A proposed diachronic revision of late Quaternary time-stratigraphic classification in the eastern and northern Great Lakes area

A succession of stratigraphic codes (1933, 1961, 1983) has guided attempts to refine classifications and naming of stratigraphic units for Quaternary deposits of the Great Lakes region. The most recent classifications for the late Quaternary of the Lake Michigan lobe (1968) and the eastern Great Lak es (1972) have been widely used, but later work has created the need for re vision. An attempt has been made to integrate the two previous classificati ons following the diachronic system of the 1983 Code of Stratigraphic Nomen clature, A new nomenclature for the higher, more broadly recognized units w as presented in 1997, We here present the diachronic nomenclature for finer subdivisions recognized in the eastern and northern Great Lakes. Following the interglacial Sangamon Episode, the three parts of the Wisconsin Episod e are further subdivided as follows: the Ontario Subepisode (former Early W isconsinan) comprises the Greenwood, Willowvale, and Guildwood phases; the Elgin Subepisode (former Middle Wisconsinan) comprises the Port Talbot, Bri mley, and Farmdale phases; and the Michigan Subepisode (former Late Wiscons inan) consists of Nissouri, Erie, Port Bruce, Mackinaw, Port Huron, Two Cre eks, Onaway, Gribben, Marquette, Abitibi, and Driftwood phases, Succeeding interglacial time to the present is the Hudson Episode. (C) 2000 University of Washington.