Ardith K. Hansel and W. Hilton Johnson
Batestown Till Member (Johnson et al. 1971b).
Batestown, a village in Vermilion County.
The Batestown Till Member of the Wedron Formation was originally defined by Johnson et al. (1971b) and described as a distinct gray till, easily recognized by its texture, structure, and color in the Decatur Sublobe area (Johnson et al. 1971b). They correlated the Batestown Till Member with unit 2 of Kempton et al. (1971) in the McLean County area to the west. McKay (1975) traced the Batestown Till Member westward into the Peoria Sublobe area and concluded it to be equivalent to the lower part of the Malden Till Member (Willman and Frye 1970). On the basis of McKay's study (1975), Johnson (1976) included the Batestown Till Member with the middle, medium textured tills of the Wedron Formation and correlated it with the lower part of the Malden Till Member of northeast and central Illinois (fig. 7). On the 1979 state Quaternary map compiled by Lineback, silty till in the eastern part of the Bloomington, Normal, Eureka, and Fletchers Moraines of the Peoria Sublobe area was mapped as the Batestown Till Member (figs. 5, 13). Similarly, Johnson et al. (1986) mapped the loam till south of the Illiana Morainic System as the Batestown Till Member, and extended the member to include the loam till in the Peoria Sublobe area. They concluded the Decatur Sublobe area (like the Peoria Sublobe area) was inundated by the Lake Michigan Lobe, rather than by a coalesced Huron-Erie Lobe.
In this report, the Batestown Till Member of the Wedron Formation is reclassified the Batestown Member of the Lemont Formation. On the basis of the previous work discussed above and in an attempt to make the classification system simpler by avoiding two names (Malden and Batestown) for the same lithostratigraphic unit in different sublobe areas, the name Batestown Member is the designation for all the gray loam diamicton units of the lower glacigenic sequence(s) of the Lemont Formation in the Decatur and Peoria Sublobe areas and part of the Princeton Sublobe area (figs. 7, 13). The lower, medium textured diamicton units of the former Malden Till Member are classified as the Batestown Member, whereas the upper, finer textured diamicton units of the former Malden Till Member are included in the revised Yorkville Member. Although the term Malden takes precedence over the term Batestown, we choose to use the term Batestown for the member name because the Malden Till Member as defined by Willman and Frye (1970) carries little meaning in regard to lithology. The Malden Till Member included all diamicton units stratigraphically above the Tiskilwa Till Member and beyond the Marseilles Morainic System (Yorkville Till Member). Diamicton texture in these units ranges from very fine to coarse. To avoid such lithic ambiguity, we have elected to reserve the term Batestown Member for the more medium textured diamicton of the lower part of the Lemont Formation; it crops out beyond the margin of the Arlington, Varna, El Paso, and Newtown Moraines (fig. 13). Locally in the Peoria Sublobe area, particularly at or near the surface, diamicton of the Batestown Member contains more clay than diamicton of type-Batestown. Because we interpret this clayier diamicton to reflect a facies change, it is treated herein as an informal facies of the Batestown Member. Similarly, we interpret lateral variation in diamicton texture along the strike of moraines that extend into the northern part of the Princeton Sublobe area to reflect facies changes, and we do not subdivide the Lemont Formation in that area (fig. 13). This avoids the 45-kilometer (28 mi) offset of member boundaries present on the 1979 state Quaternary map north and south of the Illinois River (fig. 5).
Emerald Pond Section near Danville in Vermilion County; good for contacts and lithology, but deteriorating.
Higginsville Section (fig. 14); good for contacts and lithology. Wedron Section (fig. 12); good for contacts and lithology.
The Batestown Member is the medium textured, lowermost unit of diamicton in the Lemont Formation. Diamicton of the Batestown Member generally consists of dark gray to gray silt loam to loam that oxidizes to brown or olive brown.
Diamicton of the Batestown Member is generally distinguishable from the redder, less illitic, and clayier diamicton of the underlying Tiskilwa Formation. In the Peoria Sublobe area, however, a vertical boundary is used at the front of the Normal Moraine because diamicton in the eastern part of the Bloomington Morainic System is similar to that of the Batestown Member (fig. 13). Similarly, in the Decatur Sublobe area a vertical boundary along the Champaign-Pesotum-Arcola moraine front is used for mapping purposes to distinguish diamicton of the Piatt and Delavan Members (Tiskilwa Formation) from that of the Batestown Member. The contact of the Batestown Member with the overlying Yorkville Member is readily distinguishable in the Decatur Sublobe area. It is less clear in the central part of the Peoria Sublobe area where a finer textured facies of the Batestown diamicton occurs. For mapping purposes, a vertical boundary is used at the front of the El Paso Moraine to separate the Yorkville and Batestown Members. West of the St. Charles Moraine in the northern part of the Princeton Sublobe area, the Batestown and Yorkville Members are indistinct, and the Lemont Formation is not subdivided.
Extent and thickness
The Batestown Member forms a wedge-shaped deposit that overlaps the Tiskilwa Formation and pinches out beneath the Yorkville Member to the north and east. It crops out in the shape of a crescent, which has a reentrant in the area where the Decatur and Peoria Sublobes met (fig. 13). The Batestown Member is up to about 25 meters (82 ft) thick in some end moraines (see for example, Wickham 1979a).
The Batestown Member of the Lemont Formation consists of calcareous, gray, medium textured (loam) diamicton (fig. 23) that contains lenses of gravel, sand, silt, and clay. Typically, it oxidizes to brown, olive brown, or yellow brown. Locally in the Peoria and Decatur Sublobe areas, diamicton of the Batestown Member is finer and texturally similar to diamicton of the Yorkville Member. This finer textured diamicton is retained in the Batestown Member because of lateral continuity, but it should be mapped, where appropriate, as an informal facies.
Lower boundary: the contact with the undivided Tiskilwa Formation (fig. 24), the Delavan or Piatt Members (Tiskilwa Formation; fig. 14), tongues of the Henry and Equality Formations (fig. 25), or older units. Upper boundary: the contact with the Yorkville Member (Lemont Formation; figs. 14, 24), tongues of the Peoria Silt (fig. 12) and the Henry and Equality Formations, or postglacial units.
Age and correlation
The Batestown Member was deposited during the later part of the Shelby Phase (central Decatur Sublobe area) and the Putnam Phase of the Michigan Subepisode, probably between about 18,500 and 17,700 radiocarbon years ago (Hansel and Johnson 1992; fig. 10). It correlates with the Batestown Till in Indiana (fig. 11).
Environments of deposition
The Batestown Member is interpreted to be the subglacial and ice-marginal facies of one or more glacigenic sequences; it consists predominantly of till. Evidence from the Wedron Section and the surrounding region in the area near the Princeton and Peoria Sublobe boundary (Johnson and Hansel 1990, Hansel and Johnson 1992) indicates that deposition of the Batestown Member followed a fairly significant readvance (75 km; 47 mi) of the ice margin. At the Wedron Section, the Batestown Member lithology (medium textured, gray diamicton) suggests a more local source (Illinois and Lake Michigan basin) than does the underlying Tiskilwa Formation lithology. In the area of the Decatur and southern part of the Peoria Sublobes, the lithological change to a more local source likely took place earlier in the glacial history and more gradually. For example, in color, matrix grain size, and clay-mineral composition, diamicton of the Piatt Member of the Tiskilwa Formation is intermediate between diamicton of the Delavan Member of Tiskilwa Formation and that of the Batestown Member of the Lemont Formation. Diamicton in the Bloomington Morainic System east of Bloomington, Illinois, classified herein as undivided Tiskilwa Formation, is similar to diamicton of the Batestown Member (fig. 13).
Reclassified and redescribed unit. Name changed to Batestown Member of the Lemont Formation, and unit description broadened to include lithologically similar and stratigraphically equivalent diamicton in the lower part of the former Malden Till Member of the Peoria and Princeton Sublobe areas. Formerly classified as the Batestown Till Member of the Wedron Formation (Johnson et al. 1971b).
HANSEL, A. K., and W. H. JOHNSON, 1992, Fluctuations of the Lake Michigan Lobe during the late Wisconsin Subepisode: Sveriges Geologiska Undersoekning, Series Ca 81, p. 133-144.
JOHNSON, W. H., 1976, Quaternary stratigraphy in Illinois—Status and current problems, in W. C. Mahaney, editor, Quaternary Stratigraphy of North America: Dowden, Hutchinson, & Ross, Inc., Stroudsburg, PA, p. 169- 196.
JOHNSON, W. H., D. L. GROSS, and S. R. MORAN, 1971b, Till stratigraphy of the Danville region, east-central Illinois, in R.P. Goldthwait, J.L. Forsyth, D.L. Gross, and F. Pessl, Jr., editors, Till, A Symposium: Ohio State University Press, Columbus, p. 184-216.
JOHNSON, W. H., and A. K. HANSEL, 1990, Multiple Wisconsinan glacigenic sequences at Wedron, Illinois: Journal of Sedimentary Petrology, v. 60, no. 1, p. 26-41.
JOHNSON, W. H., D. W. MOORE, and E. D. McKAY, III, 1986, Provenance of late Wisconsinan (Woodfordian) till and origin of the Decatur Sublobe, east-central Illinois: Geology Society of America Bulletin, v. 97, no. 9, p. 1098-1105.
KEMPTON, J. P., P. B. DuMONTELLE, and H. D. GLASS, 1971, Subsurface stratigraphy of the Woodfordian tills in the McLean County region, Illinois, in R. P. Goldthwait, J. L. Forsyth, D. L. Gross, and F. Pessl, Jr., editors, Till, A Symposium: Ohio State University Press, Columbus, p. 217-233.
LINEBACK, J. A., 1979, Quaternary Deposits of Illinois (Map): Illinois State Geological Survey, scale 1:500,000.
McKAY, E. D., 1975, Stratigraphy of glacial tills in the Gibson City reentrant, central Illinois: M.S. thesis, University of Illinois at Urbana-Champaign, 59 p.
WICKHAM, J. T., 1979a, Glacial Geology of North-Central and Western Champaign County, Illinois: Illinois State Geological Survey Circular 506, 30 p.
WILLMAN, H. B., and J. C. FRYE, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.
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