STRUCTURAL DEVELOPMENT OF THE POTATO HILLS: HOW MESO- AND MACRO-SCALE STUDIES AID IN THE UNDERSTANDING OF THE DEVELOPMENT OF THE OUACHITA OROGENY, SOUTHEASTERN OKLAHOMA

The Ouachita Mountains in southeastern Oklahoma represent a portion of a 2000+ km long fold and thrust belt that record a long history of Paleozoic, clastic-dominated deposition prior to the closure of the Iapetus Ocean during the final assembly of Pangea. The Potato Hills region in the central Ouachitas exposes Ordovician to Mississippian stratigraphic units that are otherwise only exposed in the Black Knob Ridge area and the Broken Bow Uplift. Understanding the processes that led to the formation of the Potato Hills in southeastern Oklahoma is critical to our understanding of the overall development of the Ouachita Mountains. The Central Ouachitas are characterized by large open folds of Late Mississippian and to Early Pennsylvanian strata. The Potato Hills, in contrast, consist of tightly-folded and highly-fractured Ordovician through Mississippian siliceous shales and cherts. The elliptical Potato Hills exposure reflects the overall doubly-plunging anticlines and synclines that trend approximately 065-075°. During the course of this study, previously undocumented Womble shale was found in the hanging wall of the Potato Hills Thrust on the northern side of the window. The mapping and mesostructural analyses also document the consistent north vergence of the mesoscale folds both within the window (footwall) and outside the window (hanging wall). Finally, new exposures (courtesy of gas exploration) reveal the presence of a weakly-developed cleavage in selected shale intervals. To summarize, our new 1:24,000 scale geologic map and structural analyses, aided by the recent exploration, provides data that help to resolve the structural history of the Potato Hills. Our research confirms that the Potato Hills structure is an erosional window through a folded thrust sheet domed up by deeper thrust duplexing.