Glaciation of WisconsinLee Clayton, John W. Attig, David M. Mickelson, - PDF document

Glaciation of WisconsinLee Clayton, John W. Attig, David M. Mickelson, Mark D. Johnson, and Kent M. SyversonFigure 1. Phases of glaciation. A event rather than a period of time. Most phases represent at least a minor advance of the edge of the Laurentide Ice during a phase of glaciation. For example, during the Johnstown Phase of the Wisconsin Glaciation, the g. 4 for lobe locations) of the Laurentide Ice Sheet advanced to the line marked ÒJohnstownÓ in south-central Wisconsin; gure 3 shows that this occurred approximately 16,000 shown at any location. Area glaciated between approximately 30,000 and 9,500 years before presentArea glaciated prior to 30,000 years before presentArea may have been glaciated, but direct evidence is lackingglacial movement Originally published in 1991; revised in 1992. Figure 3. Correlation of Ice Age events and lithostratigraphic units in dif-ferent parts of Wisconsin. The events are shown in italics, and the lithostrat-igraphic units (members and formations) are shown in upper-case letters. A lithostratigraphic unit is a layer of geologic material having a characteristic c position within a sequence of units. Most lithostrati- gure contain till (glacial sediment) and meltwa-ter-stream sediment and some glacial-lake sediment. The vertical axis represents time; the time scale is irregular before 17,000 years before present. When a speciÞ c event was responsible for a speciÞ c lithostratigraphic unit, the event is bracketed with the lithostratigraphic unit. Lobes are shown in Þ gure 4.