--> Abstract: Severe Tropical Weather in West Texas During the Early Late Cretaceous?, by Brian E. Lock and Fleur S. Bases; #90078 (2008)
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Severe Tropical Previous HitWeatherTop in West Texas During the Early Late Cretaceous?

Brian E. Lock and Fleur S. Bases
Geology, University of Louisiana, Lafayette, LA

The Cenomanian-age, terrigenous clastics of the Del Rio Formation are unusual within the Cretaceous of West Texas, which is otherwise dominated by carbonate sediments. The Del Rio consists of calcareous shales and argillaceous limestones, with scattered quartzose sandstones. The shales contain an abundant but relatively restricted fauna dominated by exogyrid oysters, and the large, distinctive agglutinating foraminiferan Cribitina texana. The sandstone beds have current-oriented prod marks and other sole marks, possible hummocky cross-stratification in places, and well-developed meter-scale sand waves elsewhere. The sand waves contain quantities of reworked oysters. The sandstone beds are only scarcely burrowed and at least one has well-preserved wrinkle-structure (Kinneyia) microbial mat on its upper surface.

It is postulated that the sands are products of major storm-surge relaxation currents, which would suggest tropical cyclone conditions in the region during the late Cretaceous. The limited literature is consistent in assigning a shallow subtidal to intertidal origin for Kinneyia. Like other Phanerozoic microbial mats, the bacterial consortium in question is believed to be opportunistic - the bacteria are common and widely distributed so that mat development tends to follow quickly after natural disruptions such as storms, and the mat survives subsequent predation only if adverse environmental conditions (in this case probably freshwater influx) persist until the mat is buried.

The Del Rio Formation environment is suggested to have been a shallow, near-shore shelf experiencing introduction of large quantities of suspended sediments with run-off from the nearby land, with fluctuating salinities such that oysters and agglutinating foraminiferans were the most abundant macrofossils. Periodic storms reworked the bottom sediments and brought in sand flows.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas