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Lithofacies and sequence stratigraphy of the Barnett Shale in east-central Fort Worth Basin, Texas

Mohamed O. Abouelresh and Roger M. Slatt
Lithofacies and sequence stratigraphy of the Barnett Shale in east-central Fort Worth Basin, Texas
AAPG Bulletin (January 2012) 96 (1): 1-22

Abstract

Ten Barnett Shale lithofacies have been recognized in a 223-ft (68-m)-long core from Johnson County, Texas. Eight of these lithofacies match those previously identified in the main producing area of the Newark East (Barnett Shale) field in the northern part of the Fort Worth Basin, but two new lithofacies have been identified in this core, resedimented spiculitic mudstone lithofacies and lag deposits, both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits. The recognition of cyclical stacking patterns of the lithofacies, condensed sections (CSs), and transgressive surfaces of erosion were the keys to establishing the sequence-stratigraphic framework in these fine-grained rocks, which consists of seven stratigraphic intervals in the lower Barnett Shale and nine stratigraphic intervals in the upper Barnett Shale. Spectral gamma-ray uranium and thorium logs aided in this objective and are recommended for future sequence-stratigraphic studies of these and other shales. The sequence-stratigraphic framework reveals that the lower Barnett Shale in this area was deposited mainly in a low-energy, relatively deep-water environment, somewhat far from a terrigenous source area, which probably lies to the northwest. By contrast, the upper Barnett Shale was deposited in an oxygenated shallower water environment, which had a source area from the west and southwest sides of the basin. The higher frequency of sea level fluctuation during development of the upper Barnett Shale most probably indicates periodic tectonic activity, perhaps associated with a structural high that was susceptible to sea level fluctuations. Alternatively, it could have resulted from the onset of glaciations in Gondwanaland during this time. This higher frequency may indicate that the upper Barnett is Chesterian in age, because cyclicity was higher than during the Osagean and Meramecian stages. If so, there may be more high-frequency cycles than recognized in this core. Siliceous sponge spicules are more common in this core than in more northerly cores, so more brittle facies might prevail in the southern part of the Fort Worth Basin. High gamma-ray log responses, which are caused by a high total organic carbon, and/or in-situ phosphate minerals are commonly found in CSs and can be used for regional correlations. However, high gamma-ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement. Correlation of the Barnett stratigraphic intervals now provides a north-to-southeast stratigraphic framework along the Fort Worth Basin. Relative hydrocarbon potential (RHP) is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions. We recommend continued testing and use of the RHP parameter for high-frequency sequence-stratigraphic analysis of unconventional gas shales.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 96
Serial Issue: 1
Title: Lithofacies and sequence stratigraphy of the Barnett Shale in east-central Fort Worth Basin, Texas
Affiliation: University of Oklahoma, Institute of Reservoir Characterization, Norman, OK, United States
Pages: 1-22
Published: 201201
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 32
Accession Number: 2012-059276
Categories: Economic geology, geology of energy sourcesStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., strat. cols., 1 table, sketch maps
N32°08'60" - N32°34'60", W97°37'00" - W97°05'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201231
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