M. C. McCartney
Residuals Management Technology
1406 East Washington Avenue
Madison, WI 53706
The purpose of this field trip is to examine some of the exposures of red tills in eastern Wisconsin and to discuss their stratigraphic relationships and implications to the late-glacial history of the area. The distribution of till sheets in the area is shown on Figure 1. We will examine deposits of the eastern limb of the Green Bay Lobe (at De Pere and Brillion) and of the western limb of the Lake Michigan Lobe (at Valders and Two Creeks). The till names used in this field trip guide are informal; the Wisconsin Geological and Natural History Survey is planning to publish formal descriptions and definitions. This report is largely a summary of the information in papers by Acomb, et al., (in preparation) and McCartney and Mickelson (in preparation).
When Chamberlin (1877) first reported on the red clay of the Lake Michigan shoreline, he correctly described the deposit at Milwaukee as stratigraphically below a similar red clay in northern Manitowoc and Kewaunee Counties. Goldthwait (1907, 1907, 1908) described the Two Creeks Forest Bed and recognized the red clay as a till. He interpreted the forest bed as documenting the retreat and readvance of ice. Alden (1918) erroneously assigned an Illinoian age to the lower red till. Thwaites (1943) mapped a single red till and gave it the name Valders for the red till at the Valders quarry. Thwaites and Bertrand (1957) extended the term to include the red till over the Two Creeks Forest Bed and the red till they mapped in the Green Bay Lobe deposits. The term Valders or Valderan was subsequently used for red till in the Green Bay lowland, for red till as far south as Milwaukee, Wisconsin and for tills in Michigan (e.g. Black, 1966, 1969; Bretz, 1951; Melhorn, 1954). Frye and Wilirnan (1960), Frye et al., (1968) and Wilirnan and Frye (1970) assigned the name Valderan Substage to the time span represented by the till and lacustrine deposits over the Two Creeks Forest Bed; the time span represented by the forest bed was named the Twocreekan Sub- stage.
Figure 1. Distribution of tills in the Green Bay Lobe and adjacent Lake Michigan Lobe in eastern Wisconsin. Large letters are till units, Italic letters are locations (D=De Pere, B=Brillion, V=Valders, TC=Two Creeks), arrows indicate ice-flow direction.
Recent studies on the red till stratigraphy in eastern Wisconsin (Evenson, 1973; Evenson and Mickelson, 1974; Lineback, et al., 1974; Acomb, 1978; McCartney, 1979) suggest there are several post-Middle Woodfordian red till sheets. One of these units, the Two Rivers till, is stratigraphically above the Two Creeks horizon and, in the Lake Michigan Basin, three till sheets are below the forest bed (Acomb, 1978; Acomb, et al., in preparation). Two red till sheets underlie the forest bed in the Green Bay Lobe deposits (McCartney, 1979; McCartney and Mickelson, in preparation). These lower till units are presumed to be Port Huron or Late Woodfordian age. (about 13,000 years B.P.). Evenson. (1973) used geomorphic evidence, and Acomb (1978) traced the stratigraphic and areal extent of the till sheet to demonstrate that the Valders till is stratigraphically below the Two Creeks horizon. Proof of this relationship requires one section, in which the Valders till definitely underlies the forest bed, but such a section has not been found. However, McCartney and Mickelson (in preparation) have, on the basis of geomorphic evidence also noted by Black (1979), correlated the Valders till with a till in the Green Bay Lobe deposits. This Green Bay Lobe till (Chilton till) has been found under the forest bed in two places.
Evenson et al., (1976) suggested replacing the time term Valderan with Greatlakean to minimize the confusion that could result from rock and time terms with the same name that are not the. same age. Lineback et al., (1974, 1979) and Black (1966, 1979) have argued against the conclusions of Evenson et al. (1976) and the change in the terminology has not yet been fully accepted. However, the investigations of Acomb (1978), McCartney (1979), McCartney and Mickelson (in preparation) and Acomb et al., (in preparation) support the basic conclusions of Evenson (1973) and further indicate that the time term Valderan should be. replaced.
A major result of the work by Evenson et al., (1976) is that "the Two Creeks and Valders are no longer viewed, as outstanding events of Lake Michigan Lobe history. Instead of one major readvance of the ice, the red tills represent minor readvances of a generally receding ice front. Further, the Gary-Port Huron Interstade preceding the advance of the ice. which deposited the red tills is now recognized as an event of major significance in the Lake Michigan Lobe. Thus, the history of the Lake. Michigan Lobe since the Middle Woodfordian includes a major deglaciation (Gary-Port Huron Interstade) followed by readvances (Port Huron) of somewhat less magnitude than the Gary about 13,000 years B.P. with a minor deglaciation (Twocreekan) and a final period of minor readvance (Greatlakean) about 11,800 years, B.P. According to Saarnisto (1974), the Lake Michigan Basin became ice-free around 11,000 years B.P.
The interpretation of the Lake Michigan Lobe late-glacial history is now consistent with what is known about the area to the east. That is, the Gary-Port Huron Interstade is now considered an important event in the Lake Michigan Lobe. This retreat has long been recognized in the eastern Great Lakes (Evenson and Drelmanis, 1976). In Michigan it is represented by the Cheboygan byrophyte bed which is buried by red till of Port Huron age (Farrand et al, 1969). Further, the Twocreekan Substage is now considered to be a minor event. This is consistent with the pollen evidence which indicates progressive deglacliation without major reversals in the northward advance of plant communities (Evenson et al, 1976).
The tills of the Green Bay Lobe correlate with those of the Lake Michigan Lobe; however, because the two lobes traversed different bedrocks, correlated till sheets differ llthologically. On that basis, separate rock- stratigraphic nomenclature is required for the two lobes. For the same reasons, separate nomenclature is also required for the western and eastern limbs of the Green Bay Lobe.
Table I summarizes the till stratigraphy and correlations of the Green Bay and Lake Michigan Lobes. Advances of the Green Bay Lobe deposited at least three red till sheets which are Late Woodfordian age and younger. In the western part of the lowland, the tills are distinguished on the basis of stratigraphic position, texture, color and depth of leaching. In the central part of the lowland, tills are covered by lacustrine sediment, but on the east side a similar sequence of tills is present. Here till units are distinguished on the basis of texture and magnetic susceptibility. In the Lake Michigan Lobe, four Late Woodfordian age and younger tills are distinguished by differences in stratigraphic position, grain-size distribution, and clay mineral content. The Chilton till of the Green Bay Lobe, which is overlain by Twocreekan wood at two localities, correlates with the Valders till of the Lake Michigan Lobe. In both lobes, a Greatlakean till overlies the forest bed at several localities.
Table I: Correlation Of Till And Forest Bed Units Of The Green Bay And Lake Michigan Lobes
|Time Stratigraphy||Stages of Glacial Lake Chicago||Western Green Bay Lobe (McCartney, 1979)||Eastern Green Bay Lobe (McCartney and Mickelson, in prep.)||Western Lake Michigan Lobe (Acomb et al., in prep.)||Lake Michigan (Lineback et al., 1974)||Eastern Lake Michigan Lobe (Farrand et al., 1969; Evenson, 1973, Taylor, 1978)|
|Greatlakean||??||Middle Inlet||Glenmore||Two Rivers||Two Rivers||Two Rivers|
|Ca. 11,800||Twocreekan||Calumet||Two Creeks Forest Bed||Two Creeks Forest Bed||Two Creeks Forest Bed|
|Glenwood||Kirby Lake||Chilton||Valders||Manitowoc||Inner Port Huron (Manitowoc)|
|Silver Cliff||Branch River||Ozaukee||Shorewood||Outer Port Huron (Shorewood)|
|Ca. 13,000||Cheboygan bryophyte bed|
In the western limb of the Green Bay Lobe, the red till units overlying the brown, sandy, Middle Woodfordian Mapleview till are, in ascending order, the Silver Cliff, the Kirby Lake, and the. Middle Inlet tills (Figure 1). In the eastern limb of the lobe, the corresponding units overlying the brown, sandy, Middle Woodfordian Wayside till are the Branch River, the Chilton, and the Glenmore tills. The tills on either side of the lobe are physically separated by sediment of Glacial Lake Oshkosh (Figure 1). The Silver Cliff till is a dull, reddish-brown, sandy loam, which is slightly siltier (Figure 2) than the underlying Mapleview till. The Silver Cliff, and the Kirby Lake till which overlies it, are Late Woodfordian (Port Huron) age. The Kirby Lake till is finer grained (less than 50% sand) and usually redder than the other units. This till has more variability than tills above and below, and it is possible that it represents two ice advances, which deposited till of similar composition. The Kirby Lake till is overlain by the Middle Inlet till, which is dull reddish brown to dull brown, sandy loam. This till is very similar to the Silver Cliff and is best distinguished from it by its stratigraphic position. Where Silver Cliff till or Middle Inlet till are present at the surface, they can be distinguished by depth of carbonate leaching. Carbonates are leached deeper than 1 m in the Silver Cliff till and less than 30 cm in the Middle Inlet till. A number of sites (McCartney, 1979) show two or three till units in one section, and the stratigraphic position of the units is well established.
Figure 2. Triangular diagram showing sand/silt/clay percentages of the 4 tills on the western side of the Green Bay lowland. Shaded areas show distribution of 54 samples of Middle Inlet till, 33 samples of Kirby Lake till, 33 samples of Silver Cliff till and 32 samples of Mapleview till.
Figure 3. Plot of sand (2 - 0.0625mm) fraction vs. magnetic susceptibility of the less than 2mm fraction of tills on the east side of the Green Bay lowland. Magnetic susceptibility measured on 30gm samples.
Other lithologic properties of the tills are shown in Table II. Additional lithologic information and trend-surface analyses of lithologic parameters are given in McCartney (1979).
The western limit of the Silver Cliff till is the red-till boundary of Green Bay Lobe deposits as mapped by Leverett (1929), and its age apparently correlates with one of the outer red till units in the Lake Michigan lowland which are Late Woodfordian (Port Huron) age. The Kirby Lake is also Late Woodfordian age, and its western boundary is the edge of the Valders of Thwaites (1943). The western limit of the Middle Inlet till, which was deposited during Greatlakean time, coincides with the Athelstane moraine (Thwaites, 1943).
On the east side of the Green Bay lowland a similar sequence of tills is present, but here grain size and magnetic susceptibility are used to characterize the tills (Figure 3). The sandy Branch River till with high magnetic susceptibility is the oldest Port Huron till and can be seen overlying the Middle Woodfordian Wayside till at several localities. Above this is the finer grained (Figure 3) Chilton till, which directly underlies the forest bed at two localities (Figure 4). Like its counterpart at the west side. of the lowland, this unit may represent more than one ice advance. Its texture is more variable than either of the other red tills (Figure 3). Depth of the carbonate leaching on the Branch River and Chilton tills is deeper than 70 cm.
The Greatlakean Age Glenmore till is leached a maximum of 75 cm although depth of leaching is generally considerably less. In addition, the Glen- more till has consistently lower magnetic susceptibility than the pre- Twocreekan units (Figure. 3). Other characteristics of these tills are given in Table II.
The four red till units in the Lake Michigan Lobe are in ascending order, the Ozaukee, the Haven, the Valders, and the Two Rivers. The Ozaukee till is distinguished from the other red tills by its fine grain-size distribution (Figure 5, Table II). This till is also distinguished by its consolidation. The Ozaukee till is normally consolidated to slightly overconsolidated, but the younger red tills are significantly overconsolidated. This may be due to the presence of permafrost during deposition of the Ozaukee till (Mlckelson et_al., 1979). The Haven till, which overlies the Ozaukee, is siltier than the Ozaukee till and has a clay mineralogy nearly identical to it (Figure 5, Table II). The Haven is the red-to-gray till exposed below the Two Creeks Forest Bed, and in almost every shoreline exposure it is overlain and underlain by lake sediments up to the Glenwood level (640'). The Valders till can be distinguished from the underlying Haven and Ozaukee tills by its clay mineralogy and grain size (Figure 5, Table II); clay mineralogy differentiates the Valders from the Two Rivers till. The Two Rivers till can be differentiated from the Haven and Ozaukee tills by grain-size distribution. Depth of carbonate leaching in the Two Rivers till is much shallower than in the older red tills (Mickelson and Evenson, 1975). The stratigraphic relationship of these red tills is shown in Figure 6.
Characteristics Of Lake Michigan Lobe Red Tills. First Parenthesis is Standard Deviation, Second Parenthesis is Number Of Samples
|% Sand||% Silt||% Clay||% Illite||Expandable||% Chlorite-Kaolinite||Calcite-Dolomite Ratio||% Total Carbonate||Magnetic Susceptibility||Predominant Color|
Figure 6. Correlation of tills in the Two Rivers, Two Creeks, Valders area. Tills (large letters); TR, Two Rivers; V, Valders; H, Haven; 0, Ozaukee; U, Unnamed (Gary). Other (small letters); g, gravel; 8, sand; sl, slit; c, clay; dol, dolomite. Location of section shown by symbol on Figure 1.
Three of the four red tills in the Lake Michigan Lobe are believed to be Late Woodfordian or Port Huron in age: the Ozaukee, the Haven, and the Valders. The Two Rivers till is post-Twocreekan or Greatlakean in age. The Valders till is interpreted to be pre-Twocreekan because it is correlative with the Chilton till which has been found below the forest bed. The age-equivalency of these two tills is based on geomorphic evidence. The Valders till has a clear ice margin with unpitted outwash where it overrides the Branch River and Wayside tills (Figure 1); however, where the Valders abuts the Chilton till there is no distinct ice margin and no unpitted outwash. This evidence suggests there was ice in both lobes at the time the Valders and Chilton tills were deposited (Black, 1979; McCartney and Mickelson, in preparation).
The age of the Valders till is the major source of disagreement in interpretations of the late-glacial history of eastern Wisconsin. The change in terminology from Valderan to Greatlakean for post-Twocreekan time is required because of the "non-Valderan" age of the Valders till. Some workers (Lineback t a., 1974, 1979; Black, 1966, 1969, 1979) are not convinced that the Valders till is pre-Twocreekan and have not adopted the . new terminology. Recent investigations (Acomb, 1978; McCartney, 1979; McCartney and Mickelson, in preparation; Acomb, et al. in preparation) support Evenson's (1973) conclusion that the Valders till is pre-Twocreekan.
As previously mentioned, proof that the Valders till is pre-Twocreekan requires an exposure with both the Valders till and the forest bed. Although no such section has been found, the weight of evidence suggests a pre- Twocreekan age for the Valders till. In particular, the presence of pre- Twocreekan Glenwood shorelines (Eschman and Farrand, 1970) cut into the Valders till surface north, of Manitowoc (Evenson, 1973) and the correlation of the Valders with the clearly pre-Twocreekan Chilton till (McCartney and Mickelson, in preparation) are the most cogent of several arguments (Acomb, et_ al.. in preparation) In favor of the pre-Twocreekan age of the Valders till. Other evidence includes significantly greater depth of carbonate leaching on the Valders and Chilton till surfaces than on the Two Rivers and Glenmore tills (Mickelson and Evenson, 1975; McCartney and Mickelson, in preparation) and the occurrence of forest beds buried by till only within the limit of the Two Rivers-Glenmore-Middle Inlet boundaries. Finally, although the Valders till has not been found below the forest bed, ' neither has it been found above it. The Chilton till, however, has been found below the forest bed, and this till is interpreted to be the time- equivalent of the Valders (Black, 1979; McCartney and Mickelson, in preparation) .
Created 31 August 2004, Last Update 17 November 2011
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