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 un subdivision would seem quite applicable to the rocks successful attempts. Trust in particular lithologic as in northern Michigan, there remain the same questions pects (as in the original definitions of the Archean and of actual time significance that plagued Leith and led Algonkian) and a shield-wide unconformity (the him to abandon Archean and Algonkian. The rocks Eparchaean interval) has been shown to have been of many, if not most, areas of the Canadian shield can misplaced; it now seems safe to say that virtually all be placed in two main groups separated by a profound the familiar time and time-stratigraphic terms Ar unconformity. But is this unconformity of the same chean, Algonkian, Laurentian, Keewatin, Algoman, age in each area ? May it not be that the rocks beneath Huronian, and Killarney have become so beclouded by the unconformity in one area are actually time- misuse they are of dubious value except in the type equivalent to rocks above a comparable unconformity areas (Gill, 1955). in another area? What of the interval represented by The monograph studies of the Lake Superior region, the unconformity itself? And in some districts pro summarized by Van Hise and Leith (1911), employed found unconformities separate the rocks into three or a standard twofold classification of Precambrian time more groups. How are the rocks then to be classified into two major units the Archean and the Algonkian. in a twofold time sense ? Emphasis was placed on the complex, crystalline nature Only one term Precambrian is now used in a strict of the Archean system, and upon the profound uncon time sense in reports of the U. S. Geological Survey; formity that separated the Archean from the Algoni- the terms Archean and Algonkian were abandoned more kian. Subsequent work in the Canadian shield was to than 20 years ago. For a region in which at least 2,000 show that in many places the Archean contains thick million years of geologic history is recorded in the rocks sequences of only weakly metamorphosed sedimentary exposed at the surface and for which the geologic rec rocks and that the "Eparchaean" unconformity is not ord locally has been worked out in as great detail as in readily defined. The increased uncertainty as to the many well-studied younger terranes, the situation ob precise correlation of rocks in separated areas finally viously is unsatisfactory. Time was an element equally led Leith (1934), in his scholarly review of the Pre important prior to Olenellm as it was later, and the cambrian, to propose that the terms Archean and Al analysis of geologic events demands a greater subdi gonkian be used only in a relative sense essentially to vision than that permitted by the single term Precam indicate the nature of the lithology. Leith, Lund, and brian. Yet it seems equally evident that until gross Leith (1935) adopted the scheme whereby only one subdivisions can be placed in an actual time scale by term Precambrian is used in a strict time sense, age determinations, they have little general value and and Archean-type and Algonkian-type were used to in fact may lead to many incorrect conclusions regard characterize Precambrian rocks but without definite ing regional problems. Fortunately, many laboratories time significance. This method of designation has not are perfecting methods of geochronology; the number been followed by other workers in the region, chiefly of absolute age determinations is increasing rapidly, because unless the terms have time sense they are of and methods such as potassium-argon permit determi no value; with less confusion one may refer to a ter- nation of the age of rocks other than those of intrusive rane as consisting simply of an older sequence and a origin. Within a decade, perhaps, it may be possible to younger sequence of rocks. Furthermore, many truly define major subdivisions of time in terms of adequately older ("Archean") rocks are not "Archean-type", mapped and geologically understood rock sequences in whereas some younger rocks elsewhere are. the Canadian shield. In 1934, a special committee of Section IV of the Until an adequate basis for time division is available, Eoyal Society of Canada (Alcock, 1934) recommended informal subdivisions such as Lower Precambrian, that the terms Archean and Proterozoic be used in Middle Precambrian, and Upper Precambrian are used Canada for Early and Late Precambrian, respectively, by the U. S. Geological Survey. Strictly speaking, these which were the terms then in current usage by the Geo are meant to apply only to rock units within a given logical Survey of Canada. The base of the Bruce area, not a subdivision of time (hence Lower and series (lower Huronian) was proposed as the dividing Upper, rather than Early and Late), and the designa line between the two major divisions. The Geological tions apply only to the particular area under discussion. Survey of Canada follows the recommended termi Inevitably, however, because of the overriding need for nology, but with recognition of the difficulty of applica subdivisions of time, the terms are used informally in tion in some areas and recognition of the uncertainty a time sense and, regardless of qualifications held by the as to the exact position of the dividing line between originators, they will be so interpreted by others (see, the Archean and the Proterozoic (J. M. Harrison, for example, Wilson, 1956). Furthermore, unless the 30 SHORTER CONTRIBUTIONS' TO GENERAL GEOLOGY implication of time is heeded, workers within the same brian (James, 1955), which is equally justifiable on the region or even in adjoining areas presumably could, basis of the geology of that area. Until enough absolute on the basis of local geology, place a recognized cor age determinations are available properly to define gross relative unit in different categories. Indeed this has subdivisions of time for the region, this obviously un already happened: Grout, Gruner, Schwartz, and Thiel satisfactory situation seemingly must be endured; all (1951) place the Biwabik and Gunflint formations in that can be done to minimize the confusion is to define the Late Precambrian an eminently justifiable de usages as clearly as possible and to apply the same terms cision considering the area whereas in Michigan the to time-equivalent units, so far as this is possible with agreed correlatives are referred to the Middle Precam the means at hand.
TABLE 1. Lithologic sequence of Precambrian rocks in Iron and Dickinson Counties, Mich. [New stratigraphic names are Indicated by asterisks]
Upper Precambrian Keweenawan series Diabase dikes and sills (probable age about 1,100 million years) -Intrusive contact Granitic intrusive rocks (probable age at least 1,400 million years) Intrusive contact- Metadiabase and metagabbro -Intrusive contact- Fortune Lakes slate* Stambaugh formation* Paint River group* Hiawatha graywacke* Riverton iron-formation* Dunn Creek slate*, with Wauseca pyritic member* Badwater greenstone* Michlgamme slate Baraga group* Fence River formation Amasa formation Middle Precambrian Hemlock formation, with Mansfield iron-bearing slate member and Bird iron- Animikle series bearing slate member* Goodrich quartzlte -Unconformity- Precambrian Loretto slate member Ourry iron-bearing member Vulcan iron-formation Menominee group* Brier slate member Traders iron-bearing member Felch formation -Unconformity- Randville dolomite Saunders formation Ohocolay group* Sturgeon quartzlte Fern Greek formation Unconformlty- Gneisslc granite and other crystalline rocks -Intrusive or replacement contact??- Six-Mile Lake amphibolite* Dickinson group* Solberg schist*, with Skunk Hardwood gneiss* Creek member* position uncertain Margeson Greek gneiss Lower Precambrian (position uncertain) East Branch arkose* Quinnesec formation Unconformity- (position uncertain) Granite gneiss Quartzlte and schist (small bodies included in granite gneiss)
For the rocks of northern Michigan, the gross subdivisions that will be followed are given in comparison with previously used terminology.
Van Hise and Leith 1911 Leith, Lund and Leith 1935 Grout et al. (Minnesota) 1951 Present Geological Survey usage for northern Michigan
Upper Precambrian Algonkian Algonkian-type Late Precambrian Proterozoic Precambrian Precambrian Middle Precambrian
Middle Precambrian Archean Archean-type Lower Precambrian Early Precambrian PRE-KEWEENAWANI ROCKS IN PAETS OF NORTHERN MICHIGAN 31 Most of the recent work of the Geological Survey in group is named. Magnetic green schist believed corre Michigan has been confined to Iron and Dickinson lative with the Dickinson group occurs in the Kiernan Counties (fig. 2), an area which includes the Iron ,and Lake Mary quadrangles to the northwest (Gair and River-Crystal Falls, Menominee, Felch Mountain, and Wier, 1956, p. 27; R. W. Bayley, 1956, p. 13). Detailed Calumet districts. The stratigraphy of the Precam- mapping by Lorin D. Clark and C. A. Lamey has shown brian rocks of this area, including terms that will be that the group can be divided into three formations in defined later in the present report, is summarized in central Dickinson County. These formations East table 1. Branch arkose (oldest), Solberg schist, and Six-Mile Lake amphibolite are defined below. The rocks are LOWER PRECAMBRIAN ROCKS steeply dipping or vertical and the sequence is believed The subdivisions of Lower Precambrian rocks, given to be conformable. in table 1, have been defined on the basis of detailed mapping in central Dickinson County, chiefly by Lorin EAST BRANCH ARKOSE D. Clark, C. A. Lamey, F. J. Pettijohn, Jacob Freed- The strata here named the East Branch arkose are man, and James Trow. Preliminary descriptions of well exposed in broad glacially polished outcrops in some parts of this area have been made available sees. 17 and 18, T. 42 N., R. 28 W., along the East (Clark, 1953; Lamey, 1946, 1947, 1949; Pettijohn, Branch of the Sturgeon River (Clark, 1953). Many 1951) and a general report on the entire area is in prep other excellent exposures occur for about two miles aration (James, H. L., Lamey, C. L., Clark, L. D., and both east and west of this area. The strata comprise others). arkose, arkosic conglomerate, and interbedded meta morphosed basalt flows and basic tuffs. The sedi OLDER GRANITE GNEISS AND INCLUDED BODIES OF QUARTZITE AND SCHIST mentary rocks are characterized by coarseness of grain, poor sorting, and beds of conglomerate. The pebbles A strongly deformed granite gneiss is exposed in the of the conglomerate are deformed into elliptical bodies northern part of T. 42 N., Ks. 28, 29, and 30 W. and is in the plane of foliation. About 75 percent of the overlain unconformably by the East Branch arkose fragments more than an inch long are quartzite, but (table 1). The rock is described by Clark (1953, p. 10) pebbles similar or identical to the underlying granite as follows: gneiss are abundant. The arkosic beds have been re Although the composition and texture of the gneiss range constituted to a gneissic-appearing rock but cross- widely, a coarse brick-red to very light-red rock of porphyritic bedding is well preserved; the beds are steeply dipping aspect is most common. The largest phenocrysts are 1% inches or vertical, and the top direction is consistently to the long and are microcline or albite. A marked cataclastic texture with strong secondary foliation is characteristic of the red south. porphyritic granite. Many of the large feldspar grains are The actual contact with the older granitic gneiss has fractured and rounded. They are separated by laminae of not been observed, though in some places the two rock micaceous or chloritic minerals in which are embedded micro units are exposed but a few feet apart. The younger cline fragments and thin, tabular quartz grains. age of the arkose is shown by the presence of granitic Less common varieties of granitic gneiss exposed in T. gneiss pebbles in the conglomerate and by the absence 42 N., R. 28 W. include fine-grained granite and quartz- of any metamorphic effects that can be related to the rich granite. contact. The strata previously have been referred to The gneiss is especially well exposed in the north part the Sturgeon quartzite of the Huronian series by of sec. 7, T. 42 N., E. 28 W. and in adjoining parts of earlier investigators (W. S. Bayley, 1899, p. 471; Van adjacent sections. Foliation trends easterly and is Hise and Leith, 1911, p. 301), who assumed it to under nearly vertical. lie Randville dolomite that is exposed a short distance Inclusions of schist and of quartzite measurable in to the north. The pre-Animikie age for the arkose is tens of feet in width and length are sparsely distributed shown by the following facts: in the granite gneiss. They are the only known 1. In much of the area, the two formations are sep remnants of the terrane in which the granite was arated by a wedge of granite gneiss. emplaced. 2. The top directions in the arkose are consistently to DICKINSON GROUP the south, away from the dolomite that was as The rocks here named in the Dickinson group occur sumed to overlie it conformably. in an easterly trending belt about four miles wide in the 3. The arkose shows strong internal deformation, in central part of T. 42 N., Rs. 28, 29 and 30 W. This area contrast to the absence of such deformation in is in the central part of Dickinson County, for which the the adjacent dolomite. In the SW*4 sec. 3, T. 449221 58 2 32 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 42 1ST., R. 28 W., for example, fine-grained dolo hornblende and plagioclase, with strong preferred mite with undef ormed algal structures occurs only planar and linear orientation of the minerals. The a few hundred feet north of broad outcrops of amphibolite is basaltic in composition and represents arkosic conglomerate in which the arkose is a metamorphosed sequence of flows and possible tuffs. gneissic in appearance and texture and in which The amphibolite grades to the south (across the strike) the pebbles of the conglomerate are flattened into a mile-wide zone of banded gray gneiss that is the discs. product of reaction between the amphibolite and post- The East Branch arkose, after .making due allowance Dickinson gneissic granite, a granite that forms the for structural complications, is believed to be at least basement to the Animikie series in parts of the area. 1,000 feet thick in the type area. The thickness of amphibolite is about 3,000 feet, but a considerably greater original amount can be inferred SOLBEKG SCHIST from the widespread occurrence of amphibolite as relict bodies in the gneiss the granite adjoining to the south. The unit here defined as the Solberg schist is named for Solberg Lake, in sees. 17 and 20, T. 421ST., R. 29 W., HARDWOOD GNEISS east of which the rock is exposed in scattered outcrops for about 10 miles in a belt 1 to 2% miles wide. The The rock here named the Hardwood gneiss is ex more northerly (stratigraphically lower) parts of the posed principally in sections 5 and 8, T. 411ST., R. 27 W., unit are dark fine-grained hornblende and biotite Dickinson County, a short distance west of the com schists. Some exposures show a banding, parallel or munity of Hardwood for which the unit is named. Ex nearly parallel to the steeply dipping foliation that cellent exposures occur along and adjacent to highway may represent original layering. The more southerly M69, within an area mapped in detail by Jacob Freed- exposures are of massive gray quartz-mica schist and man, 1951 (written communication). micaceous quartzite. The gneiss contains some highly distinctive rocks, Interlayered with the Solberg schist is a bed of iron- many of which are quite unlike any others in northern formation, here named the Skunk Creek member. It is Michigan known to me. Much of the rock is strongly named for Skunk Creek, a tributary of the East Branch layered in units a fraction of an inch to a few feet in of the Sturgeon River, which crosses the iron-rich thickness. The principal rock is dark, medium-grained member near the SE cor. sec. 17, T. 42 1ST., R. 28 W. gneiss composed of hornblende, plagioclase, and py The rock is exposed only in a small outcrop in the ISTE^ roxene, which is interlayered with dark fine-grained sec. 23, T. 42 1ST., R. 29 W., but the magnetic anomaly gneiss, beds of light-colored gneiss with light and dark caused by the rock has been traced for more than 20 laminae, garnet-quartz-mica schist, and light-colored miles and the bed has been drilled in several places by rock that resembles quartzite but which probably is the M. A. Hanna Company. The drill core shows the volcanic in origin. The layering in general dips east rock to consist principally of three interlayered rock erly at angles less than 40° but many exposures show types: (a) biotite-hornblende schist with magnetite complex crumpling. layers; (b) a distinctive thin-bedded rock consisting of The gneiss, which represents original volcanic and alternating layers of metachert and magnetite; and (c) tuffaceous rocks of basic to intermediate composition various mixtures of hornblende, biotite, grunerite, gar together with some interbedded rock of sedimentary net, and epidote. The Skunk Creek member is about origin and intrusive metagabbro sills, may well be 100 feet thick. equivalent to or part of the Dickinson group, but ex The aggregate thickness of the Solberg schist is diffi posures are inadequate to establish relationships. The cult to determine accurately, but it is about 3,000 feet. known thickness, including metagabbro sills, is not Some interbedding with the East Branch arkose is in great possibly no more than several hundred feet. dicated in exposures near the south edge of sec. 18, T. 42 1ST., R. 28 W. The Skunk Creek member is about QTJINNESEC FORMATION 1,000 feet below the top of the formation. The term Quinnesec formation applies to green stone, amphibolite, and schist that form a belt in the SIX-MILE LAKE AMPHIBOLITE southernmost part of Dickinson County and adjacent The Six-Mile Lake amphibolite is named for Six-Mile parts of Wisconsin. These rocks, under the name Lake, in sec. 22, T. 42 1ST., R. 29 W. The rock is well Quinnesec schists, were referred to the Archean by Van exposed in low knobs and ridges immediately south of Hise and Bay ley (1900), but later (Van Hise and the lake and for several miles to the east and west. It Leith, 1911) were assigned a late Huronian age. Leith, is a massive dark fine- to medium-grained aggregate of Lund, and Leith (1935) changed the designation to PRE-KEWEENAWAN1 ROCKS IN PARTS OF NORTHERN MICHIGAN 33 Quinnesec greenstone and doubtfully assigned the unit beneath the recognized Silurian strata on the north to the middle Huronian. shore of Lake Huron. The beds, which consist of con The type area of the Quinnesec formation has been glomerate, quartzite, limestone, and tillite, have an mapped in detail recently by W. C. Prinz (1957, aggregate thickness on the order of 20,000 feet, and written communication), who finds that rocks placed were described in some detail by Logan (1863). Re- in the Quinnesec formation by previous workers com study of the area by Collins (1925) showed that the prise metavolcanic rocks and younger metagabbro sills. strata were divided by an unconformity into two units, The term Quinnesec formation is retained for the meta the lower of which is now referred to as the Bruce series volcanic rocks, which are clearly older than the gran and the upper as the Cobalt series. itic rocks that form a mass of batholithic dimensions to Correlation between the Marquette district of Mich the south. Relationships of the Quinnesec formation igan and the type area of the Huronian was early pro and of the granitic rocks to known Animikie strata posed by Van Hise (1891). The Lower Marquette are not clear; the metavolcanic and granitic rocks are series of the Marquette range consisting principally believed to be pre-Animikie, and are so shown in table of the rocks now called the Mesnard quartzite, the Kona 1, but until absolute age measurements are made this dolomite, the Ajibik quartzite, the Siamo slate, and the conclusion is only tentative. The younger metagabbro Negaunee iron-formation was correlated with the sills are intrusive into the Quinnesec formation and are Lower Huronian (Bruce series of the type area) ; and younger than the granitic rocks to the south. They are the Upper .Marquette series of the Marquette range tentatively correlated with the post-Animikie meta- consisting chiefly of the rocks now called the Goodrich diabase and metagabbro. quartzite and Michigamme slate was correlated with the Upper Huronian (Cobalt series of the type area). POST-DICKINSON GNEISSIC GRANITE Subsequently, A. E. Seaman (see plate 19 in Van Hise Large areas of northern Michigan are underlain by and Leith, 1911) discovered an unconformity within masses of pre-Animikie gneissic granite and related Van Hise's Lower Marquette series, at the base of the rocks which are surrounded by or contain infolded Ajibik quartzite, and as a result the strata in the Mar Animikie strata. In central Dickinson County it has quette range were divided into three unconformable been established that the large mass of crystalline rocks units rather than two. An international committee re between the Felch and Calumet troughs of Animikie viewed the problem and accepted a proposal for a three strata is of post-Dickinson age. The basement rocks to fold division of the Huronian (Van Hise, Adams, Bell, the Animikie series in many other parts of the region and Leith, 1905), in which the Huronian was divided probably are equivalent to this post-Dickinson granite, into three units, only two of which the lower and the rather than to the pre-Dickinson granite, but proof is middle are represented in the type area. The Ani not available. The pre-Animikie Margeson Creek mikie group of the Thunder Bay area of Ontario was gneiss of northeastern Iron County (Gair and Wier, to form the third unit (upper), which was correlated 1956, p. 18-26) is in this category; it could be either with the Goodrich and Michigamme sequence of the post-Dickinson or pre-Dickinson in age. Marquette range on the basis of lithologic similarity. The term "Algoman," commonly used in the Lake The latter sequence, therefore, while retaining the desig Superior region in reference to upper pre-Animikie nation of upper Huronian, actually received an entirely granitic rocks, may be applicable to the post-Dickinson different correlation from that originally proposed; in granite gneiss, but in the absence of actual determina stead of being correlative with the Cobalt series of the tions of age this assignment should be considered type Huronian, it was made post-Cobalt in age. This tentative or doubtful. scheme was followed in Monograph 52, the final report of the U. S. Geological Survey series of monographs on MIDDLE PRECAMBRIAN ROCKS the region (Van Hise and Leith, 1911). Although Middle Precambrian rocks are represented by a thick many geologists raised objections see, for example, ar sequence of metasedimentary and metavolcanic rocks ticles by Collins, Lawson, Coleman, and others in the and by scattered bodies of metagabbro and of granitic proceedings of the 12th International Geological Con rocks. The metasedimentary and metavolcanic sequence gress (1914) the revised classification received and has been referred to the Huronian series for over 60 still receives fairly wide acceptance. A later report by years. This designation is now changed in favor of the (Canadian) National Committee on Stratigraphic Animikie series. Nomenclature, however, reinstated Upper Huronian as The term Huronian was applied by Logan and Hunt a designation for the Cobalt series of Canada (Alcock, (1855) to a sequence of sedimentary rocks that lies 1934, p. 118). 34 iSHORTER CONTRIBUTIONS TO GENERAL GEOLOGY Marsden (1955) has suggested that the Mesnard- 2. The probable age of the granitic rocks that cut the Kona sequence of the Marquette district is "Middle Middle Precambrian sequence of Michigan is more Huronian", but otherwise few major objections have than 1,400 million year. (See p. 39-40.) On the been raised to the fundamental matter of correlation of north side of Lake Huron, the Wavy Lake granite the Huronian of the type area with the strata of the (Lake Huron sheet, Map 155-A, Canadian Geo Marquette district about 200 miles to the west. Yet no logical Survey) appears to be essentially a part iron-formation such as the Negaunee is present in the of the Killarney granite of post-Huronian age. Huronian of the type area, nor, except by indirect cor Its age has been determined as 1,025 million years relation, can relationship be established between the by the potassium-argon method and 1,075 million Upper Huronian of the Marquette district, the Ani years by the rubidium-strontium method mikie group of the north shore of Lake Superior, and (Wetherill, Davis, and Aldrich, 1957, pp. 39-40). the Huronian of the type area. The correlation is based East of this area the Cutler batholith is known almost entirely upon supposed lithologic similarity be to cut the Sudbury series of probable pre- tween the Bruce series (lower Huronian of the type Huronian age, but though the granite is adjacent area) and the Mesnard quartzite and Kona dolomite se to the basal Mississagi quartzite of the Huronian quence of the Marquette range, and upon similarities in series, no direct evidence of crosscutting has been structural and igneous history. found. Age determinations on rocks from the Actually, the lithologic similarity between the Bruce batholith are given by Wetherill, Davis, and series of Canada and the Mesnard-Kona sequence of Aldrich (1957, p. 40) as 1,325, 1,760, and 1,750 Michigan is not close. If trust is to be placed in litho million years by the rubidium-strontium method, logic similarities a questionable procedure at best and 1,380, 1,420, and 1,350 million years by the other correlations can be made that are of at least potassium-argon method. The Cutler batholith, equal validity. One of the most distinctive rocks in therefore, which may well be overlain uncon- the Huronian sequence of the type area is the Gowganda formably by the basal formation of the Huronian, tillite, which forms the base of the Cobalt series of appears to be of comparable age to the granitic Canada. The tillite is overlain by the thick massive rocks that cut the supposed Huronian series in vitreous white Lorrain quartzite. In Dickinson County, Michigan. Michigan, tillite of virtually identical appearance forms The arguments for retention of the term Huronian part of the Fern Creek formation (Pettijohn, 1943), for the Michigan strata are essentially negative name and the Fern Creek formation is overlain by the Stur ly that the correlation has not actually been disproved geon quartzite, which is a thick vitreous quartzite com and that the term is deeply entrenched in the literature. parable in thickness and lithology to the Lorrain Because there are equally plausible alternatives to the quartzite that overlies the Gowganda tillite. If this correlation, it is our view that continued designation correlation were to be accepted, it would imply that the of the Michigan strata as Huronian is not justified. entire "Huronian" sequence of Michigan is post-Bruce Application of the term Animikie to the Michigan in age, but other equally plausible correlations could strata is open to far fewer major objections. The term be made. was used originally in the Thunder Bay area on the A second view is that the Michigan strata are pre- Huronian in age. The argument in favor of this view northwest side of Lake Superior (Hunt, 1873) to strata that underlie the Keweenawan series. On the basis of is as follows: physical continuity and bed-by-bed correlation, it has 1. In the type Huronian area, the two principal been accepted as a group name - by Grout, Gruner, quartzite formations the Lorrain and the Missis- Schwartz, and Thiel (1951), for strata in Minnesota sagi contain abundant pebbles and fragments of that previously had been referred to the Huronian. chert and jasper, material which is relatively These authors use Animikie rather than Huronian be scarce in the surrounding pre-Huronian terrane. cause (p. 1042) "* * * the Minnesota outcrops are well Crossbedding in these two units indicates north erly and westerly sources for the clastic material correlated with the original Animikie locality and not (Pettijohn, 1957, p. 471). The abundance of jas well correlated with the type locality of the Huronian." per and chert suggests that major chert-bearing The strata assigned to the Animikie group by Grout units were undergoing erosion during Huronian and his associates can be correlated with the Michigan time; the iron-formation strata of Michigan are strata with reasonable assurance, chiefly because of the possible sources. presence of major units of iron-formation. The Gun- PRE-KEWEEOSTAWAN ROCKS EST PARTS OF NORTHERN MICHIGAN 35 flint of the type Animikie area and of adjacent parts of these strata the Fern Creek formation, which is de Minnesota, the Biwabik of the Mesabi district, the scribed in more detail by Trow (1948). Iron wood of the Gogebic district (Wisconsin and Mich In parts of Iron and Dickinson Counties the only unit igan), the Negaunee of the Marquette district (Mich of the Chocolay group is the Randville dolomite (in igan), and the Vulcan of the Menominee district southern Iron County, its partial correlative the Saund- (Michigan) are accepted as at least approximately ers formation). Whether the Sturgeon is absent be equivalent in age (Leith, Lund, and Leith, 1935). In cause of nondeposition or whether the dolomite in these general, therefore, the extension of the term Animikie areas is time-equivalent to both Sturgeon and Randville to the Michigan strata rests on far firmer grounds than is uncertain. the extension of the term Huronian. MENOMINEE GROUP The Animikie is given series rank in application to the Michigan strata because it probably includes some The Menominee group is named for the Menominee rocks that are older and some that are younger than district of southern Dickinson County, Michigan. It those in the type area, and because it is divided into is to be noted that the term Menominee series was used four groups. Using the generalized sequence repre in Monograph 46 (Bayley, 1904) and discarded seven sented in Iron and Dickinson County for comparison, years later in Monograph 52 in favor of Huronian the relationship between the Animikie group of Minne (Van Hise and Leith, 1911). The present definition sota and the Animikie series of Michigan is given in covers only the middle part of the Menominee series as table 2. originally defined. In the type locality this group consists of two forma TABLE 2. Comparison of the stratigraphic position of the Ani mikie group of Minnesota with the Animikie series as defined for tions the basal Felch formation, and the Vulcan iron- part of Michigan. formation. The latter formation is made up of four members which are, in ascending order, the Traders Minnesota (Mesabi Michigan (Iron and Dickinson Counties) district) iron-bearing member, the Brier slate member, the Curry iron-bearing member, and the Loretto slate mem Paint River Fortune Lakes slate group Stambaugh formation ber. The Loretto was defined originally by Alien Hiawatha graywacke Riverton iron-formation (1919) as a post-Curry unit preserved only locally; in Dunn Creek slate most places it was removed by erosion prior to disposi Baraga group Badwater greenstone * «> o Michigamme slate tion of the overlying Goodrich quartzite or equivalent Virginia slate "&..S Fence River and Amasa formations Hemlock formation rocks. The existence of the Loretto is confirmed by Animikiegroup 0> Ift Goodrich quartzite
BADWATEB GREENSTONE tween the Badwater greenstone and the Michigamme slate permits or demands redefinition of the strati- Large areas of southern Iron County, northern graphic position of the strata in the Iron River- Florence County (in Wisconsin, immediately south of Crystal Falls district. In previous reports these Iron County, Mich.), and southwestern Dickinson strata, which include productive iron-formation, gen County are underlain by greenstone. The formation erally were considered part of the Michigamme slate is hlere named the Badwater greenstone for the extensive (Leith, Lund, and Leith, 1935). The Iron River- exposures in sees. 1, 2, and 11, T. 40 N., R. 31 W., in the Crystal Falls district is a deep tightly folded major vicinity of Badwater Lake, southern Dickinson County. synclinal structure incompletely bounded by Badwater The greenstone in the adjacent area of southeastern greenstone. In the area immediately east of Crystal Iron County, Dickinson County, and Florence County Falls, greenstone is absent and the strata of the dis (Wisconsin) has been referred to as the Mastadon- trict proper rest directly on the Michigamme slate, Spread Eagle-Lake Antoine belt (Leith, Lund, and which doubtless is the reason they were previously con Leith, 1935, p. 4). The greenstone in the eastern part sidered an extension of that unit. Recognition of the of this belt was assigned to the Archean by Bayley stratigraphic position of the Badwater greenstone (1904), but in Monograph 52 (Van Hise and Leith, 1911, forms the basis for definition of a new group, here p. 345) the statement is made: named the Paint River group for the Paint River, This area of schists at the time the Menoruinee monograph which drains the northern and eastern part of the dis was written, was supposed to be equivalent in age to the Quin- trict. The five formations that comprise the group nesec schist of Menominee River, then regarded as Archean. are the youngest strata of the Animikie series in Iron Later work by G. W. Corey and C. F. Brown (unpublished field notes, 1905) has shown that they are really intrusive and ex and Dickinson Counties, and probably are the youngest trusive in the upper Huronian or in part contemporaneous flows. Animikie strata preserved in northern Michigan. Some Leith, Lund, and Leith (1935) doubtfully assigned the of their characteristics have been described in previous papers (James, 1951, 1954). greenstone to the Middle Huronian. Detailed mapping in the northern part of the Me DTJNN CREEK SLATE nominee district by C. A. Lamey, and in the Common The basal formation of the Paint River group is a wealth quadrangle of southern Iron County and ad sequence of siltstones and slates here named the Dunn joining areas of Wisconsin south of the Brule River Creek slate. The name derives from Dunn Creek, in by C. E. Dutton, K. L. Wier, and the .writer has eastern Iron County south of Crystal Falls, in the 38 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY vicinity of which are abundant exposures of the unit. The formation consists dominantly of interbedded The rocks in this area have been described by Petti- chert and siderite. Its thickness ranges from less than john (1947). Much of the Dunn Creek is graywacke 100 feet in the western part of the district to about 600 and slate that are physically indistinguishable from feet in the eastern part. Locally the upper part of the rocks of the Michigamme slate, but in the type area formation is absent because of erosion prior to deposi of eastern Iron County the formation is thicker and tion of the overlying Hiawatha graywacke, but most of more complex; it contains one or more layers of slaty the variation in thickness is to be ascribed to the nature sideritic iron-formation. The probable maximum of sedimentation. thickness is about 800 feet; the probable minimum, HIAWATHA GRAYWACKE about 400 feet. The uppermost part of the Dunn Creek, immediately Overlying the Riverton iron-formation, locally with underlying the productive iron-formation, is a black minor unconformity, is a unit of clastic rock, here named pyritic graphitic slate, probably 30 feet or less in true the Hiawatha graywacke. The name is taken from the thickness but commonly much greater or less because of Hiawatha mine at Iron River, near which the rocks are squeezing and shearing. The rock typically contains exposed in scattered outcrops and in which the forma 35 to 40 percent pyrite, extremely fine grained, and 5 tion is crossed by extensive mine workings. As the name to 10 percent free carbon (James, 1951). This distinc implies, graywacke is the dominant rock, but it is inter- tive rock is exposed at only one place, a road cut south bedded with considerable amounts of slate, particularly of the town of Alpha (Pettijohn, 1947; 1948), but is in the western part of the district. The lower part of known from test pits, mine workings, and drill holes the formation quite commonly is a breccia that consists throughout the district. It is here named the Wauseca of scattered angular chert fragments in a graywacke pyritic member, for the Wauseca mine at Iron River, in matrix (see photographs in James, 1951, pi. 2). This which the unit is exposed in thousands of feet of mine rock is locally well exposed along the course of the Paint workings. The member itself is subdivided into two River at the north edge of the town of Crystal Falls or three parts in the detailed geologic mapping of the (Pettijohn, 1952). mines. One of these subunits is of particular interest. The formation ranges in thickness from 50 feet or less It is a chaotic breccia that ranges from a foot or so to in the eastern part of the district to 400 feet or more in about 50 feet in thickness and is composed of small (less the western part the reverse of the thickness aspect than 1 inch diameter) fragments of pyritic slate in a of the underlying Riverton iron-formation. The for matrix of the same composition. The uniform composi mation also becomes more arkosic in composition toward tion of the rock, the complete lack of extraneous mate the west. STAMBAtJGH FORMATION rial, and its occurrence over distances measurable in miles strongly suggest that the rock is the product of The strata here named the Stambaugh formation are a widespread submarine slump. If so, the unit is pre iron-rich rocks that range from chlorite mudstone and cisely time equivalent over the entire district. slate to a laminated cherty siderite-magnetite rock. The distinctive feature of the formation is that it is mag RIVERTON IRON-FORMATION netic (the only formation that is consistently so over The productive iron-formation of the Iron River- most of the district) and as a result can be traced by Crystal Falls district the host rock for the ore bodies magnetic methods. Tedious though the magnetic sur is here named the Riverton iron-formation. The veying is, it has been of inestimable value in working name is taken from the Riverton mine at Iron River, out the map patterns in this structurally complex area the first site of mining in the district about 75 years ago. of poorly exposed rocks. The distribution of the mag The formation is visible in the walls of the caved work netic slate, as it is called locally, is better known than ings of the old mine and the original discovery of iron in that of any other unit in the district. The formation is named for the town of Stambaugh, the district about 100 years ago was in one of the few in the western part of the district. The hill on which natural exposures of the formation in the Iron River the town is built is in large part underlain by the for area, within a hundred feet of the old mine. Small ex mation (here compressed into a tight complex syncline) posures are widespread in the eastern part of the dis and numerous small exposures can be seen on the trict (Pettijohn, 1947; Good and Pettijohn, 1949; Petti grounds of the Stambaugh High School. Better ex john, 1952), but much of the knowledge concerning the posures are present in the eastern part of the district formation is derived from the hundreds of miles of mine (Pettijohn, 1947; 1952), but like most units of the Paint workings and the thousands of diamond-drill holes that River group, a large part of the information has come have intersected the rock. from mining explorations and developments. PRE-KEWEENAWAN ROCKS IN PARTS OF NORTHERN MICHIGAN 39 FORTUNE LAKES SLATE quette district (1933). In subsequent papers he ex The strata underlying the central part of the Iron tended this term and concept to include the large areas Eiver-Crystal Falls synclinal basin are very poorly of granitic rock in Dickinson County (Lamey, 1934; known, but they underlie a larger area than any other 1937). Dickey (1936) took issue with this conclusion unit of the Paint River group. The main areas of ex and reaffirmed a pre-Huronian age. Later Dickey posure are between Crystal Falls and Fortune Lakes, (1938), on the basis of the intrusive relationships of for which the unit here is named, and in the area be granite to quartzite in the Ford River area of northern tween Alpha and the Brule River. The exposed rocks Dickinson County, introduced the possibility of a post- consist mostly of slate and minor graywacke, with Lower Huronian granite (post-Chocolay of this re characteristic thin beds (10 feet or less) of coarse mas port) for the Republic granite. At that time, how sive graywacke about 300 feet above the base. Sideritic ever, Dickey was not aware of the existence of the pre- slate is present in some areas between Crystal Falls and Animikie sedimentary sequence in the Norway Lake Alpha, and in one exposure near Fortune Lakes oxidized area (Clark, 1953) a few miles south of the area studied chert-siderite rock (iron-formation) is present. The by him. The Ford River area has been examined by character of the bulk of the formation is not known, the writer and his colleagues. The quartzite referred however, because of lack of exposure. to by Dickey almost certainly is pre-Animikie rather The aggregate thickness of the unit probably is at than Sturgeon, and the pre-Aiiimikie age for the gran least 4,000 feet. This estimate is based on structural itic rock was established by finding an exposed un- inferences rather than any measured thickness. conformable contact of Randville dolomite on the granite in the NE^SE^, sec. 15, T. 43 N, R. 29 W. MIDDLE PRECAMBRIAN IGNEOUS ROCKS Petti John's conclusions (1943) on the age relations The Middle Precambrian igneous rocks of northern of the main bodies of granitic rock in southern and Michigan fall into two principal groups metadiabase central Dickinson County have been borne out by the and metagabbro of Animikie or post-Animikie age, detailed mapping of the area by the U. S. Geological and granite and allied rocks that are younger than the Survey, in which Dr. Lamey has participated. These metadiabase and metagabbro. Other Animikie or post- conclusions are in essential agreement with the earlier Animikie igneous rocks appear to be exceedingly studies summarized by Van Hise and Leith (1911), scarce. but the detailed mapping has also shown that post- The metadiabase and metagabbro were metamor Animikie granite is more abundant than previously phosed during the post-Animikie, pre-Keweenawan in recognized. terval (James, 1955). Several large bodies of meta The Republic area has not been mapped in detail gabbro have been mapped; one, the West Kiernan sill during the present study, but a study of the metamor- (Gair and Wier, 1956; R. W. Bayley, 1956) of the Lake phism of northern Michigan (James, 1955) indicates Mary and Kiernan quadrangles of eastern Iron County, that in the type area of the Republic granite described is a differentiated sheet, now vertical but originally by Lamey the main mass of the granite is not post- horizontal, that is about a mile thick. Huronian (post-Animikie) but rather is pre-Animikie, The granitic rocks are believed relatively minor in although some post-Animikie granite is present. With surface expression but are widely distributed. Narrow Lamey's concurrence, it is recommended that the term dikes of granite and pegmatite are common in the Republic granite be abandoned because of the practical Felch area (where they cut Animikie strata as well as difficulty in distinguishing older from younger granite. older rocks) and a complex mass, perhaps several miles Measurements of absolute age have been made on across, occurs in the southern part of the Lake Mary several samples of the post-Animikie granite of Michi quadrangle of eastern Iron County (R. W. Bayley, gan by the lead-alpha (zircon) method, the potassium- 1956). argon method, and the strontium-rubidium method. The existence of post-Animikie granite in northern Determinations by the lead-alpha method on zircon Michigan has been known almost since geologic work concentrated from a post-Animikie granite body near was begun more than a hundred years ago, but con siderable debate has arisen as to its extent. Lamey the town of Crystal Falls by H. W. Jaffe were earlier (1931, 1933, 1934, 1937) contended that some of the reported to yield an age of 820 million years (James, large areas of granitic rocks regarded by others as 1955, p. 1458). Potassium-argon determinations on pre-Huronian (pre-Animikie of this report) are in post-Animikie granite from the Felch area were re fact post-Huronian, and introduced the term Republic ported by Wasserburg, Hay den, and Jensen (1956, p. granite for the rock between Republic and the Mar- 158-159), as follows: 40 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
Apparent age granitic rocks in Michigan, but the validity of this Branching (million Locality Material ratio years) designation is uncertain. Wetherill, Davis, and Aid- Pegmatite quarry in sec. Muscovite.. 0.126 1,610 rich (1957) report that the apparent age of the Wavy 19, T. 42 N., R. 29 W., Lake granite of Ontario, which is near the type area Dickinson County. of Killarney, is between 1,000 and 1,100 million years. As above..______Microcline_. .085 1,490 If this is actually the age of the Killarney granite As above.. Microcline. . .085 1,450 Groveland mine, sec. 31, Total granite .085 1,410 proper, the post-Animikie, pre-Keweenawan rocks of T. 42 N., R. 29 W., (mica free). Michigan are distinctly older, and the term Killarney Dickinson County. is not applicable.
The value of the branching ratio (0.085) used by REFERENCES CITED Wasserburg and his associates to compute the ages of Alcock, F. J., 1934, Report of the National Committee on strati- the microcline and the granite is an empirical value graphic nomenclature: Royal Soc. Canada Trans. 3d ser., assumed to correct for loss of argon. The value of 0.126 (Sec. iv), v. 28, p. 113-121. used for the mica determination is a maximum value Alien, R. C., 1919, Correlation of formations of Huronian group and the age so computed is a minimum. Unpublished in Michigan: Am. Inst. Mining Metall. Engineers Bull. 135, determinations made by L. T. Aldrich, G. W. Wetherill, p. 2579-2594; Am. Inst. Mining Metall. Engineers Trans., v. 63, p. 188-212 [1920]. and G. L. Davis by the strontium-rubidium method on Baadsgaard, H., Nier, A. O. C., and Goldich, S. S., 1957, Investi micas from several samples of metamorphosed Animikie gations in A^/K 40 dating: Am. Geophys. Union, program strata and from post-Animikie, pre-Keweenawan gra abstracts for annual meeting, Washington, D. 0., April 29- nitic rock yield values of about 1,400 million years, and May 2,1957, p. 40. feldspar from the same pegmatite reported on by Balsley, J. R., James, H. L., and Wier, K. L., 1949, Aeromagnetic survey of parts of Baraga, Iron, and Houghton counties, Wasserburg, Hayden, and Jensen yields a value near Michigan, with preliminary geologic interpretation: U. S. 1,750 million years (L. T. Aldrich, oral communication, Geol. Survey, Geophys. Inv. Prelim. Kept. 1957). Bay ley, E. W., 1956, Preliminary report of geology of Lake Mary Eecent determinations by the potassium-argon meth quadrangle, Iron County, Michigan: U. S. Geol. Survey open- file rept. od on rocks from the Lake Superior region have been Bayley, W. S., 1899, The Sturgeon River tongue: Chap. 6, vn reported by Goldich, Nier, and Baadsgaard (oral pres Clements and Smyth, U. S. Geol. Survey Mon. 36. entation and program abstract for the annual meeting 1904, The Menominee iron-bearing district of Michigan: of the American Geophysical Union, at Washington, U. S. Geol. Survey Mon. 46, 513 p. D. C., April 29-May 2,1957). Mica from granite near Canada Geological Survey, 1933, Lake Huron Sheet, Map 155A Crystal Falls, Mich., yielded an age of 1,700 million (3d ed.) : Pub. 1553. Clark, L. D., 1953, Precambrian geology of the Norway Lake years, as computed using the branching ratio of 0.118 area: U. S. Geol. Survey open-file rept. that now appears most suitable for mica. Baadsgaard, Clements, J. M., and Smyth, H. L., Jr., 1899a, The Crystal Falls Nier, and Goldich (1957) also report determinations on iron-bearing district of Michigan: U. S. Geol. Survey, 19th microcline from Dickinson County, Mich., probably Ann. Rept., pt. 3, p. 45-63. from the same localities from which the samples run by Clements, J. M., and Smyth, H. L., Jr., 1899b, The Crystal Falls iron-bearing district of Michigan: U. S. Geol. Survey Mon. Wasserburg, Hayden, and Jensen (1956) were obtained. 36, 512 p. The values of A 40/K 40 are closely comparable, but the Collins, W. H., 1925, North shore of Lake Huron: Canada Geol. age calculation using a branching ratio of 0.118 (as Survey Mem. 143. compared with 0.085 by Waserburg, Hayden, and Jen- Dickey, R. M., 1936, The granitic sequence in the southern com sen) yields values of 1,210, 1,200, 1,220, and 1,210 plex of Upper Michigan: Jour. Geology, v. 44, p. 317-340. 1938, The Ford River granite of the southern complex million years. These values, considering the probable of Michigan: Jour. Geology, v. 46, p. 321-335. argon leakage, are likely to be significantly lower than Button, C. E., 1949, Geology of the central part of the Iron River the true ages. district, Michigan: U. S. Geol. Survey Circ. 43. The net results to date of work on absolute ages 1950, Progress of geologic work in Iron and Dickinson suggest that the age of the post-Animikie, pre-Keween Counties, Michigan: U. S. Geol. Survey Circ. 84. Button, C. E., and Lamey, C. A., 1939, Geology of the Menominee awan epoch of diastrophism, metamorphism, and gran range, Bickinson County, Michigan: Michigan Dept. Con- ite intrusion is more than 1,400 million years. For serv., Geol. Survey Biv. Progress Rept. 5,10 p. comparison, the age of the Keweenawan or post-Ke- Button, C. E., Park, C. F., and Balsley, J. R., 1945, General weenawan intrusive rocks (Duluth gabbro and related character arid succession of tentative divisions in the stra rocks) is about 1,100 million years (Goldich, Nier, and tigraphy of the Mineral Hills district: U. S. Geol. Survey Prelim, rept. Baadsgaard, 1957). The term Killarney commonly has Gair, J. E., and Wier, K. L., 1956, Geology of the Kiernan quad been applied to the post-Animikie, pre-Keweenawan rangle, Michigan: U. S. Geol. Survey Bull. 1044, 88 p. PRE-KEWEENAWAN ROCKS IN PARTS OF NORTHERN MICHIGAN 41 Gill, J. B., 1955, Precambrian nomenclature in Canada: Royal Marsden, R. W., 1955, Precambrian correlations in the Lake Soc. Canada Trans.3dser. (Sec. iv) v.49,p.25-30. Superior region in Michigan, Wisconsin, and Minnesota: Goldich, S. S., Nier, A. O. C., and Baadsgaard, H., 1957, A^/K40 Geol. Assoc. Canada Proc., v. 7, pt. 2, p. 107-116. dating of rocks of the Lake Superior region: Am. Geophys. Pettijohn, F. J., 1943, Basal Huronian conglomerates of Me- Union, program abstracts for annual meeting, Washington, nominee and Calumet districts, Michigan: Jour. Geology, D. 0., April 29-May 2,1957, p. 41. v. 51, p. 387-397. Good, S. B., and Pettijohn, F. J., 1949, Magnetic survey and 1947, Geology of the Crystal Falls-Alpha iron-bearing geology of the Stager area: U. S. Geol. Survey Circ. 55. district, Iron County, Michigan: U. S. Geol. Survey Prelim. Grout, F. F., Gruner, J. W., Schwartz, G. M., and Thiel, G. A., Rept. 3-181. 1951, Pre-Cambrian stratigraphy of Minnesota: Geol. Soc. Pettijohn, F. J., 1948, Magnetic and geological data of parts of America Bull., v. 62, p. 1017-1078. Crystal Falls iron-bearing district: Michigan Dept. Con- Hunt, T. S., 1873, The geonostical history of the metals: Am. serv., Geol. Survey Div. Inst. Mining Metall. Engineers., Trans., v. 1, p. 331-395. 1951, Geology and magnetic anomalies of T. 42 N., R. 30 James, H. L., 1948, Field comparison of some magnetic instru W., Dickinson County, Michigan: U. S. Geol. Survey open- ments, with analysis of Superdip performance: Am. Inst. file rept. Mining Metall. Engineers Tech. Pub. 2293; Trans., v. 178, 1952, Geology of the northern Crystal Falls area; U. S. p. 490-500. Geol. Survey Circ. 153. 1951, Iron formation and associated rocks in the Iron 1957, Paleocurrents of Lake Superior Precambrian River district, Michigan: Geol. Soc. America Bull, v. 62, quartzites: Geol. Soc. America Bull. v. 68, p. 469-480. p. 251-266. Royce, Stephen, 1936, Geology of the Lake "Superior iron 1954, Sedimentary facies of iron-formation: Econ. deposits: Lake Superior Mining Institute, Proc. v. 29, p. 86. Geology, v. 49, p. 235-293. Trow, J. W., 1948, The Sturgeon quartzite of the Menominee 1955, Zones of regional metamorphism in the Precam district, Michigan: Unpublished Ph. D. thesis at the Uni brian of northern Michigan: Geol. Soc. America Bull., v. versity of Chicago, 60 p. 66, p. 1455-1488. Van Hise, C. R., 1891, An attempt to harmonize some apparently James, H. L., and Dutton, C. B., 1951, Geology of the northern conflicting views of Lake Superior stratigraphy: Am. Jour. part of the Iron River district: U. S. Geol. Survey Circ. 120. Sci., v. 41, p. 117-137. James, H. L., Smith, L. E., and Clark, L. D., 1947, Magnetic Van Hise, O. R., Adams, F. D., Bell, J. M., and Leith, C. K., 1905, survey and geology of the Ice Lake-Chicagon Creek area: Report of the special committee for the Lake Superior U. S. Geol. Survey Prelim. Rept. 3-213. region: Jour. Geology, v. 13, p. 89-104. James, H. L., and Wier, K. L., 1948, Magnetic survey and Van Hise, C. R., and Bayley, W. S., 1897, The Marquette iron- geology of the eastern and southeastern parts of the Iron bearing district of Michigan: U. S. Geol. Survey Mon. 28, River district: U. S. Geol. Survey Circ. 26. 608 p. Lamey, C. A., 1931, Granite intrusions in the Huronian for Van Hise, C. R., and Bayley, W. S., 1900, Description of the mations of northern Michigan: Jour. Geology, v. 39, Menominee special quadrangle, Michigan: U. "8. Geol. Sur p. 288-295. vey Atlas, folio 62. 1933, The intrusive relations of the Republic granite: Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Jour. 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K., 1934, The pre-Cambrian: Geol. Soc. America 31, p. 191-195. Proc. 1933, p. 151-180. Wier, K. L., Balsley, J. R., and Pratt, W. P., 1953, Aeromagnetic Leith, C. K., Lund, R. J., and Leith, A., 1935, Pre-Cambrian survey of Dickinson County, Michigan, with preliminary rocks of the Lake Superior region * * *: U. S. Geol. Sur geologic interpretation: U. S. Geol. Survey Geophys. Inv. vey Prof. Paper 184, 34 p. Map GP-115. Logan, W. B., 1863, Report of progress of the Geological Sur Wier, K. L., and Kennedy, B. E., 1951, Geologic and magnetic vey of Canada from its commencement to 1863: Geol. Sur data of the Sholdeis-Doane and Red Rock explorations, Iron vey of Canada. County, Michigan: U. S. Geol. Survey open-file rept. Logan, W. B., and Hunt, T. S., 1855, Bsquisse geologique du Wilson, M. B., 1956, Precambrian classification and correlation Canada * * * a 1'Exposition Univ. de Paris [Geol. Sur in the Canadian Shield (abs.): Geol. Soc. America Bull., vey of Canada]. v. 67, p. 1743.
INDEX
Page Page Acknowledgments ___.______28 Qeochronology.. 29 Algoman______29,33 Gneissic granite______- __ - 32,33 Algonkian ______29 Goodrich quartzite 35-56 Amasa formation, general description______36-37 outcrop 36 mines ____...... __... 36-37 Granite, age of. _ -__ -...... - - 34,39-40 name . ______36 Granite gneiss, general description 31 rocks in ______37 stratigraphy______.______36 Hardwood gneiss, general description 32 thickness..______37 composition. 32 Animikie . .__ .....__...... ___...... _ 32,33,34-35 dip 32 Archaean ______.______29 name_____ 32 Archean...... 29,32,37 outcrop__... 32 thickness____-_...._____~ _ - 32 Badwater greenstone ______. ______36,37 Hemlock formation, general description . -.. 36 name ___..______37 name __ 36 origin . ______37 rocks in. _ __ . 36 outcrop ______...... ______37 thickness______- 36 stratigraphy______37 Hiawatha graywacke, general description. 38 thickness.._._____.______37 name.-__.______-___ 38 Baraga group.______35-37 outcrop____ .. 38 name . __...... _..__...._. 35 rocks in.._ . . 38 rocks in . ______35-36 thickness_.. - - 38 Bird iron-bearing member, general description______.___ 36 Huronian....-..___... _ - ... 29,33,35 outcrop ______36 correlation with the strata of the Marquette district. . 33-34 stratigraphy______.____ 36 rocks - 33 thickness...... ______36 subdivisions 33 Brace series ...... ______... 29,33,34 thickness___... - - 33 Lower, rocks in...... 33,34 Canadian shield_____. ______28-29 Upper, rocks in__ __ _ 33,34 Chaotic breccia______38 See Frecambrian rocks, Middle. composition of______38 thickness... __._____...______38 Iron River-Crystal Falls district, stratigraphy...- . . 37 Chocolay group__...... ______35 structure____ 37 name. ______35 rocks in______35 Keewatin . - 29 Clark, quoted______31 Keweenawan rocks, pre 28 Cobalt series. .. _..... ______..... 33,34 Killarney . 29,40 Konadolomite. _ - - . .. 33,34,35 Dickinson gneissic granite, post_____ . ______32,33 Dickinson group ______31-32 Lake Huron, north shore, unconformity 33 dip...... __.__...._...._...... ____...... 31 Lake Superior region 29,35 name.- ______31 Laurentian_____.. . 29 Dunn Creek slate, general description ______. 37-38 Lead-alpha _...... 39 name ______37 Location of area covered by report 31 outcrop __.______38 Lorrain formation, appearance 34 rocks in..______37,38 thickness______38 Magnetic rocks___ . - - - 31,32,36,38 Mansfield iron-bearing slate member, general description 36 East Branch arkose, general description__.______31-32 name_____ - - 36 dip . ..-...... -...... -..-.-...-...... - ...... - 31 rocks in.__ 36 evidence of pre-Animikie age. _... . ______^____ 31-32 thickness_ - 36 outcrop -______.....______31 See Hemlock formation. rocks in . . __._.. .___.... 31 Marquette district, correlation with type area Huronian 33-34 thickness______32 See Frecambrian rocks, Middle Eparchaean interval______29 Marquette series, Lower, rocks in... 33 unconformity 33 Felch formation...... ______.___.__ 35 Upper, rocks in 33 rocks in ______.... ______.______35 Menominee group 35 stratigraphy.______.______.______35 formations in. - 35 See Menominee group. name. __ - 35 Fence River formation______36 Mesnard quartzite 34,35 name. ______....______36 Metadiabase...... __ 33,39 outcrop..._____....______36 Metagabbro ...... 33,39 Fern Creek formation. ______34,35 Metasedimentary rocks 33 Fortune Lakes slate, general description..-______39 Metavolcanic rocks 33 name - _____.______.______39 Michigamme slate 36,37 outcrop______39 rocks in______... . 37 rocks in_. ______39 thickness____.... .___.. . . -. . 37 thickness__....______...______.. 39 Mississagi formation, composition . 34 43 44 INDEX
Page Page Paint River group______37-39 Skunk Creek member, general description__ . 32 name ...... _.._..__._....._ 37 composition 32 See Iron River-Crystal Palls district. magnetic anomaly Potassium-argon. _ _ ...______._ 29,34 name. Precambrian, divisions of.__ ..______29 outcrop_ - 31 Precambrian igneous rocks, Middle.____-______39-40 thickness__ , 32 groups. . ___ 39 Solberg schist, general description_ 31,32 Precambrian rocks, Middle______33-35 composition.. 32 rocks in . . ..____...... ____.. 33 name___------32 See Huronlan, Marquette district. outcrop. ------32 Precambrian rocks, Lower______.______31-33 thickness -.-- Proterozoic______29 See Skunk Creek member. Stambaugh formation, general description . Quartzite. _ _ .. __.. 31,34 name . Quinnesec formation . ..__.....______32-33 outcrop ,- age . ______33 rocks in.._ . 38 rocks in. ...._ __.__.....______32 Strontium-rubidium . 40 Sturgeon quartzite... . 31 34,35 Randville dolomite______.______._.______.__ 31,35 References cited . .._ ___. _. _ 40-41 U. S. Geological Survey, Precambrian subdivisions- 29 Riverton iron-formation, general description. ..______38 composition ______38 Van Hise and Leith, quoted 37 name. ______38 Vulcan iron-formation 35,36 outcrop.______38 members__ 35 thickness ______.______38 See Menominee group. Royal Society of Canada, nomenclature of... - ______... 29 Rubidium-strontium______.______34 Wauseca pyritic member, general description. 38 composition 38 Six-Mile Lake amphibolite, general description. ..____...______31,32 name- 38 composition . ______..______.______32 outcrop_ 38 name. _____.______32 subdivisions of... . . - 38 outcrop_..______32 thickness..______. . . 38 thickness ...... -....-.-.__...._.. 32 See Dunn Creek slate.
U. S. GOVERNMENT PRIUT1NS OFFICEt 1918