Vincent N. DiRenzo, Jr. Petrology and depositional environments of
the Little Valley Limestone (Upper Mississippian) Washington County,
Virginia. (Under the direction of Dr. Donald W. Neal) Department of
Geology, April 1, 1986.
The Upper Mississippian Little Valley Limestone is a natural gas
producing unit of mixed carbonate and siliciclastic composition
transitional between largely terrigenous units below and carbonate
units above. It was deposited during the inundation of the Virginia-
Carolina delta complex. The Little Valley Limestone is approximately
220 meters thick in the study area, which is located in the Greendale
Syncline in Washington County, Virginia. Petrographic point count
data, geophysical logs and detailed hand sample characterization were
used in both environmental and diagenetic determinations.
Seven microfacies are recognized: (1) lime mudstone, (2) lime
wackestone, (3) lime packstone, (4) lime grainstone, (5) calcareous
muddy sandstone, (6) calcareous mudrock and (7) secondary gypsum.
These microfacies were deposited during a marine transgression and
represent three distinct environments. They are, in ascending
stratigraphic order: (1) restricted, high intertidal mudflat to
bordering supratidal sabkha containing algal-laminated evaporites
(gypsum and anhydrite) and dolomitic shales; (2) low intertidal to
shallow subtidal, s i 1 icicl astic shoal containing interbedded
calcareous-sandstones and raudrocks with a sparce biota; and (3) open
marine, subtidal, with shelf lagoons characterized by lime- mudstones,
wackestones, packstones and grainstones with an abundant stenohaline
fauna.
Diagenetic alteration of this unit consists of tnicri tization,
calcite and aragonite stabilization, microspar development, syntaxial
overgrowths, and bladed and blocky spar cement formation, framboidal
pyritization, dolomitization, silicification, secondary gypsum
formation, stylolitization and vein and microfault formation.
PETROLOGY AND DEPOSITIONAL ENVIRONMENTS OF THE
LITTLE VALLEY LIMESTONE (UPPER MISSISSIPPIAN),
WASHINGTON COUNTY, VIRGINIA
A Thesis
Presented to
The Faculty of the Department of Geology
East Carolina University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science in Geology
by
Vincent N. DiRenzo, Jr.
PETROLOGY AND DEPOSITONAL ENVIRONMENTS OF THE
LITTLE VALLEY LIMESTONE (UPPER MISSISSIPPIAN),
Ù>
WASHINGTON COUNTY, VIRGINIA
By
Vincent N. DlRenzo, Jr.
APPROVED BY:
THESIS DIRECTOR
COMMITTEE MEMBER Ai
Dr'. Scott W. Snyder
COMMITTEE MEMBER
COMMITTEE MEMBER
Dr . Charle s S Bartlett, ?nJr
DEAN OF THE GRADUATE SCHOOL
ACKNOWLEDGEMENTS
The author is grateful to Charles S. Bartlett, Jr. (President and
Chief geologist of Bartlett Energy Exploration Inc.) for his time and
concern for this project. He was an invaluable reference to the
geology of Washington County, Virginia. I would also like to thank
him for generously providing me with much information and hospitality.
Roger Sharp (Staff geologist for U.S. Gypsum) and U.S. Gypsum
(Plasterco, Virginia) for providing me with drillers' logs and a cored
section of a portion of the Little Valley Limestone and Maccrady
Shale.
Scott Snyder and Lee Otte (both from East Carolina University)
who graciously consented to serve on my thesis committee. I would
like to express my thanks for their help and guidance.
Don Neal (East Carolina University), who served as thesis
advisor, worked with me many hours deciphering the complexities of
this "mixed" unit. His experience with Mississippian-aged
transitional units and his detail oriented perspective greatly
contributed to this study, detailed project to occur.
Lastly, the author would like to particularly thank Vincent N.
DiRenzo Sr. (father), E. Linda DiRenzo (mother) and especially my wife
Sharon C. DiRenzo for their patience, support and understanding which
made the completion of my goals possible.
TABLE OF CONTENTS
PAGE
ABSTRACT i
ACKNOWLEDGEMENTS iii
INTRODUCTION 1
PREVIOUS WORK 2
OBJECTIVES 3
GENERAL STRATIGRAPHY 4
STRUCTURE 6
METHODS 8
STRATIGRAPHY 12
PETROLOGY 15
MATRIX 15
Carbonate Components 15
Micrlte 15
Slliciclastlc Components 16
Clays 16
Muscovite 18
Silt and Sand Sized Quartz 18
CONSTITUENT PARTICLES 19
Introduction 19
Major Allochems 19
Brachiopods 19
Bryozoans 20
Echinoderms 21
Bivalves 21
Other Allochems 23
Ooids 23
Foraminifers 25
Corals 25
Ostracodes 26
Trilobites 28
Gastropods 28
Intraclasts/Extraclasts 29
Other Constituents 29
Conodonts 29
Plant Fragments 31
ORTHOCHEMS 31
Microspar 31
Dolomite 32
Syntaxial Overgrowths 33
Bladed and Blocky Spar 33
Silica 35
Secondary Gypsum 36
Fraraboidal Pyrite 38
MICROFACIES 40
INTRODUCTION 40
Lime Mudstone Microfacies 43
Lime Wackestone Microfacies 49
Lime Packstone Microfacies 53
PAGE
Lime GrainsCone Microfacies 59
Calcareous Muddy Sandstone Microfacies 64
Calcareous Mudrock Microfacies 69
Secondary Gypsum Microfacies 76
DEPOSITIONAL ENVIRONMENTS 81
REGIONAL 81
LOCAL 82
DIAGENETIC PROCESSES AND THEIR ENVIRONMENTS OF FORMATION 90
INTRODUCTION 90
MICRITE ENVELOPES 90
CALCITE STABILIZATION 93
MICROSPAR 94
ARAGONITE 96
SYNTAXIAL OVERGROWTHS 97
BEADED AND BLOCKY SPAR 98
FRAMBOIDAL PYRITE 99
DOLOMITE 100
SILICIFICATION 102
SECONDARY GYPSUM 104
VEINS 105
STYLOLITES 106
MICROFAULTS 108
SUMMARY OF CONCLUSIONS 110
REFERENCES CITED 112
APPENDIX A 119
APPENDIX B 144
APPENDIX C 147
TABLE OF ILLUSTRATIONS
PAGE
FIGURES
1. Location map of field area 5
2. Mississippian Stratigraphy in the Greendale Syncline 7
3. Structure cross section ^
4. Sample location map 10
5. Stratigraphie cross section of Little Valley Limestone ... in pocket
6. Generalized lithologies of the Little Valley Limestone 13
7. Microfacies constituents 42
8. Environmental location of lime mudstone deposition 45
9. Environmental location of lime wackestone deposition 54
10. Environmental location of lime packstone deposition 57
11. Environmental location of lime grainstone deposition 61
12. Environmental location of calcareous muddy sandstone 67
13. Environmental location of calcareous raudrock 73
14. Environmental location of secondary gypsum 80
15. Stratigraphic cross section of the Little Valley Limestone's
environments 83
16. Depositional model 89
17. Plot of predominant fauna versus insoluable residues in pocket
18. Diagenetic environments 91
TABLE
1. Summary of microfacies point count data 41
PLATES
1. Photomicrograph of a grumose texture 17
2. Predominant brachiopods 22
3. Photomicrograph of bryozoans 22
4. Predominant bivalves 24
5. Posidonomya? sp 24
6. Predominant foraminifers 27
7. Coral Syringopora Virginica Butts 27
8. Photomicrograph of gastropods 30
9. Photomicrograph of ooid extraclasts 30
10. Photomicrograph of xenotopic-P dolomite 34
11. Photomicrograph of syntaxial overgrowth 34
12. Photomicrograph of silica replacement 37
13. Chert nodules from outcrop 37
14. Photomicrograph of secondary alabastrine gypsum 39
15. Photomicrograph of pyrite fraraboids 39
16. Photomicrograph of lime mudstone 44
17. Photomicrograph of lime mudstone fauna 44
18. Lime wackestone in core 51
19. Photomicrograph of lime wackestone fauna 51
20. Brachiopods bearing lime packstone 58
21. Photomicrograph of broken and abraded allochems in lime
packstone 58
22. Echinoderm bearing lime grainstone 63
PLATES PAGE
23. Photomicrograph of lime grainstone 63
24. Outcrop of calcareous muddy sandstone 70
25. Photomicrograph of siliciclastic components of calcareous
muddy sandstone microfacies 70
26. Photomicrograph of calcareus raudrock 77
27. Secondary gypsum and anhydrite 79
28. Photomicrograph showing formation of secondary gypsum through
anhydrite rehydration 79
29. Photomicrograph of satin spar gypsum vein 107
INTRODUCTION
The Little Valley Limestone is an Upper Mississippian (Meraraecian
Series) unit which correlates with the lowermost member of the
Greenbrier Group (Cooper, 1961) and is geographically limited to
southwestern Virginia and southeastern West Virginia. Outcrops of the
Little Valley Limestone occur within the Greendale Syncline in the
Valley and Ridge physiographic province of Virginia. Here it is part
of one of the most fossiliferous and complete exposures of
Mississippian rock (greater than 2,134 meters) in North America
(Cooper, 1948). The Little Valley Limestone is a natural gas
producing, argillaceous unit which contains sandstones and evaporite
units. It represents a "mixed"-composi tion transitional unit, lying
stratigraphically between a lower predominantly terrigeneous system
and an upper predominantly carbonate system.
The Little Valley Limestone is economically important in the
Early Grove Anticline, a small flexture within the Greendale Syncline,
in both Scott and Washington Counties, Virginia. It produces natural
gas from granular anhydrite beds in the lower portion of the
formation (Bartlett and Biggs, 1982). Production from the Early Grove
Gas Field first began in 1931 from the Elkin 1 Ridgeway well with a
flow rate of 1,750 million cubic feet per day. From 1942 until 1957,
seven producing wells supplied gas to the Bristol, Virginia area. The
field was subsequently abandoned due to low production. It was
reopened in March of 1980, with production from the Lower
Mississippian Price Sandstone. Additional wells were drilled and
2
completed in the Price Formation and in the anhydrite zone of the
Little Valley Limestone, which had near virgin pressures of 1,200 to
1,400 pounds per square inch. Production continues within the Early
Grove Gas Field.
PREVIOUS WORK
The Little Valley Limestone has not previously been the subject
of a detailed study; however, many reports dealing with the Central
and Southern Appalachians make reference to it. Butts (1940),
reporting on the geology of the Virginia Appalachian Valley, briefly
described the character and distribution of Warsaw-age rocks (Little
Valley Limestone). Similar regional studies by Cooper (1948),
Bartlett and Webb (1971), Blancher (1974), deWitt and McGrew (1979),
Gathright and Rader (1981), and characterized the stratigraphy and/or
depositional and tectonic systems of the Mississippian System in
Virginia. Little is known of the petrology of the Little Valley
Limestone.
Economic interest in the Little Valley Limestone and bounding
units spawned many Virginia Geological Survey publications. Two of
the most pertinent are Butts' 1927 report summarizing the oil and gas
potential of the Early Grove area of Scott County, Virginia, and
Averitt's 1941 report on the Early Grove Gas Field in Scott and
Washington Counties, Virginia.
Butts' report was significant for it contained the initial description
of the Warsaw-age unit, whereas Averitt's study formally named the
Little Valley Limestone and produced the first detailed map of Upper
3
Mississippian units in the area. Although relevant information on the
Little Valley Limestone was presented by Butts and Averitt, there was
little descriptive detail. Similarly, Huddle et al. (1956),
Withington (1965), LeVan (1981), Bird (1981), Bartlett and Biggs
(1982), LeVan and Rader (1983) and Sweet (1983) presented historical
and updated reports on Virginia's economic minerals and oil and gas
deposits.
Cooper (1966) discussed the geology of the salt and gypsum
deposits within the Maccrady and Little Valley Formations in Smyth and
Washington Counties, Virginia. De Witt and Mcgrew (1979) noticed local
accumulations of evaporites (mainly gypsum and halite) in the lower
portion of the Little Valley Limestone in the vicinity of Saltville,
Virginia.
The faunas within the Little Valley Limestone have been recorded
by Butts (1927, 1940, and 1941) and Bartlett and Webb (1971). Chaplin
(1975) studied the conodont biostratigraphy of the Little Valley and
Hillsdale Limestones in southwestern Virginia.
OBJECTIVES
The objectives of this study are: (1) to characterize the
mineralogy and petrology of the Little Valley Limestone (especially
the bedded gypsum recognized in the lower Little Valley Limestone);
(2) to characterize microfacies and determine the nature and extent of
diagenetic change within each microfacies; and (3) to determine the
depositional and tectonic history of the Little Valley Limestone. The
study is limited to Washington County, Virginia where good exposures
4
of Little Valley Limestone are present (Fig. 1).
GENERAL STRATIGRAPHY
Stose (1913) included Warsaw-age carbonates (the Little Valley
Limestone) within the Maccrady Formation of the Greendale Syncline,
Smyth County, Virginia. He defined the lithologies of the Maccrady as
red and gray shales, sandstones, black carbonaceous shales, and gray
limestones. The incorporation of the Little Valley Limestone within
the Maccrady'Formation was questioned by Butts ( 1927 ) because the
upper portion of the
Maccrady Formation contained a destinct Warsaw-aged fauna. The
fauna included Anlstrypa tuberculata, Fenestralia sancti-ludovici,
Hemitrypa proutana, and Produc tus altonensis ; all of which are
confined to the Warsaw and are correlative with other Warsaw faunas.
Butts also pointed out that the Maccrady shale not only had a fauna of
New Providence age, but that it was separated from Warsaw-aged
Limestones by an unconformity. As a result. Butts suggested that the
use of "Maccrady" be restricted to the red beds.
Averitt (1941) formally separated the Warsaw-age lithologies from
the Maccrady Formation based on distinct lithologic and faunal
differences. Averitt designated the Warsaw-aged unit the "Little
Valley Limestone" because of its low topographic expression in Little
Valley, Scott County, Virginia.
The Little Valley Limestone, according to Blancher (1974), is
equivalent to the lowest beds of the Greenbrier Limestone of West
Virginia. The Greenbrier Limestone was designated by Rogers (1379)
[Üi] GREENBRER GROUP
Fig. 1. Location map of field area and outcrop belt.
6
for limestones exposed along the Greenbrier River, Pocahontas County,
West Virginia. Blancher (1974) suggested that the Greenbrier
Limestone of the Greendale Syncline consists of, in ascending order.
Little Valley Limestone, Hillsdale Limestone, Ste. Genevieve Limestone
and the Gasper Limestone.
The Little Valley Limestone represents a unit of "mixed"
lithologies transitional between predominantly siliciclas tic rocks
below and carbonate rocks above (Fig. 2). The underlying Maccrady
Formation consists primarily of interbedded, soft, maroon and light
green, micaceous shale or thinly bedded mudstone with minor amounts of
maroon siltstone and light gray to red, fine-grained sandstone
(Bartlett and Webb, 1971). The Hillsdale Limestone overlies the
Little Valley Limestone and is predominantly composed of dense, light-
to dark-gray, fine-grained, fossiliferous limestone which contains
bedded and nodular chert. Oolitic and argillaceous beds are sparse,
but are also present (Bartlett and Webb, 1971).
STRUCTURE
Most major structural features in Washington County are oriented
northeast-southwest with beds dipping to the southeast. Included are
portions of the Greendale and Beaver Creek Synclines, the Early Grove
Anticline and the Saltville, Pulaski-Staunton, Spurgeon and Bristol
Thrust-fault Blocks.
The Little Valley Limestone and other Mississippian to Silurian-
age units have been folded in the Greendale Syncline (a northeast
trending southwest, plunging fold) by movement of Cambro-Ordovician
7
GENERAL THICKNESS
FORMATIONS LITHOLOGIES (m«l«r«)
PENNINGTON 407
COVE CREEK 306-372
FIDO
OIRKM
SI*. GENEVIEVE 361-367
HCLSOALE I. I T'T ,1. 84 Î
LITTLE VALLEY 173-220
! T I
MACCRAOY JSJ
PRICE 172
BIG STONE GAP 300
Fig. 2 Outcrop stratigraphic sequence of the Mississippian Formations
of the Greendale Syncline of Washington County, Virginia.
8
carbonates of the Saltville thrust sheet (Fig. 3). The thrust sheet
covers the southeastern limb of the syncline (a total displacement of
over 4,878 meters), placing the Mississippian Pennington Formation in
contact with the Lower Cambrian Rome Formation and the Middle Cambrian
Honaker Dolomite in the southwestern portion of the county and the
Maccrady Formation in the northeastern portion of the county (Bartlett
and Webb, 1971).
METHODS
The procedures used in this investigation encompass both
fieldwork and laboratory operations. The field operations include
detailed measurement and description of the Little Valley Limestone
from outcrop and core. Outcrop samples were taken at a road cut one-
eighth of a mile south of the North Fork of the Holston River along
U.S. Highway 19 and Alternate 58, and at five exposures along Virginia
State road 622 (Fig. 4). The basis for outcrop selection was the
extent of exposure (at least 4.5 meters) because complete sections of
the Little Valley Limestone are not available. The core, Bonnie-Dell
(BD) 61-5, was obtained from United States Gypsum in Plasterco,
Virginia, and contains approximately 83.8 meters of the basal Little
Valley Limestone. Lithologies, fossils, textures and sedimentary
structures, along with overall stratigraphic relationships, were
studied and samples were taken that best represent the lithologies
present. Samples from both outcrop and core were taken at changes in
lithology and/or every 1.5 to 2.0 meters within uniform lithologies
Pig. 3. Cross section of the overturned portion of tlie (ireendale Syncline through Saltville,
Virginia showing core location (modified from Cooper, 1966).
WASHINGTON
10
I I •-SAMPLE LOCATIONS
KILOMETERS
Fig. 4. Sample locations
11
(Appendix A). Using this method, 250 samples were collected. Photos
were taken of each outcrop and of core samples.
Laboratory operations involved examination of constituents and
fabrics of the rocks in thin sections and polished hand samples. Thin
sections from each sample were stained with a solution of Alizarin Red
S and potassium ferricyanide in a 0.05 molar solution of hydrochloric
acid. This technique stains calcite red and ferroan calcite mauve,
while dolomite does not stain and ferroan dolomite and ankerite stain
blue. Petrographic analysis involved 235 thin sections, 160 of which
were point counted by Dunham's (1962) "grain bulk" method such that
any material or open pore space within a particle is counted as the
particle. Three hundred points per slide were counted. All thin
sections were classified according to the system devised by Dunham
(1962).
Scanning electron microscopy was used to aid in petrographic
determinations. Weight percents of insoluble residues were obtained
for 106 samples from both the U.S. Highway 19 outcrop and the Bonnie
Dell core (Appendix B). The insoluble residues were obtained by
dissolving approximately 20-25 grams of sample in industrial grade
hydrochloric acid until carbonate was fully leached. Residue was then
weighed and a weight percent was calculated for each sample.
STRATIGRAPHY
The Little Valley Limestone is approximately 220 meters thick
within the Greendale Syncline. Individual outcrops of the Little
Valley exhibit anywhere from 6 to 150 meters of exposure (Fig. 5,
enclosed in pocket).
Stratigraphically, the Little Valley Limestone can be informally
subdivided, based on lithology, into an upper and lower section (Fig.
6). The lower section of the contains interbeds of medium-to-1ight
gray, calcareous to dolomitic shale and siltstone with argillaceous
lime mudstone and lime wackestone. The base of this lower section
also contains bedded gypsum and anhydrite. Fossils are scarce and are
predominantly composed of algae, ostracodes, and thin-shelled
pelecypods. Locally abundant zones of bryozoans, echinoderms and
brachiopods are found. This lower section of the Little Valley
Limestone contains varying bed thicknesses ranging from a few
centimeters to greater than 30 meters without a discernable break.
The degree of interbedding between the different lithologies in this
section is variable, however, thicker, more uniform lithologic
compositions prevail. Outcrop exposures of this section are typically
highly weathered (especially muddier compositions), appearing fissile
and friable.
The upper section of the Little Valley Limestone largely consists
of interbedded, medium-to-dark argillaceous lime mudstones, lime
wackestone and lime packstone. This section also contains localized
beds of black carbonaceous shale, cherty limestone, lime grainstone
GENERALIZED LITHOLOGIES OF THE
LITTLE VALLEY LS.
..IME MUDSTONES CALCAREOUS a DOLCMITIC shales
_IME WACKESTONES [3 CALCAREOUS SANDSTONES
_IME- PACKSTONES a 9RA1NST0NES EVAPORITES
. 6. Characteristic lithologies of the Little
Valley Limestone with informal lower and
upper subdivisions.
14
and calcareous fine-to-medium sandstone. Fossils are very abundant in
most lithofacies with brachiopods, bryzoans and echinoderras
predominating, but also containing localized occurances of pelecypods,
corals, forarainifers, stromatolitic algae and conodonts. Similar to
the lower section, the upper section of the Little Valley Limestone
contains varying bed thicknesses (centimeters to tens of meters),
however, the upper section's lithologies are highly interbedded.
Outcrop exposures of the upper section characteristically weather less
severely than the lower section (although the muddier lithologies are
similarly fissile and friable) containing resistant lime
packs tones,lime grainstones and calcareous sandstones. The lime
packstones and lime grainstones commonly contain fossils exposed on
weathered surfaces and silicified zones. The lime packstones of the
upper most portion of the upper section of the Little Valley Limestone
are commonly interbedded with a black, fossi1iferous shale and are
highly petroliferous. Therefore, forming excellent marker beds for
recognition of the upper section.
PETROLOGY
The petrology of the Little Valley Limestone involves the
characterization of both carbonate and siliciclastic components due to
the "mixed" nature of this unit. Depositional characteristics of
"mixed" lithologies cause problems with interpretation because
uniquely carbonate or siliciclastic depositional features do not
exist. Diagenetic overprints are also invariably controlled by the
high percentage of terrigeneous material. Therefore, in order to more
precisely characterize "mixed" features, a thorough description of all
components from both hand sample and thin section is necessary.
Petrologically, constituents of the Little Valley Limestone can
be subdivided into three major categories: (1) matrix, (2)
constituents (both carbonate and silciclastic) and (3) orthochems
(cement).
MATRIX
The main components composing the matrix within the Little Valley
Limestone can be subdivided into two groups: (1) carbonate
components, which include micrite, and (2) siliciclastic components
containing chlorite, illite, muscovite and silt-and sand-sized quartz.
Carbonate Components
Micrite
Micrite within the Little Valley Limestone is usually dark brown
16
to dark gray colored, has a grain size of less than 1 micron, and
commonly contains a tightly cemented, grumous texture (patchy,
clotted fabric of the matrix). Its clotted texture is caused by a
complex mixture of terrigenous clays and silts with neoraorphic
microspar and dolomite. Framboidal pyrite is also a common associate.
The micrite matrix is rarely homogeneous. Micrite is common to nearly
every microfacies (especially lime mudstone and wackestone) and is
considered the precursor to most, if not all, microspar in this unit.
The formation of the micrite within the Little Valley Limestone
is thought to have occurred by one or all of the following processes:
(1) bioerosion associated with organism borings and/or ingestion; (2)
mechanical breakdown of skeletal grains, principally by wave or
current activity; (3) direct inorganic precipitation in the form of
"whitings"; and (4) organic production of micrite sized skeletal
grains by algae and other calcite- and aragonite-secreting organisms.
Siliciclastic Components
Clays
Two prominent clays (illite and chlorite) were identified by x-
ray diffraction from samples of the Little Valley Limestone. Kaolinite
is also present in minor amounts. Texturally, phy1losi1icates are
usually homogeneously intermixed with carbonate muds, although they
are sometimes concentrated between microspar crystals and in localized
pockets within the matrix (possibly caused by bio turbation). The most
prominent fabric created by the mixture of phyllosllicates and
carbonate mud is a grumose texture (Plate 1).
17
PLATE 1. Photomicrograph of a grumosa texture. 1 cm = 0.25 mm.
18
Clay mineralogy is useful as an environmental indicator, but the
Paleozoic contains an illite-dominated clay mineralogy (as does the
Little Valley Limestone)(Bla11, 1972). Several theories have been
suggested for this dominance: (1) increase in silicic crystalline
rocks (plagioclase source), (2) change in the biologic controls of
chemical weathering, (3) climate (temperate in illite's case) allowing
for preferential clay mineral formation and (4) diagenetic alteration
due to increased temperatures and depths of burial.
Because the Little Valley Limestone has been buried to depths
probably greater than 1,200 meters and exposed to temperatures greater
than 100 degrees centigrade (as determined from Chaplin's (1975)
conodont CAI studies) diagenesis is thought to have been the major
cause for high concentrations of illite.
Muscovite
Muscovite is common within the more argillaceous units of the
Little Valley Limestone where its elongate, A-axis is oriented
parallel to bedding. Petrographically, muscovite is colorless to
pale green, exhibits excellent cleavage (001), and is biaxial negative
with fourth order interference colors. Its crystals range in size
from 0.01 to 0.2 mm. Muscovite is an important constituent in the
calcareous mudrock and calcareous muddy sandstone microfacies.
Silt and Sand Sized Quartz
Quartz silt and sand are pervasive throughout the Formation,
ranging from less than 1% to nearly 80% of any particular rock. The
individual grains are subrounded to angular, usually highly pitted and
19
range in size from .03 to 0.5 mm. Petrographically, quartz is
colorless and is uniaxial positive with first order interference
colors. Quartz grains may also be polycrysta 11ine and/or
monocrystalline exhibiting an undulóse extinction. Quartz is commonly
associated with feldspar and chert grains.
CONSTITUENT PARTICLES
Introduction
The constituent particles within the Little Valley Limestone can
be subdivided into carbonate allochems and noncarbonate particles.
Allochems found in the Little Valley Limestone include very fine sand-
sized (0.075 mm) and larger fossils, ooids, intraclasts and
extraclasts. The most abundant allochems within this unit are fossils,
predominantly brachiopods, bryozoans, echinoderms and ostracodes.
However, foraminifers, corals, trilobites and gastropods, although
less abundant, are locally common. Similarly, nonfos si1iferous
allochems (ooids. Intraclasts and extraclasts) also lack ubiquity but
predominate locally. Conodonts and plant fragments, not considered
allochems, are locally common within the Little Valley Limestone.
Major Allochems
Brachiopods
Brachiopods are diverse and prolific within the Little Valley
Limestone. The following brachiopods were identified:
Syringothrididae, Inflata ?sp., and Produc tus (Dictyoclostus)
inflatus McChesney. Brachiopods in the Formation are very well
20
preserved, probably due Co their original calcitic composition. They
are commonly whole but may be fragmented, and they range in size from
0.05 cm to greater than 8.0 cm in maximum dimension. Their shell
characteristics include plications, smooth to spinose surfaces and
various overall morphologies.
Petrographically, brachiopods were identified by their "fibrous"
texture (composed of oblique calcitic layers) and their external
morphology. Both endopuctaCe and pseudopunctate forms were common.
Variations in microstructural organization were recognized, especially
in calcitic layer orientation (8-10 variations seen), associated with
different shell characteristics (Plate 2).
Bryozoans
Bryozoans are another prevalent fossil found throughout the
formation. Generally, bryozoans are structurally well preserved (due
to an original calcitic composition), although they are commonly
partially or entirely recrystallized and/or pyritized. Colonies are
commonly fragmented, except for robust cryptostome varieties.
Tile two predominant types of bryozoans associated with the Little
Valley Limestone are (1) fenestrate varieties characterized by
regularly spaced, bifurcating branches and fronds containing large
amounts of zooecia; and (2) cryptostome varieties containing thickly
branched (stick-like) colonies with zooecia radially or uniformly
spaced. Microstructurally, the bryozoans' wall structure is a thinly
to thickly laminated, fibrous layer which is longitudinal and
tangential to its architectural form. The cryptostomes are usually
21
very finely laminated forms and appear fibrous to structureless.
Fenestrate varieties show a diagnostically coarse, fibrous
microstructure (Plate 3).
Echinoderms
The term "echinoderm" includes any invertebrate belonging to the
phylum Echinoderraata. These are solitary, marine organisms
characterized by radial endoskeletons composed of crystalline calcite
plates (or ossicles) and a water-vascular system (Bates and Jackson,
1980). The most common subphyla within Echinodermata are echinozoans,
crinozoans and blastozoans.
Within the Little Valley Limestone, echinoderms are not usually
the most abundant fossils, but they are the most cosmopolitan. Well
preserved echinoderm fragments are found in lime grainstones,
packestones, mudstones and even calcareous mudstones.
Petrographically, echinoderm fragments are easily identified by their
single unit extinction under crossed niçois and by their dusty
appearance (due to mud inclusions within their porous structure).
Morphologically, echinoderm fragments can have various shapes ranging
in size from 0.01 to 2.0 cm but are often circular and/or columnar in
section.
Bivalves
Bivalves are benthic mollusks characterized by two approximately
equal valves joined by a hinge. Within the Little Valley Limestone,
they are commonly well preserved, with smooth to plicated external
shell morphologies. Their test thickness ranges from very thin (0.4
22
PLATE 2. Brachiopods common to the Little Valley Limestone.
1 cm = 1.7 cm.
PLATE 3. Photomicrograph of bryozoans (bryozoan 1.5 mm in
cross section).
23
mm) to thick (1.0 mm), while their maximum dimensions vary from 0.25
to 6.0 cm. Pelecypods identified include Posidonomya or
Caneyella?sp., Tetrachamera?sp. and AviculopectenTsp.
Microstructurally, two dominant shell characteristics are
observed: (1) a smooth, parallel interlaminations which make
bivalves seemingly structureless; and (2) a prismatic structure which
has polygonal calcite blocks arranged in a columnar fashion (both
simple and composite columns) oriented normal to the shell surface.
Bivalve preservation was greatly enhanced in muddier microfacies
where whole or nearly whole specimens are found. In contrast,
bivalves associated with sandier (whether carbonate or silciclastics)
microfacies are generlly highly fragmented and contain only a
prismatic columnar raicrostructure (Plates 4 and 5).
Other Allochems
Ooids
Ooids are carbonate grains, subspherical to spherical in shape
and composed of one or more uniform concentric laminae encompassing a
particulate nucleus. The ooids within the Little Valley Limestone
range in size from 0.15 to 0.5 mm. They invariably have a radial
fabric, possibly due to recrystallization, and range from light brown
to a darker carbonized black. Ooids are mostly very mature,
containing many uniform concentric laminations, although some
superficial ooids are also present. Ooid nuclei are composed of
various particles, but the most abundant particles in any raicrofacies
(sand-sized quartz, fossil fragments, etc.) are usually Che core
constituent. Ooid maturation affects Che size variance between
24
PLATE 4. Bivalves common to the Little Valley Limestone.
1 cm = 2 cm.
PLATE 5. Posidonomya ?sp., a bivalve common to the upper section
of the Little Valley Limestone. 1 cm = 2 cm.
25
eoliths. Mature ooids are nearly uniform in size, while immature
ooids show the greatest size variance.
Most of the black, highly carbonized ooids, individually or in
clusters, contain a conspicuous darker, spar cement than the
surrounding spar cement. Therefore, they are thought to be intra- or
extraclasts.
Forarainifers
The foraminifers within the Little Valley Limestone are benthic
varieties. In thin section, foraminifers are characterized by their
test morphology, which is subcircular to circular, planispiral to low
trochospiral, regular to irregular coiling, raulticharabered and ranging
in size from 0.5 to 1.0 ram. Microstructurally they have a
raicrogranular test with a dark and dusty textural appearance caused by
complete raicritization. The dominant type of foraminifers identified
include EndothyranopsisTsp. E.compressa., Brunsia?sp., Zellerina
designata and PseudoammodiscasTsp.
The foraminifers are unusually well preserved, suggesting an
original calcitic test composition. Some recrystallization and
pyritization has occurred (Plate 6).
Corals
Two types of coral are found in the Formation: (1) a horn coral,
thought to he Lithostrotionella proliféra (Hall), and (2) a branching
coral identified as Syringopora virginica Butts. The horn coral is an
elongate form which tapers away from the calycine and has parallel
26
costae running the length of the coral. Horn corals range in size
from 4.0 to 6.0 era, and are found in localized patches. Branching
corals are thin (0.3 cm), elongate, irregularly intergrown corallites
which range in size from 14.0 to 17.0 cm and generally occur in
localized patches.
Petrographically, horn corals are characterized by an outer wall
and an internal network of radially arranged septa perpendicular to
the outer wall. Well preserved corals contain a fine fibrous
microstructure, although a lack of microstructure is more common due
to complete recrystallization. Generally, corals are associated with
high porosities where multiple stages of calcite spar growth and
silica partially infill (plate 7).
Os tracodes
Ostracodes are bivalved arthropods which are cosmopolitan in the
Little Valley Limestone. Though they never predominate, ostracodes are
present in most lithologies throughout the formation. They are
recognized by their thin, overlapping carapaces which are generally
smooth and lack ornamentation.
The microstructure of ostracodes is characterized by radial-
fibrous calcite crystals which, under crossed niçois, show a
diagnostic sweeping extinction. Ostracodes range in size from 0.3 to
1.5 mm and are mostly disarticulated, although articulated specimens
due occur. The thickness of carapace walls varies. Ostracodes in
this unit are very well preserved due to their original calcitic
composition.
27
PLATE 6. Photomicrograph of foraminifers (0.7 mm in maximum
dimension)•
PLATE 7. The coral Syringopora virginica Butts (12.0 cm in
maximum dimension.
28
Trilobites
Trilobites fragments are sparse and only locally present. Their
raicrostructural characteristics are similar to those of ostracodes,
having a silky textured, calcitic radial-fibrous structure which
shows sweeping extinction bands under polarized light. In contrast to
ostracodes,the shell morphologies of trilobites are commonly sinuous
to convolute shaped (sometimes resembling a shepard's crook). The
trilobites are very well preserved, showing little recrystallization,
but some have been broken and abraded. Trilobite fragments range from
1.5 to 8.0 mm in maximum dimension.
Gastropods
Gastropods are rare within the Little Valley Limestone, possibly
owing to lack of preservation rather than initial absence. These
gastropods which are preserved are highly recrystallized to calcite
spar, thereby, reveal no raicrostructural properties. Their
diagnostically coiled shells (which are much larger than foraminifers)
range from highly spired (large whorl translation along their coiling
axis) to nearly planospiral, which are much rounder and flatter
(little whorl translation). Two species of gastropods are identified
from the Little Valley Limestone: Bellerophon sublaevis Hall and
Streophostylus carlexanus Hall. They range in size from 1.0 to 3.5
mm (Plate 8).
29
IntraciasCs/Extraelasts
Intraclasts are reworked carbonate particles from a previous
weakly lithified substrate within the basin of deposition. In the
Little Valley Limestone they are subrounded to angular, elongate,
sometimes dolomitized, lime mud particles probably produced by
dessication and/or wave and current activity in a low intertidal and
supratidal environment. They range in size from 0.5 to 3.5 mm.
Extraclasts are similarly defined except that they are derived
from a source area outside the depositional basin. Extraclasts here
are black, highly carbonized ooids and clusters of cemented ooids
which range in size from 0.1 to 0.5 mm (Plate 9). The conspicuously
dark color of the ooids and their remnant spar cement, in contrast to
the other much lighter allochems and cements, allows for easy
identification. In addition, the dark extraclasts occur together with
terrigenous particles, particularly quartz and feldspar fragments.
According to Flugel (1982), distinct color differences along with
siliciclastic associations are indicative of extraclasts.
Other Constituents
Conodonts
Conodonts within the Little Valley Limestone are light-to-dark
brown (in plane light) cones or serrated bars which range in size from
0.5 to 2.0 ram and contain faint concentric inner laminations
(especially in their basal areas). Due to their calcium phosphate
composition, conodonts are isotropic in polarized light. Conodonts
are most commonly associated with black carbonaceous shales of the
30
PLATE 8. Photomicrograph of gastropods (1.5 mm in maximum
dimension).
PLATE 9. Photomicrograph of ooid extra- intraclasts (0.5 mm
in diameter) containing darker spar cement.
31
upper Little Valley Limestone.
Plant Fragments
Plant fragments are black, carbonaceous and/or pyritized
particles which have fibrous to netted morphologies. According to
Horowitz and Potter (1971), preservation of plants or plant fragments
occurs from the infiltration of numerous mineral types, especially
calcite, quartz and pyrite, into internal porosity or molds. Within
the Little Valley Limestone the plant fragments are primarily
preserved through pyritization, allowing only gross morphologies to be
Identified.
ORTHOCHEMS
Orthochems are precipitates, recrysta 11ized sedimentary
components and replacement minerals formed by direct chemical action
within a depositional basin or diagenetically within the sediment.
The Little Valley Limestone is characterized by many orthochems, but
microspar, dolomite and silica are predominant.
Microspar
Microspar is one of the most prominent matrix components in the
Little Valley Limestone, occurring diagenetically by the aggradational
neomorphism of micrite and/or one step neomorphic calcitization of
aragonitic mud to microspar (Lasemi and Sandberg, 1984). Microspar is
distinguished from micrite by its slightly larger crystal size (0.005
to 0.01 mm) and its higher birefringence. Microspar crystals are
32
anhedral containing irregular crystal boundaries, especially when in
contact with raicrite and/or phyllosilicate muds. Therefore, microspar
texturally creates a tightly cemented grumous fabric characterized by
a patchy mixture of various sized constituents. Microspar
predominates in lime mudstone, lime wackestone, and calcareous raudrock
microfacies.
Dolomite
Two distinct types of dolomite occur in the Little Valley
Limestone: (1) large, euhedral crystals ranging in size from 0.025
to 0.5 mm and associated with gypsum and anhydrite, and (2) finely
disseminated to densely packed (crystal supported) anhedral dolomite
which is generally less than 0.25 mm in size and commonly situated
within lime mudstones, wackestones, packstones and calcareous raudrock
raicrofacies.
The large euhedral dolomite most common in the lower Little
Valley Limestone is classified using Gregg and Sibley's (1984)
textural classification into idiotopic-E and idiotopic-P dolomite.
Idiotopic-E dolomite is characterized by nearly uniform euhedral
rhombs which are crystal supported and contain terrigenous muds in
open intercrystalline areas.' Idiotopic-P dolomite is characterized by
euhedral crystals suspended in a matrix of terrigenous mud gypsum and
anhydrite.
Fine-grained dolomite most common in the upper Little Valley
Limestone (not associated with the evaporites) is characteristically
anhedral and texturally classified (again according to Gregg and
33
Sibley's classification) into (1) xenotopic-P, finely dessirainated and
clustered anhedral dolomite (doloraicrospar) suspended in micrite and
muds; and (2) xenotopic-A, tightly packed anhedral dolomite crystals
with covered and pitted crystal boundaries. Within the Little Valley
Limestone, xenotopic-P dolomite frequently surrounds sil tier units or
zones (laminations or burrows) within lime mudstones. Xenotopic-A
dolomite is most commonly associated with lime wackestones and
packstones (Plate 10).
Syntaxial Overgrowths
Syntaxial overgrowths are early diagenetic cements which are in
optical continuity with a carbonate particle. Within the Little
Valley Limestone syntaxial overgrowths (which occur mostly on
echinoderm fragments) are restricted to the lime grainstone
microfacies where they are commonly associated with other fresh water
phreatic cements, particularly bladed and blocky spar which coarsen
towards the center of the pore (Longman, 1980). Though syntaxial,
bladed and blocky cement occur together, syntaxial cements predominate
the interparticle area. In rare instances, syntaxial overgrowths
include two or more echinoderm fragments forming a poikilotopic cement
(Plate 11).
Bladed and Blocky Spar
Bladed and blocky spar cements of the Little Valley Limestone are
most characteristic of lime grainstone and packstone microfacies.
Within interparticle pore spaces the cementation sequence progresses
from an isopachous, nonferroan, bladed spar into an equant, sometimes
34
PLATE 10. Photomicrograph of finely disseminated xenotopic-P
dolomite associated with gypsum. 1 cm = 0.25 mm.
PLATE 11. Photomicrograph of a syntaxial overgrowth on a
echinoderm fragment. Echinoderm 0.7 mm in diameter.
35
ferroan, blocky spar. The isopachous bladed spar precipitated first
around allochems as relatively equant xenotopic crystals ranging in
size from 0.02 to 0.1 mm. Towards interparticle pore centers, bladed
crystals grade to equant blocky spar. Equant blocky calcite crystals
are fine-to-medium crystalline (0.062 to 0.5mra), hypidiotopic to
xenotopic, and increase in size towards the pore center.
Silica
Silicification is pervasive in the Little Valley Limestone. Most
samples have silica partially or completely replacing some allochems.
Although rare, some samples have complete silicification of both
allochems and matrix forms chert nodules and/or bands.
Silica replacement of allochems is usually in the form of chert
and megaquartz. Depending on type of allochem, composition and
microstructural characteristics, distinct replacment textures occur
(Kuslansky and Friedman, 1981; Schmitt and Boyd, 1981; and Neal et
al., 1984). Fibrous calcitic microstructure in brachiopods and
bryozoans is commonly replaced by subhedral raegaquartz and chert. The
megaquartz and chert usually mimic the fibrous microstruetoral
characteristic by nucleating and replacing the calcitic layers
parallel to the elongate axis of the megaquartz. Echinoderms most
commonly contain spotted, circular chert nucléations in their single
calcite crystal composition. According to Kuslansky and Friedman
(1981), calcite nucléations selectively replace echinoderms along the
calcite crystals cleavages, thus attributing to silica's spotted
nucléations (Plate 12).
36
Where silicification of both allochems and matrix has occurred,
chert and megaquartz are predominating forms of silica, although
chalcedony also occurs (Plate 13). Chert nodules and bands within the
Little Valley Limestone protrude from the unit's weathered surfaces,
and are located stratigraphica 11y above calcareous sand and
siltstones.
Secondary Gypsum
Secondary gypsum occurs through the hydration of original
(primary) anhydrite. The preserved anhydrite is characteristically
nodular or "chicken wire" form. Hydration obliterates nearly all
original morphology. The two prominent gypsum textures within the
Little Valley Limestone include: (1) prophyroblastic and (2)
alabastrine (similar to Holliday's 1970 terminology). The
porphyroblastic gypsum is anhedral to euhedral containing corroded
anhydrite relics. It creates no volume increase. This form of
secondary gypsum forms during early diagenesis (Holliday, 1970).
Recently, secondary gypsum has been found forming
penecontemporaneously in anhydrite deposits of the Trucial Coast
(Shearman, 1978).
Alabastrine secondary gypsum shows a variety of textures due to
some degree of lattice disorder associated with hydration. This form
of gypsum was most common in the Little Valley Limestone and can be
subdivided into two types of alabastrine, which are texturally
gradational between each other: (1) individual "feathery" gypsum
grains in which poorly defined crystals have undulóse or irregular
37
PLATE 12. Photomicrograph of silica nucléations on an echinoderm
fragment (0.7 mm in maximum dimension).
PLATE 13. Chert nodules exposed on weathered outcrop surface.
38
extinctions, and (2) granoblastic secondary gypsum with interlocking
(curved or reentrant boundaries), well defined, anhedral, but
equidimensional grains. Alabastrine gypsum forms during a late stage
of diagenesis associated with hydration by near surface ground waters
(Plate 14).
Framboidal Pyrite
Pyrite framboids (FeS ) are microscopic, spheroidal aggregates of
pyrite which normally form in clusters. Pyrite framboids are common
to all lithofacies within the Little Valley Limestone, although they
are most abundant in darker lime mudstones and calcareous mudrocks.
Coalescence of framboids ordinarily occurs in both matrix and
allochems. Dense clusters of framboids primarily exist in sheltered
pore spaces under convex upward allochems. Although rare, complete
pyritization of allochems and algal laminations also occurs (Plate
15).
39
PLATE 14. Photomicrograph of secondary alabastrine gypsum and
a satin spar gypsum vein. 1 cm = 0.25 mm.
PLATE 15. Photomicrograph of disseminated pyrite framboids in a
lime mudstone. 1 cm = 0.25 mm.
MICROFACIES
INTRODUCTION
A microfacies, as defined by Flugel (1982), is the comprehensive
classification of thin sections, peels and polished slabs,
paleontological and sedimentalogical components. More specifically,
this includes allochems, matrix, cements, fabrics and textural
characteristics of the particles, and fossil types including their
associated structures and fossil associations. Because limestones are
highly susceptible to neoraorphic crystallization, diagenetic
alterations such as mineralogical replacement and cementation are
included in microfacies descriptions.
Microfacies in this study include the most abundant lithologic
types according to Dunham's classification. Thus, frequency of matrix
and/or cements, and particle types are the distinguishing factors for
different microfacies (Appendix C). Microfacies within the Little
Valley Limestone are subdivided into two classes: (1) carbonate
microfacies, which only include rocks with greater than 50% carbonaté
material and (2) noncarbonate raicrofacies which only contain rocks
with less than 50% carbonate material (Table 1). The carbonate
raicrofacies compose the majority of the Little Valley Limestone and
include lime mudstones, wackestones, packstones and grainstones;
while noncarbonate raicrofacies include calcareous muddy sandstone,
calcareous mudrocks, and secondary gypsum. A graphical comparison of
the percentage of raicrofacies constituents is presented in Figure 7.
Within this section, specific diagenetic characteristics corresponding
to particular raicrofacies are characterized.
SUMM!\RY OF MICROFACIES POINT COUNT DATA (TOTAL AVERAGE PERCENT)
TABLE 1
Carbonate Microfacies
T.ittip t^idstone Microfacies Lime Packstone Microfacies
Matrix 88.0% Matrix 35.0%
A1 lochems 2.0% Allochems 57.5%
Terrigenous Sand— 10.0% Terrigenous Sand— 2.8%
100% Calcite Spar 4.7%
100%
Lime Wackestone Microfacies Lime Grainstone Microfacies
Matrix 73.4% Nfatrix 3.3%
Allochems 19.8% Allochems 60.3%
Terrigenous Sand— 5.6% Terrigenous Sand— 4.7%
Calcite Spar 0.2% Calcite Spar 31.7%
100% 100%
Noncarbonate Microfacies
Calcareous Muddy Sandstone Microfacies
Matrix 28.0%
A1lochems 5.0%
Terrigenous Sand— 58.8%
Calcite Spar 8.2%
100 %
Calcareous Mjdrock Microfacies
Matrix 82.3%
Allochems 3.3%
Terrigenous Sand— 13.4%
Calcite Spar 1.0%
100%
Secondary Gypsum Microfacies
Matrix 32.0%
Evaporites 68.0%
100%
42
e^AOi BHirOZ CCMN OSTRA CORAL Uf*-F0S CORT CKXOS tN/EX T-SAMO MCAlTC SPAR
60
40
20
60 •
40-
20 ?
60
LIKC P0CKSTT>C Matonees
40 ?
20-
60 -
40-
20-
60 -
40-
20 -
60 -
40 -
20 -
60 -
40 -
20 -
Fig. 7. Average total percentage of constituents of
each microfacies.
43
LIME MUDSTONE MICROFACIES
The lime mudstone microfacies consists of 88% matrix, 2%
allochems, 10% very fine sand-sized quartz and feldspar and trace
amounts of pyrite, spar cement and plant fragments. One lime mudstone
sample in the lower Little Valley Limestone contains 3% gypsum. The
matrix is predominantly composed of microspar/micri te (68%),
phyllosilicates (15%) and mud sized (0.02 mm and less) dolomite
(4.8%). The microspar/micrite commonly has a grumose texture, and
comprises the majority of this microfacies, ranging from 34% to nearly
96% of any given sample. Dolomite and phyllosilicate muds compose
only 30% of the rock. Allochems comprise a small percentage of this
raicrofacies where brachiopods, bryozoans and echinoderras predominate.
These fossils are preferentially oriented preferentially parallel to
bedding in condensed zones (zones composed almost entirely of fossils
and fossil fragments) and/or sparsely disseminated throughout the
matrix.
Two prominent types of lime mudstone occur within this
microfacies: (1) a light gray, cryptalgally laminated and/or silty
laminated, bioturbated, argillaceous lime mudstone containing
disseminated fossils and localized gypsum accumulations; and (2) a
dark gray, cryptaIga 11y-1o-fine 1y laminated, fossi1iferous,
bioturbated lime mudstone containing disseminated and condensed zones,
where fossils are oriented parallel to bedding (Plates 16 and 17).
Based on composition and stratigraphic position, a subdivison of this
microfacies into shallow intertidal and deeper subtidal deposits
A4
PLATE 16. Algal laminated lime mudstone.
PLATE 17. Photomicrograph of ostracodes (0.25 mm in maximum dimension).
Fig. 8. Location of the lime mudstone depositional environments. 4>
46
(corresponding to Wilson's (1975) standard microfacies (SMF) numbers
19 and 20, respectively) is possible (Fig. 8).
Lime mudstones, associated with the lower Little Valley
Limestone, are virtually unfossiliferous (except for an occassional
fossil fragment and/or algae), argillaceous and silty, and represent
an intertidal mixed carbonate-siliciclastic mudflat. Irwin's (1962)
model of epeiric, dear-water sedimentation applies to this study in
that sightly fossiliferous lime mudstones are classified as shallow
intertidal deposits. He suggested that the lack of fossils is due to
poor water circulation associated with a diminished nutrient supply.
Blue green algae, however, can survive in this type of environment.
He considered the restricting mechanism to be very shallow water
conditions which promote unstable environmental conditions. The
shallow water depth also aids in dissipation of wave and current
activity allowing muds to accumulate, although higher energy pulses
must have occurred in order for very fine sand and silt layers to be
deposited.
Within the Little Valley Limestone this type of lime mudstone is
usually located stratigraphica 1ly above or interbedded with
unfOSSi1iferous, calcareous, very fine grained, ripple laminated
sandstones and siltstones that represent shoaling intertidal deposits.
Stratigraphically below the lime mudstones are unfossiliferous,
calcareous siltstones and algal-laminated dolomitic mudstones
containing bedded evaporites (gypsum, anhydrite, and halite). These
deposits are interpreted as a low intertidal-supratidal deposit.
The stenohaline fauna, especially brachiopods, bryozoans, and
47
echinoderms, found in these lime mudstones are derived from open
marine, subtidal environments, while the in situ fauna (identied by
life positioning and well preserved delicate structures) is composed
almost exclusively of ostracodes, which are cosmopolitan. The
ostracodes are smooth shelled varieties found most commonly in
restricted marine environments (Benson, 1961). Therefore, the
combined faunal and lithologic characteristics of this lime mudstone,
along with stratigraphically adjacent lithologies, indicate a
restricted, shallow water, mixed siliciclastic- carbonate intertidal
environment. Similar intertidal lime mudstone environments exist in
the Upper Mississippian Newman Group in east- central Kentucky
(Ettensohn, 1975) and in the Greenbrier Group within the Hurricane
Ridge Syncline of southwestern Virginia (Blancher, 1974).
The second lime mudstone associated with the upper Little Valley
Limestone, contains horizontally laminated, terrigenous clays and
silts, with 1) large disseminated fossils and 2) smaller
preferentially oriented fossils within condensed zones. Although the
overall percentage of allochems within this microfacies is low,
samples within condensed zones contain more than 65% of the fossils
within the raicrofacies. Predominant fossils include brachiopods,
bryozoans and echinoderms. Although ostracodes are not abundant, they
are pervasive in these lime mudstones. Disseminated in a fine grained
matrix, large productid brachiopods and fenestellid bryozoans
characteristically retain their delicate skeletal components (spines
and fronds, respectively), suggesting in situ accumulation in a quiet
48
water environment. Stromatolitic algae and vertical burrow strutures
are locally significant within this microfacies. In the past, the
presence of stromatolitic algae was misinterpreted as a diagnostic
indicator of an intertidal environment, despite other atypical
intertidal characteristics (abundant biota). Monty (1977) discounted
the limitation of stromatolites to intertidal environments stating
that during the Paleozoic and Mesozoic, stromatolites also grew in
open marine, fauna-rich subtidal environments, such as lagoons,
shelves and reefs.
Condensed zones of fossils, sedimentary boudinage structures and
the lack, of very fine sand and silt sized quartz grains are highly
suggestive of a quiet water, subtidal environment. Condensed fossil
zones are interpreted as storm deposits which swept biota out of
shallower, highly fossiliferous subtidal environments into more
restricted environments. Flugel (1982) and Wilson (1975) recognized
similar discontinuity planes associated with condensed faunal zones in
deeper marine environments. Sedimentary boudinage structures occur
due to differential compaction (in this case between argillaceous lime
muds and purer lime muds). This type of structure has been recognized
by Wilson (1969, 1975) as a deeper marine deformational feature.
Finally, the lack of silt or larger sized detritus (quartz grains in
particular) characterizes a quieter, deeper water marine environment
(Heckel, 1972). A deeper water (further offshore) enviroment lacks
the water energy to retain the silt and sand sized particles in
suspension, so they must have been deposited inshore before reaching
this environment.
49
Stratigraphically bordering these lime mudstones above are
fossiliferous lime- packstones and wackestones, which are associated
with a rich stenohaline fauna typical of open marine subtidal
environmental conditions. Interbedded with the lime- packstones,
wackestones and mudstones is a 70 cm bed of highly organic black shale
which contains sparse fossil fragments (mostly brachiopods and
echinoderms) and an abundance of conodonts. The constituents of the
black shale and its stratigraphic position between marine lime-
packstones and mudstones suggests a subtidal environment with anoxic
bottom water conditions. The semi-restricted, reducing nature of the
upper lime mudstone is suggested by its dark color (preserved organic
matter) and a high percentage of pyrite. The upper lime mudstone
biota, sedimentary structures and lithologic associations are
interpreted to represent a deeper subtidal, semi-restricted shelf or
lagoonal environment which remained within the photic zone.
The lime mudstone microfacies of the Little Valley Limestone has
undergone a complex and variable diagenetic history which includes:
neomorphism of both matrix and allocheras, various generations of spar
cement growth infilling intraparticle pore spaces, dolomitization,
silicification, pyritization, continuous and discontinous irregular
stylo1itization and calcite vein, microfault and gypsum vein
formation.
LIME WACKESTONE MICROFACIES
The lime wackestone microfacies consists of 73.0% matrix, 19.0%
allochems, 6.0% quartz and feldspar grains, 1.0% spar cement and 0.3%
50
organic material. The matrix is composed of raicrospar/micrite
(46.3%), dolomite (14.2%) and p hy 11 o s i 1 i c a t e muds (8.0%).
Micrite/microspar range from a high of 75.3% to trace amounts in
certain samples. Dolomite ranges from a high of 49% to zero in
individual samples. Only a few samples contain terrigenous muds,
however, when present, they sometimes comprise 25% of the sample
(Plates 18 and 19).
The allocheras represent approximately 19% of this raicrofacies
and include brachiopods (5.1%), bryozoans (4.2%), echinoderms (3.3%),
unidentifiable fossil fragments (3.2%), ostracodes (1.3.%), ooids
(1.3%), and cortoids (1.0%). Fo r amini f e r s, conodonts, trilobites
and intraclasts are also present though combined they comprise less
than 0.5% of this raicrofacies. Although forarainifers only appear as a
small percentage of the total raicrofacies, they compose as much as
4.0% of individual samples. The larger fossils within this
microfacies are usually broken and abraded. Overall, preferential
allignraent of elongate fossils parallel to bedding is common,
especially when they are broken and abraded.
Quartz and feldspar grains are subrounded to subangular,
moderately sorted and range in diameter from 0.025 to 0.5 mm. Quartz
is always more abundant than feldspar. The exact composition of the
feldspar grains is impossible to determine optically because of their
size. Albite twinning suggests that they are some type of
plagioclase.
Spar cement is rare within this raicrofacies occurring in only
51
P ri •
j,
r
c. ; ^
PLATE 18. Cored section of a typical lime wackestone (5.0 cm
in diameter).
PLATE 19. Photomicrograph of a lime wackestone 1. cm = 0.25mm.
52
one sample. The spar is composed of nonferroan calcite, comprises
approximately 12% of that sample and is found within the siltier
zones.
Organic fragments make up only a small portion of this
microfacies, but individual samples may contain as much as 2.0%
organic matter. These fragments are highly carbonized and/or
pyritized and are thought to be plant fragments. Structurally, these
fragments contain a netted fibrous network with an irregular outline.
Environmentally, the lime wackestone microfacies is closely
related to Wilson's (1975) standard microfacies (SMF) numbers 8 and 9,
representing a shelf environment with open water circulation. The
predominance of brachiopods, bryozoans and echinoderms combined with a
high percentage of mud is indicative of a subtidal, shelf enviroment
with open circulation. Brachiopods, bryozoans and particularly
echinoderms thrive in normal marine conditions (stenohaline) ;
Horowitz and Potter, 1971; Heckel, 1972; Tucker, 1981; and Flugel,
1982) associated with efficient water circulation. Both brachiopods
and echinoderms can exist in environments associated with soft
substrates and relatively high accumulations of mud (Tasch, 1973).
Bryozoans, however, prefer a firm substrate. Bryozoans probably used
accumulations of brachiopod and echinoderm skeletal debris as the
substrate on which they developed.
The dominant component of this raicrofacies is matrix, which
comprises nearly 75%.of the rock. Lower energy, tranquil water is
necessary for the accumulation of fine-grained matrix material. These
muds were deposited into deeper (or protected) portions of a shallow
53
marine shelf subject to constant temperatures and salinities.
Therefore, they were able to sustain a more diverse biota as long as
currents replenished nutrients and kept the bottom oxygenated. Fossil
orientation within this microfacies is highly suggestive of moderate
wave and/or current activity (Fig. 9).
The lime wackestone microfacies contains a variety of diagenetic
modifications. The major diagenetic alterations include:
silicification, stylolitization, spar infilling, neomorphism of both
allochems and matrix, dolomitization, microfaulting, pyritization,
calcite veins and micritic enveloped gypsum replacement.
LIME PACKSTONE MICROFACIES
The lime packstone microfacies is consists of 35% matrix, 56%
allochems, 5% spar cement and 3% fine-to-medium quartz and feldspar
sand. The matrix predominantly consists of microspar/micrite (23.4%),
dolomite (9.8%) and terrigenous muds (1.8%). Microspar/micri tes range
from a high of 75% (although still grain supported) to only trace
amounts. Dolomite crystals are subhedral to anhedral and 0.04 mm and
less in size. Dolomite ranges from only trace amounts to a high of
46%. Terrigenous mud is rare within this microfacies.
The allochems account for greater than half of the constituents
of the lime packstone microfacies. Three major allochems comprise
nearly 50% of this microfacies: brachiopods (21%), bryozoans (19%) and
echinoderms (10%). Other allochems, including bivalves, ostracodes,
trilobites, foraminifers, corals, conodonts, gastropods, ooids.
OPEN MARINE LOW INTERTIDAL RESTRICTED, HIGH INTERTIDAL
TO
SHALLOW
SUBTIDAL
Fig. 9. Location of the lime wackestone depoaltional environment. Ln
55
cortoids and intraclasts, individually make up less than 1% and
combined approximately 2% of this microfacies. Ooids occasionally
comprise greater than 5% of a particular sample. Allochems are mostly
benthic sessile varieties which range from whole and well preserved to
highly broken and abraded. Elongate allochems are preferentially
oriented parallel to bedding.
Spar cement is a minor component in this microfacies, although a
few samples exceed 30% spar. The spar cement is composed of 0.03 to
0.5 mm long bladed to drusy calcite crystals, which rarely form
syntaxial overgrowths and poikilotopic cements on echinoderm
f ragments.
Quartz and feldspar grains are subrounded to subangular, poorly
sorted and range in size from 0.025 mm to 1.0 mm. Some of the quartz
grains suggest metamorphic source terrains due to their
polycrystalline, semi-composite nature and their strong undulóse
extinction. Chert grains are also commonly associated with quartz.
Feldspar within this microfacies is considered to be from the
plagioclase group because it contains albite twinning. No feldspar
compositional determinations were made because of the lack of a
statistically valid sample. Within packstones, quartz is more
abundant than feldspar or chert. Although quartz and feldspar grains
make up only a small percentage of this raicrofacies, some samples
contain nearly 23% quartz and feldspar.
Sedimentary features within this microfacies include ripple-
laminations, moderate sorting, preferential orientation of elongate
allochems, graded bedding and geopetal structures, all of which are
56
indicative of shallow subtidal environments influenced by wave or
current activity.
Environmentally, the lime packstone microfacies within the Little
Valley Limestone is most similar to Wilson's (1975) standard
microfacies 5, which he locates on a shelf bordering a shoaling
environment. This microfacies is interpreted as a shallow subtidal
(at or below wave base), normal marine deposit, as evidenced by its
large percentage of fossils, the majority of which are stenohaline
varieties (brachiopods, bryozoans, echinoderms and corals) (Fig. 10).
Another feature indicative of this environment is increased diversity
and slighly lower predominance of the biota in this microfacies as
compared to the microfacies previously discussed. Lithologies are
characterized by an abundance of fossils which are larger, grain
supported and associated with a lime mud matrix. Similarly, Tyrrell
(1969) found the shallow shelf-edge environment of the Capitan
Formation to consist of lime- wackestones, packstones and boundstones
which commonly contain large skeletal material (pebble sized and
larger) in a fine grained matrix. The distinctive Capitan shelf-edge
biota includes red algae, bryozoans, and calcareous sponges, with
brachiopods, crinoid debris and forminifers being common. To a lesser
extent, corals and trilobites are also present. Heckel (1972) also
characterized deep water environments which are well oxygenated and
below wave base as having diverse biota (sand sized or coarser) within
a mud matrix (Plates 20 and 21).
Fig. 10. Locations of the lime packstone depositional environments on either side of the carbonate shoal.
58
PLATE 20. Cored section of a brachiopod bearing lime packstone
(5.0 cm in diameter).
PLATE 21. Photomicrograph of broken and abraded allochems
common to lime packstones. 1 cm = 0.4 mm.
59
This microfacles exhibits a complex diagenetic history comprising
various types of alteration. The major processes of diagenesis
include: silicification, neomorphism of both allochems and matrix,
infilling of intra- and interpore areas by spar, dolomitization,
pyritization, calcitic veins and stylolitization.
LIME GRAINSTONE MICROFACIES
The lime grainstone microfacies consists of 3.0% mud-sized
material (0.0625 mm and less), 60% allochems, 32% spar cement and 5%
very fine sand and silt sized quartz and feldspar. The mud sized
material is composed of both micrite and siliciclastics. Major
allochems include bryozoans (21%), echinoderms (15%), intraclasts
(6%), brachiopods (4.5%), unidentifiable fossil fragments (4%), ooids
(3%), cortoids (2%), and ostracodes (2%). Other allochems
individually and combined comprise less than 1% of this total
microfacies, and include trilobites, foraminifers, bivalves and
gastropods.
Allochems are large with a predominance of robust forms ranging
in size from 0.05 cm to greater than 5.0 cm. Fossils are generally
well preserved, although some are broken and abraded. Elongate
allochems are preferentially oriented parallel to bedding. Sorting of
allochems and the quartz and feldspar grains is bimodal, such that
allochems are 0.5 mm and greater whereas quartz/feldspar grains range
from 0.15 mm to 0.25 mm.
Quartz and feldspar grains are subrounded to subangular and
moderately to well sorted. The assemblage of quartz, feldspar and
60
trace amounts (less than 1%) of chert grains is highly suggestive of a
metamorphic source terrain. Furthermore, quartz grains are both
polycrystalline and monocrystalline and exhibit undulóse extinction.
Feldspar grains commonly exhibit albite twinning and are considered to
be within the plagioclase group (no compositional determination was
made due to insufficient sample size). Quartz is much greater in
abundance than feldspar.
Spar cement is a major component, composing nearly one third of
rocks in this microfacies. Spar usually occurs in a three generation
progression into open pores spaces: (1) fibrous, (2) bladed and (3)
drusy or blocky. Occasional poikilotopic spar cements form syntaxial
overgrowths on echinoderra grains.
Environmentally, the lime grainstone microfacies within the
Little Valley Limestone is interpreted as a very shallow subtidal
deposit, most similar to Wilson's (1975) standard microfacies SMF - 11
(agitated shoal environment) (Fig. 11). Indicators of this
environment include broken and abraded allochems, thicker and larger
shelled (greater than 0.625 mm), more robust forms of fossils
(especially bryozoans and ostracodes), decrease in brachiopods
(inhospitable sessile environment), increase in cortoids, ooids and
intraclasts, and siliciclastic sands.
In shallower water zones (within reach of effective wave base)
higher water energies inhibit mud accumulation, allowing sand sized
and coarser material to settle out. A lack of detrital influx allows
largely skeletal debris from a relatively diverse fauna to be
concentrated by water agitation. Typically, skeletal material becomes
1 1
1 1
' 1
OPEN MARINE 1 LOW INTERTIDAL | RESTRICTED, HIGH INTERTIDAL
TO 1
SHALLOW 1
1 SUBTIDALj
Fig. 11. Location of the lime grainstone depositional environment.
62
more robust, especially in bryozoans and ostracodes, with increasing
water agitation in order to protect against high wave energy. Many
fossils are fragmented and abraded, showing moderate to poor rounding
and sorting. The decrease in sessile-benthic fauna requiring stable
substrates suggests an inability to adapt to the high energy
conditions. This is particularly reflected in the brachiopods, which
significantly decrease in abundance within this facies.
Increases in cortoids (allochems containing micritized coatings
due to boring endolithic algae), ooids and intraclasts also suggest
increased water agitation. According to Flugel (1982), cortoids can
be used in microfacies determination as evidenced by distribution
patterns of ancient shelf reef carbonates where cortoids occur
preferentially in lime grainstones of high energy, shallow shoal
environments. Ooids and intraclasts similarly originate within higher
energy conditions where at least periodic strong water movements
occur. Siliciclastic matrix within this microfacies is generally free
of mud-sized material. According to Heckel (1972) both abraded
calcarenites and quartz sand collect in zones of agitated water above
wave base where abrasion of large grains and winnowing of fine grains
occurs (Plates 22 and 23).
Diagenetic alteration within this microfacies is similar to the
other microfacies. Neomorphism of both allochems and micrite,
progressive growth of spar (fibrous, bladed to blocky) in
intraparticle pore spaces, silicification of allochems, partial
pyritization of allochems, syntaxial overgrowths, micrite envelopes,
63
PLATE 22. Cored section of a echinoderm bearing lime grainstone
(5.0 cm in diameter).
PLATE 23. Photomicrograph of a lime grainstone. 1 cm = 0.25 mm.
64
localized stylolites, calcita veins and localized dolorai tization of
spar.
CALCAREOUS MUDDY SANDSTONE MICROFACIES
The calcareous, muddy sandstone microfacies is positioned
within the lower section of the Little Valley Limestone and consists
of approximately 28% matrix, 5% allochems, 58% terrigenous very fine
to fine sand-sized grains, 8.2% spar and trace amounts of organic
fragments and pyrite. Gypsum was encountered in two samples within
this microfacies, in one of which it constitutess just less than 10%
of the total sample. The matrix is predominantly composed of
phy1losi1icates, including clay minerals and muscovite (19%),
micrite/microspar (5.8%) and dolomite (3.5%). Illite and chlorite (as
determined by x-ray diffraction), comprise the majority of the
phyllosilicates in this microfacies. Muscovite grains are
characteristically elongate flakes containing fourth order
interference colors and ranging in size from 0.03 to 0.06 mm.
Micrite/microspar is seen as very fine grains comprising a grumose
texture. Dolomite (xenotopic-P) is the least significant matrix
component. Its distinguishing features include subhedral and anhedral
crystals which range in size from 0.01 to 0.05 mm and do not stain
when subjected to Alizarin Red S stain.
The most prominent allochems include ooids (2%) and echinoderms
(1.4%). Brachiopods, bryozoans and trilobites comprise less than 2%
of this microfacies.? Ooids, the most abundant allochem of this
microfacies, are characteristically highly recrystallized (containing
65
a radial axial texture) and range in size from 0.3 mm to 0.5 mm.
Their nuclei are either quartz or plagioclase grains, although an
occasional echinoderm fragment can also be recognized.
Echinoderms are the second most abundant allochem and the most
abundant fossil type within this microfacies. The echinoderms present
are fragmented plates and ossicles which are recognized by their
porous microstructure and their unit extinction in polarized light.
The brachiopods, bryozoans and trilobites are generally highly
fragmented and abraded, although rarely, large brachiopods also are
present.
Terrigeneous sand sized grains, which include quartz, chert and
feldspar, comprise greater than half of this microfacies. The quartz
grains are the predominant constituent, comprising greater than 55% of
this microfacies. Quartz grains are subrounded to subangular,
moderately to well sorted and range in size from 0.075 mm to 0.2 mm.
The quartz grains are generally monocrystalline and contain strong to
moderate undulóse extinction. Trace amounts of biotite and subhedral
grains of zircon are also present. Chert comprises only 1.5% of the
microfacies. Chert grains are subrounded to subangular-, ranging in
size from 0.5 mm to 0.75 mm. Within this microfacies feldspar grains
are the least abundant of the terrigeneous sand grains, comprising
just over 0.5%. Feldspar grains are subrounded to subangular, albite
twinned and range in size from 0.075 mm to 0.1 mm.
Spar cement is common to this microfacies where it grows in
stages (bladed to blocky) or forms poikilotopic cements. Both ferrous
66
and nonferrous calcite varieties of spar exist, with nonferroan being
the most common. In some instances, calcitic spar has been partially
to totally dolomitized, with preservation of the pre-existing crystal
forms.
Although not abundant, gypsum is present within this microfacies,
characteristically in satin spar veins (associated with
remobilization) and/or within calcite veins. Depositional forms of
gypsum or any other evaporite mineral were not observed within this
microfacies.
The depositional environment for the calcareous muddy sandstone
microfacies within the Little Valley Limestone is a shallow intertidal
environment most similar to Wilson's (1975) standard facies belt 8
(Fig. 12). Specific lines of evidence within this unit which suggest
this type of environment include ripple marks, tangential
crossbedding, highly fragmented and abraded allochems, sparse
occurrences of ooids, low fossil content, interbedded terrestrial muds
and sands, cryptalgal laminations, high bioturbation and pyritized
plant fragments. Stratigraphically adjacent lithologies include
underlying algal-laminated, dolomitic and terrigenous mudrocks with
mudcracks and evaporites, interpreted as high intertidal or supratidal
flat deposits; and overlying serai-restricted shelf lagoonal deposits
associated with lime- mudstones and wackestones containing a less
restricted biota.
The sedimentary structures and the abundance of sand-sized
s i 1 iciclastic components are sedimen tologically characteristic of
shallow, agitated water conditions in which the substrate is above
1 1
1 1
' 1
OPEN MARINE 1 LOW INTERTIDAL | RESTRICTED, HIGH INTERTIDAL
' TO 1
SHALLOW 1
1 subtidal|
Fig. 12. Location of the calcareous muddy sandstone depositional environment.
68
wave base. Although rare, due to extensive bio turbation, ripple
laminations are present, averaging approximately 5.0 cm in wave length
and 1.0 cm in amplitude. The ratio of sand sized grains to mud-sized
grains is 2.25 to 1.0 Although there is nearly 30% mud-sized material
within this microfacies, it should be noted that muds are generally
concentrated in thin beds, ranging in thickness from 0.05 cm to 2.5
cm. This interbedded relationship of sands and muds suggests
deposition from nonuniform water energies (discontinuous corapentency)
such that higher energy pulses are associated with winnowing fines and
deposition of coarser material, whereas waning energy episodes allow
fine grained material to settle out of suspension.
Fossils, although rare within this raicrofacies, are primarily
restricted to muddy interbeds within the sands, although highly
fragmented and abraded brachiopods and echinoderms are found within
the sands. The muddy units are characterized by brachiopods,
bryozoans, ostracodes and cryptagal laminations. The overall lack
of biota within this microfacies suggests stressed environmental
conditions associated with intense water agitation, and/or major
salinity fluctuations. More common to this microfacies are plant
fragments which are usually completely pyritized. The plant fragments
suggest relatively nearshore environments (Flugel, 1982).
Bioturbation is extensive within this raicrofacies where vertical
burrows have nearly or completely homogenized the sediments.
Therefore, increase of quartz sand and phyllosilicate mud, decrease
in marine faunal diversity and increase in plant material imply a
69
barrier in close proximity to the coastline (Flugel, 1982) (Plates 24
and 25).
The calcareous muddy sandstone microfacies is diagenetically
characterized by partially silicified allochems, syntaxial calcitic
overgrowths of echinoderms, neomorphism of micrite and allochems,
partially pyritized allochems, dolomitization of allochems (especially
brachiopods and bryozoans) and cement, localized stylolites, bladed to
blocky poikilotopic spar cements, ferroan calcitic spar cements,
calcite veins (some gypsum associated with them), gypsum interpore
areas and micro-normal faulting (displacement of 2.5 mm).
CALCAREOUS MUDROCK MICROFACIES
The mudrock microfacies consists of 82% matrix, 3.3% allochems,
13% quartz sand and trace amounts of spar and organic fragments. The
matrix consists of phyllosilicates (61%) and micrite/raicrospar (20%).
Dolomite (1.4%), is never present in high concentrations but is found
throughout the microfacies.
The phyllosilicates are dominated by terrigeneous clays. Illite
and chlorite were identified by x-ray diffraction. Muscovite is
also present, composing approximately 2% of this raicrofacies.
Muscovite is found as elongate, bladed grains exhibiting fourth order
interference colors and ranging in size from 0.03 to 0.06 mm.
Generally, muscovite grains are oriented with their elongate axes
parallel to bedding.
Micrite is dark brown-to-gray and lacks any birefringene, whereas
microspar has similar colors (although lighter) but has slightly
70
PLATE 24. Cored section of a bioturbated, muddy calcareous sandstone
(5.0 cm in diameter).
PLATE 25. Photomicrograph of a calcareous muddy sandstone.
1 cm = 0.25 mm.
71
higher birefringence. A gruraose texture is observed. Dolomite is the
least abundant matrix constituent even though it is present in nearly
all samples. Non-ferroan dolomite is characteristic of this
microfacies. Dolomite is finely disseminated through the matrix as
very fine, anhedral crystals which are approximately 0.02 mm and less
in size.
All the allochems individually comprise less than 1.0% of this
microfacies. Bryozoans (fenestrate varieties) are the most abundant,
making up 0.6%. Echinoderms, although composing only a small
percentage of this microfacies (0.3%), are present in most samples.
Allochems are generally whole and well preserved, although some are
broken and abraded.
Quartz is subrounded to subangular, moderately to well sorted and
ranges in size from 0.02 to 0.1 mm. Monocrystalline quartz is most
abundant, and most of it has an undulóse extinction. Nonferroan
calcite spar is rare, making up less than 1.0% of this microfacies.
Spar is primarily associated with siltier zones (especially burrow
structures) where it infills interpore areas.
Plant fragments are also rare, composing less than 1.0% of this
microfacies. Although plant fragments are completely pyritized, an
elongate, finely netted raicrostructure is still observable. The plant
fragments are restricted to the calcareous mudrock of the lower
(rather than the upper) Little Valley Limestone where they comprise
only a small percentage of the total rock, but they are present in
most samples.
72
The calcareous mudrock microfacies of the Little Valley Limestone
are representative of two different environments based on both
compositional and adjacent lithologic and/or microfacies differences.
The lower calcareous mudrocks are associated with the lower section
of the Little Valley Limestone, where it is interbedded with the lower
lime mudstone microfacies.
The environmental interpretation of the lower calcareous mudrock
microfacies is a shallow intertidal, mixed siliciclastic-carbonate
mudflat (Fig. 13). This environment is most similar to Wilson's
(1975) standard microfacies belts 23 and 19. The overall lack of
fauna, with the exception of smooth shelled ostracodes, and the
predominance of algal laminations suggest shallow water (within the
photic zone), restricted marine conditions ( Heckel, 1972; Wilson,
1975; and Flugel, 1982). The presence of ripple marks, interbeds of
mud and silt-sized material, dolomitic rip-up clasts (thought to be
derived from dessication features within the adjoining nearshore
supratidal environment) and plant debris are considered indicators of
coastal proximity. In this case, calcareous mudrocks were deposited
in restricted marine conditions associated with very shallow water
behind offshore sandy shoals. The combined effect of the outer sand
barrier and shallow water depths caused dissipation of both wave and
current activity and allowed for subsequent deposition of finer
grained material. Silty interlaminations represent storm deposits
where outer sands were swept landwards into the shallower, intertidal
areas. The stratigraphically adjacent lithofacies of the lower
calcareous mudrock include: 1) underlying low in te r t idal/sup ra t ida 1
1 1
1 1
' 1
OPEN MARINE 1 LOW INTERTIDAL | RESTRICTED, HIGH INTERTIDAL
TO 1
SHALLOW ¡
1 SUBTIDALJ
B’ig. 13. Location of the calcareous mudrock depositional environment.
74
deposits associated with unfossiliferous siltstones and algal-
laminated, dolomitic mudstones containing bedded evaporites; and 2)
overlying calcarous, fine grained, ripple-laminated sandstones and
siltstones representing a deeper water intertidal deposit.
The upper calcareous mudrock is associated with the upper Little
Valley Limestone and is characterized by more than twice the number of
fossil taxa and approximately half as much terrigenous silt and/or
sand-sized material as the lower mudrock. The upper calcareous
mudrock is much darker colored and contains more micrite. Conodonts
and other phosphatic-intraclasts are also found within the upper
mudrock, while plant fragments are no longer present. The upper
calcareous mudrock's stratigraphically adjacent lithofacies and/or
microfacies are also very different from these of the lower calcareous
mudrock. Underlying units, lime wackestones and lime mudstones
containing a relatively diverse stenohaline fauna are interpreted as
an innershelf, lagoonal facies. The overlying lithofacies including
lime wackestones, packstones and limited grainstones associated with a
diverse normal marine fauna, is interpreted as a subtidal, open marine
environment (at or near wave base). Based on compositional and
lithofacies environments, the upper calcareous mudrock is interpreted
to represent deeper, semi-restricted subtidal shelf environments,
similar to the lime mudstone microfacies of the upper Little Valley
Limestone. A modern analogy to this environment exists behind the
Florida reef tract in the Hawk Channel ( a localized depression in the
continental shelf) and in lows across the Great Pearl Bank of the
75
Persian Gulf (Scholle et al., 1983).
Generally, the upper calcareous mudrock is dark gray in color.
This unit also contains small localized chert nucléations which are
randomly dispersed. A single 0.5 meter unfossiliferous, black
fissile shale containing conodonts and scattered fish scales is found
interbedded with the mudrock. The deposition and preservation of this
black shale can only occur under reducing conditions, such as an
anoxic environment in which oxygenating processes have ceased
destruction of organic matter and/or iron sulfide. Oxygenated bottom
waters are caused by effective current movement, and inhibition of
this current activity causes a change in circulation of oxygenated
waters. Two possible mechanisms explaining loss of circulation
include: (1) density stratification where less dense (lower salinity)
water flows on top of more dense (higher salinity) water, thus
stopping vertical water movement and promoting the development of
anoxic bottom water conditions; (2) a topographic barrier, such as a
bar or mound, the migration of which interrupts a previously developed
circulation pattern and causes a diversion of oxygenated waters from a
particular area, which eventually stagnates. Similarly, Evans (1967)
interpreted the black shales of the Pennsylvanian-aged Heebner Shale
of Kansas and adjacent states to be a stagnated, deep-silled sea. He
recognized a submarine barrier as a stagnating device which inhibited
circulation across a portion of the mid-continent sea.
In summary, this calcareous mudrock microfacies can be subdivided
into two distinctly different environments: (1) calcareous mudrocks
of the lower Little Valley Limestone associated with marginal marine.
76
mixed siliciclastic-carbonate mud flats; and (2) calcareous raudrocks
associated with serai-restricted shelf lagoons (Plate 26).
Diagenetically this microfacies is characterized by neomorphism
of both allocheras and matrix, dolomitization of both allochems and
matrix, partial pyritization of allochems, interparticle pore areas
infilled with bladed and blocky spar, partial to complete
silicification of allochems and calcite veins.
SECONDARY GYPSUM MICROFACIES
The secondary gypsum microfacies consists of 32% matrix, 10%
nodular anhydrite and 58% secondary gypsum. The matrix is primarily
composed of dolomite (19.8%) and phyllosilicates (11.9%). Micrite is
rare (present only in one sample), composing less than 1% of this
raicrofacies. Dolomite crystals are subhedral to euhedral, contain an
idiotopic-E texture and are 0.025 mm and less in size (although rare,
some dolomite crystals range from 0.25 to 0.5 mm). Dolomite crystals
are nonferroan and considered to be a primary depositional phase.
The phyllosilicates consist of muscovite and illite. Muscovite
crystals are elongate and tabular, containing fourth order
interference colors and ranging in size from 0.03 to 0.1 mm. Illite,
with its 10 A basal spacing, was recognized through x-ray diffraction
procedures.
The evaporice minerals anhydrite (9.9%) and secondary gypsum
(58%) comprise the majority of this microfacies. Anhydrite crystals
are elongate and tabular, bedded or in nodules, exhibit fourth order
77
PLATE 26. Laminated calcareous mudrock.
78
interference colors, have pseudocubic cleavage and range in size from
0.02 to 0.06 mm. Although anhydrite is not the most abundant mineral
within this raicrofacies, it is thought to represent the original
depositional form of the evaporites. The exact origin of anhydrite
(primary or secondary) is of question (Bush, 1973; Schreiber, 1978).
Depositional characterisitics have been altered by subsequent (late
diagenesis) rehydration, thus allowing for the pervasive development
of alabastrine secondary gypsum (Holliday, 1970). The gypsum grains
are characterized by irregular extinctions, poorly defined grain
boundaries and remnant corroded anhydrite inclusions. With these
types of characteristics, the gypsum is considered to have a Type 1
hydration texture (Holliday, 1970) (Plates 27 and 28).
Environmentally this microfacies is interpreted as a high
intertidal/supratidal deposit (Fig. 14). This microfacies is most
similar to Wilson's (1975) standard microfacies 23. The nearly total
lack of biota (except for algae), together with its stratigraphic
positioning between 1) underlying red beds with much thicker and more
complete evaporites of a sabhka environment (Maccrady Formation) and
2) an overlying mixed siliciclastic carbonate mudflat lithofacies,
supply the necessary evidence for interpretation of this microfacies.
Similiarly, Presley and McGillis (1982) dolomites, evaporites and red
beds of the Clear Fork and Glorieta Formations (Permian) of the Texas
panhandle to be characteristic of nearshore and supratidal deposits
along an arid coast.
79
PLATE 27. Cored section of secondary gypsum and anhydrite
(5.0 cm in diameter).
PLATE 28. Photomicrograph of the formation of secondary gypsum
through the rehydration of anhydrite. 1 cm = 0.25 mm.
OPEN MARINE LOW INTERTIDAL | RESTRICTED, HIGH INTERTIDAL
TO I
SHALLOW I
SUBTIDALj
Fig. 14. Location of the secondary gypsum depositional environment.
DEPOSITIONAL ENVIRONMENTS
REGIONAL
The Appalachian Basin during early Meramecian time underwent a
decrease in tectonic activity corresponding to a reduction of its
eastern border lands (to lowlands) and flooding of the southern two
thirds of the basin by a sea (DeWitt and McGrew, 1979). Rising seas
entered the basin from the south and spread north along the basin axis
and northwest along the shelf areas. Although tectonic quiescence
prevailed during Meramecian time, subsidence exceeded terrigenous
detritus influx (DeWitt and McGrew, 1979). This is recognized by 1)
the sporadic occurrence of thin interbeds of shale and sandstone
within thick limestone sequences in the eastern Applachian Basin, and
2) the near absence of siliciclastic rocks in much of the shelf area
to the west.
During the Warsaw Epoch, the Meramecian sea inundated the
Greendale Syncline and surrounding areas, depositing Warsaw-aged
lithologies the full length of the syncline from northeastern
Tennessee to southwestern Virginia (Butts, 1940). Maximum water
depths during mid-Meramecian time were associated with the St. Louis
sea. The Greendale Syncline's lithofacies during the Meramecian
consisted primarily of a thick accumulation of argillaceous and sandy
carbonates derived from shallow marine shelf environments within a
subtropical to tropical (15 degrees south latitude) climate (DeWitt
and McGrew, 1979).
82
LOCAL
Based on lithologies (microfacies assemblages), biota and
sedimentary structures, the Little Valley Limestone can be subdivided
into three distinct depositional environments: (1) restricted, high
intertidal mudflats to bordering supratidal sabkha; (2) low intertidal
to shallow subtidal, siliciclastic shoal and; (3) open marine
subtidal, shelf lagoon. Figure 15 shows the stratigraphic distribution
of these environments through Washington County.
Environment 1 represents a restricted, high intertidal, mixed
siliciclastic - carbonate mudflat bordering a supratidal sabkha. It
comprises the uppermost Maccrady Formataion and the lowermost Little
Valley Limestone. This environment includes the secondary gypsum,
lower lime mudstone and lower calcareous raudrock microfacies. As
described in the previous section, these microfacies contain a
restricted biota (generally ostracodes and algae) and shallow water
sedimentary structures including ripples and horizontal to wavy
(cryptalgal) laminations. Intermittent subaerial exposure occurred,
as evidenced by dessication cracks and associated dolomitic rip-up
clasts. Mineralogically, these microfacies have a high percentage of
phyllosilicate muds, idiotopic-E and-P dolomite, secondary gypsum and
primary anhydrite.
The feature causing restriction for this environment is
considered to be either an offshore siliciclastic bar or shoal
associated with the destructive phase (inundation) of the pre-
existing Virginia-Carolina deltaic complex. This shoal, a topographic
high on a very shallow, broad shelf aided wave and current
1
90
IM) ^
ol- ? —
0 LC
IKM)
RESTRICTED. HIGH INTERTIDAL
LOW INTERTIDAL TO SHALLOW SUBTIOAL
OPEN MARINE
00
U)
Fig. 15. Stratigraphic cross section of the depositional environments of
the Little Valley Limestone through Washington County, Virginia.
84
dissipation. The decrease in water circulation caused by the shoal
created low oxygen and nutrient concentrations within waters of the
mudflat area. Therefore, the biota included only groups able to exist
in stagnating water conditions. With continued restriction in back
bar/shoal areas, hypersaline waters developed through evaporation and
concentration of brines. When brines reached sufficiently high
concentrations, anhydrite and gypsum precipitation occurred with
anhydrite being the initial depositional form of evaporite.
Precipitation of anhydrite occurred in thin beds and nodules, whereas
gypsum occurred as small (0.1 to 0.5 cm) lensoid crystals, both of
which are common in intertidal to supratidal evaporites similar to
those of the Persian Gulf (Schreiber, 1978; Achauer, 1982). The
evaporites were interbedded within algal-laminated, dolomitic,
siliciclastic muds. Farther offshore, evaporites are replaced by
interbedded lime mudstones and calcareous mudrocks. These lithofacies
frequently contain thin (2.0 - 3.0 cm) silty beds suggestive of
overwash of the outer shoal (barrier) area by storm surges that swept
coarser grained siliciclastic material inland.
Environment 2, low intertidal to shallow subtidal, comprises the
higher energy siliciclastic shoals and/or bar associated with the
reworking of the Virginia - Carolina deltaic complex. Similar
destructive deltaic morphologic features are described by Reading
( 1978) for the Nile and Ebro deltas. This environment includes the
muddy calcareous sandstone and upper calcareous mudrock microfacies.
These raicrofacies contain ooids, intraclasts and vertical burrows and
85
are characterized by a lack of skeletal debris. Ripple marks and
cross-bedding are very abundant within these microfacies.
The subdivision of the marine shoal environment into two distinct
raicrofacies signifies varying environmental conditions associated with
1) interbedded, relatively clean quartz sands and 2) phyllosilicate
muds. This is thought to represent undulating shoal-surface
topography where sands represent topographic highs subject to more
turbulent water, while muds represent topographic lows in low energy
water. Shoal migration is evidenced by the interbedded nature of
these microfacies. Enos (1983) described similar microfacies
relationships within shelf-intertidal shoals of Florida and Texas.
Additional evidence for a shoaling environment includes
lithologies and sedimentary structures present in these microfacies.
The calcareous sandstones are composed primarily of quartz grains
which are moderate to well sorted, subrounded, ripple-laminated and
cross-bedded. They represent bar crests and/or areas influenced by
higher energy conditions. Ooids, although not very abundant in this
microfacies, suggest shallow, agitated marine waters. Ooid formation
in this environment was probably inhibited by conditions not conducive
to for carbonate formation (high siliciclastic conditions). In
contrast to the calcareous sandstones, calcareous mudrocks primarily
are composed of rippled phyllosilicate muds associated with troughs or
low energy areas (between the cleaner quartz sands). Within
interlarainated terrigenous sand and mud zones bioturbation is
extensive, dominated by vertical burrows which are generally
associated with higher energy environments. Shoal-trough muds
86
contain the highest percentage of fossilized material, including
brachiopods, echinoderms, ostracodes and plant fragments, although
the overall fauna is sparse. This siliciclastic marine shoal aided in
the formation of restricted landward intertidal environments landward
and trapped most of the sand- and silt-sized terrigenous grains.
Suspended terrigenous muds, however, escaped into the offshore marine
environments. Offshore of the siliciclastic shoal are lime-
grainstones, packstones, wackestones and mudstones of more open marine
origin.
Environment 3 is an open marine subtidal shelf which contains
shelf lagoons. This environment includes the following microfacies:
upper lime mudstone, upper calcareous raudrock, lime— wackestone,
packstone and grainstone. The biota within this environment,
although overall very abundant, is predominantly comprised of a
variety of stenohaline organisms. These assemblages have become
progressively more diverse from Environment 1 to 3 where brachiopods,
bryozoans, and echinoderms predominate and bivalves, corals,
foraminifers, stromatolitic algae (LLH) and conodonts are locally
present. The water was normal marine with effective wave or current
activity supplying sufficient oxygen and nutrients to support a
diverse biota.
The seaward progression of microfacies upward from Environment 2
begins with lime- grainstone to packstone and interbedded lime-
wackestone and mudstone raicrofacies. The lime grainstone and lime
packstone microfacies represent carbonate environments at or just
87
below wave base (carbonate shoal) where fines were winnowed and sand
or larger bioclasts were concentrated. Bryozoans and echinoderms are
common to the lime grainstone and packstone microfacies due to their
need for a stable substrate and vigorous water circulation.
Interbedded lime wackestones, lime mudstone and calcareous mudrock
microfacies are interpreted to be deposits formed on an undulating
shelf topography where relatively unfossiliferous lime mudstones were
deposited in low areas across the shelf, while lime wackestone
microfacies represent normal marine shelf areas. Lime mudstones and
calcareous mudrocks were deposited in shelf lagoons restricted by
water depth, which caused poor water circulation and stagnation of
the environment. This is reflected in its darker color and restricted
biotic assemblage, which is characterized by a small percentage of
bivalves, brachiopods and ostracodes. The more normal marine lime
wackestone microfacies developed on mid-shelf areas within well
oxygenated and nutrient rich waters associated with current activity.
Therefore, it has a more diverse fauna, including abundant
brachiopods, bryozoans and echinoderms, with localized occurrences of
coral communities, foraminifers and stromatolitic algae. Similar
microfacies environmental determinations were made by Scholle et al.
(1983) for the Florida reef tractwhere a broad, shallow-shelf, marine
environment exists.
In conclusion, the overall lithologic and environmental
progression from restricted, high intertidal mudflats bordering a
supratidal sabkha to low intertidal or shallow subtidal siliciclastic
shoals to more open marine subtidal, mid-shelf environments is
88
representative of a marine transgression (Fig. 16). This
transgressive event had a direct effect on the predominant fauna and
the relative percent of terrigenous grains (insoluble residues)
throughout the Little Valley Limestone. As seen in Figure 17
(enclosed in pocket), the abundance of the predominate fauna
fluctuates locally in response to terrigenous influx and increases
overall towards the top of the Formation. The Little Valley Limestone
represents a mixed carbonate-silieiclastic formation bordering the
destructive phase of the Virginia - Carolina delta (involving the
Price and Maccrady Formations) at its base and a normal marine shelf
environment at its top.
89
model of DEPOSITIONAL ^NVf^ONMENTS
OPEN S08TDAL.
with lagoons
LOW INTERTIDAL TO SHAL
SUBTOAL, SILlCiCLASTlC St-
Bordering
SUPRATIDAL sabkma
Fig. 16. Sequential depositional model for the Little
Valley Limestone.
DIAGENETIC PROCESSES AND THEIR ENVIRONMENTS OF FORMATION
INTRODUCTION
Diagenesis includes all physical, chemical and biological
variations, excluding weathering and raetaraorphism, occurring in
sediments after initial deposition. Carbonate rocks may undergo
constructive (carbonate aggradation) and/or destructive (carbonate
degradation) diagenetic changes. The most common is constructive
diagenesis associated with cementation or lithification of the
carbonate sediments. Many factors influence the rate and/or extent of
alteration in carbonates. The primary factors include: time,
temperature, depth of burial, sedimentary composition, porosity,
permeability, tectonic terrain and environment of deposition. Because
of the complexity of the factors controlling diagenetic alterations,
the sequence and environment of these alterations is difficult and
sometimes impossible to determine. Where possible, the following
discussion will position diagenetic events in a sequential order
(early to late) with respect to their depositional environments (Fig.
18).
MICRITE ENVELOPES
Micritization of allochems is an early diagenetic event
associated with microbiotic borings that result in the formation of
micritic envelopes. Micrite envelopes develop within shallow marine
waters at or near the sediment-water interface (Bathurst, 1975 and
Flugel, 1982). Micro-organisms that bore include endolithic blue
green, green and red algae, fungi and lichens that catalyze the
EARLY LATE
Fig. 18. Diagenetic environments of the Little Valley Limestone.
92
inorganic precipitation of calcium carbonate through physiologic
activity, thereby infilling the microborings with unoriented micrite
(Schneider, 1977). Microborings, usually centripetally oriented,
consist of straight to curved tubes ranging in size from less than 1
micron to 50 microns. They are oriented perpendicular to the
carbonate particle surface. Micrite, according to Schneider,
precipitates as aragonite with a magnesium/calciura ratio greater than
1.0. Microbiota create micrite envelopes relatively quickly, such
that envelopes approximately 500 microns thick can be bored in
approximately one year (Flugel, 1982). If uninhibited, the
microboring organisms can completely micritize a carbonate particle,
destroying all or most of the grain's m i crostructura 1
character!si tics.
Within the Little Valley Limestone micrite envelopes are present
in higher energy, shoaling environments encompassing lime- packstone
and grainstone microfacies. Micrite envelopes are found on most
varieties of allochems, some of which are subrounded particles
referred to as cortiods. According to Kendall and Skipwith (1969),
extensive raicritization of an allochem accelerates its susceptibility
to rounding by weakening and loosening the carbonate around its outer
boundary. Foraminifers undergo complete m i critiza11on which
obliterates their microstructural characteristics, but they do retain
their overall test morphology. Micrite envelopes are resistant to
recrystallization, such that they remain microcrystalline while
associated allochems undergo complete recrystallization.
93
CALCITE STABILIZATION
Most allochems and carbonate matrix that formed before the
Tertiary Period are considered to have a magnesium calcite composition
(Loreau, 1979), although some aragonitic allochems and matrix did
occur. Magnesium calcite is differentiated from calcite based upon
its mole percent magnesium which ranges from 4 to 20 (Flugel, 1982).
High magnesium calcite stability fluctuates with changes in
environment, such that it is stable under normal marine conditions
(marine photic zone), but it is unstable in meteoritic or freshwater
(fresh phreatic zone). Unless subjected to well circulating mixing
zone conditions and/or high magnesium concentrated fluids, magnesium
calcite will neomorphose to low magnesium calcite by expelling
magenesium ions (Bathurst, 1975). Magnesium calcite stabilization
occurs by exsolution of magnesium ions to form calcite or by
absorption to form dolomite. According to Longman (1977), to produce
a 30% dolomite, it takes a minimum of several thousand pore volumes of
mixed marine-fresh water to pass through the carbonate sediment.
Within the Little Valley Limestone, calcite stabilization is not
restricted to a particular environment, but it is considered an early
diagenetic feature. The most prominent components having initially
high-magnesium calcite compositions include: micritic envelopes,
echinoderms, ooids, algae and some foraminifera. All of the above
allochems retained their original microstructural characteristics
after neomorphism from magnesium calcite to calcite. However,
localized dolomite nucléations did occur on echinoderm grains.
94
Magnesium calcite muds of the matrix (commonly associated with
terrigenous clays) probably stabilized to low magnesium calci te by
absorption of their excess magnesium by existing clays, Clay
participation in calcite stabilization is thought to be most
significant.
MICROSPAR
Microspar, formed by the aggradational neomorphism of micrite and/or
neomorphic calcitization of aragonite, is characterized by calcite
crystals ranging from 5 to 10 microns in size. According to Folk
(1973, 1974), microspar forms in normal marine conditions from micrite
which was originally composed of high magnesium calcite or aragonite.
Upon burial and diagenesis, the unstable high magnesium calcite and
aragonite expel magnesium ions and invert to a more stable low
magnesium calcite phase (Longman, 1977). Longman also emphasized that
most expelled magnesium ions from the micrite attach to the surfaces
of the now low magnesium calcite crystals. Magnesium, an impeder of
calcite growth, must be removed before the production of raicrospar can
occur. Magnesium ions can be removed from the microcrystalline
calcite by (1) clay absorption, (2) dolomitization and (3) freshwater
movement (associated with high porosities and permeabilities)
(Longman, 1977).
The second process of microspar formation involves the direct
neomorphic calcitization of aragonite to microspar without a micrite
precursor (Laserai and Sandberg, 1984). This process of microspar
formation
95
was recognized by Laserai and Sandberg (1984) through scanning electron
microscopy, which revealed consistent numbers of relic aragonite
crystals in all crystal sizes of neomorphic calcite. According to
Lasemi and Sandberg (1984), the similar amounts of aragonite relics in
various sized neomorphic calcite crystals proves that aggradational
neomorphism does not exclusively form by solution-reprecipitation
(since this process causes a large reduction in the abundance of
aragonite crystals).
The reason for the pervasive occurrence of raicrospar within the
Little Valley Limestone, whether aggradational neomorphism or
neomorphic calcitization of aragonite, is unknown. If raicrospar is
aggradational, then it is thought to be primarily controlled by the
abundance of terrigenous clays in close association with the
carbonate muds. Chlorite, one of the dominant clays within the Little
Valley Limestone, has been recognized by Longman (1977) as a magnesium
ion "sump". The presence of chlorite, therefore, is very effective in
removing the inhibiting magnesium ions from microcrystalline calcite
crystals. Finely disseminated dolomite within the matrix also
influenced microspar development. Freshwater movement within the
Ste. Genevieve Limestone, as described by Choquette and Steinen
(1980), similarly affected raicrospar production within the Little
Valley Limestone. Microspar formation must have been early since
porosities and permeabilities needed for the transportation of
freshwater would have been greatly reduced by cementation and the high
degree of compaction associated with late burial.
96
Environmentally, raicrospar is ubiquitous in all depositional
environments, although it was more prominent in lower energy subtidal
shelf areas. Microspar is primarily associated with the lime-
mudstone, wackestone and calcareous mudrock microfacies.
ARAGONITE
Aragonite is a polymorphic phase of calcite having an
orthorhombic crystal system and a very low magnesium content (less
than 5000 ppm). Aragonite's stability field ranges from 25 degrees C
at 4 kb pressure to a lower limit of 600 degrees at 14 kb pressure
(Clark, 1957). The lower symmetry of aragonite in comparison to pure
calcite causes aragonite's much higher solubility, but aragonite in
shallow normal marine water is less soluble than magnesium calcite
(Bathhurst, 1975). Three prominent types of alteration of aragonite
occur due to its high susceptibility for reaction and its unstable
nature: (1) polymorphic inversion, (2) dissolution and (3)
replacement (Folk, 1974 and Lasemi and Sandberg, 1984). Aragonite's
polymorphic inversion to calcite is characterized by retention of its
original composition and a modification of its original crystal
structure (from orthorhombic to rhombohedral). Complete dissolution
of an aragonitic allochem creates moldic porosity (as long as a mold
of the particle was made before dissolution), usually infilled by
sparry calcite. Replacement of aragonite with another mineral of
different composition can occur. Dolomite, calcite, silica and pyrite
are the most common replacement minerals.
Environmentally, aragonite within the Little Valley Limestone was
97
most common to the subtidal shallow shelf where lime- mudstone and
wackestone prevail. This environment is characterized by the highest
percentage of mud sized material (micrite/microspar) and contains
possible aragonitic fossils.
The two most common aragonitic fossils include bivalves and
gastropods. Bivalves are commonly replaced by blocky spar crystals
which obliterate most of their original structure, although their
outer prismatic calcitic layer is generally preserved. Gastropods
are always entirely replaced by blocky spar, thus retaining no
microstructural characteristics. Both of these allochems were
probably diagenetically altered by both polymorphic inversion and
dissolution.
SYNTAXIAL OVERGROWTHS
Syntaxial cements most commonly form on echinoderm fragments in
the active fresh water phreatic zone where they are associated with
very rapid growth rates (Longman, 1980). The high rate of syntaxial
cement growth associated with echinoderm fragments is evidenced by the
large amount of interparticle pore space incorporated by syntaxial
cements in comparison to adjacent cements (bladed and/or blocky
calcite spar) associated with other types of allochems. The large
calcite crystal (echinoderm grain) on which the overgrowth nucleates
also aids in cement development. Although syntaxial overgrowths are
most common to the fresh phreatic zone, they rarely occur in the fresh
vadose and later deeper diagenetic environments. However, syntaxial
overgrowths on echinoderms occur only very rarely, if at all, in
98
marine phreatic zones. Instead, fibrous aragonite or magnesium calcite
form (Longman, 1980).
Syntaxial overgrowths are restricted to lime grainstone
microfacies of the carbonate shoal environment, and are commonly
associated with fresh water phreatic cements. Other fresh phreatic
cements include bladed and blocky spar which coarsen towards the
center of the pore.
BLADED AND BLOCKY SPAR
Bladed and blocky spar are early diagenetic cements which are
most common to an active fresh water phreatic environment. These
types of spar cement are associated with lime- grainstone and
packstone microfacies of the shallow subtidal shelf (at or near wave
base). Blocky ferroan calcite is diagnostic of a fresh water phreatic
environment due to the low interstitial Eh conditions (Flugel, 1982).
Correspondingly, Longman (1980) suggested that abundant, equant and
isopachous bladed calcite cements occurring as interlocking crystals
which coarsen towards pore center are characteristic of early
diagenesis within a fresh water phreatic environment.
Active fresh water phreatic and/or deep connate water
environments associated with bladed and blocky equant spar cements
must have magnesium to calcite ratios below 2 to 1, and optimally
between the 1 to 10 and 1 to 2 (Folk, 1974). Deeper connate water
systems contain waters of marine origin characterized by low magnesium
calcite ratios (1 to 2 through 1 to 4) due to magnesium ion removal by
clay minerals and by the formation of dolomite (Folk, 1974; Bathurst,
99
1975; Flugel, 1982). Following the removal of magnesium ions (calcite
growth inhibitors), sparry calcite will be allowed to precipitate.
FRAMBOIDAL PYRITE
Pyrite authigenically forms in marine environments during early
diagenesis of organic rich, anoxic sediments. The key components for
pyrite formation are hydrogen sulfide, which is derived from bacterial
reduction of dissolved sulfate through decomposition of organic
matter, and free iron (Blatt et al., 1972). Although the
compositional origin of pyrite is understood, much controversy
(Schneiderhohn, 1923 and Love, 1957) arose over the origin of
framboidal texture. Love and Schneiderhohn originally suspected a
biogenic origin in which the framboid represents fossilized micro-
organisms. Further studies disproved this hypothesis. Berner
(1970), through laboratory experimentation, inorganically synthesized
framboidal pyrite at low temperatures (65 degress C) and at a neutral
pH (7.8). Berner concluded that elemental sulfur is required for the
formation of pyrite if organic matter and micro-organisms are absent.
Pyrite framboids of the Little Valley Limestone are common
throughout all microfacies, although they are most abundant in darker
lime mudstones and calcareous mudrocks of the deeper subtidal shelf
lagoons. Lime wackestone and packstone microfacies associated with
high organic productivity commonly have pyrite infillings in sheltered
pore spaces under convex upward allocheras. This probably occurs due
to trapping of hydrogen sulfide gases and/or volatile organic matter
(undergoing decomposition) which is later converted to pyrite by
100
exposure to ferrous ions.
DOLOMITE
Dolomite found in the Little Valley Limestone is considered to
have been formed both early and late in its diagenetic history. The
timing of dolomite formation is reflected by the crystal morphology of
the dolomite. According to Gregg and Sibley (1984), dolomite which
crystallizes below the "critical roughing temperature" (CRT, a
theoretical temperature) forms smooth euhedral dolomite crystals, and
dolomite crystallizing above the CRT favors the formation of rough
anhedral crystals. Through experimentation, they determined the CRT
to lie between 50 and 100 degrees C. Therefore, euhedral, idiotopic
textures characterized by slow atomic building of the dolomite
crystal, which creates smooth crystal faces are associated with
surface or near surface conditions. Conversely, anhedral, xenotopic
dolomite textures involving random addition of atoms to the dolomite
crystal faces occurs in deeper subsurface conditions (Jackson, 1958
and Gregg and Sibley, 1984).
Two major textural types of dolomite occur in the Little Valley
Limestone: (1) idiotopic-E and -P (diagenetically early dolomite) of
the lower Little Valley Limestone and (2) xenotopic-P and -A
(diagenetically late dolomite) of the upper Little Valley Limestone.
The lower section of the Little Valley Limestone was subjected to
lower temperature dolomite crystallization characteristic of early
diagenesis, similar to that described by Purser and Evans (1973) in
the sabkhas of the Persian Gulf. This dolomite most likely
101
precipitated as a calcium-rich phase of dolomite (protodolomite) from
hypersaline waters by elevation of the magnesium calcite ratios
corresponding to gypsum and/or anhydrite (Tucker, 1981). Later
neomorphic processes allowed stabilization of the calcium rich
protodolomite to a more stoichiometric phase without destroying the
original rhombohedral crystal form (Lumsden and Chimahsky, 1980).
The upper section of the Little Valley Limestone was subjected to
high temperature that produced dolomite crystal textures thought to be
indicative of late stage diagenesis. Two plausible models for late
stage dolomitization are considered. The first is localized high
magnesium pore fluids created by neomorphic aggradation of micrite to
microspar, which not only draws calcium from the pore waters but also
releases magnesium ions into it (Longman, 1977). Thus, localized
dolomite nucléations as well as more extensive doloraitization are
confined to more porous and permeable zones usually containing
terrigenous silt and sand. Within the lime- mudstone and wackestone
microfacies of the upper Little Valley Limestone dolomitization
frequently occurs in close proximity to zones or thin beds of quartz
silt. Similarly, Choquette and Steinen's (1980) investigation of
dolomitization within the Ste. Genevieve Limestone of the Illinois
Basin revealeded lime mudstone sequences overlain by carbonate sands
which have gradational dolomitization trends that lessen with distance
from the contact. They also recognized extensive dolomitization
associated with silty burrows within lime mudstones. The second
doloraitizing model involves formation water movements which are
capable of dolomitization when they have a molar calcium/magnesium
102
ratio of less than 15 and a temperature of approximately 300 degrees C
(Land, 1980). Therefore, late stage diagenetic alteration can occur
by infiltration of hydrothermal fluids into more porous and permeable
zones, causing dissolution and/or replacement of the calcite crystals
(more soluable than dolomite at higher temperatures) by dolomite
(Land, 1980). Evidence within the Little Valley Limestone for this
hydrothermal dolomitizing model are calcite veins which contain
dolomite in their centers.
Dolomitization within the Little Valley Limestone occurs in most
microfacies (independent of depositional environment), although
dolomite within the lower portion of the Formation corresponds to the
low intertidal-supratidal depositional environments.
SILICIFICATION
In some form, silicification occurs throughout the Little Valley
Limestone. Silica can be derived from either organic or inorganic
sources. Organic sources of silica have been considered the most
common to marine environments and include sponges, radiolarians,
[diatoras, silicoflagellate0 and some terrestrial plant materials
(Williams and Creror, 1985). However, inorganic sources also occur,
primarily from the diagenesis of phyllo- and tecktosilicates. The
primary source of silica within the Little Valley Limestone is thought
to be inorganic. The lack of evidence of siliceous organic material
and the high concentrations of both phyllo- and tecktosilicates
support this interpretation. The relatively close association of
siliciclastic material with carbonate material (matrix and allochems)
103
allows for an i n t r a f o r tna t i o na 1 source of silica, although
extraforraational silica solutions are locally significant in the
formation of chert nodules. The diagenesis of phyllosilicates (mainly
montmori11inite to illite) and tecktosilicicates with pressure
solution, dissolution of feldspar (Smale, 1973; Tucker, 1981) and the
transformation of feldspar to kaolinite provide sources of
intraformational silica (Tucker, 1981). Clay minerals may also supply
silica by the leaching of magnesium ions and absorption of hydrogen
ions, resulting in an increase of pH of the solution. This creates an
alkaline halo around clays which, then dissolve quartz grains in
contact with them (Thompson, 1959). Solutions which are highly
oxidizing (pH of 9-10) can dissolve silica in the form of chert and
quartz. In thin section, the boundaries of quartz and feldspar grains
are highly pitted and sharp, which is suggestive of dissolution.
According to Meyers and James (1978), varying forms of silica are
associated with groundwater which is initially saturated with silica
(greater than 125 ppm). Precipitation of opal CT in micropores of
matrix and allochems allows the solution to become lower in silica
concentrations (25 to 125 ppm), permitting micro- and mega-quartz to
precipitate. The recrystallization of the unstable opal CT forms
microquartz varieties (chert and chacedony). Likewise, groundwaters
permeating the lower siliciclastic zones (source of silica) within the
Little Valley Limestone are thought to have permeated along
fossi1iferous zones where porosities allowed for complete
silicification of both matrix and allochems. The time of diagenesis
104
is considered late since adequate amounts of silica derived from
inorganic sources require higher temperatures and pressures for
increased solubility of silica. No substantial correlations between
silicification and depositional environment were noted.
SECONDARY GYPSUM
Secondary gypsum occurs through the hydration of original
anhydrite. According to Hardie (1967), three main hydration
mechanisms allow diagenetic alteration of anhydrite to secondary
gypsum: (1) solution-precipitation, (2) direct hydration by the
addition of structural water and (3) stepwise hydration through the
formation of the intermediate sulfate mineral bassinate. Mechanisms 1
and 2 are most favorable for the hydration of the anhydrite within the
Little Valley Limestone. Mechanism 1 is associated with the
dissolution and hydration of calcium sulfate, and its later
precipitation as a hydrated calcium sulfate in the form of subhedral
to anhedral, porphyroblastic secondary gypsum. The transformation of
anhydrite to secondary gypsum is associated with a considerable
increase in volume due to the larger unit cell of gypsum. Therefore,
by mechanism 1, volume equilibrium is maintained by the reraobilization
of some of the hydrated calcium sulfate in the form of satin spar.
Mechanism 2 involves situ incorporation of water into the calcium
sulfate structure to form an alabastrine gypsum.
Within the Little Valley Limestone secondary gypsum is restricted
to high intertidal-supratidal environments. Within this environment
evaporation was sufficient for brine concentrations to precipitate
105
anhydrate and gypsum. Secondary gypsum comprises its own microfacies,
although it is also associated with lower Little Valley calcareous
raudrocks,
VEINS
Veins are found within all environments of the Little Valley
Limestone where they have various sizes, orientations and interstitial
mineralogies. Calcite veins are generally more abundant in lime-
packstones and grainstones as compared to calcareous mudstones and
lime wackestones of the upper Little Valley Limestone. However,
gypsum veins commonly dissect dolomitic mudstones and gypsiferous
mudstones of the lower Little Valley Limestone. Overall, the veins
cut obliquely across bedding and through allocheras and other
diagenetic textures, except well developed stylolites. Veins range in
size from 0.5 to 2.0 cm in maximum thickness and can mineralogically
contain the following associations: (1) calcitic blocky spar, (2)
calcitic blocky spar with dolomite in its center, (3) calcite with
pryite in its center and (4) gypsum in the form of satin spar. The
most prominent vein mineralogy is blocky or drusy calcite. The
calcitic fluids develop from dissolution and/or pressure solution of
carbonate rocks (includes allocheras, matrix and cements) during
compaction. Interstitial waters (connate waters) transport the
highly calcitic fluid through fractures or planes of weakness derived
from tectonism, precipitating equant calcite spar upon reaching
supersaturation. Calcitic veins associated with dolomite in the
center are primarily caused by two different mechanisms. The first
106
involves depletion of calcium in the vein solution, thus allowing
super-saturation of magnesium ions with respect to cations and
precipitation of dolomite as the last phase within the vein. The
second mechanism involves the precipitation of two different
generations of vein infill. Pyrite, also associated with the centers
of sparry calcite veins, is interpreted as hydrocarbon mobilization
through open pore areas inhibiting spar growth and allowing
precipitation of pyrite in open pore spaces. The last type of vein
mineralogy is satin spar gypsum, which occurs due to the hydration and
remobilization of the lower anhydrite beds. The gypsum veins form
from the excess sulfate removed in solution during gypsification
and/or tectonism (Plate 29).
STYLOLITES
Stylolites are thin solution seams produced in carbonate rocks
due to overburden or tectonic pressure. The irregular morphologic
pattern of solution seams is attributed to discontinuities in particle
strength. Therefore, dissolution seams incorporate most calcite
grains and matrix and concentrate less soluble material such as
dolomite, opaques, quartz, phyllosilicates and ferrous oxides along
their boundaries. The black opaque materials lining stylolites are
insoluble residues which include a mixture of clay minerals and
organic matter (Tucker, 1981). Stylolites may occur early (before
cementation) or late (cutting across all other diagenetic fabrics).
Tectonic stylolites develop normal to stress and commonly cut across
and displace diagenetically late stylolites (Purser, 1978). Flugel
107
PLATE 29. Photomicrograph of a satin spar gypsum vein (1.5 mm
in width).
108
(1982) subdivide stylolites into two classes based on stylolitic
amplitudes: (1) aggregate stylolites, characterized by amplitudes
greater than the grain diameters of the host rock; and (2)
intergranular stylolites with amplitudes less than the grain diameter
of the host rock. Stylolites also have varying patterns due to
discontinuities within host.rocks. Stylolites may be columnar,
irregular, hummocky, etc., and configurations or sets of stylolites
may be arranged in parallel sets, conjugate sets, anastomosing sets,
etc.
Within the Little Valley Limestone discontinuous, aggregate, and
irregular to hummocky individual stylolites are most common, although
irregular anastomosing sets occur rarely. These solution seams
commonly contain pyrite, dolomite, allochems, quartz grains and opaque
films concentrated along their borders. Stylolites within this
formation are diagenetically late since they cut across all other
diagenetic fabrics except for calcite veins. They have no particular
environmental correlations.
MICROFAULTS
Microfaults are limited to the lime mudstones of the lower Little
Valley Limestone. They occur due to the remobilization of evaporite
minerals, mainly gypsum, underneath the overlying lime mudstones
and/or by tectonic movements. Remobilization of the evaporites (by
density differential flowage and/or by dissolution from groundwater
movement) causes voids to develop into which overlying material (lime
mudstones in this case) collapses, resulting in the development of
109
collapse breccias and inicrof aul ting (Goldstein and Collins, 1984).
Tectonic evidence for microfaulting within this unit is the close
proximity of microfaulted intervals to the Saltville fault décollement
zone within the upper portion of the Maccrady Formation. The
microfaults characteristic to the lower Little Valley lime mudstones
have displacements ranging from 0.25 mm to 1.25 mm. Nonferroan sparry
calcite commonly infills between fault surfaces.
lio
SUMMARY OF CONCLUSIONS
1) The Little Valley Limestone is an Upper Mississippian natural gas
producing, " mixed"-composition, transitional unit lying
stratigraphically between underlying predominantly terrigenous
lithologies including the Price and Maccrady Formations and overlying
predominantly carbonate lithologies encompassing the remainder of the
Greenbrier Group.
2) Seven microfacies are discernable from the Little Valley
Limestone. They are: lime- mudstone, wackestone, packstone,
grainstone, calcareous and muddy sandstone, calcareous mudrock and
secondary gypsum. The combination and stratigraphic pattern of these
microfacies allowed for identification of depositional environments.
3) The depositional environments of the Little Valley Limestone as
interpreted from its microfacies, represent a marine transgression
proceeding from a restricted, high intertidal mudflat or bordering
sabkha to a low intertidal-shallow subtidal, siliciclastic shoal,both
containing a paucity of fauna, to an open marine subtidal shelf with
shelf lagoons containing a diverse stenohaline fauna.
4) The Little Valley Limestone represents the initial marine
inundation of the Virginia-Carolina delta complex during a period of
tectonic quiesence. Sedimentation was characterized by mixed
carbonate-siliciclastic deposition.
Ill
5) Various types of diagenetic alteration occured in the Little
Valley Limestone and, to some degree, were controlled by the high
concentration of siliciclastic components, the depth of burial and
tectonism. Most of the gypsum in this unit is a secondary rehydration
phase formed from an anhydrite precursor. Because of the complexity
of diagenetic overprinting the sequence and environments of diagenetic'
alteration are extremely difficult to decipher.
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APPENDIX A MEASURED SECTIONS
FROM OUTCROP AND CORE
120
Hillsdale Formation D£PTH (m«Mr«)
1: 1 D.W. Dorton sample log with gamma rav log
(provided by Bartlett Energy) .
121
Price Fm.
2: Outcrop at Horseshoe Bend.
122
OUTCRCP AND (DRE DESCIIIPTIONS
2: HSB - Sançiles from Horse Shoe Bend
Sanple No. Descriptions Thickness (Inters )
F lime nudstone, fine grained, rasdium bedded,
slightly friable, brachiopods show on weathered
surface, fresh surface is a medium light gray
(N6) weathering to a light gray (N7). 1.8
E Packstone, fine grained, thinly bedded, dense,
crinoids show on weathered surface, fresh surface
is a medium dark gray (N4) weathering to a medium
gray (N5). 0.5
B, C, D Line nudstone, very fine grained, medium bedded,
friable, no fossils seen, fresh surface is an olive
gr^ (5Y 4/1) weathering to a light olive gray
(5Y 6/1). 4.6
A lime nudstone, fine grained, mediun bedded, dense,
brachiopods show on weathered surface, fresh
surface is a medium gray (N5) weathering to a light
olive gray (5Y 6/1). 1.5
Hillsdale Fm.
123
Road cut Highway 19.
124
OUICRœ AND OORE DESCRIPTIONS
3: LVL- samples from Highway 19
SampleNo. Description Thickness (meters)
20L lime Mudstone, fine grained, medium bedded, dense,
contains small laminations of silt sized quartz
grains, fresh surface is medium dark gray (ÎH+)
weathering yellowish gr^ (5Y 7/2). 1.2
20E, 20E1 Calcareous sandstones, very fine grained, medium
bedded, contains small tangential cross-beds,
fresh surface is light gray (N-7) weathering
to a yellowish gray (5Y 7/2). 2.4
20D Ifeckestone, fine to medium, bedded, contains
contains brachiopods and crinoids, fresh
surface is a dark, gray (N3) weathering to a
light olive gray (5Y 5/2). 1.8
20M Packstone, fine to lœdium grained, medium
bedded, crinoids on weathered surface.
Fresh surface is medium dark gray (N4)
weathering to a olive gray (5Y 4/1). 1.2
20S Wackestone, fine to medium grained, medium
bedded, wdth medium dark gray (N4) bedded and
nodular silicified zones, contains brachiopods,
bryozoans and echinoderras, fresh surface is
dark gray(N3) weathering to medium gray (N5). 3X)
20T Packstone, fine to medium grained, tædium
bedded, brachiopods and echinoderras exposed
on weathered surface, fresh surface is
brownish gray (5YR 4/1) weathering to a light
brownish gray (5YR 6/1). 1.8
19T, 19A lime nudstone, fine to medium grained, fissile
and friable, brachiopods and bryozoans show on
weathered surface, fresh surface medium dark gray
(N4) weathering to an olive gray (5Y 4/1). 3.4
18D, 18E, 18F Packstone, fine to lœdiim grained, interbedded
18G, 18H dense mid friable units, brachiopods, bryozoans
and crinoids show on weathered surface, fresh
surface medium dark gray (N4) weathering to a
tædium gray (N5). 7.9
125
SampleNo. Description Thickness (meters)
17Y, 17A, 17C lime nudstone, very fine to medium grained,
16A, 16B, 16C thinly interbedded, friable and dense units,
161, 16D brachiopods and bryozoans show on weathered
surface, fresh surface is a medium dark gray
(N4), weathering to an olive gray (5Y 4/1). 15.9
15 Calcareous sandstone, fine grained, veil
rounded and sorted grains, nedium bedded, fresh
surface is a very light gray weathering to a
moderate yellowish brown (10 YR 5/4). 1.5
14E, 14F, 14G Lime nudstone, very fine grained, thin to
medium bedded, highly friable, possible algal
laminations, fresh surface is a medium dark
gray weathers to a medium light gray (N6). 4.3
14D lime nudstone, fine to medium grained, medium
bedded, dense, localized zones of silicification,
fresh surface is a dark gray (N3) weathering to
a light olive gray (5Y 6/1). 0.6
14B, 14C, Packstone, fine to medium grained, medium bedded,
moderately friable crinoid and brachiop>ods show
on weathered surface, disrupted laminations, fresh
surface is a medium dark gray (N4) weathering to
a light olive gray (5Y 6/1). 1.8
14A Lime nudstone, very fine grained, medium bedded,
highly friable, fresh surface is an olive gray
(5Y 4/1) weathering to a medium light gray (N6). 1.5
14T Grainstone, fine to nEdium grained, medium bedded,
dense brachiopods and crinoids show on weathered
surface, fresh surface is a pale brown (5YR 5/2)
weatherging to a light olive gray (5Y 6/1). 1.8
13A, 13B, 13C Line nudstone, fine to medium grained, fissile
at top grading to a more dense nedium bedded
unit at its base, contains zones of brachiopods,
fresh surface medium dark gray (N4) weathering to
medium light gray (N6). 6.1
12T, 12R, 12C line nudstone, very fine to fine grained, nedium
IID bedded, very friable, contains rippled laminations,
fresh surface is a nedium gray (N5), weathering to
a nedium light gray. 77..00
126
Sample No. Descriptions Thickness (Meters)
lie Lime nudstone, fine grained, tædium bedded, algal
laminations, friable, fresh surface is medium dark
gray weathering to an olive gr^ (5Y 4/1). 1.5
IIB Lime nudstone, very fine grained, thinly bedded,
fresh surface is moderate greenish gr^ (5G 6/1)
tæathering to a medium light gray. 1.5
IIT Wackestone, fine to medium grained, medium bedded,
bryozoan and brachiopods show on weathered surface,
fresh surface is medium dark gr^ (N4) weathering to
a medium light gr^ (N6) or a yellowish gray
(5Y 7/2). 1.8
Covered' interval, no sanple. 13.7
lOB, lOTM, Wackestone, fine to medium grained, interbeds of
IOC fissile and dense medium units, brachiopods and
crinoids show on weathered surface, fresh surface
is medium gray (N5) weathering to a light olive gray
(5Y 6/1). 2.4
9E Packstone, fine to medium grained, medium bedded,
dense, bryozoans and brachiopods show on weathered
surface, fresh surface is medium dark gray (N4)
weathering to a light olive gray (5Y 6/1). 1.5
9, 9T, 9C, Wackestone, fine to medium grained, medium bedded,
9D friable, brachiopods and crinoids show on weathered
surface, fresh surface is medium dark gray (N4)
weathering to a light gray (N7). 6.1
8U, 8M, 8B Wackestone, medium grained, medium bedded, dense
near base becoming more friable near unit's top,
abundant bryozoan stems show throughout, some
brachiopods also present, slight sulfur odor on
fresh break, fresh surface tædium gray (N5)
weathering to a light olive gray (N7). 5.0
7L, 7T, 7M Lime nudstone, medium to thinly bedded, friable
7B near base, becoming more dense near unit's top
localized linear zones of brachiopods following
bedding, brachiopods, gastropods and bryozoans
also show on væathered surface, fresh surface is
tædium dark gray (N4) weathering to a medium
gray (N5). 4.0
127
Sanple No. Descriptions Thickness (î>feters)
6Br, 6D Lime mudstone, medium bedded, slightly friable,
no fossils seen, fresh surface is a medium gray
(N5) weathering to a yellowish gray (5Y8/1). 2.7
6T Slightly sandy packstone, fine to medium grained,
medium bedded, scattered fossil fragments, fresh
surface is a medium dark gray (N4) weathering to
a light brownish gray (5YR 6/1). 1.5
5, 5B, 5P, Lime mudstone, fine to medium grained, medium
51 bedded, contains spheroidally \Æathered denser
lenses, scattered brachiopods, fresh surface is
a medium gray (N5) weathering to a medium light
gray (N6). 1.2
4J, 4B Packstone, fine to noedium grained, medium bedded
strong petroliferous odor, contains small black
stain calcite irregular stringers, brachiopod
molds, gastropods and crinoid molds show on
weathered surface, fresh surface is a medium dark
gray (N4) weathering to a yellowish gray (5Y 7/2). 3.7
4.5 Shale, fine grained, one thin bed, highly contorted,
no fossils seen, fresh surface gr^sh black (N2)
weathering to a dark gray (N3) with a lustrous
surface. : 0.3
4, 4K Packstone, fine to lœdium grained, rtedium bedded,
strong petroliferous odor, crinoids and brachiopods
sliow on weathered surface, slightly friable, fresh
surface is a medium dark gray (N4) weathering to a
medium light gray (N6). 4.9
3 Lime nudstone, very fine grained, fissile friable,
no fossils seen, laminated, fresh surface is a
medium dark gray (t'}4) weathering to a medium
gr^ (N5). 3.0
IB, 2 Packstone, fine to medium grained, medium bedded,
ripple laminated, brachiopods, bryozoans and corals
show on weathered surface, fresh surface pale
yellowish brown (lOYR 6/2) weathering to a pale
yellowish orange (lOYR 8/6). 0.6
1 Lime mudstone, fine to naedium grained, medium
bedded, friable, brachiopod molds and bryozoans
show on weathered surface, fresh surface is a
medium Kght gray (N6) weathering to a light gray
(N7). 2..7
(O
(T
iLl 15
h-
UJ
2
O
ílaccrady Fm.
4: Jackson School Outcrop.
129
OUTCRœ AND CORE ASCRIPTIONS
4: JS - Sanples from Jackson School
Sanple No. Descriptions Thickness (Ffeters)
D, E, lime nudstone, very fine grained, interbedded
F friable thin bedded and denser medium bedded
units, no fossils seen, fresh surface is a
medium light gray (í'í6) weathering to a yellowish
gray (5Y 8/1). 2.7
C Lime sandstone, very fine grained, thinly bedded,
no fossils seen, fresh surface is a light bluish
gray (5B 7/1) weathering to a greenish gray (5G 6/1). 0.9
B lime mudstone, very fine grained, medium bedded,
no fossils seen, fresh surface is medium light gray
(N6) to grayish orange (lOYR 7/4) in localized
areas weathering to a yellowish gray (5Y7/2). 1.2
130
Hillsdale Fm,
A
B
Ct
Ce
c
V) O
cc
UJ E
I- F
ÜJ
Z C
HOLSTW RIVER
5: UKa - Samples from road cut on S.R. 692.
131
OLTTCKCF AND œRE DESCRIPTIONS
5: UKa - Sanples from Roadcut on S. R. 692
Sanple No. Descriptions Thickness (îfeCers)
Covered.
G Lime nudstone, fine grained, medium bedded,
bryozoans and brachiopods show on weathered
surface, fresh surface is an olive gray (5Y 4/1)
weathering to a gr^dsh orange (lOYR 7/4). 0.6
Covered. 3.0
F Lime nudstone, fine grained, medium bedded,
brachiopods show on weathered surface, fresh
surface is a medium light gray (N6) gathering
to a light olive gray (5Y 6/1). 0.9
E lime nudstone, fine grained, medium bedded,
slight petroliferous odor upon fresh break,
fresh surface is a medium dark gray (N4)
weathering to a grayish orange (lOYR 7/4). 1.5
Covered. 2.4
Packstone, fine to medium grained, medium bedded,
strong petroliferous odor upon fresh break, crinoids
show on weathered surface, fresh surface is a medium
gr^ (N5) weathering to a pale yellowish brown
(lOYR 6/2). 0.9
G Wackestone, fine to medium grained, medium bedded,
B ripple laminated, contains brachiopods, bryozoans,
and crinoids, fresh surface is a light gray (N7)
weathering to a pale yellowish brown (lOYR 8/2). 1.5
C lime nudstone, very fined grained, medium bedded,
T no fossils seen, fresh surface is a light olive
gray (5Y 6/1) vreathering to a very pale orange
(lOYR 8/2). 1.5
B Wackestone, fine to medium grained, medium bedded,
brachiopods and bryozoans show on weathered surface,
fresh surface is a light olive gray (5Y 6/1)
weathering to a pale yellowish brown (lOYR 6/2). 1.5
132
Sample No. Description Thickness (meters)
A Wackestone, fine to medium grained, medium bedded,
brachiopod molds, bryozoans and corals show on
weathered surface, fresh surface is a light olive
gray (5Y 6/1) weathering to a gr^ish orange
(lOYR 7/4). 1.5
133
Price Fm.
6: River Bend Outcron.
134
OUTCROP AND GORE EESCRIPTIONS
6: RB - Sanples from River Bend School
Sample No. Descriptions Thickness (Ifeters)
11, 12 Lime nudstone, very fine grained nedium bedded,
slightly friable, ostracode fragments seen,
fresh surface is a medium dark gray (M)
weathering to a light olive gray (5Y 6/1). 1.5
10 Calcareous sandstone, very fine grained, thinly
bedded, dense, crinoids show on weathered surface,
fresh surface is a medium gray (N5) weathering
to a light olive gray (5Y 6/1). 0.6
9 Sandy packstone, find grained, lœdiura bedded,
friable, ooids, crinoids and fossils fragments
abundant, fresh surface is medium gray (N5) to
light brownish gray (5YR 6/1) weathering to a
medium light gray (N6). 0.3
8 Calcareous sandstone, very fine grained, medium
bedded, slightly rippled laminated, friable, no
fossils seen, fresh surface is a light olive
gray (5Y 6/1) weathering to a yellowish gr^
(5Y 7/2). 2.7
Covered. 1.8
7B Packstone, fine to medium grained, nEdiura bedded,
friable, crinoids show on weathered surface, fresh
surface is a nedium light gray (N6) weathering to
a yellowish gray (5Y 7/2). 1.2
7 Grainstone, fine to nedium grained, medium bedded,
partially silicified, crinoids and bryozoans show
on weathered surface, fresh surface is a light
bluish gray (5B 7/1) weathering to a very light
gray (N8). 1.5
Covered. 1.2
6B Packstone, fine to medium grained, medium bedded,
contains chert nodules at its base, rugose" corals
and crinoids show on weathered surface, fresh
surface is a brownish gray (5YR 4/1) weathering to
a yellowish gray (5Y 7/2). 0.9
135
Sample No. Description Thickness (meters)
6 Lime nudstone, very fine grained, medium bedded,
dense, contains mary calcite veins, fresh surface
is a medium gray (N5) weathering to a yellowish
gr^ (5Y 8/1). 0.9
5 Wackestone, fine to medium grained, thinly
bedded, friable, contains highly fossiliferous
zones fcMch parallel bedding, fresh surface is
pale blue (5B 6/2) to a pale yellowish brown
(lOYR 6/2) weathering to a very pale orange
(lOYR 8/2). 0.6
Covered. 16.8
4 Slightly sandy lime nudstone, fine grained,
medium bedded, friable, fresh surface is a
medium light gr^ (N6) weathering to a light
brownish gray (5Y 6/1). 3.0
3 Packstone, fine to medium grained, medium bedded,
slightly friable, brachiopods and crinoids show
on weathered surface, fresh surface is a
medium light gr^ (N6) weathering to a light
olive gr^ (5Y 6/1). 0.9
2 Line nudstone, very fine grained, thinly bedded,
slightly silty, contains bedded chert nodules,
no fossils seen, fresh surface is a light brownish
gr^ (5YR 6/1) «gathering to a grayish orange
(lOYR 7/4). 0.3
1 Lime packstone, fine to coarse grained, medium
bedded, friable, corals and crinoids show on
weathered surfaces, fresh surface is a medium
gray (N5) weathering to a light olive gray (5Y 6/1). 1.5
136
7 : UKb Samples from road cut 622.
137
OUTCROP AND ODRE DESCRIPTIONS
7 : UKb - Samples from Roadcut 622
Sample No. Descriptions Thickness (Maters)
1 tiadstone, very fine grained, thinly bedded,
friable, brachiopods show on weathered surface,
fresh surface is a lœdium dark gr^ (N4)
weathering to a grayish orange (lOYR 7/4). 0.6
IB Packstone, fine to medium grained, medium bedded,
dense, strong petroliferous odor upon fresh break,
brachiopods show on weathered surface, fresh surface
is a nedium dark gray (N4) weathering to a yellowish
gray (5Y 7/2). 0.9
1C Packstone, fine to medium grained, strong
petroliferous odor upon fresh break, dense zones
of bryozoans show on weathered surface, fresh surface
is a medium dark gray (N4) weathering to a grayish
orange (lOYR 7/4). 0.9
1C Wackestone, fine to raediim grained, medium bedded,
2 friable, slight petroliferous odor upon fresh
break, brachiopods and bryozoans show on weathered
surface, fresh surface is a raediuim gray (N5)
weathering to a grayish orange (lOYR 7/4). 0.9
ID Wackestone, fine to medium grained, medium bedded,
friable, large brachiopod molds (1") show on weathered
surface, fresh surface is a brownish gray (5YR 4/1)
weathering to a light olive gray (5Y 6/1). 1.2
ly Lime nudstone, fine grained, medium bedded, friable,
ly-2 large brachiopod molds (1") show throughout, highly
iron stained, fresh surface is a medium dark gray
(N4) weathering to a pale yellowdsh orange
(lOYR 8/6). 3.0
Iz Packstone, fine to medium grained, medium bedded,
dense, zones of large brachiopods show on weathered
surface, fresh surface is a dark gray (N3)
weathering to a pale yellowish brovm (lOYR 6/2). 0.6
138
Sample No. Description Thickness (meters)
1 Lime mudstone, fine grained, thin bedded, fissile,
contains 2.0 cm thick beds of shale and has a
petroliferous oder when broken, fresh surface is
medium dark gray (N4) weathering to a pale yellowish
brown (lOYR 6/2). 6.0
2 Lime mudstone, fine to medium grained, medium bedded,
bryozoans and brachiopods present, fissile, fresh surface
is medium dark gray (N4) weathering to light gray (N6). 20.0
3 Calcareous nudstone, very fine grained, fissile, friable,
bryozoans and pelec57pods present, fresh surface is daric
gray (N5) weathering to a light olive gray (5Y 6/1). 30.0
4 lime wackestone, fine to nedium grained, dense.
silicified brachiopods and chert nodules exposed
on weathered surface, fresh surface is dark gray (N5)
weathering to a médium dark gray (N4) 5.0
5 Sandy, calcarecxis nudrock, fine to medium grained,
medium bedded, dense, fresh surface is dark gray (N5)
weathering to a medium dark gray (N4) 9.0
6 Calcareous nudrock, fine grained, fissile, friable,
fresh surface is nedium dark gray (N4) weathering
to a medium gr^ (N5). 5.0
139
NOTE; SAMPLES TAKEN APPttOXIMATELY
EVERY METER
Maccrady Fm.
8: Core (Bonnie Dell), Plasterco, Virginia.
140
8: BD- core sanples from Plasterco, Virginia
Sanple No. Description Thickness (meters)
16, 17 lime raudstone, fine grained medium bedded,
18, 19 dense, contains algal laminations (some
pyritized), microfaults with minor displacements
and limited brecciation. Fresh surface is medium
light gray (N6). 2.4
20, 21 lime nudstone, fine to medium grained, medium
22, 23 bedded, contains 1.0 cm thick darker lime
24, 25 mudstone laminations and condensed zones,
algal laminations, calcite veins and raicrofaults
with minor displacements (0.5 mm). Fresh surface
is medium light gray (N6). 3.7
26, 27 Doloraitic, gypsiferous, tiudrock, fine grained,
28, 29 friable, algal laminations, contains 2-5 cm thick
30, 31 gypsum beds and satin spar gypsum veins, many
microfaults (0.7 mn displacements). Fresh
surface is medium light gray (N6) 9.7
32 Calcareous, nudrock, very fine grained, medium
bedded, algal laminated containing 0.5 to 1.0 cm
solution breccia clasts, and many satin spar gypsum
veins. Fresh surface is pinkish gr^ (5YR 8/1). 2.0
33, 34 Calcareous mudrock, fine grained, medium bedded,
35, 36 algal laminated, containing sandy fossiliferous
(fragmented brachiopods and echinoderms) oolitic
beds which are 5.0 to 6.0 cm thick and calcite
veins. Fresh surface is raediun dark gray (N4). 2.4
37, 38 Time nudstone, very fine grained, medium bedded,
39, 40 •dense, fossiliferous (fragmented bryozoans and
41, 42 pelecypods), bioturbated, algal laminated,
43, 44 containing 3.0 to 4.0 cm thick beds of very
45, 46 fine grained quartz sand which is well rounded
47 and sorted. Fresh surface is mediun gray (N5). 18.0
48, 49 Ume mudstone, fine grained, medium bedded, dense,
50, 51 fossiliferous (bryozoans and echinoderms), bioturbated
52, 53 and contain 2.0 to 3.0 cm beds of calcite spar
cemented ooids and intraclasts. Fresh surface is
medium dark gray (N4X 10.0
141
Sampleno. Dsscription Thickness (meters)
54 Lime grainstone, medium grained, medium bedded,
calcite spar cemented, ooids are approximately
0.5 nm in size with many concentric laminations.
Fresh surface is medium gray (N5). 0.5
55, 56 Tdmp nudstone, medium bedded, brachiopods and
bryozoans present in zoned concentrations,
bio turbated containing thin beds (3-4 cm thick)
of terrlgeneous laods, some calcite veins which
cut across bedding. Fresh surface medium gray
(N5). 1.5
57, 58, Calcareous siltstone, fine grained, well sorted
59, 60 medium bedded, ooid bearing, bioturbated, containing
61, 62 3.0 - 4.0 cm thick beds of terrigeneous nuds and
calcite veins cutting across bedding. Fresh
surface is medium gray (N5). 3.7
63, 64 Calcareous sandstone, very fine grained, medium
bedded, bioturbated, ripple laminated, containing
2.0 - 5.0 cm thick beds of terrigeneous mud which
has satin spar veins cutting across it. Fresh
surface is a medium gray (N5). 1.2
65, 66 Calcareous nudstone, fine grained, medium bedded,
67, 68 bioturbated, containing 2.0 - 3.0 cm beds of
69, 70 quartz sand (diich is îæII rounded and sorted,
71 calcite veins are common. Fresh surface is medium
gray (N5). 4.3
72, 73 Calcareous sandstone, very fine grained, medium
74, 75 bedded, bioturbated containing terrigeneous mud
76 laminated and rippled. Fresh surface is medium
gr^ (N5). 3.0
77, 78 Calcareous nudstone, fine grained, medium bedded,
79, 80 dense, conmon quartz sand laminations, contains
81 brachiopods and echinoderras and is rippled
142
Saraple No. Description Thickness (meters)
54 Lime grainstone, medium grained, medium bedded,
calcite spar cemented, ooids are ^prcocimately
0.5 mm in size with mary concentric laminations.
Fresh surface is medium gray (N5). 0.5
55, 56 Lime nudstone, medium bedded, brachiopods and
bryozoans present in zoned concentrations,
bioturbated containing thin beds (3-4 cm thick)
of terrigeneous mods, some calcite veins which
cut across bedding. Fresh surface medium gray
(N5). 1.5
57, 58, Calcareous siltstone, fine grained, \æ11 sorted
59, 60 medium bedded, ooid bearing, bioturbated, containing
61, 62 3.0 - 4.0 cm thick beds of terrigeneous nuds and
calcite veins cutting across bedding. Fresh
surface is medium gray (N5). 3.7
63, 64 Calcareous sandstone, very fine grained, medium
bedded, bioturbated, ripple laminated, containing
2.0 - 5.0 cm thick beds of terrigeneous nud which
has satin spar veins cutting across it. Fresh
surface is a medium gray (N5). 1.2
65, 66 Calcareous nudstone, fine grained, medium bedded,
67, 68 bioturbated, containing 2.0 - 3.0 cm beds of
69, 70 quartz sand vtóch is well rounded and sorted,
71 calcite veins are connon. Fresh surface is nedium
gr^ (N5). 4.3
72, 73 Calcareous sandstone, very fine grained, medium
74, 75 bedded, bioturbated containing terrigeneous nud
76 laminated and rippled. Fresh surface is medium
gr^ (N5). 3.0
77, 78 Calcareous nudstone, fine grained, medium bedded,
79, 80 dense, common quartz sand laminations, contains
81 brachiopods and echinoderms and is rippled
laminated. Fresh surface is medium gray (N5). 3.0
82 Calcareous nudstone, very fine grained, medium
bedded, dense, slightly fossiliferous, brachiopods
and bryozoans. Fresh surface is medium gray (N5). 1.5
83, 84 Lime nudstone, medium bedded, dense, fossiliferous
85, 86 (bryozoans and echinodems). Fresh surface is
87 medium gray (N5). 3.2
143
Sançle No. Description Thickness (meters)
88 Calcareous sandstone, very fine grained, moderately
rounded and well sorted grains, medium bedded,
bioturbated, containing 3.0 - 5.0 cm beds of
terrigeneous tiuds. Fresh surface is medium gray
(N5). 10.0
89, 90 Lime packstone, medium grained, medium bedded,
91, 92 contains interbeds of lime nud, brachiopods,
93, 94 bryozoans and echinoderms are present. Fresh
95 surface is medium gr^ (N5). 4.3
96, 97 Lime nudstone, very fine grained, nedium bedded,
98 containing 5.0 - 7.0 cm calcareous nudrock
interbeds, algal and ripple laminated. Fresh
surface is medium dark gr^ (N4). - - 2.0
99 Lime packstone, fine to medium grained, medium
bedded, dense, brachiopods, bryozoans, and
echinoderms are abundant. Fresh surface is
medium dark gr^ (N4). 2.0
100, 101 Lime mudstone, fine grained, medium bedded,
dense, algal laminated, disseminated brachiopods,
bryozoans and echinoderms. Fresh surface is
medium gray (N5). 7.0
102 Lime packstone, fine to medium gray, medium bedded,
bioturbated bryozoans and crlnoids dominate and
fossils oriented parallel to bedding. Fresh
surface is medium gr^ (N5). 1.0
103, 104 Calcareous sandstone, very fine to fine grained,
105 well rounded and sorted, medium bedded, bioturbated,
rippled, cross bedded, containing thin beds (4.0 -
10.0 cm) of terrigeneous nud. Fresh surface is
medium gray (N5). — 2.0
106, 107 Lime packstone, fine to medium grained, medium
bedded, brachiopods, bryozoans and echinoderms
conmon with elongate forms oriented parallel
to bedding. Fresh surface is medium dark gray (N4). 33..00
APPENDIX B - INSOLUBLE RESIDUE DATA
FROM HWY. OUTCROP AND PLASTERCO, VIRGINIA CORE
INSOLUBLE RESIDUES
Sample No. Weight % Insolubles Sample No. Weight % Insolubles
LVL-1 64.94 LVL-14E 41.27
LVL-2 52.72 LVL-14F 38.06
LVL-3 75.09 LVL-14G 43.68
LVL-4T 26.19 LVL-15 70.25
LVL-4 20.82 LVL-16T 72.53
LVL-^I 92.61 LVL-16A 72.53
LVL-4K 19.91 LVL-16B 74.35
LVL-^BC 17.54 LVL-16C 68.02
LVL-4J 18.26 LVL-16D 73.54
LVL-^B 30.52 LVL-16I 80.88
LVL-5 59.77 LVL-17T 73.24
LVL-5I 38.48 LVL-17B 69.65
LVL-5P 29.33 LVL-17C 16.89
LVL-6T 41.15 LVL-18D 39.81
LVL-6BR 38.29 LVL-18E 31.79
LVL-6 26.17 LVL-18F 36.11
LVL-7L 41.11 LVL-18G 31.03
LVL-7M 27.97 LVL-18H 44.12
LVL-7T 31.20 LVL-19T 75.36
LVL-7B 55.12 LVL-19A 50.74
LVL-8U 47.28 LVL-20T 19.67
LVL-8M 35.89 LVL-20D 27.86
LVL-8B 30.12 LVL-20E 87.96
LVL-9T 38.13 LVL-20L 24.43
LVL-9 55.68 LVL-20M 25.42
LVL-9C 53.56 LVL-20S 58.43
LVL-9D 52.23 BD-107 48.91
LVL-9E 27.09 BD-105 81.58
LVL-IOIM 27.60 BD-101 87.01
LVL-lOB 19.99 BD-100 82.35
LVL-1IT 19.35 BD-99 37.81
LVL-1IB 90.07 BD-% 49.41
LVL-11C 38.24 BD-93 37.35
LVL-1ID 59.79 BD-91 31.13
LVL-12T 84.83 BD-89 25.22
LVL-12CA 77.04 BD-84 75.74
LVL-12C 86.23 BD-82 68.57
LVL-12R 76.42 BEH78 40.56
LVL-13T 27.86 BD-76 74.36
LVL-13A 28.48 BD-73 59.92
LVL-13B - 57.34 BD-71 17.84
LVL-13C 58.31 BD-66 27.47
LVL-14T 31.35 BD-64 69.26
LVL-14A 84.76 BD-62 88.58
INSOLUBLE RESIDUES (continued)
Sample No. Weight % Insolubles Sample No. Weight % Insolubles
LVL-14B 56.73 BD-59 91.73
LVL-14C 35.40 BD-57 77.11
LVL-14D 30.15 BD-53 62.10
BD-48 20.81 BD-30 81.28
BD-46 77.50 BD-27 85.29
BEHÍ3 81.58 BI>-24 63.48
BD-40 79.39 BD-21 35.34
BD-36 57.97 BD-19 34.23
BD-34 47.99
APPENDIX C - MICROFACIES POINT COUNT DATA
l.IMK MUDS I'ONl-: MICKDFACIKS l'ÜINI' COUNT DATA
S.imp le Braeh Hry¿ Echu Os 1 r Pele Cor 1 Fo rm Tri 1 Cono Cas t Un fos Plant Cort ooia In/Ex spar MicrL 1)0 1 o Trauíi Tsand Cyp/An
I.VL-l 2.0 0.7 1.3 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 85.7 0.0 4.3 3.3 0.0*
I.VI,-3 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 95.7 0.0 0.6 2.7 0.0
LVL-Sl 1.3 0.0 0.0 0.7 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 8 5.0 0.0 12.7 0.0 0.0
I.VL-5P 0.0 1.7 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 0.0 90.0 0.0 6.0 0.0 0.0
LVL-6BR 0.0 1.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 92.3 0.0 5.0 1.0 0.0
1.VL-7T 0.0 1.7 1.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 67.3 29.3 0.0 0.0 0.0
LVL-7L 1.3 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 75.7 20.3 T 2.0 0.0
I.VL-7M 4.3 0.7 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 84.7 8.7 0.0 0.0 0.0
LVL-7B 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 60.4 39.3 T 0.0 0.0
1.VL-8U 1.3 7.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 56.0 34.7 T 0.0 0.0
LVL-9D 2.0 1.3 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 97.7 0.0 15.0 1.4 0.0
LVL-9C 2.0 1.3 0.0 0.3 0,0 0.0 0,0 0.0 0.0 0,0 0.3 0,0 0.0 0.0 0.0 0.0 78.3 9.3 7.7 0.8 0.0
LVL-11C 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 89.0 0.0 1.0 10.0 0.0
LVL-1ID 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 58.3 0.0 41.7 0.0 0.0
I.VL-1 3T 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 90.0 0.0 10.0 0.0 0.0
1,VL-13B 2.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.3 0.0 0.0 0.0 0.0 0.0 79.7 0.0 15.0 1.7 0.0
LVL-KD 1 .0 0.0 2.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.3 0.0 0.0 0.0 0.0 0.0 81.0 0.0 2.0 11.4 0.0
LVL-14E 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 65.0 0.0 28.4 6.3 0.0
LVL-14F 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 90.0 0.0 5.0 5.0 0.0
1,VL-14G 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.3 0.7 0.0 76.3 0.0 0.4 22.4 0.0
LVL-20L 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 56.0 15.7 T 28.0 0.0
BD-105 0.0 0.0 6.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 2.3 0.0 0.0 0.0 0.0 53.7 0.0 34.0 4.0 0.0
BD-79 0.7 2.3 0.3 0.0 2.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 T 2.0 0.0 34.0 27.0 14.0 16.0 0.0
BD-78 0.0 0.0 1.0 2.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 48.7 0.0 T 48.0 0.0
BD-77 T T T 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.3 0.0 54.4 0.0 9.7 35.3 0.0
BD-75 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 62.3 0.0 2.7 35.0 0.0
BD-74 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 65.0 0.0 2.7 32.3 0.0
BD-70 0.3 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 56.3 0.0 30.0 12.0 0.0
BD-66 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 66.0 0.0 25.3 8.7 0.0
BD-65 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 68.4 0.0 8.3 19.3 0.0
BD-50 1.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 61.3 0.0 34.0 2.7 0.0
BD-41 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 59.3 0.0 26.0 14.0 0.0
BD-40 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 57.7 0.0 35.6 6.7 0.0
BD-39 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 58.6 0.0 13.0 26.7 0.0
BD-38 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 70.3 0.0 22.0 6.0 0.0
BD-37 0.0 0.0 0.0 1.7 T 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 48.7 0.0 47.6 1.0 0.0
BD-34 0.3 0.0 0.0 1.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 60.7 0.0 35.3 2.0 0.0
BI)-2 5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 49.3 28.0 20.0 T 2.7
BD-21 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 76.0 0.0 23.0 1.0 0.0
BD-20 0.0 0.7 0.7 T 3.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.7 0.0 48.7 0.0 28.2 15.0 0.0 148
BD-19 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 64.0 0.0 29.0 7.0 0.0
BD-18 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 76.3 0.0 20.7 3.0 0.0
BD-17B 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 60.7 0.0 19.0 20.3 0.0
Bl)-16 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 70.0 0.0 24.7 5.3 0.0
LIMK WACKtSTONt MICROKACIKS POINT COUNT DATA
Samp 10 Brach Bryz Echu Ostr PrilC Cor 1 Fo rm Trll Cono Cast lln fOS PlajiC Cort Oo iti Í n / E K spar M i c r 1. Do 1 o Traud Ts.and Gyp/An
LVL-8B 9.0 12.3 3.7 0.7 0.0 0.0 0.0 0.0 0.0 0.0 2.3 0.0 0.0 0.0 0.0 0.0 79.7 7.3 0.0 0.0 0.0
LVL-9T 3.7 1.3 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.3 0.0 0.0 0.0 0.0 62.0 27.7 0.0 0.0 0.0
LVL-lOB 9.7 6.3 16.0 1.0 0.0 0.0 9.0 0.0 0.0 0.0 5.0 0.0 0.0 0.0 0.3 0.0 72.7 0.0 0.0 0.0 0.0
LVL-5 20.0 11.3 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 12.0 0.0 0.0 0.0 0.0 0.0 75.3 0.0 10.0 1.0 0.0
LVL-nc 10.3 0.3 12.3 0.0 0.0 0.0 0.0 1.0 0.3 0.0 3.3 0.0 0.0 0.0 0.0 0.0 39.7 0.0 25.7 17.3 0.0
l,VL-IAC 1.0 9.3 19.3 0.0 0.0 0.0 0.0 0.3 0.0 0.0 5.7 0.0 0.0 0.0 0.0 0.0 67.7 0.0 2.7 9.0 0.0
LVL-19T 6.7 5.7 0.3 0.0 0.0 0.0 0.0 0.7 0.0 0.0 5.7 0.0 0.0 0.0 0.0 0.0 60.0 21.0 0.0 0.0 0.0
BD-71 13.3 0.0 2.7 2.7 0.0 0.0 T 0.0 0.0 0.0 0.0 2.0 0.0 T 0.0 0.0 65.3 0.0 7.0 9.0 0.0
BD-56 3.3 13.0 7.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.0 2.0 0.0 0.0 0.0 11.7 10.0 38.7 0.0 18.7 0.0
BD-52 2.3 3.0 1.0 9.7 T 0.0 0.0 0.0 0.0 0.0 0.7 1.0 0.0 0.0 0.0 0.0 92.3 37.0 0.0 8.0 0.0
BD-51 0.3 0.7 1.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 10.0 0.0 0.0 0.0 99.0 39.7 0.0 9.0 0.0
B1)-A9A 9.3 T 11.3 9.0 0.0 0.0 0.0 0.0 0.0 0.0 1.7 0.0 9.7 19.0 0.0 0.0 21.0 39.3 0.0 9.7 0.0
BÛ-23 8.3 3.0 T 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 69.3 1.7 16.0 1.7 0.0
149
I.IMK I'ACKSTONt II I CROh'AC I KS POINT COUNT UATA
Samp 1 Hracli Bryz Echn Osir Pele Corl Fo rin Trl 1 Cono Cast Un f OS Plant Cort Oo 1 li tn/Ex Spar Mlc rt Dolo Tmud Tsand Gyp/An
LVL-IB 7.7 23.0 16.0 0.3 T 0.0 0.3 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 52.3 0.0 0.0 0.0 0.0
l.VL-2 13.0 4.3 10.0 1.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 71.7 0.0 0.0 0.0 0.0
LVL-4 40.0 T 23.3 1 .0 0.0 0.0 0.0 0.0 0.3 0.3 7.3 0.0 0.0 0.0 0.0 23.3 2.7 0.0 0.0 9.0 0.0,
1,VL-4J 20.3 7.7 9.3 2.3 T 0.0 0.0 0.0 0.7 0.0 11.7 0.0 0.0 0.0 0.0 0.0 46.3 0.0 0.0 1.7 0.0
LVL-4B 16.0 16.0 8.3 2.7 T 0.0 0.0 0.3 0.Ü 0.7 5.7 0.0 0.0 0.0 0.0 0.0 49.3 0.0 0.0 1 .0 0.0
LVT-4K 18.7 7.7 23.7 0.3 0.0 0.0 0.0 0.0 0.0 0.0 11.7 0.0 0.0 0.0 0.0 24.7 13.3 0.0 0.0 0.0 0.0
LVL-4U 10.7 10.0 19.0 0.0 0.0 0.0 0.0 0.3 0.0 0.7 10.0 0.0 0.0 0.0 0.0 1.7 47.3 0.0 0.0 0.3 0.0
1.VL-6T 0.3 46.7 7.0 0.0 0.0 0.0 0.3 0.3 0.0 0.0 7.0 0.0 0.0 0.3 3.7 3.7 5.7 0.0 0.0 20.7 0.0
LVL-9E 16.0 14.7 2.0 0.0 T 0.0 0.0 0.3 0.0 0,0 4.0 0,0 0,0 0.0 0.3 0.0 62.7 0,0 0.0 0.7 0.0
LVL-IOC 12.3 5.7 4.3 T 0.7 T 0.0 0.0 0.0 0.0 1.7 0.0 0.0 0.0 0.0 0.0 75.0 0.0 0.0 0.7 0.0
l,VL-l IT 2.7 19.7 6.0 0.0 11.7 0.0 0.0 0.0 0.0 2.0 3.0 0.0 0.0 0.0 0.0 0.0 55.3 0.0 0.0 0.0 0.0
l,VL-l 3A 3.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 45.0 0.0 0.0 0.0 0.0 31.3 9.7 0.0 6.7 3.7 0.0
LVL-18D 13.7 34.0 15.3 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 23.7 0.0 0.0 1.3 0.0
LVL-18F 18.7 37.3 6.7 0.0 0.0 0.0 0.0 1.7 0.0 1.0 7.7 0.0 0.0 0.0 0.0 0.0 27.0 0.0 0.0 0.0 0.0
LVL-18G 22.3 20.7 2.7 0.3 0.0 0.0 0.0 0.0 0.0 0.0 13.0 0.0 0.0 0.0 0.0 1.7 39.3 0.0 0.0 0.0 0.0
LVL-18U 11.7 4.0 10.3 0.7 0.0 0.0 0.0 0.0 0.0 0.0 5.7 0.0 0.0 o.d 0.0 33.3 11.7 22.7 0.0 0.0 0.0
LVL-20S 23.7 10.7 0.3 0.0 0.0 0.0 0.0 1.0 0.0 0.0 6.7 0.0 0.0 0.0 0.0 0.0 11.3 36.7 0.0 8.7 0.0
I.VL-20T 59.7 8.0 4.7 0.0 0.0 0.0 0.0 7.0 1.3 0.0 10.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.0 0.3 0.0
LVL-20M 9.0 16.3 41.7 0.0 0.0 0.3 0.0 0.7 0.3 0.0 9.3 0.0 0.0 0.0 0.0 0.0 22.3 0.0 0.0 0.0 0.0
I.VL-20D 12.3 3.7 9.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.7 0.0 3.7 0.0 0.0 11.7 30.0 20.7 0.0 12.7 0.0
BD-106 19.7 23.7 4.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 39.0 0.0 13.3 0.0
BD-99 30.3 12.0 7.0 0.0 0.0 0.0 T 0.0 T 0.0 2.7 0.0 0.0 0.0 0.0 0.0 1.0 46.0 0.0 1.0 0.0
BD-94 15.7 40.3 6.3 0.0 0.0 0.0 0.0 5.3 T 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 31.7 0.0 0.0 0.0
BD-93 12.7 32.3 16.3 T 0.0 0.0 0.0 1.7 T 0.0 2.7 0.0 0.0 0.0 0.0 0.0 13.7 20.3 0.0 0.0 0.0
BD-92 18.7 28.7 6.0 0.0 2.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 42.7 0.0 1.3 0.0
BD-91 17.3 58.3 11.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 7.3 5.0 0.0 0.0 0.0
BD-90 16.7 59.7 4.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.7 17.3 0.0 0.3 0.0
BD-89 49.0 24.0 13.0 0.0 2.0 0.0 0.0 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 11.3 0.0 0.0 0.0
BD-54B 14.3 0.0 4.3 7.7 0.0 0.0 0.3 0.0 0.0 0.0 1.3 0.0 9.0 6.7 0.0 3.0 21.0 0.0 25.7 6.3 0.0
150
LIME CRAINSTONE M1CRÜEAC1ES POINT COUNT DATA
Sanple Brâch Bryz Echl n Os t r Pe Ic Cor 1 Forn Trl 1 Cono Cast Un fos Plan C Cor t Oold In/Ex Spar Mlcrc Dolo Tnuds Tsand Gyp/An
LVL-14T T 89.7 6.3 0.0 0.0 T T T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.7 0.3
LVL-Í4C 0.3 10.3 0.0 0.040.3 T T 0.0 0.01.3 0.00.0 0.0 6.0 0.0 0.0 0.0 0.0 0.6 32.0 7.3
LVL-17T 6.7 0.011.7 0.014.0 0.6 0.3 1.3 0.0T 0.0 0.0 0.0 0.0 9.0 0.0 0.0 0.0 0.0
LVL-17C 51.7 0.07.7 11.3 0.013.0 5.70.3 1.0 0.0 0.3 0.3 0.00.6 0.0 0.0 8.7 0.0 0.0 0.0 0.0
LVL-18E 49.814.3 0.027.0 0.026.3 0.6 6.70.0 0.6T 0.0 0.01.0 0.0 0.0 6.7 0.0 0.0 Ü.0 0.0 19.3 1.0 0.0
BÜ-33 0.5 0.00.0 1.0 7.3 3.80.0 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 2.3 3.3 44.0 20.3
BD-48 1.7 2.3 0.00.0 0.05.3 6.3 0.0 0.0 19.00.0 0.00.6 0.0 0.0 0.0 0.0 14.7 20.0 0.0 43.7 0.0 0.0 0.0 7.7 0.0
151
CAl.CARKOUS MUDDY SANDSTONE MICKOFACIES I’OINT COUNT DATA
Sample Br.ich Bry/. Eohii Os l r PriK: Co r 1 Ko rm Tri 1 Cast Uat'os Pl.jnt Con Oo i (i In/Ex Spar Mien Do 1 o Tidüc)
Tsand Chert Flag Gyp/An
3.7 0.0•LVL-IS 0.0 0. ) 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 29.0 0.0 0.0 0.0 56.7 9.7 0.0
0.0
LVI.-16A 0.0 0.3 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 16.3 0.0 11.0 72.3 0.0 0.0
LVL-16C 0.0
0.0
0.0 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 T 0.0 0.0 0.0 0.0 23.1 0.0 25.0 49.3 0.0 0.0
I.VL-16I 9.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.3 0.0 35.7 51.0 0.0 0.0
0.0
LVL-20E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 7.7 0.0 0.0 30.3 55.0 4.3 2.7 0.0
LVL-20E1 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 6.0 0.0 0.0 38.0 55.0 1.0 0.0 0.0
BD-102 14.3 10.3 3.3 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.3 65.3 0.0 0.0 0.0
liD-88 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 3.3 0.0 27.0 0.0 60.3 5.3 3.7 0.0
BD-8Ü o.o 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 14.3 0.0 19.3 15.3 51.0 0.0 0.0
0.0
BD-76 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 25.3 0.0 0.0 19.3 51.3 2.3 1.7
0.0
BD-7 3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 15.3 27.3 0.0 3.0 54.3 0.0 0.0
0.0
BD-7 2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 21.0 6.0 0.0 1.0 72.0 0.0 0.0
0.0
BD-69 0.0 0.0 8.7 0.0 0.0 0.0 0.0 T 0.0 0.0 0.3 0.0 0.0 0.0 20.0 0.0 0.0 27.0 33.7 0.0 0.6
9.7
0.0
BD-6 7 0.0 0.0 0.3 T 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 39.7 0.0 16.0 43.3 0.0 0.0
BD-64 0.0 0.0 9.7 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 27.0 11 .0 47.7 3.3 1.0 0.0
BD-63 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 24.0 70.3 3.0 1.0
0.0
BD-62 0.0 0.0 0.3 0.0 0.0 0.0 0.0 T 0.0 0.0 0.6 0.0 0.0 0.0 6.0 0.0 0.0 32.0 61.0 0.0 0.0 0.0
BD-61 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 1.0 0.6 0.0 4.3 0.0 5.7 0.0 0.0 21.6 66.7 0.0 0.0 0.0
BD-60 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 36.7 0.0 11.0 0.0 0.0 14.0 37.7 0.0 0.0 0.3
BD-59 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 1.3 0.0 0.0 27.3 66.3 2.0 3.0 0.0
BD-57A 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 2.0 0.0 0.0 0.0 6.0 0.0 0.0 41.0 51.0 0.0 0.0 0.0
152
CALCAREOUS MUUKOCK M1CKÜFACIKS ROI NT COUNT DATA
.S.im[) 1 e Br acli Bryz Ecliii Os L r Relc Corl Ko r m Tri 1 Cono Cast Un 1 OS Rlaiu Corl Ooid 1 n / E X Spar Mien Do 1 o Tmud Tsand (iyp/An
LV1,-A.3 1.3 T 0.3 'r 0.0 0.0 0.0 0.0 1 .0 0.0 11.,7 0.0 0.0 0.0 0.0 0.6 u.u 0.0 75.3 9.7 0.0
LVL-Sli U.O 0.0 0.0 U.O 0.0 0.0 0.0 0.0 0.0 0.0 1. 7 0.0 0.0 0.0 0.0 0.0 36.0 T 50.0 12.3 0.0
LVL-y 2.0 0.0 T T 0.0 0.0 0.0 0.0 0.0 0.0 0.,3 0.0 0.0 0.0 0.0 0.0 A6.7 0.0 50.0 1 .0 0.0
I.VL-1 IB U.O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0..0 0.0 0.0 0.0 0.0 0.0 5.0 T 95.0 0.0 0.0
LVL-12T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.,0 0.0 0.0 0.0 0.0 0.0 10.0 0.0 90.0 0.0 0.0
LVL-12C T 0.3 0.3 T 0.0 0.0 0.0 0.0 0.0 0.0 0..3 0.0 0.0 0.0 0.0 0.0 23.0 0.0 76.0 0.0 0.0
LVI.-IAA 0.0 1.0 1.0 T 0.0 0.0 0.0 0.0 0.0 0.0 2.,0 0.0 0.0 0.0 0.0 0.0 5.0 T 90.0 1 .0 0.0
LVL-16T 0.Ü 0.0 0.6 0.0 0.0 •0.0 T 0.0 0.0 0.0 0. 0 0.0 0.0 0.0 0.0 0.0 2A.0 0.0 70.1 5.3 0.0
LVL-16B 0.0 0.0 0.3 0.0 0.0 0.0 T 0.0 0.0 0.0 0.,0 0.0 0.0 0.0 0.0 0.0 AO.7 0.0 A5.0 lA.O 0.0
I.VL-16Ü 0.0 1.0 1.0 0.6 T 0.0 T 0.3 0.0 0.0 A. 3 0.0 0.0 0.0 0.0 3.7 10.7 0.0 AA.O 3A.3 0.0
LVL-17B 1.5 0.0 3.0 0.0 0.0 0.0 0.5 0.0 T 0.0 0. 0 0.0 0.0 0.0 T 0.0 AO.O 0.0 AO.O 15.0 0.0
LVL-19A 0.6 0.0 0.3 T 0.0 0.0 0.0 0.0 T 0.0 15. 7 0.0 0.0 0.0 0.0 0.0 T 0.0 68.3 15.0 0.0
BD-100 1.3 1A.7 0.6 T 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 0.0 T 7A.7 8.7 0.0
BD-68 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 20.0 0.0 A2.0 38.0 0.0
BU-58 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 1.0 0.0 T 60.6 38.3 0.0
BD-55 0.3 0.0 0.6 T 0.0 0.0 0.0 0.0 0.0 0.0 1. 7 0.6 0.0 0.0 0.0 11.7 0.0 T 72.3 12.7 0.0
BD-53 1 .0 0.6 0.3 A.O 0.3 0.0 0.0 0.0 0.0 0.0 2. 0 0.6 0.0 0.0 8.3 0.0 1 .6 0.0 65.0 16.3 0.0
BD-A7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 2.3 0.0 0.0 60.3 37.3 0.0
BD-A6 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 31.3 T A5.3 23.3 0.0
BD-A5 0.0 T T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 0.0 0.0 0.0 0.0 5.3 28.7 0.0 A3.0 23.0 0.0
BD-AA 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 0.0 0.0 0.0 0.0 0.0 3A.7 T 53.6 11.7 0.0
BD-43 0.0 T T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 27.0 T 62.0 11.0 0.0
BD-A2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 3 0.0 0.0 0.0 0.0 0.0 39.3 0.0 51.7 8.7 0.0
BD-36 0.0 T T 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 39.7 T 55.3 A.7 0.0
BD-35 0.0 0.0 T T 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 0.0 0.0 AO.O T 52.0 8.0 0.0
BD-32B T 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 3.3 0.0 3A.3 T A6.0 16.3 0.0
BU-2A 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 T 0.0 0.0 T 0.0 0.0 A6.3 A5.0 8.7 0.0
BD-22 0.0 0.0 T T 0.0 0.0 0.0 0.0 0.0 0.0 0. 0 0.0 0.0 0.0 T 0.0 23.0 0.0 77.0 T 0.0
153
SECONDARY GYPSUM MICROFACIES POINT COUNT DATA
Sample M i c r t Dolo Sec-Gyp Anhy Tmu d
BD-3 1 0.0 54.0 46.0 T 0.0
BD-29 0.0 7.0 45.7 47.3 0.0
BD-28 0.0 27.3 70.3 2.3 0.0
BD-27 0.0 0.0 54.3 T 45.7
BD-26 1 . 7 10.7 74.0 T 13.7
154
4
GEOLOGIC CROSS SECTION OF THE LITTLE VALLEY LIMESTONE
WASHINGTON COUNTY. VIRGINIA
LEGEND
I
I \
FIG. 5
VS. INSOLUBLE RESIDUES OTAL AVERAG P P RCE
TAPOVEERTRCAEGNLET
sample NUMBLKS
I
I l
FIG. 17