Petrology of the Rockport Quarry Limestone (Middle Devonian Traverse Group) Alpena, Presque Isle and Montmorency Counties, Michigan

Home , Bell Shale, Ferron Point Formation, Squaw Bay Limestone, Traverse Group

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Master's Theses Graduate College

12-1976

Charles Willard Cookman

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This Masters Thesis-Open Access is brought to you for free and open access by the Graduate College at ScholarWorks at WMU. It has been accepted for inclusion in Master's Theses by an authorized administrator of ScholarWorks at WMU. For more information, please contact [email protected]. PETROLOGY OF THE ROCKPORT QUARRY LIMESTONE (MIDDLE DEVONIAN TRAVERSE GROUP) ALPENA, PRESQUE ISLE AND MONTMORENCY COUNTIES, MICHIGAN

Charles Willard Cookman

A Thesis Submitted to the Faculty of the Graduate College in partial fulfillment of the Degree of the Master of Science

Western Michigan University Kalamazoo, Michigan December 19 76

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

The basal unit of the dominantly carbonate Traverse

Group, the Bell Shale, is gradationally overlain by the Rock-

port Quarry Limestone which has a thickness of approximately

14 m. The Rockport Quarry Limestone is composed of a dark

unrestricted marine subtidal organic-mud packstone facies,

comprised of an algal-mat-bearing coral packstone subfacies

and a shallower water crinoid-bryozoan grainstone subfacies;

a shoal-forming stromatoporoid biolithite facies; and a la-

goonal micrite facies comprised of a subtidal dense subfacies

containing gastropods, ostracods, and calcispheres, and an

intertidal to supratidal fenestral subfacies. The local fa

cies tract reconstructed for the Rockport Quarry Limestone is

interpreted to be analogous to the subtidal facies relation

ships present today in and around Rodriguez Key and within the

intertidal to supratidal environments at Andros Island and

Shark Bay, Australia. At Rockport Quarry and Grand Lake,

basal Rockport Quarry strata are comprised of extensive bio-

lithites (3 x 1000 m in cross section) composed of laminate

to tabulate stromatoporoid sheets interlaminated with subordi

nate organic-mud packstone. Higher in the section at Rockport

Quarry, the stromatoporoid biolithite facies is capped locally

by a subtidal back-shoal biolithite-micrite transition facies

containing what is thought to be the first recorded occurrence

of calcareous algae in the Middle Devonian of Michigan.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iii

Insoluble residues of the Bell Shale and organic-mud

packstones from the Rockport Quarry Limestone are mineralogi-

cally similar, but the residues from the Rockport Quarry Lime

stone are darker due to disseminated pyrite and hydrocarbons.

The dominant hydrocarbon grain type, 4 micron brown "micro

spheres," are inferred to be the fossil unicell remnants of

ancient subtidal algal mats.

Diagenetic phenomenon observed within the Rockport Quarry

Limestone indicate early marine cementation, neomorphism, so

lution and compaction, followed by later local void formation

and dolomitization. Extensive dolomite at Ocqueoc Falls pro

bably reflects dolomitization along a local fracture system.

Twenty-two taxa were encountered that were previously

unrecorded in the literature for Rockport Quarry including:

calcareous algae, cephalopod conchs, and trilobite fragments.

Three families of stromatoporoids were differentiated.

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MASTERS THESIS M-9 30 7

COOKMAN, Charles Willard PETROLOGY OF THE ROCKPORT QUARRY LIMESTONE (MIDDLE DEVONIAN TRAVERSE GROUP) ALPENA, PRESQUE ISLE AND MONTMORENCY COUNTIES, MICHIGAN.

Western Michigan University, M.S., 1976 Geology

Xerox University Microfilms, Ann Arbor, Michigan 48106

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS

It is a pleasure to acknowledge the advice and encour

agement of my research advisor, Dr. W. David Kuenzi. Dr.

Kuenzi introduced me to the problems of the Traverse Group

of the northern lower peninsula of Michigan and suggested the

study of the Rockport Quarry Limestone. I also thank Drs. Wm

B. Harrison and W. T. Straw for providing comments and criti

cism of the manuscript. Thanks are also expressed to Mr.

Wm. Mantek of Consumers Power Co., Jackson, Michigan, and Mr.

Irvin Kuehner of the Geological Survey Division of the Michi

gan Department of Natural Resources who furnished well log

data from the study area.

The study was made possible by support from the Graduate

Student Research Fund at Western Michigan University. Thanks

are expressed to Dr. Lloyd J. Schmaltz and the Geology De

partment at Western Michigan University for providing the in

tellectual training and equipment necessary to carry out the

study. Thanks are also expressed to Frank Allen and Lynn

Toohey of the Western Michigan University Libraries who pro

vided vital assistance in acquiring the research literature

required.

I am grateful to Mari Harrington for assistance in typin

of the manuscript, and Judy Robinson for processing of photo

graphs .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

INTRODUCTION ...... 1

Previous Investigations ...... 4

Methodology ...... 6

Terminology ...... 7

Petrography ...... 8

X-Ray Analysis and Other T e s t s ...... 11

FACIES ...... 17

General Statement ...... 17

Micrite Facies ...... - ...... 19

Outcrop Description ...... 19

Petrography...... 21

Dense Micrite Subfacies ...... 23

Fenestral Subfacies ...... 25

Relationships Between Subfacies of the Micrite F a c i e s ...... 28

Interpretation of the Micrite Facies ...... 29

Organic-Mcd Packstone Facies ...... 31

Outcrop Description ...... 31

Composition of the Dark Fraction ...... 35

Petrography...... 3 7

Coral Packstone Subfacies ...... 40

Crinoid-Bryozoan Grainstone Subfacies .... 43

Interpretation of the PackstoneFacies ...... 47

Stromatoporoid Biolithite Facies ...... 52

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Outcrop Description ...... 52

Petrography...... 54

Interpretation of the Stromatoporoid Biolithite F a c i e s ...... 57

Biolithite-Micrite Transition Facies ...... 58

Outcrop Petrology ...... 58

Petrography...... 59

Interpretation of the Biolithite-Micrite Transi tion F a c i e s ...... 60

Shale F a c i e s ...... 61

Subsurface Distribution of Facies ...... 63

Depositional History of the Rockport Quarry Lime stone ...... 66

Diagenesis...... 71

Solution and Compaction ...... 71

C r a c k i n g ...... 73

Cementation...... 75

Dolomitization ...... 77

Neomorphism...... 80

Diagenetic History ...... 82

PALEONTOLOGY ...... 84

CONCLUSIONS...... 101

APPENDIX 1— MEASURED SECTIONS ...... 104

APPENDIX 2— LABORATORY METHODS ...... 140

REFERENCES CITED ...... 142

PLATES ...... 148

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1. Index naps within the lower peninsula of Michigan ...... 2

2. Subcrop pattern within the study area ...... 3

3. Composition of calcite versus interplanar spacing of d(100) ...... 22

4. Diffractogram of packstone ...... 13

5. Diffractogram of insoluble residue from pack stone ...... 14

6. Distribution of facies along the outcrop belt . 20

7. Microstructure of the subtidal algal mat from the 3ahamas 3 8

8. Plot of the modal abundance of sparry calcite cement versus dark organic-mud matrix ...... 39

9. Schematic interpretation of the facies ...... 49

10. Inferred facies relationships ...... 62

11. Index map of Rodriguez B a n k ...... 70

12. Facies mosaic model ...... 72

TABLES:

1. Modal analyses of rocks from themicrite facies. 9

2. Modal analyses of non-micriticrocks ...... 10

3. Facies within the study a r e a ...... 18

4. Characteristics of rocks from the micrite fa cies ...... 30

5. Wells in Alpena, Presque Isle, and Montmorency Counties which have mechanical logs of the Rock port Quarry Limestone ...... 65

6. Diagenetic events ...... 76

7. Taxa within the Rockport Quarry Limestone . . . 85

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATES:

1. Outcrop expression at Rockport Quarry ...... 148

2. Outcrop expression at Rockport Quarry ...... 149

3. Outcrop expression at Rockport Quarry and Warren Creek ...... 150

4. Outcrop expression at Grand L a k e ...... 151

5. Outcrop expression at Ocqueoc Falls ...... 152

6. Outcrop expression at Black L a k e ...... 153

7. Calcispheres, Favosites, and Heterophrentis at Rockport Quarry ...... 154

8. Photomicrographs of rocks from the micrite f a c i e s ...... 156

9. Macrofossils from the organic-mud packstone facies at Rockport Quarry ...... 158

10. Fossils in the organic-mud packstone facies at Rockport Quarry ...... 159

11. Stromatoporoids at Rockport Quarry ...... 161

12. Fossils from the organic-mud bearing facies . . 162

13. Photomicrographs of the organic m u d ...... 164

14. Calcareous algae ...... 166

15. Outcrop expression of the stromatoporoid-biolithite facies ...... 167

16. Dolomite ...... 168

17. Macrofauna ...... 170

18. Topographic expression and sampling locations for Measured Sections 1-8 in pocket

19. Topographic Topographic expressionexpression andand samplingsampling locationslocations for Measured Sections 9-14 ...... in pocket

with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION

The Rockport Quarry Limestone crops out along a north

west-trending belt in the Lower Peninsula of Michigan where

it represents one of eleven formations comprising the Middle

Devonian Traverse Group (Figs. 1, 2). The Rockport Quarry

Limestone gradationally overlies the Bell Shale, which is the

basal formation of the Traverse Group, and is unconformably

overlain by the Ferron Point Formation (Ehlers and Kesling,

19 70). Major exposures of the Rockport Quarry Limestone in

Alpena and Presque Isle Counties occur at Rockport Quarry,

Grand Lake, Ocqueoc Falls, and Black Lake (Fig. 1; Pis. 1-6).

The formation can be traced in the subsurface from the outcrop

belt southwestward into the Michigan Basin (Figs. 1, 2). Pre

vious investigations involving the Rockport Quarry Limestone

have been concerned mainly with taxonomic paleontology and

general stratigraphy (Ehlers and Stumm, 196 7; Ver Weibe, 1926;

Warthin and Cooper, 1935). Intraformational facies variations

in the Rockport Quarry Limestone, however, have not been pre

viously investigated.

Examination of the Rockport Quarry Limestone over an area

of 4000 km^ in Alpena and Presque Isle Counties (Figs. 1, 2)

indicates that the formation is comprised of a mosaic of in-

tertonguing laterally contemporaneous shallow subtidal to su

pratidal carbonate platform facies. Facies interpretation has

been enhanced by detailed petrologic studies which have re-

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84°

84° ■45°

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Figure 1. Index maps: A, location of study area within the lower peninsula of Michigan; 3, sampling locations of the Rockport Quarry Limestone (crosses, measured section numbers are underlined) in Alpena and Presque Isle Counties (Appen dix 1). Major exposures occur at Rockport Quarry, Grand Lake, Ocqueoc Falls, and Black Lake. The location of the boreholes which produced the subsurface logs examined for this study are shown by the numbered dots (Table 4).

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Figure 2. Subcrop pattern of Paleozoic strata beneath glacial drift in Alpena, Presque Isle, and Montmorency Counties (after Ehlers and Kesling, 1970; Martin, 1957). Middle Devonian Traverse Group shown in white, except for the Rock port Quarry Limestone shown in black, pre-Traverse Devonian in vertical lines, and post-Traverse Devonian and Missis- sippian in horizontal lines. Key to stratigraphic units: Ddr, Detroit River Group; Ddd, Dundee Limestone; Drc, Rogers City Limestone; Dbs, Bell Shale; Drq, Rockport Quarry Lime stone; Dfp, Ferron Point Formation; Dgl, Lower Genshaw For mation; Dgk, Killians Member-Genshaw Formation; Dgu, Upper Genshaw Formation; Dnc, Newton Creek Limestone; Dal, Alpena Limestone; Dfm, Four Mile Dam Formation; Dnp, Norway Point Formation; Dpf, Potter Farm Formation; Dtb, Thunder Bay Limestone; Dsb, Squaw Bay Limestone; M-Da, Antrim Shale; Mb, Berea-Bedform Formation; Me, Coldwater Shale.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vealed the presence of locally abundant calcareous algae here

tofore unrecorded from the Devonian of Michigan and black, hy

drocarbon microspheres (remnants of subtidal algal mats) pre

viously unknown from the ancient rock record. It is hoped

that the local facies model developed for the Rockport Quarry

Limestone will be useful elsewhere as a general model to be

considered in the interpretation of shallow water Middle De

vonian carbonate rock sequences.

Previous Investigations

Strata now known as the Rockport Quarry Limestone were

first described by Rominger (1876), and later by Grabau (1902,

p. 184-191) who referred to these strata as the "lower beds of

the Long Lake shales and limestones of the lower Traverse se

ries." The lower beds were biostratigraphically and litholo-

gically correlated by Grabau (1902) with Romingers "Middle

Island" strata exposed at Grand Lake (PI. 4) and at the "bot

tomless sink" southwest of Ferron Point on Lake Huron (Fig. 1,

Loc. 33-9-36) .

From Romingers descriptions (Rominger, 1876) it is cer

tain that he visited the type locality of the Rockport Quarry

Limestone near the intersection of the Presque Isle-Alpena

County line and the Lake Huron shoreline (Figs. 1, 2) at least

37 years before quarrying began. At that time there existed

a natural 4.8 meter high bluff approximately one kilometer in

land from the Lake Huron shore. From the top of the bluff,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the ground surface rose inland for about 200 meters to a sec

ond terrace (Smith, 1916). By 1916, quarrying at Rockport

had begun (Smith, 1916, p. 172-175), and the harbor and docks

had been emplaced to facilitate quarrying operations. It

seems correct to assume that the names "Rockport" and "Rock

port Limestone" originated at that time (Smith, 1916, p. 172-

175). The first published field report using the name "Rock

port Quarry Limestone" was that of Warthin and Cooper (1943,

p. 580-581) who had earlier accepted the name (Cooper and War-

thin, 19 41) in an attempt to clarify nomenclature. In their

report, Warthin and Cooper (1943) were the first to consider

the strata at Ocqueoc Falls (PI. 5) and Black Lake (PI. 6) as

being equivalent to the strata at Rockport Quarry (Pis. 1, 2;

Pi. 3, Fig. A). The Rockport Quarry strata at Black Lake was

first described by Kelly and Smith (1947, p. 449) from expo

sures in the already abandoned Onaway Company Limestone Quarry

(PI. 6). Rocks described by Kelly and Smith (1947, p. 451)

along Black River are no longer visible due to flooding caused

by construction of a dam downstream of the outcrop location.

Work on the Rockport Quarry Limestone in the subsurface

has been limited. In Alpena and Presque Isle Counties (Fig.

1), the Rockport is stratigraphically equivalent to Grabau1s

unit number 14 from the "Churchill Well" (Grabau, 1901; Ver

Weibe, 1926; Ehlers and Kesling, 1970). Down dip to the south

west, the Rockport is traceable with difficulty because of in

creasing carbonate content in the overlying shales of the Fer-

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ron Point Formation. In the subsurface to the northwest, the

Rockport is highly fossiliferous (Hake and Maebius, 1937).

Near the center of the Michigan Basin, the Rockport be

comes more shaley and is interbedded with shales lithologi-

cally similar to the Bell Shale. Here the Rockport Quarry

Limestone contains chert which becomes darker to the west

(Jodry, 1957).

According to Jodry (1957), a north-scuuh trending barrier

was present in western Michigan between Range 9 West and Range

12 West during deposition of the Rockport Quarry Limestone.

The barrier is inferred to have followed a north-south line

approximately through the present shared boundary between Ne-

wago and Mecosta Counties. Evidence for the barrier includes

overlap sequences (Jodry, 1957; Hake and Maebius, 1937; New-

combe, 19 30), and the presence of evaporites in the Rockport

Quarry Limestone interpreted to have formed in a lagoon lo

cated to the west of the barrier (Jodry, 1957).

Methodology

Sixteen days were spent in the field between November,

1974 and May, 1976 measuring sections with Jacobs' staff, col

lecting oriented samples, and describing and photographing the

Rockport Quarry Limestone. A total of 14 sections (Appendix

1, Pis. 18, 19) were measured at 6 locations (Fig. 1) in Al

pena and Presque Isle Counties (Appendix 1).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7

Terminology

The definitions of facies and subfacies used herein fol

low those of Weller (1960) cited in the glossary published by

the American Geological Institute. Weller (1960) defines a

facies as "a stratigrapnic body as distinguished from other

bodies of different appearance or composition," and a sub

facies as a "subdivision of a broadly defined facies."

The combined terminology of Dunham (1965) and Folk (1959,

1962, 1965, 1974) is used to describe the facies and subfacies

comprising the Rockport Quarry Limestone. The Folk terms are

highly descriptive for micrites and provide both a composi

tional and a textural description for each rock. However,

rocks classified in the field as packstones (Dunham, 1965)

are composed of grain-supported skeletal grains (averaging

one millimeter in size) enclosed in a matrix of hydrocarbon-

bearing amorphous debris (organic mud, p. 35). Such rocks do

not strictly fit the definition of packstone or poorly washed

grainstone as defined by Dunham (1965) because of the lack of

lime-mud matrix. As used in this report, organic-mud pack

stone contains greater than 10 percent organic-mud, poorly

washed organic-mud bearing grainstones contain 1 to 10 per

cent organic mud, and grainstones contain trace amounts of

organic mud. Modifiers indicating composition are incorpo

rated into each rock name. Two typical designations would be:

fine skeletal calcirudite: poorly-washed crinoid-bryozoan or

ganic-mud bearing grainstone; and coarse skeletal calcarenite:

coral organic-mud packstone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rock colors follow the Geological Society of America

standard rock color chart (Goddard et ad., 1970).

Petrography

Petrographic investigation of the Rockport Quarry Lime

stone was accomplished by examination of specimens collected

from the measured sections (Appendix 1; Pis. 18, 19). Repre

sentative thin sections from each measured section were point

counted (Tables 1, 2). An average of 300 points were counted

per slide. Samples were prepared according to normal thin-

section procedures. From the more compacted samples plexi

glass peels (Frank, 1965) were prepared to enhance grain defi

nition (Appendix 2). When peels were prepared from poorly

indurated samples, grains pulled off into the peel; when peels

were prepared on permeable surfaces, air bubbles commonly

formed. In several cases thin sections and peels were both

prepared from the same specimens in order to cross check iden

tifications .

Dolomite, in both peel and thin section, is easily de

tectable by its brownish color and rhombic crystal form. More

over, the relief of dolomite in a peel is typically depres-

sional because of its relatively high resistance to HCl. When

necessary, duplicate thin sections were produced so that stan

dard staining techniques for thin sections and hand specimens

(Dickinson, 1965; Appendix 2) could be employed to confirm the

existence of suspected trace amounts of dolomite. Duplicate

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. thin sections were produced to provide control whenever stain

ing was done, or in order to examine insoluble residues left

on thin section epoxy by 1.5 percent HC1 (DeMeijer, 1969).

Thin sections, prepared for staining and (or) for examination

of insoluble residues, were of normal or slightly less than

normal petrographic thickness (30 microns).

X-Ray Analysis and Other Tests

Thirty samples of packstone from the Rockport Quarry Lime

stone and one sample of the Bell Shale were crushed and subse

quently ground to fine powder for x-ray analysis using a No-

relco diffractometer (type 120-102-11) equipped with a range

goniometer. All samples were mixed with equal parts fluorite

and scanned between 27.5° and 30.5° to determine the position

of the calcite peak (Harrison, personal communication). The

largest calcite peak is uniformly present in all samples at a

O dA spacing of 3.02 corresponding to a magnesium weight percent

of 6.0 (Chave, 1952; Fig. 3).

The same 31 samples were then scanned between 3° and 50°

(Fig. 4). Moreover, six of the Rockport samples and the Bell

Shale sample were subsequently treated with 10 percent HC1 to

remove the carbonate and thereby produce an insoluble residue

for x-ray analysis (Fig. 5). Analysis of the resulting x-ray

patterns (Figs. 4, 5) obtained from the Rockport Quarry Lime

stone samples indicates that the packstones and the inter-

stromatoporoid rocks are composed dominantly of calcite; and

contain trace amounts of dolomite, pyrite, quartz, and musco-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12

2 .9 8

< Z UJ 3 .0 0 H

Su. o o ^ 3 02

3 .0 4

10 20 30

WEIGHT PER CEWT MgCQ3

Figure 3. Curve showing variation in magnesium content in calcite as a function of interplanar spacing d(100) (from Chave, 1952). Point A shows the d(100) in calcite from 30 samples of packstone from the Rockport Quarry Limestone which corresponds to a magnesium carbonate weight percent of about 6.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 DEGREES 2 9

c.q

50 40 30

D EG R EES 2 6

Figure 4. Diffractogram of sample RQ3-1 (unoriented mount) from interstromatoporoid packstone of the biolithite facies at Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Mea sured Section 1, Unit 1; Table 2, number 13). Key to peaks c, calcite; q, quartz. Cu K«, radiation, 500 cps. , scanning speed 1° 20 per minute. Chart speed 30" per hour., 30 kv., 20 m a .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 10 D E G R E E S 2 6

50 4 0 3 0

D EG R EES 2©

Figure 5. Diffractogram of the insoluble residue of sample RQ3-1 from the interstromatoporoid packstone of the bioli thite facies at Rockport Quarry after 10 percent HC1 treatment (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 1, Unit 1; Table 2, number 13). Key to peaks: q, quartz; m, muscovite-illite; and p, pyrite. Cu K«- radiation 500 cps. , scan ning speed 1° 20 per minute., chart speed 30" per hour, 30 k v ., 20 m a .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15

tc-1 1 li ce in order of fccrcasir.^ relative abundance. A set

of u:::jer.tifiable unlabeled peaks is also present (Figs. 4,

When the six Rockport buarry Limestone samples were

treated with 10 percent HCi tc produce an insoluble residue

for x-ray analysis, a dark colloidal substance, similar in ap

pearance to tanic acid, was observed floating on the liquid

surface following the acid reaction, and a distinct hydrocar

bon odor was noted. One of the six Rockport samples was then

immersed in a solvent consisting of 10 percent methanol and 90

percent benzene and agitated every few hours in order to lib

erate any organic material present (Stevens et ad., 1956).

The solution turned bright orange after 24 hours. No darken

ing was observed after 4 8 hours. When the solvent was evapo

rated off in a watch glass at room temperature, the resulting

concentrate was black in mass and yellow-orange when spread

thin. The texture of the concentrate was extremely sticky,

almost asphaltic. Again a distinct hydrocarbon odor was noted.

The hydrocarbon indications from the chemical tests in

dicate that the insoluble residue contains significant amounts

of hydrocarbon in addition to the mud-sized pyrite, quartz,

and muscovite-illite detected by x-ray. This hydrocarbon ma

terial may be the source of the unidentifiable unlabeled x-ray

diffraction peaks noted above. Because of the unknown chemi

cal nature of the hydrocarbon compounds and the extremely fine

grain size of the silt and clay in the insoluble residues, an

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission 16

estimate could not be made of the relative abundance of hydro

carbon material versus terrigenous detritus.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. FACIES

General Statement

The maximum exposed thickness of the Rockport Quarry

Limestone observed in the study area is 15 meters which oc

curs at Black Lake (Fig. 1; Pis. 6, 19). All exposed sec

tions of the Rockport Quarry Limestone represent partial sec

tions resulting from erratic exposure from beneath glacial

drift. Thicknesses of the Rockport Quarry Limestone reported

from the subsurface commonly range from 15 to 18 meters.

Previous workers (Warthin and Cooper, 1943; Kelly and

Smith, 1947; Ehlers and Kesling, 1970) recognized two facies

in the Rockport Quarry Limestone based on "mud" content: 1)

the "argillaceous" or "bituminous" facies (equivalent to the

organic-mud packstone facies, the stromatoporoid biolithite

facies, and the two transitional facies of this study); and

2) the micrite facies (Table 3).

In this study three main facies are recognized: 1) the

micrite facies; 2) the organic-mud packstone facies; and 3)

the stromatoporoid biolithite facies (Table 3). The micrite

facies and the organic-mud packstone facies have each been

subdivided into two subfacies (Table 3). The micrite facies

has been divided into the fenestral subfacies and the dense

subfacies; and the organic-mud packstone facies into the cri-

noid-bryozoan grainstone subfacies and the coral packstone

subfacies (Table 3). In addition, a fourth facies, grada-

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Table 3. Facies comprising the Rockport Quarry Limestone in

the study area

Previous workers (Warthin and Cooper, 194 3; This Study Kelly and Smith, 1947; Ehlers and Kesling, 1970)

1) Micrite Facies 1) Micrite Facies

a. Dense Subfacies

b. Fenestral Subfacies

2) Argillaceous or 2) Organic-Mud Packstone Facies

Bituminous Facies a. Crinoid-Bryozoan

Grainstone Subfacies

b. Coral Packstone Subfacies

3) Stromatoporoid Biolithite

Facies

4) Biolithite-Micrite

Transition Facies

5) Bell-Rockport Transition

Facies

tional between the stromatoporoid biolithite and the micrite

facies, commonly displays laminar stromatoporoids interbedded

with micrite and is termed the biolithite-micrite transition

facies. Finally the facies transitional between the Bell

Shale and the biolithite facies, the basal facies of the Rock

port Quarry Limestone at Rockport Quarry (Fig. 1, Loc. 32-9-6)

has been designated the Bell-Rockport transition facies. The

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vertical and lateral distribution of facies along the outcrop

belt is summarized in Figure 6 (See Pis. 18 and 19) .

Gradational contact relationships between the facies and

subfacies are observed only at Rockport Quarry (Fig. 1, Loc.

32-9-6; Appendix 1, Measured Sections 1-8; Pi. 18). Here the

upper biolithite facies is gradational into the biolithite-

micrite transition facies above and the organic-mud packstone

facies below; and the biolithite-micrite transition facies is

gradational between the biolithite facies below and the mic

rite facies above. Furthermore, within the organic-mud pack

stone facies interlaminated and interlensed coral packstones

occur within the crinoid-bryozoan grainstone subfacies, and

interlaminated and interlensed crinoid-bryozoan packstones and

gr-ainstones occur within the coral packstone subfacies. The

biolithite-micrite transition facies and the coral packstone

subfacies are not present in the other outcrops of the Rock

port Quarry Limestone, and gradational contacts between other

facies are not observed.

Micrite Facies

Outcrop Description

The thickness of the micrite facies in the Rockport Quar

ry Limestone along the outcrop belt ranges from 15 m, or 99

percent of the exposed Rockport section at Black Lake (Pis.

6, 19); to 3 m, or about 30 percent of the exposed Rockport

section at Rockport Quarry (Pi. 1, Fig. A), where it occurs at

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* ^ •*» • m j* vfc

2 5 Km BR S c a le

Micrite (M) Facies Organic-Mud Packstone Facies Coral Packstone (CP) Subfacies Biolithite-Micrite Transition (T) Facies Bryozoan Packstone (BP) Subfacies

Biolithite (B) Facies Bell-Rockport Transition (BR) Facies

Covered Dolomitized

Figure 6. Distribution of facies within the Rockport Quarry Limestone along the outcrop belt in Alpena and Presque Isle Counties. Key to location of sections: A, 31ack Lake (Fig. 1, Loc. 35-2-7); B, Ocqueoc Falls (Fig. 1, Loc. 35-3-22); C, Grand Lake (Fig. 1, Loc. 34-8-31); D, Rockport Quarry (Fig. 1, Loc. 32-9-6). See Appendix 1 and Plates 18 and 19 (Measured Sections 1-8, 10-11, 13-14).

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the top of the section (Fig. 6; Pi. 18). The micrite facies

is not exposed at Ocqueoc Falls or in the Grand Lake area.

At Black Lake (Fig. 6) the contact of the micrite facies

with the organic-mud packstone facies is abrupt (PI. 6; Ap

pendix 1, Measured Section 14); however, at Rockport Quarry

the micrite facies is separated from the organic-mud packstone

facies below by a 30 cm thick stromatoporoid biolithite facies

and by a 60 cm thick biolithite-micrite transition facies con

taining laminar stromatoporoids (Fig. 6). The color of the

transitional strata gradually changes from the greyish-orange

(10 YR 7/2) of the biolithite facies to the pale yellowish-

brown (10 YR 6/2) of the sparse biomicrite above (Pis. 1, 18;

Appendix 1, Measured Sections 2-8). At Rockport Quarry (Figs.

1, 6), the micrite facies is typically pale yellowish-brown

(10 YR 6/2) near the base but grades upward into a light grey

(N7) 20 to 30 cm above the base. At Black Lake the colors

are usually more yellow than grey.

Stratification within the micrite facies is dominantly

horizontal and parallel, and ranges in thickness from 0.5 to

10 cm; however, local small disconformities are also present.

Stylolites occur subparallel to bedding and successive stylo-

lites are spaced at distances that range from 0.5 cm to 80

cm. Outcrops of the micrite facies are typically fractured

and display a blocky character (PI. 1, Fig. A; PI. 6).

Petrography

Microscopically, the micrite sequences at Rockport Quarry

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and Black Lake are composed of micrite, sparse biomicrite,

fenestral rocks composed of both pelsparite and pelmicrite,

and less abundant intrasparite and intramicrite. The micri-

tic material comprising the micritic matrix, pellets, and in

traclasts within these rocks consists of equant to elongate

crystals less than 6 microns in diameter; however, locally 25

to 75 percent of the material has been neomorphosed to 6 to

20 micron microspar. The microspar is usually elongate or

loafish as described by Folk (1965), and as shown on Plate 7

(Figs. A, B) . Crystal boundaries are usually straight. Ag

gregates of micrite and microspar commonly comprise pelloids

(Bathurst, 1975) and intraclasts (Pi. 8, Figs. B, C, F). Skel

etal allochems, in the micrite sequences, are present in trace

amounts and include: ostracods (Pi. 8, Fig. A), ca1cispheres

(PI. 7, Figs. A, B), ramose and laminar stromatoporoids, and

ramose Favosites.

Fine to medium crystalline pore-filling bladed sparry

calcite, when it occurs, commonly lines the interiors of os-

tracod shells and corallites, and forms optically continuous

syntaxial overgrowths with the skeletal walls (PI. 7, Fig. D).

Equant crystals of sparry calcite, ranging from 8 to 3000 mi

crons, often occur as patches in the micrite (PI. 7, Figs.

A, B) and commonly delineate fenestral fabrics (PI. 8, Figs.

B, D, E, F).

Variation in the form of the fenestrae within the micrite

sequences allows delineation of two subfacies: 1) a dense

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micrite subfacies lacking horizontally-oriented fenestrae,

and 2) a fenestral micrite subfacies containing horizontally-

oriented fenestrae. Sparry calcite-filled vertically-oriented

fenestrae in the form of vugs, tubes (tubular fenestrae), and

cracks occur in both the dense and fenestral subfacies. Some

vertically-oriented fenestrae with dark walls, as well as os-

tracods and corallites, exhibit geopetal fillings.

Dense Micrite Subfacies. Micritic rocks were assigned

to the dense subfacies when they showed: 1) high opacity,

2) low to no single-grain distinction (Pi. 8, Fig. A), and

3) a lack of horizontally-oriented fenestrae (Table 1, num

bers 6-11, 18, 19, 25, 27, 28, 30, 37, 45-47, 51). Generally,

the micritic rocks assigned to the dense micrite subfacies are

composed of tightly packed pelloids with little (less than 20

percent) or no very finely crystalline sparry calcite cement.

In some rocks, however, pelmicrites and pelsparites occasion

ally occur interlaminated. Pelloids generally account for 95

to 98 percent of the non-authigenic components within the

dense micrite subfacies. Locally, the micritic rocks contain

a limited variety of fossils and are sparse biopelmicrites

(PI. 8, Fig. A ) .

Organic mud, locally present in the micrite facies, is

restricted to the dense subfacies. Brown microspheres inter

preted to represent remnants of subtidal algal mats (p. 95)

are present in two samples at Black Lake (Table 1, numbers 8,

19). In both cases, the organic mud-bearing micrite occurs

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in stratigraphic contact with micrite containing vertical fe

nestrae .

Faunal diversity within the dense subfacies at Black

Lake is low. Here, the dense subfacies contains only ostra-

cods and calcispheres which comprise up to 2 percent of the

rock (Table 1). At Rockport Quarry (Fig. 6) unabraided os-

tracods, stromatoporoids and Favosites occur only in trace

amounts within the dense subfacies. Some Favosites coral-

lites occur as accumulations of disjointed debris (PI. 7,

Fig. C ) ; however, most are whole. Ramose forms of Favosites

and idiostromatids are found rarely and are usually only

slightly fragmented. At both Rockport Quarry and Black Lake,

the beds with the most diversified fauna lack tubular fene

strae .

Intraclasts in the dense micrite subfacies are rare; how

ever, accumulations of shell debris are locally present in

high percentages as lenses averaging 2 cm thick and 2 m long.

The skeletal fragments are unidentifiable because of replace

ment of shell material by single crystals of finely crystal

line neomorphic sparry calcite. They probably represent os-

tracod and brachiopod fragments.

In conclusion, the lack of fragmentation of the larger

fossils, the low faunal diversity characterized by an ostra-

cod-calcisphere association, and the lack of horizontal fene

strae and intraclasts, strongly suggests that the dense mic

rite subfacies accumulated in a restricted low-energy sub-

tidal environment.

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Fenestral Subfacies. Rocks of the fenestral subfacies

are composed of generally crudely laminated micrites and pel-

sparites (and less commonly intrasparites and intramicrites}

that commonly contain up to 35 percent fine to medium crystal

line pore-filling sparry calcite (Table 1, numbers 3, 4, 5,

12-17, 20-24, 26, 29, 31-36, 38-44, 48-50). The sparry cal

cite fills voids which in general are elongated in a horizon

tal direction. The lamination may be distinguished by verti

cal variation in grain size or by variation in the percentage

of horizontally-oriented voids filled with sparry calcite.

Vertical variation in texture on the order of 1.0 to 10 cm

produces fenestral micrites composed of interlaminated pel-

sparite and pelmicrite enclosing sparry calcite filled fene

strae (PI. 8, Figs. B, D, E, F; Table 1, numbers 3-5, 12-16,

20-24, 26, 34, 38-40, 42, 45, 48-50). Locally, pelloids with

in the pelmicrites become indistinguishable from micrite ma

trix, yielding a dense micrite with fenestrae marked by hori

zontal accumulations of sparry calcite (Table 1, numbers 17,

29, 31-33, 35, 36, 41, 43, 44).

Grains comprise up to 85 percent of the rocks comprising

the fenestral subfacies. Skeletal grains in the fenestral

subfacies include: ostracods, rare calcispheres, and skeletal

fragments. The fragments include laminar and ramose stroma-

toporoids, Favosites, ostracods, brachiopods, unidentifiable

shell fragments which are commonly replaced by single or ag

gregate crystals of finely crystalline sparry calcite, and

neomorphosed gastropods.

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Non-skeletal grains comprising rocks of the fenestral

subfacies include: pelloids which compose from 5 to 95 per

cent of the rocks and average about 85 percent, and intra

clasts which range in abundance from less than 1 percent to

as much as 80 percent in some intrasparites. Pelloids, aver

aging 50 microns in size, occur in 90 percent of the samples

collected from the fenestral subfacies and usually comprise

greater than 60 percent of the rocks in which they occur (Ta

ble 1). Intraclastic layers, composed of clasts ranging in

diameter from 0.15 mm to 2 cm, account for about 10 percent

(at most) of the micrite facies exposed at Black Lake and

Rockport Quarry. Locally, the intraclastic layers, which

range up to 15 cm in thickness, are disconformable with layers

below and locally bury a scoured erosion surface with as much

as 10 cm of local relief over a horizontal distance of 5 m.

Disoriented ramose and laminoid stromatoporoids are usually

associated with the intraclasts.

Maximum concentrations of intraclasts in modern carbonate

environments on Andros Island (Bahamas) occur within the su-

pratidal environment (Shinn, Lloyd, and Ginsburg, 1969); how

ever, local accumulations of smaller intraclasts (derived from

the supratidal zone) do occur within the intertidal and sub-

tidal zones. Maximum concentrations of intraclasts within Ho-

locene sediments at Shark Bay, Australia (Logan et a^L. , 1974)

have a similar occurrence. Thus, the intraclastic rocks of

the fenestral subfacies probably also formed within the inter

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tidal to supratidal zones. That the intrasparite beds were

associated with stress conditions is indicated by the scoured

erosion surfaces at their bases and by their low faunal abun

dance and diversity.

The horizontal fenestrae, which characterize the fene

stral subfacies can be subdivided into fine laminoid and pus

tular fabrics. By definition (Read, 1973), a fine laminoid

fenestral fabric consists of subparallel closely spaced flat

tened sparry calcite-filled voids (fenestrae) up to 1 mm high

(Pi. 8, Fig. D). A pustular fenestral fabric consists of ir

regular to subspherical equidimensional fenestrae from 1 to 5

mm in size (PI. 8, Fig. E) with some voids flattened horizon

tally (Read, 1973a, 1973b). The elongate morphology of the

intraclasts dictates that in their packing non-horizontal

voids will be created which could be filled with sparry cal

cite to form a pustular fenestral fabric.

At Shark Bay, Australia, laminoid and pustular fenestral

fabrics form today where voids are created by decay of algal

deposits within the intertidal zone (Read, 1973a, 1973b; Logan

et al. , 1974). Similar fenestral fabrics in micrites from the

Devonian Pillara Formation of western Australia have also been

interpreted as being cryptalgal indicators of intertidal de

position (Read, 1973a, 1973b), and laminoid fabrics from Pa

leozoic rocks have generally been interpreted as cryptalgal

(Gebelein and Hoffman, 1973). Horizontal fenestral fabrics

within the fenestral subfacies of the micrite facies thus pro

bably also record cryptalgal intertidal sedimentation.

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In conclusion, the fenestral fabrics, intraclasts, and

low faunal diversity within the fenestral subfacies strongly

suggest that the subfacies records intertidal to supratidal

depositional environments.

Relationships Between Subfacies of the Micrite Facies.

The vertical sequence of generally gradational facies which

comprise the Rockport Quarry Limestone most probably record

laterally contemporaneous depositional environments. At

Rockport Quarry, the micrite facies gradationally caps the

biolithite-micrite transition facies. At Black Lake the con

tact of the micrite facies with the packstone facies below is

covered; however, locally organic-mud packstone layers, up to

8 cm in thickness, are interlaminated within the micrite fa

cies (Table 2a, samples 8, 15, 19). Micritic rocks at Black

Lake, displaying horizontal fenestrae and assigned to the fe

nestral subfacies, are commonly interlaminated with micritic

rocks assigned to the dense subfacies, suggesting cyclical

repetition of intertidal and subtidal conditions. However,

at Rockport, the micrite facies is composed predominantly of

laminoid fenestral rocks (90 percent) assigned to the fene

stral subfacies and interlaminated micritic rocks assigned to

the dense subfacies comprises only about 10 percent of the fa

cies. Thus intertidal deposition apparently prevailed at the

present locality of Rockport Quarry during deposition of the

micrite facies although subtidal and supratidal deposition

also occurred locally.

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Interpretation of the Micrite Facies

Pelletal muds and sands like those recorded by the rocks

of the micrite facies are typical of protected, low energy,

subtidal to supratidal depositional environments occurring on

carbonate platforms (Shinn, Lloyd, and Ginsburg, 1969; Read,

1973a, 1973b; Bathurst, 1975; Ehlers and Kesling, 1970).

Subtidal stress conditions are suggested for the dense

micrite subfacies by the calcispheres which are typical of

subtidal hypersaline environments (Rupp, 1967), ostracods

which are typical of polyhaline stress environments (Benson,

1956), and by the calcareous blue-green alga Renalcis (PI. 15,

Fig. F) which is typical of shallow subtidal areas of normal

salinity (Wray, 1967a, 1967b, 1971; Wray and Playford, 1970).

The dense micrite subfacies was probably deposited marginal

to a normal marine environment which is suggested by the local

inclusion of normal marine fossils, Heterophrentis and Favo

si tes .

Micritic rocks within the Rockport Quarry Limestone char

acterized by horizontal fenestral fabrics and limited faunal

abundance and diversity are interpreted to record deposition

in an intertidal environment. The horizontal fenestral fab

rics are similar to those developed in Holocene pelloidal in

tertidal sediments (Logan, 1974) and Devonian rocks from Aus

tralia (Read, 1973a, 1973b) and New York (Laporte, 1967) in

terpreted to have formed in the intertidal zone. These fab

rics are thought to record algal mats formed at various po-

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Table 4. Characteristics of rocks comprising the dense sub

facies and the fenestral subfacies of the micrite facies which

are inferred to record subtidal, intertidal, and supratidal

deposition

Dense Fenestral Subfacies Subfacies

Characteristics Subtidal Intertidal Supratidal

Pelloids ------— ------

Intraclasts ------

Micrite

Fenestrae Pustular Laminar Tubular

Ostracods

Calcispheres ------

Favosites

Heterophrentis

Synhoresis Cracks

sitions within the intertidal zone (Read, 1973a, 1973b). In

traclastic layers are interpreted to represent supratidal caps

or storm and current accumulations formed within the inter

tidal or subtidal zones. The characteristics of the rocks

comprising the micrite facies which are inferred to record

subtidal, intertidal, and supratidal deposition are summa

rized in Table 4.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Organic-Mud Packstone Facies

Outcrop Description

The exposed thickness of the organic-mud packstone facie

in the Rockport Quarry Limestone along the outcrop belt (Fig.

6; see ris. 13, 19) ranges from 2 m at Rockport Quarry (Pi. 1

Fig. B; Pi. 2, Fig. A) to 8 m at Ocqueoc Falls (PI. 5) and 11

m at Grand Lake (Pi. 4). The organic-mud packstone facies at

Rockport Quarry (PI. 1, Fig. B; Pi. 2, Fig. A), the type lo

cality of the Rockport Quarry Limestone, can be subdivided

into a lower darker (greyish orange, 10 YR 7/4) more fissile

unit and an upper lighter (light olive grey, 5 Y 6/1) more

massive unit (Ehler and Kesling, 19 70; Warthin and Cooper,

1943; Appendix 1, Measured Sections 1-6; Pi. 18). The lower

darker unit is predominantly composed of coral organic-mud

packstone and is here designated the coral packstone subfa

cies ; the upper lighter more massive unit, characterized by

crinoid-bryozoan organic-mud packstones and crinoid-bryozoan

organic-mud packstones and crinoid-bryozoan grainstones, is

designated the crinoid-bryozoan grainstone subfacies.

In the lower darker coral packstone subfacies, the or

ganic-mud packstone contains solitary rugose corals, usually

Heterophrentis, which commonly lie on bedding planes and are

considerably flattened parallel to them (Pi. 7, Figs. E, F ) .

Moreover, trace amounts of blue phosphatic fragments occur in

the organic-mud packstone and at one locality four arthrodire

plates were found (Pi. 9, Fig. A). Locally, the organic-mud

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packstone encloses light-colored lenses up to 60 cm long and

10 cm thick which are richer in bryozoan and echinoderm frag

ments, and in sparry calcite. These lenses, within the lower

coral packstone subfacies, are lithologically similar to the

crinoid-bryozoan organic-mud packstone and crinoid-bryozoan

grainstone that characterize the upper lighter more massive

crinoid-bryozoan grainstone subfacies of the organic-mud pack

stone facies (PI. 1, Fig. B; Pi. 2, Fig. A). Locally in Rock

port Quarry, a discontinuous layer of lighter crinoid-bryozoan

organic-mud packstone and crinoid-bryozoan grainstone (Pi. 2,

Fig. A; Appendix 1, Measured Section 5, Unit 2), about 45 cm

thick, overlies a 15 cm thick shale unit and forms the basal

layer of the organic-mud packstone facies. This discontinuous

layer is also included within the coral packstone subfacies.

Commonly the lenses and layers of lighter crinoid-bryo

zoan organic-mud packstone and crinoid-bryozoan grainstone

within the coral packstone subfacies contain both overturned

and in situ colonial corals (Hexagonaria, Spongophyllum, bul

bous Favosites), and hemispherical stromatoporoids. The stro-

matoporoids occur attached to harder substrates such as la

mellar stromatoporoids, colonial rugose corals (PI. 11, Fig.

A), crinoidal substrates, or cephalopods (PI. 12, Fig. C).

Other lenses are comprised of coral organic-mud packstone and

contain clumps of ramose branching Favosites all preferen

tially aligned in the horizontal plane.

In the upper lighter more massive crinoid-bryozoan grain-

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stone subfacies, lighter crinoid-bryozoan organic-mud pack

stone and crinoid-bryozoan grainstone layers and lenses are

interbedded with subordinate darker more fissile organic-mud

packstone which is lithologically identical to the organic-

mud packstone that predominates in the coral packstone subfa

cies below. The gradational contact of the lower coral pack

stone subfacies with the upper crinoid-bryozoan grainstone

subfacies at Rockport Quarry is arbitrarily placed at the base

of a crinoid grainstone layer (PI. 1, Fig. B; Pi. 2, Fig. A,

Table 2, number 21) which varies from 15 cm to 45 cm thick.

Where the crinoid grainstone layer is thickest, it contains

large colonial rugose corals which are usually overturned.

Lateral variation in the modal abundance of the crinoid detri

tus in the crinoid grainstone layer ranges from 15 to 3 4 per

cent. Other crinoid grainstone and crinoid organic-mud pack

stone layers occur in the crinoid-bryozoan subfacies but these

exhibit limited continuity (PI. 1, Fig. B; PI. 2, Fig. A) and

show a pinch and swell effect. In the more fissile organic-

mud packstone, which often occurs in the pinches, tabular bry-

czoan fragments and frequently other shell fragments often

show preferred orientation (Pi. 13, Figs. A, B; Pi. 17, Figs.

C, E, F ) .

The upper 30 cm of the upper crinoid-bryozoan grainstone

subfacies at Rockport Quarry is locally comprised of darker

fissile coral organic-mud packstone; however, elsewhere,

lighter more massive crinoid-bryozoan organic-mud packstone

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and poorly washed crinoid-bryozoan grainstone comprise the top

30 cm of the subfacies (PI. 1, Fig. B; Pi. 2, Fig. A ) .

Exposures of both subfacies in the quarry walls of Rock

port commonly exhibit surficial crusts of botryoidal aggre

gates of fine to very finely crystalline sparry calcite which

disguise the outcrop (PI. 1, Fig. B). Apparently this calcite

precipitate formed as the result of evaporation of carbonate-

bearing ground water which seeped out of the quarry walls.

Outcrops of the organic-mud packstone facies elsewhere

within the study area generally exhibit the more massive char

acter displayed by the crinoid-bryozoan grainstone subfacies

at Rockport Quarry (Fig. 6). Strata at Grand Lake (PI. 4,

Fig. B; Appendix 1, Measured Sections 10 and 11; PI. 19), con

taining abundant brachiopods and bryozoans, are somewhat yel

lower (brownish-grey, 5 YR 4/1) than the crinoid-bryozoan

grainstone subfacies at Rockport Quarry, and generally lack

the outcrop fissility displayed by the coral packstone subfa

cies at Rockport Quarry. However, packstones exposed in road-

cuts at 33-8-17 and 34-6-24 (Fig. 1; Appendix 1, Measured Sec

tions 9 and 12; PI. 19) commonly are darker (dusky yellowish

brown, 10 YR 2/2) in outcrop than others in the Grand Lake

area, and exhibit fissility and brecciation due to road con

struction (PI. 3, Fig. B ) .

Strata comprising the organic-mud packstone facies at

Ocqueoc Falls (Fig. 1, Loc. 35-3-22, PI. 19) are pale yel

lowish brown (10 YR 6/2) to light olive grey (5 Y 6/1), and

include crinoid-bryozoan packstones and grainstones which are

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extensively dolomitized (Pi. 5; Pi. 12, Figs. E, F; Pi. 16,

Fig. F ) . Here, vugs are often present in the lower 90 cm of

the facies.

At Black Lake, grainstone comprises both the top and bot

tom of the exposed section (Fig. 6; Table la, numbers 1, 28;

PI. 19) .

Composition of the Dark Fraction

The coral organic-mud packstones which occur in the or

ganic-mud packstone facies and the interstromatoporoid organ

ic-mud packstones which occur in the biolithite facies are in

variably dark brown to black. Wet chemical and x-ray tests

(p. 11) indicate that the dark fraction is composed of hydro

carbons with trace amounts of mud (Figs. 4, 5). Thus the most

descriptive term for this dark fraction is "hydrocarbonaceous

terrigenous mud"; however, because such a term is unwieldy,

the term "organic mud" is used to designate the dark fraction.

When thin sections are ground below normal petrographic

thickness so that calcite shows some second and third order

birefringence (Appendix 2), the distribution of the crudely

laminated organic mud can be observed. Under low power, the

organic-mud layers mold around coarse allochemical grains to

produce a crude pinch and swell lamination (Pi. 13, Figs. A,

B). The degree of opacity is usually constant but locally it

increases within a single layer where organic-mud layers ap

pear to pinch together at contacts with larger allochemical

grains (PI. 13, Fig. A).

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Closer examination of thin sections indicates the pre

sence of skeletal grains which are embayed (PI. 13, Fig. A),

truncated, and lens shaped. Under high power, the crude la

mination and grain relationships mark sutured interconnecting

network microstylolites (Park and Schot, 1968; PI. 13, Figs.

A-E). True vertical stylolites (Park and Schot, 1968) are

present where organic content is lower (Pi. 13, Fig. B). Where

coherent stromatoporoid and crinoid grains intersect the sty

lolites, the opacity of the stylolites increases. The degree

of packing of the microstylolites and stylolites apparently

controls the fissility of the organic-mud packstones and the

interstromatoporoid sediment (of the biolithite facies).

Where the degree of packing is low, and the composition

of the organic mud can be observed in microsection, the or

ganic mud is composed of: 1) elongate dark acicular to mas

sive translucent brown to opaque phosphatic fragments; 2) 4

micron dark brown translucent brown microspheres; 3) pyrite;

and 4) amorphous aphanitic debris (PI. 13, Figs. C, D, E, F).

Locally, as mentioned previously (p. 23), the organic mud is

present as laminae within the dense subfacies of the micrite

facies. The organic mud is uniformly present in the matrix

of rocks belonging to the organic-mud packstone facies. How

ever, it is less abundant in the matrix of the interstroma

toporoid organic-mud packstones of the stromatoporoid bio

lithite facies and occurs only in trace amounts within the ma

trix of rocks belonging to the biolithite-micrite transition

facies.

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The brown microspheres are interpreted to represent fos

silized unicells of blue-green algae that record remnants of

subtidal algal mats very similar to the Schizothrix-unicell

mats (Neumann et a^l. , 1970) which form today in the Bahamas

(compare Fig. 7 with PI. 13, Figs. C, D, E, F; See p. 95 for

systematic description and interpretation).

Petrography

Thin sections indicate that rocks from the organic-mud

packstone facies (Table 2) are grain supported and contain

variable amounts of black organic mud matrix and fine to me

dium crystalline sparry calcite cement. A bivariate plot of

the abundance of sparry calcite versus the abundance of black

organic-mud matrix (Fig. 8) shows that samples from the bio

lithite facies group in the lower left hand corner indicative

of their high skeletal content relative to both sparry calcite

and organic mud. Crinoid-bryozoan organic-mud packstones and

crinoid-bryozoan grainstones which characterize the crinoid-

bryozoan grainstone subfacies (but also occur in the coral

packstone subfacies) have a relatively high sparry calcite

content and thus plot in the upper left hand portion of the

diagram. The coral-bearing organic-mud packstones which char

acterize the coral packstone subfacies (but also occur in the

crinoid-bryozoan grainstone subfacies), plot in the lower

right hand part of the diagram in reflection of their higher

organic-mud content.

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POLYCNAETE SCHIZOTNNIX UNICELLS YUBE FILAMENTS

m 5B MicrMS

Figure 7. Microstructure of the Schizothrix-unicell subtidal algal mac. from the Bahamas. Abundance of fine filaments create a rough surfaced mat lacking rigid fibrous structure but within which grains are completely enmeshed (from Neu mann et al., 19 70).

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.29

4 0 -

■30 3 0 - Crirroid-Bryozoan MODAL Grainstone Subfacies PERCENT SPARRY

CALCITE 27-

2 0 - 25-

2 1 - •26 29*

31-

■ 23 Coral-Packstone

1 0 - .22 Subfacies Biolithite 4* S . *15 Facies

•18 . 14 19-

•17

0 10 20 3 0

MODAL PERCENT ORGANIC-MUD

Figure 8. Plot of the modal abundance of sparry calcite ce ment versus dark organic-mud matrix for rocks characteristic of the biolithite facies, the crinoid-bryozoan grainstone subfacies and the coral packstone subfacies of the organic- mud packstone facies. Estimated best fit regression line (solid) for the organic-mud packstone facies showing strong negative slope. Facies boundaries are dashed. Modal analy ses of the samples (numbered) are given in Table 2.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40

Coral Packstone Subfacies. The dominant lithology com

prising the coral packstone subfacies is fine to medium skel

etal calcarenite: coral-bearing organic-mud packstone (Table

2, numbers 3-6, 8, 11, 12, 15, 19, 22); however, the subfacies

also contains subordinate lenses of crinoid-bryozoan organic-

mud packstones and crinoid-bryozoan grainstones. The coral-

bearing organic-mud packstones are composed, on the average,

of about 74 percent grains, 19 percent matrix (including or

ganic mud which ranges from 14 to 22 percent, and micrite

which averages about 1 percent), and 6 percent authigenic min

erals . The authigenic minerals include: sparry calcite which

ranges from 2 to 10 percent and pyrite which is distributed

in trace amounts throughout the matrix.

Greater than 99 percent of the grains comprising the

coral-bearing organic-mud packstones are of skeletal origin.

Intraclasts, which occur in trace amounts, are the only non-

skeletal grain type present. Identifiable skeletal grains

observed in thin section include: solitary rugose coral, 7

percent; Fenestellidae, 6 percent; crinoid ossicles, 5 per

cent; Favosites, 4 percent; brachiopods, 1 percent; and traces

of ostracods, calcispheres, clathrodictydids, stromatoporids,

forams, trilobite fragments, and phosphatic fragments. Un

identifiable grains account for about 41 percent of the coral-

bearing organic-mud packstone. Eight percent of the unidenti

fied grains are probably shell fragments based on their mor

phology, and 4 percent consist of unidentifiable crystals which

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either represent skeletal fragments or sparry calcite cement.

The remainder of the unidentifiable grains (PI. 10, Figs. A,

C, D; Pi. 13, Fig. A) do not appear to be composed of micrite

although they often contain dark inclusions (but not brown

microspherulites). They seem to be aggregates of microspar

and slightly coarser sparry calcite with poorly defined indi

vidual crystals. Some of the crystals appear to have loaf

form.

Macrofossils within the coral packstone subfacies in

clude bulbous and ramose Favosites; whole, partially fragmen

ted, and crushed Heterophrentis; colonial rugose corals; stro-

matoporoids; bryozoans; and crinoid ossicles. Locally packed

ramose Favosites or packed Heterophrentis lenses exhibit pre

ferred alignment in the horizontal plane. The ramose Favo

sites are generally nearly complete; however, accumulations

of fragments of the corallite walls indicate that the surfaces

of some specimens have been fragmented. One Heterophrentis

was observed truncated at its top edge by dark organic-mud.

Small (1 cm to 4 cm thick) laminar stromatoporoids (PI. 10,

Figs. A, C, D), hemispherical stromatoporoids, and colonial

rugose corals (dominantly Hexagonaria and Spongophyllum) are

sparsely distributed throughout the coral-bearing organic-mud

packstone and are often overturned. Fenestellid bryozoans

ire present commonly as broken fragments, and crinoids occur

as isolated ossicles with the margins of the grains commonly

polygonalized and micritized.

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The coral-bearing organic-mud packstones display a lami

nated fabric which to the uninitiated might appear cataclas-

tic. Sampling is difficult because of the high degree of fis-

sility and the tendency for the rocks to break into thin

sheets and plates. Lens-shaped grains show birefringence and

are usually single fragments (PI. 10, Figs. A, C, D; Pi. 13,

Figs. C, D). The lens-shaped grains are wrapped and molded

around by the dark organic-mud which is generally translucent

and non-birefringent (Pi. 13, Figs. C, E, F). These opaque

laminae grade laterally into microstylolites of the "sutured

interconnecting network" type (Park and Schot, 196 8) or trun

cate individual grains (PI. 13, Fig. C). Brown microspheres

and amorphous fragments are observed ubiquitously in the black

laminae under highest power (Pi. 13, Figs. C, D) except where

the microstylolites coalesce into opaque laminae (pinchouts)

in the vicinity of larger fossils such as crinoid ossicles,

Favosites, stromatoporoids, and colonial rugose corals.

Intraskeletal porosity in the coral packstone subfacies

is usually filled with medium to coarsely crystalline equant

polygonal sparry calcite displaying straight to curved crystal

boundaries (PI. 13, Figs. C, E, F). Some of the sparry cal

cite crystals are embayed by other sparry calcite crystals

and some non-equant sparry calcite is present. The size of

the sparry calcite crystals increases away from the pore

walls. In some Favosites, intraskeletal sparry calcite is

more bladed (Pi. 7, Fig. D) and forms optically continuous

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syntaxial bladed overgrowths with the average optic axis of

the cell walls. The morphology of these crystals is sugges

tive of early submarine cementation (Folk, 1974). Throughout

the subfacies, but dominantly within Favosites, some of the

sparry calcite ranges from 0 to 20 microns and is vaguely pel-

loidal suggesting current transport or faunal infilling of

the pelloids into the corallites. Geopetal structure is rarely

observed within these pelloidal infillings; however, some os-

tracods are geopetally filled (Pi. 10, Fig. C), others have

been subsequently overturned.

Intergranular porosity in the organic-mud packstones is

usually filled with very fine single equant crystals of sparry

calcite that average 10 microns in diameter. Locally, ran

domly oriented lenses up to 300 microns long and 80 microns

wide occur partially filled with very finely crystalline

equant polygonal sparry calcite and pelloids suggesting that

invertebrates within the soft organic-mud sediments left be

hind burrows partially filled with pelloids which were later

filled with sparry calcite.

Crinoid-Bryozoan Grainstone Subfacies. The crinoid-bryo

zoan grainstone subfacies is characterized by lenses and

layers of crinoid-bryozoan organic-mud packstones, poorly

washed crinoid-bryozoan grainstones, bryozoan organic-mud

packstones, poorly washed bryozoan grainstones, crinoid-or-

ganic-mud packstones, and poorly washed crinoid-bearing grain

stones all interbedded with subordinate darker and more fis-

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sile coral-bearing organic-mud packstone layers. The dominant

lithology from which the subfacies is named is medium skeletal

calcarenite to fine skeletal calcirudite: crinoid-bryozoan

poorly washed organic-mud bearing grainstone (Table 2, numbers

21, 23-29).

The crinoid-bryozoan organic-mud packstones and grain

stones are composed on the average of about 6 9 percent grains;

13 percent matrix (including organic-mud ranging from 2 to 24

percent and averaging 13 percent, and trace amounts of mic-

rite); and 19 percent authigenic minerals. The authigenic

minerals include sparry calcite which ranges from 12 to 26

percent and averages 19 percent; and trace amounts of pyrite.

The only non-skeletal grain types are pelloids and oolites

which occur in trace amounts.

Skeletal grains observed in thin section include: Fene-

stellidae, 26 percent; crinoid ossicles, 13 percent; brachio-

pod fragments, 6 percent; Favosites, 2 percent; undifferenti

ated coral, 2 percent; Cyclostomata, 1 percent; Ostracoda, 1

percent; and trace amounts of calcispheres, clathrodictyds,

stromatoporias, forams and trilobite fragments (Pi. 10, Fig.

E). Unidentifiable grains account for 20 percent of the rock;

however, 8 percent are considered to be shell fragments based

on their morphology; and 4 percent are unidentifiable crystals

that represent either skeletal fragments or finely crystalline

sparry calcite cement (Table 2).

Bryozoans in the subfacies commonly occur as fragments.

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Encrusting bryozoans locally cover macrofossils including:

Favosites, crinoid fragments, and colonial rugose corals. Cri-

noids occur as stem fragments, partially diaggregated stem

fragments with columnals stacked en echellon (Pi. 12, Fig. D),

isolated ossicles (Pi. 10, Fig. E; PI. 12, Figs. E, F; Pi. 13,

Fig. B ) , and as rare calyx plates. No whole calyxes were re

covered. Individual crinoid ossicles are polygonalized (PI.

12, Figs. E, F ) . Polygon boundaries and occasional ossicle-

matrix contacts are micritized (Pi. 12, Figs. E, F; Pi. 13,

Fig. B). Pores within the crinoid ossicles are filled with

micrite and thus are well preserved and locally micritization

has occurred immediately around the pores. Brachiopods occur

in all samples, and show positive correlation with both cri-

noids and bryozoans. The brachiopods are commonly present as

fragments but locally, such as at Grand Lake, (Fig. 1, Loc.

33-8-31; Appendix 1, Measured Section 12, Unit 3), whole ar

ticulated fragments occur. Ramose Favosites occur locally,

partially broken and lying parallel to bedding. Pelloids are

commonly present only where the dark organic-mud is sparse

such as in the corallites of Favosites. The occurrence of the

pelloids is suggestive of either current or faunal infilling

of the corallites.

Orthochemical constituents within the crinoid-bryozoan

grainstone subfacies include: 1) mediur to coarsely crystal

line equant polygonal sparry calcite, and 2) finely crystal

line bladed sparry calcite. The medium to coarsely crystal

line equant polygonal sparry calcite is composed dominantly

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of polygonal crystal units with straight to curved boundaries

that usually occur as triangular pore-filling intergranular

patches which are locally poikilitopic (PI. 10, Fig. F). Where

intraskeletal porosity is filled with the coarsely crystalline

equant polygonal sparry calcite, the crystal size of the spar

ry calcite may or may not decrease in size as the skeletal

wall is approached. Fibroradiating Favosites walls are lo

cally lined with the finely crystalline bladed sparry calcite

which forms optically continuous syntaxial overgrowths on the

coral walls. However, near the center of the corallites, me

dium to coarsely crystalline equant sparry calcite is present.

The bladed morphology suggests early submarine precipitation

of fibrous aragonite or magnesian calcite cement (now neomor-

phosed to bladed sparry calcite), followed by later precipi

tation of pore-filling equant polygonal sparry calcite from

deep subsurface or meteoric waters (Folk, 1974).

The fabric within the lenses and layers of crinoid-bryo

zoan organic-mud packstones and poorly washed crinoid-bryo

zoan grainstones which characterize the crinoid-bryozoan

grainstone subfacies is dominantly laminated but not as marked

as in the: 1) subordinate coral-bearing organic-mud pack

stones which occur interbedded with the lenses and layers and

in the 2) coral-bearing organic-mud packstone which dominate

the lower coral packstone subfacies at Rockport Quarry. Mi

cros tylolites (point counted as organic mud) are also present

but are not as tightly packed as in the coral-bearing organic-

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mud packstones, particularly where crinoids and bryozoans are

abundant. Locally, coarser grains are truncated either above

or below, and the grain boundaries are marked by opaque ma

terial (PI. 13, Fig. B). "Vertical type" stylolites (Park and

Schot, 1968) occur at these boundaries in some samples and lo

cally solution has removed material from both above and below

the coarser grains (Pi. 13, Fig. 3). Brown microspheres, com

mon to the coral packstone facies and the interstromatoporoid

rocks of the biolithite facies, are also present in this sub

facies (Pi. 13, Fig. B).

Interpretation of the Packstone Facies

The organic-mud packstone facies within the Rockport

Quarry Limestone is interpreted to record deposition of shal

low marine carbonate platform interior blanket sands (Ball,

1967, p. 573) which were locally bounded by subtidal algal

mats.

The vertical sequence of gradational facies comprising

about the upper two-thirds of the section at Rockport Quarry

(Fig- 1, Loc. 32-9-6; Appendix 1, Measured Sections 1-8) com

pares with similar sequences from the Devonian of Morrocco

(Dumestre and Illing, 1967), and Alberta and Australia (Embry

and Klovan, 1973; Klovan, 1974), which have been interpreted

to represent progradational sequences that record progres

sively decreasing water depth. At Rockport Quarry (Figs. 1,

6; Pi. 1, Fig. B; Pi. 2, Fig. A; PI. 18), a shale facies up

to 30 cm thick is overlain by Heterophrentis-Favosites bearing

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organic-mud packstones and subordinate lenses of crinoid-bx'y-

ozoan organic-mud packstones and poorly washed grainstones

which together comprise the coral packstone subfacies. These

rocks in turn are overlain by lenses and layers of crinoid-

bryozoan organic-mud packstones and poorly washed grainstones

interbedded with subordinate Heterophrentis-Favosites bearing

organic-mud packstones which together comprise the crinoid-

bryozoan grainstone subfacies. The rocks comprising the cri

noid-bryozoan grainstone subfacies are gradationally overlain

by a stromatoporoid biolithite which grades upwards into a

sparse stromatoporoid biolithite with calcareous algae (bio-

lithite-micrite transition facies), and finally into a pel-

loidal micrite (micrite facies) of probably lagoonal subtidal

and intertidal origin (Appendix 1, Measured Sections 1-8).

The iri situ hemispherical stromatoporoids that occur in

the coral-bearing organic-mud packstones within the coral

packstone and bryozoan grainstone subfacies are interpreted

to represent lower energy than the lamellar stromatoporoids

(Abbot, 197 3; which characterize the overlying biolithite fa

cies. Therefore, the coral packstone and overlying bryozoan

grainstone subfacies of the organic-mud packstone facies are

interpreted to record a progressively shallowing subtidal en

vironment adjacent to a stromatoporoid biolithite shoal (Fig.

9). In this shoaling subtidal environment, subtidal algal

mats (Neuman et al., 1970; Scoffin, 1970; Bathurst, 1975),

now recorded by concentrations of brown microspheres (probably

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Production

ensive Algal Mat

y/ y/ Production ^Extensive Local Grain Marine Biolithite-Micrite Transitional Facies Grainstone Subfacies Micrite Facies Shallow Subtidal Bg Bg Crinoid-Bryozoan Cp Coral Packstone Subfacies M B Biolithite Facies B-MT Shoal Laminar Shoal-Forming Stromatoporoid Lagoon Fenestellid Bryozoan Algal Algal Mat Crinoid

Sequence Vertical of of Facies B-MT Produced by Progradation stone stone and crinoid-bryozoan grainstone subfacies) particular in and the vertical sequence of facies observed the in upper two-thirds of the section exposed at Rock port Quarry general. in Figure 9. Figure 9. Schematic interpretation of facies the organic-mud pack (coral packstone'

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unicells produced by coccoid blue-green algae) and black or

ganic mud, were prevalent and produced a stabilized substrate

ideal for colonization by ramose and hemispherical Favosites,

Heterophrentis, hemispherical stromatoporoids and other or

ganisms. Apparently, the slightly deeper offshoal subtidal

substrates represented by the dark grey coral-bearing organic-

mud packstones, the predominant lithology of the coral pack

stone subfacies, contained the highest algal-mat concentra

tion (Fig. 9). The concentration of algal mats apparently

decreased shoalward as suggested by the more subordinate na

ture of the dark grey algal-bearing organic-mud packstones in

the overlying bryozoan grainstone subfacies. Modern algal

mats do not colonize on coarser substrates as easily as on

finer substrates (Gebelein, 1969, p. 63) which suggests that

perhaps the calcirudic nature of the crinoid-bryozoan organic-

mud packstones and poorly washed crinoid-bryozoan grainstones

which characterized the more shoalward substrates limited ex

tensive mat distribution. The general fabric of the coral-

bearing organic-mud packstones is reminiscent of algal mats

that form today within subtidal environments ranging from less

than 1 meter to 2 or 3 meters in depth in the Bahamas (Fig. 7;

Neuman et a ^ . , 1970; Bathurst, 1975) and at Shark Bay, Aus

tralia (Logan et al., 1974).

The dominantly fragmental angular skeletal sands com

prising the crinoid-bryozoan organic-mud packstone and poorly

washed crinoid-bryozoan grainstone lenses and layers that

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characterize the bryozoan grainstone subfacies are interpreted

to have been produced by in_ situ subtidal crinoid and bryozoan

grain production followed by deposition near their source of

origin as suggested by the homogenous faunal content within

individual lenses (Fig. 9). Some lenses may simply represent

crushed fragments from the same individual (Pi. 17, Fig. A).

According to McCurda (1975, personal communication), the cri-

noids probably grew very near if not within the area of ac

cumulation of their detritus. Crinoid stems in modern envi

ronments disaggregate after about a week of exposure to sub

marine currents; however, increased current activity and sca

vengers may further increase the rate of disarticulation (Li-

dell, 1975). Apparently the abundance and areal extent of

the local bryozoan and crinoid grain-producing meadows which

produced the crinoid-bryozoan packstones and poorly washed

grainstones that characterize the crinoid-bryozoan grainstone

subfacies at Rockport Quarry increased in the progressively

shallowing subtidal environment adjacent to the biolithite

shoal (Fig. 9) .

The interlaminated nature of ramose Favosites (occurring

in organic-mud packstones) and lamellar stromatoporoids in

the transition zone between the organic-mud packstone facies

and overlying biolithite facies suggests that the ramose Favo

sites , too, are nearly in situ. Colonial rugose corals in the

organic-mud packstone facies and the biolithite facies, not in

growth position, apparently have been rolled locally. Asso-

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elation of the organic-mud packstone facies with an unrestric

ted normal marine environment is indicated by the high faunal

diversity and by the faunal composition of the facies (cri-

noids, bryozoans, corals, arthrodire plates, and cephalopod

fragments).

Stromatoporoid Biolithite Facies

Outcrop Description

At Rockport Quarry, Grand Lake, and Ocqueoc Falls (Figs.

1, 6; PI. 1, Fig. B; Pi. 2, Fig. A; PI. 4, Fig. A; Pi. 5,

Figs. A, B; Pi. 18; Pi. 19) rock units comprised of tabular

to laminar stromatoporoids (30 to 60 percent) and interbedded

interstromatoporoid coral-bearing organic-mud packstones are

termed stromatoporoid biolithites and assigned to the stroma

toporoid biolithite facies (PI. 15). The biolithites range

in color from greyish-orange (10 YR 7/4) to pale yellowish

brown (10 YR 6/2); the lighter colors corresponding to higher

stromatoporoid contents. Accumulations of laminar stromato

poroids observed at Rockport Quarry (Appendix 1, Measured Sec

tions 1-8; PI. 18) range from 3 cm in thickness and 30 cm in

diameter up to 4.5 m thick and 1.5 km long. The thinnest ex

tensive biolithite at Rockport Quarry is 30 cm thick and lies

in the upper part of the section where it is overlain grada-

tionally by the biolithite-micrite transition facies. Stro

matoporoid sheets and colonies at Rockport are usually thin

(2 to 8 cm with some as thin as 1 cm), laterally extensive

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(0.3 to 2 m) , and locally contain interbedded hemispherical

stromatoporoids and colonial rugose corals (Pi. 11, Fig. B;

PI. 15, Fig. A). The laminar stromatoporoids always mold

around larger more buttressing grains (PI. 15). Corals, in

cluding Heterophrentis, Cystiphilloides, and Aulocystis, are

occasionally found between laminar stromatoporoids. Locally

ramose Favosites and other corals are completely surrounded

by stromatoporoid laminae.

At Grand Lake, hemispherical stromatoporoids, although

more common than at Rockport Quarry, remain subordinate to

laminar and tabular stromatoporoids (Pi. 15, Fig. B). The

hemispherical stromatoporoids are often overturned, and are

typical of Devonian stromatoporoid occurrences thought to re

cord deeper water reef margins and other somewhat lower energy

zones than the tabular and laminar stromatoporoids (Read,

1973a, 1973b; Embry and Klovan, 1973; Klovan, 1974; Heckel,

1974). The interstromatoporoid organic-mud packstones asso

ciated with the hemispherical forms contain abundant fragments

of laminar stromatoporoids suggesting derivation of the frag

ments in higher energy shoal areas and subsequent transport

to somewhat deeper lower energy zones. The biolithites com

prising the lower exposed units at Rockport Quarry and Grand

Lake (Fig. 6) probably are not laterally continuous, and the

biolithites at Rockport Quarry probably represent shallower

water and higher energy as suggested by the more abundant la

minar stromatoporoids (Abbot, 1973).

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All of stromatoporoid biolithite outcrops are laced with

secondary calcite veinlets that divide the rocks into 1 m

blocks. Excepting for the extensive dolomite in the bioli

thite exposed at Ocqueoc Falls, dolomite in the biolithite

facies is commonly coarsely crystalline, turbid orange brown

in color, and locally fi^ls veins as well as galleries in some

stromatoporoids (PI. 16, Figs. B, E). The dolomite filling

the veins crosscuts calcite veins indicating that the dolomite

formed after precipitation of the calcite veins. Pyrite oc

curs locally and often may be distinguished on the white stro

matoporoids by an orange limonite stain.

Petrography

The dominant lithology comprising the stromatoporoid bio

lithites is bound skeletal calcirudite: stromatoporoid bio

lithite (Folk, 1965) comprised of tabular to laminar stroma

toporoids and interbedded interstromatoporoid fine to medium

skeletal calcarenite: organic-mud packstone. The average

sizes of the grains comprising the interstromatoporoid pack

stones range from about .08 to 0.4 mm and average about .35

mm. At Rockport Quarry, the interstromatoporoid organic-mud

packstones grade into coral-bearing organic-mud packstones of

the organic-mud packstone facies with increasing organic-mud

content, and into the biolithite-micrite transition facies

with decreasing organic-mud content (Fig. 8; Table lb).

Rocks of the stromatoporoid biolithite facies are com

posed of 88 percent grains, 8 percent matrix (including or-

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ganic-mud ranging from 0 to 20 percent and averaging 8 per

cent, and trace amounts of micrite) and 3 percent authigenic

minerals. Authigenic minerals include sparry calcite which

ranges from 0 to 8 percent and averages 3 percent, and trace

amounts of dolomite and pyrite. Pelloids, present in trace

amounts, are the only non-skeletal grains within the bioli

thite facies. The skeletal grains observed in thin sections

of the biolithites include: clathrodictyds, 33 percent; stro-

matoporids, 15 percent; Favosites, 3 percent; fenestellids,

3 percent; echinoderm ossicles, 2 percent; trepostomida, 1

percent; and trace amounts of ostracods, idiostromatids, He

terophrentis , undifferentiated corals, and crinoid fragments.

Unidentifiable grains account for 19 percent of the rocks; 3

percent are considered to be shell fragments based on their

morphology and 2 percent are unidentifiable crystals, either

skeletal fragments or fine sparry calcite cement (Table 2).

Grains within the interstromatoporoid organic-mud pack

stones exhibit textures and fabrics unique to the biolithite

facies. Pelloids, when present, usually occur in grain in

terstices. A probable burrow, filled with pelloids and finely

crystalline equant sparry calcite, was probably abandoned par

tially filled with pelloids and later filled with pore-filling

sparry calcite. Crinoid fragments within the biolithite ma

trix are rarely optically continuous due to grain polygonali-

zation (Folk, 1965). Often cryptocrystalline micritic bounda

ries surround both the crinoid fragments and the polygons with

in the fragments.

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Stromatoporoids appear as aggregates of fine to coarsely

crystalline neomorphic sparry calcite marked by brown ghosts

of organic material which pseudomorph the original cell walls

(Pi. 12, Figs. A, B, C). The morphology of the neomorphic

calcite takes two forms: fibroradiating and equant. The

finely crystalline neomorphic fibroradiating sparry calcite

crystals (Pi. 12, Figs. A, B) are elongate to bladed, show ir

regular boundaries and are preferentially aligned parallel to

the original cell walls (PI. 12, Figs. A, B ) . Fine to medium

crystalline equant neomorphic sparry calcite cross cut the

original cell boundaries (PI. 12, Fig. C). Peels made of the

stromatoporoids were usually unsatisfactory because peels are

only able to replicate grain boundaries and textures but not

colors such as the brown pseudomorphs.

In the facies that contain organic-mud (organic-mud pack

stone facies, stromatoporoid biolithite facies, biolithite-

micrite transition facies) dolomite is unique to the stroma

toporoid biolithite facies except at Ocqueoc Falls where both

the biolithite and organic-mud packstone facies are extensive

ly dolomitized. In thin section, the dolomite in the bioli

thites occur either as: 1) vein fillings resulting from re

placement of calcite that originally filled veins, 2) iso

lated replacement rhombahedrons, and 3) pore-filling dolomite.

The vein fillings (Pi. 16, Fig. B) locally are composed of 50

to 250 micron crystals of baroque dolomite displaying non-

uniform extinction (Folk, 1965); however, more commonly the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57

vein fillings are composed of tuxbid dark dolomite which often

crosscuts the sparry calcite that originally lined the veins.

Rhombahedral dolomite occurs as turbid interlocked crystals

with clear rims ranging in size from 50 to 300 microns; or at

Grand Lake as isolated crystals replacing both grains and ma

trix (Pi. 16, Fig. A). Stromatoporoids at Grand Lake have a

high percent of empty surficial galleries. Approximately 40

percent of these galleries are partially filled with dolomite.

Galleries further removed from the periphery of the stromato

poroid are calcite filled (PI. 16, Fig. E). Pore filling do

lomite occurs locally at Rockport Quarry.

Interpretation of the Stromatoporoid Biolithite Facies

The relief inferred for Devonian stromatoporoid bioli

thites at the time of deposition ranges up to several hundred

feet (Heckel, 1974). The effect of the stromatoporoid bioli

thite masses (reefs) upon surrounding sediment accumulation

has been inferred to range from low (Fenton, 19 31) to great

(Heckel, 1974; Playford and Lowry, 1966; Read, 1973a, 1973b;

Dumestre and Illing, 1967). The biolithites within the Rock

port Quarry Limestone apparently record a stable gently undu

lating wave resistant substrate which probably rose gently

above the general substrate of the adjacent shallow sea floor

to form low relief reefs or biostromes (Stumm, 1967; Sanford,

196 7) that approached sea level. Without more information

from the subsurface, the three dimensional morphology of these

reefs cannot be evaluated. Similar but thicker Devonian ac

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cumulations in Morrocco and Alberta are ellipsoidal in plane

view (Dumestre and Illing, 1967).

The interbedded stromatoporoids and interstromatoporoid

organic-mud packstones and organic-mud bearing grainstones

(PI. 12, Figs. A, B; Pi. 15, Figs. A, B) indicate that sedi

mentation was contemporaneous with both horizontal and verti

cal stromatoporoid growth. Sediment was apparently deposited

in interstromatoporoid energy lees (perhaps slight topographi

lows) around the margins of individual laminar and tabular

stromatoporoid plates. These energy lees apparently served

as loci for the development of subtidal algal mats which lo

cally encroached laterally over the stromatoporoid sheets.

These areas of algal mat development in turn provided zones

for subsequent recolonization by stromatoporoids which en

croached horizontally over the interstromatoporoid substrate

and accreted vertically to produce low relief topographic

highs. Hemispherical stromatoporoids and colonial rugose cor

als which locally inhabited the interstromatoporoid algal-mat

substrate were occasionally overturned by intense current ac

tion and subsequently overgrown by laterally encroaching stro

matoporoid colonies.

Biolithite-Micrite Transition Facies

Outcrop Petrology

The biolithite-micrite transition facies occurs at Rock

port Quarry only where it gradationally overlies a thin la-

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terally extensive stromatoporoid biolithite and in turn is

gradationally overlain by micrite facies (Figs. 1, 6; PI. 1,

Fig. B; Pi. 2, Fig. A; Pi. 18; Appendix 1; Measured Section

1, Unit 5; Measured Section 2, Unit 5; Measured Section 5,

Units 5, 6; Measured Section 6, Unit 3; Measured Section 7,

Unit 3; Measured Section 8, Units 2, 3). The base of the fa

cies was arbitrarily placed where laminar stromatoporoids com

prising the biolithite decreased below 50 percent; and the top

of the facies where the abundance of Favosites and Hetero

phrentis , characteristically present in the interstromatopo

roid rocks of the stromatoporoid biolithite facies, decreased

to trace amounts.

The biolithite-micrite transition facies averages 60 cm

thick. The lower 20 cm of the facies is a sparse stromatopo

roid biolithite conspicuously lighter (light olive grey, 5 Y

6/1) and better indurated than the greyish orange (10 YR 7/2)

biolithite facies which it overlies. Upward through the tran

sition facies, the stromatoporoid content becomes sparser and

more fragmental such that only traces of stromatoporoids occur

in the upper 2 0 cm. The color of the upper 20 cm progres

sively changes upwards to the lighter grey (N7) of the micrite

facies, and Favosites and Heterophrentis gradually decrease in

abundance until they are absent in the micrite facies.

Petrography

The biolithite-micrite transition facies grades upward

from stromatoporoid biolithites to stromatoporoid-b^aring pel-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. micrites at the top of the sequence. Compositionallv these

rocks grade downward through the biolithite facies to the or

ganic-mud packstone facies with increasing organic-mud content

and upward with decreasing organic-mud and increasing pelloid

content into the micrite facies.

Rocks of the biolithite-micrite transition facies are

composed of about 88 percent grains, 8 percent matrix (in

cluding 6 percent micrite, 2 percent organic mud, and 4 per

cent authigenic minerals. Authigenic minerals include: sparry

calcite, 4 percent; and trace amounts of pyrite. Non-skeletal

grains include: pelloids, 12 percent; and intraclasts in

trace amounts. The skeletal grains observed in thin section

include: stromatoporidae, 2 8 percent; clathrodictydae, 24

percent; Favosites sp., 4 percent; echinoderm ossicles, 2 per

cent; fenestellidae, 2 percent; and trace amounts of ostra-

cods, idiostromatids (PI. 14, Fig. E), and calcareous green

algae including Vermiporella (PI. 14, Figs. A, B) and an un

identified encrusting algal form (PI. 14, Figs. C, D). Un

identifiable grains account for 14 percent of the sediment;

3 percent are considered to be some type of shell fragment

based on their morphology, and 5 percent consist of unidenti

fiable skeletal fragments comprised of fine sparry calcite.

Interpretation of the Biolithite-Micrite Transition Facies

The vertically continuous gradational sequence observed

within the biolithite-micrite transition facies at Rockport

Quarry indicates that the vertically stacked facies were at

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one time laterally contemporaneous, and that lateral migration

of facies was instrumental in their superposition.

Calcareous green algae indicate a shallow-water environ

ment of deposition with moderate energy analagous to that pos

tulated for similar species from the Middle Devonian Pillara

Formation of western Australia (Wray, 1967a, 1967b, 1971; Wray

and Playford, 1970; Read, 1973b). The amount of stromatopo

roid production decreased progressively during deposition of

the transition facies. Pe;rhaps the laterally separated stro

matoporoid plates of the biolithite-micrite transition facies

provided aereatea but protected interstromatoporoid areas ca

pable of supporting delicate calcareous algae on the lagoon-

ward-side of the stromatoporoid biolithite shoals (Fig. 9,

Fig. 10).

Heterophrentis and ramose and hemispherical Favosites

were apparently the most widely adaptable of the Rockport

fauna. They not only occur isolated in the micrite at the

top of the biolithite-micrite transition facies where they

are often unfragmented and thus possibly in_ situ (Appendix 1,

Measured Section 7, Unit 3), but also occur within the bio

lithite and organic-mud packstone facies.

Shale Facies

The top of a soft mud shale which underlies the Rockport

Quarry Limestone and contains Atrypa and other small brachio

pods, marks the contact between the Bell Shale and the over-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to CTi

vy.y

Coral Packstone Subfacies Organic Mud Packstone Facies 0 Bryozoan Grainstone Subfacies f&R

Transitional Biolithite- Micrite Facies Biolithite Facies Micrite Facies Rockport Quarry Limestone. Figure 10. Figure 10. Inferred facies relationships during shallow water deposition of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. lying Rockport Quarry Limestone. Samples of this unit are

difficult to obtain because of its softness and extensive

quarrying operations. Talus covers any possible exposure of

the formational contact in the quarry walls; however, locally

it can be found along the edges of the low blue pits formed

in the Bell Shale where quarrying operations broke through

the basal layers of the Rockport Quarry Limestone (PI. 3, Fig

A) .

Thin layers of shale lithologically similar to the Bell

Shale occur locally at Rockport Quarry within the lower stro

matoporoid biolithite, between the top of the lower stromato

poroid biolithite and the base of the coral packstone subfa

cies of the organic-mud packstone facies, and in the coral

packstone subfacies (PI. 18). The shale unit between the

lower stromatoporoid biolithite and the overlying coral pack

stone subfacies ranges up to 30 cm thick, and can be traced

in a north-south direction for at least 500 meters (PI. 18;

Appendix 1, Measured Sections 1-5). In the coral packstone

subfacies, local discontinuous 2 cm shale beds occur with a

maximum lateral extent of 2.5 m.

Subsurface Distribution of Facies

An attempt was made to investigate the subsurface distri

bution of facies in the Rockport Quarry Limestone through use

of well logs acquired from Consumers Power Company, Jackson,

Michigan, and Western Michigan University. Well logs contain

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ing the Rockport Quarry Limestone were available from 19 wells

in Alpena, Presque Isle, and Montmorency Counties (Fig. 1,

Table 5); however, cores of the unit were not available.

On mechanical well logs the Rockport Quarry Limestone is

easily distinguished from both the overlying Ferron Point For

mation and the underlying Bell Shale by its lower gamma ray

response (15 API versus 70 API), higher neutron density, and

high resistivity. Within the Rockport Quarry Limestone the

micrite and the stromatoporoid biolithite facies exhibit

higher resistivities and neutron densities because of their

higher carbonate content. The organic-mud packstone facies,

which contains significant amounts of non-calcareous matrix,

displays lower responses on both the neutron density and re

sistivity tests.

The distribution of facies in the subsurface appears spo

radic. Mechanical logs from wells separated by 1 or 2 km ex

hibited similar well log responses; however, when well logs

separated by 10 or more km were compared the more responsive

units (represented by the biolithite and the micrite facies)

locally appear and disappear. Thus the facies comprising the

Rockport Quarry Limestone in the subsurface are apparently

widespread but discontinuous in their distribution. A simi

lar conclusion is suggested by comparison of the horizontal

and vertical distribution of the facies observed in the sec

tions measured along the outcrop belt (Fig. 6; Pis. 18, 19).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65

Table 5. Wells in Alpena, Presque Isle, and Montmorency

Counties which have mechanical logs of the Rockport Quarry

Limestone (see Fig. 1 for location of wells).

imber Well Location Permit Number

1 Beamen Smith et al. 7-30N-3E 19410

2 Huron Cement Company 12-31N-8E 29138

3 Ford 1-5 5-31N-5E 25690

4 Blue Lake Ranch 1-7 7-32N-1E 29872

5 Gaylord Fishong 20-32N-1E 29837 Club 1

6 Stell-Maris 1-29 6-30N-3E 30058

7 State Montmorency 6-30N-3E 30086 1-6

8 State Allis 1-23 2 3-3 3N-2E 28083

9 Shell Zwolinski 1-12 12-33N-2E 28856

10 William Weide 1 33-3 3N-7E 24999

11 State Forest 1-34 34-34N-1E 28084

12 L. B. Smith 1 12-34N-2E n . a.

13 Paul E. Trapp 1 35-34N-5E 27920

14 Kreft 1 5-34N-5E 28337

15 Bruning 1 7-34N-5E 2 7f 74

16 Sellke 1 20-34N-5E 22638

17 Schweisow 1 27-34N-5E n . a.

18 A. Vermilya 1 29-35N-5E 27784

19 D. E. Drasey 1 29-35N-2E 27199

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 6

Depositional History of the Rockport Quarry Limestone

When the distribution and environmental significance of

the facies within the Rockport Quarry Limestone are considered

as a whole and analyzed in light of more extensively exposed

Devonian outcrops in New York (Laporte, 1967) , Morocco (Du-

mestre and Illing, 1967) and Australia (Heckel , 1974; Read,

1973a, 1973b; Klovan, 1974), it becomes apparent that the en

vironments and facies recorded by the Rockport Quarry Lime

stone developed on a carbonate platform in response to varying

water depth, energy, salinity, and terrigenous sediment in

flux .

Shale deposition, prevalent during accumulation of the

Bell Shale diminished during deposition of the Rockport Quarry

Limestone. The thin basal shaly packstones at Rockport Quarry

which underlie the lower stromatoporoid biolithite represent

a time when terrigenous mud was still periodically suspended

in the water column. This mud may represent mud brought in

from the east (Gardner, 1974) or northeast (Straw, personal

communication, 1976) or may represent Bell Shale sediment un

dergoing brief remobilization due to incomplete cover by the

Rockport Quarry Limestone carbonates. Local lenses of shale

in the stratigraphically higher organic-mud packstone and bio

lithite facies may represent incremental storm deposition fol

lowing mobilization of contemporaneous deeper water terrige

nous muds to the southeast (Gardner, 1974) or may possibly re

present terrigenous sediment periodically discharged into the

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basin from the northeast by migrating distributary channels

(Straw, 1976, personal communication).

During Rockport Quarry deposition, unrestricted subtidal

blanket sands (organic-mud packstone facies) and shallow la-

goonal subtidal to intertidal pelletal muds and sands (dense

and fenestral subfacies of the micrite facies), vied for space

with locally expanding stromatoporoid biolithite reefs that

formed shoals on a shallow carbonate platform that varied in

depth (Fig. 9, Fig. 10). In the deeper unrestricted subtidal

areas on the carbonate platform, skeletal sands were bound by

extensive subtidal algal mats. A coral community consisting

of bulbous Favosites and Heterophrentis was well adapted to

the algal mat substrate and produced extensive coral-bearing

organic-mud packstones which enclosed minor lenses of locally

produced crinoid-bryozoan organic-mud packstones and grain-

stones to form the coral packstone subfacies. In the shal

lower unrestricted subtidal areas, locally adjacent to shoals

formed by stromatoporoid biolithite reefs, meadows of cri-

noids, bryozoans, and ramose Favosites were particularly ex

tensive and responsible for local grain production which cre

ated abundant skeletal lenses and layers now represented by

crinoid-bryozoan organic-mud packstones and grainstones, and

Favosites organic-mud packstones that characterize the cri

noid-bryozoan grainstone subfacies. Between the meadows, sub

strates were covered with less extensive subtidal algal mats

that stabilized the sediment in a mucilaginous sheath. Most

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the unrestricted marine subtidal deposits preserved within

the outcrop belts of the Rockport Quarry Limestone are repre

sented by the shallower crinoid-bryozoan grainstone subfacies.

Thus the unrestricted subtidal carbonate platform deposits

preserved in outcrop are probably of relatively shallow water

origin. The coral packstone subfacies at Rockport Quarry ap

parently records a local area of somewhat deeper water on the

carbonate platform.

Local accumulations of laminar stromatoporoids (with dia

meters of 1.0 to 2.0 meters) in shoal environments grew to

gether to form low extensive reefs producing the stromatopo

roid biolithite facies. Algal mat-bearing interstromatoporoid

sediment, spread over the stromatoporoid sheets wherever ener

gy lees were created, producing complexly interlaminated in

terstromatoporoid organic-mud packstone and laminar stromato

poroids. On the leeward side of these stromatoporoid bioli

thite shoals protected lagoons were formed between the shoals

and low supratidal islands (Figs. 9, 10). Subtidal areas in

the lagoons which were shoalward and of nearly normal salinity

provided substrates for the calcareous algae (PI. 14; Figs.

A, B, C, D) and ramose Favosites and Idiostroma preserved in

the biolithite-micrite transition facies (Read, 1973a, 1973b;

Pi. 14, Fig. E ) . In the more restricted areas of the lagoons,

the muds and pelletal muds and sands were deposited in sub

tidal (dense micrite subfacies) and intertidal-supratidal en

vironments (fenestral subfacies) to produce the micrite fa

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69

cies. Ostracods occupied subtidal substrates but apparently

were frequently transported into intertidal and supratidal en

vironments bordering low islands where they became associated

with intertidal fenestral fabrics produced by a complex in

teraction between algae, sedimentation, and diagenesis.

Rodriguez Bank, an elongate flat-topped mound about one

mile east of Key Largo, Florida, is surrounded by deeper water

(Fig. 11) and seems to provide an excellent modern analogue

for the deposition of the facies of the Rockport Quarry Lime

stone exposed at Rockport Quarry (Fig. 9). At Rodriguez Bank

(Turmel and Swanson, 1964), a narrow intertidal shoal on the

windward eastern margin of the island is largely occupied by

Porites and Goniolithon, and may be similar to the shoal en

vironment implied for the biolithite facies of the Rockport

Quarry Limestone (compare Fig. 9 and Fig. 10 with Fig. 11).

The gradually deepening open marine grass and green algal zone

surrounding the bank (Turmel and Swanson, 1964) may correspond

bathymetrically to the depositional environment postulated for

the unrestricted marine organic-mud packstone facies of the

Rockport Quarry Limestone; whereas, the backshoal lagoon area

of Rodriguez Bank (Fig. 11) may be analagous to the deposi

tional environment postulated for the biolithite-micrite tran

sition facies. Moreover, the most restricted area of the

backshoal lagoon, where hypersaline or schizo-haline condi

tions may occur, could compare to the environment represented

by the dense subfacies of the micrite facies. An analogy for

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70

Goniolithon & Porites Zone

Grass and Green Algae Zone

□ Mangrove Zone

Figure 11. Index maps: A, Location of Rodriguez Bank (cross) 1 mile east of Key Largo, Florida; B, Zonation of dominant plants and animals on the surface of Rodriguez Bank. From Turmel and Swanson (1964).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the intertidal fenestral subfacies is not present at Rodriguez

Bank due to the presence of mangroves in the intertidal area;

however, fenestral fabrics similar to those found in the fene

stral subfacies of the Rockport Quarry Limestone are observed

at Andros Island, Bahamas (Shinn et. al. , 1969) and Hamelein

Pool, Sharks Bay, western Australia (Logan et a_l. , 1974) where

they form in the intertidal zone through diagenesis of laminar

and pustular algal mats and in the supratidal zone by packing

of intraclasts.

In conclusion, simple migration of the postulated envi

ronments during the time of deposition of the Rockport Quarry

Limestone can explain the facies distribution observed in the

outcrop band of the Rockport Quarry Limestone (compare Fig.

6 and Fig. 12).

Diagenesis

Diagenetic changes within the Rockport Quarry Limestone

have involved compaction, cementation, neomorphism, local do-

lomitization, and synhoresis cracking (Table 6).

Solution and Compaction

Rocks in the Rockport Quarry Limestone which have a

higher organic-mud content, commonly contain less sparry cal-

cite cement and the sparry calcite which is present generally

has a smaller average crystal size. Graphically, sparry cal

cite content shows a negative correlation when plotted against

organic-mud content (Fig. 8). The sparry calcite cement may

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. K)

Bryozoan Packstone Subfacies Organic-Mud Packstone Facies Gi Gi (5) Coral Packstone Subfacies (5)

migration. Figure 12. Figure 12. Facies mosaic model resutling from environmentally constrained facies PI PI Biolithite Facies □ Micrite Facies ™ Micrite Facies n Transitional Biolithite-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73

have been locally derived by dissolution of carbonate grains,

particularly where carbonate grains occurred in sediments con

taining relatively high proportions of easily compactible or

ganic mud. In such sediments, ferrous iron, present in inter

stitial water, could have combined with hydrogen sulfide (a

decay product of the organic mud) and produced pyrite plus

ionic hydrogen causing an increase in acidity,

2 Fe+2 + 2 H 2 S (decay product)— ►FeS2 (pyrite) + H 2 + .

The increased acidity could have in turn caused dissolution of

carbonate grains,

CaCC>3 + 2H+— *C02 + Ca+2 + H 2 O.

Such a process (Krauskopf, 1967) could have provided the chem

ical mechanism which, through dissolution of now embayed and

corroded (PI. 13) skeletal grains in contact with organic mud,

produced a local source for the sparry calcite cement preva

lent in the grain supported rocks.

Cracking

Within the micrites, short (2-5 cm) cracks roughly poly-

gonalize the sediment. The cracks are closed at both ends as

if they formed by some type of dilational effect. They dilate

a maximum of 2 mm and are filled with medium to coarsely crys

talline equant polygonal sparry calcite. A subtidal origin

for the sediments is suggested by their association with sub

tidal ramose Favosites and ostracods. Similar cracks form in

modern sediments (Thomas and Glaister, 1960) and have been re

ported from Paleozoic rocks of the Illinois basin (White,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74

1961) and Mississippian carbonate rocks in the Western Canada

Basin (Thomas and Glaister, 1960). They are interpreted to

be synhoresis cracks formed early in diagenesis because of

pressure dewatering contemporaneous with sedimentation (White,

1961). In order to preserve these cracks, it is probable that

the sparry calcite that fills the cracks was precipitated be

fore dewatering was complete (Table 6).

Individual stromatoporoid plates within the stromatopo

roid biolithite are laced with a network of short vertical

cracks which polygonalize them. Thin section evidence indi

cates that these too are filled with pore-filling medium crys

talline sparry calcite. It is hypothesized that compaction

of interstromatoporoid sediments began with the onset of de

position and continued to post lithification. Early compac

tion of the interstromatoporoid sediment may have created

cracks along pressure highs in the stromatoporoid plates caus

ing polygonalization of the plates.

Long vertical fractures within the Rockport strata with

a dilation up to 2 mm usually occur within the less fissile

layers of the Rockport Quarry Limestone (PI. 1, Figs. A, B;

PI. 2, Figs. A, B) such as the micrite facies, the biolithite-

micrite transition facies, the biolithite facies, and the cri

noid-bryozoan packstone subfacies. Where two less fissile

layers are separated by a thinner more fissile layer, usually

shale or coral-bearing organic-mud packstone, the crack often

passes through all (Pi. 9, Fig. A; PI. 10, Fig. E) . The

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75

cracking is thus a late or post-compactional feature. The

fractures are filled with pore-filling medium crystalline

equant polygonal sparry calcite.

Post-depositional compaction initially caused a decrease

in the thickness of the Rockport Quarry Limestone. With in

creasing overburden, the Rockport Quarry Limestone was frac

tured as a unit into polygons, probably partially due to in-

homogenous strain and support properties within the underlying

Bell Shale and overlying Ferron Point Formation (Table 6).

The effect of glacial overburden cannot be excluded.

Cementation

Medium crystalline pore-filling and neomorphic sparry

calcite is the dominant authigenic mineral within the Rockport

Quarry Limestone. The calcite cement within the organic-mud

packstone facies and the calcite which fills fenestrae in the

micrite facies is usually comprised of medium crystalline

equant polygonal sparry calcite with straight crystal bounda

ries (PI. 7, Figs. A-D; PI. 10, Figs. A-D, F). Locally equant

polygonal curved boundaries are present that grade into

straight crystal boundaries. Where sparry calcite is predomi

nant over organic mud (Fig. 8), allochem size averages greater

than 1.5 mm and coarsely crystalline poikilotopic equant poly

gonal precipitative sparry calcite cement often occurs (Pi.

10, Fig. F). Locally crinoid fragments serve as nuclei for

optically continuous monocrystalline sparry calcite over

growths (Pi. 10, Fig. F) . Ostracods and Favosites fragments

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. < T \ Time Partial the the Sediment Exposure Modern Dewatering of First Subareal

Time Time of Deposition

sequences sequences of diagenetic events recorded by the Rockport Quarry Inferred Event Extensive Local Fracturing of the Rockport Calcite Development of Porosity Dolomitization Submarine Cementation Synhoresis Cracking Pore-Filling Equant Poly gonal Sparry Calcite Original Submarine Cement Neomorphosed to Bladed Quarry Limestone as Unit a Compaction Cracking Table Table 6. Neomorphism of Micrite to Limestone Microspar

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77

commonly display polycrystalline overgrowths of optically con

tinuous fine to medium crystalline fibrous to bladed (Folk,

1965) calcite radiating out from skeletal walls into intra

particle pore space. The fibrous to bladed calcite grades

into coarser medium crystalline equant polygonal pore-filling

sparry calcite near the center of the void. In some speci

mens fine to medium crystalline bladed sparry calcite was ob

served as polycrystalline overgrowths optically continuous on

other allochemical components.

The fibrous and bladed sparry calcite is thought to re

present neomorphosed aragonite or magnesium calcite indicative

of early marine cementation; however, the equant polygonal

sparry calcite is interpreted to have formed from meteoric

waters or from magnesium-poor formation waters in the subsur

face (Folk 1974; Folk and Land, 1975; Bathurst, 1975).

Thus the morphology of the bladed sparry calcite cement

and the occurrence of synhoresis cracks filled with precipi-

tative equant sparry calcite suggests that cementation began

soon after deposition in the subtidal marine environment and

has continued in phases possibly throughout the diagenetic

history of the Rockport Quarry Limestone (Table 6).

Dolomitization

Dolomite in the Rockport Quarry Limestone is clearly sec

ondary. It replaces pore-filling sparry calcite at Rockport

Quarry (PI. 16, Fig. D) and Grand Lake, matrix (Pi. 16, Fig.

A) and stromatoporoids (PI. 16, Fig. E) at Grand Lake, and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78

matrix (Pi. 12, Figs. E, F; PI. 16, Fig. F) and fossil frag

ments at Ocqueoc Falls (Table 6). At Rockport Quarry (Fig. 1,

Loc. 32-9-6) and Grand Lake (Fig. 1, Loc. 32-9-6) dolomitiza-

tion is extremely minor and is restricted to the stromatopo

roid biolithite facies; however, at Ocqueoc Falls pervasive

dolomitization has replaced much of the matrix and coarse al-

lochemical components within the organic-mud packstone facies

(PI. 16, Fig. F ) .

Dolomite within the strata at Rockport and Grand Lake has

locally replaced pore-filling sparry calcite that originally

filled: 1) fenestrae (PI. 16, Figs. C, D); and 2) original

intraparticle voids in the skeletons of Favosites, ostracods,

and stromatoporoids (Pi. 16, Fig. E). The dolomite is usually

brownish and displays rhombic form in both hand specimen and

thin section (Pi. 16, Figs. A, B, E); however, when the dolo

mite occurs in aggregate the rhombic form is less pronounced

(PI. 16, Fig. D).

The extensive dolomitization of Rockport Quarry Lime

stone strata at Ocqueoc Falls is characterized by 125 micron

dolomite rhombs showing some segregation of darker materials

in the centers and at the boundaries (Pi. 12, Fig. E; PI. 16,

Fig. F). Nevertheless, the ubiquitous brown microspheres pre

sent in all non-micritic Rockport facies are still present in

the less dolomitized layers at Ocqueoc Falls (PI. 13, Fig. E).

Echinoderm ossicles and stromatoporoids are the common pre

served skeletal allochems (Pi. 12, Figs. E, F; Pi. 16, Fig.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. E). Interrhombic porosity in the dolomites at Ocqueoc Falls

ranges from 0.0 to 6.0 percent. The pores characteristically

have trapezohedral or triangular shape with straight walls

(Pi. 16, Fig. F). Landes (1946) has suggested that contem

poraneous solution and dolomitization by ground water moving

along local fracture zones has locally produced this type of

porosity.

The localized nature of the dolomitization at Ocqueoc

Falls rules out seawater-fresh-water mixing (Folk and Land,

1975) as a possible source of magnesium for dolomitization.

In southern Michigan dolomitization along the Albion-Scipio

trend is thought to have occurred when a subsurface source of

magnesium picked up by ground water was redistributed along

fault trends (Landes, 1946; Shaw, 1976). This could have

locally raised the Mg/Ca ratio in the formation waters caus

ing dolomitization of carbonate in the subsurface (Folk and

Land, 1975). Perhaps this same mechanism is responsible for

the localized dolomitization at Ocqueoc Falls.

The magnesium required for the minor dolomitization else

where in the Rockport Quarry Limestone may have been locally

expelled from abundant magnesium calcite grains (such as cri-

noids) as they underwent recrystallization to calcite during

flushing by meteoric waters (Folk and Land, 1975). The uni

form composition of the calcite (6 percent magnesium) in the

Rockport Quarry Limestone (Fig. 3) is suggestive of this mech

anism.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80

Algal mats (Gebelein and Hoffman, 1973) and clays offer

other possible sources of magnesium for the minor dolomitiza

tion in the Rockport Quarry Limestone. Organic mud in the

Rockport Quarry Limestone is probably of algal origin and thus

could provide a possible source for magnesium (Gebelein and

Hoffman, 1973). Furthermore, the Rockport Quarry Limestone

is bounded above by the Ferron Point Formation and below by

the Bell Shale. Possibly during diagenetic conversion of

clays to illite magnesium was released which allowed local

dolomitization in the Rockport Quarry Limestone.

Neomorphism

Neomorphism (Folk, 1965) has extensively altered grain

contact relationships within all facies of the Rockport Quarry

Limestone (Table 6). X-ray data indicate that calcite from

the packstone facies contains only about 6 percent MgCC>3 (Fig.

3). The magnesium content of skeletons produced by modern

marine organisms ranges from 0.0 to 30 percent MgCOg and aver

ages 10 to 20 percent (Chave, 1954). The uniformly low MgCC>3

content of the Rockport packstones probably reflects a loss

of magnesium during neomorphism.

Aggrading neomorphism has recrystallized most of the mic

rite comprising the pelloids to fine microspar averaging 6

microns in size. Loaflike crystals (Folk, 1965), indicative

of neomorphism, are occasionally discernable in the micrite

(Pi. 7, Figs. A, B). Under high power pelloid boundaries are

inpinged by small neomorphic sparry calcite crystals growing

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81

inward from the surrounding matrix (PI. 8, Fig. C). Larger

medium crystalline loaf-shaped sparry calcite crystals (Pi.

7, Figs. A, B) are probably also neomorphic (Folk, 1965) and

derived from original micritic matrix.

Skeletal grains that originally had fibroradial wall

structure (ostracods) or lamellar structure (brachiopods),

have been neomorphosed to produce a mosaic of finely crystal

line equant sparry calcite; whereas, the fibroradial shell

structure of tabulate corals has often aggraded to form bladed

sparry calcite crystals. Gastropods are represented by medium

to coarsely crystalline sparry calcite molds. The original

aragonitic shell was apparently dissolved and contempora

neously or later filled with sparry calcite (Pi. 8, Fig. A).

Within the organic-mud packstone and biolithite facies,

neomorphism has affected mainly the echinoderm fragments and

the stromatoporoids. Degrading neomorphism has polygonalized

echinoderm ossicles, and the polygon boundaries are usually

bounded by micrite (PI. 12, Figs. E, F). Original pores with

in the echinoderm fragments usually show different optical

orientation than the enclosing fragment. Either 1) the pores

were filled with a pore-filling precipitate which was not neo

morphosed with the fragment, or 2) the pores within the echi-

nodern fragments were filled with micrite and neomorphosed

along with the fragment, which exerted no control upon the

orientation of the neomorphosed pore-filling micrite. The

stromatoporoids have recrystallized by aggrading neomorphism

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (PI. 12, Figs. A, 3, C) such that the neomorpnic crystals

transect the original wall structure of the coenosteum which

is preserved as a ghost structure (PI. 12, Figs. A, B, C; Pi.

14, Fig. E).

Diagenetic History

The diagenetic history of the Rockport Quarry Limestone

began with deposition in the Middle Devonian and has contin

ued into the Holocene (Table 6). Diagenesis began with the

local formation of submarine aragonite and (or) magnesium cal

cite needle cement which was subsequently neomorphosed to

finely crystalline bladed sparry calcite (Table 6). Follow

ing original submarine cementation, but before dewatering of

the sediment was complete, synhoresis cracks v/ere filled with

equant polygonal sparry calcite that also started filling ori

ginal inter and intraskeletal porosity. As lithification of

the sediment increased, cracks originally formed only in stro

matoporoid plates and soft micritic sediment began to encom

pass lithified strata. Fracturing eventually effected the

Rockport Quarry Limestone as whole (Table 6). Perhaps such

fractures served as the avenue for dolomitization at Ocqueoc

Falls. Dolomitization in formation of the rest of the Rock

port Quarry Limestone occurred following a period of fresh

water flushing which created voids after the precipitation of

the sparry calcite cement (PI. 16, Fig. E).

To summarize, the diagenetic history of the Rockport

Quarry Limestone began with the formation of submarine cement

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the Devonian and the initiation of neomorphism, compaction,

and fracturing. Before dewatering was complete sparry calcite

cements began to form, possibly suggesting early subsurface

cementation. Cementation was locally followed by a period of

void formation which preceded local dolomitization.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEONTOLOGY

Before this study, 22 genera had been identified in the

Rockport Quarry Limestone (Ehlers and Kesling, 1970; Table

7); however, there were many omissions in the faunal lists

of the formation for all but the Brachiopoda (Imbrie, 1959)

and the Coelenterata (Stumm, 1951, 1961). In this study, 22

additional taxa were identified that have not been previously

recorded in the literature (Table 7).

Since the study was concerned primarily with the deposi-

tional facies of the Rockport Quarry Limestone and not with

the systematic paleontology of the enclosed biota, only mini

mal taxonomic hierarchy information is presented. Addition

ally, descriptions and discussions are limited to specimens

collected for this work.

Systematic Descriptions

Phylum Protozoa

Order Foraminiferida Eichwald

Family Nodosinellidae Rhumbler

Plate 10, Fig. A

Discussion. Test trochospiral, loosely evolute. Wall

structure composed of micrite with an inner finely crystal

line fibroradial layer. Only one specimen (RQ 4-2) found.

Dimensions. Chamber size, 150 to 500 microns; wall thick

ness, 40 microns including an inner wall (4 microns) and an

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 7. Taxa recorded from the Rockport Quarry Limestone.

E, Ehlers and Kesling (1967); D, Dorr and Eschman (1970); C,

Cookman, this study

Fauna Author

Coelenterata E

Rugosa E

Billingsastrea E

Cyanthophyllum E

Cylindrophyllum E

Cystiphylloides E

Heterophrentis E

Hexagonaria E

Spongophy1lum E

Tabulata

Aulocystis E

Emmonsia E

Favosites E

Trachypora E

Brachiopoda

Articulata E

Chonetes E

Longispina E

Pentamerella E

Pholidostrophia E

Chi zophora E

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Schuchertella E

Spinulicosta E

Strophodonta E

Foraminiferida C p. 84

Coelenterata E

Clathrodictydae C p. 88

Stromatoporidae C p. 89

Idiostromatidae C p. 89

Bryozoa

Fenestellidae C p. 90

Species A C p. 90

Species B C p . 90

Species C C p. 91

Trepostomata C p. 91

Species A C p. 91

Species B C p . 92

Mollusca

Cephalopoda C p. 92

Gastropoda C p. 93

Arthropoda

Trilobitomorpha C p. 93

Ostracoda C p. 93

Echinodermata

Crinoidea C p. 94

Vertebrata

Arthrodire plates D p . 158

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Cyanophyta

Brown Microspherulites C p- 95

Renalcis C p - 96

Oncolite C p- 96

Chlorophyta

Dasycladaceae

Vermiporella C p- 97

Rhodophyta C p- 98 Algae indeterminate

Calcisphera sp. A C p- 99

Calcisphera sp. B c p- 100

outer wall (36 microns); test size, 1200 microns.

Facies. Organic-mud packstone; crinoid-bryozoan grain-

stone subfacies.

Location. Measured Section 1, Unit 2 (Appendix 1, PI.

18) .

Figured specimen. Thin section RQ 4-2 = WMU 2580.

Family indet.

Plate 10, Fig. B

Description. Test biserial enrolled (mature) or sphe

roidal (juvenile). Wall structure calcareous and smooth com

posed of micrite with an outer fibroradial layer.

Discussion. Found sparsely as solitary individuals in

6 specimens.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88

Facies. Organic-mud packstone facies; micrite facies,

fenestral subfacies.

Specimens. Plexiglass peels: 34-6-24 b = WMU 2593, 33-

8-17 = WMU 2594, RB 2-3b = WMU 2597. Thin sections: 2RQl-sz

= WMU 25 81, RQ 3-3 = WMU 2595, RQ 5-2 = WMU 2596.

Dimension. Chamber size, 800 to 900 microns; wall thick

ness, 130 microns including an inner wall (70 microns) and an

outer wall (60 microns); test size 1250 x 275 microns.

Location. Measured Sections 1, 2, 4, 9, 12, 14 (Appen

dix 1, Pis. 18, 19).

Figured specimen. Plexiglass peel, 33-8-17 = WMU 2594.

Phylum Coelenterata

Order Stromatoporoidea Nicholson and Murie

Family Clathrodictydae Galloway (1957)

Plate 11; Plate 12, Fig. C

Description. Coenosteum laminar to massive composed of

laminae which are in general parallel. Galleries are higher

than the laminae are thick. Pillars usually present, con

fined between two laminae, but may be incidentally superim

posed. Tissue compact in laminae and pillars. Astorhiza pre

sent.

Neomorphism. Coarsely crystalline equant polygonal.

Dimensions. Mamellon, 1 mm; Gallery, 250 microns; Wall,

50 microns.

Facies. Organic-mud packstone, stromatoporoid biolithite,

biolithite-micrite transition.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89

Location. Measured Sections 1-8, 10 (Appendix 1, Pis.

18, 19).

Figured specimen. Field photographs Measured Section 1,

Unit 1, and Measured Section 10, Unit 1. Thin section RQ-

Ceph = WMU 2 5 89.

Family Stromatoporidae Galloway (19 5 7)

Plate 12, Figs. A, B; Plate 15, Figs. A, B

Description. Coenosteum laminar composed of laminar and

short and long pillars. Interlamellar spaces filled with sec

ondary tissue. Tissue coarsely maculate. Astrorhizae present.

Neomorphism. Fibroradial, medium crystalline.

Dimensions. Cell size, 25 micron (inter-maculate); cell

size, 250 micron (galleries); wall thickness, 10 micron.

Facies. Stromatoporoid biolithite, biolithite-micrite,

transition.

Location. Measured Sections 1-8, 10 (Appendix 1, Pis.

18, 19).

Figured specimen. Field photographs Measured Section 1,

Unit 1, and Measured Section 10, Unit 1. Thin sections RQ1-1

= WMU 2590.

Family Idiostromatidae Galloway (1957)

Plate 14, Fig. E

Description. Coenosteum cylindrical, dendroid or fasci

culate, skeleton composed of thick laminae and irregular pil

lars, mostly short. Skeletal tissue compact possibly porous.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Neomorphism. Medium crystalline equant polygonal.

Dimensions. Coenosteum length, 3 cm (maximum observed)

coenosteum diameter, 0.5 to 1.0 cm; cell size, 250 microns;

cell wall thickness, 50 microns.

Facies. Biolithite-micrite transition.

Location. Measured Section 1, Unit 5; Measured Section

2, Unit 3 (Appendix 1; PI. 18).

Figured specimen. Thin section RQ 5-3 = WMU 2586.

Phylum Bryozoa Ehrenberg

Order Cryptostomata Vine

Family Fenestellidae King

Species A

Plate 17, Fig. A

Description. Fenestrule ovoid with aperatures arranged

alternately along interfenestrule partition.

Dimensions. Aperature, 20 microns; Fenestrule, 350-400

microns.

Facies. Organic-mud packstone, crinoid-bryozoan grain-

stone subfacies.

Location. Measured Sections 1-11 (Appendix 1; Pis. 18,

19) -

Figured specimen. 34-8-31-2 = WMU 2598.

Species B

Plate 17, Fig. A

Description. Fenestrules rectangular.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91

Dimensions. Aperature, 20 microns; Fenestrule, 1000 x

37 5 microns.

Facies. Organic-mud packstone, crinoid-bryozoan grain-

stone subfacies.

Location. Measured Sections 1-11 (Appendix 1; Pis. 18,

19) .

Figured specimen. 34-8-31-2 = WMU 2598.

Species C

Plate 17, Fig. A

Description. Fenestrule ovoid, aperature not observed.

Dimensions. Fenestrule, 600 microns.

Facies. Organic-mud packstone, crinoid-bryozoan grain-

stone subfacies.

Location. Measured Sections 1-11 (Appendix 1; Pis. 18,

19) .

Figured specimen. 34-8-31-2 = WMU 2598.

Order Trepostomata

Plate 17, Fig. B

Description. Ramose zoaria with ovoid zooecia.

Discussion. Two species (A, B) identified based on di

mensional data.

Species A

Dimensions. Zoarium length, 3 cm; zoarium diameter, 125

microns; zooecium diameter, 125 microns.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Facies. Organic-mud grainstone.

Location. Measured Sections 1-14 (Appendix 1; Pis. 18,

19) .

Figured specimen. Hand specimen 34-8-31-2-ta = WMU 2599

Species B

Dimensions. Zoarium length, 3 cm; zoarium diameter,

0.5 cm, zooecium diameter, 300 x 250 microns.

Facies. Organic-mud packstone, crinoid-bryozoan grain-

stone subfacies.

Location. Measured Section 12 (Appendix 1; PI. 18) .

Specimen. Hand specimen RQ-Cr = WMU 2592.

Phylum Mollusea

Class Cephalopoda

Plate 12, Fig. C; Plate 17, Figs. C, D

Discussion. Test apparently originally aragonitic now

represented by aggregates of medium crystalline neomorphic

sparry calcite. Only protoconchs observed and collected. Al

samples crushed post-depositionally.

Dimensions. Length of test, 2 to 10 cm; diameter of

test, 1.0 to 5 cm.

Facies. Organic-mud packstone, crinoid-bryozoan grain-

stone subfacies.

Location. Rockport Quarry Measured Sections 1-8 (Appen

dix 1; Pi. 18) all specimens collected as single hand speci

mens from talus and wall rock, but from no specific measured

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93

section.

Figured specimen. RQ-Ceph = WMU 2 5 39.

Phy 1 uir. Mo llusca

Class Gastropoda Cuvier

Plate 8, Fig. A

Discussion. Ghost walls not visible implying test ap

parently was originally aragonitic and is now represented by

neomorphic sparry calcite aggregates.

Dimensions. Length of test, 500 to 2000 microns.

Facies. Micrite facies, dense subfacies.

Location . Measured Section 8, Unit 3; Measured Section

14, Units 1 and 6 (Appendix 1; Pis. 18, 19).

Figured specimen. Plexiglass peel RB l-4b = WMU 2591.

Phylum Arthropoda Seibold and Stannisis

Class Trilobitomorpha

Plate 10, Fig. E

Discussion. One complete pygidium along with several

fragments were observed.

Dimension. Length of pygidium, 2.5 cm.

Facies. Organic-mud packstone facies, crinoid-bryozoan

grainstone subfacies.

Location. Measured Section 2 (Appendix 1; Pi. 18).

Figured specimen. Hand specimen RQ-CR = WMU 2592.

Class Crustacea Pennant

Subclass Ostracoda Latreille

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94

Plate 10, Figs. E, D

Dimensions. Test length, 200 to 1000 microns.

Facies. Micrite facies, fenestral and dense subfacies;

organic-mud packstone, coral packstone subfacies.

Location. Measured Sections 1-8; Measured Section 14

(Appendix 1; Pis. 18, 19).

Figured specimen. RQ4-2 = WMU 2580.

Phylum Echinodermata

Class Crinoidea

Plate 10, Fig. E; Plate 12, Figs. D, E, F; Plate 13, Fig. B

Discussion. Observed as disaggregated ossicles, ossicles

stacked en echellon, and fragments of columnals. One partial

calyx recovered.

Dimensions. Ossicles, 0.5 mm to 7.5 mm; columnals up to

5 cm long; calyx apparently 3 to 4 cm in diameter.

Facies. Organic-mud packstone, biolithite, biolithite-

micrite transition.

Location. Measured Sections 1-14 (Appendix 1; Pis. 18,

19) .

Figured specimen. Hand specimen, RQ-CR = WMU 2592. Thin

sections 34-8-31-1 = WMU 2600, R05 = WMU 2601.

Phylum Cyanophyta

Genus and species indeterminate

Plate 13, Figs. C, D, E, F

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Description. Spherical bodies 3-5 microns in diameter

with a majority of individuals averaging 4 microns. Several

broken specimens show the existence of a wall approximately

0.5 microns in thickness. The thallus is composed of hydro

carbons of asphaltic nature.

The brown microspheres occur within the non-micritic

strata (Table 2) and commonly in the packstone in such con

centrations that the rocks take on a dark grey to black color.

In thin section the microspheres are commonly compacted to

gether so tightly that they form an amorphous mass. Indivi

duals are detected only in microsection or within uncompressed

areas, such as within the outer perimeter of Favosites coral-

lites (PI. 13, Fig. F).

Discussion. The spatial distribution of the brown micro-

spherulites is comparable to the distribution of blue-green

algal unicells within modern Australian and Bahaman subtidal

algal mats. The recent subtidal algal mats contain an abun

dance of fine filaments, coccoid algae and mucilage which can

completely inmesh the sediment (Neuman, et al., 1970; Scoffin,

1970; Logan, 1973). One type of these mats, the Schizothrix

unicell mat, is morphologically similar in its grain packing

and unicell distribution to the grain packing and distribution

of the brown microspheres observed at Rockport (compare Figure

7 and Pi. 13, Figs. C, D, E, F). It is hypothesized that

Rockport brown bodies are the unicell remnants of ancient sub

tidal algal mats.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96

Facies. Organic-mud packstone, biolithite, biolithite-

micrite transition.

Location. Rockport Quarry Limestone Measured Sections

1-14 (Appendix 1; Pis. 18, 19).

Figured specimen. Thin sections: RQ4-2 = WMU 2 5 80;

2RQ1-SZ = WMU 2581; ROl = WMU 2582; RQ-F = WMU 25 83.

Phylum Cyanophyta

Genus Renalcis Vologdin

Plate 14, Fig. F

Description. Thallus made up of irregular compound

growths of hollow inflated reniform chambers about 10 microns

high and 250 microns long. Colony is a simple 2 mm long hemi

spherical growth form containing two chambers. Walls are

thick (2500 microns) and of uniform texture, composed of a

dense micrite. The walls are characterized by a reticulate

pattern of clefts between the inner and outer margin. Clefts

average a height of 250 microns and a width of 25 microns,

may open toward the inner margin.

Facies. Micrite, fenestral subfacies

Location. Measured Section 14, Unit 17 (Appendix 1; PI.

19) .

Figured specimen. Thin section RB 3-6 = WMU 2584

Phylum Cyanophyta

Oncolite

Plate 17, Figs. E, F

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97

Description. Oblate ellipsoidal oncolite composed of con

centrically laminated close and spaced laterally linked hemi-

spheroids (Code = SS-C/LLM-C-S; Logan et al_. , 1964). Around

the margin, some of the layers are contorted and cracked. Void

space within the oncolite is filled with coarsely crystalline

equant polygonal sparry calcite (locally dolomite in trace

amounts replaced the sparry calcite). Stromatoporoid proba

bly served as the nucleus.

Dimensions. Length, 10 cm; height, 3 cm; layer thick

ness, 25-250 microns.

Discussion. Some post-depositional crushing of the sam

ple has occurred as exhibited by the disrupted layers around

the edges.

Facies. Organic-mud packstone, coral packstone subfa

cies

Location. Between Measured Section 1 and Measured Sec

tion 2 within a fine to medium skeletal calcarenite: coral

organic-mud packstone (Appendix 1; Pi. 18).

Figured specimen. RQ-On = WMU 2 5 85.

Phylum Chlorophyta Papenfus

Family Dasycladaceae Kutzin

Genus Vermiporella Stollup

Plate 14, Figs. A, B

Description. Tallus cylindrical branching of varying di

ameter. Wall of thallus is thin composed of parallel or unit

ed fibers of calcite perpendicular to thallial wall and pene-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. trated by simple circular pores oriented perpendicular to the

axis of the central stem. Pores numerous closely set and of

uniform diameter (they do not bifurcate into a second series).

Calcification very thin and restricted to angular rind. Con

sequently thalli easily broken into small fragments.

Inner structure not preserved. Observed as transverse

sections, most specimens now irregular in shape due to crush

ing .

Dimensions. Thallus diameter, 150 to 450 microns; wall

thickness, 50 microns; pore diameter, 7 to 10 microns.

Facies. Biolithite-micrite transition facies.

Location. Measured Section 1, Unit 5; Measured Section

2, Unit 3 (Appendix 1; Pi. 18).

Figured specimen. Thin sections RQ 3-5 = WMU 2587, RQ

5-3 = WMU 2586.

Phylum Rhodophyta

Algae indeterminate

Plate 14, Figs. C, D

Description. Thallus cylindrical to reniform of varying

diameter. Thallus wall composed of an outer dense micrite

margin and an inner margin of laminated calcite fibers perpen

dicular to the thallus wall. Individual chambers agglutinated

as a mass, with the outer dense micrite margin being shared by

adjacent chambers (possibly encrusting).

Dimensions. Thallus diameter, 25-135 microns; wall thick

ness, 10 microns.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99

Facies. Biolitnite-micrite transition facies.

Location. Measured Section 2, Unit 3 (Appendix 1; Pi.

18) (four colonies observed).

Algae indeterminate, Problematical Algae (Wray, 1967)

Genus Calcisphera Williamson

Plate 7, Figs. A, B

Discrete spherical bodies consisting of an inner chamber

(40 microns to 190 microns) in diameter, bounded by a calci-

tic wall (2-10 microns thick). Walls are composed of dense

micrite which under highest power shows a vague loaf-like form.

A second inner wall may be visible (Pi. 7, Fig. B). The cen

tral chamber is commonly filled with clear calcite cement,

commonly one crystal but occasionally several equant poly

gonal crystals with straight boundaries. Nonequitorial sec

tions can be distinguished from equitorial sections due to

their fuzzy outline (Stanton, 1963).

Calcisphera sp. A

Plate 7, Fig. A

Description. One form with a concentrically laminated

calcite wall was observed.

Dimensions. Cell size, 60-200 microns; wall thickness,

10 microns; inner chamber size, 40 to 180 microns.

Facies. Micrite, dense subfacies.

Location. Measured Section 14, Unit 8 (Appendix 1; PI.

19) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100

Figured specimen. Plexiglass peel RB 2-4b = WMU 2588.

Calcisphera sp. B

Plate 7, Fig. B

Description. Dense micrite wall bounded interiorly by

a second spherical wall which is delineated by a circular

train of microspar crystals. The lack of preservation of

these interior walls suggest that originally they were not

calcite (Stanton, 1963).

Dimensions. Cell size, 60-200 microns; outer wall thick

ness, 2 to 4 microns; inner wall marked by 2 micron sized mi

crospar, 6 microns within the outer wall.

Facies. Micrite, dense subfacies.

Location. Measured Section 14, Unit 8 (Appendix 1; PI.

19) .

Figured specimen. RB 2-4b plexiglass peel = WMU 2588.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSIONS

Comprehensive study of the Rockport Quarry Limestone in

Alpena, Presque Isle, and Montmorency Counties allows the

following conclusions to be made concerning the sedimento-

logy of the formation.

1. Four facies (organic-mud packstone facies, stroma-

toporoid biolithite facies, biolithite-micrite transition fa

cies, and micrite facies) record deposition of shallow sub

tidal marine algal-mat-bearing platform blanket sands, stro-

matoporoid biolithite shoals, and lagoonal subtidal to inter

tidal pelletal muds.

2. The algal-mat-bearing blanket sands are represented

by the organic-mud packstone facies. Coral-bearing organic-

mud packstone within the facies record the algal mat suben

vironment, and the crinoid-bryozoan organic-mud packstones and

poorly-washed grainstones represent local meadows of in situ

grain production. The coral packstone subfacies, characterized

by organic-mud packstone probably represent deeper water sedi

mentation and lower energy than the crinoid-bryozoan grain-

stone subfacies characterized by layers and lenses of crinoid-

bryozoan organic-mud packstone and poorly-washed grainstones.

3. The pelletal muds of the micrite facies were probably

deposited in back reef lagoons; the fenestral subfacies form

ing in the intertidal zone and the dense subfacies in the sub

tidal environment.

101

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4. The biolithite-micrite transition facies at Rockport

Quarry is transitional between the shoaling environment of the

biolithite facies and the restricted back shoal area of the

micrite facies. Locally it contains calcareous green algae

represented by Vermiporella and an unidentified encrusting

form. Renalcis, found at Black Lake in micritic rocks in

ferred to be of intertidal origin, was probably washed into

the intertidal zone from adjacent subtidal lagoonal back reef

areas. It is believed that this is the first documented oc

currence of Devonian calcareous algae in the Traverse Group

of Michigan.

5. Relative depths of the three facies present in the

Rockport Quarry Limestone are based on superpositional and

faunal indicators that compare favorably with studies of other

shallow water Devonian facies of the world. Stromatoporoid

biolithite shoals apparently separated unrestricted subtidal

marine organic-mud packstones from back shoal areas where pel

letal muds were deposited.

6. The dark component of the Rockport Quarry Limestone

("organic mud") which occurs in the organic-mud packstone fa

cies and the interstromatoporoid rocks of the biolithite fa

cies, is composed primarily of hydrocarbon but contains trace

amounts of terrigenous quartz and muscovite-illite, and dia-

genetic pyrite. The dominant hydrocarbon grain type in the

organic mud are 4 micron black spheres, termed "microspheres,"

which are interpreted to represent the unicell remnants of

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Middle Devonian subtidal algal mats.

7. Diagenetic effects within the Rockport Quarry Lime

stone began penecontemporaneously with deposition.

8. At Rockport and Grand Lake, dolomite replacement

began after the cracks and fractures were filled with sparry

calcite. The timing of the dolomitization at Ocqueoc Falls,

however, can only be stated as post-depositional, possibly

post-cementation.

9. Twenty-two additional taxa have been added to the

faunal list for the Rockport Quarry Limestone.

10. A generalized aepositional model (Fig. 10) can be

developed to account for the facies sequence observed today

in the outcrop belt that requires only simple facies migra

tion on a stable carbonate platform (Fig. 12). This model

can probably serve as a general model tc be considered in the

interpretation of shallow-water Devonian sediments elsewhere.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX 1— MEASURED SECTIONS

Fourteen sections of the Rockport Quarry Limestone were

measured at six locations in Alpena and Presque Isle Counties

using a Jacob Staff. The six locations are shown in Figure 1

where each location is identified by three elements (such as

32-9-6) which refer to the: 1) number of the Township North;

2) number of the Range East; and 3) the number of the section.

This numbering scheme was used by Ehlers and Kesling (1970,

p. 3) who listed numerous localities previously cited in pub

lications by the Michigan Geological Survey where exposures

of the Rockport Quarry Limestone could be examined. The mea

sured sections are described from southeast to northwest along

the outcrop belt.

Measured Sections 1-8, Rockport Quarry

Eight sections of the Rockport Quarry Limestone were mea

sured at the abandoned quarry of Kelly's Island Lime and Trans

port Company (formerly Great Lakes Stone and Lime Company)

near Rockport (Rockport Quarry) in the NW1/4, Sec. 6, T. 32 N.,

R. 9 E. (Fig. 1, 32-9-6). Rockport Quarry is in the type area

of the Rockport Quarry Limestone. The north end of the quarry

extends into the southeast corner of Presque Isle County in

the SEl/4, Sec. 36, T. 33 N., R. 8 E.; and west into the north

east corner of Alpena County in the NEl/4, Sec. 1, T. 32 N.,

R. 8 E. The Bell Shale crops out in drainage ditches near the

104

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. south end of the quarry, and the Ferron Point Formation is ex

posed at the top of the west wall. A sinkhole exposed in the

west wall contains Genshaw Formation fossils (Ehlers and Kes-

ling, 1970). The eight sections were measured along the west

wall of the quarry over a distance of 600 meters. Listed from

south to north they are: Measured Section 1 (RQ3); Measured

Section 2 (RQ5); Measured Section 3 (RQ4); Measured Section 4

(RQ1); Measured Section 5 (RQ2); Measured Section 6 (RQ6);

Measured Section 7 (RQ7); and Measured Section 8 (RQ8).

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Measured Section 1 (RQ3) - Rockport Quarry

Measured Section 1 (RQ3) was measured in the Rockport

Quarry Limestone along a vertical wall adjacent to a large

cave-in on the west wall of Rockport Quarry in the SWl/4,

NW1/4, Sec. 6, T. 32 N., R. 9 E. The base of the Rockport

Quarry Limestone is covered and the top has been removed

either by erosion or quarrying operations (see PI. 18 for to

pographic expression and sample locations).

Thickness M. above Unit Description______in M.______base

6. Micrite facies. Fine to medium 0.90 5.40-6.30 calcilutite: horizontally fenestral interbedded pelmicrite and pelsparite. Light grey (N6) .

5. Micrite-biolithite transition 0.30 5.10-5.40 facies gradationally overlying stromatoporoid biolithite fa cies. Laminar stromatoporoids (average 1 cm thick at base) with 50 percent interstromatoporoid fine to coarse skeletal calcarenite: organic-mud pack stone grading to poorly washed pelloidal grainstone at tops containing calcareous algae. Greyish orange (10 YR 7/4) to light grey (N7) upwards.

4. Biolithite facies. Laminar 0.30 4.80-5.10 stromatoporoids from 1 to 2 cm in thickness with interstromatoporoid fine to coarse skeletal calcarenite: organic- mud packstone. Greyish orange (10 Y 7/4)

3. Organic-mud packstone facies, 0.45 4.35-4.80 crinoid-bryozoan grainstone subfacies. Medium to coarse

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Thickness M. above Unit Description______in M. base

skeletal calcarenite to fine skeletal calcirudite: cri noid-bryozoan packstone to poorly washed grainstone. Light olive grey (5 Y 6/1) interbedded with less abun dant dark grey (N3) fine to coarse calcarenite: coral or ganic-mud packstone. Coral organic-mud packstone more abundant near the top of the unit where it contains Hetero- phrentis, Favosites, and broken laminar stromatoporoids and is gradational with stromatoporoid biolithite. A layer of medium skeletal calcarenite to fine skeletal calcirudite: crinoidal organic-mud packstone to poorly washed grainstone similar to Unit 4 (Measured Section 5; RQ2) occurs at the base. The bryozoan packstones are better indurated and ring under the hammer, they commonly exhibit 1 mm thick CaCO^ preci pitates on the exposed rock faces which may be remnant fracture fillings.

2. Organic-mud packstone facies, 1.95 2.40-4.35 coral packstone subfacies. Medium light grey (N6) (weathered) and dark grey (N3) (fresh) fine to coarse calcare nite: coral organic-mud pack stone with lenses 2 to 10 cm thick and 10 to 60 cm long of light olive grey (5 Y 6/1) (weathered) and dark grey (N3) (fresh) coarse skeletal cal carenite to fine skeletal cal cirudite: crinoid-bryozoan organic-mud packstone to poorly washed grainstone.

la. Mud shale and talus. Brownish 0.25 2.15-2.40 black (5 YR 2/1) to dark grey (N3) .

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Thickness M. above

Unit Descriotion^ - in _ M. base ------

1 . Stromatoporoid biolithite 2.15 0.00-2.15 facies. Laminar stromatoporoids interlaminated with 10 percent interstromatopcroid fine to coarse skeletal calca renite: organic-mud packstone. Dark grey (N3), greyish orange (10 YR 7/4) when weathered. Large hemispherical stromatoporoids and colonial rugose corals, locally overturned. At 60 cm above base, a 5.0 to 10 cm thick zone of thin laminar stromatoporoids averaging 1 cm in thickness forms a distinct outcrop lineation. At top of unit some stromatoporoids are truncated.

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Measured Section 2 (RQ5) - Rockport Quarry

Measured Section 2 (RQ5) was measured in the Rockport

Quarry Limestone below glacial till, 200 m south of the large

sinkhole on the west wall of Rockport Quarry in the SW1/4,

NWl/4, Sec. 6, T. 32 N., R. 9 E. The base of the Rockport

Quarry Limestone is covered and the top has been removed by

glacial scour (see Pi. 18 for topographic expression and sam

ple location).

Thickness M. above Unit Description ______in M.______base

8. Micrite facies, brecciated. 0.60 7.70-8.30 Light grey (N7).

7. Micrite facies, fenestral sub- 0.90 6.80-7.70 facies. Fine to medium calcilutite: horizontally fenestral interbedded pelsparite and pelmicrite. Light grey (N7).

6. Micrite facies, fenestral sub- 0.15 6.65-6.80 facies. Medium calciiutite to medium calcarenite: intraclast-bearing horizontally fenestral interbedded pel sparite and pelmicrite. Light grey (N7).

5. Biolithite-micrite transition 1.20 5.45-6.65 facies. Laminar stromatoporoids at base interlaminated with 50 percent interstromatoporoid fine to coarse skeletal calcarenite: organic-mud packstone grading to poorly washed pelloidal grainstone at the top. Greyish orange (10 YR 7/4) at base to light grey (N7) at the top of unit. Heterophrentis, Favo- sites, stromatoporoids (hand specimen) and calcareous algae (thin section).

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Thickness M. above Unit Description______in M. base

4. Stromatoporoid biolithite 0.65 4.80-5.45 facies similar to Unit 4 (Mea sured Section 1, RQ3).

3. Organic-mud packstone facies- 0.90 3.90-4.80 crinoid-bryozoan grainstone subfacies. Lenses of greyish orange (10 YR 7/4) medium skeletal calcarenite to fine skeletal calcirudite: cri noid-bryozoan organic-mud packstone to poorly washed grainstone (60-70%) enclosed within dusky yellowish brown (10 YR 2/2) fine to coarse skeletal calcarenite: coral organic-mud packstone. Lenses coalesce upward into layers. A medium skeletal calcarenite to fine skeletal calcirudite: crinoid organic-mud packstone to poorly washed grainstone layer at the base. Bulbous Favosites and laminar stro matoporoids more abundant near top of unit; and ramose Favosites lenses most abundant near the top but distributed in lesser amounts randomly.

2a. Organic-mud packstone facies, 0.9 0 3.00-3.90 coral packstone subfacies. Dusky yellowish brown (10 YR 2/2) fine to coarse calcare nite: coral organic-mud packstone (60-80 percent) en closing greyish orange (10 YR 7/4) medium skeletal calcare nite to fine skeletal calci rudite: crinoid-bryozoan organic-mud packstone to poorly washed grainstone. Crinoid and bryozoan frag ments more abundant near base of unit.

Organic-mud packstone facies 0.45 2.55-3.00 coral packstone subfacies. Medium skeletal calcarenite

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Thickness M. above Unit Description in M. base

to fine skeletal calcirudite: crinoid-bearing organic-mud packstone to poorly washed grainstone. Light grey (N7) weathered and dark grey (N3) fresh.

la. Shale and talus. Brownish 0.15 2.40-2.55 black (5 YR 2/1) to dark grey (N3) .

1. Stromatoporoid biolithite 2.40 0.00-2.40 facies. Laminar stromato poroids up to 10 cm in thick ness interlaminated with in ters tromatoporoid fine to coarse calcarenite: organic- mud packstone. Medium brown ish grey (5 YR 5/1); scattered ramose Favosites, Cystiphil- loides, and Heterophrentis in trace amounts; zones of lami nar stromatoporoids averaging less than 1 cm in thickness, observed at 60 and 120 cm; a layer 15 cm thick containing colonial rugose corals (Hexagonaria and Billingsastre) and abraded hemispherical stro matoporoids with locally filled erosional scours at 150 cm.

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Measured Section 3 (RQ4) - Rockport Quarry

Measured Section 3 (RQ4) was measured in the Rockport

Quarry Limestone just 50 m south of the large sinkhole on the

west wall of Rockport Quarry in the SWl/4, NWl/4, Sec. 6,

T. 32 N., R. 9 E. The base of the Rockport Quarry Limestone

is covered and the top has been removed either by glaciation

or quarrying operations (see PI. 18 for topographic expression

and sample locations).

Thickness M. above Unit Description______in M.______base

4b. Micrite facies fenestral sub- 0.20 7.00-7.20 facies. Fine to medium calcilutite: horizontally fenestral interbedded pelsparite and pelmicrite. Light grey (N7).

4a. Micrite facies, dense subfa- 0.20 6.80-7.00 cies. Fine to medium calcilutite: sparse ramose Favo sites bearing micrite. Light grey (N7) .

3b. Biolithite-micrite transition 0.20 6.60-6.80 facies gradationally overlying stromatoporoid biolithite fa cies. Laminar stromatoporoids at base interlaminated with 50 percent interstromatoporoid fine to coarse skeletal calca renite: organic-mud packstone grading to poorly washed pelloidal grainstone at top. Greyish orange (10 YR 7/4) to light grey (N7) at top.

3a. Stromatoporoid biolithite fa- 0.60 6.00-6.60 cies. Laminar stromatoporoids interlaminated at base of unit with 25 percent interstromato poroid fine to coarse skeletal calcarenite: organic-mud pack stone which increases upwards to comprise 50 percent of unit.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thickness M. above Unit Description in M. base

Greyish orange (10 YR 7/4). Gradational with organic-mud packstone facies below and biolithite-micrite transition facies above.

2b. Organic-mud packstone facies, 1.05 4.95-6 . 00 crinoid-bryozoan grainstone subfacies. Lenses of crinoid- bryozoan organic-mud pack stone and poorly washed grain stone that locally coalesce to form 2 cm to 10 cm thick layers (light olive grey, 5 Y 6/1, when weathered; dark grey, N3, when fresh) interbedded with 20 percent coral organic-mud pack stone (greyish orange, 10 YR 7/4). Bryozoan packstone layers locally centered around colonial rugose corals. Cri noid organic-mud packstone to poorly washed grainstone layer similar to that observed in Measured Section 5 (RQ2) occurs at the base. Top of unit gradational with over lying biolithite. Approxi mately 15 m to the south, the crinoid organic-mud packstone layer contains laminar stroma toporoids with associated Heterophrentis and Favosites at the base.

2a. Organic-mud packstone facies, 1.50 3.45-4.95 coral packstone subfacies. Layers of light olive grey (5 Y 6/1) fine to coarse skeletal calcarenite: coral organic-mud packstone inter bedded with lenses of medium to skeletal calcarenite to fine calcirudite: crinoid- bryozoan organic-mud packstone to poorly washed grainstone (20 percent).

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Thickness M. above Descnotior. in M. base

id. Mud shale and talus. Brownish 0.15 3.30-3.45 black (5 YR 2/1) to dark grey (.\3) ; colonial rugose corals and Favosites locally present.

1. Stromatoporoid biolithites 3.30 0.00-3.30 facies. Laminar stromatoporoids interlaminated with in- terstrom.atcporcid fine to coarse skeletal calcarenite: orgar.i c-r.ud packstone. Pale greyisr. orange (10 YR 7/4); preaom.inar.tly laminar stroma toporoids ranging from 1-6 cm and averaging 4 cm in thickness, subordinate hemispherical strc- matcpcrcids. At 150 cm, hemi spherical strcmatopcroids (45 cm in diameter) continuous with enclosing stromatoporoids at the base but discontinuous and partially eroded at top. Zones of thin (0.5-2.0 cm) laminar stromatoporoids at 1.20, 1.80,

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Measured Section 4 (RQ1) - Rockport Quarry

Measured Section 4 (RQ1) was measured in the Rockport

Quarry Limestone 25 m north of the large sinkhole on the west

wall of Rockport Quarry in the SWl/4, NW1/4, Sec. 6, T. 32 N . ,

R. 9 E. The base of the Rockport Quarry is covered and the

top has been removed through quarrying operations (see PI. 18

for topographic expression and sampling locations).

Thickness M. above Unit Description______in M.______base

2a. Brown shale and talus. 0.30 6.00 +

2. Organic-mud packstone facies, 1.65 4.35-6.00 coral packstone subfacies. Lenses of greyish orange (10 YR 7/4) medium calcarenite to fine calcirudite: crinoid- bryozoan organic-mud pack stone to grainstone ranging from 2 to 10 cm thick and 10 to 60 cm long, within dusky yellowish brown (10 YR 2/2) fissile fine to medium cal carenite: coral packstone.

la. Brown mud shale and talus. 0.30 4.05-4.35

1. Stromatoporoid biolithite 4.05 0.00-4.05 facies. Laminar stromatoporoids from 1 to 10 cm in thick ness interlaminated with interstromatoporoid fine to coarse skeletal calcarenite: organic- mud packstone containing whole and fragmented colonial and solitary rugose corals, and some hemispherical stromatoporoids. Fragments are marked by truncated chambers. Dark grey (N4) when fresh.

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Measured Section 5 (RQ2) - Rockport Quarry

Measured Section 5 (RQ2) was measured in the Rockport

Quarry Limestone 25 m north of Measured Section 4 (RQl) on

the west wall of Rockport Quarry in the NW1/4, NW1/4, Sec.

6, T. 32 N., R. 9 E. The base of the Rockport Quarry Lime

stone is covered and the top has been removed by quarrying

operations (see Pi. 18 for topographic expression and sam

pling locations).

Thickness M. above Unit Description ______in M.______base

6. Micrite facies. Light grey 0.60 6.00-6.60 (N7). Gradational contact with Unit 5 below.

5. Biolithite-micrite transition 0.75 5.25-6.00 facies gradationally overlying stromatoporoid biolithite facies (Unit 4a). Laminar stromatoporoids (average 1 cm thick at base) interlaminated with 50 percent fine to coarse calcarenite: organic-mud packstone which grades upward with decreasing laminar stromatoporoid, Heterophrentis and Favosites content to fine skeletal calcarenite: poorly washed pelloidal grainstone at top. Greyish orange (10 YR 7/4) to light grey (N7) near top of unit.

4a. Stromatoporoid biolithite 0.60 4.65-5.25 facies. Laminar stromatopo roids from 1 to 2 cm in thick ness interbedded with fine to coarse skeletal calcarenite: organic-mud packstone. Grey ish orange (10 YR 7/4). Lens of ramose Favosites enclosed in the stromatoporoid bioli-

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Thickness M. above Unit Description______in M. base

thite. Stromatoporoid con tent high at the bottom (70 to 80 percent) and lower (20 to 30 percent) near the top.

4. Organic-mud packstone facies, 1.05 3.60-4.65 crinoid-bryozoan grainstone subfacies. Dusky greyish orange (10 YR 7/4) less fis sile medium skeletal calcare nite to fine skeletal calcirudite: crinoid-bryozoan organic-mud packstone to poorly washed grainstone con taining colonial rugose corals and ramose Favosites that encloses layers of yel lowish brown (10 YR 2/2) fissile coral organic-mud packstone containing Hetero- phrentis and bulbous Favo sites . Thick laterally con tinuous crinoid-rich layer at base of unit.

3. Organic-mud packstone facies, O.SO 2. 70-3.60 coral packstone subfacies. Dark yellowish brown (10 YR 2/2) fissile fine to coarse skeletal calcarenite: coral organic-mud packstone inter bedded with dusky greyish orange (10 YR 7/4) less fis sile medium skeletal calcare nite to fine skeletal calcirudite: crinoid-bryozoan organic-mud packstone to poorly washed grainstone.

2 . Shale facies. Mud shale and 0.30 2.40-2.70 medium skeletal calcarenite to fine skeletal calcirudite: crinoid-bryozoan organic-mud packstone to poorly washed grainstone. Brownish black (5 YR 2/1) to dark grey (N3).

lc. Stromatoporoid biolithite fa- 0.60 1.80-2.40 cies. Laminar and some hemi spherical stromatoporoids in-

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Thickness A. above Unit Description ______in M. base

terlaminated with inter stroma toporoid medium skele tal calcarenite: organic-mud packstone equaling about 40 percent of unit. Greyish orange (10 YR 7/4). Unit capped by 2 cm thick laminar stromatoporoids.

lb. Stromatoporoid biolithite fa- 0.90 0.90-1.80 facies. Stromatoporoid bio lithite with predominantly laminar stromatoporoids in terbedded with interstromatoporoid medium skeletal calcarenite: organic-mud packstone equaling 40 per cent of unit.

la. Stromatoporoid biolithite fa- 0.90 0.00-0.90 cies. Stromatoporoid bioli thite with 2-10 cm thick laminar stromatoporoids that average 5 cm in thickness, and local 15 cm thick lami nar stromatoporoids, inter laminated with interstromato poroid medium skeletal cal carenite: organic-mud pack stone comprising 20 percent of unit. Thin (0.5 to 1.0 cm) laminar stromatoporoids in the upper 2 8 cm of the unit give a shaley appearance to the outcrop.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 6 and 7 (RQ6 and RQ7) - Rockport Quarry

Measured Sections (6, 7) were measured in the Rockport

Quarry Limestone at a location on the west wall 50 m north

of Measured Section 5 (RQ2) in the NW1/4, NW1/4, Sec. 6, T.

32 N ., R. 2 E . , Alpena County. Section RQ7 is laterally con

tinuous with and 20 m north of Section RQ6. Due to the simi

larities in the sections/ both are presented together. The

bottoms of both sections are covered; the tops have been re

moved by quarrying operations (see PI. 18 for outcrop expres

sion and sampling locations).

Thickness M. above Unit Description______in M.______base

7. Micrite facies, fenestral RQ6 1.19 3.38-4.57 subfacies. Very fine to RQ7 0.90 3.75-4.65 fine calcarenite: inter bedded horizontally fene stral pelsparite and pelmicrite with yellow calcite-filled vugs near the top. Light grey (N7).

6a. Micrite facies, fenestral RQ6 not present subfacies. Coarse cal RQ7 0.15 3.60-3.75 carenite: intrasparite. Light grey (N7) .

6. Micrite facies, fenestral RQ6 0.58 2.80-3.38 subfacies. Very fine to RQ7 0.75 2.85-3.60 fine calcarenite: inter bedded pelsparite and pelmicrite and very fine to fine calcilutite: micrite. Dominantly horizontally fenestral. Local 6 cm high cross beds present. Light grey (N7) .

5. Micrite facies, fenestral RQ6 0.30 2.50-2.80 subfacies. Very fine to RQ7 0.30 2.55-2.85 fine calcarenite: inter-

with permission of the copyright owner. Further reproduction prohibited without permission. 120

Thickness M. above Unit Description______in M. base

bedded pelsparite (domi nant) , pelmicrite, and local very fine to fine calcilutite: micrite. Yellowish grey (5 Y 8/1) to light olive grey (5 Y 6/1).

4. Micrite facies, fenestral RQ6 0.60 .90-2.50 subfacies. Very fine to RQ7 0.65 .90-2.55 fine calcarenite: inter bedded pelsparite, pelmicrite and local very fine to fine calcilutite: mic rite. Light grey (N7) ; Favosites in lower part of unit.

Biolithite-micrite transi RQ6 0.60 ] .30-1.90 tion facies. Laminar RQ7 0. 55 .35-1.90 stromatoporoids at base interlaminated with 50 per cent interstromatoporoid fine to coarse skeletal calcarenite: organic-mud packstone grading to poorly washed pelloidal grainstone at top. Light grey (N7) to light olive grey (5 Y 6/1); profusion of in situ corals (Favosites and Heterophren- tis j and some stromatopo roid fragments.

Stromatoporoid biolithite RQ6 0.55 C .75-1.30 facies. Laminar stromato RQ7 covered poroids (70 percent) inter laminated with 30 percent interstromatoporoid fine to coarse skeletal calcare nite: organic-mud pack stone that decreases in organic mud and increases in micrite content upwards. Light olive grey (5 Y 6/1).

Organic-mud packstone fa- RQ6 0.75 C .00-0.75 cies, bryozoan packstone RQ7 covered subfacies. Lenses (2 to 10 cm thick and 10 to 60

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Thickness M. above Unit Description______in M. base

cm long) of light olive grey (5 Y 6/1) medium skele tal calcarenite to fine skeletal calcirudite: cri noid-bryozoan packstone coalesced into layers (10 to 30 cm thick) interbedded with 20 to 30 percent dark grey (N3, when fresh; and medium light grey, N6, when weathered) fine to coarse skeletal calcarenite: coral organic-mud packstone layers.

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Measured Section 8 (RQ8) - Rockport Quarry

Measured Section 8 (RQ8) was measured in the Rockport

Quarry Limestone on the west wall of Rockport Quarry in the

NW1/4, NWl/4, Sec. 6, T. 32 N., R. 9 E., by a large cave-in

30 m north of Measured Section RQ7. The top of the section

has been removed by quarrying operations and the bottom of

the section is covered. Numbered units correspond to stra-

tigraphically equivalent strata in sections RQ6 and RQ7 (see

PI. 18 for outcrop expression and sampling locations).

Thickness M. above Unit Description______in M.______base

7. Micrite facies, fenestral 1.20 2.75-3.95 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and pelmicrite locally grading to very fine to fine calcilutite: micrite. Llvjl.L. grey (N7) . Highly frac tured because of quarrying oj. arations.

6. Micrite facies, fenestral 0.50 2.25-2.75 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and pelmicrite locally grading to very fine to fine calcilutite: micrite. Light grey (N7); corals in trace amounts.

51. Micrite facies, fenestral 0.15 2.10-2.25 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and coarse calcare nite: intrasparite. Light grey (N7) .

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5. Micrite facies, fenestral 0.45 1.65-2.10 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and pelmicrite, and locally very fine to fine calcilutite: micrite. Light grey (N7); 330 x 10 cm stromatoporoid near the base; vertical stylolites spaced 5-7 cm apart.

4. Micrite facies, fenestral 0.70 0.95-1.65 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and pelmicrite, and locally very fine to fine calcilutite: micrite. Light grey (N7). Favosites present in trace amounts near the top of the unit; some vertical fenestrae present.

3. Biolithite-micrite transi- 0.35 0. 60-0.95 tion facies. Laminar stroma toporoids interbedded with fine to coarse skeletal cal carenite: Favosites bearing organic-mud packstone at base, grading upward into sparse biomicrite and poorly washed pelloidal grainstone. Light grey (N7). Fragmental stromatoporoids at the base gradually decrease upward in abundance from 50 to 20 percent.

2. Biolithite facies. 70 per- 0.60 0.00-0.60 cent laminar stromatoporoids interlaminated with 30 per cent interstromatoporoid fine to coarse skeletal calcarenite organic-mud packstone. Light grey (N7) to light olive grey (5 Y 6/1) when fresh and

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Thickness M. above Uni t Description______in M.______base

greyish orange (10 YR 7/4) when weathered. Ramose and bulbous Favosites present in abundances up to 20 per cent.

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Measured Section 9 - South Grand Lake Area

Measured Section 9 was measured in the Rockport Quarry

Limestone in the roadcut along U. S. Highway 2 3 at short dis

tance north of where Warren Creek enters the southwest corner

of Grand Lake near the center of El/2, Sec. 17, T. 32 N., R.

8 E., Presque Isle County (Fig. 1, Loc. 33-8-17). The base

of the Rockport Quarry Limestone is covered and the top of the

section has been removed by erosion (see PI. 19 for topogra

phic expression and sample locations).

Thickness M. above Unit Description______in M.______base

1. Organic-mud packstone facies, 3.48 0.00-3.48 crinoid-bryozoan grainstone subfacies. Fine calcirudite: crinoid-bryozoan organic-mud packstone. Brownish grey (5 YR 4/1) when weathered, greyish brown (5 YR 3/2) when fresh; Favosites, Heterophren- tis, and Aulocystus; stromato poroids randomly distributed near the base; bryozoans and crinoids uniformly present as fragments in thin section. The morphology of the outcrop highly fragmented from road construction.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126

Measured Sections 10 and 11 - Grand Lake Area

Measured Sections 10 and 11 were measured in the Rock

port Quarry Limestone near the middle of the western shore of

Grand Lake, near the center SE1/4, SW1/4, Sec. 31, T. 34 N.,

R. 8 E., Presque Isle County.

Measured Section 10 - Grand Lake Area

Measured Section 10 was measured in the Rockport Quarry

Limestone in a roadcut along U. S. Highway 23 at the top of

the hill near the center of SE1/4, SWl/4, Sec. 31, T. 34 N.,

R. 8 E., Presque Isle County. The road to the shore of Grand

Lake intersects U. S. 2 3 at the extreme west end of the expo

sure. The bottom of the section is covered, the top of the

section is partly covered with soil mostly removed by ero

sions (see Pi. 19 for outcrop expression and sampling loca

tions) .

Thickness M. above Unit Description ______in M.______base

3. Organic-mud packstone facies, 1.80 4.95-6.75 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: bryozoan-crinoid organic-mud packstone to poorly washed grainstone. Brownish grey (5 YR 4/1) when weathered, light grey (N7) when fresh; contains Aulocystus, Cystiphilloides, and ramose Favosites locally with branches between 10 and 15 cm long.

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Thickness M. above Unit Description inM. _base

2 . Organic-mud packstone facies, 1.95 3.00-4.95 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone to poorly washed grainstone. Pinkish grey (5 YR 4/1) when weathered, dusky yellowish brown (10 YR 4/2) when fresh. Laminated, easily eroded; numerous brachiopods and bryozoan fronds in float.

1 . Organic-mud packstone facies, 0.30 2.70-3.00 crinoid-bryozoan packstone subfacies. Medium to coarse skeletal calcarenite : cri noid-bryozoan organic-mud packstone to poorly washed grainstone. Yellowish grey (5 Y 7/1) when weathered, brownish black (5 YR 2/1) when fresh.

Stromatoporoid biolithite 2.70 0.00-2.70 facies. Pale yellowish brown (10 YR 6/2) when weath ered, light brownish grey (5 Y 7/1) when fresh. Basal 60 cm composed of laminar stromatoporoids with thick nesses ranging from 5 to 15 cm; interbedded with interstro matoporoid medium to coarse skeletal calcarenite: organic- mud packstone ranging from 20 to 75 percent and averaging 50 percent. Contains Cysti- philloides, ramose Favosites, overturned colonial rugose corals, and brachiopods be tween 60 and 165 cm; hemi spherical stromatoporoids occur interbedded with laminar stromatoporoids and are locally overturned. Between 165 and 270 cm, biolithite contains

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Thickness M. above Unit Description______in M.______base

only laminated stromatopo roids with 40 percent inter stromatoporoid medium to coarse skeletal calcarenite: organic-mud packstone con taining ramose Favosites, Cystiphilloides, Sjpongo- phyllum, and colonial rugose coral.

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Measured Section 11 - Grand Lake Area

Measured Section 11 was measured in the Rockport Quarry

Limestone along bluffs near the middle of the western shore

of Grand Lake near the center of SEl/4, SW1/4, Sec. 31, T.

34 N ., R. 8 E., Presque Isle County. Take road at west end

of Measured Section 10 directly to the exposure. Top and

bottom of section covered with soil; 1.65 to 5.85 m covered

with soil and talus (see Pi. 19 for outcrop expression and

sampling locations).

Thickness M. above Unit Description______in M.______base____

5. Organic-mud packstone facies, 0.90 9.90-10.80 crinoid-bryozoan grainstone subfacies. Medium skeletal calcarenite to coarse skele tal calcirudite: crinoid- bryozoan grainstone and poorly washed grainstone. Pinkish grey (5 YR 8/1) when weathered, brownish grey (5 YR 4/1) when fiash.

4. Organic-mud packstone facies, 1.35 8.55- 9.90 crinoid-bryozoan grainstone subfacies. Medium to coarse skeletal calcarenite: cri noid-bryozoan organic-mud packstone and poorly washed grainstone. Pinkish grey (5 YR 8/1) when weathered, brownish grey (5 YR 4/1) when fresh; contains Cysti- philloides, ramose and bul bous Favosites, 2 cm thick laminar stromatoporoid at 900 cm, upright hemispherical Hexagonaria at 840 cm.

3. Organic-mud packstone facies, 1.2 0 7.3 5-8.55 crinoid-bryozoan grainstone subfacies. Coarse skeletal

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Thickness M. above Unit Description in M. base

calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone and poorly washed grainstone. Brownish grey (5 YR 4/1) when fresh, light grey (N7) when weathered. Contains Aulo- cystus concentration at 800 cm; upright colonial rugose corals and crinoid and bryozoan fragments observable in hand specimen.

2 . Organic-mud packstone facies, 1.50 5.85- 7.35 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone to poorly washed grainstone. Pinkish grey (5 YR 4/1) when weathered, dusky yellowish brown (10 YR 4/2) when fresh; bryozoans and crinoid ossicles observable in hand specimen.

la. Talus covered slope. 4.20 1.65- 5.85

1 . Organic-mud packstone facies, 1.65 0.00- 1.65 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone to poorly washed grainstone. Medium light grey (N6) when weathered, brownish black (5 YR 2/1) when fresh. Pos sibly equivalent to Units 1, 2, or 3 in Section 10.

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Measured Section 12 - North Grand Lake Area

Measured Section 12 was measured in the Rockport Quarry

Limestone in the bluff and road cut on the south side of U. S.

Highway 23 1.8 miles east of Trout River, 1.2 miles west of

junction with CO 427, and about 4.8 miles east of Liske, in

the NEl/4, Sec. 24, T. 34 N., R. 6 E., Presque Isle County

(Fig. 1, Loc. 34-6-24). The top of the Rockport Quarry has

been removed by erosion, the bottom of the section is covered

(see Pi. 19 for outcrop expression and sampling locations).

Thickness M. above Unit Description______in M.______base

2. Organic-mud packstone facies, 3.00 2.00-5.00 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud-bearing poorly washed grainstone. Light olive grey (5 Y 5/1) when weathered, dusky yel lowish brown TlO YR 2/2) when fresh. Talus slope from road construction.

1. Organic-mud packstone facies, 2.00 0.00-2.00 crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone. Light olive grey (5 Y 5/1) when weathered, dusky yellow ish brown (10 YR 2/2) when fresh. The contact with Unit 2 is covered and the thick nesses reported are based on a more resistant layer at 200 cm which is inferred to mark the contact between the two units.

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Measured Section 13 - Ocqueoc Falls

Measured Section 13 was measured in the Rockport Quarry

Limestone at Ocqueoc Falls in the Ocqueoc Falls Forest Camp

ground along the Ocqueoc River just north of Ocqueoc Falls

highway (M 68), 4 miles north of Millersburg (near the center

Sl/4, Sec. 22, T. 35 N . , R. 3 E., Presque Isle County). The

top and bottom of the formation are covered by soil. The sec

tion has been completely dolomitized (see PI. 19 for outcrop

expression and sampling locations).

Thickness M. above Unit Description______in M.______base

8. Talus covered probably simi- 0.15 7.95-8.10 lar to Unit 7.

7. Organic-mud packstone facies, 0.75 7.20-7.95 crinoid-bryozoan grainstone subfacies. Coarse calcare nite: dolomitized bryozoan- crinoid organic-mud packstone. Pale yellowish brown (10 YR 6/2) when weathered, greyish orange pink (5 YR 7/2) when fresh; trace amounts of ramose and bulbous Favosites and Heterophrentis, locally broken.

6. Organic-mud packstone facies, 1.50 5.70-7.20 crinoid-bryozoan grainstone subfacies. Fine calcirudite: dolomitized crinoid-bryozoan organic-mud packstone. Pale yellowish brown (10 YR 6/2) when weathered, dusky brown (5 YR 2/2) when fresh; grada tional contacts with units above and below; stromatopo roid observed 15 cm above the contact with Unit 5.

5. Stromatoporoid biolithite 0.90 4.80-5.70 facies. Medium to coarsely crystalline dolomitized

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Thickness M. above Unit Description______in M. base

stromatoporoid biolithite and 60 percent medium to coarsely crystalline dolo mitized interstromatoporoid poorly washed grainstone. Light olive grey (5 Y 6/1) when weathered, yellowish grey (5 Y 8/1) when fresh. Interstromatoporoid dolo mite contains ramose Favo sites , Heterophrentis, Cystiphilloides, and over turned and in situ colonial rugose corals including Hexagonaria and Spongo- phyllum.

4. Organic-mud packstone facies, 1.50 3.30-4.80 crinoid-bryozoan grainstone subfacies. Coarsely crystal line dolomitized crinoid- bearing organic-mud packstone to poorly washed grainstone. Pale yellowish brown (10 YR 6/2) when weathered, brown (5 YR 4/2) when fresh.

3. Organic-mud packstone facies, 0.30 3.00-3.30 crinoid-bryozoan grainstone subfacies. Medium crystal line dolomitized bulbous Favosites-bearing organic- mud packstone. Pale yel lowish brown (10 YR 6/2) when weathered, pale grey ish brown (5 YR 4/2) when fresh.

Organic-mud packstone facies, 0.45 crinoid-bryozoan grainstone subfacies. Medium crystal line dolomitized poorly washed organir-mud-bearing grainstone. Pale yellowish brown (10 YR 6/2) when weathered, pale greyish brown (5 YR 4/2) when fresh.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thickness M. above Unit Description in M. base

l a . Talus and soil. 1.35 1.20-2.55

1 . Organic-mud packstone facies. 1.20 0 . 00- 1.20 Coarsely crystalline dolomitized organic-mud packstone. Pale yellowish brown (10 YR 6/2) when weathered, pale greyish brown (5 YR 4/2) when fresh. Contains 2 5 percent laminar stromatoporoid frag ments averaging 1 cm in dia meter.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 14 - Black Lake

Measured Section 14 was measured in the Rockport Quarry

Limestone in the abandoned quarry of the Onaway Limestone

Company on the shore of Black Lake, NW1/4, Sec. 7, T. 35 N.,

R. 2 E., Presque Isle County. Top and bottom of section is

covered (see Pi. 19 for topographic expression and sampling

locations).

Thickness M. above Unit Description______in M.______base____

17. Organic-mud packstone facies: 14.10 + crinoid-bryozoan grainstone subfacies. Medium skeletal calcarenite to fine skeletal calcirudite: crinoid-bryo zoan organic-mud packstone. Occurs as talus at the top of the section.

16. Micrite facies, dense sub- 0.20 14.10-14.30 facies. Medium skeletal calcarenite: crinoidal bio- pelmicrite. Greyish orange (10 YR 7/4) when fresh.

15. Micrite facies, fenestral 1.80 12.30-14.10 subfacies. Coarse calcare nite: pustular fenestral interbedded intramicrite and intrasparite. Orangish brown (10 YR 7/2) when weathered, pale yellowish brown (10 YR 6/2) when fresh. Intraclasts range from 0.2 to 1.0 mm and average 0.6 mm.

14. Micrite facies, fenestral 0.30 12.00-12.30 subfacies. Very fine to fine calcarenite: pustular fenestral interbedded pel sparite and pelmicrite. Dusky yellowish brown (10 YR 2/2) when fresh, dark

with permission of the copyright owner. Further reproduction prohibited without permission. 136

Thickness M. above Unit Description______in M.______base

yellowish brown (10 YR 4/2) when weathered; laminated and shaley with more fissile shale bounding top and bottom of unit.

13. Micrite facies, dense sub- 1.20 10.80-12.00 facies. Very fine to fine calcilutite: Favosites- bearing biomicrite. Pustu lar fenestral intrasparite at top of unit. Very pale yellowish orange (10 YR 7/2) when weathered, pinkish grey (5 YR 8/1) when fresh.

12. Micrite facies, dense sub- 0.90 9.90-10.80 facies. Very fine to fine calcilutite: micrite and biomicrite. Pale yellowish brown (10 YR 6/2) when weathered, very pale orange (10 YR 8/2) when fresh; with Favosites, Heterophrentis, and lamxnar stromatoporoid clasts. Some pustular fenestrae near the top.

11. Micrite facies, dense sub- 0.30 9.60- 9.90 facies. Very fine to fine calcilutite: micrite. Pale yellowish brown (10 YR 6/2) when weathered, dusky yellow ish brown (10 YR 2/2) when fresh.

10. Micrite facies, dense sub- 1.20 8.40- 9.60 facies. Very fine to fine calcilutite: micrite. Light orange (10 YR 8/4) when weathered, light grey (N7) when fresh.

9. Micrite facies, fenestral 1.50 6.90- 8.40 subfacies. Very fine to fine calcarenite: pustu lar fenestral interbedded pelsparite and pelmicrite.

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Thickness M. above Unit Description______in M.______base____

fenestral interbedded pel sparite and pelmicrite. Pale orange brown (10 YR 3/2) when weathered, pale orange brown (10 YR 7/2) when fresh. Similar to Unit 4. Contact between units 4 and 5 marked by a 4 cm zone with shale partings.

4. Micrite facies, fenestral 1.35 2.70- 4.05 subfacies. Very fine to fine calcarenite: pustu lar fenestral interbedded pelmicrite and pelsparite. Moderate yellowish brown (10 YR 3/2) to yellow orange (10 YR 8/4) when weathered, dark yellowish brown (10 YR 4/2) to pale yellowish brown (10 YR 6/2) when fresh. Stylolites and tubular fenestrae more abundant near top of unit; shale partings present at the base where in contact with Unic 3.

3. Talus and soil covered. 0.45 2.25- 2.70

2. Micrite facies, fenestral 1.50 0.75- 2.25 subfacies. Very fine to fine calcarenite: laminoid fenestral interbedded pel sparite and pelmicrite. Pale yellow brown (10 YR 6/2) when weathered, yellow grey (5 Y 7/1) when fresh; occurs as scabby outcrops on the quarry floor.

1. Vegetation covers quarry 0.75 0.00- 0.75 floor at north end of quarry near the waterline of Black Lake making lithologic dis crimination difficult. Two facies observed: stromato-

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Thickness M. above Unit Description______in M.______base____

Greyish orange (10 YR 7/4) to black when weathered, yellowish brown (10 YR 7/2) when fresh; tubular fenestrae abundant at 780 cm above base locally with drusy calcite fillings.

8. Micrite facies, fenestral 0.90 6.00- 6.90 subfacies. Very fine to fine calcarenite: lami noid fenestral interbedded pelsparite and pelmicrite. Pale yellowish brown (10 YR 6/2) when weathered, dark yellowish brown (10 YR 4/2) when fresh; 4 to 7 cm thick shaley zone near top of unit.

7. Micrite facies, fenestral 0.90 5.10- 6.00 subfacies. Very fine to fine calcarenite: lami noid and pustular fene stral pelmicrite grading locally to very fine to fine calcilutite: micrite containing synhoresis cracks. Pale yellowish brown (10 YR 6/2) when weathered, dark yellowish brown (10 YR 4/2) when fresh.

6. Micrite facies, dense sub- 0.45 4.65- 5.10 facies. Very fine to fine calcarenite: ostracod- bearing pelmicrite. Pale yellowish brown (10 YR 6/2) when weathered, dark yel lowish brown (10 YR 4/2) when fresh. Contact with Unit 5 marked by a 4 cm thick zone with shaley partings.

5. Micrite facies, fenestral 0.60 4.05- 4.65 subfacies. Very fine to fine calcarenite: laminoid

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thickness M. above Unit Description ______in M. base

poroid fragment-bearing organic-mud packstone (sam ple 1-la; greyish orange, 10 YR 7/4, when weathered; pale yellow brown, 10 YR 6/2, when fresh); and micrite facies, very fine to fine calcarenite: pelsparite; (sample 1-lb; orangish-brown, 10 YR 7/2, when weathered; pale yellow brown, 10 YR 6/2, when fresh).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. APPENDIX 2— LABORATORY METHODS

Plexiglass peels (Frank, 1965) were used to examine the

Rockport Quarry Limestone microscopically. Peeling with plexi

glass is preferable to acetate peeling in that plexiglass will

provide a replicate equal to acetate but will not roll. Fur

thermore, plexiglass peels need not be covered and therefore

can be studied under high power. Like acetate peels, these

peels are as large as the available polished surface, but

peels larger than 3 x 7 cm were found to be unwieldy. Peels

were referenced to and supplemented by tradational thin sec

tions .

To peel a cut slab, it must be polished smooth with 600

grit carborundum before etching for 10 to 20 seconds with 10

percent HCl. Ethelene dichloride or dichloroethelvene is then

poured over the sample to form a meniscus. The plexiglass is

then placed on one side of the specimen and let down so that

the meniscus is forced to travel to the other side of the spe

cimen. The peel is then left to cure for at least two hours

before being pulled. Sample numbers can be applied with a

simple scribe.

After the slabs were polished and etched during the peel

ing procedure, they were repolished and etched in 10 percent

HCI for 20 seconds in preparation for staining. Thin sections

were etched in 1.5 percent HCl for 20 seconds before staining.

140

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. before staining. The etched slabs and thin sections were

placed in 0.5 Alazarin Red S solution containing 1.5 percent

HCl (Dickinson, 1965; Carver, 1971). After 30 or 45 seconds

calcite stained red; dolomite took no stain. Slabs and thin

sections thus prepared were examined under binocular and pet-

rographic microscopes.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES CITED

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Dunham, R. J., 1962, Classification of carbonate rocks accord ing to depositional texture: in_ Classification of Carbo nate Rocks, (Ham, W. E., editor) Am. Assoc. Petrol. Geol. Mem. 1, p. 108-121.

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Logan, B. W . , Rezak, R., and Ginsburg, R. S., 1964, Classifi cation and environraental significance of algal stromato lites: Jour, of Geol., v. 72, p. 68-83.

Newcombe, R. B., 1930, Middle Devonian unconformity in Michi gan: Geol. Soc. Amer. Bull., v. 41, p. 725-738.

Neuman, A. C., Gebelein, C. D., and Scoffin, T. P., 1970, The composition, structure, and erodihility of subtidal mats, Abaco Bahamas: Jour, of Sedimentary Petrology, v. 40, p. 274-297.

Park, W. D., and Schot, E. H., 1968, Stylolites: Their nature and origin: Jour, of Sedimentary Petrology, v. 38, p. 179-191.

Playford, P. E., and Lowry, D. C . , 1966, Devonian Reef Com plexes of the Canning Basin Western Australia: Geologi cal Survey of Western Australia, Bull. 118, 141 p.

Read, J. F., 1973a, Carbonate cycles Pillara Formation (Devo nian) Canning Basin, Western Australia: Bull. Can. Petroleum Geology, v. 21, p. 38-51.

Read, J. F . , 1973b, Paleoenvironments and paleography Pillara Formation (Devonian), Western Australia: Can. Petroleum Geologist Bull., v. 21, p. 344-394.

Rominger, C. L., 1876, Geology of Lower Peninsula of Michigan, in Lower Peninsula 1873-1876 accompanied by a geological map: Geol. Survey Mich., v. 3, pt. 1, 22 5 p.

Rupp, A. J . , 1967, Origin, structure, and environmental sig nificance of recent and fossil calcispheres: Geol. Soc. Amer. Special Paper 101-186.

Sanford, B. V. , 1967, Devonian of Ontario and Michigan: In ternational Symposium on the Devonian System, Oswald, D. H., (ed.), Alberta Society of Petroleum Geologists, Calgary, Alberta, v. 1, p. 973-1000.

Scoffin, T. P., 1970, The trapping and binding of subtidal sediments by marine vegetation in Bimini Lagoon, Bahamas: Jour, of Sedimentary Petrology, v. 40, p. 249-274.

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Shaw, B., 1976, Structural Development of the Albion-Scipio Trend, Southern Michigan: in Geol. Soc. Amer. Abstracts with Programs, v. 8, p. 508-509.

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Outcrop expression of the Rockport Quarry Limestone in the type area of the formation at Rockport Quarry (Fig. 1, Loc. 32-9-6). Rod for scale subdivided into 30 cm (1 ft) divisions.

Figure A. Rockport Quarry Limestone (Drq) overlain by Fer- ron Point Formation (Dfp). Exposed facies of the Rock port Quarry Limestone, in ascending order, include: bg, crinoid-bryozoan grainstone subfacies of the organic-mud packstone facies; b, stromatoporoid biolithite facies; t, biolithite-micrite transition facies; and m, micrite facies (Appendix 1, Measured Section 6, Units 1 to 7; PI. 18).

Figure B. Rockport Quarry Limestone exhibiting in ascend ing order: b, stromatoporoid biolithite facies; cp, coral packstone subfacies and bg, crinoid-bryozoan grainstone subfacies of the organic-mud packstone fa cies; b, stromatoporoid biolithite facies; t, bioli thi te-micrite transition facies; and m, micrite facies (Appendix 1, Measured Section 3, Units 1 to 4; Pi. 18)

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EXPLANATION FOR PLATE 2

Outcrop expression of the Rockport Quarry Limestone in the type area of the formation at Rockport Quarry (Fig. 1, Loc. 32-9-6).

Figure A. Stromatoporoid biolithite facies (b) disconform- ably overlain by the organic-mud packstone facies (cp and bg) which in turn is gradationally overlain by stromatoporoid biolithite facies (b) . Key to subfacies of the organic-mud packstone facies: cp, coral pack stone subfacies; and bp, crinoid-bryozoan grainstone subfacies (Appendix 1, Measured Section , Units to ; PI. 18). Rod for scale subdivided into 30 cm (1 ft) divisions.

Figure B. Coral packstone subfacies of the organic-mud packstone facies. Lenses of bryozoan grainstone (bg) enclosed within more fissile coral packstone (cp) (Ap pendix 1, Measured Section 4, Unit 2; PI. 18). Hammer for scale.

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EXPLANATION FOR PLATE 3

Outcrop expression of the Rockport Quarry Limestone.

Figure A. View east looking over Rockport Quarry (Fig. 1, Loc. 32-9-6) in the type area of the formation. Pits in the foreground are at the Bell Shale-Rockport Quarry Limestone contact.

Figure B. Exposure of crinoid-bryozoan grainstone subfacies of the organic-mud packstone facies at Warren Creek (Fig. 1, Loc. 33-8-17; Appendix 1, Measured Section 9; Pl. 19). Rod for scale subdivided into 30 cm (1 ft) divisions.

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EXPLANATION FOR PLATE 4

Outcrop expression of the Rockport Quarry Limestone at Grand Lake (Fig. 1, Loc. 34-8-31).

Figure A. Lower Rockport strata exposed at Grand Lake along U. S. 23. Stromatoporoid biolithite facies (b) gradationally capped by the crinoid-bryozoan grainstone sub facies (bg) of the organic-mud packstone facies (Appen dix 1, Measured Section 11, Units A to 2; Pi. 19).

Figure B. Upper Rockport strata exposed as bluffs along the shore of Grand Lake. Crinoid-bryozoan grainstone sub facies of the organic-mud packstone facies (Appendix 1, Measured Section 12, Units 1 to 5; Pi. 19).

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Outcrop expression of the Rockport Quarry Limestone at Ocqueoc Falls (Fig. 1, Loc. 35-3-22).

Figure A. Ledges of the Rockport Quarry Limestone along the Ocqueoc River forming Ocqueoc Falls.

Figure B. Exposure of the Rockport Quarry Limestone (cri noid-bryozoan grainstone subfacies of the organic-mud packstone facies) as bluffs at Ocqueoc Falls (Appen dix 1, Measured Section 13, Units 1 to 7; PI. 19).

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Exposures of the Rockport Quarry Limestone at Black Lake in the old Onaway Stone Company Quarry (Fig. 1, Loc. 35-2-7). The quarry walls are comprised of the micrite facies (m); the crinoid-bryozoan grainstone subfacies (bp) of organic-mud packstone facies is exposed on the quarry floor and at the top of the section (Appendix 1, Measured Section 14, Units 1 to 17; Pi. 19).

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Calcispheres, Favosites, and Heterophrentis in the Rockport Quarry Limestone at Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1).

Figure A. Micrite facies, dense subfacies. Calcisphere- bearing pelmicrite largely neomorphosed to microspar (RB 2-4a = WMU 2588; Table 1, number 15). Plexiglass peel x 600 (1 cm = 16.6 microns) from Black Lake (Fig. 1, Loc. 35-2-7; Appendix 1, Measured Section 14, Unit 8; PI. 19). Pelloids (p) with intersertal microspar (ms) of probable micritic origin (Folk, 1965) enclos ing a type ”A" calcisphere (a) with finely crystalline fibroradial chamber fillings of sparry calcite. Ob serve the loaf form (1) exhibited by the microspar and the micrite comprising the pelloids.

Figure B. Micrite facies, dense subfacies. Calcisphere- bearing pelmicrite largely neomorphosed to microspar. Same sample as Figure A but showing a type "B" calci sphere (b) exhibiting an inner wall (i) .

Figure C. Biolithite-micrite transition facies. Favosites (RQ 7-3 = Vi MU 2605) . Plexiglass peel x 30 (1 cm = 333 microns). Specimen shows brecciation around the edges (br). Voids filled with pore-filling fine to medium crystalline equant sparry calcite (sc) (Appendix 1, Measured Section 7, Unit 3).

Figure D. Biolithite-micrite transition facies. Favosites (RQ 7-3 = WMU 2605; same sample as Figure C). Plexi glass peel x 30 (1 cm = 333 microns). Preferred growth of pore-filling finely crystalline bladea syntaxial overgrowths of sparry calcite parallel to the original optic axis of the corallite walls (ec) sug gestive of an early phase of submarine cementation. The corallites were later completely filled with me dium to coarsely crystalline equant polygonal sparry calcite (epsc) suggestive of cementation by meteoric or deep subsurface waters (Folk, 1974).

Figure E. Organic-mud packstone facies. Heterophrentis, apical view. Sample on left (WMU 2606) comes from the coral packstone subfacies at Rockport Quarry. Note the marked flattening (f). Sample on the right (WMU

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2607) comes from the faryozoan grainstone subfacies at Rockport Quarry. Note the evidence of frequent reju venation (rb). Scale is 8 cm long.

Figure F. Same samples as Figure E. Calical view. Scale is 8 cm long.

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Photomicrographs of rocks from the micrite facies of the Rockport Quarry Limestone.

Figure A. Dense subfacies. Pelsparite or neomorphosed pelmicrite (RB l-4b = WMU 2591). Thin section in plane light x 30 (1 cm = 333 microns) from Black Lake (Fig. 1, Loc. 35-2-7; Appendix 1, Measured Section 14, Unit 5; Pi. 18). Key: neomorphosed gastropod (g); ostracods (o); pelloids (p); and s, pore-filling finely crystalline equant sparry calcite.

Figure B. Fenestral subfacies. Intraclast-bearing pel sparite (RQ 5-6 = WMU 2602). Thin section in plane light x 30 (1 cm = 33 3 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 2, Unit 6; Pi. 18). Key: fenestrae (f) filled with fine to medium crystalline equant sparry calcite; pelloids (p); and intraclasts (i).

Figure C. Fenestral subfacies. Intraclast-bearing pel sparite. Same sample as Figure B with medium crystal line rhombic dolomite replacing both matrix (dm) and sparry calcite (df) that originally filled fenestrae.

Figure D. Fenestral subfacies. Interlaminated horizon tally fenestral-bearing pelmicrite (pm) and pelsparite (ps) (RQ 8-6a = WMU 2603; Table 1, number 33). Plexi glass peel x 30 (1 cm = 333 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Sec tion 8, Unit 6; PI. .18). Pellets enclosed in micrite (pm) ; interbedded with fenestrae containing higher amounts of calcite spar (ps) locally neomorphosed to microspar.

Figure E. Fenestral subfacies. Pustular to horizontal fe nestral-bearing pelmicrite with local interbedded pel sparite (RQ 5-7 = WMU 2604). Thin section in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 5, Unit 7; Pi. 18). Pelmicrite (pm) containing horizon tally oriented voids filled with fine to medium crys talline equant sparry calcite (sc). Pelsparite when present is somewhat discontinuous.

Vflfc E T A L P 8 EXPLANATION FOR PLATE 8 (Cont.)

Figure F. Fenestral subfacies. Random fenestral intra clast-bearing pelmicrite (RQ 5-6 = WMU 2602). Thin section in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Mea sured Section 2, Unit 6; PI. 18). Pelmicrite (pm) with fenestrae (f) oriented at angles to the horizon tal. Intraclasts are locally present (i).

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Macrofossils from organic-mud packstone facies, Rock- port Quarry (Fig. 1, Loc. 32-9-6).

Figure A. Organic-mud packstone facies, coral packstone subfacies. Coral-bearing fine to coarse calcarenite: organic-mud packstone. Field specimen (WMU 2609) with surface parallel to stratification showing cracks (c), Arthrodire plate (ap) and Heterophrentis (h). Hammer for scale.

Figure B. Organic-mud packstone facies, bryozoan packstone subfacies. Hand specimen of Favosites (WMU 2610) showing rejuvenation (r). Scale is 8 cm long.

Figure C. Organic-mud packstone facies, bryozoan packstone subfacies. Hand specimen of Hexagonaria (WMU 2611) showing rejuvenation (r). Scale is 8 cm long.

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EXPLANATION FOR PLATE 10

Fossils in the organic-mud packstone facies at Rock- port Quarry (Fig- 1, Loc. 32-9-6; Appendix 1).

Figure A. Organic-mud packstone facies, coral packstone subfacies. Coarse skeletal calcarenite; organic-mud packstone (RQ 4-2 = WMU 2580; Table 1, number 15). Thin section in plane light x 30 (1 cm = 333 microns) from Rockport Quarry (Eig. 1, Loc. 32-9-6; Appendix 1, Measured Section 4, Unit 2). Skeletal sand containing a type "A" foram (a), bound by a matrix of organic-mud (om) .

Figure B. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Fine skeletal calcirudite: or ganic-mud packstone (WCk = WMU 2594; Table 1, number 23) . Plexiglass peel x 30 (1 cm = 333 microns) from Warren Creek in the Grand Lake area (Fig. 1, Loc. 33- 8-17; Appendix 1, Measured Section 9). Skeletal sand containing a type "B" foram (b) bound by precipitated medium crystalline equant sparry calcite and organic m u d .

Figures C and D. Organic-mud packstone facies, coral pack stone subfacies. Medium skeletal calcarenite: or ganic-mud packstone (RQ 4-2 = WMU 25 80; Table 1, num ber 15). Thin sections in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9- 6; Appendix 1, Measured Section 4, Unit 2; Pi. 18). Coral packstone exhibiting preferred orientation and consisting of: F, Favosites fragments; Is, laminar stromatoporoids; o, ostracods (with "go" indicating geopetally filled); and other debris all bound by or ganic-mud (om) .

Figure E. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Fine skeletal calcirudite: crinoidal organic-mud packstone to crinoidal organic- mud bearing grainstone (RQ-Cr = WMU 2592; Table 2, number 21). Skeletal sand containing crinoid ossicles (o) and trilobite pygidium (t), cemented by sparry calcite. Light band (c) is a crack filled with medium crystalline sparry calcite.

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l x p l a :. 10 (Cv

Figure F. Organic-nud packstone facies, u-cryozoar. grainstone subfacres. Fine skeletal caici n i l te : crinoidal orgar.ic-xud bearing grainstone. Same sample as Figure £ out thin section under crossed nicols x 3 0 (1 err. - 333 microns}. Poikilotopic pore-: i- 11 n g me — dium to coarsely crystalline sparry calcit e . spj cement within crinoidal organic-mud bearing g r a ms tone containing crinoid (cj and bryozoan (b) :r ag me .'its .

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EXPLANATION FOR PLATE 11

•: :• .1 toporoids at Rockport Quarry (Fig. 1, Loc. 32-9-

F . ;_:o A. Hemispherical stromatoporoid (hs) that has grown ever colonial rugose coral (c) in the crinoid-bryozoan grainstone subfacies of the organic-mud packstone fa cies. Key to rock types: bg, crinoid-bryozoan grain stone and cp, coral packstone (Appendix 1, Measured Section 5, Unit 2; PI. 18).

Figure 5. Hemispherical stromatoporoid (hs) that has grown over laminar stromatoporoid (Is) within the stromato poroid biolithite facies (lower biolithite). Note the local irregular erosion surface (e) separating the hemispherical stromatoporoid from younger strata.

EXPLANATION FOR PLATE 12

Fossils from the organic-mud bearing facies of the Rockport Quarry Limestone.

Figure A. Stromatoporoid biolithite facies. Fine skeletal calcarenite: organic-mud packstone (RQl-1 = WMU 2590; Table 2, number 1). Thin section in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 1, Unit 1; Pi. 18). Organic-mud (om) bearing interstromatoporoid sediment (is) enclosing a stromatoporid stromatoporoid (Sts) displaying maculate fabric.

Figure B. Stromatoporoid biolithite facies. Fine skeletal calcarenite: organic-mud packstone. Same sample as Figure A. Thin section under crossed nicols. Observe neomorphic fibroradial finely crystalline sparry cal cite (fr) .

Figure C. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies (RQ-Ceph = WMU 25 89). Thin sec tion in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6). Clathrodic- tydid stromatoporoid (cs) growing on a cephalopod fragment (c). The wall structure of the stromatopo roid, represented by an organic ghost, is locally cut by individual neomorphic medium crystalline equant sparry calcite crystals (n).

Figure D. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Crinoidal fine skeletal calci rudite: crinoid-bearing organic-mud packstone to or ganic-mud bearing grainstone (RQ-Cr = WMU 2592; Table 2, number 21). Hand specimen from Rockport Quarry (Fig. 1, Loc. 32-9-6) showing: ramose Favosites (rf) and en echellon stacked crinoid ossicles (ec). Scale is 8 cm long.

Figure E. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Bryozoan-bearing medium cal carenite: organic-mud packstone (RQ5 = WMU 2612; Table 2, number 34). Thin section in plane light x 20 (1 cm = 500 microns) from Ocqueoc Falls (Fig. 1, Loc. 35-3-22, -27; Appendix 1, Measured Section 13,

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EXPLANATION FOR PLATE 11

L T . i t 5] containing: calcite crmciu :: a. rar.ts icc) in a dolomitized matrix (dm).

Figure F. Same sample as Figure E. Inin see: ion under crossed .nicols x 20 (1 cm = 5CC microns, snowing polygon boundaries (p).

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Photomicrographs of the organic mud occurring in the biolithite and organic-mud packstone facies.

Figure A. Biolithite facies. Coarse skeletal calcirudite: Biolithite (RQ 3-1 = WMU 2608; Table 2, number 13). Thin section in plane light x 20 (1 cm = 500 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 1, Unit 1; PI. 18). Stromatoporoids (s) in interstromatoporoid organic-mud packstone caus ing opaqueness in a pinchout (p). Note innerconnect- ing network stylolites in the matrix (is).

Figure B. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Coarse skeletal calcarenite: organic-mud packstone (34-8-31-1 = WMU 2600; Table 2, number 29). Thin section in plane light x 30 (1 cm = 333 microns) from Grand Lake (Fig. 1, Loc. 34-8-31; Appendix 1, Measured Section 11, Unit 1, PI. 19). In- nerconnecting network stylolites (is) grading into a single vertical type (v) near coarser grains: c, crinoid fragment; and b, punctate brachiopod fragment.

Figure C. Organic-mud packstone facies, coral packstone subfacies. Medium skeletal calcarenite: organic-mud packstone (RQ 4-2 = WMU 2580; Table 2, number 15). Thin section in plane light x 600 (1 cm = 16.6 mi crons) from Rockport Quarry (Fig. 1, Loc. 32-9-6; Ap pendix 1, Measured Section 3, Unit 2; PI. 18). Black organic-mud matrix exhibits: a, amorphous debris; and mi, microspheres.

Figure D. Organic-mud packstone facies, coral packstone subfacies. Coral-bearing medium skeletal calcarenite: organic-mud packstone (2RQl-sz = WMU 2581; Table 2, number 22). Thin section in plane light x 600 (1 cm = 16.6 microns) from Rockport Quarry (Fig. 1, Loc. 32-9- 6; Appendix 1, Measured Section 4, Unit 2; Pi. 18). Key the same as Figure C.

Figure E. Organic-mud packstone facies, crinoid-bryozoan packstone subfacies. Dolomitized fine skeletal calci rudite: organic-mud packstone (R01 = WMU 2582; Table 2, number 39). Thin section in plane light x 600 (1 cm = 16.6 microns) from Ocqueoc Falls (Fig. 1, Loc. 35-3-22; Appendix 1, Measured Section 13, Unit 1; Pi. 19). Key same as Figure C.

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Figure F. Organic-mud packstone facies, coral packstone subfacies- Coral (RQ-F = WMU 2583). Thin section with less than normal petrographic thickness in plane light x 600 (1 cm = 16.6 microns) from Rockport Quarry (Fig. 1, Loc. 32-9-6). Microspheres (mi) within a Favosites corallite. "C" shaped body (c) at right center indicates that the spheres are hollow. Aci- cular fragments (af) and amorphous debris (a) also present.

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Calcareous algae from the biolithite-micrite transi tion facies (Figs. A-E) and from the fenestral subfacies of the micrite facies (Fig. F). Figures A-E from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Sections 1 and 2; PI. 18); Figure F from Black Lake (Fig. 1, Loc. 35-2-7; Appendix 1, Measured Section 14, Unit 15; PI. 19).

Figure A. Organic-mud and pellet-bearing poorly washed biosparite (RQ 3-5 = WMU 2587; Table 2, number 9). Thin section in plane light x 30 (1 cm = 333 microns). Key: v, Vermiporella; p, pelloids; and other debris, cemented locally with finely crystalline equant sparry calcite (sc) (Appendix 1, Measured Section 1, Unit 5).

Figure B. Organic-mud and pellet-bearing poorly washed biosparite (RQ 5-3 = WMU 2586; Table 2, number 18). Thin section in plane light x 20 (1 cm = 500 microns). Key: v, Vermiporella; p, pelloids; b, brachiopod fragments; and other debris, cemented locally with finely crystalline equant sparry calcite (sc) or bound by organic mud (om) (Appendix 1, Measured Section 2, Unit 3) .

Figures C, D, and E. Organic mud and pellet-bearing poorly washed biosparite (RQ 5-3 = WMU 2586; same sample as Figure B). Thin sections in plane light: Figs. C, D x 600 (1 cm = 16.6 microns); Fig. E x 20 (1 cm = 500 microns). Key: I, idiostromatid stromatoporoids; S, stromatoporid stromatoporoids; ai, algae incertae; p, pelloids; and sc, sparry calcite.

Figure F. Fine to medium pelletal calcarenite: irregu larly fenestral pelsparite (RB 3-6 = WMU 2584; Table 1, number 3). Thin section in plane light x 30 (1 cm = 333 microns). Key: r, Renalcis; if, irregular fenestrae; and p, pelloids (Appendix 1, Measured Section 1 4 , Unit 1 5 ) .

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•v % S?PL ’- - - » A • i> W • » L''”' A W IT-* * r: » LT * * t*. \ rr> * t' ^

tcroc expression ;ne st: :r,atc: ii te

• ; ,-ure A. Exposure of the stromatoporoid Liol ithi te facies at Rockport Quarry (Fig. 1, Loc. 32-9-6; Appendix 1, Measured Section 1, Er.it 1). Laminar stronatoporoids (Is) interbedded with interstromatoporoid coral-bear ing organic-mud packstone (iss) that locally molds around buttressing hemispherical stronatoporoids (hs).

Fiuure B. Exposure of the stromatoporoid biolithite at Grand Lake (Fig. 1, Loc. 34-8-31; Appendix 1, Measured Section 10, Unit 1; Pi. 19). Key is the same as Fig ure A.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission PLATE 15

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission EXPLANATION FOR PLATE 16

Dolomite in the Rockport Quarry Limestone.

Figure A. Biolithite facies. Medium skeletal calcarenite: organic-mud packstone (RGA = WMU 2613). Thin section in plane light x 30 (1 cm = 333 microns) from Grand Lake (Fig. 1, Loc. 3 4-8-31; Appendix 1, Measured Sec tion 10, Unit A; Pi. 19). Isolated dolomite rhombahedrons (d) replacing both skeletal grains and matrix. Calcite-dolomite definition exhanced by Alzarin Red S stain (Dickinson, 1965).

Figure B. Biolithite facies. Hand specimen from Grand Lake (Fig. 1, Loc. 34-8-31; Appendix 1, Measured Sec tion 10, Unit A; Pi. 19). Hemispherical stromatopo roid (WMU 2614) with a fracture filled secondarily by coarsely crystalline dolomite (d) which locally re placed earlier precipitative medium crystalline equant sparry calcite. Scale is 8 cm long.

Figure C. Micrite facies, fenestral subfacies. Fine pelletal calcarenite: horizontally fenestral pelsparite (RQ 6-7a = WMU 2615; Table 1, number 48). Hand speci men from Rockport Quarry (Fig. 1, Loc. 32-9-6; Appen dix 1, Measured Section 6, Unit 7). Dolomite replac ing sparry calcite filled fenestrae. Scale is 8 cm long.

Figure D. Same sample as Figure C; thin section in plane light x 30 (1 cm = 3 33 microns). Replacement dolomite (d) showing euhedral crystal boundaries cross cutting sparry calcite (c). Calcite-dolomite grain definition in both figures C and D enhanced by Alazarin Red S stain (Dickinson, 1965).

Figure E. Biolithite facies. Dolomitized stromatoporoid- baaring medium skeletal calcarenite: organic-mud pack stone (RGA = WMU 2613). Thin section in plane light x 20 (1 cm = 500 microns) from Grand Lake (Fig. 1, Loc. 3 4-8-31; Appendix 1, Measured Section 10, Unit A; PI. 19). Galleries in stromatoporoid fragment were first filled with pore-filling medium crystalline equant sparry calcite (c), subsequently voided (v) and then locally refilled with pore-filling medium crystalline rhombic dolomite (d) .

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PLATE 16

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169

EXPLANATION FOR PLATE 16 (Cont.)

Figure F. Organic-mud packstone facies. Dolomitized cal carenite: organic-mud packstone or grainstone (R04a = WMU 2616; Table 1, number 36). Thin section in plane light x 30 (1 cm = 333 microns) from Ocqueoc Falls (Fig. 1, Loc. 35-3-22, -27; Appendix 1, Measured Sec tion 13, Unit 4; PI. 19). Medium crystalline rhombic replacement dolomite (d) with interrhombic void spaces (v) typically trapezohedral in shape.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPLANATION FOR PLATE 17

Macrofauna of the Rockport Quarry Limestone.

Figure A. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Medium skeletal calcarenite: organic-mud packstone (R34-8-31-2 = WMU 2598). Hand specimen from Grand Lake (Fig. 1, Loc. 34-8-31; Appen dix 1, Measured Section 11, Unit 2; Pi. 19) exhibiting three fenestellid bryozoan species: sp. A (a); sp. B (b); and sp. C (c). Scale is 4 cm long.

Figure B. Organic-mud packstone facies, crinoid-bryozoan grainstone subfacies. Trepostomids sp. (WMU 2599) from Grand Lake (same location and stratigraphic posi tion as Figure A). Scale is 3.5 cm long.

Figure C. Organic-mud packstone facies, crinoid-bryozoan packstone subfacies. Crinoid-bearing fine skeletal calcirudite: organic-mud packstone. Top view of cephalopod (WMU 2617) from Rockport Quarry (Fig. 1, Loc. 32-9-6) 30 m west of Measured Section 1 (Appendix 1). Scale is 8 cm long.

Figure D. Same sample as Figure C. End view showing crushing (cr). Scale is 8 cm long.

Figure E. Organic-mud packstone facies, coral packstone subfacies. Oncolite (WMU 2585) from Rockport Quarry (Fig. 1, Loc. 32-9-6) between Measured Section 1 and Measured Section 2 (Appendix 1).

Figure F. Same sample as Figure E. Thin section in plane light x 20 (1 cm = 500 microns) showing the concentri cally laminated close and spaced laterally linked hemispheroids (Logan et al., 1964) that compose the oncolite.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. P L A T E 1 7

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPJ

Topographic expression, sam pling locations, and

stone, Rockport, M ichigan {Fig. 1, Loc. 32-9-6; Apj used in Figure 6.

Measured Section 2

7 Measured Section 1 6 M e a s u r e d

- •••: v-:2x4 \ R Q 5 - 3

4 4

3 - «J6 ‘-

- R Q 3 - 2 2 a * * Q 5 - 2 ^ p - 8 0 3 - 1 2 r»v l a "la l a

- R Q 5 - 1

‘ R Q 3 - 4

Measured Section 6 M(

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPLANATION FOR PLATE 18 kr* • ■ ** locations, and facies d istrib utio n at the type lo cality of the Rockport Quarry

32-9-6; Appendix 1, Measured Sections 1-8). Facies symbols are the same as t| li .

Measured Section 3 Measured Section 5

— S Q 5 - 3

B Q 4 - 3

m m R Q 2 - 3 *§i05-2 RQ4-2 ?\»(v «?';

^.x»v^jcsyc»0£j . R Q 2 - 2

■*®Q5-1 R Q 2 - l i

— R Q 2 - 1 4 — R Q 4 - l b

Measured Section 8 M easured section 7

— **- tiUifiiiiSBS t m m m Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. j:‘tkt the type lo c a lity o f the Rockport Quarry Lime- 1-8) . Facies symbols are the same as those

Measured Section 5

S e c t i o n

4 a - » • $ 4a

1-1

Measured Section 8

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 6

r R Q 6 - 7 c R Q 6 - 7 b

R Q 6 - 7 a

3 m - 6 R Q 6 - 6

5 R Q 6 - 5

2 m- R Q 6 - 4 b 4

0 mJ 1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 8 MMsured Section 7

RQ8

R Q 8 - 3

EXPLANATION

Numbered sections correspond MEASURED SECTION 1 to described measured sections (Appendix 1)

Number refers to unit described 2 in measured sections

Short hatchures mark 1 m eter 1 RQ1 i n t e r v a l s

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EXPLANATION

Lons correspond MEASURED SECTION 1 m easured sections

to un it described 2 s e c t i o n s ' S a m p l e subjected to is m ark 1. m eter 1 -RQi-1 petrographic o r x - r a y a n a l y s i s

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Topographic expression, sam pling locations, aaad sym bols are the same as tnose used in Figure 6.

3 4 - 8 - 3 ^

M easured Sectios \ \ \

33-8-17

Measured Section 9

; K s \ -- R-WCK-3 3-8-17 V?®. r A > C:

& 4 & Gt'&Q

3 5 - 3 - 2 2

Measured Section 13

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ESfum xatm rom p l a t e 1 9

1 felons, and facie* dlstxibufeion w ithin Measured Sections 9-14 (Appendix 1). Fi 6 .

3 4 - 8 - 3 1

rated Section 10

3 4 - 8 - 3 1 i \ \ Measured Section 11 \ R G 34-8-31-5

\ RG34-8 -31 -4 & \ 3 4 - 6 - 2 4 M easured Section R G 34-8-31-3

* M RG34-8 -31 -2b I

R G 34-8-31-2a

■ V& \ > r •

• v- ' O *•

\ S$> i .n'Cri 'X*m!Vi

R G 34-8-31-1

3 5 - 2 - 7

M easured Section 14

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Sections 9-14 (Appendix l) • F*cxc*

inrtd Section 11

R G 34-8-31-5

*:* •&•.s '

R G 34-8-31-1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 5 - 3 - 2 2

Measured Section 13

8 .*aiVOn 7 • H D 7 17

- R D 6 16

. iw] ■R05 1 5 1 »

14 • Srlr v‘°7&<«T RD4b R04a 13 SBEKSaaBSjH 12

0 * 11 la

— R 0 1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 14

R B 3 - 7 17

1 6 10 A

- R B 3 - 6 *X5 R B 2 - 5 b

1 4 R B 3 - 5 /

R B 3 - 4 3 6 1 3 — R B ^ 4 a

12 — ^ & 3 - 3

11 ^ R B 3 - 2

EXPLANATION

Numbers correspond to sam pled 3 4 - 8 - 3 1 locations (Fig. 1)

Numbered sections correspond MEASURED SECTION 1 to described m easured sections

(Appendix 1)

Number refers to u n it described in m easured sections

Short hatchures mark 1 m eter R G l - l i n t e r v a l s Y

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Measured Section 14

- R B l - 4 a

- R B l - 3 c R B 2 — 5 b - R B I - 3 b

- R B l r 3 a

RB2-4b

— R B 2 - 4 — RBI-2

R B l - l a , b

EXPLANATION

tpond to sam pled 3 4 - 8 - 3 1 ¥• D

Ions correspond MEASURED SECTION 1 Measured sections

too u n it described 2 f e l o n s S a m p l e subjected to m ark 1 m eter 1 RG1-1 petrographic o r x - r a y E a n a l y s i s

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.