Algal) Material in the Middle Devonian Rockport Quarry Limestone of the Northeastern Portion of Michegan's Lower Peninsula

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Master's Theses Graduate College

12-1981

The Paleoecology of Carbonaceous (Algal) Material in the Middle Devonian Rockport Quarry Limestone of the Northeastern Portion of Michegan's Lower Peninsula

Jeffrey Dean Spruit

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Recommended Citation Spruit, Jeffrey Dean, "The Paleoecology of Carbonaceous (Algal) Material in the Middle Devonian Rockport Quarry Limestone of the Northeastern Portion of Michegan's Lower Peninsula" (1981). Master's Theses. 1820. https://scholarworks.wmich.edu/masters_theses/1820

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]. THE PALEOECOLOGY OF CARBONACEOUS (ALGAL) MATERIAL IN THE MIDDLE DEVONIAN ROCKPORT QUARRY LIMESTONE OF THE NORTHEASTERN PORTION OF MICHEGAN'S LOWER PENINSULA

Jeffrey Dean Spruit

A Thesis Submitted, to the Faculty of the Graduate College in partial fulfillment of the requirements for the Degree of Master of Science Department of Geology

Western Michigan University Kalamazoo, Michigan December I98I

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE PALEOECOLOGY OF CARBONACEOUS (ALGAL) MATERIAL IN THE MIDDLE DEVONIAN ROCKPORT QUARRY LIMESTONE OF THE NORTHEASTERN PORTION OF MICHIGAN’S LOWER PENINSULA

Jeffrey Dean Spruit, M.S.

Western Michigan University, I98I

The Rockport Quarry Limestone of the Lower Traverse Group represents

a sequence of laterally contemporaneous carbonate platform sediments

characterized in outcrop by four facies: (l) stromatoporoid biolithite,

(2) organic-mud packstone, (3 ) biolithite-micrite transition, and (4)

micrite. In facies (l), (2) and (3 ) dark brown 4-micron microspheres are

found grouped or singly in wispy seams of brown carbonaceous material.

Three species of filamentous blue-green algae were discovered in insol

uble residues of facies (l) and (2 ). Numerous lamellar stromatoporoids

and solitary corals occur with the carbonaceous-rich sediment in facies

(l). Coalescing lenses of crinoid and bryozoan debris occur with the

carbonaceous sediment in facies (2). Algal-laminated sediments* calcar

eous red algae, and calcareous blue-green algae are present in facies

(4), as well as two new foraminifers in facies (l) and (3 ). The size

range and morphology of the non-nueleated microspheres suggest that they

are coccoid blue-green algae. The kerogenous material composing the

seams probably represents fossilized sheath material secreted by the

algae. The carbonaceous seams, microspheres, and algal filaments are

interpreted as subtidal algal mats that provided a firm substrate upon

which stromatoporoids could grow.

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

I would like to thank Dr. William B. Harrison III for his invalu

able guidance during the course of the study, his encouragement when

difficulties were encountered, and his helpful suggestions toward the

manuscript. Heart-felt thank you's also go to Dr. W. Thomas Straw for

his thought-provoking debriefing concerning proposed hypotheses and

Dr. John-G. Grace for their reading the manuscript} also, to Gary

Furman and Steven Subocz for their assistance and companionship in the

field, and last but not least, to my loving sister who with painstaking

dedication turned chicken-scratch handwriting into a professionally

typed manuscript.

Jeffrey Dean Spruit

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! SPRUIT, JEFFREY DEAN THE PALEOECOLOGY QF CARBONACEOUS (ALGAL) MATERIAL IN THE MIDDLE DEVONIAN ROCRPORT OUARRY LIMESTONE OF THE NORTHEASTERN POR;TION OF *ICHIGAN*S LOWER PENINSULA. WESTERN MICHIGAN UNIVERSITY, M . S . , 1'981

COPR. 1981 SPRUIT, JEFFREY DEAN University Microfilms International 300 N. ZEEB RD., ANN ARBOR. Ml 48106

JEFFREY DEAN SPRUIT

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

ACKNOWLEDGEMENTS ...... ii

LIST OF ILLUSTRATIONS ...... iv

INTRODUCTION...... 1

PREVIOUS INVESTIGATIONS ...... 5

METHODOLOGY...... 7

Field Methods ...... 7

Laboratory Methods ...... 7

DESCRIPTION OF FACIES ...... 10

ORGANIC MATERIAL ...... 17

Biologic Affinity ...... 17

PALEOECOLOGY OF THE ALGAE AND ASSOCIATING ORGANISMS ...... 23

Stromatoporoid Biolithite Facies - Lower Unit .... ;...... 23

Organic-Mud Packstone Facies ..... 36

Coral Packstone Subfacies ...... 36

Crinoid-Bryozoan Subfacies ...... 4l

Stromatoporoid Biolithite Facies -Upper Unit ...... 43

Biolithite-Micrite Transition Facies ...... 46

Micrite Facies ...... 55

Dense Subfacies ...... 55

Fenestral Subfacies ...... 63

SYSTEMATIC PALEONTOLOGY ...... 68

DISCUSSION...... 78

CONCLUSIONS ..... 82

BIBLIOGRAPHY ...... 84

iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIS T OF ILLUSTRATIONS

Figure 1 Stratigraphic succession of Devonian strata in Michigan 2

Figure 2 Location Map 3

Figure 3 Major exposures of Rockport Quarry 4

Figure 4 Measured sections from Rockport Quarry 8

Table 1 Dissolution procedure 9

Table 2 Microsphere abundance chart 11

Figure 5 Total microspheres per facies and subfacies 13

Figure 6 Average amount of microspheres perfacies and subfacies 14

Figure 7 Microstructure of Schizothrix mat 22

Figure 8 Relation of sedimentary structure to current volocity 25

Figure 9 Initial algal mat stabilization 26

Figure 10 . Stromatoporoid encroachment 27

Figure 11 Algal mat growth within energy lees 29

Figure 12 Algal mat encroachment 30

Figure 13 Present configuration of the algal-stromatoporoid consortium 31

Figure 14 Biqlithite turbulent environment 32

Figure 15 Encrusting bryozoans within the algal mat 35

Figure 16 Facies tract of the stromatoporoid biolithite facies 37

Figure 17 Coral packstone subfacies 39

Figure 18 Crinoid-bryozoan grainstone subfacies 42

Figure 19 Facies tract of the organic-mud packstone facies 44

Figure 20 Facies tract of the upper unit of the stromatoporoid biolithite facies 47

Figure 21 Origin of sand- and mud-size material in the biolithite- micrite transition facies 5^

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF ILLUSTRATIONS (CONT.)

Figure 22 Vertical fenestrae 60

Figure 23 Facies tract from the biolithite-micrite facies through the micrite facies 62

Figure 24 Typical microsphere 68

Figure 25 Algal filament, Genus "A" 69

Figure 26 Algal filament, Genus "B" 70

Figure 27 Algal filament of the Family Nostochopsidae 72

Figure 28 Calcareous blue-green alga, encrusting form 73

Figure 29 Calcareous blue-green alga, unattached form 73

Figure 30 Solenoporacean alga 74

Figure 31 Flask-shaped foraminiferan 75

Figure 32 Encrusting foraminiferan 76

Table 3 Energy conditions and environments of the Rockport Quarry Limestone 79 & 80

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Rockport Quarry Limestone is one of eleven formations consti

tuting the Middle Devonian Traverse Group (fig. l). It gradationally over

lies the B&sal Traverse Bell Shale, and lies unconformably below the

Ferron Point Formation (Ehlers and Kesling, 1970). The outcrop belt of

the Rockport Quarry Limestone is a northwest-trending arc in the north

ernmost tier of counties in the lower peninsula of Michigan (fig. 2).

Major exposures (fig. 3) occur at Rockport Quarry, Grand Lake, Ocqueoc

Falls and Black Lake. The exposures at Rockport Quarry and Black Lake

are complete sections measuring 26 feet and 43 feet respectively.

Numerous minor exposures are present along U.S. 23 northeast of Grand

Lake and along M-68 between Rogers City and Ocqueoc Falls,

The bulk of previous studies have been concerned with the taxonom

ic paleontology (Kesling, 1953i Imbrie, 1959; and Stumm and Taylor,

(1964) and general stratigraphy (Grabau, 1902; Ver Weibe, 1927; Warthin

and Cooper, 1943; and Ehlers and Kesling, 1970), although more recent

examinations have been concerned with intraformational facies varia

tions (Cookman, 1976) and subsurface studies (Jodry, 1957 and Cookman,

1976). Paleontologic (Cookman, 1976) and paleoecologic studies of

macro- and micro-organisms, in particular, have been either investigated

lightly or virtually ignored.

This investigation attempts to bridge this gap by proposing paleo

ecologic interpretations of each of the facies established by Cookman

in 1976 and identifying new organisms encountered. Examination of over

one hundred thin sections and insoluble residues have revealed a rather

restricted microflora that formed algal mats in the shallow subtidal

environment. Calcareous algae, fenestral fabrics, encrusting foramin-

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

ANTRIMAnd NORWOOD SQUAW BAY THUNDER BAY Concealed bcdi

POTTER FARM

NORWAY POINT 45 FOUR MILE D A M 20

ALPENA

79 NEWTON CREEK

Killiin* member

116

FERRON POINT 37 ROCKPORT QUARRY 40

BELL

ROGERS CITY

Figure 1. Stratigraphic succession of Middle Devonian strata in' Michigan depicting the stratigraphic position of the Rockport Quarry Limestone id thin the Traverse Group. Numbers on the right side of the chart indicate stra tigraphic thicknesses in feet. Modified from Warthin and Cooper (19^3)•

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

Traverse Group

& quarry

□ Rockport Quarry

Figure 2. Location map of the Rockport Stone Quarry within the north west trending outcrop belt of the Rockport Quarry Lime stone .

ifers calcispheres, and algal laminated sediments are present in the

intertidal and supratidal regimes. Algal mats, along with other en

crusting organisms, bound, and thereby stabilized, the sediment thus

facilitating the succession of other organisms that required a rela

tively firm substrate.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A.Shub RQ . gl o f ' b l • r1 ------r1 ------h 0 40 80 KILOMETERS 0 25 50 MILES (RQ), Grand "Lake (GL), Grand(RQ), "Lake Ocqueoc Falls (OF), andElack Lake (BL). Figure 3- Locationmap of primary exposures of the Rockport Quarry Limestone. Rockport Quarry

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

The Rockport Quarry Limestone was" first described in 1841 by D. C.

Douglass as a black sub-slaty limestone, highly-charged with bituminous

material and very fossiliferous in parts. He attributed the bituminous

character of the unit to "animal matter from the fossils". Grabau (1902)

correlated these strata biostratigraphically and lithologically with his "lower beds of the Long Lake shales" and limestones of the lower Trav

erse Series that he described at Grand Lake.

R. A. Smith (1916, Pg. 175) was the first geologist to assign the

name Rockport Limestone to these strata. This formation was renamed the

Rockport Quarry Limestone by Cooper and Warthin (1941, Pgs. 259-260)

because two other formations held the same name. They also designated

the Kelly Island Rock and Transport Company Quarry at Rockport (in the

northeast comer of Alpena County) as the type locality of the formation.

Warthin and Cooper (1943, Pgs. 585-586) recognized the biostromal nature

of the lower Rockport Quarry Limestone, one of the first investigations

acknowledging this fact. Other investigations concerning the lithology

and stratigraphy of the Rockport strata include: Lane (l895)» Grabau

(1901), Ver Weibe (1927), Pohl (193°), Hake and Maebius (1938), Kelly

and Smith (19^7), and Kelly (1949). % Most of the above investigations also considered the taxonomic

paleontology of the macroscopic invertebrate fauna of the Rockport Quarry

Limestpne and the other formations of the Traverse Group. Other studies

regarding the paleontology of various macro-organisms found in the Rock

port. Quarry Limestone include: Kesling (1953)» Imbrie (1959)» Stumm and

Taylor (1964), and Ehlers and Kesling (1970),

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. One of the first subsurface studies involving Traverse strata was

that of Lane (1895) in which he pieced together the stratigraphy of the

entire lower peninsula using deep borings". Grabau (1902) correctly

equated bed 14 of the Churchill well near Alpena to the Rockport Quarry

Limestone as did Ver Weibe (1927) and Ehlers and Kesling (1970). Cook

man (1976) concluded, by use of mechanical well logs, that the subsurface

distribution of facies within the Rockport Quarry Limestone is "wide

spread but continuous". During deposition of this formation a barrier

existed in western Michigan at the present Newaygo-Mecosta County border

(Jodry, 1957). Overlap sequences (Jodry, 1973? Hake and Maebius, 1938;

and Newcombe, 1930) and the presence of lagoonal evaporites in the Rock

port Quarry Limestone west of the barrier (Jodry, 1957) have been inter

preted as evidence for it.

Cookman's study in 1976 was multidimensional in scope, involving

not only the nature of the intraformational facies changes and their in

ferred depositional history, but the subsurface facies distribution

(using mechanical well log data), and the taxonomic paleontology of the

invertebrate fossils of the Rockport Quarry Limestone. His petrologic

studies revealed the presence of locally abundant calcareous algae and

remnants of what he believed to be subtidal algal mats, both previously

unreported in the literature. Although, at least one study considered

the paleoecology of the invertebrate fossils contained within the whole

Traverse Group (Ehlers and Kesling, 1970).

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

Field Methods

Between August, 1978 and November, 1979» fifteen days were spent

in the field collecting oriented samples, measuring sections with a

Jacob’s staff, field checking the measured sections of previous inves

tigators, and photographing the Rockport Quarry Limestone. A total of

five sections were measured at Rockport Quarry (fig. 4). From these

sections forty-eight oriented samples were collected, from which thin

sections were made.

Laboratory Methods

One hundred five thin sections were prepared from the samples

collected. The thin sections were ground down to less than

standard thickness (30 microns), to facilitate the study of the

hydrocarbonaceous material contained within the rocks. The slides

were examined with a Leitz Ortholux binocular polarizing microscope

with an attached Orthomat camera for photomicrography.

Insoluble residues from the organic-inud packstone facies and the

interstromatoporoid sediment from the stromatoporoid biolithite facies

were prepared using standard dissolution procedures (table l). The

residues were then analyzed in vitro under the same microscope-camera

set-up used for thin-section analysis.

Thin-section analysis included: (l) a point count of algal spher

es to determine their relative abundance in each facies; (2) a grain-

size analysis of all facies other than the biolithites, for which

Cookman's (1976) data was available; and (3 ) documentation of micro-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ’i? Sample locations

LEGEND Fcncstral Subfacies Transition Facies Subfacics Stromatoporoid Biolithite Facies Packstone Facies Crinoid-Bryozoan Coral Packstone Organic Mud Grainstone Subfacies Shale I I Biolithite-Micrite i i Dense Subfacies | | ,_W V .JL_ + tT' + U I 2 5 - —10 usedas the datum plane. the smallnumbers represent sample locations. Tie lines were drawn to showthe same - 2 C majorfacies in each section; the top of the lower stromatoporoid biolithite facies was Figure 4. Measured sections from Rockport Quarry. The large numbers represent scale; the vertical,

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

Table 1 Dissolution of Carbonate Sediment

I Sample Preparation

A. Separate out organic-rich sediment from the stromatoporoid biolithite samples.

B. Crush/Break the above and organic-inud packstone samples into marble-sized fragments.

II Dissolving Procedure

A. Place rock fragments into dissolving trays; no more than one layer of rock fragments per tray.

B. Pour in diluted Glacial Acetic Acid until all fragments are immersed.

C. When all reaction ceases:

1 . Temporarily remove undissolved fragments.

2. Decant spent acid and rinse residues into another container.

3. Return fragments to trays and add fresh acid.

D. Repeat step C until all rock fragments are dissolved.

E. Let residues settle overnight.

F. Very carefully pour off spent acid and add distilled water to rinse residues.

sphere-sediment relationships.

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

Four distinct facies can be recognized in the Rockport Quarry Lime

stone (fig. 4), two of which have been subdivided into sub-facies: (l)

stromatoporoid biolithite, occurring at the base of the formation and

between the organic-mud packstone and biolithite-micrite transition;

(2 ) organic-mud packstone, divided into a lower coral packstone and an

upper crinoid-bryozoan grainstonej (3 ) biolithite-micrite transition;

and (4) micrite, divided into a dense micrite interbedded with a fenes-

tral micrite. These lithosomes are believed to represent a sequence of

laterally contempraneous shallow subtidal to supratidal carbonate plat

form facies (Cookman, 19?6 ).

The stromatoporoid biolithite is characterized by an abundance of

lamellar stromatoporoids (over 50 percent by volume) and a detrital

interstromatoporoid, dark-brown, organic-rich fine to medium skeletal

calcarenite. This sediment contains, by weight, an average of 7.15 per

cent insoluble residue (Cookman, 1976), which is mostly organic mater

ial. Over 4300 microspheres per slide (on the average) are found in

this organic ijiaterial (table 2). Solitary and colonial corals, fenes

trate and stony bryozoans, and occasional hemispherical stromatoporoids

are found within the interstromatoporoid sediment. In a few scattered

places, where small accumulations of overturned colonial coral heads

and hemispherical stromatoporoids are found, little organic material

exists in the sediment. The contact with the overlying organic-mud

packstone is sharp and occasionally marked by the presence of a thin

seam of poorly indurated black shale.

The coral packstone subfacies is represented by a dark brown to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0 00 ON ro ro ro «a 481.7 M 1-1 ro VO 4,300.3 - 12,015.3 0 M CO -V3 -O -0 n O H O H ro NO «• J f — O ON Ov H O H N> UO VO TOTALAVERAGE CO OS O Ov V_n Un UO Un Un 655 452 338 6,052 7,774 2,227 1,460 22,220 17,931 14,032 31,090 10,800 37,306 10,450 NO. NO. OF SPHERES TABLE 2 Middle Middle THIN SECTION -6 -8 Microsphere abundance chart RQII RQ-UE 1 Top RQ-UB 1 Top RQ1-5 Top RQ-EMT 2 Top RQ-EMT 1 Pottom RQ VI-4 Bottom RQ-UB 2 Bottom RQ-BMT 2 Top RQ 1-6 Top RQII1-1 Bottom RQ VI RQ VI-1 Top 9,214 RQII-1 Middle *RQ V-4 Bottom Grainstone SUB-FACIES Bryozoan

was thicker than average Coral Packstone Crinoid- energy conditions; an increase in microspheresa decrease indicates indicates higher lower energy energy conditions.conditions whereas n e

° T Mud The slide FACIES Organic- Note. The chart displays trends in microsphere content within the facies. These trends reflect upper oroid Micrite Stromatop * Transition \ oroid Biolithite- Biolithite Stromatop Biolithite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 black organic-rich very fine skeletal calcarenite with numerous solitary

corals with minor amounts of crinoid and fenestrate bryozoan fragments,

hemispherical stromatoporoids, and colonial corals, making up the de-

trital portion. Lenses of medium to dark brown crinoid-bryozoan grain-

stone containing, minor amounts of hemispherical stromatoporoids and

solitary and colonial corals are distributed throughout the coral pack

stone subfacies in outcrop. A layer of crinoid-bryozoan grainstone

delineates the contact between the coral packstone subfacies and repre

sents the lowermost part of the overlying crinoid-bryozoan grainstone

subfacies.

The crinoid-bryozoan grainstone subfacies is a medium to dark

brown organic-rich fine calcarenite that contains much crinoid and

fenestrate bryozoan debris with minor amounts of hemispherical strom

atoporoids and solitary and colonial corals. Lenses and layers of dark

brown to black coral packstone are found throughout the crinoid-bryozoan

grainstone subfacies. These darker lenses and layers of packstone con

tain the same types of fossils as the coral packstone subfacies. The

organic-mud packstone as a whole contains, by weight 10.23 percent in- % soluble residue (Cookman, 1976), which is mostly organic material. The

organic-mud packstone facies, on the average, contains more microspheres

than all the other facies (figs. 5 & 6) 20,000 per slide, with over

19,000 per slide for the coral packstone subfacies and over 21,000 per

slide for the packstone lenses in the crinoid-bryozoan grainstone sub

facies (table 2). The contact with the overlying stromatoporoid bio

lithite (upper unit) is sharply delineated by the sudden occurrence of

lamellar stromatoporoids.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120-

110 -

100 1 2

90-

80-

70 o o 60-

5 0 -

40-

30-

20 -

10-

Figure 5. Microsphere abundance chart. A histogram shows the total amount of microspheres per facies and subfacies based upon the data from Table 2.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26-

24-

2 22- > AVERAGE FOR FACIES 2 ^ CM o 1

»V*%%VXV«V*V»V»*X*X >*X*X*X*X*X*XvX*X*** 18- l l l l l l ! m S M !‘X*XsvXvXvXvXvI vX 'X 'X vX 'X vX ’Xv. 16-

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;XvXvXvXvX*XvX 6 - vXv!*X»XvX*Xv!v!v ;!;y ;Xv !v Xv !v Xv !v ! \ i x*x»yx*X‘X vX vX #x 4 - V.V.J.V m X*X X*XvXvXvX*X*X*X* *•*•*»* X#X*X*XvX*X*X*X*X* 2- X vX \ •XvXvXvXvXvXv! :<*: v .v!v *X*X*X*X*X*X*«*X*X*X 4 •* X*X ■::x*XvX:x*:vA v& v: x\vx*xvx*x*x*xv: Figure 6. Microsphere abundance chart showing a histogram represent ing the average number of microspheres per facies and sub facies. Based upon data from Table 2.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 The upper unit of the stromatoporoid biolithite closely resembles

the lower unit except for a few minor differences. It generally has a

slightly larger grain size (medium-grained) than the lower unit (fine-

to medium-grained). In many areas the entire thickness (approximately

two feet) of the upper unit consists of overturned hemispherical strom-

atoporoids and colonial corals and fragmented lamellar stromatoporoids.

This unit contains foraminifera whereas the lower unit does not. The

interstromatoporoid sediment in these areas contains relatively little

organic material. In general, organic matter decreases from the bottom

to the top of the upper unit. This is shown in table 2 by an upward

decrease in the microsphere content. The upper unit of the stromatopor

oid biolithite grades into the overlying biolithite-micrite transition.

The biolithite-micrite transition is a medium to light brown medium

to coarse skeletal calcarenite that is separable from the underlying

biolithite because it contains less than 50 percent lamellar stromatop

oroids by volume. The coral heads and hemispherical stromatoporoids

present are smaller than those found in the other facies. Solitary cor

als are quite common. Ostracods and foraminifera are also found in

this facies.' Very little organic material is present in this facies;

only a few organic-rich stringers can be seen in hand specimen. This

is reflected in thin section where slides average only 481 microspheres

per slide (table 2). This facies contains fewer microspheres than the

rest of the facies except for the micrite facies which contains no car

bonaceous material. The biolithite-micrite transition grades into the

overlying micrite.

The dense micrite subfacies is characterized by tightly packed pel-

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

micrites with little or no sparry calcite cement. Occasionally pelspar-

ites are interbedded with the pelmicrites. Biopelmicrites containing a

limited variety of fossils are present locally. Individual rhombs and

clusters of dolomite are widely scattered throughout the subfacies. A

sparse fossil community of ostracods, ramose stromatoporoids, calcareous

blue-green algae, and calcispheres is present. Occasionally, vertical fen-

estrae can be seen along different horizons in outcrop. The dense micrite

subfacies is found interbedded with the fenestral micrite subfacies.

The fenestral micrite subfacies is represented by pustular or hori

zontally elongated fenestrae within crudely laminated micrites, pelspar-

ites and intrasparites. Horizontal fenestrae separate micrite laminae

and are occasionally connected by vertical micro-stringers of calcite

spar. In some areas the micrite laminae may be broken and slightly

curled upward. The laminae can be distinguished from each other by grain

size and textural differences such as some displaying slightly larger

grain size, some having a higher micrite content, and some displaying

graded bedding, reverse graded bedding or neither. Dolomite is more

common in this subfacies than in the dense micrite subfacies. The dolo-

\ mite is present as individual rhombs or irregular patches occurring in

zones that are relatively loosely packed. The most common fossil re

mains in the fenestral micrite are ostracods and calcispheres with minor

amounts of ramose stromatoporoids and unidentifiable skeletal fragments.

Just a few fragments of calcareous red algae (Solenopora) are seen in

thin section. A zone approximately one inch thick, composed of very

thin lamellar stromatoporoids is present in outcrop between sections II

and V at the Rockport Stone Quarry (see figure 4).

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

A dark brown to black carbonaceous substance is present in the

three facies underlying the micrite facies. The stromatoporoid biolith

ite and organic-mud packstone facies contain so much carbonaceous mater

ial that these lithologies appear medium brown to black in outcrop. This

material is distributed throughout the sediments as wispy seams winding

between, and frequently enveloping the indigenous detrital carbonate

grains. In thin section the carbonaceous seams are translucent to op

aque and many such seams contain single, or clumps of, minute dark brown

to black spheres.

The microspheres range in diameter from two to ten microns and

average four microns. The wall thicknesses range from 0.5 to i micron.

The microspheres display no ornamentation nor do any display internal

organization, structures, or organelles.

Biologic Affinity of the Organic Material

Cookman (1976) while investigating the petrology-petrography of the

Rockport Quarry Limestone, discovered the microspheres and suggested

that they may be some form of blue-green algae. Other possible inter

pretations for the affinity of these includes (l) bacteria, and (2)

spores/pollen.

Schopf (1969, p. 145-146) suggested that

When the various major groups of ancient organisms are considered in relation to their supposed origins, sharp lines of definition and distinction are lack ing ... and probably very few lines of real distinc tion ever did exist .... Most major groups of organisms may contribute microfossil remains, but these may be so very much alike that assured recognition is problem-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18

matic .... When we consider the taxonomic sub division of very ancient biotic assemblages in which morphologic evidence is at a minimum we inevitably encounter uncertainties .... Class ification of ancient microfossils must be based largely upon inferences derived from morphologic evidence.

Because of the smooth, ornament-free outer surface,, spherical shape,

and the apparent lack of nuclei a bacterial origin for the inicrospheres

seemed possible. However, bacteria are barely visible under a polariz

ing microscope even at the highest of magnifications. Bacteria are gen

erally much smaller (less than one micron in diameter) than the Rockport

microspheres. Walcott (1915) reported Algonkian spherical bacteria

0.95 to 1.3 microns in diameter.

Spores or pollen sometimes occur as spherical bodies. Land plants

had developed by middle Devonian time producing spores and pollen for

propagation. They are usually carried to remote areas by wind, and it

is conceivable that these reproductive bodies could have been carried

by offshore breezes and deposited on the middle Devonian shallow carbon

ate shelf that became the Rockport Quarry Limestone. Spores and pollen

are similar to the spherical bodies only in that they display no intern-

v al organization. The smallest pollen grains and spores range down to

ten microns in diameter; only one microsphere was observed with a ten

micron diameter. ■ .

The liklihood that the microspheres represent unicellular algae

seems greater than the possibility of their being either bacteria or

spores/pollen. The size range of the microspheres corresponds excep

tionally well with those reported for ancient and recent blue-green

algae. Awramik (1976) reported two size populations of unicellular

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 blue-green algae within the Precambrian Gunflint Formation. One popu

lation included forms less than three microns in diameter, the other

included forms ranging from 5 to 10 microns in diamter. Bathurst.

(1976) stated that a m o d e m unicellular blue-green alga, genus Entophy-

salis, ranges from one to two microns in diameter. Goccoid blue-green

algae measuring seven microns in diameter forming subtidal mats in

Bermuda were reported by Gebelein (1969). Newmann and others (1970)

reported a modem Bahaman unicellular blue-green alga, genus Anacystis,

that was two to three microns in diamter. The size range (2-5 microns

in diameter with a single 10 micron microsphere) of the Rockport micro-

spheres matches those of both ancient and m o d e m forms.

As previously stated, the Rockport bodies exhibit no internal struc

ture. The procaryotic or non-nucleated nature of blue-green algae is

well documented (Tilden, 1935» Drouet, 19515 Chapman, 1964; and Chapman

and Chapman, 1973)* The external morphology of the Rockport microspheres

is like that of the blue-green algae: spherical and devoid of any orna

mentation.

Most unicellular and filamentous blue-green algae secrete sheaths

of mucilage (Drouet, 19515 Shearman and Skipwith 1965; and Wray, 1977)-

These sheaths are used to protect the algal community from excessively

intense electromagnetic radiation (Tilden, 1935 and Drouet, 1951) and

desiccation (Fogg et al, 1973 and Prescott, 1968) during periods of

exposure. The sheath material is very sticky, promoting adhesion of

clay- through sand-size material that normally would be swept away

(Ginsburg and Lowenstam, 1959» Wray, 1971; Monty, 1972; and Golubic,

1976). The distribution of the Rockport bodies and detrital material

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 within the carbonaceous seams strongly suggests an algal affinity for

the microspheres with the carbonaceous seams representing a residue of

the gelatinous sheath material. Shearman and Skipwith (1965) found

mucilaginous "organic matter" in recent, sediments of the Trucial Coast

and also found a similar material in partially cemented Pleistocene

limestone beneath the floor of the Persian Gulf. They concluded that

ancient organic matter, usually classed as kerogen, contained within

Paleozoic limestones may be the derivative of ancient algal secretions.

Gebelein and Hoffman (1973) state sheath material is very stable, that

it does not decompose until long after deposition or even lithifica

tion.

The carbonaceous seams of the Rockport Quarry Limestone are present

in two forms: (l) quasi-filamentous and (2 ) compact. In the former

case the material appears pellucid and filamentous on the edges of

thin section slides in areas where holes occur along the seams and

wherever the seams are very thin. The compact carbonaceous seams appear

very dense and opaque in thin section, light is transmitted through

them only near the edges where breaks occur.

If the Rockport carbonaceous seams and spheres do have an algal

affinity algal filaments should also be present; but no filaments were

seen in thin-section. Examination of insoluble residues from the.

stromatoporoid biolithites and organic-mud packstone facies did yield

three types of filaments ranging in size from 25 to over 600 microns in

length, and 1.5 to 7*5 microns in diameter, some displaying few cells

and others displaying many cells. Newmann and others (1970) reported

modem Bahaman blue-green algal filaments 1 to 1.5 microns in diameter

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and Wolf (1965) reported Devonian blue-green filaments from New South

Wales ranging from 5 to 20 microns in diameter. The Rockport filaments

range in color from green-brown to brown and are translucent. They

possess a surface sculpture, but are not ornate like fungal threads.

It is reasonable to conclude that they represent filamentous algae.

All three filament types belong to the Glass Hormogoneae (Golubic,

1976). Two forms are found as homocystous trichomes, lacking hetero

cysts and branching; they are probably representatives of the Order

Oscillatoriales. The third form is heterocystous and exhibits true

branching of the T-ramification (Golubic, 1976), placing it within the

Order Stigonematales. Some cells in this filament type, located near

the ends of filaments, are longer (up to 10.8 microns) than the average

cell (5 .^ microns). These are areas of filament growth, characterized

by very rapid cell division and multiplication. Sometimes heterocysts

are found at the ends of these meristematic zones. Chapman (196^)

describes heterocysts as enlarged cells which possess thickened walls,

particularly at their poles, usually occurring singly, Croft and

George (1959) reported middle Devonian filamentous blue-green algae

from Scotland possessing spherical heterocysts that were smaller than

surrounding cells. Tilden (1935) showed some sketches of filaments with

disc-like heterocysts. The full extent of their functions are not known

however they do seem to determine the breaking up filaments into hormo-

gones thus forming a means of vegatative reproduction among the fila

ments (Chapman, 196^).

The presence of carbonaceous seams engulfing the microspheres and

carbonate detritus, and the discovery of heretofore unreported filaments

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the Rockport Quarry Limestone indicates that these materials most

likely represent the remains of subtidal mats dominated by unicellular

blue-green algae such as the subtidal Schizothrix-unicell mat (fig. 7)

reported by Neumann and others (1970) in the Bahamas, as proposed by

Cookman (1976) for the Rockport. Carbonate detritus that was washed

over the mats by currents was bound by the intertwinning activity of

the filaments and by the sticky nature of the mucilage secreted by the

unicells and filaments. In light of the available data and the inferenc

es presented here it seems reasonable to assign most of the organic

matter to algal categories.

POLYCHAETE SCHIZOTHRIX UNICELLS TUBE FILAMENTS

50 microns

Figure 7 Microstructure of Schizothiix mat. Abundance of fine fila ments and. mucilage create a rough-surfaced mat lacking rigid fibrous structure but within which grains are completely en meshed. After Neumann et al (1970).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PALEOECOLOGY OF THE CARBONACEOUS (ALGAL) MATERIAL AND ASSOCIATED ORGANISMS

Stromatoporoid Biolithite Facies - Lower Unit

The mat-forming algae, and, to a lesser extend fenestrate bryozoans,

were very effective in binding the interstromatoporoid sediment of the

biolithites. A consequence of this activity was the development of a

firm substrate upon which other organisms, specifically lamellar stroma

toporoids could grow. Hemispherical stromatoporoids, found in zones

where there are fewer organic seams (fewer algal mats), preferred to use

other objects as growth nuclei, such as lamellar stromatoporoids, brach-

iopod shells, and coral and stromatoporoid debris. Solitary corals are

found throughout the section, but never in growth position, so one can

not definitely say whether they grew here and were then toppled or were

washed in. Where the carbonaceous seams are sparse compound rugose

corals and some favositid corals are present locally, but usually not in

growth position.

According to Abbott (1973) there has been much dispute among paleon

tologists concerning the environmental significance of stromatoporoid

growth forms. The lamellar growth form, for example, has been thought

to represent a moderately low energy to a high energy growth form depend

ing upon the investigator. They agree, basically, that hemispherical

forms grew and lived in high energy environments (James, 1979)- It is

obvious that other factors have to be considered to determine the paleo-

ecology of lamellar stromatoporoids.

The presence of stromatoporoid debris associated with intact strom

atoporoids indicates very shallow water or higher energy conditions,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24

but fine sediment associated with stromatoporoid biostromes indicates

relatively quiet offshore waters (Lecompte, 1956). The Rockport bio

lithites show evidence of both of these conditions.

The stromatoporoid biolithite facies probably represents biostromes

of lamellar stromatoporoids that grew in the subtidal zone and neared

surf base. The lamellar forms are intimately associated with the

algal mats in moderate energy environments; in higher energy environ

ments the algal mats are present but not as prevalent. Modem sub

tidal algal mats in the Bahamas, as demonstrated by Neumann and others

(1970) can withstand current velocities three to nine times as high as

the maximum tidal currents (13 cm/sec) in that area. Gebelein (1969)

has described algal colony growth forms associated with different cur

rent velocities (fig. 8). Using Gebelein's data, the Rockport algal

mats represented by the carbonaceous seams would have existed with

surface currents less than 15 - 20 centimeters per second due to the

fact they are essentially flat. Although no algal oncolites were found

in the Rockport Quarry during the course of this study, Cookman (1976)

reported several. With oncolites occuring in the Rockport Quarry

Limestone the surface currents present in those layers would have been

1 - 11 centimeters per second by Gebelein's scheme. It is reasonable

to assume, that the algal mats and lamellar stromatoporoids co-existed

in a moderate to high energy environment.

It appears that the proposed algal mats played the role of pioneer

species. The following sequence of events originally proposed by Cook

man (1976), displayed in figures 11 through 15, illustrate the develop

ment of the stromatoporoid biolithite. The algal mats rapidly colonized

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

SEDIMENTARY STRUCTURE ' SURFACE CURRENT SEDIMENT MOVEMENT VELOCITY l e m / M e l ( gm / hr/foot)

RIPPLED SAND

ALGAL MAT

ALGAL DOME High total • udlmant accumulation 8-60 ALGAL BISCUIT Law total uodlmont accumulation

THICK ALGAL MATS

ALGALISCUITS

ALGAL DOMES

ALGAL MAT, THICKENING UPWARD

RIPPLED SAND WITH FLA T PEBBLE CONGLOMERATE

Figure 8 (a) Relation of sedimentary structure to current velocity and sediment movement. (t>) Interpretation of vertical sequences of stromatolitic structures. From Gebelein (1969).

the substrate, binding and stabilizing the bottom sediments in the Rock- % port biolithites (fig. 9)• Soon after, lamellar stromatoporoids, the

opportunistic species, took advantage of the stabilized substrate pro

vided by the algal mats by colonizing the surface and proliferating

(fig. 10). Currents coursing over the stromatoporoids brought in nutri

ents essential for this growth. Most of the lamellar forms usually grew

to a thickness of 5 “ 6 centimeters, although some reached 15 centi-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N> ON A.Shub Wave and Current Direction Initial Algal Mat Stabilization withinthe'stromatoporoid. biolithite facies during Middle Devonian time. Figure 9• Initial stabilization of the Rockport Quarry sediment surface by subtidal algal mats

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ro Stromatoporoid Stromatoporoid Encroachment continuedto grow within these energy lees. formation of energy lees between adjacent stromatoporoids. The algal mat survivedand Figure 10. Subsequent encroachment of the algal mat surface by lamellar stromatoporoids and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28

meters. Energy lees "between adjacent stromatoporoids were created by

the few centimeters of relief of the stromatoporoids and the underlying

mat surface (fig. 10). The algal mats thrived in these energy lees

(fig. 11) instead of being stifled by the encroaching stromatoporoids.

As the mats continued to grow and bind sediment brought in by currents,

the mats eventually encroached upon the stromatoporoids (fig. 12).

They constantly competed for space, neither one completely domin

ating for very long (fig. 13)• The lamellar stromatoporoids probably

tolerated slightly higher current velocities than the algal mats as

evidenced by the presence of lamellar stromatoporoids and sparcity of

carbonaceous seams in areas of the biolithites where coarse stromatop

oroid debris and overturned stromatoporoid and coral heads are found

(fig. 14). Together, the algal mats and lamellar stromatoporoids formed

a climax community that produced the Rockport biolithites.

Hemispherical and some lamellar stromatoporoids are widely scattered

in the stromatoporoid biolithite facies where the carbonaceous seams are

sparse and sometimes absent; the sediment in these areas is coarser and

full of stromatoporoid debris. The sparsity of mats and the presence

of coarse stromatoporoid debris indicates a higher energy environment

(see fig. 14). Colonial coral heads, indicative of higher energy envi

ronments, are found in these areas. Both hemispherical stromatoporoids

and colonial corals are most often found overturned. Solitary corals

are also found in these zones; they are never in growth position and

commonly display surface abrasion. These high energy zones represent

areas where the stromatoporoid biostromes grew to surf base and were

subjected to some turbulence.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N> \o Mat Mat Growth Within Energy Lees ment hy the algal mats during times of reducedwave and current activity. Figure 11. Continuedgrowth of the algal mat within the energy lees allowed incipient encroach

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. c A.Shub Algal Mat Encroachment tendedperiods of wave and current activity. Figure 12. The algal mats eventually completely encroached the lamellar stromatoporoids after ex

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. AShub After Many Repititions Rockport Quarry. displayedin the upper andlower stromatoporoid biolithite facies in the exposure at in interbedded organic-rich sediment between superposedlamellar stromatoporoids as . . Many repetitions of the sequence of events displayedin Figures 9 through 12 resulted 13 Figure

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ro ). ). 2 ) and) colonial coral heads (C 2 Biolithite Turbulent Environment Colonial corals (0^). Wispy organic (algal) seams (W). edimmediately beneath lamellar stromatoporoidsoidsand ) and between overturned lamellar (Si hemisphericalstromatopor stromatoporoids (S lowerunit of the stromatoporoid biolithite facies. Algal mats (A) are most pronouncmats are Thefound algal- as mere wisps of organic material amidthe biostromal debris. Figure 14. Sketch of a quarry wall from Rockport Quarry depicting a turbulent environment in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33

Solitary corals are found not only in these high energy zones but,

throughout the biolithites. Even in the zones representing areas of

quiet water conditions the solitary corals are not found in growth po

sition; they are all lying prostrate, incorporated in the mats. Be

cause they are not found in growth position, it is uncertain whether or

not they grew within the facies or were washed in. Upon examination,

they show little, if any, abrasion. It becomes evident that mature

forms with their narrow bases and their height (2.3 to 15 centimeters)

would be fairly unstable as growth proceded and could be easily toppled

by currents. By the fact that corals and stromatoporoids are found in

the same types of environments (Lecompte, 1956), and the fact that the

Rockport forms show little or no abrasion, suggest they grew in the

environments represented by the facies in which they are found and were

felled by current and or storm action. In the Rockport Quarry Lime

stone the solitary corals played the role of an opportunistic species

of ineffective competitors (Raup & Stanley, 1978).

Fenestrate bryozoans are found occasionally in the algal-bound

interstromatoporoid sediment of the lower biolithite unit. The capa-

bility of bryozoans providing biohermal frameworks to build bioherms

was pointed out by Pray (1958). Although they are not abundant enough in

the Rockport strata to be considered biohermal or biostromal builders,

it seems likely that bryozoans could have aided in the trapping of sedi

ment through a baffle effect with their upright frond-like forms. Deel-

man (1957) also reported little bryozoan material in limestones compos

ed predominantly of algae, sponges, and stromatoporoids. At Rockport

Quarry bryozoans occur in relatively low numbers near the top of algal

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3^ .mats, and near the bases of some overlying stromatoporoids (fig. 15).

The low number of bryozoans found in the Rockport strata may be

explained by competition with the algal mats for surface area on the

substratum. Algal mats are known to bind relatively large volumes of

sediment in relatively short time intervals (Monty, 1965, 1967, 19?6j

Gebelein, 1969, Neumann et al., 1970? and Golubic, 1973)* With this

rapid expansion of algal mats it is easy to see how bryozoans would

soon be engulfed and stifled by the mats, thus inhibiting their estab

lishment in this environment. Another factor that could have prevented

bryozoans from expanding in this environment is that the soft surface

of algal mats is not conducive to attachment by young bryozoa. The few

bryozoans found in the biolithite may have attached to hard objects

previously trapped by the algal mats or to hard objects located in bare

spots of algal mats that were soon engulfed .by the mat.

Environmental factors that could have prevented the establishment

of bryozoans in the Rockport biolithites are water depth and agitation.

The water in the stromatoporoid biolithite facies may have been too

shallow for bryozoans to tolerate. Most writers suggest substrates

favored by bryozoans were slightly below wave base (Duncan, 1957)* At

any rate, the bryozoans represent an opportunistic species, like .the

.corals, that was a poor competitor. The presence of higher energy zones

(fig. 14) indicate the environment represented by the biolithite was at

or near surf base, probably too shallow for optimal bryozoan growth.

Also, water conditions here most likely would be too agitated for del

icate fenestrate bryozoans. Water temperature and salinity could not

have been factors since algae, stromatoporoids, corals and bryozoans

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. !!!5 !l!!!!!!!!!lllllia i|iiiiiiiiiiiiiiiiSiiiiSSSSSSSSMS!SBlla"'”''*"la,l'^*>SiSiSaS!il!!!l 2l,a11'" ''”*

500x

Figure 15. Thin sections depicting fenestrate bryozoans (B) incor porated in algal mats very close to the bases of overlying lamellar stromatoporoids (Sj).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36

have similar optimal temperature and salinity ranges.

The stromatoporoid biolithite represents an ecological succession

typified by a climax community composed of an exceptionally competitive

opportunistic species of lamellar stromatoporoids and an equally compet

itive pioneer species of algal mats that thrived in the subtidal envi

ronment. Together, they built biostromes under moderate energy condi

tions that eventually built up near surf base, typified by higher energy

conditions where hemispherical stromatoporoids and colonial corals, both

competitive opportunistic species, competed successfully for space with

the stromatoporoid algal mat climax community (fig. 16).

Organic-Mud Packstone

Coral Packstone Subfacies

This lithosome representing the lower of the two subfacies

that comprise the organic-mud packstone, is a packstone that is almost

black with carbonaceous seams surrounding lighter-colored lenses of

grainstone. The packstone contains solitary corals and some overturned

colonial coral heads and hemispherical stromatoporoids especially with-

in the lower two feet of this unit. The grainstone lenses contain

abundant crinoid debris and fenestrate bryozoans with solitary and

colonial corals, hemispherical stromatoporoids and hardly any carbon

aceous seams.

As in the biolithites, the organic rich sediment in the coral pack

stone subfacies represents extensive algal mat growth. Algal mats

covered almost the whole bottom except for local crinoid and bryozoan

gardens (Cookman, 1976). During the time of deposition of this lith-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O j -x) V A.Shub

Subfacies Coral Packstone Inter-Biostromal Depression

Biolithite Facies Outer Biostrome colonial coralheads (Cp)* crinoids (Cr), bryozoans (B;. Arrows indicate the pre dominant wave and current direction. "biolithite facies. "biolithite Landwardfrom lies the an "biostrome inter-"biostromal depression stromatoporoids (S^), hemispherical stromatoporoids (So), solitary corals (C^), representedby the coral packstone andbryozoan grainstone subfacies. Lamellar Lower Stromatoporoid Figure 16. Sketch shoringan representingouter"biostrome the lowerunit of the stromatoporoid

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. osorae of the Rockport Quarry Limestone the sea floor would be covered

by algal mats and localized crinoid-bryozoan gardens (fig. 17).

The gardens were initiated by crinoids and bryozoans colonizing

bare spots in the mats proximal to the stromatoporoid biostrome or on

spots where debris was washed in from the biostrome. H. L. Clark (1921)

showed that m o d e m reef crinoids at Maei Island, Torres Strait, Austra

lia, lived in water in reef flats from a few inches to three feet deep.

It seems possible that the crinoids of the organic-mud packstone facies

could have lived in this quiet water zone between the two stromatoporoid

biostromes represented by the biolithites. Middle Paleozoic crinoid

biocoenoses consist of tightly knit gregarious units, whereupon the

resulting thanatocoenoses often consist of thick, lenticular burial

assemblages of almost all crinoidal debris (Laudon, 1957). Laudon

(1957) also reported that nearly complete disarticulation can occur in

areas of relatively minor bottom agitation in the burial environment.

Bryozoans are more abundant here than in the stromatoporoid bio

lithite facies, suggesting quieter water conditions. The presence of

abundant crinoidal debris also suggests this. Ulrich (1911) stated

bryozoans flourish in relatively quiet waters seaward of zones of higher

energy. O s b u m (1957) stated that the majority of m o d e m bryozoan

species are limited to comparatively shallow waters of coastal shelves

from the low tide mark to 100 or 200 fathoms. Stach (193&) stated that

fenestrate bryozoans are most abundant in the sublittoral zone. Ulrich

(1911) also indicated that they too were gregarious forms as their dis

persal was greatly facilitated by currents. So, as the Rockport crin

oids and bryozoans established their "gardens" they flourished and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ). ). Hemispherical stromatoporoids (So) also grewon the low 2 colonial coral heads (C algal mats and (A) localized crinoid-bryozoan gardens. Solitary corals (Cp) and a few mounds of debris built bythe crinoids (Cr) andbryozoans (E). Figure 17. The coral packstone subfacies of the organic-mudpackstone facies displaying extensive

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 0

slowly built up low mounds of debris created by dead bryozoan fronds

and disarticulated crinoids. The crinoids and bryozoans flourished and

the mounds became larger, creating more space for the crinoids and

bryozoans, as well as, solitary and a few colonial coral heads along

with hemispherical stromatoporoids.

The presence of extensive algal mats, crinoids, and bryozoans sug

gest quiet water conditions, most likely quieter than the stromatoporoid

biolithite. The presence of solitary and colonial corals and hemispher

ical stromatoporoids in this quiet water environment initially appears

contradictory to the paleoecological interpretations of the stromatopor

oid biolithite. However, there are recent analogues of species living

in two rather different energy regimes. In the Florida reef tract one

finds patch reefs consisting of hemispherical coral heads (Montastrea

annularis. Porites asteroides. and Siderastrea sp.) with some small

corals growing between the heads such as flower corals (Eusmilia fasti-

giata and Mussa angulossa) and finger corals (Porites sp.), (Ginsburg,

1972, p. 33-44). Many of these forms are found at the reef front as

well as in the patch reefs of the back reef environment. This author

has even observed a head of Montastrea sp. surviving in the quiet con

fines of Coupon Eight behind the Florida Keys. Although the water depth

and energy conditions are quite different in these two modem environ

ments the coral' species are able to tolerate the variation. Appar

ently some species found in the Rockport Quarry Limestone were equally

tolerant of exceptional energy conditions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Crinoid-Bryozoan Subfacies

The gregarious- habits of the crinoids and bryozoans of the coral

packstone subfacies brought about the radiation of this competitive

community in that subfacies. As more individuals thrived and expired,

their remains were accumulated into low mounds on the substrate creat

ing more living space. The local gardens soon coalesced and spread,

relegating the algal mats, to local patches in the crinoid-bryozoan

grainstone subfacies, the upper subfacies of the organic-mud packstone .

facies. This is evidenced by the dominance of crinoid-bryozoan pack-

stones and grainstones and only minor amounts of organic-mud packstone

in this subfacies (fig. 18). The algal mat community, dominant in the

coral packstone subfacies, is subordinate in the crinoid bryozoan sub

facies while the crinoid-bryozoan communities are poorly represented in

the coral packstone subfacies and are dominant in the crinoid-bryozoan

grainstone subfacies.

The organic-mud packstone facies is located in a depression between

the two biostromes defined by the lower and upper units of the stroma-

toporoid biolithite facies. The outer stromatoporoid biostrome (lower % stromatoporoid biolithite) shielded this environment from most current

and wave action. Since only isolated areas of the outer biostrome neared

surf base, some current and wave action was allowed to enter the inter-

biostromal depression as illustrated in figure nineteen. There was

enough circulation to allow hemispherical stromatoporoids, and both

solitary and colonial corals to grow, but gentle enough to allow quiet

water organisms such as crinoids and bryozoans to thrive. The crinoid-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the coalescedcrinoid-bryozoan gardens. algal mats to local patches, As thelow gardens spots amidcoalescedthe gardens. they relegated the See figure 17 for an expla nation of characters. Figure 18. The crinoid-bryozoan grainstone subfacies ofthe organic-mud packstone facies shoring

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. k3

bryozoan grainstone (fig. 19) is located at the back of the depression

where the current activity is more direct. Overturned hemispherical

stromatoporoids and colonial corals occur near the base and top of the

organic-mud packstone facies. They were once living on the surrounding

biostromes and were toppled by current and wave action and washed into

the depression.

Stromatoporoid Biolithite - Upper Unit

The upper unit of the stromatoporoid biolithite facies resembles

the higher energy zones of the lower biolithite. The unit, only 1.8

feet in thickness, contains many overturned coral heads, prostrate sol

itary corals, hemispherical stromatoporoids, and associated coral and

stromatoporoid debris in addition to lamellar stromatoporoids (some up

to 6 inches thick). The content of algal seams gradually decreases up

ward from the base of the facies, indicating higher energy conditions

at the top.

Ostracoda make their first appearance in the Rockport Strata in

this unit of the stromatoporoid biolithite, These ostracods appear to % be smooth-shelled and somewhat elongated, with their length approx

imately twice their height. According to Benson (l96l) and Tasch (1973)

the carapaces of burrowers living in fine-grained sediments are smooth

and elongate. The carapaces of swimmers are smooth, light-weight, and

high in proportion to their length (Benson, 1963 and Tasch, 1973), ruling

out the possibility of the Rockport ostracods being swimmers. Also, the

majority of the Rockport forms were not broken (the carapaces of swimmers,

being lightweight, would most likely be broken) indicating they had

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. £ A.Shub ______I I I Subfacjes I Organic-Mud Packstone Facies Inter-Biostromal Inter-Biostromal Depression coalesce^ crinoid-bryozoan gardens. The arrows at the top of the sketch algal mats; the portion representedby the crinoid-bryozoan grainstone sub facies is characterizedby localized crinoid-bryozoan gardens and extensive facies. The portion of the depression representedby the coral packstone sub facies is characterized by localizedpatches ofalgal mats and extensive indicate current direction. See figure 17 for an explanation of characters. Coral Packstone Subfacies I Crinoid-Bryozoan Grainstone Figure 19. The inter-biostromal depression represented by the entire organic-mud packstone ______

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. heavier and sturdier carapaces common to burrowers. The Rockport ostra

cods exhibit no ornamentation of the carapace, ruling out'their being

crawlers, which usually display various ornaments (frills, keels, venters

or spines). The Rockport ostracods probably represent burrowing organ

isms that lived in the sediment and fed upon in situ organic detritus.

Most ostracods are omnivorous, feeding on detrital material, algae, and

tiny animals contained within the sediment (Moore et al., 1952).

The Foraminifera also made their first appearance in the upper bio

lithite unit of the Rockport strata. An encrusting form was observed.

It possesses a wall thickness of 3-7 to 8 microns and displays a rather

constant chamber size of 51 1° 95 microns across. Johnson (1968) reported

a lower Devonian encrusting foraminiferan resembling Wetheredella sp.

that has a wall thickness of 8 to 12 microns and a chamber size of 0 to

25 microns. The overall morphology and chamber shape of Johnson's Wether-

edella-like foraminiferan strongly resembles those of the Rockport en

crusting foraminifera. Cookman (1976) reported an alga, Algae indeter

minate, that strongly resembles the Rockport encrusting forams in every

respect. They are, in fact, encrusting foraminifera, not algae. The % Rockport encrusting foraminifera possess walls composed of tiny fibro-

radial crystals of calcite oriented perpendicular to both external and

internal surfaces of the wall and appear translucent in thin-section.

Many genera of Foraminifera have tests of tiny crystals of fibrous cal

cite which have their c-axes normal to the outer wall surface (Moore et

al., 1952 and Tasch, 1973)* Most calcareous blue-green algae display

no wall microstructure} the walls are usually composed of dense micro

crystalline calcite (Wray, 1977)* The fibroradial microstructure of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. . 46

the encrusting foraminifera is often difficult to see due to frequent

replacement by microcrystalline calcite which would make misidentifica-

tion quite easy. These encrusting foraminifera represent a new species.

Gross (1972, pg. 464) states that Foraminifera are one of the major

sediment contributors in the reef environment. Although the environment

of the upper biolithite unit does not represent a reef per se, it does

represent a biostrome that was built up very close to surf base. It

has been reported that the relative abundance of benthic foraminifera

increases as the littoral environment is approached (Moore et al.f

1952). This supports the idea that the upper biolithite represents a

biostrome closer inland than the biostrome represented by the lower

unit of the stromatoporoid biolithite since the upper unit contains

Foraminifera and the lower unit does not.

So the upper unit of the stromatoporoid biolithite represents an

inner biostrome that was closer to surf base and closer inland than

the outer biostrome represented by the lower biolithite unit (fig. 20).

The algal-stromatoporoid relationships are generally identical to those

of the lower biolithite as are the effects of higher energy conditions

upon the algal mats and stromatoporoids. This biostrome was also the

habitat of some solitary and colonial corals, encrusting foraminifera,

and endopsammic ostracods. This biostrome created a quieter water zone

on its leeward side than the outer biostrome because it was closer to

surf base than the latter.

Biolithite-Mlcrite Transition

The transition is a medium to coarse skeletal calcarenite. Common

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. - p - - o A.Shub

Biolithite- Micrite Transition Facies Backwater Backwater Zone

Biolithite Facies characters. Ramose stromatoporoids (S*j). See figure 17 foran explanation for the rest of the facies anda backwater zone represented by the biolithite-micrite transition facies. Inner Inner Biostrome Upper Stromatoporoid Figure 20. The innerbiostrome therepresented upper unit by' of the stromatoporoidbiolithite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sedimentary constituents include lamellar stromatoporoids, corals and

their debris at the base, whole and fragmented ostracod carapaces,

and fine-grained skeletal debris. The lamellar stromatoporoids in

the transition are not as abundant as they are in the biolithites.

The main criterion used to distinguish the transition from the under

lying biolithite is the base of the transition facies is arbitrarily

placed where the lamellar stromatoporoid content decreases below 50

percent (Cookman, 1976). At the base of the facies some of the lamel

lar stromatoporoids show signs of abrasion. Stromatoporoid debris in

the medium to coarse sand-size fraction exists in the interstromatop-

oroid sediment and occurs as a stromatoporoid wackestone along with

ostracod carapaces and other skeletal debris. Except for ostracod

shells, the amount and grain size of skeletal debris decreases near

the top of the facies.

Colonial (mostly Favositid) and solitary (Heterophrentis) corals

are more prevalent at the base of the facies. The decrease of corals

to trace occurrences defines the upper bounding surface of the transi

tion facies (Cookman, 1976). The favositid corals in the transition > are smaller in size than those in the other facies; they are rarely

over three inches across in the transition, whereas in the other facies

they may be up to twice that size. The solitary corals display no

size difference in these facies.

The distribution of the organisms within the transition facies re

flects the need for water movement by these organisms. Organism density

is greatest at the base of this facies, proximal to the inner stromatop

oroid biostrome where the water was more turbulent. Skeletal debris is

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. also more prevalent at the base of the transition facies, p r o b a b l y washed

in from the. stromatoporoid biostrome. The transition facies represents

an environment not unlike those occurring immediately behind modern reef

systems by the energy conditions, the species found there, and their com

munity structure. Most of these environments are typified by rather heavy

sediment fallout and good water circulation proximal to the reef where

•reef-loving organisms prosper with a gradual decrease in water circu

lation and finer sediment fallout occurring farther inland of the reef

where the reef-loving ozganisms decrease in number and size (Multer, 1977).

Enough water circulation occurred immediately behind the biostrome to

allow stromatoporoids and corals to grow here but it was not strong

enough to allow favositid corals to grow larger. This water movement

probably rapidly waned lagoonward behind the biostrome. This decrease in

water movement would hamper the lifestyles of organisms such as stromatop

oroids and corals that depend upon aerated, moving water. As the water

movement decreased lagoonward organisms decreased in number and size.

The transition facies contains very little organic matter, although

a few algal seams are seen in thin-section and even less are noticed in % outcrop. The lack of algal seams and spheres probably results from a

combination of two factors: (l) algal mats were not as abundant in

this environment as they were elsewhere and (2) the mats that did grow

here were not preserved as effectively as they were in the other envi

ronments. Being located behind a biostrome at or near surf base' a great

deal of debris washed into this "back-biostrome" environment. There

was probably too much sedimentary fallout, both coarse and fine, for

many mats to grow. They literally became choked with sediment and

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. could not keep up with the sedimentation rate. The few that could sur

vive were subjected to grazing by herbivorous organisms and scavengers

and to bacterial action that would reduce the preservability. Under

comparable rates of primary production, the ratio of aerobic (complete)

and anaerobic (incomplete) decomposition largely determines the over

all organic accumulation. Near-aerobic decomposition, along with fewer

mats habitating this environment, resulted in the reduced number of or

ganic seams in the biolithite-micrite transition facies. By the same

token the high number of organic seams preserved in the biolithites and

the organic-mud packstone facies can be explained by a combination of

vast carpets of algal mats thriving in those environments.along with

anaerobic (incomplete) decomposition. Algal peats with partially pre

served cellular structures and pigmentation have been found after 8,000

years of burial in Abu Dhabi (Golubic, 19?6).

Other organisms preserved within the biolithite-micrite transition

facies include endopsammic ostracods, planktonic and encrusting Foramin

ifera, ramose stromatoporoids, and calcareous algae. The ostracods

found in the transition facies are the same forms as those found in the

upper unit of the stromatoporoid biolithite facies.

The foraminifera include those described by Cookman (1976) along

with an encrusting form like the one found in the upper biolithite and

a previously undescribed form. This new form has a flask-shaped agglu

tinated test composed of fine carbonate sediment. The wall can be seen

in some areas where the surrounding micritic sediment is sparse. The

earliest known Foraminifera (Lower Ordovician to Middle Silurian) poss

essed simple arenaceous or agglutinated tests. The variety and abundance

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of these earliest' forms clearly indicate that "by Ordovician time the'

Foraminifera had evolved many genera and species that could make agglu

tinated tests (Shrock and Twenhofel 1953» P« 59)* This flask-shaped

form averages 6.79 millimeters in length by 3*25 millimeters in width.

In shallow tropical waters many foraminifera are large, having diameters

between 5 a*id 20 millimeters (Moore et al., 1952, p. 53)- Some fossil

forms have been found as large as 2k millimeters in diameter (Buchsbaum,

1962, p. 50). It seems reasonable to assume that these flask-shaped

organisms represent benthic foraminifera that incorporated the bottom

sediment into their tests.

Ramose stromatoporoids were also observed in the transition in trans

verse and longitudinal sections. As expected they were found in the low

er part of the facies where the energy conditions were less intense than

those found in the biolithites. Ramose stromatoporoids are found in en

vironments that had moderate to quiet energy conditions (Abbott, 1973).

Fragments of a calcareous red alga, Solenopora sp., were observed.

The specimens were not in very good condition although the irregular

spaced cross partitions of cell threads, typical of Solenopora sp,, were

clearly visible. Solenopora is comparable to m o d e m corralline algae,

but is not as wide ranging in its depth and temperature ranges as the

corallinaceae (Wray, 1977). Solenopora is common in back reef facies

but rare in sublagoonal facies (Tsien and Dricot, 1977). In the upper

Devonian of Western Australia, Solenoporacean algae in some localities are

found in facies immediately behind the reef facies (Wray, 1977). The

biolithite-micrite transition facies is a backwater zone behind the in

ner biostrome (fig. 20). These two fragments could probably have lived

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52

in the back-biostrome but due the low amount of debris one cannot be

certain.

The sediment at the base of the transition is characterized by an

abundance of skeletal debris in the medium to coarse sand size fraction,

most of which is unidentifiable but containing stromatoporoid and coral

fragments. The base of the transition represents the part of this en

vironment that was nearest to the more turbulent inner biostrome. It

follows that a lot of material would be deposited in the lagoon proximal

to the inner biostrome, the washed-in debris would be coarser proximal

to the biostrome and would decrease in grain size farther landward.

This is in fact the case. At its base the biolithite-micrite transition

facies is predominantly clastic with little micrite. At the top of the

unit it is predominantly micrite with "floating" clasts, a wackestone.

Micrite can originate from inorganic chemical precipitation, dis

integration of organisms into their constituent crystallites, precipi

tation by microorganisms, or from mechanical and/or biological abrasion

of skeletal material (Folk, 1974). In the lee of reefs, conditions are

relatively calm and much of the mud formed in the reef environment comes > out of suspension (James, 1979» p. 129).

The possibility of organisms producing the micrite cannot be ruled

out. Most lime mud is organically derived and a common product of

shallow, tropical waters (Wilson, 1975» P* 4). Some species of codi-

acean green algae such as Penicillus. Riphocephalus, and Udotea are

lightly calcified and produce aragonite mud upon post-mortem disintegra

tion (Ginsburg, 1972; Neumann and Land, 1975; Bathurst, 1976, p. 278-

284; and Multer, 1977i p. 71)• Considering that the above modern green

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algae disintegrate completely to unidentifiable mud-size carbonate ma

terial upon death (Stockman et al., 1967) comparable ancient'forms are

possible sources of much of the lime mud that is so abundant in many

ancient deposits (Heckel, 197^-). The degree to which inud-producirig

organisms produced the micrite found in this facies or any micrite, is

very difficult to determine. The organisms that produce this mud live

in semi-restricted, to restricted environments. On a recent field excur

sion to the Florida Keys the author observed abundant codiacean green

algae growing in Florida Bay and around Rodriguez Key. The presence of

the skeletal debris mixed with the micrite in the transition facies in

dicates there was enough circulation to wash in debris and to support

and disintegrate mud-producing organisms.

Some of the micrite in the transition facies was derived from the

biological erosion of skeletal debris as evidenced by the micrite envel

opes surrounding skeletal grains and some totally micritized ostracod

shells. Micrite envelopes are caused by boring organisms, mostly algae,

that upon death leave behind micrite-filled tubules (Bathurst, 1976,

p. 381 - 392). These borings commonly riddle skeletal grains, thus aid-

ing mechanical abrasion immensely (Bathurst, I969, 1976, p. 381)• Some

micrite in the transition facies was most likely derived chiefly from

mechanical abrasion occurring in the inner biostrome environment,'the

micrite produced was put into suspension by wave and current activity

and was washed into the tranquil transition facies and deposited (fig.

2l). Micrite was probably also produced, but to a lesser extent by the

disintegration of mud-producing flora and by bioerosion.

The biolithite-micrite transition facies represents a backwater

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A.Shub Transition Biolithite-Micrite ’ ’ Suspended Mud-Sized. Material Saltating Material Saltating Suspended Sand-SizedMaterial o . o. ‘ transition facies from the upper stromatoporoid-biolithiteformed chiefly from mechanical facies. abrasion andfrom bioerosion The micrite of skeletal debris. Upper Upper Biolithite Figure 21. Sketch showing mud- andsand-size material washedinto "being the biolithite-micrite

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 '

environment located in the lee of the inner hiostrome (fig. 20). The

energy conditions were considerably more tranquil than those of the

inner biostrome, although some activity would be expected proximal to

the biostrome. The wave and current activity rapidly waned landward

(up section) from the biostrome. The presence of arenaceous foraminif-

erans in this facies indicates a nearshore environment (Raup and Stanley,

1978, p. 260). The environment also supported the life habits of lamel

lar and ramose stromatoporoids, colonial and solitary corals, ostracods,

and a few algal mats. The scarcity of algal mats can be attributed to

sedimentary choking and an increase in anaerobic (complete) decomposi

tion. This is the last subtidal environment in the Rockport section.

Micrite Facies

This facies is composed of two subfaciess a pelmicritic dense sub

facies and a crudely laminated fenestral subfacies, which are often

interbedded.

Dense Subfacies

The fauna and flora in the dense subfacies is sparse, and con

sisting chiefly of ostracods (whole and fragmented carapaces), calci-

spheres and a minor amount of ramose stromatoporoids and local accumu

lations of fragmented trilobite carapces, probably washed into the en

vironment from elsewhere.

The ostracods are the most abundant of the organisms found in the

dense subfacies. They are similar in all respects to the forms found

in the upper unit of the stromatoporoid biolithite facies and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. biolithite-micrite transition facies.

Ramose stromatoporoids are found locally within the dense subfacies.

They range from one millimeter up to 7.75 millimeters in diameter. Very

thin lamellar stromatoporoids, less than 10 millimeters in thickness,

are also locally present-(one zone approximately one-inch thick).

Ramose stromatoporoids are commonly found in back-reef facies (Heckel,

197^). Klovan (196^) found the slender stick-like stromatoporoid

Amphipora sp. in a lagoonal facies of the Redwater Reef complex of

Alberta, Canada. Krebs (197^0 also reports ramose stromatoporoids

(Amphipora and Stachyodes sp.) in back-reef lagoons from .Devonian car

bonate complexes of central Europe. The presence of ramose stromatop

oroids, then, indicates a lagoonal environment, or at least an indica

tion of relatively low energy conditions.

Fragmented trilobite carapaces are observed in varying amounts in

almost every thin section of the dense subfacies. Their distribution

within the subfacies appears patchy; some slides display a profusion of

carapaces where others exhibit a marked reduction in carapace content.

The fragmentation of the carapaces indicates that the trilobites lived

and grew outside of this environment represented by the dense subfacies

and were washed in by wave or current action during periods when energy

conditions were more vigorous. Once suspended, the shape of tiil'obite

carapaces, like brachiopod shells, will sink slower than an object of

comparable mass but of more compact shape.

Coral and crinoid fragments are found in trace amounts. Because

these two organisms are only found in fragments and are so scarce in

this environment it seems unlikely that they inhabited this facies.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 These fragments were probably washed into this environment from the

inner biostrome.

Spongy micritic structures, believed to represent previously undes

cribed calcareous algae, are observed; one is found encrusting a ramose

stromatoporoid and another is found free within the sediment. The en-

cruster forms a rind ranging in thickness from 0.019 to O .665 milli

meters that completely encircles the diameter of a ramose stromatoporoid.

The crust consists of reticulating walls that range in thickness from

0.009 to 0.033 millimeters. This network of walls forms ovoid chambers

- ranging from 0.014 to 0.105 millimeters in maximum dimension - that

are either completely or at least partially filled with calcite.

The free form is triangular in shape with its base 1.62 millimeters

long and 0.95 millimeters high from base to apex. This form has thick

er walls than the encrusting form - its reticulating walls range in

thickness from 0.024 to O.O67 millimeters and the maximum chamber di

mension ranges from 0.019 to 0.24? millimeters. The majority of the

chambers, as with the encrusting form, are completely filled with cal

cite. The walls of both forms are composed of dense micrite. Neither % form displays any type of wall microstructure.

These two structures may represent some type of calcareous algae,

probably a blue-green alga related to Renalcis sp. They resemble'

Renalcis in the following ways: (l) the nature and composition of the

walls (dense and micritic); (2 ) the complete absence of any wall micro

structure; and (3) growth habits (Renalcis is found both free in the

sediment and as an encrustation. The chambers of the Rockport micritic

structures range in size from 14 to 105 microns and wall thicknesses

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58

range from 9 to 33 microns. The chambers of Renalcis sp. commonly dis

play great variation in size (50 to 400 microns) and possess, wall thick

nesses ranging from 39 to 80 microns (Wray, 1977). Although the Rock

port structures possess slightly thinner wall thicknesses than those of

Renalcis sp., the overlapping of size ranges of the chambers of the

Rockport structures and Renalcis, the wall composition, the lack of wall

microstructure, and the similar growth habits of the two forms indicate

that the Rockport structures are at least related to Renalcis sp.

Calcispheres are found in trace quantities in all facies of the

Rockport Quarry Limestone, except for the micrite facies where they are

one of the major organic components. The only organisms more abundant

in the two subfacies of the micrite facies are the ostracods. Calci

spheres are fossil remains of unknown affinity. Four opinions exist

regarding their taxonomic affinity: (l) Foraminifera, (2 ) Radiolaria,

(3 ) Dasycladacean algae, or (4) inorganic structures (Konishi, 1956).

The wall microstructure of the Foraminifera does not bear any resemblance

to the wall microstructure of the calcispheres as described by Cookman

(1976). Radiolarian tests are composed of silica, whereas calcispheres % are composed of calcite. Stanton (1963) believed calcispheres probably

represent some form of plant spore or reproductive body with their

exact affinities remaining uncertain. Baxter (i960, plate 144, fig. 12)

observed a calcisphere containing "spore-like' bodies" and suggested it

may represent some type of reproductive structure. Calcispheres are

often found in limestones believed to be deposited under conditions sim

ilar to those under which the sediments of the Bahama Banks are being

deposited today (Beales, 1956 and Baxter, i960). This type of environ-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ment is conducive to the growth and proliferation of Dasycladacean al

gae. Konishi (1958) demonstrates that some calcispheres are attribut

able to Charophyta, a green alga closely related to the Dasycladaceae.

The Dasycladacean, Acetabularia sp., produces small spherical calcar

eous reproductive bodies strongly resembling calcispheres (Wray, 1977i

p. 1C&). Two form-species of calcispheres can be observed in the mi

crite facies: (l) Galcisphaera with its spherical, dark calcite exter

ior rim and (2) Parathurammina with thick pentagonal to hexagonal walls.

The Calcispheres range from 60 to 225 microns in external diameter,

with wall thickness ranging from 3 to 30 microns. The microstructure

of the Rockport microspheres appears too complex (spherical wall, often

multilayered) to be the result of inorganic processes such as trapped

air bubbles filled with calcite as suggested by Pia (1937» P* 803).

The Rockport calcispheres most likely represent the reproductive bodies

of some marine plant. The derivative plants from which these spherical

bodies originated must disintegrate upon death since only the calci

spheres are preserved. The most likely derivative, plant would be a

Dasycladacean alga.

The dense micrite is sublithographic in character and occasionally

displays a lumpy or mottled appearance; in other areas flaser bedding

can be seen, although it is not that common. Some intraclasts (flat

pebble) can also be seen. Although the dense micrite is sublithograph

ic in character, occasional vertical fenestrae can be observed. Ver

tically oriented fenestrae often affect the millimeter thick lamina

tions in the surrounding sediment (fig. 22). These fenestrae are filled

with sparry calcite or dolomite and taper in the downward direction.

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

0 .5mm

Figure 22. Vertical fenestrae in the dense subfacies and their effect upon millimeter laminations in the sediment of the dense micrite subfacies. In most cases the laminae are down- tumed as they near the fenestrae; sometimes the laminae are distorted. Laminations not affected are shown at the bottom of the sketch. The fenestrae are filled with sparry calcite or dolomite. The downward tapeiing of the fenestrae and their effect upon the surrounding sediment indicate they may represent root casts.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The vertical fenestrae more often than not distort the millimeter lamin

ations of the sediment. These laminae either curl downward near the

fenestrae or are not affected by them. The downward tapering of the

fenestrae and the downwarping of sediment laminae indicate that the ver

tical fenestrae probably represent root or stem casts of some marine

plant, probably a marine grass similar to Thallassia sp., living in a

shallow intertidal lagoon. When the plants died and started to decom

pose CO2 was liberated which, under the proper conditions, aided in the

precipitation of calcium carbonate, even dolomite if enough magnesium

ions were available. Conversely, if the vertical fenestrae represent

burrow structures they would not taper downward and would be filled

with micrite, also if the vertical fenestrae resulted from escaping gas

bubbles the fenestrae would not taper downward and would cause the

laminae to curl upward, if at all.

The dense micrite subfacies is an example of an intertidal mud flat

environment where endopsammic ostracods and ramose stromatoporoids lived

(fig. 23). Marine plants were present, as evidenced by the presence of

calcareous algae, calcispheres, and downward tapering vertical fenes-

v trae with associated downwarped laminae. Shinn (1968) states that birds-

eye structures are preserved in supratidal sediments, sometimes in inter

tidal sediments, and never in subtidal sediments. Friedman (1969) sug

gests that lumpy structures, flaser structures, sporadic birdseyes, and

flat pebble conglomerates indicate intertidal environments. Although

the dense subfacies is a sublithographic micrite, lumpy structures,

flasers, fenestrae and flat intraclasts all occur locally, implying in

tertidal conditions.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ON ro A.Shub

Marsh Supratidal e s e Subfacies Fenestral Micrite Flats Mud

marshes Subfacies and Dense Micrite intertidal supratidal The Foraminifera (F), calcareous algae (A), and solitary corals (Ci). Figure 23- The intertidal and supratidal marshes representing the micrite facies. Encrusting-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 Fenestral Subfacies

The other micrite subfacies is the fenestral subfacies, character

ized by horizontal fenestrae and a sparse flora and fauna. The fauna is

represented mainly by ostracods and occasional trilobite carapaces; the

flora is represented by calcispheres and calcareous algae. Intraclasts,

"stromatactis" structures, and laminae that differ from one another due

to grain size and textural inconsistencies are sedimentary structures

commonly found in the fenestral subfacies.

Very few trilobite carapaces were observed in the fenestral facies.

Most of the carapaces were badly fragmented probably from transport by

tidal currents. The remains of red algae, a Solenoporacean, are en

countered in this subfacies as sparsely scattered fragments. These frag

ments appear rounded indicating they may have been washed into this envi

ronment. Johnson (i960) suggests they prefer areas of good water circu

lation where clastic sediments are absent or in limited quantities.

Since this subfacies does not appear to have had good water circulation

(very sparse fauna and lacking organisms that enjoy good circulation) the

calcareous algal fragments must have been washed into this environment.

Locally, sediment resembles the dense micrite subfacies, but is

mostly pelloidal in nature. Floral and faunal fragments, lithoclasts

and unidentifiable calcareous material are abundant and arranged in thin

laminae. Different laminae can be discerned by grain size and textural

differences. These laminae may coarsen upward, fine upward, or may have

a fairly uniform grain size differing slightly from that of the overlying

and underlying laminae. Some laminae may contain micrite in varying

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64- amounts where others may be micrite free.

As the name suggests, fenestrae are a major characteristic, of the

fenestral subfacies. Horizontally elongate fenestrae are the dominant

type present and are commonly present between the millimeter laminae.

Pustular fenestrae are also found in the subfacies but are not as abun

dant as the horizontally elongate fenestrae. The horizontal fenestrae

follow any undulations the laminae may make. Occasionally, fenestrae

from different levels are connected to each other by vertical "dike

like" stringers of sparry calcite. Some spar-filled voids have flat .

bottoms; these are stromatactoid structures. Some stromatactoid struc

tures are laterally connected to horizontally elongate fenestrae.

The fenestrae may have originated in several ways: (l) primary al

gal mat vugs; (2) blisters formed from gas produced by decaying organic

material; (3 ) infaunal activity; or (4) dessiccation. The only infaunal

organisms found within this subfacies are ostracods. Judging by their

size and numbers it seems unlikely they could have produced so many

horizontal fenestrae of the shape of those found in this micrite sub

facies. Other possible origins are (l) primary algal, (2 ) gas blisters,

and (3 ) desiccation. All three of these would produce pustular to hori

zontally elongate fenestrae in sufficient numbers as seen in the fenes

tral micrite subfacies. All three of these possible origins probably

occurred. Desiccation probably produced horizontal fenestrae and the

connection of fenestrae from different levels by vertical stxingers.

The upper fenestrae in these cases contain small buildups of sediment

at the point where the vertical stringers enter the upper fenestrae,

indicating upward percolation of water during evaporation and desic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cation, Gas bubbles produced by decaying organic material would produce

predominantly pustular fenestrae (Shinn, 1968). The coalescing of indi

vidual gas bubbles to form pustules and eventually elongated vugs would

explain the complete lack of.circular fenestrae and low number of pustu

lar fenestrae. The primary voids present in modem algal mats and both

modem and ancient stromatolites have the configuration of coalescing

pustules into horizontally elongated fenestrae. In algal mats and strom

atolites gas produced as a photosynthetic by-product and by decaying al

gae is trapped below the uppermost algal layer. The possible coexistence

of these three origins seems real.

Evidence lending credence to the algal origin lies in the sediment

making up the laminae between the horizontally elongate fenestrae. What

can cause the consistent textural and grain size differences between the

laminae? Some laminae display reverse grading where others show normal

grading. The sorting within the laminae ranges from poor to well sorted.

The grain sizes of the laminae vary from very fine sand to medium sand

from lamina to lamina. Laminae of finer sediment alternate with laminae

of coarser material. The grain size differences between superposed v laminae are abrupt despite the grading of some laminae.

Tidal currents could have created graded or reverse bedding within

certain laminae but could not have been responsible for the alternating

laminae of coarser and finer material found within the fenestral micrite

subfacies. This alternation of grain size combined with pervasive hori

zontally elongated fenestrae leads this author to believe that these

laminae represent algal-laminated sediments. The overall appearance of

this subfacies in thin-section resembles that of ancient stromatolites

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66

with their alternating laminae of differing grain size and associated

horizontally elongated fenestrae. Wray (1977)* showed several examples

of ancient and modem stromatolites with laminations and horizontally

elongated fenestrae. The finer grained laminae represent the horizons

where algae grew prolifically with carbonate material adhering to the

mucilaginous sheaths or becoming entwined by filamentous forms present.

Tidal currents or storm events subsequently washed in relatively coarser

material over the algal mats. The algae then grew up through this

coarser material and re-established the mat over the coarser laminae,

continuing to trap finer sediment. The fenestrae were probably formed

by both escaping gas from decaying algae that could not grow through the

veneer of coarser sediment and desiccation during times of exposure

during intervals of low tide. Wolf (1965)1 in his study of the Nubrigyn

Reef complex suggested that fenestral fabrics associated with algal lime

stone indicate shallow water conditions, if not specifically littoral

environments.

Some thin-sections show gently upturned laminae strongly resembling

curled-up pieces of supratidal algal mat observable on Crane Key in

Florida Bay (personal observation, 1980; Ginsburg, 1972, 19^7, 19^0).

In some thin-sections of this subfacies almost the entire slide is com

posed of carbonate clasts cemented predominantly by sparry calcite with

a few areas cemented by cryptocrystalline calcite and lesser amounts of

dolomite. .On modem tidal flats clasts are commonly cemented by crypto

crystalline calcite, and characteristically contain fine crystalline

dolomite (James, 1979)* These are common occurrences in upper inter

tidal to supratidal environments, and some parts of the fenestral

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. micrite subfacies seem to indicate at least a supratidal influence,

probably isolated islands. The absence of evaporite minerals in this

facies indicates that the chlorinity of the water in this enviromhent

was probably between 39 °/oo and 65 °/oo. This can occur by having an

influx of fresh water from inland sources thereby diluting hypersaline

groundwater or fresh water flooding during rainy seasons (James, 1979).

Terrigenous windblown sand would be common in the sediment of the

supratidal zone (James, 1979); some thin-sections of the fenestral-

micrite subfacies show minor amounts of very fine quartz which is most

likely terrigenous.

The fenestral micrite subfacies seems to represent an upper inter

tidal environment with some areas indicating supratidal marsh condi

tions. The subfacies is almost devoid of indigenous organisms other

than ostracods and algae; all other biotic elements appear to have

originated elsewhere due to their broken and rounded condition. The

sediment characterized by laminae of alternating grain size texture,

horizontal fenestrae, minor amounts of terrigenous quartz, and occas

ional curled laminae was probably produced by algae in the extreme

upper intertidal to supratidal zones (see fig. 23). The algae respon

sible for the production of the calcispheres were probably not sub-

aerially exposed as often as the algae producing the algal-laminated

sediments.

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

Algae

Divisions Cyanophyta

Class: Coccogoneae

Order: Chroococcales

Family: Chroococcaceae (Figure 24)

Figure 24. Typical microsphere at a magnification of 625 x.

Description: Dark "brown translucent to opaque microspheres averaging

between 3 to5 microns in diameter. The average cell wall thickness is

0.5 microns. No nuclei seen in any cells. Found in clumps and singly,

within carbonaceous seams in the stromatoporoid biolithite, organic-

mud packstone, and the biolithite-micrite transition facies.

Discussion: It has been suggested by Cookman (1976) that these micro-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. spheric algal forms are subtidal mat formers. Their algal affinity is

supported by the fact that no other spherical microscopic life form be

it bacterium, fungus, or pollen possesses a comparable size range;

their size ranges are either less than or greater than the Rockport

microspheres. It has been well documented that algal mats are common

ly composed of a number of forms of algae that secrete mucilagineous

sheaths to protect themselves and also trap sediment (Gebelein, 1969

and Neumann et al, 1970). These microspheric algae, along with fila

mentous forms, formed subtidal mats in the Rockport Quarry Limestone

and the carbonaceous seams that these forms are found in represent the

the last vestiges of sheath material.

Class s Hormogoneae

Order: Oscillatoriales

Family: Oscillatoriaceae

Genus: "A" (Figure 25)

Figure 25. Blue-green algal filaments belonging to the Oscillator iales (Genus "A") at a magnification of 1250 x.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Description: Yellow-green translucent filaments averaging between 1.5 to

2 microns in diameter and extremely long. They are very often observed

in "tangled masses" making length measurements very difficult to ob

tain. Branching is absent. The filaments cannot be seen in thin-sec-

tion, only in insoluble residues of the stromatoporoid biolithite and

the organic-mud packstone facies.

Discussion: The discovery of this and other filamentous forms within

the Rockport Quarry Limestone reinforces the hypothesis that hydrocar-

bonaceous seams found in the lower Rockport strata represent the remain

ing traces of subtidal algal mats composed of coccoid and filamentous

algae.

Family: Oscillatoriaceae

Genus: "B" (Figure 26)

Figure 26. A blue-green algal filament belonging to the Oscillator- iales (Genus "B") at a magnification of 625 x.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Descriptions Brown translucent filaments 7-5 microns in diameter found

as short trichomes 25 microns long composed of short wide cells, each

averaging 4.2 microns long. Branching is absent. The filaments are

only seen in insoluble residues of the stromatoporoid biolithite.

Order: Stigonematales

Family: Nostochopsidaceae (Figure 2?)

Description-: Yellow-green to green-brown translucent filaments averag

ing 2.7 to 4 microns in diameter found as short trichomes of 27 to 66

microns in length. Branching is present as incipient sidward growths

to moderately developed branches. True branching of the "T" ramifica

tion is displayed. Heterocysts are developed but not always apparent.

Found in insoluble residues of the stromatoporoid biolithite facies.

Problematical Algae

(Figures 28 and 29)

Diagnosis: Thalli found attached (fig. 28) as crusts or free (fig. 29)

as low conical forms. Chambers ovoid in shape, forming single layer in

the encrusting form or forming several layers in unattached forms.

Description: The attached form has reticulating walls, ranging in

thickness from 0.009 millimeters to 0.033 millimeters, forming ovoid

chambers ranging in maximum dimension from 0.014 to 0.105 millimeters;

forms a crust, ranging in thickness from 0.019 to 0.665 millimeters,

upon other biological remains of larger size. The network of walls of

the unattached form range in thickness from 0.024 to 0.067 millimeters

and form ovoid chambers ranging in maximum dimension from 0.019

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72

Figure 27. A blue-green algal filament belonging to the Stigonematales at a magnification of 625 x.

to 0.24? millimeters; appears triangular in thin section (1.62 milli

meters long along the base and 9*95 millimeters high from base to apex),

probably a low conical thallus in three dimensions. The walls of both

forms are composed of dense micrite lacking any microstructure. Found

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

Figure 28. The encrusting form of a calcareous blue-green alga form ing a crust upon a hemispherical stromatoporoid at a magnification of 43.75 x.

Figure 29. The unattached form of a calcareous blue-green alga at a magnification of 43.75 x.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the dense micrite subfacies.

Discussion! The chamber size (l4 to 247 microns), wall thickness (9

to 67 microns) and overall colony size (O.67 to I .67 millimeters) are

all comparable to the dimensional data typical of Renalcis (chamber

sizes 50 to 400 microns, wall thickness: 30 to 80 microns, and

colony sizes up to 2 millimeters, Wray, 1977)- However, the forms

encountered in the Rockport Quarry Limestone in no way resemble Renal

cis found in the Rockport strata by Cookman in 1976. Cookman's Renal

cis is larger in size (2 millimeters across), has thicker walls

(2500 microns) that possess clefts, and has fewer chambers (two).

The problematic forms just described are probably calcareous blue-

green algae which may be related to Renalcis.

Divisions Rhodophyta

Family: Solenoporaceae (Figure 30)

Figure 30* A fragment of the calcareous red alga, Solenopora sp., at a magnification of 125 x.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Descriptions Small nodular mass composed of radiating filaments. Cell

walls separating filaments distinct; cell partitions within filaments

inconspicuous or absent,. Found in the fenestral micrite subfacies.

Phylum: Protozoa

Orders Foraminifera.

Familys Saccamminidae (Figure 3l)

Figure 31. A flask-shaped foraminiferan belonging to the Family Sac-

caminidae at a magnification of 12.5 x.

Descriptions Test single flask-shaped chamber (3*96 millimeters long

by 2.26 millimeters across; extreme examples 9-61 millimeters long by

4.24 millimeters wide). Wall pseudochitinous and densely covered with

agglutinated material; aperture terminal on neck. Found in the biolith-

ite-micrite transition facies.

Discussions In some areas along the test the wall is difficult to

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. discern as it is composed mostly of carbonate mud from the surrounding

sediment. The larger form has a shell fragment incorporated into its

wall on the end opposite the aperture indicating this foraminiferan

was not extremely selective in using materials for its tests.

Orders Foraminiferida

Family: Ptychocladiidae (Figure 32)

Figure 32. An Encrusting foraminiferan belonging to the Family Pty-

cocladiidae of a magnification of 125 x.

Description: Test attached consisting of irregular aggregates of, cham

bers? wall composed of microgranular crystals of calcite arranged fi-

broradially. Average chamber size is 60.5 microns, average wall thick

ness is 6.1 microns, and the average size of aggregates is 699 microns

long by 278 microns high, Found in the upper stromatoporoid biolithite

and biolithite-micrite transition facies.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Discussion: Cookman's (1976) Algae indeterminate is probably an en

crusting foraminiferan belonging to this family.

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

The Rockport Quarry Limestone represents a portion of a shallow

marine carbonate shelf with the contained rock facies representing a

spectrum of environments, energy conditions and organism communities,

from the shallow subtidal zone up through the extreme upper intertidal

to supratidal zones (table 3)* The lower and upper stromatoporoid

biolithite facies, the organic-mud packstone facies and the biolith-

ite-micrite transition facies represent a subtidal zone. In the bio-

lithites stromatoporoids and algal mats constructed biostromes that

neared surf base. The organic-mud packstone facies represents a quiet

area between the biostromes where crinoid-bryozoan gardens successfully

competed with algal mats for space. The innermost biostrome represent

ed by the upper unit of the stromatoporoid biolithite facies existed

closer to surf base than the outermost biostrome and thereby was sub

jected to higher energy conditions. Behind the innermost biostrome a

subtidal backwater zone existed where stromatoporoids and corals de

clined in numbers due to the influx of micrite and organic debris wash

ed in from thfe inner stromatoporoid biostrome. Benthic organisms such

as ostracods and foraminifera thrived here.

Lagoons represent the intertidal zone in the lower and upper por

tions and supratidal algal marshes in the upper portions of the micrite

facies. Ostracods and calcispheres flourished here. Vertical spher

ical, and pustular fenestrae are abundant in the micrite facies. The

vertical fenestrae most likely represent the root casts of intertidal

plants, possibly algae, with the spherical and pustular structures rep-

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. - o vo ______ENERGY CONDITIONS coral debris, and stromatoporoid debris. Excellent circulation.- circulation to allow crinoids, Bry- ozoans, and colonial as well as solitary corals to growin local oroids to grow orto destroy exten conditions helowsurf Base existed; zoans coalescing relegating the subtidal algal mats to local patch es. Adequate circulation for cer that are more intense, closerto algal mats in the interstromatoporoid sediment Become more sparse as the top of the unit is approached. in localized areas the Buttresses Low energy conditions with enough lation to allowlamellar stromatop sive algal mats. Adequatelati£n_f£r_C£rtain_organisms:_ circu- Generally, moderate to high energy Lowenergy conditions as aBove with the gardens of crinoids and Bryo- Moderately high energy conditions nearedsurf Base as evidencedBy Brecciatedlamellar stromatoporoids. izedgardens But not enough circu Abundant overturned coral heads, tain organisms surf Base, than lower Biolithite; Good circulation. ______TABLE3 MAJORBIOTA CoccoidBlue-green Algae Ostracods Coccoid Ilue-greenAlgae CoccoidBlue-green Algae Crinoids CoccoidBlue-green Algae Colonial Corals Colonial Corals Crinoids oroids Colonial Corals oroids oroids oroids Solitary Corals Lamellar Stromatoporoids Lamellar.Stromatoporoids Solitary Corals Hemispherical Stromatop Hemispherical Stromatop Solitary Corals Hemispherical Stromatop Hemispherical Stromatop Fenestrate Eryozoans Fenestrate Bryozoans Foraminifera ENVIRONMENT zone shallow subtidal zone shallowsubtidal shallowsubtidal shallow suBtidal innerButtress Buttress zonfe inter-Buttress inter-Buttress Energy Conditions andEnvironments of the Rockport Quarry Limestone Upper Grainstone SuBfacies FACIES Crinoid-Bryo- zoan Eiolithite Biolithite C 0 0 Coral Pack- M D P T Stromatoporoi d Stromatoporoi U S Stromatoporoid ^stone A SuBfacies A K N N K

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 00 o ENERGY CONDITIONS oroid and coral debris at the base of the unit fining upwardto micrite ergy conditions towards the top of Wateralso too shallowfor crinoids andbryozoans. Plenty of stromatop too high for crinoidand bryozoaris. nearthe topindicating waningen the unit. spherical fenestrae and fewerver bedding, intraclasts, and dolomite differences indicate algal marsh es; micrite sediment with some dol omite andquartz indicates upper Lowto moderate energy conditions; Lowenergy conditions; some small tical fenestrae, lumpy and'flaser indicate alternating wet anddry Lowenergy conditions; abundant pustularto horizontal fenestrae foundin laminatedsediments dis playing grain size and textural intertidal isolatedlagoons. £onditions_in th£intertidal_zone. Table 3 (Cont.) Algae Ramose Stromatoporoids Ostracods Calcispheres Calcareous Blue-green Ramose Stromatoporoids Ostracods Calcispheres Calcareous RedAlgae LamellarStromatoporoids ENVIRONMENT MAJORBIOTA shallowsubtidal backwater zone upperintertidal lowerintertidal back buttress lagoon lagoon to supra tidal marshes sedimentary features displayedby the facies and subfacies ofthe Rockport Quarry Limestone. Subfacies FACIES Micrite Micrite Dense Micrite Subfacies Fenestral I C Transition I T Biolithite- M E Note. The environment and energy conditions were determinedfrom the fossil assemblages and various .R

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. resenting voids created by gases liberated from decaying plant or animal

matter.

Horizontal fenestrae associated with alternating laminae of carbon

ate debris of differing grain sizes and textures characterize the algal

marshes. These laminae with the associated horizontal fenestrae repre

sent sediments deposited by mat-forming algae under the influence of

tidal action. Some areas of the algal marsh sediments seem to have been

subaerially exposed for long periods of time as some slightly upcurled

chips of sediment are found. Sprinkled within these sediments are very

fine quartz particles of terrigenous origin, indicating a supratidal

influence.

The carbonaceous seams pervade the stromatoporoid biolithites and

organic-mud packstone facies to the degree that the rocks of these fac

ies are dark-brown to black and liberate a strong petroliferous odor

when cut with a rock saw. The organic material, a solid amorphous sub

stance typically refered to as kerogen, appears dark-brown to black and

translucent to opaque in thin section. So much of this material exists

that the upper and lower units of the stromatoporoid biolithite facies % and the organic-mud packstone facies could be good sources for petrol

eum in deeper portions of the Michigan Basin.

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

The environmental interpretations of the facies of the Rockport

Quarry Limestone were based largely upon the paleoecology of the con

tained. flora and fauna augmented by observations of the sedimentologic

characteristics of the rocks in outcrop, hand specimens, and thin-sec-

tion. The facies represent laterally contemporaneous shallow marine

carbonate environments that become vertically stacked as they shifted

with a drop in sea level within the Michigan Basin during middle

Devonian time.

The findings of this study are as follows:

(1) the lack of nuclei, size range, and lack of ornamentation support

Cookman's (1976) idea that the Rockport microspheres represent blue-

green algae;

(2) algal filaments in insoluble residues of both units of the strom

atoporoid biolithite facies and the organic-mud packstone facies;

(3 ) the kerogenous material composing the carbonaceous seams most

likely represents the fossilized protective sheath material secreted

by the algae 'that constructed the subtidal mats;

(*f) Cookman's Algae indeterminate is probably misnamed; it is most

likely an encrusting foraminiferan probably belonging to the family

Ptychocladiidae;

(5) other newly discovered organisms include

(a) a calcareous blue-green alga, possibly related to Renalcis.

(b) fragments of the calcareous red alga, Solenopora sp.,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83

(6) algae Influenced, the paleoecology in the Rockport Quarry Limestone by

(a) stabilizing a potentially shifting substrate of.medium to

fine sand allowing organisms that require a stable substrate to

colonize and proliferate,

(b) binding large volumes of sediment in relatively-short time

intervals and thereby engulfing encrusting organisms such as

bryozoans that may have attached to debris incorporated in the

algal mat and preventing their colonizationj

(?) The stromatoporoid biolithites and the organic-mud packstone facies

of the Rockport Quarry Limestone have the potential to be good source

rocks for petroleum if the Rockport Quarry Limestone is present in the

subsurface of the Michigan Basin.

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

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