BIOSTRATIGRAPHIC CONSTRAINTS ON THE TIMING OF VALLEY INCISEMENT AND DEPOSITION OF THE LOWER MISSISSIPPIAN BLACK HAND SANDSTONE OF OHIO

The Black Hand Sandstone Mbr. of the Cuyahoga Fm. is up to 60 m thick and consists almost entirely of nonmarine, cross-bedded, coarse-grained, conglomeratic sandstone. We interpret the Black Hand as braided river sediments filling incised-valleys within finer-grained marine sediments of the Cuyahoga. Available biostratigraphic data points to late Kinderhookian incision followed by an early Osagean transgression.

By combining previous biostratigraphic studies (e.g., Fagadau, 1952; Hyde, 1953; Rodriguez, 1961; Manger, 1971, 1979; Thompson et al., 1971; Gordon and Mason, 1985; Coleman and Clayton, 1987; Clayton et al., 1998; Sandberg, Mason, and Work, 2002) on various taxa (brachiopods, ammonoids, conodonts, miospores) it can be demonstrated that the overlying Logan Fm., and the equivalent Borden Fm. of eastern KY, is early Osagean (Tn3) age. The age relationships of the various members of the Cuyahoga are more complex. In general, the Cuyahoga is time-transgressive from north to south. In northern Ohio nearly all reported species from the Orangeville, Sharpsville, and Meadville members are restricted to the Kinderhookian (Tn2) (Szmuc, 1957). In southern Ohio, near the Ohio River, ammonoids and conodonts in the basal Henley Member indicate the Cuyahoga is predominantly early Osagean age (Sandberg, Mason, and Work, 2002). In central Ohio the Kinderhookian-Osagean (K-O) boundary is thought to occur within the upper Cuyahoga, but precise correlation is equivocal because of missing time within the unconformity at the K-O boundary in the Mississippi Valley.

Based on: A) the above age relationships, B) the unconformity at the K-O boundary of the Mississippi Valley, C) reports of Tournaisian (Tn2) tillites on Gondwana (Crowell, 1999), and D) the positive C13 anomaly in the late Kinderhookian (Mii et al., 1999; Saltzman, 2002) the following can be inferred. 1) a glacial eustatic drop in sea level in the late Kinderhookian produced incised valleys in the Cuyahoga Fm.; 2) the valleys filled with braided stream deposits during an early Osagean sea level rise; and 3) the continued rise in sea level flooded the top of Black Hand, where marine fossils occur, and deposited the overlying Logan Fm.