PRELIMINARY MULTITAXA BIOSTRATIGRAPHY AND SEQUENCE STRATIGRAPHY OF THE PŘíDOLí (LATE SILURIAN) AND LOCHKOVIAN STAGES (EARLY DEVONIAN) IN THE APPALACHIAN STANDARD SUCCESSION OF NEW YORK

The Devonian System (Lochkovian Stage) begins in New York in the upper Green Vedder Mbr. (GVM), a HST within the otherwise peritidal facies of the Manlius Fm. (Helderberg Grp.). Recognition of this event is based on the coeval occurrence of a strong positive δ¹³C excursion within the zone of the Icriodus woschmidti group (Kleffner et al. 2006) and the epibole of scyphocrinitid loboliths (Matteson and Ebert 2011). These factors indicate that the Klonk Event occurs in the upper portion of the GVM., placing the lower GVM and Thacher Mbr. of the Manlius Fm. in the Late Silurian (likely Přídolí) and the Olney through Jamesville members (Manlius Fm.) and the Coeymans Fm. in the early Lochkovian (uniformis graptolite zone).

Conodonts of the I. postwoschmidti group (Kleffner et al. 2006) indicate an early Lochkovian age for lower Kalkberg Fm. A second HST represented by the New Scotland Fm. is middle Lochkovian in age (upper eurekaensis or lower delta conodont zones; praehercynicus graptolite zone) based on the occurrence of Pterochitina megavelata, Cingulochitina ervensis, Eisenackitina bohemica and Margachitina catenaria (Bevington, Ebert and Dufka 2010). These strata include a K-bentonite dated at 418 Ma (Tucker et al. 1997). Chitinozoans from the New Scotland corroborate earlier assignments of these beds to the praehercynicus zone based on brachiopods (Johnson and Murphy 1969) and correlation with the Indian Point Fm. (Chaleurs Grp.; Gaspé, Québec) based on the co-occurrence of K-bentonites and M. praehercynicus in the Rosebush Cove and Petit Portage Mbrs. (Ebert, Matteson and Natel 1997). A late Lochkovian assemblage of chitinozoa (hercynicus graptolite zone) including E. bohemica, Fungochitina lata (Bevington, Ebert and Dufka 2010) and M. tenuipes (?)(late Lochkovian – mid-Pragian) is present in the Becraft Fm.

This biostratigraphic framework provides a temporal context for Helderberg sequence boundaries and early signals of Acadian orogenesis. The Mine Lot Falls (Rondout/Thacher) and Clockville (Thacher/GVM) unconformities occur in the Late Silurian. The GVM represents a HST that straddles the S/D boundary. The Terrace Mountain (GVM/Dayville), Howe Cave (sub-Ravena) and Punch Kill (sub-Kalkberg) unconformities occur in the early Lochkovian and the New Scotland HST occurred during the mid-Lochkovian.