TECTONIC SUBSIDENCE ANALYSIS OF THE MIDLAND BASIN AND EASTERN SHELF: INFORMING ANCESTRAL ROCKY MOUNTAIN EVOLUTION

The Midland Basin of West Texas is an intracratonic basin that began to form in the Early Pennsylvanian due to the collision between Laurentia and Gondwana. Contemporary basins such as the Anadarko, Paradox, and Orogrande also formed as a part of the Ancestral Rocky Mountains (ARM). The evolution and deformation of ARM basins is widely debated. The application of subsidence analysis to the Midland Basin and Eastern Shelf are used to illuminate basin evolution and provide constraints for the proposed ARM tectonic models. Chronostratigraphic data must be obtained to construct subsidence curves; however, this aspect is commonly a challenge in ARM basins due to poor biostratigraphic data, lack of coeval volcanic activity, and Cenozoic thermal overprinting.

This research utilizes chronostratigraphic surfaces constructed from >2000 fusulinid biostratigraphic reports across the Midland Basin. These chronostratigraphic surfaces represent time-surfaces of each stage within the Pennsylvanian and early Permian. Three locations within the axis of the basin and three locations along the shelf have been chosen to apply backstripping, utilizing the regional chronostratigraphic surfaces for age control.

Preliminary results yielded tectonic subsidence curves similar to the two-phase subsidence model produced for the Anadarko Basin. The two phases are represented as the initiation of subsidence in the Atokan through peak subsidence in the Canyon (Missourian) and reduced subsidence in the Cisco (Virgilian). The Wolfcampian demonstrates an uptick in subsidence compared to the Cisco (Virgilian). Additionally, the resulting subsidence rates in the basin are approximately six times greater than the rates of subsidence observed on the shelf. The Canyon (Missourian) shows the greatest rate of subsidence throughout the Pennsylvanian and Permian on both the shelf and in the basin. From the decompacted thickness curves, it is apparent that the basin was starved of sediment until the Permian when the basin experienced a greater influx of sediment. Future work includes using the graphic correlation method to plot the last appearance datums at the six locations to determine their correlation as well as comparing decompacted thicknesses to determine sediment accumulation rates and patterns.