Sedimentology and Provenance of the 

Early Proterozoic Michigamme Formation and 

Goodrich Quartzite, Northern Michigan 

Regional Stratigraphic Implications and 

Suggested Correlations

U.S. GEOLOGICAL SURVEY BULLETIN 1904-R
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Chapter R

Sedimentology and Provenance of the 

Early Proterozoic Michigamme Formation and 

Goodrich Quartzite, Northern Michigan 

Regional Stratigraphic Implications and 

Suggested Correlations

By RICHARD W. OJAKANGAS

U.S. GEOLOGICAL SURVEY BULLETIN 1904

CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION 

P.K. SIMS and L.M.H. CARTER, Editors
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U. S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1994

For sale by

USGS Map Distribution 

Box 25286, Building 810 

Denver Federal Center 

Denver, CO 80225

Library of Congress Cataloging-in-Publication Data

Ojakangas, Richard W.

Sedimentology and provenance of the Early Proterozoic Michigamme Formation 

and Goodrich Quartzite, northern Michigan: regional stratigraphic implications and 

suggested correlations / by Richard W. Ojakangas.

p. cm. (U.S. Geological Survey bulletin; 1904-R) 

(Contributions to Precambrian geology of Lake Superior region; ch. R)

Includes bibliographical references.

Supt. of Docs, no.: I 19.3:1904

1. Geology, Stratigraphic Proterozoic. 2. Geology Michigan. 

3. Michigamme Formation (Mich. and Wis.). 4. Goodrich Quartzite 

(Mich.). I. Title. II. Series. III. Series: Contributions to Precambrian geology 

of Lake Superior region; ch. R. 

QE75.B9 no. 1904-R 

[QE653.5]

557.3 s dc20 93-30526 

(551.7'15'09774] CIP
CONTENTS

Abstract Rl

Introduction Rl

General field description, Michigamme Formation R4

Slate members R4

Bijiki Iron-formation Member R7 

Drill hole descriptions R7

Clark Creek basin drill hole R8

Dead River basin drill hole R8

East Baraga basin drill holes R8

Amasa drill hole RIO

Gwinn area drill hole RIO 

Petrography RIO 

Chemistry R13 

Paleocurrent analysis R16

Metagraywacke and metasiltstone R16

Goodrich Quartzite R18 

Sedimentation R19

Introduction R19

Goodrich Quartzite R21

Lower slate member, Michigamme Formation R22

Bijiki Iron-formation Member, Michigamme Formation R22

Upper slate member, Michigamme Formation R22 

Tectonic model and provenance R23 

Stratigraphic implications R27 

References cited R28

FIGURES

1. Correlation chart for rocks in the Early Proterozoic Animikie basin R2

2. Generalized geologic-tectonic map of Precambrian rocks, Lake Superior 

region R3

3. Generalized geologic map of Precambrian rocks, northern Michigan and

northwestern Wisconsin R5 

4-6. Photographs showing:

4. Graywacke beds in roadcut south of Covington, Michigan R6

5. Graded graywacke beds with refracted cleavage, roadcut east of 

Covington, Michigan R6

6. Graywacke beds, measured section southeast of Crystal Falls, 

Michigan R6

7. Generalized logs of drill holes DL-4 and DL-5, northern Michigan R9

8. Q/F/L plots of modal analyses of Michigamme Formation graywacke and

Goodrich Quartzite RIO 

9-12. Photomicrographs of:

9. Graywacke, showing abundance of matrix R13

10. Graywacke, showing felsic volcanic rock fragments R13

11. Graywacke, showing fresh and altered plagioclase R14

12. Goodrich Quartzite, composed mostly of rounded quartz grains R14

Contents III
13-17. Paleocurrent plots of:

13. Michigamme Formation in northern and southern areas R17

14. Copps Formation and Tyler Formation R18

15. Michigamme Formation in northern and southern areas, with all 

measurements replotted together to interpret direction R19

16. Goodrich Quartzite outcrops in northern Michigan R20

17. Goodrich Quartzite outcrops with all measurements replotted together to 

interpret direction R21

18. Photograph of lower slate member of Michigamme Formation in drill 

core R22

19. Q/F/L plots of average modal analyses of gray wacke-slate units of Lake 

Superior region R23

20. Schematic cross section depicting deposition of Michigamme Formation R24

21. Schematic map of paleogeography at time of sedimentation of Michigamme 

Formation R26

TABLES

1. Sedimentological data from measured sections of Michigamme Formation R7

2. Modal analyses of samples of graywacke from northern exposures of 

Michigamme Formation and from Goodrich Quartzite Rll

3. Modal analyses of graywackes from southern exposures of Michigamme 

Formation R12

4. Chemical analyses of samples from southern exposures of Michigamme 

Formation R15

5. Chemical analyses of samples from northern exposures of Michigamme 

Formation (drill cores) R16

IV Contents
CONTRIBUTIONS TO PRECAMBRIAN GEOLOGY OF LAKE SUPERIOR REGION

Sedimentology and Provenance of the 

Early Proterozoic Michigamme Formation and 

Goodrich Quartzite, Northern Michigan Regional 

Stratigraphic Implications and Suggested Correlations

By Richard W. Ojakangas 1

Abstract

The Early Proterozoic Michigamme Formation of northern Michigan was deposited in the southeastern part of the 

Animikie basin. The formation conformably overlies the Goodrich Quartzite and comprises three widespread members a 

lower member of thin-bedded shale, siltstone, and sandstone; 

the Bijiki Iron-formation Member; and an upper member of turbiditic graywacke, siltstone, and mudstone and a few local 

members. The Goodrich Quartzite is interpreted as having 

been deposited in a tidally influenced shallow marine environment. The lower member of the Michigamme is interpreted as 

having been deposited in a tidally influenced environment, the 

iron-formation member as having been deposited below wave 

base in somewhat deeper water, and the upper member as having been deposited in still deeper water with turbidity currents 

being a major depositional mechanism.

Several lines of evidence including paleocurrents, paleogeographic setting, and neodymium isotopes suggest that the 

graywacke of the southern part of the outcrop area was derived 

from the south (Early Proterozoic Wisconsin magmatic terranes, Archean miniplates, and older Early Proterozoic sedimentary units formed on the continental margin), and that the 

graywacke in the northern area was derived from an Archean 

terrane to the north. The tectonic model that best fits the available data is a northward-migrating foreland basin.

INTRODUCTION

The Early Proterozoic, dominantly clastic Marquette 

Range Supergroup (fig. 1), deposited in the eastern part of 

the Animikie basin in the Upper Peninsula of Michigan and

'Department of Geology, University of Minnesota Duluth, Duluth, 

MN 55812, and U.S. Geological Survey.

adjacent Wisconsin, consists of, in ascending order, the 

Chocolay, Menominee, and Baraga Groups (Cannon and 

Gair, 1970). A fourth group, the Paint River Group, may be 

the youngest sequence (Cannon, 1986), but it could instead 

be remnants of a thrust sheet and therefore not the stratigraphically youngest unit (Cambray, 1987; Sims, 1990; 

Sims and Schulz, 1992). The entire succession comprises a 

continental margin assemblage deposited on the south edge 

of the Archean Superior province. The Menominee Group 

contains the iron-formations that have long been of economic significance. The Michigamme Formation, the uppermost unit in the Baraga Group of James (1958), is a darkgray to black turbiditic graywacke, siltstone, and mudstone 

sequence several thousand meters thick. The Tyler and 

Copps Formations in the vicinity of the Gogebic range in 

northwesternmost Michigan and adjacent Wisconsin, both 

also deposited in the Animikie basin, are generally considered correlative with the Michigamme Formation because 

of proximity and lithologic similarity.

The Michigamme, Tyler, and Copps Formations are 

present in the southeastern segment of the Animikie basin 

(fig. 2), on the east side of the 1,100 Ma Midcontinent rift 

system (Morey, 1983a, b). Most of the outcrop area of the 

Michigamme Formation is within the Iron River I°x2° 

quadrangle (Cannon, 1986), and in several llk' quadrangles 

of the western part of the Marquette syncline. In some recent 

publications (Southwick and Morey, 1991; Hoist, 1991), the 

southeastern segment of the Early Proterozoic basin has been 

called the Baraga basin, but in this report the southeastern 

segment is considered part of the larger Animikie basin.

Correlations within the larger Animikie basin have been 

a concern for the last century, largely because of the ironformations in the seven iron ranges of the Lake Superior

Michigamme Formation and Goodrich Quartzite, Northern Michigan R1
Northwest segment

Gunflint range, 

Minn. -Ontario

Goodwin, 1958

\ (Group Animikie 

^-\_-'-^_-^-^

Rove 

Formation

Gunflint 

Ironformation

Basal con- 

, glomerate 

 \member

Mesabi range, 

Minnesota

White, 1954

-^ ^_^''~\ " \_^

Virginia 

Formation

Biwabik 

Ironformation

Pokegama 

Quartzite

Cuyuna range, 

Minnesota

Morey, 1978

Rabbit Lake 

Formation

Trommald 

Formation

(Mille Group(( Lacs -^

/lahnomen 

-ormation

^-\_^~--\-_- -- ^

^frouTCake" 

Formation

Little Falls 

Formation

Glen Township 

Formation

Denham

Southeast segment

Western part 

Gogebic range, 

Wisconsin

Aldrich, 1929

Tyler 

Formation

Ironwood 

Ironformation

Palms 

Formation

-- - -^~~- ^~~~- 

"§ Bad River

>, Sunday 

_<5 Quartzite

o , '

0 /

o , x 

o <^

Eastern part 

Gogebic range. 

Michigan

Sims and 

others, 1984

Formation\ ^-_^-^~^ ^~-^_-^^

Emperor / 

Volcanic /

// Creek 

/^Formation

Palms 

Formation

'~~-^-_^^~\_^^~~^_ ~* 

^-^DoJornjle^^^,

Western 

Marquette 

range, Michigan

Cannon, 1986

~^-~~~ ^ ^- -^-~-~ 

Michigamme 

Formation

Goodrich

Quartzite -^^~*~^^~~-^-^--~,

Negaunee Fronformation

Siamo Slate

Ajibik 

Quartzite ~^_-^""^ ^~

Eastern 

Marquette range, 

Michigan

Gair and 

Thaden, 1968

Goodrich 

Quartzite

Negaunee ironformation

Siamo Slate

Ajibik

Quartzite ~ ^- -~~-^^~-~ ^~~~^

Wewe Slate

Kona Dolomite

Mesnard 

Quartzite

Enchantment 

Lake Formation

Reany Creek 

Formation

Amasa uplift. 

Michigan

Cannon, 1986

Badwater 

Greenstone

Michigamme 

Sfate ^~\_^- ^^ ^

Amasa and 

Fence River 

Formations

Hemlock 

Formation

--^\-^^^^-^ \_

Iron RiverCrystal Falls 

range, Mich.

Cannon, 1986

Fortune 

Lakes Slate

Stambaugh 

Formation

Hiawatha 

Graywacke

Riverton 

Iron-formation

Dunn Creek 

Slate

Badwater 

Greenstone

Michigamme 

Sfate 

-^ - - -^~~- ^~-

Amasa and 

Fence River 

Formations

Hemlock 

Formation

Menominee 

range, 

Wisconsin

Bayley and 

others, 1966

-~^_^'^-_^~\^^~- 

Badwater 

Greenstone

Michigamme 

Sfate 

- ^ ~ - - ^^_

Vulcan Ironformation

Felch 

Formation

-^ - \_^^

Randville 

Dolomite

Sturgeon 

Quartzite

Fern Creek 

Formation

\0araga Grp./Group Paint River Group nee 

|Menom Chocolay Group

Marquette Range Supergroup

Archean rocks, undivided

Figure 1 . Correlation chart for sedimentary and volcanic rock units of Early Proterozoic age in the Animikie basin. From Morey 

and Van Schmus (1988). The Animikie basin as used herein follows the usage of Morey and Van Schmus (1988) and differs from 

the more restricted usage of Southwick and Morey (1991). Southwick and Morey (1991) have shown that the formations within the 

Mille Lacs Croup on the Cuyuna range are mainly fault bounded; a fault separates the Denham Formation from the Glen Township 

and Little Falls Formations, and the latter two formations are separated from the Trout Lake Formation by another fault. Also recently, workers have correlated the Paint River Group with the Baraga Group on structural grounds (Sims and Schulz, 1992) and 

have correlated the Badwater Greenstone and the Hemlock Formation (Sims, 1992). Sims (1991) also has placed the Reany Creek 

Formation in the Late Archean.

region. (See, for example, Van Hise and Bayley, 1897; Leith 

and others, 1935; James, 1958; Cannon and Gair, 1970; 

Cannon and Klasner, 1975.) In the most recent synthesis 

(Morey and Van Schmus, 1988), the Michigamme, Tyler, 

and Copps Formations of the southeastern segment are correlated with units in the northwestern segment, that is, the 

Rove, Virginia, and Rabbit Lake Formations of the Gunflint, 

Mesabi, and Cuyuna ranges, respectively (fig. 1). The Thomson Formation of east-central Minnesota, which has a similar 

lithology, has also generally been considered correlative of 

these graywacke units (Morey and Ojakangas, 1970), However, recent structural interpretations complicate the correlations of these units, for northward thrusting has juxtaposed 

units of differing Early Proterozoic ages in both east-central 

Minnesota (Southwick and others, 1988; Southwick and 

Morey, 1991) and the Upper Peninsula of Michigan (Klasner 

and others, 1991; Gregg, 1993). Southwick and Morey 

(1991) discussed and illustrated correlation problems 

between the northwest and southeast segments of the 

Animikie basin.

Geochronologic data are somewhat equivocal because of 

the lack of datable crosscutting dikes of Early Proterozoic 

age. The data, summarized in Morey and Van Schmus 

(1988), indicate that the Marquette Range Supergroup was 

deposited during the interval 2,100-1,900 Ma. The age of 

the Michigamme Formation is probably closer to the 

younger figure; Sims and Schulz (1992) reported an age of 

1,930 Ma on a carbonate-apatite bed in the iron-formation 

member of the Michigamme Formation in the East Baraga 

basin. Southwick and Morey (1991) suggested that the correlative Animikie Group in Minnesota may be younger than 

1,900 Ma and older than late-tectonic to post-tectonic intrusions 1,820(?)-1,770 Ma.

The rocks of the southeastern segment of the Animikie 

basin (the study area), which include metavolcanic rocks 

as well as the thick sequences of metasedimentary rocks, 

are bordered on the south across the Niagara fault zone 

(fig. 2) by the younger («1,850 Ma) 200-km-wide 

sequence of granitoid and metavolcanic rocks of the Wisconsin magmatic terranes (Morey and Van Schmus, 1988;

R2 Precambrian Geology of Lake Superior Region
97° 96C 95° 94° 93° 92° 91 C 90°

<e

II

ft9

S"

I

49C

^^ """ - -.__,.__ Wabigoon subprov

| ^w

48C

47 C46C

QUETICO FAULT

Rainy Lake area

1 Wisconsin magmatic terranes ^^

Middle Proterozoic

Volcanic, sedimentary, and plutonic rocks of Midcontinent rift system (R:l,100 Ma)

Early Proterozoic 

Turbidites overlying shelf deposits (Animikie basin)

Plutonic and volcanic rocks

Complex continental-margin sequences (Animikie basin)

EXPLANATION 

Archean

Rocks of greenstone-granite terrane 

(Superior province)

Rocks of gneiss terrane

Contact High-angle fault

^ Transcurrent fault Showing relative horizontal movement

 ^ ^ Thrust fault Sawteeth on overthrust block

- - - Trace of Great Lakes tectonic zone (GLTZ)

Trend of magnetic anomaly

Figure 2. Generalized geologic-tectonic map showing distribution of Precambrian rocks and structural elements of the Lake Superior region. The Michigamme Formation of Michigan and Wisconsin is part of the unit "turbidites overlying shelf deposits." (Modified from Sims, 1991; Sims and Day, 1993.) A, Amasa uplift; C, 

Covington; 1C, Iron River-Crystal Falls range; M, Menominee range.
Sims and others, 1989). Whereas the trace element patterns from basaltic volcanic rocks of the Marquette Range 

Supergroup are characteristic of continental tholeiites (rift 

volcanics), those of the Wisconsin magmatic terranes (a 

bimodal suite of basaltic and rhyolitic rocks) are characteristic of tholeiitic and calc-alkalic volcanic rocks of oceanic island arcs (Schulz, 1983; Sims and others, 1989).

The Michigamme Formation was folded, faulted, and 

metamorphosed during the Penokean orogeny. (See for 

example, Cannon, 1973; Klasner, 1978; Alton and Klasner, 

1989; Klasner and others, 1991; Hoist, 1991; Gregg, 1993.) 

The Penokean orogen in northern Michigan has been divided 

into two structural domains (Klasner and others, 1988; Klasner and Cannon, 1989; Klasner and Sims, 1993). The northern domain, north of the Marquette syncline (fig. 3), consists 

of a foreland-basin thrust belt in which deformation was 

largely thin skinned (Gregg, 1993); the southern domain, 

south of the Marquette syncline, consists of a basement arch 

in which deformation was primarily thick skinned, that is, it 

involved the Archean basement as well as the Early Proterozoic rocks (Klasner and Sims, 1993). Details on specific 

areas are presented by Cannon (1974), Puffett (1974), Cannon and Klasner (1980), Foose (1981), Sims and others 

(1984), Klasner and others (1991), and Gregg (1993), among 

others.

Klasner and others (1991) interpreted the presence of 

numerous north-verging folds, thrust faults, and multiple 

deformation in northern Michigan as the product of collisional tectonics. Hoist (1991) compared similar structures in 

east-central Minnesota to those in Michigan, and Southwick 

and Morey (1991) also made such comparisons. Because of 

rather poor outcrops, it is likely that thrusting has disrupted 

the stratigraphy to a greater extent than has been documented.

The rock units of the southeastern Animikie basin, 

including the Michigamme Formation, have been metamorphosed to varying degrees; most rocks are in the chlorite 

zone of the greenschist facies, but higher grade rocks crop 

out in the southern and eastern parts of the study area (James, 

1955; James and others, 1961; Cannon, 1973; Klasner, 1978; 

Morey, 1978). A Rb/Sr isochron age of 1,820±50 Ma (Sims 

and others, 1984) gives a minimum age for the metamorphism. The metamorphism and deformation occurred during 

the Penokean orogeny, about 1,850 Ma. (See for example, 

Sims and Peterman, 1983; Hoist, 1991; Klasner and others, 

1991.)

The Late Archean Great Lakes tectonic zone (fig. 2; 

Sims and others, 1981; Sims, 1991), which separates an 

Archean greenstone-granite terrane to the north from a 

southern gneiss terrane as old as 3,600 Ma (Sims and 

Peterman, 1983), divides the Early Proterozoic basin into 

a northern stable cratonic zone and a southern more 

mobile zone. North of the tectonic front, the Early Proterozoic sedimentary rocks generally have been subjected 

to only low-grade metamorphism and moderately weak

folding, whereas south of it the rocks are intensely 

deformed by multiple deformations and locally are metamorphosed to amphibolite facies.

GENERAL FIELD DESCRIPTION, 

MICHIGAMME FORMATION

The Michigamme Formation has been divided into three 

major members. In ascending order, these are the lower slate 

member, the Bijiki Iron-formation Member, and the upper 

slate member (Leith and others, 1935; Tyler and Twenhofel, 

1952; Cannon and Klasner, 1977). In specific areas, local 

members such as the Greenwood Iron-formation Member 

and the Clarksburg Volcanics Member have been designated 

(Cannon, 1974; 1975). A generalized columnar section for 

the Michigamme Formation in the Dead River basin, north 

of the Marquette trough, was presented by Puffett (1974).

Slate Members

Determining the stratigraphic position of graywacke-siltstone-slate (metamorphosed graywacke, siltstone, and mudstone) in the scattered outcrops in the large area between the 

Marquette syncline and the Gogebic range is generally not 

possible, because of (1) generally broad open folds that may 

repeat the section over broad areas; (2) the presence of thrust 

faults (Klasner and others, 1991; Gregg, 1993); and (3) 

multiple deformation. Consequently, the drill holes 

described following are invaluable for establishing the 

lithology of the lower and upper members of the formation. 

Briefly, examination of the cores indicates that the lower 

member is finer grained than the upper member and that the 

upper member, although dominantly fine grained, contains 

several graded graywacke beds.

Various sedimentary features are present in the 

graywacke beds, including graded beds with internal Bouma 

intervals, mud chip (rip-up) layers, load features, concretions, and flat soles with a lack of primary scour and tool 

marks. Cleavage is prominent in all exposures, and refracted 

cleavage is the rule in the graywacke-slate sequences.

The best exposures of well-developed beds of graywacke 

and slate are roadcuts along U.S. Highway 141 from Covington (fig. 3) southward for 20 km (fig. 4) and a few 

kilometers along Michigan Highway 28 both east and west 

of the junction at Covington with U.S. Highway 141. Other 

accessible outcrops showing excellent beds are present at 

Little Mountain just south of L' Anse; near the west end of 

Lake Michigamme (here the formation contains staurolite 

crystals as much as 1 cm long); at Little Bull Rapids on the 

Paint River south of Crystal Falls,; and at Hemlock Rapids, 

also on the Paint River, northeast of the town of Iron River.

R4 Precambrian Geology of Lake Superior Region
90

0)3.9- 

o 

g3. H. 

ff

I

LAKE SUPERIOR LAKE SUPERIOR

East Bara 9a Basin

'a1 - Clark Creek Basin

Northern ' " -.-':' .' £Complex ; ' '.''.

.................. .. .

,, " ., X

.. KS" IS

, Copps ;r\

Wakefield 'FormationN\;Lafce Gogebic

IRON RIVER- - 

CRYSTAL FALLS orence RANGE Horencel, .

Iron Mountain*. '^x^TSsL.

Paleozoic rocks

Midcontinent rift system rocks

Middle 

Proterozoic

EXPLANATION

Mostly Michigamme Formation, but includes other Early Proterozoic rocks Iron-formation in blackArchean rocks

Contact

Paleocurrent locality

X Drill hole

[ 1 Measured section

Figure 3. Generalized geologic map of Precambrian rocks, northern Michigan and northwestern Wisconsin, showing locations of measured sections, drill holes, and paleocurrent localities. Compiled by R.W. Ojakangas, 1992. Early Proterozoic Wisconsin magmatic terranes lie to south of map

area.
Figure 4. Roadcut showing 1- to 2-m-thick graywacke beds 

of Michigamme Formation. Stratigraphic tops are to right 

(south). The void spaces at upper right are result of the weathering out of concretions. Roadcut on U.S. Highway 141 about 

4.3 km south of the town of Covington (5 km south of the intersection of Michigan Highway 28 and U.S. Highway 141). 

Outcrops total about 4 m high.

Figure 5. Graded graywacke beds of Michigamme Formation 

with refracted cleavage. Tops are to left (north). Roadcut on 

Michigan Highway 28 about 1.6 km east of the town of Covington (5 km west of the intersection of U.S. Highway 41 and 

Michigan Highway 28). Pencil for scale (about 0.8 cm wide).

The Michigamme Formation is fine grained and predominantly slaty over much of the study area, and especially 

north of an east-west line positioned a few kilometers north 

of Covington (figs. 2,3) and including the East Baraga basin 

(fig. 3). This facies relation is shown on the geologic map 

of the Iron River I°x2° quadrangle (lat 46°-47° N., long 

88°-90° W.; Cannon, 1986). Cannon mapped unit Xbms 

(slate) in the northern part of the quadrangle, and unit Xbmg 

(metamorphosed graywacke) occupies the southern twothirds of the quadrangle. Cannon implied by the mapped 

Stratigraphic sequence in the Lake Michigamme area on the 

east edge of the quadrangle that unit Xbms is the lower

Figure 6. Graywacke beds of Michigamme Formation in 

measured section at Little Bull Rapids on the Paint River, about 

10 km southeast of town of Crystal Falls. Tops are to left, so 

beds are slightly overturned. Hammer is 27 cm long.

member of the Michigamme and that unit Xbmg is the upper 

member; the two units are separated by an iron-formation 

unit. However, drill-hole data cited herein following suggest 

that unit Xbms of Cannon is instead largely the upper member, rather than the lower member. It is noteworthy that 

Cannon's metamorphosed graywacke unit (Xbmg) is dominantly fine grained to medium-grained graywacke with 

abundant intercalated slate; even those graywacke beds that 

are several meters thick are fine grained.

In the roadcuts along a 20-km-long stretch of U.S. Highway 141 south of Covington, graywacke is dominant over 

slate, as is indicated on the Iron River I°x2° quadrangle 

(Cannon, 1986). Beds as much as 3 m thick are common, 

and a few are as much as 6 m thick; nevertheless, all beds 

are fine grained or medium grained. Grading is common (fig. 

5) and Bouma A (A-E), B, and A-B beds are the norm; the 

soles of the beds are generally very flat and have sharp 

contacts with the underlying slate. A few sole marks are 

present, as is small-scale crossbedding. Pseudo-sole marks, 

pseudo-ripple marks, and pseudo-flame structures are the 

products of bedding-cleavage intersections. Ubiquitous concretions are generally rotated into cleavage, as are rare mudchips. Also present are clastic dikes (subparallel to 

cleavage), convolutions, soft-sediment deformation features, 

and load features.

Two well-exposed sections of graywacke-slate were 

measured and studied in detail (table 1). One is a 75-m-thick 

section at the dam on the Paint River at Little Bull Rapids, 

about 10 km southeast of Crystal Falls (N'6SW>/4 sec. 24, 

T. 42 N., R. 32 W.), as shown in figure 6, and the other is 

a 13-m-thick section at the west end of Ramsey Island in the 

central part of Lake Michigamme (fig. 3). A third measured 

section, 60 m thick, was studied in less detail in the gorge 

on Silver River (NW corner sec. 26, T. 51 N., R. 32 W.), 11 

km northeast of L'Anse. At the latter locality, pseudo-sole

R6 Precambrian Geology of Lake Superior Region
Table 1 . Sedimentological data from measured sections of Michigamme Formation

[Grain size: M, medium; F, fine. Leader (-), statistically none, locality II; not determined, locality III. Proximality index is the percentage of 

graywacke beds starting with Bouma A plus one-half of the percentage of beds starting with Bouma B (Walker, 1967)]

Section total thickness (meters)

Number and percent graywacke beds

Percent thin siltstone and sandstone

Percent argillite

Graywackes: Percent graded

Average grain size

Average thickness (centimeters)

Range, thickness (centimeters)

Number and percent,

Bouma A beds

AB beds

ABC beds

B beds

Number ungraded, massive

Number ungraded, laminated

Proximality index

I 

Little Bull 

Rapids

74.25

63 (30.7 pet.)

(68.9)

(0.4)

70

M-F

36

8-385

21 (33 pet.)

16 (25)

1(1)

6(10)

8(13)

11 (17)

86

Locality

II 

Lake 

Michigamme

12.7

14 (99.5 pet.)

-

(0.5)

100

F

90

30-240

12 (86 pet.)

-

2(14)

-

-

-

100

III 

Silver River 

Falls

60

(18 pet.)

) A}9\ \ 18ZJ

few

F

<10?

2-120

-

-

few

-

many

-

-

marks, formed by the intersection of bedding and cleavage, 

are present on graywacke beds; the soles are generally very 

flat, grading is not well defined, and load casts, zones of 

soft-sediment deformation, and convolutions exist.

Bijiki Iron-formation Member

The Bijiki Iron-formation Member of Van Rise and Bayley (1897) is a relatively thin (as much as 60 m), lithologically variable unit. It is fine grained, thin bedded, and cherty 

(white and black); it contains black slate (cleaved), varicolored argillite-siltstone (lacking cleavage), iron carbonate, 

and, locally, iron oxides or grunerite. More than 5 million 

tons (2,000-pound tons) of high-grade iron oxide ore has 

been produced from the formation (Klasner and Cannon, 

1978). The unit is best developed in the vicinity of Lake 

Michigamme, at the west end of the Marquette syncline, and 

can be traced westward around the west end of the northern 

complex of the Marquette district in drill cores as well as by 

geophysical means. The extent of the member is best displayed on a map by the Cleveland-Cliffs Iron Company 

(1975). The occurrence of iron-formation at several horizons 

in the Michigamme Formation creates a stratigraphic problem. Structural repetitions may be responsible for at least

some of these occurrences; correlation, therefore, is difficult. 

For further detail, see the description of map units in the 

Iron River I°x2° quadrangle (Cannon, 1986).

In the Negaunee quadrangle (Puffett, 1974), iron-formation is present at the approximate stratigraphic position of 

the Bijiki; exposures in sec. 15, T. 48 N., R. 26 W. (Puffett, 

1974, p. 37) consist of thinly bedded chert, goethite-limonite, and argillite. The Greenwood Iron-formation Member 

in the Greenwood quadrangle (Cannon, 1974) also is 

approximately stratigraphically equivalent to the Bijiki. The 

Bijiki can be traced as a magnetic high across the northern 

part of the Witch Lake 15' quadrangle (Cannon and Klasner, 

1976a).

Phosphorite has been described from iron-formation at 

two localities in the Baraga basin (Mancuso and others, 

1975), as well as elsewhere in the lowermost 100-200 m of 

the Michigamme Formation (Cannon and Klasner, 1976b).

DRILL HOLE DESCRIPTIONS

A few drill holes penetrate much or all of the Michigamme Formation in the study area. Six vertical holes (fig. 

3) were drilled in 1977-1978 by Bendix Field Engineering

Michigamme Formation and Goodrich Quartzite, Northern Michigan R7
Corporation, which was subcontracted by the Michigan 

Geological Survey and funded by the U.S. Department of 

Energy. J & L Steel Company drilled one vertical hole, and 

Cleveland-Cliffs Mining Company and Minatome Corporation drilled an inclined hole in 1983. These eight holes were 

drilled as stratigraphic test holes2 for assessment of uranium 

potential (Trow, 1979). In general, the same three members 

of the formation that crop out in the area are present in the 

drill holes (1) the lower slate member, (2) the Bijiki Ironformation Member, and (3) the upper slate member. The 

cores consist largely of black slate, metasiltstone, and minor 

metagraywacke; carbon and sulfide minerals are common. 

Trow (1979) has described the cores and presented some 

chemical data. The iron-formation in most of the drill cores 

consists of thin beds of white chert, brown-tinged iron carbonates, and minor iron oxides. Iron sulfides are locally 

present. The Bijiki in the drill cores was described in detail 

by Trow (1979, p. 24-26).

Clark Creek Basin Drill Hole

Bendix's drill hole DL-5 in the Clark Creek basin (fig. 

3) was logged and sampled (fig. 7). The hole penetrated 233 

ft of the upper slate member, 47 ft of the Bijiki Iron-formation Member, 146 ft of the lower slate member, and 94 ft of 

the Goodrich Quartzite before ending in Archean metarhyolite.

Argillite and siltstone are dominant in the upper member, 

but some graded graywacke beds (Bouma A, A-B, B, and 

A-B-C) as much as 10 cm thick are present. The Bijiki 

consists of chert and carbonate with interbedded black slate; 

a possible stromatolite layer 30 cm thick was logged in the 

original study (Trow, 1979), but this may be a tectonically 

deformed carbonate layer.

Graywacke is essentially absent in the lower member. 

Rather, thin (less than 2 cm thick) siltstone beds alternate 

with thin argillite beds, and black shale partings alternate 

with thin light-tan sandstone beds that are similar to those 

in the underlying Goodrich Quartzite.

Dead River Basin Drill Hole

Bendix's drill hole DL-4 (4A and 4B) in the Dead River 

basin (fig. 7) intersected 2,890 ft (2,630 ft actual thickness 

according to Trow, 1979) of the upper member, 40 ft of the 

Bijiki, and 93 ft of Goodrich Quartzite; it penetrated weathered Archean tonalite basement at 3,119 ft. I reinterpreted 

the upper 33 ft of the Goodrich as assigned by Trow as being

2These drill holes were logged in feet and are reported herein in feet. 

To convert to meters, multiply feet x 0.3048.

the lower member of the Michigamme Formation, for it 

closely resembles that member in hole DL-5. Thus, the 

thickness of the Goodrich is about 60 ft.

The upper member in hole DL-4 is markedly coarser 

grained than in the other holes, as was noted by Trow (1979, 

p. 34). Slate is the dominant lithology, but medium- to 

coarse-grained graded graywacke beds are abundant. Bouma 

A, A-B, A-B-C, and A-B-C-D beds are present; many beds 

are as thick as 1 meter, and a few are 2-3 m thick. However, 

many beds lack grading. Because of the great thickness of 

the upper member (2,630 ft) and its general uniformity, I did 

not log the entire member; only the lower 400 ft was 

inspected box-by-box, and only every sixth core box (each 

with 15 ft of core) was inspected for the bulk of the member.

The Bijiki Iron-formation Member is a unit of variable 

lithology, consisting of white cherty-carbonate rock, pyritic 

black slate with massive sulfide beds as much as 8 cm thick, 

and minor graphite-rich beds.

The underlying lower slate member as reinterpreted consists of laminated argillite and thin sandstone.

The lowest unit in the drill hole, the Goodrich Quartzite, 

consists of an upper zone of thin-bedded sandstone interlayered with very thin black shale, and a lower zone of thicker 

massive gray sandstone with sparse black shale partings. The 

contact with the underlying Archean tonalite is sharp and 

unconformable, and the tonalite is only slightly weathered.

East Baraga Basin Drill Holes

Three holes DL-1, DL-3, and DL-7 were drilled by 

Bendix in the East Baraga basin, as designated in figure 3. 

Hole DL-1 penetrated nearly 2,100 ft (1,978 ft actual thickness according to Trow, 1979) of the upper slate member, 

which contains only a few graywacke beds; it did not reach 

Archean basement. Hole DL-3 was terminated at 1,634 ft 

after penetrating 1,471 ft of the upper member. Hole DL-7 

penetrated 326 ft (285 ft actual thickness according to Trow, 

1979) of the upper slate member, 86 ft of Bijiki Iron-formation Member, and, below, weathered Archean granite. 

Apparently neither the lower member of the Michigamme 

Formation nor the Goodrich Quartzite was deposited here; 

this area must have been a topographic high during Goodrich 

and early Michigamme time, as noted by Trow (1979).

About 21 km northwest of hole DL-7, J & L Steel 

Company drilled hole DDH-116 as a uranium test. This drill 

hole penetrated 847 ft of the upper member, which consists 

of carbonaceous, chloritic, and pyritic argillite with only 

minor graywacke; 70 ft of Bijiki Iron-formation Member; 

and bottomed in Archean granite (Burns, 1975). As in drill 

hole DL-7, the lower slate member is missing, presumably 

because of nondeposition.

R8 Precambrian Geology of Lake Superior Region
DEAD RIVER BASIN 

DL-4

CLARK CREEK BASIN 

DL-5

METERS FEET

150 500- 

300 1000-

450 1500- 

600 2000- 

750 2500- 

900 3000-

'O'.&b

 

«« *

1 « * » 

 

 _! -. .

 _._..

 

_

 . i

X X

x x x

Michigamme Formation

_

upper slate 

member

/

Bijiki Iron-formation 

Member

/ / lower slate 

/ / member

-"-""''^ Goodrich Quartzite

Late Archean

METERS FEET 

0 0 -

150 500 -

O

Pleistocene glacial 

deposits

0)

II

to co

.9>E 

to

300 1000-

X X

x x 

x x

VAVW

upper slate 

member

Bijiki Iron-formation 

Member

lower slate 

member

Goodrich Quartzite

Late Archean

Figure 7. Generalized logs of drill holes DL-4 and DL-5, northern Michigan. Locations shown in figure 3. Total depth not given.

Michigamme Formation and Goodrich Quartzite, Northern Michigan R9
Amasa Drill Hole

Bendix's hole DL-6 was drilled about 14 km northnorthwest of the town of Amasa (fig. 3). It was terminated 

at 1,093 ft after penetrating a true stratigraphic thickness of 

286 ft of alternating carbon-rich and carbonate-rich chloritic 

graywacke and argillite intercalated with cherry and slaty 

layers of iron-formation (Trow, 1979). Trow interpreted the 

cherty and slaty layers of iron-formation to be either the 

Bijiki Iron-formation Member or the lower slate member.

Gwinn Area Drill Hole

Drill hole C-8, an inclined 900-ft hole near the town of 

Gwinn (fig. 3), about 32 km south of Marquette, was drilled 

jointly by Cleveland-Cliffs Mining Company and Minatome 

Corporation in 1983 in search of uranium. The upper 102 ft 

of conglomerate, in which chert and hematite clasts, gritstone, and sandstone are arranged into 15 fining-upward 

(fluvial?) sequences, is likely post-Proterozoic in age, for 

Paleozoic rocks blanket the area just 3 km to the south of 

the drill hole. A thickness of about 100 ft of black slate and 

minor graywacke beds overlies about 140 ft of iron-formation. These rocks overlie about 400 ft of black graphitic slate 

with minor pyritic laminae and thin beds of graywacke; 36 

ft of basal arkose lies on Archean granite. The penetrated 

granite contains a number of "fresh" granite zones and 

altered shear zones, features which may indicate the presence of a major shear zone at the base of the Proterozoic 

section.

PETROGRAPHY

Most of the graywacke from the Michigamme Formation 

is too fine grained, recrystallized, cataclasized, or altered to 

allow determination of the original ratios of constituents; 

therefore, most petrographic observations are qualitative. 

Some petrographic information gleaned from drill cores has 

been provided by Trow (1979). One of Trow's observations 

was that the upper member lacks potassium feldspar; however, I noted orthoclase and microcline in many thin sections, and I verified their presence by staining thin section 

heels. Much potassium feldspar has undoubtedly been 

altered to sericite.

A total of 28 thin sections of better preserved Michigamme graywacke were point-counted (600 points each) 

(tables 2, 3). Fourteen samples are from the "northern area" 

(north of the arbitrary east-west line through Covington), 

including three drill core samples, and 14 are from the 

"southern area." Of the 28 samples, 19 plot on a Q/F/L 

diagram as arkosic graywackes, 7 as feldspathic graywackes, 

and 2 as sublithic graywackes (fig. 8); however, these rock 

names probably do not reflect the original compositions of 

the graywackes, as discussed following.

Q/F/L ratios (quartz/feldspar/lithics or rock fragments) 

were calculated for each of the 28 samples. Prior to making

Subfeldspathic 

graywacke

Quartz wacke

Sublithic 

graywacke

EXPLANATION

 Northern Michigamme graywacke 

® Mean of northern Michigamme

graywacke samples 

o Southern Michigamme graywacke 

© Mean of southern Michigamme

graywacke samples 

A Goodrich Quartzite

Figure 8. Q/F/L plots of modal analyses of 28 thin sections of 

graywacke of Michigamme Formation and 5 thin sections of 

Goodrich Quartzite. Q-pole, common (monocrystalline) 

quartz; F-pole, all feldspars; L-pole includes volcanic and 

metamorphic rock fragments. The rock fragments include polycrystalline quartz grains and metachert. Triangle modified from 

Petti John and others (1987).

the Q/F/L determinations, I made two adjustments of the 

original point-count data (tables 2, 3): (1) The plutonic rock 

fragment percentages were divided equally between feldspar and quartz, because the "L" component in standard 

sedimentological procedures generally excludes plutonic 

fragments. (2) Polycrystalline quartz (recrystallized and 

sutured types) and chert were counted as metamorphic rock 

fragments in 15 of the 28 samples. The other 13 samples 

contain large quantities of recrystallized quartz interpreted 

to indicate deformation after deposition rather than derivation from metamorphic source rocks; therefore, this quartz 

was not plotted as rock fragments on the "L" pole. The 14 

northern samples have an average Q/F/L ratio of 61:27:12, 

and the 14 southern samples have an average Q/F/L ratio of 

60:31:9. Thus, there is no appreciable difference between 

the average compositions of sample? from the two areas, 

although differences might have existed prior to postdepositional changes. Note that the ranges of the three constituents are large (tables 2, 3).

The fine-grained matrix of chlorite, sericite, biotite, epidote, and fine-grained quartz-feldspar in the Michigamme 

Formation samples totals from 20 to 77 percent (X = 53 

percent) in the 28 samples (fig. 9). This matrix may be in

RIO Precambrian Geology of Lake Superior Region
Table 2. Modal analyses of samples of graywacke from northern exposures of Michigamme Formation and from Goodrich Q

[x, less than 1 percent; leader (-), not identified]

Graywacke

Sample Number 78-

M-39D M^2

2

f

3

n

o1

£5*

i.

^

§_2. n'

3-

o 

g

1.

z

o

^

i

QUARTZ

Common

FELDSPAR

Plagioclase

Orthoclase

Microcline

Perthite

Total

ROCK FRAGMENTS

Volcanic, felsic-intermediate

Volcanic, intermediate-mafic

Plutonic1

Metamorphic

Mica pellets2

Total

MISCELLANEOUS GRAINS

MATRIX-CEMENT

Quartz

Carbonate

Sericite3

Chlorite3

Biotite3

Fine quartz and feldspar

Epidote

Total

Q/F/L Q

F

L

18

6

8

-

-

14

-

x

(3)

2

-

2

x

.

X

12

17

.

28

9

 

66

53

41

6

34

13

7

1

-

21

2

.

(3)

7

-

9

-

-

4

12

8

-

9

3

 

36

53

33

14

M-5

20

9

6

-

1

16

3

4

(3)

3

-

10

-

-

_

.

16

25

9

3

 

53

46

37

17

M-6

40

14

15

x

x

30

1

x

(9)

8

-

9

x

-

X

6

6

4

3

1

 

20

51

37

12

M-10

39

10

9

-

1

20

8

x

(3)

x

-

8

-

.

_

.

7

11

15

-

 

33

57

30

13

M-ll

23

7

5

-

-

12

1

(2)

7

-

8

1

.

x

14

9

28

5

 

56

53

29

18

82-

M-18D

29

-

1

-

-

5

4

.

(2)

-

(7)

4

5

-

.

27

27

-

3

x

57

74

11

15

M-18F

39

-

3

x

-

6

5

.

(1)

-

(6)

5

2

-

.

30

13

-

6

x

49

83

13

4

M-18G

31

3

x

3

-

6

2

.

(1)

-

(3)

2

x

-

.

30

20

4

5

x

59

77

17

6

M-18K

37

3

1

x

1

5

3

.

(x)

-

(5)

3

2

.

_

28

13

8

3

-

52

80

12

8

M^JE

29

14

13

2

-

29

2

.

(9)

4

-

6

1

.

10

.

20

5

x

35

45

46

9

4A-346

25

2

7

-

-

9

1

x

-

4

-

5

4

-

1

41

8

-

6

x

56

63

24

13

DL4B-996

28

6

6

.

-

12

5

.

(2)

5

-

10

5

-

x

32

4

-

9

-

45

57

24

19

4B-1

1

4

4

x

(x

2

4

20

3

15

75

55

29

1

1 Recounted as quartz and feldspar. Parentheses refer to the recounting.

2Recounted as feldspar and felsic volcanic rock fragments. Parentheses indicate recounting.

3Sericite, chlorite, and biotite counted together but divided here on estimated abundances.
Table 3. Modal analyses of graywackes from southern exposures of Michigamme Formation 

[x, less than 1 percent; leader (-), not identified]

Sample Number

QUARTZ:

Common

FELDSPAR:

Plagioclase

Orthoclase

Perthite

Total

ROCK FRAGMENTS:

Volcanic, felsic-intermediate

Volcanic intermediate-mafic

Plutonic1

Metamorphic

Total

MISCELLANEOUS GRAINS:

MATRIX-CEMENT:

Carbonate

Sericite2

Chlorite2

Biotite2

Fine quartz & feldspar

Epidote

Total

Q/F/L Q

F

L

78-M112A

23

6

7

X

13

-

X

(6)

9

9

X

-

17

17

-

20

-

53

49

30

21

113B

18

7

8

-

15

3

-

(4)

5

8

X

2

.

22

-

25

10

59

42

36

22

122B

10

3

3

-

6

3

-

(1)

4

7

-

-

32

16

-

28

1

77

45

24

31

124

23

4

6

-

10

X

-

(x)

-

X

X

4

20

11

-

30

1

66

70

29

1

140B

16

8

9

-

17

-

-

(x)

1

1

X

1

.

.

47

14

4

66

48

50

2

141B

13

6

7

-

13

2

-

(2)

5

7

x

3

36

17

-

10

1

67

40

40

20

142

21

4

3

x

7

-

x

(x)

3

3

x

1

29

.

-

32

8

70

69

22

9

143A

41

8

4

-

12

-

x

(6)

1

1

x

5

12

5

5

18

-

45

76

21

3

151B

30

7

5

x

12

1

x

(4)

4

5

1

x

13

12

12

14

-

51

62

26

12

Recounted as quartz and feldspar. Parentheses indicate recounting.

2Sericite, chlorite, and biotite counted together but divided here on estimated abundances.
Figure 9. Photomicrograph of graywacke of Michigamme 

Formation showing abundance of matrix. Most distinguishable 

sand grains in this view are quartz. Field of view about 1.8 mm 

wide. Sample 78-M-141B from roadcut on U.S. Highway 141 

about 8 km south of town of Covington.

Figure 10. Photomicrograph of graywacke of Michigamme 

Formation showing abundance of felsic volcanic rock fragments, as at upper right and lower left. A more mafic chloritized (greenstone) volcanic rock fragment is dark grain near 

center. Microcline grain at lower middle right and altered feldspar at upper left. Field of view about 1.8 mm wide. Sample 

86-MI-12B from Falls River just west of town of L'Anse.

part or totally a product of alteration and recrystallization of 

felsic volcanic rock fragments, other soft rock fragments 

such as intraformational shale chips, and possibly even feldspar. A total of 24 of the 28 samples contain felsic-intermediate volcanic rock fragments, varying in amount from a 

trace to 16.8 percent (X = 4.4 percent) in the 14 northern 

samples (fig. 10) and from zero to 12.9 percent (X =2.8 

percent) in the 14 southern samples. In four of the northernmost graywacke samples from L'Anse, 3-7 percent of the 

grains are "mica pellets," which are interpreted as totally 

altered felsic volcanic rock fragments or possibly feldspar 

grains.

Plagioclase and potassium feldspar (orthoclase, microcline, and minor perthite) are present in subequal amounts; 

most is altered, but some is fresh (fig. 11). Plutonic 

("granitic") rock fragments of plagioclase-quartz or

potassium feldspar-quartz average 6.8 percent of the grains. 

Metamorphic rock fragments (argillite-slate-schist) are 

present in small amounts in five northern samples and six 

southern samples; in tables 2 and 3, polycrystalline quartz 

grains (recrystallized and sutured types) are listed as metamorphic rock fragments, and these grains constitute the 

majority of this component.

Five modal analyses of the basal Proterozoic (Goodrich) 

quartzites are included in table 2 and on the triangle of figure 

8. A representative microscopic field of view is shown in 

figure 12.

CHEMISTRY

Major element analyses are sparse for the Michigamme 

Formation. The most complete chemical data are given by

Michigamme Formation and Goodrich Quartzite, Northern Michigan R13
Figure 11. Photomicrograph of graywacke of Michigamme 

Formation showing fresh plagioclase (center) and altered plagioclase (lower right). Other sand- and silt-sized grains are 

quartz and feldspar. Field of view about 1.8 mm wide. Sample 

78-M-141B from roadcut on U.S. Highway 141 about 8 km 

south of town of Covington.

Figure 12. Photomicrograph of Goodrich Quartzite. Composed mostly of rounded quartz grains. Fresh plagioclase at upper left; fresh microcline at lower left. Minor silica cement and 

sericite matrix. Field of view about 1.8 mm wide. Sample from 

Arvon Hill about 17.7 km east-northeast of town of L'Anse.

Sims and others (1984) for samples from the area of Watersmeet (fig. 3); six of their Michigamme analyses are included 

with a few others in table 4.

The CIA (chemical index of alteration) of Nesbitt and 

Young (1982) can be used to indicate the weathering history 

of a sediment. For example, it can be used to determine 

whether a graywacke-mudstone sequence had a direct volcanic origin or is derived from a weathered volcanic terrane. 

(See Bailes, 1980; Ojakangas, 1986.) The indices for the 

Michigamme and related samples (all from the southern 

outcrop area of the Michigamme) range from 49.2 to 71.3 

(table 4), perhaps indicating considerable variation in the 

amount of chemical weathering in the source areas, assuming the samples have not undergone chemical alteration during diagenesis, metamorphism, and (or) recent weathering. 

However, the CIA values undoubtedly also vary with grain

size: those with more original clayey matrix should have 

higher amounts of Na2O and K^O and hence lower CIA 

values.

As for the northern exposures of the Michigamme, no 

samples were available for chemical analyses, except for 5- 

ft composite samples from drill holes (table 5), which were 

analyzed. These samples are included here even with their 

composite nature, and the analyses were used for the calculation of the CIA index because of their low CaO values. 

They indicate a lack of diagenetic or metamorphic calcite.

The Badwater Greenstone and the Hemlock Formation, 

both bimodal volcanic units within the Baraga Group 

(Cannon and Klasner, 1975), have compositions similar to 

that of continental and oceanic basalts (Schulz, 1983,1984). 

Schulz interpreted these rocks as indicating a rift environment, comparable to volcanic rocks in the Keweenawan

R14 Precambrian Geology of Lake Superior Region
Table 4. Chemical analyses of samples from southern exposures of Michigamme Formation 

[CIA, chemical index of alteration]

Sample 

SiO2

A1A

FeA

FeO

MgO

CaO

Na2O

K2O

H2O

TiO2

P205

MnO

CO2

CIA

1

57.94

18.88

1.26

6.73

3.21

.91

1.69

3.45

3.93

.92

.22

.07

.06

69.8

2

60.03

17.85

1.14

7.16

3.15

.44

1.64

3.41

3.74

.95

.09

.03

.12

71.3

3

58.03

15.00

3.67

5.82

1.64

.26

3.52

3.60

4.30

.64

.16

.09

.03

59.6

4

63.2

16.4

1.2

3.7

1.6

3.9

4.4

2.4

1.06

.70

.24

.06

.02

49.2

5

58.5

16.4

.33

9.3

3.0

2.0

3.1

2.0

2.85

.87

.14

.06

.08

60.1

6

67.6

14.6

.61

6.0

2.4

1.8

3.4

1.5

1.85

.70

.13

.04

.02

58.2

7

60.1

16.0

2.0

7.1

3.0

2.9

2.8

1.9

1.77

.85

.13

.09

.08

57.2

8

63.3

16.8

1.3

5.9

2.7

1.9

3.4

2.6

1.96

.79

.19

.03

.01

58.6

9

66.4

14.9

.82

5.4

2.3

1.7

4.6

.51

2.07

.70

.12

.03

.02

57.0

SAMPLE DESCRIPTIONS

1. Nanz, 1953, table 1, analysis 8, roadcut U.S. Highway 141, about 10 km S. of Covington.

2. Nanz, 1953, table 1, analysis 9, roadcut U.S. Highway 141, about 5 km S. of Covington.

3. Nanz, 1953, table 1, analysis 33, slate from footwall strata of Crystal Falls district, sec. 8, T. 42 N, R. 32 W.

4. Sims and others, 1984, table 7, sample No. D2433, Marenisco-Watersmeet area. 

5-9. Sims and others, 1984, table 7, sample Nos. D2434, D2435, D2436, D2437, and D2440, respectively.

Midcontinent rift system and the Triassic basins of eastern 

United States.

Neodymium isotopic data (Barovich and others, 1989) 

from three northern samples and four southern samples of 

Michigamme Formation (the former presumably from the 

lower member of the Michigamme Formation and the latter presumably from the upper member of the formation) 

have been interpreted by Barovich and others to indicate 

that the northern samples had an Archean source (e Nd(t) 

values from -10.8 to -6.6) and that the southern samples 

had an Early Proterozoic source (e Nd(T) values from -0.9 

to +1.3). However, the designation of all three northern 

samples as being from the lower member is likely erroneous. Sample 5 of Barovich and others (1989) (sec. 8, T. 47 

N., R. 27 W.), taken from west of Ishpeming, is indeed

from the lower member, but their sample 6 (sec. 9, T. 50 

N., R. 33 W.), taken from Little Mountain, may have 

come from a thrust block (Klasner and others, 1991); if so, 

its original stratigraphic position within the Michigamme 

Formation is uncertain. Their sample 7 (sec. 26, T. 51 N., 

R. 32 W.) is from the Silver River Falls locality at the 

west end of the East Baraga basin. Inasmuch as drill holes 

DL-1, DL-3, and DL-7, as well as DDH-116 (Burns, 

1975), all from the East Baraga basin (fig. 3), contain only 

the upper member of the Michigamme (deposited upon 

iron-formation), the lower member is absent. Accordingly, 

their sample 7 is likely to come from the upper member of 

the Michigamme rather than the lower member of the 

Michigamme. Similar stratigraphic conclusions were 

reached by Trow (1979, p. 21).

Michigamme Formation and Goodrich Quartzite, Northern Michigan R15
Table 5. Chemical analyses of samples from northern exposures of Michigamme Formation (drill cores)

Sample ~

SiO2

A1A

Fe203

MgO

CaO

Na2O

K.O

TiO2

P205

MnO

CIA

1

60.4

18.9

8.55

3.33

.40

1.55

4.07

.84

.11

.04

71.1

2

65.2

16.9

9.21

3.10

.32

2.62

2.82

.77

.10

.03

68.0

3

67.9

16.3

6.04

2.86

.66

2.28

3.26

.66

.11

.03

65.8

4

64.7

16.7

7.92

3.07

.22

2.42

2.69

.69

.02

.03

69.6

5

61.0

19.8

8.16

2.65

.23

.82

5.01

.73

.03

.02

73.3

6

64.7

15.1

6.75

3.12

.77

3.44

1.58

.61

.11

.05

63.2

7

65.8

15.8

7.53

3.86

.40

.62

3.08

.53

.04

.04

75.7

8

57.9

21.5

7.04

3.32

.27

1.43

5.20

.69

.12

.03

71.7

9

62.2

18.0

8.08

3.19

.71

3.22

2.66

.78

.11

.06

65.6

	SAMPLE DESCRIPTIONS

1. Trow, 1979, Appendix, sample 1-224-229, p. 96, 5 ft composite, Hole DL-1, East Baraga basin.

2. Trow, 1979, Appendix, sample 1-1244-1249.

3. Trow, 1979, Appendix, sample 3-504-509, p. 97, 5 ft composite, Hole DL-3, East Baraga basin.

4. Trow, 1979, Appendix, sample 3-1314-1319.

5. Trow, 1979, Appendix, sample 5-454-459, p. 98, 5 ft composite, Hole DL-5, Clark Creek basin.

6. Trow, 1979, Appendix, sample 4-709-714, p. 99, 5 ft composite, Hole DL-4, Dead River basin.

7-9. Trow, 1979, Appendix, samples 4-1069-1074, 1-2059-2064, 4-2239-2244, respectively.

Therefore, the conclusion of Barovich and others 

(1989) that the lower part of the Marquette Range Supergroup had an Archean source and the upper member of the 

Michigamme Formation had an Early Proterozoic source 

needs some modification. One and possibly two of the 

samples from the northern Michigamme are stratigraphically from the upper member of the Michigamme; therefore, both the lower part of the Marquette Range 

Supergroup and the upper, member of the Michigamme 

Formation in the northern outcrop area had Archean 

sources. Furthermore, the tectonic scenario is so complicated (Gregg, 1993) that some of the samples from the 

southern Michigamme of Barovich and others (1989) 

could be upthrusted lower Michigamme rather than upper 

Michigamme. The available data indicate that the northern 

samples had an Archean source and the southern samples 

had an Early Proterozoic (southern) source, regardless of 

stratigraphic position within the Marquette Range 

Supergroup. However, it would be desirable to have a 

larger Michigamme Nd data base.

PALEOCURRENT ANALYSIS

Metagraywacke and Metasiltstone

Paleocurrent indicators are uncommon in the metagraywacke beds of the Michigamme Formation, and only 51 

paleocurrent features were measured (fig. 13). A total of 15 

sole marks was measured; 7 of these are flute casts (scour 

marks) and 8 are various elongate sole marks, mostly groove 

casts and scour channels. The bottoms (soles) of most beds 

are very flat and featureless, except for cleavage-bedding 

intersections that have produced abundant "pseudo-sole 

marks."

A few small-scale crossbeds were measured in the C 

intervals of Bouma A-B-C beds. Small-scale crossbedding 

in thin metasiltstone-slate sequences found between thicker 

metagraywacke beds provided most of the 35 crossbed measurements; such metasiltstone beds could be distal parts of 

turbidite beds (Bouma C beds). One low-relief scoured channel was also measured.

R16 Precambrian Geology of Lake Superior Region
wNORTHERN AREA 

N

WSOUTHERN AREA

EXPLANATION 

Crossbeds

Flute cast

Groove cast

Scour channel

Total number of measurements

Figure 13. Paleocurrent plots of measurements in graywackeslate units of northern and southern exposures of the Michigamme Formation. Note that groove casts and scoured channels are plotted on both sides of diagrams, as they do not 

indicate a unique current sense.

Of the 51 measurements, 13 are from four outcrop areas 

in the northern part of the study area, and 38 are from six 

outcrop areas in the southern part of the study area; Covington is the approximate east-west dividing line (fig. 3). The 

paleocurrent plots for the northern and southern parts of the 

study area are summarized in figure 13.

Locations of outcrops of Michigamme Formation from 

which paleocurrent measurements were obtained, plus types 

of measured sedimentary structures, are as follows: 

"Northern area" outcrops:

1. Silver River Falls area, NW corner sec. 26, T. 51 N., 

R. 32 W. (two crossbeds and two flute casts).

2. Falls River, upstream from Highway 28 bridge at 

L'Anse, sec. 9, T. 50 N., R. 33 W. (one crossbed and two 

flute casts).

3. Slate River, south of bridge on road to Skanee, C W. 

edge sec. 9, T. 51 N., R. 31 W. (two crossbeds).

4. Tibbett's Falls on Sturgeon River, SW»/4 sec. 5, T. 

48 N., R. 34 W. (one flute cast, two groove casts, and one 

channel scour). 

"Southern area" outcrops:

1. Roadcuts on Highway 141, south of Covington, 

NWV4SEV4 sec. 36, T. 47 N., R. 34 W. (six crossbeds, one 

flute cast, and one groove cast).

2. Roadcuts on Highway 141, south of Covington, 

W&NW1/4 sec. 12, T. 47 N., R. 34 W. (one flute cast 

and three groove casts).

3. Roadcut on Highway 141, just south of railroad 

tracks in Covington (two crossbeds).

4. Roadcut, C S»6 sec. 16, T. 46 N., R. 35 W. (14 

crossbeds).

5. Hemlock Rapids on Paint River, SEi/4 NE»/4 sec. 23, 

T. 44 N., R. 34 W. (one crossbed, one flute cast, and one 

groove cast).

6. Little Bull Rapids, dam area, on Paint River, 

N1&SW/4 sec. 24, T. 42 N., R. 32 W. (seven crossbeds).

For each outcrop from which measurements were made, 

the master bedding was rotated back to a horizontal configuration around the strike of the beds. Only this one-tilt 

rotation was utilized, because the fold axes throughout most 

of the study area are subhorizontal or have only moderate 

plunges. Probable northward thrusting and multiple deformation in the region (Klasner and others, 1991; Gregg, 1993) 

may have affected the readings to some degree. In interpreting the measurements, this possible error should be borne in 

mind. Also, the total number of measurements is obviously 

too small for statistical analysis.

The correlative Copps Formation between Lake Gogebic 

and Wakefield (fig. 3) yielded only 11 paleocurrent measurements; 9 are small-scale crossbeds (mostly in siltstone 

beds, but a few are from the C interval of Bouma beds), and 

2 are sole marks (flute casts). The paleocurrent plot gives a 

very broad paleocurrent trend to the west, north, and east 

(fig. 14A). Lineations are problematical in the Copps outcrop

Michigamme Formation and Goodrich Quartzite, Northern Michigan R17
CORPS FORMATION 

N

TYLER FORMATION

EXPLANATION 

 Flute cast

I Crossbeds 

Groove cast

f 11 j Total number of measurements

Figure 14. Paleocurrent plots of measurements in A, Copps 

Formation, and B, Tyler Formation. (Data on Tyler Formation 

from Alwin, 1976.)

area, so the effect of folding is unknown; however, only a 

one-tilt correction was applied to the data.

In a study of the correlative Tyler Formation on the 

Gogebic range (fig. 3), Alwin (1976) found a prominent 

northwestward paleocurrent trend (fig. 14). Lineations in the 

Tyler are generally subhorizontal so only a single tilt correction was deemed necessary. It is possible that the Tyler 

Formation was thrust northward and that the Tyler outcrop 

belt is allochthonous (Klasner and others, 1991). Nevertheless, I assume that the Tyler behaved as a block and that the 

paleocurrent indicators were not rotated relative to each 

other, nor was the entire block rotated either clockwise or 

counterclockwise.

In summary, the measurements from the metagraywacke-metasiltstone-slate sequences of the Michigamme and correlative formations have an apparent 

dominant southerly trend in the northern outcrop areas and 

an apparent dominant northerly trend in the southerly areas, 

as shown in figure 15. The paleocurrent data of figure 13 

are generalized in figure 15, with all the measurements plotted on two rose diagrams. The total numbers of measurements in the northern and southern areas (only 13 and 38, 

respectively) are small; nevertheless, fairly strong unimodal 

patterns are evident.

Goodrich Quartzite

Paleocurrent indicators in the gently dipping basal 

quartzite beds of the exposed Early Proterozoic succession, 

considered as Goodrich Quartzite by Cannon (1986) and by 

me, were measured at four localities near the west end of 

the Archean northern complex. Figure 16 shows detailed 

paleocurrent plots divided out by sedimentary structure 

from these four localities, and figure 17 is a map showing 

the localities and generalized data combined into one rose 

diagram per locality.

At Canyon Falls on the Sturgeon River, the southernmost 

of the four quartzite localities, the pattern indicates that 

currents were toward the north, west, and south (based on 

24 measurements). Parallel beds as much as 30 cm thick 

dominate at this locality, but planar crossbeds as much as 8 

cm thick and trough crossbeds as much as 20 cm thick are 

present. Very fine mud drapes (flaser bedding) are rare. At 

the "Near Canyon Falls" locality, about 1.6 km north-northeast of Canyon Falls, the pattern (n=17) is similar; currents 

were to the southwest and northwest, both trough and planar 

crossbeds are present; troughs are as much as 2 m wide and 

crossbed sets are 10-50 cm thick.

At Pike's Peak, about 25 km north-northeast of Canyon 

Falls, feldspathic quartzite and conglomerate of the Goodrich contain trough-type crossbeds; troughs are on the scale 

of 1 m wide and crossbed sets are 15-30 cm thick. The 

paleocurrent pattern (n=20) is toward the northwest.

R18 Precambrian Geology of Lake Superior Region
IRON RIVER- ' 

CRYSTAL FALLS 

RANGE

EXPLANATION 

Paleozoic rocks 

Midcontinent rift system rocks (Middle Proterozoic)

Rocks of Marquette Range Supergroup

(Early Proterozoic) Mostly Michigamme Formation. 

Heavy black lines and areas, iron-formation

Archean rocks 

Contact 

Paleocurrent localities

Figure 15. Interpretive plot of paleocurrent data (shaded area) of Michigamme Formation graywackes shown in figure 13. 

Replotted onto northern and southern rose diagrams (combined with crossbed data) with flute casts, groove casts, and scour channels shown as single directions, even though the latter two types of sedimentary structures do not yield a unique current sense.

At Arvon Hill, about 10 km southeast of Pike's Peak, the 

pattern (n=25) is strongly bimodal-bipolar, with currents 

toward both the northwest and the southeast. The crossbedding is trough-type; troughs range from 10 cm to 1 m wide 

and crossbed sets are 5-30 cm thick. A white quartzite, 

which apparently dips outward from the top of the small hill, 

passes upward into dark-gray quartzite and then into black 

metagraywacke and slate.

In summary, the dominant paleocurrents in the Goodrich 

Quartzite flowed outward from the west end of the Archean 

northern complex, towards the southwest, west, and north.

SEDIMENTATION

Introduction

The Baraga Group, consisting of the Goodrich Quartzite 

and the Michigamme Formation in the western Marquette 

range (fig. 1), is the product of the third and final cycle of 

deposition in the Marquette Range Supergroup (Sims and 

others, 1981). The sedimentation of the lower slate member 

of the Michigamme Formation is closely related to the sedimentation of the underlying Goodrich Quartzite. This

Michigamme Formation and Goodrich Quartzite, Northern Michigan R19
w-

-E WCANYON FALLS 

N

-E W

PIKE'S PEAK

EXPLANATION

Trough axis 

Crossbeds 

Asymmetrical ripple

NEAR CANYON FALLS 

N

ARVON HILL

Symmetrical ripple trend 

Flute cast

 - Groove cast ^\ 

20 ) Total number of measurements

Figure 16. Paleocurrent plots of four outcrops of Goodrich Quartzite in northern Michigan. Localities shown and data generalized in figure 17. Canyon Falls, C S. edge sec. 19, T. 49 N., R. 33 W.; "Near Canyon Falls," SW. cor. sec. 17, T. 49 N., R. 33 W.; 

Pike's Peak, C and EI& sec. 11, T. 51 N., R. 32 W.; Arvon Hill, C sec. 28, T. 51 N., R. 31 W.

R20 Precambrian Geology of Lake Superior Region
 ^ Keweenawan rocks of * 

Midcontinent rift system

46°30'

10 KILOMETERS

I

Figure 1 7. Locations of four outcrops of Goodrich Quartzite near west end of the Archean northern complex. Paleocurrent plots 

are generalized from figure 16 to interpret direction, but symmetrical ripple trends and the lone groove cast were not plotted on 

rose diagram A. A, Canyon Falls; B, "Near Canyon Falls"; C, Pike's Peak; D, Arvon Hill.

relationship is most evident in drill holes DL-4 (Dead River 

Basin) and DL-5 (Clark River Basin), where the quartzite 

and graywacke units are gradational. In outcrops in the 

Negaunee SW7V2 ' quadrangle (Clark and others, 1975) and 

the Negaunee llk' quadrangle (Puffett, 1974), the Goodrich 

Quartzite (not formally named by Puffett, 1974) is overlain 

by the lowermost Michigamme unit, an "interbedded finegrained quartzite and siltstone" that becomes finer grained 

upward; in turn this rock is overlain by iron-formation and 

graywacke-slate. As outlined following, the sequence indicates changes upward from a shallow-water environment 

(the Goodrich and lower member of the Michigamme) to a 

transitional somewhat deeper water environment in which 

the Bijiki Iron-formation Member was deposited below 

wave base, and finally to a still deeper water environment 

in which turbidity-current deposition was intermittently 

imposed into a regime of slow suspension settling of fine 

particles (upper member of the Michigamme). This interpretation is slightly at variance with Cannon and Klasner's

(1977) interpretation that the lower member of the Michigamme, the Bijiki, and the lower part of the upper member 

are relatively shallow water deposits, whereas the remainder 

of the upper member of the Michigamme is a deeper water 

turbidite deposit.

Goodrich Quartzite

The Goodrich Quartzite is the basal Proterozoic sedimentary unit in the area west and northwest of the Marquette 

syncline; it lies directly on Archean basement, commonly 

with an intervening regolith. The quartzite was studied at 

four localities on the west and northwest edges of the 

Archean northern complex (fig. 16), as well as in drill cores 

DL-4 and DL-5 (fig. 7). A detailed study of the Goodrich 

Quartzite in the Marquette syncline (to the east) was beyond 

the scope of this project.

The paleocurrent data at three localities are unimodal, 

radiating outward from the Archean basement complex

Michigamme Formation and Goodrich Quartzite, Northern Michigan R21
toward the southwest, west, northwest, and north (fig. 17). 

At the fourth locality (Arvon Hill), the plot is bimodalbipolar with modes to the northwest and southeast (figs. 16, 

17), an arrangement that can be interpreted as being the 

product of a tidal environment. The three unimodal plots, 

although not distinctly suggestive of a tidal influence, could 

nevertheless be tidal, formed under the influence of strong 

ebb tides. The mineralogical (table 2) and textural maturity 

of the sands in the basal quartzite unit also fit such an 

interpretation, as a tidal environment results in long and 

continued abrasion and maturation of sand (Klein, 1975, p. 

50). Because the Goodrich is the basal Proterozoic unit in 

the area, it probably was deposited in a sea that transgressed 

onto a low-lying landmass of Archean rocks. This landmass 

stood above sea level and influenced tide- and wind-generated current systems. Because the Goodrich Quartzite is thin, 

it is likely that the landmass had little relief and therefore 

shed only a modest amount of sediment into the adjacent 

sea. A regional analog is the Early Proterozoic Palms Formation, the basal terrigenous clastic unit on the Gogebic 

range, 80-160 km to the west, which I have interpreted as 

the product of a tidally influenced nearshore environment in 

a transgressing sea (Ojakangas, 1983).

Lower Slate Member, Michigamme Formation

The lower slate member of the Michigamme, where it 

can be stratigraphically placed unequivocally above the 

Goodrich Quartzite and below the Bijiki Iron-formation 

Member, as in drill cores DL-4 and DL-5, consists of thin 

light-tan sandstone beds, similar to the sandstone of the 

underlying Goodrich, separated by thin dark shale partings 

(fig. 18). Also present are thin siltstone beds alternating with 

thin argillite beds. These lithologic variants are the products 

of alternating low-energy and higher energy conditions, typical of a tidally influenced environment. As noted just previously, the Palms Formation (middle member) on the 

Gogebic range is an analog.

Bijiki Iron-formation Member, 

Michigamme Formation

The Bijiki is very fine grained and thin bedded. Evidence 

is lacking for either high-energy or alternating low- and 

higher energy conditions, as in the lower member of the 

Michigamme. The overlying upper member, as interpreted 

following, has characteristics of a turbidite sequence deposited in relatively deep water. It seems likely that the iron 

minerals of the Bijiki were precipitated out of surface waters 

and settled into a low-energy environment below wave base 

in relatively deep water. On the Mesabi range in Minnesota 

(Ojakangas, 1983), a fine-grained and thin-bedded iron-formation facies (that is, lower and upper slaty members) is 

interpreted as a deeper water shelf deposit formed seaward

Figure 18. Part of drill core DL-5, showing lower slate member of Michigamme Formation. Footage is 845 ft, near the middle of the lower member. (Figure 7 describes drill core.) 

Stratigraphic tops are towards the top.

from a coarser grained and crossbedded facies (the lower 

and upper cherty members). If the structures logged as stromatolites in the cores (Trow, 1979) are indeed stromatolites 

rather than deformational features, they provide further support for a relatively shallow water regime of less than about 

60 m depth, the depth of sunlight penetration. However, I 

think these structures are suspect (that is, deformational in 

origin), and that the water depth is indeterminant.

Upper Slate Member, Michigamme Formation

The graded graywacke beds in the upper member of the 

Michigamme are characteristic of deposition by turbidity 

currents. The dominant mudstones (now slates) between the 

graded beds would have been formed by the slow settling 

of fine-grained sediment (clay and silt) during the time intervals between turbidity currents. Deposition was below storm 

wave base, likely in relatively deep water, and possibly on

R22 Precambrian Geology of Lake Superior Region
or near submarine fans. The measured sections (table 1) 

reveal additional details on the sedimentation by turbidity 

currents. The graywacke beds are classic turbidites, with an 

apparent lateral continuity, good grading, and very flat soles.

In the 74-m-thick measured section at Little Bull Rapids 

(fig. 6) near Crystal Falls, 70 percent of the 63 graywacke 

beds are graded, and the proximality index of Walker (1967) 

is a high 86, suggesting that the section is proximal to the 

originating point of the turbidity currents. The proximality 

index as used here in a generalized way is given by the 

percentage of graywacke beds starting with Bouma A plus 

one-half of the percentage of beds starting with Bouma B 

(Walker, 1967). The sequence in this measured section fits 

turbidite facies C, comprised of proximal turbidites (Walker 

and Mutti, 1973). Not shown in table 1 is the observation 

that the entire section is a crudely thinning upward and fining 

upward sequence, with the coarser beds in the lower twothirds of the section. Within this thinning-upward sequence, 

three thickening-upward sequences 2, 4, and 26 m thick can 

be distinguished, although as pointed out by Walker (1984, 

p. 183), such sequences can be "in the eyes of the beholder," 

depending upon which beds thin or thick are interpreted 

as the beginning of a sequence. This measured section may 

be interpreted as indicating either the shifting of a suprafan 

lobe or the filling and migration of a middle fan channel 

(Walker and Mutti, 1973; Walker, 1984).

Measured section II, on Ramsey Island in Lake Michigamme, near the west end of the Marquette syncline, consists of 14 thick, graded graywacke beds with a proximality 

index of 100. These are classical proximal turbidites of 

Walker (1967) and turbidite facies C of Walker and Mutti 

(1973) and Walker (1984). The short section could be interpreted as consisting of either a few thinning-upward 

sequences or a few thickening-upward sequences. The interpretation is the same as for measured section I.

Measured section III at Silver River Falls, east of L'Anse 

in the northernmost Michigamme exposures, contains much 

less graywacke than do sections I and II, and the beds are 

thinner and finer grained. Soles are very flat and sharp. This 

section fits turbidite facies D, with pelagic mud dominant 

over graywacke. It appears to be a part of a distal turbidite 

sequence, deposited on the lower part of a fan or as a basin 

plain sequence.

The graywacke beds in the roadcuts along U.S. Highway 

141 south of Covington (fig. 5) appear to be proximal turbidites of facies C and may belong to the middle fan lobe 

association.

In summary, the graywacke-siltstone-mudstone 

sequences, now metagraywacke-metasiltstone-slate 

sequences, appear on the basis of a few short measured 

sections and countless observations to be submarine fan 

deposits. Alternatively, they could be ramp deposits, laid 

down along the margins of a basin below a major break in 

slope, without the presence of submarine fans. The generally 

fine grain size, the general lack of sole marks, and the very

EXPLANATION

1 Northern exposures of Michigamme Formation

2 Southern exposures of Michigamme Formation

3 Copps Formation

4 Tyler Formation

5 Thomson Formation

6 Rove Formation

7 Virginia Formation

8 Goodrich Quartzite

Figure 19. Averages of modal analyses of graywackes from 

northern and southern outcrops of Michigamme Formation 

and the Copps, Tyler, Thomson, Rove, and Virginia Formations, as well as the Goodrich Quartzite, plotted on a Q/F/L triangle depicting tectonic provenance. Triangle modified from 

Dickinson and others (1983). Note that the modes are probably 

considerably modified from what they were prior to diagenesis 

and metamorphism. Tyler average calculated from Alwin 

(1976); Rove average calculated from Morey (1967); Virginia 

average calculated from Lucente and Morey (1983); Thomson 

average calculated from Morey and Ojakangas (1970).

flat nature of the soles of graywacke beds over much of the 

area (measured sections I and II are exceptions) suggest that 

many beds were deposited on distal portions of fans or on 

an abyssal plain.

TECTONIC MODEL AND PROVENANCE

Sandstone compositions, when plotted on a Q/F/L triangle, can be assigned to tectonic source areas. A triangle 

utilized by Dickinson and others (1983) indicates three main 

source terranes for North American Phanerozoic sandstones cratonal, recycled orogen, and magmatic arc. The 

plots of figure 8 are transferred to such a triangle in figure 

19. Whereas the modes of the Michigamme graywackes are

Michigamme Formation and Goodrich Quartzite, Northern Michigan R23
SOUTH NORTH

FOLD-AND-THRUST 

BELT

FORELAND BASIN 

migrating to north PERIPHERAL BULGE

. 

north

" '",, Basal quartzose sands, 

.and iron-formationvv

Figure 20. Schematic cross section depicting deposition of the Michigamme Formation in a foreland basin, with sediment derived 

from both north and south. The southern source area, the fold-and-thrust belt, comprises a complex assemblage including (1) accreted Early Proterozoic volcanic and plutonic rocks of the Wisconsin magmatic terranes, (2) accreted Archean miniplate terranes, 

(3) older Early Proterozoic passive-margin sedimentary rocks and volcanic rocks produced during initial rifting of the continental 

margin, both scraped off the southward-subducting Archean Superior craton, and (4) recycled initial foredeep deposits, possibly 

including basal shallow water sandstones deposited in the transgressing sea of the northward-migrating foreland basin. The peripheral bulge comprises a source-rock assemblage of Archean granitic rocks and Archean volcanic-sedimentary (greenstone) belts. 

The faults in the fold-and-thrust belt are related to the Niagara fault zone (suture). Compare with figure 21. Partly based on Hoffman 

(1987), Southwickand others (1988), and Southwick and Morey (1991). Scale is approximate.

probably not representative of original compositions, as 

discussed in the "Petrography" section of this report, they 

can be partially interpreted with regard to the average plots 

of the presumed correlative Rove, Thomson, Virginia, and 

Tyler Formations (also shown in figure 19), which are somewhat less metamorphosed and deformed than the Michigamme and therefore more representative of their primary 

sandstone compositions. The Rove Formation was derived 

entirely from the cratonal region to the north (Morey, 1967), 

as were the Thomson (Morey and Ojakangas, 1970) and 

Virginia Formations (Lucente and Morey, 1983); the northern exposed part of the Michigamme Formation probably 

also has a similar cratonal parentage.

In contrast, the southern Michigamme graywackes and 

the Tyler Formation probably had their source areas in the 

collisional zone to the south, a zone made up of Early Proterozoic volcanic-arc rocks, Archean basement rocks, and 

cover rocks of the craton margin. Yet, on the Q/F/L triangle 

(fig. 19), the southern graywackes plot with the northern 

graywackes. This coincidence is discussed following.

Several workers have interpreted the Animikie basin as 

an elongate easterly trending intracratonic basin, with sediment supplied from both the north and south sides. (See, for 

example, Sims and others, 1981; Ojakangas and Matsch, 

1982, p. 43; Morey, 1983a, b.) Other workers proposed a 

subduction model on a continental margin to explain the

asymmetry and the distribution of rock types, including the 

volcanic rocks to the south in Wisconsin. (Here, see Van 

Schmus, 1976; Cambray, 1978; Van Schmus and Bickford, 

1981; Larue, 1983; LaBerge and others, 1984.)

Hoffman (1987) proposed a foreland basin model combined with a southward-dipping subduction zone to explain 

the interrelation of Early Proterozoic iron-formations, mafic 

volcanic rocks, and thick turbidite sequences, with the asymmetric basin being the product of loading by the northwardverging Penokean fold-and-thrust belt. A similar model, and 

also a back-arc basin model with northward subduction, 

were proposed to explain lithologic and structural relationships in east-central Minnesota detailed by Southwick and 

others (1988) and Southwick and Morey (1991).

I accept the foredeep model, with associated southward 

subduction and the collision of a volcanic arc (the Wisconsin 

magmatic terranes) with the craton to the north, as the model 

that can best explain the origin of the Michigamme Formation, as well as that of the correlative Copps and Tyler 

Formations (fig. 20). However, as noted previously, the elastics in the southern part of the Michigamme Formation 

appear to have had a different source than those in the 

northern part of the Michigamme.

Several lines of evidence support derivation of the clastic 

sediments in the southern outcrops of the Michigamme from 

a combination of a craton (Archean terrane) and a recycled

R24 Precambrian Geology of Lake Superior Region
orogen (Wisconsin magmatic terranes) to the south. (1) 

Paleocurrent plots of the Tyler, Copps, and the southern 

exposed part of the Michigamme suggest source areas to the 

south rather than to the north. (2) The Nd data of Barovich 

and others (1989) support an Early Proterozoic source for 

the Michigamme graywacke-slate sequence of the southern 

area. (3) Q/F/L plots for the graywackes are suggestive of 

cratonal and recycled erogenic sources rather than direct 

magmatic arc sources for the detritus (fig. 19). (4) The CIA 

values (table 4) imply a moderate amount of weathering in 

the source areas and provide argument against a major direct 

volcanic source. (5) Regional paleogeography indicates that 

the Wisconsin magmatic terranes, south of the Niagara fault, 

together with Late Archean gneiss terranes, also to the south 

(fig. 2), were the likely source areas. These source rocks 

apparently comprised part of an imbricate sequence of northverging thrusts that formed a high-relief area. Interestingly, 

petrographic studies do not show the volume of clastic volcanic material that might be expected in sediments derived 

in part from the Wisconsin magmatic terranes. Possible 

explanations for this deficiency are (1) destruction of volcanic clasts by weathering in the source areas, (2) diagenetic 

and metamorphic alteration of the volcanic clasts, (3) 

destruction of the volcanic clasts by tectonic recycling and 

resedimentation, or (4) the failure of significant volumes of 

eroded volcanic detritus to reach the foreland basin. In the 

latter scenario, volcanic ash from the colliding arc could 

have been deposited in the basin, and this ash could have 

provided the Early Proterozoic source imprint (Nd data) to 

the sedimentary rocks.

In the vicinity of the Michigan-Wisconsin border, lensoid 

exposures of quartzite exist within the Michigamme Formation (Sims and Schulz, 1992). The "Pine River member" 

(quartzite conglomerate of Nilssen, 1965), for example, can 

be either an older (Chocolay? Group) continental margin 

sedimentary unit or the basal quartzite (Goodrich Quartzite 

equivalent of an earlier stage of the northward-migrating 

foreland basin) incorporated into the fold-and-thrust belt. A 

roadcut on Wisconsin Highway 12, 20 km south of Covington, exposes possibly analogous sandstone lenses in muddy 

rock and thin sandstone beds with thin mud drapes or flasers; 

these are comparable to sedimentary structures in the lower 

member of the Michigamme, which are attributed herein to 

a tidal environment; these data suggest the possibility that 

the lower member of the Michigamme Formation exists in 

this area.

In contrast, the northern exposures of the Michigamme 

Formation are interpreted to have had a source to the north, 

for the following reasons: (1) The paleocurrent data, 

although sparse, support a northern source; (2) the Nd data 

of Barovich and others (1989) support an Archean source 

for the sediment of the northern Michigamme sequence; (3) 

Q/F/L plots for the graywacke, in spite of likely postdepositional changes, indicate a cratonic or recycled orogen 

source; (4) CIA values (table 5) indicate a moderately

weathered source area; and (5) regional paleogeography supports the Archean granite-greenstone terrane of northern 

Minnesota and Ontario and the Archean northern complex 

of Michigan as plausible, likely source areas. The Dead 

River, Clark Creek, East Baraga, and Gwinn basins (fig. 3) 

are small down-folded and down-faulted erosional remnants 

(Sims, 1991, fig. 1) of the widespread and once continuous 

Michigamme sequence.

Paleocurrent indicators in the Rove Formation on the 

north side of Lake Superior, in Minnesota and Ontario, show 

a strong mode toward the south (Morey, 1967; fig. 21), 

similar to that of the northern segment of the Michigamme 

Formation. Any paleogeographic reconstruction, however, 

must allow for the spreading that occurred during the formation of the 1,100 Ma Midcontinent rift system, which is 

situated in the Lake Superior basin between Michigan and 

Minnesota-Ontario (fig. 2). The amount of spread between 

the two Archean-Early Proterozoic terranes has been estimated to be 60-100 km (Klasner and others, 1982; Chandler, 

1983). If the regional paleogeography is restored to its preMidcontinent rift position by moving the block situated 

southeast of the Midcontinent rift system a distance of 100 

km in a northwesterly direction (perpendicular to the trend 

of the rift), the distance between the northern Michigamme 

exposures and the southernmost Rove exposures is reduced 

to an estimated 65-100 km. It seems probable that the finegrained northern Michigamme is "distal Rove Formation," 

deposited on the distal portion of a southward-thinning submarine fan or on the basin plain, for both formations have 

paleocurrent patterns towards the south and an Archean 

provenance (fig. 21). In this interpretation, both the Rove 

and the northern Michigamme were deposited on the north 

side of the asymmetric foreland basin (on the continental 

foreland or the peripheral bulge), whereas the southern 

Michigamme was deposited nearer the axis of the asymmetric foreland basin. Note that this restoration (fig. 21) also 

results in the alignment of the fold-and-thrust belts of Minnesota and Wisconsin-Michigan.

Whereas the Michigamme graywacke and slate were 

probably derived from relatively distant source areas, the 

basal quartzose sandstone underlying the Michigamme Formation (the Goodrich Quartzite) was evidently derived 

locally. Its composition includes potassium feldspar and plutonic rock fragments (table 2). These components, when 

coupled with the paleocurrent data (figs. 16, 17) that show 

paleocurrents radiating southwestward, westward, and 

northward from the Archean northern complex, indicate 

local derivation from these Archean granitoid rocks. The 

sands composed of quartz, feldspar, and plutonic rock fragments were apparently reworked in a shallow-water tidal 

environment, thereby becoming mineralogically and texturally mature. These shallow-water deposits can be interpreted 

to have been deposited along the northern shoreline (on the 

continental foreland or the peripheral bulge) of the northward-migrating foreland basin.

Michigamme Formation and Goodrich Quartzite, Northern Michigan R25
Wisconsin u v,, v 

magmatic terranes

J

46°-

EXPLANATION

Early Proterozoic

Turbidites overlying shelf deposits

Plutonic and volcanic rocks

Complex continental-margin sequences 

Archean

Rocks of greenstone-granite terrane (Superior province)

Rocks of gneiss terrane

 Contact

 ^ ^ ^- Thrust fault Sawteeth on overthrust block

 High-angle fault

Sedimentary transport direction 

G LTZ Great Lakes tectonic zone

---------- Outline of present Upper

Peninsula of Michigan

Figure 21 . Schematic hypothesized paleogeography at time of sedimentation of the Michigamme Formation. The rocks of the 

Midcontinent rift system have been removed, and Michigan is positioned 100 km closer to Minnesota-Ontario. Arrows denote generalized transportation directions of sediment from major source areas. Compare with figures 2 and 20. Map modified from Sims 

(1991) and Southwick and Morey (1991).

The island landmass in the Early Proterozoic sea, now 

constituting the northern complex (fig. 17), probably was 

eventually totally submerged and covered with sediments. 

On the southern part of this landmass, the stratigraphic 

sequence is complete, as in drill holes DL-4 and DL-5 in 

the Dead River and Clark Creek basins (figs. 3, 7). To the 

north in the East Baraga basin, the Goodrich Quartzite and 

the lower slate member of the Michigamme Formation were 

not deposited, as shown by drill holes DL-7 and DDH-116 

(locations, fig. 3; text, p. 8). Evidently this part of the

landmass was topographically higher than the area to the 

south, and was onlapped only by the higher stratigraphic 

units (the Bijiki Iron-formation Member and the upper slate 

member). By late Michigamme time, the entire landmass 

was submerged and covered by the upper slate member. 

Subsequent uplift and erosion of the cover rocks exposed 

most of this landmass of Archean rocks, except where the 

cover rocks were downfaulted and preserved in three small 

structural basins the Dead River, Clark Creek, and East 

Baraga basins.

R26 Precambrian Geology of Lake Superior Region
STRATIGRAPHIC IMPLICATIONS

This study raises numerous stratigraphic questions that 

challenge the long-accepted correlations shown in figure 1. 

Some revisions of regional correlations seem to be required, 

as discussed following.

The stratigraphic sequence in outcrop and drill core in 

the northern part of the study area comprises the Goodrich 

Quartzite and the overlying Michigamme Formation, consisting of the lower slate member, the Bijiki Iron-formation 

Member, and the upper slate member. A similar stratigraphic 

sequence occurs on the Gogebic range, which is 120-160 

km to the west-southwest and is on depositional and tectonic 

strike with the western Marquette district (fig. 3). On the 

Gogebic range, the relevant stratigraphic units, from oldest 

to youngest, are the Palms Formation, the Ironwood Ironformation, and the Tyler and Copps Formations. Not only 

are the lithologies generally similar between the two ranges, 

but the interpreted depositional environments are similar. 

These units were likely deposited contemporaneously in the 

northward-transgressing Early Proterozoic (Animikie) sea 

situated in the developing foreland basin. The proposed correlations between the Gogebic and the western Marquette 

ranges are, therefore, as follows:

Gogebic range Western Marquette range

Tyler and Copps Formations 

Ironwood Iron-formation

Upper slate member, 

Michigamme Formation.

Bijiki Iron-formation Member, 

Michigamme Formation.

Palms Formation Lower slate member,

Michigamme Formation. 

Goodrich Quartzite.

The stratigraphic sequences to the north on the Gunflint 

and Mesabi ranges (fig. 2) are also similar to those on the 

Gogebic range and the western Marquette range, in both 

lithologies and environments of deposition. On the Mesabi, 

the basal unit (the Pokegama Quartzite) fits a tidal model, 

the two "cherty" members of the Biwabik Iron-formation 

have shallow-water attributes, and the two "slaty" members 

have deeper water attributes (White, 1954; Ojakangas, 1983; 

Morey, 1983a). The overlying Virginia Formation was 

deposited below wave base by turbidity currents and suspension settling on the outer or middle parts of a submarine 

fan complex (Lucente and Morey, 1983). The lowermost 

unit on the Gunflint range, the Kakabeka Quartzite, which 

lies unconformably upon Archean basement, is at most only 

a few meters thick and hence its environment of deposition 

is difficult to interpret. However, the overlying Gunflint 

Iron-formation has shallow-water tidal attributes (Goodwin, 

1956; Shegelski, 1980), and the uppermost unit, the Rove 

Formation, has characteristics of turbidity current deposition 

on a prograding submarine fan (Morey, 1969). Therefore,

the depositional histories on the Mesabi and Gunflint ranges, 

which are on depositional strike with each other and very 

likely were continuous before intrusion of the 1.1 Ga Duluth 

Complex, are very similar; and lithostratigraphic correlations between these two ranges are unequivocal.

Although correlations can be made, on the one hand, 

between the western Marquette range and the Gogebic 

range, and on the other hand, between the Mesabi and Gunflint ranges, can correlations be made among all four of these 

ranges? The lithologies, environments of deposition, and 

stratigraphic sequences are indeed similar, indicating a 

strong case for correlation. However, diachronous relationships between the western Marquette and Gogebic ranges to 

the south and the Mesabi and Gunflint ranges to the north 

are required. If the model of a northward-migrating foreland 

basin is utilized (figs. 20, 21), with the basal terrigenous 

clastic units and the iron-formations deposited on the peripheral bulge and the turbidite sequences deposited both on the 

bulge and in the deeper parts of the foreland basin, the Palms 

Formation-Ironwood Iron-formation and Goodrich Quartzite-lower member of the Michigamme Formation-Bijiki 

Iron-formation Member were deposited prior to deposition 

of the more northerly Pokegama Quartzite-Biwabik Ironformation and the Kakabeka Quartzite-Gunflint Formation. 

If it is instead assumed that the basal terrigenous clastic units 

and the iron-formations were deposited on a stable shelf 

prior to the development of the foreland basin with its turbidite fill, northward-migrating depositional environments 

were also probable, with the southern units deposited prior 

to deposition of the northern units. In both models, it can be 

assumed that the terrigenous clastic units and the overlying 

iron-formations form essentially continuous sheetlike deposits across the basin, between Wisconsin-Michigan and Minnesota-Ontario.

However, as discussed previously in this report, the 

upper slaty member of the northern part of the Michigamme 

Formation and the Rove Formation of Minnesota-Ontario 

are the same age, and perhaps integral parts of the same large 

submarine fan. A further correlation consequence of this 

model (stated just previously) is that the Virginia Formation 

of the Mesabi range and the Thomson Formation just west 

of Duluth, both on tectonic and depositional strike with the 

Rove Formation (see figs. 2, 21), are approximately equivalent in age to the upper slaty member of the Michigamme 

Formation. No direct means exists to determine whether the 

graywacke-slate units having general northward-directed 

paleocurrent patterns (the Tyler and Copps Formations and 

the southern Michigamme Formation) are younger or older 

than the Virginia, Thomson, and Rove Formations and the 

upper slaty member of the Michigamme Formation; it can 

be assumed, however, that they are all approximately the 

same age, and correlative. However, there exist two main 

qualifying points, as follows.

1. In a foreland basin such as that which probably 

existed for several million years and which was receiving

Michigamme Formation and Goodrich Quartzite, Northern Michigan R27
sediment from both north and south, units will inevitably be 

different in age.

2. In the foreland basin model, the fold-and-thrust belt 

and the asymmetric foreland basin to the north developed 

as a result of the collision of the Wisconsin magmatic terranes with the craton. The collision caused the Penokean 

orogeny, which is dated at about 1,850 Ma. Thus, the 

southerly derived graywacke-slate units were deposited 

about 1,850 Ma.

Of prime concern, therefore, are the contacts of the southerly derived graywacke-slate units with the underlying ironformations. Are the relationships conformable or nonconformable? If conformable, the ages of the Ironwood Iron-formation and the Bijiki Iron-formation Member of the 

Michigamme Formation would not be much older than 1,850 

Ma. If unconformable, the iron-formations and the terrigenous clastic units that underlie them could be considerably 

older. I have seen no evidence in outcrop or in drill core for 

an unconformable relationship between the Bijiki Iron-formation Member and the overlying upper slate member of 

the Michigamme Formation. The Tyler Formation-ironwood Iron-formation relationship has been described by 

Schmidt (1980, p. 68-70), who reviewed the various viewpoints of geologists regarding the contact. Schmidt regarded 

the "basal conglomerate" of the Tyler Formation as an 

intraformational unit of no great stratigraphic significance, 

and emphasized that both the presence of iron-formation a 

few hundred meters above the base of the Tyler and the ironrich nature of the lower part of the formation indicated a 

gradational contact.

However, the Copps Formation just to the east of the 

Tyler on the eastern Gogebic range, and surely correlative 

with it, has a basal conglomerate that contains iron-formation clasts. Thus, the contact between the Copps and the 

Ironwood Iron-formation is probably unconformable (Gene 

LaBerge, oral commun., 1992). This appears to be a local 

rather than a regional unconformity.

The Virginia Formation-Biwabik Iron-formation contact 

on the Mesabi range is gradational over several tens of 

meters (Lucente and Morey, 1983), and the Rove Formation-Gunflint Iron-formation boundary also is gradational 

(Morey, 1969).

Thus, the precise ages and therefore the correlation of 

several Early Proterozoic units are uncertain. Crosscutting 

dikes of Early Proterozoic age are lacking. Many K-Ar and 

Rb-Sr ages probably reflect metamorphism. Faure and 

Kovach (1969) reported a whole-rock Rb-Sr isochron age of 

1.6410.2 Ga for the deposition or diagenesis of the Gunflint 

Iron-formation in Ontario, and Stille and Clauer (1986) 

determined a Sm-Nd isochron age of 2.0810.25 Ga for deposition of the same unit. A Sm-Nd whole rock isochron for 

the lower half of the Biwabik Iron-formation indicated an 

age of 2,11010.52 Ma (Gerlach and others, 1988).

Essential to the resolution of the correlations discussed 

herein will be the acquisition of better ages from within the

sequences. Zircons for precise U-Pb age dating should be 

present in the metamorphosed ash beds of the Virginia Formation and the Biwabik and Gunflint Iron-formations. Volcanic rocks within the Thomson Formation could yield 

zircons. Perhaps a detailed search of the Michigamme in 

drill cores would yield zircon-bearing ash beds. If the felsic 

parts of the Emperor Volcanic Complex at the east end of 

the Gogebic range are shown to be unequivocally intercalated with the Ironwood Iron-formation, U-Pb dates for zircons of that unit would be invaluable.

Until reliable age data on units within the Early Proterozoic sequences are available, correlations will necessarily remain subjective, and interpretive errors will be 

perpetuated.

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____1989, Segment 2 Geology of the Marquette Range 

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sedimentology of the Lower Proterozoic Virginia Formation, 

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____1969, The geology of the Middle Precambrian Rove 

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Nanz, R.H., Jr., 1953, Chemical composition of Pre-Cambrian 

slates with notes on the geochemical evolution of lutites: 

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Ojakangas, R.W., 1983, Tidal deposits in the early Proterozoic 

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____1986, An early Proterozoic metagraywacke-slate turbidite 

sequence The Tampere Schist Belt, southwestern Finland: 

Bulletin Geological Society of Finland, v. 58, p. 241-261.

Ojakangas, R.W., and Matsch, C.L., 1982, Minnesota's geology: 

Minneapolis, Minn., University of Minnesota Press, 255 p.

Pettijohn, F.J., Potter, P.E., and Siever, R., 1987, Sand and 

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Puffett, W.P., 1974, Geology of the Negaunee quadrangle, 

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Schulz, K.J., 1983, Geochemistry of the volcanic rocks of 

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___1984, Early Proterozoic Penokean igneous rocks of the 

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Shegelski, R.J., 1980, Stratigraphy of the Gunflint Formation, 

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Iron Mountain and Escanaba I°x2° quadrangles, 

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Geological Survey Miscellaneous Investigations Series Map 

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___1991, Great Lakes tectonic zone in Marquette area, 

Michigan Implications for Archean tectonics in northcentral United States: U.S. Geological Survey Bulletin 

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Sims, P.K., compiler, 1992, Geologic map of Precambrian rocks, 

southern Lake Superior region, Wisconsin and northern 

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early Proterozoic basins of the Great Lakes region, in 

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R30 Precambrian Geology of Lake Superior Region
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Manuscript approved for publication July 12,1993 

Published in the Central Region, Denver, Colorado 

Photocomposition by Shelly A. Fields 

Graphics by Gayle M. Dumonceaux

Michigamme Formation and Goodrich Quartzite, Northern Michigan R31

i, U.S. GOVHaWENT HUNTING OFFICE: 1994- 573-038/86036

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