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Map showing publication footprint
  • Usage in publication:
    • Rock Grove substage
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Limestone
    • Dolomite
  • AAPG geologic province:
    • Iowa shelf
Publication:

Belanski, C.H., 1927, The Shellrock stage of the Devonian of Iowa: American Midland Naturalist, v. 10, no. 10, p. 317-370., See also Amer. Midland Naturalist, v. 11, no. 5, p. 165-170, Sept. 1928 [Available online, with subscription, from AGI georef (CSA Illumina): http://ca1.csa.com; and JSTOR: http://jstor.org]


Summary:

Rock Grove substage. Magnesium limestone, shaly limestone, and impure dolomite, 21+ feet thick, unconformably underlying First ACTINOSTROMA zone of Nora limestone [redefined] and unconformably overlying Mason City substage [restricted use of Mason City]. Divided into SCHIZOPHORIA zone above and PARACYCLAS zone below. Is middle substage of Shell Rock stage, which is assigned to Upper Devonian.
Typically developed on east (left) bank of Shell Rock River a short distance southeast of Nora Springs. Named for great development in Rock Grove Twp., Floyd Co., IA.

Source: US geologic names lexicon (USGS Bull. 896, p. 1829).


Map showing publication footprint
  • Usage in publication:
    • Rock Grove member
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Iowa shelf
Publication:

Stainbrook, M.A., 1944, The Devonian System in Iowa, IN Symposium on Devonian stratigraphy: Illinois Geological Survey Bulletin, Illinois Mineral Industries Conference, Nov. 14-16, 1940, no. 68, p. 182-188, (incl. geologic maps)


Summary:

Pg. 187. Shellrock [Shell Rock] comprises (ascending) Mason City, Rock Grove, and Nora members.

Source: US geologic names lexicon (USGS Bull. 1200, p. 3310).


Map showing publication footprint
  • Usage in publication:
    • Rock Grove Member
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Iowa shelf
Publication:

Witzke, B.J., Bunker, B.J., and Rogers, F.S., 1988, Eifelian through lower Frasnian stratigraphy and deposition in the Iowa area, Midcontinent, U.S.A., IN McMillan, N.J., Embry, A.F., and Glass, D.J., eds., Devonian of the World; proceedings of the 2nd international symposium on the Devonian System; Volume I, Regional synthesis: Canadian Society of Petroleum Geologists Memoir, 14, p. 221-250.


Summary:

Assigned as the middle member of Shell Rock Formation, upper formation (of 4 named formations) of Cedar Valley Group (revised). Overlies Mason City Member of Shell Rock. Underlies Nora Member of Shell Rock. Graphic sections, nomenclature charts. Is dominated by pelleted to skeletal limestone and dolomite, in part vuggy. Poorly fossiliferous. Cross-bedded calcarenites locally in upper beds. Also includes shales and shaly limestones. Strata may be laminated, intraclastic, brecciated, mudcracked, birdseye-bearing. Minor evaporites in central IA (map). Varies from 2.5 to 8 m thick. Of Late Devonian, Frasnian age.

Source: GNU records (USGS DDS-6; Denver GNULEX).


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

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

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