Pennsylvanian-Early Permian chronostratigraphic evolution of the eastern shelf of the Midland Basin; implications for subsidence patterns across the Ancestral Rocky Mountains

This article utilizes over 3000 biostratigraphic reports of fusulinid taxa in the Midland Basin to produce a series of chronostratigraphic surfaces that show shelf-to-basin profiles from the end of the Atokan to the end of the Leonardian. The position of the shelf-edge break along the Eastern Shelf was geometrically reconstructed for each of the chronostratigraphic surfaces. Comparing the location of the shelf edges produced in this study to published examples resulted in significant disagreement for some time intervals, especially the Wolfcampian. These discrepancies are inferred to be predominantly the result of lithostratigraphic-based vs. biostratigraphic-based data. Assessing shelf-edge trajectory through the Pennsylvanian into the Early Permian indicates that (1) tectonic and eustatic increases in shelf accommodation resulted in retrogradation of the shelf edge during the Pennsylvanian, and (2) Early Permian progradation was the likely result of cessation in tectonic subsidence that allowed bypass of the shelf and passive filling of the basin center. When placed into the context of the Ancestral Rocky Mountains, subsidence analysis of the Midland Basin agrees with tectonic models that portray a synchronous start rather than an east-to-west migration of peak subsidence. Additionally, a relatively synchronous apex of tectonic subsidence occurred in the Middle to Late Pennsylvanian.