INFERRED END-DEVONIAN TECTONIC, SEA-LEVEL, AND PALEOCLIMATIC EVENTS AS OBSERVED IN NORTHERN OHIO AND ADJACENT PENNSYLVANIA

Cleveland-area stratigraphy is dominated by the thick, black Cleveland Shale succession (expansa - praesulcata conodont zones), which includes the record of the global Dasberg event and possibly the Hangenberg black shale marker, as yet undiscovered, near its top. It marks an eastward-southeastward overspread of anoxia above distal neritic deposits of the Chagrin Shale. We are currently looking for key taxa (conodonts, palynomorphs) in Upper Famennian deposits at the Bradford, Pennsylvania meridian for the possibility that marine deposits of the Oswayo Formation, above marginally marine red beds of the Cattaraugus Formation, may be a shoreward expression of this same transgression.

Ongoing work in Ohio shows a dynamic pattern of northwestward, progradational downlap of divisional units of the Bedford Formation towards the top-Cleveland Shale–basal Bedford Formation erosional contact across the greater Cleveland area. This culminated in deposition of enigmatic, red-brown mudstone deposits of the topmost Bedford succession, well within the zonal time-slice of the global Hangenberg biocrisis. This facies, indicative of either parallic deltaic conditions or an offshore, oligotrophic, marine setting, remains poorly understood. Post-Bedford sea-level drop is indicated by a widespread disconformity that floors the top-Devonian Cussewago-Berea Sandstone succession across the Ohio – northwest Pennsylvania region. The Cussewago fills a major lowstand paleovalley centered near the OH/PA state line; these gravelly, valley-fill deposits yield numerous basement clasts including granite and gneiss. This immaturity stands in marked contrast to other area conglomeratic units, which are quartz-dominated. Hence, the basal Cussewago is believed to record unusually rapid, dissection of sediment source terrains, consistent with reports of glacial and periglacial deposits in this time-slice by others.