Process Regime Change From Wave-Modified and Tidally-Influenced to Wave-Dominated Deltas Across Growth Faults in the Paleogene Lower Wilcox Guadalupe Delta, South Texas Gulf Coast
The Wilcox Group in Texas is a 3000 m (9900 ft) unit of clastic sediments deposited along the northern margin of the Gulf of Mexico during late Paleocene-early Eocene time. This study integrates core facies analysis with subsurface well-log correlation and 3D seismic interpretation to document the stratigraphy and sedimentology of the Lower Wilcox Guadalupe Delta. Detailed core descriptions show that bedding type, sedimentary and biogenic structures reflect a transition from wave-modified and tidally influenced to wave-dominated deposition as deltas approached the shelf edge. Seismic stratal slices revealed characteristic geomorphologic patterns of tidal-influenced and wave-dominated deltas. Growth faults within the lower Wilcox section influenced sediment pathways, controlled sediment partition and provided increased accommodation for deltaic depocenters. During deltaic progradation the structural and depositional systems migrated and adjusted as sedimentation rates kept pace with fault displacement rates. Increased local accommodation due to fault subsidence slowed shoreline progradation and favored a stronger wave regime on the outer shelf due to unrestricted fetch and water depth. As the shoreline advanced during deltaic progradation, relatively more sediment was deposited on the downthrown side of faults and reworked along shore by wave processes. The sedimentary succession in downthrown basins in outer shelf and shelf edge areas is characterized by repeated vertical stacking of shoreface deposits and pronounced increase in sediment thickness (up to 4 times) adjacent to the fault. The change in depositional environment from tide-influenced and wave-modified to wave-dominated deltas in growth-faulted compartments indicates that significant volumes of sediments were trapped on the outer shelf. The locally enhanced subsidence with pervasive wave reworking because of the decreased shoreline progradation generates thick and relatively clean shoreline- associated reservoirs.
AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016