MALOTT, VINCENT E., and DONALD F. REASER, University of Texas at Arlington, Arlington, TX

ABSTRACT: Facies and Depositional Environments of the Lower Cretaceous (Middle Albian) Finlay Limestone, Western Trans-Pecos Texas

The Finlay is a prominent carbonate rock body exposed over a large part (>30,000 sq km) of western Trans-Pecos Texas. There, it can be divided into a lower slope-forming unit that is transitional with the subjacent Cox Formation and an upper ridge-forming unit that is in sharp contact with the superjacent Benevides/Kiamichi formations. The strata were deposited across a differentially subsiding shelf that probably reflected recurrent movement between the Diablo platform on the east and Chihuahua trough on the west. Differential subsidence across the shelf resulted in the limestone thickening westward from 10-100 m on the platform to more than 165 m in the trough.

The Finlay is interpreted as an aggradational carbonate sequence which kept pace with or exceeded the regional subsidence rate on the shelf. The carbonate succession in the trough consists mostly (>85%) of mollusk lime mudstone deposited in a slowly subsiding basin. On the Diablo platform, the limestone is composed primarily of (1) mollusk-algal wackestone (50%), (2) Dictyoconus-algal-peloid packstone (20%), and (3) rudist wackestone (5%) that represent deposition on a shallow shelf. Sandy lime mudstone and terrigenous, fine-grained quartz sandstone dominate the sequence along the updip margin of the shelf. An episode of increased subsidence along the tectonic hinge line at the close of Finlay deposition resulted in the accumulation of rudistid-fragment sand bars along the western argin of the hinge area; concurrently, miliolid-peloid wackestone was deposited updip on the platform in a partly restricted, shallow-shelf environment.

AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.