Equality Formation

Lithostratigraphy: Mason Group >>Equality Formation
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

Equality Formation (Willman and Frye 1970).

Derivation

Equality, a village in Gallatin County, southeastern Illinois.

History/background

The Equality Formation was defined by Willman and Frye (1970) to include lake sediment that occurs at the surface or underlies loess or Holocene deposits. Tongues of equivalent lake sediment interfingered with till units of the Wedron and Winnebago Formations were separated from the Equality Formation by vertical boundaries and classified as part of the till units.

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  Figure 3 -- Diagram shows Willman and Frye's (1970) use of arbitrary vertical boundaries to avoid intertonguing of till members with sorted-sediment units in classification of the deposits of the Wisconsinan Stage.

Willman and Frye (1970) divided the Equality Formation into two members, the Carmi and Dolton, representing fine-grained and coarse-grained facies respectively.

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  Figure 9 -- History of the litho-stratigraphic classification of the Mason Group deposits with respect to the Wedron Group deposits: (a) Peoria and Roxana Silts, (b) Henry Formation, and (c) Equality Formation. Vertical lines indicate part of section missing due to erosion.

Two former formations, the Lake Michigan and the Peddicord, are now classified within the Equality Formation.

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  Figure 12 -- Intertongued sorted-sediment units of the Mason Group and diamicton units of the Wedron Group at Wedron Quarry pit 1. Mason Group units are shaded.
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  Figure 12 Diagram.

Type section

Type location

Saline River Section, 4 miles southwest of Equality.

Reference section

Reference location

Core 9V, Lake Michigan; Wedron and Charleston Sections.

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  Figure 15 - Lower tongues of the Mason Group Henry and Equality Formation (Ashmore and Peddicord, respectively) beneath the Wedron Group Tiskilwa Formation (Delavan Member) at Charleston Quarry.

Stratigraphic relationships

The Equality Formation consists of gray to red silt and clay with bedding structures and intertongues with diamicton units and other formations of the Mason Group.

Extent and thickness

The Equality Formation is widespread but discontinuous, occurring beneath Lake Michigan and across much of Illinois, especially in low-lying and valley areas.

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  Plate 1 -- Quaternary Deposits of Illinois

Lithology

The Equality Formation consists predominantly of bedded silt and clay, with occasional lenses of sand, gravel, and organic material.

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  Figure 31 -- Ripple and planar bedded silt, clay, and fine sand of the Equality Formation.

Contacts

Lower boundary: contact with Wedron Group or older units. Upper boundary: contact with younger deposits or land surface.

Age and correlation

Deposited during the Wisconsin and Hudson Episodes, ranging from about 26,000 years ago to modern.

Environments of deposition

Fine-grained lacustrine sediment deposited in glacial and postglacial lakes, often showing varved structures.

Remarks

Redescribed unit.

References

(unchanged)

ISGS Codes

ISGS Code and Symbol

Stratigraphic Code	Geo Unit Designation
0220	e