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W. F. CANNON U.S. Geological Survey, Washington, D. C. 20242 J. E. GAIR

A Revision of Stratigraphic Nomenclature for

Middle Precambrian Rocks in Northern

ABSTRACT GEOLOGY The name Marquette Range Supergroup is The middle Precambrian Stratigraphic sec- proposed to supplant the term Animikie Series tion in the Northern Peninsula of Michigan is for middle Precambrian strata of the Northern composed of metasedimentary and metavol- Peninsula of Michigan and adjacent areas of canic rocks which lie unconformably on domi- . The Marquette Range Supergroup nantly granitic basement rocks and are uncon- consists of the Chocolay, Menominee, Baraga, formably overlain by upper Precambrian and Paint River Groups, as defined in previous Keweenawan igneous and sedimentary rocks. literature. We feel that this new name to apply Radiometric age determinations (Goldich and to Northern Peninsula rock units is appropri- others, 1961; Aldrich and others, 1965) indicate ate, as continued investigations have failed to an age of about 2.5 b.y. for the granitic base- show unequivocal correlation between middle ment rocks, and an age of about 1.9 b.y. for Precambrian rocks of Michigan and the Hu- regional which has affected all ronian Supergroup of Ontario. Although the the middle Precambrian rocks. equivalence of the Animikie Group in Ontario Figure 1 shows the distribution of middle and with parts of the Michigan Precambrian rocks. The section has been rocks is likely, the Stratigraphic complexity of divided into four groups by James (1958). From the Michigan sequence requires supergroup oldest to youngest, these are the Chocolay, rank. The inherent confusion of an Animikie Menominee, Baraga, and Paint River Groups. Group in Ontario and Minnesota, and an A general Stratigraphic section based on previ- Animikie Supergroup in Michigan, makes a ously published work is presented in Figure 2. local name such as Marquette Range Super- The Baraga Group has, by far, the widest group preferable to Animikie for the middle geographic distribution; the other groups are Precambrian rocks of Michigan. largely confined to synclinal or monoclinal structures commonly referred to as ranges. INTRODUCTION The Marquette Range is a westward-trending A sequence of metasedimentary and meta- synclinorium in which the Chocolay, Menom- volcanic rocks whose age is bracketed by inee, and Baraga Groups are well exposed. The radiometric dates of 1.9 and 2.5 b.y. occurs Paint River Group is restricted to the throughout much of the west half of the River-Crystal Falls district about 30 mi south- Northern Peninsula of Michigan and adjacent west of the Marquette Range. areas of Wisconsin. This paper proposes the name Marquette CORRELATION AND Range Supergroup for these rocks. The new NOMENCLATURE name is preferable to older names which either Although the rock units cannot all be di- imply unsubstantiated correlations with other rectly traced between the ranges in Michigan, sequences in the upper Great Lakes region, or the correlation of the Chocolay, Menominee, violate the Stratigraphic code and result in and Baraga Groups is generally agreed upon. confusion by using the same name for a single Correlation is less certain or doubtful between group and for several groups together. rocks in Michigan and other homotaxial se-

Geological Society of America Bulletin, v. 81, p. 2843-2846, 2 figs., September 1970 2843

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EXPLANATION

Paleozoic rocks

Upper Precambrian (Keweenawan) rocks Includes some probable Cambrian racks

Middle I'recambn, 47° — Iran-fornxttnin sAow

Figure 1. Geologic sketch map of western part of Northern Peninsuk of Michigan, showing location of iron ranges. quences in the upper Great Lakes region, such have not produced sufficient evidence for cor- as the Huronian Supergroup on the north relation of the two sequences. Therefore, we shore of Lake Huron and the Animikie Group agree with fames (1958) that the term Hu- in western Ontario and Minnesota. ronian is inappropriate for the Michigan rocks. The rocks in Michigan were long considered The term Animikie for the sequence in correlatives of the Huronian but James (1958) Michigan also has inherent drawbacks. The correlated them with the Animikie Group, Animikie Group is a well-defined sequence of owing principally to similar occurrences of the Gunflint Range in Ontario and the Mesabi iron-formation in both the Animikie and Mich- Range in Minnesota. The Animikie Group of igan rocks and the general absence of iron- those areas is probably correlative with the formation in the type Huronian. He proposed Menominee Group and part of the Baraga the name Animikie Series, which has been used Group, but the presence of the additional by the U.S. Geological Survey since 1958, for groups above and below these rocks in the the middle Precambrian sequence in Michigan. Michigan sequence requires a supergroup des- Following recommendations of the American ignation for the entire sequence. The designa- Commission on Stratigraphic Nomenclature tion of both the middle Precambrian group in (1961) these rocks must now be considered as Ontario and Minnesota and the middle Pre- a supergroup rather than a series. cambrian supergroup in Michigan by the term Continued detailed investigations of both Animikie would be confusing and in violation the Huronian Supergroup and the middle Pre- of the Stratigraphic code. cambrian rocks in Michigan by many geologists Recent age determinations by Faure and

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Iron River- Marquette Range Menominee Range Crystal Falls District

Upper Volcanic, intrusive, Keweenawan Intrusive diabase Intrusive diabase Intrusive diabase Precambrian and sedimentary rock Fortune Lakes Paint Stambaugh Formation River Hiawatha Graywacke

Group Riverton Iron-Formation Dunn Creek Slate

Badwater Greenstone Badwater Greenstone Mjchigamme Slate Michigamme Slate Michigamme Slate Bijiki Iron- Amasa Formation Formation Member Hemlock Formation araga Clarksburg Group Volcanics Member Greenwood Iron- Marquette Formation Member Middle Goodrich Quartzite Range Precambrian Supergroup LOCAL UNCONFORMITY I Off DISCONFORMITY v"'CC'"C™'n UNCONFQRMI f Y

Menotninee Negaunee Iron-Formation Vulcan Iron-Formation Ironwood Iron-Formation Siamo Slate Felch Formation Palms Quartzite Group Ajibik Quartzite

UNCONFORMITY C UNCONFORMITY OP DISCONFORMtTY

Wewe Slate Chocolay Kona Dolomite Saunders Formation Randville Dolomite Bad River Dolomite Mesnard Quartzite Sturgeon Quartzite Sunday Quartzite Group Enchantment Lake Fern Creek Formation Formation

UMCONf OR Ml TY

Lower Greenstone Gneiss (strati graphic Gneiss Gneiss Precambrian Greenstone position uncertain)

Figure 2. Stratigraphic sections of Precambrian rocks in parts of northern Michigan. Compiled from Leith and others, 1935, table facing p. 10; James, 1958, p. 30; and Gair and Thaden, 1968, Table 1. Kovach (1969) cast some doubt on the correla- Local terms for rock units seem most appro- tion of the Animikie Group with the Michigan priate at this time as they imply neither corre- sequence. Ages of about 1.6 b.y. have been lation nor lack of correlation between similar obtained from the Gunflint Range, which but geographically isolated sequences. Such Faure and Kovach interpret as the age of usage should avoid future confusion in termi- sedimentation. If this is correct, the rocks of nology as possible correlations are either sub- the Gunflint Range are considerably younger stantiated or disproved. than their supposed correlatives in Michigan, all of which predate the 1.9 b.y. old meta- morphism. REFERENCES CITED MARQUETTE RANGE Aldrich, L. T., Davis, G. L., and James, H. L., SUPERGROUP 1965, Ages of minerals from metamorphic and We here propose the name Marquette Range igneous rocks near Iron Mountain, Michigan: Supergroup to supplant the term Animikie Jour. Petrology, v. 6, Pt. 3, p. 445-472. Series for the middle Precambrian sequence of American Commission on Stratigraphic Nomen- the Northern Peninsula of Michigan and adja- clature, 1961, Code of Stratigraphic nomencla- cent areas of Wisconsin. The supergroup is ture: Am. Assoc. Petroleum Geologists Bull., v. 45, no. 5, p. 645-665. composed of the Chocolay, Menominee, Faure, Gunter, and Kovach, Jack, 1969, The age of Baraga, and Paint River Groups defined by the Gunflint Iron Formation of the Animikie James (1958). The name is intended to be Series in Ontario, Canada: Geol. Soc. America restricted to the middle Precambrian rocks Bull., v. 80, no. 9, p. 1725-1736. south of . Gair, J. E., and Thaden, R. E., 1968, Geology of

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the Marquette and Sands quadrangles, Mar- 27-44. quette County, Michigan: U.S. Geol. Survey Leith, C. K., Lund, R. J., and Leith, Andrew, Prof. Paper 397, 77 p. 1935, Pre-Cambrian rocks of the Lake Superior Goldich, S. S., Nier, A. O., Baadsgaard, Halfdan, region: U.S. Geol. Survey Prof. Paper 184, Hoffman, J. H., and Krueger, H. W., 1961, 34 p. The Precambrian geology and geochronology of Minnesota: Minnesota Geol. Survey Bull. 41, 193 p. MANUSCRIPT RECEIVED BY THE SOCIETY MAY 5, James, H. L., 1958, of pre-Ke- 1970 weenawan rocks in parts of northern Michigan: PUBLICATION AUTHORIZED BY THE DIRECTOR, U.S. Geol. Survey Prof. Paper 314-C, p. U.S. GEOLOGICAL SURVEY

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