Do Upper Wilcox Incised Valleys Support Paleogwne Gulf of Mexico (GOM) Isolation?
Deeply incised Upper Wilcox valleys along the mid-Texas gulf coast are renamed as non-generic canyons. They incise two stratigraphic horizons within the MFS bounded Upper Wilcox. Seismic data show they are incisions not lateral facies changes. They are predominately shale filled, deep (770' near the shelf edge), and cut the Yoakum MFS below. They are shelf incised and linked to slope canyons. Canyon fill shales overtop the incisions. Clinoforms fill the Anna Barre slope canyon. Canyon fill facies include stacked shoreface, stacked canyon fill delta, channel sandstones, lagoonal shales, and marine shales. The shoreface sandstones (240') are strike parallel, bar the canyon shelf entrance, and have a shale break where the canyon is deepest. The canyon fill deltas (190') consist of a small lower sequence and a more broadly deposited upper system. Channel sandstones (135' thick) have a meandering geometry, and occur 310' from the canyon top. They are one seismic cycle thick with a flat top and bottom. Canyons originate as shelf incised submarine canyons. The canyon fill facies represents a relative sea level rise and transgression. This implies a previous relative sea level fall within the canyon. Facies thicknesses indicate relative sea level changes in excess of those for the Paleogene world ocean. Isostatic rebound is insufficient to explain this large relative change. Other explanations, including consideration of GOM isolation from the world ocean are needed.
AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013