Seismic Interpretation of Mass-Moved Sediments within the Upper Oligocene Frio Formation, South Texas Gulf Coast
Mass transport of sediments initiated by reactivated growth faults involving coastal-plain and shelf deposits has been described in several parts of the world, particularly in the Niger Delta in West Africa, offshore Trinidad, and the Mexican Gulf Coast. We investigated one such mass-movement event in the Oligocene Frio Formation of the South Texas Gulf Coast. We integrated well logs and 3D seismic data, covering about 1,142 km2 and employing seismic amplitudes, seismic attributes, and spectral decomposition to describe a wedge of deformed upper Frio sediments lying above a major bed-parallel décollement. Reactivation of an earlier listric growth fault resulted in local slope instability and mass wasting of shelfal sediments. Movement of sediments caused the otherwise regularly bedded, railroad-track seismic signatures typical of highstand and transgressive systems tract sediments to be deformed into mounded, chaotic/hummocky, subparallel to parallel seismic internal reflections. Spontaneous potential (SP) wireline-log motifs observed within the undeformed Upper Frio Formation show regularly bedded alternating sands and shale, whereas the SP log motif from within the deformed sediments is erratic, making correlation difficult within this interval. Our results further show that in the area proximal to the main listric fault, smaller, strike-parallel normal faults controlled transport and deposition of sediments. These mostly antithetic faults are strike oriented, paralleling the main listric fault that set off late Frio deformation. Preferred orientation of associated mass-wasted sediments is parallel to these faults. Interpreted water depths from biostratigraphic data ranged from 60′ to120′ in a shallow neritic environment. In contrast, the distal area of the mass-wasted deposits is less fault controlled, resulting in mostly dip oriented sediments. Interpreted water depth for the distal area ranges from 120′ to 300′ in a middle neritic environment. Collapse and subsequent deformation of the upper Oligocene Frio Formation led to a number of events, such as (1) creation of paleo-lows for subsequent deposition of turbidites during transgression of the overlying Anahuac shale and (2) compressive deformation of sediments leading to intense folding, faulting, and localized rotation.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009