The Wisconsinan Stage
The names of the Huron, Erie, and Ontario Lobes imply that glaciers followed these lake depressions, but the flow patterns of these lobes were complex and changed several times during the Wisconsin glaciation. The sublobes of the southwestern part of the so-called Erie Lobe were more often an extension of the ice coming down Huron Basin, and ice from both basins participated in these sublobes. A review of the studies of Wisconsin-age deposits in the area of the three lobes indicates the emphasis that has been placed on investigations of tills by multiple methods, on paleontological studies of the interstadial and late-glacial deposits, and on radiocarbon dating. A threefold time-stratigraphic division of the Wisconsin Stage in this area is based upon synchronous fluctuations by several glacial lobes, and upon climatologic inferences from paleontologic studies. Early and late Wisconsin experienced maximum glacial advances; middle Wisconsin was dominated by interstadial retreats.
The first Wisconsin glacial advance reached into the St. Lawrence Lowland only, and was followed by a glacial retreat during the St. Pierre Interstade about 65,000 radiocarbon yrs B.P. The second major glacial advance (by several lobes) went farther, but did not reach as far south as the late Wisconsin glaciation in Indiana and Ohio. In Pennsylvania and New York it was more extensive than the late Wisconsin, if the Olean Drift is indeed of early Wisconsin age. The source of ice was centered in the eastern Canadian Laurentide area.
Mid-Wisconsin glacier margins retreated several times far into the Huron and Ontario Basins, or even north of them. Three main retreats were probably interrupted by two readvances which reached into the Erie Basin but not south of the Lake Erie watershed. Mid-Wisconsin time began more than 50,000 yrs B.P. and ended about 23,000 yrs B.P.
During late Wisconsin time the major glacial advance in the western part of the region investigated reached its farthest extent south in at least three pulses: 21,000, 19,500, and 18,000 yrs ago. The oscillating retreats were interrupted by three documented readvances: about 17,000, 15,000, and 13,000 yrs B.P. The source of ice was primarily in the western Laurentide center. No evidence has been found here for the Valders readvance which took place in the Lake Michigan Lobe.