END-DEVONIAN (LATEST FAMENNIAN) SUCCESSION IN WESTERN AND CENTRAL OHIO: POTENTIAL DEPOSITIONAL CONTINUITY THROUGH THE HANGENBERG TIME-ROCK INTERVAL AND ITS REGIONAL IMPLICATIONS

In Ohio, the end-Devonian succession is represented by the black, organic-rich Cleveland Member of the Ohio Shale, by enigmatic, gray-green and red mudstones of the succeeding Bedford Formation, and by a major sandstone succession of the, still higher, Berea Formation. Bedford and Berea deposition is understood to have occurred within the upper part of the praesulcata conodont Zone within the inferred time-rock interval of global Hangenberg biotic extinctions and paleoclimate disruption. However, Cleveland Member deposition occurred mainly prior to this crisis within the underlying expansa conodont Zone with only an unknown upper portion of this unit correlating to the praesulcata Zone. Hence, it is apparent that this topmost Cleveland division records the onset of the global crisis and may be a regional expression of the Hangenberg Black Shale of global workers. Alternatively, all Cleveland Member strata equivalent to the Hangenberg Black Shale are absent, owing to erosive beveling below the base-Bedford disconformity across northern and northeast Ohio.

Recent observation of stream and core sections across northern and central Ohio (Amherst, Lorain County southward to Gehanna near Columbus) shows that the Cleveland Member-Bedford Member contact is distinctly conformable and gradational across this region, in contrast to sections to the east and south of Cleveland where significant removal of Cleveland Member strata is evident near the inferred structural basin margin. The newly examined continuous sections suggest that strata correlative to the base-Hangenberg event should indeed be present in this structural, depositional basin setting. Ongoing field mapping and biostratigraphic sampling is directed to finding the zonal base (or physical basal contact) of the Hangenberg black shale interval within the greater, undivided Cleveland Member succession across this region.