The Pennsylvanian Marmaton Group Granite Wash located in the southern Anadarko Basin is a fan delta system that consists of stacked arkosic sandstones, conglomerates, and shale, and within Washita County, Oklahoma, are known to be a prolific hydrocarbon producer. The Marmaton Group in Washita County, though, has a variable and largely unestablished stratigraphic framework and sudden changes in lithology throughout the region, both horizontally and laterally. This combined with a lack of core or outcrop data has created confusion in the subsurface, and the Marmaton Group has remained largely unstudied in southern Washita County, OK.
This study examined two sets of core, correlated over 90 wells logs, and examined thin sections to determine the characteristics of the Marmaton Group in Washita County, Oklahoma. Tops were determined for each of the Marmaton Group intervals (A-F), along with the Skinner Shale. These data were used to create thickness and structure maps of the formations. The two sets of core show a series of interbedded conglomerates, and coarse- through fine-grained sands, topped with shales, indicating rising and falling sea level affecting the delta fan, and creating the unique and striking sediment packages typically observed in fan delta systems. These sediments consist of high amounts of arkosic material sourced just south of the study area from the Amarillo-Wichita Uplift, as confirmed by the thin sections. These arkosic materials give an atypical well log reading due to the potassium and lithic fragment content of the conglomerates and sandstones, creating a higher-than-normal gamma ray reading. This in turned complicates the boundaries between shale, sandstones, and conglomerate zones in the gamma ray well logs. Density porosity logs, Neutron Porosity logs, and Caliper logs were relied upon to accurately determine the interval boundaries
