New Interpretation on the Structural Geology of Strata in Chapel Creek and Berlin Heights, North-Central Ohio
The bedrock geology of Chapel Creek and Old Woman Creek near Berlin Heights in north-central Ohio displays unusual structural deformation in the Devonian-age Ohio Shale, Bedford Shale, Berea Sandstone, and the Mississippian-age Cuyahoga Formation. These folded and faulted units are partially exposed as anticlines and synclines along these creeks. Past studies of this area proposed Pleistocene ice movement as a deformation mechanism, but this cannot explain the extent of layer displacement or the contradiction between the southwest travel direction of the ice sheet and the sense of motion on the folded units. Our new interpretation using field data and constructing geologic profiles explains development of these structures. The Chappell Creek site study is focused on four partially-exposed anticlines, with synclines in between. Anticline axes and their limbs trend NW – SE or N – S. Three southern fold limbs dip 15°–30°; one limb dips 70°. The northern fold is an overturned anticline and its axis dips south with faulted and imbricated Ohio Shale in the core. Bedford Shale is locally thin and mostly covered by debris. Overturned Berea Sandstone outcrop at the NE limb of the anticline dips 55° to SW resting on shale layers of the Cuyahoga Formation. Toward the north, Berea Sandstone and Ohio Shale are exposed in the north limb of the overturned syncline dipping SE. Structural analysis of the anticlines shows that they are formed above the incompetent Chagrin Shale, which acted as a décollement zone. The Old Woman Creek site is a classic example of décollement in the Bedford Shale between the Berea Sandstone and Ohio Shale. Low-relief folds in the Ohio Shale were formed above the Chagrin Shale. At the upper level of the bluff, Berea Sandstone as a low-relief broad anticline sits on imbricated and internally folded and faulted Bedford Shale. A low angle thrust at the base of the Berea Sandstone cuts off internal folds of the Bedford Shale. The presence of allochthonous blocks of fissile black Ohio Shale within the lower part of the Bedford Shale shows that the top of the Ohio Shale anticline is truncated by a horizontal thrust fault and hosted in the Bedford décollement zone. Analyses of both sites show that the folds were created by regional shallow thin-skinned tectonic forces during the late Paleozoic. The folds trend generally NE – SW and abnormal fold and stress trends are the result of local stratigraphic variations and accommodation of the incompetent layers.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019