Structural and lithologic data indicate that, while deposited under actively moving ice, considerable portions of three muddy calcareous subglacial tills in the Great Lakes region probably experienced some component of ductile deformation. Viscous till flow and ductile shear are invoked to explain a combination of features such as recumbent isoclinal folds, unlithified sediment clasts, mixed ostracode shells, reversed stone lee ends, girdle and transverse fabrics, irregular stone pavements, fine striae following stone curves, and inconsistent stone striae and a-axes. Deforming, fine-textured subglacial till is considered as a subhorizontal shear zone, rheologically layered with associated structures (in descending order): ductile (e.g., isoclinal folds), brittle–ductile (e.g., fissility), and brittle (e.g., till wedges). Rheology would be controlled mainly by till pore water content, matrix texture, and stone content. Spatial and temporal superposition of rheologies and subglacial processes probably occurred while some fine tills were forming. Fine deformation till may be especially common around areas of the Great Lakes region where proglacial mud and weak bedrock were remoulded as ice travelled along major basins and troughs. In such areas, under a wet-based glacier, resulting till would have been too weak to sustain a large shear stress or inhibit rapid ice flow over it. Instead, in these places, the till was probably water saturated, accounting for most of the glacial flow, and protected the substrate from extensive deformation while effectively acting as a lubricant to overriding ice. Areas of fine deformation till probably represent areas of former low subglacial fluid conductivity and rapid glacial flow. In other areas, subglacial sheet flow of meltwater may have accelerated glacial flow. These two types of areas may have been connected at times under zones of ice streaming and (or) surging.
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 71
Detailed field mapping, till fabric, granulometric, and thin section investigations indicate that a 500 m long unit of laminated tills and interstratified glaciofluvial and glaciolacustrine sediments, belonging to the Catfish Creek Formation and exposed along the north shore of Lake Erie, Ontario, were deposited contemporaneously into a proglacial lake by coherent subaqueous mass flows of till (subaquatic flow tills) accompanied by glaciofluvial and glaciolacustrine contribution from supra‐ and/or subglacial and ice marginal sources. Comparison with descriptions of other stratified tills suggest that several of them may have a similar origin.
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 Lakes (1972) have been widely used, but later work has created the need for revision. An attempt has been made to integrate the two previous classifications following the diachronic system of the 1983 Code of Stratigraphic Nomenclature. A new nomenclature for the higher, more broadly recognized units was 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 Episode are further subdivided as follows: the Ontario Subepisode (former Early Wisconsinan) comprises the Greenwood, Willowvale, and Guildwood phases; the Elgin Subepisode (former Middle Wisconsinan) comprises the Port Talbot, Brimley, and Farmdale phases; and the Michigan Subepisode (former Late Wisconsinan) consists of Nissouri, Erie, Port Bruce, Mackinaw, Port Huron, Two Creeks, Onaway, Gribben, Marquette, Abitibi, and Driftwood phases. Succeeding interglacial time to the present is the Hudson Episode.
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