--> Silurian Through Middle Devonian Far-Field Tectonics during the Appalachian Orogen in Ohio

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Silurian Through Middle Devonian Far-Field Tectonics during the Appalachian Orogen in Ohio


As part of the Midwestern Carbon Sequestration Partnership’s characterization of CO2 reservoir and sealing units, the Ohio Department of Natural Resources Division of Geological Survey created eight detailed isochore maps of the Llandovery to Middle Devonian strata of Ohio. The time represented by the mapped strata is coeval with the Taconic orogeny, Salinic disturbance, and Acadian orogeny of the Appalachian orogen at the continental margin of Laurentia. Variation of thicknesses at the same locations throughout time show far-field tectonics influence in the Appalachian Basin. Paleozoic strata in Ohio typically dips <3o; however, detailed mapping of Paleozoic surfaces shows two dominate structural fabrics in Ohio: 1) subparallel to the Outlet fault system (~N50oW); and 2) subparallel to the Parkersburg-Lorain syncline (~N20oW). Ohio is far from the Appalachian fold and thrust belt, and Paleozoic structures are typically generated by Proterozoic basement faults. In Ohio, these faults likely formed during the Midcontinent Rift System (Outlet fault strike) and the Grenville Orogen (Parkersburg-Lorain strike). Thinning of the Clinton/Medina sands show a paleo-high north of the Akron-Suffield fault during the third tectophase of the Taconic orogeny. Thickening of the overlying Clinton Group north of the Akron-Suffield fault indicates a reversal of throw during the second tectophase of the Salinic orogeny. Large scale thinning of the Clinton Group over the Parkersburg-Lorain syncline indicates that the syncline occupies the position of a Silurian arch, and/or the area arched after Clinton deposition, causing differential compaction of the Clinton shales. As the second tectophase of the Salinic orogeny continued, the Lockport Dolomite reef trends show right lateral offset along the Akron-Suffield faults. The initiation of the Acadian orogeny is marked by the unconformity on top of the Helderberg Limestone. Thickness variation of the Helderberg show the rectilinear pattern of the underlying paleotopography. In northeastern Ohio, the Onondaga Limestone interval thickness shows a tongue of strata from the Michigan Basin near the Chatham Sag. The thickest portion of the tongue is controlled by the Suffield and Highlandtown faults, indicating the faults were a depositional barrier. Overall, changes of regional stress directions within the Appalachian Basin reactivated Proterozoic crustal weaknesses, resulting in variation of depositional/erosional patterns of Paleozoic strata.