Orchard Creek Shale Member
Lithostratigraphy: Maquoketa Shale Group >>Scales Shale >>Orchard Creek Shale Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Cincinnatian Series >>Maysvillian Stage
Allostratigraphy: Tippecanoe Sequence
Primary source
Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.
Contributing author(s)
H. B. Willman and T. C. Buschbach
Name
Original description
The Orchard Creek Shale Member of the Scales Shale (Savage, 1909, p. 515).
Derivation
Named for a small exposure along Orchard Creek, 2 miles south of Thebes, Alexander County. This section is now covered.
Other names
History/background
Type section
Type location
The Orchard Creek is exposed in the Mississippi River bluffs a mile north of Thebes (SE 5, 15S-3W), where it is 27 feet thick, overlies the Thebes Sandstone Member, and is overlain by the Girardeau Limestone.
Type author(s)
Type status
Reference section
Reference location
Reference author(s)
Reference status
Stratigraphic relationships
Extent and thickness
The Orchard Creek Shale Member is exposed locally in and near the Mississippi bluffs in Alexander County from Gale southward almost to Fayville. It is 10-30 feet thick in the outcrop area.
Lithology
The Orchard Creek Member is largely blue-gray shale, but in the thickest exposures the upper part is interbedded with fine-grained limestone. The Orchard Creek is probably a lateral equivalent of part of the Elgin Shale Member, but its precise position is uncertain, and it could be equivalent even to the Brainard Shale. It is differentiated only where it overlies the Thebes Sandstone Member.
Core(s)
Photograph(s)
Contacts
Well log characteristics
Fossils
The Orchard Creek contains a large fauna (Savage, 1917). It was long assigned to the Silurian System, but the presence of Climacograptus putillus indicates Cincinnatian age (Pryor and Ross, 1962).
Age and correlation
Environments of deposition
Economic importance
Remarks
References
PRYOR, W. A., and C. A. Ross, 1962, Geology of the Illinois parts of the Cairo, La Center, and Thebes Quadrangles: Illinois State Geological Survey Circular 332, 39 p.
SAVAGE, T. E., 1909, Ordovician and Silurian formations in Alexander County, Illinois: American Journal of Science, v. 28, p. 509-519.
SAVAGE, T. E., 1917, Thebes sandstone and Orchard Creek shale and their faunas in Illinois: Illinois Academy of Science Transactions, v. 10, p. 261-275.
ISGS Codes
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