SURFICIAL GEOLOGIC MAP OF WEATHERSFIELD, VERMONT: GLACIAL HISTORY AND IMPLICATIONS FOR GROUNDWATER RESOURCES

The town of Weathersfield, Vermont lies in southeastern Vermont between the Black River and Connecticut River valleys. The town is underlain by a complex variety of metamorphic and igneous rocks including Proterozoic gneisses and marble, Cambro-Ordovician schists, Silurian-Devonian phyllites, and Cretaceous intrusions (the Ascutney and Little Ascutney stocks). Surficial geologic mapping was conducted during the summer of 2016 to update the current 1960’s era map, to compliment recent bedrock mapping, and to better understand the glacial history in the region and the town’s groundwater resources.

Most glacial striations indicate ice flow to the south, parallel to the Connecticut River valley. At least two subparallel eskers occur in the Black River/North Branch valley and a third in the Connecticut River valley. In some areas these are distinct, mapable landforms. In other areas they are exposed in gravel pits or buried beneath younger sediments and mapped via water well logs and the GPR profiles.

Current work indicates that Glacial Lake Hitchcock lay at an elevation of ~570–600 ft (174–183 m) in this area. Fluvial sediments in these valleys suggest that much of the North Branch and Black River valleys were filled with a delta system that rapidly filled the lake as the delta prograded southward towards Springfield. Similarly, the Sugar River delta partially filled the Connecticut River valley. These delta sediments which bury esker and esker fan deposits host large groundwater reserves.

Quiet water lacustrine deposits primarily occur in the Connecticut River valley and consist mostly of fine to very fine sand intermixed with silt. The sparseness of silt/clay deposits may reflect the narrowness of the lake in this area and/or sediment input into the lake from the Sugar River delta. While these sediments may not be fine enough to confine an aquifer in the eskers, they do serve to filter/adsorb many potential contaminants from entering these potential groundwater sources.