Lithostratigraphy, multi-taxa biostratigraphy, and sequence stratigraphy of the Heidelberg Group (Přídolí – Lochkovian) in New York State
Authors: Ebert James , Matteson Damon 
Published: July 2024

Historically, the Helderberg Group has been an important unit including some of the earliest paleontologic and stratigraphic studies in North America. Once interpreted as a series of coeval facies, most formations and even some members of the Helderberg Group are separated by disconformities and regionally angular unconformities. The Green Vedder Member (new) is defined within the Manlius Formation and the Dayville Member is reassigned from the Coeymans to the Manlius Formation. The name Ravena member of the Coeymans Formation is abandoned because it coincides entirely with the redefined Coeymans Formation. Two new members, Jefferson Heights and Leeds Gorge, are recognized within the New Scotland Formation. A cluster of tephra beds occurs in the Kalkberg Formation, the upper Jefferson Heights and lower Leeds Gorge members of the New Scotland Formation. Strata formerly described as an “upper tongue of the Kalkberg Formation” are referred to as the Old Stone Fort Member (new) of the Becraft Formation. The Deansboro, formerly a member of the Coeymans Formation, is raised to formational rank owing to its physical and biostratigraphic separation from the Coeymans Formation. Reef-bearing strata may still comprise a part of the Deansboro Formation or may be removed and referred to as the Mosquito Point Formation (new). Strata that overlie the Deansboro Formation in central New York that had been regarded as part of the Kalkberg Formation differ lithologically and are significantly younger than the Kalkberg. They are therefore redefined as the Buckley Mill Formation (new). Major unconformities occur between the Chrysler Member of the Rondout Formation and the Thacher Member of the Manlius Formation (Mine Lot Falls Unconformity), between the Thacher and Green Vedder members of the Manlius Formation (Clockville Unconformity), and between the Green Vedder Member and the Olney and Dayville members (Terrace Mountain Unconformity). The Columbia Center Unconformity separates the Olney from the overlying Dayville Member. The Howe Cave Unconformity marks the base of the Coeymans Formation and is basin-wide in its extent. The Punch Kill Unconformity caps the Coeymans Formation and is onlapped by four subunits of the Kalkberg Formation. The Getman Corners Unconformity marks the base of the Deansboro Formation and erosionally separates this unit from the Helderberg Group. The Silurian–Devonian boundary interval (base of the Lochkovian Stage) occurs in the upper portion of the Green Vedder Member of the Manlius Formation. The co-occurrence of scyphocrinitid loboliths and a positive δ13C excursion (Klonk Event) in facies that represent deeper, dysoxic conditions characterize the boundary interval. The Judds Falls Bentonite Bed is constrained to the middle Lochkovian (upper bohemica Zone) by a somewhat diverse chitinozoan fauna. A mid- to late Lochkovian age for the Becraft and Alsen formations is indicated by chitinozoans. Additional chitinozoan data suggest that the Lochkovian–Pragian boundary occurs in the Port Ewen Formation. Pragian conodonts from the Deansboro Formation mark a maximum age for the bioherms that have been grouped with the Deansboro. A Pragian age is also likely for the Buckley Mill Formation that overlies the Deansboro Formation, but chitinozoan studies from this unit are not yet completed. Seven epiboles of various crinoids and cystoids are recognized and are important marker horizons in the revised stratigraphy. The sequence stratigraphic framework of the Helderberg Group suggests that the stratigraphic architecture is strongly controlled by episodic, tectonically-driven subsidence produced by crustal loading during a pre-Tectophase I episode of Acadian orogenesis. During deposition of the Thacher Member of the Manlius Formation, maximum subsidence occurred in the region around Cherry Valley, New York. During deposition of the overlying Green Vedder Member, a low arch developed in this region, separating two sub-basins. The Cherry Valley Arch disappeared during deposition of the Dayville Member of the Manlius Formation and maximum subsidence was centered near Columbia Center, New York. The Cherry Valley Arch was reactivated and broadened to extend between Cherry Valley and the area around West Berne during deposition of the Elmwood through Jamesville members of the Manlius Formation. The Cherry Valley Arch disappeared as subsidence increased during deposition of overlying Helderberg units. Post-Manlius formations document eastward migration of the axis of maximum subsidence and bathymetric axis of the basin through time. This pattern reversed during deposition of the lower part of the Becraft Formation in which deeper water facies (Old Stone Fort Member) were deposited in the Schoharie region and shallower environments developed in the Hudson Valley. This transposition was short-lived as maximum subsidence migrated into the Hudson Valley region once again and persisted during deposition of the upper Becraft and the overlying Alsen and Port Ewen formations. The newly developed sequence stratigraphy and biostratigraphy in the Appalachian Standard Succession (New York State) enable revised correlations within the Central Appalachian Basin.