Petersburg Silt
Lithostratigraphy: Petersburg Silt
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Pleistocene Series
Primary source
Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.
Contributing author(s)
H. B. Willman and John C. Frye
Name
Original description
Petersburg Silt (Willman, Glass, and Frye 1963).
Derivation
The Petersburg Silt was named for Petersburg, Menard County.
Other names
History/background
Type section
Type location
The type section is a roadcut (supplemented by an auger boring) at the south edge of the city and is called the Petersburg Section (table 6), NW NW NE Sec. 23, T. 18 N., R. 7 W.
Table 6 -- Stratigraphic Sections
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Malden South Section (cont.), New Salem Northeast Section, and Petersburg Section
Type author(s)
Type status
Reference section
Reference location
Reference author(s)
Reference status
Stratigraphic relationships
The silt rests on the Yarmouth Soil and is overlain by till of the Glasford Formation of Illinoian age.
The Petersburg Silt was previously included in the Loveland Loess (Leighton and Willman, 1950; Wanless, 1957). In this report it is separated from the Loveland by a vertical cuttoff at the outer limit of till in the Glasford Formation. This relationship is shown diagrammatically in figure 7.
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Fig. 7 -- Diagrammatic cross section showing the relations of formations and members of Illinoian age in western Illinois.
The Petersburg Silt is described in the Petersburg Dam, Pryor School, Rock Creek Township, and Rushville (2.4W) Sections (table 7), and in other stratigraphic sections.
Table 7 -- Described Stratigraphic Sections Previously Published
Extent and thickness
Lithology
The formation consists of gray to yellow-tan to purplish tan, calcareous silt with some fine sand and clay. The upper part is generally massive and loess-like, but the lower part is distinctly bedded in places.
Core(s)
Photograph(s)
Contacts
Well log characteristics
Fossils
It commonly contains fossil snail shells.
Age and correlation
The Petersburg Silt is in the early part of the Liman Substage of the Illinoian Stage. It is a pro-glacial deposit of the advancing earliest Illinoian glacier and includes outwash, loess, and some locally derived sediment.
Environments of deposition
Economic importance
Remarks
References
LEIGHTON, M. M., and H. B. WILLMAN, 1950, Loess formations of the Mississippi Valley: Journal of Geology, v. 58, no. 6, p. 599-623. (Reprinted as Illinois State Geological Survey Report of Investigations 149)
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois Geological Survey Bulletin 82, 233p.
WILLMAN, H. B., H. D. GLASS, and J. C. FRYE, 1963, Mineralogy of Glacial Tills and Their Weathering Profiles in Illinois, Part 1—Glacial Tills: Illinois State Geological Survey Circular 347, 55 p.
ISGS Codes
| Stratigraphic Code | Geo Unit Designation |
|---|---|
|
0990 |
pb |