CAMBRIAN-ORDOVICIAN STRATIGRAPHY OF THE SOUTHERN CHAMPLAIN VALLEY, NEW YORK AND VERMONT: RECONCILING GEOLOGIC MAPPING OF FORMATIONS

With a goal of compiling seamless geologic maps across political boundaries and our current geologic mapping at 1:24,000 scale in the southern Champlain Valley of New York and Vermont, we developed a stratigraphic column of Cambrian and Ordovician formations based our ability to robustly map them at this scale. The Cambrian and Ordovician stratigraphic framework throughout the Appalachians is complex and has a complicated history of locally and regionally assigned names for lithostratigraphic units. The Cambrian-Ordovician Great Carbonate Bank (GCB), which extends along the eastern part of North America and is represented in the Champlain Valley, contains stratigraphic units that can be traced for hundreds of miles along strike. However, facies changes and discontinuities have led to recognition of numerous local and regional units. The stratigraphy of the Champlain Valley of New York and Vermont has been confounded by more than a century of work on stratigraphy, paleontology and geologic mapping resulting in a confusing nomenclature of geologic units. Some formations were defined on their paleontologic content where others were defined through geologic mapping of lithologies. To reconcile the lithostratigraphy and the mappable formations of the southern Champlain Valley of NY and VT, we considered the history of the nomenclature and correlations, mappability, petrology, biostratigraphy, and the genesis of the units based on paleoenvironmental interpretation. For the current geologic mapping, the authors carefully considered the history of stratigraphic names used in previous mapping and examined outcrops and type sections or other reference localities to develop a stratigraphic column. This Cambrian-Ordovician stratigraphy for the southern Champlain Valley records a transition from syn-rift clastic sediments and shallow-water carbonate buildups (Potsdam Sandstone and Ticonderoga Formation) to peritidal dolostones and limestone (Whitehall Formation, Cutting Dolomite, Fort Cassin Formation, and Providence Island Dolomite), to gradually deeper water peritidal to subtidal mostly limestone units (Crown Point Limestone, Valcour Limestone, and Orwell Limestone) and ultimately to deeper-water shelf carbonates (Glens Falls Limestone and Stony Point Formation).