A PAC Analysis Of The Manlius-Coeymans Formational Boundary Helderberg Group Of New York State

Abstract

Application of the PAC hypothesis to the Thacher Member of the Manlius Formation has resulted in its di­vision into eleven correlative PACs, shallowing-upward cycles produced by sedimentary aggradation following rap­id episodic base-level rises. The eleven Thacher PACs are organized into two sequence so Manlius PACs 1-5 contain predominantly intertidal facies; Manlius PACs 6-11 are comprised mainly of subtidal and supratidal facies. These sequences are discernible at all locali­ties in the Hudson Valley and central New York State. This study demonstrates that certain distinctive facies found in PACs of the upper Thacher sequence de­veloped laterally persistent horizons, an observation made earlier by Rickard (1962), The PAC 8 algal laminite horizon, which corresponds to the waterlime datum of Rickard (1962, figure 2), provides the primary time and environmental datum for the upper Thacher PAC sequence. Correlation of upper Thacher PACs demonstrates that the Manlius-Coeymans formational contact is unconformable. in eastern New York State. The thickness of section and number of PACs in the upper Thacher decreases progressively from west to east. Erosion responsible for the missing section and PACs is attributed to differential tectonic uplift of the eastern basin margin prior to any Coeymans deposition.