RE-EXAMINATION OF THE TYPE ITHACA FORMATION FRASNIAN USING A SEQUENCE STRATIGRAPHIC APPROACH: IMPLICATIONS FOR CONTROL OF AN ANACHRONISTIC FAUNA

Chronostratigraphic refinement of the early Frasnian (Genesee Group) succession in New York has been ongoing for over 150 years. While recent work has recognized key horizons that may have temporal significance (e.g., sequence boundaries, condensed sections, flooding surfaces) in western New York sections, correlation of such horizons into the vicinity of Ithaca, New York has been a key challenge. This study focuses on detailed examination of the Ithaca Formation of east-central New York in its type area, using a sequence stratigraphic approach to describe and correlate these strata. We summarize progress in characterizing small-scale sedimentary cycles within the Ithaca Formation, as well as the identification of potential horizons and/or beds that appear to be correlative with those previously recognized in western New York sections. These include fossil-rich calcareous siltstone and limestone beds that probably record sediment-starved intervals associated with small-scale transgressions. The latter appear to correlate into condensed, styliolinid-rich pelagic limestones in western New York. New correlations provide a high-resolution framework for examining changes in Appalachian Basin faunas that are found in these strata, including not only the Frasnian “Ithaca Fauna”, but also a recurrent “anachronistic” fauna dominated by taxa typical of the Middle Devonian (Givetian) Hamilton Group. This recurrence occurred iteratively long after these taxa had apparently gone extinct in other parts of the world following the global Taghanic Bioevent; this suggests the long-term persistence of faunal associations, which may re-appear in “Lazarus” fashion when conditions appropriate to their survival return to a particular region, provided that they do not become biogeographically isolated. Furthermore, these results suggest that sea level fluctuation is a key factor influencing faunal migration into the study area. Examination of facies gradients and the position of these faunas within a sequence stratigraphic framework may allow us to infer the location and nature of refugia for this relict “Hamilton-like Fauna” during times of “Ithaca Fauna” dominance.