FINAL MOVEMENTS ASSOCIATED WITH LATE ANCESTRAL ROCKIES DEFORMATION

The easternmost Ancestral Rockies (AR), the Wichita Mountains and the Arbuckle Mountains of southern Oklahoma, contain an interesting paleogeomorphic and stratigraphic record documenting amount and style of tectonism near the end of the AR series of events. For example, in the Wichita Mountains area there is reasonable evidence that ~1000m of vertical uplift, and then subsidence, occurred in the Early Permian (Wolfcampian and Leonardian). Perhaps 3X that amount of horizontal displacement is possible based on work of Donovan. These offsets are distinct from the larger and earlier Pennsylvanian uplifts of 5-7km which formed the AR. It suggests that the tectonism responsible for the AR was episodic and probably far-field. The subsidence is even more striking than the uplift: 1)it shows that movement was concentrated locally along existing faults and did not affect the adjacent Oklahoma Permian basin; 2)it documents a relaxation (extensional) event not long after the earlier compressive event.

These conclusions are based on an understanding of the Permian paleotopography of the Wichita Mountains and of the origin of the Permian Post Oak Conglomerate (POC). The character of this locally derived unit (POC) implies a pre-existing low-relief plain. Regional Permian stratigraphy shows that this plain was near sea level. All relief related to the initial Pennsylvanian uplift had been worn away, implying some substantial time between uplift (tectonism) and formation of the plain on the uplifted block. Thus the Permian tectonism is distinct in time from the Pennsylvanian tectonism. Detailed correlations need to be made with events farther west, and east, to potentially tie this Permian event to larger regional ones.

Gilbert (2004) has argued that crustal thickening of the paleorift, the Cambrian Southern Oklahoma Aulacogen, occurred during the Pennsylvanian compression related to the formation of these Ancestral Rockies. It is not clear how this later event, the Early Permian one, is related, if at all, to this thickening process. However, because the Permian offsets seem to be specific to those existing faults bounding the paleorift, one could argue for whole crust involvment.