Ardith K. Hansel and W. Hilton Johnson
Kewaunee Formation (Mickelson et al. 1984).
Kewaunee County, Wisconsin.
Frye et al. (1968) defined the Wedron Formation to include the glacial tills and intercalated deposits between the Morton Loess and the top of the till below the Two Creeks forest deposit at Two Creeks, Wisconsin. At that time, the red till above the Two Creeks forest deposit was believed to correlate with the red Valders till of eastern Wisconsin. The Valders till was inferred to extend as far south as Milwaukee (Thwaites 1946, Thwaites and Bertrand 1957). Accordingly, Frye et al. (1968) applied the name Valderan to the deposits above the Two Creeks forest deposit, and thereby introduced a threefold Woodfordian-Twocreekan-Valderan Substage division of the upper part of the Wisconsinan Stage (fig. 1).
Later, Willman and Frye (1970) defined several members of the Wedron Formation in Illinois, the youngest of which was the Wadsworth Till Member (fig. 7). Subsequent work by Lineback et al. (1974) indicated that four lithologically distinct till units (one gray and three red) occur beneath Lake Michigan. The gray till unit occurs in the southern portion of the lake basin, and Lineback et al. (1974) correlated it with the Wadsworth Till Member. On the basis of changes in color and clay-mineral and carbonate compositions, they also defined and mapped the distribution of three younger, red till members under the lake from oldest to youngest: the Shorewood, Manitowoc, and Two Rivers Till Members. Although they noted in seismic profiles a moraine on the lake floor and pinch-outs of some till units beneath younger ones, they mapped the distribution of till units predominantly on the basis of the lithology of samples from cores. Lineback et al. (1974) interpreted the Shorewood and Manitowoc Till Members to be older than the Two Creeks forest deposit; thus, they classified those till members as part of the Wedron Formation. They correlated the Two Rivers Till Member (named Two Rivers by Evenson 1973a) with the red till above the Two Creeks forest deposit at Two Creeks, Wisconsin, and assigned it to an unnamed formation of the Valderan Substage.
At about the same time, Evenson (1973a), Evenson and Mickelson (1974), and Mickelson and Evenson (1975), on the basis of work in eastern Wisconsin, suggested the type-Valders till was older than the Two Creeks forest deposit, which led Evenson et al. (1976) to conclude that the name Valderan Substage was misleading as a time-stratigraphic term for the red till overlying the Two Creeks forest deposit in Wisconsin. Evenson et al. (1976) proposed the term Greatlakean as a replacement name for Valderan. Further, they presented stratigraphic and geomorphic evidence that deemphasized the significance and extent of ice-margin fluctuations associated with the Two Creeks' and Valders' events. Recognition of pre-Twocreekan red tills obviated the necessity for a post-Two Creeks ice-margin advance as far south as Milwaukee. Instead, they argued, on the basis of the Cheboygan bryophyte site near the Straits of Mackinac (see Farrand et al. 1969, Farrand and Eschman 1974), that a major fluctuation of the ice margin occurred between the events represented by the formation of the Lake Border and Port Huron moraines (a fluctuation that coincided with a change from gray to red till).
Evenson et al. (1974) were uncertain as to how the type-Valders till correlated with other pre-Twocreekan red tills in eastern Wisconsin and Lake Michigan. Subsequent work on stratigraphic relationships of the red till units in eastern Wisconsin (Acomb 1978, McCartney 1979, Dagle et al. 1980, Acomb et al. 1982, McCartney and Mickelson 1982) culminated in the definition and description of the Kewaunee Formation (Mickelson et al. 1984), which contains all the red brown tills and associated deposits of the Lake Michigan and Green Bay Lobes that overlie the Holy Hill and Oak Creek Formations in Wisconsin (fig. 11). Diamicton of the Kewaunee Formation is typically redder than the underlying formations, and although diamicton units of the Kewaunee Formation vary in grain size, they generally contain more silt and clay than those of the Holy Hill Formation (Mickelson and Syverson, in press). Mickelson et al. (1984) differentiated ten members in the Kewaunee Formation, four in the Lake Michigan Lobe area and six in the Green Bay Lobe area. The latter are not discussed in this report.
More recently, Foster and Colman (1991) used high-resolution seismic-reflection profiles collected in the southern two-thirds of Lake Michigan to study the late Quaternary glacial and postglacial stratigraphy and map the distribution of seismic sequences and facies under the lake. Their seismic profiles and cores confirmed the presence of the four till members recognized by Lineback et al. (1974); however, unlike Lineback et al., they mapped the till members on the basis of the distribution of the seismic units. As a result, some of their unit boundaries are different from those of Lineback et al. In figure 8, we follow Foster and Colman (1991) for lithostratigraphic unit boundaries in Lake Michigan.
Kewaunee Section, located in the lake bluff at south edge of the town of Kewaunee in Wisconsin; good for lithology of the Ozaukee, Haven, and Two Rivers Members of the Kewaunee Formation in Wisconsin and the correlative units in Lake Michigan (Shorewood, Manitowoc, and Two Rivers Members).
Cedarburg Lake Bluff Section; good for lower boundary and lithology of the Shorewood-equivalent Ozaukee Member of the Kewaunee Formation.
The Kewaunee Formation is the uppermost succession of red diamicton units of the Wedron Group. Three members were differentiated in the Lake Michigan basin: a basal, red gray to pink gray, silty clay diamicton (Shorewood Member), a middle, brown to red brown, silty clay diamicton (Manitowoc Member), and an upper, red brown, silty clay diamicton (Two Rivers Member).
Diamicton of the Kewaunee Formation is redder and less illitic than that of the underlying Wadsworth Formation in the lake basin or the Wadsworth-equivalent Oak Creek Formation in Wisconsin. Beneath Lake Michigan, it is readily distinguished from the overlying bedded sediment of the Equality Formation.
Extent and thickness
The Kewaunee Formation (and equivalent units in Michigan) is beneath about the northern three-quarters of Lake Michigan and is the surface drift in moraines along the lake basin that extend as far south as Milwaukee, Wisconsin, and Muskegan, Michigan (fig. 8). It also extends into the northern part of the Green Bay Lobe area in Wisconsin. Thicknesses greater than 19 meters (62 ft) were reported in some exposures along the lake bluffs in Wisconsin (Mickelson et al. 1984) and thicknesses up to 49 meters (161 ft) were reported beneath Lake Michigan (Lineback et al. 1974).
The Kewaunee Formation consists of calcareous, red gray, pink gray, red brown, or brown, fine to medium textured diamicton units that contain lenses of sand, gravel, silt, and clay. The matrix grain size is predominantly silty clay in the lake basin, but equivalent members on land (e. g., the Valders and Two Rivers Members) contain more sand (Mickelson et al. 1984). Typically, diamicton of the Kewaunee Formation oxidizes to red brown, yellow brown, or brown.
Lower boundary: the contact with tongues of the Equality and Henry Formations, the Wadsworth or Holy Hill Formations, or older units. Upper boundary: the contact with upper tongues of the Equality and Henry Formations, or postglacial units.
Age and correlation
The Kewaunee Formation was deposited during the later part of the Michigan Subepisode after about 13,500 radiocarbon years ago, when the Lake Michigan Lobe ice margin first melted back far enough north to open a lower outlet for ancestral Lake Michigan at or near the north end of the basin. Readvances of 300 km (186 mi) to the outer Port Huron moraine and 200 km (124 mi) to the Two Rivers moraine occurred at about 13,000 and 11,800 radiocarbon years ago (Port Huron and Two Rivers Phases; figs. 8, 10). The Kewaunee Formation of Wisconsin and Lake Michigan correlates with drift (Monague, Riverton, and Orchard Beach tills) of the Port Huron and Manistee moraines in Michigan (fig. 11).
Environments of deposition
The Kewaunee Formation is interpreted as the subglacial and ice-marginal facies of multiple glacigenic sequences deposited during the late phases of the Michigan Subepisode. The formation consists predominantly of till and debris-flow sediment, some of which was redeposited in a subaqueous environment. In this classification system, interfingering sorted sediments, including the interstadial organic debris (Two Creeks forest deposit) that accumulated as forest litter and was redeposited by water in some cases, are treated as tongues of the Equality and/or Henry Formation(s) of the Mason Group rather than as part of the Kewaunee Formation, as it is in the Wisconsin classification of Mickelson et al. (1984). In its type area along the lake bluffs in eastern Wisconsin, the Two Creeks forest deposit represents the OA horizon of an incipient soil and reflects a short interval of subaerial weathering under cool climate conditions. Radiocarbon ages for the Two Creeks forest deposit in eastern Wisconsin indicate that conditions conducive to the development of a weak soil prevailed in parts of the area between about 12,200 and 11,500 radiocarbon years ago.
Redescribed unit. Extended to include red diamicton units beneath Lake Michigan (Shorewood, Manitowoc, and Two Rivers Members). These units originally classified as the Shorewood and Manitowoc Till Members of the Wedron Formation and the Two Rivers Till Member of an unnamed formation (Lineback et al. 1974). Defined in Wisconsin (Mickelson et al. 1984).
ACOMB, L. J., 1978, Stratigraphic relations and extent of Wisconsin's Lake Michigan Lobe red tills: M.S. thesis, University of Wisconsin-Madison, 63 p.
ACOMB, L. J., D. M. MICKELSON, and E. B. EVENSON, 1982, Till stratigraphy and late glacial events in the Lake Michigan Lobe of eastern Wisconsin: Geological Society of America Bulletin, v. 93, no. 4, p. 289-296.
DAGLE, M., D. M. MICKELSON, L. J. ACOMB, T. EDIL, and S. PULLEY, 1980, Shoreline Erosion and Bluff Stability Along Lake Michigan and Lake Superior Shorelines of Wisconsin, Appendix 7, Northern Manitowoc, Kewaunee, and Door County Shorelines of Lake Michigan: Wisconsin Coastal Management Program, Shore Erosion Study Technical Report, 116 p.
EVENSON, E. B., 1973a, A reevaluation of the "Valders" limit in the Lake Michigan Basin, in E. B. Evenson, D. F. Eschman, and W. R. Farrand, editors, The "Valderan" Problem, Lake Michigan Basin: Midwest Friends of the Pleistocene, 22nd Annual Field Conference Guidebook, Ann Arbor, Michigan, p. 1-29.
EVENSON, E. B., W. R. FARRAND, and D. F. ESCHMAN, 1974, Late Pleistocene shorelines and stratigraphic relations in the Lake Michigan basin— Reply: Geological Society of America Bulletin, v. 85, no. 4, p. 661-664.
EVENSON, E. B., W. R. FARRAND, D. F. ESCHMAN, D. M. MICKELSON, and L. J. MAHER, 1976, Greatlakean Substage— A replacement for Valderan Substage in the Lake Michigan Basin: Quaternary Research v. 6, no. 3, p. 411-424.
EVENSON, E. B., and D. M. MICHELSON, 1974, A reevaluation of the lobation and red till stratigraphy and nomenclature in part of eastern Wisconsin, in J. C. Knox, and D. M. Mickelson, editors, American Quaternary Association Third Biennial Meeting, July 28-August 2, 1974, University of Wisconsin Guidebook, Late Quaternary Environments of Wisconsin: Wisconsin Geological and Natural History Survey, p. 102-117.
FARRAND, W. R., and D. F. ESCHMAN, 1974, Glaciation of the southern peninsula of Michigan— A review: Michigan Academician, v. 7, no. 1, p. 31-56.
FARRAND, W. R., R. ZAHNER, and W. S. BENNINGHOFF, 1969, Cary-Port Huron interstade— Evidence from a buried bryophyte bed, Cheboygan County, Michigan: Geological Society of America Special Paper 123, p. 249-262.
FOSTER, D. S., and S. M. COLMAN, 1991, Preliminary Interpretation of the High-Resolution Seismic Stratigraphy Beneath Lake Michigan: United States Geological Survey Open File Report 91-21, 42 p.
FRYE, J. C., H. B. WILLMAN, M. RUBIN, and R. F. BLACK, 1968, Definition of Wisconsinan Stage: U.S. Geological Survey Bulletin 1274-E, p. E1-E22.
LINEBACK, J. A., D. L. GROSS, and R. P. MEYER, 1974, Glacial Tills Under Lake Michigan: Illinois State Geological Survey Environmental Geology Notes 69, 48 p.
McCARTNEY, M. C., 1979, Stratigraphy and compositional variability of till sheets in part of northeastern Wisconsin: Ph.D. thesis, University of Wisconsin-Madison, 147 p.
McCARTNEY, M. C., and D. M. MICKELSON, 1982, Late Woodfordian and Greatlakean history of the Green Bay Lobe, Wisconsin: Geological Society of America Bulletin, v. 93, no. 4, p. 297-302.
MICKELSON, D. M., L. CLAYTON, R. W. BAKER, W. H. MODE, and A. F. SCHNEIDER, 1984, Pleistocene Stratigraphic Units of Wisconsin: Wisconsin Geological and Natural History Survey Miscellaneous Paper 84-1, 107 p.
MICKELSON, D. M., and E. B. EVENSON, 1975, Pre-Twocreekan age of the type Valders till, Wisconsin: Geology, v. 3, no. 10, p. 587-590.
MICKELSON, D. M., and K. M. SYVERSON, in press, Pleistocene Geology of Ozaukee and Washington Counties, Wisconsin: Wisconsin Geological and Natural History Survey Bulletin 91.
THWAITES, F. T., 1946, Outline of Glacial Geology: 41 Roby Road, Madison, WI, 129 p.
THWAITES, F. T., and K. BERTRAND, 1957, Pleistocene geology of the Door Peninsula, Wisconsin: Geological Society of America Bulletin, v. 68, no. 7, p. 831-879.
WILLMAN, H. B., and J. C. FRYE, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.
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