The American Upper Ordovician Standard. XIX. A Middle and Upper Ordovician reference standard for the eastern Cincinnati region

A 1,200-foot core (designated CA-38) drilled by Cominco American, Inc., just east of Minerva, Mason County, Kentucky, provides an essentially complete section from near the top of the Fairview Formation (Upper Ordovician, Maysvillian) to the base of the Middle Ordovician High Bridge Group. The lowest 850 feet of the core penetrates a part of the Ordovician section that is not exposed in the eastern Cincinnati region, and the uppermost 350 feet provides a more nearly complete stratigraphic record than is exposed in a single surface section. Thus we suggest that core CA-38 be a primary reference standard for stratigraphic units in the eastern Cincinnati region. As a first step in estab-lishing such a standard, we present for the uppermost 665 feet of the core a shale-percentage log, a clastic-ratio log, and a log showing the ranges and relative abundances of important conodont species. This portion of the core represents the stratigraphic interval above the base of the Lexington Limestone. Correlation and nomenclature of units in the upper-most 665 feet of core CA-38 is effected by comparing the logs with similar ones for im-portant surface and subsurface sections elsewhere in the Cincinnati region