RECONSTRUCTING THE EVOLUTION OF THE MIDLAND BASIN WITH CHRONOSTRATIGRAPHIC SURFACES DERIVED FROM FUSULINID BIOSTRATIGRAPHY

The Midland Basin is the easternmost basin within the greater Permian Basin hydrocarbon-bearing province. The basin began accumulating sediments in the Pennsylvanian and was completely filled by the Guadalupian. This project aims to reconstruct the Pennsylvanian-early Permian sediment infill history of the Midland Basin, with special emphasis on the Eastern Shelf. To date, 2127 biostratigraphic reports from wells across 50 counties have been archived. Each biostratigraphic reports contains the depth of fusulinid occurrences that allow mapping the top of five biozones, namely the Wolfcampian, Canyon, Cisco, Strawn, and Lower Strawn. Using sea level as a datum, the tops of each biozone forms a regional chronostratigraphic surfaces that demonstrate the geometry of the basin at the end of the specific time interval. We infer in this study that the point of maximum curvature in the shelf-to-basin transition approximates the shelf edge at that time. Thus, comparison of shelf edge locations through time allow reconstruction of the basin filling history.

Three cross sections of the eastern shelf of the Midland Basin along the northeastern shelf, the middle eastern shelf, and finally the southeastern shelf, demonstrate the progradational and aggradational history of the eastern shelf into the Midland Basin. The northern cross section showed continuous aggradational trends from the Atokan through Leonardian. The middle cross section showed general aggradation through the Pennsylvanian, but progradation in the Leonardian and Wolfcampian structural maps. The southeastern cross section mimicked the Pennsylvanian aggradation as seen in the other two cross sections, but depicted significantly more magnitude of progradation during the Wolfcampian and Leonardian. These results imply that the during the Pennsylvanian the Midland Basin was creating accommodation, likely through subsidence, at similar rates that sediment was delivered to the basin. However, the subsidence rate must have greatly decreased relative to the sediment delivery rate by Permian time.