed at this site. Materials deposited by viscous and fluidal

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107
debris flows, and by mud flows, are present. The absence of evidence for surface

exposure, except in one unit in BLa, combined with the non-erosional contacts, indicates
that the sequences at the Bradley site were deposited in a relatively continuous fashion.
Apparently there were no major interruptions in the depositional episodes.

The overall fabric of the deposits is isotropic. One subset of the clasts in viscous
flows, probably those transported near the bottom of the flow, shows a tendency for a
weak (gentle dip) upslope imbrication. The orientation of a second subset of clasts, those
transported higher up in the flow, is influenced by their position with respect to the front of
the flow. The fabric of only one unit formed by a fluidal debris flow was studied. It is very
different from the fabric of the units produced by viscous flows. It is disorganized and has
a steep (47°) imbrication downslope.

The orientation of the long axis of the clasts is influenced by flow direction and the
local slope. The fabric of the deposits, as expressed by the ratio of eigenvalues, is weak. It
is comparable in strength to other debris flow deposits described in the literature. However,
fabric strength is not a diagnostic property of debris flows because other types of colluvium
can possess a weak fabric as well.

Settling of clasts and bioturbation may change the original fabric of debris flow
deposits. Fabric analyses of debris flow colluvium would, therefore, benefit from more

information on the change in fabric over time.

108
6 SOILS

6.1 Literature review

6.1.1 Morphology

Uncultivated soils on the Blue Ridge Front of North Carolina often have a complete
O—A-E-B-C profile (Graham et al., 1990a). Some of these soils have developed entirely in
saprolite or colluvium; most have developed in both materials. Nevertheless, Graham et al.
(1990a) did not indicate the existence of lithologic discontinuities in their pedon
descriptions. Argillic horizons had formed more quickly in fresh regolith upslope than in
highly weathered colluvium on low slope positions (Graham et al., 1990a).

Soils in the Joyce Kilmer Memorial Forest in western North Carolina are deep
(>90cm) (Daniels et al., 1987a). The A horizons of the soils in this area area thicker and
contain more organic matter on north-facing slopes than on south-facing slopes. On north
aspects significant amounts of the organic matter are mixed deeply into the subsoil. Weak
structural development in the subsoil is attributed by Daniels et al. (1987a) to the absence of
wet - dry cycles. Surface horizons however, particularly those on north aspects, have better
structure. Sometimes the original rock structure extends well up into the profile, but depth
to bedrock is frequently >l.3 m. Relatively few coarse fragments are present in most of
these soils, typically <10% by weight. Soils at higher elevations, on the other hand, often
contain a dense gravelly subsurface layer (Feldman et al., 1991b).

Literature reviewed by Feldman et al. (199 lb) led them to believe that the uniform
morphology of high elevation soils of the Southern Blue Ridge has resulted from the
dominance of climate in pedogenesis through its effect on slope instability, and that the
influence of rock type is secondary. Norfleet and Smith (1989) concur with Feldman et al.

(1991b) in that slope and climate are the main factors responsible for differences in soil

109
morphology, rather than parent material, vegetation or age. They reached this conclusion

after studying Typic Hapludults on steep to very steep slopes in the Blue Ridge of South

Carolina.

6.1.2 Physical and chemical properties.

6.1.2.1 Clay content

Soils of the Blue Ridge Front that have at least partially developed in saprolite have
the most distinct clay-enriched zones, while entirely colluvial soils have more gradual clay
increases (Graham et al., 1990b). Fine/total clay ratios indicate that much of the clay in the
Bt horizons of the saprolitic soils is due to illuviation. Clay contents decrease sharply in the
saprolite itself (Cr horizon) (Graham et al.,1990b). Enrichment of clay in a B horizon has
not taken place, however, in soils under virgin hardwood forest, probably because the
climate was too wet (Daniels et al., 1987a). Whole soil clay contents of these soils are
higher on north-facing slopes than on south-facing slopes (Daniels et al., 1987a). The
accumulation of clay in a thin rind just above the contact of the R horizon was seen by the

authors as evidence for illuviation.

6.1.2.2 Bulk density

The bulk densities of A horizons of soils in the region are quite low (<1.0 g cm'3)
due to high organic matter contents and porous structure (Daniels et al., 1987a; Norfleet
and Smith, 1989; Graham et al., 1990b). In the Blue Ridge Front bulk densities of the B
horizons are higher than those of underlying saprolite (1.6 g cm'3 as opposed to 1.4 g
cm'3) (Graham et al., 1990b), but Daniels et al. (1987a) found that bulk densities generally

remained below 1.4 g cm'3 through the porous B horizons, before increasing in the

saprolite.

6.1.2.3 Base saturation

110
In the Blue Ridge Front the dominant exchangeable bases of soils are K and Mg,

but low levels of Ca are also present (Graham et al., 1990b). Base saturation is low in the
acid surface horizons (< 10 %) but increased in the B horizons of the soils (12 - 40 %). On
lower slope positions where cations carried downslope by throughflow have accumulated,
base saturation is particularly pronounced (i 40 %) (Graham et al., 1990b).

In other areas of the Southern Appalachians, exchangeable bases are found to be
very low (Norfleet and Smith, 1989; Daniels et al., 1987a). Potassium, directly released
from feldspars, is relatively abundant (0.1 - 1 cmolC kg‘l) but Ca and Mg are virtually

undetectable in most horizons (Daniels et al., 1987a).

6.1.2.4 Free iron content

Parent material has a clear influence on the free (sodium citrate-bicarbonate-
dithionite (CBD) extractable) Fe content of soils in the region. In the Blue Ridge Front,
soils that are derived from gneiss have less free Fe than those that are derived from schist
because the schist has a higher proportion of Fe-bearing minerals (Graham et al., 1990b).
High elevation soils in micaceous parent material contain higher levels of CED-extractable
Fe than those formed from more siliceous parent material (Feldman et al., 1991b). Soils in
colluvium have a more uniform distribution of free Fe due to the colluvial homogenization
of preweathered material (Graham et al., 1990b; Daniels et al., 1987b).

Free Fe generally reaches a maximum in B horizons but in some pedons there is a
decreasing trend with depth (Daniels et al., 1987b; Norfleet and Smith, 1989). Deviations
from the expected bulge of free Fe in the B horizons could be attributed to small scale
variations in parent material composition and depth of weathering (Norfleet and Smith,
1989).

Daniels et al. (1987a) observed that soils on north-facing slopes are consistently

higher in extractable Fe than those on opposing south-facing slopes. There also appeared to

111
be a trend of decreasing Fe with increasing elevation. However, the authors did not

consider the effect of aspect or slope position on soil chemistry to be strong.

6.1.3 Mineralogy and weathering.

6.1.3.1 Biotite

The mineralogy of the sand fraction of some soils in the Southern Blue Ridge of
South Carolina is comprised of quartz, feldspar, sericite and muscovite (Norfleet and
Smith, 1989). The biotite content increases with depth or there are indications (high
amounts of hydroxy-interlayered-vermiculite (HIV)) that it has in the past. In soils of the

Blue Ridge Front, biotite has transformed into an interstratified biotite/vermiculite phase

(Graham et al., 1989a, b).

6.1.3.2 Chlorite

Primary chlorite is present in soils of the Blue Ridge Front (Graham et al., 1989a;
b). More chlorite is found in colluvial soils than in saprolitic soils. Comminution during
transportation of sand sized primary chlorite may reduce this mineral to the clay fraction,
where it persists unaltered (Graham et al., 1989b). The unaltered state can be explained by
a lack of intensive weathering. This can account for the difference between colluvial and
saprolitic soils but does not explain why there is a relatively large amount of fresh chlorite

as compared to other primary mineral contents (Graham et al., 1989b).

6.1.3.3 Vermiculite and HIV

Surface horizons of some soils in the region are dominated by vemticulite and
hydroxy-interlayered minerals (Daniels et al., 1987b; Norfleet and Smith, 1989). The
vermiculite and interlayered minerals decrease with depth, while mica increases (Daniels et

al., 1987b). At other sites regularly interstratified mica-vermiculite (RMV) predominates in

112
surface horizons and HIV increases with depth (Feldman et al., 1991b). The authors

associated RMV with podzolization processes. The absence of HIV in surface horizons
reflects both the mobility of Al-organic complexes out of surface horizons of these
mountain soils and the inability of hydroxy-Al interlayers to form in the presence of organic
acids (Feldman et al., 1991b). HIV seems considerably less stable at higher elevations than
at lower elevations.

Colluvial soils usually contain more vermiculite and (HIV) than do saprolitic soils
(Daniels et al., 1987b; Graham et al., 1989b). Soils studied by Norfleet and Smith (1989)
also had an abundance of vermiculite. The authors did not explicitly state whether or not the
parent materials were transported, but the paper leads the reader to believe that they were
not. If this is true, their finding is different from that of Daniels et al. (1987b) and Graham
et al. ( 1989a, b). The higher precipitation in the study area of Norfleet and Smith (1989)

most likely caused a more intense weathering of the micas.

6.1.3.4 Kaolinite

Kaolinite in the soils of the region was produced by different processes. In the Blue
Ridge front most kaolinite was probably formed as a pseudomorphic alteration product of
sand-sized biotite. Comminution later released it into the clay fraction (Graham et al.,
1989a). In the Southern Blue Ridge of South Carolina kaolinite contents vary greatly and
have no fixed relation with gibbsite contents (Norfleet and Smith, 1989). This could
indicate that kaolinite could have been produced by dissolution of primary minerals and
subsequent precipitation in a silica-rich soil. In other, more silica-poor, environments
kaolinite could form from direct alteration of primary minerals (Norfleet and Smith, 1989).
Kaolinitization of sand-sized biotite was considered to be the most likely transformation
process by these authors. The kaolinite content in the clay fraction of high elevation soils is
nearly constant with depth (Feldman et al., 1991b). Its presence in the non-clay fraction

suggests again that it is the result of more than one process, i.e. feldspar alteration in

113
addition to desilication of 2:1 minerals higher in the profile. The low kaolinite content in

soils of southwestern North Carolina could be explained by the fact that the soils seldom
dry out, thereby limiting kaolinite precipitation (Daniels et al., 1987b). Daniels et al.

(1987b) did not find a strong influence of aspect or slope position on soil mineralogy.

6.1.3.5 Gibbsite

Gibbsite is most abundant in the clay fraction of C and Cr horizons of saprolitic
soils and decreases in abundance toward the surface (Daniels et al., 1987b; Graham et al.,
1989a; b; Norfleet and Smith, 1989; Feldman et al., 1991). Occasionally, it reaches its
maximum in the Bt horizon and then decreases with depth. Norfleet and Smith (1989)
concurred with Graham et al. (1989a, b) in attributing the formation of gibbsite to
reprecipitation in lower horizons of Al released by weathering of aluminosilicate minerals.
In colluvial soils gibbsite comprises a much lower proportion of the clay fraction and a
decreasing trend toward the surface is less evident (Graham et al., 1989a; b). Possible
reasons are a homogeneous distribution of previously weathered minerals in the colluvium
and a lack of time.

The total amount of gibbsite does not change with depth in some soils of the
Southern Appalachians, because the clay content decreases with depth (Daniels et al.,
1987b; N orfleet and Smith, 1989). This indicates that it is fairly stable in the environment
of the South Carolina Blue Ridge (Norfleet and Smith, 1989). The interpretation of Daniels
et al. (1987b) was that either gibbsite remains in place following direct conversion from
feldspars and is diluted as the soil weathers or that additional gibbsite is forming near the
surface. No silt- or sand-sized gibbsite was observed by Daniels et al. (1987b). The
decreasing clay contents with depth supports the hypothesis of rapid weathering and
desilication from the surface downward.

The presence and abundance (approximately 20 % by weight) of gibbsite was noted

in weathering profiles of the Coweeta Hydrologic Laboratory area (Campione et al., 1992).

114
According to the authors, the presence of gibbsite in the profiles emphasizes the importance

of solution-reprecipitation of Al-rich phases in temperate climates. It suggests that the
activity of silica was more critical than the regional climate in controlling regolith formation
(Campione et al., 1992). These weathering profiles lack a clear vertical zonation. This may
reflect variations in bulk composition of the parent rock and/or variations in the
composition of ground water.

Bryan (1994) on the other hand, who worked in the same area, found that kaolinite
rather than gibbsite was the most abundant secondary clay mineral. Gibbsite was present in
the saprolite (C horizons) and declined in abundance upward in the profile. Similar trends
are reported by Graham et al. (1989b), Norfleet and Smith (1989) and Daniels et al.
(1987b) (see above). Bryan (1994) suggested that the trend was caused by pH and
permeability differences between the saprolite and solum. It was not clear why kaolinite

would dominate over gibbsite.

6.1.3.6 Iron oxides

Hematite and goethite have been observed to coat almandine grains in soils of the
Blue Ridge Front (Graham et al., 1989b). Some of the Al released during weathering of the
almandine precipitates as gibbsite, a minor component in the grain coatings. Graham et al.
(1989b) suggested that the Fe released from etch pits may have locally exceeded the
solubility product of ferrihydrite which then precipitates and is altered to hematite. Other
parts of the crystal may release Fe more slowly, resulting in lower localized concentrations
of Fe, thereby favoring the formation of goethite, which has a lower solubility product than
ferrihydrite. Graham et al. (1989b) partly rejected the conclusions of Velbel (1984) that
coatings form in saprolite weathering under inorganic circumstances while biochemical
processes in the soil produce etch pits and removed earlier formed coatings.

The occurrence and abundance of clay-sized hematite in these soils is strongly

dependent on the parent rock mineralogy (Graham et al., 1989a, b). Soils derived from

1 15
almandine-bearing parent materials (schists) have higher hematite contents than those

developed in material without almandine (gneisses). It has been argued that rock structure,
texture and other compositional elements could possibly affect the abundance of hematite in
these soils (Bryan, 1994). Colluvial soils have the most evenly distributed hematite,
probably as the result of homogenization of preweathered material during colluvial
transport (Graham et al., 1989a; b). Although goethite is also a weathering product of
almandine, it is found in the clay fraction of all soils, whether or not they are derived from
almandine bearing rocks. The additional Fe may have come from the alteration of biotite to
kaolinite (Graham et al., 1989a; b).

The sites at the Coweeta Hydrologic Laboratory studied by Bryan (1994) differed
from those in the Blue Ridge Front (Graham et al., 1990a; b) in that they contained more
goethite and less hematite. This can be explained by the smaller crystal size and faster
weathering in the Blue Ridge Front but also by climatic and pedologic variations between
the two sites (Bryan, 1994). Coweeta is cooler and wetter than the Blue Ridge Front, and

thus has conditions that favor the formation of goethite rather than hematite.

6.1.4 Genesis.

Graham et al. (1990a) described pedogenesis on the Blue Ridge Front explicitly as
a function of regolith type. In the construction of their model of soil formation the authors
relied heavily on an earlier model of pedogenesis by Rebertus and Buol (1985). This model
can be summarized as follows. In fresh saprolite an initial flush of clays occurs when
readily weatherable minerals alter to clays. This clay is illuviated and gradually produces an
argillic horizon. The soils then enter a period with little illuviation during which some of the
cutans are destroyed by pedoturbation. When biotite becomes extensively kaolinized a new
illuviation period starts and the argillic horizon continues to develop. This is followed by
another period of minimal illuviation and destruction of cutans. Kaolinitization of

muscovite then starts a third period of clay illuviation. Erosion can, of course, interrupt this

116
orderly progression at any time and mix the soil material. At first, clay sized material is

produced by physical disruption of weathered minerals during transportation. After
deposition of the eroded material, illuviation starts again. Depending on residence time,
degree of preweathering and initial clay content, a cambic or argillic horizon forms. During
geomorphic remobilization events, clays become depleted and soil development is
inhibited. Clay accumulation in the B horizon resumes but it is slower. Finally the material
stabilizes. Weatherable minerals are depleted but, given sufficient time, an argillic horizon
develops. All pedons in the study area of Graham et al. (1990) in the Blue Ridge Front of
North Carolina could be fit into this model.

In high—mountain soils of the Southern Blue Ridge, geomorphic processes have
resulted in younger, less weathered soil materials overlying older, more chemically
weathered soils (Feldman et al., 1991b). Formation of clay minerals from primary
aluminosilicates, mixed throughout the soil, was considered to be controlled by biotic and
climatic factors by the authors. In most surface horizons the genesis of secondary clays
was primarily the result of mica transformation in the following sequence:

mica (biotite)--->hydrobiotite--->RMV-—->vermiculite--->smectite.

The soils were thought to be undergoing the early stages of podzolization and
therefore are very different from adjacent low elevation soils (Feldman et al., 1991b). They
are typically associated with refugia of spruce-Fraser fir forests.

Elevation also affects the genesis of soils in the South Carolina Blue Ridge through
its influence on precipitation (Norfleet and Smith, 1989). The most important factor
affecting the removal of silica from these soils is rainfall. High precipitation results in more

gibbsite and less kaolinite in the clay fraction (Norfleet and Smith, 1989; Daniels et al.,

1987b).

1 17
6.1.5 Classification

The deepest soils of the Blue Ridge Front have formed where colluvium has
accumulated on the footslopes. These soils are, however, weakly developed and classified
as Typic Dystrochrepts or very weakly expressed Hapludults (Graham et al., 1990a). On
the slopes and the summits in the Blue Ridge Front the soils are thin and classify as
Hapludults. They belong to the Typic group in all landscape positions except on the
backSIOpe where they may be Ruptic, Lithic or Entic. Typic Hapludults generally have
developed in saprolite parent material (Graham et al., 1990a). The soils with the reddest
and most clay—rich Bt horizons are Typic Hapludults on backslopes.

At high elevations of the Southern Blue Ridge most soils classify as Typic
Haplumbrepts (Feldman et al., 1991b). Some of these soils show the development of a
weak, spodic-like horizon.

Most soils in the Joyce Kilmer Memorial Forest in western North Carolina contain a
cambic horizon and classify as Typic Haplumbrepts on north-facing slopes and as Umbric
Dystrochrepts on south-facing slopes (Daniels et al., 1987a). Yellowish-red Typic
Hapludults are observed by the authors over Fe-rich phyllites. These Typic Hapludults are
a major component of the soils on south-facing slopes below 800 m.

Norfleet and Smith (1989) and Daniels et al. (1987b) encountered a soil
classification problem in their study areas. Mineralogically, most of the soils studied by
these authors could be classified in the oxidic class. This class was intended to group
intensively weathered soils together. But, some of the soils also classified as Inceptisols,
genetically young soils, or had considerable amounts of easily weatherable minerals. In
both cases this apparent contradiction was seen as the result of a flaw in the Soil Taxonomy
(Norfleet and Smith 1989, Daniels et al. 1987b). None of the authors checked if there was
a correlation between parent material (i. e. saprolite or colluvium) and how well a soil fit

into a given mineralogy class.

118
Ms

6.2.1 Data collection

As discussed in section 5.2. 1, pits were located on the foot and/or the apex of the
deposits. At each location the soil was described and sampled in accordance with Soil
Survey Laboratory Staff (1992) and Soil Survey Division Staff (1993) procedures.
Morphological properties described for each horizon included horizon boundaries, texture,
structure, redoxymorphic features, cutans and coarse fragment content. Estimates of the
coarse fragment content were made in volume percent. Duplicate bulk density samples were
taken from the horizons with the core method (Soil Survey Laboratory Staff, 1992).

Geomorphic features such as slope, aspect, slope geometry and erosion were also

recorded.

6.2.2 Data analysis

Air dried soil samples were manually crushed with a mortar and pestle. Particle size
analysis was performed by dry sieving for the sand and fine gravel (8 - 2 mm) fractions
and by the pipette method for the clays. Procedure 3A1 of Soil Survey Laboratory Staff
(1992) was followed but without filtering after organic matter removal. Bulk density of the
soil samples was obtained by subtracting the weight of the >2 mm particles from the oven
dry weight of the sample, and by dividing the difference by the volume of the cores
(procedure 4A3 of Soil Survey Laboratory Staff (1992)). Bulk density was also determined
for rock fragments collected on the slopes above the deposits. Their volume was
determined by immersing them in water in a volumetric flask. Free iron was extracted with
the sodium citrate-bicarbonate-dithionite (CBD) method (Mehra and Jackson, 1960) (see

section 10.2.2 for details).

119
For clay mineral identification X-ray diffractometry (XRD) was employed. A

subsample large enough to yield about 4 g of clay was separated from every horizon-based
sample. The appropriate size of the subsample was estimated on the basis of the particle
size data. Organic matter was oxidized with H202 at approximately 60° C (Anderson,
1963). The procedure was stopped when frothing disappeared completely. Iron oxides
were removed with sodium CBD (Mehra and Jackson, 1960) (see section 10.2.2 for
details). The sample was then added to a cylinder, deionized water was added to make the
volume 1 L and the mixture was shaken vigorously for one minute. The time required for
particles > 2 mt to settle to a certain depth was calculated. After that period of time had
elapsed, the clays were siphoned off, the cylinder was filled with water again and the
sedimentation and siphoning procedure was repeated. This procedure was repeated until
most clays had been removed from the mixture. The clays were then transferred to
centrifuge tubes for Mg saturation as described in Whittig et al. (1987). Slides were
prepared by adding as much of a concentrated mixture of saturated clays and deionized
water to a slide as could be held by surface tension. X-ray analyses were performed on a
Philips XRG 3100 scanning diffractometer with Cu Ka radiation. The clay mounts were
scanned in 2 sec steps of 005° over a 20 range of 2 to 32°.

The relative abundance of the clay minerals was determined with a method based on
Rieck et al. (1979) and Griffin and Ingram (1955). First the ratios of the intensity of the
7.15 A, 10 A and 14 A XRD peaks to the intensity of the highest peak were calculated.
(For a discussion of the minerals that correspond to these (001) peaks the reader is referred
to section 7.2.3). The ratio was then assigned a code of 1 if it was <33 %, 2 if it‘was
>33 % and <66 %, and 3 if it was >66 %. This code reflects the relative abundance of the
minerals in each sample. Rieck et al. (1979) argued that when ratios of intensities are used,
and when the intensities are obtained from the same diffractograms, semi-quantitative
comparisons between samples can be made. Therefore, while not a quantitative measure for

the mineralogical composition of the samples, the code calculated here permits

120
semi-quantitative comparisons between samples to be made. Markewitch and Pavich

(1991) recently employed a similar method, based on peak height ratios, to study relative

abundances of clay minerals.

6.3 Results

6.3.1 Soil morphology and classification

6.3.1.1 Alarka site

The soils at the Alarka site are very deep. Sola are more than 187 cm thick in three
of the four pedons (Table 4). The C horizon was only encountered in AUa, at 161 cm. An
A horizon rich in organic matter is present in all pedons, but only on the lowest deposits of
the sequence (pedons ALfl and ALf2) is it underlain by an B horizon. (For the
nomenclature of pedons the reader is referred to table 2). ALf2 has a 30 cm thick argillic Bt
horizon that has a few distinct clay skins. Other B horizons at the Alarka site also have a
few distinct clayskins, but they do not classify as argillic horizons because of the low clay
enrichment. All B horizons at this site have a hue of 7.5YR (Table 4) and usually have a
soil structure with a medium grade.

The non-argillic B horizons have an extremely flaggy or gravelly fine sandy loam
texture while the argillic Bt horizon has an extremely gravelly sandy clay loam texture.
Surficial horizons (A, AE, E, BA) usually have a loam texture.

The pedons at ALfl, ALf2 and AUa classify as loamy-skeletal, mixed, mesic
Umbric Dystrochrepts. Because of the presence of an argillic horizon in ALf2 the pedon

classifies as a loamy-skeletal, mixed, mesic Typic Hapludalf.

121
6.3.1.2 Hidden Valley site

The pedons on the lowest deposit at Hidden Valley have relatively thin sola (Table
4). At HLf the C horizon was encountered at 62 cm and at HLa the solum was only 111 cm
thick. At the other four pedons the upper limit of the C horizon was encountered at
>211 cm. HLf and HLa, and one pedon in Bradley (BLf), are the only soils with thick,
gleyed horizons. The gleying indicates that the water table is relatively shallow during a
major part of the year and probably impedes a further development of the soils.

HMa is the only pedon of the Hidden Valley site in which an B horizon was
observed. It also is the only pedon that contains a buried profile and the only one in which
a Cr horizon could be observed.

In all Hidden Valley pedons except HLf, Bt horizons with cutans and a soil
structure with medium grade were observed. Most of these Bt horizons classify as argillic.
In the highest pedon, HU a, only the deepest B subhorizon described was argillic. The
argillic horizons, except the one at HUa, have a clay texture. The B horizons have hues of
5YR or 2.5YR, redder than the B horizons of the soils at the other two sites.

The texture of the soils in Hidden Valley is also distinctly different from that at the
other two sites (Table 4). The pedons in Hidden Valley, except for the lowest one (HLf),
are dominated by clay loam and clay textures. The lowest pedon has a loamy solum and
sandy loam C horizons, the lowest of which is extremely gravelly. This is similar to the
textures of horizons at the two other sites which are dominated by loams and fine sandy
loams.

Taxonomically the pedons on the highest and lowest deposits classify as loamy,
mixed, mesic Typic Hapludults. The pedons HMf and HMa are clayey, mixed, mesic
Typic Hapludults.

122
6.3.1.3 Bradley site

The lowest pedon in Bradley is similar to its counterpart in Hidden Valley, in that it
is shallow (depth C horizon = 59 cm) and has a gleyed horizon, indicating a high water
table. The depth to the C horizon in the other two Bradley pedons is >187 cm. An E
horizon was only observed at BLa. Bw horizons are described without cutans and with a
weakly developed structure. Consequently, no argillic horizons were identified at Bradley.
The hue of the B horizons is 7.5YR (Table 4). Superficial horizons generally have a loamy
texture while most of the subsurface horizons are coarser textured.

The lowest and highest pedons classify as loamy, mixed, mesic Typic

Dystrochrepts while HLa is a loamy-skeletal, mixed, mesic Umbric Dystrochrept.

6.3.2 Physical and chemical properties

6.3.2.1 Alarka site

Clay enrichment in the B horizons of the soils in Alarka is minimal (Figure 24).
Only ALf2 has an argillic horizon. The BC horizons of pedon AUa, which is at the apex of
one deposit, contain less clay than the overlying and underlying horizons (Figure 24). The
clay content of the BC horizon is comparable to the clay content of the BC horizons of
AUf, which is located on the foot of the same deposit, but the content is considerably less
than in the horizons of AUf that are at the same depth. The bulk density of AUf is
consistently lower than that of AUa (Figure 25).

Other properties, such as percentage clayfree silt (Figure 26), do not show any
systematic difference between foot and apex of a deposit nor do they show a consistent
depth trend.

The most striking feature of the soils at the Alarka site is the high amount of coarse
fragments (Table 4). Pedons ALfl and ALf2 have horizons with more than 80 % coarse
fragments. The highest deposit at Alarka (pedons AUf and AUa) has about 50 % coarse

123

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126
fragments. The trends with depth of the total amount of coarse fragments are almost

completely reflected in the fine gravel (8 - 2 mm) fractions (Appendix 3). In ALfl there is a
sudden increase in the fine gravel below 50 cm.

The depth profiles of the free iron mass in AU] and ALf2 are very similar (Figure
27). The maximum amount of free iron is reached in the Bt horizons at about 80 cm depth.
The depth profiles of free iron mass for AUf and AUa are also similar to each other but
different from those of ALfl and ALf2. In AUf and AUa there is a steep increase in the
amount of free iron just under the surface, with the maximum being reached at less than 60
cm. The steep increase immediately below the surface suggests that erosion may have
removed eluvial horizons on the higher deposit at the Alarka site.

The results of the particle size fractionation show that there is large variation in the
fine gravel and sand fractions between adjacent horizons, especially in ALfl and ALf2

(Appendix 3).

6.3.2.2 Hidden Valley site

In Hidden Valley, pedons HMf and HMa have the highest clay enrichment in the Bt
horizon (Figure 28). The argillic horizons of these pedons that have developed in saprolite
have from 18 % to 25 % more clay than the overlying eluvial horizons. The Cr horizon of
HMa has considerably less clay than the overlying horizons. On the lowest and the highest
deposits (HLf, HLa and HUf, HUa respectively), clay enrichment in the Bt horizons
ranges from 2 % to 16 %. In pedons Hmf and Hua an increase in the clay content can be
observed near the bottom of the soil pit. This increase produces a second, deep, maximum
of the clay content.

No systematic difference in the clay content is present between the pedons located
on the foot and the apex of the deposits. On the lowest deposit the pedon on the foot has
less clay than the pedon on the apex, while on the highest deposit the pedon on the foot has

more clay than the one on the apex. The trend with depth of the clay mass in the two

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129
pedons on the lowest deposit is very similar and shows a well pronounced clay maximum

(Figure 28). This trend is typical of mature soil profiles. The absence of eluvial horizons
near the surface may point to their removal by erosion. At HMa deposition occurred and a
more complete profile, with an eluvial horizon, became buried (Table 4, Figure 28).

Bulk density values show a difference between the foot and apex of deposits but the
difference is not consistent (Figure 29). As in Alarka, the pedon on the foot of the lowest
deposit (HLf) has a lower bulk density than the pedon on the apex, but the situation is
reverse for the highest deposit in Hidden Valley. In pedons HMf and HMa minimum bulk
density values are not observed in the A horizon, as was the case in all other pedons
studied, but in the AB horizon.

The pedons in Hidden Valley have considerably less coarse fragments than those at
Alarka and Bradley (Table 4). Only HLf has a horizon (2Cg) with very many coarse
fragments (90 %) but the horizon is only 25 cm thick.

The free iron mass distribution on the lowest deposit is very irregular (Figure 30).
The maximum free iron in the other pedons at Hidden Valley (HMf, HMa, HUf, HUa) is
reached in the Bt horizon. The higher in the landscape the pedon is located, the deeper in
the soil this maximum is found.

As at the Alarka site, many large changes occur with depth in the amount of fine
gravel and sand at HLf, HLa, HUf and HUa (Appendix 3). At BUa and Br4 there are only
very gradual variations in the texture of adjacent horizons. The only large change in textural

composition in these pedons can be observed between the AB and Ab horizons of HMa.

6.3.2.3 Bradley site
As evidenced by the absence of argillic horizons, clay translocation is low at this
site. The highest pedon, BUa, has two Bw horizons (2Bw2 and 3Bw3) that have less clay

than the over and underlying horizons (Figure 31). At the Bradley site clay enrichment

130

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133
decreases with increasing elevation of the pedon. For bulk density values, a clear trend

with depth could not be identified.

The amount of coarse fragments in the soils at Bradley is more variable than at the
other two sites (Table 4). The highest amounts (>80 %) are reached in the two lowest
pedons.

Free iron mass has similar depth profiles in all three pedons (Figure 32). The
maximum is reached in the first Bw horizon at about 40 cm depth. The highest pedon has a
secondary maximum at the bottom of the described soil profile. At this site, as well as in
most pedons of the other two sites (see above), a clear eluvial horizon is absent. This can
point to removal of surficial horizons by erosion.

Texturally, the pedons in Bradley are more heterogeneous than those in the other
two sites (Appendix 3). Large changes in the fine gravel and sand subfractions occur with
depth throughout the pedons. This reflects the sedimentological complexity of the parent

material.

6.3.3 Clay mineralogy

6.3.3.1 General

Kaolinite was recognized by its 7.15 A and 3.57 A XRD peaks and mica was
identified by its first order 10 A peak. The 14 A minerals theoretically include chlorite,
smectite, vermiculite and hydroxy-interlayered minerals. Identification of each of these
species is impossible with the data available but some can be excluded from the list.
Chlorite, which is distinguishable from kaolinite by its second order 7.08 A peak and third
order 3.54 A peak was not found in the samples. The presence of smectite cannot be
excluded on the basis of the data but its occurrence is unlikely in the high intensity

weathering environment of the Blue Ridge and in these well drained soils (Borchardt,

134

Free iron mass as a function of depth, Bradley site

 

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135
1989). The 14 A minerals present are, therefore, most likely to be vermiculite and hydroxy-

interlayered minerals.

In general terms, the clay mineralogy varies little within each site but presents clear
differences between sites (Table 11). The Alarka site contains more 14A minerals and less
kaolinite than the other sites. The Hidden Valley site contains almost no mica, few 14 A
minerals but high amounts of kaolinite. The Bradley site has, proportionally, as much mica

as the Alarka site, but it has more kaolinite.

6.3.3.2 Alarka site

All pedons at the Alarka site contain relatively little mica (Table 11). Kaolinite is present in
small to intermediate amounts at AU] and ALf2 and in intermediate to high amounts at
AUf and AUa. The relative abundance of 14 A minerals is variable. The BC and C
horizons have small to intermediate amounts of 14 A minerals, while higher amounts

usually occur in surficial horizons (A, AE, E, BA) (Appendix 4).

6.3.3.3 Hidden Valley site

The clay spectrum at the Hidden Valley site is dominated by kaolinite (Table 1 l). Kaolinite
is abundant in every horizon of this site. Mica is absent in most horizons. Only pedon HUf
has low amounts of mica (Appendix 4). Some 14 A minerals are present in proportionally
low amounts in almost all horizons. They are absent from one B horizon in HMa and HUa

and have an intermediate abundance in the A horizons of HLf and HUa.

6.3.3.4 Bradley site
Kaolinite is also abundant in every horizon of the Bradley site (Table 11). Mica has a low
abundance in every horizon (Appendix 4). The relative abundance of the 14 A minerals is

higher than at the Hidden Valley site but lower than at the Alarka site. It is intermediate in

136
the A, and E, horizons of BLf and BLa and low in all other horizons of these two pedons.

At BUa, 14 A minerals are intermediate in abundance in all horizons.

  

 

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14 A minerals Mica Kaolinite

2.0 1.0 1.8

2.3 1.0 2.0

2.0 1.0 2.6

AUa 2.1 1.0 2.5

Mean of site 2.1 1.0 2.2

HLf 1.0 0.3 3.0

Hla 1.0 0.3 2.9

Hle 1.0 0.1 3.0

HMa 1.0 0.3 3.0

HUf 1.0 0.8 2.9

HUa 1.2 0.2 3.0

Mean of site 1.0 0.3 3.0

BLf 1.3 1.0 3.0

BLa 1.3 1.0 3.0
BUa 1.9 1.0 3.0 II

Mean of site 1.5 1.0 3.0

* Values in table are pedon averages. Increasing number indicates
increasing relative abundance. See section 6.2.2 for definition of

codes.

6.4 Discussion

6.4.] Saprolite

In HMa a Cr horizon occurred near the bottom of the pit. There were no indications
in the particle size distributions for the existence of a lithologic discontinuity higher up in

the profile. In HMf a Cr horizon was not identified but the morphology of this pedon is

137
very similar to that of HMa. The B/C horizon of HMf is similar to the C/B horizon of

HMa. These horizons consist of highly weathered, reddish, clay-rich seams surrounding
angular, brownish yellow fragments of rock that are little weathered. These observations
suggest that pedons HMf and HMa have developed entirely in saprolite.

Although bulk density does not gradually increase with depth in the saprolite, there
is a gradual transition from the bottom of the solum to the bedrock. The bulk density
increases from about 1.36 g cm"3 in the C/B and B/C horizons to 1.41 g cm'3 in the BC
horizon and to 1.45 g cm'3 in the Cr horizon. Fresh bedrock samples from the Hidden
Valley site, which are likely to be similar to the parent material of the saprolite, yielded bulk
densities of about 2.65 g cm‘3. The difference in bulk densities between the bedrock and
the various transitional horizons represents the loss of mass that accompanies saprolite
formation. Assuming isovolumetric weathering the mass losses are 48 % for C/B and B/C
horizons, 46 % for BC horizons and 44 % for Cr horizons. This loss in mass is similar to
that reported for the Piedmont by Cleaves (1974), for the Blue Ridge Front by Graham et
al. (1990a), and for the Blue Ridge of Virginia by Stolt er al. (1992).

6.4.2 Lithologic discontinuities

Particle size data for most colluvial soils show that many large variations in the
abundance of the sand subfractions exist (Appendix 3). This may be interpreted as evidence
for the existence of lithologic discontinuities. At the Alarka site and at [-11.3 and HUa,
however, no evidence for discontinuities was observed in the field. There was no evidence,
such as buried paleosols, distinct differences in coarse fragment content, or differences in
sediment characteristics, for the presence of lithologic boundaries. Clay mineralogy data
support the lack of lithologic discontinuities at the Alarka site and at HLa and HUa. The
clay mineral spectrum changes with depth (section 6.4.4) but the changes are not closely

associated with changes in particle size. The irregular trend with depth of other soil

138
properties, such as clayfree silt content (Figure 26), are not related to clearly distinct

variations in particle size distribution either. The apparent discontinuities observed in the
particle size distributions at the Alarka site and at HLa and HUa are, therefore, interpreted
to be the result of internal variations within the deposit of a single flow, rather than being
the result of different deposits stacked on top of each other. Consequently, the numeral
prefixes assigned to horizons of the Alarka site and HLa and HU a represent differences in
parent material from a pedogenic point of view but they do not necessarily indicate the
existence of different depositional units. The internal variations in the deposits can be due
to different shear zones in the flows. As shown in section 5.3, the heterogeneity of the
parent material at the Bradley site is due to the presence of different sedimentary units.
Graham et al. (1990b) and Daniels et al. (1987b) found a more uniform distribution
of free iron in colluvium than in saprolite. In the present study, however, no clear
difference exists between the trends of free iron in the saprolite and the debris flow
deposits. The homogenization of preweathered material during colluvial transport, that
Graham et al. (1990b) and Daniels et al. (1987b) use to explain their observations, did not
take place in the debris flows. This is confirmed by the particle size data which indicate

that, within one flow, vertical differentiation rather than homogenization occurred.

6.4.3 Clay content

The soils that have developed in the saprolite have higher clay contents and
experienced more clay enrichment than the pedons that have developed in debris flow
colluvium (all other pedons studied). In the Cr horizon of HMa, the clay content decreased
considerably (from 30 to 1 1 %). Similar observations were made by Graham et al. (1990a)
for colluvium of soil creep and slope wash. In the saprolitic soils, changes of free-iron
mass with depth closely follow the depth trend of clay mass (correlation coefficient =

0.91). Because free iron tends to move with fine clay in well drained soils, like those

139
studied here (Eswaran and Sys 1970, Soileau and McCracken 1967), and because fine clay

is indicative of illuviation, the free iron trend suggests that the clay enrichment in HMf and
HMa is primarily due to illuviation.

The difference in clay content between the pedons in saprolite and colluvium is
related to the type and age of the parent material. As will be shown below (part III), the
soils in saprolite appear to be older than those in colluvium, and thus more time has been
available for weathering, clay production and clay translocation. Other factors that influence
clay formation and translocation, such as climate, vegetation, topography and drainage are
similar at the three sites and probably did not play a major role. The soils on the highest
deposit in Hidden Valley appear to be similar in age to the saprolitic soils (part III) but have
thicker sola. The thick sola reflect clay enrichment over a wide zone and result in a high
total clay mass when the amount of clay is integrated for the whole solum (see also figure
35). This suggests that, in saprolitic soils, relatively thin but very clay-rich B horizons
often develop, while in colluvial soils thicker, but less clay-rich B horizons form.

The highest pedons at the Hidden Valley and Bradley sites (HUa and BUa
respectively), and to some extent the lower saprolitic soil (HMf), have a depth trend with
two local clay maxima (Figures 28 and 31). One usually expects to find an increase in the
clay content in the upper B horizon. In these two pedons, however, the clay content
reaches a minimum in the intermediate B horizons and increases both upward and
downward from there. At Alarka, C horizons were encountered in the highest soil pit
(AUa) and a second clay maximum was not observed.

Bisequal soils, with two clay maxima, have been observed elsewhere (Birkeland
1984, Kesel and Spicer 1985, Farming and Farming 1989, Gamble 1991). The two
maxima have been linked to different parent materials (Kesel and Spicer 1985, Gamble
1991). As mentioned in section 5.3, lithologic discontinuities are clearly present at BUa.
Sedimentary unit 2 (horizon 4Bw4, Figure 21), which is part of the second, deep, clay

maximum, contains less coarse fragments, less clayfree very coarse, coarse and medium

140
sand, and more clayfree silt than the overlying unit (Appendix 3). It therefore seems

reasonable to assume that textural differences of the parent materials, i.e. more clay in unit
2, determined at least in part the origin of the second, deep, clay maximum at BUa.
Consequently, the first, shallow maximum (horizon Bw l) is considered to be most
characteristic of pedogenic development at this locality.

In Typic Haplorthox that had developed on alluvial fans, Kesel and Spicer (1985)
also found profiles with two clay maxima. In these soils, as in the HMa and HUa pedons
of the present study, there was no compelling evidence for the presence of lithologic
discontinuities. Kesel and Spicer (1985) attributed the relatively low amount of clay
between the two maxima to intense and prolonged weathering, of the clays, and subsequent
leaching of the weathering products. If the explanation of Kesel and Spicer (1985) applies
to HMf and HUa, a clay maximum may have existed in these soils between the two
observed bulges in clay content. Therefore, data of the horizon with the highest clay
content, whether it belongs to the shallow or deep maximum, will be used hereafter to
characterize the most clay-rich horizon of these pedons. More firm conclusions about the
origin of the second clay maxima in HMf, HUa and BUa, and the bisequal nature of these
soils, could possibly be drawn if textural and fine clay data were available for all horizons,
including the C horizons.

The most clay-rich horizon (Bwl in BUa, see above) is shallower in soils on the
foot of the deposits than in the corresponding soils on the apex of the deposits. In a more
general sense it is also true that on these debris flow deposits, and on the saprolite, the clay
maxima occur at greater depths in higher landscape positions (Figure 33). For the lowest
deposits at the Hidden Valley and Bradley sites this increase in depth with elevation can be
explained by a relatively shallow water table at the foot of the deposits. Because the other
soils are well drained differences in drainage are not likely to have determined the depth of
the clay maxima on the other deposits and the saprolite, although some influence can not be

completely excluded. Considering that higher deposits are younger than lower deposits at

141

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142
the same site (see Part HI), the depth of the clay maximum may be related to age. Age

dependence of the depth to clay maximum has been reported from a variety of
environments (Levine and Ciolkosz 1983, McFadden and Weldon 1987, Fanning and
Farming 1989).

The shallow position of the clay maximum in the highest pedons at Alarka (AUa)
and Bradley (BUa) (Figure 33) may be due to erosion. It has been argued above (6.3.2.1
and 6.3.2.3), based on the depth profile of free iron, that erosion may have removed
surficial horizons at these locations. The shallow position of the clay maximum at AUa and
BUa supports this notion. Additionally, pedon BUa is located on the steepest slope at the
Bradley site (19 %), which indicates that increased surficial erosion may occur at this

location.

6.4.4 Clay mineralogy

Although chlorite is present in some of the bedrock at the study sites, it was not
found in any of the soil samples. Considering the weatherability of chlorite and the high
intensity weathering environment of the area, chlorite has probably been altered to other
14 A minerals. Chlorite was detected in other types of colluvium in the Blue Ridge Front
but its presence was hard to explain (Graham et al., 1989b). Slightly higher amounts of 14
A minerals (probably vermiculite and hydroxy-interlayered minerals) are present in surface
horizons than in subsurface horizons. This trend is best expressed at Alarka and Bradley. A
similar trend was observed by Daniels et al. ( 1987b) and Norfleet and Smith (1989) and
was related to an increasing trend with depth of mica. Both trends are explained by these
authors by intense alteration of mica to 14 A minerals in surface horizons. In this study, no
depth trend for mica was found at Alarka and Bradley and mica was absent at Hidden
Valley. The lack of a trend for mica is most likely due to the advanced degree of weathering

of the soils. Mica may be present in amounts so small that any variation in its abundance is

143
below the resolution of the quantification method that was used. Colluvial soils have been

found to contain more (Daniels et al., 1987b; Graham et al., 1989b) and less (Norfleet and
Smith, 1989) vermiculite and HIV than saprolitic soils. In this study, however, there is no
difference in the relative amount of vermiculite and hydroxy-interlayered minerals in
colluvium and saprolite.

Mica has been shown to weather, here and elsewhere, to 14 A minerals such as
vermiculite and hydroxy-interlayered minerals (Daniels et al., 1987b; Norfleet and Smith,
1989; Feldman et al., 1991). From common weathering sequences, it is known that upon
alteration, 14 A minerals can produce kaolinite. This suggests that the soils at Alarka,
which have more mica than the soils at the other two sites, have undergone less weathering
than those at the Hidden Valley site, which has proportionally the most kaolinite and the
least micas. The degree of weathering is usually related to bedrock composition, time and
climate (Ollier, 1984). Differences in bedrock composition are most likely not the main
factor that determines the differences in degree of weathering in this case. The bedrock
composition at the three sites is similar and variations in the composition within one site are
of the same magnitude as the variations between sites (Table 7). If bedrock composition
were a chief factor, one would expect clay mineralogy to be variable within each site. That
is not the case. Climate is not considered to be an important factor either, because the
climate at the three sites is very similar. Detailed climatological observations are not
available for the sites but the three sites are located in the same general region, at
approximately the same elevation and have comparable aspects and slope. Therefore, the
principal factor influencing the degree of weathering, and thus the clay mineral
composition, of the studied deposits is time (age of the deposits). This is supported by the
results of the relative dating (see part IH).

The mineralogical composition of the clays at the Alarka site, and to some extent the
Bradley site, includes minerals associated with initial stages of weathering. Their presence

suggests that inheritance of clays may have been low in these debris flow deposits, unless

144
both the source material and the described soils are very young. If the source material was

very young, and therefore relatively unweathered, it also seems reasonable to assume that

inheritance of clays was not high.

6.5 Conclusions

Two of the pedons studied have developed in saprolite; these two pedons have
higher clay contents and more clay enrichment than do the other colluvial soils. This
difference in clay content and clay enrichment is at least in part due to a difference in age
(see below).

Many lithologic discontinuities exist in the debris flow deposits. The discontinuities
at the Alarka site and in two Hidden Valley pedons do not appear to represent
sedimentological boundaries, but variations within the deposit of one event. Considering
the sedimentological properties of the deposits, the variations can be linked to different
shear zones in the flows. At the Bradley site the discontinuities represent lithologic
discontinuities in the strict sense and correspond to boundaries between distinct
sedimentary units. This variability in the parent material indicates that debris flows render
the regolith more heterogeneous rather than homogeneous, as was observed in other
colluvium (Graham et al., 1990b).

The heterogeneity of the parent material affects the depth trends of most
morphological properties of the soils. The only characteristic that shows a systematic trend
is the depth to maximum clay and free iron accumulation. The trend is directly related to the
topographic position of the pedon, higher pedons having maximum accumulation at greater
depths: Depth to maximum clay and free iron accumulations in pedons on the apex of the
deposits occur at greater depths than in pedons on the foot of the same deposit. The most
likely explanation is an impeded drainage at the lowest topographic positions where vertical

water movement in the soils may be restricted, and relative age. The presence of shallow

145
clay maxima in soils on the steepest slopes and the absence of eluvial horizons in some

pedons may point to surficial erosion.

The clay mineral assemblages show very little variation between the horizons of one
pedon, and between pedons at each site. Only 14 A minerals show a weak, decreasing,
trend with depth. This trend can not be explained by a more intense alteration of mica to
14 A minerals in surface horizons, as was the case in colluvium studied by Daniels et al.
(1978b) and Norfleet and Smith (1989). The relative abundance of 14 A minerals in the
soils on the debris flow deposits does not differ from that of nearby saprolitic soils. This
finding is different from that of Daniels et al. (1987b) and Graham et al. (1989b) who
found that other colluvial soils in the region usually contained more 14A minerals than did
saprolitic soils. The main factor influencing the clay mineral assemblages of the soils on the
debris flow deposits is time/age.

To better understand pedogenesis on debris flow colluvium, more information on
the characteristics of its parent material is required. These characteristics, i.e. texture, clay
mineralogy and possibly depth profiles of chemical and physical properties, may be
inherited from source materials and may be affected by transportation in the flow. It is
therefore suggested that pedologic studies comparing recent debris flow deposits and their

source material can further the knowledge of pedogenesis on debris flow colluvium.

PART III: RELATIVE-AGE DATING

146

147
7 INTRODUCTION

Several approaches used to date Quaternary geomorphic surfaces rely upon absolute
ages. Often-used methods include thermoluminiscence, fission track, radiocarbon and other
radioisotope dating methods (Kochel and Johnson, 1984; Shafer, 1984; 1988; Kochel,
1990). In the absence of suitable material for absolute-age dating, relative-age dating
techniques have been used. Relative-age dating techniques have been employed to
quantitatively estimate the age of a surface, using knowledge of rates of soil formation
(Knuepfer, 1988), and to compare qualitatively the ages of a series of surfaces for which
no rate information is available (Whitehouse et al., 1986; Harrison et al., 1990; Phillips,
1990; Birkeland and Berry, 1991; Markewitch and Pavich, 1991; Whittecar and Ryter,
1992; Woodward et al., 1994).

Relative-age dating techniques utilizing soils data are based on the principle that the
degree of soil development is dependent on five soil-forming factors (Jenny, 1941).
Harden (1990) argued that the general magnitude of soil development strongly depends on
the time factor, surface stability and possibly parent material. She submitted that the effect
of the other factors (vegetation, climate and topography) is less apparent. Even if Harden's
(1990) statement underestimates the importance of the other soil forming factors, soil
development can be used to compare the relative ages of soils in different locations when
those other factors remain more-or-less constant at all sampled locations.

In this research, a qualitative (comparative) approach will be used. Clast
weathering, color, clay content and iron species will serve as proxies for the degree of soil
development and weathering. As argued above (sections 3.2, 3.3.3 and 6.4.4), the climate,
vegetation, topography and parent material of the soils at the three sites are similar. Because
the sites are located within 13 km of each other, the first three factors can be expected to

have been similar in the past as well.

148
Although the mode of origin and the general nature of the parent material is the

same, with the exception of the saprolitic soils, variations in the colluvial parent material
may be due to compositional differences of the source material of the flows. It cannot be
ascertained that the source materials of the different debris flows had the same degree of
weathering and soil formation at time zero. Therefore it is conceivable that some of the
characteristics of the soils on the debris flow deposits partly reflect the composition of the
source material. However, as will be demonstrated in chapter 8, the degree of weathering
of the clasts in the deposits is unlikely to have been influenced by preweathering of the
source material. The similarity of the results for the other proxies to those of clast
weathering suggests that the other proxies, too, may not have been influenced to a large
extent by inheritance from the source material. It therefore seems reasonable to assume that
time has been the chief factor in the determination of differences in soil development at the
three sites, and that relative-age dating techniques can be applied without major obstacles.

Strictly speaking, relative-age indicators give an estimate of the relative age of the
soil and the present day geomorphic surface on which the soil developed (Phillips, 1990).
However, it is assumed here that the mode of origin and the geomorphic evolution of the
deposits is similar, and hence, that the relative-age relationships of the soils can be
extended to the deposits as well. Therefore, "soil" and "deposit" will be used
indiscriminately when references to relative-age are made hereafter.

The purpose of the application of relative-age dating techniques is to provide an
assessment of the relative ages of the deposits. Although relative ages of other colluvial
deposits in the Southern Blue Ridge have been reported (King, 1964; Michalek, 1968;
Gryta and Bartholomew, 1977; Mills, 1981), many of them were based on the degree of
weathering and/or topographic position of the deposits. One of the very few soil
chronosequence studies in the Southern Blue Ridge was carried out by Leigh (1995) on
alluvial terraces just south of the present study area. In general, chronosequence studies

from warm to hot, humid environments are scarce (Birkeland, 1990). This part of the

149
research may, therefore, contribute to the understanding of pedogenetic pathways in this

type of physical environment.

1 50
8 CLAST WEATI-IERING

8.1 Literature review
8.1.1 General

Clast weathering has often been used as a means of relative age dating of soils and
deposits (Chinn, 1981; Colman and Pierce, 1981; Mills, 1982; Whitehouse et al., 1986;
Knuepfer, 1988; Mills, 1988; Whittecar and Ryter, 1992). In many cases granitic boulders
have been studied because they decompose relatively rapidly and uniformly in most
environments (Birkeland, 1984). Various properties of clasts have been used to represent
their degree of weathering. Most frequently, weathering rind thickness has been employed,
but percent weathered boulders and depth of near-circular weathering pits have also been

used (Birkeland, 1984).
8.1.2 Weathering rind thickness

In New Zealand, Chinn ( 1981) showed that the thickness of weathering rinds on
cobbles on Holocene geomorphic surfaces increases rapidly with time, described by a
power function. Whitehouse er al. (1986) suggested that rind growth is not predicted by a
power function for surfaces older than 20 ka because for those surfaces the rate of
weathering approaches the rate of inward rind migration.

Variations in annual precipitation and minor variations in lithology and mineralogy
were found to produce little variation in the rate of weathering rind growth (Colman and
Pierce, 1981; Knuepfer, 1988). Knuepfer (1988) observed that even the weathering of
chlorite schist occurred at rates comparable to those of other lithologies, i.e. graywacke and

high grade metamorphic rocks. The weathering of metamorphic rocks was different from

15 1
that of clasts of other lithologies because metamorphic rocks decomposed principally along

foliation planes rather than by inward rind thickening. Nevertheless, weathering rinds on
high grade metamorphic rocks have been used with success as a relative age indicator
(Mills, 1983).

Weathering rind thickness was found to be strongly dependent on depth of rock
burial (Birkeland, 1984; Knuepfer, 1988; Mills, 1988). Initial weathering was
characterized by rates of subaerial weathering that exceeded those of subsurface
weathering; with time, subsurface rates became greater, although more variable than near-
surface rates (Birkeland, 1984; Knuepfer, 1988).

Measurements of weathering rind thickness have also been used successfully to
date mass movements such as rock avalanches in New Zealand (Whitehouse, 1983) and
debris flows in the Blue Ridge (Mills, 1983; Whittecar and Ryter, 1992). Mills (1983)
identified three topographic levels of debris flow deposits and concluded that the age of the
deposits increased from the lowest to the highest level. Weathering rind thickness increased
consistently with increasing age. It was, however, not possible to unequivocally assign a
deposit to a topographic level on the basis of weathering rind thickness alone because there
was some overlap of the rind thickness of adjacent levels (Mills, 1983). Whittecar and
Ryter (1992) obtained very similar results. They identified two groups of debris flow
deposits at different topographic levels. Greenstone clasts in the soils of the higher level
had significantly thicker weathering rinds than the clasts of the lower level, and were
interpreted to be older. Other soil properties, such as maximum clay content and maximum
free iron content, pointed to a similar age relationship between the two groups of debris

flow deposits.

152
8.1.3 Percent weathered clasts

The relative amount of weathered clasts has been used most frequently for relative-
age dating of moraines (Mahaney, 1978; Burke and Birkeland, 1979; Miller, 1979). Mills
(1981; 1982a; b; 1988) employed the method to determine the relative ages of colluvium in
the Southern Blue Ridge of North Carolina and the Valley and Ridge of Virginia. Mills
(1981; 1982a; 1988) defined a weathered clast as one that could be broken apart by hand.
In the Blue Ridge, deposits considered to be young occurred at lower elevations and had
considerably fewer weathered clasts than older deposits (Mills, 1981). The percentage
weathered clasts correlated well with another relative age indicator, soil color, but did not
correlate with the percent clay, which also has been used as a relative age indicator (see
chapter 9). This lack of correlation was thought to be due to the breakdown of clasts and
the subsequent incorporation of the component grains into the soil matrix (Mills, 1981). In
colluvium of the Valley and Ridge the percent weathered clasts was also deemed an
accurate measure for discriminating between older and younger deposits (Mills, 1988). In
the same environment, however, sandstone weathering rinds proved too variable to use as

a weathering index (Mills, 1988).

8.2 Methods

As explained in section 5.2.1, 50 clasts were collected at random from 11 pedons.
The horizons from which the clasts were collected are listed in Table 3. The clasts were
characterized by size, sphericity, roundness, lithology and weathering. Almost all clasts
were metamorphic (Table 7) and did not show weathering rinds. Therefore, the percentage
weathered clasts was considered as an alternative proxy for relative age. A similar approach

was used by Sharp (1969).

153
Determining the percentage weathered clasts has traditionally involved classifying

clasts as either weathered or not weathered. In this research project, there was enough
variability in the weathering of the clasts to assign them semi-objectively to one of three
groups; little, intermediate, and highly weathered. The allocation of a clast to a certain
group was based on (i) the physical soundness of the clast as determined by a sharp blow
with a rock hammer, (ii) the dominant color of the inside of the Clast and (iii) the alteration
of minerals as seen under a 10X hand lens. Clasts in the "little weathered" category
typically needed many (> 4) hard blows to be broken, did not show oxidation colors on
broken surfaces although staining in cracks was sometimes present, and had no clear
alteration of minerals. Clasts in the "intermediately weathered" group did not need many (2-
4) hard blows with a hammer to be broken, had oxidation colors over most of the broken
surfaces and had visible alteration of some minerals. The highly weathered clasts were easy
to break with S2 gentle strikes with a hammer, were completely brownish or reddish inside
and had many crystals that were visibly altered or completely dissolved.

For each pedon, the percentage of clasts in each weathering group was determined.
The results were then analyzed visually and by cluster analysis of standardized values.
Both methods were used in conjunction because it is important to have control over the
physical meaning of observations and conclusions. while it is also critical to keep a sense of
objectivity. Harbor (1986) also concluded that, for mathematical reasons, it is important to
combine a clustering procedure with a subjective analysis of individual data distributions.
For the cluster analysis a K-means procedure, with 50 iterations and 4 groups, was used.
This procedure produces non-hierarchical clusters by maximizing between-cluster, relative

to within-cluster, variation.

154
8.3 Results and discussion

The use of clast weathering as a relative—age indicator assumes that all clasts were
equally weathered when the deposits were formed and that they have weathered at
comparable rates since deposition. In the case of debris flow deposits the first assumption
seems warranted. During transportation in debris flows, clasts interact with each other, the
matrix, and obstacles on the surface and in the path of the flow. It seems therefore
acceptable to assume that weathered clasts are destroyed during transportation and that
primarily fresh clasts are incorporated in deposits. Mills (1983) and Graham et al. (1989a,
b) also concluded that destruction of preweathered material occurred in debris flows.

The rate of weathering (related to the second assumption above), depends chiefly
on climate, vegetation, topography and bedrock composition. As argued in the introduction
(chapter 7), the climate, vegetation and topography at the three sites are very similar. The
lithology of the clasts encountered in the various deposits is also fairly uniform (Table 7).
Most sites are dominated by gneisses that usually show little foliation. The main deviation
of this mode was observed at AUf and AUa where metasandstone was the dominant
lithology. The metasandstone is quartz-rich and thus, more resistant to chemical weathering
than most other lithologies that were encountered. However, since most gneisses also
contain relatively high amounts of quartz and are better crystallized, the influence of the
abundance of metasandstone in the one Alarka deposit may not be large. This is confirmed
by the presence of relatively fresh schist at the Alarka site. Schists generally are susceptible
to weathering and their presence suggests that the unweathered nature of the metasandstone
is not due to its composition alone. In fact, the presence of schist at the Alarka site and its
absence in Hidden Valley could be the result, not the cause, of the difference in age
indicated in the results of this chapter. For the above reasons, the rate of weathering of the
clasts at the three sites will be assumed to be similar.

The abundance of the clasts in the three weathering classes is listed in Table 12.

155

There are clear differences in the degree of weathering of the clasts at the three sites. At the

Alarka site many clasts are little weathered, intermediate amounts are moderately weathered

and few clasts are highly weathered. In Hidden Valley, most clasts belong to the

interrnediately or highly weathered classes and very few clasts show little weathering. At

the Bradley site clasts are distributed more evenly over the three weathering classes.

l:ITable 12: Clast weathering data, all sites.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon- Low Medium High Cluster
Horizon % % %
ii ALfl 50 42 8 1
ALf2 57 37 6 l
AUf 20 54 26 2
AUa 18 59 22 2 1'
HLf 27 48 25 2
HMf 4 14 82 4
HUf-2Bt2 3 63 34 3
HUf-3Bt3 8 38 54 4
HUa 5 26 69 4 I
BLf 14 55 3 l 2
BLa-2Bw2 25 5 l 24 2
BLa-43 W4 5 l 49 0 1
BUa-3Bw3 26 52 22 2
BUa-5Bw5 l 5 70 l 5 2

 

Within the Alarka and Hidden Valley sites there is a systematic variation in degree

of weathering of the clasts between the lowest and highest deposits. Pedons ALfl and

ALf2, which are in the lower landscape position at the Alarka site, have more little-

weathered and less highly-weathered clasts than AUf and AUa, which are located on the

higher deposit. The same trend can be observed at Hidden Valley, where HLf has more

156
little weathered and less highly weathered clasts than the other (higher) pedons. HMf has

many more intensely weathered clasts than any of the other locations. Its greater relative
age is corroborated by the existence of saprolite at this location (see section 6.4)

Three pedons (HUf, BLa and BUa) are represented by samples from two different
horizons. Although there is a difference between the two samples from within each pedon,
the variation is neither large nor systematic. The only noteworthy difference is the larger
amount of little weathered clasts in BLa-4Bw4 (1 1-187+ cm) as compared to BLa-2Bw2
(45-79 cm). This observation can be explained by the generally accepted notion of
decreasing weathering intensity with depth.

The results of the cluster analyses confirm these visual observations (Table 13). All
but one pedon at the Hidden Valley site are concentrated in two clusters. In these two
clusters, samples from the other two sites are not represented. These two clusters represent
pedons with high amounts of highly weathered clasts. Also all but one pedon of the
Bradley site are concentrated in one cluster (cluster #2). In Alarka the two lowest Alarka
pedons, AU] and ALf2, do not co-occur with the two higher Alarka pedons. The lowest
pedon of Hidden Valley (HLf) was grouped together with the two higher pedons of Alarka
and several Bradley pedons. The general concentration of the pedons of one site in one or

two groups seems to indicate that the within-site relative-age difference is small.

8.4 nclusions

Although the results of this chapter will be combined with those following, they
point to the existence of distinct differences in age within and between the three sites. The
Alarka site has the least number of weathered clasts and therefore appears to be the
youngest of the three. The Hidden Valley site, and especially the saprolite in HMf, has
many highly weathered clasts, indicating an older age. All but one of the Hidden Valley

pedons were classified in separate clusters, suggesting a similarity in age but also ages that

157
are unlike those of the other two sites. At the Bradley site none of the three weathering

classes clearly dominates over the other two, which indicates that the age may be

intermediate between the Alarka and Hidden Valley sites.

Table 13: Cluster anal ses of clast weatherin ; data.

 

 

 

 

 

 

 

 

 

 

 

 

 

Cluster* Pedons Variable Standardized mean
(Clast weatheringgroup)

1 ALfl, ALf2, BLa-4Bw4 Low 1.65
Medium -0.29
High -1.07
2 AUf, AUa, HLf, BLf, Low -O.13
BLa-2Bw2, BUa-3Bw3 Medium 0.58
BUa-5Bw5 High -O.27
3 HUf-2Bt2 Low -1.12
‘ Medium 1.09
High 0.18
l 4 HMf, HUf-3Bt3, HUa Low -0.97
Medium -1.42
Hih -l.63

 

 

 

 

* A higher cluster number indicates an older relative age.

At the Alarka site the higher deposit appears to be older than the lower deposit. In
the cluster analyses the higher deposit was grouped together with the deposits of the
Bradley site, suggesting that it may be similar in age to the Bradley deposits. The highest
deposit at the Hidden Valley site also appears to be older than the lowest deposit at that site.

In summary, the results of this chapter, which have to be considered preliminary,
show that there is a difference in age between the three sites, Alarka being the youngest and
Hidden Valley being the oldest. At the Alarka and Hidden Valley sites, the lowest deposit is

younger than the highest.

l 5 8
9 SOIL DEVELOPMENT

2.1 Literature review

Soil morphological properties have been used extensively, and successfully, as
tools for relative-age determination in geomorphic studies (e.g. Birkeland, 1978; Levine
and Ciolkosz, 1983; Harden, 1990; Birkeland et al., 1991; Markewitch and Pavich, 1991;
Woodward et al., 1994; Leigh, 1995). Many soil morphological properties have been used
to assess the relative age of soils, including percent clay in B horizons (Leigh, 1995), color
(Meixner and Singer, 1981; Harden, 1982; Dethier, 1988; Leigh, 1995), decalcification
depth (Woodward et al., 1994), clay illuviation (Dethier, 1988; Markewitch and Pavich,
1991; Woodward et al., 1994), solum thickness (Dethier, 1988; Markewitch and Pavich,
1991; Vidic et al., 1991; Leigh, 1995), organic matter in B horizons (Woodward et al.,
1994), overall texture (Van Wambeke, 1962; Meixner and Singer, 1981; Harden, 1982;
Harrison et al., 1990), consistence (Meixner and Singer, 1981; Harden, 1982) and
structure (Harden, 1982; Phillips, 1990).

Several problems, however, are associated with the use of soil development as a
relative age indicator. Switzer et al. (1988) pointed out that the technique assumes that soil
development is continuous but that, on small timescales, soil development may be episodic.
Harrison et al. (1990) showed that the degree of variability of soil properties for a given
surface and landscape position can be sufficient to raise questions about the usefulness of
quantification of soil - time relationships. Phillips (1990) cautioned against the use of soil
development as an indicator of the relative age of the parent material of the soil because
surficial processes (i. e. erosion and deposition) may have inhibited pedologic development.
He argues that soil development should be used to characterize the relative age of
contemporary geomorphic features. Harden (1990) came to a similar conclusion and added

that an improved comprehension of intrinsic, soil-driven mechanisms is needed to better

159
evaluate soil development. Nevertheless, she concluded that soil morphology has proven to

be a convenient tool for assessing degree of development.

Most chronosequence and relative-age dating studies of soils have been carried out
on moraines or in semi—arid environments. Few studies from humid areas in general, and
from the southeastern US in particular, have been performed. Most work in the
southeastern US was carried out on the Coastal Plain (Daniels, 1978; Markewitch et al.,
1986; 1987; 1988; 1989; Phillips, 1990; Markewich and Pavich, 1991).

Markewitch and Pavich (1991) investigated the usefulness of chronosequence
studies in a low relief area with a temperate to subtropical, humid climate. They found that
in their area soils had developed along two different pathways; one resulting in the
formation of Spodosols and one in Ultisols. No clearly distinguishable age trends could be
identified in the Spodosols but the morphological properties of Ultisols could be utilized to
characterize surface material alteration through time. The best indicators of the degree of
soil development among soils of Pleistocene age were solum thickness, thickness of the
argillic horizon, color of the B horizon, clay mass in a unit column of the solum and several
chemical characteristics. The most useful properties for age comparison of older soils
included solum thickness, clay mass and color (Markewitch and Pavich, 1991). These
properties increased with increasing time. Properties of Holocene soils were variable and
sometimes could be confused with geologic properties of the parent material. This problem
was in particular true for horizonation, structure and texture. Clay mass was considered to
be the best overall relative age indicator by Markewitch and Pavich (1991). Leigh (1995)
studied floodplain and terrace soils about 45 km southwest of the study area of the present
research. The floodplain and the lowest terrace were dated by 14C to 1.9-0.6 ka and 13.3
ka respectively. Floodplain soils were Entisols, on the lowest terrace Alfisols had
developed and on the higher terraces Ultisols were observed. The B horizons of the higher,
and therefore older, terraces contained progressively more clay and were redder than those

of lower terraces.

160
221mm

9.2.1 Selection of relative-age indicators

The selection of the most appropriate relative age indicators is mainly based on
findings by Markewitch and Pavich (1991) and Leigh (1995). Both studies took place in
soils and climates that are similar to those of this research. Furthermore, Leigh's (1995)
study area is located in the Southern Blue Ridge.

Both Markewitch and Pavich (1991) and Leigh (1995) judged soil color and clay
content to be good relative-age indicators. To represent color, Markewitch and Pavich
(1991) used Munsell hue while Leigh (1995) used the Hurst index. The amount of clay
was characterized by Markewitch and Pavich as clay mass in g cm'2, integrated through the
thickness of the solum, which is associated with the degree of weathering. Leigh (1995)
used the percent clay in the most developed B horizon. Markewitch and Pavich (1991) also
ranked thickness of the solum and the argillic horizon as good indicators. All the above
observations are not in contradiction with generally accepted principles (Birkeland, 1984),
and therefore, the focus of the rest of this chapter will be on color (rubification) indices and
measures of clay content as relative-age indicators.

Thickness of the solum is not a suitable parameter for this study because the C, and
even BC, horizon was not reached in four of the 13 pedons. Moreover, thickness of the
solum is sometimes difficult to assess because horizon boundaries may be gradual or
diffuse. As an alternative for solum thickness, the depth of maximum clay content will be
considered as a thickness criterion. An argillic horizon is only present in six pedons and in
the soil pit of two of these, the bottom of the argillic horizon was not encountered. It

therefore seems more appropriate to consider presence of an argillic horizon rather than its

thickness.

161
9.2.2 Data collection and analyses

Field data were collected and basic calculations performed as explained in sections
5.2 and 6.2. Results of these operations are reproduced in Table 4 and Appendices 3 and 4.

The most frequently used rubification indices in chronosequence studies are the
Buntley-Westin index (Buntley and Westin, 1965), Hurst index (Hurst, 1977) and the
redness rating (Torrent et al., 1983). The Buntley-Westin index (BW) quantifies the hue
(10R = 7, 2.5YR = 6, 5YR = 5, 7.5 YR = 4), which is then multiplied by chroma. It is
closely allied with the intensity of weathering, stage of soil development and drainage
(Buntley and Westin, 1965). The Hurst index (HI) quantifies hue (10R = 10, 2.5YR =
12.5, 5YR =15, 7.5YR = 17.5) and multiplies it by the value/chroma fraction. The H1 is a
crude proxy for the total amount of iron in a soil (Hurst, 1977). The redness rating (R) is
calculated by the formula (10-YR hue) x chroma/value. The R has been linked to hematite
content (Torrent et al., 1983; Graham et al,. 1989a). As mentioned in 9.2.1, Munsell YR
hue has also been used as a color index (Markewitch and Pavich, 1991), but it is a less
refined measure than the above three indices.

The calculations were performed on the Munsell color of the reddest horizon of
each profile. Because the HI decreases with increasing redness, and presumably increasing
age, and the BW and RR increase with increasing redness, the reciprocal of the HI was
graphed in Figure 34.

To represent the clay content of the soils, three parameters were calculated; percent
clay in the most clay-rich horizon (Bwl for BUa, see section 6.4.3), the clay mass of the
most clay-rich horizon, expressed in g cm'3 (Bwl for BUa, see section 6.4.3), and the
clay mass in g cm‘z, summed over the thickness of the solum. The clay mass was obtained
by multiplying the bulk density of the most clay-rich horizon by the percent clay. (An
underlying assumption is that all particles in a soil have the same density.) Clay mass is

considered to be a better measure for the amount of clay than percent clay because clay

162
mass is an absolute value that permits quantitative comparisons. The clay mass per cm2 of a

solum-thick column was derived by multiplying the clay mass of each horizon by its
thickness and by integrating the results over the horizons in the solum. A cluster analysis
identical to the one explained under 8.2 was performed on the six variables.

As mentioned above, the bottom of the solum was not reached in all pedons.
Therefore, the clay mass per square centimeter has to be regarded as a minimum value in

the case of the two highest pedons at Hidden Valley and Bradley (HUf, HUa, BLa, BUa).

9.3 Results and discussion

9.3.1 Rubification

The results of applying the three rubification indices to the various pedons are very
similar (Figure 34). The lowest values are present in the Alarka pedons, intermediate values
can be observed at the Bradley site and the highest indices are for the pedons at Hidden
Valley. The values at the Bradley site are somewhat closer to the values at Alarka than to
those at Hidden Valley.

The three indices show identical relationships for pedons within the Alarka site;
Pedons AU 1, ALf2 and AUa have the same value and AUf, which is on the highest
deposit, has a slightly higher value. At Bradley there is no consistent relation between the
three pedons. The R increases with increasing elevation but the HI and BW show no
trend with elevation. At Hidden Valley the highest value is always reached for HMa, one of
the soil pits that was in saprolite. As compared to the other Hidden Valley pedons, HLf and
HLa, which are on the lowest deposit, have lower values for the HI and RR and

intermediate values for the BW.

163

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164

A systematic difference between pedons in toe and apex positions is not apparent
(Figure 34). In Alarka, pedon AUf, which is in a toe position, has higher values than the
pedon on the apex of the same deposit (AUa). In Hidden Valley there is no difference
between the pedons on the toe and apex of the lowest deposit (HLf and HLa) and highest
deposit (HUf and HUa), except for the BW of the highest deposit. In the latter case the
pedon on the toe has a lower value than the pedon on the apex. As mentioned above, a

systematic trend with elevation or geomorphic position is not present in the Bradley site.

9.3.2 Clay content

In general, the three parameters representing clay content show the same trends
(Figure 35). The lowest values are observed at Alarka, the pedons at Bradley have
comparable to slightly higher values, and the highest values are reached at Hidden Valley.
The presence of argillic horizons at the Hidden Valley site, and their general absence at the
other two sites, substantiates this observation. The highest clay content in a B horizon is at
HMf, one of the saprolitic soils, while the highest clay mass in a solum is at HUf. The clay
mass in the most clay-rich B horizon and the clay mass in the solum have opposite trends in
Alarka but the same trend in Hidden Valley. This indicates that at the Alarka site the B
horizons are either clay rich or thick while at the Hidden Valley site they are usually both
clay rich and thick.

The clay content of the B horizon and clay mass of the solum of pedons on the toe
and the apex of a deposit do not show a systematic difference (Figure 35). However, at
Alarka the clay content of the B horizon is higher in the apex position (AUa) than in toe
position (AUf) while on the saprolite and the highest deposit of Hidden Valley it is lower in
the apex position. The low amount of clay in the sola of HLf and BLf is due to a shallow

water table which prevents the sola from developing further downward. This means that at

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166
these two locations time is not the prime factor that has determined the clay mass in the

profile.

No inferences can be made for the clay mass in the sola on the highest deposit in
Hidden Valley (HUf, HU a) and Bradley (BLa, BUa) because at these locations the lower
boundary of the solum was not encountered. This does not, however, appear to influence
the conclusions to a large extent. Values for clay mass in the solum of HUf and HUa are
among the highest encountered anyway. The results for BLa and BUa indicate that the
internal relationship of the site, as indicated by the other two parameters, does not hold for
the clay mass in the solum, regardless of the magnitude of the underestimation for BLa and
BUa. The results for the two latter pedons, obviously, does affect between-site
comparisons.

The cluster analysis, which was run on all six soil development indices, grouped
the Alarka and Bradley pedons into one cluster. The second cluster contained pedons HLa,
HMf, HUf and HUa. Pedons HMa and HLf were each assigned to a one-member cluster.
A cluster analyses with three groups classified HLf together with the Alarka and Bradley
pedons. This would have left HMa as the pedon that is most different (older) from the other

pedons.

2.4 Conclusions

The variation in relative age, as indicated by soil development indices, is larger and
more consistent between sites than within sites. But, conclusions about the implications of
within-site relative-age variations should be evaluated more cautiously than the conclusions
about between-site variation (Harrison et al., 1990).

Between-site variations consistently point to a relatively young age for the soils at
Alarka, an intermediate age for those at Bradley and an older age for the soils at Hidden

Valley. Assuming that the rate of increase with time of the color indices and clay content is

167
not logarithmic, the soils at the Hidden Valley site appear to be considerably older than

those at the other two sites.

Most indices indicate that pedon AUf is slightly older than the other Alarka pedons.
This is, however, not confirmed by the clay content in the B horizon. Pedon AUf also was
grouped together with the other Alarka pedons in the cluster analyses. At Hidden Valley,
there is some evidence to suggest that, at this site as well, the highest deposit is older than
the lowest deposit. The saprolite at Hidden Valley, which topographically is located
between the two deposits, appears to be older than any of the deposits. The results for the
lowest pedon in Hidden Valley, HLf, are typical of relatively young soils. This pedon was
grouped singly by the 4-group cluster analysis. Its assignment to the group of the Alarka
and Bradley pedons by the three-group cluster analysis suggests that HLf is similar in age
to the pedons at these two sites.

The lack of systematic variation between pedons on the toe vs. apex of the deposits
points to the effectiveness for relative-age dating of the chosen variables. Although there
are morphologic differences between pedons on toe and apex positions (see chapter 6),
relative-age indicators should show less difference between soils on a single geomorphic
surface. Nevertheless, if the relative ages postulated in chapters 8 and 9 (Hidden Valley
older than Alarka, higher deposits slightly older than lower deposits) are correct, some of
the variations in clay content on a geomorphic surface may be related to age. The available
data suggest that B horizons on the apex of a deposit contain more clay than B horizons on
the toe of the deposit in young soils but that in old soils they contain less clay on the apex

than on the toe.

1 68
10 [RON SPECIES

10.1 Literature review

10.1.1 General

Many authors have concluded that certain iron species, their abundance and ratios
thereof correlate well with soil age and profile development. The most frequently used iron
species include total ferric iron (Fed, extractable with sodium dithionite), ferric iron present
in poorly crystalline oxyhydroxide phases and organic complexes (Feo, extractable with
acid ammonium oxalate), and total iron (Fet). Regularly employed iron species ratios
include Fed/Fet, Fed-Feo/Fet, and Feo/Fed.

This literature review summarizes the climatologic, pedologic and geomorphic
settings of studies by Alexander (1974), Torrent et al. (1980), Alexander and
Holowaychuk (1983a, b), Arduino et al. (1984, 1986), Rebertus and Buol (1985),
McFadden and Weldon (1987), Graham et al. (1989a) and Leigh (1995).

Alexander (1974) examined a sequence of terraces in a sub-humid climate. The
soils on the floodplain were Cumulic Haploxerolls and those on the terraces classified as
Typic Argixerolls. In the Typic Argixerolls samples were taken from the argillic horizon.
Torrent et al. (1980) studied trends of Fed, Feo, Fed/Fet and Feo/Fed with age in xeric
Alfisols on two terrace sequences. The authors sampled the upper part of the Bt horizon
because it usually had the most pronounced red color. Alexander and Holowaychuk
( 1983a, b) studied a chronosequence on terraces under a hot, humid climate. The soils on
the floodplain were Aquents and Aquepts; on the intermediate terraces they classified as
Ustults, and on the highest terrace an Ustox had developed. Arduino et al. (1984) sampled
the most weathered horizons of Alfisols, Entisols and Inceptisols on terraces under a

Mediterranean climate. The age of the terraces ranged from Middle Pleistocene to

169
Holocene. Rebertus and Buol (1985) studied Hapludults and Dystrochrepts in regolith of

the Piedmont and Blue Ridge of North Carolina. Some of the study sites were located 120
km NE of the study area of the present research. Arduino et al. (1986) examined Alfisols,
Inceptisols and Entisols on three terrace levels under a Mediterranean climate. The
maximum age of the highest terrace was estimated to be 300 ka while the youngest terrace
was thought to be at least 10 ka. McFadden and Weldon (1987), working in a
Mediterranean climate in SW California, had good absolute age control for 11 terraces
ranging in age from 500 ka to 47 a. Characteristics of the area and soils studied by Leigh

(1995) were discussed in section 9.1.

10.1.2 Fed and Feo

Torrent et al. (1980), who studied two terrace sequences, found an increase with
age of Fed, but not of Feo, in soils on one of the sequences. They did not find a trend for
these two species in the other sequence. Alexander and Holowaychuk (1983a, b)
concluded that the amount of Fed was very similar in the soils they studied, although their
data and their discussion indicated that Fed increased as soil age increased. The amount of
Feo decreased with terrace age in this study. Arduino et al. (1984) stated that in their study
area there was an increasing trend with age of Fed and a decreasing trend with age of Feo.
Knuepfer (1988) noted an increase of Feo in young soils (<12-14 ka) but a decrease in
older soils, probably due to re-solution of amorphous Fe. Rebertus and Buol (1985) and
Leigh (1995) reported that the Fed of B horizons showed an increase with soil
development, and thus with soil age.

McFadden and Weldon (1987) noted that Fed, Feo and Fet maxima of Holocene
soil profiles were reached in the A or Bw horizons and that in Pleistocene soils maximum
concentrations of Fed and Feo were reached deeper in the profile, usually in B horizons.

From a graph presented by Alexander and Holowaychuk (1983) and from the data of

170
Arduino et al. (1986), similar conclusions about progressively deeper Fe maxima can be

drawn. In the study of McFadden and Weldon (1987) Fed content was highly correlated
with terrace age (1:094).
Fed content often correlates well with soil redness. Graham et al. (1989a) observed

a strong correlation of this species with the redness rating and McFadden and Weldon
(1987) observed one with the Hurst index (r=0.76 to 0.92 at 0L=2.5% level).

10.1.3 Fed/Fet, (Fed-Feo)/Fet and Feo/Fed

In one terrace sequence Torrent et al. (1980) found an increase in Fed/Fet with age
but Feo/Fed did not show a trend. In the other sequence there were no apparent age trends
of iron minerals but instead a high (i 0.80) Fed/Fet ratio was observed. Torrent et al.
(1980) concluded that this implies that the parent materials of the soils must have had
similar, and high, Fed/Fet ratios, and thus must have been highly weathered. The sequence
that showed trends for Fed/Fet also had increasing amounts of goethite and hematite with
increasing terrace age.

Feo/Fed is an index of crystallization of secondary forms of iron that in the initial
stages of weathering and soil development, when the release of iron from minerals may
exceed the rate of crystallization, increases. Thereafter, the ratio decreases with increasing
soil age. In the study by Alexander and Holowaychuk (1983a; b) the best age trend was
obtained for this index. Feo/Fet decreased as age increased but also decreased substantially
from the surface to the subsoil and thence increased slightly below the solum.

Arduino et al. (1984) obtained the best trend with age with (Fed-Feo)/Fet. This
ratio is a measure of the amount of ferric iron in crystallized phases, as a proportion of the
total amount of iron. The largest proportions of Fed-Feo were present in the oldest terraces,

indicating that progressively more iron was released from silicates as time advanced

17 1
(Arduino et al., 1984). The ratio was independent of the total amount of iron in the samples

and therefore of the general lithology of the basin (Arduino et al., 1984).

Rebertus and Buol (1985) concluded that the Fed/Fet ratio was a sensitive indicator
of profile development, and therefore, of soil age. The Fed/Fet ratios in the B horizons
were much better indicators of relative soil development than those from either C or A
horizons. The Fed/Fet ratio also changed nearly systematically with particle size class and
solum thickness. As age increased, Fed/Fet and solum thickness increased and overall
texture became finer.

Arduino et al. (1986) found that both Fed/Fet and Fed-Feo/Fet served to distinguish
soils of different age. In this study Feo/Fed was generally found to be only a crude
indicator of soil age. McFadden and Weldon (1987) noted that the Fed/Fet ratio of
Holocene soils increased slightly with age, while in Pleistocene soils Fed/Fet increased
significantly with age. The average Feo/Fed ratio for the solum increased for Holocene and
latest Pleistocene soils but decreased for older soils (McFadden and Weldon, 1987).
Alexander (1974) observed a similar trend for Feo/Fed. The breakpoint where the trend
changed from increasing to decreasing with age occurred after "several thousand years".
McFadden and Weldon (1987) concluded that, in their study area, iron oxide content was a

potentially excellent indicator of age of Middle Pleistocene or younger deposits.

1 2 8

10.2.1 Selection of relative-age indicators

As shown by the literature review, Fe species ratios are generally considered to be
better relative age indicators than are individual species data alone. Ratios have the
advantage that variations in the parent material are compensated for. If, for instance, a high

amount of Fed is the result of a high Fet content in the parent material, and not of the

172
degree of weathering, dividing Fed by Fet will eliminate the influence of the parent

material. Therefore, the ratios can be considered "standardized" values.

To better compare the effectiveness of the various ratios (Feo/Fed, Fed/Fet and
Fed-Feo/Fet) as a relative age indicator, I calculated the ratios that were not determined by
the authors. I determined Fed-Feo/Fet for the data of Torrent et al. (1980) and Fed/Fet and
Feo/Fed for the data of Arduino et al. (1984). Other authors did not provide raw data that
allowed me to determine other ratios than those that they had calculated.

Among the authors that discussed Feo/Fed, only Alexander and Holowaychuk
(1983), working on soils in a hot humid climate, considered this ratio to be a good relative
age indicator. For the data of Arduino et al. (1984) I did not find a good correlation of
Feo/Fed with age. Therefore, this ratio will not be used in the present research.

Other authors obtained the best relative-age dating results with Fed/Fet and/or Fed-
Feo/Fet. From the data of Arduino et al., the ratio calculated by me (Fed/Fet) had a trend
that was very similar to the Fed-Feo/Fet trend used by the authors. For the data of Torrent
et al., I found a trend for Fed-Feo/Fet that was comparable to the trend of Fed/Fet obtained
by the authors. Together with the results from the literature review, this pre-analysis
procedure suggests that trends for Fed/Fet and Fed-Feo/Fet are closely related, and that in
many cases the ratios lead to similar results. Unfortunately, a quantitative comparison of
the effectiveness of the two ratios can not be made because of a lack of quantitative age
data.

Rebertus and Buol (1985) worked in the Southern Blue Ridge of North Carolina, in
a clirnatologic and geologic environment that is very similar to that of the present study.
Because they attained better results with Fed/Fet than with Fed-Feo/Fet, the former ratio

will be used in the present study.

173
10.2.2 Data collection and analysis

Field data and samples were collected as explained in sections 5 .2 and 6.2.
Procedures for extracting Fed and Fet were according to Jackson et al. (1986) (procedure
64.3) and Lim and Jackson (1982) (procedure 1-5) respectively. For each horizon a
sample of about 10 g was separated from the main sample with sample splitters to obtain a
representative sample. The 10 g sample was ground to silt size in an agate mortar. Replicate
subsamples of about 4 g were taken for Fed analysis, replicate samples of about 0.2 g were
taken for Fet analysis.

The subsample for Fed analysis was transferred to a centrifuge tube and a 5:1
mixture of 0.3 M sodium citrate (N a3C6O7.2H20) and 1 M sodium bicarbonate (NaHCO3)
was added. Subsequently, the mixture was heated to 75 to 80° C, at which time about 1 g
of sodium dithionite (N a2S204) powder was added. After a 15 minute digestion period
under repeated stirring, the tube was placed in a centrifuge, spun at 2000 rpm for 6
minutes, and the supernatant decanted. This procedure was repeated to remove any ferric
iron that might have been left by the first extraction. The supematants of the two extractions
were combined and diluted for measurement on a directly coupled plasma spectrometer.

The 0.2 g subsample for Fet analysis was first mixed in a polypropylene bottle with
1 ml of aqua regia (3 parts 12 N HCl and 1 part 15 N HNO3). After about one hour, 10 ml
of 48 % hydrofluoric acid (HF) was added and the bottle capped immediately. The mixture
was then shaken overnight to dissolve the sample. Afterwards, 100 ml of saturated boric
acid was added to decompose any metal fluorides that might have formed and the bottle
was shaken again for 6 to 8 hours. Subsequently, the contents of the bottle were diluted to
200 g and analyzed on a directly coupled plasma spectrometer.

Results for Fed, Fet and Fed/Fet are provided in Appendix 8. Because there was
variation in the Fed/Fet ratio with depth (Figure 36), the profile weighted mean ratio for

each pedon was computed. The mean was calculated by the formula

174

(2(ratioi*thicknessi))/solum thickness, where i designates the horizons in the solum. By
using the solum, rather than the bottom of the soil pit, C horizons were excluded from the
calculations. (C horizons were not encountered in all soil pits). Including them for some
pedons only, would have biased the average of those pedons towards a lower value
because, generally, C horizons have lower Fed/Fed ratios than do B horizons.

A cluster analysis identical to the one explained under 8.2 was performed on the
solum means. In this one dimensional case, the routine simply provides a grouping of the
pedons along a single axis, providing an objective alternative to the visual assignments of

groups on a histogram.

1 . R sults and discussion

The general variation of Fed/Fet with depth, demonstrated in Figure 36, can be
observed in saprolitic (HMf, HMa) and colluvial (all other pedons) soils alike. This
indicates that weathering products do not gradually decrease with depth in these soils. This
finding can possibly be explained by variations in the composition of the soil water. As
argued above, the effect of compositional changes in the parent material is expected to be
small because the ratio has the total amount of iron (Fet) in its denominator.

Figure 37 shows that the pedons of the Alarka site have the lowest Fed/Fet ratio and
that those at the Hidden Valley site generally have the highest values. The pedons at
Bradley have intermediate values. The values within the Alarka site are very similar (25 -
28 %). Also within the Bradley site there is little variation although the ratio slightly
decreases as elevation increases. This may be an artifact of the misrepresentation of the
ratio at BLa and BUa where the bottom of the solum was not encountered. At the Hidden
Valley site the pedons on the lowest deposit have the lowest values (HLf and HLa). The
ratio is maximal in one of the saprolitic soils (HMf) and slightly lower in the pedons on the

highest deposit (HUf, HUa).

 

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177
The cluster analysis classified all four pedons of Alarka and HLf and BUa, in one

group. The three highest pedons in Hidden Valley (HMa, HUf, HU a) were grouped in a
second cluster. The third cluster consisted of HLa, BLf and BLa, while pedon HMf was in
a cluster alone. When three clusters only were used, HMf was added to the group of HMa,
HUf and HUa. These results confirm that there is little variation within the Alarka site and
that the pedons on the lowest deposit in Hidden Valley are more similar to pedons in the

Alarka and Bradley site than to the other four deposits in Hidden Valley.

10,4 Cooolusions

The variation of Fed/Fet with depth, in both saprolitic and colluvial soils, is
irregular. However, the results of this chapter corroborate conclusions of earlier chapters.
The pedons of the Alarka site have relatively small Fed/Fet ratios, which generally are
associated with relatively young soils. The pedons at the Hidden Valley site have Fed/Fet
ratios characteristic of older soils. Based on the Fed/Fet ratio, the relative age of the soils at
the Bradley site appears to be intermediate to those of the other two sites.

The within-site variation at Alarka is smaller than the within-site variation at Hidden
Valley and the between-site variation of the three sites. At the Alarka and Bradley sites there
is no evidence that the higher deposits are older. In Hidden Valley the lowest deposit has
lower Fed/Fet values and therefore appears to be younger. For the Bradley and Hidden
Valley sites this conclusion is consistent with the results of chapters 8 and 9. The highest
Fed/Fet value was reached in HMf, one of the saprolitic soils.

As was the case for the clast weathering and soil development indices, conclusions
regarding Fe species ratios have to be considered as partial. They will be combined with

other results to come to a firmer end result.

178
11 DISCRIMINANT ANALYSES

11.1 Literature review

Qualitative evaluation of relative-age characteristics and data has been the classical
approach to the grouping of geomorphic sites (e. g. Sharp, 1969). More recently, various
multivariate statistical operations have been used to classify relative-age data into
meaningful groups. Miller (1979) used custom-built software to develop an age
classification of stations according to six relative-age dating criteria. Mills (1982) applied
discriminant analysis to relative-age data from three sites in the Southern Blue Ridge but
then evaluated the results subjectively. Switzer et al. (1988) used existing absolute age
information and maximum likelihood classification to establish calibration curves and to
estimate the age of undated soils. The majority of statistical classifications, however, have
been carried out with principal component (PCA), cluster and discriminant analyses.

A paper by Dowdeswell and Morris (1983) was one of the first to review these
three methods. The authors argued that PCA was an important preliminary step to the
grouping of sites through cluster analysis. Advantages were thought to be that PCA
routines standardized scores, filters noise and produces orthogonal (independent) new
variables. Harbor (1986) agreed with these advantages but pointed out that a major
assumption of PCA was that each original variable is normally distributed. In most relative-
age studies, however, the ages of deposits are expected to be concentrated in distinct
groups that represent different geomorphic surfaces. Therefore, most relative-age data sets
will not have a normal distribution.

Cluster analysis is usually used to group sites on the basis of PCA scores or
standardized values of the relative-age indicators. Most cluster routines combine sites into a
hierarchy of groups of decreasing similarity (Dowdeswell and Morris, 1983). A visual

inspection of the classification is performed to select the most appropriate level of

179

clustering. If there is no a priori reason to assert that all groups have the same level of
internal variance, clusters from different levels may be chosen for further interpretation
(Dowdeswell and Morris, 1983). Because cluster algorithms are sensitive to small changes
in the data, the technique should be accompanied by a subjective evaluation of the results
(Harbor, 1986).

The quality of clustering at any level can be tested with discriminant analysis.
Discriminant analysis can be considered to be the opposite of clustering because it uses
existing groups and constructs functions (new variables) that produce maximum difference
between those groups (Davis, 1986). The statistical significance of the separation between
the groups produced by the discriminant functions, and thus the quality of the initial
grouping, can be assessed by Wilks's lambda (Dowdeswell and Morris, 1983) and
Hotelling's T2 test (Davis, 1986). Harbor (1986) submitted, however, that there is a
circularity in the testing of the output of cluster analysis by discriminant analysis. He
contended that, because of purely mathematical reasons, discriminant analysis always gives
a high significance between groups derived from cluster analysis when the data set
conforms to all assumptions of the methods. Harbor (1986), therefore, stated that the only
valid means of using discriminant analysis with groups of relative-age data is to use one set
of data to generate the clusters and another to test them, or to use groups based on personal
judgment. In other words, discriminant analysis can be used as a quality check for a non

statistical grouping of data into discrete classes.

11 Met ds

11.2.1 Construction of relative-age groups

Not all relative-age indicators used in this study are normally distributed (Lilliefors

test, or = 10 %). Therefore, it seemed best not to use PCA, and subsequently cluster

1 80
analysis, to group the pedons. It seemed better to use subjective but physically meaningful

data, rather than objective but statistically inappropriate data, for further grouping and
processing. Furthermore, considering the caution by Harbor (1986) about the appropriate
use of dicriminant analyses, I chose to group the pedons based on the findings of the
previous three chapters.

All relative-age proxies indicated that, in general, the youngest deposits were
present in Alarka and the oldest in Hidden Valley. Within the Alarka site clast weathering
data clearly pointed to a greater age for the highest deposit (AUf, AUa) than for the lowest.
The soil development indices seemed to confirm this for AUf but not for AUa. The iron
species ratio showed very similar values for all Alarka pedons. These observations are
inconclusive but because of the strong evidence from clast weathering, the pedons of the
Alarka site were separated in two groups. Pedons ALfl and ALf2 were classified in the
youngest group (G1) and AUf and AUa were the first members of a slightly older group
(G2).

Within the Hidden Valley site all relative-age indicators (clast weathering, soil
development, iron species ratio) pointed to a younger age for the pedons on the lowest
deposit (HLf, HLa), as compared to the higher pedons. The cluster analyses reported in the
previous three chapters systematically grouped HLf with the pedons of the Alarka site.
Pedon HLf was therefore classified in G2. Because of the similarity of HLa to HLf, it too
was classified in G2. The other four Hidden Valley pedons (HMf, HMa, HUf, HUa) were
assigned to a separate group (G3) that may contain the oldest soils.

At the Bradley site there is no apparent age difference between deposits at different
topographic levels. The clast weathering and soil development data indicate that the ages of
the three Bradley deposits may be similar. It was therefore decided to classify the three
Bradley pedons together. The results from chapters 8 and 10 show that they are more
closely associated with G2 than with G] or G3. It would be possible to assign a new group

to these soils. However, it is not clear whether this new group would be slightly younger

181
or older than G2. Because the resolution of the employed methods probably does not

permit to make this distinction, the soils of the Bradley site were classified in group G2.

11.2.2 Data analysis

Once the three groups above were delineated, three variables were excluded from
the discriminant analysis to avoid redundancy. In chapter 8 the number of clasts in three
weathering classes was expressed as a percentage of the total number of clasts. This
implies that the value of the third class is completely determined by the outcome for the two
other classes. One of the classes (medium weathered) was therefore eliminated from the
data set. The three rubification indices (chapter 9) had very similar trends. To avoid an
undue influence of the color as a relative-age indicator, one of the indices was removed
from the data. I chose to remove Buntley-Westin index because it was developed for
grassland soils, which have a morphology that is quite different from the soils studied here.
However, the similarity of the three color indices (Figure 34) indicate that removing any
one of them would have been acceptable. The percent clay in the most developed B horizon
and the clay mass in the most developed B horizon both provided very similar trends as
well (chapter 9). One of these two variables, percent clay, was therefore excluded from the
data set.

The seven variables remaining (two weathering classes, two color indices, two
parameters for clay content and Fed/Fet) and a dummy variable for the group assignment
were then submitted to the discriminant analysis routine of SYSTAT. Mathematically, the
computation of the discriminant functions is similar to that of principal components. The
discriminant functions can be considered as new variables which maximize between group
variance and minimize within group variance. To visually represent the groupings as
described by the new variables, the scores for the discriminant functions were plotted on a

graph (Figure 38). The scores are the new values of the pedons for the new variables.

182
11.3 Rosults and oiscossion

The grouping explained above (G1, G2, G3) was described by the discriminant
functions in a statistically significant manner (W ilks's lambda, T2, or = 1 %), indicating
that there is not only a subjective, physical base for the assignment of the pedons to their
respective groups, but that there also is an objective, statistical justification to do so as well.

Figure 38 illustrates the quality of the classification. Discriminant function 1 by
itself could provide a good means of separating the three groups. The scores of G3 on
function 1 are clearly different from the scores of the other groups. Although the scores of
G1 and G2 on function 1 are distinct, these two groups can be better separated when the
discriminating power of function 2 is added. The graph also shows that although there is
considerable variation in group G2, splitting it in two or more distinct groups would be
difficult. This confirms the subjective notion, mentioned in section 11.2.1, that subdividing
G2 would not be appropriate. This does not imply that the ages of the pedons in G2 are
equal; they obviously are not. It implies that the ages are sufficiently similar to be
unseparable with the methods used.

As a test, three other grouping schemes were subjected to discriminant analysis. In
the first, the saprolitic soils were assigned to a separate group. In the second, the Bradley
site was classified separately, and in the third test HLf was added to G1. Separation of the
new groups in the three tests was not achieved by the discriminant analysis with the
statistical confidence observed in the initial run. Also the plots of the scores showed that the
discriminating power of the functions was less than in the original run. This indicates that

the statistically most appropriate grouping was chosen in the initial classification.

183

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184

11. Esti ati n f solut a es

Studies in the Southern Blue Ridge and in the Blue Ridge of Virginia have tried to
relate relative-age data to absolute ages (Mills, 1983; Whittecar and Ryter, 1992; Leigh,
1995). This was accomplished by comparing soil morphological properties and relative
ages to characteristics of dated soils. This kind of comparison is tenuous and probably can
only provide order of magnitude estimates of the ages. Nevertheless, even very
approximate numerical ages could help evaluate the results of the cosmogenic radiosiotope
dating discussed in the part IV.

Soils with hues redder than 2.5YR were inferred to be older than 100 ka by
Whittecar and Ryter (1992) and Leigh (1995), and about 375 ka by Mills (1983). In the
Valley and Ridge of Virginia, Mills (1988) estimated soils with similar colors to be >600 ka
old. These soils had well developed argillic horizons (Whittecar and Ryter, 1992), with
>45 % clay (Mills, 1983). Since pedons HMf, HMa, HUf and HUa have hues of 2.5YR
and 10R, well developed argillic horizons and >40 % clay in at least one B subhorizon, the
age of the saprolitic soils and of the highest deposit at the Hidden Valley site is estimated at
>100 ka, and even could be >600 ka.

Soils in the Southern Blue Ridge that were dated by 14C to 13 ka were Alfisol-like,
and had about 20 % clay and a 10YR color in the B horizon (Leigh, 1995). Soils in the
Blue Ridge of Virginia that were estimated to be about 10 ka by Whittecar and Ryter (1992)
had weak argillic horizons, many unweathered clasts, and about 25 % clay and a 5YR hue
in the B horizon. Soils judged to be of the same age had about 20 % clay and 7.5 to 10 YR
colors in the B horizon (Mills, 1983). These characteristics are comparable to those of the
pedons at the Alarka and Bradley sites, which therefore could be of the order of 10 ka old.

It would be inappropriate to further distinguish between these soils with this method.

185
11.5 Conclusions

Evaluation of clast weathering, soil development and iron species ratios allowed for
a classification of the debris flow deposits in three age-related groups. Discriminant
functions were effective in distinguishing between the three groups of deposits. Testing of
the discriminant analysis indicated that the grouping was statistically significant at a high
level of confidence. Other tested groupings could not be accepted with the same level of
confidence. This indicates that the proposed, physically based, qualitative grouping of the
deposits is statistically the most appropriate. Based on comparison with soils of known age
in the region, the absolute age of the youngest group (ALfl , ALf2) can be expected to be of
the order of 10 ka. The oldest soils (HMf, HMa, HUf, HMa) may be >100 ka, and even
>600 ka old.

1 86
12 CONCLUSIONS

The results of the various relative-age proxies used in the previous chapters are in
good agreement. They classified the deposits into uniform groups that were physically
meaningful and statistically significant.

The proxies for relative age indicate that the deposits of the three sites were
emplaced at different periods in time. Generally, the debris flows at the Alarka site occurred
more recently than those at the Hidden Valley site. The lowest deposits at these two sites
appeared to be younger than the highest deposits. Other investigators working in the Blue
Ridge have found a similar association between relative age of debris flow deposits and
topographic position (Mills, 1981; 1983; Whittecar and Ryter, 1992). A distinction in age
between the oldest (higher) deposit at Alarka and the youngest (lowest) deposit of Hidden
Valley could not be made. The discriminant analysis showed that assigning a similar age to
these deposits is statistically meaningful. The deposits at the Bradley site appear to be
comparable in age to the higher deposit at Alarka and the lowest at Hidden Valley. The soil
and weathering characteristics of the saprolite at the Hidden Valley site point to a greater
age for the exposure of this saprolite than for any of the colluvial deposits.

Most relative-age proxies show larger within-site variation at the Hidden Valley site
than at the other two sites. If this inference is correct, it indicates that either there is a
greater difference in age of the deposits at the Hidden Valley site or that as soils become
older more variation is introduced in their development. Acceptance of the latter option
would contradict the principle of converging pedogenetic pathways. Mills (1982)
mentioned, however, that perhaps small differences in parent material and
microenvironment of deposits may become more important with greater age and hence may
introduce more variation. Absolute dating of the deposits could possibly resolve this

contention.

187

Two soil properties discussed in chapter 6 conform to these age relationships. Clay
mineralogy (Table 1 1) showed that more kaolinite was present at the Hidden Valley site
than at the Alarka site and that the higher deposit at the Alarka site contained more kaolinite
than the lower deposit. Because a high kaolinite content is usually associated with an
advanced degree of weathering, and thus an older age, these observations strengthen the
age relationships postulated above. The clasts at the Hidden Valley site are smaller and less
abundant than at the Alarka site (Table 5, Figure 17). Although this may reflect the size and
abundance of the clasts in the source material, it also could be the result of longer
weathering of the Hidden Valley deposits.

If, as postulated above, the paucity of clasts at the Hidden Valley site is the result of
longer weathering, and was not inherited from the source material, the term "mud flow"
assigned to these deposits in section 5.4.3 may not be appropriate. If these deposits
originally contained large amounts of coarse fragments, "debris flow" may be the best
designation after all.

The soil properties used in this research as proxies for relative age may have been
inherited, in part, from the source material of the debris flows. However, the close
agreement of the results of the various, independent, relative-age indicators, suggests that
inheritance did not affect these soil properties considerably. A study comparing pedogenic
characteristics of source areas and deposits of very recent debris flows could establish the

importance of inheritance for pedogenesis on debris flow colluvium more firmly.

PART IV: CONCLUSIONS

188

189
Debris flow deposits are a common geomorphic phenomenon in the landscape of

the Southern Blue Ridge of North Carolina. In this study, sedimentary, pedological and
age characteristics of these debris flow deposits were examined. In spite of the widespread
occurrence of the deposits, detailed investigations of these properties have not often been
carried out in the region, nor have they been carried out frequently in other temperate to
warm humid environments. Part of the relevance of this study, therefore, lies in the
generation of characterization data of previously poorly understood landforms. In addition,
this study was designed to help understand pedogenesis on debris flow deposits and to
identify periods of increased landscape stability/instability in the region through an analysis
of relative ages of the deposits.

A reconnaissance survey showed that colluvial deposits occur commonly in many
landscape positions throughout the Little Tennessee River basin. Debris flow deposits are
most prevalent in relatively small, low order stream valleys with steeply-sloping
backslopes. Typically, these deposits have a lobate topography, and large boulders, many
more than a meter in diameter, can often be observed at their surface. Three sites with
debris flow deposits were selected for further study based, among other criteria, upon the
presence of a sequence of deposits at the site, degree of surface erosion, differences in
degree of soil development in and between sites and the uniformity of the local bedrock.

The sedimentary characteristics of the deposits show that most were formed by
debris flow activity. They typically consist of massive, matrix supported diamicts, a facies
often observed in debris flows by other researchers. In some soil pits of the Hidden Valley
site very few clasts were encountered. These deposits are interpreted to be mud flow
deposits. However, this site also had the oldest relative age and the paucity of coarse
fragments may be due to prolonged weathering.

Facies characteristics indicate that the viscosities of the debris flows at the three
sites were different. The Alarka site appears to have experienced the most viscous flows, as

evidenced by the fabric, lobate topography and thickness of the deposits. At the Hidden

190
Valley and Bradley sites more fluidal debris flows occurred. In the case of Hidden Valley

this may be due to a finer texture of the source material. The finer texture may relate to
more intense weathering of the source material, and/or could point to a greater stability for
this basin. The Bradley site has the most heterogeneous sediments. Various sedimentary
units are present in the three pits at this site. However, there is no evidence for prolonged
surface exposure. This suggests that there were no major interruptions in the most recent
depositional episode at Bradley.

Particle size fractionation data show that the parent materials of the soils are very
heterogeneous. This heterogeneity was reflected in many pedons by the presence of
lithologic discontinuities. These lithologic discontinuities were in most cases interpreted as
the result of internal variations within one flow, rather than the result of the stacking of
consecutive flows. It is postulated that the internal variations represent different shear zones
in the flows. The presence of shear zones is consistent with the results of the sedimentary
fabric analysis. The observation of heterogeneous parent materials in debris flow deposits
contrasts with those of Daniels et al. (1987) and Graham et al. (1990b) who observed
homogenization in colluvial soils. Although these authors did not completely describe the
origin of the colluvium they studied, this contrast indicates that pedogenesis is not uniform
in all colluvial deposits of the region.

The only parameter that shows a systematic spatial trend is the depth to maximum
clay accumulation. Depth to maximum clay accumulation increases as elevation increases.
This pattern holds for situations when two pedons are located on one deposit and also for
two deposits within one site. The trend most likely reflects impeded vertical movement of
vadose water in lowest topographic positions and age differences between the deposits.
Shallow clay maxima on steep slopes and apparently incomplete soil profiles point to
removal of surficial horizons by erosion at some locations.

Two of the pedons that were studied in Hidden Valley have developed in saprolite.

These pedons showed no evidence for lithologic discontinuities and contain more clay and

191
have more pronounced clay maxima than do colluvial soils. The difference in clay content

and accumulation may in part be due to a greater age of the saprolitic soils.

The clay mineralogy within every pedon varies little. Of the principal clay mineral
groups, only 14 A minerals show a decreasing trend with depth. No consistent trends with
depth were apparent for the other clay minerals. Within the Alarka site there was a small
difference in the clay mineral assemblages between the lower and higher deposit. Larger
differences exist between sites. These within and between site differences most probably
relate to differences in age of the deposits.

The qualitative and statistical analysis of the various relative-age proxies produced
very consistent results. This consistency and the accordance of the results with sediment
and soil characteristics, such as content and size of coarse fragments, and clay mineralogy,
indicate that the results are dependable. It also suggests that the chosen variables are
appropriate relative-age indicators for debris flow deposits in warm to temperate humid
environments.

This research, as well as studies by Mills ("1981; 1983) and Whittecar and Ryter
(1992), shows that higher deposits are slightly older than lower deposits in the same area.
In the Little Tennessee River basin the within-site variance in age is smaller than the
between-site difference in age. In spite of the generally large between-site differences, one
deposit at each of the three sites appeared to have a relative age that was very similar to that
of one deposit at the other sites. This similarity in age may be due to an inadequate
resolution of the applied relative-age dating methods. However, if real, the similarity would
suggest that an external factor, operative across all the three sites, triggered the debris flows
at approximately the same time. In the tectonically stable Southern Blue Ridge this factor is
most likely to be climate (Mills, 1981; 1982b; Kochel and Johnson, 1984; Velbel, 1987).

The two most recent deposits are present at the Alarka site. Deposits of comparable
age were not observed at the other two sites. It is not likely that deposits of that age have

been present at those other sites, they cannot be covered and would have been exposed to

192
less erosion than the older deposits. Their absence at the Hidden Valley and Bradley sites

therefore suggests that climate alone cannot explain the occurrence of debris flows in the
region. Local, intrinsic factors must affect the timing of debris flow activity.

Further study of relative ages of debris flow deposits in the region could help to
identify the relative importance of intrinsic and external factors that produce debris flows.
Large numbers of deposits of the same relative age would point to a dominance of external
over internal factors.

Absolute ages would allow for temporal correlations between sites on a larger
spatial scale and could clarify during which periods in geologic history the climate of the
Southern Blue Ridge was most favorable for the formation of debris flows. Considering
that materials datable with traditional methods, such as 14C, are absent from the studied
deposits, it is suggested that methods based on the decay of cosmogenic radioisotopes may

be the only viable dating approach in the near future.

PART V: APPENDIXES

APPENDIX 1

Generalized description of selected pedons of reconnaissance survey

193

194
Table 14: Field ' of selected of reconnaissance
orrzon orst

cm Munsell consistence fragments
color

 

none
none
CW’

e“!
e“!
conunon
none
none

none
none
none
none
none
none

e“!

Table 14: Field
orrzon

 

   

'on of selected

cm

195

Olst
Munsell
color

multicolored

multicolored

of reconnaissance

cont

 

consistence fragments

none ew
none

many

none
common
common
ew

196
Table 15: Particle size of selected of reconnaissance

Pedon Horizon exture Sand Silt Clay VCS CS MS FS VFS
of fine % % % % % % % %

earth1

         

197
Table 15: Particle size anal of selected of reconnaissance cont'

Pedon Horizon Texture Sand Silt Clay VCS CS MS FS VFS
of fine % % % % % % % %

earthl

       

   

Abbreviations for texture class: 1 = loam, c = clay, cl = clay loam, 31 = sandy loam,
scl = sandy clay loam.

APPENDIX 2

Longitudinal profiles, Alarka and Bradley sites

198

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APPENDIX 3

Particle size fractionation data

201

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N.o_. Ndr o.w m4. mé VKF m.mm 56v NS 0.0 Q< mDm

 

 

o.w adv 3: m.o_. m6 v.33: 0.0m m.om N4; N4; vgmw

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

«.«3 «.«3 « « « « «.« «.«« «.«« «.«« 3.3 «.« «;m«

3.« 3.3 «.33 «.«3 «.«3 «.«3 «.«« «.«« «.« «.« «;m«

3.« «.«3 «.« «.« «.« «.«3 «.«« «.3« «.« «.« 3;«

3.« «.3 «.« «.« «.« «.«3 «.«« «.«3. 3.3. 3.« m

«.« «.«3 «.« «.« «.3. «.«3 «.«« «.«3. «.« «.« «< Sm
«E3: «vq «:8 «3.« 30 ..«o «.32 30 «x.

 

 

 

 

 

«Us _ mm _ «s. _ «o _ «o> _ «so _ Em _ «3.«« EE 3.-« EE «-3. .3555: «88

 

«383 «««w =« ««.«« «Na «38 ”«3 «BS

 

Table 17: Clayfree

article size data, all sites

207

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon sand I silt I VCS] (B I NB 1 FS 1 VFS
* % offfine earth 1<2 mm) (Clal ree)

ALf1 A 62.6 37.4 3.6 7.5 15.1 23.1 13.3
AE 55.7 44.3 3.8 7.8 13.6 20.5 10.0

2E 62.2 37.8 6.6 7.7 14.1 22.3 11.4

ZBt 68.2 31.8 6.6 10.7 16.6 23.0 11.4

3801 76.3 23.7 13.2 15.4 18.9 19.6 9.1

3802 88.1 11.9 14.8 21.1 24.6 20.3 7.2

ALf2 A1 64.1 35.9 4.4 8.6 18.0 23.0 10.2
A2 62.3 37.7 5.5 8.7 14.7 22.5 10.9

E 62.8 37.2 6.8 8.7 14.0 20.6 12.7

ZBt 66.7 33.3 7.5 9.2 14.9 24.2 11.0

2801 74.2 25.8 7.0 10.7 16.1 25.7 14.8

3802 78.1 21.9 10.2 13.8 18.7 23.8 11.5

AUf A 58.7 41.3 5.6 8.4 13.3 21.4 9.9
E 62.9 37.1 5.6 7.9 13.9 27.3 8.2

8w1 63.2 36.8 6.5 8.8 13.9 21.7 12.4

Bw2-2 65.1 34.9 5.1 8.7 14.1 25.2 12.0

Bw2-1 72.3 27.7 6.3 8.8 15.8 25.4 16.1

2801 71.4 28.6 10.3 10.9 15.3 22.0 12.9

2802 69.5 30.5 6.3 9.6 16.1 25.5 11.9

AUa A 62.1 37.9 5.2 8.2 13.9 23.7 11.1
Bw-2 62.1 37.9 7.8 9.6 14.1 20.8 9.8

Bw-1 64.1 35.9 6.5 7.9 14.3 22.9 12.4

Bt 70.0 30.0 8.1 9.4 14.7 25.1 12.7

2801 59.0 41.0 6.7 8.7 13.2 22.0 8.3

2802 68.9 31.1 6.7 10.2 15.3 22.5 14.2

20 69.6 30.4 10.6 10.8 14.6 20.8 12.8

30 65.7 34.3 5.4 9.5 14.4 21.9 14.5

HLf A 63.2 36.8 5.0 11.5 16.5 20.6 9.7
Bw 60.3 39.7 4.5 12.0 15.8 18.7 9.3

80 63.4 36.6 4.4 10.8 17.3 20.7 10.2

_01 84.0 16.0 4.4 10.4 22.1 34.4 12.7

2293 87.6 12.4 11.0 20.5 26.4 22.2 7.5

30 63.2 36.8 3.9 10.8 15.2 21.5 12.0

 

 

 

 

 

 

 

 

Table 17: Clayfree

208

particle size data, all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon sand I silt I VCS I (B I NB I PS I VFS
3 °/o of fine earth (<2 mm) (clar ree)

HLa A 57.4 42.6 5.9 11.6 14.5 17.7 7.7

B/A 44.0 56.0 3.2 5.6 11.8 14.7 8.7

811 50.7 49.3 7.3 7.3 11.4 16.2 8.6

Bt2 45.0 55.0 1.3 5.3 11.1 16.8 10.5

H: 46.5 53.5 2.3 8.8 13.7 15.2 6.4

C 63.6 36.4 3.0 11.7 16.8 20.7 11.4

2C 79.4 20.6 6.4 15.3 21.7 25.2 10.8

301 49.9 50.1 1.5 6.8 10.0 17.7 13.8

4C 75.4 24.6 5.7 11.7 19.0 27.7 11.3

509 73.6 26.4 6.9 11.1 18.3 24.7 12.6

HMf A 60.0 40.0 6.4 9.6 15.8 19.8 8.4

AB 59.2 40.8 5.0 9.7 16.8 19.2 8.4

311 58.9 41.1 6.2 10.8 14.5 19.4 7.9

812 61.5 38.5 6.6 12.6 14.2 16.9 11.3

B/C-2 69.8 30.2 9.4 14.5 13.7 21.4 10.8

B/C-1 68.4 31.6 6.8 1517 16.4 18.6 11.0

H) 61.4 38.6 8.4 13.2 13.0 18.7 8.2

HMa A 62.7 37.3 4.2 10.1 18.4 21.8 8.3

AB 60.9 39.1 4.3 8.8 16.2 22.8 8.8

Ab 64.8 35.2 5.4 10.4 17.7 21.4 9.9

51b 57.2 42.8 4.8 7.5 14.5 19.8 10.5

E2b 60.0 40.0 4.0 7.4 15.9 23.1 9.7

Btb-2 66.0 34.0 3.7 9.1 16.5 24.0 12.8

Btb-1 71.3 28.7 2.7 9.8 19.2 26.3 13.3

C/Bb-2 79.9 20.1 2.6 11.6 20.9 31.5 13.3

C/Bb-1 82.6 17.4 6.2 16.1 21.7 25.8 12.6

Clb 85.8 14.2 10.2 19.5 22.1 24.4 9.6

HUf A 55.7 44.3 4.3 10.8 15.4 17.5 7.7

BA 57.9 42.1 4.0 10.8 15.3 18.9 8.9

BW1 61.8 38.2 4.8 13.6 16.3 19.2 7.9

28w2-2 65.3 34.7 5.3 14.6 17.4 19.5 8.4

2Bw2-1 63.7 36.3 4.2 13.9 16.5 18.9 10.1

3Bt3-2 69.9 30.1 9.5 13.3 16.0 21.6 9.5

3Bt3-1 67.9 32.1 11.6 11.7 15.1 21.5 8.0

4Bt4 65.8 34.2 7.9 10.7 16.0 19.6 11.6

 

 

 

 

 

 

 

 

209

Table 17: Clayfree particle size data, all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon sandI silt | vcs | <8 I MS | F8 | vr=s
% of fine earth j<2 mm) (clar ree) 3

HUa A 63.7 36.3 5.0 10.1 18.2 21.1 9.3
BA 65.7 34.3 5.0 10.6 19.6 22.4 8.0

Bw1 67.9 32.1 5.7 12.9 19.8 20.1 9.4

8w2 68.2 31.8 7.1 15.9 19.2 18.0 7.9

28w3 60.8 39.2 4.8 13.3 17.0 16.8 8.9

38w4 60.2 39.8 7.2 10.6 15.5 21.4 5.4

SBt 65.2 34.8 6.5 11.3 16.9 21.0 9.4

BLf A 54.9 45.1 6.7 6.5 10.0 19.6 12.2
8w 56.4 43.6 6.1 7.4 11.0 17.6 14.4

Q‘L 63.3 36.7 4.5 7.1 11.8 27.4 12.3

2gL2 70.1 29.9 7.6 10.8 15.6 27.0 9.1

BLa Ap 56.5 43.5 5.5 5.8 9.6 23.2 12.4
E 51.7 48.3 5.8 5.5 8.3 17.5 14.7

8w1 55.5 44.5 6.9 5.8 9.5 17.8 15.5

28w2 64.2 35.8 7.6 9.0 12.7 23.4 11.3

38w3 52.4 47.6 5.1 5.5 8.3 17.2 16.3

48w4 59.8 40.2 12.0 8.9 9.8 16.6 12.4

BUa Ap 51.8 48.2 5.5 6.7 10.3 18.2 11.1
8w1 55.9 44.1 10.8 8.8 10.1 15.9 10.3

28w2 63.9 36.1 12.1 11.6 11.6 18.6 10.1

38w3 67.4 32.6 12.2 12.8 13.8 17.8 10.8

4Bw4 48.9 51.1 2.8 4.6 8.2 19.9 13.2
58w5-2 65.0 35.0 11.5 12.1 13.1 18.4 9.9
58w5-1 72.1 27.9 17.0 14.8 14.8 16.9 8.6

 

 

 

 

 

 

 

 

 

 

APPENDIX 4

Sorting and bulk density data

210

211

Table 18: SortinLand bulk density data, all sites

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon 01 I 03 sortin; bulk density estimated?
mm 9 cm-3
ALf1 A 0.017 0.230 3.68 0.97 n
AE 0.017 0.220 3.60 1.18 n
E 0.017 0.230 3.68 1.38 y
231 0.018 0.290 4.01 1.38 y
3301 0.045 0.550 3.50 1.38 y
3BC2 0.070 0.660 3.07 1.38 y
ALf2 A1 0.017 0.260 3.91 0.98 n
A2 0.017 0.240 3.76 1.01 n
E 0.015 0.240 4.00 1.05 n
281 0.002 0.240 10.95 1.20 y
2BC1 0.025 0.300 3.46 1.20 y
3BC2 0.038 0.430 3.36 1.20 y
AUf A 0.016 0.230 3.79 0.80 n
E 0.020 0.240 3.46 1.25 n
BW1 0.017 0.240 3.76 1.45 y
BW2-2 0.022 0.240 3.30 1.45 y
BW2-1 0.017 0.240 3.76 1.45 y
2BC1 0.040 0.490 3.50 1.45 y
28C2 0.040 0.330 2.87 1.45 y
AUa A 0.013 0.230 4.21 1.10 n
BW-2 0.002 0.240 10.95 1.18 n
BW-1 0.009 0.230 5.06 1.38 y
31 0.018 0.270 3.87 1.38 y
2BC1 0.027 0.260 3.10 1.38 y
2BC2 0.036 0.320 2.98 1.38 y
2C 0.036 0.380 3.25 1.38 y
3C 0.027 0.260 3.10 1.38 y
HLf A 0.012 0.270 4.74 1.38 n
BW 0.005 0.260 7.21 1.52 n
H: 0.005 0.260 7.21 1.53 n
99 0.040 0.330 2.87 1.57 n
2C9 0.100 0.610 2.47 1.65 y
3C 0.033 0.280 2.91 1.65 y

 

 

 

212

: Sorting and bulk density data,all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 18
Pedon Horizon Q1 I Q3 sorting bulk density estimated?
mm 9 cm-3

HLa A 0.005 0.240 6.93 1.45 n

B/A 0.004 0.090 4.74 1.48 n

811 0.002 0.125 7.54 1.44 n

Bt2 0.002 0.060 5.35 1.40 n

H) 0.003 0.125 7.07 1.31 n

C 0.003 0.220 8.86 1.36 n

20 0.006 0.370 7.85 1.48 n

3C}; 0.004 0.120 5.48 1.35 n

4C 0.008 0.300 6.12 1.44 n

5C9 0.012 0.300 5.00 1.45 y

HMf A 0.015 0.260 4.16 1.29 n

AB 0.003 0.240 8.94 1.28 n

Bt1 0.002 0.120 7.75 1.49 n

Bt2 0.002 0.150 8.66 1.54 n

BIC-2 0.002 0.160 8.94 1.37 n

BIC-1 0.002 0.230 10.72 1.36 n

a) 0.002 0.230 10.72 1.41 n

HMa A 0.003 0.210 9.17 1.31 n

AB 0.003 0.200 8.94 1.29 n

Ab 0.003 0.250 9.13 1.43 n

E1b 0.006 0.210 5.92 1.45 n

E2b 0.003 0.210 8.37 1.58 n

Btb-2 0.002 0.170 9.22 1.41 n

Bib-1 0.002 0.170 9.22 1.41 n

C/Bb-2 0.003 0.240 9.80 1.35 n

C/Bb-1 0.003 0.330 11.49 1.35 n

Crb 0.066 0.520 2.81 1.45 n

HUf A 0.003 0.220 8.56 1.33 n

BA 0.003 0.180 8.49 1.45 n

Bw1 0.002 0.190 9.75 1.38 n

2Bw2-2 0.003 0.190 8.72 1.44 n

28w2-1 0.003 0.210 9.17 1.44 n

3Bt3-2 0.002 0.220 10.49 1.47 n

3813-1 0.002 0.220 10.49 1.47 n

4Bt4 0.002 0.200 10.00 1.54 n

 

 

 

213

Table 18: SortinLand bulk densiy data,all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon Q1 I 03 sorting bulk density estimated?
mm gem-3
l-Ma A 0.010 0.290 5.39 1.16 n
BA 0.008 0.280 5.92 1.47 11
BM 0.016 0.340 4.61 1.50 n
8w2 0.026 0.420 4.02 1.55 n
28w3 0.010 0.330 5.74 1.62 n
38w4 0.003 0.210 9.17 1.66 n
381 0.003 0.240 8.94 1.56
BLf A 0.011 0.190 4.16 1.39 n
Bw 0.005 0.190 6.16 1.58 n
091 0.022 0.220 3.16 1.46 n
2093 0.031 0.330 3.26 1.50 y
BLa Ap 0.015 0.190 3.56 1.27 n
E 0.015 0.240 4.00 1.52 n
Bw1 0.015 0.330 4.69 1.58 n
2Bw2 0.027 0.410 3.90 1.37 n
38w3 0.010 0.150 3.87 1.59 n
4Bw4 0.027 0.400 3.85 1.57 n
BUa Ap 0.016 0.200 3.54 1.15 n
Bw1 0.016 0.180 3.35 1.38 n
28w2 0.022 0.200 3.02 1.47 n
38w3 0.026 0.260 3.16 1.46 n
4Bw4 0.014 0.170 3.48 1.45 n
SBw5-2 0.022 0.450 4.52 1.48 n
58w5-1 0.016 0.250 3.95 1.48 n

 

 

 

 

 

 

 

 

APPENDIX 5

Stereograms for Clast a-axis

214

215

Stereograms of long axis of 018318,
lower deposits at Alarka site

ALfl

Pro ectian . . . . . . . . . Schmidt
Num6er oF Sample Paints 30

151 Eigenvalue . 0 580
2nd Eigenvalue 0 251
3rd Ei envalue . . . . . . 0.169
LN l E / E2 1 . 0 839
LN 1 E2 / E3 ) . 0 396
(LNlEl/EZl] / 1LNlE2/E3ll . 2.116
S herical variance . 0 4456
Rgar . . 0 5544

o Clast a-ax1s orientation

 

ALf2

Pro ectian . . . . , Schmidt
Num6er aF Sample Points 30
let Eigenvalue . 0 624
2nd Eigenvalue . 0 250
3rd Ei envalue . . . . . . 0.125
LN l E / £2 1 . 0 915
LN 1 E2 / E3 1 . . . . . 0.690
(LNlE1/E21] / [LNlEZ/EEll . 1 325
S herical variance . 0 6618
R or . . . . . . . . . . . . 0.3382

. Clast a-axi: orientation

 

. Figure 41

216

Stereograms of long axis of clasts,
higher deposit at Alarka site

N AUf

Pro ectron Schmidt
Num6er of Sample Paints . . 30

151 Eigenvalue . . . . . . . 0.550
2nd Eigenvalue . 0.313
3rd E1 envolue . . . . . . . 0.137
LN I E / E2 1 . 0.564
LN ( E2 / E3 1 . 0.827
lLNiEl/EZl] / lLNiEZ/E3ll . 0.681
S herical variance . 0.5727
R or . . 0.4273

+ Clast a-axrs orientation

AUa

Pro ection . . . . . . . . . Schmidt
Num er oF Sample Paint: 30

lst Eigenvalue ’ . 0.505
2nd Eigenvalue . 0.276
3rd E1 envalue . . . . . . . 0.219
LN ( E / E2 1 . 0 606
LN 1 E2 / E3 1 . 0.228
lLNlEl/EZl] / lLNlE2/E3ll . 2.657
S herical variance . 0.5330
850r . . 0.4670

0 Clast a-axis orientation

 

Figure 42

217

Stereogram of long axis of clasts,
Hidden Valley site

HUf

Pro ectian Schmidt
Num6er oF Sample Points . . 29

lst Eigenvalue . . . . . , . 0.469
2nd Eigenvalue . 0 352
3rd Ei envalue . 0 179
LN ( E / E2 1 . . . . . 0.287
LN 1 E2 / £3 1 . 0 678
(LNlEl/EZl] / lLNlEZ/E3ll . 0.424
S herical variance 0 4080
REar 0 5920

o Clast a-aXis orientation

 

Figure 43

218

Stereograms of long axis of clasts,
Bradley site

BLa

Pro ection ..... . . . . Schmidt
Num er oF Sample Points 1

lst Eigenvalue ....... 0.592
2nd Eigenvalue . 0 315
3rd Ei envalue . 0 093
LN 1 E / E2 1 . . . . . . . 0.630
LN 1 E2 / E3 1 . 1 221
1LN1El/E211 / 1LN1E2/E3ll . 0.516
S herical variance 0 6406
850r . 0 3594

4 Clast a-oxis orientation

 

BUa

Pro ection . . . . . . . . . Schmidt
Num er of Sample Pr 113 31

lst Eigenvalue . 0 500
2nd Eigenvalue . 0 354
3rd Ei envalue . . . , . . . 0.146
LN 1 E / E2 1 . 0 347
LN 1 E2 / E3 1 . 0 884
1LN1E1/E21] / 1LN1E2/E3ll 0.392
S hericol variance 0 6157
Rgar . 0 3843

a Clast o-axis orientation

 

Figure 44

22159

Stereograms of long axis of clasts, subpopl

1LN1E1/EZ)] / iLNiEZ/Eaii‘
Spherical variance
8 or

[\Iafl
Pro ectian . . . . . . . . Schmidt
Num6er of Sample Paints . 16
Mean Lineatian Azimuth 76.2
Mean Lineatian Plunge . . . 30.4
lst Eigenvalue . 0 748
2nd Eigenvalue 0 152
3rd Ei envalue . . 0.100
LN 1 E / E2 1 1 592
LN 1 E2 / E3 1 . 9.421
0
0

o Clast o-axis orientation

 

lLNlEl/EZl] / (LNiEZ/EBJI
S erical variance . .
R or

IXIJEZ
Pro ection . . . . . . . . . Schmidt
Num er 0? Sample Paints 13
”can Lineatian Azimuth 103 1
Neon Lineatian Plunge . . . 18.8
let Eigenvalue . 0 885
2nd Eigenvalue . . . 0 081
3rd Ei envalue . . . 0.034
LN 1 E / E2 l . 2 390
LN 1 E2 / E3 1 . . 0 878
(LNlEl/EZl] / 1LN1E2/E3ll 2 720
S herical variance 0 0631
R or . . . . 0.9369
9 Clast a-axis orientation
Atllf
Pro ection Schmidt
Num er oF Sample Points 13
neon Lineatian fizimuth . . . 60.2
Neon Lineatian Plunge 15 4
lst Eigenvalue . 0.896
2nd Eigenvalue 0.091
3rd Ei envalue 0 013
LN 1 E / E2 1 . . 2.292
LN 1 E2 / E3 1 {.914

. 0.

0.

2 Clast a-OXis orientation

 

Figure 45

220

Stereograms of long axis of clasts, subpop 2

ALfl

Pro ectian . . . . Schmidt
Num er aF Somple Paints . 13
Great Circle Azimuth . . . . 232.0
Great Circle Plunge . 32 3
lst Eigenvalue . 0 532
2nd Eigenvalue . . . . . . 0.406
3rd Ei envalue . 0 062
LN 1 E / E2 l . 0 270
LN 1 E2 / E3). 1.878
1LN1E1/Ele / 1LN1E2/E3ll 0 144
Spherical. variance . . . . 0 4223
. . . . . . . . . 0 S777

. Clast a-axis orientation

ALf2

Pra ectian . Schmidt
Num er 0F Sample Paints . . 15
Great Circle Azimuth . . . . 231.7
Great Circle Plunge 25 6
lst Eigenvalue . . . . . . 0.598

2nd Eigenvalue . 0 363
3rd Ei envalue . 0 039
LN 1 E /E2 1 . . . . . . 0.499
LN 1 E2 / E3 l . 2 241
1LN1E1/E2l] / 1LN1E2/E3ll 0 223
S herical variance . . . 0 3462
WE . 0 6538

. Clast O‘OXIS orientation

AUf
Pro ectian . . . . Schmidt
Num er aF Sample Points 16
Great Circle Azimuth . . . 181.7
Great Circle Plunge 33 8
lst Eigenvalue 0 529
2nd Eigenvalue . . . . . . . 0.426
3rd Ei envalue 0 044
LN 1 E /E2 l 0 216
LN 1 E2 / E3 1 . 2 262
1LN1E1/E2l] / 1LN1E2/E3ll 0 096
S herical variance . . . . 0.3453
WE . . . . . 0 6547

o Clast a-axis orientation

Figure 46

APPENDIX 6

Stereograms for Clast a-b plane

221

222

Stereograms of poles of a-b plane,
lower deposits Alarka site

ALfl
Projection Schmidt
Number of Sample Paints . . 30
lst Eigenvalue . . . . . . 0.612
2nd Eigenvalue . 0 219
3rd Ei envalue . . . . . . 0.169
(E / E2 l . 1 026
LN 1 E2 / E3 1 0 262
1LN1E1/E2l] / 1LN1E2/E3ll 3 910
S herical variance 0 2718
R or . 0 7282

o Orientation of a-b plane

 

ALf2
Pro ectian Schmidt
Num er of Sample Points 0
lst Eigenvalue . 0 691
2nd Eigenvalue . . . . 0.173
3rd Ei envalue . 0 137
LN 1 E / E2 l . . . . . . . 1.386
LN 1 E2/ E3 l . 0.234
1LN1E1/E21] / 1LN1E2/E3ll 5 919
S herical variance . . . . 0.1989
WE . . . . 0.8011

0 Orientation aF a-b plane

 

Figure 47

223

Stereograms of poles of a-b plane,
upper deposit at Alarka site

AUf

Pra ectian . . . . . . . Schmidt
Num6er of Sample Paints 30

lst Eigenvalue . . . . . . . 0 584
2nd Eigenvalue . 0 317
3rd Ei envalue . 0 099
LN 1 E / E2 1 . . . . . . . 0 610
LN 1 E2 / E3 1 . 1 166
1LN1E1/E2ll / 1LN1E2/E3ll 0 523
Spherical variance . . . . . 0.3072
Rbor . . 0 6928

a Orientation of o-b plane

 

AUa

Pro ectian Schmidt
Num er 0F Sample Points 28

lst Eigenvalue . 0 622
2nd Eigenvalue . 0 219
3rd Ei envalue . 0 160
LN 1 E / E2 1 . . . . . . . 1 044
LN 1 E2 / E3 1 0 316
1LN1E1/E2l] / 1LN1E2/E3ll 3 300
S herical variance . . . . 0.2440
R or . 0 7560

a Orientation of a-b plane

 

Figure 48

224

Stereograms of poles of a—b plane,
Bradley site

BLa

Pro ectian Schmidt
Num6er of Sample Paints . . 29

let Eigenvalue . 0 660
2nd Eigenvalue . . . . 0.217
3rd Ei envalue . . . . . . 0.124
LN 1 E / E2 l . 1 113
LN 1 E2 / E3 l . . . . . . 0.561
1LN1E1/E2)] / 1LN1E2/E3ll 1 983
S herical variance 0 2202
R or . . . . . . . . . 0.7798

0 Orientation 0F a-b plane

 

AUa

Pro ectian . . . . . Schmidt
Num6er aF Sample Paints 29

lst Eigenvalue . 0 730
2nd Eigenvalue . . . 0.227
3rd Ei envalue 0 043
LN 1 E / E2 1 1 166
LN 1 E2 / E3 l . . . . . . . 1.673
1LN1E1/E2l] / 1LN1E2/E3ll 0 697
S herical variance 0 1776
Rgar . . . . . . . .. . . . 0.8224

0 Orientation 0F a-b plane

 

Figure 49

APPENDIX 7

Clay mineralogy data

225

226
Table 19: data
Pedon Horizon 14 minerals mica kaolinite

 

 

relative abundance*

ddNOOOJN
NN-‘NNN

101003me
NNNNNN

2 2
3 3
2 2
1 2
2 3
2 3
2 3

NM-‘NNQNW
Add—L—L—L—Ld
NNWNQQWN

A—L—L—L-LN
AOOOO-‘
0303030003“)

227
Table 19: data cont'
Pedon Horizon 14 min mica kaolinite

       

relative abundance*

d—t—L—L-‘d—L—t—t—L
C-‘doo
wwwwwwwwmw

HOOD

OCOOOO-e
0003003000303

1 1
1 0
1 O
1 1
1 0
1 0
1 O
1 0
1 1

ODODODCDCDODODCDCO

d-l-J-‘d—A—L—b
4044404.;
wwwwwwmw

228

Table 19: Cla data cont'
Pedon 14ofizon 14 nfin nflca kaofinfie

     

relative abundance*

Bw1
2Bw2
38w3
4Bw4
58w5-2
58w54

* See section 6.2.2 for definition

APPENDIX 8

Iron species data

229

230

Table 20: Iron species data. all sites

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon % Fed‘ % Fet" 100'Fed/Fet
ALf1 A 0.78 2.41 32.4
AE 0.66 2.53 26.1
E 0.73 2.71 26.9
2Bt 1.00 3.86 25.9
3BC1 0.90 3.75 24.2
3BC2 0.84 3.58 23.4
ALf2 A1 0.89 2.84 31.4
A2 0.77 2.72 28.4
E 0.80 2.94 27.0
2Bt 1.24 4.07 30.4
2BC1 1.02 4.02 25.3
3BC2 0.80 3.68 21.7
AUf A 0.74 3.50 21.1
E 1.03 4.34 23.8
Bw1 1.35 4.51 29.8
8w2-2 1.09 4.33 25.2
Bw2-1 1.14 3.56 32.2
2BC1 1.18 3.57 33.2
28C2 0.99 3.57 27.6
AUa A 0.96 2.91 33.0
Bw-2 1.20 4.31 27.7
Bw-1 1.12 4.08 27.4
Bt 0.98 5.06 19.3
2BC1 1.07 4.12 25.9
2BC2 0.92 3.44 26.7
2C 0.76 3.31 22.9
3C 0.85 3.85 22.2
HLf A 1.45 3.84 37.7
Bw 1.86 7.77 23.9
m 1.27 4.81 26.5
Cg 0.83 3.76 21.9
2Cg 0.79 3.30 23.9
3C 4.83 7.82 61.8

 

 

 

 

 

 

231
Table 20: iron species data, all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon % Fed‘ % Fet' 100‘Fed/Fet
HLa A 1.95 5.66 34.4
B/A 2.35 6.50 36.2
Bt1 1.80 8.81 20.4
Bt2 4.06 9.17 44.3
E) 2.35 8.38 28.0
C 1.97 7.28 27.1
2C 2.26 6.06 37.3
309 1.48 ~ 4.79 30.9
40 2.56 6.25 41.0
5Cg 0.85 4.54 18.8
HMf A 1.72 4.19 41.1
AB 1.86 4.54 40.9
Bt1 3.45 6.85 50.3
Bt2 3.71 7.43 49.9
BIC-2 3.37 6.79 49.7
BIC-1 3.03 6.58 46.0
K) 3.70 7.83 47.2
HMa A 2.67 5.41 49.4
AB 2.12 4.86 43.6
Ab 2.35 6.28 37.3
E1b 1.79 ' 4.06 44.0
E2b 1.98 4.80 41.2
Btb-2 2.70 6.10 44.3
Btb-1 3.13 5.17 60.6
C/Bb-2 1.94 5.70 34.0
C/Bb-1 2.42 6.54 36.9
Crb 1.55 4.26 36.5
HUf A 1.95 4.84 40.4
BA 2.29 5.80 39.5
Bw1 1.80 6.31 28.5
2Bw2-2 2.19 6.35 34.5
2Bw2-1 2.80 6.55 42.8
3B13-2 3.82 8.16 46.9
3Bt3-1 3.59 . 6.83 52.5
4Bt4 2.91 7.31 39.8

 

 

 

 

 

 

232
Table 20: Iron species data, all sites (cont'd)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pedon Horizon % Fed" °/o Fet* 100*Fed/Fet
HUa A 2.01 5.72 35.1
BA 2.20 6.03 36.5
Bw1 2.29 5.48 41.8
Bw2 1.98 4.68 42.3
28w3 1.99 6.73 29.6
3Bw4 2.45 4.99 49.1
3Bt 2.69 6.64 40.5
BLf A 1.26 3.84 32.8
Bw 1.46 4.43 33.1
091 1.20 4.34 27.6
2092 1.04 4.27 24.4
BLa Ap 1.11 3.74 29.7
E 1.35 4.19 32.2
Bw1 1.68 4.80 34.9
2Bw2 1.52 4.54 33.5
38w3 1.49 _ 4.47 33.4
4Bw4 1.14 4.02 28.2
BUa Ap 1.19 3.72 31.9
Bw1 1.26 4.05 31.2
2Bw2 1.10 3.77 29.2
38w3 1.04 3.43 30.3
4Bw4 1.07 3.77 28.4
5Bw5-2 1.29 4.17 30.9
5Bw5-1 1.41 5.36 26.3

 

 

 

 

 

 

* Weight °/o of fine fraction

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