INVESTIGATION OF LAST INTERGLACIAL SEDIMENT IN WEYBRIDGE CAVE, VERMONT, USA

A complex latest-Quaternary history has been reconstructed for the Champlain Valley in western Vermont, including a series of proglacial lakes in front of the retreating Laurentide ice sheet, submergence beneath a marine embayment during a period of high relative sea level, and establishment of the modern-day Lake Champlain. However, very few records of climatic conditions exist for northern New England prior to the retreat of ice ~14 kyr ago.

A detailed chronological, sedimentological and geochemical examination of clastic sediment within Weybridge Cave, on the floor of the Champlain Valley, could begin to fill this gap. This cave, developed in Ordovician limestone with over 450 m of passage, is one of the larger known solution caves in the region. Passages of the cave closer to the surface are floored with erratic cobbles washed in from the glacial till and proglacial lake sediment that mantles the surrounding landscape. In contrast, the deepest level of the cave (~35 m below surface) is partially filled with fine, laminated sediments. The majority of this sequence (>2 m) consists of silty clay (mean grain size of 10 µm) with mm-scale and sub-mm scale laminations. Several exposures contain local concentrations of rip-up clasts and a mélange containing intact blocks of finely laminated clays, indicating that deposition of this fine-grained unit was punctuated by higher-energy discharge events. Optically Stimulated Luminescence (OSL) evidence from sand layers that bracket the section suggests that the laminated fines were deposited after 133 ± 22 ka, but before 62 ± 15 ka­, which corresponds to the Sangamon interglacial. Paleomagnetic data were unable to further refine these age estimates, but suggest that the sequence covers a lengthy (>15 ka) time period. The sediments described here offer a paleoenvironmental record that could aid further interpretation of New England landscape evolution prior to the most recent glaciation.