PENNSYLVANIAN-EARLY PERMIAN SUBSIDENCE PATTERNS OF SOUTHWESTERN LAURENTIA CRATONIC BASINS

Intracratonic deformation began to affect the Laurentian continent in the Early Pennsylvanian. Deformation manifested as high-angle, basement-involved reverse faults that resulted in a collage of generally northwest-trending structural uplifts and adjacent sedimentary basins. Historically, this episode of deformation is referred to as the ancestral Rocky Mountains (ARM) and is commonly portrayed as a cohesive pattern of deformation that continued from Early Pennsylvanian initiation to the middle Permian. Here, outcrop and subsurface relationships coupled with 1D subsidence curves are utilized to demonstrate that while the Pennsylvanian period of deformation resembles a more cohesive pattern of subsidence across the greater ARM region, the Permian period of deformation is spatially disjointed. With the exception of the Anadarko Basin, Pennsylvanian subsidence across the orogen began in the middle Bashkirian and generally increased until the Late Pennsylvanian. Subsidence history curves during this period are consistent with a fixed-load foreland basin consistent with the classical ARM tectonic style. In contrast, basins in the northern region of the ARM were largely tectonically quiet after the earliest Permian, whereas basins in the southern region of the ARM continued to subside variably. The amount of early Permian (Wolfcampian) subsidence is spatially coincident with a crustal block that is inferred to record the spatial extent of the Cambrian-aged southern Oklahoma Aulocogen, such that basins situated atop the aulocogen subside more than those located more distally. In the late part of the early Permian (Leonardian), basins along the southwestern periphery of the greater ARM began to subside more rapidly. This last phase of deformation is probably linked to plate interactions along the southwestern margin of Laurentia, as closure of the central Pangean suture along the southeastern margin was mostly complete. Notably, subsidence analysis here does not demonstrate any east-to-west subsidence migration patterns and such previous defined subsidence patterns are likely the artifact of updated geological time scales and using sedimentation accumulation rates as a proxy for subsidence.