THE EARLY EVOLUTION OF LAKE CHAMPLAIN AS RECORDED IN ST. ALBANS BAY, VT

Sediment cores collected along a transect in St. Albans Bay, located in the Northeast Arm of Lake Champlain, VT record the transition from Champlain Sea to Lake Champlain. In this area of the lake, this transition is represented by an unconformity overlain by a peat horizon. The cores we collected allow us to better constrain the spatial extent, thickness and age variability of the peat layer within the bay. Palynological evidence spanning the period of peat deposition reveals a changing climate, with pollen assemblages transitioning from Pine-dominated (cooler climate), to Pine and Hemlock/hardwood-dominated (warmer climate), followed by a return to a Pine-dominated community. These transitions may represent a warming climate related to the onset of the Hypsithermal, briefly interrupted by a short-lived period of cooling, possibly related to the “8.2ka” cooling event.

The peat horizon suggests the presence of a widespread wetland and a lake level 8-9 m lower than the present during the early Holocene. Radiocarbon dating indicates that this paleo-wetland occupied the entirety of the inner basin of St. Albans Bay from ~ 9,600-8,600 cal yr BP. The pattern of peat deposition is time-transgressive, reflecting increasing water levels due to differential tilting of lake basin due to isostatic rebound following the end of the Champlain Sea period. Examination of peat fossil assemblages indicates that the wetland formed in an entirely freshwater environment that was established post-Champlain Sea.

An increase in grain-size observed in the Champlain Sea sediments directly below the peat horizon likely represents a low-stand and the end of Champlain Sea deposition in this area of the Champlain Valley. The combination of an episode of cooler temperatures and water level rise during the establishment of Lake Champlain lead to decreased productivity and a transition from submerged macrophytes and peat deposition to algal production and more typical fine-grained lake sediment.