Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events

The glacial stratigraphy and geomorphology of the western Lake Superior region record a complex sequence of late Wisconsinan ice advances and retreats of the Laurentide Ice Sheet from accumulation centers in Quebec and Hudson Bay. Geomorphic evidence indicates that three major late Wisconsinan events occurred, each marked by gradual buildup of ice, formation of a prominent moraine, and subsequent rapid ice retreat. The established radiocarbon chronology indicates that these three events culminated ca. 23-21, 16-15.5, and 13 ¹⁴C ka, indicating that major glacial advances culminated immediately prior to Heinrich events H-2 and H-1, and that ice underwent rapid retreat during Heinrich events. The possible linkage between western Lake Superior region ice dynamics and Heinrich events is supported by the presence of indicator rock types in drift associated with each major glacial recession. These indicators suggest that progressive southward shifts of the Laurentide Ice Sheet ice divide accompanied each rapid giacial recession. Furthermore, lithologic evidence indicates that there were two episodes of ice divide shifts: one ∼400-600 km occurring during H-2, and a smaller shift occurring during H-l.