ASSESSING THE ROLE OF DEEP STRUCTURES ON SHALLOW DEFORMATION IN THE POTATO HILLS, CENTRAL OUACHITA MOUNTAINS, OKLAHOMA

The Ouachita Mountains of southeastern Oklahoma are part of the larger Ouachita Orogenic System. Paleozoic shallow to deep-water deposition on the rifted margin of Laurentia was replaced by convergent processes in the late Paleozoic. The Potato Hills region in the central Ouachita Mountains represents a structural window through the uppermost folded thrust sheet. The Potato Hills are unique in that they expose moderately to strongly deformed Ordovician to Mississippian rocks within what is otherwise only mildly deformed Mississippian to Pennsylvanian rocks. Unlike many orogenic belts, there is not clear/convincing evidence for basement involvement in the Ouachita orogenic system. Recent natural gas exploration and production has focused interest on this structural anomaly and provided access to well-logs and high-resolution aeromagnetic data. Together with recently completed 1:24000 scale geologic mapping, this offers an opportunity to reassess the role that deep structures played in the deformational history of this portion of the Ouachita orogenic system.

Geologic mapping and mesostructural analyses document tightly-folded and highly-fractured Ordovician through Mississippian siliceous shales and cherts throughout the Potato Hills that reflect the overall doubly-plunging, east-northeast trending anticlines and synclines. Previously undocumented Womble Shale in the hanging wall of the Potato Hills Thrust, together with consistent north vergence of mesoscale folds both within the window (footwall) and outside the window (hanging wall), further supports the window interpretation. Preliminary analysis of the aeromagnetic data suggests that surface and near surface structures (recorded during geologic mapping) can be traced to deeper levels. Mapping demonstrates that the "pre-window" geometry consists of a thrust fault that cuts up-section both to the north (in the transport direction) as well as laterally from east to west. Lineations in the magnetic data offer insight into the cause for lateral ramping and suggest a correlation between the position/geometry of shallow structures and deeper levels. Ultimately, this research may offer the first clear and convincing evidence for true basement-involved structures in the Ouachita Mountains.