MAPPING AND INTERPRETING THE SURFICIAL GEOLOGY OF THE NEWPORT QUADRANGLE,NORTHEASTERN VERMONT

Detailed surficial geologic maps help to inform land use, hazard assessments, economic opportunities, the movement of pollutants, particularly important in this area which hosts the state’s largest landfill, and provide the basis for interpreting the glacial history of the area. During summer 2023 we mapped the Newport Quadrangle which lies along Vermont’s border with Québec. A total of 2,220 geolocated surficial field observations, 355 bedrock outcrops, and 3 glacial striations were recorded with the Fulcrum mobile app. These observations along with a LIDAR hillshade baselayer and aerial imagery were used to construct a surficial geologic map of the quadrangle using GIS software.

The bedrock in the area is mainly the Waits River Formation which consists primarily of phyllite and limestone. In the southeastern half of the quadrangle there is a large unit of the Derby pluton which consists of mainly granodiorite. Three glacial striations were observed all indicating southern movement of the glacier. Data from nearby quadrangles show striations suggesting NW to SE movement which suggests that the glacier changed direction as it receded from the mountains and became confined in the valley. Generally lacustrine fine-grained sediments occur below 1000 feet and glacial till above 1000 feet. This suggests the level of the Glacial Lake Memphremagog to be roughly 1000 feet. In the northern portion of the quadrangle there is a SW to NE esker recording subglacial water flow in this direction. In addition, there appears to be an unconsolidated assortment of till and fine to coarse grained lake sediments slightly SE of the esker just above 1000 feet which suggests some sort of ice contact deposits where a piece of ice broke off the glacier as it receded into the valley. On the eastern edge there is a large outwash deposit suggesting a considerable flow of water off of the receding glacier. In addition, there are numerous abandoned channels where water coming off the receding glacier likely incised down through the landscape. Some of these channels are still being used today. Evidence of this is found in alluvial terraces which are perched above the current river indicating where an older river used to flow. The observations found above help give us a better understanding of the glacial history of the state.