HELDERBERG-TRISTATES GROUP STRATA IN SOUTHEASTERN NEW YORK STATE

The boundary between the Helderberg and Tristates groups of the Lower Devonian in eastern North America (NA) records several major transitions: 1) a change from passive margin deposition into a time of active tectonics associated with the beginning of a major influx of siliciclastics into the region; 2) a global sea level fall and subsequent rise; 3) a major transition in sea floor communities recognized as a boundary between two Evolutionary-Ecological Subunits; and 4) somewhere in this interval lies the Lochkovian-Pragian stage boundary of the Lower Devonian. While the record of the Devonian Period in NY is the geological standard for all NA, not every portion of the interval is perfectly preserved across the state. The time with the least amount of rock deposited across the state through the Devonian is in that area near the boundary of the Helderberg and Tristates groups in the Lower Devonian. While this dynamic interval is missing across most of NY, strata in the southeastern NY/northeastern PA (between Kingston, NY in the north and Stroudsburg, PA in the south) record nearly continuous deposition through this interval.

Recent preliminary investigation of strata across the Helderberg/Tristates boundary in SE- NY has revealed the following findings: 1) a key index fossil for this interval is the terebratulid brachiopod Nanothyris subglobosa, occurring across carbonate and siliciclastic facies and seemingly restricted to the uppermost portion of the Helderberg Group; 2) carbonate facies in slightly deeper-water settings are preserved near Port Jervis at the NY/PA boundary while siliciclastic facies dominate to the north near Kingston; 3) the Port Jervis Formation of SE-NY at the top of the Helderberg Group is likely equivalent to the lowermost portion of the Connelly Formation in the Kingston Region to the north and the Central Valley Sandstone in the Skunnemunk Outlier to the northeast; and 4) uppermost Helderberg Gp. strata are missing north of Kingston, NY.