--> Abstract: Seismic Imaging of Sediment Ridges in Growth-Faulted Subbasins of the Oligocene of the South Texas Gulf Coast—Are They Shale, Salt, Or Seismic Artifacts?, by Ursula Hammes and Osareni Ogiesoba; #90078 (2008)
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Seismic Imaging of Sediment Ridges in Growth-Faulted Subbasins of the Oligocene of the South Texas Gulf Coast—Are They Shale, Salt, Or Seismic Artifacts?

Ursula Hammes and Osareni Ogiesoba
Bureau of Economic Geology, University of Texas, Austin, TX

The Oligocene Frio Formation of the south Texas Gulf Coast is dominated by mobile, mud-influenced tectonics, which resulted in growth-faulted subbasins originating during sea-level lowstands. Coarse clastic deltaic sedimentation, shifted basinward during 3rd-order sea-level lowstands, was deposited onto unconsolidated slope muds that had been mobilized into ridges. Associated growth faults developed along the ridges, as well as synthetic and antithetic accommodation faults typically located in crestal positions of growth-fault rollover. Imaging these ridges seismically has proven difficult because of deep burial to approximately 20-25,000 ft and subtle velocity differences. The growth fault typically creates a seismic shadow zone, further obscuring the seismic Previous HitsignatureNext Hit of the sediment ridge. The south Texas Gulf Coast has typically been associated with shale tectonics, as compared with the salt-dominated tectonics of the northern Texas Gulf Coast. Indeed, although salt has not been encountered in any of the South Texas wells, some of the seismic Previous HitsignatureNext Hit indicates remnants of salt and/or salt welds. These signatures might explain some of the salt/shale withdrawal features that are evident on seismic, such as collapse features of overlying strata and bright amplitudes resembling salt welds.

Poststack processing was conducted to enhance stratigraphic and structural features of the sediment ridge and associated faults and sedimentary features such as onlap and detachment surfaces. To further enhance definition of these features, we applied several poststack filtering algorithms such as fx-Previous HitdeconvolutionTop and tau-p to the 3D seismic data. The filtering processes helped reveal some of the internal architecture within sediment ridges behind the growth faults (i.e., on the upthrown sides of the growth faults) and address salt/shale withdrawal processes.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas