The Cleveland Shale Member is the uppermost member of the Ohio Shale that was deposited on the western edge of the Catskill Delta. This delta is underlain by middle and upper Devonian strata. The sediments were derived from the Acadian Mountains that were formed as a result of a collision between the Euramerica plate and the Europe plate at about 390 Ma. Because of the rise of the Acadian Mountains, large volumes of sediments were eroded and delivered to a marine environment called the Appalachian Basin. During the Late Devonian period, the Ohio Shale was deposited in that basin.
This study is based on lithofacies analysis from three outcrops located around the city of Cleveland and from five well cores obtained from four counties in northeast Ohio. There are 161 samples collected from the outcrops and the well cores. A total of 33 thin sections, 11 from sandstones and 22 from mudstones, were prepared and analyzed to determine the textural properties, sedimentary structures, and microstructures. In addition, 12 samples were analyzed using SEM methods for mineralogy, surface textures, and microfacies analysis. Paleocurrent analysis is based on 56 measurements from groove casts located at the base of tempestites, and these indicate flow direction from NE to SW.
Analysis of the outcrops and cores identified 14 lithofacies which are classified into seven lithofacies associations, four mudstone lithofacies associations and three sandstone lithofacies associations. The green-gray claystone lithofacies association was mostly observed in the lower part of the Cleveland Shale Member with mean thickness of 51cm. It consists of light green-gray planar laminated siltstone (lithofacies SSl), medium green-gray planar laminated clayshale (lithofacies Cl), and dark green-gray massive claystone (lithofacies Cm). The green-gray siltstone and mudshale rhythmite lithofacies association is observed in the middle part starting after a bundle of event deposits. This lithofacies association consists of light green-gray planar laminated siltstone (lithofacies SSl) and dark green-gray planar laminated mudshale (Lithofacies Ml) and has a mean thickness of 19 cm. The dark blue-gray mudrock lithofacies association, which has a mean thickness of 52 cm, is found in the middle and upper parts, consisting of medium blue-gray planar laminated mudshales (¿lithofacies Ml), concretionary massive mudstone (lithofacies Mc), and dark blue-gray planar laminated clayshales (lithofacies Cl). The mudshale and clayshale rhythmites are only observed in the upper part, consisting of medium blue-gray planar laminated mudshale (lithofacies Ml) and dark blue-gray planar laminated clayshale (lithofacies Cl). These rhythmites have a mean thickness of 23 cm.
Three types of event layers are interbedded with the deposits described above. They represent 12% of the total outcrop thickness. First, there are storm deposits, known as tempestites, which consist of massive -to- normally graded sandstone (lithofacies Smg), overlain by hummocky stratified sandstone (lithofacies Sh), overlain by planar laminated sandstone (lithofacies Sl), and topped by ripple laminated sandstone (lithofacies Sr). This lithofacies association is observed seven times, having a mean thickness of 13 cm. Second, there is a distal turbidite lithofacies association which consist of massive to normally graded sandstone (lithofacies Smg), overlain by planar laminated sandstone (lithofacies Sl), overlain by rippled sandstone (lithofacies Sr), and covered by laminated siltstone (lithofacies SSl). This lithofacies is identified five times, having a mean thickness of 14 cm. The third lithofacies association consists of hyperpycnites which has a mean thickness of 1.74 cm. Each hyperpycnite consists of massive to normally graded sandstone (lithofacies Smg), overlain by planar laminated sandstone (lithofacies Sl), overlain by rippled laminated sandstone (lithofacies Sr), overlain by planar laminated siltstone (lithofacies SSl), overlain by siltstone and claystone rhythmites (lithofacies SSCl), and/or topped by planar laminated clayshale (lithofacies Cl). A Neonereites trace fossil was identified from the base of a turbidite layer. In addition, a Chagrinichnites fish fossil was observed at the base of a tempestites. The fossilized remains of 60% of a lower part of this fish fossils indicates rapid burial in a storm event.
The results of this study support the interpretation that the Cleveland Shale Member depositional environment received clastics from the northeast, which were primarily transported westward as density underflows (turbidities and hyperpycnites). The deposits of mudstone and turbidite indicate deposition occurred on a clastic marine shelf at water depths deeper than fair weather wave base (FWWB). However, the presence of significant storm deposits (tempestites) within the Cleveland Shale Member indicates deposition occurred at water depths shallower than storm weather wave base (SWWB). Together, these results indicate a shallow muddy shelf, in contrast to the pelagic models suggested by other workers.