Sea Level Events Associated with Lower Oligocene Vicksburg Formation of Texas Gulf Coastal Plain, as Determined from Depositional Systems Analysis

Janet Coleman, William E. Galloway

The lower Oligocene Vicksburg Formation of the Texas Gulf coastal plain was deposited in a regressive setting characterized by prograding, sand-rich coastal systems--deltaic, barrier, and strand plain. These paralic units were deposited considerably seaward of the latest Eocene coastal facies of the Jackson Group. The depositional loci of the Vicksburg deltaic systems in the Houston Embayment and along the central Texas coast were situated on the upper Eocene shelf platform, while in the Rio Grande Embayment the locus of deltaic deposition was the relict Eocene platform margin-upper continental slope. Barrier and strand-plain systems linked the deltaic headlands.

On dip cross sections, the locations of the paralic sands of the Vicksburg, Jackson, and other Paleogene formations trace regional coastal onlap curves for the early Tertiary. Comparison of these curves with the coastal onlap curves of Exxon and with Paleogene curves from around the Gulf of Mexico reveals both correspondences and conflicts. For example, in Texas the contact between the Vicksburg Formation and the Jackson Group is marked by a distinct fall in relative sea level. This event most closely matches a prominent downward shift in coastal onlap at the Eocene-Oligocene boundary on the Exxon coastal onlap curve. In contrast, this same time horizon corresponds to a surface of maximum transgression (condensed section) in the Paleogene stratigraphy of Alabama as demonstrated in 198 by Mancini. Such intrabasinal discrepancies may reflect increased rates of subsidence/uplift and sediment influx in south Texas due to concurrent tectonic activity in west Texas. Carbonate (eastern Gulf) vs. clastic (northwestern Gulf) sedimentation rates and compaction/subsidence styles also might result in different relative sea level curves under similar eustatic conditions.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.