RECONSTRUCTING PALEOGEOGRAPHY OF A PALEOZOIC SEDIMENT ROUTING SYSTEM: A SUBSURFACE STUDY OF PENNSYLVANIAN CLASTS AND COARSE-GRAINED FACIES IN WASHITA AND BECKHAM COUNTIES, ANADARKO BASIN, OKLAHOMA

Analysis of sedimentary fabrics and composition within basin sediments is key to unravelling the unroofing history of tectonic uplifts and the configuration of the paleogeography where sediments originate. During the late Paleozoic assembly of Pangea, regional compression and transpression resulted in uplifts, rapid basin subsidence, and accumulation of > 3,600 meters of Pennsylvanian sediments deposited northeast of the Wichita-Amarillo uplift within the Anadarko foreland basin. This study’s aim is to compare vertical and lateral variations in sedimentological facies, clast size and composition within coarse-grained Pennsylvanian deposits in Beckham County, OK, with deposits in Washita County, OK, to identify temporal and spatial variation in depositional mechanisms, paleoenvironments, and lithology of source catchments. Although these sediments have been studied by many entities in the energy industry, published literature which documents evolution of clast composition through the Pennsylvanian is sparse.

Published literature and thickness maps of Pennsylvanian “Granite Wash” deposited directly adjacent to the Wichita-Amarillo Uplift, suggest that several subaqueous depositional systems may be represented. This sedimentological study utilizes data collected from subsurface borehole cores to evaluate the hypothesis that the Desmoinesian subaqueous fans in Beckham County were shed from smaller catchments along the Wichita Uplift, whereas the fan in Washita County was fed by a larger catchment. Observations were recorded for lithofacies, sedimentary structures, and conglomerate clast size and composition. Preliminary data from this study suggests a wider range of clast lithologies within conglomerates of the Washita fan in comparison to Beckham County fans. The diversity of clast lithology, in conjunction with sedimentary fabrics, sediment volume and fan areal extent (based on published work) suggest the coarse-grained submarine fan in Washita County was sourced from a large catchment and nearby shallow water shelf. The results of this study reveal insights into catchment paleogeography and the Pennsylvanian unroofing of the Wichita-Amarillo Uplift, filling a gap in the prior literature about this ancient sediment routing system.