CONODONT BIOSTRATIGRAPHY, δ13C CHEMOSTRATIGRAPHY, AND RECOGNITION OF SILURIAN/DEVONIAN BOUNDARY IN THE APPALACHIAN BASIN AT CHERRY VALLEY, NEW YORK

Icriodus woschmidti is recognized for the first time in Silurian/Devonian (S/D) boundary strata in the Cherry Valley, New York region of the Appalachian Basin.  The first appearance (FAD) of I. woschmidti is near the base of the Dayville Member of the Coeymans Formation, just slightly above the Terrace Mountain Unconformity (TMU).  The Pa element representing I. woschmidti appears to be an early form, suggesting that the FAD of that species in the Cherry Valley region is close to its actual FAD.  Many previous studies have used the FAD of I. woschmidti to approximate the S/D boundary in sections lacking Monograptus uniformis.  However, The FAD of I. woschmidti is known to be within the Pridoli, and possibly even within the range of Monograptus transgrediens.  The newly recognized FAD of I. woschmidti in Cherry Valley suggests that the S/D boundary can be no lower than the base of the Dayville, and more likely higher in the Dayville, or in the overlying Ravena Member of the Coeymans.  A 0.8-m thick unit of the Manlius Formation, bounded by the Clockville Unconformity (CU) below and the TMU above, preserves the record of a positive excursion of d¹³C, with values of +3.59, +3.57, and +3.46 from near the base to near the top, respectively. d¹³C values in the subjacent Thacher Member range from a low of +0.99 near the base to a high of +2.72 just below the CU, whereas d¹³C values in the suprajacent Dayville Member of the Coeymans gradually decline from +3.05 at the level of the FAD of I. woschmidti to +2.15 just below the Howe Cave Unconformity (HCU), which separates the Dayville from the overlying Ravena Member.  d¹³C values for the Ravena are consistently around +2.00. A positive excursion of d¹³C across the S/D boundary has been recognized globally, beginning in the late Pridoli, with peak values typically in the earliest Lochkovian, above the FAD of I. woschmidti.  The position of the positive d¹³C excursion recorded in the S/D boundary strata of the Appalachian Basin in the Cherry Valley region does not correlate well with the position of the global S/D d¹³C excursion as it is currently recognized.