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Stratigraphy of Pre-Keweenawan Rocks in Parts of Northern Michigan

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Stratigraphy of Pre-Keweenawan Rocks in Parts of Northern Michigan Stratigraphy of Pre-Keweenawan Rocks in Parts of Northern Michigan GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-C Prepared in cooperation with the Geological Survey Division, Michigan Department of Conservation Stratigraphy of Pre-Keweenawan Rocks in Parts of Northern Michigan By HAROLD L. JAMES SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-C Prepared in cooperation with the Geological Survey Division, Michigan Department of Conservation UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1958 UNITED STATES DEPARTMENT OF THE INTERIOR FRED A. SEATON, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 20 cents (paper cover) CONTENTS Pace Page Abstract...._______________________________________ 27 Middle Precambrian rocks Continued Introduction. ____________________________________ 27 Baraga group.________________ 35 Subdivision of Precambrian time________-_-__-_--___ 28 Goodrich quartzite._ ______ 36 Lower Precambrian rocks__________________.________ 31 Hemlock formation __________ 36 Older granite gneiss and included bodies of quartzite Fence River formation._ 36 and schist_____________________________ 31 Amasa formation__ ________ 36 Dickinson group____________________________ 31 Michigamme slate. _________ 37 East Branch arkose_____-___-_--______-__-_- 31 Badwater greenstone _________ 37 Solberg schist.__________________________.__ 32 Paint River group______------___ 37 Six-Mile Lake amphibolite.-____-_---______-_ 32 Dunn Creek slate__________ 37 Hardwood gneiss.______________________________ 32 Riverton iron-formation ______ 38 Quinnesec formation________________. ____________ 32 Hiawatha graywacke.________ 38 Post-Dickinson gneissic granite_.____--______-____ 33 Stambaugh formation ________ 38 Middle Precambrian rocks._________________________ 33 Fortune Lakes slate.____.___ 39 Chocolay group______________________________ 35 Middle Precambrian igneous rocks_____ 39 Menominee group__________________________ ___ 35 References cited________-__--_- _.__ 40 Index._____________________________ 42 ILLUSTRATION Page FIGURE 2. Generalized geologic map of northern Michigan. 28 TABLES TABLE 1. Lithologic sequence of Precambrian rocks in Iron and Dickinson Counties, Michigan____________ __ __ 30 2. Comparison of the stratigraphic position of the Animikie group of Minnesota with the Animikie series as defined for part of Michigan.. __________ __ __ _ _______ 35 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY STRATIGRAPHY OF PRE-KEWEENAWAN ROCKS IN PARTS OF NORTHERN MICHIGAN By HAROLD L. JAMES ABSTRACT stone; and (d) the Paint River group, which comprises the The Precambrian rocks of northern Michigan are placed in Dunn Creek slate, Riverton iron-formation, Hiawatha gray- three major categories Lower Precambrian, Middle Precam­ wacke, Stambaugh formation, and Fortune Lakes slate. The brian, and Upper Precambrian. This report summarizes strat- strata of the Paint River group, which occur chiefly in the igraphic nomenclature used by the U. S. Geological Survey for Iron River-Crystal Falls district, previously have been con­ the Lower and Middle Precambrian rocks that occur in Iron and sidered part of the Michigamme slate. Dickinson Counties. The Animikie strata were deformed, metamorphosed, and in­ A sequence of Lower Precambrian rocks Archean of older truded by dikes, stocks, and sills of gabbroic to granitic com­ reports is established on the basis of detailed mapping in position in a pre-Keweenawan erogenic interval. Recent de­ central Dickinson County; it consists of metamorphosed sedi­ terminations of A^/K40 and Rb'YSr87 indicate a probable age mentary and volcanic rocks, herein named the Dickinson group. of at least 1,400 million years for the granitic rocks, which com­ These strata rest unconformably on an older granite gneiss, monly have been referred to as "Killarney", on the basis of and in turn have been invaded by granitic rocks of batho- assumed equivalence in age with the Killarney granite of the lithic dimensions. The pre-Dickinson granitic gneiss contains north shore of Lake Huron. Recently reported ages of rocks inclusions of quartzite and schist, relics of a still older sedi­ from near the type area of the Killarney granite indicate that mentary sequence. The Dickinson group is divided into three the assumed equivalence is not valid. formations East Branch arkose (oldest), Solberg schist with the interbedded iron-rich Skunk Creek member, and the Six- INTRODUCTION Mile Lake amphibolite. Separated by a covered interval from Since 1943, the U. S. Geological Survey, in coopera­ strata of the Dickinson group are rocks herein designated the Hardwood gneiss, which may be in part or wholly equivalent tion with the Geological Survey Division of the Mich­ to the Dickinson group. The absolute age of the post-Dickinson igan Department of Conservation, has been engaged in granitic rocks is not known. restudy of the iron-bearing districts of northern Mich­ Middle Precambrian rocks consist chiefly of the Animikie igan (fig. 2). In cooperation with the State of Wis­ series (Huronian of older reports) and post-Animikie, pre- consin, this study has recently been extended into Keweenawan igneous rocks. The term Huronian, used in the adjoining areas of Wisconsin. A number of reports on region for nearly 60 years, is not used because of the uncertainty of correlation with the type Huronian of Canada. various aspects of the work have been published (Dut- The strata previously correlated with the Huronian are now ton, Park, and Balsley, 1945; Petti John, 1947; James, referred to the Animikie, here expanded from group to series Clark, and Smith, 1947; James, 1948; Pettijohn, 1948; rank, on the basis of accepted correlations with the strata of James and Wier, 1948; Dutton, 1949; Good and Petti­ the Mesabi district of Minnesota, which have been traced into john, 1949; Balsley, James, and Wier, 1949; Dutton, the type Animikie of the Thunder Bay area of Canada. The Animikie series rests with profound unconformity on 1950; Wier, 1950; James, 1951; James and Dutton, the eroded surface of Lower Precambrian (post-Dickinson) 1951; Pettijohn, 1952; Wier, Balsley, and Pratt, 1953; granitic rocks in many places in northern Michigan. The James, 1954; James, 1955; Gair and Wier, 1956) and Animikie is divided into four groups that are defined in this several more have ben placed on open file (Lamey, 1946; report. In order of age (oldest to youngest) these are (a) the Lamey, 1947; Lamey, 1949; Wier and Kennedy, 1951; Chocolay group, comprising the Fern Creek formation, Stur­ geon quartzite, and Randville dolomite, and their stratigraphic Pettijohn, 1951; Clark, 1953; Bayley, 1956). Eeports equivalents; (b) the Menominee group, which in the type area on the Lake Mary quadrangle (E. W. Bayley), Central consists of the Felch formation (Felch schist and equivalent Dickinson County (James, Lamey, Clark, and others), rocks of older reports) and the Vulcan iron-formation, with the Iron Eiver-Crystal Falls district (James, Petti­ the Traders, Brier, Curry, and Loretto members; (c) the john, and Dutton), and Southern Dickinson County Baraga group, comprising the Goodrich quartzite, Hemlock formation, Fence River formation and its probable equivalent (Bayley, Lamey, and Dutton) are in various stages of the Amasa formation, Michigamme slate, and Badwater green­ preparation for publication. Most of the early reports 27 28 SHOETEK CONTRIBUTIONS TO GENERAL GEOLOGY Upper Precambritm (Keweenawan) rocks ^^^"Tk" A/-*Di£rRICT< FIGURE 2. Geologic sketch map of northern Michigan. and all those placed on open file were preliminary in Prinz, James Trow, and K. L. Wier. Each of these nature; stratigraphic names were used in conformity men criticized preliminary drafts of the manuscript with existing terminology or were described only in and their suggestions have been incorporated. Com­ terms of lithology, without formal designation. The plete unanimity of view on all points is not to be reports now in preparation, however, will contain many expected, but we are in agreement on all major aspects new stratigraphic names and revisions of terminology of the stratigraphy. The final responsibility for the of the pre-Keweenawan rocks. The present paper is statements made herein is mine, but the report is a joint written so that the problem can be reviewed in its en­ effort and I hope it will be so regarded. tirety rather than piecemeal; in part it will summarize that which will be presented in more detail in later SUBDIVISION OF PRECAMBRIAN TIME reports on individual areas. Unlike the situation with respect to post-Precam- The conclusions summarized in this brief report are brian time, there exists no widely accepted reference based on more than 200 man-months of field work. In framework of eras and periods to which Precambrian preparing the report I have drawn heavily on the lithologic units and geologic events can be related. The published and unpublished work of my colleagues: principal reasons, of course, are obvious: lack of diag­ R. W. Bayley, L. D. Clark, C. E. Button, Jacob Freed- nostic fossils and the greater degree of deformation man, J. E. Gair, C. A. Lamey, F. J. Petti John, W. C. and metamorphism. Even within the Canadian shield PRE-KEWEENAWAN ROCKS IN PARTS OP NORTHERN MICHIGAN 29 no satisfactory subdivision has been achieved, although 1957, written communication). Although the two-fold the literature is strewn with the debris of many
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