MIDDLE-LATE GIVETIAN CHRONOLOGY IN THE TYPE TAGHANIC ("TULLY FORMATION") SUCCESSION, NEW YORK AND PENNSYLVANIA

The Tully Limestone is an anomalous clean carbonate unit within the overall siliciclastic succession in central and western New York that has been a focus of study for 170 years (Vanuxem, 1842; Hall, 1843). It is now understood to record an inferred major shift in local water mass conditions (warm, saline water incursion and water column stratification) linked to the global Taghanic Biocrisis (Aboussalam, 2003; Zambito et al., 2012). As depicted on the Rickard (1975) Silurian-Devonian correlation chart, it was placed within a window of time-rock uncertainty for the “Middle Devonian/Upper Devonian boundary” within the ranges of “Polygnathus varcus” (conodont) and Pharciceras amplexum (ammonoid) occurrence. Subsequent refinement (Huddle, 1981; Klapper, 1981; Ziegler et al., 1976) places the lower and middle parts of the Tully within the uppermost Po. ansatus Zone. The upper Tully (Moravia and Fillmore Glen beds interval), yielding Oz. semialternans and the ammonoids Pharciceras amplexum, followed by Schmidtognathus latifossatus, marks the base of the Oz. semialternans Zone = topmost zone of the Middle Givetian substage (Becker, 2007; House, 1978; Ziegler et al., 1976).Stratigraphy for the relatively condensed Tully carbonate deposits of western and west-central New York, recorded on the Rickard chart, and mapped by Heckel (1973), remains largely valid. However, correlations within coeval, off-platform siliciclastic deposits in east-central New York and central Pennsylvania depocenters, have been characterized in much more detail (Baird and Brett, 2003, 2008; Baird et al. 2003). Moreover, Taghanic event-specific chamosite deposits, bordering the carbonate shelf, are understood to be linked to unusual warm water incursion-, and sediment-starvation-related, conditions at this time (Baird et al. 2012; Zambito et al. 2012). On the Rickard chart, the Tully was complexly equated westward to the Leicester Member (formerly “Tully Pyrite”). This diachronous, detrital pyrite lag deposit is now found to be eastwardly (and temporally) coeval to the post-Tully deep-basinal, Geneseo black shale interval and to overly a major hiatus marking entire Tully removal west of Canandaigua Lake (Baird and Brett, 1986).