MIDDLE HAMILTON GROUP STRATA (LOWER GIVETIAN) OF THE EASTERN OUTCROP BELT IN NEW YORK STATE

Lower Givetian strata of the Hamilton Group east of the ~74.75° West meridian in NYS, aligning roughly with a north-south line drawn from the Otsego-Schoharie county border along the northern Hamilton Group outcrop belt to exposures in the south along the Delaware River near Port Jervis, Orange County, present a challenging puzzle compared to time-equivalent strata to the west in NYS. This region preserves Hamilton Group rocks ranging from shallow-marine open-water facies, near-shore and shore-face facies (Mount Marion, Panther Mountain, and Cooperstown fms.), into transitional marine-terrestrial to pre-redbed terrestrial facies (Ashokan Fm.), eventually passing into terrestrial flood plain and river channel facies with redbeds (Plattekill and lower Manorkill fms). Middle Hamilton strata in the Helderbergs in the north transition from fully marine facies to fully terrestrial facies heading south to the vicinity of Catskill. Continuing along the outcrop belt to the southwest, Hamilton marine strata climb up-section again, and transition back to fully marine facies approaching Port Jervis, a pattern very similar to that along the northern outcrop belt near the Schoharie-Otsego county border.

Challenges to correlating with the standard Hamilton succession in central/western NYS include: 1) overall less abundant and complete exposure; 2) preservation of varied lateral facies changes over short distances; 3) a thicker package of sediments, with less vertical heterogeneity and more gradational facies changes within the vertical succession; 4) anomalous faunas (e.g., the brachiopods Schizophoria and Orthospirifer), and; 5) lack of clear biostratigraphic data. Additional significant problems are the homogeneity of nearshore facies and little recognition of distinct, traceable marker units. Furthermore, very few workers have carried out stratigraphic and paleontologic studies within this region within the last 150 years, as opposed to the myriad of studies carried out in west/central NYS on age-equivalent strata. All of these factors result in a paucity of knowledge about this broad area. This report summarizes our current understanding of the strata of this region and proposes several possible lines of correlation to western strata in an attempt to establish a preliminary stratigraphic framework.