Abstract: Another Strike at Bee Bluff

John A. Breyer

Two surfaces within sediments of the Wilcox Group (Paleogene) exposed at Bee Bluff in Zavala County, Texas, have been interpreted as thrust faults formed when a meteor struck South Texas in the early Tertiary. The surfaces are instead a disconformity and a normal fault. The disconformity is the edge of an incised valley cut into sediments of the Wilcox Group during a fall in relative sea level in the early Tertiary. A paleosol can be traced from the ancient divide that bordered the valley into the valley-fill sequence, demonstrating that no displacement has taken place along the surface since the strata were deposited. The disconformity is a type 1 sequence boundary that separates coal-bearing strata of the Wilcox Group from the overlying Carrizo Sand--not a thrust fault. The displacement across the second surface mapped as a thrust fault cannot be directly ascertained because none of the strata exposed in the bluffs can be traced across the fault. However, the drag on the fault and movement on small antithetic faults suggest extension, not compression. This fault is most likely the continuation of a normal fault that offsets the Lituola taylorensis zone (Cretaceous) in the subsurface beneath Bee Bluff. The offset of the L. taylorensis zone probably resulted from sediment compaction above the flank of a serpentine plug intruded in the late Cretaceous. Neither of the surfaces mapped as thrust faults shows evidence for compressional movement, and neither surface provides support for the notion of a meteor strike at Bee Bluff.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas