The Vicksburg Formation of Texas: Depositional Systems Distribution, Sequence Stratigraphy, and Petroleum Geology

The lower Oligocene Vicksburg Formation of the Gulf Coastal plain contains major petroleum reservoirs in the Rio Grande embayment and is an economically viable target in other areas of Texas. Knowledge of the distribution of Vicksburg depositional systems is essential to understanding sandstone concentrations and, therefore, is fundamental to effective exploration and production of the Vicksburg section. The depositional setting of the Vicksburg reservoirs, their position in a sequence stratigraphic framework, and the influence these factors have on the petroleum geology of the Vicksburg are the focus of this paper. Surface and subsurface geological and geophysical data provided the framework for an analysis of the depositional systems and the petroleum geology of the Vic sburg. The two primary Texas Vicksburg depocenters, the Rio Grande embayment and the Houston embayment, are separated by the San Marcos arch, a deep-rooted structural nose. Within the embayments, sand-rich deltaic complexes merged along strike with barrier/strand plains. Contemporaneous growth faulting controlled depositional patterns of shelf-edge deltas in the Rio Grande embayment, but had only a minor effect on the configuration of the shelfal deltas in the Houston embayment. Smaller wave-dominated shelf delta complexes interspersed with barrier/strand plains extended across the San Marcos arch. Updip of these sandy paralic depocenters, fluvial systems traversed mud-rich coastal plain units. Seaward of the paralic systems, sand and mud deposits prograded across and built up over the r lict Jackson shelf and shelf-margin shales. These depositional complexes are contained in the systems tracts of one eustatic (Exxon) sequence. Vicksburg production from each of the three structural regions of Texas is characterized by reservoirs from different systems tracts and of distinct, different depositional origins.