Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005
Control of Third-Order Growth Faulting on Lowstand Slope and Basin-Floor Sedimentation: A Geomorphologic Evaluation of Oligocene Deep Frio Strata, South Texas Gulf Coast
Architecture of slope- and basin-floor-fan systems in growth-faulted subbasins along the south Texas Gulf Coast developed as a result of interplay between synsedimentary tectonics and sedimentation during third-order sea-level lowstands. These subbasins, or intraslope basins, have not been adequately explored for their slope and basin-floor-fan potential, as have the intraslope basins in salt-dominated areas in the Gulf of Mexico. Exploration has concentrated on lowstand prograding-wedge and highstand shelf deposits in the Frio Formation. Growth-faulted subbasins set up by gravity failure along the upper slope generated syndepositional faults that displaced and mobilized muds basinward of the growing lowstand sedimentary wedge. These growth faults are generally parallel to Frio shelf edges. The subbasin in the Corpus Christi area under investigation is characterized by a basin-floor-fan complex and slope/leveed channel complexes. These gravity deposits were fed by incised rivers that spilled sandy bedloads onto slopes at different locations, resulting in deepwater systems along the entire Frio shelf edge, including (1) slope systems with amalgamated slope channels and levees deposited immediately downdip of an incipient structural high and (2) basin-floor fans fed by channels contouring along slope and depositing their load into the eastwardmost part of the subbasin. Interfan locations seem to be void of channel and levee sedimentation. Unlike most geomorphologic studies conducted on the seafloor or in a shallow seismic section, this study deals with seismic data of greater than 3 seconds in which stratal slices show evolution from basin-floor-fan to slope-fan to prograding-wedge systems during one lowstand third-order cycle.