U-PB DATING OF DOLOMITE FROM THE CHAMPLAIN VALLEY SEQUENCE, WESTERN VERMONT

The Champlain Valley is a broad lowland separating the Adirondack Mountains of New York from the Green Mountains of Vermont. The basin is floored by the Champlain Valley Sedimentary Sequence, grading upwards from coarse sandstones, to fossil-poor dolomites, shallow water reef limestones, and shale. Although the uppermost portion of the section contains fossil-rich limestones of indisputable Ordovician age, a lack of abundant well-preserved fossils leaves significant uncertainty around the age of the lowermost units such as the Potsdam Sandstone, the Ticonderoga, and Whitehall formations. Our work uses petrography, SEM analysis, and U-Pb dating of dolomite to explore the age of these lowermost units. Preliminary results suggests that they are Neoproterozoic in age, perhaps as old as Late Cryogenian. However, significant lithologic variability coupled with scatter in the U-Pb ages leaves many questions to be resolved.