NEW CHRONOSTRATIGRAPHIC DATA FROM THE TELYCHIAN (LLANDOVERY; SILURIAN) OF THE NORTHERN APPALACHIAN BASIN AND ITS IMPLICATIONS FOR EXISTING SEQUENCE STRATIGRAPHIC FRAMEWORKS

In recent years, the chronostratigraphic framework for lower Silurian strata in the northern Appalachian Foreland Basin has been greatly refined by the application of δ¹³C chemostratigraphy and conodont biostratigraphy. These techniques have been employed to discern globally recognized signals, including the mid-Telychian Valgu Excursion, which has been identified in the Waco Member of the Alger Formation. New and published data have been summarized and integrated here toward the goal of a unified sequence and chronostratigraphic framework linking the northern margin of the basin (upstate New York) and the western margin of the basin (central Kentucky and Ohio).

Traditionally, the base of a major stratigraphic sequence (S-IV) in eastern North America has been placed at the lower contact of the Westmoreland Hematite in east-central New York, the Second Creek Bed in west-central New York, the Waco Member of the Alger Formation in Kentucky and south Ohio, and the Dayton Formation of west Ohio. However, the new data discussed here suggest a Pt. eopennatus Zone (stage slice Te2) assignment for the Waco, a Pt. angulatus Zone (stage slice Te3) assignment for the Second Creek Bed, and a Pt. am. amorphognathoides Zone (stage slice Te4-Te5) assignment for the Westmoreland and Dayton. A long-standing inference that the Waco and Dayton were laterally equivalent units is challenged by the new conodont data as well. Although stage slices Te1-Sh1 in Ohio and Kentucky have recently been assigned to S-IV, the presumed lateral equivalents of these strata in New York (where the Silurian sequences were originally defined) apparently encompass S-IV and much of the underlying S-III ("middle Clinton") as well. Additional work is underway to more fully constrain these sequence stratigraphic hypotheses regionally and to refine age assessment of “lower” and “middle Clinton Group” strata in central New York State.