16-9 Surficial Geology of the Westmore Quadrangle, Northern Vermont

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

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Abstract:

Surficial geologic mapping is useful for guiding land use planning and understanding geologic history. In this project we mapped the surficial geology of the 7.5 minute Westmore Quadrangle in northern Vermont, which includes the northern half of Lake Willoughby. This work contributes to a larger effort to update the surficial geologic maps across northeastern Vermont. The surficial deposits preserve a detailed record of Laurentide Ice Sheet retreat across the area ~13,800 - 13,500 years ago. We conducted 4 weeks of field work collecting observations of surficial materials and landforms. We used these observations along with LiDAR-derived hillshade imagery to produce a detailed map of the surficial geology. Additionally, we drew 3 geologic cross-sections across major valleys, constraining the underlying geology with both water well logs and Tromino (passive seismic) survey points.

These findings provide insight into the region’s glacial history, as well as how the landscape is being altered by modern geologic processes. Crag and tail structures, only visible in new LiDAR imagery, provide evidence for local NW to SE glacial flow, parallel to the rare glacial striations observed in the area. Widespread glacial till overlies Silurian-Devonian metasedimentary rocks and granite bedrock. One esker was mapped on the western edge of the quadrangle indicating organized subglacial drainage systems flowing south-southeast during retreat. Successive sets of abandoned meltwater channels were eroded along the retreating ice margin reflecting shifting drainage pathways between a proglacial lake that filled the adjacent Clyde River Valley and the Lake Willoughby valley. Fine-grained lacustrine sediments, delta deposits, and shoreline deposits record the presence of Glacial Lake Willoughby at two lake levels above the modern lake. The modern lake formed when the ice sheet retreated over the drainage outlet into the Black River valley, north of modern Lake Willoughby. As lake level dropped, the Clyde and Willoughby Rivers formed, flowing at very low gradients across former lake bottom sediments. Extensive wetlands across the valleys and modern delta and alluvial fan deposits characterize the recent geologic processes that shape the current landscape.

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