Lake Michigan Member
Lithostratigraphy: Mason Group >>Equality Formation >>Lake Michigan 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
Lake Michigan Formation (Willman and Frye 1970).
Derivation
Lake Michigan.
Other names
History/background
The Lake Michigan Formation was defined by Willman and Frye in 1970 to include the lacustrine deposits of modern lakes. Additional members were later defined based on cores and seismic data.
-
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.
Subsequent studies grouped lower red and upper gray units and reinterpreted their depositional relationships and stratigraphic significance.
Type section
Type location
Southern Lake Michigan cross section based on multiple core samples.
Reference section
Reference location
Cores 5p and 9v; both good for lithology and boundaries.
Stratigraphic relationships
The Lake Michigan Member consists of gray to brown laminated silt and clay above a major unconformity or gradational contact with underlying red laminated sediment.
Extent and thickness
The unit forms much of the lake floor beneath Lake Michigan and varies in thickness, reaching significant accumulations in basin areas.
Lithology
The Lake Michigan Member consists of laminated clay and silt, with occasional sand, gravel, and organic debris.
Core(s)
Photograph(s)
Contacts
Lower boundary: truncational or gradational contact with underlying units. Upper boundary: lake floor or nearshore sediment.
Well log characteristics
Fossils
Age and correlation
The Lake Michigan Member is postglacial and correlates with equivalent lake deposits in the Great Lakes region.
Environments of deposition
Deposited in postglacial lacustrine environments, primarily from river input and shoreline erosion.
Economic importance
Remarks
Revised unit.
References
(unchanged)
ISGS Codes
| Stratigraphic Code | Geo Unit Designation |
|---|---|
|
0225 |
e-l |