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THE-“9'9

-' LIBRARY " "

Egflicbigan Stare
Unaw-

     

This is to certify that the

thesis entitled

CONICAL STRUCTURES IN THE MIDDLE PRECAMBRIAN
MICHIGAMME FORMATION

presented by
KATHRYN JEANNE MUSSER

has been accepted towards fulfillment
of the requirements for

M.S. demcm GEOLOGY

Major professor

 

 

Date 2-16-81

 

0-7 639

 

 

 

OVERDUE FINES:
25¢ per day per item
RETURNING LIBRARY MATERIALS:

Place in book return to remove
charge from circulation records

 

 

CONICAL STRUCTURES IN THE MIDDLE PRECAMBRIAN MICHIGAMME FORMATION

By

Kathryn Jeanne Musser

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Geology

1981

ABSTRACT
CONICAL STRUCTURES IN THE MIDDLE PRECAMBRIAN MICHIGAMME FORMATION

By

Kathryn Jeanne Musser

Small conical structures that were tentatively considered to be
algal stromatolites, a shallow water sedimentary feature, are found
in black slates and graywackes, interpreted as deep water turbidity
current deposits. The inconsistency of how an organosedimentary
structure which depends on light for its existence could form in the
non-illuminated depths of a marine basin was finally dismissed, be-
cause the structures showed a greater resemblance to cone-in-cone
structure, a post-depositional feature that does not require light
to form. Examination of core segments and thin sections proved that
the structures could neither be stromatolites in growth position,
nor stromatolites transported as elastic debris.

The methods used in this study involved petrographic analysis

of core segments and thin sections, staining, and microprobe analysis.

ACKNOWLEDGMENTS

The writer wishes to thank Dr. James W. Trow, Chairman of the
Committee, for his suggestion of and interest in this study, and for
his infinite patience and understanding.

Gratitude is extended to Dr. Robert L. Anstey and Dr. Chilton E.
Prouty, for their valuable criticisms and helpful suggestions.

In addition, thanks are due to Tom Taylor, who assumed responsi-
bility for the microprobe data; and to Jack Van Alstine, John Jaykka,

and John Jaakola, who helped start this project.

11.

LIST OF TABLES

Measurements of orientation, size, and apical angle
of conical structures.

Stratigraphic height of conical structures.

Percentages of CaCOB, MgCO3, and FeCO3 in conical
structures.

iii.

Page

11

17

18

11.

12.

13.

14.

15.

16.

17.

LIST OF FIGURES

Index map of the East Baraga, Clark Creek, and
Dead River Basins.

Stratigraphic column of the Marquette District.

Evolution of terminology in the Marquette Dis-
trict.

Alternating carbonate and organic laminae of
Conophyton.

Photograph of core segment 2774-4.
Photograph of core segment 2761-4.

Modified Bouma Sequence.

Profile of conical structure in 2039c-1 top.
Profile of cone-in-cone structure.

Transverse section of conical structure, from
2774-4 #1.

Transverse section of cone-in-cone structure.

The diagram depicts two layers of cone-in-cone
in a concretion.

Core segment 2761-4 exhibiting a possible off-
shoot from the primary layer to the right.

Offshoots from the primary cone-in-cone layer.

Photograph of 2861-4 M illustrating the contact
between the conical structures and the argillite.

Diagram showing cone-in-cone structure developed
in argillaceous matrix.

Conophxtons from the Dismal Lakes Group.

IV.

Page

25

30
3O
32
34
34

36

36

37

38

38

39

39

41

Figure Page

18. Laminae of the Conophyton from the Dismal Lakes Group. 42

V.

TABLE OF CONTENTS

LIST OF TABLES 111.
LIST OF FIGURES v.
INTRODUCTION
STATEMENT OF THE PROBLEM 1.
LOCATION 2.
GEOLOGY OF THE STUDY AREA 2.
TERMINOLOGY ' 4,

SAMPLE COLLECTION, PREPARATION, AND EXAMINATION

SAMPLE COLLECTION 8.
THIN SECTION PREPARATION 8.
THIN SECTION EXAMINATION 9.
STRATIGRAPHIC HEIGHT COMPUTATIONS 15.
IDENTIFICATION OF CARBONATE BY MECROPROBE AND STAIN 15.
ENVIRONMENT OF DEPOSITION OF THE UPPER SLATE MEMBER 19.

DESCRIPTION OF STRUCTURES

TURBIDITES 22.
STROMATOLTTES 23.
CONE-IN-CONE STRUCTURES 26.

IDENTIFICATION OF CONICAL STRUCTURES

IDENTIFICATION OF CARBONATE IN CONICAL STRUCTURES 28.
STROMATOLITES IN GROWTH POSITION 29.
STROMATOLITES AS CLASTIC DEBRIS 31.

vi.

ARE THESE CONE-IN-CONE STRUCTURES?
ORIGIN OF CONE-IN-CONE STRUCTURES
FORMATION OF CONE-IN-CONE STRUCTURES AND STYLOLITES
PARAGENESIS
CONCLUSION
SUMMARY AND CONCLUSION
RECOMMENDATIONS FOR FURTHER STUDY
BIBLIOGRAPHY
THIN SECTION DESCRIPTIONS

MICROPROBE DATA

vii.

31.

43.

45.

48.
48.
50.
57.

81.

INTRODUCTION

STATEMENT OF THE PROBLEM

In the Baraga Basin of Baraga County, Michigan, Mancuso, Lougheed,
and Shaw (1975) strongly suggest the presence of columnar branching al-
gal stromatolites in cherty carbonate iron-formation of the Marquette
Range Supergroup of Middle Precambrian age. Eastward along strike in
this basin and in other portions of northern Marquette County, the im-
mediately overlying Upper Slate Member of the Michigamme Formation con-
sists of gray to black graywacke, argillite, and slate, containing thin
layers of small conical laminate structures, tentatively considered to
be Conophyton-type stromatolites when view macroscopically in diamond-
drill cores (Trow, 1979). However, these graded-bedded clastics appear
to be Bouma-type turbidite sequences deposited in a reducing, deep-water
environment as suggested by sedimentary type and by the presence of pres-
ent-day abundant pyrite and graphite. Such a sedimentary setting tra-
ditionally is not considered to be favorable for the growth of stroma-
tolite-producing algae, which presumably could not grow at such light-
free depths. Several questions arise: 1) Are these small cones paleo-
biologically significant Conophyton-type stromatolites which grew‘ig
§i£2.at hitherto unrecognized depths in a relatively light-free reduc-
ing environment? 2) Are these layers of small cones elastic fragments
of stromatolites deposited as rip-up clasts by turbidites, shifted basin-
ward to deep water from shallow platform growth area, and hence are of
no paleobiological igngigg significance? 3) Are these small cones some-

1.

2.
thing else, such as cone-in-cone structures, as suggested by A. T.
Cross (1980, personal communication)?

4) What is the origin of these cone-bearing layers and their
laminations? 5) When were they formed? 6) Do they have any stratigra-
phic significance that could be useful in correlating strata of the
Michigamme Formation of the Marquette Range Supergroup, which is dated

between 1900 and 2000 Ma (Van Schmus, 1976).

LOCATION

Samples used in this study were taken from four of the six drill
cores obtained during the DOE--Bendix--Michigan Geological Survey
Upper Peninsula Precambrian Project (Fig. l), which are now stored at
the Michigan Department of Natural Resources #1 Regional Headquarters,
Marquette, Michigan. Sites selected for those four Precambrian Project
drill holes were section 5, T. 50 N., R. 28 W. for drill core 1; section
2, T. 48 N., R. 28 W. for drill core 4; section 16, T. 49 N., R.27 W.
for drill core 5; and section 4, T. 50 N., R. 28 W. for drill hole 7
in Marquette County, Michigan. Samples from drill hole 5 were not in-
cluded in this study after preliminary investigation revealed a lack
of possible algal structure. Of significance to this study are the 10-
cations of drill holes 1 and 7 in the East Baraga Basin, and the location

of drill hole 4 in the Dead River Basin.

GEOLOGY OF THE STUDY AREA

Both the Baraga Basin in northwestern Marquette County and the
Dead River Basin in north-central Marquette County are located north of
the Marquette Synclinorium. They are sedimentary basins containing
Middle Precambrian Baraga Group ”metasediments... of quartzite, cherty

iron-formation, graywacke, slate, and argillite" (p. 7, Burns), and

/

CREEK BASIN

OOH-5,

DEAD RIVER BASIN
I u ~‘Iu 'u ,'

r'

OOH—4

 

Figure 1. Index map of the East Baraga, Clark Creek, and Dead River
Basins (after Trow, 1979). This map shows the sites of diamond drill
holes 1, 3, 4, 5, and 7; and the inset shows the location of the map
in the Upper Peninsula of Michigan.

4.
slate, respectively (Seaman, 1910; Burns, 1975), which behaved indepen-
dently until Bijiki time when seas inundated the entire area (Trow,
1979). The sediments in each are believed to correlate with the Michi-
gamme Formation (Van Rise and Leith, 1911; Burns, 1975).

Drill core 1 penetrated glacial overburden and the Upper Slate
Member of the Michigamme Formation, while drill core 7 penetrated over-
burden, the Upper Slate Member, Bijiki Iron Formation Member, and Pre-
cambrian W granite. Drill core 4 was drilled through overburden, Pre-
cambrian Y diabase, Upper Slate and Bijiki Iron Formation Members of
the Michigamme Formation, Goodrich Quartzite, and Precambrian W tonal-
ite (Trow, 1979). The stratigraphic column of the Marquette District
is provided as a reference (Fig. 2).

The Bijiki and Upper and Lower Slate Members intercepted by drill-
ing contrast with the Michigamme Formation of the Marquette Synclinor-
ium, which contains the Clarksburg Volcanics Member and the Greenwood
Iron Formation Member in addition to these three members (Cannon and
Klasner, 1975). In contrast to the more varied lithology of the Mar-
quette Trough, (Boyum, 1975), macroscopic examination showed pertinent
core segments to be composed primarily of argillite and graywacke as-
signed to the chlorite zone of metamorphism (James, 1955).

One final item that deserves mention is the stratigraphic horizon
of the conical structures, which seems to be the lower part of the Up-

per Slate Member of the Michigamme Formation (Trow, 1979).

TERMINOLOGY
Because revisions of terminology by other researchers have led to
the use of "Michigamme Formation", "Upper Slate Member", "Precambrian

W, X, and Y", and "argillite" in this study, a brief discussion of that

 

 

 

 

 

 

 

 

 

 

>4
g s-
.E g diabase dikes and plugs
8 é’
3 S2
0...
Michigamme Formation
Upper Slate Member -- metagraywacke, schist,
and slate
Bijiki Iron Formation.Member -- cherty sili-
cate iron formation
m a. Lower Slate Member -- black slate, quartzite,
g0 g argillite
8:5 Clarksburg Volcanics Member -- mafic to inter-
” mediate pyroclastics
Greenwood Iron Formation Member -- magnetic
silicate iron formation
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g Goodrich Quartzite -- quartzite, conglomerates,
>< $3 argillite
a a UNCONFORMITY
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a. o
3 ;§ Ajibik Quartzite -- quartzite, local conglomerate
g beds
3 UNCONFORMITY
£3 Wewe Slate -- gray sericitic and quartz-sericite
slate
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'3 E and cherty dolomite
0
or:
5 Mesnard Quartzite -- vitreous white quartzite
Enchantment Lake Formation -- Reany Creek Formation
metasediments
UNCONFORMITY
:3
c
3
,§ gneiss and schist
8
2’.
a.

 

 

 

 

Figure 2. Stratigraphic column of the Marquette District. (Cannon
and Gair, 1970; Boyum, 1975; Cannon and Klasner, 1975).

6.

history is in order. James (1958) subdivided the Precambrian rocks of
northern Michigan into Lower Precambrian rocks corresponding to the
Archeanétype, and Middle and Upper Precambrian rocks corresponding to
the Algonkian-type of the older literature (Leith, Lund, and Leith,
1935). He also revised ”Huronian” to "Animikie Series", because of
a lack of correlation of the Huronian type section with other districts
in the Lake Superior region (Figure 3). Cannon and Gair (1970) replaced
”Animikie Series" with "Marquette Range Supergroup", which encompasses
James's Chocolay, MenOminee, Baraga, and Paint River Groups, the last
of which is now recognized by some researchers (Cambray, 1978; Trow,
personal communication) as equivalent to the Menominee and Baraga
Groups. As a replacement of "Michigamme Slate", which they considered
to be a misnomer, Cannon and Klasner (1975) resurrected Van Hise's
terminology (1897) "Michigamme Formation" to include an Upper Slate
Member, the Bijiki Iron Formation Member, a Lower Slate Member, the
Clarksburg Volcanics Member, and the Greenwood Iron Formation Member.
Cannon (1974) combined the Marquette Range Supergroup with Jamesls
interim scheme (1972), resulting in the classification of the Michi-
gamme Formation and the Baraga Group as Precambrian X rock units.

As a final point, the term "argillite" is restricted to a low
rank metamorphosed shale without slaty cleavage, while slate refers
to a metamorphosed shale possessing slaty cleavage (Flawn, 1953;

Meorehouse, 1959).

SAMPLE COLLECTION, PREPARATION, AND EXAMINATION

SAMPLE COLLECTION

Drill cores obtained from DOE--bendix--Michigan Geological Survey
Precambrian Project which presently are stored at the Department of
Natural Resources Headquarters in Marquette, Michigan, were used for
this study. Appropriate samples were selected by consulting the En-
gineering Reports which denoted footages of algal-bearing core. Drill
core extending fifteen feet both above and below each algal-appearing
section was sampled to determine the lithology in which the structures
were embedded. With the aid of a 13 W 4000 Rock Trimmer, the cores
were split and half was left in the storage boxes, at the request of
Jack van Alstine.

The samples and thin sections are identified by a five-digit
hyphenated number. The first four digits refer to the depth cored, and
the fifth digit refers to drill core 1, 4, 5, or 7. Letters refer to
multiple samples from a single foot of core: 276lA-4 is stratigraphically
above 27613-4, which is above 2761C-4, and so on; all are from a depth
of 2761 feet in drill core 4. "Top" and "bottom" also refer to relative
positions within a designated footage. The letters M, N, O, P, W, X,
Y, Z, K, and L indicate the thin section is a replacement of one that
was damaged. A sixth number, such as in 2769-4 #4 indicates the thin
sections is one of four taken from that depth. Thin sections are often

more precisely identified than core segments.

THIN SECTION PREPARATION
Sixty-seven thin sections were originally prepared from the samples

collected, but more slides were necessary because of damage, or incom-

8.

9.
plete coverage of a structure. Thin sections were to have been made
parallel or perpendicular to bedding planes, but they would have repre-
sented too small a surface area. Instead, orientations were chosen to
record as large a sample as possible on the slide. Bedding, therefore,
shows only an apparent and not a true thickness.

The thin sections were chosen to illustrate possible algal struc-
tures, the contacts between the structures and the adjacent lithology,
and the adjacent lithology, to determine if they were perhaps clasts of
the Bouma sequence. At depths of 2039 feet in drill core 1, and 2769,
2774, and 2861 feet in drill core 4, pieces of drill core were missing
at the DNR; consequently only the lower contact of the upper layer of
structures and the upper contact of the lower layer of core segment
2774-4 are preserved. There are gaps in core segments 2039-1, 2769-4,
and 2861-4, because these footages were previously sampled for DNR
thin sections; and not all the structure can be said to have been docu-
mented with certainty. A sample taken from 2856 feet in drill core 4
made reconstruction of the core somewhat uncertain, but the most logi-
cal sequence downward stratigraphically is 2856-4 K, 2856-4 L, 2856-4 M,
and 2856-4 N. At 2774-4, the prOper sequence proceeding downward is
286l-M, 2861-N0, 2861-4 0, and 2861-4 P; at 2907 feet in drill core 4
the sequence is 2907-4 X, 2907A-4, and 29073-4, proceeding downward.

The aim of documenting the top and bottom of the algal structures
was not reached with segment 2861-4, because what was preserved in the
core was a side of the structure. It is assumed that the entirety of

the structure was represented in all other segments.

THIN SECTION EXAMINATION

Thin sections were examined petrographically at the following mag-

10.
nifications: 40, 100, 200, and 400, and their descriptions are included
in Appendix A.

Samples once thought to contain structures, from 1992 feet in drill
core 1, and from 682-683 feet in drill core 5, are believed to lack
conical structures and were not used for further study.

Point counts were made of all slides, except those of primarily
carbonate lithology. Rock fragments were counted as such, and not as
constituent minerals. Because of the fine-grained nature of the sam-
ples, it was often difficult to determine what constituted a rock frag-
ment; and in such cases individual minerals were counted. Different
point totals resulted from the samples' unequal surface areas. When
the cross hairs fell on grain boundaries, the point was assigned to one
of the two lithologies, and was not discounted.

Concerning 2867-4, the percentage of pyrite depended on the posi-
tion of the slide in the point counter, but actually it appears to be
bedded pyrite within the argillite, and a larger sample is needed for
a more accurate point count.

Measurements of the apparent angle between the axis of symmetry
of the conical structure and the bedding planes in the argillite were
taken from thin sections (Table 1). The reading may appear greater
than the actual angle, because of the orientation of the axes and the
bedding planes in thin section. The purpose of the measurements is
to help determine if the structures are in growth position (approxi-
mately 90°) or if they were brought in from another source (all orien-
tations ranging from 0°, where one axis is parallel to bedding, to 90°,

where structures are both right-side up and upside down).

11.

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14.

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15.
Apical angles were also determined from thin section by rotation of the

stage.

STRATIGRAPHIC HEIGHT COMPUTATIONS

Stratigraphic height or thickness above the top of the Bijiki Iron
Formation Member was computed by multiplying the cosine of the angle
between the bedding and a plane perpendicular to the core axis, by the
difference in depths between the top of the Bijiki Iron Formation Mem-
ber and the particular occurrence of conical structures.

The angles between the core axis and bedding, obtained by measure-
ing core segments with a protractor, yielded angles of 34° for segment
2761-4, 320 for 2769-4, 17° for 2861-4, 31° for 2039-1, and 36° for
483-7. Obliterated bedding prevented such measurements in 2774-4,
2856-4, and 2907-4, In the first two cases, the values for the angles
in core segments 2769-4 and 2861-4 were used (320 and 17°, respectively)
because of proximity. 170 was also used for 2907-4, because bedding was
assumed to have a constant dip to the base of the Upper Slate Member.

In Table 2, 2507 feet is a theoretical depth computed from the
assumption that Precambrian W rocks would be intercepted at 2599 ft.

(Trow, 1979).

IDENTIFICATION OF CARBONATE BY MICROPROBE AND STAIN

Thin sections 2039-1, 2761C-4, 2769-4 #1, 2774-4 Y, 2856-4B (bor-
rowed from the DNR), 28613-4 (transverse section, not previously list-
ed), 2907A-4, and 483-7 were analyzed for magnesium, manganese, calcium,
zinc, and iron by Tom‘Taylor with an ARL electron microprobe using an
accelerating potential of 10 kv. and 0.05 milliamperes beam current.

Percentages of CaC03, MgCO3, and FeC03 that he computed are given in

16.

Table 2. Stratigraphic height of conical structures.

DDH-l DDH-4

Stratigraphic height of 401 _ 170
conical structures above

the top of the Bijiki 167

Iron Formation Member,

in feet 162

105

100

56

Depth to the top of the 2507 2966

Bijiki Iron Formation
Member, in feet

DDH-7

70

569

17.
Table 3.
All samples containing the structures were tested in at least one

thin section for calcite with alizarin red stain.

18.

Table 3. Percentages of CaC03, MgC03, and FeCO3 in conical structures.

 

 

 

 

 

 

 

 

 

 

SAMPLE % Gaco3 % FeCO3 z F6003
2039-1 52 4o 8
49 42 9
47 34 19
43 38 19
2761-4 53 41 6
52 41 7
2769-4 47 38 15
96 2 2
45 10 10
2774-4 57 37 6
55 38 7
53 35 12
2856-4 56 26 18
55 27 18
2861-4 45 31 24
46 4o 14
2907-4 50 37 13
483-7 49 49 2
57 41 2
51 41 8

 

 

 

ENVIRONMENT OF DEPOSITION OF THE UPPER SLATE MEMBER

Environmental conditions suitable for the deposition of black muds
and their preservation as black shales have been discussed by numerous
researchers (Strfim, 1939; Twenhofel, 1939; James, 1951; Krumbein and
Garrels, 1952; Pettijohn, 1957). The sequence involves organic matter
preserved in the bottom of a sedimentary basin as a result of toxic,
oxygen-depleted water. This reducing environment, illustrated by the
Black Sea and Norwegian fjords, is brought about by restricted circulae’
tion of bottom water and bacteria that reduce sulfate to sulfide and
generate HQS in the process. Otherwise known as an euxinic environment
and characterized by a low oxidation-reduction potential or Eh, (Petti-
john, 1957), it is believed to be the environment of deposition of black
graphitic slate (low-grade metamorphic counterpart) of the Michigamme
Formation in Iron, Baraga, and Marquette Counties (James, 1951; Petti-
john, 1957; Olmsted, 1962; Burns, 1975).

The alternation of great thicknesses of black shales, argillites,
and slates, with graywackes (Tyler and Twenhofel, 1952) has led to the
interpretation of the Michigamme Formation's Upper Slate Member as a
product of turbidity currents (Cannon and Klasner, 1977; Trow, 1979; La-
rue and $1083, 1980). Samples from a depth of 2761 feet from drill core
4 contain such features as rock and argillite fragments, which may be
rip-up clasts, and reinforce this interpretation (Stanley, 1963). Thin
sections are too small to permit observation of grading, elsewhere
suggested as evidence for the turbidity current origin of the Michigamme
Formation (Base, 1957; Cannon and Klasner, 1977). Trow's suggestion
(1979), that the clastic source for turbidites during deposition of the

Upper Slate Member was from the south because there is a northward-

19.

20.
fining of grain sizes, is consistent with Alwin's conclusion (1979)
that paleocurrent indicators of the Tyler Formation in Wisconsin and
Michigan, of which the upper lithology is correlative with the Michi-
gamme Formation (Leith, Lund, and Leith, 1935; Sims, 1976), imply
movement of turbidity currents "toward the west-northwest....from a
single source area for all of Tyler time” (p. 225).

The Baraga Group has been attributed to primarily geosynclinal
(James, 1954; Hase, 1957, Pettijohn, 1957) and more specifically,
eugeosynclinal sedimentation (Cannon, 1973). Proceeding to a more
inclusive view, Pettijohn (1957) integrated the depositional environ-
ments of black shales and geosynclinal graywacke into one model:

The elastic facies recognized are an expression of the tec-
tonic stability or instability of the site of deposition....
Rapid subsidence carries the site below the wave base. If
ample elastic materials are available they will consist of
muds, settled from above, and immature sands introduced by
turbidity underflows. The result is a rhythmically inter-
layered and even-bedded accumulation of graywackes and
shales (p. 631).
More recently, Van Schmus (1976), Cambray (1978), and Larue and 81055
(1980) have interpreted the data in the light of plate tectonic theory,
where sedimentary basins were simultaneously filling and subsiding
into passive continental crust, later to be structurally deformed into
the Marquette, Felch, and Menominee Synclines by a continental colli-
sion. This theory may be extended upon further investigation to the
East Baraga, Dead River, and Clark Creek Basins.

If the conical structures found in the Michigamme Formation are

stromatolites, then one of two issues is raised:

1) If the structures are in growth position, how did photosynthe-

tic algae flourish in a toxic, reducing environment to form stromatolites?

21.
2) If the structures are not in growth position, were they trans-

ported into the basin as rip-up clasts by turbidity currents?

DESCRIPTION OF STRUCTURES
Structures anticipated in the Upper Slate Member are turbidites
Conophyton, which may be confused.with cone-in-cone structure. Descrip-

tions are provided to facilitate identification in thin section.

TURBIDITES

For this study the concept of turbidity current deposits as de-

fined by walker and Mutti (1978) will be used:

Collectiyely, a group of turbidites in outcrop will be very
regularly bedded, and consist of alternating coarse and fine
beds.... The coarse layers are normally sandstones....

The fine layers are shales.... Individually, each coarse
layer has a sharp or erosive base with an assemblage of sole
marks.... Internally the sandstone is commonly graded....
(p. 120).

Several salient points indicate why the Bouma Sequence is in fact
considered a turbidity current deposit:

1) The Bouma sequence contains graded bedding, which has been
argued (Kuenen and Migliorini, 1950) and experimentally demonstrated
(Kuenen and Menard, 1952; Kuenen, 1953; and Middleton, 1967) to be a
product of turbidity currents.

2) Both "convolute ripple lamination and convolute lamination"
are included within the current ripple interval of the Bouma Sequence
(Bouma, 1962). Dzulynski and walton (1965) produced convolute lamin-
ations with small-scale turbidity currents; and from.observations of a
fluvial environment, Harms and Fahnestock (1965) theorized current
ripple lamination to result from the decreasing flow regime of a tur-
bidity current.

3) Sole marks such as flute casts and tool marks, that are now
included in a modified version of the Bouma Sequence (Stanley, 1963),

were produced experimentally by turbidity currents in glass tanks

22.

23.
(Dzulynski and Walton, 1965).

4) The actual sequence of intervals in the Bouma Sequence
(Middleton and Hampton, 1973) could result from bedforms produced by
a waning turbidity current (p. 109, Harms and Fahnestock, 1965).

Stanley (1963) modified the original Bouma Sequence to include
rip-up clasts that "represent non-consolidated muds....ripped off
the floor of the basin and transported and redeposited downslope by
the passing current" (p.787). Bouma (1962) also described sequences

where the bases and upper layers were absent.

STROMATOLITES

Walter (1972) describes stromatolites as "layered organosedimen-
tary structures", formed when microbialcommunities trap and bind
sediment in order to survive (Golubic, 1976; Awramik, Margulis, and
Barghoorn, 1976). Once preserved in the sediments, these algal mats
consist of layers of the organic remains of algae and bacteria (Monty,
1976) alternating with layers of detrital and chemically precipitated
carbonate. CyanOphytes or blue-green algae, eucaryotic algae, photo-
synthetic bacteria, and various heterotrophic bacteria (Golubic, 1976)
are present-day stromatolite-building organisms, which may include the
microboring alga Plectonema terebrans (Smith, 1951; Drouet, 1968),
which has been collected from depths of 370 meters (Lukas, 1978).

Stromatolites are currently forming in subtidal and intertidal
environments (Gebelein, 1976; Playford and Cockbain, 1976), freshwater
marshes (Eggleston and Dean, 1976), hot springs (welter, 1976), and
sabkhas (Kinsman and Park, 1976). Furthermore, the fossil record docu-
ments shallow water forms (Playford et. al., 1976; Haslett, 1976;

Horodyski, 1976). Hoffman (1976), however, has argued on the basis of

24.
stratigraphic analysis for the existence of deep-water forms, report-
ing that Conophyton-like columns...grew in foreshelf basins of water
tens or even humdreds of meters deep" (p. 611).

Hoffman's findings are controversial when data regarding the low-
er limit of light necessary for the growth of algae and bacteria are
considered. Brock (1976) reported 2100 - 2800 lux as the minimum for
blue-green algae and eucaryotic algae to flourish, but Sverdrup's cal-
culations (1942) show that light diminishes to 2500 lux in the clear-
est ocean water (p. 776) at 100 meters (Brock, 1976). The difficulty
of how algae survive at depths below 100 meters, or the equivalent in
normal ocean.water which is 50 meters, when there is not enough light
for photosynthesis is not explained.

The classification of stromatolites is not only confused because
of uncertainty of the "nature of the material classified” (p. 33,
Krylov), but usage of the Linnean system of nomenclature is also de-
bated (Logan et. al., 1964), because entities that are not entirely
organic are being classified with a system developed for biological
forms. Nevertheless, the term "conOphyton" is understood to mean
"columnar and pseudocolumnar stromatolites characterized by conical
laminations....with a distinctive axial zone" (p. 523, Donaldson; p.
34, Krylov). Conophyton in the generic sense used by Maslov is ital-
icized and capitalized (Cloud and Semikhatov, 1969), and refers to a
group ("genus") subdivided into forms ("species") on the basis of
differences in the axial zone. This paper uses the term in the more
general sense, unless specifically indicated.

Figure 4 shows alternating carbcnwme and organic laminae of

Conophyton.

25.

 

Figure 4. Alternating carbonate and organic laminae of Conophyton
(after Walter, 1977).

26.
CONE-IN-CONE STRUCTURES

Cone-in-cone structures, a sedimentary feature composed of layers
of circular concentric cones separated by thin films of intercone clay,
are presumably due to pressure-solution (Tarr, 1932; Pettijohn, 1957),
although a few questions regarding their origin still remain. They
have been observed in radial arrangements with apices pointing inward
(Harker, 1892; Garwood, 1898), in double-layered lenses where apices
point toward each other, and at the ends of lenses pointin in all di-
rections. values for apical angles range between 15° and 100°, while
height normally varies from 1 to 200 millimeters (Tarr, 1932).

Cone-in-cone structures have been reported in coal beds, under-
clays, shales, slates, and limestones (Bartram, 1941; Cole, 1892;
Garwood, 1892; Gresley, 1892). They have been reported with fossil
fish, bivalves, and trilobites (Newberry, 1885; Gresley, 1887; Brown,
1954), but are primarily associated with concretions (Hall, 1843;
Gresley, 1894), and concretions are found in the Michigamme Formation
(James, 1955; James, Clark, Lamey, and Pettijohn, 1961; James, Dutton,
Pettijohn and Wier, 1968). Composition ranges from calcium.carbonate,
magnesium limestone, and siderite, to gypsum and coal (Cole, 1893;
Grimsley, 1903-04; Tarr, 1932; Hendricks, 1937; Bartrum, 1941). Occur-
ences range from the Cambrian (Utah) to the Tertiary (Tarr, 1932).

A comparison of Conophyton and cone-in-cone structure reveals they
are composed primarily of carbonate, and due to the continuity of layers
of adjacent columns, apices point both up and down (Cloud and Semikhatov,
1969; Hill, 1963). They differ in their associations: cone-in-cone ...
structures are found associated with concretions, and stromatolites are

found associated with other stromatolites or bioherms (Krylov, 1976).

27.
Cone-in-cone structures are frequently found in double-layered lenses,
with apices pointing toward the opposite layer, while columnar 9229-
phyggg frequently grade into other stromatolitic forms (Donaldson, 1976,
Hoffman, 1976; and Serebryakov, 1976).. Also, epigenetic (Tarr, 1932)
cone-in-cone structures contain layers exhibiting transverse ribs
(Dawson, 1868; Gresley, 1894) presumably due to pressure - solution
(Tarr, 1932), whereas the laminae of Conophyton, a morphologically-
related structure that forms in place, are merely thicker in the axial

zone (Walter, 1976).

IDENTIFICATION OF CONICAL STRUCTURES

IDENTIFICATION OF CARBONATE IN CONICAL STRUCTURES

Microprobe analysis revealed a close relation of 2039-1 to the
dolomite standard (Appendix B) plus a high iron content, suggesting
ferroan dolomite. Staining thin sections 2039-l bottom, 2039-1 top,
2039-1, and 2039a-1 with alizarin red dye revealed no calcite.

Staining thin sections 276lA-4, 27618-4, 276lC-4, 276lD-4, and
276lE-4 proved the absence of calcite. Microprobe analysis of 2761C-4
showed high iron content with small amounts (much less than 1%) of
zinc and manganese, and values of calcium and magnesium similar to the
dolomite standard, indicating the mineral is probably ferroan d01omite.

2769-4 #2, 2769-4 #3, and 2769-4-#4 were stained and revealed the
presence of calcite. 2769-4 #1 was subjected to microprobe analysis
and values were obtained similar to those of the calcite standard,
confirming the results of the stain test. A small amount of iron was
found.

2774-4 #1, 2774B-4, and 2774-4 #2 revealed the presence of calcite
after they were stained with alizarin red dye. Results of microprobe
analysis of 2774-4B were mixed: values for calcium‘were low but were
very high for magnesium and high for iron compared to the calcite stan-
dard. This means that it could be considered dolomite with a low con-
tent of magnesium and high amounts of calcium. Much less than 1% zinc
and manganese are present,

2856-4 revealed no calcite after being stained with alizarin red
dye. 2856-4 was analyzed by microprobe, revealing values comparable
for dolomite, except the iron content is very high and the magnesium

content very low. Perhaps this is ferroan dolomite.

28.

29.

Alizarin red did not reveal calcite in slides 2861B-4 and 286lC-4.
Microprobe results for 2861B-4 showed values for cabcium and magnesium
comparable to dolomite, but values for iron were much in excess of
those of the dolomite standard. This suggests very iron-rich dolomite.

2907A-4 and 2907-4 Y were stained for calcite with alizarin red,.
but the test proved negative. Values for calcium and magnesium in
2907A-4 are low, but high for iron in comparison with the dolomite
standard, so the sample may be closer to iron-rich dolomite than to
any other carbonate.

483-7 was stained with alizarin red but revealed no calcite.
Micr0probe results of 483-7 showed values comparable to calcium and
magneaium of the dolomite standard, but values for iron were high.

This implies the presence of iron-rich dolomite.

STROMATOLITES IN GROWTH POSITION

Do the samples contain stromatolites in growth position? Core
segments from drill core 4 at depths of 2761 and 2774 feet each pre-
serve two sets of conical structures with apices pointing toward each
other. Consideration of growing conical stromatolites in Yellowstone
National Park (Walter, Bauld, and Brock, 1976) implies that the bases
of Conophyton occur on the stratigraphically lower side. This is in
contrast to the samples, where the bases occur on the lower side of the
lower set of structures, and on the upper side of the upper set. The
asymmetric nature of grain sizes in the intervening clastics precludes
the possibility of isoclinal folding, so the structures cannot be a
single layer of stromatolites doubled back on itself after the stromat-
olites had grown with their apices pointing in one direction. The forms

are not stromatolites in growth position.(Figures 5 and 6)-

Figure 3. Evolution of terminology in the Marquette District.
The sixth and seventh columns show stratigraphic sections of
the Minnesota Gunflint and Mesabi Ranges.

 

Mesabi Range

 

Horey (1972)

 

 

 

 

 

 

 

 

 

Htary and Upper Sedimentary and
J3 rocks Precambrian Keweenawan igneous rocks
rmation Virginia Formation
Middle Animikie
Precambrian Group
t Iron Formation Biwabik Iron Formation
1 Quartzite Pokegama Quartzite
DNFORHITY UNCOHFORHITY
)NFORMITY UNCONFORHITY
Lower
and metamorphic rocks Precambrian

 

 

igneous and metamorphic rocks

 

 

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Figure 5. Photograph of core segment 2774-4. The diameter of the
segment is 1.9 inches.

 

Figure 6. Photograph of core segment 2761-4. The arrow is approxi-
mately 1.2 inches.

31.

STROMATOLITES AS CLASTIC DEBRIS

Do the samples contain stromatolitic elastic debris transported
from growth positions? Structures in samples from drill core 4 at
depths of 2761, 2774, 2856, 2861, and 2907 feet, from drill core 1 at
2039 feet, and from drill core 7 at 483 feet form an abrupt contact
with argillite, but scattered debris is not present in the argillite.
Deformation and secondary mineralization have obliterated much sedi-
mentary structure at a depth of 2856 feet in drill core 4, but an
abrupt contact between argillite and conical structures is preserved.
Structures from core segments 2761-4 and 2774-4 grade through argillite
and graywacke to structures at the Opposite ends.. Proving the presence
of stromatolitic rip-up clasts in these two segments requires that
pieces of stromatolites occur in all orientations,.similar to those in
Figure 7, as part of the lowermost interval of the Bouma Sequence
(Bouma, 1962; Stanley, 1963). They are not, therefore, randomly orie
ented.

Macroscopic examination shows that segments 2761-4 and 2774-4 do
not contain clasts of conical stromatolites (Fig. 5 and 6).

The absence of rip-up clasts and the current ripple and convolute
lamination interval suggests that the sedimentary sequence observed
in these two core segments does not match with the Bouma Sequence, and
that the structures are not elastic debris transported from growth po-

sitions by turbidity currents.

ARE THESE CONEelN-COHE STRUCTURES?
Conical structures are composed in part of black graphitic or car-
bonaceous opaque layers arranged in short (several millimeters in height)

conical stacks (2039c-1 top), which have both smooth and serrated appear-

STRUCTURES

ORGANIC TRACKS

(HORIZONTAL CASTSI

RIP-UP CLASTS

SAND-FILLED BURROW

32.

VERTICAL SEQUENCE

SHALE AND ARGILLITE
"PELAGIC" HORIZON

HORIZONTA L LAMINATION

 

CURRENT RIPPLE AND
CONVOLUTE LAMINATION

 

HORIZONTAL LAMINATION

   

 

GRADED BEDDING

scoua FILLN o

(GRAVELS RARELY > IO MM)

SOLE MARKINGS (CASTSI

Figure 7. Modified Bouma

 
 

 

Sequence (after Stanley, 1963).

33.
ances (Fig. 8). Layers of stacks are superpositioned on other layers
as in 2774-4 #2, 27610-4, and 2907-4 X, but their axes are not neces-
sarily aligned from layer to layer. Discontinuities in or the absence
of graphitic layers are partly due to replacement of graphite or car-
bonaceous matter by quartz and chlorite (2856-4). Actual widths of '
layers vary between 0.01 and 0.25 mm., and apical angles range from
10° to 63°, while structures as a whole at their bases range in size
from 0.5 - 6 mm., and from 0.2 - 11 mm. in height.

Opaque layers in cone-in-cone structure (Fig. 9) have been de-
scribed as muddy, clayey material, and as clay consisting of illite,
chlorite, and a mixed layer mineral; and have been shown to display
both smooth and corrugated surfaces (Gresley, 1887; Gresley, 1894;
Cole, 1892; Tarr, 1932; Gilman and Metzger, 1967). The layers are
frequently superpositioned, but stacks of conical layers have also
been reported (Dawson, 1868; Gresley, 1887; Cole, 1892). Cone-in-cone
structures range in height from less than 1 mm. to 20 cm., with apical
angles commonly varying between 300 and 60° (Tarr, 1932).

The non-Opaque portions of the conical structures are composed
primarily of anhedral grains of carbonate. Calcite was found at depths
of 2769 and 2774 feet in drill core 4, and ferroan dolomite was found
in all other samples. Quartz exhibiting replacement texture is found
along contacts between conical structures and argillite in drill core
4 at depths of 2761, 2769, and 2774 feet, while chlorite is found
along contacts at 2856 and 2861 feet in the same drill core. Quartz
frequently replaces portions of carbonate in the structures (2761A-4,
2774-4 #1, 2856-4 #1, 2861-4 M, 2907-4 X, 2039a-1, and 483-7).

Although gypsum (Grimsley, 1903-04) and coal (Young, 1886;

serrated graph-
itic matrix

carbonate

. .
. :-

‘r' I
\

, .". _..\“'1‘- .‘Le‘: ‘. ‘
3:3 I '1; re: .

 

1;. '
y“;

Figure 8. Profile of conical structure in 2039c-1 top.

annular depressions

 

clayey matrix

calcite

 

Figure 9. Profile of cone-in-cone structure (after Cole, 1892).
XS.

35.
Bartrum, 1941) cone-in-cone structures have been reported, the pre-
vailing composition is calcite (Tarr, 1932), in some cases with traces
Of iron carbonate (Cole, 1892). Outer surfaces show annular grooves,
the nature of which is made distinct by thin films of Opaque matrix
adhering between crystalline surfaces of adjacent cones (Cole, 1892;
Tarr, 1932).

Transverse sections of conical structures and cone-in-cone struc-
tures (Figs. 10 and 11) are inserted to display the similarity in form
from another view.

Other comparisons to be made are Optical continuity, dispensation
of structures in double layers, contact, and surrounding strata. Sweep-
ing extinction under crossed nicols of carbonate is Observed in some
conical structures (2039-l DNR large, 2039-1 DNR small, 2774a-4), and
is reported in some cone-in-cone structures (Cole, 1892; Gilman and
Metzger, 1967). Core segments from depths Of 2861 and 2774 feet from
drill core 4 display two sets Of conical structures with apices point-
ing toward each other, separated by argillite and graywacke (Figs. 5
and 6). Cone-in-cone structures have been associated with concretions
(Tarr, 1932; Gilman and Metzger, 1967) with apices pointing toward
each other, the area between the layers being filled by argillite or
siltstone (Fig. 12). A core segment from drill core 4 from 2761 feet
where part of the structure appears bifurcated and infilled by argillite
invites comparison with "tongues or Offshoots" (Gresley, 1894) of a
layer of cone-in-cone structure (Figs. 13 and 14). The contact between
argillite and conical structure observed in samples 2039a-1, 276lA-4,
2769-4 #1, 2856-4 M, and 2861-4 M (Fig. 15) is similar to the contact

between some cone-in-cone structure embedded in argillaceous matrix

36.

graphitic matrix carbonate

 

Figure 10. Transverse section of conical structure, from 2774-4 #1.

clayey matrix

calcite

 

Figure 11. Transverse section of cone-in-cone structure (after Cole,
1892). X 12.

37.

    
    

 
   

 
   

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“MY
W“) \t) “l at

-- 14’0“!“ ‘n

   

  

    
   
     
       

   

(ll'lfil'fl’ll'l :2

T: 2'. '3?“ \‘g I“ \\‘
i a...» 3‘ I‘ o [I‘I'I \‘j’I'I‘ ".nfi‘“ ‘\~\\ \
11%” 'f/b’j/ I50 ~35 Ir‘

Mil/7‘ I III MAI. q'\\‘\'\\\ \\\\\\\\N“

Figure 12. The diagram depicts two layers of cone-in-cone in a

concretion. The apices point in the direction of the opposite layer
(after Gilman and Metzger, 1967).

  
       

        

   

38.

 

Figure 13. Core segment 2761-4 exhibiting a possible offshoot from
the primary layer to the right. Core diameter is 1.9 inches.

 

Figure 14. Offshoots from the primary cone-in-cone layer (after
Gresley, 1894). 1/8.

 

conical structure contact
P—4
argillite 0.1 mm.

Figure 15. Photograph Of 2861-4 M illustrating the contact between
the conical structures and the argillite.

cone-in-cone structure
contact

shale matrix

 

Figure 16. Diagram showing cone-in-cone structure developed in ar-
gillaceous matrix (after Cole, 1892). X 18.

40.
(Cole, 1892), which is abrupt, well-defined, and uneven due to the mul-
tiplicity of levels of the various bases (Fig. 16).

Cone-in-cone structures are found primarily in shales and marls
(Tarr, 1932) and all occurrences of the conical structures are present
in argillite, the metamorphic equivalent of shale. Slide 27610-4 re-
veals apices of conical structure pointing in the direction of the ad-
jacent graywacke, as cone-in -cone structures pointed to a medial silt-
stone or sandstone layer in some concretions (Gresley, 1894; Gilman and
Metzger, 1967).

Conical structures bear a superficial resemblance to Conophytons
in gross morphology (Fig. 17), yet comparisons concerning laminae are
hard to draw because of diagenetic effects (Fig. 18; Donaldson, 1976).
The similarity ends, however, because bases of Conophyton occur only

on the lower surface; and Conophytons which are postulated to have a

 

subtidal origin because of associations with such sedimentary features
as oolites, intraformational conglomerates, cross bedding and ripple
marks, grade into other stromatolitic forms (Donaldson, 1976). A
consideration of form, composition, and associations with other lith-
ologic types and sedimentary features leads to the belief that there
is a greater resemblance between conical structures of the Michigamme

Formation and cone-in-cone structures.

41.

 

Figure 17. Conophytons from the Dismal Lakes Group. The hammer in
the lower center provides a scale (after Donaldson, 1976).

42.

fix. 9?.
.. . a ., 1
. . .nfl‘. ..\ U C. .t . I

.v.

, .. . .. w 4...-..
E pt . A
. . , ... .. l . . {to
. m t . t ... . uxévra.:$ t .
s . . . a; .
. . .. .. x .. .H. .
. . I u .. . 1'1. 1 . ...
, .. _ I . ... _ w... 1.....1 37,;
. , .. . I . we; . . . . .......I 2.6.5.4.. .. .. I . ....
.no~ ..I I . I I I .. , . i, .J . , . 4 ,. ... t
. ..— .In - ,.... .

 

.V‘ «.I. ..

. . . , k . w. I I. .I. v. . 4 us I. . .
, . . O a 1 I .. . . .. ,. . . ., .. . . .
Jflffié. K. . . , . . . I: I

Laminae of the Conophyton from the Dismal Lakes Group

(after Donaldson, 1976).

Figure 18.

ORIGIN OF CONEf-IN-CONE STRUCTURES

FORMATION OF CONEle-CONE STRUCTURES AND STYLOLITES

Gilman and Metzger (1967) use the continuity of the medial silt-
stone layer into a concretion as proof of its "syngenetic character",
while Pettijohn argues the presence of this layer implies epigenetic
formation of concretions (1957). If the graywacke and argillite in
footages 2761 and 2774 of drill core 4 are medial layers of concree
tionary cone-in-cone structures, this continuity has a bearing on their
formation. Bilateral symmetry of concretionary cone-in-cone structures
does not suggest, contrary to Gilman and Metzger's conclusion, that
”sedimentation of clay was going on at the time the carbonate concre-
tioniwas developing" (p. 94), but implies that deposition had ended.
One would expect differences between the upper and lower layers if
concretions were syngenetic (Pantin, 1957).

A syngenetic origin (Shaub, 1937) which requires a continuation

of sedimentary processes (deposition) for the formation of cone-in-

cone structures where the apices are necessarily directed downward is
inadequate to explain the occurrence of cone-in-cone structures in the
Michigamme Formation. Shaub studied the molds of the conical structures
preserved in unconsolidated sediments, and not the actual cones or casts
of the molds. He concluded that the preservation of cones would re-
quire filling these conical molds with sediment that would later con-
vert to carbonate, and which would be overlain by a second layer of
mudstone or siltstone. The samples from the Michigamme Formation are
believed to be turbidites, and it is not understandable how cone-in-cone
structures could be preserved by Shaub's method and still be turbidites.

Other theories of the origin of cone-in-cone structures include

43.

44.
l) the gaseous theory, 2) the crystallization theory, and 3) the
pressure - solution theory as developed by Tarr, although debate
regarding the source of the pressure continues (Tarr, 1932). Pres-
ent-day researchers with few exceptions favor the pressure - solution
theory. Carbonate was reorganized into layers along bedding planes,
and pressure from the weight of overlying beds caused fractures in
the recrystallited carbonate. Either a second or a continuation of
the first episode of pressure-solution caused more dissolution of
carbonate, resulting in the clayey residues left as intercone clay
and stylolites.

Whether the origin of intercone clay is entirely by pressure-
solution (Tarr, 1932; Pettijohn, 1957) or by pressure pushing semi-
consolidated shale into conical fractures (Gilman and Metzger, 1967)
is debated, but pressure forcing shale along the entire length of the
conical fractures isn't believable. Stylolites observed in slides
2039-l, 2039c-l and 483-7 indicate pressure-solution has been active
in the rock (Stockdale, 1922), and the fact that they grade into inter-
cone clay in some instances implies the simultaneous formation of sty-
lolites and intercone clay.(Tarr, 1932).

Thin sections 2039-l top, 276lA-4, 2761 c-4, 2769-4 #1, 2769-4 #3,
2774a-4 top, and 2856-4 exhibit argillite continuing into the intercon-
ical clay; 276lA-4, 276lC-4, 2774a-4 top, and 27743-4 bottom, contain
fragmented cone-in-cone structures embedded in argillite; and graphitic
and argillitic conical laminae are present in 2774-4 X. These three
Observations are essentially the same as those made by Gilman and
Metzger (1967), which they interpreted as the soft, plastic shale being

deformed by solid cone-in-cone structures.

45.

Layers of cone-in-cone structures appear conformable with bedding
in segments 2039-1, 483-7, 2769-4, and 2774-4, which do not possess
slaty cleavage. In segment 2761-4, bedding is deformed, and the rela-
tionship of cone-in-cone structures to bedding or slaty cleavage is
equivocal, as it is in segment 2856-4. Layers of cone-in-cone struc-
ture don't appear to follow either bedding or slaty cleavage in 2861-4,
where structures appear to deflect bedding. Layers of cone-in-cone
structure apparently are unrelated to slaty cleavage in 2907-4.

Parallelism of layers of conical structures with slaty cleavage
would imply that slaty cleavage formed prior to the cone-in-cone struc-
tures, which it would have guided. The significance of layers parallel
to bedding may indicate that cone-in-cone structure formed under the
weight of overlying strata before the onset of deformation and metamor-
phism of the Penokean Orogeny during an episode(s?) Of pressure-
solution responsible for the stylolites. Whether they are diageneti-
cally formed while shales were relatively unindurated, or epigenetic
as Tarr thinks (1932), is unresolved but the fact that stylolites tran--
sect cone-in-cone structures (2039-1 top) implies that stylolites con-
tinued to form after the construction of cone-in-cone structure had

ceased.

PARAGENESIS

The origin of the carbonate in the cone-in-cone structures is
probably not a sedimentary lamination of micrite (Burns, 1975), but
from recrystallization of interstitial carbonate present in the ar-
gillite (Trow, personal communication), which dissolved and reprecip-
itated as carbonate during diagenesis before the metamorphic peak of

the Penokean Orogeny, Carbonate veins in the cores show that carbonate

46.
was in solution after lithification of sediments.

Although cone-in-cone structure is found in-ooncretions, (Gresley,
1894; Gilman and Metzger, 1967) and calcareous concretions have been
reported in the Michigamme Formation (James, 1955; James, Clark, Lamey,
and Pettijohn, 1961; James, Dutton, Pettijohn, and Wier, 1968), the
cone-in-cone structures found in the Upper Slate Member samples have
not been proved concretionary. If these samples are part of concretions,
Klasner's belief (1978) that calc-silicate concretions were "originally
calcareous" (p. 716) strengthens the Observation that cone-in-cone
structures were originally carbonate, because at depths of 2761, 2769,
and 2774 feet in drill core 4, the amount of silica is very small in
fairly-well preserved carbonate cone-in-cone structures, while at all
other depths of cone-in-cone structures, carbonate is present with
recrystallized quartz which obliterates much of the structures.

~ Cone-in-cone fragments do not represent a reorganization of ar-
gillite by pressure-solution into carbonate, because this process
produces rhombs. The formation of the layers of carbonate prior to
the formation of cone-in-cone structures is not questioned in this
study. Argillite in slide 2769-4 exhibits carbonate rhombs whose
upper and lower edges are defined by thin carbonaceous layers, and
whose lateral edges grade into the surrounding argillite. The carbon-
aceous layers may be an insoluble residue formed as carbonate crystall-
izes at the expense of argillite. Indicative of their secondary ori-
gin is the observation that bedding appears to pinch out above and be-
low these rhombs, which could have formed synchronously with the car-
bonate of the structures.

A small amount of pyrite present as irregular grains in the Michi-

47.
gamme Formation argillite (slides 2856-4 and 2911-4) is presumably
of diagenetic origin (James, 1966; Curtis and Spears, ;968). Forming
prior to the lithification of sediments at or below the sediment -
water interface in a reducing environment of low Eh values (Krumbein
and Carrels, 1952; Pettijohn, 1957; Curtis and Spears, 1968; Berner,
1970), it probably formed as FeS and later converted to pyrite. Py-
rite transected by stylolites (2039-1, 2907-4, and 2856-4) obviously
antedates pressure-solution.

A second episode of pyrite formation during Keweenawan time
(Trow, personal communication) is implied by pyrite grains replacing
carbonate, recrystallized quartz, and cone-in-cone structure (2774a-4,
2774b-4, 2856-4 M, and 2907-4 X) and stylolites (2856-4, 2861-4, 2907-4,
483-7, and 2039-1), and pyrite aggregates injected into slaty cleavage
formed during the Penokean Orogeny and along Keweenawan faults.

Chert is present as elastic grains in argillite and graywacke in
samples from all three drill cores, presumably from the Bijiki Iron
Formation Member. An episode of grain growth for quartz in slide
2039c-l top is indicated where finer-grained quartz does not obliterate
structure, but the coarser-grained quartz does eradicate structure.
Silica may have been present or introduced from another source during
Keweenawan time, but an episode of quartz recrystallization possibly
during the Penokean Orogeny postdates the formation of cone-in-cone
structure .

The formation of chlorite along contacts between cone-in-cone
structure and argillite, and as a replacement of the intercone clay
(2856-4 M) occurred after the formation of cone-in-cone, probably

during the metamorphism of the Penokean Orogeny.

CONCLUSION

SUMMARY AND CONCLUSION

Structures once thought to be stromatolites of questionable
shallow water origin are believed to be cone-in-cone structures. The
idea that they were stromatolites in growth position was ruled out by
the fact that within two core segments, the apices pointed toward each
other, but in the absence of isoclinal folding.

The pieces of cone-in-cone structure do not necessarily have a
elastic origin, for these fragments may be explainable as normal out-
growths of the formative processes of cone-in-cone structure. More
evidence is accumulated in favor of their identity as in §i£g_cones,
such as carbonate cones with serrated layers of intercone clay and
graphite, sweeping extinction of some structures under crossed nicols,
apices of double layers found associated with calcareous argillite,
and the nature of the contacts with the argillite.

Because these forms are probably not stromatolitic, the question
of a deep water origin for algal stromatolites together with the impli-
cations for photosynthesis is dismissed. However, stromatolites of
bacterial origin are known to exist and it is not inconceivable that

such could exist in a deep water environment (Hoffman, 1976).

RECOMMENDATIONS FOR FURTHER STUDY

Further study should extend to the conical structures of the
Bijiki Iron Formation Member, to gauge any similarities with the Upper
Slate Member. Problems remaining to be solved are: l) was the shale
plastic or indurated at the time of origin of the cone-in-cone struc-

tures? 2) Why is calcite present in the cone-in-cone structures at

48.

49.
depths of 2769 and 2774 feet in drill core 4, but ferroan dolomite
present in the other structures? Paragenesis Of minerals and their
relationships to orogeny and deformation may yield a more precise

time of formation of these cone-in-cone structures.

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Stockdale, P. B., 1922, Stylolites: Their nature and origin: Indiana
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Strbm, K. M., 1939, Land-locked waters and the deposition of black
muds, in Recent marine sediments: Am. Assn. Pet. Geol., p. 356-
372.

Sverdrup, H. U., Jehnson, M. W., and Fleming, R. H., 1942, The Oceans:
Prentice-Hall, Inc., New York, 1087 p.

Tarr, W. A., 1932, Cone-in-cone, In: W. H. Twenhofel, Treatise on
Sedimentation. Dover Publications, New York, p. 716-733-

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formation in the Middle Precambrian basins, in the western portion

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Assn. Pet. Geol. Bull. v.23, p. 1178-1198.

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56.

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APPENDIX A

THIN SECTION DESCRIPTIONS

THIN SECTION DESCRIPTIONS

2031-1

Argillite, laminate, gray. This sample contains quartz, anhedral
grains, 0.5 mm. maximum dimension, approximately 5%; graphite, matrix,
approximately 43%; sericite, 50%; plagioclase, elastic, exhibiting
polysynthetic twinning, alteration, and graphite inclusions, 0.1 mm.
maximum dimension, less that 1%, dolomite, subhedral to anhedral cry-
stals, 0.06 mm. maximum dimension, less than 1%; calcite, anhedral
crystals, 0.05 mm. maximum dimension, less that 1%; chlorite, anhedral,
0.13 mm. maximum dimension, less that 1%. rock fragments, rounded, 0.23
mm. maximum dimension, composed of quartz, carbonate, sericite, plagio-
clase, and graphite, less than 1%. Sericite-rich layers alternate with

thicker graphite-rich layers.

2039-l DNR small Sample
This slide contains carbonate, with conical structure and stylolites,
and argillite. The carbonate in the columm of conical structure ex-
hibits sweeping extinction under crossed nicols, embayed boundaries
with quartz (chalcedony) forming a cement on pyrite. Pyrite occurs as
irregular grains, attains 0.87 mm. maximum size, and exhibits boundaries
embayed by quartz. Graphite occurs as stylolitic seams and as part of
the conical structure in the fornxof conical laminae, with an irregular-
ly shaped "v" appearance in thin section. Chlorite is associated with
graphite in stylolites. Quartz is pseudomerphous after pyrite, and
obliterates conical structure.

The argillite consists of a graphite matrix in which are embedded

carbonate, sericite, and quartz grains. Bedding, defined by elongated

57.

58.

grains, appears compressed where argillite thins.

2039-l DNR large sample

This slide exhibits conical structure and stylolites. Carbonate
comprises the greater part of the conical structure, and exhibits
sweeping extinction under crossed nicols in some structures, and dis-
plays embayed boundaries. Graphite occurs as stylolites, seams in
conical structures, and smaller irregular grains, 0.75 mm. maximum
dimension. Chlorite, usually in patches, is associated with stylolitic
graphite. Pyrite is uncommon, but occurs as irregular grains, 0.75 mm.
maximum dimension.

Shapes and orientations of conical structure vary within the slide.
Graphite in coaxial "v" shapes 3.5 mm. in height suggest profiles, while
2.5 mm. diameter rosette-shaped graphite indicates transverse sections.
Penetration through successively higher and higher layers of one struc-
ture is implied by progression from the innermost center ring to the

outermost ring.

2039a-1

This slide contains argillite and conical structure. Argillite is
composed of graphite as matrix, approximately 75%, quartz, angular to
subrounded anhedral grains, 0.21 mm. maximum size, 10%; sericite, laths,
0.7 mm. maximum size, 1%; carbonate, irregular grains, 0.1 mm. maximum
dimension, 23%; and rock fragments, rounded, 0.16 mm. maximum dimension;
composed of chert, graphite, and carbonate. The bedding is defined by
long axes of muscovite grains, and streaks of quartz and carbonate grains,
and exhibits deformation.

The conical structure is composed primarily of quartz, carbonate,

and pyrite. Quartz (60%) is partly a replacement of carbonate and pyrite,

59.

since it exhibits embayed boundaries, and masses of quartz interrupt
conical structure. It is also a cement on pyrite. Anhedral plagioclase
grains,displaying polysynthetic twinning, are angular to rounded, and
reach a maximum size of 0.65 mm. Pyrite (1%) occurs as cubes and
irregular grains with 1.75 mm. as a maximum dimension. Carbonate
occurs as rhombs and anhedra, and constitutes 26%. Sericite is present
as laths, and chlorite occurs as aggregates; both add up to less than
1%. Graphite is present as stylolites (13%).

The contact is well-defined at magnifications of 40, 100, and 200.
Graphite matrix is in contact with the carbonate or quartz at a fairly

sharp planar boundary.

2039c-l top

This slide of conical structure is composed of carbonate, quartz,
graphite, and pyrite. Quartz, from 0.025 mm. to 0.25 mm., is bimodal
in size distribution, and larger recrystallized textures of quartz
obliterate and replace conical structure. Pyrite occurs as irregular
grains, 1 mm. maximum dimension; and graphite composes stylolites and
the conical layers of the structures. In addition to graphite, frag-
ments of carbonate not yet removed by pressure-solution are present in
some of the thicker sty101ites.

The argillite at the tap of the slide is composed of graphite,
quartz, sericite, and carbonate. Quartz grains are anhedral; the larg-
est measures 0.05 mm. Carbonate occurs as irregular grains, with a
0.05 mm. maximum dimension. Bedding defined by long axes of sericite
and quartz grains, exhibits deformation due to the carbonate lithology
that pushed into it. The deformed zone is 3mm. in length. Dark, car-

bonaceous matter of the argillite grades into stylolites of the coni-

60.
cal structures, whose boundaries are cross-cut by stylolites.

The contact between argillite and conical structure is sharp and
well-defined, and nearly planar.

Conical structures measure from 1 to 2.25 mm. at their bases, and
individual columns of "coaxial v's" range from 2 mm. to more than 2 cm.
in height. Structures are obliterated in the l - 3 mm. wide zone ad-
jacent to the largest seam, but it is not clear whether they belong to
the same column. While defining the conical structure in thin section,
some of these graphitic "coaxial v's" appear serrated or jagged on one
side. "Coaxial v's" grade into stylolites and larger seams.

A twenty-two millimeters thickness of a stylolite from 0.5 to 2 mm.
wide is represented on the slide, and appears to separate portions of con-
ical structure. The seam is composed of amorphous masses of graphite
ranging in size form 0.13 X 0.25 mm. to 1.3 X 2.0 mm., appearing as if
they were laid end-to-end in thin section. A twelve millimeters thick-
ness of a second seam occurs in another zone of obliteration of struc-
ture from 7-10 mm. in a downhole direction from the first. It appears
as amorphous masses of graphite on the sides and apices of the struc-
tures that grade into stylolites and layers of the conical structure.

Stylolites are abundant, but generally do not exceed 0.25 mm. in

width, or 10 mm. in length.

2039c-1 bottom

This graphitic carbonate is largely a transition from the carbonate
above; the stylolitic zone shows vague definition of "coaxial v" shapes,
but instead of conical structure the graphite forms parallel anastomos-
ing seams with 0.02 mm. maximum width below the stylolites. Quartz is

present in patches; as a replacement of carbonate, it exhibits embayed

5,1.
boundaries. It comprises 6.7%, compared to carbonate which makesuup
50%. Graphite (42%) is present as amorphous masses and seams, which
cross-cut veins of calcite and quartz. Muscovite comprises less than
1%, and attains 0.04 mm. maximum size. Carbonate is present as anhedral

grains.

2043-1

Argillite, laminated, gray. It contains graphite as matrix, approx-
imately 70%; muscovite, 24%, 0.03-0.6 mm. long laths; plagioclase, less
than 1%, anhedral, twinned, altered, angular to rounded, 0.1 mm. maxi-
mum dimension; chlorite, irregular grains, 9.5 mm. maximum dimension,
less than 1%; quartz, anhedral grains, angular to subangular, 0.25 mm.
maximum dimension, 1.5%; carbonate, rhombs and irregular grains, 0.45
mm. maximum dimension, less than 1%; rock fragments, angular to rounded,
0.6 mm. maximum dimension, 4%, composed of chlorite, sericite, graphite,
chert, and carbonate.

Bedding is defined in thin section by linear arrangement of grains
of quartz, carbonate, and rock fragments. Sericite-rich layers alter-

nate with graphite-rich layers.

2750-4

Argillite, gray, bedded. This sample contains quartz, angular to
subrounded, anhedral, 0.4 mm. maximum size, 2.5%; muscovite, laths, 0.1
mm. maximum length, and flakes; graphite, irregular grains, 0.05 mm.
maximum dimension, 0.1%; pyrite, irregular grains, less than 1%; carbon-
ate, 2.3%, rhombic, 0.38 mm. maximum.dimension, and irregular grains,
partially replaced by Quartz; chlorite, irregular grains, 1.8%, 0.15 mm.

maximum dimension; plagioclase, 0.25 mm. maximum dimension, angular to

62.
subrounded, anhedral to subhedral, polysynthetic twinning, altered to
sericite, 0.5%; rock fragments, rounded, 0.4 mm. maximum dimension,
composed of muscovite, quartz, graphite, and chlorite, less than 1%.
Clastic laminae of coarser-grained quartz, plagioclase, rock frag-

ments, and carbonate are present in a quartzose, sericitic matrix.

276lA-4

The rock contains graywacke, carbonate, and argillite. The gray-
wacke is composed of quartz, 0.4 mm. maximum dimension, 21%; carbonate,
rhombs to irregular grains, 0.4 mm. maximum dimension, partly replaced
by quartz, 23%; rock fragments, rounded, 0.5 m. maximum dimension, com-
posed of chert, carbonate, and graphite, 0.6%; chlorite, irregular
grains, and laths, 0.75 mm. maximum diemsnion, 4%; plagioclase, partly
replaced by carbonate, anhedral, 0.3%, twinned, 0.05 mm. maximum dimen-
sion; graphite, stringers, 0.5 mm. maximum length, and irregular grains,
0.2 mm. maximum dimension, 15%; The smaller grains serve as the matrix
in this graywacke. Graphite defines conical structures, layers of which
are embedded in this siltstone; the apices point in a downhole direction.

Argillite, laminated and massive, is composed of graphite, string-
ers, 2.5 mm. maximum length, and irregular grains, 0.11 mm. maximum.
length, 38%; sericite, 50%; quartz, 4%, 0.03 mm. maximum dimension, an-
hedral, angular. Laminated argillite associated with the conical strucq
tures shows graphite stringers alternating with layers of quartz, seri-
cite, and graphite grains.

The conical structures are composed of carbonate which is being
replaced by quartz. Pyrite is present as irregular grains, 0.3 mm.

‘maximum dimension, and is being replaced by quartz. Graphite layers

63

defining the structures have been replaced to a large extent by chlor-
ite. Apices point in a downhole direction.

The contact between argillite and conical structure is well-defined
and consists of irregular grains of carbonate bordering the argillite.
Some 0.005mm. to 0.01 mm. wide graphitic stringers are present between
the carbonate and the argillite.

The contact between conical structure and graywacke is distinct.
Conical structures are outlined by argillite, or else the carbonate of
the conical structures makes a sharp contrast under crossed polars with
the graywacke.

The contact between the argillite and graywacke is obvious at 40
magnification, but is less distinct at 100 and 400 magnification, it

is remarkably planar considering the small grain size.

27613-4

The two lithologies represented are graywacke and graphitic carbon-
ate. The carbonate consists of a graphite-sericite-carbonate matrix
with an anastdmosing network of veins containing sericite, quartz, and
chlorite.

The graywacke is composed of quartz, anhedral, angular, to sub-
rounded, 0.15 mm. maximum dimension, 2%; rock fragments, rounded, 0.25
mm. maximum dimension, containing chert, plagioclase, carbonate, and
sericite, less than 1%; chlorite, elongated irregular grains, 0.15 mm.
maximum dimension, 40%1 sericite, laths, 0.2 mm. maximum length, and
flakes, 8%; graphite, irregular grains and stringers constituting the

matrix.

27610-4

64-

Argillite is composed of graphite, quartz, carbonate, and sericite.
Carbonate occurs as rhombs, less than 1%, 0.25 mm. maximum dimension,
and irregular grains. Quartz is present as angular anhedra, 0.05 mm.
maximum dimension. Graphite, 52%, occurs as irregular grains, 0.08 mm.
maximum dimension, and tiny stringers, 0.15 mm. maximum length, that
define either foliation or bedding planes by parallel alignment of
long axes. Sericite, 49%, and elongated quartz grains also help de-
fine this foliation. Quartz is present in the 0.04 mm. size range
along the contact, possible as a replacement mineral.

The conical structures consist of carbonate and layers of graphite
and chlorite. In some, the graphite layers have a serrated appearance,
and measure 5 mm. in length. Apices point in an uphole direction.

The argillite pinches out into graywacke. This is composed of
quartz grains, angular to subrounded, with some recrystallization tex-
ture, 0.32 mm. maximum length; chlorite, laths and irregular grains;
carbonate, anhedral crystals, 0.63 mm. maximum dimension; graphite,
irregular grains and clots; and plagioclase, subhedral, polysynthet-
cally twinned, 0.05 mm. maximum dimension.

The contact between argillite and conical structure is frequently
a graphite stringer, from 1 mm. in length to individual grains. Where
no graphite is present, fine grains (0.025 mm. maximum dimension) of
anhedral quartz occur. At 40 magnification the resolution is very in-
distinct for this fine-grained rock's contacts and grain boundaries.

The contact between conical structure and graywacke is a well-

defined break that grades into a % mm.'wide zone of carbonate.

2761D-4

Argillite, laminated, gray. This sample is mineralogically com-

65.

posed of quartz, angular to rounded, 0.20 mm. maximum dimension, an-
hedral to elongated grains, also as a cement on carbonate grains, 13%;
carbonate, rhombs, 19%, 0.3 mm. maximum dimension, partial replacement
by quartz, present in all laminae; sericite, 0.18 mm. maximum length,
30%, laths and flakes; graphite, irregular grains, 37%, 0.09 mm. max-
imum dimension, and stringers, 2.5 mm. maximum length; chlorite, laths
and aggregates, 0.25 mm. maximum dimension, less than 1%; plagioclase,
incipient alteration to sericite, polysynthetic twinning, 0.25 mm. max-
imum dimension, less than 1%; rock fragments, composed of quartz, car-
bonate, graphite, and are rounded, with a 0.25 mm. maximum dimension.

Clastic beds of silt size quartz and plagioclase alternate with
laminae that are finer grained. Quartz veins are also present in the

argillite.

2761E-4

Argillite with graywacke. Argillite is composed of graphite, ire
regular grains, 0.075 mm. maximum dimension, 40%; sericite, 36%; quartz,
angular, anhedral grains, 0.03 mm. maximum dimension, 3.5%; chlorite,
laths, 0.025 mm. maximum length, and irregular grains, 0.4%; carbonate,
rhombs and irregular grains, 0.2 mm. maximum dimension, 19%.

The graywacke contains rock fragments, less than 1%, rounded, 0.2
mm. maximum size, composed of chart and sericite; plagioclase, polysyn-
thetically twinned, 0.18 mm. maximum dimension, 3.4%; carbonate, rhombs,
0.35 mm. greatest dimension, 9.5%; sericite, shreds, 1.1 mm. maximum
length; 22%; pyrite, irregular grains, 0.6 mm. maximum.dimension, 2%;'
graphite, irregular grains, 0.08 m. maximum dimension, 12%; chlorite,
irregular grains and laths, 0.5 mm. maximum dimension, 3.2%; and quartz,

also in the form of chert, angular to subrounded grains, 0.58 mm. maximum

66.

dimension, also a replacement of carbonate, 47%.

2764-4

Argillite, gray. It consists of graphite, irregular grains, 0.1
‘mm. maximum, some stringers, 60%; carbonate, rhombs, 0.2 mm. maximum
dimension, 18%; quartz, anhedral, anhedral grains, 0.01 mm. maximum
dimension, less than 1%, sericite, 20.5%, pyrite, irregular grains,
less than 1%.

A quartz vein, approximately 0.01 mm.'wide, and a carbonate vein,

approximately 0.125 mm. wide, are present.

2769-4 #1

This slide contains conical structure and argillite. Mineralogi-
cally it consists of carbonate in the conical structure, rhombs and
parts of rhombs in the argillite, 0.075 mm. maximum dimension, 18%;
graphite, composing layers of conical structure, and laminae in the ar-
gillite, 10 mm. maximum length X 0.1 mm. maximumnwidth, irregular
grains in argillite, 0.075 mm. maximum dimension, 64%; chlorite, aggre-
gates, associated with and partially replacing graphite in stylolites
and layers in conical structures, less than 1%; pyrite, in irregular
grains, 0.25 mm. maximum dimension, associated with the contact, 0.5%;
chalcopyrite, irregular grains, associated with the contact, 0.125 mm.
maximum dimension, less than 1%; and quartz, associated with the contact,
and with pyrite in the argillite, 3.4%, with embayed boundaries.

Conical structures are defined by graphitic layers, frequently with
a serrated appearance, or straight appearance, from 0.075 mm. to 2.5
mm. in length. The bases range from 0.5 mm. to 4 mm. and heights vary

from 0.75 mm. to 8 mm. The shape in thin section is a "coaxial v", with

67-
a rounded apex, which is expected in an oblique section intermediate
between a transverse section and a profile. Some fragments are embed-
ded in the argillite and point in the uphole direction.
The basal contact between the bases of the conical structures and
argillite is clearly-defined, planar, and jagged due to the protrusion
of structures. At 400 magnification, the resolution isn't great e-

nough to see grain boundaries.

2769-4 #4

Argillite is composed of quartz, 5%, angular anhedra, 0.25 mm.
maximum dimension; carbonate, rhombs, 18%, 0.275 mm. maximum dimension;
graphite, irregular grains 0.07 mm. maximum dimension, and layers
at least 1 mm. long, 40%; sericite, laths, 36%, 0.1 mm. maximum length;
chlorite, laths, 0.2 mm. maximum length, less than 1%. The bedding is
defined by long axes of phyllosilicate grains and graphite stringers.
Some pyrite is being replaced by quartz and carbonate.

Argillite is contained in the coaxial cones that define the conical
structures. They are smaller and more fragmented compared to those in
sample 2769-4 #1, although both exhibit some obliteration of fine struc-
ture, indicated by faint, diffuse layers. Apices point inva downhole
direction, and vary in size from 0.2 mm. to 2.5 mm. in height, and from
0.3 mm. to approximately 2.5 mm. in width. Structures are also composed
of carbonate.

The third lithology is graphitic carbonate containing carbonate as
irregular grains, 46%, 0.12 mm. maximum dimension; sericite, laths,

0.08 mm. maximum length, 1.1%; and graphite, 54%, in seams, layers, and
irregular grains.

Fragmentary conical structures are obliterated and grade downward

68.
into graphitic carbonate with much less carbonate, where they are no
longer discernable. The upper contact can be considered a 2 mm. wide
zone where discrete and commonly obliterated structures are embedded

in argillite.

2773-4

Argillite, gray. This is composed of a fine-grained matrix of
quartz, sericite, and graphite, with larger grains of carbonate and
graphite. Quartz occurs as angular anhedra, 0.02 mm. maximum dimen-
sion, 1%; sericite, comprises 38%, and graphite, 45%. Carbonate occurs
as rhombs and irregular grains, 0.23 mm. maximum dimension, 17%.
Bedding is defined by parallel arrangement of long axes of sericite

grains, 0.125 mm. maximum length.

2774-4 #1

This transverse section of conical structure consists of carbonate,
graphite in rosette-shaped arrangements, 2-7 mm. in diameter; pyrite,
1 mm. maximum dimension, irregular grains; chlorite, irregular grains,
0.1 mm. maximum dimension, also as a replacement of graphite; and

quartz, exhibiting embayed boundaries and recrystallization texture.

2774-4 w

This slide is composed of conical structure and fragments of coni-
cal structure that grade downward into argillite. Structures contain
carbonate; chlorite, in irregular grains and.aggregates commonly replac-
ing graphite; and graphite, forming conical laminae. The largest struc-
tures measure 2-5 mm. at their base, and 6 mm. in height; while the
smallest fragments' dimensions are 0.23 mm.X 0.23 mm. The largest

structures' apices point down.

69.
Argillite is composed of graphite, irregular grains, 0.1 mm.
maximum dimension, and stringers; carbonate, generally in the form of
anhedral grains, but rhombs are also present; and phyllosilicate in

the forms of sericite and chlorite.

2774-4 K

Conical structures with apices pointing upward gradually dimin-
ish in size so that in a % cm. wide zone, structures grade into car-
bonate-rich argillite. At the base of the slide conical structures
range from 7 mm. high to a few millimeters wide at the distance of
greatest separation of graphitic conical laminae, where bases are not
present. These grade upward to fragments measuring 0.125 mm. (base)
X 0.15 mm. high. Graphite and argillite define conical structures,
and some of these have a serrated appearance. A single axis common to
multiple conical structures is found and the structures form a column.
In other cases, graphite layers serve as a common side to adjacent
conical structures, and nested structures without a single axis of sym-
metry prevail. At the base of the slide, graphite layers fade into

carbonate.

2774-4 Y

This profile of conical structures consists mainly of carbonate
that includes a few layers of graphite grading into stylolites of graph-
ite and phyllosilicate. Pyrite occurs as irregular grains measuring
0.4 mm. as a maximum dimension. Orientation and other measurements can
not be determined from this thin section due to a lack of defining

layers 0

2774-4 #3

70.

Conical structure consists of carbonate, graphite, and layers of
phyllosilicate, both sericite and chlorite. Pyrite is present as irreg-
ular grains, cubes, and aggregates. Quartz occurs as cement on some
pyrite grains, and replaces carbonate and pyrite, as indicated by em-
bayed boundaries and recrystallization texture.

Argillite consists of quartz, angular anhedra, 5%, 0.05 mm. max-
imum dimension; carbonate, 8%, as irregular grains and rhombs, 0.23 mm.
maximum dimension; graphite, 22%, irregular grains and layers, 0.75 mm.
maximum dimension; muscovite, laths, 65%, 0.125 mm. maximum length; and
chlorite, 0.43 mm. maximum length, less than 1%.

Pyrite and recrystallized quartz are present along the abrupt and
well-defined contact between argillite and conical structures. The
zone of quartz and pyrite ranges between % mm. and 2 mm. wide, and ob-

scures the original contact.

2778-4

Argillite, gray, composed of larger irregular grains of pyrite and
carbonate. Pyrite attains 1.25 mm. maximum dimension, and carbonate
rhombs reach 0.125 mm. maximum dimension, and comprise 7%. The matrix
is composed of quartz, 0.015 mm. maximum, 0.3%; graphite comprises
38%, and is present as irregular grains and stringers; and sericite

totals 55%.

2844-4

Argillite, gray, massive. This is composed of a graphite matrix,
81%; in ‘which are embedded quartz grains, 0.05 mm. maximum dimension,
13%, anhedral, angular; carbonate, rhombs, 1.4%; sericite, 6%; rock

fragments, containing chert, sericite, and graphite, rounded, 1.75 mm.

71.

maximum dimension, less than 1%.

2856-4 K

Conical structures consist of crystalline carbonate, in irregular
grains, 0.05 mm. maximum dimension; quartz, Which obliterates conical
structure; graphite, as irregular grains, 0.05 mm. maximum, and string-
ers, distinct to diffuse, serrated and smooth, 5.75 mm. long X 0.12 mm.
wide maximum, and stylolites. Pyrite is present as irregular grains
and aggregates several millimeters in diameter, and its embayed bound-
aries show it is being replaced by quartz and carbonate. Chlorite oc-
curs in aggregates at the base of the structures, and in layers of con-
ical graphite. Apices of structures point down, and in place of dis-
crete symmetric structures are multiple structures, possibly a result
of joining at the sides of two or more single structures. This is indi-
cated by the multiple occurrence of apices without the graphite layers
defining the individual sides of structures. Lower layers fade into
carbonate, and upper layers define several apices.

Laminated and crenulated argillite consists of graphite, 69%, a1-
ternating with patches of recrystallized quartz, 20%; sericite, 11%,
and graphite grains. QUnrtz is present as angular, anhedral grains,
0.05 mm. maximum dimension, and disrupts the lamination of the argillite
where it occurs as a replacement. Graphite occurs in irregular grains,
0.1 mm. maximum dimension.

The generally rounded but smooth contact consists of chlorite aggre-
gates adjacent to graphitic laminae of the argillite. One relatively
defined structure is oriented so its axis does not form a right angle

with the bedding. The contact's jagged appearance in places is due to

this fact andeflso to stylolites or graphite that define the conical

72.

layers grading into the argillite.

2856-4 L

Semi-preserved conical structure is composed of graphite, quartz,
and carbonate. Graphite layers appear serrated, and the recrystalliza-
tion of quartz has obliterated conical structure. Graphite is also
present as stylolites. Irregular pyrite grains measuring several milli-

meters in diameter are present.

2856-4 M

Both obliterated and preserved conical structures are present.

The largest bases measure 0.75 mm. - 1 mm. across, and some columns
appear to reach 2 mm. in height; apices point upward.

A six to eight millimeter wide zone of interbedded argillite with
which the structures form a contact is composed of graphite, matrix,
76%; quartz, angular anhedra, 16%, 0.2 mm. maximum dimension; carbonate,
anhedral, 6%; and sericite, less than 1%. Bedding is defined by planar
arrangement of quartz and carbonate grains. The jagged contact is a-
bruptly marked by the presence of two distinctively different lithol-
ogies.

Below the argillite is a 1 cm. wide bed of carbonate containing
obliterated conical structures with the exception of several fairly-
well defined shapes. The carbonate contains amorphous masses of ar-
gillite, which possibly are incipient stylolites. Structures do not
occur below this zone. The contact between the argillite and 1 cm.
'wide carbonate is a transition zone, 0.75 mm. - 1.0 mm.‘wide, contain-

both graphite and carbonate.

73.
2858-4

Argillite contains graphite, 87%, as matrix, in which are quartz
grains that are angular to subangular, deformed and elongated, and
reach 0.125 mm. maximum dimension. Quartz veins are present, with
8 mm. long X 0.07 mm. wide as a maximum size observed. Other mineral
constituents include rock fragments, 5.6%, composed of chert, chlorite,
sericite, and graphite, and are rounded, some elongated, with 2.25 mm.
as a maximum dimension; sericite, 5%, laths and flakes; carbonate,
2.4%, as irregular grains, 0.1 mm. maximum dimension, and chlorite,
2.7%, as irregular grains and aggregates, 0.1 mm. maximum dimension.
Quartz comprises approximately 40%.

Bedding in argillite is defined by subparallel arrangement of long
axes of quartz, sericite, and rock fragments.

The approximately 7 mm. thick carbonate bed contains carbonate,
pyrite as irregular grains and aggregates, ranging upward to 1.5 mm.,

and graphite as irregular grains and stringers, 2 mm. maximum length.

2861-4 M

The conical structure consists of carbonate and quartz exhibiting
embayed boundaries and recrystallization texture. The layers defining
the structures are composed of chlorite in irregular grains and aggre-
gates, and graphite, as irregular grains and seams reaching a maximum
size in thin section of 0.025 nm. wide X 2.5 mm. long. Pyrite is pres-
ent in irregular grains, 4 mm. maximum dimension, being replaced by
quartz, and with islands of quartz. Sericite is also noted.

Some conical structures are defined by graphite and chlorite in
general outline; in others spikey-appearing layers of graphite are pre-

served; still in others graphite and chlorite aggregates form masses

74.
and consequently detail is difficult to discern. Quartz has recrystal-
lized and obliterated some conical structure.

The argillite consists of a graphite matrix, 66%; quartz grains,
angular, anhedral, frequently elongated, 0.125 mm. maximum dimension,
17%; carbonate, irregular grains or rhombs, 9%; and sericite, laths,
0.05 mm. long, and flakes. Bedding is defined by long axes of elongat-
ed grains in parallel alignment, and is deformed in some places. A
few tiny quartz veins occur, 1.75 mm. long X 0.075 mm. wide, maximum
size.

The contact is distinct and planar, consisting of chlorite aggre-
gates at the bases of many structures adhacent to the argillite. The

jaggedness results from the bases being at different heights.

2861-4 0

This slide of conical structures consists of quartz, carbonate,
graphite, chlorite, and pyrite. Quartz replaces conical structures.
Graphite defines conical layers several millimeters in height, and
ranging in.width from 0.01 mm. to approximately 0.25 mm. Pyrite is
present as irregular grains several millimeters in diameter. Carbon-
ate is present as rhombs that have grown and pushed aside the carbon-
aceous matter.

Layers are often discontinuous along a side or at an apex, where
quartz is present; and they commonly have a straight or serrated
appearance. Apices are rounded to pointed, and point both uphole and
downhole, since many structures share a single side. Graphite layers
form conical laminae, but some structures have been annihilated to the

point where graphite layers are subparallel.

75.
28613-4

Annihilated conical structures contain carbonate, graphite,
chlorite, pyrite, and quartz which replaces conical structures. Graph--
ite occurs as layers of conical structures which are several millimeters
in length, ranging up to 0.25 mm. in width, and ofter are spikey-appear-
ing. Chlorite is present in aggregates along the contact between the
structures and argillite, and along some graphite seams. Enough struc-
ture is present to show apices pointing away from the argillite.

The laminated argillite is composed of a graphitic matrix, 56%;
carbonate, rhombs, approximately 0.04 mm. maximum dimension; quartz,
angular, spherical to elongated grains, 0.06 mm. maximum dimension, 2%;
sericite, 16%; rock fragments, 0.09 mm. maximum dimension, 1%, composed
of carbonate, chert, and muscovite. ‘Bedding is defined by parallel
alignment of long axes of grains.

The argillite and chlorite form an abrupt, uneven contact.

28610-4

Argillite, gray, laminated. It consists of quartz, angular, anhe-
dral grains, 0.23 mm. maximum dimension; chert, 0.12 mm. maximum dimen-
sion of grains; together chart and quartz total 6.4%. Carbonate is
present as irregular grains and patches, less than 1%; muscovite is pres-
ent as shredS,0.2 mm. maximum length, 6%; graphite matrix, 82%; and
plagioclase, anhedral to subhedral, with polysynthetic twinning, 0.2 mm.
maximum length, less than 1%.

Pyrite is present as irregular grains, 0.35 mm. maximum size, less
than 1%. Rock fragments compose 5%, are rounded to angular, and consist

of chert, carbonate, chlorite, and sericite, and graphite. Two elastic

76.

beds of 0.5 mm. and 1.5 mm. thickness are faulted and offset by approx-

imately 2.75 mm.

2867-4

Argillite, massive. It consists of graphite, matrix, 24%; quartz,
0.125 mm. maximum dimension, angular, anhedral grains, 27%; muscovite,
laths and parts of flakes, 0.1 mm. maximum length, 36%; plagioclase,
anhedral to subhedral, 0.05 mm. maximum dimension, twinned and altered
to sericite, less than 1%; pyrite, aggregates, approximately 10%; car-
bonate, 4%, irregular grains; rock fragments, rounded, anhedral, 0.1 mm.

maximum dimension, containing sericite, chert, and carbonate.

2903-4

This is a massive argillite composed of quartz, graphite, carbonate,
and sericite. Quartz is anhedral, angular, and attains 0.05 mm. maxi-
mum size; together with chert the total percentage is 20%: Sericite
occurs as flakes and laths, 0.06 mm. maximum size, 15%. Carbonate
occurs as irregular grains, 0.08 mm. maximum size, and constitutes less
than 1%. Graphite occurs as irregular grains and masses comprising the

matrix, 64%.

2907-4 X

Conical structures are composed of quartz, carbonate, graphite,
and muscovite. Quartz replaces conical structure and occurs as cement
on pyrite. Graphite occurs primarily as layers of the conical struc-
tures, but is also present as amorphous masses among them. Pyrite oc-
curs as irregular grains, reaching 1.75 mm. maximum dimension, with in-

clusions of quartz and carbonate, and obliterating conical structures.

Chlorite is present along the contact in aggregate form.

77.
Apices point in the uphole direction, and some graphitic layers

have a serrated appearance, but most seem to be of a uniform thickness
between 0.01 mm. and 0.12 mm. A few seem to grade into stylolites.
The argillite is composed of chert, in patches, 21%. Graphite,
62%, constitutes matrix, in amorphous masses and as layers. Muscovite,
occurs as laths and flakes, 0.1 mm. maximum dimension, 17%. Bedding
is defined by parallel graphite layers, and lenses of quartz, musco-
vite, and graphite.
The contact between conical structures and argillite is abrupt,
where 0.01 mm. thick layers of graphite form the bases of structures,
but elsewhere the transition occurs as a % - % mm. thick interval of

carbonate, graphite, and quartz.

2907A-4

This slide of conical structures contains carbonate, quartz, py-
rite, graphite, and sericite, with quartz replacing the conical struc-
tures, pyrite, and graphite. Graphite is present as irregular grains
and amorphous masses, ranging upward in size from 0.005mm., and as seams
and layers of conical structures, and in stylolites. Muscovite occurs
as laths, 0.05 mm. maximum length, and pyrite occurs as irregular grains
that contain inclusions of quartz and carbonate, with a maximum dimen-
sion of 1.25 mm.

Apices and conical forms are suggested by the convergence of ser-
rated-appearing layers, where discontinuity in layers exists, and point
in both uphble and downhole directions. Form is obscured in some struc-

tures, because of the diffuse and indefinite nature of the layers.

29078-4

78.

This slide of conical structure consists of carbonate, quartz,
graphite, and pyrite. The crystalline portion is composed of carbonate,
and quartz which replaces conical structure land pyrite. Graphite oc-
curs as irregular grains, ranging upward from 0.005 mm., to layers of
conical structures. Pyrite is present as irregular grains, 1.25 mm.
maximum dimension, with inclusions of quartz and carbonate.

Conical structures are defined by graphite layers, and gteater
amounts of quartz and carbonate than are present in the mixture of
graphite, quartz, and carbonate filling in among the structures. Apices
of most of the separate structures point in a downhole direction, al-
though the zigzag pattern of graphite, in the middle of the slide makes
this determination difficult. The pattern may reflect stacking of

structure, in very close proximity, and apices here may point downhole.

2908-4

This slide represents soft sediment deformation in a zone of ar-
gillite; and contains chert, carbonate, sericite, graphite, and pyrite.
Graphite occurs as deformed layers and some disseminated clots and
grains. Pyrite is present as irregular grains and cubes, 0.75 mm. max-
imum dimension; it obliterates other structures, but is also cross-cut,
fractured, and filled with quartz inclusion. Carbonate occurs as veins
and is being replaced by quartz. Argillite exhibits deformed bedding,

shredded boundaries, and severed quartz veins.

2911-4
Argillite and graywacke. Argillite is composed of graphite, mus-

covite, quartz, and carbonate. Graphite occurs as irregular grains,

I
O

1.5 mm. maximum.dimension, 44%; quartz, 19%, occurs as angular to sub-

79.
rounded grains, as vein filling, and as chert. Sericite occurs as
laths and flakes, 36%, 0.01 mm. maximum dimension, and carbonate oc-
curs as rhombs, 0.25 mm. maximum.dimension. Carbonate and graphite
occur in both lithologies, but carbonate is more abundant in the gray-
wacke, comprising less than 1% in the argillite.

4 Graywacke is composed of quartz, graphite, carbonate, sericite,
plagioclase, and argillite. Quartz is detrital, 0.25 mm. maximum di-
mension, but also a replacement of carbonate, and comprises 49%. Seri-
cite is present as laths and flakes, 0.08 mm. maximum dimension, com-
prising 8%; and argillite clasts are present With a maximum dimension
of 0.1 mm. Plagioclase occurs as subhedral to anhedral grains with
polysynthetic twinning and slight alteration to sericite, 3%, reach-
ing 0.11 m. maximum size. Carbonate is present as rhombs and anhedral

grains, 20%, 0.5 mm. maximum dimension.

478-7

Argillite, laminated, gray. This sample is composed of graphite,
69%, forming a matrix of clots and stringers; quartz, 0.05 mm. maximum
dimension, anhedral grains, angular to subangular, 6.4%; sericite, 7.4%,
0.1 mm. maximum length; rock fragments, 17%, rounded and composed of
chert and muscovite, 0.075 mm. maximum dimension; and carbonate, anhe-
dral grains, 0.04 mm. maximum dimension, 0.4%. Graphite-rich layers al-

ternate with muscovite-rich layers.

483-7
The first zone is argillite containing lenses of chert embedded in
graphitic matrix. Carbonate occurs as irregular grains and patches.

Sericite is present as flakes and laths, 0.05 mm. maximum length. The

80.

lenses define bedding by parallel arrangement of their long axes.

The second zone of conical structures is composed of carbonate,
graphite, and chert that obliterates conical structure. Graphite is in
the form of irregular grains ranging upward from 0.005 mm., and layers
that vary in width from 0.01 mm. to 0.25 mm. that commonly grade into
stylolites. Pyrite is present as cubes and irregular grains, 0.3 mm.
maximum dimension.

The conical shape is indistinctly defined by graphite layers, and
the direction in which the apices apparently pointe is downhole. Much
of the graphitic structure has been obliterated by the recrystallization
of quartz, but the "coaxial v" shapes and familiar zigzag patterns are
present.

The upper contact is well-defined. Bases of conical structures
are in contact with the clastic lenses of the argillite.

The third zone contains carbonate and graphite, now as stylolites
and disseminated grains. and conical structures partially obliterated
by quartz. The contact between the second and third zones can be con-
sidered where conical structure is absent.

The fourth zone contains chlorite, graphite, and carbonate.
Chlorite is present in flakes, and carbonate and graphite are present
as irregular grains. The well-defined contact occurs as a % mm.‘wide

interval marked by7the absence of chlorite.

APPENDIX B

MICROPROBE DATA

Ca Fe
DOLOMITE STD.
00001581 00000007
00002537 00000009
00002608 00000005
00002696 00000007
00002679 00000011
00002613 00000008
SIDERITE STD.
00000058 00000925
00000055 00000880
00000060 00000899
00000048 00000989
00000066 00000917
CALCITE STD.
00005321 00000012
00005024 00000007
00004974 00000008
00005111 00000007
00004936 00000008
28618-4

Ca Fe
00001997 00000248
00002305 00000310
00002189 00000338
00002273 00000131
00002290 00000173
00002421 00000199
00001626 00000070
00001756 00000076
00002508 00000238
00001540 00000147

MICROPROBE DATA

M8

00001569
00002046
00002070
00002073
00001991
00002140

00000145
00000142
00000111
00000105
00000106

00000022
00000019
00000021
00000012
00000017

“3

00001127
00001080
00000883

00001446
00001080
00001492

00001108
00001237

00001237
00000748

time
(sec.)

00009.79
00009.82
00009.81
00009.92
00009.97
00009.97

00009.86
00009.86
00009.79
00009.86
00010.01

00009.94
00010.12
00010.12
00010.10
00010.04

00009.98
00009.96
00009.92

00009.88
00009.98
00009.96

00009.81
00009.87

00009.76
00010.26

81.

Ca

00002721
00002720
00002442
00002446
00002320
00002414

Ca

00002552
00002690
00002723
00002606

483-7
Ca

00001916
00001942
00002128
00001260

00002397
00002345
00002201
00002231
00002128

2039-l
Ca

00001765
00002064
00001454

00002047
00002147
00002301

Ca

00000793
00002379
00002381
00002285

Mb

00000007
00000011
00000012
00000026
00000020
00000022

Zn

00000022
00000021
00000021
00000019

Fe

00000027
00000017
00000012
00000030

00000021
00000020
00000083
00000090
00000067

Fe

00000090
00000081
00000068

00000123
00000092
00000112

Mn

00000012
00000023
00000019
00000022

M8

00001161
00001174
00001161
00001111
00001147
00001143

M8

00001166
00001166
00001060
00001113

M8

00001383
00001487
00001457
00001196

00001319
00001343
00001399
00001327
00001248

M8

00001209
00001181
00001176

00001954
00001454
00001433

“8

00000734
00001447
00001340
00001307

82.

time
(sec.)

00010.21
00010.18
00010.19
00010.17
00010.20
00010.17

00010.05
00010211
00010.15
00010.12

00010.23
00010.25
00010.23
00010.00

00010.09
00010.19
00010.17
00010.08
00010.00

00009.95
00009.89
00009.90

00009.80
00009.76
00009.91

00010.08
00010.01
00009.96
00009.92

Ca

00002138
00002135
00002121

Ca

00001884
00002311
00002145
00002221

2907A-4
Ca

00001527
00002108
00001714
00001762
00001425

2769-4
Ca

00001577
00002507
00003612
00003235
00002597
00001821
00001841

2774-4B
Ca

00003026
00003022
00003076
00003133
00003151

00002884
00002953
00002950

Zn

00000025
00000024
00000016

Fe

00000192
00000236
00000237
00000224

Fe

00000106
00000144
00000141
00000200
00000067

Fe

00000180
00000169
00000021
00000020
00000006
00000120
00000079

Fe

00000099
00000084
00000091
00000090
00000098

00000173
00000176
00000135

M8

00001528
00001505
00001318

M8

00001086
00001161
00001323
00001508

M8

00000885
00001138
00000854
00000741
00000921

M8

00001260
00001209
00000037
00000051
00000048
00001363
00003170

M8

00001571
00001436
00001620
00001620
00001612

00001343
00001397
00001407

83.

time
(sec.)

00010.02
00010.00
00009.97

00009.94
00009.93
00009.98
00009.99

00010.19
00010.19
00010.21
00010.18
00010.13

00009.85
00009.85
00010.04
00009.93
00009.90
00009.89
00009.95

00009.84
00009.87
00009.87
00009.92
00010.02

00009.92
00009.89
00009.85

Ca

00002939
00002958

Ca
00003137
00003046
00002260
2856-4

Ca
00002542
00002519
00002519
27610-4

Ca
00002461
00002801
00002752
00002767
00002690
00002573

Ca
00002804
00002815
00002315
00002771

Ca
00002768

00002895
00002475

Mn

00000024
00000036

Zn

00000025
00000022
00000026

Fe

00000208
00000203
00000176

Fe

00000065
00000079
00000064

00000090
00000073
00000071

Mb

00000004
00000010
00000019
00000021

Zn
00000026

00000025
00000024

M8

00001270
00001308

M8

00001421
00001383
00001285

M8

00000818
00000866
00000857

M8

00001407
00001625
00001605

00001642
00001666
00001554

M8

00001670
00001589
00001374
00001562

M8

00001727
00001630
00001538

84.

time
(sec.)

00010.00
00009.99

00009.85
00009.86
00009.91

00010.22
00010.06
00010.04.

00009.99
00010.01
00009.99

00010.02
00010.00
00009.92

00010.01
00010.02
00010.06
00010.07

00010.16
00010.05
00010.02