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This is to certify that the

thesis entitled

The Influence of Climate and Relief on
Lithic Fragment Abundance in Modern Fluvial
Sands of the Southern Blue Ridge Mountains,

North Carolina

presented by

Jeremy Hummon Grantham

has been accepted towards fulfillment
of the requirements for

 

 

Mas te r degree in Geo logy

///7Z¢r/M::/i//J

Major professor

Date /2///./’7>’

0-7639 MS U is an Afirtmfin Action/Equal Opportunity Institution

 

 

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RETURNING MATERIALS:
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THE INFLUENCE OF CLIMATE AND RELIEF ON LITHIC FRAGMENT
ABUNDANCE IN MODERN FLUVIAL SANDS OF THE SOUTHERN
BLUE RIDGE MOUNTAINS, NORTH CAROLINA

BY

Jeremy Hummon Grantham

A THESIS

Sumitted to
Michigan State University
in partial fulfillment of the requirement
for the degree of

MASTER OF SCIENCE

Department of Geological Sciences

1986

ABSTRACT

THE INFLUENCE OF CLIMATE AND RELIEF ON LITHIC FRAGMENT
ABUNDANCE IN MODERN FLUVIAL SANDS OF THE SOUTHERN

BLUE RIDGE MOUNTAINS, NORTH CAROLINA

BY

Jeremy Hummon Grantham

Chemical weathering imprints are observed in sediments
derived from a variable humid climate in the Coweeta basin,
North Carolina. 0f the four grain types studied;
monocrystalline quartz, polycrystalline quartz, mica, and
lithic fragments, these imprints are best developed in the
lithic fragments because these are the grains that are most
sensitive to chemical degradation. The extent of chemical
weathering is a function of the duration and intensity of
chemical weathering in the source area. In the Coweeta
basin, the intensity of chemical weathering is directly
related to the climatic variability across the basin, while
duration of chemical weathering is inversely related to the
average topographic slope of a watershed. Therefore, in
the Coweeta basin, watersheds with low slope and high
discharge per unit area have the highest extent of chemical
weathering, and sediments derived from these watersheds

contain the lowest percentage of lithic fragments.

ACKNOWLEDGEMENTS

I would first like to thank Dr. Michael A. Velbel for his
guidance in developing and seeing through this project, it
could not have been done without him. I would also like to
thank Dr. Duncan F. Sibley and Dr. Grahame Larson for their
advice and suggestions. Many thanks go to all of the
friends that I have made over the past two years,
especially to John, Tim, Mike, and Al who reminded me what
the really important things in life are. Finally I would
like to thank Laura for her love and support throughout
this endeavor, we did this together.

ii

TABLE OF CONTENTS

LIST OF TABLES ......... ..... ...... ..............

LIST OF FIGURES

INTRODUCTION

PREVIOUS WORK 0.0.0.IOOOOOOOOOOOOOOOOOOOOOO..0...

STUDY AREA

Topography

Climate

Bedrock Geology

and HYdrOIOgy OOOOOOOOOOOOOOOIOOOOOO

GeOChemistry OOOOOOOOOOIOOIOOIOOOOOO

METHODS O00......00.000.000.000...0.00.0000...0..

Field Sampling

Test for Effect of Rock Homogeneity

Sample Prepariation and Point Counting
Test for Effect of Transportation

RESULTS 00.00....O0.000000000COOOOOOOOOOOOO0.0...

Effects

and Transportation
Results of Point Counting

DISCUSSION

of Parent Rock Homogeneity

Are Sediment Transport and Parent

Rock Variability Significant Factors?

Do Climatic Imprints Exist in the

Sediments From the Coweeta Basin?

SUMRY 0......OOOOOOOOOOOOOOOOOOOOOOOOOO00......

UNANSWERED QUESTIONS FOR FURTHER RESEARCH

APPENDIX A

Data from Point Counts .............

APPENDIX B

Plots of Grain Type Abundance Versus

Discharge, Slope, and Discharge/Slope

BIBLIOGRAPHY

iii

10
12

14
16

19
19
19
20
20
22

22
24

28
28
31
43

44

45

53

78

Table

Table

Table

Table

Table

Table

LIST OF TABLES

page
Data for watersheds used in study ...... 13
Lithologies and mineral assemblages
in the Tallulah Falls Formation ........ 15

Lithologies and mineral assemblages
in the Coweeta Group ................... l7

Undulosity of quartz as an indicator
of parent rock homogeneity ...... .,..... 23

Weathering rinds on garnets as indicators
of the effect of transportation ........ 23

Correlation coefficients (r), slopes (a)

and y intercepts (b) for linear regressions
through each size fraction of grain

types versus discharge, slope and
discharge/slope ........................ 34

iv

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

10

LIST OF FIGURES

page
Variation in composition of Holocene

fluvial sand in the size range

-l¢ to 4D ................. ............ 4
Comparison of size-composition

plots for soils and Holocene

fluvial samples ....................... 6

Four variable plot of quartz

population in Holocene sand

derived from source rock indicated

by symbols ............................ 8

Map of the Coweeta Hydrologic
Laboratory ............................ 11

Variation in composition of fluvial
sand from watersheds draining the
Coweeta Group bedrock ................. 26

Variation in composition of fluvial
sand from watersheds draining the
Tallulah Falls Formation bedrock ...... 27

Percent lithic fragments versus
discharge/slope for watersheds

draining the Tallulah Falls

Formation source rock ................. 36

Percent lithic fragments versus
discharge/slope for watersheds

draining the Coweeta Group

sourre rock ........................... 37

Percent mica versus discharge for
watersheds draining the Tallulah
Falls Formation source rock ..... ...... 39

Percent mica versus discharge for
watersheds draining the Coweeta
Group source rock ..................... 40

INTRODUCTION

The effects of provenance upon the composition of sands
and sandstones have been a subject of great interest for
many years. Obviously, the composition of the parent rock
has a large influence upon the sediments which are derived
from it; however, other factors also greatly affect the
composition of the sediments eroded from a source area.
Mann and Cavaroc (1973), Young et a1. (1975), and Mack and
Suttner (1977) have all shown that the composition of the
sediments is largely affected by the climate in the source
area. Specifically, Young et al. (1975) showed that
lithic fragments are relatively more abundant in sediments
derived from source areas with an arid climate than those
derived from source areas with a humid climate. Young et
al.(1975), and Suttner et al. (1981) suggested that more
intense chemical weathering of lithic fragments in the
soils of the more humid source area accounts for the
lesser abundance of lithic fragments relative to sediments
derived from an arid source.

The purpose of this study is to examine in more detail
the relationship between the lithic fragment abundance in
Holocene stream sediments and the climatic variability
within a source area. This study differs from previous
studies of this nature (Young et al. 1975; Basu, 1976:
Mack and Suttner, 1977)) in three fundamental ways.

First, this study is confined to one small, topographic

basin with considerable climatic variability across its
length. This provides better control on factors such as
the distance of sediment transport and source rock

variability which otherwise might influence the results.

Secondly, this study examines the effect of chemical
weathering on sand size sediments within a variable humid
climate. Unlike previous studies (e.g. Young et a1.,
1975) which have compared only the extreme climatic
conditions of arid and humid, this study will focus on a
range of humid rainfall conditions (170-250cm/yr), to
determine whether climatic imprints on sediment
composition can be differentiated at this more refined
level.

Thirdly, this study specifically investigates the effect
of climate on lithic fragments in the sand size fraction
of the sediments, since these are thought to be the best
indicators of climatic variability (Basu, 1976). However,
other mineral grains in the samples are also studied for
evidence of climatic imprinting.

The results of this study indicate that, in a controlled
study area where the effect of parent rock variability and
transportation are minimal, climate alone does not control
the composition of the sediments. Instead, a combination
of the climate and topographic slope exert an integrated
weathering imprint upon the sediments. Of the grain types
studied in the samples, lithic fragment abundance best

reflects this weathering imprint from the source area.

PREVIOUS WORK

For over the last decade, numerous studies have
investigated the effect of climate on the petrology of
Holocene sands (Mann and Cavaroc, 1973; Young et a1., 1975;
Basu, 1976; Mack and Suttner, 1977; and Suttner et a1.,
1981). Young et al. (1975) observed climatic imprinting
from the source area in recent fluvial sediments derived
from low-rank metamorphic, high-rank metamorphic and
plutonic source rocks. They found that major petrographic
distinctions exist in sediments derived from the same
source rock types between the humid southeastern 0.8. and
the arid northwestern U.S. Lithic fragments were much more
abundant in all the sediments derived from the arid climate
(see figure 1), while monocrystalline and polycrystalline
quartz were more abundant in sediments derived from the
more humid climate. Young et al. (1975) explained these
results by suggesting that rock fragments are easily
destroyed by rigorous chemical weathering in a more humid
environment, whereas quartz (mono- or polycrystalline) is
much more resistant to chemical weathering and actually
increases in relative abundance in the more humid climates
because of the release of quartz grains from the weathering
of the lithic fragments. Basu (1976) therefore concluded
that, of the sand size fraction in fluvial sediments,

lithic fragments are the best climatic indicators since

 

 

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they are most sensitive to destruction by chemical
weathering.

To accurately interpret the effect of climate on lithic
fragment abundance in fluvial sediments, other factors
which might affect the composition of these sediments must
also be evaluated. Young et al. (1975) and Suttner et a1.
(1981) studied the effect of transportation upon sediments
by comparing sand-size stream sediments to the sand-size
fraction of the soil from both a gneissic and plutonic
soucre area. They found that the sand fraction of the soil
and fluvial sand from the same parent rock had very similar
compositions (see Figure 2) and concluded that the effect
of transportation over short distances is relatively minor
in fluvial sands in comparison to the importance of
chemical weathering in the source area. Basu (1976)
concurred and noted that even in high gradient streams, the
effect of short fluvial transportation on igneous rock
fragments is negligible. Further, Breyer and Bart (1978)
suggested that granitoid rock fragments can undergo more
than 600 km of transportation with very little physical
breakdown.

The mechanical durability of schistose rock fragments is
more questionable. Cameron and Blatt (1971) found that
schistose lithic fragments are easily broken down in
relatively short distances of transport. However, Mann and
Cavaroc (1973) found that although micaceous rock fragments

are drastically reduced by chemical weathering in the

 

 

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source area, they showed no detectable effects from
transportation.

The effect of parent rock lithology on fluvial sand
composition has also been studied by several workers. In
particular, Mann and Cavaroc (1973) compared Holocene
fluvial sands released from granitic, metamorphic and first
cycle sedimentary source rocks and found that the sediments
derived from each were discernable in subtle ways. The
first cycle sedimentary rock was derived from a metamorphic
and granitic source so that the sediments from it differed
from the others only in that they contained fewer labile
grains and were more enriched in quartz. The sediments
derived from the metamorphic source could be distingushed
from the granitic sands by the higher percentage of
polycrystalline quartz and gneissic lithic fragments in the
coarse sands, and the extremely high percentage of
monocrystalline quartz in the fine grained sands.

Basu et al. (1975) showed that the crystalline source
rock for a sediment can be determined by plotting relative
percentages of (1) undulose quartz, (2) non-undulose
quartz, (3) polycrystalline quartz with two to three
crystals per grain, and (4) polycrystalline quartz with
more than three crystals per grain, on a diamond diagram
(see figure 3). Sediments derived from a low rank.
metamorphic source rock tended to have more undulatory
quartz, and polycrystalline quartz with greater than three

crystals per grain. Sediments derived from a plutonic

 

 

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(2-3 cr stal units per grain, 75%
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at total polycrystalline quartz)

 

 

Figure 3. Four variable plot of quartz population in
Holocene sand derived from source rocks indicated by

symbols (From Basu et al., |975).

source have more non-undulatory quartz, and polycrystalline
quartz with less than three crystals per grain. Sediments
from a middle to high rank metamorphic source have
monocrystalline and polycrystalline quartz which plots
between the quartz from the plutonic and low rank

metamorphic sources.

STUDY AREA

The study area for this project is the Coweeta Hydrologic
Laboratory, located in the Blue Ridge Mountains of
Southwestern North Carolina (see Figure.4). The laboratory
is a 1625 hectare basin managed by the U. S. Forest
Service, and is used primarily to investigate the effect of
varying practices of forest management on the hydrology and
nutrient flow in the basin (Douglass and Swank, 1975; and
Swank and Douglass, 1977).

The area was chosen for this study principally because of
the large variability of precipitation across the basin.
More important than rainfall, however, the stream discharge
from the areas of high precipitation is over double that
from areas of low precipitation and actually represents the
water involved in the chemical weathering of the source
rock.

The Coweeta Hydrologic Laboratory is very well suited to
this study because of the large amount of background
information and data that is available. This includes
stream discharge and precipitation data for most of the
individual watersheds (USDA Forest Service, unpublished
data), detailed geochemistry of the watersheds, including
mineral weathering data (Velbel, 1984a), and a complete
geologic map (Hatcher, 1980) and detailed descriptions of
geologic units present in the Coweeta basin (Hatcher, 1971,

1974, 1976, 1979).

10

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and bo

 
 

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Figure 4. Map of the Coweeta Hydrologic Laboratory

12

TOPOGRAPHY

 

The relief in the Coweeta basin is quite rugged with
elevations ranging from 5200 feet (1585 meters) at Albert
Mountain on the western border to 2200 feet (670 meters) in
the valley of Coweeta Creek in the east. The average slope
across this part of the whole basin is 36% 3 however,
average slopes in the individual watersheds studied are
much higher, ranging from 50% to 100% (see Table 1. Note:
the discharge/slope column will be discussed in the

Discussion section).

CLIMATE AND HYDROLOGY

Average annual precipitation at the Coweeta Hydrologic
Laboratory is among the highest in the eastern United
States, with precipitation ranging from 67.0 inches (170
centimeters) at the lower elevations to 98.5 inches (250
centimeters) at the higher elevations (Swank and Douglass,
1975). The precipitation is distributed fairly evenly
throughout the year with only a minor amount falling as
snow. The mean annual temperature for the area is 55°F
(12.8°C), with average maxima and minima of 92°F (33°C) and
1°F (-17°C) respectively (Douglass and Swank, 1975).

Streamflow in the basin is perennial, ranging from 27 to
68 inches (69 to 173 centimeters) per unit area per year,
and is a function of precipitation and evapotranspiration

within each individual watershed. Base flow is sustained

13

Table 1. Data for watersheds used in study.

1 2 3 4
WS No. Prec Disc Slope DiscASlope Bedrock

 

2 68 32 81 40 Tallulah Falls
10 - 42 53 80 Tallulah Falls
34 77 47 60 78 Tallulah Falls
41 81 53 90 59 Tallulah Falls
13 74 42 56 75 Coweeta Group
27 94 68 82 83 Coweeta Group
32 85 55 51 108 Coweeta Group
37 88 64 100 64 Coweeta Group

1. Average annual precipitation (inches/unit area)
calculated over a 20 year period from 1954 to 1973 for each
watershed (USDA Forest Service, unpublished data).

2. Average annual discharge (inches/unit area) calculated
over the interval that each watershed was monitered (USDA
Forest Service, unpublished data).

3. Average slope (%) calculated from the maximum relief
divided by the maximum length of each watershed.

4. Taken from Hatcher (1980).

14

by extended drainage of unsaturated soil and saprolite
(Hewlett, 1961) so that by late summer flows tend to be
lowest and most stable. Direct runoff only occurs in
disturbed watersheds and is usually less than 10% of total

runoff (Swank and Douglass, 1977).

BEDROCK GEOLOGY

 

The study area is situated in the metamorphosed Blue
Ridge of North Carolina. The bedrock consist of two Upper
Precambrian lithostratigraphic units, the Tallulah Falls
Formation and the Coweeta Group, which are juxtaposed along
the Shope Fork Thrust Fault (Figure 4). The Tallulah Falls
Formation, the older of the two units, consist
predominantly of metagraywackes, muscovite and biotite
schists and amphibolites (Hatcher, 1971,1976). A list of
the mineral assemblages and lithologies in the Tallulah
Falls Formation is given in Table 2.

Hatcher (1979) divides the Coweeta Group into three
formations. The oldest of these formations is the
Persimmon Creek Gneiss, a massive oligoclase-quartz-biotite
gneiss with minor amounts of metasandstone and schist near
the top of the unit. The Coleman River Formation overlies
the Persimmon Creek Gneiss and is composed predominantly of
metaarkose and quartz-feldspar gneiss with interlayers of
pelitic schist. The Ridgepole Mountain Formation is the

uppermost unit of the Coweeta Group and contains the

Table 2.

15

Lithologies and mineral assemblages in the

Tallulah Falls Formation (from Hatcher, 1976).

 

 

 

 

 

Member/Lithology Assemblage*
Quartzite-Schist

Quartzfte Q M P Mi B C Mt Z T E

Schist M B Q P Mt T
Graywacke-Schist

Metagraywacke Q B P M Mt S 2 A T E G

SChist M B Q P Mt
Garnet-Aluminous Schist

, Aluminous Schist M G Q K (or Si) P B Mt

Metagraywacke Q B P M Mt S 2 A T E G

Amphibolite H P Q E Mt G S A B
Graywacke-Schist Amphibolite

Metagraywacke Q B P M Mt S 2 A T E G

Schist M B Q P Mt

Amphibolite H p Q E Mt c s A B

Q - Quartz E - Epidote (or Clinozoisite)

P - Plagioclase Mt - Magnetite

Mi - Microcline H - Hornblende

M - Muscovite A - Apatite

B - Biotite T - Tourmaline

Si - Sillimanite Z - Zircon

S - Sphene G - Garnet

* Minerals listed in order of decreasing abundance.

16

greatest variety of lithologies, including pelitic and
biotite schists, clean quartzites to muscovite-chlorite
quartzites and metasandstones (Hatcher, 1979). A list of
the mineral assemblages and lithologies in the Coweeta
Group is given in Table 3.

The major difference between the Tallulah Falls Formation
and the Coweeta Group is that the sedimentary protoliths
for the Tallulah Falls Formation were less mineralogically

mature than for the Coweeta Group (Hatcher, 1979).

GEOCHEMISTRY

 

Velbel (1985) suggested that the dissolved load of the
streams in the Coweeta basin is affected by two variables,
parent rock type and flushing rate. He contends that the
greater the maturity of the parent rock protolith, as in
the Coweeta Group rocks, the lower the abundance of
weatherable minerals, and thus the lower the concentrations
of dissolved weathering products in the stream water.
However the Tallulah Falls protoliths are mineralogically
less mature, so that these rocks have more weatherable
minerals, resulting in higher dissolved concentrations in
streams draining the Tallulah Falls Formation relative to
streams draining the Coweeta Group rocks for watersheds
with comparable discharges. The dissolved load in the
streams in the Coweeta basin is also affected by the
flushing rate at which the water is percolating through the

watersheds. Velbel (1985) suggests that with a high

17

Table 3. Lithologies and mineral assemblages in the
Coweeta Group (from Hatcher 1979).

 

 

 

 

Unit/Lithology Assemblages*
Ridgepole Mountain Formation
Biotite- Garnet Schist B M G C Q P
Quartzite Q M C E G B St Mt
Pelitic Schist M B G Ky C
Coleman River Formation
Metasandstone Q P M B E C G Mt
Quartz-Feldspar Gneiss Q P M B G
Pelitic Schist M B Q G Ky St Mt
Persimmon Creek Gneiss
Biotite Gneiss P Q B M E G C Ap Mt
Metasandstone Q P M B E C G Mt
Pelitic Schist M B Q G Ky St Mt
Q - Quartz K - Kyanite
M - Muscovite St - Staurolite
B - Biotite E - Epidote (or Clinozoisite)
G - Garnet Mt - Magnetite
P - Plagioclase A - Apatite
C - Chlorite

* Minerals listed in order of decreasing abundance.

18

flushing rate, there is less opportunity for the water to
acquire solutes, so that the limiting factor may be the
rate at which cations are contributed to the percolating

solution.

METHODS

FIELD SAMPLING

 

Sand-size stream sediments were collected across the
Coweeta basin in two transects, one sampling sediments
derived from the Tallulah Falls Formation and the other for
sediments derived from the Coweeta Group. These transects
ran roughly East-West, with elevation and watershed
discharge increasing to the West. Table 1 lists stream
discharge, average topographic slope, and bedrock type for
the watersheds which were sampled. No watersheds were used
in this study that were recently disturbed or altered, so
the effects of varied biota on chemical weathering in the
source area are minimal.

Each watershed was sampled 40 to 60 feet above the weir
at 3 intervals 20 to 30 feet apart to test for homogeneity
of the sediments. To minimize the effect of
transportation, all samples were collected from streams
which are first or second order and less then one-half mile

in length.

SAMPLE PREPARIATION AND POINT COUNTING

 

The samples were wet sieved into three fractions, coarse
(-l¢ to l¢), medium (10 to 20) and fine (20 to 40).
Portions of each fraction were vacuum impregnated with
epoxy and thin sectioned. -Samples were not stained for
potassium feldspar determination since its occurrence in

the parent rocks is minimal. Each thin section was then

19

20

point counted (Chayes, 1949) for monocrystalline quartz,
polycrystalline quartz, lithic fragments, mica, garnet,
plagioclase, heavy minerals and others at about 300 points
per thin section . Lithic fragments are defined following
Suttner et al. (1981). Modal percentages of
monocrystalline quartz, polycrystalline quartz, lithic
fragments, and mica were then recalculated to 100 percent

for the remaining analysis.

TEST FOR EFFECT OF TRANSPORTATION

Garnet grains have been shown to develope a
gibbsite-goethite weathering rind in saprolites from the
Coweeta basin (Velbel, 1984b). These rinds are relatively
fragile and can withstand little high-energy
transportation. To determine the effect of transportation
upon the sediments, garnets were counted as having complete
rinds, partial rinds, or no rinds in the coarse sediment

fraction from each watershed.

TEST FOR PARENT ROCK HOMOGENEITY

Parent rock homogeneity between watersheds would have a
large effect upon the sediment derived from these areas.
For example, if the parent rock in watershed X was 80%
schist and 20% quartzite while the parent rock in watershed
Y was 20% schist and 80% quartzite, then one would expect
to see major differences in the petrology of the sediments

between these two areas.

21

To determine roughly the degree of homogeneity of the
parent rock between watersheds underlain exclusively by the
Tallulah Falls Formation or the Coweeta Group rocks, a
simple test for parent rock homogeneity was devised by the
author following the work of Young et al. (1975).
Approximately 300 monocrystalline quartz grains from the
medium sand size fraction of each watershed were point
counted on a flat stage and classified as either undulose
(>5o extinction) or nonundulose (<5o extinction). These
relative percentages for each watershed were compared
between sediments derived from the same parent rock to
determine roughly the homogeneity of bedrock within the

Coweeta Group and the Tallulah Falls Formation.

RESULTS

EFFECTS OF PARENT ROCK HOMOGENEITY AND TRANSPORTATION

The results of the tests for parent rock homogeniety are
given in Table 4. These are presentedn as the percent
undulose quartz to total monocrystalline quartz in the
medium-sized sands from sediments across the Coweeta
basin. Samples from watersheds 2, 41, 10 and 34 were
derived from parent rock consisting of only the Tallulah'
Falls Formation, while samples 13, 27, 32, and 37 were
derived from only the Coweeta Group parent rock. The
percent undulose quartz to total monocrystalline quartz in
the medium-sized sand fraction of the sediment draining the
Tallulah Fall Formation parent rocks varies by only 3%
among the four watersheds 2, 41, 10, and 34, while among
the four watersheds (13, 27, 32, 37) draining the Coweeta
Group rocks, the percent undulose to total monocrystalline
quartz in the medium-sand sized fraction varies by only
4%. However, the percent undulose quartz varies by over
20% between sediments derived from the Tallulah Falls
Formation and Coweeta group rocks.

The results of the test for the effect of transportation
show that a large number of all the garnets from the
watershed draining both Tallulah Falls Formation rocks (ws
2,41,10,34) and Coweeta group rocks (ws l3,27,32,37) have
whole or partial gibbsite-goethite weathering rinds (see

Table 5). The average relative percent of garnets with

22

23

Table 4. Unudulosity of quartz as an indicator of parent

rock homogeniety.

Tallulah Falls Watersheds

 

 

Watershed No. Undulose
WS#2 49%
WS#lO 47%
WS#34 46%
WS#41 46%

Ave. 47%

Coweeta Watersheds

 

 

Watershed No. Undulose
WS#13 28%
WS#27 27%
WS#32 24%
WS#37 28%

Ave. 27%

Nonundulose

 

Ave.

51%
53%
54%
54%
53%

Nonundulose

 

72%
73%
76%
72%
73%

Ave .

Table 5. Weathering rinds on garnets as indicators of the

effect of transportation.

Tallulah Falls Watersheds

 

 

Watershed No. Whole Rind
WS#2 45%
WS#lO 48%
WS#34 46%
WS#41 43%

Coweeta Watersheds

 

 

Watershed No. Whole Rind
WS#13 60%
WS#27 52%
WS#32 52%
WS#37 39%

 

 

Partial Rind No Rind
33% 22%
43% 9%
42% 12%
31% 26%

Partial Rind No Rind
29% 11%
32% 16%
33% 15%
34% 27%

24

whole rinds in sediments derived from the Tallulah Falls
Formation rocks is 45%, with 83% of the garnets showing at
least a partial rind. For the sediments derived from the
Coweeta group rocks, the average relative percent of
garnets with a complete weathering rind is slightly over
50%, while 83% of these garnets show a partial rind or
more. The occurrence of garnets with partial or no rinds
does not necessarily imply that these were eroded off
during transportation since not all garnets in the
weathering profile form gibbsite-geothite weathering
rinds. These rinds form primarily in the saprolite horizon
of the weathering profile but are often chemically removed
once the garnets migrate into the soil horizon (Velbel,

1984b).

RESULTS OF POINT COUNTING

The results of the point counts are compiled in Appendix
A. Modal percents of lithic fragments, monocrystalline
quartz, polycrystalline quartz, and mica were recalculated
to 100% and these values are used in the remaining
analyses. The average modal abundance of each grain type
was calculated from the point counts of the three samples
taken from each watershed. These were then plotted against
grain-size (coarse, medium, and fine) following the work of
Young et al.(1975) for each group of sediments derived
either from the Tallulah Falls Formation or Coweeta Group

rocks. 0f the four grain types plotted, only the modal

25

percentage of mica shows a relationship to the climatic
variability in the source area for both the Tallulah Falls
and Coweeta Group sediments. Climatic variability is
measured not as precipitation per unit area as done in most
previous studies (Young et al., 1975: Basu, 1976; and Mack
and Suttner, 1977), but rather as stream discharge per unit
area per year since this more accurately represents the
water which is involved in the chemical weathering of the
source rock.

The discharge per unit area for watersheds underlain by
Coweeta Group rocks increases from 13 to 32 to 37 to 27;
this corresponds to an increase in the modal abundance of
mica in these sediments (Figure 5) except in the fine
fraction of watershed 27. The same basic relationship
holds between discharge and the micas in the sediments
derived from the Tallulah Falls Formation rocks; as the
discharge per unit area increases between watersheds, the
modal abundance of mica in the sediments also increases
except for the medium and fine fractions in watershed 41
(Figure 6).

From Figures 5 and 6, there is no other obvious
relationship between the climatic variability (discharge
per unit area) and the modal abundance of monocrystalline

quartz, pollycrystalline quartz or lithic fragments.

26

 

 

 

 

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DISCUSSION

ARE SEDIMENT TRANSPORT AND PARENT ROCK VARIABILITY
SIGNIFICANT FACTORS?

The purpose of addressing this question is to determine
if climatic variability is the only factor affecting the
sediment composition from a particular geologic unit, e.g.,
Coweeta Group or Tallulah Falls Formation, in the Coweeta
Basin. After studying the results of these tests, this
author believes that other factors do affect the sediment
composition, but that these effects are relatively minor in
comparison with the effect of chemical weathering in the
source area.

Numerous other studies (Mann and Cavaroc,l973; Young et
al., 1975; and Basu, 1976) have concluded that the physical
effects of short distances of transportation, up to several
miles, are relatively minor in fluvial sands. ,The overall
results of this study's test for the effect of
transportation on sediments within the Coweeta basin also
show that little mechanical breakdown has occurred between
the source area and the sampling stations. This conclusion
is based on the occurrence of very fragile
gibbsite-goethite weathering rinds on garnets in sediments
within the sampling area, less than one-half mile from the
source areas, but at distances of three miles or greater

downstream, weathering rinds are completely absent on any

28

29

garnets (Velbel, personal communication). This suggests
that mechanical breakdown by transportation within the
study area is minimal, but that continued transportation
outside the study area is affecting the most labile grains
such as these gibbsite-goethite weathering rinds.

0n the other hand, by comparing the discharge per unit
area of a watershed to the relative percent of garnets with
complete weathering rinds, it appears that some mechanical
breakdown by transportation is occurring in the study area.
In watersheds with high discharges and slopes there are
fewer garnet grains with complete weathering rinds (see
Table 5; e.g., watersheds 37 and 41) than in the other
watersheds studied. The author interprets this as
indicating that mechanical destruction of the
gibbsite-goethite weathering rinds on garnets occurs more
rapidly in watersheds with higher energy streams.

This, however, does not necessiarly mean that other
detrital grains are also affected by short fluvial
transport. The fact that these rinds are totally absent on
garnets in the sediments three miles from the source area
while other labile grains such as lithic fragments still
occur in abundance suggests that these gibbsite-goethite
rinds are ultra-sensitive to mechanical degradation and
that limited transport may affect them without affecting
other detrital grains. If, in fact, these rinds are
ultrasensitive to mechanical degradation, then the

occurrence of partial or whole gibbsite—goethite

3O

weathering rinds on 83% of the garnets observed would imply
that the overall effect of fluvial transportation in the
study area is negligible.

The influence of parent rock variability upon the
sediments is much less certain. From Tables #2 and #3, it
can be seen that the individual lithologies in both the
Coweeta Group and the Tallulah Falls Formation are quite
varied. However, the question of parent rock variability
is not concerned with the diversity of lithologies within a
major unit, but rather, whether these lithologies are
distributed homogeneously throughout that unit. Obviously
the best way to determine this would be to compile a
detailed lithologic map of both the Coweeta Group and
Tallulah Falls Formation in the Coweeta basin. This,
however, is not feasible, since a thick soil-saprolite
weathering profile covers most of the bedrock, and intense
structural deformation has caused numerous repeated
sections so that estimating lithologic abundances and
distributions is very difficult. Therefore an alternative
method was applied which used the undulosity of
monocrystalline quartz grains in the sediments as a very
crude indicator of parent rock homogeneity.

Although the degree of undulosity in quartz is governed
not only by the lithology but also by the metamorphic grade
and deformational history of the rock, the result of this
test suggests that some sort of homogeneity exists within

each of the two major lithologic units that does not exist

31

between these groups. This is supported by the uniformity
of the percent undulose quartz in the sediments between
watersheds underlain by one geologic unit, either the
Tallulah Falls Formation or the Coweeta_Group. However,
this uniformity does not exist when comparing the percent
undulose quartz between the two major geologic unit. As
stated above, undulosity is not directly related to
lithologic type. However, both quartz undulosity and
metamorphic lithologies are directly related to the
deformational history, degree of metamorphism, and
protolithic types of the unit, so that indirectly, the
uniformity of undulose quartz in a lithologic

unit may roughly estimate the homogeneity of the parent
rock. Further detailed studies need be done to confirm this

preliminary result.

DO CLIMATIC IMPRINTS EXIST IN THE SEDIMENTS FROM THE
COWEETA BASIN?

The results of the plots of modal abundance of grain type
to grain size indicate that only the mica grains seem to be
affected by the climatic variability (discharge) across the
Coweeta basin. This contradicts the original hypothesis
that lithic fragments are the most sensitive to climatic
variability. To resolve this contradiction, the specific
factors which are affecting the sediment composition in the
Coweeta basin must first be examined. The effects of

transportation and parent rock homogeniety have already

32

been discussed in the previous section; the affect of
climate on sediment composition will now be examined in
more detail. As previously mentioned, discharge per unit
area for each watershed more closely represents the effect
of climate on weathering in the source area since this is
the water which actually interacts with the soil,
saprolite, and parent rock. Precipitation would include
not only the water which is discharged from the watershed,
but also water which is recycled as evapotranspiration
without ever reaching the weathering horizon.

Secondly, it is very important to realize that in a study
of this nature where the effects of transportation and
parent rock variability are considered minimal, the modal
abundances of grain types reflect the total amount of
chemical weathering which occurs in the source area, of
which climate is only a part. It has been shown that the
extent of chemical weathering, as measured by chemical or
mineralogical changes, is dependant upon 1) the intensity
of the weathering, and 2) the duration over which the
weathering occurs (Krynine, 1942; Pettijohn et al., 1972;
and Suttner et al., 1981). In its simplest form, the

relationship is as follows:

DURATION X INTENSITY = EXTENT

Franzinelli and Potter (1983) showed that quartz arenite

sands could be produced from granitic bedrock in a low

33

relief, humid climate region of the Amazon basin by
chemical weathering alone. Likewise in the Coweeta basin,
watersheds with high discharges and low topographic slopes
would have the highest extent of chemical weathering, while
low discharge, high relief watersheds would have the lowest
extent of chemical weathering. The intensity of chemical
weathering in the Coweeta basin is largely dependent upon
the climate, while the duration of weathering appears to be
inversely related to the relief in the source area since
high relief areas would have higher erosion rates and thus
reduce the residence time that material is in the
weathering profile. Relief is measured here as the average
topographic slope (%) across the length of each watershed.
The equation for the extent of chemical weathering in

watersheds from the Coweeta basin can then be written as
l/SLOPE x DISCHARGE/UNIT AREA = TOTAL CHEMICAL WEATHERING

The total chemical weathering for each watershed was then
plotted against the modal abundance of each grain type.
Plots were also constructed of average watershed slope
versus modal abundance and discharge per unit area versus
modal abundance of each grain type (Appendix B). Linear
regressions were calculated for each grain size (coarse,
medium, and fine) for all plots with correlation
coefficients, slopes, and y intercepts given in Table 6.

These results showed that of all of the plots, the best

Table 6.

34

Correlarion coefficients (r), slopes (a), and y
intercepts (b) for linear regressions through each size
fraction of grain type versus discharge, slope and
discharge/slope.

SEDIMENTS DERIVED FROM THE COWEETA GROUP SOURCE ROCK

Mono Qtz

Coarse
Medium
Fine
Poly Qtz
Coarse
Medium
Fine
Mica
Coarse
Medium
Fine
Lithics
Coarse
Medium
Fine

 

Mono Qtz
Coarse
Medium
Fine

Poly gtz
Coarse
Medium
Fine

Mica
Coarse
Medium
Fine

Lithics
Coarse
Medium
Fine

Discharge Slope Discharge/Slope
r b a r b a r b a
56.0 58.3 -.55 93.0 59.9 -45.9 86.0 -17 .52
6800 7804 -045 9500 7501 -3104 7000 2809 028
28.0 69.7 —.12 78.0 74.8 -l6.4 78.0 46.5 .20
49.7 11.5 .28 0.0 27.8 -.5 44.5 14.7 .15
44.0 5.8 .09 40.5 7.9 4.0 18.7 12.8 -.02
28.0 0.5 .03 18.9 2.9 1.0 44.7 6.0 -.03
76.6 -10.0 .27 53.7 -1.9 9.4 10.0 5.5 -.01
82.0 -l.5 .31 58.6 8.3 11.2 30.0 18.3 -.02
79.9 12.6 .19 71.4 17.4 8.6 15.1 25.4 -.02
0.0 40.0 .01 66.4 14.1 37.0 96.8 95.6 -.66
7.7 18.2 -.03 67.2 9.6 14.5 84.9 38.6 -.23
17.0 12.3 -.05 51.3 4.8 6.8 91.9 22.1 -.15
SEDIMENTS DERIVED FROM THE TALLULAH FALLS SOURCE ROCK
Discharge Slope Discharge/Slope
r b a r b a r b a
69.8 1.46 0.38 8.90 16.1 2.46 35.6 12.0 0.91
89.0 23.3 0.40 36.7 34.8 8.51 22.8 37.7 0.05
22.8 48.1 0.20 80.0 82.5 -36.1 81.9 34.8 0.34
86.3 62.8 -.67 43.5 45.8 -17.3 14.5 37.0 -.05
6400 4001 -048 7000 3801 -2609 2206 1309 008
16.4 6.7 -.24 7.0 6.0 -.59 0.0 5.7 0.0
9101 -1304 053 301 809 101 5101 06 014
59.5 1.5 .35 39.2 25.1 -11.8 68.5 4.5 .19
54.0 8.2 .28 18.1 16.8 4.7 18.7 17.3 .05
54.0 49.3 -.24 60.1 29.1 13.8 85.8 50.5 -.18
39.9 36.2 -.30 78.8 1.9 30.1 92.4 44.3 -.33
43.2 35.4 -.43 78.5 -6.9 33.4 99.1 42.1 -.39

 

 

 

 

 

 

35

correlation exists between the modal abundance of lithic
fragments and the total chemical weathering for both the
Tallulah Falls sediments (Figure 7) and the Coweeta Group
sediments (Figure 8). These plots show that as the total
chemical weathering increases, the modal percent lithic
fragments in all three size fractions decreases for both
the Tallulah Falls and the Coweeta Groups sediments. This
is the expected result since lithic fragments are
considered the most labile grains (Basu, 1976) of those
counted in this study and therefore would be the most
susceptible to chemical weathering in the source area.

This relationship could not be due to mechanical
degradation during transportation since lithic fragment
abundances decrease with increasing discharge and
decreasing slope. If transportation were affecting the
sediments, lithic fragment abundance would decrease with
both increasing discharge and increasing slope.

Numerous reasons may exist why only the lithic fragments
in the sediments reflect the extent of chemical
weathering. Foremost is the fact that polyminerallic
grains have heterogeneous crystal boundries which are
avenues for fluid movement and eventually cause physical
breakdown of these grains. This would be especially true
in foliated, metamorphic rocks where planar and non-planar
crystals, e.g., mica and quartz respectively, have
physically weak crystal boundries. Secondly, chemical

dissolution of certains minerals such as quartz occurs at

36

TF LITH
48.0+

 

 

32.0+
2400+
: r= 92
16.0+
_ r? 99
8.0+
36.0 45.0 74.0 53.0 72.0 31.0

DISCHARGE/SLOPE

F 7. Percent lithic fragments versus discmrge/slme
fciiig’uilgtersheds draining the Tallulah Falls Fonmtion source
rock (r=correlation coefficient for each grain size).

37

C: Li I... I T H

{2’} C’ -) 'i'

   

.3:- l\
\J A) ‘3

i-i-l

40.

il-i-iii

30.

l+llil+il

12’. O .

10.

tl+tll

O
+li

DISCHARGE/SLOPE

Figure 8. Percent lithic fragnents versus discharge/slam
for watersheds draining the Coweeta Group source rock
(r=correlation coefficient for each grain size).

38

such a slow rate in the weathering profile that the
duration of weathering may be too short to see any chemical
weathering imprints on these monominerallic grains.
However, the chemical destruction of one labile crystal in
a polyiminerallic grain may cause a more rapid physical
breakdown of that grain and thus make lithic fragments more
prone to develope chemical weathering imprints while still
in the source area.

The results of this new plot differ from the preliminary
results of this study which found that the micas were the
best indicators of climatic differentation across the
Coweeta Basin. However by comparing the correlation
coefficients of the lithic fragment abundance versus the
total chemical weathering (Figures 7 and 8) to the mica
abundance versus the discharge (Figures 9 and 10), it
becomes evident that the correlation between the modal
abundance of lithic fragments and the total chemical
weathering is the most statistically valid (significant at
the 1% level) for all three size fractions in both the
Coweeta Group and Tallulah Falls Formation sediments.

These results are interpreted to mean that the modal
abundance of lithic fragments in the sediment is very
strongly correlated with the total weathering in the source
area, but that the modal abundance of mica in the sediment
is correlated only with the discharge or intensity of,
weathering in the source area. Other good correlations

exist between certain grain types and the slope, discharge,

39

TF MICA
3000+

.. i F r= 55

 

m-_1 m *m+w__”_mu1-+_mmwumm_*+-2m_“__-_+—_-~*g--a+

00’0-
.. :1“ '3?
30.0 35.0 40.0 wu.0 50.0 00.0

DISCHARGE

Figure 9. Percent mica versus discharge for watersheds
draining the Tallulah Falls Forrmtion source rock
(r=correlatlon coefficient for each grain size).

4O

r= 80

_. M r= 82

 

r= 77

 

0.0+ 3

+......_..........................+._...............................+......................._..........+...................................+....._-..........................+

DISCHARGE

Figure 10. Percent mica versus discharge for watersheds

draining the Coweeta Grow source. rock (r—-correlation
coeffic ent for each grain size).

41

or discharge/slope (see Table 6), however these
correlations are either not consistent between grain sizes
or not consistant between the Coweeta Group sediments and
the Tallulah Falls sediments and therefore are considered
much less significant.

In a very recent paper, Basu (1985) also proposes that
topographic slope and climate have a combined affect upon
sediments derived from a source area. He shows, using
recalculated data from Ruxton (1970), that the material on
the crest of hills is more highly weathered than the
material on the slopes.

This study produced similar results to Basu (1985) but
took a somewhat different approach. First, the duration of
chemical weathering in this study area was estimated from
the average topographic slope across the length of each
watershed. Although the topographic slope within an
individual watershed would vary greatly, this author feels
that the average slope is the best estimate for predicting
the duration of chemical weathering over a large area.
Secondly, the intensity of chemical weathering in the
Coweeta basin can best be estimated from the average
discharge per unit area in an individual watershed. By
combining the average discharge per unit area and slope of
a watershed into the chemical weathering equation, the
total chemical weathering can be determined for that
watershed, and the modal abundance of lithic fragments can

be predicted from the regression line for each of the three

42

grain sizes. The reverse should also be true with the
total chemical weathering of a watershed being predicted
from the modal abundance of lithic fragments in the
sediment.

The theory behind these results is far reaching; however,
further work need be done in this field to determine if
these same factors control the extent of chemical
weathering in other source areas, and how this relationship

might relate to ancient sediments.

SUMMARY

The abundance of lithic fragments in sand-sized sediment
derived from a source area with a variable humid climate in
the southern Appalachians is not correlated with climate
but instead is correlated with the total extent of chemical
weathering in the source area. This weathering imprint is
best observed in the lithic fragment portion of the
sediments, and is a function of the duration and intensity
of the chemical weathering in the source area. Duration of
chemical weathering is inversely related to the average
topographic slope of a watershed, while intensity is
directly related to the climate.

43

UNANSWERED QUESTIONS FOR FURTHER RESEARCH

1) Does the relationship between chemical weathering in
the source area and lithic fragment abundance apply to
other geographic areas?

2) What are the thresholds of this relationship?

3) Why does this relationship appear to be linear?

4) What are the ranges of sand composition that can be

produced by chemical weathering alone?
5) What is the relative importance of chemical weathering
in the source area to transportation for sands derived from

the Coweeta basin or other source areas?

6) How is this applicable to the ancient?

44

APPENDIX A

Data from point counts

APPENDIX A

Data from point counts

WATERSHED 2
draining Tallulah Falls Formation bedrock

 

 

 

Coarse Medium Fine
Sample ZAC ZBC 2CC 2AM 28M ZCM ZAF 28F 2CF
Total Pts 286 297 293 365 289 290 336 307 311
Mono Qtz 33 33 37 114 98 96 156 125 131
Poly Qtz 99 106 101 83 45 53 18 13 16
Lithics 108 117 113 89 78 88 75 65 76
Mica 7 9 12 37 31 27 49 47 48
Garnet 18 17 18 5 9 2 1 1 2
Heavies 16 13 8 31 22 15 33 40 25
Plag 5 3 4 6 6 9 4 8 1
Other - - - - - - - 8 12

Modal Percent of Total

Mono Qtz 11.5 11.1 12.6 31.2 33.9 33.1 46.4 40.7 42.1
Poly Qtz 34.6 35.7 34.5 22.7 15.6 18.3 5.4 4.2 5.1
Lithics 37.8 39.4 38.6 24.4 27.0 30.3 22.3 21.1 24.4
Mica 2.4 3.0 4.1 10.1 10.7 9.3 14.6 15.3 15.4
Garnet 6.2 5.7 6.1 1.4 3.1 .7 .3 .3 .6
Heavies 5.6 4.4 2.7 8.5 7.6 5.2 9.8 13.0 8.0
Plag 1.7 1.0 1.4 1.6 2.1 3.1 1.2 2.6 .3
Other - - - - - - - 2.6 3.8

Modal Percent of Monqggtz, Polyggtz, Lithics, and Mica
Recalculated to 100%

Total Pts 247 265 263 323 252 264 298 250 271
Mono Qtz 13.4 12.5 14.1 35.3 38.9 36.4 52.3 50.0 48.4
Poly Qtz 40.0 40.0 38.4 25.7 17.9 20.0 6.0 5.2 5.9
Lithics 43.7 44.1 43.0 27.7 31.0 33.4 25.2 26.0 28.0
Mica 2.8 3.4 4.6 11.5 12.3 10.3 16.4 18.8 17.7

45

46

WATERSHED 10 '
draining Tallulah Falls Formation bedrock

 

 

 

Coarse Medium

Sample 10AC 108C 10cc 10AM 108M 10CM
Total Pts 318 279 312 300 264 292
Mono Qtz 47 54 48 108 91 106
Poly Qtz 101 91 117 70 63 65
Lithics 75 91 100 47 53 39
Mica 17 23 35 40 32 55
Garnet 18 8 6 5 2 3
Heavies 12 7 3 15 16 13
Plag 6 2 5 10 2 3
Other 9 3 7 5 5 8
Modal Percent of Total

Mono Qtz 14.8 19.4 15.0 36.0 34.5 36.3
Poly Qtz 31.8 32.6 36.4 23.3 23.9 22.3
Lithics 33.9 32.6 31.5 15.6 20.0 13.3
Mica 5.3 8.2 10.9 13.3 12.1 18.8
Garnet 5.7 2.9 1.9 1.7 .7 1.0
Heavies 3.8 2.5 .9 5.0 6.1 4.4
Plag 1.9 .7 1.5 3.3 .7 1.0
Other 2.8 1.1 2.1 1.6 1.9 2.7

Modal Percent of Mono Qtz ,Polyggtz,

LithicsLiand Mica

 

 

Recalculated to 100%

Total Pts 273 259 290 265
Mono Qtz 17.2 20.8 16.5 40.7
Poly Qtz 37.0 35.1 40.3 26.4
Lithics 39.6 35.1 34.5 17.7
Mica 6.2 8.8 8.6 15.1

239
38.1
26.4
22.2
13.4

265
40.0
24.5
15.0
20.7

Fine

10AF loBF 10CF
288 281 297
160 147 144
14 18 16
30 26 29
51 37 73

3 6 2

19 4O 24

1 2 3

10 5 6
55.5 52.3 48.5
4.9 6.4 5.4
10.4 9.3 9.8
17.7 13.2 24.6
1.0 2.1 .6
6.6 14.2 8.1
.4 .7 1.0
3.5 1.8 2.0
255 228 262
62.7 64.4 55.0
5.5 7.9 6.1
11.8 11.3 11.1
20.0 16.2 27.9

47

WATERSHED 34
draining Tallulah Falls Formation bedrock

 

 

 

 

 

 

Coarse Medium Fine
Sample 34AC 34BC 34CC 34AM 348M 34CM 34AF 34BF 34CF
Total Pts 340 328 344 311 293 338 341 312 357
Mono Qtz 59 46 65 118 119 126 197 199 197
Poly Qtz 92 101 110 48 57 56 12 17 14
Lithics 111 106 95 50 54 56 33 32 37
Mica 53 37 37 74 50 78 63 43 69
Garnet 5 8 6 6 1 1 1 - -
Heavies 16 9 5 7 7 17 33 20 38
Plag 2 7 2 6 1 1 - - -
Other 2 4 4 2 4 3 2 1 2
Modal Percent of Total
Mono Qtz 17.3 14.0 18.9 37.9 40.6 37.3 57.7 63.8 55.1
Poly Qtz 27.0 30.8 31.9 15.4 19.4 16.5 3.5 5.5 3.9
Lithics 32.6 35.4 33.4 16.1 18.4 16.5 9.6 10.3 10.4
Mica 15.6 11.3 10.7 23.8 17.0 23.0 18.7 13.7 19.3
Garnet 1.5 2.4 1.7 1.9 .3 .3 .3 - -
Heavies 4.7 2.7 1.5 2.3 2.4 5.0 9.7 6.4 10.6
Plag .6 2.1 .6 1.9 .3 .3 - - -
Other .6 1.2 1.2 .6 1.4 .9 .6 .3 .6
Modal Percent of Mono Qtz, Poly Qtz, Lithics, and Mica
Recalculated to 100%
Total Pts 315 300 327 290 280 316 305 291 317
Mono Qtz 18.7 15.3 19.9 40.7 42.5 39.6 64.6 68.3 62.2
Poly Qtz 29.2 33.6 33.6 16.6 20.3 17.7 3.9 5.8 4.4
Lithics 35.3 38.6 35.1 17.4 19.3 17.7 10.8 11.0 11.7
Mica 16.8 12.3 11.3 25.2 17.7 24.7 20.6 14.7 21.7

48

WATERSHED 41
draining Tallulah Falls Formation bedrock

 

 

 

 

 

 

Coarse Medium Fine
Sample 41AC 418C 41CC 41AM 418M 41CM 41AF 4lBF 41CF
Total Pts 293 307 358 328 314 317 310 332 247
Mono Qtz 39 76 56 122 125 129 146 134 107
Poly Qtz 57 55 85 26 38 42 13 13 15
Lithics 91 97 118 72 69 74 55 52 37
Mica 33 36 39 48 46 43 62 78 42
Garnet 38 16 30 15 11 18 - 6 4
Heavies 19 16 22 25 18 13 30 43 35
Plag 16 11 8 18 7 14 3 3 2
Other - - - - - - 1 3 5
Modal Percent of Total
Mono Qtz 13.3 24.8 15.6 37.2 39.8 40.7 47.1 40.4 43.3
Poly Qtz 19.4 17.9 23.7 7.9 12.1 8.2 4.2 3.9 6.0
Lithics 31.1 31.6 33.0 22.5 22.023.3 17.7 15.6 15.0
Mica 11.3 11.7 10.9 14.6 14.6 13.6 20.0 23.5 17.0
Garnet 13.0 5.2 8.4 4.6 3.5 5.6 - 1.8 1.6
Heavies 6.5 5.2 6.1 7.6 5.7 4.1 9.7 13.0 14.2
Plag 5.4 3.6 2.2 5.5 2.2 4.4 1.0 .9 .8
Other - - - - - - .3 .9 2.0
Modal Percent of Mono Qtz, Poly Qtz, Lithics, and Mica
Recalculated to 100%
Total Pts 220 264 298 .270 278 272 276 277 201
Mono Qtz 17.7 28.8 18.8 45.2 45.0 47.4 52.9 48.3 53.2
Poly Qtz 25.9 20.8 28.5 9.6 13.7 9.6 4.7 4.7 7.4
Lithics 41.3 36.7 39.5 27.3 24.8 27.1 19.8 18.8 18.3
Mica 13.0 13.6 13.1 17.9 16.5 16.0 22.5 28.1 21.0

49

WATERSHED 13

draining Coweeta Group bedrock

 

 

 

 

Coarse Medium Fine

Sample 13AC 138C 13CC 13AM 13PM 13CM 13AF 13BF 13CF
Total Pts 318 340 359 283 270 282 300 285 320
Mono Qtz 98 86 96 147 147 147 162 163 163
Poly Qtz 62 72 80 28 25 22 12 8 11
Lithics 130 154 151 51 53 56 32 30 27
Mica 2 2 3 30 23 40 51 51 52
Garnet 10 7 15 2 - - 2 - -
Heavies 9 12 9 16 13 14 34 31 58
Plag 1 1 2 3 1 l 1 1 -
Other 6 6 3 6 8 2 6 1 9
Modal Percent of Total

Mono Qtz 30.8 25.3 26.7 51.9 54.4 52.1 54.0 57.2 51.0
Poly Qtz 19.5 21.2 22.3 9.9 9.2 7.8 4.0 2.8 3.4
Lithics 40.9 45.3 42.1 18.0 19.6 19.8 10.6 10.5 8.4
Mica .6 .6 .8 10.6 8.5 14.2 17.0 17.9 16.3
Garnet 3.1 2.1 4.2 .7 - - .7 - -
Heavies 2.8 3.5 2.5 5.7 4.8 5.0 11.3 10.9 18.1
Plag .3 .3 .6 1.1 .4 .4 .3 .4 -
Other 1.9 1.8 .8 2.2 3.0 .7 2.0 .3 2.8

Modal Percent of Mono Qtz, Polyggtz,

Lithicsi and Mica

 

Recalculated to 100%

Total Pts 292 314 330 256 248
Mono Qtz 33.6 27.4 29.1 57.4 59.3
Poly Qtz 21.2 22.9 24.2 10.9 10.1
Lithics 44.5 49.0 45.8 19.9 21.4
Mica .7 .7 .9 11.7 9.3

265 257 252 253
55.5 63.0 64.7 64.4
8.3 4.7 3.2 4.3
21.1 12.5 11.9 10.7
15.1 19.8 20.2 20.5

50

WATERSHED 27

draining Coweeta Group bedrock

 

 

 

 

 

 

Coarse Medium Fine
Sample 27AC 278C 27CC 27AM 278M 27CM 27AF 27BF 27CF
Total Pts 296 307 248 300 315 290 284 271 276
Mono Qtz 65 58 43 138 137 132 167 160 160
Poly Qtz 91 80 90 28 44 27 7 4 7
Lithics 97 112 81 48 49 45 22 19 20
Mica 11 36 16 58 59 53 61 59 60
Garnet 10 4 2 3 1 2 - - 1
Heavies 6 7 1 15 7 8 20 22 20
Plag 16 9 9 6 15 20 6 4 4
other - 1 4 4 3 3 1 3 4
Modal Percent of Total
Mono Qtz 22.0 19.0 17.3 46.0 43.5 46.5 58.8 59.0 58.0
Poly Qtz 30.7 26.0 36.3 9.3 14.0 9.3 2.5 1.5 2.5
Lithics 32.7 36.6 32.6 16.0 15.5 15.5 7.7 7.0 7.2
Mica 7.7 3.7 11.7 19.3 18.7 18.2 21.5 21.8 21.7
Garnet 3.4 1.3 .8 1.0 .3 .7 - - .4
Heavies 2.0 2.3 .4 5.0 2.2 2.8 7.0 8.1 7.2
Plag 5.4 2.9 3.6 2.0 4.8 6.9 2.1 1.5 1.4
Other - .3 1.6 1.3 1.0 1.0 .3 1.1 1.4
Modal Percent of Mono Qtz, Poly Qtz, Lithics, and Mica
Recalculated to 100%
Total Pts 264 286 230 272 289 257 257 242 247
Mono Qtz 24.6 20.3 18.7 50.7 47.4 51.3 65.0 66.0 64.8
Poly Qtz 34.5 28.0 39.1 10.3 15.2 10.5 2.7 1.7 2.8
Lithics 36.7 39.2 35.2 17.6 16.9 17.5 8.6 7.9 8.1
Mica 4.2 12.5 7.0 21.3 20.4 20.6 23.7 24.4 24.3

51

WATERSHED 32

 

 

 

draining Coweeta Group bedrock

 

 

 

Coarse Medium Fine
Sample 32AC 328C 32CC 32AM 328M 32CM 32AF 328E 32CF
Total Pts 312 250 247 283 291 287 278 299 304
Mono Qtz 117 94 100 145 156 168 181 184 180
Poly Qtz 90 73 64 24 25 31 7 10 10
Mica 9 8 17 47 41 34 63 66 65
Garnet 10 5 5 2 3 3 1 2 1
Heavies 8 6 3 18 8 5 7 18 31
Plag 1 1 2 2 3 3 1 2 1
Other 1 - - 2 12 - - 1 -
Modal Percent of Total
Mono Qtz 37.5 37.6 40.5 51.2 53.6 58.5 65.6 61.5 59.2
Poly Qtz 28.8 29.2 25.9 8.5 8.6 10.8 2.5 3.3 3.3
Lithics 24.3 25.2 22.7 15.1 15.5 12.5 6.1 6.0 5.6
Mica 3.1 3.3 7.1 18.1 15.4 12.0 23.5 23.7 23.9
Garnet 3.2 2.0 2.0 .7 .3 3.5 - - -
Heavies 2.6 2.4 1.2 6.4 2.7 1.7 2.5 6.0 10.2
Plag .3 .4 .8 .7 1.0 1.0 .3 .7 .3
Other .3 - - .7 4.1 - - .3 -
Modal Percent of Mono Qtz, Poly Qtz, Lithics, and Mica
Recalculated to 100%
Total Pts 292 238 237 259 267 269 268 278 272
Mono Qtz 40.1 39.5 42.2 56.0 58.4 62.4 67.5 66.2 66.2
Poly Qtz 30.9 30.7 27.0 9.3 9.4 11.5 2.6 3.6 3.7
Lithics 26.0 26.5 23.6 16.6 16.9 13.4 6.3 6.5 6.3
Mica 3.1 3.3 7.1 18.1 15.4 12.0 23.5 23.7 23.9

52

WATERSHED 37
draining Coweeta Group bedrock

 

 

 

 

 

 

Coarse Medium Fine
Sample 37AC 37BC 37CC 37AM 378M 37CM 37AF 37BF 37CF
Total Pts 398 346 364 315 315 318 303 336 315
Mono Qtz 62 43 43 130 124 120 154 158 156
Poly Qtz 84 58 90 26 38 38 11 17 11
Lithics 197 177 167 76 79 80 34 37 36
Mica 19 29 15 56 41 57 79 77 65
Garnet 12 7 29 7 4 7 - 2 2
Heavies 6 10 4 3 10 15 17 27 28
Plag 16 21 15 14 16 12 4 17 13
Other 2 1 1 3 3 1 4 1 4
Modal Percent of Total
Mono Qtz 15.5 12.4 11.8 41.3 39.4 37.7 50.8 47.0 49.5
Poly Qtz 21.1 16.8 24.7 8.2 12.1 11.9 3.6 5.1 3.5
Lithics 49.4 51.0 45.9 24.1 25.1 25.2 11.2 11.0 11.4
Mica 5.2 9.4 4.7 19.4 14.5 19.3 28.4 26.6 24.2
Garnet 3.0 2.0 8.0 2.2 1.3 2.2 - .6 .6
Heavies 1.5 2.9 1.1 1.0 3.2 4.7 5.6 8.0 8.9
Plag 4.0 6.1 4.1 4.4 5.1 3.8 1.3 5.1 4.1
Other .5 .2 .3 1.0 1.0 .3 1.3 .3 1.3
Modal Percent of Mono gtz, Polyggtz, Lithics, and Mica
Recalculated to 100%
Total Pts 362 307 315 288 282 295 278 289 268
Mono Qtz 17.1 14.0 13.7 45.1 44.0 40.7 55.4 54.7 58.2
Poly Qtz 23.2 18.9 28.6 9.0 13.4 12.9 4.0 5.9 4.1
Lithics 54.4 57.7 53.0 26.4 28.0 27.1 12.2 12.8 13.4
Mica 5.2 9.4 4.7 19.4 14.5 19.3 28.4 26.6 24.2

APPENDIX B

Plots of grain type abundance versus
discharge, slope, and discharge/slope

APPENDIX B

Plots of grain type abundance versus
discharge, slope, and discharge/slope

Abbreviation used in Appendix B:

CW = sediments derived from the Coweeta Group source rock

TF = sediments derived from the Tallulah Falls Formation
source rock

MQTZ = % monocrystalline quartz

PQTZ = % polycrystalline quartz

MICA = % mica

LITH = % lithic fragment

= coarse fraction

medium fraction

fine fraction

Designates where two samples lie on or near the same

point.

Designates where three samples lie on or near the same

point.

N’IJSO

U
I

53

54

TF MQTZ
704+
-— F
—- F F
- F F
604+
- F
- F
- F F
50o+ F
- 2
- M
404+ 2 2
r M N
* 2
304+
* C
204+ C C
* C C 2
* C C
- :3
r C
104+
+ ————————— + ~~~~~~~~~ + ~~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ +
30.0 3540 40.0 45. 50.0 55.0

DISCHARGE

TF

55

MQTZ
70.+
.. F‘
.... F‘ I:
~ F F
60.+
.. I:
~ F
~ F F
30.+ F
- F 2
~ 2
~ M
40.+ 2 2
._ n M
" 2
30.+
~ C
20.+ C C
.. C C 2
.. C C
” 2
~ C
10.+
+ ————————— + ~~~~~~~~~~~~ + ~~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ +~~~
0480 0460 9640 9720 0800 9880

SLOF'E

56

TF MQTZ
70.+
_ F
r F F
“ F F
éO.+
“ F
- F
1 F F
UO.+ F
F 2
I 2
r M
40.+ 2 2
_ M M
r 2
30.+
* C
20.+ C C
- 2 C C
r C C
~ 2
r C
10.+
+ --------- + ~~~~~~~~~ + ~~~~~~~~~ + ----------- + ~~~~~~~~~ +
36.0 45.0 54.0 63.0 72.0 81.0

DISCHARGE/SLOPE

57

DISCHARGE

TF PQTZ
40.0+ 2 C
1 C
r C
r C
“ 2
32.0+
r C C
~ M 2 C
24.0+ M
1 M M C
1 M M
16.0+ M
r M
3 :2
8.0+ F F
1 2 F F
~ F F F 2
~ F
0.0+
+ ~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ + ********* + --------- +
30.0 35.0 40.0 45.0 0.0 55.0

58

TF PQTZ
40.0+ C 2
“ C
2 C
~ C
~ 2
32.0+
_ C C
~ 2 M C
24.0+ M
- M M C
_ M M
16.0+ M
r M
~ 2
8.0+ F F
- F F 2
~ F F F 2
- F
0.0+
+ ~~~~~~~~~ + ---------- + ------------ + ~~~~~~~~~~ + ~~~~~~~~~ +~~~
.480 .560 .640 .720 .800 .880

S L O F' E

59

TF PQTZ
40.0+ 2 C
1 C
1 C
“ C
1 2
32.0+
- C C
.1 M C 2
24.0+ M
1 M C M
1 M M
16.0+ H
r M
I 2
8.0+ F F
-- :2 F F
- F 2 F F
-- F
0.0+
+ ~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ + ————————— + ————————— +
36.0 45.0 54.0 63.0 72.0 81.0

DISCHARGE/SLOPE

60

TF LITH
48.0+
1 C
1 2
* C
40.0+ C C
r C
“ C
* 2 2
- M
32.0+
- M
r F
1 M 2
1 2
24.0+ M
r M
~ M 2
1 M 2 F
16.0+
r M
w 2 3
- F
8.0+
+ ~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~~ i ~~~~~~~~~~ +
30.0 35.0 40.0 45.0 50.0 50.0

DISCHARGE

61

TF LITH
- C
1 2
~ C
40.0+ C C
- C
r C
- :2 2
r M
32.0+
~ M
1. F.
- M :3
- :2
24.0+ M
1 M
: M 2
1 M 2 F
16.0+
~ M
1 2 3
- F
8.0+
+ ~~~~~~~~~ + ~~~~~~~~~~ + ~~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ +---
.480 .560 .640 .720 .800 .880

TF LITH

48.0+

no.

40.0+

32.0+

fa} {'3-

X

{03713

62

ix)

71 In)

DISCHARGE/SLOPE

C

f-J 3

3

IO

TF MICA

3 F.) :"J 1'1

001—}

OCII“*~*"~~O~—

63

F‘
F
M
M
F'
F F
2 F
M M
F c M
M 2
F
c
c
2
c:

DISCHARGE

64

SL OF'E

TF MICA
30.0+
.... I:
.. F
- M
24.0+ M
- F
- F F
~ 2 F
18.o+ M F M
— F c 2 M
~ M 2
— F
— M 2
12.0+ c 2
— C M
I 2
6.0+ c
— 8
~ 0
— c
0.0+
+ ————————— + ~~~~~~~~~ + ————————— + ~~~~~~~~~ + ~~~~~~~~~ +-~~
.480 .560 .640 .720 .800 .880

TF MIcn
30.0+
"" F
- F
- M
24.o+ H
-— F
- F F
- F 2
18.0+ F M M
- 2 M c F
- 2 M
- F
- 2 M
12.o+ 2 c:
1 M C
- 2
6.0+ c
—- c
-- C
- c
0.0+
+ --------- + ~~~~~~~~~ + ————————— + ~~~~~~~~~~ + ~~~~~~~~~ +
36.0

65

DISCHARGE/SLOPE

66

CH MQTZ
70.+

{-.J T!

r 3

60.+

I
T! f-J

33

I
{a} O

40.+

30.+ C

DISCHARGE

CH MQTZ
70.+

60.+

50.+

40.+

30.+

20.+

67

F'
2 2
3 F
M
M
M M F
M M F
F
M
M
M
M
M
C
2 M
C
C
C
C
C
C C
2
+ ~~~~~~~~~ + ~~~~~~~~~~ + --------- + ~~~~~~~~~ + ~~~~~~~~~ +
.50 .60 .70 .80 .90 1.00

SLOPE

CU MQTZ
70.+

no.
on-
.-

60.

+

40.+

30.+

68

F‘
2 2
3 F
M
M
F M M
F M M
F
M
M
M
M
M
c
M 2
c
c
c
c
c
r: C
2
+ ~~~~~~~~~ + ~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ +
60. 7o. 80. 90. 100. 110.

DISCHARGE/SLOPE

69

CU PQTZ
40.0+
C C
‘ C
32.0+
‘ 2
* C C
“ C
24.0+ C
- C C
- C
- C
16.0+
" M
“ 2
* H M M
* M 2 M
8.0+ H M
* F
- 2 2
- F 3 2
* F
0.0+
+ --------- + ********** + ---------- + ********** + ~~~~~~~~~ +
42.0 48.0 54.0 60.0 66.0 72.0

DISCHARGE

CU PQTZ
40.0+

70

c:
c
:3
C c
c:
c
c c
c:
C
M
:2
M M M
2 M M
M M
F
2 :2
:5 F :2
F
+ ~~~~~~~~~~ + ~~~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ + ~~~~~~~~~ +
.50 .60 .70 .80 .90 1.00

SLOPE

CU PQTZ

40.0+

71

c
c
2
C C
c
c
c c
c
c
M
2
M M M
M M 2
M M
F“
2 2
F 2 3
F"
+ ~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ +
60. 7o. 80. 90. 100. 110.

DISCHARGE/SLOPE

72

cu LITH
60.+
~ C
2 2
50.+
— c
.. 2
40.+ C
~ 2
30.+
2 2
~ 2
- c M
~ 2
2o.+ M
m 2
- 2 M
.. M F
~ 2 2
10.+ F
~ 3
_ 3
0.+
+ ~~~~~~~~~~ + ~~~~~~~~~ + ~~~~~~~~~~ + ----------- + ~~~~~~~~~ +
42.0 48.0 4.0 60.0 66.0 72.0

DISCHARGE

cw LITH
60.+

40.+

30.+

10.

i-i-l

0 IO

I h)

{A

73

c
2
c
2
c
2
2
M
2
M
2
M
F.“
2 2
F
3
------ +~~~—~—~»~+~~~-—~6~~+-—-—~—~~~+~--—~~~--+
.60 .70 .80 .90 1.00

SLOPE

aw LITH

(I!) O + +

40.+
30.+
2.0.:-

O++

{'3

ix} ‘1

IO 0

Z :’-J

74

id

32 f-J

DISCHARGE/SLOPE

{"3 IO

3: rd

{>3

cw MICA

30 -> 0 +

18.0+

12.0+

flrJ

{a}

UISCHARGE

1'.)

to I

cw MICA
30.0+

76

F
F
3 3 F
N
2 2
F M
M H
M M
H
M H C
M
C
C C
C 2
2
3
+ ********* + ********* + ********* + --------- + ---------- +
.50 .60 .70 .80 .90 1.00

SLOPE

CU MICA
30.0+

77

F‘
F
F 3 3
M
2 2
M F
M M
M M
M
M c M
M
c:
c c
2 c
2
3
+ ~~~~~~~~~ + --------- + ~~~~~~~~~ + ~~~~~~~~~ + ————————— +
60. 7o. 80. 90. 100. 110.

DISCHARGE/SLOPE

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79

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