CONODONT AND MAGNETIC SUSCEPTIBILITY STRATIGRAPHY OF THE MARCELLUS SHALE AND PLACEMENT OF THE EIFELIAN-GIVETIAN BOUNDARY, MIDDLE DEVONIAN, NORTHERN APPALACHIAN BASIN

The Eifelian-Givetian (E-G) boundary, associated with the globally recognized Kačák-otamari events, is defined by the first occurrence of the conodont Polygnathus hemiansatus Bultynck; this horizon at the global section and stratigraphic point at Jebel Mech Irdane, Morocco, is above a black shale interval (otamari-shale) and the Late Eifelian Magnetic Susceptibility Event. In New York and eastern Pennsylvania three widespread black shales occur in the Marcellus Subgroup close to the E-G boundary. In the absence of Polygnathus hemiansatus the boundary is resolved to be between the Cherry Valley Member and below the Dave Elliot and Halihan Hill beds in which the lowest macrofauna of Givetian character are found. An abrupt and significant rise in magnetic susceptibility (MS) values from 1.5E-8 to 5E-8 m³/kg 40 cm above the base of the East Berne Member (top of the Cherry Valley) and before the brachiopod/conodont bearing beds in the Genesee River Valley, and elsewhere across central New York, are similar to the MS shift measured in Morocco at the GSSP. The E-G boundary is provisionally placed where this shift stabilizes above the Cherry Valley Member at the base of or within the black shale of the lower East Berne Member, Oatka Creek-Mount Marion formations.