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THESIS 1987 L454 GEOL

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DUE RETURNED

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· .. ( . ·'.· :L fiffD .. -... PALEOENVlRONMENTAL SIGNIFICANCE OF BENTHIC FORAM INIFERAL

BIOFACIES IN THE YEGUA FORMATION (MIDDLE EOCENE),

SOUTHEAST TEXAS To Rose PALEOENVIRON.MENTAL SIGNIFICANCE OF BENTHlC FORAMINIFERAL

BIOFACIES IN THE YEGUA FORMATION (MIDDLE EOCENE),

SOUTHEAST TEXAS

by

THOMAS BRUCE LAYMAN, B.S.

THESIS

Presented to the Faculty of the Graduate School of

The University of Texas at Austin

in Partial Fulfillment

of the Requirements

for the Degree of

MASTER OF ARTS

THE UNIVERSITY OF TEXAS AT AUSTIN

DECEMBER 1987 ACKNOWLEDGEMENTS

I would like to thank the members of my supervising committee, Drs.

Martin B. Lagoe, William E. Galloway, and Amos Salvador. Special thanks are extended to Martin Lagoe for serving as committee chairman and for his guidance and encouragement during the past two years.

I also wish to thank Exxon Company, U.S.A. for the release of information. Eleanor Hoover of Exxon's Exploration Department provided helpful discussions and sifted through the Exxon files to locate the wells with samples used in this study.

I gratefully acknowledge the friendship and assistance offered by my fellow graduate students and the staff of the Department of Geological Sciences.

Harold Billman deserves special thanks for many helpful discussions and the generous loan of reference materials. I would like to thank the Dorothy Ogden

Carsey Scholarship Fund for financial support.

Finally, I would like to thank my family for their understanding and support throughout my graduate program. Of course, my wife, Rose, deserves all the thanks in the world for her extraordinary patience and word processing abilities. She was especially understanding during the times when everything that

I saw somehow looked like a foram.

October 1, 1987

IV ABSTRACT

Foraminiferal data analysis and lithofacies analysis of a three-well transect through the Middle Eocene Yegua Formation in southeast Texas provide insights into the depositional and paleoenvironmental history of the Gulf of

Mexico Basin. Vertical and downdip changes in the lithology of the Yegua

Formation in the three wells represents the depositional environments of a delta system that prograded onto the continental shelf, updip from the shelf margin.

Two progradational episodes and two marine transgressions of the Yegua delta

system occurred within this interval of the Yegua Formation in southeast Texas.

Factor analysis of benthic foraminiferal census data reveals five major recurring assemblages of benthic fora min ifera. These assemblages, or biofacies, occupied environments ranging from marginal marine to normal marine, middle­ to-outer shelf environments. The stratigraphic relationships of the five biofacies show paleoenvironmental complexities that are not readily apparent from the lithofacies analysis. Integration of lithologic data and nonforaminiferal paleontologic data with the foraminiferal data produces a detailed paleoenvironmental reconstruction of the Yegua shelf in dip direction.

Comparison of the forarninifera! data from the Yegua Formation with

modern forarninifer al data from the Gulf of Mexico indicates that several

properties of modern forarninifera! assemblages are similar to the foraminiferal

v assemblages of the Yegua Formation. Generic predominance, species diversity, and planktic to benthic ratios of modem foraminifer al assemblages can be used to help determine the paleoenvironmental significance of the Yegua foraminiferal assemblages. These properties of modern foraminifer al assemblages are not exact analogs for Middle Eocene assemblages and should be applied with caution.

Vl TABLE OF CONTENTS

INTRODUCTION 1

Objectives 2

Area of Study 3

Previous Work 5

Stratigraphic and Geologic Setting 6

1vf.ETHODS 15

DATA ANALYSIS 18

Lithofacies Analysis 18

Well A - Humble Sam Houston Area Council No. 1 19

Well B - Kathryn M. Hines No. 1 20

Well C - Humble Foster Lumber Company No. 1 21

Exxon Conroe Field Unit Well No. 2720 22

Lithofacies Interpretation 24

Foraminifera 26

Factor Analysis 27

DATA INTERPRETATION 37

Biofacies Interpretation 37

Biofacies of the Cored Interval 42

Vll Planktic Foraminifera 43

Yegua Foraminiferal Relationships vs Modem 43 Foraminifera I Relationships

Paleobathymetry of the Yegua Biofacies 52

SUMMARY AND CONCLUSIONS 54

ANN OTA TED SPECIES 56

BIBLIOGRAPHY 69

Vlll LIST OFTABLES

Table 1. V arimax. factor loadings of the five factors. 29

Table 2. The distributions of planktic and benthic foraminifera 44 within the Yegua Formation of Wells A, B, and C.

Table 3. Values of the Shannon-Wiener infonnation function 51 H(S) for selected samples from the five Yegua Formation biofacies.

lX LIST OF FIGURES

Figure 1. Location of wells used in this study. 4

Figure 2. Correlation chart for the Yegua Formation. 7

Figure 3. Outcrop of the Yegua Formation in Texas. 8

Figure 4. Depositional systems of the Yegua Formation in 12 southeast Texas.

Figure 5. Thickness of the Yegua Formation. 13

Figure 6. Well log of the Exxon Conroe Field Unit Well No. 2720. 23

Figure 7. Contoured factor plot for Factor 1. 31

Figure 8. Contoured factor plot for Factor 2. 32

Figure 9. Contoured factor plot for Factor 3. 33

Figure 10. Contoured factor plot for Factor 4. 34

Figure 11 . Contoured factor plot for Factor 5. 35

Figure 12. Distribution of the five factors for each regressive and 36 transgressive phase shown on Plate 6.

Figure 13. Generic Predominance Facies among the marine benthic 49 foraminiferal cornrnunity of the Gulf of Mexico.

x LIST OF PLATES

Plate 1. Scanning electron micrographs. 63

Plate 2. Scanning electron micrographs. 65

Plate 3. Scanning electron micrographs. 67

Xl LIST OF INSERTS IN MAP POCKET

Insert 1. Cross section A-A'.

Insert 2. Species checklist of benthic and planktic foraminifera for Well A.

Insert 3. Species checklist of benthic and planktic forarrUnifera for Well B.

Insert 4. Species checklist of benthic and plank.ti c foraminifera for Well C. lnsen 5. Species checklist of benthic and planktic foraminifera for the Cored Well.

Insert 6. Lithofacies cross section.

XII INTRODUCTION

Foraminiferal biofacies are powerful tools for paleoenvironmental reconstructions in terms of paleobathymetry, type of substrate, and water mass structure. Many paleoenvironmental models and interpretations using forarninifera are based upon comparisons with distributions of modern foraminifera. However, past environments and their related biofacies may not be similar to modem conditions, because oceanic conditions underwent dramatic evolutionary changes during the Cenozoic (Berger et al., 1981 ). The oxygen isotopic record for the Cenozoic in deep sea sediments shows an overall cooling trend punctuated by periods of rapid cooling during the Late Eocene and Middle

Miocene (Berger et al., 1981 ). The rapid cooling trend mostly affected the high latitudes, while the tropical regions were relatively unaffected (Berger et al.,

1981) . The change in pole-to-equator temperature gradients caused major changes in oceanic water mass structure and thermohaline deep water circul ation

(Douglas and Woodruff, 1981 ).

Changes in benthic faunas have been related to changes in marine environments during the Cenozoic. Species abundance, bathymetric distribution, and geographic distribution have varied in the deep sea and on the continental margin in response to changing oceanic conditions during the Cenozoic (Douglas,

1979). Therefore, modern analogs must be applied cautiously to the 2

interpretation of ancient environments, and attempts should be made to interpret ancient biofacies distributions independently of the modem analogs.

This study examines the distributions of benthic foraminiferaJ biofacies of the Middle Eocene Yegua Formation in the subsurface of southeast Texas.

Benthie foraminiferal biofacies are recurring assemblages of benthic foraminifera that characterize samples of the Yegua Formation. The biofacies of the Yegua

Formation are determined by quantitative analysis of benthic foraminiferal census data. The paleoenvironmental significance of these biofacies is evaluated from:

1) stratigraphic and biofacies relationships revealed by quantitative analysis, 2) lithologic data, and 3) nonforaminiferal paleontologic data with paleoenvironmental significance. The biofacies and paleoenvironmental interpretations are compared with modem benthic foraminiferal biofacies in the

Gulf of Mexico to see how the modem analog can be applied to Middle Eocene environments.

Objectives

The objectives of this study are as follows:

1. Document the distribution of benthic forarniniferal biofacies across a

portion of the Yegua shelf in the dip direction.

2. Determine the paleoenvironmental significance of Yegua benthic

foraminifera I biofacies. 3

3. Relate Yegua biofacies and paleoenvironments to lithostratigraphy.

4. Integrate the benthic foraminifera I biofacies with planktic foraminifer al

biostratigraphy for better chronostratigraphic control.

5. Compare Yegua benthic forarniniferal biofacies to modern biofacies

structure in the Gulf of Mexico.

Area of Study

A transect through the Yegua Formation in Montgomery and Harris

Counties in southeast Texas was chosen because this area is within a major hydrocarbon producing trend of the Yegua Formation, and consequently, the entire Yegua section has been penetrated by the drill. Two oil fields producing from the Yegua Formation are adjacent to the transect: I) Conroe field to the nonheast in Montgomery County, and 2) Tomball field to the southwest in Harris

County. Exxon Company, U.S.A. provided well cuttings and well logs for three wells which constitute the traverse through the Yegua Formation in the dip direction (Figure 1). Well A, Humble Oil and Refining Company Sam Houston

Area Council No. 1, and Well B, Humble Oil and Refining Company Kathryn M.

Hines No. 1, are located in Montgomery County. Well C, Humble Oil and

Refining Company Foster Lumber Company No. 1, is located in nonheastern

Harris County. A cored section of the Yegua Formation from the Exxon Conroe

Field Unit Well No. 2720 in Montgomery County was also made available for 4

~ -----1 \ . / / • t. ."'\ .>-·-( '( ' \ ./ <

N

~ OU TCROP O~ ~ YEGUA FORMATION

0 10 20 30 40 50 mi

0 25 50 ~m

Figure 1. Location of wells used in this study.

A-A' is the line of section for Insert 1. Dashed lines show approximate shelf edge from WinkJer and Edwards (1983). Dotted lines show approximate position of the flu vial/delta plain transition from Fisher (1969). 5

inspection and paleontologic sampling by Exxon Company, U.S.A.

Previous ·work

Published paleontologic studies of the Yegua Formation in Texas are limited. Dumble (1918) was the first to list marine megainvertebrate fossils from the type section of the Yegua Formation in Lee County, Texas. Gardner (1927) considered the molluscan fossils from the type section of the marine Yegua

Formation for correlation. Foraminifera and ostracodes picked from the samples collected by Gardner were later described by Stadnichenko (1927). The most recent study of foraminifera from the type locality of the Yegua Formation was done by Cushman and Applin (19-+3 ).

Subsurface micropaleontologic work on the Yegua Formation was first reported by Weinzierl and Applin (1929). They described foraminifera of the

Claiborne Formation (ponions of which are now considered part of the Yegua

Formation) from well cuttings from Harris County, Texas. Further subsurface work was done by Israel sky ( 1935) who proposed a foraminiferal zonation of the subsurface Claiborne of Texas and Louisiana. Koenig ( 1979) presented a summary of surface and subsurface index foraminifera of the Yegua Formation.

Several nonpaleontologic studies of the Yegua Formation have also been published. Stenzel (1939) and The Houston Geological Society (1954) provide concise chronologies of the surface mapping and definition of the Yegua 6

Formation. More recent mapping, stratigraphic, and depositional systems studies involving the Yegua Formation are those of The Houston Geological Society

( 1962, 1979), Fisher ( 1964, 1969) and LeBlanc ( 1970).

Stratigraphic and Geologic Setting

The Yegua Formation is the uppermost unit of the Middle Eocene

Claiborne Group (Figure 2). The type section of the Yegua Formation are near the mouth of Elm Creek, a branch of Yegua Creek, in Lee County, Texas. The outcrop of the Yegua Formation extends across the Upper Gulf Coastal Plain of

Texas, as a belt that ranges from one to twenty miles in width (Figure 3).

Between the Colorado and Sabine rivers, the Yegua Formation is composed mainly of sands, interbedded clays, numerous thin lignites, and silts of nonmarine origin (Stenzel, 1939). In southern Texas, the outcrops of the Yegua Formation contain mostly clay with minor amounts of sand, lignite, and limestone (Eargle,

1968).

The upper boundary of the Yegua Formation in eastern and central

Texas is marked by a disconformity between the overlying marine sands and shales of the Caddell Formation of the Late Eocene Jackson Group and the lignitic nonmarine sands, silts, and clays of the Yegua Formation (Stenzel, 1939).

However, marine fossils are found in the the uppermost portion of the Yegua

Formation in eastern Texas along the Sabine River in Sabine County (Deussen, 7

Lithostratigraphic units Epoch Group Texas Louisiana

Whisett Yazoo Q) Jackson Group Mc Elroy _Jro

Caddell Moody's Branch

Yegua Cockfield

~ Crockett ~ Cook Mountain

Q) Sparta Sparta :0 :2 Claiborne Group :E Weches

Queen City Cane River

Reklaw

Figure 2. Correlation chart for the Yegua Formation. 8

98° 96°

SABINE UPL IFT \

)

SAN ANTONI•O

N \

0 25 50 75 IOO m1 0 50 IOO km

Figure 3. Outcrop of the Yegua Formation in Texas. (modified from Eargle, 1968) 9

1918). In 1933, J. A. Cushman and A. C. Ellisor named a new species of benthic foraminifera from this locality on the Sabine River, Nonionella cockfieldensis.

This new species became an index fossil of the marine Cockfield Formation.

Stenzel (1939) observed that the upper part of the Yegua in eastern Texas is a sequence of interbedded marine, brackish and nonmarine deposits, and he argued that the Cockfield represents the marine equivalent of the nonmarine Yegua deposits of central Texas. Stenzel (1939), therefore, placed the beds from the

Sabine River that contain Nonionella cockfieldensis within the Yegua Formation and proposed that the name Cockfield be dropped.

The definition of the lower boundary of the Yegua Formation has been a source of confusion. Stenzel (1939) argued that, on the basis of lithologic and paleontologic evidence, the lower boundary of the Yegua Formation in central

Texas is the base of a thick nonmarine sand which overlies the marine clay of the

Crockett Formation (Cook Mountain Formation). In the subsurface, the base of the Yegua Formation is placed at the top of the glauconitic marine clay of the

Crockett Formation. However, in the downdip direction, the Yegua sands shale out and the lower boundary, thus defined, moves up in the section (Eargle, 1968).

The Yegua Formation in the subsurface has also been incorrectly defined on biostratigraphic criteria. Israelsk.')' (1935) proposed a benthic forarniniferal zonation of the Claiborne for use in subsurface correlation. Two foraminifera from his proposed zones are now used by the oil industry as index 10

fossils for the upper and lower boundaries of the Yegua Formation (The Houston

Geological Society, 1954). The first down-hole appearance of the index fossil,

Nonionel/a cockfieldensis, marks the top of the Yegua Formation, while the first down-hole appearance of the index fossil, Ceratobulimina eximia, is used to mark the base of the Yegua Formation. In this study, the Yegua Formation is defined by these two index fossils. Insert 1 is a stratigraphic cross section of the Yegua

Formation through the study area.

The principal depositional and rock units of the Yegua Formation were described by Fisher (1964) in a study of sedimentary cycles in the Eocene deposits of the northern Gulf Coast. He described the Yegua and other Eocene deposi ts observed in outcrops in terms of two general phases: 1) a marine transgressive phase, and 2) a nonmarine regressive phase. He observed that the

Yegua Formation in Texas contains a basal arenaceous nonmarine regressive unit composed of medium-grained, cross-bedded sands. This basal unit grades vertically into an argillaceous nonmarine phase consisting of deltaic, lagoonal, and nonmarine lignitic clays and silts. On top of the nonmarine regressive phase are glauconitic, fossiliferous marine sands, and restricted marine clays of an initial marine transgressive phase that preceded the main marine transgression of the Jackson age sea.

Fisher (1969) continued his studies of the depositional systems of the

Yegua Formation in the subsurface of the Texas Gulf Coast. He concluded that 11

the rocks of the Yegua Formation, between the Sabine River and the Colorado

River, are an example of a high-constructive delta system with an updip fluvial system and downdip delta plain, delta front, and prodelta-embayment facies. This delta system has an average thickness of approximately 1,500 feet and a

maximum net sand thickness of approximately 1,000 feet (Fisher, 1969;

Figure 4).

Maps constructed by LeBlanc (1970) of the subsurface Yegua in

southeast Texas differ from what Fisher reported in that they show a lower net

sand thickness, a generally thinner section, and a thinning of the section to the

west, east, and south. Thinning of the section is also shown by the stratigraphic

cross-sections of The Houston Geological Society (1954). LeBlanc's map of total

thickness of the Yegua (Figure 5) shows two lobate areas in Montgomery, San

Jacinto, Polk, and Tyler Counties that he suggested may be the depocenters of

two deltaic systems.

The Yegua Formation between the Sabine River and the Colorado

River dips to the southeast in the subsurface and is cut by many faults. Normal

faults with displacements of approximately fifty feet have been found in delta­

front environments where sand was probably deposited rapidly on unstable, water

saturated prodelta muds (Berg, 1986). Salt diapirs and deep-seated salt

movement have caused faulting with up to several hundred feet of displacement

in Austin, Waller, Harris, Montgomery, and Liberty Counties along the nonhern 12

N

Study 0,..0

EXPLANATION (]]} r ~ol 1y1lt m (mo1n chonnol ortOI ) D Otlto- ploin I ~ Ito - Iron! foc;u} Oe lto ~ Pro ~ lto /tml>oymtnl fo d u Sylltm ~ L09oon tyste m 0 Borr it ' bor / 1 hOl'ldplo1n sys tem 8!,'3 Sond 1y1t1m -2'00/Sond itolllh (fl) 0 20 40rni 0 30 60km

Figure 4. Depositional systems of the Yegua Formation in southeast Texas. (modified from Fisher, 1969) 13

N

~~· ~ ••llA r•MT•• --·~- C. L • tW 0 10 20 30 40 '° ..,; 0 2, ,o,.

Figure 5. Thickness of the Yegua Fonnation. (modified from LeBlanc, 1970) 14

portion of the Houston Salt Basin (Galloway et al., 1983).

The complex faulting and Yegua delta system sandstones have contributed to the accumulation of significant quantities of petroleum in the

Yegua Formation. Over 900 million barrels of oil have been produced from the

Yegua Formation sands in southeast Texas and recovery efficiencies are high.

Galloway et al. (1983) present more detail on the structural complexity and production history of oil fields in southeast Texas that produce from the Yegua

Formation. 15

METHODS

Washed residues from ditch samples collected at approximately thirty foot intervals from Wells A, B, and C were made available for study by Exxon

Company, U.S.A. The volume of each residue sample was usually less than 20

3 cm . The residues were sieved at 149 µm, and the foraminifera were picked.

Residues less than 149 µm were also examined to verify that no taxa of foraminifera were overlooked. Very few foraminifera less than 149 µm were picked in order to avoid juvenile forms that could cause identification problems.

Down-hole contamination of the foraminifera is another source of problems and is always a possibility whenever ditch samples are used for paleontologic study. In each well, several samples above the top of the Yegua

Formation were examined in an attempt to clearly distinguish the Caddell

Formation faunas from the Yegua Formation faunas. From the examination of the Caddell Formation faunas, the presence of misplaced foraminifera in the samples from the Yegua Formation was judged to be minor.

Whenever possible, three hundred specimens of benthic foraminifera were picked to facilitate the quantitative analysis of the census data. The preservation of the benthic forarninifera in the samples used was generally good.

The abundance of the benthic foraminifera is reported as the number of specimens per taxon per sample. 16

Planktic foraminifera were generally not common or were absent in the samples that were studied. Planktic foraminifera present in the residues were typically poorly preserved. A comprehensive species checklist of benthic and planktic foraminifera from each well is included in the appendix (Inserts 2-4).

In addition to the foraminifera, other fossils and nonfossiliferous materials with possible paleoenvironmental significance were picked from the residues and tabulated on the species checklist. Various other fossils examined include: echinodenn fragments, gastropods, bivalves, other mollusc fragments, ostracodes, fecal pellets, fish remains, shark teeth, radiolaria, diatoms, and petrified wood. Nonfossiliferous materials picked include glauconite, lignite, pyrite, and chert.

A total of 120 residue samples were picked from the three wells: Well

A - 32 samples, Well B - 39 samples, and Well C - 49 samples. The residues from sand intervals in the three wells typically contained less than 50 benthic foraminifera, while residue samples from shale intervals usually contained more than 50 benthic foraminifera. This resulted in Wells A and B (each of which contained over 1,200 feet of gross sand thickness) being picked at 60 foot intervals, and Well C (which was predominantly shale) being picked at 30 foot intervals.

In addition to the residues from ditch samples, approximately 154 feet of Yegua Formation core from Conroe Field Unit Well No. 2720 were examined, 17

and 7 samples were taken for paleontologic study. Each sample contained approximately 500 cm3 of rock. The samples were crushed and then soaked for

24 hours in Quaternary "O'' solution to break down the clays. Samples were boiled for 30-60 minutes and then wet sieved at 63 µm. Approximately 20-50 cm3 of residue was dried and sieved at 149 µm, and then the foraminifera were picked. A species checklist for the core samples is included in the appendix

(Insert 5). 18

DATA ANALYSIS

Lithofacies Analysis

The lithologies of the Yegua Fonnation were assessed primarily from the electric log responses of Wells A, B, and C. The vertical sequences and bedding architecture for each well were detennined from the shapes of the sp.':>ntaneous potential (SP) and resistivity logs using the approach of Galloway and Hobday (1983). Three types of bedding architecture, aggradational, progradational, and lateral accretion were interpreted from the logs. Each bedding style has a characteristic textural trend and vertical sequence that can be interpreted from the elecuic logs (Galloway and Hobday, 1983 ). Aggradational bedding often has erratic textural trends that produce serrated or barrel shaped SP and resistivity curves. Progradational bedding is characterized by an upward­ coarsening textural pattern that produces funnel shaped SP and resistivity curves.

The funnel shaped log response may also be due to an upward increase in bedding thickness. Bedding produced by lateral accretion generally has an upward-fining textural pattern that produces a bell shaped SP curve. A bell shaped SP curve response may also be due to an upward decrease in bedding thickness.

Interpretation of lithology from electric logs must be done with caution, because well logs do not directly measure lithology or grain size. Therefore, one hundred and fifty four feet of Yegua core were examined to integrate lithology 19

and log response, and the residues from the three wells provided additional lithologic information. Using this integrated approach, a more detailed lithologic interpretation was made.

Well A - Humble Sam Houston Area Council No. 1

Well A is located approximately 2 miles east of Conroe field in

Montgomery County (Figure 1). The gross lithology of the Yegua Formation in

Well A was interpreted from the electric log to be a series of interbedded sandstones and mudstones. The 200 foot interval at the base of the Yegua

Formation in Well A shows a funnel shaped SP curve characteristic of progradational bedding architecture (Insert 6). The top of this interval is a 35 foot thick sand which has a blocky SP curve. Above this progradational interval, the remaining section of the Yegua Formation in Well A shows barrel shaped SP and resistivity curves characteristic of aggradational bedding. Several sand bodies within this interval are up to forty feet thick and show both blocky and serrated

SP curves. Other sand bodies within the aggradational interval show bell shaped and funnel shaped SP curve deflections indicating lateral accretion or upward­ thinning sequences, and progradation or upward-thickening sequences.

The residues from Well A often contained millimeter size grains of lignite, glauconite, and pyrite. Glauconite and pyrite were found in trace amounts scattered throughout the section. Lignite inclusions and laminations were also 20

found in trace amounts in many of the residues, but the largest amounts of millimeter size blockly fragments of lignite were found in the residues from the sandy interval above 5,500 feet. The species checklist for Well A (Insert 2) shows the distribution of lignite, glauconite and pyrite within this section of the

Yegua Formation.

Well B - Kathryn M. Hines No. 1

Well B is located in Montgomery County approximately 11 miles southeast of Well A (Figure 1). The electric log patterns of Well B are very similar to the log patterns of Well A (Insert 6). The lithology of the Yegua

Formation in Well B was also interpreted to be a series of interbedded sandstones and mudstones with minor amounts of lignite. The 300 foot interval at the bottom of the Yegua Formation in Well B has a funnel shaped SP curve indicative of progradational bedding. The top of this progradational interval also has a sand with a blocky SP curve as in Well A, but the blocky sand in Well B is much thicker, up to ninety feet thick. Above the progradational interval, the remaining portion of the Yegua Formation is an aggradational interval as shown by the barrel shaped SP and resistivity curves. This interval is very similar to the aggradational interval of Well A in that the SP curve of Well B shows blocky and serrate patterns. Within the aggradational interval are individual sands that show bell shaped and funnel shaped SP deflections that suggest lateral accretion or 21

upward-thinning sequences, and progradation or upward-thickening sequences.

The distributions of lignite, glauconite, and pyrite in the residues of

Well B were very similar to those in Well A. Glauconite and pyrite were found throughout the section, and the largest amounts of lignite were found in the upper sandy interval of Well B. Detrital chert grains up to 2 millimeters in size were found in the residues of the progradational interval at the base of the Yegua

Formation in Well B. The species checklist of Well B (Insert 3) shows the

distribution of lignite, glauconite, pyrite, and chert within this section of the

Yegua Formation.

Well C - Humble Foster Lumber Company No. 1

Well C was drilled in northeastern Harris County approximately 15

miles southeast of Well B (Figure 1 ). The log responses of Well C are very

different from those of Wells A and B (Insert 6). The barrel shaped, serrated SP

curve for the Yegua interval suggests aggradational bedding architecture. The

predominant lithology is mudstone with individual sand bodies that are thinner

and less abundant in Well C than the sands in Wells A and B.

The residues from Well C contained less lignite and pyrite but more

glauconite than the residues from Wells A and B. The lignite found in the

residues of Well C was mostly in the form of laminations and inclusions. The

species checklist for Well C (Insert 4) shows the distribution of li gnite, 22

glauconite, and pyrite within this section of the Yegua Formation.

Exxon Conroe Field Unit Well No. 2720

This well is located in the north central portion of Conroe Field in

Montgomery County (Figure 1). Three cores totaling 154 feet were cut through the portion of the upper Yegua or "Main Conroe" sands that produce the majority of oil in the field (see Insert 1 for the position of the cored interval in the Yegua

Formation). Figure 6 shows the SP and induction resistivity curves for this cored interval. The interval consists of a series of interbedded sandstones, shaley sandstones, and mudstones. The basal sand (5046'-64') is fine-grained, burrowed, and has trough cross stratification. This sand is upward-fining into very fine-grained sands and bioturbated mudstones (5023'-5046') with thin lignite streaks. Above this un it are medium to fine-grained sandstones and shaley sandstones that are upward-fining (4964'-5023'). Ophiomorpha burrows are common in this interval. On top of these sands are 8 feet of bioturbated mudstone

(4956'-4964'). Above this mudstone are 8 feet of fine-grained, burrowed sandstones (4948'-4956') that are upward-fining into another mudstone that was not cored (4940'-4948'). The upper portion of the cored interval (4900'-4935') consists of sandstones that are upward-fining and have trough cross-stratification.

These sands do not contain Ophiomorpha burrows. The top of the core

(4898' -4900') is a black, organic rich, laminated shale with thin, very fine- 23

~ "O .s:: c: > ~ "O 0 i5. ~ v: ·c: v 0 v: 0... "O t>v v v:: a u v: ct:: ..

, ..

6000 . ....

C=:J Sand•tone I- -j Muduone

- Lignite

1010 ... ..

Figure 6. Well log of the Exxon Conroe Field Unit Well No. 2720. 24

grained sandstone laminations and occasional burrows.

Lithofacies Interpretation

The three-well transect through the Yegua Fonnation in southeast

Texas shows a downdip change in lithology from a thick sequence of sands updip to predominantly mudstones downdip. Wells A and Beach have over 700 feet of net sand, while Well C has less than 200 feet of net sand. Integration of the core data and log responses of the three wells indicates that the sands are medium to fine-grained and often shaley. Sand bodies within the progradational and aggradational intervals of Wells A and B can be correlated, but correlation of sand bodies between Wells B and C is more difficul t.

The downdip change in lithology between the three wells fits into

Fisher's (1969) model of the high-constructive Yegua delta system (Figure 4).

The three wells contain delta front, delta plain, and prodelta/embayment environments. Within the delta front environment are distributary mouth bar, distributary levee, marine reworked distal bar, and marginal delta front sub­ environments. The delta plain environment typically includes swamp, marsh, and bay sub-environments that can be subject to n:anne influence and reworking.

Prodelta/embayment environments consist mostly of marine muds, silts, and thin sands that are deposited in front of the delta, between deltaic lobes, or at the margins of the delta. These three depositional environments have been projected 25

into adjacent wells (Insert 6).

The prograding Yegua delta system produced complex relationships

among depositional environments, but generalized relationships can be

interpreted. The basal sands and mudstones in Wells A and B represent delta

front deposits of the initial progradation of the Yegua delta system onto the shelf.

The thin sands in Well C may be the distal bar sands and frontal splays into

prodelta muds. In the three wells, the first down-hole appearance of

Ceratobulimina eximia (index fossil for the base of the Yegua Formation) varies

within the initial progradational deposits. In Well B, Ceratobulimina eximia was

found in samples at the base of the initial progradation, but in Wells A and C, this

index fossil was picked from samples above the initial progradational deposits.

This variation in the first down-hole appearance of Cerarobulimina eximia may

indicate that the distribution of this fossil was environmentally controlled. If this

was the case, then Ceracobulimina eximia is not a good index fossil for the base

of the Yegua Formation in southeast Texas. The regional resistivity marker

(Inserts 1 and 6) probably represents a better local time line than the first down­

hole appearance of Ceratobulimina eximia.

The aggradational intervals above the delta front deposits in Wells A

and B probably represent delta plain deposits. Within the aggradational intervals

of Wells A and B is a thin mudstone that may represent a minor marine

transgression caused by abandonment of a Yegua delta lobe (Insert 6). The delta 26

plain deposits in Wells A and B above the thin mudstone represent another progradation of the Yegua delta system (Insert 6). Glauconite in the residues from this interval and Ophiomorpha burrows in the lower sands of the cored well indicate marine reworking of some of the delta plain sediments possibly caused by abandonment of a delta lobe. The uppermost mudstone interval of the Yegua

Formation is present in all three wells and represents what Fisher ( 1964) called the initial marine transgression of the Jackson age sea.

Foraminifera

One hundred and twenty samples from Wells A, B, and C were picked for this study. Of these samples, 98 were selected for identification of the forarninifera, including several samples immediately above the Nonionella cockfieldensis marker and several samples below the Ceratobulimina eximia marker. A total of 89 benthic taxa and 10 planktic. taxa were identified from the samples. The annotated species list provides a comprehensive list of all the benthic and planktic species and species groups.

The original census data were reported as actual numbers of specimens per taxon per sample. These data were converted to relative abundances and then transformed to numerical values for quantitative analysis as follows: 27

Census data Relative Abundance Numerical Value

I specimen/sample ~ Very Rare ~ 1

2-9 specimens/sample ~ Rare ~ 6

10-32 specimens/sample ~ Few ~ 21

33-100 specimens/sample ~ Common ~ 66

> 100 specimens/sample ~ Abundant ~ 99

Factor Analysis

Factor analysis is a multivariate quantitative technique that reduces a

complex multivariate data set to a few factors. These factors are linear

combinations of the original variables and account for the majority of variance

and covariance between the original variables (Davis, 1986). In this study, the

variables are the species and species groups of benthic foraminifera, and the

factors are used to help define the benthic foraminiferal biofacies structure of the

Yegua Formation.

Before the factor analysis was run, the number of taxa of benthic

foraminifera was reduced from 89 to 40 to eliminate very rare and rare species

from the analysis. The number of samples was also reduced from 98 to 88 to

include only those samples from the Yegua Formation in each well.

This reduced data set was entered into the computer and used in the

factor analysis. Eleven factors with eigenvalues greater than one were retained 28

by the analysis (for more detail on the procedures of the factor analysis, see Frane et al., 1985). These eleven factors account for 74% of the cumulative variance in

the reduced data set. Of these eleven factors, the first five factors account for

54% of the cumulative variance in the data set and show meaningful relationships

between the variables (taxa). The varimax factor loadings for the five factors are

presented in Table 1. The factor loadings show that the factors are related to the

following species associations:

FACTOR 1 - Bathysiphon eocenica, Bulimina jacksonensis, Eponides

mexicanus, Eponides yeguaensis, Gyroidina ocrocamerara,

Lenriculina mexicana, Lenriculina spp. and Texrularia

claibornensis

FACTOR 2 - Bolivina jacksonensis, Eponides jacksonensis, Flori/us spissa s. !.,

Fursenkoina dibollensis, Glandulina ovara, Qui11q11eloculina spp.

and Siphonina jacksonensis

FACTOR 3 - Anomalina spp., Dentalina spp., Lenriculina propinqua,

Marginulina texasensis, Uvigerina cocoaensis species group and

Uvigerina topilensis

FACTOR 4- Haplophragmoides spp., Nonion chapapotense, Texrularia

hockleyensis, and Texrularia spp.

FACTOR 5 - Ammobaculites hockleyensis and Texrularia dibollensis 29

Species Number Factor I Factor 2 Factor 3 Factor4 Factor 5 Epon.i&.s muicafUl.S II 0.830• Tu:twltJria claibonsen.sis 33 0.766• Epon.i&s yegwaen.sis 12 0.731• Gyroidina octocamerata 16 0.686• 0.336 Bathysip>iott toctttica 5 0.645• 0.265 Lett1icwlina spp. 21 0.620• 0.483 Lettticwlina muicatta 19 0.590• 0.507 Bwlimina jack.sotten.sis 8 0.575• 0.298 Florilus hantutti 13 0.845• Ep01tides jack.s01ttn.sis 10 0.825• GlattdJdina ovata 15 0.764• Bolivina jaclcsotten.sis 7 0.682• Siphottina jack.sotttn.sis 31 0.668• 0.356 F w su1J:oina dibollen.sis 14 0.635• 0.291 Quinquelocwlitta spp. 28 0.305 0.564• 0.331 0.303 Uvigerina topiltn.sis 42 0.150• Uvigerina cocoatn.sis species group 40 0.306 0.729• De111alina spp. 9 0.673• Attomalina spp. 4 0.458 0.651 • Lettticwlina propittqua 20 0.374 0.644• Marginulina ltzastttSis 22 0.358 0.534• Ttuwl4ria lwckleytttSis 35 0.843• Ttl'.lwl4ria spp. 37 0.817• Haplophragmoides spp. 18 0.778• Nottictt chapapoltttSt 24 0.671• .A.mmobacwlitts JwckleytttSis 3 0.817• Ttl'.lwitJria dibolltttSis 34 0.790• Bolivina gracilis 6 0.308 0.253 Uvigerina pertgrina 41 0.376 0.476 TrochanUtta spp. 39 0.297 Nottiotttlla mawrictttSis 26 0.401 Ttl'.lwltJria ada/la 32 0.412 Siphottina claiborttettSis 30 0.412 0.389 Ttl'.lwlaria mississippitttSis 36 0.442 0.300 0.295 0.363

Table 1. Varimax factor loadings of the five factors. * denotes important species 30

The factor scores for each sample of the three wells can be plotted in cross section and contoured. Figures 7-11 are the contoured factor plots for each factor. Factors 1 and 3 (Figures 7 and 9) most commonly occur in the downdip well, Well C. Factors 2 and 5 (Figures 8 and 11) occur mainly in the updip wells,

Wells A and B. Factor 4 (Figure 10) occurs predominantly in Well B. The factor plots show that none of the factors occur in the lower portion of Well A. This may be due to the fact that the samples from this interval contained less than 45 benthic forarninifera per sample. However, the fauna from this interval closely resembles the assemblage of Factor 5. Figure 12 shows the distribution of the five factors for each regressive and transgressive phase on the lithofacies cross

section (lnsen 6). 31

NW SE A B c 6600 7600 ·•

6600

1000

1000

t OO O IO:r0 I • I. I. t600

Figure 7. Contoured factor plot for Factor 1. Contour interval variable. 32

NW SE A B c

71100

eooo

8000

8000 8500 IO:r0 2 ..... I.

8500 7000

Figure 8. Contoured factor plot for Factor 2. Contour interval variable. 33

NW SE A B c

1500

5500

eooo

eooo e soo

.. e soo 7000

Figure 9. Contoured factor plot for Factor 3. Contour interval variable. 34

NW SE A B c

7500

5500

800 0

e ooo

0 t .... IO:r..

9800

Figure 10. Contoured factor plot for Factor 4. Contour interval variable. 35

NW SE A B c 6600 7600

6600

8000

1 000 8600

0 2 .. 1. IO:r..

8500 7000

Figure 11. Contoured factor plot for Factor 5. Contour interval variable. 36

3

2

C) MARINE TRANSGRESSIVE PHASE

5

B) UPPER REGRESSIVE PHASE

A) LOWER REGRESSIVE PHASE

Figure 12. Distribution of the five factors for each regressive and transgressive phase shown on Insert 6. 37

DATA INTERPRETATION

Biofacies Interpretation

Quantitative analysis of the benthic foraminiferal census data of the

Yegua Formation indicates that five biofacies are present (fable 1).

1. Eponides mexicanus biofacies - The important species in this biofacies

include: Eponides mexicanus, Texrularia claibornensis, Eponides

yeguaensis, Gyroidina ocrocamerata, Ba1hysiphon eocenica,

Lenriculina spp., Lenticulina mexicana, and Bulimina jacksonensis.

Subordinate species are Quinqueloculina spp., Uvigerina cocoaensis

species group, Lenricu/ina propinqua, Margi1111/ina rexasensis, and

Siphonina claibornensis.

2. Flori/us hanrkeni biofacies - The major species of the Flori/us ha:ukeni

biofacies are: Flori/us hanrkeni, Eponides jacksonensis, Glandulina

ovara, Bolivina jacksonensis, Siphonina jacksonensis, Fursenkoina

dibollensis, and Quinqueloculina spp. Other species include:

Anomalina spp., Texrularia mississippiensis, Nonionella mauricensis,

Uvigerina peregrina species group, and Bolivina gracilis.

3. Uvigerina spp. biofacies - The major species of the Uvigerina spp.

biofacies are: Uvigerina ropi/ensis, Uvigerina cocoaensis species

group, Denralina spp., Anomalina spp., Lenriculina propinqua, and 38

Marginulina texasensis. Subordinate species in this biofacies are

common to the Eponides mexicanus biofacies and include:

Barhysiphon eocenica, Bolivina gracilis, Bulimina jacksonensis,

Fursenkoina dibollensis, Gyroidina octocamerara, Lenriculina

mexicana, Lenriculina spp., Quinqueloculina spp., Siphonina

claibornensis, Textularia mississippiensis, and Uvigerina peregrina

species group.

4. Texrularia spp. biofacies - Agglutinated species are the major

components of the Texrularia spp. biofacies and include: Texcularia

hockleyensis, Texrularia spp. and, Haplophragmoides spp. The only

calcareous species, Nonion chapaporense, is the final major component

of the biofacies. Subordinate species of the Texrularia spp. biofacies

are also agglutinated species aAd include: Troclzamina spp. and

Texrularia mississippiensis.

5. Ammobaculites hockleyensis biofacies - Two agglutinated species,

Ammobaculites hockleyensis and T excularia dibo/lensis are the

dominant species of the Ammobaculites hockleyensis biofacies.

However, the subordinate species are both calcareous and agglutinated

species and include: Quinqueloculina spp., Siphonina jacksonensis,

Texrularia adalta and, Textularia mississippiensis. Of these

subordinate species, Textularia adalra is the only species that is not a 39

component of one or more of the other biofacies.

The paleoenvironmental significance of these biofacies is evaluated from:

1. Stratigraphic and biofacies relationships shown by the factor analysis.

2. Generalized lithofacies interpretation.

3. Nonforaminiferal paleontologic data obtained from the residues.

The location of the three-well transect in this study (Figure 1) lies downdip from the Yegua ftuvial to delta plain transition and updip from the

Yegua shelf edge. The position of the transect on the Yegua shelf indicates that

Well A should contain, at any one time, the shallowest water biofacies, and that

Well C should contain the deepest water biofacies. The distribution of the biofacies (Figure 12) shows that the Ammobaculites hockleyensis biofacies is most common in the updip well, Well A, and the Uvigerina spp. biofacies is most common in the downdip well, Well C. The Ammobaculices hocklcyensis biofacies represents the shallowest water biofacies, and the Uvigerina spp. biofacies represents the deepest water biofacies. This updip/downdip geometry of the five Yegua biofacies indicates that the distribution of biofacies on the Yegua shelf from shallowest to deepest water was as follows: 1) Ammobaculites hockleyensis biofacies (Factor 5), 2) Flori/us hanckeni biofacies (Factor 2), 3)

Textularia spp. biofacies (Factor 4), 4) Eponides mexicanus biofacies (Factor 1), and 5) Uvigerina spp. biofacies (Factor 3). 40

With the relative positions of the five biofacies established, nonforaminiferal paleontologic data from the residues also helped to provide additional paleoenvironmental information for a more complete interpretation.

Marine fossils including mollusc fragments, echinoderm fragments, ostracods, gastropods, and fecal pellets were picked from the residues of the Yegua

Formation. Glauconite, which is indicative of marine deposition, was also picked from the residues. Marine fossils and glauconite were most common in the residues from the Uvigerina spp., Eponides mexicanus, Texrularia spp., and

Flori/us hanrkeni biofacies. The residues from the Ammobaculites hockleyensis biofacies rarely contained glauconite or fewer marine fossils. The distribution of marine fossils and glauconite indicates that the Ammobaculites hockleyensis biofacies was a brackish to normal marine salinity assemblage, while the other four biofacies were normal marine assemblages.

Incorporation of the lithofacies interpretation with the sample biofacies and water mass distributions refines the paleoenvironmental interpretations. The

Ammobaculires hockleyensis biofacies most commonly occurs in the delta plain deposits of Wells A and B (Figure 12 and Insert 6). Brackish to normal marine environments of the delta plain include marshs or bays, and therefore, the

Ammobaculires hockleyensis is interpreted to have occupied a brackish to normal marine marsh or bay within the Yegua delta plain. 41

The Flori/us hanrkeni biofacies also occurs within the delta plain facies, but only in the mudstones that may be associated with minor marine transgressions. The most common occurrence of the Flori/us hantkeni biofacies is within the marine transgressive mudstones (Figure 12 and Insert 6). Therefore, the Flori/us hantkeni biofacies is interpreted to have occupied the normal marine phase of an interdeltaic embayment, or a normal marine shelf environment associated with the initial marine transgression of the Yegua delta.

The Textularia spp. biofacies occurs in the marine transgressive, delta front, and delta plain environments of Well B (Figure 12 and Insert 6). This distribution of the Texrularia spp. biofacies indicates that the species in this group were able to tolerate a wide range of environments, from the marginal marine environments of the delta front and delta plain to the normal marine environments of the shelf.

The distribution of the Eponides mexicanus biofacies falls within the mudstones of the prodelta/embayment environments in Well C, and within the mudstones of the marine transgressive environment in Wells A and C (Figure 12 and Insert 6). The distribution of the Eponides mexicanus biofacies within these mudstones indicates that this assemblage occupied a normal marine environment in front of, or at the margins of, the prograding Yegua delta system.

The deepest water biofacies, the Uvigerina spp. biofacies, has a similar distribution to the Eponides mexicanus biofacies. The Uvigeri11a spp. biofacies 42

typically occurs in the prodelta/embayment environments of Wells B and C, and in the marine transgressive environment of Well C, but does not occur in Well A

(Figure 12 and Insert 6). The downdip distribution of this biofacies indicates that the Uvigerina spp. biofacies occupied a normal marine shelf environment.

The distribution of the biofacies in the three-well transect (Figure 12 and Insert 6) show an increase in marine influence and water depth in the downdip direction. Well A also shows an increase in marine influence and water depth from the base to the top of the Yegua Formation. Even though the log patterns and lithofacies interpretations of Wells A and B are similar, the biofacies interpretations indicate a more marine influence in Well B than in Well A. The downdip well, Well C, is characterized by the deepest water marine biofacies and environments of the transect throughout the deposition of the Yegua Formation.

Biofacies of the Cored Interval

The species checklist (Insert 5) for the cored well, Exxon Conroe Field

Unit Well No. 2720, shows that very few benthic foraminifera were obtained from the entire interval. As previously mentioned in the core description, the sands below 4935' contain Ophiomorpha burrows indicating marine deposition, while the sands above 4935' are not burrowed indicating more fluvial/fresh water influence. The mudstones from the cored interval that were sampled contain

Ammobaculires hockleyensis almost exclusively. The presence of Ammobaculires 43

hock/eyensis indicates that the mudstones and marine sands were deposited in a marginal marine environment. The thin lignite streaks in the mudstones and the overlying fiuvial sands may further indicate that the cored interval represents a crevasse splay that has prograded into a marginal interdeltaic embayment.

Planktic Foraminifera

Planktic foraminifera were most abundant in the downdip well, Well C.

Table 2 shows the planktic to benthic ratio for each sample in the three wells.

The largest ratio values are from the samples representing the most marine facies and the facies farthest from the shoreline: the prodelta/embayment facies and the marine transgressive facies.

Although planktic foraminifera were not abundant in the residues and were generally poorly preserved, enough planktic species were identified to apply the planktic foraminiferal zonations of Stainfonh et al. (1975) and Blow (1969).

The presence of the planktic species, Globigerinarheka semiinvolura, in the samples above the top of the Yegua Formation (Nonionella cockfieldensis zone), and the absence of this planktic species within the Yegua Formation, establishes that the Yegua Formation falls within the Truncororaloides rohri zone of

Stainforth et al. ( 1975) and the P l 4 zone of Blow (1969).

Yegua Foraminiferal Relationships vs Modern Foraminiferal Relationships

While the present may not always be the key to the past, interest and 44

WELL A Sample Depth Number of Number of Planktic to (in feet) Planktics Benthics Benthic Ratio 5,064-5,094 7 327 .021 5,094-5,1 25 7 367 .019 5,125-5,1 55 3 36 .083 5,155-5,184 0 91 .000 5,184-5,2 15 2 324 .006 5,246-5,278 2 325 .006 5,338-5,368 1 296 .003 5,399-5,430 0 293 .000 5,460-5,490 4 262 .015 5,551-5,582 0 320 .000 5,612-5,643 6 226 .027 5,675-5,705 1 26 .038 5,736-5,767 2 44 .045 5,828-5,859 4 154 .026 5,890-5,921 3 133 .023 5,95 1-5,982 1 66 .015 6,012-6,043 0 29 .000 6,073-6, 103 2 14 .143 6, 134-6, 165 0 24 .000 6, 195-6,226 0 14 .000 6,258-6,288 1 11 .091 6,3 18-6,349 0 25 .000 6,3 79-6,410 0 44 .000 6,440-6,472 0 239 .000 6,4 72-6,502 0 234 .000 6,502-6,534 0 65 .000

T able 2A. The distributions of plank tic and benthic foraminifera within the Yegua Formation of Wells A, B, and C. 45

WELLE

Sample Depth Number of Number of Planktic to (in feet) Planktics Benthics Benthic Ratio 5,466-5,497 0 224 .000 5,497-5,528 1 180 .005 5,528-5,559 0 252 .000 5,559-5,590 1 143 .007 5,590-5,621 0 152 .000 5,621-5,652 7 246 .028 5,652-5,683 14 306 .046 5,683-5,714 13 303 .043 5,714-5,735 11 295 .037 5,735-5,766 10 338 .030 5,766-5,797 4 278 .014 5,828-5,859 12 238 .050 5,890-5,921 11 245 .045 5,952-5,983 16 275 .058 6,014-6,045 8 231 .035 6,107-6,138 8 222 .036 6, 169-6,200 27 365 .079 6,231-6,262 3 160 .019 6,262-6,293 2 133 .015 6,355-6,386 2 112 .018 6,417-6,448 0 53 .000 6,479-6,501 3 187 .016 6,563-6,594 2 83 .024 6,594-6,625 2 91 .022 6,625-6,656 1 150 .007 6,656-6,686 0 98 .000 6,716-6,746 1 100 .010 6,777-6,808 2 172 .012 6,808-6,839 1 119 .008 6,839-6,870 0 93 .000 6,870-6,901 1 78 .013 6,901-6,932 0 74 .000 6,932-6,963 0 78 .000 6,963-6,994 3 118 .025 6,994-7,025 1 102 .010 7,025-7,056 0 116 .000

Table 2b. The distributions of planktic and benthic foraminifera within the Yegua Formation of Wells A, B, and C. 46

WELLC Sample Depth Number of Number of Planktic to (in feet) Plank tics Benthics Benthic Ratio 7,445-7,476 82 318 .256 7,476-7,508 101 320 .316 7,508-7,539 112 317 .353 7,539- 7,563 62 339 .183 7,563-7,594 82 309 .265 7,594-7,625 44 315 .140 7,625-7,656 29 313 .093 7 ,656-7 ,687 38 315 .121 7 ,687-7 ,718 31 294 .105 7,718-7,749 80 318 .252 7,749-7,780 32 309 .105 7 ,825-7 ,856 33 311 .106 7,856-7,888 39 294 .133 7,888-7,919 33 310 .106 7,919-7,951 31 302 .103 7,951-7,983 42 296 .142 7,983-8,014 32 314 .102 8,014-8,046 34 244 .139 8,046-8,077 36 313 .115 8,077-8,128 19 302 .063 8, 128-8, 159 11 238 .046 8,159-8,190 11 270 .041 8,190-8,221 35 317 .110 8,221-8,252 80 329 .243 8,252-8,283 20 320 .063

Table 2c. The distributions of planktic and benthic foraminifera within the Yegua Formation of Wells A, B, and C. 47

confidence in applying modem foraminiferal relationships to ancient assemblages is widespread (Poag, 1986). Seven properties of modem benthic forarniniferal communities are summarized by Poag (1986) include: 1) depth limits, 2) characteristic associations, 3) predominance facies, 4) species richness, 5) equitability, 6) benthic percentage, and 7) ecophenotypic gradients. Three of these properties of modem foraminifera (generic predominance, species richness, and benthic percentage) vary from nearshore to offshore and can be compared with the changes in foraminiferal distributions across the Yegua shelf.

The generic predominance of the Yegua biofacies can be compared to the generic predominance facies of the modem Gulf of Mexico compiled by Poag

(1981). The Yegua biofacies are interpreted to have occupied marginal marine to normal marine shelf environments. Each of these proposed Yegua environments has a modem analog in the northwestern Gulf of Mexico.

Marginal marine environments in the modem Gulf of Mexico most commonly occur in bays, lagoons, and estuaries. The agglutinated Ammocium predominance facies is present in the freshwater/river influenced areas, while the calcareous Ammonia and Elplzidium predominance facies occupy the more saline areas. None of these genera are present in the Yegua samples, but Ammorium is very similar (homeomorphic) to Ammobaculites of the Yegua samples. This homeomorphy between the two genera may indicate that Ammobaculices hockleyensis occupied environments similar to the environments that Ammocium 48

occupies today. The modern relationships between agglutinated species in more brackish waters and calcareous species in the more saline waters may also be applicable to the Yegua. The Ammobaculites hockleyensis biofacies, which is interpreted to have occupied marginal marine environments, is a mixed assemblage of predominantly agglutinated species and a few calcareous species.

The inner to middle shelf of the northwestern Gulf of Mexico has a complex generic predominance facies pattern (Figure 13). Several of these modem genera are present in the Yegua biofacies interpreted to have occupied the middle shelf. However, one notable difference is the presence of the

Saccammina-Ammobaculites predominance facies on the middle shelf. As stated earlier, the Ammobaculites hockleyensis biofacies of the Yegua Formation is interpreted to have occupied a marginal marine environment. This is not an unexpected difference. The evidence from this study supports the interpretation for the Ammobaculires hockleyensis biofacies. Perhaps Ammobaculires has been subsequently displaced seaward by the Ammonia and Elphidium biofacies. This type of problem could be addressed with continued research on the benthic foraminiferal biofacies structure of Paleogene and Neogene sediments of the Gulf

Coast.

The modem outer shelf is characterized by Brizalina and Brizalina­

Uvigerina predominance facies . Several species of Uvigerina occur in the Yegua samples, and the Uvigerina spp. biofacies is dominated by Uvigerina topilensis 49

96° 94° 92°

I \

'

c

...J

0 100 200 MI. I I I I Focies 0 200 ~00' KM

Figure 13. Generic predominance Facies among the marine benthic foraminiferal community of the Gulf of Mexico. (modified from Poag, 1981) 50

and the Uvigerina cocoaensis species group. This Yegua biofacies is interpreted to have occupied normal marine shelf environments. In this case, it appears that the modern analog of generic predominance could be successfully used for paleobathymetric interpretation.

The second property of modern forarninifer al assemblages to be compared with the Yegua assemblages is the observation that species richness or diversity increases from the shoreline to the outer shelf. One measure of species diversity is the Shannon-Weiner information function. This function measures the average diversity per individual and is given by the equation:

H (S) = L Pi In Pi (Gibson and Buzas, 1973). The term Pi is the proportion of

1 the i h species, and S is the number of species. Samples or assemblages with low species diversity will have low H (S) values, and samples with higher species diversity will have higher H (S) values.

Four samples from each of the five biofacies were picked for the calculation of H (S) values. The samples each have a high positive factor score for only one biofacies, and therefore, clearly represent that biofacies. The H (S) values for the samples are presented in Table 3. The Ammobaculites hock/eyenis biofacies samples show the lowest average H (S) value indicating the lowest diversity assemblage. The Uvigerina spp. samples show the highest average

H (S) value indicating the highest diversity. These H (S) values for the five 51

Biofacies Sample Depth (ft) Well H(S) Average H(S)

Eponides mexicanus 7,749-7,780 c 3.419 7,888-7,919 c 3.119 7,919-7,951 c 3.485 7,951- 7,983 c 3.113 3.284

Flori/us hanrkeni 5,064-5,094 A 3.196 5,094-5,125 A 3.284 5,184-5,215 A 3.164 4,246-5,278 A 3.265 3.227

Uvigerina spp. 7,508-7,539 c 3.329 7 ,594-7 ,625 c 3.436 7,687-7,718 c 3.283 7,828-7,856 c 3.609 3.414

Textularia spp. 5,497-5,528 B 2.307 5,621-5,652 B 2.799 6,479-6,501 B 3.148 6,777-6,808 B 3.031 2.821

Ammobaculites hockleyensis 5.551-5,582 A 3.038 5,612-5,643 A 2.400 6,440-6,472 A 2.786 6,472-6,502 A 2.670 2.724

Table 3. Values of the Shannon-Wiener information function H(S) for selected samples from the five Yegua Formation biofacies. 52

Yegua biofacies indicate an increase in diversity with depth, and show that the modern analog of species richness can be applied to the Yegua assemblages.

The final property of the modem analog to be compared with the Yegua assemblages is the offs hore increase in the planktic to benthic ratio (similar to benthic percentage of Poag, 1986). Within the Yegua Formation, there is a general downdip increase in the planktic to benthic ratio from Well A to Well C

(Table 2). The planktic to benthic ratio of the samples interpreted to represent the shallowest environments (Factor 5) range from 0.0 to 0.05, and ratios for the deepest environments (Factors 1 and 3) range from 0.10 to 0.35. Therefore, the modern analog of the planktic to benthic ratio also can be applied to the Yegua assemblages.

Pa leobat hymet ry of the Yegua Biofacies

The paleobathymetry of the five Yegua biofacies has been presented only in general terms. However, the position of the transect on the shelf has paleobathymetric implications. The five biofacies will be assigned one of the following water depth ranges:

1. Marginal marine: 0-10 m; 0-35 ft. This zone includes bays, lagoons,

and estuaries.

2. Inner neritic: 0-10 m; 0-35 ft. This zone extends from the shoreline to

the fair weather wave base. 53

3. Middle neritic: 10-50 m; 35-165 ft. This z.one extends from the fair

weather base to the storm weather wave base.

4. Outer neritic: 50-150 m; 165-490 ft. This z.one extends from the

storm weather wave base to the shelf edge.

These water depth ranges were obtained from the literature and are approximate.

Obviously, the fair weather wave base, the storm weather wave base, and the water depth at the shelf margin are variable.

Biofacies Paleobathymetry

Ammobaculires hockleyensis Marginal marine

Flori/us hanrkeni Inner neritic

Texrularia spp. Inner to middle neritic

Eponides mexicanus Middle neritic

Uvigerina spp. Middle to outer neritic 54

SUMMARY AND CONCLUSIONS

The benthic foraminifera I biofacies analysis and the lithofacies analysis of the Yegua Formation in southeast Texas provide insights into the depositional and paleoceanographic history of Gulf of Mexico Basin. The vertical and downdip changes in lithology are interpreted to represent the depositional environments of a delta system that prograded onto the continental shelf, updip from the shelf margin. Two progradational episodes and two marine transgressions are identified by the lithofacies analysis. The results of the lithofacies analysis also indicate that the distribution of Cerarobulimina eximia may have been environmentally controlled, and that this fossil should be used with caution as a marker for the base of the Yegua Formation in southeast Texas.

Factor analysis of the benthic f?raminiferal census data reveals five major recurring biofacies that exhibit complex stratigraphic relationships. These biofacies occupied environments ranging from marginal marine to normal marine, middle-to-outer neritic environments. The stratigraphic relationships of the biofacies indicate paleoenvironmental complexities that are not readily apparent from the lithofacies analysis. Integration of lithologic data and nonforaminiferal paleontologic data with the foraminiferal data produced a detailed paleoenvironmental reconstruction of the Yegua shelf in the dip direction.

Comparison of the foraminiferal data from the Y egua Formation with the data from the modem Gulf of Mexico indicates that several properties of 55

modern foraminifera! assemblages are similar to the foraminifera! assemblages of the Yegua Formation. Generic predominance, species diversity, and the planktic to benthic ratio of modern foraminiferal assemblages can be used to help determine the paleoenvironmental significance of the Yegua foraminiferal assemblages. These properties of the modem assemblages are not exact analogs for Middle Eocene assemblages and should be applied with caution. More research is needed to document the changes m Paleogene and Neogene foraminiferal assemblages of Gulf Coast sediments. 56

ANN OT ATED SPECIES LIST

* Indicates species that are illustrated. Benthic Foraminifera *Ammobaculites agglucinans (d'Orbigny) = Spirolina agg lurinans d'Orbigny, 1846, Forarn. Foss. Vienne, p. 137, pl. 7, figs. 10-12. Ammobaculites hock/eyensis Cushman and Applin, 1926, AAPG Bull., v. 10, no.2,p. 163,pl.6,figs. 2a-2b. Ammobaculires spp. *Anomalina spp. Anomalina umbonara Cushman, 1925, AAPG Bull., v. 9, no. 2, p. 300, pl. 7, figs. 5-6.

Astacolus crepidulus (Fichte! and Moll) = Nautilus crepidula Fichte! and Moll, 1803, Test. Mier., p. 107, pl. 9, figs. g-i. *Barhysiplzon eocenica Cushman and Hanna, 1927, Calif. Acad. Sci. Proc., ser. 4, v. 16, no. 8, p. 210, pl. 13, figs. 2- 3. Bolivina gardnerae Cushman, 1926, Contr. Cushman Lab. Foram. Res., v. 2, part 2, no. 27, p. 31 , pl. 4, fig. 7. Bolivina gracilis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 167, pl. 7, figs. 1-2. *Bolivina jacksonensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 167, pl. 7, figs. 5-6. Bolivina spp. Bulimina cooperensis Cushman, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 12, pl. 1, fig s. 32a-32b. *Bulimina jacksonensis Cushman, 1925, Contr. Cushman Lab. Foram. Res.,v. 1, part 1, p. 6, pl. 1, figs. 6-7. Bulimina ovara d'Orbigny, 1846, Forarniniferes fossiles du bassin tertiare de Vienne, p. 185, pl. 11 , figs. 13- 14. Bulimina spp. Included in this group are elongate to ovate high trochospiral, multichambered, calcareous foraminifera. They are rare in the samples and generally crushed or broken. More than one genus may be represented. 57

Cassidulinoides spp. *Ceratobulimina eximia (Rzehak) = Pulvinulina eximia Rzehak, 1888, Ann. K. K. Nat. Hofmuseums, v. 3, part 3, p. 263, pl. 11, figs. 7a-7c. Cibicides spp. Cornuspira spp. Dentalina spp. Included in this group are fragments of the species of Dentalina cocoaensis (Cushman), = Nodosaria cocoaensis Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, p. 66, pl. 10, figs. 5,6; Denralina cooperensis Cushman, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 8, pl. 1, fig. 17; and Denralina jacksonensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 170, pl. 7, figs. 14-16. Discorbis spp. Discorbis yeguaensis Weinzierl and Applin, 1929, Journal of Paleontology, v. 3, p. 405, pl. 44, figs. 5a-5c. Eponides jacksonensis (Cushman and Applin) = Pulvinulina jacksonensis Cushman and Applin, 1926, AAPG, v. IO, no. 2., p. 181, pl. 9, figs. 24-25. *Eponides mexicanus (Cushman) = Pufrinulina mexicana Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, part 3, p. 300, pl. 7, figs. 7-8. Eponides guayabalensis Cole, 1927, Bull. Am. Pal., v. 14, no. 5 1, p. 29, pl. 2, fig s. 17-19, is placed in synonymy with Eponides mexicanus. Eponides spp. *Eponides yeguaensis (Weinzierl and Applin) = Eponides guayabalensis Cole, var. yeguaensis Weinzierl and Applin, 1929, Journal of Paleontology, v. 3, p. 406, pl. 42, figs. 2a-2c. *Flori/us hanrkeni (Cushman and Applin) This tax.on is used sensu faro. The samples studied probably contain Flori/us hantkeni (Cushman and Applin) = Nonionina hantkeni Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 182, pl. 10, figs. 10--11 and Flori/us spissa (Cushman) = Nonionella hantkeni (Cushman and Applin) var spissa Cushman, 1931, Contr. Cushman Lab. Foram. Res., v. 7, p. 58, pl. 7, figs. 13a-13c. Flori/us spp. *Fursenkoina dibollensis (Cushman and Applin) = Virgulina dibollensis Cushman and Applin, 1926, AAPG Bull., v. IO, no. 2, p. 168, pl. 7. 58

Fursenkoina recta (Cushman) = Virgulina recra Cushman, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 12, pl. 1, figs. 3la-3lb. Gaudryina sp. *Glandulina ovata (Cushman and Applin) = Glandulina laevigata d 'Orbigny, var. ovata Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 169, pl. 7, figs. 12-13.

Globulina gibba (d'Orbigny) = Polymorphina gibba d 'Orbigny, 1826, Ann. Sci. Nat., ser. 1, tome 7, p. 266.

Guttulina irregularis (d'Orbigny) = Globulina irregularis d'Orbigny, 1846, Foraminiferes fossiles du bassin tertiare de Yienne, p. 226, pl. 13, figs. 9-10. Guttulina spicaeformis (Roemer) = Polymorphina spicaeformis Roemer, 1838, Neues Jahrb. p. 386, pl. 3, fig. 31. Gyroidina ocrocamerata (Cushman and G. D. Hanna) = Gyroidina soldanii d 'Orbigny, var. ocrocamerata Cushman and G. D . Hanna, 1927, California Acad. Sci. Proc., ser. 4, v. 16, p. 223, pl. 14, figs. 16-18. Hap/ophragmoides dibollensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 163, pl. 6, figs. 1a-1 b. *Haplophragmoides spp. This group of planispiral, multichambered, agglutinated foraminifera probably contains several species and possibly more than one genus. They are often common in the samples studied, but generally poorly preserved.

Lagena cosrara (Williamson) = Enrosolenia costata Williamson, 1858, Recent Foraminifera of Great Britain, p. 9, pl. 1, fig. 18. Lagena sp.

Lenticulina gutticosrara (Gumbel) = Robulina gurricosrara Gumbel, 1868, K. Bayer A1cad. Wiss. Miichen, C 1.2, Abh., v. 10, p. 643, pl. 1, fig. 74. This tax.on is used sensu faro to include the varieties Lenriculina gutticosrara (Gumbel) var. cocoaensis (Cushman) = Crisrellaria gutticosrara (Gumbel) var. cocoaensis Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, p. 67, pl. 10, fig. 11; Lenticulina gutticostara (Gumbel) var. yazooensis Cushman, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 4, pl. 1, fig . 8.

*Lenticulina mexicana (Cushman) = Robulus mexicana (Cushman) = Crisrellaria mexicana Cushman, 1925, AAPG Bull., v. 9, no. 2, p. 299, pl. 7, figs. 1-2. 59

Lenticulina propinqua (Hanrken) = Cristellaria propinqua Hanrken, 1875, K. Ungar. Geol. Anst. Mitt. Jahrb., Bd. 4, Heft 1, p. 52, pl. 5, fig. 4. Lenticulina spp. Marginulina jacksonensis (Cushman and Applin) = Cristellaria jacksonensis Cushman and Applin, 1926, AAPG Bull., v. 10, p. 172, pl. 8, fig. 10. Marginulina spp. *Marginulina texasensis (Cushman and Applin) = Cristellaria fragaria Gumbel var. texasensis Cushman and Applin, 1926, AAPG Bull., v. 10, p. 171, pl. 8, figs. 5-7. Massilina spp.

*Melonis planatum (Cushman and Thomas) = Nonion planatum Cushman and Thomas, 1930, Journal of Paleontology, v. 4, p. 37, pl. 3, figs. Sa-Sb. Melonis spp. Nodosaria mexicana Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, part 1, p. 5, pl. 1, figs. 3-4. Nodosaria!Dentalina spp. Fragments of calcareous uniserial foraminifera are rare in the samples studied. These two genera are probably represented. Nonion advenum (Cushman) = Nonionina advena Cushman, 1922, U. S. Geological Society Prof. Paper 129, p. 139, pl. 32, fig. 8. *Nonion chapapotense Cole, 1928, Bull. Am . Paleontology, v. 14, no. 58, p. 210 (10), pl. 1, figs. 18-19. Nonion spp. *Nonionella cockfieldensis Cushman and Ellisor, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 95-96, pl. 10, fig s. 11 a-1 lc. *Nonionella mauricensis Howe, 1939, Louisiana Geological Survey Bull., no. 14, p. 59, pl. 7, figs. 19- 21. Nonionella spp. *Nummulires spp. This taxon includes species of Operculina of previous authors. Planulina kniffeni Howe, 1939, Louisiana Geological Survey Bull., no. 14, p. 86-87, figs. 1-3. Polymorphina advena Cushman, 1922, U. S. Geological Survey Prof. Paper 129, p. 132, pl. 31, fig. 4. 60

Pseudonodosaria sp. Pseudopolymorphina decora (Reuss)= Polymorphina decora Reuss, 1863, Acad. roy. sci. Belgique Bull., ser. 2, v. 15, p. 152, pl. 3, fig. 41. Pseudopolymorphina dumblei (Cushman and Applin) = Polymorphina compressa d'Orbigny var. dumblei Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2,p. 173,pl.9,figs. 4-5. Quinqueloculina spp. Specimens from the samples studied were often poorly preserved and specific determination was not attempted. Saracenaria hantkeni (Cushman) = Saracenaria arcuata (d'Orbigny) var. hanrkeni Cushman, 1933, Contr. Cushman Lab. Foram. Res., v. 9, p. 4, pl. l, figs. 11-12. Saracenaria sp. Sigmomorphina pseudoirregularis Cushman and Thomas, 1929, Journal of Paleontology, v. 3, p. 178, pl. 23, figs. 5a-5c. Sigmomorphina sp. Siphonina eocenica (Cushman and Applin) = Siphonina advena Cushman var. eocenica Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 180, pl. 9, figs. 16-19. Siphonina claibornensis Cushman, 1927, U. S. Nat. Mus. Proc., v. 72, p. 4, pl. 3, figs. 5a-5c. *Siphonina jacksonensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 180, pl. 9, figs. 20-23. Siphonina spp. *Textularia adalta Cushman, 1926, Contr. Cushman Lab. Foram. Res., v. 2, p. 29, pl. 4, figs. 2a-2b. Texru/aria claibornensis Weinzierl and Applin, 1929, Journal of Paleontology, v. 3, p. 392, pl. 44, figs. 1a-1 b. Texrularia dibol/ensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 165, pl. 5, figs. 12-19. This taxon is used sensu faro to include the variety Textularia dibollensis Cushman and Applin var. humblei Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 164, pl. 6, figs. 7-8. *Textularia hockleyensis Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 164, pl. 6, figs. 3-6. 61

*Texrularia mississippiensis Cushman, 1922, U. S. Geological Society Prof. Paper 129, p. 90 and 125, pl. 14, fig. 4. This taxon is used sensu Lato to include the varieties of this species. This taxon may also include species of the genus Spiroplectamina and its variants, but no well developed initial coils were observed in the specimens examined. Texrularia recta Cushman, 1923, U. S. Geological Survey Prof. Paper 133, p. 17, pl. 1, fig. 2. Textularia spp. Triloculina mindenensis Howe, 1939, Louisiana Geol. Survey Bull., no. 14, p. 37, pl. 3, figs. 11-13. Triloculina spp. Trochamina spp. *Trochamina teasi Cushman and Ellisor, 1931, Contr. Cushman Lab. Foram Res., v. 7, pt. 3, p. 52, pl. 7, fig. 3. *Uvigerina cocoaensis species group. This species group of clinal variants is similar to the one defined by McDougall (1980) and includes Uvigerina alara Cushman and Applin, 1926, AAPG Bull. , v. 10, no. 2, p. 176, pl. 8, fig s. 11-13; Uvigerina cocoaensis Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, part 3, p. 68, pl. 10, fig. 12; Uvigerina conrinuosa Lamb, 1964, Micropaleo., v. 10, no. 4, p. 462; Uvigerina jacksonensis Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, part 3, p. 67, pl. 10, fig . 13. Uvigerina dumblei Cushman and Applin, 1926, AAPG, v. 10, no. 2, p. 177, pl. 8, fi g. 10. *Uvigerina peregrina species group. This group consists of spinose-costate clinal members defined by Lamb and Miller (1984) and includes: Uvigerina gardnerae Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 175, pl. 8, figs. 16-17; Uvigerina gardnerae Cushman, MS., var. texana Cushman and Applin, 1926, AAPG Bull., v. 10, no. 2, p. 175, pl. 8, fig. 18; Uvigerina peregrina Cushman, 1923, U. S. Nat. Mus. Bull., no. 104, p. 166, pl. 42, figs. 7-10. Uvigerina spp. *Uvigerina ropilensis Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, part 1, p. 5, pl. 1, figs 5a-5b. 62

Planktic Foraminifera Chiloguembelina sp. *Globigerina linaperta species group. This is the species group used by Stainforth et al. (1975) and includes Globigerina linaperta Finlay, 1939, Royal Soc. New Zealand Trans., v. 69, p. 125, pl. 13, figs. 54-56; Globigerina eocaena Gumbel, 1868, Bayer. Akad. Wiss. Abh., Math.-Physik. Kl., v. 10, pt. 2, p. 662, pl. 2, fig. 109; Globigerina corpulenta Subbotina, 1953, Vses. Neft. Nauchno-Issled. Geol.-Razved. Inst. Trudy, n. ser., p. 76, pl. 9, figs. 5-7; and Globigerina triparita Koch, 1926, Eclogae Geol. Helvetiae, v. 19, p. 746, fig. 21 a-21 b. *Globigerinarheka barri Bronnimann, 1952, Contr. Cushman Lab. Foram. Res., v. 3, p. 27-28, fig. 1. *Globigerinarheka index (Finlay) = Globigerinoides index Finlay, 1939, Royal Soc. New Zealand Trans., v. 69, p. 125, pl. 4, figs. 85-88.

*Globigerinatheka mexicana (Cushman) = Globigerina mexicana Cushman, 1925, Contr. Cushman Lab. Foram. Res., v. 1, p. 6, pl. 1, fig. 8. *Globigerinarheka semiinvolura (Keijzer) = Globigerinoides semiivolurus Keijzer, 1945, Utrecht Univ. Geogr. Geol. Meded., Physiogr.-geol. Reeks, ser. 2, no. 6, p. 206, pl. 4, fig. 58.

Globororalia cerroazulensis cerroazulensis (Cole) = Globigerina cerro-azulensis Cole, 1928, Bulls. Am. Paleontology, v. 14, p. 17, pl. 1, figs. 11-13. *Globororalia cerroazulensis pomeroli Toumarkine and Bolli, 1970, Rev. Micropaleontologie, v. 13, p. 140, pl. 1, figs. 10-18, pl. 2, figs. 11-19. Hantkenina sp. *Pseudohastigerina micra (Cole) = Nonion micrus Cole, 1927, Bull. Am. Paleontology, v. 14, no. 51, p. 22, pl. 5, fig. 12. 63

PLATE 1.

Scanning electron micrographs

Ammobaculires hockleyensis (d'Orbigny) oblique side view, x 55. 2 Barhysiphon eocenica Cushman and Hanna side view, x 31. 3 Haplophragmoides sp. A side view, x 94. 4, 8 Trochamina rea si Cushman and Ellisor 4, dorsal view, x 80; 8, ventral view, x 73. 5 T exrularia adalra Cushman side \·iew, x 46. 6 Texrularia hockleyensis Cushman and Applin side view, x 39. 7 Texrularia mississippiensis Cu shman side view, x 60. 9-10 Anomalina sp. A 9, dorsal view, x 112; 10, ventral view, x 130. 11 - 12 Anomalina sp. B 11, dorsal view, x 89; 12, ventral view, x 142. 13 Bolivina jacksonensis Cushman and Applin side view, x 112. 14 Bulimina jacksonensis Cushman side view, x 89. 15-16 Cerarobulimina eximia (Rzehak) 15, dorsal view, x 59; 16, ventral view, x 83.

65

PLATE 2

Scanning electron micrographs

1-2 Eponides mexicanus (Cushman) 1, dorsal view, x 42; 2, ventral view, x 77. 3-4 Eponides yeguaensis (Weinzierl and Applin) 3, dorsal view, x 77; 4, ventral view, x 77. 5 Flori/us hanrkeni (Cushman and Applin) side view, x 136. 6 Fursenkoina dibol/ensis (Cushman and Applin) side view, x 77. 7 Glandulina ovara (Cushman and Applin) side view, x 77. 8 Lenriculina mexicana (Cushman) side view, x 77. 9 Marginulina texasensis (Cushman and Applin) side view, x 48. IO Melonis planarum (Cushman and Thomas) side view, x 112. 11 Nonion chapaporense Cole side view, x 106. 12-13 Nonionella cockfieldensis Cushman and Ellisor 12,dorsal view, x 118; 13, ventral view, x 124. 14 Nonione/la mauricensis Howe ventral view, x 100. 15 Nummulites sp. A side view, x 35. 16-17 Siphonina jacksonensis Cushman and Applin 16, dorsal view, x 112; 17, ventral view, x 100.

67

PLATE3

Scanning electron nticrographs

1-3 Uvigerina cocoaensis species group side views of three clinal variants; 1, x 77; 2, x 40; 3, x 77. 4-5 Uvigerina peregrina species group side views of two clinal variants; 4, x 11 8; 5, x 74. 6 Uvigerina topilensis Cushman side view, x 42. 7-8 Globigerina linaperta species group ventral views of two clinal variants; 7, x 118; 8, x 142. 9 Globigerinacheka barri Bronnimann side view, x 124. 10 Globigerinacheka index (Finlay) side view, x 124. 11 Globigerinacheka mexicana (Cushman) side view, x 118. 12 Globigerina semiinvoluca (Keijzer) side view, x 118. 13-14 Globorocalia cerroazulensis pomeroli Tourmarkine and Bolli 13, ventral view, x 106; 14, dorsal view, x 106. 15 Pseudohascigerina micra (Cole) side view, x 142.

69

BIBLIOGRAPHY Barker, R. W., 1960, Taxonomic notes on the species figured by H. B. Brandy in his report on the forarninifera dredged by H. M. S. Challenger during the years 1873-1876. Society of Economic Paleontologists and Mineralogists, Special Publication No. 9, 238 p. Berg, R. R., 1979, Stratigraphy of the Claiborne Group, in D. G. Kersey, ed., Lower Tertiary of the Brazos River Valley, Houston Geological Society Guidebook, p. 5-11. Berg, R. R., 1986, Slumped, delta front reservoir sandstone in the Eocene Yegua Formation, East Sour Lake Field, Southeast Texas. Gulf Coast Association of Geological Societies Transactions, v. 36, p. 401-407. Berger, W. H., E. Vincent, and H. R. Thierstein, 1981, The deep sea record: Major steps in Cenozoic ocean evolution, in J.E. Warme, R. G. Douglas, and E. L. Winterer, eds., The Deep Sea Drilling Project: A Decade of Progress. Society of Economic Paleontologists and Mineralogists, Special Publication No. 32, p. 489-504. Blow, W. H. , 1969, Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. International Conference of Planktonic Microfossils, First Proceedings, v. 1, p. 199-422. Boersma, A. , 1984, Handbook of common Tertiary Uvigerina. Microclimates Press, New York, 207 p. Bronnimann, P., 1952, Globigerinoira and Globigerinarheka, new general from the Tertiary of Trinidad, B.W.I. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 3, p. 25-28. Cole, W. S., 1927, A foraminiferal fauna from the Guayabal formation in Mexico. Bulletin of American Paleontology, v. 14, no. 51, 46 p. Cole, W. S., 1928, A forarniniferal fauna from the Chapapote Formation in Mexico. Bulletin of American Paleontology, v. 14, no. 53, p. 1-32. Curtis, N. M., Jr., 1955, Paleoecology of the Viesca Member of the Weches Formation at Smithville, Texas. Journal of Paleontology, v. 29, no. 2, p. 263-282, pis. 30, 31. Cushman, J. A., 1922a, Foraminifera of the Byram calcareous marl at Byram, Mississippi. ~. S. Geological Survey Professional Paper 129, p. 87-122. 70

Cushman, J. A., 1922b, Forarninifera of the Mint Spring calcareous marl member of the Marianna limestone. U.S. Geological Survey Professional Paper 129, p. 123-152. Cushman, J. A., 1923, The forarninifera of the Atlantic Ocean: Part 4 - Lagenidae. U.S. National Museum Bulletin, no. 104, 228 p. Cushman, J. A., 1925a, An Eocene fauna from the Moctezuma River, Mexico. American Association of Petroleum Geologists Bulletin, v. 9, no. 2, p. 298-303. Cushman, J. A., 1925b, Eocene forarninifera from the Cocoa sand of Alabama. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 1,no. 3,p.65-69. Cushman, J. A., 1925c, New forarninifera from the upper Eocene of Mexico. Contribution from the Cushman Laboratory, v. 1, no. 1, p. 4-8. Cushman, J. A., 1926, Some new foraminifera from the upper Eocene of the southeastern Coastal Plain of the United States, Contributions from the Cushman Laboratory for Foraminiferal Research, v. 2, part 2, p. 29-36. Cushman, J. A. , 1927, Foraminifera of the genus Siphonina and related genera. U.S. National Museum Proceedings, v. 72, no. 2716, art. 20, 15 p. Cushman, J. A., 1931, Three new upper Eocene foraminifera. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 7, part 3, p. 58-59. Cushman, J. A., 1933, New foraminifera from the upper Jackson Eocene of the southeastern Coastal Plain Region of the United States. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 9, part l, p. 1-21. Cushman, J. A., 1935, Upper Eocene foraminifera of the southeastern United States. U.S. Geological Survey, Professional paper 181 , 88 p. Cushman, J. A., and A. C. Ellisor, 1931, Some new Tertiary foraminifera from Texas. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 7. pt. 3, p. 51-58. Cushman, J. A., and A. C. Ellisor, 1933, Two new Texas foraminifera. Contributions from the Cushman Laboratory for Foraminiferal Research, v. 9, p. 95-96, pl. 10. Cushman, J. A., and E. R. Applin, 1926, Texas Jackson foraminifera. American Association of Petroleum Geologists Bulletin, v. 10, no. 2, p. 154-189. 71

Cushman, J. A., and E. R. Applin, 1943, The fora min ifera of the type locality of the Yegua Formation of Texas. Contributions from the Cushman Laboratory forforaminiferal Research, v. 19, no. 245, p. 28-46. Cushman, J. A., and G. D. Hanna, 1927, Forarninifera from the Eocene near Coalinga, California. California Academy of Sciences Proceedings, 4th ser., v. 16,no. 8,p.205-228. Cushman, J. A., and N. L. Thomas, 1929, Abundant forarninifera of the east Texas greensands. Journal of Paleontology, v. 3., p. 176-184. Cushman, J. A., and N. L. Thomas, 1930, Common foraminifera of the east Texas greensands, Journal of Paleontology, v. 4, no. 1, p. 33-41. Davis, F. E., 1941, Textularia from the Texas Tertiary. Journal of Paleontology, v. 15, no. 2, p. 144-152. Davis, J. C., 1986, Statistics and data analysis in geology - second edition. John Wiley and Sons, New York, p. 468-615. Deussen, A., 1914, Geology and underground waters of the southeastern part of the Texas Coastal Plain. U. S. Geological Survey, Water-Supply Paper 335, 365 p. Douglas, R. G. , 1979, Benthic forarniniferal ecology and paleoecology: A review of concepts and methods, in J. H. Lipps, W. H. Berger, M. A. Buzas, R. G. Douglas and C. A. Ross, eds., Foraminiferal ecology and paleoecology. Society of Economic Paleontologists and Mineralogists, Short Course No. 6, Houston, Texas, p. 21-53. Douglas, R. G., and F. Woodruff, 1981, Deep sea benthic foraminifera, in C. Emiliani, ed., The oceanic lithosphere, The Sea. Wiley-lnterscience, New York, v. 7, p. 1233-1327. Dumble, E. T., 1918, The geology of east Texas. University of Texas Bulletin 1869, p. 102-106. Eames, F. T., F. T. Banner, W. H. Blow, and W. J. Clark, 1962, Fundamentals of Mid-Tertiary stratigraphical correlation. Cambridge University Press, Cambridge, 163 p. Eargle, D. H., 1968, Nomenclature of formations of Claiborne Group, middle Eocene coastal plain of Texas. U.S. Geological Survey Bulletin, 1251-D, 25 p. Fichtel, I. von, and J. P. C. von Moll, 1803, Testacea microscopica al laque minute ex generibus Argonauta et Nautilus. Wien, Osterreich, p. 107. 72

Finlay, H.J., 1939, New Zealand fora.m.inifera; key species in stratigraphy. No. 2: Royal Soc. New Zealand Transactions, v. 69, p. 89-128, pls. 11-14. Fisher, W. L., 1964, Sedimentary patterns in Eocene cyclic deposits, northern Gulf Coast region. Kansas State Geological Survey Bulletin, v. 1, p. 151-170. Fisher, W. L., 1969, Facies characterization of Gulf Coast Basin delta systems with some Holocene analogies. Gulf Coast Association of Geological Societies Transactions, v. 19, p. 239-261. Frane, J., R. Jennrich, and P. Sampson, 1985, Factor analysis, in W. J. Dixon, ed., BMDP Statistical Software Manual. University of California Press, Berkeley, California, p. 480-499. Galloway, W. E., and D. K. Hobday, 1983, Terrigenous elastic depositional systems. Springer-Verlag, New York, 423 p. Galloway, W. E., T. E. Ewing, C. M. Garrett, N. Tyler, and D. G. Bebout, 1983, Atlas of major Texas oil reservoirs. Bureau of Economic Geology, p. 8-11. Gardner, J., 1927, The correlation of the marine Yegua of the type sections. Journal of Paleontology, v. 1, no. 3, p. 245-251. Gernant, R. E., and R. Y. Kesling, 1966, Foraminiferal paleoecology and paleoenvironmental reconstruction of the Oligocene middle Frio in Chambers County, Texas. Transactions - Gulf Coast Association of Geological Studies, V. 16, p. 131-158. Gevirtz, J. L., R. A. Park, and G. M. Friedman, 1971 , Paraecology of benthonic foraminifera and associated micro-organisms of the continental shelf off Long Island, New York. Journal of Paleontology, v. 45, no. 2, p. 153-177. Gibson, T. G.! and M.A. Buzas, 1973, Species diversity: patterns in modern and Miocene fora.m.inifera of the eastern margin of North America. Geological Society of America Bulletin, v. 84, p. 217-238. Gumbel, C. W ., l 868a, Beitrage zur Fora.m.iniferen fauna der nordalpinen Eocangebilde. K. Bayer. Akad. Wiss. Munchen, Math.-Physik. Kl., Abh., Munchen, Deutschland, Bd. 10, Abt. 2, p. 643. Gumbel, C. W., 1868b, Beitrage zur Foraminiferen fauna der nordalpinen, filtern Eocagebilde oder der kressenberger Nummulitenschichten. Bayerische A.lead. Wiss. Abh., Math.-Physik. Kl., v. 10, pt. 2, p. 579-730, pis. 1-4. 73

Hantkeni, M . von, 1875, Die Fauna der Clavulina szaboi - Schichten; Theil I - Foraminiferen. Hungary, K. Ungar. Geol. Anst., Mitt. Jahrb., Budapest, Ungarn, Bd. 4, Heft 1, p. 52. Houston Geological Society Study Group, 1954, Stratigraphy of the upper Gulf Coast of Texas and strike and dip cross sections upper Gulf Coast of Texas. Houston Geological Society Study Group Repon 1953-1954, 26 p. Houston Geological Society Study Group, 1962, Yegua and Wilcox potential upper Texas Gulf Coast. Gulf Coast Association of Geological Societies Transactions, v. 12, p. 27-37. Howe, H. V., 1939, Louisiana Cook Mountain Eocene foraminifera. Louisiana Geological Survey Bulletin, no. 14, 122 p. Israelsky, M. C., 1935, Tentative foraminiferal zonation of subsurface Claiborne of Texas and Louisiana. American Association of Petroleum Geologists Bulletin, v. 19, no. 5, p. 689--695. Jackson, M. L. W., and L. E. Garner, 1982, Environmental geology of the Yegua-Jackson lignite belt, southeast Texas. Bureau of Economic Geology, Report of Investigations No. 129, 36 p. Keijzer, F. G., 1945, Outline of the geology of the eastern part of the Province of Oriente, Cuba (E. of 76° W. L.), with notes on the geology of other parts of the island. Utrecht Univ. Geogr. Geol. Meded., Physiogr.-geol. Reeks, ser. 2, no. 6, 238 p. Keller, G ., 1983, Paleoclimatic analyses of middle Eocene through Oligocene planktic foraminiferal faunas. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 43, p. 73-94. Koch, R. E., 1926, Mitteltertiare Foraminiferen aus Bulongan, Ost.-Borneo. Eclogae Geol. Helvetiae, v. 19, p. 722-751. Koenig, K. J., 1979, Micropaleontologic biostratigraphy of the Claiborne Group, in D. G. Kersey, ed., Lower Teniary of the Brazos River Valley. Houston Geological Society Guidebook, p. 14-17. Lamb, J. L ., and T. H. Miller, 1984, Stratigraphic significance of uvigerinid foraminifers in the western hemisphere. University of Kansas Paleontological Contributions, art. 66, 99 p. LeBlanc, R. J., Jr., 1970, Environments of deposition of the Yegua Formation (Eocene), Brazos County, Texas. Texas A & M University, unpublished M.S. thesis, 157 p. 74

LeBlanc, R. J., Jr., 1979, Depositional systems in the Yegua Formation, Brazos County, Texas, in D. G. Kersey, ed., lower Tertiary of the Brazos River Valley, Houston Geological Society Guidebook, p. 18-25. Loeblich, A. R., and H. Tappan, 1964, Treastise on Invertebrate Paleontology: Part C - Protista 2. The Geological Society of America and The University of Kansas Press, v. 1 and 2, 900 p. Loucks, R. G., M. M. Dodge, and W. E. Galloway, 1986, Controls on porosity and permeability of hydrocarbon reservoirs in Lower Tertiary sandstones along the Texas Gulf Coast. Bureau of Economic Geology, Report of Investigations No. 149, 78 p. McDougal, K., 1980, Paleoecological evaluation of late Eocene biostratigraphic zonations of the Pacific Coast of Nonh America. Society of Economic Paleontologists and Mineralogists, Special Publication No. 2, 238 p. Members of the New Orleans Paleoecologic Committee, Gulf Coast Section, Society of Economic Paleontologists and Mineralogists, 1966, Forarniniferal ecological zones of the Gulf Coast. Gulf Coast Association of Geological Society Transactions, v. 16, p. 345-347. Orbigny, A. d', 1826, Tableau methodique de la classe des Cephalopodes. Ann. Sci. Nat., Paris, France, ser. 1, tome 7, p. 266. Orbigny, A. d', 1946, Forarniniferes fossils du bassin tertiarre de Yienne, p. 137. Park, R. A., 1974, A multivariate analytical strategy for classifying paleoenvironments. Mathematical Geology, v. 6, no. 4, p. 333-352. Phleger, F. B., and F. L. Parker, 1951, Ecology of forarninifera, northwest Gulf of Mexico. The Geological Society of America, Memoir 46, 152 p. Poag, C. W., 1981, Ecologic atlas of benthic forarninifera of the Gulf of Mexico. Marine Science International, Woods Hole, Massachusetts, 175 p. Poag, C. W., 1986, Forarniniferal characteristics of late Cretaceous and Cenozoic bathyal lithtopes. Gulf Coast Association of Geological Societies Transactions, v. 36, p. 533-539. Poag, C. W ., and P. C. Y al en tine, 1976, Biostratigraphy and ecostratigraphy of the Pleistocene Basin Texas - Louisiana continental shelf. Gulf Coast Association of Geological Societies Transactions, v. 26, p. 185-256. Postuma, J. A., 1971, Manual of planktonic forarninifera. Elsevier Publishing Company, Amsterdam, 420 p. 75

Roemer, F. A., 1838, Die Cephalopoden des Nord-Deutschen tertiaren Meersandes. Neues Jahrb. Min. Geogn. Geol. Petref.-Kunde, Stuttgart, Deutschland, p. 386. Reuss, A. E., 1863, Les foraminiferes du Crag d'Anvers. Acad. Roy. Sci. Lettres. Beaux-Arts Belgique, Bull., Bruxelles, Belgique, ser. 2, V. 15, p. 152. Rzehak, A., 1888, Die Foraminiferen des Kieseligen Kalkes von Nieder - Hollabrunn und des Melettamergels der Umgebung von Bruderndorf in Niederosterreich. Vienna, Nat. Hofmuseums, Ann., Wien, Bd. 3, p. 263. Siesser, W. G., 1984, Paleogene sea levels and climates: U.S. A. eastern Gulf Coastal Plain. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 47, p. 261-275. Skinner, H. C., W. E. Steinkraus, C. C. Albers, et al., H . C. Eppert, Jr., and G. C. Glaser, 1972, in H. C. Skinner, ed., Gulf Coast stratigraphic correlation methods with· an atlas and catalogue of principal index foraminifera. Louisiana Heritage Press, New Orleans, 213 p. Stadnichenko, M. M., 1927, The foraminifera and ostracoda of the marine Yegua of the type sections. Journal of Paleontology, v. 1, no. 3, p. 221-242. Stainforth, R. M., J. L. Lamb, Hanspeter Luterbacher, J. H. Beard, and R. M. Jeffords, 1975, Cenozoic plank.tonic foraminiferal zonation and characteristics of index forams. The University of Kansas Paleontological Contributions, art. 62, 162 p. Stenzel, H. B., 1939, The Yegua Problem. The University of Texas Publication No. 3945, p. 847-910. Stuckey, C. W., Jr., 1978, Milestones in Gulf Coast economic micropaleontology. Gulf Coast Association Geological Society Transactions, v. 28, part 2, p. 621-625. Subbotina, N. N., 1953, Iskopaemye foraminifery SSSR; Globigerinidae, Hantkeninidae i Globorotaliidae: Vses. Neft. Nauchno-Issled. Geol.­ Razved. Inst. Trudy, n. ser., no. 76, 296 p. Tourrnarkine, M., and H. M. Bolli, 1970, Evolution de Globorotalia cerroazulensis (Cole) dans l'Eocene moyen et superieur de Possagno (Italic). Rev. Micropaleontologie, v. 13, p. 131-145. Tourrnarkine, M., and Hanspeter Luterbacher, 1985, Paleocene and Eocene planktic foraminifera, in H. M . Bolli, J. B. Saunders, K. Perch-Nielsen, eds., Plankton Stratigraphy, Cambridge University Press, Cambridge, p. 87-154. 76

Weinzierl, L. L., and E. R. Applin, 1929, The Claiborne Formation on the coastal domes. Journal of Paleontology, v. 3, p. 384-410. Winkler, C. D., and M. B. Edwards, 1983, Unstable progradational elastic shelf margins. Society of Economic Paleontologists and Mineralogists, Special Publication No. 33, p. 139-157.

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Key to symbols: P =Present C = Common

Insert 2. Species checklist of benthic and planktic foraminifera for Well A. Mlt.M1•·f\\ f '••l1Ult'(iV l f\l•f!i°:f'1Hl11'f r11 F"I\• , ..,, N'I Of C· I , ,,1 °" 1r''' ~r· 11 Nr-rc;­ UNl\/l kSll 1 OF inns Ai llUSTIN

EXAl"IJNED 8Yt !:~~~!~~~------·-- DA1Et NOTES•

II

Agglutinated Benthics Calcareous Benthics Plank tics Accessory Materials

5435- 5•66 17 10 JO 4.\ 5 16 9 14 3 b 3 • p p p p p p 54b6- 54«17 2• 27 • :so 12 45 7 .. p :t•~5-!i«lbb 'I 11 9 2 3 p p p p p 5•9?- 5 528 20 31 ? •I 9 17 23 I .. p ~•bb - ~11-57'H 11 6 15 18 22 18 3 2 20 13 " • :1e90 .. :sq21 6 21 B :s 27 3 I 3 2 '2 2 2 10 c c p p S829-50:59 21 8 12 12 2< 19 1 2 I 17 ~ " 5 3 5952- 5993 9 12 lb 13 3 l 3 27 B e • 5 2 I I 2 2 II p p p p !5890•5nl 20 21 15 15 19 26 3 3 l 27 12 10 2 9 • b014-b045 2 31 4 6 I 5 I 10 2 3 2 13 ) p p p p 5952· :1993 31 9 14 20 13 IB 3 2 15 12 bl0?-6138 2 39 3 2 8 3 5 2 I 6 2 p p p p p p p p p b014 b04~ 34 9 19 12 20 17 6 5 2 I 17 • 6169- 6200 31 28 27 10 20 25 ~7 ~3 ~ 2 2 42 3 2 14 I I • 6 7 4 I 2 :z 6 I p p c c p c p 1>107 bl39 I I 29 I 2 24 16 18 12 4 • ,. 6231 -6262 19 ., 10 17 6 16 i: ; I 34 :s 3 17 5 2 2 18 9 B 2 23 8 p c p c p blb~ · b200 I I 3 10 8 " 2 6262-6293 19 15 9 10 • 5 7 7 3 I 15 3 3 I :;: 3 7 2 r P p b231- b21>2 I II 3 !I • 3 1>355-6396 • I 16 7 2 I I I I I p p p 6262·62'13 10 e • 12 9 1:s 2 I 7 b b417-b448 4 3 I 4 2 7 2 p p bl55- •38b 9 4 I 5 I 8 2 6 2 2 • 2 4 2 3 2 I 4 p p p p 6417-b448 1>•79-6:101 18 12 10 10 15 19 3 5 2 17 3 2 8 b 2 2 4 12 2 3 p p p 0,479 ... ~~0 l 65b3-b594 7 5 6 2 I 7 7 3 • 5 1 2 8 6 2 I 3 3 3 9 p p p 6563- 6594 6:S94-6b25 13 4 5 7 3 2 2 14 l 2 I 2 6 3 B 2 p p ti594- bb:.t5

Key to symbols: P =Present C =Common

Insert 3. Species checklist of benthic <>.nd planktic foraminifera for Well B. 111n, u1 ·n 1 l ,lN'10I Hr·V 1. nHJIU,ltlh V ,,,., b OlttrNt nr r.r n 1. n r.: 1r"1 r..c-11 Nrrr. UNIVCnsnv or- l rlAS Al l\USllN

[XA.'1JNED ev. T. B. LAY.. AN NOlES• ------··---

------·------..4 ------:------··------.... ------... ------

Agglutinated Benthics Calcareous Benthics Planktics Accessory Materials

7413-7445 7413-7445 15 I 4 12 17 2 6b 20 I 2 3 9 2 16 I 31 3 2 6 2 B 6 7 39 23 I 7445-7476 7445- 7476 • 4 3 18 16 2 55 16 2 14 6 I 18 4 39 2 5 10 • 47 23 3 4 2 I• I 5 .. 7476-7509 7476-7508 9 4 16 5 16 6 4 7 14 I 2 7 5 2 14 32 8 4 4 2 14 3 38 20 12 II 2 ·3 · I 8 2 7508-7539 18 3 7 3 7 • 7:508 - 7~39 38 13 b 10 8 I 24 4 31 3 I I 5 • 5 47 17 - 7 7 5 7 4 3 7539-7563 "/539·75 b3 17 I 10 22 e 4 2 2 I 63 18 5 10 2 . 15 5 28 3 I I 15 6 44 16 4 12 I 2 6 4 I 3 2 I 7563- 7594 7563-7594 II 4 • 12 12 4 4 I 2 52 10 I 2 7 13 5 39 3 14 I 2 3 14 8 2" 15 6 8 2 8 I I 2 I 5 7~94-76::?5 759•·7b25 17 4 e J4 s~ 2 4 65 II 4 e 21 3 25 2 I 17 4 23 20 5 3 I 2 2 9 3 3 I 4 I 2 I I 2 7625-7656 7625-7656 10 4 8 8 17 2 3 2 2 40 12 I 5 I 2 27 I 36 3 2 4 l'I I 41 12 4 6 2 13 5 2 I I 11 2 5 I 2 76:i6-7687 7656- 7687 12 2 4 4 12 I I I 4 :14 16 I 2 3 3 I 10 5 3? 2 3 3 7 6 53 • I I 15 12 I 3 2 2 7 2 7687-7718 7687-7718 17 3 • 10 15 5 2 ::lb 7 .7 2 2 • 2 2 II 8 17 4 3 13 s 46 6 7 2 3 6 4 2 4 2 8 16 7718-7749 7718-7749 JS:? u. .. 8 3 4 I 22 12 10 4 8 I 2 33 3 42 3 3 13 2 36 10 I 4 25 :z 5 2 10 3 6 7749-7780 774.. · 7780 • 2 3 10 6 I II I 2 25 9 4 4 47 2 20 3 31 I 7 2 20 I 30 14 2 2 4 • 3 12 3 7825-7856 78~5-7856 7 4 15 4 4 2 I 40 10 I 40 2 3 2 12 6 4 1> I 2 7 3 25 15 5 3 2 14 I I 2 4 4 2 7851>-7888 78:16-7888 8 • II 2 3 2 2 30 6 3 3 39 9 - 17 4 28 5 6 2 17 I 30 7 5 I I 12 4 2 I 4 2 3 I 7888-7919 7888-7"1'1 15 3 • 8 10 3 2 2'1 15 I 34· 4 3 I 10 5 34 5 14 4 55 II 3 :z 2 5 I 3 2 •8 3 791'1-7951 7'119-7951 7 3 10 5 s 4 3 •5 3 2 21 s 3 .· 47 I 3 15 I 46 5 3 16 2 28 13 2 I I 4 2 3 2 3 2 II 3 4 3 79:11-7983 7'1:11-7983 9 2 8 13 3 4 6 5 13 • I :z 10 • 52 6 7 2 56 4 5 3 2 6 3 I 14 2 2 47 7983-8014 7983-8014 15 2 7 6 2 • 2 :i 37 6 I 4 2 . 4 14 I 37 7 2 14 I 4 0 13 5 I II 3 6 3 5 31 8014· 8046 eo14·8046 10 I ••II 8 6 5 I 20 S I I 4 4 .2 .. I 3 5 2 53 19 3 I 2 4 3 2 3 8 2 I II 8046-8077 8046-8077 10 s 9 13 •1 6 3 4 2 32 21 3 13 3 8 4 44 2 I 12 41 14 • 3 3 14 4 2 II 3 2 8077-8128 8077-8128 3 8 3 s 13 4 2 57 II 2 • ... 5 :z I 2 :27 I 6 2 39 17 4 17 5 2 2 18 8128-8159 8128-81:1'1 2 .. s 10 3 7 ~ 3 2 I 51 8 :z I II 3 IB I I 6 3:; l'I 3 I 10 3 4 2 16 8159-8190 3 3 • 8 I · 3 81'!5'1-8190 16 13 I 2 .. :z 5 5 2 30 I B 2 45 24 I 2 21 2 3 4 13 8190-8221 8190-8221 5 I 6 11 :n S I 58 7 4 2 5 4 39 I 3 I 8 2 45 29 10 14 2 3 •2 I 3 14 8221-8252 I 3 8 8221-8:'52 s 13 2 3 I 49 :z :z 6 3 2 II 3 22 4 2 12 I 76 11 11 • 2 3 2:2 2 3 2 3 4 I 2 4 IS 8Z52·8283 8252-8283 • 6 5 15 s 6 7 5 28 14 4 60 :z 8 I 2 I 16 I e 6 57 9 II I 10 7 I ; I 2 3 8283 - 831~ 8283-8315 3 3 20 • 1 8 s 3 2 :23 7 2 4 9 25 3 e 4 2 2 8 8315-8344 831:1-83•6 8 • 23 34 I 24 • 4 21 22 5 14 4 I 2

Key to symbols: P =Present C=Common

Insert 4. Species checklist of benthic and planktic foraminifera for Well C. 11 1CllOP"'-&:OHTO..CIOV t..A-ATORV DEPART11ENT OF GEO..DOICAt. SCIEM:EB UNlllEJ!!llTV OF T'EXA!I AT AUSTIN

l'ROJECT• Y£UUA FDl'MTtON BIOFACIES -.vs 1s-T'Dl9 'OESll SECTIOH/WEU.•--- CONRlll>- --· --FIELD UNIT wELL Ml.- 2720 AA£A OR FIEl..Ot ---COHR0£ FIELD - ----· SECTIOHt' --TOWNSHtp;--- --RiiHii£-;- 8"• COUOITY • IOONTGOfERV------STATii:• fX-- - FOR weu.s=KiELEVATtONr------TDTl'l. o£..- -TH-t------F OR SECTIONS- TOTAl. THICKNESS1'iS4- l'IETHOD OF "EASUiiiP£~--- EXMINED BY• T.8. LAY­ DATE1 SD'TE"BER I '197 NOTES1 ------

(/) () .... (/) VJ ..c () .µ ..... ~ i:: 11) .s ·c i:: m 11) £ "d C1) m .... (/) ~ cd ::s e:- i:: 0 0 ·a C1) (/) ::s (/) ...... ~ 11) bl) () t>.Q ~ 8 <( I u I <(

Ul.. Ulz I.II > Ul I.II .J 0.. a. -Ul :..: 0.. a. z CJ Ul Ul I.II 0 z :x: Ul QC .J ;i: Ul CJ :x: I.II z UI w 0 .... w m 0 a -:> ...... 0 .J z -z QC z r a. -..J 0 Li.I -QC r 0 a. :x: >

Insert 5. Species checklist of benthic and planktic foraminifera for the Cored Well. N\tV SE A . 0 A' 0 Cl) 0 N (\j 1 2 eni._ 53 mi. A c . . I

RL . ------Explanation

mi. RES. MARKER oJ---d T = Marine transgressive phase RU = Upper regressive phase RL = Lower regressive phase 200 ] DF = Delta front environment * 21314 ft. DP = Delta plain environment PD/E = Prodelta/Embayment environments MT = Marine transgressive shelf environment 1 = Eponides mexicanus biofacies 2 = Flori/us hantkeni biofacies 3 = Uvigerina spp. biofacies 4 = Textularia spp. biofacies Insert 6. Lithofacies cross section. 5 = Ammobaculites hockleyensis biofacies See Figure 1 for location of wells. Dashed line is the base of the Yegua Fonnation.