THE VICKSBURG FORMATION OF TEXAS - DEPOSITIONAL SYSTEMS DISTRIBUTION,SEQUENCE STRATIGRAPHY, AND PETROLEUM GEOLOGY

The lower Oligocene Vicksburg Formation of the Gulf Coastal plain cont ains major petroleum reservoirs in the Rio Grande embayment and is an economically viable target in other areas of Texas. Knowledge of the d istribution of Vicksburg depositional systems is essential to understa nding sandstone concentrations and, therefore, is fundamental to effec tive exploration and production of the Vicksburg section. The depositi onal 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. Surfac e and subsurface geological and geophysical data provided the framewor k for an analysis of the depositional systems and the petroleum geolog y of the Vicksburg. The two primary Texas Vicksburg depocenters, the R io Grande embayment and the Houston embayment, are separated by the Sa n Marcos arch, a deep-rooted structural nose. Within the embayments, s and-rich deltaic complexes merged along strike with barrier/strand pla ins. 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 emba yment. Smaller wave-dominated shelf delta complexes interspersed with barrier/strand plains extended across the San Marcos arch. Updip of th ese sandy paralic depocenters, fluvial systems traversed mud-rich coas tal plain units. Seaward of the paralic systems, sand and mud deposits prograded across and built up over the relict Jackson shelf and shelf -margin shales. These depositional complexes are contained in the syst ems tracts of one eustatic (Exxon) sequence. Vicksburg production from each of the three structural regions of Texas is characterized by res ervoirs from different systems tracts and of distinct, different depos itional origins.