Historical:Vandalia Till Member
H. B. Willman and John C. Frye
The Vandalia Till Member of the Glasford Formation was informally named the Vandalia till by Jacobs and Lineback (1969, p. 12) for the south-central Illinois region. It was named for Vandalia, Fayette County.
The type locality is the Vandalia Bridge Section (Jacobs and Lineback, 1969; MacClintock, 1929), NW NE SE Sec. 16, T. 6 N., R. 1 E.
The Vandalia overlies the Mulberry Grove Silt, or the Smithboro Till in the absence of the Mulberry Grove Silt. Where the two tills are in contact, the sandy till of the Vandalia can be readily differentiated from the silty till of the Smithboro. The Vandalia Member is overlain by the Hagarstown Member or the Roby Member, and where these are absent the Sangamon Soil is developed in its top. The Vandalia Till is judged to be equivalent in part to the Hulick Till Member of western Illinois.
Extent and thickness
It is commonly 25 to 50 feet thick, but it is probably much thicker in some of the deep valleys. Its extent has not been determined, but it probably is the surface till throughout most of the area of Illinoian drift in southeastern Illinois.
It is a relatively sandy, gray, compact till, and the mineral composition has been described by Jacobs and Lineback (1969).
Age and correlation
The Vandalia Till Member is within the Monican Substage of the Illinoian Stage. In the Vandalia area, the till fabric suggests deposition by a glacier advancing from the northeast, probably part of the Lake Michigan Lobe (Lineback, in press). Its dolomite-calcite ratio is not as high as is typical for the Lake Michigan Lobe nor as low as is usual for the Lake Erie Lobe, which suggests a source in the Saginaw Lobe.
JACOBS, A. M., and J. A. LINEBACK, 1969, Glacial geology of the Vandalia, Illinois, region: Illinois State Geological Survey Circular 442, 24 p.
MacCLINTOCK, PAUL, 1929, I. Physiographic divisions of the area covered by the Illinoian drift-sheet in southern Illinois. II. Recent discoveries of pre-Illinoian drift in southern Illinois: Illinois State Geological Survey Report of Investigations 19, 57 p.
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