POTENTIAL LINKAGE OF THE LATE FAMENNIAN CLEVELAND MEMBER TO THE GLOBAL DASBERG TRANSGRESSION: NEW STRATIGRAPHIC OBSERVATIONS IN NORTHERN OHIO

The organic-rich, black Cleveland Member, recording anoxic, marine conditions, occurs in a roughly north-south, arcuate, basinal belt across west-central Ohio. In northern Ohio, it overlies the gray, marginally neritic Chagrin Member and underlies sparsely fossiliferous gray and red strata of the Bedford Formation. Cleveland deposition was mainly coincident with the global expansa conodont Zone with the upper part extending into the praesulcata Zone. As such, this unit temporally correlates with the global Dasberg transgression, with the topmost portion approaching, or exceeding, the earliest phase of the end-Devonian Hangenberg biocrisis interval.

Recent detailed examination of known Cleveland sections, coupled with the discovery of numerous additional outcrops, shows that the Cleveland Member thins dramatically southeastward across the Cleveland, Ohio region toward an inferred basin margin and an upslope erosional limit. A gray shale marker unit within the Cleveland Member, herein designated the Penitentiary Glen Bed, appears to show that part of the southward Cleveland Member thinning is due to regional onlap of Cleveland strata onto a ramped, submarine disconformity surface; basal black Cleveland strata pinch out onto the disconformity as the overlying Penitentiary Glen descends southward to that contact, only to disappear, in turn, along the same surface. This base-Cleveland erosion surface terminates downslope (basinward) to continuity, where it overlies a coarse, turbiditic unit of the topmost Chagrin at the Rocky River Metropark section in west Cleveland. This coarse sediment bundle appears to have been a lowstand fan, timed with a pre-Cleveland regression event that preceded black shale onlap.

This onlap pattern should reveal that basal Cleveland strata are measurably diachronous, and that this regional drowning episode is related to the global Dasberg transgression. Moreover, the top-Chagrin turbiditic unit at Rocky River may be the proximal phase of a basin-wide, lowstand signal that may correlate southwestward to the base- Cleveland “Three Lick Bed” marker of southern Ohio and Kentucky workers.