Croixan Series

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Chronostratigraphy: Paleozoic Erathem >>Cambrian System >>Croixan Series

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)

T. C. Buschbach


Original description

Croixan Series (Winchell, 1873, p. 70; 1900).


Named for the St. Croix River in eastern Minnesota.

Other names

The Croixan Series has also been called the Upper Cambrian, the St. Croix, and the St. Croixian Series.


Type section

Type location

The type section consists of all strata of Cambrian age (about 600 feet) exposed in the St. Croix Valley.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

In the St. Croix Valley, Cambrian strata overlie Precambrian rocks, and the uppermost Cambrian formation, the Jordan Sandstone, is overlain by the Oneota Dolomite, the oldest Ordovician formation in that area. The Croixan Series is subdivided into the Dresbachian (oldest), Franconian, and Trempealeauan Stages (fig. Є-3). Information about Cambrian rocks in extreme southern Illinois is scarce and middle, or even lower, Cambrian strata may be present in that part of the Illinois Basin.

Extent and thickness

All Cambrian strata in Illinois are assigned to the Croixan Series. Therefore, the thickness of the Croixan is the same as that for the Cambrian System (1000-3500 feet) (fig. Є-2).





Well log characteristics


The Croixan Series is defined on the basis of its trilobite faunas; it extends from the Cedaria Zone at the base to the Plethopeltis Zone (Howell et al., 1944) or the Saukia Zone (Raasch, 1951) at the top.

Age and correlation

Environments of deposition

Economic importance



HOWELL, B. F., et al., 1944, Correlation of the Cambrian formations of North America: Geological Society of America Bulletin, v. 55, p. 993-1003.
RAASCH, G. O., 1951, Revision of Croixan dikelocephalids: Illinois Academy of Science Transactions, v. 44, p. 137-151 ; Illinois State Geological Survey Circular 179.
WINCHELL, N. H., 1873, Potsdam Sandstone: Minnesota Geological and Natural History Survey 1st Annual Report (1872), p. 68-80.

ISGS Codes

Stratigraphic Code Geo Unit Designation