Year of Publication
Master of Science (MS)
Arts and Sciences
Earth and Environmental Sciences (Geology)
Dr. Frank R. Ettensohn
The Cleveland Shale displays a characteristic and distinctive pattern of promontories and recessed intervals on weathered outcrops, which appears to represent cyclicity. This weathering pattern can be observed in other shales, both within and outside the Appalachian Basin; so determining the nature of these cycles may be critical for understanding the origin of, not only the Cleveland Shale, but also of black shales in general. Cyclicity in the Cleveland was examined on a decimeter-to-meter scale using lithologic characterization, gamma-ray stratigraphy and x-ray fluorescence, and on a millimeter-to-centimeter scale using organic petrography. Lithologic characterization and gamma-ray stratigraphy revealed Milankovitch-band fourth- and fifth-order cyclicity related to changes in the earth’s orbital eccentricity (100 ka) and obliquity of the earth’s axis (42 ka), respectively. Sedimentological changes associated with these cycles were identified through organic petrography and x-ray fluorescence. A depositional model was developed from these data sets, which suggests that cyclic changes in local climate — from cold and wet to warm and dry — controlled advancing and retreating glaciation in the adjacent Acadian mountains as well as concomitant sea-level rise and fall in the Black-Shale Sea. Such changes would have controlled sediment influx to the sea and are thought to be reflected in the cycles.
O'Bryan, Alice C., "THE NATURE AND ORIGIN OF CYCLICITY IN THE CLEVELAND MEMBER OF THE OHIO SHALE (UPPER DEVONIAN), NORTHEASTERN KENTUCKY, U.S.A." (2014). Theses and Dissertations--Earth and Environmental Sciences. 21.