Peddicord Tongue

Lithostratigraphy: Mason Group >>Equality Formation >>Peddicord Tongue
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

Peddicord Formation (Willman et al. 1971).

Derivation

Peddicord School in La Salle County, northeastern Illinois.

History/background

Fine grained laminated sediment below the pink Tiskilwa till of the Bloomington Morainic System occurs along the Illinois Valley between LaSalle and Morris. These deposits were previously referred to as the "Kickapoo beds" and later as "Lake Kickapoo deposits." Subsequent work reinterpreted their stratigraphic position and depositional history, leading to formal recognition as the Peddicord Formation and later reclassification as the Peddicord Tongue of the Equality Formation.

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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.

Type section

Type location

Wedron Section, Wedron Silica Company quarries at Wedron, Illinois; good for contacts and lithology.

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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.

Reference section

Reference location

Charleston Section, Charleston Stone Quarry pits; good for boundaries and lithology.

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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.
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  Figure 32 -- Lacustrine silt of the Pedicord Tongue of the Equality Formation above forest litter (including spruce stumps) of the Farmdale Geosol developed in the Robein Member of the Roxana Silt at Charleston Quarry.

Stratigraphic relationships

The Peddicord Tongue consists of stratified silt and clay of the Equality Formation beneath diamicton units of the Tiskilwa Formation or Delavan Member. It may interfinger with other Mason Group units such as the Ashmore Tongue or Morton Tongue.

Extent and thickness

A discontinuous subsurface unit occurring in low-lying areas beneath glacial deposits; up to about 10 meters thick.

Lithology

Fine-textured stratified sediment, predominantly silt and clay, with occasional organic material and wood fragments.

Contacts

Lower boundary: contact with Morton Tongue, Ashmore Tongue, Robein Member, or older units. Upper boundary: contact with Ashmore Tongue, Morton Tongue, Delavan Member, or undivided Tiskilwa Formation.

Age and correlation

Deposited during advance of the Tiskilwa ice margin between about 26,000 and 19,500 radiocarbon years ago. Correlates with similar stratigraphic units in surrounding regions.

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  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).
• 
  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.

Environments of deposition

Low-energy lacustrine sediment within a glacigenic sequence, typically part of a coarsening-upward proglacial succession.

Remarks

Revised unit. Formation lowered in rank and redefined as the Peddicord Tongue of the Equality Formation.

References

BERG, R. C., et al., 1985...
JOHNSON, W. H., and A. K. HANSEL, 1990...
JOHNSON, W. H., et al., 1985a...
LEONARD, A. B., and J. C. FRYE, 1960...
MICKELSON, D. M., et al., 1984...
SAUER, C. O., 1916...
WAYNE, W. J., 1963...
WILLMAN, H. B., and J. C. FRYE, 1970...
WILLMAN, H. B., et al., 1971...
WILLMAN, H. B., and J. N. PAYNE, 1942...

ISGS Codes

ISGS Code and Symbol

Stratigraphic Code	Geo Unit Designation
0610	e-p