Genetic stratigraphic sequence analysis of the Upper Wilcox, Gulf Basin, Texas

The Upper Wilcox genetic sequence (UWGS) is a transgressively bounded unit that represents the last major progradational episode associated with Wilcox (Paleocene-Eocene) deposition in the Texas Gulf Coast basin. The UWGS includes at outcrop, the Sabinetown Formation, the Carrizo Formation and the lower Reklaw Formation, and in the subsurface it includes the upper part of the Middle Wilcox Subgroup, all of the Upper Wilcox Subgroup and the lower part of the Reklaw Formation. UWGS depositional systems in the Rio Grande embayment (South Texas) include two large but distinct delta complexes, the Rosita and Burgos deltas. The Rosita delta system contains the Duval, Massive, and Live Oak deltas which were fed by the Carrizo fluvial system. The Burgos delta system contains the Fandango and the Zapata deltas and was fed by an unnamed and unmapped fluvial system originating from northern Mexico. Depositional systems within the UWGS in the Houston embayment (East Texas) include two small delta systems, the Columbus and the Jasper, and an intervening strandplain system, the Harris. The Columbus delta was supplied by the Jewett fluvial system and the Jasper delta by an unnamed and unmapped fluvial system originating in Louisiana. UWGS deposition began following the transgression of the Lower Wilcox shelf margin and the deposition of a regional marine mudstone containing a maximum flooding surface (MFS). An influx of sediment from the west from the last pulse of the Laramide Orogeny (55ma) began deltaic progradation in the Rio Grande embayment. At approximately the same time, delta systems in the Houston embayment first prograded and then were transgressed as the trunk fluvial system shifted to the southwest. The resulting transgressive deposits include the Yoakum shale, which defines the top of the Sabinetown Formation. A fall in sea level at the end of the Yoakum/Sabinetown transgression extended the delta systems in the Rio Grande embayment to the shelf edge; the smaller delta systems in the Houston embayment shifted basinward. A slow relative rise followed as the systems in both embayments continued to prograde/aggrade and then were progressively transgressed. A transgressive shelf with isolated sands ('Atkinson' sands) developed over the drowned basin margin. The Bigford barrier/lagoon complex marked the maximum landward migration of the shorelineGeological Science