Sedimentary Facies and Biota of Early Permian Deep-Water Allochthonous Limestone, Southwest Reagan County, Texas
John P. Hobson, Jr., Craig D. Caldwell, Donald F. Toomey, 1985. "Sedimentary Facies and Biota of Early Permian Deep-Water Allochthonous Limestone, Southwest Reagan County, Texas", Deep-Water Carbonates: Buildups, Turbidites, Debris Flows and Chalks—A Core Workshop, Paul D. Crevello, Paul M. Harris
Download citation file:
Conventional cores from four wells in and near Gunnx Field, southwest Reagan County, Texas, recovered interbedded limestone conglomerates, intraclast and bioclast limestones, calcarenite, and shale. Twenty-one lithologies are grouped into six lithofacies based on the study of slabbed cores: lithoclast rudstone/floatstone; porous, bioclast-lithoclast rudstone/floatstone; bioclast wackestone; intraclast floatstone/rudstone; thin-bedded grainstone/packstone (calcarenite); and dark gray shale. The strata are assigned an Early Permian Wolfcamp age based on analysis of large and small foraminifera, algae, and Problematica. Environment of deposition interpretation is based on petrologic characteristics, biota, regional stratigraphic setting, and local facies stratigraphy. The cored sequence is interpreted as a complex of debris flow sheets overlain by interbedded thin carbonate turbidites, thin debris flow sheets, and shale. The lowermost debris flow was deposited on a thin, generally undated shale. The lower part of the shale where cored in nearby West World Field is dated as Late Pennsylvanian and is interpreted as representing starved, basin floor deposition. Carbonate detrital components were derived probably from a Wolfcamp platform to the west in the Central Basin platform area and were emplaced by a variety of submarine, gravity flow processes. The allochthonous components may have been transported into a basin floor setting more than 16 km from the platform margin during a time of deep-seated faulting. Although the allochthonous carbonates do not appear to represent slope or toe-of-slope aprons based on present mapping of the platform, accurate delineation of platform margin and slope that existed during their deposition is difficult with present well control.
Figures & Tables
Deep-water carbonates represent on the few frontiers remaining for carbonate exploration and research. The last decade has experienced a rapid evolution in concepts of depositional models and diagenesis which underscores the importance of these deposits as significant reservoirs and source rocks. This workshop displayed cores selected to provide subsurface geologic examples of deepwater carbonates from a variety of depositional settings. Several papers discuss depositional models, platform-to-basin reconstructions, and diagenetic sequences that are important in the development and exploration of Paleozoic carbonate debris flow and turbidite reservoirs of the Palo Duro, Delaware and Midland Basins. Many other examples are included from several different regions.