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Volumetric Partitioning of Growth-Faulted Subbasins and High-Resolution Sequence Stratigraphic Architecture of the Oligocene Frio Formation in the Corpus Christi Area of South Texas

Bonnaffe, Florence 1; Hammes, Ursula 1
1 Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas, Austin, TX.

A high-resolution, regional, sequence-stratigraphic architectural study, using wireline logs, seismic, core, and biostratigraphic data, was conducted on the Oligocene Frio Formation along the southern Texas Gulf Coast, where it is more than 15,000 ft thick. Historically, most production has been from highstand and transgressive systems tracts of the Upper Frio; however, compartmentalized reservoirs in lowstand prograding-wedge, slope-, and basin-floor fan deposits of the Lower Frio have been recognized as important reservoirs. Evaluating potential downdip plays of the Frio requires an understanding of the regional sequence-stratigraphic architecture. On the basis of high-resolution sequence stratigraphy, six third-order sequences were recognized in six growth-fault-bounded subbasins. Growth-fault activation created subbasin-confined sedimentation differentiation during sea-level lowstand and ceased its influence during subsequent transgression and highstand. The combination of eustasy and tectonic controls on available accommodation space and sediment accumulation created a strong volumetric partitioning between the lowstand slope and basin and the transgressive and highstand shelf. Because genetically similar but noncontemporaneous lowstand depositional systems successively filled each subbasin, unraveling the stratigraphic architecture of these seaward-stepping, progressively younger basinward Frio subbasins requires careful examination and integration of sedimentological data, wireline-log response, and biostratigraphic data using a sequence-stratigraphic-based approach. Our study focuses on evaluation of four consecutive subbasins: Nueces, Encinal (Corpus Christi), Red Fish, and Mustang Island over a four-county area in the South Texas coastal area. We constructed sets of isopach, net-sand, and gross-sand maps of individual systems tracts for each of the six sequences within each subbasin and across subbasins. System-tract-specific isopach maps illustrate strong volumetric partitioning of Frio lowstand to highstand sequences and allow identification and prediction of potential zones of sand-rich reservoirs for each subbasin.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009