Yorkville Member

Lithostratigraphy: Wedron Group >>Lemont Formation >>Yorkville 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

Yorkville Till Member (Willman and Frye 1970).

Derivation

Yorkville, a village in Kendall County.

History/background

The Yorkville Till Member of the Wedron Formation was originally defined by Willman and Frye (1970). It was described as a very clayey gray till that commonly exhibits a green cast and is slightly darker than other gray tills. It was mapped across several sublobe areas and later expanded to include related fine-textured diamicton units previously assigned to other members. Subsequent studies demonstrated that these units form a single lithologic entity, leading to retention of the Yorkville name and reclassification as a member of the Lemont Formation.

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  Figure 4a -- Lobe and sublobe boundaries in Illinois during the last glaciation (from Willman and Frye 1970). Locations of the ancient Mississippi and Iowa Rivers added.
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  Figure 4b -- Areal distribution of predominant Quaternary formations and members in Illinois (from Willman and Frye 1970).
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  Figure 5 -- Areal distribution of the Wedron Formation till members and the Trafalgar Formation (after Lineback 1979).
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  Figure 7 -- History of lithostratigraphic classification of the Wedron Group deposits.

Type section

Type location

Roadcut at the intersection of Illinois Highways 71 and 47.

Type status

No longer exposed.

Reference section

Reference location

Higginsville Section; Wedron Section; Core 7815.

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  Figure 14 -- The Yorkville and Batestown Members of the Lemont Formation, Delavan Member of the Tiskilwa Formation, Robein Member of the Roxana Silt, and Glasford Formation at Higginsville Section.
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  Figure 26 -- Modern soil developed in diamicton of the Yorkville Member of the Lemont Formation above a sand and gravel tongue of the Henry Formation at Wedron Quarry pit 1.

Stratigraphic relationships

The Yorkville Member is a fine-grained diamicton unit within the Lemont Formation. It is typically dark gray and silty clay to silty clay loam in composition and oxidizes to olive brown. It is generally finer textured than the underlying Batestown Member and much finer than the Haeger Member.

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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.

Extent and thickness

The Yorkville Member forms a widespread wedge-shaped diamicton unit that overlaps older formations and pinches out beneath younger units. Thickness may reach up to 60 meters in major moraine systems.

Lithology

The Yorkville Member consists of calcareous, gray, fine-textured diamicton containing lenses of sand, gravel, silt, and clay. It typically oxidizes to olive brown and commonly contains dolomitic pebbles.

Contacts

Lower boundary: contact with underlying Batestown Member, Tiskilwa Formation, or older units. Upper boundary: contact with overlying Haeger Member, Wadsworth Formation, or younger deposits.

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  Figure 24 -- Silty clay diamicton of the Yorkville Member and silt loam diamicton of the Batestown Member (Lemont Formation) overlie clay loam diamicton of the undivided Tiskliwa Formation at Fox River Stone Quarry, St. Charles, Illinois. The diamictons are interpreted to be subglacial tills.
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  Figure 27 -- Upper tongues of the Peoria Silt and Henry Formation above diamictions of the Yorkville and Batestown Members of the Lemont Formation and the undivided Tiskilwa Formation, which overlie the Elwood Dolomite (Silurian) at the Fox River Stone Company Quarry, St.Charles, Illinois.
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  Figure 27 Diagram

Age and correlation

The Yorkville Member was deposited during the Livingston Phase of the Michigan Subepisode.

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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).
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  Figure 11 Correlation of the Wedron Group formations and members in the Lake Michigan Lobe area (units in Wisconsin from Mickelson et. al. 1984, Mickelson and Syverson, in press; units in Indiana from Bleuer et al. 1983, N.K. Bleuer, Indiana Geological Survey, personal communication, 1994; units in Michigan from Monaghan and Larson 1986, Monaghan et al. 1986, Taylor 1990).

Environments of deposition

The Yorkville Member represents subglacial and ice-marginal deposition within glacigenic sequences that include lacustrine, fluvial, and debris-flow sediments.

Remarks

Reclassified and redescribed unit.

References

(unchanged)

ISGS Codes

ISGS Code and Symbol

Stratigraphic Code	Geo Unit Designation
0430	l-y