National Geologic Map Database

Geologic Unit: Castlewood


Castlewood Limestone Member of Spechts Ferry Formation of Decorah Group (IL*,MO*-notably in St. Louis region)
Castlewood Limestone Member of Decorah Formation of Galena Group (IL*)


Deicke K-bentonite Bed (IL*,MO*).

Geologic age:

Late Ordovician (Mohawkian; Turinian)*

Type section, locality, area and/or origin of name:

Type section: exposure in south bluff of Meramec River along St. Louis-San Francisco RR, 0.25 mi northeast of Mincke Siding, near center E/2 SE/4 SE/4 sec. 21, T. 44 N., R. 4 E., Manchester 7.5-min quadrangle, St. Louis Co., eastern MO. Named from village of Castlewood, St. Louis Co., eastern MO, 1.5 mi northeast of type section (Templeton and Willman, 1963).
Reference sections in MO: (1) roadcut on U.S. Interstate Highway I-55, mileage 182, in NW/4 SW/4 NW/4 sec. 6, T. 41 N., R. 6 E., Herculaneum 7.5-min quadrangle, Jefferson Co.; (2) roadcut on north frontage road of U.S. Interstate Highway I-44, west of Allenton-Six Flags exit, in sec. 33, T. 44 N., R. 3 E., western St. Louis Co.; (3) exposure on St. Louis County Road W., 1 mi south of Eureka, in NW/4 NW/4 NE/4 sec. 12, T. 43 N., R. 3 E., Pacific 7.5-min quad; and (4) roadcut on U.S. Highway 61 north of bridge over Spencer Creek, in SE/4 SE/4 sec. 21, T. 55 N., R. 4 W., Ralls Co. (Thompson, 1991).

AAPG geologic province:

Illinois basin*
Ozark uplift*

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).