TEXTURAL AND COMPOSITIONAL VARIATIONS IN LATE WISCONSIN PROGLACIAL LAKE AND MARINE DEPOSITS AS PROXIES FOR CHANGING SEDIMENT PROVENANCE AND FRESH-WATER OUTFLOW SOURCES IN THE CHAMPLAIN LOWLAND, NEW YORK

Sedimentological and compositional trends in late Wisconsin proglacial lake and marine sediment in the Champlain Lowland reflect deglacial changes in water level, lake and meltwater outflow routes, intrabasinal and extrabasinal sediment supply, and salinity. The Coveville Phase of proglacial Lake Vermont expanded northward into the Champlain Lowland as the ice margin receded northward across the Hudson-Champlain drainage divide. Lake Vermont was largely isolated from meltwater and proglacial lake outflow and sediment discharges from Great Lakes and other western sources during this phase. Coveville Phase sediment properties reflect intrabasinal sediment-supply such as changes in proglacial lake outflow from the adjacent Adirondack and Taconic-Green Mountain uplands, proximity to the receding ice margin, and sediment and iceberg trapping mechanisms. The breakout of Lake Iroquois rerouted outflow from the Great Lakes basins through the Champlain Lowland and caused Lake Vermont to fall more than 40 meters from the Coveville to Fort Ann level. The abrupt upward change from thin, debris-poor rhythmites to thicker, debris-rich rhythmites and concomitant changes in sediment mineralogy and geochemistry in a core from Whallonsburg may record this event in the mid-Champlain Lowland. An erosional unconformity overlain by a 0.1–1.5 m thick, massive to ripple-bedded medium to fine sand layer marks the breakout event in cores from the northwestern Champlain Lowland near Plattsburgh.

Connection to Great Lakes and other western sources of meltwater and proglacial lake outflow persisted through later proglacial lake and marine phases in the Champlain and St. Lawrence lowlands. Abrupt variations in sedimentological, compositional and paleontological proxies across the Lake Vermont–Champlain Sea transition occur in several cores from the Plattsburgh area. These variations reflect intrabasinal changes in depositional environment, such as shoreline regression associated with water-level changes and changes in salinity, and extrabasinal sediment supply associated with changes in ice-margin provenance and proglacial lake outflow from the Great Lakes basins and other western sources.