Abstract: A Regional Subsurface Study of the Expanded Yegua Formation in the Houston Embayment of the Upper Texas Gulf Coast

Richard E. Goings, Richard Smosna

The Eocene Yegua Formation, one of a series of Tertiary clastic wedges, thickened significantly basinward of the platform margin as it prograded across the Houston diapir province of southeastern Texas. Sandstones of the expanded Yegua represent neritic, distal mouth-bar and shelf environments downdip from the strandline. Structural movements (growth faulting and salt diapirism) were contemporaneous with deposition and exerted a strong influence on patterns of sand dispersal, while sedimentation in turn mobilized the underlying salts and triggered faulting over the unstable shelf edge. Major depocenters became established along strike-parallel growth faults, sourced by dip-oriented feeder systems from the northwestern shelf. The faults, which trend northeast through Liberty and Hardin counties, served to localize thicker sand sections on their downthrown side. Salt diapirism created a major depocenter over a large withdrawal syncline in south-central Liberty County, assumed to be the source for most piercement features in the study area. Thick sand sections also accumulated in other low areas due to salt withdrawal or sediment loading and to damming behind growing domes. In contrast, salt domes and ridges were generally positive topographic highs, which channeled sand into interdomal conduits. Diapirism has therefore compartmentalized the depocenters. Multiple Yegua sandstones now occur in several favorable structural positions (especially along the shelf-edge growth faults and over the central salt-withdrawal syncline), and these areas of thick sand accumulation cons itute primary targets for petroleum exploration.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994