CORRELATION OF UPPER CAMBRIAN CARBONATE STRATA FROM SOUTHEASTERN NEW YORK AND WESTERN MASSACHUSETTS

The correlation of Upper Cambrian carbonate strata in the northern Appalachians poses many uncertainties, as these strata are commonly poorly fossiliferous, dolomitized and/or metamorphosed. Regional stratigraphic correlation is additionally hampered by structural complications, including thrusting of basinal over platform successions in multiple allochthons. Previous correlations of these Upper Cambrian strata have relied on lithologic evidence and biostratigraphic indicators in overlying and underlying strata, but the exact ages of many Cambrian sedimentary successions remain poorly constrained.

This study focuses on the Pine Plains Formation (southeastern New York) and parts of the metamorphosed Stockbridge Formation (western Massachusetts), carbonate platform deposits, which have been interpreted as coeval lateral equivalents. The lithologic indicator for their correlation is the presence of significant coarse siliciclastic material (quartz sand) in the carbonate succession. This study proposes that increased siliciclastic input, coupled with other shallow water indicators, may be related to a sea level fall at the Dresbachian/Franconian boundary in the Late Cambrian (Steptoean stage), which produced the Sauk II/Sauk III unconformity on the craton.

This time interval is also characterized by a globally recorded positive carbon-isotope excursion (d¹³C=4 to 5‰ VPDB). Future study of the Pine Plains and Stockbridge Formations will evaluate the validity of the proposed lithostratigraphic correlation by applying carbon isotopes as a tool for high-resolution stratigraphy. In addition, carbon-isotope stratigraphy will be applied in correlating the platform deposits of the Pine Plains Formation to their proposed basinal equivalents in the Schodack (Germantown) Formation, which are lithologically distinct and contain rare documented late Dresbachian and early Franconian fossils (Bird and Rasetti, 1968). This approach will critically evaluate the application of carbon isotopes in making stratigraphic interpretations beyond the resolution possible by using lithologic and biostratigraphic markers.