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Paleocene-Eocene Marine Transgression in the Upper Calvert Bluff Formation, Wilcox Group, Bastrop County, Texas

Thomas E. Yancey¹, Andrew Dunham², and Kevin Durney³
¹Department of Geology and Geophysics, Texas A&M University, MS 3115, College Station, Texas 77843–3115
²10707 Mourning Dove Dr., Austin, Texas 78750
³3701 Trailhead Ct., Cedar Park, Texas 78613

Deposits of the Sabinetown transgression in the upper Calvert Bluff Formation, Bastrop County, Texas, contain a record of Wilcox-age marine flooding and a diverse new Wilcox fossil assemblage. Sediments contain fossils of open-neritic marine environments. Winnowed, sparsely fossiliferous lowstand sandstones are capped with a lag deposit of marine vertebrates and an ironstone transgressive horizon and overlain by upward- coarsening sediments. Concentrations of shark teeth, bivalves Venericor and Litorhadia, gastropods Turritella and Athleta, scaphopods, and echinoderms demonstrate full marine conditions. Presence of fossiliferous ironstones with phosphate nodules and bioeroded shell indicates sediment starvation. Aragonite shell (including otoliths) is preserved in a 1m thick (3 ft) unit above the ironstones. These deposits are in the Sabinetown transgression (pre-Carrizo) that overlies the Rockdale depositional system in the Houston Embayment. These marine deposits are located on the northeast margin of the South Texas shelf system and are an extension of that depositional system. Palynological analysis of the Sabinetown transgression in the subsurface dates it as basal Eocene, and vertebrate fossils correlate to the basal Eocene Red Hot biota of the Bashi Formation in Mississippi, indicating that the Paleocene-Eocene boundary at Bastrop occurs below the fossil horizon.

 

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012