Geologic Unit: Joachim

Usage:

Joachim Dolomite (AR*,IL*,IN,KY,MO*)
Joachim Dolomite of Ancell Group (IL,IN)
Joachim Formation (KY,MO)

Subunits:

(alphabetical): Abernathy Member (IL,KY,MO), Augusta Member (IL,MO), Boles Member (IL,MO), Defiance Member (IL,MO), Matson Member (IL,MO), Metz Member (IL,MO).

Geologic age:

early Late Ordovician (late Whiterockian to Mohawkian; late Chazyan to Turinian)*

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

Type section: exposures along Plattin Creek [misidentified as Joachim Creek], in NE/4 sec. 8 and NW/4 sec. 9, T. 40 N., R. 6 E., Festus 7.5-min quadrangle, Jefferson Co., eastern MO (Winslow, 1894; corrected by Grohskopf, 1948).
Reference sections in MO:
(1) roadcut on U.S. Interstate Highway I-55, 1.5 mi south of MO Highway Z interchange at Pevely, in SW/4 SW/4 sec. 19 and NW/4 NW/4 sec. 30, T. 41 N., R. 6 E. (projected), Herculaneum 7.5-min quadrangle, Franklin Co. (Thompson, 1991);
(2) roadcuts on U.S. Interstate Highway I-44 east of Pacific interchange, in NE/4 NW/4 sec. 12 and SE/4 SE/4 sec. 1, T. 43 N., R. 2 E., Pacific 7.5-min quadrangle, and abandoned railroad cut immediately east of Glencoe, in center NW/4 sec. 19, T. 44 N., R. 4 E., Manchester 7.5-min quadrangle, both in St. Louis Co. (Thompson, 1991);
(3) at interchange of I-44 and MO Highway 109 just east of Eureka, in SW/4 sec. 31, T. 44 N., R. 4 E., Manchester 7.5-min quadrangle, St. Louis Co. (Thompson, 1991); (4) Berg quarry, near Matson, in NE/4 sec. 8, T. 44 N., R. 2 E., Labadie 7.5-min quadrangle, St. Charles Co. (Martin and Wells, 1966).

AAPG geologic province:

Arkoma basin*
Forest City basin*
Illinois basin*
Ozark uplift*
Upper Mississippi embayment*