2023 GCAGS Journal, Vol. 12
TITLE
Unraveling the “Eaglebine”: A Sequence Stratigraphic Framework for the Eagle Ford Group in the East Texas Basin
AUTHOR(S)
A. D. Donovan, P. Johnson, S. R. Gifford, M. J. Meyer, S. Dangtran, and M. Pope
ABSTRACT
A major stratigraphic problem presently exists in the southern East Texas Basin. Geoscientists working in the subsurface in this region are no longer sure, as to what strata, between the Buda Formation and Austin Group, are equivalent to the Woodbine and Eagle Ford groups, as defined along the outcrop belt. As a result, this stratal succession is now commonly just referred to as the “Eaglebine.” To resolve this dilemma, a regional grid of well-log cross-sections, tied to petrophysical and geochemical data from (1) two shallow subsurface government research cores and (2) a deeper subsurface industry core, was used to unravel the “Eaglebine.” This research revealed that the “Eaglebine” in the southern East Texas Basin actually consists of a vertical succession four petrophysically and geochemically distinct unconformity-bounded sequences (sequences 1 to 4, from the base up), all of which (1) have a sharp basal contact and (2) display underlying stratal terminations, on the grid of regional well-log cross-sections. The lowermost “sequence 1,” which is interpreted as the False Buda, is a moderate gamma ray (GR)/ resistivity unit, that is rich in Ca, but poor in total organic content (TOC), Al, and Ti. “Sequence 2,” which is interpreted as the Pepper Formation (Woodbine Group), is a low-resistivity unit, that is poor in Ca and TOC, but rich in Al and Ti. “Sequence 3,” which is interpreted as the Lower Eagle Ford Formation (LEF), is a high-resistivity/GR unit, that overall is enriched in Ca and TOC, but poor in Al and Ti. The uppermost unit, “Sequence 4,” which is interpreted as the Lower Member of the Upper Eagle Ford Formation (UEF), is primally a low-resistivity unit, that is rich in Al and Ti, but overall poor in Ca and TOC. In general, across the study area, Ca– and TOC–rich, high-resistivity LEF mudstones separate more Al–rich, as well as Ca– and TOC– poor strata, of both the Woodbine Group/Freestone delta (below) from the UEF/Harris delta (above).
PAGE(S)
106-134
DOI
https://doi.org/10.62371/ABPO7316
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