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ABSTRACT: Depositional Systems Distribution of the Lower Oligocene Vicksburg Formation, TX

Janet Coleman, William E. Galloway

The lower Oligocene Vicksburg Formation of Texas is situated between the upper Eocene Jackson Group and the upper Oligocene Frio Formation. The paleogeography of the Texas Gulf coastal plain during the early Oligocene is typical of a progradational passive continental margin. However, a detailed regional depositional systems analysis of stratigraphic units, such as the Vicksburg, within a mature petroleum basin can yield results beneficial in both exploration and development. Stratigraphic plays are determined from the distribution of depositional systems, and reservoir characteristics are heavily influenced by conditions of sedimentation. Two primary depocenters (and exploration fairways) of the Texas Vicksburg were the Houston Embayment and the Rio Grande Embayment; the were separated by a deep-rooted structural nose in central Texas: the San Marcos arch. Within the embayments, deltaic depositional systems merged along strike with barrier/strand plain systems. Updip, fluvial systems traversed coastal plain units. On the seaward edge of the paralic systems, sand and mud deposits prograded across, and built up over, the relict Jackson shelf and shelf margin. Contemporaneous growth faulting controlled deltaic depositional patterns in the Rio Grande Embayment and, to a lesser degree, in the Houston Embayment. A barrier/strand plain system within an interdeltaic coastal bight extended across the northern flank of the San Marcos arch. Several minor wave-dominated delta complexes were interspersed within this regional setting. The southern flank of the arch w s influenced by the fluvial systems of the Rio Grande Embayment that established another wave-dominated delta. Deposition of the Vicksburg progradational paralic sediments was initiated seaward of the Jackson coastal position. A brief, minor transgression interrupted the progradational pattern during middle Vicksburg deposition.. Aggradational deposition characterizes the lower Frio deposits, but sedimentation was continuous across the Vicksburg-Frio boundary.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990