--> New Interpretation of the Cambridge Arch and Parkersburg-Lorain Syncline in Ohio

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New Interpretation of the Cambridge Arch and Parkersburg-Lorain Syncline in Ohio


The Cambridge Arch (CA) and Parkersburg-Lorain Syncline (PLS) are two of the most prominent structural features in Ohio. The CA is a northwest-striking arch that is most pronounced from Washington to Coshocton counties (> 94 km). The CA was first recognized at the surface over 130 years ago. Currently, the basement faults related to the CA are known as the Cambridge cross-strike structural discontinuity. The PLS was first mapped around 1909 and was more formally described in 1935. Located to the west of and striking parallel to the CA, the PLS extends over 220 km, from Parkersburg, West Virginia to Lorain County, Ohio. Two primary interpretations of the CA’s origins have been proposed. A surprisingly persistent hypothesis is that a gravity-slide in the Appalachian Basin formed the CA with a décollement in the salt of the Silurian Salina E unit (which coincidentally halite is absent west of the CA). The second and more modern interpretation is that the CA is a Proterozoic basement-fault generated feature that has influenced Paleozoic stratigraphy. This interpretation of the CA is based off mapping subsurface units, seismic interpretation, and few deep-well penetrations along the structure. Near the PLS in Coshocton County, previous investigators noted that east-dipping Proterozoic seismic reflector patterns change direction to west-dipping reflectors of the Coshocton Zone. The change of reflector dip is separated by a chaotic zone of reflectors. This expression of deep reflectors near the PLS has been interpreted as an intra-Grenville Province suture. After interpretation of available modern seismic data, detailed Silurian Salina salt correlation, mapping of Paleozoic intervals, and review of radiometric age dates, the CA initiates at the Proterozoic surface as series of basement fault-related arches, influencing Paleozoic thickness patterns and structure. The faults bounding the CA at depth should be renamed the Cambridge fault system because they do not share the geometry of a cross-strike structural discontinuity. The reflector pattern interpreted as an intra-Grenville suture is expressed along the axis of the PLS from Coshocton County south to Washington County (67 km). The PLS suture amalgamated older Mazatzal-aged crust during the Grenville orogeny to proto-Laurentia. The CA is the conjugate structure of the PLS, representing a back-arc terrane of the PLS suture.