Origin and depositional environment of some Central Ohio Devonian black shales based on clay mineralogy

Abstract

The clay mineralogy of an outcrop of the lower Ohio Shale sequence near Worthington, Ohio has been studied by x-ray diffraction. Illite was found to be the dominant clay mineral. Both illite and kaolinite vary in abundance as a function of stratigraphic position and clay particle size. Theories of the origin and depositional environment of this shale are reviewed. It is suggested in this paper, according to the results of this study, that the Ohio Shale originated from parent soils displaying similar clay mineralogy characteristics. This type of soil would have developed best on a topography of low relief. The shale was deposited by the reworking of these soils by the transgressing Devonian sea west and northwest of the Appalachian geosyncline. Deposition occurred in the deepening water to the east of the western edge of this sea.