Pleistocene geology of northeastern Maine

There is evidence in northeastern Maine for at least two glacial phases represented by two tills. The older till unit is the St. Francis, a blue-gray deposit observed in the St. John and Hammond Brook Valleys. At Golden Rapids, the St. Francis till is overlain by a younger brown till with a different clast lithology. The surface of the St. Francis till section at Hammond Brook exhibits a weathered zone, 30 to 45 cm thick, and is overlain by approximately 6 m of stratified sediments. Erratics of Canadian Shield provenance in the surface till indicate advance of the Laurentide Ice Sheet into Maine at least in late Wisconsinan time. Indicator fans, stoss-and-lee forms, drumlins, and striae imply southerly to southeasterly ice flow during the late Wisconsinan maximum. Moraines in southern Aroostook and northern Penobscot Counties and associated outwash and eskers record the northward to northwestward recession of the ice sheet from coastal Maine. Deglaciation in the study area occurred after the formation of the Pineo Ridge Moraine in southern Maine and after the emplacement of the St. Antonin segment of the Highland Front moraine complex of the St. Lawrence Valley in Quebec. A relict ice cap occupied northeastern Maine during the last phase of late Wisconsinan deglaciation. This ice cap had a northeast-southwest trending axis and occupied a perimeter defined by the Aroostook River Valley and by the Fish River, St. Froid, Eagle, Square, Cross, Mud, and Long Lakes. Late Wisconsinan ice flow south of the Aroostook River Valley was generally southeastward. In northern Aroostook County, the flow eventually became northwestward as a consequence of ice drawdown following the incursion of the marine waters into the St. Lawrence Lowland. The radiocarbon age (averaged from several samples) of a sheared and convoluted peat layer associated with a diamicton near Oxbow, Maine, suggests that deglaciation of the area was complete by approximately 10,500 years B.P.