Chronology of Late Wisconsinan deglaciation of coastal Maine

Forty-two radiocarbon dates on shells, seaweed, and organic sediments provide the basis for a tentative chronology of Late Wisconsinan deglaciation of coastal Maine. The dates comprise two general categories: (a) those that can be directly related to positions of the retreating ice margin, and (b) those that are related to the interval of late-glacial marine submergence, but without a clearly defined temporal relationship to retreating ice. Available dates span the interval 13,800 B.P. to 11,400 B.P., with the majority of dates clustering between 12,300 B.P. and 12,500 B.P. Time-distance curves depicting ice retreat from coastal Maine were constructed on the basis of the forty-two available dates; separate curves were drawn for the eastern coastal zone and the southern and central coastal zone. In eastern Maine, the rate of ice retreat from the coast was on the order of 0.2 km/yr. A value of between 0.35 km/yr and 0.5 km/yr is postulated for the rate of retreat in eastern Maine if readvance to PineoRidge at 12,700 B.P. is accommodated. The rate of ice retreat in southern and central coastal Maine was probably between 0.2 km/yr and 0.25 km/yr, though inclusion of a date of 13,000 B.P. from Embden Pond would require ice retreat at a rate of 0.5–0.6 km/yr. Form lines constructed on the basis of field evidence and information from time-distance curves outline the pattern of ice retreat and indicate the following general sequence of events: (a) At 13,800 B.P., the retreating ice margin occupied a position at the present coastline in southwestern Maine but was well seaward of the coast in eastern Maine, (b) By 13,200 B.P., ice stood at the position of the present coastline in eastern Maine. Ice was still seaward of the central coast but had begun to withdraw inland from the coast in southwestern Maine. Coastal highlands, such as Mt. Desert Island, had been uncovered by ice at this time. (c) The ice front had reached a position above the marine limit along its entire extent between 12,600 B.P. and 12,400 B.P. The late-glacial marine transgression reached its maximum extent at this time, (d) Emergence of the coastal zone, resulting from isostatic recovery, was complete by 12,000 B.P. in eastern Maine and by 11,500 B.P. in southern Maine.