MAGNETIC SUSCEPTIBILITY BASED PLACEMENT OF THE EIFELIAN-GIVETIAN BOUNDARY IN THE MARCELLUS SHALE OF THE LOWER HAMILTON GROUP IN NEW YORK STATE

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 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, which is assigned to the kockelianus Zone based on the occurrence of the nominative taxon, and below the Dave Elliot and Halihan Hill beds where 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, is similar to the MS shift measured in Morocco at the GSSP and other localities. 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 in central and western New York. At Hannacroix Creek in the Hudson River Valley the East Berne Shale is much thicker than at localities to the west. Here, the boundary is probably more than 28 meters below the Dave Elliot Bed, compared to less than a meter at West Limestone Creek near Syracuse.