The Reany Creek 

Formation 

Marquette County 

Michigan

By WILLARD P. PUFFETT

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1274-F

Prepared in cooperation with the 

Geological Survey Division 

Michigan Department of Conservation

Description of a new formation of 

Precambrian age in northern Michigan

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 25 cents (paper cover)
CONTENTS

Page

Abstract_ _____._____-___-_______-__.._.____.._.____________.____ Fl

Introduction._____________________________________________________ 1

General Geology._________________________________________________ 2

Previous work _____-_____-..__.__-_._.__..___.___..-_.____.__._._ 2

Reany Creek Formation__________________________________________ 5

Location. -_____________._________._-_____..._.____.__-_____.. 5

General description..__________________________________________ 5

Basal conglomerate__--_-____--_-_____---_________--__--_----__ 6

Graywacke and slate with disrupted beds of arkose and dispersed

boulders of granitic rock (middle unit)_________________________ 9

Slate.------..--------..--------.-.---.---.--------------. 9

Graywacke.___--_-._______--_______--_______--_-____----_ 9

Arkose.__________________________________________________ 9

Dispersed granitic megaclasts.______________________________ 11

Interbedded arkose, slate, graywacke, conglomerate, and quartzite.. 13

Arkose---.---------._____________________________________ 13

Conglomerate----__--___-_--------_--_-__--------------_-- 13

Quartzite.._______________________________________________ 15

Thickness ___________ _______________________________________ 15

Chemical composition._________________________________________ 15

Origin______________________________________________________ 19

Correlation and age-_--_----_-.-------------------------------- 21

References cited._______________.___________-_-_____----_____-----_ 23

ILLUSTRATIONS

Page 

FIGURE 1. Map showing general geology of part of northern Michigan. __ F3

2. Map showing general geology of the east end of the Dead 

River basin, including the location of the Reany Creek 

Formation..._________________________________________ 4

3. Map showing three subdivisions of the Reany Creek Formation__.-.___-.___--___._-_-_--------_--_-___-__---_- 6

4. Photographs of granitic boulders in basal conglomerate of the

Reany Creek Formation______________________________ 8

5. Sketch of granite boulder in arkose and slate beds..--------- 10

6. Sketch of broken beds of arkose in slate__-_-------_-------- 12

7. Photographs of conglomerate in upper part of the Reany Creek

Formation____-_.___.._-_-..___-_______----_____------ 14

8. Map showing areas underlain by the Cobalt Series in Canada 

and the Reany Creek and Fern Creek Formations in 

Michigan.-.--._...._-__....-_-_-_..------------------ 23
IV

Page

TABLE 1. Chemical analyses of slate from the Reany Creek Formation 

compared with graywacke and argillite from other dispersed 

conglomerates of Precambrian age_________--------_______ F16

2. Average chemical composition of slates and argillite in dispersed

conglomerates and of other pelitic rocks._____-___-_______ 17

3. Chemical analyses of lower Precambrian rocks in the Negaunee

7^-minute quadrangle.__..__..___________-_-___---_---__- 17

4. Semiquantitative spectrographic analyses of slate from the 

Reany Creek Formation compared with spectrographic 

analyses of argillite from the Gowganda Formation._____._ 18
CONTRIBUTIONS TO STRATIGRAPHY

THE REANY CREEK FORMATION 

MARQUETTE COUNTY, MICHIGAN

By WlLLARD P. PUITETT

ABSTRACT

The Reany Creek Formation, a new stratigraphic unit, crops out in a narrow 

belt north of Dead River in and west of the Negaunee T^-niinute quadrangle, 

Marquette County, Mien. It is divided into three units : (1) a basal conglomerate, 

(2) a middle sequence of graywacke and slate containing disrupted beds of arkose 

and dispersed pebbles and boulders of granitic rock, and (3) an upper unit of 

arkose, quartzite, slaty graywacke, and conglomerate. Maximum thickness of 

the formation is 3,000-3,500 feet. The formation unconformably overlies massive 

greenstone and layered arnphibolite of the Mona Schist of early Precambrian 

age. The upper part of the Reany Creek Formation is faulted against sheared 

metavolcanic rocks of the Mona Schist.

The middle sequence, which consists of slate and graywacke containing dispersed boulders of granitic rock, is similar in composition to other formations in 

the Lake Superior region that are believed to be of glacial origin. Chemical 

composition of the slate is similar to that of the matrix of the Gowganda 

Formation, reported to be of glacial origin, and to the graywacke and argillite 

in Timiskaming rocks that contain granitic boulders. All these rocks are distinctly different from average Precambrian slates in that Na20 greatly exceeds 

K2O, CaO is lower, and ferrous iron exceeds ferric iron.

The age of the Reany Creek Formation is not known, but it is presumed to be 

middle Precambrian because it is intruded by Keweenawan dikes and rests unconformably on lower Precambrian rocks.

The similarities between the Reany Creek Formation in Michigan and the 

Gowganda Formation in Canada suggest a correlation between these two units.

INTRODUCTION

The Reany Creek Formation is a new stratigraphic unit north of 

Dead River in the Negaunee T^-minute quadrangle, Marquette 

County, Mich. The distinguishing feature of this formation is a chloritic slate containing widely scattered pebbles and boulders of granite 

and sparse to abundant intraclasts of arkose. Coarse conglomerate 

occurs locally at the base, and quartzite, arkose, graywacke, and bedded

Fl
F2 CONTRIBUTIONS TO STRATIGRAPHY

and nonbedded conglomerate occur in the upper part. The formation 

rests unconformably on rocks of early Precambrian age; the upper 

part is in fault contact with sheared metavolcanic rocks also of early 

Precambrian age. Comparison of this formation with formations elsewhere suggests that the Reany Creek Formation is of middle Precambrian age and is in part of glacial origin.

The Reany Creek Formation was mapped in 1966 during the study 

of the Negaunee 7^-minute quadrangle; this investigation is part 

of a restudy of the Marquette Iron Range by the U.S. Geological Survey in cooperation with the Geologic Division of the Michigan Department of Conservation. Areas underlain by the Reany Creek Formation 

west of the Negaunee T^-minute quadrangle were not mapped in 

detail.

GENERAL GEOLOGY

The general geology of the area in which the Reany Creek Formation 

occurs is shown in figures 1 and 2. Dead River basin (fig. 1) is a 

topographic lowland underlain by metasedimentary rocks of middle 

Precambrian age and bordered by highlands underlain by lower Precambrian rocks.

The geology in and around the east end of the Dead River basin is 

shown in figure 2. The Mona Schist, the oldest rock in the area, has 

been intruded by granitic gneiss in the northeastern part of the area 

and by syenite-diorite-granodiorite in the southern part. The Michigamme Slate has been deposited on an erosional unconformity that cuts 

across the granodiorite. Near its east limit, the slate has been folded 

into a northwest-plunging syncline. A broad zone of shearing, in which 

the exposed rocks are rhyolite, tuff, and greenstone of the Mona Schist, 

borders the north edge of the Michigamme Slate and has truncated 

the granodiorite. The Reany Creek Formation occupies the area 

between the broad zone of shearing and the greenstones and amphibolites of the Mona Schist to the north. Metamorphism has affected all 

the rocks in the area shown in figure 2, including the rocks of the Reany 

Creek Formation and Michigamme Slate, which have been metamorphosed to the chlorite zone by post-Huronian pre-Keweenawan 

regional metamorphism (James, 1955, pi. 1).

PREVIOUS WORK

The Dead River basin has been studied much less than the Marquette syncline, a few miles to the south, and references to conglomerates within the basin are few. Published maps do not show conglomerate underlying the north flank of the basin. Rominger (1881, p. 13) 

described conglomeratic rock with bright red granite pebbles in sec,
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F3

2, T. 48 N., E. 26 W., near the east end of the area mapped as the 

Reany Creek Formation. Wadsworth (1893, p. 85, 115) correlated 

a conglomerate at the Holyoke mine in sec. 2, T. 48 N., R. 27 W. 

(nearly a mile west of the Negaunee 7y2-minute quadrangle) with one 

in sec. 15, T. 48 N., R. 26 W., and named it the Holyoke Formation. 

Van Hise and Leith (1911, p. 288) assigned this conglomerate to 

the base of the upper Huronian (now the Michigamme Slate).

Engel (1954) described conglomerate and slate along the north 

side of the Dead River Storage Basin between the north central part 

of sec. 7, T. 48 N., R. 26 W., and the Holyoke mine. He called these 

rocks the Holyoke Formation, suggested that the formation was in 

part of glacial origin, and tentatively correlated it with the basal 

middle Precambrian Fern Creek Formation of Dickinson County, 

Midi. Engel suggested also that it might be correlative with either 

the Timiskaming metasediments or the Gowganda Tillite of Ontario, 

Canada.

47 C

Negaunee 7W 

quadrangle 

Figure 2

EXPLANATION

Upper Precambrian 

and younger rocks

Middle Precambrian 

rocks

Lower Precambrian 

rocks

FIGURE 1. Generalized geology of part of northern Michigan and 

location of the Negaunee 7%-minute quadrangle.
F4 CONTRIBUTIONS TO STRATIGRAPHY

T. 49 N 

T. 48

Contact

where approximately 

located;dotted where concealed 

_______D__

U

High-angle fault 

Dashed, where approximately 

located; dotted where concealed. 

U, upthrown aide; D, downtkrown 

aide

Axis of syncline, showing 

plunge

l 65

Strike and dip of beds

A 75

Strike and dip of foliation

Zone of general shearing

FIGURE 2. General geology of the east end of the Dead River basin, including the 

location of the Reany Creek Formation. (For location of area in Negaunee 

7%-ruinute quadrangle, see figure 1.)
THE RE ANY CREEK FORMATION, MARQUETTE CO., MICH. F5

The Holyoke Formation, orginally introduced as a stratigraphic 

name by Wadsworth (1893, p. 85), has never been adopted for use 

by the U.S. Geological Survey. The rocks described by Engel as the 

Holyoke Formation are here included in the Reany Creek Formation.

REANY CREEK FORMATION 

LOCATION

The Reany Creek Formation is here named for the stream that flows 

across the formation in the eastern part of the area (fig. 2). The 

formation crops out north of the Dead River in Marquette County, 

Mich., in an elongate belt extending west from sec. 12, T. 48 N., R. 26 

W., to near the northeast corner of sec. 2, T. 48 N., R. 27 W., about a 

mile west of the Negaunee TV^-nrimite quadrangle. The maximum 

mapped width of the formation is about 1 mile; the average width is 

about 2,000 feet. Outcrops are generally small and widely separated. 

Glacial deposits obscure more than 75 percent of the bedrock, and 

water in the Dead River Storage Basin covers much of the formation 

west of sec. 8, T. 48 N., R. 26 W. There is no continuous exposure of a 

complete section of the formation. Some of the best exposures are along 

a line that extends north from the shore of Dead River Storage Basin 

about 400 feet west of the east boundary of sec. 7, T. 48 N., R. 26 W. 

Exposures along this line include arkose and interbedded conglomerate and slate in the upper part of the formation, chloritic slate containing granitic boulders in the middle unit, and coarse conglomerate 

in the lower unit that is in contact with greenstone of the Mona Schist. 

This line of exposures, which extends north from the Dead River 

Storage Basin for about 1,750 feet, is here designated the type section. 

The top of the formation is not defined since the upper part is in fault 

contact with sheared felsic rocks of the Mona Schist (p. F13).

GENERAL DESCRIPTION

The Reany Creek Formation is divided into three units: (1) a basal 

conglomerate, (2) a middle sequence of graywacke and slate with 

disrupted beds of arkose and dispersed pebbles and boulders of 

granitic rock, and (3) an upper unit of interbedded arkose, quartzite, 

slaty graywacke, and conglomerate (fig. 3). The middle sequence is the 

most widely distributed of the three units; the basal conglomerate is 

known only from two widely separated areas, and the upper unit 

crops out only in the western part of the area underlain by the formation. The formation rests on a well-defined unconformity, under 

which are the massive greenstone and layered amphibolite of the Mona 

Schist. The upper part is faulted down against the sheared metavol319-846 O 68 2
F6 CONTRIBUTIONS TO STRATIGRAPHY

R. 27 W. R. 26 W.

Conglomerate, slate, 

arkose, and quartzite

EXPLANATION

Slate and graywacke with disrupted arkose beds and dispersed granite pebbles and 

boulders

Coarse basal 

conglomerate

Contact 

Dashed where approximately located

D Fault

Dashed where approximately

located. U, upthrown side;

D, downthrown side

FIGURE 3. Three subdivisions of the Reany Creek Formation in the Negaunee

71/2 -minute quadrangle.

canic rocks of the Mona Schist; thus the top of the Reany Creek Formation is not exposed.

BASAL CONGLOMERATE

The eastern lens of conglomerate (fig. 3) is about 7,500 feet long. 

The beds dip 65°-85°S., and the calculated maximum thickness of the 

lens is nearly 2,000 feet. The best exposure of the conglomerate extends 

about 800 feet northwestward on a conspicuous hill 2,800 feet east and 

500 feet north of the southwest corner of sec. 2. The conglomerate contains many rounded and angular boulders of granitic rock and greenstone in a matrix of poorly sorted coarse-grained arkose that is subordinate in volume to the boulders. The granitic rock in the boulders 

is light gray to reddish gray and ranges from pegmatite to fine-grained 

felsic porphyry. Some boulders are as much as 25 inches in diameter, 

but more commonly the boulders are about half this size. There are a 

few clasts of vein quartz as much as 2 inches in diameter and a few of

chert-magnetite rock less than 2 inches across. The arkosic matrix is 

tightly cemented, is poorly sorted, and contains large angular grains 

of feldspar and chloritized mafic minerals, quartz grains, and rock
THE RE ANY CREEK FORMATION, MARQUETTE CO., MICH. F7

fragments including a chert-magnetite rock, vein quartz, a quartzfeldspar rock, and metabasalt. All the rock types represented in the 

boulders occur in about the same proportion in the smaller fragments 

of the matrix. Bedding or foliation is obscure, and there is no systematic gradation in size of boulders from the base of the unit upward.

Widely separated outcrops of conglomeratic arkose and graywacke 

are in the south-central part of sec. 3, near the west limit of the eastern lens. The arkose and graywacke contain fragments of granite and 

vein quartz that are about 12 inches in diameter near the base of the 

lens; clast size decreases upward, and near the top of the lens, clasts 

average about 1 inch in diameter. The graywacke is fine grained to 

medium grained, is tightly cemented, and commonly breaks conchoidally. It consists of angular to subangular grains of sericitized plagioclase, rather fresh microcline, angular to subrounded quartz grains, 

fragments of igneous rocks ranging in composition from basalt to 

granite, and fine-grained pyrite and magnetite. Feldspar is equal to 

or more abundant than quartz. The matrix of the graywacke is a 

cloudy claylike material and chlorite; the chlorite has corroded the 

margins of many of the quartz grains. In the east-central part of sec. 3, 

thin quartz-chalcopyrite veins and sparingly disseminated chalcopyrite occur within the graywacke.

The contact between the conglomerate of the Reany Creek Formation 

and the amphibolite of the Mona Schist is not exposed, but it apparently coincides with a drainage line in the west-central part of sec. 2 

and the central part of sec. 3. There is a large angular discordance 

between the base of the conglomerate and the well-defined layering in 

the amphibolite. The curving trend of the contact suggests that the 

conglomerate was deposited in a U-shaped valley at least 2,500 feet 

deep.

The western lens of conglomerate (fig. 3) is well exposed near the 

crest of a steep slope in the southern third of sec. 6, T. 48 N., R. 26 W. 

The lens is about 3,800 feet long and has a maximum thickness of 250 

feet. The west limit of the lens is well exposed at the top of a steep 

slope in the southeastern part of sec. 1, T. 48 N., R. 27 W., but the 

east limit is less well defined. Conglomerate less than 100 feet thick 

is possibly concealed in a covered interval at the base of steep greenstone cliffs in sec. 5.

The western conglomerate lens is composed of boulders of granitic 

rock and greenstone in a chloritic matrix. A boulder 10 feet long was 

reported by Engel (1954); however, most of the boulders are 1^4 

feet in diameter and, regardless of size, range from well rounded to 

very angular (fig. 4). The western conglomerate differs from the eastern conglomerate in containing more greenstone and more chertmagnetite rock and in having a chloritic rather than arkosic matrix.
F8 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 4. Granitic boulders in basal conglomerate of the Reany Creek Formation, SW% sec. 6, T. 48 N., R, 26 W. A. Rounded boulder. #. Sharply angular 

boulder.
THE RE ANY CREEK FORMATION, MARQUETTE CO., MICH. F9

The unconformity at the base of the western conglomerate has 

truncated northwest-trending dikes of metadi abase and beds of crystal 

tuff in the Mona Schist. At least three Keweenawan (upper Precambrian) diabase dikes strike northeastward across the conglomerate 

and extend into the underlying greenstone.

GBAYWACKE AND SLATE WITH DISRUPTED BEDS OF ABKOSE AND 

DISPEBSED BOULDEBS OF GBANITE BOCK (MIDDLE UNIT)

The middle unit is the most widespread of the three units of the 

Reany Creek Formation. The best exposures are in the NWi/4 sec. 

12, T. 48 N.j R. 26 W., and along a steep slope west from the southwest corner of sec. 5, T. 48 N., R. 26 W.

SLATE

Slate is the most common rock in the middle unit. It is pale olive 

green, is thinly foliated, and lacks evidence of bedding. It contains 

a few angular grains of cloudy feldspars and rounded to angular 

grains of quartz sparingly dispersed in a matrix of chlorite, sericite, 

and an unidentified cloudy claylike material. Two samples of this rock 

were chemically analyzed (table 1), and the results are discussed 

later in this report (pp. F16-F18).

GRAYWACKE

Dark-gray-green graywacke forms a few outcrops. Bedding is generally obscure, but in a small exposure near the center of sec. 12, thin 

alternating layers of slate and graywacke resemble varves. Small 

rounded pebbles of granite, generally less than an inch in diameter, 

occur in an outcrop less than 20 feet from the interlaminated exposure. 

The graywacke is composed of angular to subrounded grains of cloudy 

plagioclase, relatively fresh microcline, quartz, some margins of which 

are corroded by chlorite, fragments of chloritized mafic rock, and 

relatively fresh quartz-feldspar rock fragments, all dispersed widely 

through a matrix of chlorite, sericite, and unidentified claylike material. Detrital zircon was identified in some thin sections.

ARKOSE

Pinkish-gray medium- to fine-grained firmly cemented arkose forms 

thin beds in the lower part of the slate-gray wacke unit and interclasts 

of small knots and rootless folds in many exposures elsewhere. The 

grains in the arkose are tightly packed and fairly well sorted. Clouded 

feldspar is about twice as abundant as quartz. Zircon, leucoxene, 

chloritized mafic minerals, and carbonates are accessories. In composition, the arkose differs from the graywacke chiefly by the smaller 

proportion of matrix to rock fragments.
F10 CONTRIBUTIONS TO STRATIGRAPHY

Arkose beds, a few inches to about a foot thick, are interbedded with 

greenish-gray chloritic slate in u few small outcrops near the south 

edge of the SW% sec. 2, T. 48 N., R. 26 W. In part, the arkose beds

are folded and broken resulting in an intermixture of slate and arkose. 

In one exposure (fig. 5), beds of arkose and slate are draped over a 

granite boulder about 22 inches in diameter. A few hundred feet east 

of this exposure the arkose beds are folded and broken, but there are 

no boulders.

2 FEET

EXPLANATION

Arkose Slate Granite

FIGURE 5. Sketch (from photograph) of granite boulder surrounded by disrupted 

beds of arkose and chloritic slate. Outcrop is about 2,000 feet east of southwest 

corner of sec. 2, T. 48 N., R. 26 W., and is near the base of the middle unit of the 

Reany Cre'ek Formation. Symmetrical draping of beds over the boulder possibly 

resulted from compaction during lithificatioi? of sediments deposited after 

emplacement of boulder; however, the overturned beds in lower right of 

sketch suggest forceful emplacement of the boulder into preexisting beds. Beds 

below boulder appear to be undisturbed.' Distortions in arkose beds above 

boulder resulted from slump. There are no other granite boulders in the exposure ; the outcrop extends a few feet to the left and right from the limits of 

the sketch.
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. Fll

The method of emplacement of the granite boulder is uncertain, but 

it could be attributed to gravity movements such as slumping or mudflows ; however, the surrounding rocks, even though folded and broken, 

do not appear to have been sufficiently disrupted for such an origin. 

Perhaps the boulder was ice rafted, and the sediments now forming the 

slate and arkose were deposited over it. Overturned arkose beds near 

the lower part of the boulder could have resulted from lateral displacement of the boulder, either at the time of original emplacement 

or later.

Near the east boundary of sec. 1, T. 48 N., R. 27 W., small rootless 

folds of arkose a few inches in diameter are widely scattered in the 

slate on and near the crest of a steep slope. These fragments of arkose 

appear similar to the arkose exposed in sec. 2, and thus it is assumed 

that they are of intraformational origin. There is a general decrease 

in size and abundance of the arkose intraclasts upward from the base 

of the slate. Evidence of bedding in some of the larger fragments 

indicates they were formerly part of a bed or series of beds (fig. 6). 

However, bedding is not common in the smaller pieces of arkose; possibly they were never part of extensive beds, but were deposited as 

isolated small pods in what is now slate. The folded and broken fragments of arkose may have resulted from slumping, mudflows, slip 

folding within the slate, or possibly from disruption of beds by ice in a 

till-like deposit.

Features somewhat similar to the disrupted beds and fragments of 

arkose have been reported in the Gowganda Formation. Schenk (1965, 

p. 312-314) described formerly well-laminated interbedded argillite 

and quartzite in the Gowganda Formation that have been extremely 

swirled, although the laminae in the surrounding rocks are undisturbed. He ascribed these features to deformation caused by slumping.

A. T. Ovenshine (written commun., 1967) described rootless folds 

of medium- to coarse-grained poorly sorted pink arkose dispersed 

through finer grained sediments in the Gowganda. He could not attribute these folded inclusions to tectonism, because the enclosing 

beds dip only a few degrees and no secondary planar structures are 

found. He also noted that similar features have been found in permafrost soils.

DISPERSED GRANITIC MEGACLAS.TS

Granitic pebbles and boulders, ranging from less than an inch to 

as much as 22 inches in diameter, are widely dispersed in the slate 

and graywacke and are the distinguishing feature of the Reany Creek 

Formation. The pebbles and boulders can be found in most outcrops 

even if the exposure is only a few square feet in area. In some large 

outcrops, however, careful search is required to find one or two granitic
F12 CONTRIBUTIONS TO STRATIGRAPHY

EXPLANATION

Arkose Chloritic slate

FIGURE 6. Sketch of outcrop of slate containing broken beds of arkose from near 

the base of the middle unit of the Reany Creek Formation. Outcrop is near the 

top of a steep slope in the SE% sec. 1, T. 48 N., R. 27 W. Well-defined bedding is 

evident in larger fragments of arkose; it is at a high angle to the foliation in 

the slate and is oriented differently in each fragment.

clasts in an outcrop area of as much as several hundred square feet. 

Some boulders, as much as several inches in diameter, appear completely isolated from other megaclasts. Where several pebbles and 

boulders are found in a small area, they commonly are crudely alined 

parallel to the foliation in the slate. Most of the larger boulders are 

round, but some are subangular to angular. There is no systematic 

change in size or abundance of the granitic boulders along or across 

the strike of the formation. Moreover, sedimentary features in the 

slates surrounding these boulders provide no clues as to their origin. 

Ice rafting seems to be the most reasonable method of emplacement; 

however, no striated boulders have been found.
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F13

INTERBEDDED ARKOSE, SLATE, GEAYWACKE, CONGLOMERATE.

AND QUARTZITE

The upper unit in the Reany Creek Formation (fig. 3) consists of 

interbedded arkose, slate, graywacke, conglomerate, and quartzite. 

The outcrops south of it are of sheared metavolcanic rocks of the 

Mona Schist against which the Reany Creek Formation has been 

faulted. The only exposure of the contact between the two formations 

is in Reany Creek about 1,000 feet north of the center of sec. 10, T. 48 

N., R. 26 W. The easternmost exposure of this unit is in Reany Creek 

in sec. 10; other outcrops are in a belt 500-800 feet wide that extends 

west to the edge of the area shown in figure 2.

ARKOSE

Beds of massive pinkish-gray arkose crop out south of Reany 

Creek in the north-central part of sec. 9, T. 48 N., R, 26 W.; on the 

north edge of the county road on the north side of Dead River near 

the east border of sec. 7; and in a small southeast-draining valley at 

the north edge of Dead River Storage Basin, about 1,500 feet west 

of the east edge of sec. 7, T. 48 N., R. 26 W. Foliated coarse-grained 

pinkish-gray arkose is exposed on the north and south edges of 

Dead River Storage Basin in sec. 1, T. 48 N., R. 27 W. In the easternmost exposure of arkose in sec. 9, feldspar is dominant over quartz, 

as it is in the disrupted beds of arkose in the slate-gray wacke unit, but 

to the west in sees. 1 and 7, the arkose contains as much as 75 percent 

quartz.

CONGLOMERATE

Conglomerate is exposed along the north shore of Dead River Storage Basin in sec. 7, T. 48 N"., R. 26 W.; near the east boundary of sec. 1, 

T. 48 N., R. 27 W.; and in Reany Creek north of the center of sec. 10, 

T.48N.,R.26W.

Several beds of conglomerate, 1-3 feet thick and separated by 

3-5 feet of chloritic slate and coarse-grained graywacke, are exposed 

on the shore of Dead River Storage Basin west of a small inlet 300 

feet west of the east edge of sec. 7. A photograph of one of the beds is 

shown in figure 7. The beds are relatively well sorted, being composed 

of clasts ranging from 3-5 inches in diameter; the matrix of chloritic 

slate forms only a very small percentage of the beds. A few large 

boulders, some as much as 15 inches in diameter, occur along the 

beds. In some places, the beds abut such boulders, and in other places, 

layers of the smaller sized material bend around the large boulder. 

The most common boulders are light-gray medium-grained granite, but 

there are also large clasts of greenstone and a few boulders of finegrained quartzite.
F14 CONTRIBUTIONS TO STRATIGRAPHY

B

FIGURE 7. Conglomerate in the upper part of the Reany Creek Formation. Exposed along the north shore of the Dead River Storage Basin in the NEJ/4 sec. 7, 

T. 48 N., R. 26 W. A. Nonbedded dispersed conglomerate with slaty graywacke matrix. B. Interbedded conglomerate and graywacke.
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F15

The conglomerate east of the small inlet in the northeast corner 

of sec. 7 is not bedded, but consists of pebbles and boulders of granite 

that are broadly dispersed throughout a chloritic slate matrix containing a few thin lenses of gray fine-grained quartzite. The distribution of the pebbles and boulders appears to be random, and the 

exposure has the general aspect of an indurated till. The foliation in 

the slate is bent or compressed near the margins of many of the larger 

boulders, but there is no definite evidence of penetration such as 

might be expected from ice-rafted erratics dropped into soft sediment. 

(Figure 7A is from this locality.)

QTJARTZITE

Fine-grained gray feldspathic quartzite is exposed 1,000 feet west 

and 1,800 feet south of the northeast corner of sec. 8, T. 48 N., R. 26 W., 

and north of the arkose in the northeastern part of section 7. Large 

lenses of very fine grained light-gray quartzite occur in chloritic 

slate on the north border of Dead Kiver Storage Basin along the east 

boundary of sec. 7. In all these exposures, the quartzite is relatively 

massive, bedding is indistinct, and there is a suggestion that it forms 

lenticular bodies.

Fine-grained gray and light-gray quartzite, with some thin interbeds 

of sericitic slate, crops out near the crest of a hill on the south side of 

Dead River Storage Basin in sec. 1, T. 48 N., R. 27 W. This quartzite is 

included within the Reany Creek Formation; however, no conglomerate beds are exposed on this hill, and future work may show that this 

quartzite south of the storage basin is not part of the Reany Creek.

THICKNESS

The thickness of the Reany Creek Formation can be determined only 

within broad limits. The estimated thickness of different parts of the 

formation are as follows: The eastern basal conglomerate is 1,800- 

2,000 feet thick; the western basal conglomerate is 250 feet thick; the 

middle unit is about 600 feet thick at the west boundary of the 

Negaunee 714-minute quadrangle and about 1,000 feet thick in the 

eastern part of the quadrangle; and the upper conglomerate, arkose, 

and quartzite is 300-400 feet thick. Maximum thickness of the formation in the quadrangle is between 3,000 and 3,500 feet.

CHEMICAL COMPOSITION

The slate in the middle member of the Reany Creek Formation is 

similar in chemical composition to the slates containing boulders in 

other Precambrian formations in the Lake Superior region (table 1), 

but differs from average Precambrian slate (table 2). The slates
F16 CONTRIBUTIONS TO STRATIGRAPHY

containing boulders have a high Na2O: K2O ratio but a low Fe2O3 : FeO 

ratio; they are low in CaO. This composition, which is similar to that 

of sandstone (graywacke) of a eugeosyncline (Middleton, 1960, p. 

1017), suggests deposition from a source in which mechanical weathering was predominant and chemical weathering was minimal. The high 

Na2O content of the slate of the Keany Creek Formation might be due 

either to source rocks rich in Na2 0 (table 3) or to postdepositional 

albitization.

TABLE 1. Chemical analyses, in weight percent, of slate from the Reany Creek 

Formation compared with graywacke and argillite from other dispersed conglomerates of Precambrian age

TiOi...... ............... ..

A12 03 -----.--. -------------

Fe2 03 

FeO--~ --------------

MnO- ------------------

MgO -- . 

CaO- -- --------

N&tO.... ................ ..

 K,O. ......................

HtO+ .. ....................

H2 0--. .---------- --

COz-..-. ---------

PtOi... ....................

S03 

PI

F... .......................

S-..~- 

BaO - ------------

C.. . --------------

Total.--.. -----------

1

-...--....--... 63.7

 .53

 ... 15.9

 1.0

.-..--......... 4.6

. - -... .03

 3.2

--..-..-..--... .85

------------ 4.5

............... 2.3

 _ 2.6

....... ........ .00

............... .35

-.-...-.....-. .16

. . 100

2

65.6

.52

15.2

1.3

3.7

.11

3.4

' .57

4.2

2.4

2.5

.02

.15 .

.15 .

100

3

61.98

.60

17.20

1.42

4.49

.10

3.27

1.00

5.27

2.04

2.70

.10

100. 17

4

61.68

.49

16.48

1.73

5.61

.09

3.18

.53

3.99

2.62

2.95

.08

.12

.20

.01

.01

.05

.11

.04

.00 .

99.97

5

58.82

.73 .

16.46 .

1.10 .

7.20 .

.09 .

4.92 .

.76

4.03

1.60

3.73 .

.11 .

.01 .

.17 .

.02 .

.03 .

.04 .

.05 .

.00 .

99.87 .

6 7

61. 54 70. 0

........ .6

....... 13.2

....... 1.0

........ 3.9

....... .1

........ 2.9

.84 .7

4. 73 4. 0

2. 84 1. 2

........ 2.0

........ .1

........ 99.7

8

61.0

.4

18.0

1.2

4.6

.1

4.0

1.4

3.2

2.3

3.6

.1

Trace

99.9

1. Reany Creek Formation. Slate with widely dispersed pebbles and boulders of granite. SEMSEM sec. 6, 

T. 48 N., E. 26 W. Sample No. P-310a-66. Lab. No. W-167403. U.S. Geological Survey Rapid Rock 

Analysis. P. Elrnore, L. Artis, G. Chloe, H. Smith, S. Botts and J. Glenn, analysts.

2. Reany Creek Formation. Slate with widely dispersed pebbles and boulders of granite. SWJ^NE}^ sec. 

11, T. 48 N., R. 26 W. Sample No. P-642a-66. Lab. No. W-167404. U.S. Geological Survey Rapid Rock 

Analysis. P. Elmore, L. Artis, G. Chloe, H. Smith, S. Botts, J. Glenn, analysts.

3. Gowranda Formation. Matrix of boulder conglomerate. Section 4, Thompson Township, Ontario, Canada. 

M. F. Conner, analyst (Collins, 1925, p. 66).

4. Cobalt Series (Gowganda Formation). Varved argillite. Wells Township, Ontario, Canada. L. N. Tarrant, analyst. (Pettijohn and Bastron, 1959, p. 595).

5. Cobalt Series (Gowganda Formation). Varved argillite. Olive Township. M. Balazs, analyst. (Pettijohn 

and Bastron, 1959, p. 595).

6. Cobalt Series (Gowganda Formation). Argillite from Lily Lake in the Gowganda district, Ontario, 

Canada. Partial analysis. (Wilson, 1913, p. 139).

7. Timiskaming graywacke, near Porcupine Lake, Ontario, Canada. H. B. Wiik, analyst. (MacPherson, 

1958, table 1, p. 76).

8. Timiskaming argillite, Ogden Township, Ontario, Canada. H. B. Wiik, analyst. (MacPherson, 1958, 

table 1, p. 76).

The two analyzed samples of slate from the Keany Creek Formation 

are from outcrops nearly 4 miles apart one from near the southeast 

corner of sec. 6 and the other from about 1,000 feet northeast of the 

center of sec. 11. Both outcrops are of uniformly fine grained chloritic 

slate containing widely scattered granitic boulders. Semiquantitative 

analyses of the two samples are given in table 4, together with spectrographic analyses of two samples of argillite from the. Gowganda 

Formation. The trace-element content of the two formations is similar 

except for the higher Ba and Cu content of the Reany Creek 

Formation.
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F17

TABLE 2. Average chemical composition, in weight percent, of slates 

and argillite in dispersed conglomerates and of other pelitic rocks

SK>2--- -------------------

Ti02.----...-. .......

MtOt...... ...............

Ye^----- ---------------

FeO......................

MnO. ....................

MgO.. ...................

CaO......................

Na20.....................

K2 0. .....................

HzO*..--.. --.-.-.-. 

HsO-.. .... ...............

C02------.-.-----.-.

P2 0s.--. .. ...

S03 -.. ...................

................. 64.6

................. .53

................. 15.5

................ 1.1

................. 4.2

................. .07

................ 3.3

................ .71

................. 4.3

................. 2.3

................. 2.6 

................ .01

................. .20

................ .16

60.83

.61

16.71

1.42

5.77

.09

3.79

.76

4.43

2.09

3.13 

.10

.07

.18

.02

56.30

.77

17.24

3.83

5.09

.10 ..

2.54

1.00

1.23

3.79

3.311 

.381

.84

.14

.28

58.10

.65

15.40

4.02

2.45

2.44

3.11

1.30

3.24

5.00

2.63

.17 ..

.64 ..

60.64

.73

17.32

2.25

3.66

2.60

1.54

1.19

3.69

J3.51 

\ .62

1.47

Total.............................. 99.58 100.00 96.84 99.15 99.22

1. Average Reany Creek Formation (average of 1 and 2, table 1).

2. Average Gowganda Formation (average of 3, 4, and 5, table 1).

3. Average Precambrian slate, 33 analyses (Nanz, 1953, p. 58).

4. Average shale (Clarke, 1924, p. 34).

5. Average slate (Eckel, 1904, p. 26).

TABLE 3. Chemical analyses, in weight percent, of lower 

Precambrian rocks in the Negaunee 7%-minute quadrangle

[U.S. Geological Survey Rapid Rock analyses. P. Elmore, H. Smith, L. Artis, 

G. Chloe, S. Botts, and J. Glenn, analysts]

8102 ------------

Ti02----~ 

Ah03.. ..................

F&Ot. ..................

FeO. ................ ....

MnO.. .

MgO.. . ---------

CaO.... . ................

Na2 0 .... ...... 

K20... ..... ...... ..

H20+.... . _ . . 

H8 0-. . ............. ..

C02 --.- ---------

P2 05 .. ...... ............

.. .... 72.9

.- ...- .23

. 14.6

...... - .67

. .66

...... .04

.... .--. .56

............... 1.4

..... . 5.0

............... 2.9

............... .58

-------- .15

...._ - <.05

.-. ... - .13

49.7

.77

15.8

2.3

9.6

.02

6.6

7.0

3.7

.70

2.7

.00

.31

.06

64.0

.62

15.1

.82

4.8

.04

3.5

2.2

3.0

2.2

2.8

.00

.18

.20

65.3

.43

15.2

1.0

1.6

.06

2.5

1.8

3.6

5.1

1.2

.06

1.8

.41

Total......................... 100 99 99 100

1. Granitic gneiss. SWJ4NE}i sec. 35, T. 49 N., R. 26 W. Sample No. P-226-66. 

Lab. No. W167842.

2. Layered amphibolite, Mona Schist. SE^SWJi sec. 4, T. 48 N., R. 26 W. Sample 

No. P-676a-66 Lab. No. W167400.

3. Sericite, chlorite, quartz-feldspar schist, Mona Schist. SWJ^SW^ sec. 18, T. 

48 N., R. 26 W. Sample No. P-173C-65. Lab. No. W167405.

4. Granodiorite. SE^SE^, sec. 15, T. 48 N., R. 26 W. Sample No. P-213-64. 

Lab. No. W164096.

Petti John and Bastron (1959, p. 596-598) suggested that the 

sodic nature of the argillites of the Cobalt Series is due to postdepositional changes. They compared the Na20: K20 ratio with that of 

average detrital sediments and found it is similar to that of gray wacke. 

The sodic nature of the graywacke is regarded as an original characteristic inherited from its source rocks, but they believed the pelitic 

rocks of the Cobalt Series should contain about 4r-5 percent CaO if they
F18 CONTRIBUTIONS TO STRATIGRAPHY

were the result only of glacial abrasion of the average rock of the 

Canadian Shield. They concluded that the high Na2O: K2O ratio and 

low CaO content indicate postdepositional albitization of the detrital 

plagioclase that resulted in loss of CaO and addition of Na2O.

TABLE 4. Semiquantitative spedrographic analyses of slate 

from the Reany Creek Formation compared with spedrographic 

analyses of argillite from the Gowganda Formation

[Results of Semiquantitative spectrographic analyses are reported in percent to 

the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, and 0.1, etc., which 

represent approximate midpoints of interval data on a geometric scale. The 

assigned interval for Semiquantitative results will include the quantitative 

value about 30 percent of the tune. Elements looked for but not detected in the 

Semiquantitative spectrographic analyses: Ag, As, Au, Bi, Cd, Eu, Ge, Hf, 

Hg, In, Li, Nd, Pd, Pr, Pt, Re, Sb, Sin, Sn, Ta, Te, Th, Tl, U, W. Elements 

looked for in the spectrographic analyses but not found: Ag, As, Au, Bi, Cd, 

Ce, Ge, Hg, In, Nb, Pd, Pt, Re, Rh, Ru, Sb, Sn, Ta, Te, Th, Tl, U, W. Dashes 

(..--) indicate element looked for but not detected]

B. ...................

Ba._ .................

Be-.... ...... .....

Co..................

Cr.... .................

Cu. ..................

Ga..... ...............

La........----..--...

Mo. ............... ...

Nb._ .................

Ni... .................

Pb._ .................

Sc.. .....-------....

Sr_. ...................

V... ...................

Y. ...................

Yb..-.. ......... ..

Zn. ...................

Zr.. ...................

.................. 0.1

.................. .002

.................. .02

...-..--.- ..-. .02

.................. .001

.................. .005

.................. .0003

.................. .0005

.................. .007

.................. .0007

.................. .0015

.................. .02

.................. .02

.-.....---...---.- .001

.................. .0001

.................. .015

0.1

.0015

.015

.01

.001

.003

nnna

.0007

.005

.0003

.0015

.015

.015

.001

.0001

.015

0.002

.03

.0002

.002

.02

.006

.001

.005

.004

.0005

.002

.005

.009

.003

.0001

.02

.009

0.002

.02

.0002

.002

.02

.0006

.001

.007

.006

.0006

.002

.01

.02

.003

.0002

.01

.01

1. Reany Creek Formation. Slate. Sample No. P-310a-66. Lab. No. W-167403. 

W. B. Crandell, analyst.

2. Reany Creek Formation. Slate. Sample No. P-642a-66. Lab. No. W-167404. 

W. B. Crandell, analyst.

3. Gowganda Formation. Varved argillite, Cobalt Series, Wells Township, 

Ontario, Canada. Harry Bastron, analyst (Pettijohn and Bastron, 1959, 

p. 595).

4. Gowganda Formation. Varved argillite, Cobalt Series, Olive Township, 

Ontario, Canada. Harry Bastron, analyst (Pettijohn and Bastron, 1959, 

p. 595).

The high Na2 0 content of the slate in the Eeany Creek Formation 

may be mainly the result of rapid mechanical weathering, with only 

minor chemical weathering, of source rocks in which the Na2 0: K2 0 

ratio is high. Lower Precambrian rocks similar to those in the Negaunee T1/^-minute quadrangle probably were the source for much of the 

sediment in the Keany Creek Formation. The analyses given in table 

3 show that the Na2O: K2O ratio is high in all samples except the 

granodiorite and that CaO exceeds Na2O only in the layered amphibolite. If rocks similar to those given in table 3 were the main 

source rocks for the slate of the Keany Creek Formation, then postdepositional albitization, as suggested by Pettijohn and Bastron 

(1959, p. 596-598) for the Gowganda Formation, might not have been
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F19

necessary to produce a Na2 0-rich sediment. To obtain a Na2 0-rich 

sediment from Na2 0-rich source rocks, however, a rather specialized 

environment would be required, in which chemical weathering would 

have to be inhibited to prevent leaching of the Na2 0. A glacial 

environment, such as that postulated for the Gowganda Formation 

(Collins, 1925; Schenk, 1965; Wilson, 1913), might have prevailed 

during deposition of the Reany Creek Formation, and this environment could have allowed the retention of Na2 0 in the slate.

ORIGIN

The broad range of rock types in the Reany Creek Formation indicates a variety of depositional conditions, but the same general 

environment probably prevailed during most of Reany Creek time. 

The coarse basal conglomerate required a source area with high 

initial relief, the well-sorted beds of arkose and quartzite represent 

fluvial deposits, and the very fine grained slate must have accumulated 

in either deep water or a restricted basin that had virtually no currents. 

The beds of conglomerate suggest torrential fluvial conditions; possibly they are outwash from glaciers. The boulders widely dispersed 

through the slate required a somewhat unique transporting medium, 

such as ice rafting. The disrupted beds of arkose in slate possibly 

resulted from slumping on an unstable slope. The local concentrations 

of pebbles and boulders in slate, which grossly resemble till, suggest 

glacial conditions. A rugged coastline from which glaciers extended 

into the sea over a relatively steep submarine slope could well have been 

the environment in which the sediments of the Reany Creek Formation 

accumulated.

The distinctive lithology of the middle sequence of the Reany Creek 

Formation slate and graywacke with widely dispersed boulders of 

granitic rock and the till-like deposits of pebbles and boulders in 

slate in the upper part are the most significant features in determining 

the origin of the formation. Precambrian formations in Canada with 

similar lithologies are believed to be of glacial origin (Collins, 1925, 

p. 73; Dott, 1961, p. 1303, Wilson, 1913, p. 140), and it is here suggested 

that the Reany Creek Formation is at least in part of glacial origin.

The glacial origin of some pebbly mudstones has been questioned in 

recent papers by Crowell (1957, 1964) and Dott (1961). They suggested that turbidity currents dispersed the coarser material in the 

fine-grained sediments. According to Dott (1961, p. 1301), the most 

convincing evidence for glacial origin is a widespread and polished 

pavement beneath till-like deposits. Striated boulders have been considered supporting evidence, although Winterer (1964, p. 175) has 

shown that these are not always of glacial origin. Crowell (1964, p.
F20 CONTRIBUTIONS TO STRATIGRAPHY

88) considered the best evidence for Precambrian glaciation to be 

the presence of megaclasts that clearly have been dropped into bottom 

sediments; moreover he stated that a glacial pavement is rarely preserved in a terrestrial environment.

Large clasts can be dispersed in fine-grained sediments by processes 

other than by ice rafting. Turbidity currents, mudflows, submarine 

slumping, thrust faults, and collapse of submarine escarpments can 

result in mixtures of fine and coarse material. Most of these dispersing processes produce features that aid in determining the origin of the 

anomalous boulders and pebbles. Some of these features include sole 

markings, convolute bedding, graded beds, and lenses consisting of 

poorly sorted mixtures that include fragments of the enclosing rocks. 

None of these features, however, are found in the Reany Creek 

Formation.

A glacial origin for at least part of the Reany Creek Formation 

is postulated because of the presence of widely dispersed pebbles and 

boulders of granitic rock in a matrix of slate and gray wacke and because of the lack of evidence for any other origin. Also, most of the 

larger clasts are of a granitic rock type that is not known to be in 

contact with the Reany Creek Formation, unless possibly under Pleistocene deposits in the eastern part of the area; thus this feature fits 

Mansfield's (1907) criterion that conglomerates of glacial origin contain boulders from a distant source. Other factors supporting a glacial 

origin are largely negative in nature. Because of an absence of obvious 

bedding surfaces, no determination can be made that megaclasts were 

dropped into and deformed soft bottom sediments. The contact of 

the Reany Creek Formation with the underlying formation is exposed 

at only a few places, and the nature of the surface on which the Reany 

Creek Formation rests cannot be determined. The disrupted beds of 

arkose in the lower part of the slate-graywacke unit could have resulted either from overriding glacial ice or from slump along steep 

submarine slopes.

The environment at the time of deposition of the Reany Creek 

Formation is believed to have been a rugged coastline bordered by 

steep submarine slopes. Piedmont glaciers on the highlands are envisaged as having fingers that extended toward the sea, gouging out 

U-shaped valleys that were later filled with coarse conglomerate. At 

the coastline or at the "buoyancy line" (Carey and Ahmad, 1961, p. 

873), subglacial streams deposited arkosic sand that oversteepened 

the upper submarine slopes, causing local slumping. Icebergs are 

believed to have carried boulders out to sea and dropped them into 

fine-grained bottom sediments. The environment was probably similar 

to that along modern coasts in subarctic regions.
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F21

CORRELATION AND AGE

The age of the Reany Creek Formation is indicated by its lithology, 

its mode of origin, its relationship to rocks of early Precambrian age, 

and its chemical composition. Comparison with other formations in the 

Lake Superior region suggests that the Reany Creek Formation is of 

middle Precambrian age, is in part of glacial origin, and is possibly 

correlative with tillite in the Gowganda Formation of Ontario, 

Canada. The correlation cannot be precise, however, because the Reany 

Creek Formation is not in contact with other known sedimentary 

formations of Precambrian age, and no radiometric dating has been 

done on it or adjacent formations.

It is not definite that the Reany Creek Formation is post early 

Precambrian in age, but the marked unconformity between it and 

the Mona Schist and the presence of Keweenawan dikes suggest a 

middle Precambrian age. Alternatively, the Reany Creek Formation 

could conceivably be equivalent to the Timiskaming, that is, older 

than the Animikie Series, but younger than other pre-Animikie lower 

Precambrian rocks in the area.

Evidence for glacial action in other Precambrian rocks in Michigan 

is described by Murray (1955, p. 344). He reported striations, gouges, 

grooves, polishing, and friction cracks in the Michigamme Slate 

near L'Anse, Mich., about 35 miles northwest of the Dead River basin. 

He did not indicate that any till-like sediments overlie the striated 

surfaces. At the present time, the evidence of glaciation reported 

by Murray does not seem to be related to that suggested by the sediments in the Reany Creek Formation.

J. E. Gair (U.S. Geological Survey, 1962, p. A24) described pebbles 

and cobbles of granite that may have been ice rafted and deposited 

in thinly layered, possibly varved, muds of the Wewe Slate (Animikie 

Series) in the Marquette syncline. This occurrence is about 10 miles 

southeast of outcrops of the Reany Creek Formation, but at the present 

time, the two formations cannot be correlated. It is of interest that 

the deposits of the Marquette syncline show evidence of possible glaciation in Precambrian time, and future work might prove that the deposits are broadly synchronous with those of the Reany Creek 

Formation.

The dispersed conglomerate in the Reany Creek Formation is similar 

to that described in the Fern Creek Formation of Dickinson County, 

Mich. (Pettijohn, 1943), the Gowganda Tillite of the Cobalt Series 

in Canada (Collins, 1925; Schenk, 1965), the Timiskaming Series in 

Ontario, Canada (Collins, 1937), and parts of the Knife Lake Group 

in northern Minnesota (Leith and others, 1935, p. 8; Grout and others, 

1951, p.1035).
F22 CONTRIBUTIONS TO STRATIGRAPHY

It is doubtful that the Reany Creek Formation can be correlated 

with the Knife Lake Group. Leith, Lund, and Leit'h (1935, p. 16) 

thought it highly improbable that the Knife Lake Group ever extended 

south of Lake Superior. Grout, Gruner, Schwartz, and Thiel (1951, 

p. 1075) stated that the correlation of the Knife Lake Group with the 

Huronian is not certain and that the relation of the Knife Lake Group 

to the Timiskaming cannot be ascertained until the relations of the 

Timiskaming beds to the older and younger rocks are better understood. Goldich, Nier, Baadsgaard, Hoffman, and Krueger (1961, 

p. 154) believed that the Knife Lake represents a sedimentary cycle 

of the Timiskaming period. It now seems probable that the Knife 

Lake Group and the Timiskaming are pre-Huronian in age and thus 

older than the Gowganda Formation.

The Fern Creek Formation is lithologically similar to the Reany 

Creek Formation, and both formations rest unconformably on rocks 

of early Precambrian age. The granitic gneiss on which the Fern 

Creek Formation rests may correlate with the granitic rocks that 

intrude the Mona Schist. Young (1966, p. 209) suggested that the 

Fern Creek Formation is correlative with the Cobalt Group the 

group that includes the Gowganda Formation on the north side of 

Lake Huron. Frarey (1966, p. 998) believed that such a correlation 

is very unlikely and, on the basis of published isotope dates, suggested 

that the Huronian in Canada belongs to an earlier cycle than the 

Animikie Series in Dickinson County, Mich.

The Reany Creek Formation crops out about 50 miles north of 

the Fern Creek Formation and about 160 miles west of the nearest 

outcrop of the Cobalt Series (fig. 8). The total length of outcrop of 

the Reany Creek Formation is about 7 miles. It hardly seems justified 

to project it over the distance required to connect it with either the 

Fern Creek Formation or the Gowganda Formation.

The Reany Creek Formation has, however, many features similar 

to those in the Gowganda Formation. Significant lithologic similarities 

include the irregularly shaped rootless folds of arkose and the dispersed pebbles and boulders of granite in slate. The chemical composition of the slate in the Reany Creek Formation is almost identical 

with that of the argillite and matrix of the boulder conglomerate in the 

Gowganda. Both formations rest unconformably on rocks of early 

Precambrian age. Wilson (1913, p. 123) reported that the general 

succession in the Cobalt Series is from basal conglomerate through 

graywacke, argillite, and arkose to an upper conglomerate. This succession is like that found in the Reany Creek Formation. Schenk (1965. 

p. 311) reported that in the Gowganda Formation of Vogt Township, 

Ontario, massive conglomeratic graywacke and laminated ft
THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F23

84° 82° 80°

MICHIGAN Fern Creek 

' Formation

FIGURE 8. Areas underlain by the Cobalt Series in Canada and the Reany 

Creek and Fern Creek Formations in Michigan.

quartzite alternate through at least 10,000 feet of strata; each of the 

two rock types appears three times, so the formation is divisible into 

six members. The base of the formation is represented in places by a 

seventh member granitic conglomerate. Possibly, the tripartite Reany 

Creek Formation, including the well-developed basal conglomerate, 

corresponds to Schenk's lower three members of the Gowganda Formation. The Cobalt Series in Canada trends nearly due west near the 

southeast tip of Lake Superior (fig. 8), and an extension of this trend 

would possibly include the area underlain by the Reany Creek 

Formation.

The lithologic and chemical similarities between the Reany Creek 

Formation and the Gowganda Formation seem sufficient to suggest a 

tentative correlation. To correlate them, however, would suggest reassignment of some strata in northern Michigan to the Huronian, and 

James (1958, p. 34-35) has concluded that the middle Precambrian 

rocks in northern Michigan should be assigned to the Animikie Series 

and not to the Huronian. Refinements in radiometric dating techniques 

will certainly be an aid in resolving correlation problems, but at 

present there are no meaningful radiometric ages to assist in the correlation of the Reany Creek Formation with formations near Lake 

Superior in Canada.

REFERENCES CITED

Carey, S. W., and Ahniad, Naseeruddin, 1961, Glacial marine sedimentation:

Tasmania Univ. Dept. Geology Pub. 87, p. 865-894. 

Clarke, F. W., 1924, The data of geochemistry [oth ed.]: U.S. Geol. Survey Bull.

770, 841 p.
F24 CONTRIBUTIONS TO STRATIGRAPHY

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Lake Superior region ; a review of newly discovered geologic features with a 

revised geologic map: U.S. Geol. Survey Prof. Paper 184, 34 p.

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THE REANY CREEK FORMATION, MARQUETTE CO., MICH. F25

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