GEOLOGIC AND PALEOECOLOGIC EVIDENCE OF ICE-MASS ADVANCE IN NORTHERN MAINE DURING THE YOUNGER DRYAS COLD REVERSAL

During the 1000-year Younger Dryas chronozone in northern Maine, a residual or newly formed ice mass advanced to override and deform frontal sand and gravel exposed at Oxbow, Maine. The advancing ice margin continued southeastward beyond the Oxbow exposure for another kilometer, where several moraine segments mark the termination of the readvance. In the Oxbow stratigraphic section, below the basal till of the readvance, the sand and gravel unit contains deformed peat with four samples dating to an average of 10,500 14C yr B.P. Lake sediment cores from northern and eastern Maine demonstrate a climate change signal characterized by a unique magnetic susceptibility pattern, an associated sharp reduction in organic content, an increase in spruce pollen and Dryas leaves, and chironomid assemblages consistent with colder July temperatures. This zone has been well-dated to the Younger Dryas chronozone. Along the ice-flow line of the re-advance, this Younger Dryas signal is present in lake sediments 5 km south of the termination of the re-advance, but absent in Cranberry Pond sediments, 1.2 km east of the Oxbow exposure and in Perch Pond in the Deboullie highlands northeast of the Oxbow site. High carbonate influx peaks following Younger Dryas sediment deposition at Pennington Pond and Little Machias Lake in northern Maine suggest carbonate leaching from recently deposited, ice-transported tills. Evidence of ice re-advance during the Younger Dryas chronozone in the region of two Paleoindian sites dated to Younger Dryas time at nearby Munsungan Lake demonstrates the presence of Paleoindians in an ice-margin environment. As chironomid-derived temperature estimates for northern Maine and geologic evidence of Younger Dryas ice margin advance are applied to a northern Maine ice cap model, we can better define the Younger Dryas climate in northeastern North America.