REORIENTATION ANALYSIS OF DEGLACIAL FEATURES IN SOUTHERN MAINE

Southwestern Maine was glaciated at the last glacial maximum, and deglaciated between 15 and 13 ka. Glacial retreat was simultaneous with isostatic uplift, marine onlap, and influence of topography on flow during final thinning phases. Three disparate morphologies (multiple till drumlins, large meltwater channels in bedrock, and an isolated rock-cored drumlin of exaggerated length aspect) clustered within an 80 km² area on the Mt. Agamenticus upland have nearly identical orientations. We examined flow-parallel orientations for the surrounding area (n=173) to test the hypothesis that these features are closely related to one another and were perhaps created within a coherent drumlinization zone with a specific ice center of mass. Orientation data were gathered from the Surficial Geology map sets of the Maine Geological Survey. Student's t-test, which allows the comparison of small samples with normal distribution, was used to test area sub-samples. Results support the interpretation of a single population of flow-parallel orientations, but only in the area known to be below the inland marine limit. This suggests a single upflow center of mass, however distant, for the ice that occupied the isostatically depressed coastal zone and which carried out the work of drumlinization. At Mt. Agamenticus, the lowland ice thinned substantially, then produced a population of minor recessional moraines with a radically new northerly orientation before disappearing. This analysis identifies a sequence of local deglacial activity: 1) massive grounded ice with upflow connection, 2) thinning grounded ice pinned and isolated on Mt. Agamenticus and 3) reoriented actively receding ice shelf complex. This work applies to regional models of ice retreat (e.g., Retelle and Weddle, 2001) in a controversial zone between western New England and central and eastern Maine. It also is a link between the terrestrial and offshore records of deglaciation.