Thesis Proposal:

Salt Reconstruction and Study of Depositional History, Upper Jurassic, East Texas

Basin

By: Krista Mondelli

Advisor: Dr. Chris Liner

April, 2009

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Introduction

The East Texas Basin covers a large part of eastern Texas, and is approximately

100 square miles, as seen in Figure 1. According to Goldhammer and Johnson (2001), it

is part of the eastern Gulf of Mexico tectono-stratigraphic province, meaning that during

the Middle and Upper Jurassic, it was undergoing rifting due to the opening of the Gulf

of Mexico. The tectonic evolution of this area had an impact on its unique structures and

contributed to and influenced sedimentary deposition throughout the region. The East

Texas Basin is bounded to the east by the Sabine Uplift, while the Talco Fault Zone

forms the northern and western edges, and the Angeline Flexure contains the southern

area.

Since the initial discoveries in the 1930s, the Upper Jurassic rocks of the East

Texas Basin and northern Louisiana have proven to be major producers of hydrocarbons,

producing over 20 TCFG and 900 MMBO (Ewing, 2001). Today, researchers are

looking to expand their studies of the hydrocarbon potential through a better

understanding of salt tectonics and rifting in the area. While there are several published

interpretations of the depositional environments of the formations of the East Texas

Basin, there are varying ideas and conflicting models. The purpose of this study is to test

these published interpretations by recreating the paleotopography and depositional setting

as each formation was formed in hopes of learning more about the impact of the

underlying salt and its affect on basin development at each depositional stage. This study

will focus on reconstructing the base of salt on regional (2D) and local (3D) seismic lines

across Freestone, Leon, and Houston counties in Texas (Figure 2). The aim is to gain a

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better understanding of basin history and the influence of salt tectonics on deposition and

hydrocarbon potential of the Bossier Formation.

Objectives

The focus of this study is to clarify the depositional environments during Bossier

and Cotton Valley time by reconstructing the basin history. The depositional models

described below will be tested by recreating the salt surface at the time of deposition and

estimating accommodation space, sediment supply, and timing of subsequent

depositional events. These models will serve as guidelines in the reconstruction process,

but they will also be challenged to assure that they agree with and fit both the geological

and geophysical models.

I will evaluate the interplay between salt movement and Upper Jurassic deposition

in the East Texas Basin. The post-salt formations of interest, in depositional order, are

the Cotton Valley Limestone, the Bossier and Cotton Valley sands. The Cotton Valley

Limestone marks the top of the Louark Group and is regionally underlain by the Buckner,

Smackover, and Norphlet Formations respectively (Williams et al., 2001). The Bossier

shales and sands represent the first deposits of the Cotton Valley Group and are overlain

by the Cotton Valley Sandstone and the Knowles Limestone (Figure 3).

Salt tectonics was both influenced by younger deposition and controlled the

topography over which the subsequent formations were distributed. The Louann Salt was

deposited in the Middle Jurassic during the rifting of Pangea and the opening of the Gulf

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of Mexico (Goldhammer and Johnson, 2001). At the time of deposition, the Louann Salt

was laid down in a restricted marine environment and reached thicknesses of

approximately 5,000 feet, but over time, through dissolution and post-depositional

halokinesis, the salt dissipated in many areas leaving a highly variable surface for future

deposition (Maione and Pickford, 2001). This surface, figure 4, controlled the

distribution of the overlying formations and changed through time with sediment loading

and salt movement. Pillow structures, diapirs, and turtle structures are a few of the

elements left behind that have influenced later deposition. With the help of 2D

restoration, these can be reconstructed to depositional time to better illustrate the timing

and methods of salt movement. These structures are also of interest as hydrocarbon traps.

Depositional Models

The Middle Jurassic was marked by the opening of the Gulf of Mexico and the

deposition of the Luann Salt. During the Upper Jurassic, four major river systems

supplied sediment to the East Texas, North Louisiana, and Mississippi regions, which

cradled several salt filled post-rift basins. The ancestral Red River supplied sediments

from the northwest, while the ancestral Ouachita River came in from the north, the

ancestral Mississippi River from the northeast, and the ancestral Alabama River from the

east (Ewing, 2001). Via these river systems, the Norphlet Formation was deposited

during the Late Jurassic as a thin siliciclastic fluvial and eolian formation over eastern

Texas, northern Louisiana, Mississippi, and Alabama. Overlying the Norphlet is the

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Smackover Formation, which is Oxfordian in age and consists of limestones and a belt of

oolite shoals deposited as part of a carbonate ramp system.

Above the Smackover, lies the Kimmeridgian aged Buckner evaporites. Due to a

limited supply of terrigenous sediments from the north and northwest during

Kimmeridgian time, the Buckner was deposited as part of a restricted carbonate platform-

facies that allowed for development of evaporites behind carbonate belts (Ewing, 2001).

A sequence boundary has been interpreted at the top of the Buckner to mark the transition

into the Haynesville/Gilmer/Cotton Valley Lime Formations.

The top of the Louark Group is defined by the Cotton Valley Limestone

Formation, which sits atop the Buckner Formation and in this study, is synonymous with

the Haynesville and Gilmer Formations. Similar to the Smackover Formation, the Cotton

Valley Lime consists of oolitic shoal complexes. However, they are found more seaward

than the Smackover shoals and beyond them the Cotton Valley Lime is present in the

form of pinnacle reefs. The shoals reflect a pattern of deposition along the pre-

Smackover structural highs, specifically Sabine and Wiggins Islands, as well as older salt

and basement highs. The shoals and reefs of the Cotton Valley Lime are structurally

complex as they were strongly impacted by salt movement (Ewing, 2001). Seismic

reconstruction along this horizon will help to determine the overall influence of salt

movement on the Cotton Valley Lime as well as its affect on the deposition of overlying

sediments.

The end of Kimmeridgian deposition is marked by a flooding surface representing

a major transgression in which carbonate deposition ceased across the region

(Goldhammer and Johnson, 2001). Above the Cotton Valley Lime, the Bossier Formation

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marks the beginning of the Tithonian aged Cotton Valley Group, which includes the

Bossier, Cotton Valley Sandstone, and Knowles Formations. At the beginning of Cotton

Valley time, due to the major flooding event, fine-grained marine shales of the Bossier

Formation were deposited. Above these shales are several sand-rich parasequences that

represent a lowstand progradation and comprise the Bossier sands (Williams et al., 2001).

Following the deposition of the Bossier, there is a transition from lowstand to highstand

in which there is a shift from deposition of deep marine shaly units to more sand-rich

shallow marine complexes. This corresponds to an increase in siliciclastics from the

ancestral Red, Ouachita, and Mississippi Rivers, which created fluvial and progradational

deltaic complexes known as the Cotton Valley Sands (Klein and Chaivre, 2002 and

Williams et al., 2001). Both the Bossier and Cotton Valley Sand Formations are proven

hydrocarbon reservoirs in the East Texas Basin, and are a main point of interest in my

study to determine how salt tectonics influenced their deposition and hydrocarbon

potential.

The youngest formation in the Cotton Valley Group and the last of interest in this

study is the Knowles Limestone. It was deposited at the end of Tithonian time during a

period of marine transgression, and it is interpreted to be a shelf-edge carbonate ramp that

covers the southeastern portion of the East Texas Basin (Ewing, 2001).

These depositional models will be tested and refined during the reconstruction

process. At each stage of the process, these models will be examined to see how well

they fit with the paleo-restoration, and they will be revised as needed.

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Methodology

Several interpretations have been published regarding the depositional history of

the East Texas Basin. With the help of seismic, this area has been studied extensively.

However, there are still inconsistencies in interpretation and many missing pieces. Klein

and Chaivre, 2001 published an interpretation of one of the same lines that this study will

attempt to reconstruct (Figure 5). Their interpretation will serve as a scenario to test and

balance as the layers are rebuilt.

For this study, one regional 2D seismic line, approximately 60 miles in length, has

been selected and is currently being reprocessed to enhance data quality. There is also

newly acquired 3D coverage over the areas of interest and applicable 3D lines will be

implemented as needed.

Using Geologic Systems Lithotect software, it is possible to reconstruct the base

of salt on seismic lines in this area in order to rebuild the foundation upon which the

sediments were deposited (Figure 6). By hypothetically reversing geologic time, the

methods and timing of deposition, transportation, structural and depositional deformation

can be studied. This will aid in predicting depositional characteristics and structural

trends within the formations and supply valuable insight into basin development,

reservoir distribution, and hydrocarbon potential in the basin.

Well log information and isopachs of the Cotton Valley and Bossier Formations

are available, and will be used to help correlate the seismic and sequence stratigraphic

models. They will also be tied into the restoration process to clarify uncertainties and

provide a better model.

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Summary

In conclusion, the purpose of this study is to confirm the depositional

environments of the Upper Jurassic formations and how salt movement influenced

accommodation space, reservoir distribution, structural and depositional trends and

impacted the overall basin history. It will include geophysical interpretation of seismic

data along with sequence stratigraphic modeling and seismic reconstruction of 2D and 3D

seismic lines over Freestone, Leon, and Houston counties in the East Texas Basin. This

project will build upon previous research and present a refined and comprehensive

picture of the depositional environments of the Upper Jurassic formations, while focusing

on the Bossier Formation and its relation to salt tectonics and the resulting influence on

basin development and hydrocarbon potential.

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Timeline

April – May, 2009

- Reprocess regional 2D seismic line

- Research depositional models and hydrocarbon systems in the basin

- Become familiar with LithoTect software

o Complete tutorials and establish workflow

o Load seismic line and create stratigraphic column

Summer, 2009

- Begin reconstruction process

- Build models in LithoTect

- Add 3D lines as needed

- Start to develop basin history

o Work from local area to more regional view

- Begin compiling citations and generate thesis introduction and background

Fall, 2009

- Complete reconstruction

- Apply reconstruction to basin history model and framework

- Compile results and compare models

o Compare results with published interpretations

o Assess which models are the most balanced, and which fit with the

geological and geophysical models the best

- Incorporate results and finalize thesis discussion and conclusions

Spring, 2010

- Complete first draft of thesis

- Review and make revisions until finalized

- Defend thesis

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Works Cited

Ewing, Thomas E, 2001, Review of Late Jurassic Depositional Systems and Potential Hydrocarbon Plays, Northern Gulf of Mexico Basin: Gulf Coast Association of Geological Societies Transactions, v. LI, p. 85-96.

Goldhammer, R. K., and C. A. Johnson, Middle Jurassic-Upper Cretaceous

paleogeographic evolution and sequence-stratigraphic framework of the northwest Gulf of Mexico rim, in C. Bartolini, R. T. Buffler, and A. Cantú-Chapa, eds., The western Gulf of Mexico Basin: Tectonics, sedimentary basins, and petroleum systems: AAPG Memoir 75, p. 45-81.

Jackson, M.P.A. and S.J. Seni, 1983, Geometry and evolution of salt structures in a

marginal rift basin of the Gulf of Mexico, east Texas: Geology, v. 11, p. 131-135. Klein, George D. and Kenneth R. Chaivre, 2002, Sequence and Seismic Stratigraphy of

the Bossier Formation (Tithonian), Western East Texas Basin: Gulf Coast Association of Geological Societies Transactions, v. 52, p. 551-561.

Maione, Steven J. and Scott Pickford, 2001, Discovery of ring faults associated with salt

withdrawal basins, Early Cretaceous age, in the East Texas Basin: The Leading Edge, August issue, p. 818-829.

Williams, Ralph A., Marc C. Robinson, Edward G. Fernandez, and Robert M. Mitchum,

2001, Cotton Valley/Bossier of East Texas: Sequence Stratigraphy Recreates the Depositional History: Gulf Coast Association of Geological Societies Transactions, v. LI, p. 379-388.

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Figure 1: Regional and structural setting of the East Texas Basin. http://payperview.datapages.com/data/bulletns/1999/05may/0707/Images/figure01.htm

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Figure 2: Approximate location of seismic line reconstruction.

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MFS

164 mya

160 mya

154 mya

151 mya

SB

Figure 3: Stratigraphic column of the East Texas Basin. The red box denotes the main formations of interest. SB = sequence boundary, MFS = maximum flooding surface. Modified from http://www.prescocorp.com/projects/east%20texas/stratcolumn.html.

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Figure 4: Salt structures present within the East Texas Basin. (Jackson and Seni, 1983)

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Figure 5: Klein’s and Chaivre’s interpretation of the regional seismic line in this study. (Klein and Chaivre, 2002)

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Figure 6: Example of LithoTect software. Modified from LithoTect “Getting Started Tutorial”.