GLACIAL HISTORY OF THE BLACK RIVER AND NORTH BRANCH VALLEYS, WEATHERSFIELD, VERMONT

The Black and North Branch Rivers in Weathersfield, VT are tributaries of the Connecticut River. We mapped the surficial geology of these valleys during the summer of 2016 as interns for the Vermont Geological Survey with the purpose of making a surficial geologic map and cross-section that we use here to outline the glacial history of the area. The underlying bedrock geology contains an intrusion of the White Mountain Igneous Suite from the Lower Cretaceous called Little Ascutney Mountain. This pluton intrudes into schists, gneisses, and marble/calc-silicates that vary in age from Proterozoic to Devonian.

Field observations were recorded using a smartphone application called Fulcrum. Using QGIS, geologic contacts were drawn between areas underlain by differing surficial materials. Water wells observed in the field were marked using GPS. Each well has an identification tag that can be matched to well log data online. Other well locations and subsurface stratigraphic data came from the Vermont Agency of Natural Resources’ “Natural Resources Map.” The 3D cross section was drawn across the valley using observations from the field and water well data.

The Laurentide ice sheet was the dominant mover and sorter of surficial material in Weathersfield. In addition to creating eskers and kettles, it also deposited large amounts of till at elevations greater than 700 ft. Eskers are found in valley bottoms as well-sorted sand and gravel sediments that have been partially or fully buried by outwash and modern alluvium. Glacial flow indicators discovered in the field reveal that the ice sheet travelled in both NW-SE and N-S trends. This directional shift from SE to S occurred when the ice sheet thinned and began flowing parallel to the Connecticut River valley. Ice sheet recession some 17,000 years ago facilitated the creation of a narrow proglacial lake, Glacial Lake Hitchcock, which extended up the Connecticut River valley into the Black River and North Branch valleys. The shallow lake in these valleys rapidly filled with deltaic sediments that prograded southwards until the lake drained.