Paleoenvironments of Late Albian Stage (Early Cretaceous) of Eastern Trans-Pecos, Texas: ABSTRACT

Abstract

Upper Albian rocks in eastern Trans-Pecos Texas consist of a depositional sequence that records a major transgressive-regressive cycle, beginning with an initial transgression of the early late Albian seas over a regionally disconformable surface and ending with the onset of late Albian regression. The history of these events is recorded in rocks of the Fort Lancaster Formation and its western equivalent, the Boracho Limestone. These rocks were deposited in several depositional systems that developed on the Comanche shelf and an associated shelf basin called the Fort Stockton embayment. These depositional systems include the carbonate-shelf system, the shelf-basin system, and the carbonate-shoal system. Each system is recognized by unique suites of lithofacies, differentiated on the basis of petrographic and outcrop characteristics: skeletal wackestone, interbedded shale and wackestone, oyster packstone/shale, skeletal grainstone, and calcareous shale. Associated with these lithofacies are the following biofacies: Protocardia-Macraster, Globigerina, Nuculana-Syncyclonema, Texigr phaea, Lopha, and Miliolina. Within a biostratigraphic framework based on ammonite zones, the geographic and stratigraphic distribution of a depositional systems and their associated lithofacies and biofacies indicate that late Albian deposition primarily was influenced by periodic terrigenous influxes from the northwest over the Comanche shelf. This was coupled with tectonically controlled subsidence in the Fort Stockton embayment. The depositional sequence culminated in the development of widespread carbonate sand shoals prior to the onset of emergence. End_of_Article - Last_Page 461------------