A LITHOSTRATIGRAPHIC, BIOSTRATIGRAPHIC, AND PETROGRAPHIC ANALYSIS OF MIDDLE AND UPPER ORDOVICIAN STRATA IN THE SOUTHERN CHAMPLAIN VALLEY, NEW YORK, AND A PRELIMINARY 1:24,000 SCALE GEOLOGIC MAP OF THE PORT HENRY QUADRANGLE

The Middle and Upper Ordovician stratigraphic framework throughout the Appalachian orogen is complex and for over a century has led to confusion relative to the regional extent of older nomenclature and the designation of type sections for contemporary names. A better understanding of the depositional environments and facies changes in this mostly carbonate rock sequence can define a more precise local and regional lithostratigraphic framework. To achieve this goal in the southern Champlain Valley of New York and Vermont, new 1:24,000 scale geologic mapping from the Crown Point, Ticonderoga, and Port Henry quadrangles is integrated with new and previously measured sections, conodont biostratigraphy, and microfacies analysis. Previous workers have made detailed measurements of representative sections throughout this region, and those measurements and descriptions are compared with our work in the Champlain Lowlands. Samples of dolostones and limestones were selected for detailed petrographic characterization of framework grains, matrix, cement, porosity, and characterization of microfacies, which is used to improve the selection of samples for conodont biostratigraphy. The recovery of new conodont elements facilitated regional conodont biostratigraphic correlations and aided in the correlation of various microfacies and formational contacts throughout the region along and across strike. A comparison of measured sections shows that issues arising from inconsistent nomenclature, which often predate the North American Stratigraphic Code persist into recent research. Our research in Middle and Upper Ordovician Appalachian stratigraphy includes a multi-faceted analysis of stratigraphic sections, providing a model for future use that reconciles discrepancies relating to stratigraphy and nomenclature throughout the central and northern Appalachians.