Piatt Member

Lithostratigraphy: Wedron Group >>Tiskilwa Formation >>Piatt Member
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Pleistocene Series

Primary source

Hansel, Ardith K., and W. Hilton Johnson, 1996, Wedron and Mason Groups: Lithostratigraphic Reclassification of Deposits of the Wisconsin Episode, Lake Michigan Lobe Area: Illinois State Geological Survey Bulletin 104, 116 p.

Contributing author(s)

Ardith K. Hansel and W. Hilton Johnson

Name

Original description

Piatt Till Member (Wickham 1979a).

Derivation

Piatt, a county in east-central Illinois.

History/background

The Piatt Till Member of the Wedron Formation was defined by Wickham (1979a) in Champaign County. It was described as sandier and more illitic than the underlying Fairgrange Member of the Wedron Formation.

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  Figure 5 -- Areal distribution of the Wedron Formation till members and the Trafalgar Formation (after Lineback 1979).

Because of its similarity to the Batestown Till Member, the Piatt Till Member was grouped with medium-textured tills of the Wedron Formation. In this report, however, the Piatt Member is classified within the Tiskilwa Formation.

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  Figure 7 -- History of lithostratigraphic classification of the Wedron Group deposits.
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  Figure 13a -- Areal distribution of moraines and boundaries of formations and predominant members of the Wedron Group and the Trafalgar Formation in Illinois. (Names of formations and members are labeled on 13b.) Sublobe areas of the Lake Michigan Lobe and the Huron-Erie Lobe are shown on inset map: (1) Harvard; (2) Princeton, (3) Joliet; (4) Peoria; (5) Decatur; and (6) Huron-Erie (sublobe areas and moraines are modified from Willman and Frye 1970).
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  Figure 13b -- Names of Wedron Group formations and members in Illinois.

Type section

Type location

Mahomet Interstate 74 Bridge Section along the Sangamon River.

Type status

Overgrown and poorly exposed.

Reference section

Reference location

Mahomet North Section; Core 4943; Wedron Section.

Stratigraphic relationships

The Piatt Member is the upper gray, loam diamicton facies of the Tiskilwa Formation.

Extent and thickness

Forms a wedge-shaped deposit over part of the Delavan Member.

Lithology

Gray loam diamicton containing lenses of sorted sediment; locally shows pink or violet cast.

Contacts

Lower boundary: contact with Delavan Member or undivided Tiskilwa Formation. Upper boundary: contact with Batestown Member or younger deposits.

Age and correlation

Deposited during the Shelby Phase of the Michigan Subepisode.

• 
  Figure 10 -- Geochronological units, chronostratigraphic units and diachronic units in the Lake Michigan Lobe in a transect from south of Peoria, Illinois, to north of the Straits of Mackinac in Michigan (geochronologic and chronostratigraphic units are after Frye et al. 1968, as modified by Follmer et al. 1979, Curry and Follmer 1992, and Evenson et al. 1976; upper part of time-distance diagram and phases of the Michigan Subepisode are after Hansel and Johnson 1992).

Environments of deposition

Subglacial till and ice-marginal redeposited sediment within glacigenic sequences.

Remarks

Reclassified unit.

References

FORD, J., 1973, Surficial Deposits of Coles County, Illinois: Illinois State Geological Survey Open File Report, 73 p.
HANSEL, A. K., and W. H. JOHNSON, 1992, Fluctuations of the Lake Michigan Lobe during the late Wisconsin Subepisode: Sveriges Geologiska Undersokning, 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.
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.
WICKHAM, J. T., 1979a, Glacial Geology of North-Central and Western Champaign County, Illinois: Illinois State Geological Survey Circular 506, 30 p.

ISGS Codes

ISGS Code and Symbol

Stratigraphic Code	Geo Unit Designation
0490	t-p