› › Chemostratigraphy Of The Eagle Ford Formation South Texas




Geochronologic and Chemostratigraphic Record of Cenomanian-Turonian Eagle Ford, South Texas

Author : Michael Anthony Nieto

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Page : 366 pages

File Size : 10,54 MB

Release : 2016

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The Eagle Ford Shale of South Texas is an organic-rich, calcareous mudrock succession which was deposited on the Comanche Platform during the earliest Late Cretaceous. Many academic and industry sponsored Eagle Ford studies over the past 10 years have concentrated their efforts on trying to understand the rock fabrics, facies architecture and heterogeneities present in the succession. However, despite heavy economic and academic interest in the system, few studies focus on trying to understand timing and source of the many bentonite ash beds present in the Eagle Ford; which serve as regional chronostratigraphic markers across South Texas. One of the primary goals of the study is the determination of U-Pb age dates in bentonite-rich ash beds from a group of subsurface cores that penetrate the Eagle Ford Formation in Atascosa County, Texas. Absolute age dates provide a chronostratigraphic framework that is used to estimate the depositional timing of variable Eagle Ford facies, as well as define the timing, duration and magnitude of isotopic events in the region. Secondly, age estimates are utilized to determine and calculate Eagle Ford accumulation rates across South Texas. Absolute age dates are incorporated with lithofacies definitions to better 1) understand the cyclic relationship between dominant Eagle Ford lithologies, 2) identify the controls responsible for the cyclic mode of deposition, and 3) determine the lateral continuity of key lithofacies and lithologic units. Lastly, elemental (XRF) data are utilized to describe the subtle paleoceanographic and sediment source conditions that persisted across the entire Eagle Ford section. These findings are integrated with stable carbon ([delta]13C) isotopic data, which allow for the accurate definition of Ocean Anoxic Event 2 (OAE 2) in the study area and provide a basis for regional correlation with previous studies. Recent studies have suggested that anoxic conditions experienced within the Western Interior Seaway during this time were asynchronous with the well-documented global OAE 2 event. The present study compares local U-Pb age dates, isotopic and elemental results with regional studies to better define the onset timing and paleoceanograpic conditions associated with Eagle Ford Shale deposition.





Chemostratigraphy of the Late Cretaceous Eagle Ford Group, South Texass

Author : Robert Francis Nikirk

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Page : 60 pages

File Size : 24,68 MB

Release : 2014

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Strata of the Eagle Ford Group of South Texas, deposited during the Cenomanian and Turonian of the Late Cretaceous, are largely characterized as mixed siliciclastic and carbonate mudrocks rich in organic carbon. The Eagle Ford Group records deposition within the Maverick Basin, along the Comanche Shelf, at the southern margin of the Western Interior Seaway in present-day South Texas. In recent years, the Eagle Ford has emerged as one of the premiere petroleum plays, as it has been proven to be capable of producing significant volumes of dry gas, wet gas/condensates, and oil. It is believed the Eagle Ford represents deposition during the globally correlative Ocean Anoxic Event #2, characterized by the accumulation and preservation of vast amounts of organic carbon due to the expansion of large deep-water oxygen minimum zones. This study integrates geochemical analyses of six drill cores from Gonzales, Guadalupe, La Salle and Wilson counties of South Texas. These cores were studied to determine bulk geochemistry, redox conditions, and degree of basin restriction and deepwater renewal times in order to provide a detailed assessment of the chemostratigraphy and paleoceanography of the Eagle Ford Group. Each core was scanned at one foot intervals with a handheld X-ray fluorescence (XRF) spectrometer to obtain quantitative measurements of major elements, such as Ca, Al and Si, as well as redox sensitive trace metals, such as V, Zn, Ni and Mo. In addition, some cores were analyzed for total organic carbon (TOC), total inorganic carbon (TIC), and stable isotope ([delta]13C and [delta]18O) signatures of the inorganic, carbonate component. The elevated levels of redox sensitive trace metals of the Lower Eagle Ford, represented here by the Lake Waco and Pepper Shale Formations, reveals deposition during a time of anoxic or euxinic conditions leading to the preservation of large amounts of organic carbon (~5% TOC). The South Bosque Formation, representing the Upper Eagle Ford, displays reduced levels of these trace metals, suggesting a return to a more oxygenated environment prior to the deposition of the overlying, fully oxygenated and heavily bioturbated Austin Chalk. The physical paleoceanography of the Eagle Ford is revealed to be restricted at times and more open at others with lower deep-water renewal times, yet remained mainly within an anoxic or euxinic state. In regard to the inorganic stable isotopic data, the [delta]13C carb values, which other studies have shown to display a positive excursion at the time of OAE2, suggest this event is not preserved within the cores analyzed.



Chemostratigraphy of the Upper Cretaceous from Central and South Texas with Focus on the Eagle Ford Group

Author : Brett Huffman

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Page : pages

File Size : 13,44 MB

Release : 2013

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The fine-grained organic-rich rocks of the Eagle Ford (Cenomanian-Turonian) were deposited during the Upper Cretaceous in the shallow waters of the Western Interior Seaway. Five drill cores recovered from two counties, four from Travis County, Texas and one from Frio County, Texas, have been scanned from between two foot and half foot intervals with a hand-held energy-dispersive x-ray fluorescence (HH-ED-XRF) spectrometer to acquire major (e.g. Ca, Si, Al) and trace (e.g. Mo, V, Ni) element data for quantitative analysis. Additionally, gamma ray logs have been analyzed for two of the cores. Major element geochemistry indicates the Eagle Ford deposited in South Texas is different from the Eagle Ford deposited in Central Texas. South Texas Eagle Ford is much more Ca (carbonate) rich, with a noticeably lower Al (clay) content. South Texas and Central Texas Eagle Ford both have low Si (quartz) content relative to the Al and Ca content, indicating a negligible siliciclastic contribution during deposition. Trace element analysis reveals the redox conditions of the bottom waters during deposition. Mn -- an element which becomes mobile and may be removed from an open system in reducing conditions -- levels are much higher in the Austin Chalk and Buda with notably lower values in the Eagle Ford in both Central Texas and South Texas. Mo, an element which tends to bind with organic matter or sulfides during reducing conditions, is notably higher in the Eagle Ford of both South Texas and Central Texas. The correlation of decreased Mn levels and increased Mo levels suggests that the Eagle Ford was deposited in reducing conditions in an open system capable of removing mobilized Mn. Geochemical analysis of major and trace elements obtained from ED-XRF may be used in the petroleum industry in concert with XRD, electric logs, and standard core analysis to give a more complete picture of the depositional environment, clay type and volume, geophysical rock properties, and areal extent of a potential unconventional shale reservoir for hydrocarbon extraction. XRF data offers insight about the rocks, leading to improved understanding of the depositional environment and chemical makeup. Applying these technologies to the Eagle Ford helps unlock the potential of this significant hydrocarbon source and reservoir.



Chemostratigraphy of the Austin Chalk and Upper Eagle Ford Shale, South Central, TX

Author : Zain Abdi

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Page : 49 pages

File Size : 50,55 MB

Release : 2014

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A single drill core from La Salle, TX was analyzed for its chemical composition and percent concentration of both major and trace elements in order to understand depositional environments and local tectonic activity of the Balcones Fault Zone. The drill core contained the entirety of the Austin Chalk and the upper portion of the Upper Eagle Ford Shale. Samples were taken from 47 boxes at 3 inch intervals which accumulated in a total of 1,680 samples. Each sample was analyzed using a handheld x-ray fluorescence instrument which provided quantitative analysis of the following elements: Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, S, Si, Ti, and V. Furthermore, x-ray diffraction analysis was conducted at every 7 feet of the Austin Chalk and every 4 feet of the Upper Eagle Ford Shale. Calcium values ranged from 5% to 40% with the former values arising from the Upper Eagle Ford Shale and the latter values coming from the Austin Chalk. Sulfur percent composition ranged from 0%-20% and had similar trends as Magnesium which had values from 0.04% to 4.8%. The Austin Chalk contained great values of pyrite, illite, quartz, calcite, and dolomite. Trace element concentrations suggest that the depositional environment had periods of anoxic or euxinic events. Mineralogical and major elemental geochemistry suggests a carbonate rich Austin Chalk and calcareous Eagle Ford Shale.



Chemostratigraphy of the Eagle Ford Formation

Author : Timothy J. Kearns

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Page : pages

File Size : 36,60 MB

Release : 2011

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The Late Cretaceous Eagle Ford Formation contains the Cenomanian-Turonian Boundary (CTB). It crops out along the Red River and extends southward through the Dallas-Fort Worth Area of Texas, Waco, Austin and west towards Del Rio and Big Bend. The outcrops were not sampled. Sampling was conducted on cores located at the Bureau of Economic Geology (BEG). The cores were collected from Zavala, La Salle, Frio, Gonzalez, De Witt, and Bee Counties. The Austin Chalk Formation is located above the Eagle Ford Formation and the Buda Formation is located below it. Deposition of the Eagle Ford Formation occurred in the southern portion of Western Interior Seaway (WIS) of North America during a period of high temperature due to greenhouse warming stemming from enhanced volcanism and associated CO2 input. Increased CO2 input ultimately resulted in enhanced continental solubility or weathering and enhanced primary productivity, which resulted in stagnant, oxygen, depleted waters. The effect of the former was to possibly cause the second (OAE-2) of six global ocean anoxic events that occurred during the Cretaceous Period. A combination of enhanced carbonate precipitation from primary productivity and enhanced preservation caused by ocean anoxia led to the deposition of highly carbonaceous organic-rich mudrock. All the samples were measured using a Bruker XRF handheld device. Select samples were measured for %TIC, %TOC, %N, %S, ð13C and ð15N. The data revealed that sampled population included not only the upper and lower portion of the Eagle Ford Formation, but the overlaying Austin Chalk and underlying Buda Formations. This was primarily determined by the Molybdenum concentration. Molybdenum concentration less than or equal to 5 ppm indicate the presence of oxic to suboxic water column conditions. Molybdenum concentration that is greater than or equal to 5 ppm, but less than 20 ppm indicates anoxic water column conditions. Molybdenum concentration that is equal to or greater than 20 ppm indicates euxinic water column conditions. The Eagle Ford Formation was deposited mostly under anoxic to euxinic conditions. The overlying Austin Chalk Formation and underlying Buda Formation were both deposited under dominantly oxic to suboxic conditions. Analyses of the results indicate upwelling was prevalent during much of the deposition of each core. Upwelling is indicated by the enrichment of Phosphorus and depletion of Manganese. Increased continental weathering and upwelling were the likely primary controlling influences that caused anoxic-euxinc water column conditions. Such conditions facilitated enhanced organic matter preservation during the deposition of the Eagle Ford Formation.





High Resolution Geochemistry of the Cretaceous Eagle Ford Shale, Bee County, Texas

Author : Lisa Michelle Moran

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Page : pages

File Size : 50,16 MB

Release : 2012

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The Eagle Ford Formation of Bee County, Texas is a sporadically laminated carbonaceous dark mudrock. The depositional area of the Eagle Ford Formation stretches across the state of Texas in a northeast-southwest trend. Early studies of the Eagle Ford found the deposits to be rich in organic material but could not fully describe the formation due to the lack of outcrop exposure. Recent studies of the Eagle Ford Formation have begun to explore the sub-surface nature of the formation. Geochemical analyses of the J.A. Leppard #1 core from the southwestern portion of the formation was conducted to further constrain the sub-surface geochemical signatures of the Eagle Ford Formation. Major and trace element compositions were all measured using a hand- held X-ray fluorescence spectrometer. Bulk geochemistry, trace metal enrichments, inferred mineralogy and geochemical relationships were used as proxies to define the depositional paleoenvironment and degree of basin restriction. The Eagle Ford Formation was deposited under mostly anoxic/euxinic conditions with intermittent pulses of oxygenation. The basin was mostly restricted, but with significant periods of a more open marine setting. Dark mudstones associated with similar depositional histories have previously been linked to global Cretaceous oceanic anoxic events (OAEs). Earlier studies inferred that the Eagle Ford Formation preserved in the J.A. Leppard #1 core preserved a record of the Cenomanian-Turonian boundary. However, biostratigraphic evidence questions the original timing of sedimentation at the core location. It is now believed that the chemostratigraphic patterns could be related to marine preconditioning episodes of anoxia/euxinia prior to a major OAE.