Chapter 2

Late Pleistocene Glacial History of

the Central Upper Peninsula, Michigan

48

ABSTRACT

In the central Upper Peninsula of Michigan, little detailed work has been done to

describe the age, origin, or distribution of glacial landforms, or to interpret the history of

glacial ice movements during the late Pleistocene. Detailed analysis of texture and

lithology of 69 till samples, striation measurements, field reconnaissance and interpretation

of geomorphic characteristics, and landform analysis using topographic maps confirmed

previous interpretations that two lobes once occupied the study area, and that each lobe

was responsible for a different set of moraines. It was also confirmed that the moraines

are separated by a hummocky topography, sandy interlobate deposit. Till samples from

moraines south of the interlobate feature are distinctly different from samples taken from

north of the feature. Laboratory analysis shows that till south of the interlobate feature is

fine-grained and composed of Ordovician limestone and Cambrian sandstone grains in the

eastern part of the study area (bedrock lithologies the ice passed over in its westward

advance), and coarser-grained and rich in granite/gneiss toward the western part of the

study area (the bedrock underlying that area). Drumlins of the Menominee drumlin field

(in the southeastern pan of the study area) and bedrock striation measurements south of

the interlobate feature indicate S50°W ice movement in the eastern part of the study area,

becoming due west, then more northerly farther toward the west. Striations in the western

part of the drumlin field are perpendicular to the north-south oriented, curvilinear sets of

moraines and ice-contact scarps. The continuous change in orientation of drumlins and

striations and their relationship to the terminal moraine, along with till composition and

49

texture, suggests that a lobe moved initially from the northeast and spread out toward the

west.

North of the interlobate feature, sediments are coarse-grained, and composed of

Archean and Proterozoic-aged metamorphic and igneous lithologies. Fewer grains of

Paleozoic age were found in till north of the interlobate feature. Striation measurements

north of the interlobate feature show ice movement was dominantly from N50°E. Such

evidence supports the interpretation that different ice lobes occupied the region north and

south of the interlobate feature.

One additional moraine and outwash plain pair is located about ten kilometers

south of the Lake Superior shoreline and does not conform to the above model. These

deposits overlie older sediments and buried trees of the Gribben forest (C14 dated at 9,850

years before present) and represent a final, significant, re-advance of a single lobe out of

the Lake Superior basin.

From the evidence described above, and through correlation of the newly

described GLU's with deposits of known age west and south of the study area, it is

interpreted that the two ice lobes that contemporaneously advanced into the study region

correlate with the previously named Green Bay and Michigamme lobes of the Laurentide

ice sheet. During its earliest recorded advance across the study area, the Green Bay lobe

moved from the east and occupied the area south of the interlobate deposit, while the

Michigamme lobe moved from the northeast and occupied the area north of the interlobate

deposit. Retreat from their terminal positions began about 12,500 YBP. At this time, the

Green Bay lobe deposited the late Sagola moraine, while the Michigamme lobe deposited

50

the Republic moraine in the westernmost part of the study area. After east and

northeastward retreat from those positions, respectively, and subsequent re-advance at

11,850 YBP, the Green Bay lobe deposited the Green Hills moraine and the Michigamme

lobe deposited the Ishpeming moraine. The Ishpeming outwash plain formed distally to

both lobes and forms a continuous surface between the moraines. Downslope recession of

both lobes resulted in deposition of four additional minor ice-contact scarps and moraines,

each with small outwash plains on their distal sides. Both lobes retreated into the Lake

Superior basin, clearing the south shore of present Lake Superior about 11,000 YBP.

At about 10,000 YBP, the Superior lobe advanced onto the Upper Peninsula and

deposited the Marquette moraine that roughly parallels the modern shoreline of Lake

Superior. Sediments carried away from the moraine formed the Sands outwash plain and

buried the trees of the Gribben forest. No other advances of glacial ice are recorded in the

area after the Superior lobe retreated into the Lake Superior basin.

51

INTRODUCTION

This study documents the movement of glacial ice and the spatial distribution of

glacial features in southern Marquette and northern Dickinson counties, Michigan through

combined digital image processing and traditional field and laboratory techniques. Image

processing of Digital Elevation Model (DEM), Landsat Thematic Mapper (TM) and Side-

looking Airborne Radar (SLAR) data provided information for the initial interpretation of

the distribution of glacial landforms, while field and laboratory analysis were used to verify

and confirm the interpretations.

The study area is in the Upper Peninsula (U.P.) of Michigan, bounded by the

parallels 46° OO'N and 46° 30'N latitude, and the meridians 87° 15'W and 88° OO'W

longitude (Figure 1). This area encompasses the western 3/4 of the Gwinn, Michigan

1:100,000 topographic sheet. Little detailed glacial geologic mapping has been done in

this area, though several people have contributed to the general understanding of its

glacial history (Chamberlain, 1878; Russell, 1905, 1907; Leverett, 1909, 1911, 1929;

Bergquist, 1931; Martin, 1957; Farrand, 1960; Black, 1969; Hughes, 1971; Wright, 1971;

Hughes and Merry, 1978; Drexler, 1981; Farrand an Drexler, 1985; Peterson, 1986, etc.).

The central U.P. was affected by glacier ice moving across the area from the

northeast and east. Retreat toward the northeast gradually uncovered the study area

between the period beginning at 13,000-12,500 YBP and ending at about 9,500 YBP,

when the ice cleared the modern Lake Superior shoreline for the last time (Hughes and

Merry, 1978). The oldest deposits in the present study area were documented by Peterson

(1985, 1986), who mapped the Saint Johns and Sagola moraines (in the extreme western

MICHIGANUPPER PENINSULA

Lake Superior

Ishpening'Republic

1 Gwinn

Ralph . "NorthlandStudy Area

KJ

Figure 1. Study area. Portions of Marquette and Dickinson counties are included in the study. This area corresponds tothe western 3/4 of the Gwinn 1:100,000 scale U.S.G.S. topographic quadrangle.

53

portion of the current study area). He attributed them to deposition by the Michigamme

and Green Bay lobes of the Woodfordian Substage (approximately 13,000-12,500 YBP)

which entered the area from the northeast and east, respectively. Based on morphological

evidence, he suggested lobe movements were synchronous. Peterson's mapping officially

covered the Iron River 1° X 2° quadrangle, but carried over the east border slightly (into

the present study area) to draw attention to the existence of one significant moraine

segment northeast of the Saint Johns moraine and two segments east of the Sagola

moraine in the western part of the present study area. The author postulated that these

moraines are slightly younger than deposits of the maximum advances, and that the

younger of the two moraines east of the Sagola moraine may be time-equivalent to the

MacDonald moraine, which was deposited by the Ontonagon lobe in the western U.P. of

Michigan about 11,000 YBP. In contrast, Clayton (1984) correlates the southeastern

segment of the Sagola moraine with the late Athelstane moraine in eastern Wisconsin.

The late Athelstane moraine was deposited during the Greatlakean advance (11,850 YBP).

Clayton's interpretation is supported in this study. Thus, the younger of the two moraines

east of the Sagola moraine (in the present study area) was likely deposited during the

significant Greatlakean advance.

Russell (1904, 1907) and Leverett (1911, 1929) also recognized the moraine

segments and outwash plains deposited during the Greatlakean advance within the present

study area, but offered little explanation for their origin. They were disadvantaged in

making interpretations, as they had no large-scale topographic maps, aerial photographs,

or satellite imagery to study. However, both authors described a major variation in till

54

(composition and color) south of a series of northwesterly-trending moraines in northern

Marquette County. Limestone-rich till in the southern part of the county was attributed to

deposition by the Green Bay lobe. In contrast, they noted that till in northern Marquette

County was composed of igneous and metamorphic clasts. According to Leverett, the

Green Bay lobe entered the area from the east, carrying a great abundance of Paleozoic

sedimentary rocks. A second lobe entered from the northeast, carrying crystalline igneous

and metamorphic rock fragments. His interpretation is supported by the present study.

Russell, however, contended that much of the deposits in the southeast part of the current

study area, in a drumlinized landscape, are re-worked drift from an earlier, southeast-

oriented advance. His suggestion is based largely on the occurrence of native copper,

silver, and banded iron formation (BIF) he found in the till. Copper and silver were

presumed by Russell to have been derived from the Keweenaw Peninsula area, and the

BIF from northern Marquette County. In the present study, clasts of lithologies unique to

northern Marquette County were also found in till in the southern part of the present study

area. The clasts were found well south of the mapped extent of their (presumed)

provenance and incorporated throughout the sedimentary masses, not just at the surface or

just buried by other sediments. The significance of the exotic clasts is unclear because the

last motions of the ice masses were from northeast-to-southwest, not north-to-south as

their provenance suggests. Additionally, there are no distinct landforms or sedimentary

structures found in the present study area to confirm Russell's hypothesis.

Stuart et al. (1954), in a groundwater resources study, noticed that several

outwash terraces exist south of Negaunee and Ishpeming at elevations between 470 and

55

388 meters (1550 and 1280 feet). The most prominent terraces he identified exist at 442

m (1460 feet), 424 m (1400 feet) and 394 m (1300 feet) elevation, respectively.

Successively lower surfaces were postulated by Stuart to have formed by erosion of the

higher outwash plains, and subsequent deposition at a lower base level. This

interpretation is not supported by findings of the current study because the surface slope

of each terrace is toward the west, opposite of what would be expected if sediments were

derived from the west. Black (1966, 1969) also recognized the outwash plains (terraces)

south of Ishpeming. He used the spatial positions of the plains (and the moraines at their

edges) to help him trace the Valders (now named Greatlakean) ice margin from northeast

Wisconsin to the Upper Peninsula of Michigan. To aid in this task, he used striae

orientation measurements and the unbroken array of drumlins that extend from a known

Valders position north of Green Bay, Wisconsin to Northland, Michigan.

The most recent glacial advance to affect the region was not well-documented

until Hughes and Merry (1978) discovered an in situ forest of spruce and tamarack buried

by outwash at the Gribben tailings basin in Marquette County. Wood samples taken from

trees in the forest were C14 dated at 9,850 YBP. Based on this evidence, they described a

significant, new re-advance of ice out of the Lake Superior basin, and introduced the name

Marquette Stadial for the advance, and Marquette moraine (outer and inner) for the end

moraine(s) deposited at the ice front during its tenure. The moraine was mapped by

previous researchers, but its significance eluded them. Saarnisto (1974) mapped the

position of the Marquette (which he called Sands) moraine, but incorrectly gave 11,000

YBP as the time of deposition because he traced the margin to the outer Cartier belt south

56

of Sault Ste. Marie, Michigan. Leverett (1929) also recognized the impressive Marquette

Moraine, but was unaware of its significance. Once the Marquette advance was

documented, Drexler (1981) correlated the Marquette moraines eastward to a pair of

moraines near Munising, Michigan, which he called Grand Marais I & II. Further, he

cites evidence of a moraine younger than the inner Marquette moraine (Grand Marais III)

near the shore of Lake Superior in the Munising area. An equivalent to this moraine does

not extend into the present study area.

Hughes (1971, 1989) described channels southeast of Marquette that formed

during discharge events from the proglacial Duluth and post-Duluth Lakes in the western

Lake Superior basin. Eastward drainage of these lakes was allowed when the Marquette

ice front receded northward from the face of the Huron Mountains, exposing eastern

outlets for the lakes. Additional details regarding the drainageways were described by

Drexler (1981) and Drexler et al (1983).

METHODOLOGY

End moraines and contemporaneously-formed outwash plains, ice stagnation

landforms, drumlins, and other glacial features have been shown to indicate ice-marginal

positions (Flint, 1971;Koteff, 1974; Sugden and John, 1985), allowing interpretations

about relative ice movements. In this study, remote sensing imagery was the primary tool

used to identify and map the spatial distribution and relationships of these macro-scale

glacial landscape features.

57

For the remote sensing component of this study, both digital and paper forms were

used. Landsat Thematic Mapper (TM), Side-Looking Airborne Radar (SLAR), and

Digital Elevation Model (DEM) data were used in digital format. Paper products include

Landsat TM and SLAR photo-images at 1:100,000 scale. Photogeologic techniques

(interpretations based on color and tone, texture, and spatial relationships) were used to

initially identify features and ultimately to map their extent (after field verification and

sample analysis). Topographic maps (7 !/2 minute series U.S.G.S.) were the primary tool

for detailed field analysis.

Field study was conducted during two summer seasons to examine features that

were identified using remote sensing information or described by others. Samples were

collected from areas where detailed information was required, or to assess a feature of

unknown origin. Each collection site was identified after examination of remote sensing

imagery and topographic maps, and through field reconnaissance. Gravel pits, roadcuts,

and unique glacially formed features were located and exposures were examined.

Sedimentologic or stratigraphic data that could be related to changes in ice dynamics or

depositional environments were logged in detail. After surface investigation of such

features, soil borings were made using a hand auger, or pits were dug. Photographs of

key features were also taken.

Sediment samples (approximately 1 kg each) were collected to assess the

distribution and type of till at 69 sites across the study area (their location is symbolically

denoted on Plate 1). Samples were oven-dried, and split into halves. One half of the

sample was sieved to extract the 2 mm fraction only, which was analyzed for lithologic

58

composition using the grain-counting technique of Lucas et al (1978). The second half of

the sample was reserved for textural analysis. Data derived from grain counts were

entered into a database, and categorized into groupings that correspond to the major

bedrock lithologies found within, and around the study area. The data were then entered

into a spreadsheet and exported to statistical graphics and contouring software. Data

were finally plotted on ternary diagrams and as an isoline map. The percentage of

Paleozoic-age limestone and sandstone in samples was used as an indicator of the

direction ice came from, and to map the geographic extent of the ice lobes. Paleozoic-age

lithologies (sandstone and limestone) were used as the indicator lithologies because they

are easily identifiable under the microscope and are distinctly different than lithologies

derived from the northern part of the study area (Archean-age igneous and metamorphic,

and Proterozoic-age sedimentary and metamorphic rocks). Color of the till samples was

measured in the field using a standard Munsell color chart.

Particle size analysis (texture) was performed to aid in comparing sedimentary

deposits from different lobes and for stratigraphic information. The U.S.D.A. Natural

Resources Conservation Service (NRCS, formerly Soil Conservation Service, SCS)

hydrometer method was employed. Texture of the till samples varied widely, but most

were classified as sand to sandy loam. In general, the coarsest-grained till was present

above granitic bedrock and the finest-grained till was present over limestone bedrock.

Many samples collected over limestone bedrock were classified as loam to silt-loam on the

NRCS textural triangle.

59

To determine the direction of ice motion, the azimuths of striations were measured

in the field at many locations, and flute and drumlin orientations were measured from

topographic maps and TM imagery. The azimuths of directional features are shown on

Plate 1.

Data from water-well logs, geophysical investigations, and water-resources reports

were employed to gain overburden thickness/bedrock topography, and some stratigraphic

information. Resistivity studies conducted by Young et al. (1982) in the western portion

of the study area provided overburden thickness information where there were insufficient

water-well data. Bedrock topography maps were constructed from these data sources.

Eight-hundred ninety-three data points consisting of location, thickness and surface

elevation (meters above mean sea level interpolated from topographic maps) were entered

into a spreadsheet software program. Thickness was subtracted from surface elevation to

derive bedrock elevation. The location and bedrock elevation data were exported into a

contouring software application and kriged to produce a regularly spaced grid of output

values (dimensions = 500 lines by 500 columns). Topographic maps and perspective

views were produced from this data set. Figures that resulted from this procedure are a

generalization of overburden thickness and bedrock topography, because the distribution

of data points across the study area was non-uniform. It is thought to be an adequate

representation of such conditions on a glacial landscape scale.

60

GEOLOGIC SETTING

Bedrock Geology

The bedrock of the study area consists of three general lithologic/stratigraphic

units (Figure 2). In the central and west-central portion of the study area, Archean

granite/gneiss is present. It is generally termed the southern complex. Across the entire

northern portion of the study area are Proterozoic X metasediments, including the

Negaunee Iron Formation. Also, remnant patches of the Jacobsville Formation, a

Proterozoic Z or Cambrian sandstone, are found there. Cambrian sandstone (Munising

Formation) and Ordovician limestone (Au Train and Trempeleau Formations) comprise

the bedrock in the southeast and east-central part of the study area. These Paleozoic

rocks are the basal formations of the Michigan Basin series. They thin northward and

westward over the Archean and Proterozoic rocks.

Bedrock Topography

Bedrock topography is interpreted to have exerted significant control on the

movement of ice within the study area. It is instructive to examine the bedrock relief to

better understand the movement of ice and resulting distribution of geomorphic features in

the region. Figure 3 shows a contour map (3a) and a perspective view (3b) of bedrock

topography. In the perspective view, the azimuth of the look-direction is west-northwest.

The slope of the bedrock surface in most of the study area is to the southeast (except in

the extreme northeast where the slope locally faces the northeast). Elevations of the

bedrock surface in the extreme western portion of the study area exceed 450 meters, while

61

•Granite PiLakeSuperior

Prtsqut Isle Ft

Shot Pi&£*

5 4 3 2 10 N

543210 5 10 15Kilometers

O - Ordovician limestone

C - Cambrian sandstone

Xm - Proterozoic metasediments

Agn - Archean granite/gneiss

Figure 2. Bedrock Geology. Archean granite and gneiss compose the bedrock in thewest-central part of the study area, Proterozoic-aged metasediments are found in theextreme north and in the southwest, and Paleozoic sandstone and limestone composethe southeastern third (after Morey, et al., 1982).

62

Drunlins

Strlatlons430000 440000 450000 460000 470000 480000

UTM meters eastingcontour intervol in neters

- 500,00-(LJ>

*a 400,00-tuW

* 300.00-&o

£ 200,00-u•fHi

5" 100,00sv

Michigammelobe

Green Baylobe

NE

Figure 3. Bedrock topography. Paths of the Green Bay and Michigamme lobes areindicated by drumlin and striation orientation symbols, and by bold arrows.3 (a) Contour map of bedrock topography. Contour interval is 25 meters.3(b) Perspective view of bedrock topography. Note the general south-to-southeasterlyslope of the bedrock surface, except in the northeast, where the slope is much greater andtoward the northeast.

63

those in the southeast are about 200 meters (horizontal distance about 40 km). The

surface elevation of Lake Superior in the extreme northeast corner of the study area is 183

meters. The Paleozoic rock surface in the southeast is relatively low-relief, whereas the

surface of the granitic rocks, and especially the Proterozoic rocks in the north, are higher-

relief. High-relief, high elevation bedrock impedes ice flow. Because of this, only

vigorous advances could breach the rugged bedrock areas in the north, and the ice

preferentially followed the path of least resistance; it flowed southward through the

Paleozoic bedrock lowlands. The Green Bay lobe followed this path and extended farthest

south during the Woodfordian and Greatlakean advances, the latter burying trees near

Two Rivers, Wisconsin (Attig et a/., 1985).

Striation, drumlin, and flute orientations (Figure 3a, and Plate 1) demonstrate the

influence of bedrock topography on ice motion. Ice movements from the northeast were

southwest-oriented (S50°W, commonly). Striae formed by the Michigamme lobe in the

north part of the study area are uniformly oriented in that direction, while southwest-

oriented striations formed by the Green Bay lobe exist only in the extreme eastern portion

of the study area. Drumlins in the far eastern portion of the study area also maintain a

southwesterly orientation. West-to-northwest (S60°W to N45°W) oriented striae,

drumlins, and flutes are only found south of the relatively high-relief Proterozoic bedrock.

They formed as the Green Bay lobe "fanned-out" south of the bedrock high area in the

north. Where the lobes met, striation orientations are nearly perpendicular to each another

(N50°E beneath the Michigamme lobe and N45°W beneath the Green Bay lobe). Thus,

striation evidence shows that the ice lobes converged along an east-west trending zone

64

near the center of the study area. Other supporting evidence for the lobes merging in that

locale are the change in orientation of drumlins and moraines, and the variation in clast

lithology within the drift on either side of the convergence zone (both are described in the

next section).

DATA AND INTERPRETATION

This section presents data collected from field and laboratory study, and

interpretations of landform origins. First, topography, sediments, and morphology of the

region are described, then soils and specific site data are presented. In the section

following this one, temporal movements of glacial ice are interpreted from this

information.

Topography

A perspective view of the surface topography within the study area (Figure 4) and

an west-east profile of surface elevations across the center of the study area (Figure 5) aid

in the visualization of landscape units. The view direction in Figure 4 is toward the west-

northwest and the profile (Figure 5) is along the line-of-sight of the perspective view.

Both images were derived through image processing of DEM data for the region. The

most striking features apparent in both figures are the series of stair-step like terraces.

Note that there are at least four major terraces and several minor ones decreasing in

elevation toward the east (there are eight different surfaces recognized but they could not

all be shown on a single profile). The features are interpreted as outwash plains that

Figure 4. Perspective view derived from image processing of digital elevation model (DEM) data for the study area.Note the outwash terraces (described in the text).

VNW Profile of surface elevation ESE

600

Upper Peninsulaof Michigan

250

10000 Distance (meters) 20000 30000

Figure 5. West-east surface profile across the study area. The line of the profile is indicated in the inset box. Note thedistinct stair-step like profile formed by the outwash plains (terraces) at successively lower elevations toward the east. In all,eight levels were recognized within the study area.

ONON

67

represent deposition of fluvial sediments in front of either active or stagnant ice. The

slope of the plains is toward the west. At the eastern edge of each surface, east-to-

northeast facing escarpments are present. They represent the ice-marginal position when

the terrace was forming. The escarpments are either moraines or ice-contact slopes. Each

successively lower surface, and the escarpment that forms its eastern edge (toward the

east) was deposited later than those higher in elevation because ice retreated from west to

east (if features in the east were deposited first they would have been destroyed by

vigorous advances toward the west), and provides a distinct record of ice retreat. Thus,

the assemblage of landscape features forms a significant pattern interpreted as a result of

episodic retreat of ice from west to east.

Sediments

Drift in the area can be divided into three general types, based mainly upon the

mode of deposition and the underlying bedrock lithology. In the north, central and

western portions of the study area, sandy, reddish-colored till and glaciofluvial deposits,

such as outwash plains, are the most common glacial sediments. Both are cut by fluvial

channelways in many places. In the southeast part of the study area, calcareous-rich till

and glaciofluvial deposits are found, which comprise a drumlinized landscape. The major

differences between these two drift associations are their lithologic constituents and

texture. In the north, lithologies reflect the crystalline and metasedimentary bedrock the

ice passed over, in the southeast, drift lithologies mainly reflect the underlying sedimentary

limestone and calcareous sandstone. Till found in the southeast is also typically much

68

finer-grained (silt loam) and lighter-colored (gray) than till in the north-central and

western portions (red hues).

The third type of drift is mainly of lacustrine origin, consisting of sand and silt,

with minor amounts of eolian sand and sandy till. The most recent glacial advance into the

region was responsible for these deposits (Hughes, 1971; Hughes and Merry, 1978;

Drexler, 1981). Some fluvial sand and gravel also exist in channels within the lacustrine

assemblage. This complex of lacustrine and associated fluvial and eolian sediments are

found mainly near Lake Superior in the northeast part of the study area and occupies a

small percentage of the study area. They were deposited in ice marginal lakes, along the

shores of those lakes, and in streams carrying discharge from proglacial lakes in the

western Lake Superior basin that were flowing eastward through the Marquette, Michigan

area (Hughes, 1971).

Figure 6 shows all 69 till samples plotted on a textural triangle. Samples collected

from deposits of each of the three major lobes are denoted by these symbols; "G" for the

Green Bay lobe, "M" for the Michigamme lobe, and "S" for the Superior lobe. Note that

there is significant overlap between till deposited by all three major lobes, with the

exception of Green Bay lobe till that was collected over limestone bedrock, which is much

finer-grained ("G" plotted in the loam to silt-loam area of the ternary plot). Most samples

could not be differentiated by texture alone. Till deposited by the Michigamme and

Superior lobes do not vary much in texture. Many are classified as sand to sandy-loam.

In Figure 7, a ternary plot of Archean, Proterozoic, and Paleozoic grain

percentages in till for each of the major lobes that transected the area, note that there is a

69

C l a y

G - Green BayM - MlchlganneS - Superior

Figure 6. Textural triangle showing till samples taken from 69 sites within the study area.Samples are differentiated according to the ice lobe from which they were deposited(G=Green Bay, M=Michigamme) S=Superior). Green Bay lobe samples taken overlimestone bedrock had the highest percentage of silt and clay, all the remaining sampleswere very sandy-textured.

70

Paleozoic

G - Green BayM = MichiganneS - Superior

Archean Proterozoic

Figure 7. Ternary plot of percentages of Archean, Proterozoic, and Paleozoic coarse sand(2 mm) grains in till samples. Because the Green Bay lobe passed exclusively over thePaleozoic-age sandstone and limestone, percentages of these lithologies in till may be usedto discriminate Green Bay lobe deposits from deposits of the Michigamme lobe, butdeposits of the Superior and Michigamme lobe were indistinguishable based only on grainlithologies.

71

clustering of elements near the Paleozoic apex of the triangle for Green Bay lobe samples.

These samples were collected directly over sandstone and limestone bedrock. The relative

percentage of Paleozoic lithologies in sediment samples, as compared to Archean and

Proterozoic lithologies in the Green Bay lobe till, decreases away from their provenance.

Michigamme and Superior lobe till contained few Paleozoic-lithology grains and could not

be differentiated from one-another based on lithology of the grains alone. Thus, sediments

deposited by the Green Bay lobe are lithologically distinct from others found in the study

area. Figure 8 shows the spatial distribution of the percentage of Paleozoic-age lithologies

found in till samples. Note that extremely high percentages occur in the southeast, directly

over Paleozoic limestone and sandstone bedrock. Most samples collected there had nearly

100% limestone and sandstone grains. The percentage of these lithologies decreases

gradually from the southeast toward the west, but decreases very rapidly toward the north.

Notably, the area of maximum rate of decrease of percent Paleozoic lithologies occurs in

the central portion of the study area along an east-west oriented trend. This is where the

Green Bay and Michigamme lobes met.

The color of most till in the study area varies in reddish hues (i.e., 5YR typically)

but intensity and chroma varied as a function of the underlying bedrock. Very red (10R)

and lowest value and highest chroma till (3/7) is found close to Proterozoic iron

formations, while highest value and lowest chroma till (10YR7/4) is situated above, and

down-ice from, areas of limestone bedrock. Both the Michigamme lobe and Green Bay

lobe till are similar in color and cannot be differentiated by color alone. However, Green

72

5145000-

5135000-

.c 5125000H

5115000-

5105000-

5095000-

425000 435000 445000 455000

UTM Easting

465000 475000

Figure 8. Contour map of the percentage of Paleozoic-age lithologies in the 2 mm sandfraction of till samples. Note the highest percentages of sandstone and limestone arefound directly over bedrock of those lithologies, except in a westerly-trending zone in thesouth-central of the study area. This anomaly is created by subglacial channels beneath theGreen Bay lobe that transported water and sediments that originated in the Paleozoic-bedrock zone toward the margin. Striation (arrows) and drumlin orientations are shownon the map.

73

Bay lobe till over limestone bedrock has unique coloration (less red hue and high values of

intensity and chroma) and is easily identified.

Moraines, ice-contact features, and outwash plains

The oldest moraines, ice-contact features, and outwash plains studied are located

in the extreme western part of the study area. Peterson (1986) established that the

Michigamme Lobe advanced southwestward across the Upper Peninsula from the Huron

Mountain area north of Marquette, and the Green Bay Lobe moved southwest, then

westward from the eastern Lake Superior and the Lake Michigan basins. At their terminal

position late in the Woodfordian substage, the Green Bay Lobe constructed the Sagola

Moraine and the Michigamme Lobe constructed the Saint Johns moraine (Peterson, 1986).

The Sagola moraine is composed of red, sandy till with inclusions of stratified sand and

gravel in many places. The Saint Johns moraine is composed of sandy, brown till with

lesser amounts of stratified sand and gravel. The till deposited by both lobes at this time

probably correlates with the Silver Cliff member of the Kewaunee Formation (McCartney

'and Mickelson, 1982) in eastern Wisconsin although the till found within the present study

area is coarser-grained. Because these sediments have been correlated with deposits of

known age in Wisconsin (Clayton, 1984) their age is estimated to be about 12,500-12,300

YBP. The deposits of the main Sagola moraine also mark the westernmost edge of the

"red drift" noted by Russell (1907), Leverett (1929) andThwaites (1943). Black (1966)

recognized, however, that the red drift of the Valders (Greatlakean) Stadial becomes

"brown, sandy, and stony to the north" (in Shawano County, Wisconsin), and claimed that

74

the former ice margin could not be mapped on drift color, texture, or composition alone.

He said that the distribution of landforms must be incorporated when mapping the

Greatlakean border, and that drift characteristics are extremely variable. This assertion is

supported by findings in the present study. Generally, the drift color of the Green Bay

lobe deposits is variable; 10R4/4 in the west, commonly 5YR4/4 throughout much of the

area, and more pale (10YR6/4) to the east. The change reflects the increasing influence of

limestone bedrock on the color of the till toward the east.

A formerly unnamed moraine parallels the Saint Johns moraine and is located

about 10 kilometers to the northeast. It is a small but distinct feature, herein called the

Republic moraine, as it nearly passes through the village of Republic, MI. Also, branching

to the east of, and paralleling the main Sagola moraine at its northernmost extent is a

second moraine. The eastern segment of the northeastern 10 km of the Sagola moraine is

a distinct landform, so the name "late" Sagola moraine is used for that part. It is variable

in width, typically at least 1-5 km wide, and it ranges from 10-20 m in height. A relatively

small outwash plain (about 10 km2) formed distally to the Republic and late Sagola

moraines and is continuous between them. It slopes toward the southwest. It is

represented as terrace "#1" on Figures 4 and 5, and on other figures throughout this paper.

Till of the Republic moraine is very sandy and grey-brown in color (7.5YR5/4).

Large boulders and cobbles of granite lithology are concentrated at the surface in many

places. Lithologic constituents of the drift closely reflect the type of bedrock the ice

passed over (Proterozoic metasediments and Archean granite). Foliated, compact basal

till below about 1 m of sandy ablation till was discovered in several roadcuts north of

75

Republic, in a position within 1 km up-ice (northeast) from the Republic moraine. In one

pit (SW 1/4, T47N, R29W), the basal till overlies a different, sandy-grained till, deposited

during an earlier advance.

Sediments of the outwash plain that formed distally to the Republic and late Sagola

moraines pinch out against bedrock high areas in the north, and against previously

deposited drift (the main Sagola moraine) to the west. Figure 9 shows a typical

relationship of sandy, fluvial deposits overlying coarse-textured, bouldery till in the

Republic area, at the western edge of the outwash plain. Note the lag of boulders in the

upper part of the till sequence, at the till/sand interface. The finer component was eroded

from the till by meltwater, before the outwash sand was deposited. The lag surface

represents this event.

Another ice-contact position to the east of the late Sagola moraine was identified

on topographic maps and satellite imagery. This moraine, about 5 km east of and

paralleling the late Sagola moraine, is continuous and curvilinear (concave toward the

east), and generally oriented in a north-south direction. This feature was recognized by

Peterson (1986), but was left unnamed. It is called the Green Hills moraine in this study

because it begins at the prominent "Green Hills" of the Green Hills U.S.G.S. quadrangle.

Till of the Green Hills moraine is very coarse-grained and composed of mostly Archean

granite clasts. Some sandstone and lesser amounts of limestone (derived from the east)

were also found in the till. Color of the drift is variable, but is commonly 7.5YR4/4.

Basal till overlying outwash deposits was also recognized in two separate exposures, both

up-ice (east) a short distance from the Green Hills moraine. In Figure lOa, a photo taken

Figure 9. Photo of exposure located south of Republic, Michigan. Fluvial sand overlies bouldery, sandy till. Note thereverse grading in the till deposit. A lag of boulders atop the section of till marks an erosion surface.

Figure 10(a). Photo of sediment exposure taken about 1.5 km east of the Green Hills moraine. At the bottom of thesection is cross-bedded coarse sand. Directly above and in sharp contact is approximately 2 m of foliated, compactbasal till. The upper 1 m of the section is sandy ablation till. A large boulder caps the section. Shovel is about 1 mlong.

78

1.5 km east of the Green Hills margin, highly-sheared, extremely compact basal till

overlies stratified sand. The till was so compact, it took many blows with the pick end of

a rock hammer to dislodge fist-sized clasts from the till (Figure lOb). The basal till is

composed of clay to boulder-size clasts that grade into a finer-grained, contorted, compact

till at the top of the bed. A deposit of ablation till about one meter thick caps the

sequence. Remarkably, primary sedimentary structures in the sand at the base of the

section, such as foresets and bedding planes, remained intact despite the ice movement and

shearing of basal till over it. A very large boulder (>2 m diameter) rests at the surface of

the pit, lying atop about 1 m of ablation till. The sequence of deposits is interpreted to

reflect a re-advance of the ice to the Green Hills position. The ice sheet likely overrode

outwash deposited during an earlier retreat from the (late) Sagola moraine position and

deposited the basal till over the top of it. Wastage of the ice from that position resulted in

the accumulation of ablation till. If this interpretation is correct, the basal till of the Green

Hills moraine likely corresponds to the Middle Inlet member of the Kewaunee Formation

in northeastern Wisconsin (Attig et al, 1986).

In the northern part of the study area, at the northernmost extent of the Green Hills

moraine, a small, but prominent linear scarp branches to the northwest. It parallels the

Republic moraine that is located about 5 km to the northeast. The scarp is about 8-15

meters high and is composed of sand and gravel. There is no hummocky topography or

till at the scarp, but many boulders of granitic composition dot the surface near its crest.

Tracing the scarp several kilometers to the northwest, it changes into a moraine. Thick

accumulations of till interspersed between bedrock knobs form hummocky topography

Figure 10(b). Close-up of foliated basal till taken from area just to right of the location shown in Figure 10(a).Lens cap is about 60 mm diameter.

80

there. Thus, the feature is called the Ishpeming moraine (and ice-contact position in its

southern part) in this study. A large outwash plain formed to the west of the Green Hills

and Ishpeming ice-contact positions. It is interpreted to have been deposited by both the

Green Bay and Michigamme lobes. The surface of the terrace is approximately 450 m

elevation and slopes to the west-southwest. It is named the Ishpeming outwash plain

(terrace #2 on Figures 4 and 5) in this study.

It is unclear whether movements of both lobes were synchronous as the Ishpeming

and Green Hills moraines were being deposited. However, one landform suggests the

Green Bay lobe occupied the area to the west of the Green Hills moraine, then retreated to

the east before stabilizing. A few kilometers southwest from the Ishpeming moraine, in

the Ishpeming outwash plain, tributary channels to the modern Escanaba River take on an

unusual pattern. They exhibit a parallel drainage pattern that is perpendicular to the main

river (Figure 11). Also notable is that the trend of the modern Escanaba River lies

precisely along the northeastward continuation of the trend of the Green Hills Moraine.

The tributary streams cut channels into the plain that are perpendicular to the main channel

on its southeast side, but not on the northwest side. Usually, parallel drainage occurs in

fine-grained sediments on evenly sloping terrain (Way, 1978). The outwash plain where

this pattern is found is nearly completely composed of sand and generally slopes

perpendicular to the orientation of the parallel channels, not parallel to them as one would

expect. Thus, it is likely that the geometry of the current drainage system reflects some

older, pre-existing pattern. Parallel drainage patterns in the plain, and the trend of the

Escanaba River suggests that the Green Bay lobe occupied the area of the plain southeast

81

Figure 11. Tributary (parallel) channels of the Escanaba River. Northwest-southeastoriented tributary channels to the Escanaba river maintain parallel orientation even thoughthe regional slope is to the northeast. The trend of the Green Hills moraine isperpendicular to the parallel drainage pattern.

82

of the present-day course of the Escanaba River, where it deposited a moraine, and then

later retreated. Streams flowing from the ice at the time the moraine was being deposited

may have cut channels through the moraine, perpendicular to the moraine's orientation.

As retreat continued, sedimentation beyond the margin of both ice lobes buried the

northernmost extent of the moraine, and formed the Ishpeming outwash plain. Holocene

streamflow may then have preferentially followed the moraine because it impeded any

eastward flow. Tributary channels to the main trunk continued to occupy pre-existing

channelways cut into the northwest side of the Green Hills moraine. As an alternative

hypothesis, bedrock exposed at the floor of the Escanaba River channel in many places

may have influenced drainage patterns. Overburden thickness in this area ranges from 0-

20 meters, but is extremely variable, due to the undulating bedrock surface. Not enough

depth-to-bedrock information is available to determine if there is a correlation between the

drainage pattern and bedrock. Thus, the cause or significance of the unusual drainage

pattern is not clear, but the drainage pattern suggests that the Green Bay and Michigamme

lobe movements were not synchronous over short intervals of time.

Several pairs of small moraines and ice-contact scarps with outwash plains on their

western (distal) sides were identified to the east of the Green Hills and Ishpeming

moraines. They record episodic, synchronous downslope retreat of both ice lobes into the

Lake Superior basin. Similar relationships between moraines, ice-contact scarps and

outwash plains were reported in the Munising area (about 100 kilometers east of the

present study area) by Blewett and Rieck (1987). They recognized scarps composed of

outwash sand and gravel that form the edges of outwash plains as "heads-of-outwash".

83

They represent distinct ice-marginal positions, but contain little till. Features such as these

are incorporated in a conceptual model called a "morphosequence", first introduced by

Jahns (1941) and later used by Koteff (1974). According to the morphosequence model

(Koteff, 1974), a series of small outwash terraces may form beyond the margin of stagnant

ice as the active zone within a glacier moves in an up-ice direction. They form at an

elevation controlled by a temporary base level. The terraces described in this study are

similar to those predicted by the morphosequence model. For example, other outwash

terraces east and north of the Green Hills and Ishpeming moraines, respectively, occur at

430 m, 415 m, 400 m (T46N, R27W), and 375 m elevations (T45N, R26W) and generally

slope toward the west. Scarps found at the eastern and northeastern edges of the terraces

mark the ice position while the terraces were forming. Each of these features are

relatively small (3-5 meters high and up to 10 km long). Some boulders and till were

found at the scarps, but as a rule, the deposits are composed mostly of sand. The outwash

terraces are referenced by the numbers #3, #4, #5 and #6 in Figures 4 and 5.

In the northeasternmost part of the study area, the prominent Marquette moraine

(Hughes and Merry, 1978) is present. The moraine actually consists of two separate

moraines that are parallel, and very close to each other. They are called the outer (older)

and inner (younger) Marquette moraines, respectively. They are prominent landforms

about 10 km south of Marquette, Michigan. Both moraines trend north-north west. The

outer Marquette moraine is the larger of the two, and has a maximum relief of about 30

meters. Maximum relief of the inner moraine is about 20 meters. Sediments deposited by

the Marquette advance are mostly very sandy, reddish till. In many places, especially near

84

the moraine, it is difficult to establish the mode of deposition based on the sediment

texture alone. Sediments that comprise morainal forms deposited by the Marquette ice are

often over 90% sand, unlike the "typical" till. Refer to Figure 6, the textural triangle that

shows the percentages of sand, silt, and clay of till samples. Twelve samples were

collected along the Marquette moraine (the letter "S" for Superior lobe). Note that most

are clustered very near to the sand apex of the triangle. No samples contained significant

amounts of clay. Although the till is commonly quite sandy and could be misinterpreted

as being fluvial in origin, boulders and cobbles are found throughout the deposits, and the

deposits are not stratified or normally graded. The high percentage of sand in the till

deposits of the Marquette moraine likely reflects reworking of outwash and lacustrine

sediments deposited in the Lake Superior basin during recession of the Greatlakean ice. A

re-advance of the Marquette ice overrode the sediments, incorporating them into its

deposits, resulting in the large, sandy, Marquette moraine. In some places, the till is fine-

grained containing a high percentage of silt. In these areas, the ice likely advanced over

previously deposited lacustrine sediments, incorporating them into the till.

The Sands outwash plain was constructed distal to the outer moraine. It is about

500 sq. km in area, and slopes gently to the southwest. A smaller outwash plain, lower in

elevation and located to the east of the Sands plain, formed distally to the inner Marquette

moraine. Those outwash plains are called outwash terraces #7 and #8 in this study (see

Figures 4 and 5). Tracing the outer moraine to the south, its crest gradually decreases in

elevation until it is entirely buried by the younger outwash plain. For example, near

Gwinn, Michigan, only a small portion of the outer Marquette moraine rises above the

85

sedimentary cover formed while the ice was at the inner Marquette moraine position.

Sand and gravel deposits in the plain attributable to the Marquette advance average only

about 10-30 m thick, although the total thickness of the plain often exceeds 100 m

(Granneman, 1984).

Interlobate deposits

At the confluence of the late Sagola and Republic moraines, a conical-shaped,

hummocky deposit is found. Because of its spatial relationship to surrounding features, its

topography, and its coarse-grained sedimentary characteristics, it is interpreted as an

interlobate deposit. It is about 5 km2 in size, relatively high-relief, and pocked with

dozens of kettles throughout its extent. The largest of the kettles are a kilometer wide,

though most are much smaller.

At the junction of the Green Hills and Ishpeming moraines, there is another very

thick conical-shaped accumulation of sediment called the Green Hills on the Green Hills,

MI (U.S.G.S.) 7 1/2 minute quadrangle (Figure 12). No evidence of bedrock could be

found in the feature, so it is likely composed mostly of sediments. Total relief of the hill

above surrounding terrain is over 50 m, making it one of the most prominent relief

features in the area. It is interpreted as an interlobate deposit because of its spatial

relationship with nearby moraines (parallel, northwest trending moraines north of and

southwest trending moraines south of the deposit merge there) and its composition

(abundant deposits of coarse-grained sand and gravel).

Figure 12. Green Hills topographic map (north part). This map shows the ice-marginal positions of the Green Bay andMichigamme lobes beginning with construction of the Ishpeming moraine (and ice-contact scarp) by the Michigamme lobeand the Green Hills moraine by the Green Bay lobe. The Green Hills interlobate deposit and Ishpeming outwash plainformed at this time. The lobes retreated and stabilized at the eastern ice-contact scarp/moraine and formed outwash terrace#3. Further retreat and stabilization of the lobe formed outwash terrace #4.

00Os

87

Trending eastward from the Green Hills interlobate deposit is a linear, hummocky

chain of hills that extends nearly to Gwinn, Michigan, a distance of about 30 km (Figure

13). The hills contain many kettles and kettle lakes that Leverett (p. 36, 1929) described

as "a fosse of unusual length". Because the feature is easily discriminated by the lakes that

occupy kettles along its extent, it is called the "chain-of-lakes" in this study. It is

interpreted as an interlobate deposit because the northwest and north-south trending

moraines and ice-contact scarps merge there, and the outwash surfaces west of the

moraine-pairs are continuous across the interlobate feature. Total relief of the chain-of-

lakes interlobate feature is about 20-30 meters on the south side, while on the north side,

total relief is only about 10-20 meters. Slopes on the south side of the feature are also

generally steeper than on the north side. Thus, it is asymmetrical about its east-west axis.

Sediments composing the feature are almost entirely sand and gravel although

many boulders dot the surface. Most of the deposits are interpreted to be fluvial in origin,

because they contain abundant trough cross-bedding and graded bedding, and are

composed of sand and gravel. Some structures were extremely contorted and suggest

collapse over stagnant ice or slumping. Some till was also found in the interlobate feature,

but it is less common than the sand and gravel. At the westernmost end of the feature, in

the Green Hills, many large erratics (mostly granite lithology) were found at the surface.

Southward-flowing meltwater along the toes of both lobes cut across the

interlobate deposits at successively lower elevations toward the east. The many

abandoned valleys that trend southward through the eastern part of the interlobate tract

are evidence of this streamflow (Figure 13). Many channels are no longer intact, due to

1•bate tra»V

, f,fS^T.and^^^4^y3^/4<.r., % ,„-.-* > 4, JJ "-^HCr^

• tr\*-**u ~^Js

- fev Lake-*

? t

Figure 13. Portion of the Cataract Basin quadrangle showing the interlobate tract, chain-of-lakes, moraines and outwashterraces, and meltwater channels. As the lobes wasted farther eastward, several small, unnamed moraines and outwashterraces (#5 and #6, for example) were formed. The interlobate tract and chain-of-lakes are especially well-preserved here,with the exception of the eastern part, where meltwater channelways are found. The location of the boulder field describedin the text is indicated on the figure.

COCO

89

collapse of surrounding and overlying sediments. One channel located in Sections 26 &

35, T45N, R26W, and shown in Figure 13, is deeply incised into the interlobate sediments,

and has at least one hanging channel well above the floor of the main channel. This is

interpreted as evidence that the channel was active for of a long period of time despite

changing flow conditions and local base levels. The main channel is about 10m deep and

400 m wide and possesses steeply-sloping walls. Sediments at the floor of the channel

have a mean grain size of about 4 mm and D95 of about 8 cm. This channel probably acted

as a drainageway during the initial stages of the Marquette advance of ice out of the Lake

Superior basin (Drexler, 1981). Two additional minor recessional moraines, outwash

terraces #5 and #6, and the interlobate tract, chain-of-lakes, and drainage channels are also

shown on Figure 13. The eastern end of the chain-of-lakes interlobate feature is an

impressive accumulation of clast-supported boulders that form a boulder train (Figure 14).

Some boulders are 3 meters in diameter, though most are 2 meters in diameter or less.

Sediments of the matrix are mostly sand and gravel. This feature is the last distinguishable

landform that can be attributed to retreat of the Greatlakean ice, because spatially, it is at

the same elevation as the last outwash terrace (#6) and ice-contact position of the

Greatlakean retreat. There were probably later stillstands than the ones described to this

point, but were destroyed by the next ice advance out of the basin.

Proglacial lake landforms

Scarps were found eroded into sand and till deposits on the east side of the Green

Hills moraine and one of the younger recessional moraines of the Green Bay lobe. The

Figure 14. Boulder train. Clast-supported, linear accumulation of boulders in the interlobate tract. The accumulation isthe result of smaller clasts winnowed out by competent meltwater flowing through the interlobate region.

91

scarps are linear, are at a constant elevation, and have well-sorted, sandy sediments at

their base. They are interpreted to have formed by wave action along the shore of a small

proglacial lake. Soil augering in Sec. 28 of T45N, R28W revealed laminated, planar-

bedded silt and very-fine sand deposits. They were likely deposited at the bottom of the

lake, which formed distally to the ice margin. Several two-to-three meter high mounds of

well-sorted sand found on the east side of the Green Hills moraine, and west of the

shoreline just described, are interpreted as sand dunes. Several small deltas in T45N,

R27W of the Green Hills quadrangle show the level of the lake (390 m), and support the

lacustrine interpretation. Deltas are identified by their shape (flat surface and delta-shape

in plan view), position (at the ends of valleys cut into the moraines) and their similarity in

elevation, and their composition (mostly sand).

Figure 15 shows the southern part the Green Hills topographic map and some of

the features just described. The Green Hills moraine is located just west of the left margin

of the figure. The lakes are interpreted to have formed because southerly drainage of

meltwater was impeded by the thick ablation deposits, westward drainage was impeded by

the regional slope, and eastward drainage was impeded by ice of the Green Bay lobe. A

deeply incised channel trending southeastward across the small, unnamed moraine carried

water into the lake that formed proximal to the then active recessional moraine. Drainage

through the channel probably started when the lake surface was at 390 m elevation, as

evidenced by the small deltas. After the lake drained, a younger stream flowing along the

channel caused further downcutting, and eroded part of the delta. Reduced competence at

the floor of the former lake caused the post-lake stream to deposit its load of sediment,

92

S Ti A" "t;-E

Figure 15. Green Hills topographic map (south part) showing glacial lake deltas,interlobate tract, chain-of-lakes, and a moraine. A proglacial lake filled the area betweenthe Green Bay lobe and the moraine shown in the figure. Several small deltas show thelake level to have been 390 m elevation. After the lake drained, a stream incised a channelinto the unnamed moraine and deposited a fan along the southeast edge of the moraine. Asmall portion of a moraine deposited by the Michigamme lobe can be seen in the upperright corner of the figure (unlabeled). The interlobate tract and chain-of-lakes show thelocation of the confluence of the two lobes.

93

which formed an alluvial fan (located on the figure at the tip of the arrow pointing the

Green Bay lobe ice movement direction) of several square kilometers extent (See's. 21 &

28, T45N, R27W). The modern Bryan Creek continues to erode into the fan.

In the northeastern part of the study area, another large proglacial lake developed

between the higher, outer Marquette moraine and the ice margin when it was located at

the position now occupied by the inner Marquette moraine. Until the ice receded slightly

from the inner Marquette position, the lowest outlet from the lake was over part of the

outer moraine. When the lake surface reached that elevation (360 m), water breached the

crest and cut a pair of channelways (Figure 16). The channels were downcut into the crest

of the moraine in stages, as indicated by one hanging channel located about 10 m above

the floor of the main channel. Some of the lower channel (the more southerly channel in

Figure 16) is now occupied by Powell Lake (south of the geographic extent of the figure).

Drexler (1981) postulated that this channel carried eastward discharge from the post-

Duluth lakes in the western Lake Superior basin to the Marquette area, then southward

into the Lake Michigan basin.

Ablation hills

South of the Green Hills interlobate deposit, in the central portion of the study

area, stagnant-ice, ablation landforms formed by the retreating Green Bay lobe are present.

Most of the features are found within ten kilometers (up-ice) of the Green Hills moraine.

Typical of this landscape are very large hummocky mounds, typically several kilometers in

length, slightly smaller in width, and several tens of meters in height. They are weakly

94

Sands outwbsh.,. "• pfoin |,.-'; ̂ errace .̂ 7);

Figure 16. Portion of the Sands topographic quadrangle showing segments of the outerand inner Marquette moraines and the Sands outwash plain (outwash terraces #7 & #8).Outlet channels from a lake that occupied the area between the outer moraine and the iceas the inner moraine was constructed are also shown.

95

oriented parallel to the direction of ice flow. Sediments in the features are mostly sandy

till, though many have some stratified sand and gravel within them. Bouldery ablation till

veneers the surfaces. In the southwest portion of the study area, some similar-appearing

features are bedrock-cored. Radar and TM imagery reveal faint flutings on the surface of

many of these features. The flutes are oriented in the direction of ice flow and are

perpendicular to the Green Hills moraine. The ablation hills of the present study area

resemble the "Spooner Hills" of northwestern Wisconsin that are described by Johnson

(1996). Johnson suggested that Spooner hil ls form by subglacial erosion of existing

sediments because they contain sediment types representing a wide variety of depositional

environments, and they oriented in the direction of ice flow. The ablation hills in the

present study area have similar characteristics to those described by Johnson.

Drumlins

Eastward from the ablation hills, in an up-ice direction, an assemblage of drumlin

and fluted forms developed beneath the Green Bay lobe. The landscape is known as the

Menominee drumlin field. There are over 1,000 drumlins in the field, along with

transitional forms, such as combinations of drumlins and flutes. In the eastern part of the

study area, most of the drumlins are oriented with their long axes south-southwest but in

the western-central portion of the study area the drumlins smoothly change orientation to

westerly, and then northwesterly (see Figure 3a or Plate 1). In the western part of the

field, they are oriented perpendicular to the Green Hills moraine. According to Sugden

and John (1985), drumlins typically form several tens of kilometers upglacier from the ice

96

margin in the warm-based zone of the glacier. Drumlins and flutes of the Menominee

drumlin field are oriented approximately normal to, and between 15-45 km up-ice from,

the Green Hills moraine. The relationship between the drumlins and the Green Hills

moraine conforms to the Sugden and John model and suggests that both features

developed contemporaneously.

Loess

Loess overlies the glacial sediments in some areas, particularly in the extreme

western portion of the present study area. Thickness of the loess cap ranges from 0-1

meters, but typically is less than 50 cm. A small channel filled with loess to a thickness of

about 2 meters (Figure 17) was found about 1 km north of Republic, Michigan. No

structures (such as foreset bedding or bedding planes) were found in the deposit, but it is

probably of eolian origin. Loess is generally not found east of the late Sagola and

Republic moraines.

TEMPORAL MOVEMENTS OF GLACIAL ICE

As the late Wisconsinan ice sheet began its retreat from the northern part of

Wisconsin, it gradually uncovered the present study area in the central part of the Upper

Peninsula of Michigan. When the generally retreating ice margins temporarily stabilized,

or even locally re-advanced within the study area, moraines and outwash plains were

constructed that left a record of the event. Because the regional slope within the present

study area is to the east (in the direction of ice retreat), pro-glacial landforms that resulted

Figure 17. Loess filling a small postglacial channel incised in till to a depth of about 2 meters. Photo taken about 5km southeast of Republic, Michigan.

98

from each subsequent stillstand are lower in elevation than the ones formed earlier. The

net result of the retreat is a series of distinct landscape units that decrease in elevation

toward the east.

Figure 18 shows an interpretation of the ice-marginal positions, starting with

stabilized ice margins at the beginning of their retreat from the maximum extent of

Woodfordian ice (about 12,500-12,300 YBP) through about 11,000 YBP. This

represents the period from when Green Bay lobe constructed the late Sagola moraine and

the Michigamme lobe constructed the Republic moraine (Figure 18a), to the time the

retreating ice cleared the shoreline of Lake Superior and allowed Lake Aggasiz to drain

eastward along the ice front (Drexler et al, 1983). The Gribben forest and the Marquette

advance are younger than the events outlined in this section and are discussed later in this

paper.

Retreat from the late Sagola and Republic moraines

In the study area, the first recorded movement of the Michigamme and Green Bay

lobes is their retreat northeast of the Republic moraine and east of the late Sagola moraine,

respectively. This retreat was followed by a re-advance to the positions shown in Figure

18(b). During the re-advance, the Green Bay lobe formed the Green Hills moraine. The

time-equivalent deposit of the Michigamme Lobe is the Ishpeming moraine (and ice-

contact position). Neither moraine accumulated to the size of the late Sagola or Republic

moraines which suggests the ice margin did not remain adjacent to the Green Hills or

Ishpeming moraines as long as it was present at the edge of the Sagola and Republic

99

Mlchigomme lobe

Green Bay lobe

Q

Mlchlgammelobe

Green Baylobe

c

ProgLacial lake

Inierlobate andmoraine sedinents

ISHPEHING ""•sS;

Mtchigonme lobe

Green Boy lobe

b

Proglacial drainage

Modern lakes

Figure 18(a-d). Interpretation of ice marginal positions, construction of outwash plains,and proglacial lakes as the Woodfordian and Greatlakean ice retreated across the studyarea. In (a) the Woodfordian ice built the late Sagola moraine (Green Bay lobe) and theRepublic moraine (Michigamme lobe). A significant re-advance of both lobes at about11,850 YBP is expressed in (b). At this time, the Green Bay lobe deposited a largemoraine, herein called the Green Hills moraine, as it emanates southward from the GreenHills (an interlobate deposit). The Michigamme lobe formed the Ishpeming moraine,which in part is an ice-contact scarp. The large Ishpeming outwash plain formed at thistime. Figures 10(c-d) shows the positions of moraines and ice-contact scarps as outwashterraces were constructed in front of the rapidly stagnating ice margins. The outwashplains formed distal to the stillstand positions and formed terraces #3-#4 (of 8) describedin the text.

100

moraines. The Green Hills interlobate deposit formed at the junction between the Green

Bay and Michigamme lobes during the re-advance. It is difficult to establish whether the

Green Hills and Ishpeming moraines formed contemporaneously. No sedimentologic or

stratigraphic evidence, such as till from one lobe overlying till from the other lobe, was

found to conclusively discern the relative timing of lobe movements. Because the

Ishpeming outwash plain is a continuous surface between both moraines, it is likely both

moraines were formed contemporaneously just before retreat.

Retreat from the Green Hills and Ishpeming positions

Evidence for the retreat of both the Green Bay and Michigamme lobes from the

Green Hills/Ishpeming positions are the pairs of separate, small outwash terraces and ice-

contact scarps described earlier (the oldest two are shown in Figures 18c and 18d) that

decrease in elevation toward the east. It is questionable whether either lobe was active

during this interval because no significantly large moraines were constructed.

Additionally, the ice lobes were generally wasting downslope into the Lake Superior basin,

an environment characterized by abandoned masses of stagnant ice. Sandy-grained till and

outwash aprons bounded by ice-contact scarps and small, discontinuous moraine segments

are all that remain to show the former ice positions. As the ice margins receded

downslope through the study area, meltwater outlets opened at lower elevations, forming

new base levels. Thus, contemporaneous ice-contact scarps and terraces that formed after

the Green Hills and Ishpeming moraines appear to conform to the morphosequence model

(Blewett and Rieck, 1987). In fact, the topographic expression of the scarps and terraces

101

is greatly enhanced by the regional slope toward the northeast, in the direction of ice

retreat. As the Green Bay lobe retreated eastward from the Green Hills position to lower

elevations, southward drainage of meltwater was temporarily impeded for short periods of

time. The void space left by the retreating ice filled with meltwater. Landforms and

sediments on the east side of moraines and scarps suggest that at least one lake of several

square kilometers extent must have existed for a significant period, during a time when the

ice margin stabilized at a new, lower elevation position.

As the ice lobes continued to retreat, meltwater was discharged southward through

successively lower outlets at the front of the progressively retreating margins. The

Michigamme lobe margin likely retreated more quickly, because the ice was probably

thinner (it is interpreted that the ice did not extend as far to the south because it passed

over bedrock with much higher relief and elevation). The Green Bay lobe partly blocked

southward water movement from the Michigamme lobe, and was partially buried by fluvial

sediments of the interlobate tract in its northern extent. As the Green Bay ice continued to

ablate, more easterly drainageways opened at lower elevations, stranding earlier, higher

elevation channelways. All the while the two lobes were retreating, fluvial sediments

accumulated at their confluence, forming the "chain-of-lakes" interlobate deposit.

Continued northeastward retreat of the Greatlakean ice into the Lake Superior basin

probably left additional deposits, but they were buried by deposits of the next advance.

The ice-free period was named the Gribben Interstadial and the re-advance was called the

Marquette Stadial by Hughes and Merry (1978). They are described in the following

sections.

102

Gribben Interstadial

Futyma (1981) postulated that an ice lobe occupied the Lake Superior basin until

the Holocene. Saarnisto (1974) described carbon dates from organic sediments and

proposed that the Valders (Greatlakean) ice retreated from the Upper Peninsula region

slowly, from 11,000 to 10,100 YBP. From palynological data, he concluded that tundra

vegetation dominated the Lake Superior region during this interval, and that vegetation

moved northward following retreat of the ice margin. He suggested a stow retreat of the

ice out of the area, although at the time evidence reflecting a younger major advance had

not been discovered.

It is now known that the Greatlakean ice must have retreated at least into the

Lake Superior basin in order for the Duluth lakes to drain into the eastern Lake Superior

basin. Drexler et al. (1983) suggested the ice retreated north of the Huron mountains

between 11,000 and 10,600 YBP, allowing glacial Lake Agassiz to drain through the Lake

Superior basin and then through an outlet at Sault Ste. Marie. This implies that the

average rate of ice retreat, from the terminal position in Wisconsin until the margin cleared

the south shore of modern Lake Superior, was only 0.36 to 0.24 km/yr. The rate of

retreat was not likely uniform, as evidenced by the many moraines, ice-contact features

and outwash surfaces that formed after the deposition of the Green Hills and Ishpeming

moraines. If the calculated average rate is reasonable, and the ice continued to retreat

until 10,000 YBP (approximately the start of the next advance), this places the ice margin

near the north shore of Lake Superior. Melting of ice within the basin and drainage from

surrounding areas may have provided enough water to nearly float the ice within the basin.

103

If the ice was even partially supported by water, shear strength along its base could have

been reduced, resulting in a surge (Goodwin, 1988; Mayo, 1989; Russell, 1989). This is a

potential mechanism that aided the next advance, called the Marquette Stadial (Hughes

and Merry, 1978).

Before the Marquette Stadial, the Gribben forest encroached on the area of Upper

Michigan formerly occupied by the Greatlakean ice. Tree growth rate decreased

immediately preceding the movement of ice into the area. Merry (unpublished data, 1978)

noted a significant decrease in the width of 30-40 tree rings at the outer extremities of the

trees. He interpreted the decrease in growth rate to show a rapidly cooling climate,

influenced by the proximity of the glacial ice. Termination of growth resulted as the trees

were flooded by an advancing and deepening proglacial lake.

Gribben forest

The main evidence for an advance younger than those described to this point is the

discovery of a buried forest 15 km south of Marquette, Michigan. In 1976 and 1977, and

again in 1994, while outwash sand was being excavated for a tailings basin by the

Cleveland Cliffs Iron Mining Company, several hundred trees in growth position were

encountered at a depth of about 5-8 m below the modern surface, in lacustrine deposits

and outwash sand and gravel. Hughes and Merry (1978) first described the forest of black

spruce and tamarack at the Gribben tailings basin. The present author had the opportunity

to examine trees and soils of the forest when it was recently unearthed for expansion of

the basin. The trees were buried by glacial lacustrine and outwash sediments, and provide

104

evidence of the most recent ice advance to occupy the Upper Peninsula of Michigan

(described later). There were at least 150 yearly growth rings on the largest tree (60 cm

diameter, one meter above the base) uncovered in the excavation, indicating the minimum

age of the forest. Radiocarbon dates for five wood specimens and spruce needles in the

soil at the base of the trees furnished a mean age of 9,850 YBP (Hughes and Merry, 1978)

and are presented below;

Table 1. Radiocarbon ages for wood and spruce needles collected in the Gribben tailingsbasin (after Hughes and Merry, 1978).

Sample Age (YBP) +/- error Description

Dal-338 10,220 215 Outer layers of Spruce woodDal-340 9,545 225 White Spruce conesW-3866 9,850 300 Outer layers of Tamarack woodW-3896 10,230 300 Black Spruce conifer needlesW-3904 9,780 250 Sapling piece.

Recently acquired samples of wood from the outer extremities of a 50 cm diameter buried

tree were C14 dated at 9,650 +/-50 YBP (Glen Mroz, Michigan Technological University,

personal comm., 1995). This date corresponds well with earlier dates.

Figure 19 shows the distribution and size of trees unearthed in the pit. Note that

the frequency of tree diameters does not favor any particular size and that there are many

young trees clustered in small groups. Also note the spacing between trees is large. Thus,

the forest was not very densely populated, which implies that the forest was not very

healthy and was not growing under favorable conditions (although this could be a relict of

preservation).

105

GRIBBEN BASIN BURIED FORESTPrinter, Michigan

510152025303540

45

Figure 19. Location and size of trees unearthed in the Gribben Basin in 1978 (afterHughes and Merry, 1978).

106

The forest grew on a Spodosol with Entisol-like characteristics that formed during

the interstadial. The soil developed to a thickness of about 10-20 cm. Soil profiles from

two different locations were described after it was first exposed (Berendt, 1978,

unpublished data). The profiles depict the sedimentological conditions that buried the

forest, and imply the climatological conditions the forest grew in. For comparison, the soil

at the present-day surface is Croswell sand on the knolls and Roscommon sand in the

swales. The Croswell series is a sandy, mixed, frigid Oxyaquic Haplorthod. The

Roscommon series is a mixed, frigid, Mollic Endopsamment. The first description of the

paleosol begins about 35 centimeters above the buried surface and is presented below

(Table 2). The second description of the paleosol is similar to the first. It was classified

as a sandy, mixed, frigid, ortstein, Aerie Endoaquod. The technical description downward

from the top boundary of the "C" horizon overlying the paleosol (about 2 m below the

modern surface) follows (Table 3).

107

Table 2. Gribben Basin Paleosol description #1.

Horizon D£plh

Cl 0-20cm

C2

IIC3

20-30cm

30-35cm

Top of PaleosolIIIAllb 35-43cm

IVA12b 43-51cm

IVClb 51 -66cm

IVC2b 66-94cm

IVC3b 94cm+

Description

Light brown (7.5 YR 6/4) sand, single grained, loose,extremely acid, abrupt smooth boundary.

Light brown (7.5 YR 6/4) sand, thin horizontal streaks ofstrong brown (7.5YR 5/8) and yellowish red (SYR 5/8),single grained, loose, extremely acid, abrupt smoothboundary.

Reddish-brown (SYR 5/3) loamy very fine sand, thin verydark gray (10YR 3/1) streaks in upper part, massive, firm,extremely acid, abrupt smooth boundary.

Very dark gray (10YR 3/1) sandy loam, massive, friable, 10to 15% partly decomposed spruce needles, extremely acid,abrupt smooth boundary.

Dark brown (7.5YR 3/2) sand, common fine distinct verydark gray (10YR 3/1) and common medium faint brown(10YR 4/3) mottles, weak medium granular structure, veryfriable, extremely acid, abrupt smooth boundary.

Light yellowish brown (10YR 6/4) sand, common mediumfaint yellowish brown (10YR 5/4) and dark grayish brown(10YR 4/2) mottles and streaks, single grained, loose,extremely acid, clear smooth boundary.

Light yellowish brown (7.5YR 6/4) sand, single grained,loose, extremely acid, abrupt smooth boundary.

Light brown (7.5YR 6/4) sand, single grained, loose,extremely acid.

108

Top of PaleosolVAllb 904-909cm

Table 3. Gribben Basin Paleosol description #2.

Horizon Dfiplh DescriptionC1 200-518cm Light yellowish brown (10 YR 7/4) sand, single grained,

loose, strongly acid, abrupt, smooth boundary.C2 518-640cm Pale brown (10YR 6/3) sand, single grained, loose, 15%

gravel, strongly acid, abrupt smooth boundary.IIC3 640-793cm Light reddish brown (5YR 6/4) stratified very fine sand,

single grained, loose, very strongly acid, abrupt smoothboundary.

IIIC4 793-869cm Stratified light brown (7.5YR 6/4) very fine sand andbrown (7.5YR 5/2) loamy very fine sand, massive, firm,thin yellowish brown (10YR 5/4) stain between individualstrata, mildly alkaline, abrupt smooth boundary.

IVC5 869-904cm Brown (7.5YR 5/2) silt loam, common medium distinctyellowish brown (10YR 5/4) mottles, massive, firm, fewscattered woody remnants (twigs), mildly alkaline, abruptsmooth boundary.

Brown (10YR 5/3) mucky fine sandy loam, weak mediumplaty structure, friable, 60-70 percent spruce needles,rubbing reduces amount of needles to 10 percent and givesa color of very dark gray (IOYR 3/1), mildly alkaline,abrupt smooth boundary.

VIA 12b 909-934cm Dark grayish brown (1OYR 4/2) mucky fine sandy loam,weak medium platy structure, friable, 25 percent spruceneedles and twigs, rubbing reduces needle and twig contentto 5 percent and gives a color of very dark gray (IOYR3/2), mildly alkaline, abrupt smooth boundary.

VIA13b 934-937cm Very dark gray (IOYR 3/1) mucky sandy loam, massive,friable, mildly alkaline, abrupt smooth boundary.

VIIB21 b 937-942cm Dark brown (7.5YR 4/2) loamy sand, massive, friable, fewroot fragments, mildly alkaline, abrupt smooth boundary.

VIIB22b 942-962cm Dark brown (7.5YR 4/2) sand, very few dark (IOYR 3/1)organic stains, weak medium subangular blocky structure,parting to weak fine granular structure, very friable, fewroot fragments, 5 percent fine gravel, mildly alkaline,abrupt smooth boundary.

VIIC1 b 962-972cm Light brown (7.5YR 6/4) sand, single grained, loose,neutral, abrupt smooth boundary.

VIIIC2b 972-983cm Brown (7.5YR 5/4) cobbly sand, single grained, loose, 20percent cobbles, neutral, abrupt smooth boundary.

IXC3b 983-1069cm Light brown (7.5YR 6/4) sand, single grained, loose.

109

The "C" horizons underlying the forest floor are mostly sand with some cobbles.

These show the forest grew upon mostly outwash deposits. The sand and gravel were

probably deposited following retreat of the Greatlakean ice into the Lake Superior basin.

Water levels in the soils were probably high, as evidenced by mottles and the fact that

black spruce and tamarack lived there; both favor very moist soils. The "C" horizons

overlying the forest soil "A" horizons depict conditions as the next advance approached

the forest. Immediately overlying the "A" horizons in both profiles are 5-35 cm thick

deposits of loam to very fine loamy sand. These were interpreted by Hughes and Merry

(1978) as lacustrine deposits. They reflect ponding of water on the forest floor as a

proglacial lake encroached upon the area. The second profile shows stratified very fine

sand overlying the loam. This suggests filling of the lake with fine-grained sediments.

Stratigraphically higher, the sediment texture becomes coarser, until gravel appears in the

section, nearly 400 cm above the former forest floor.

Figure 20 shows a photograph of an in situ tree unearthed in the pit and Figure 21

is a cross section of that exposure. Approximately 1.5 meters of its trunk were encased in

a sequence of inverse-graded lacustrine silt and sand. An abrupt contact between the

lacustrine sediments and overlying cross-bedded fluvial gravel and sand indicates the

presence of an erosion surface at that level. The trees extend slightly into the overlying

deposit with pointed, eroded tips that uniformly point southward. Cross-bedding and tree

orientations record southward-moving streamflow through the area. Branches are bent

downward because of the weight and compaction of the overlying sediments.

Stratigraphically above the gravel beds, southward-oriented cross-bedding in several

I l l

:H_-H_H_H-:H-:Mndern soil

Cross-bedded sand

Coarse sand andv e l - f i l l e d channe l

Some varves /_acustr!ne -

-^—- - T. zn- " - -;

-Pre-Marquette

2 meters

Figure 21. Cross section showing the relationship between sediments and standing treesunearthed at the Gribben site. Black spruce and tamarack were rooted in a Spodosol withEntisol-Iike characteristics. Trunks were encased in a sequence of reverse-gradedlacustrine silt and sand ranging from a few centimeters to 3 meters in thickness. Somevarves were found in the uppermost portion of the encasing sediments of some exposures(after Hughes and Merry, 1978).

112

meters of fluvial sand suggests continued fluvial sedimentation. Modern soils developed in

this parent material.

Marquette Stadia!

The Marquette Stadial is the name given to the re-advance of ice out of the Lake

Superior basin that terminated the Gribben Interstadial (Hughes and Merry, 1978).

Evidence for the re-advance is the Marquette moraine and Sands outwash plain

geomorphic features, the interpretation of the stratigraphy at the Gribben site, and the

radiocarbon dates derived from the Gribben trees. Farrand and Drexler (1985) call the ice

that re-advanced out of the Superior basin the Marquette Phase of the Superior lobe.

Although the Marquette moraine and associated outwash plain have long been recognized

(Leverett, 1929, p.40 for example), its significance eluded previous researchers. Black

(1969) and Saarnisto (1974) called it the Sands Moraine, and placed deposition at late

"Valders" time (about 11,000 YBP). Of course, before 1976, the Gribben forest had not

yet been discovered.

Figures 22 and 24 through 28 show an interpretation of the sequence of events

leading to burial of the Gribben trees and development of the Marquette moraine and

Sands outwash plain (Hughes and Merry, 1978). In Figure 22, at about 10,200 YBP, the

Gribben forest extended over a large area (of unknown extent), spreading into the space

that was formerly occupied by the retreating Greatlakean ice. The forest must have been

fairly extensive. Organic materials, including buried trees with comparable C'4 dates, have

been found at many other locations in the Upper Peninsula (Figure 23). The distribution

113

— \esediments

Gribben forest

Goose Lake

T.47N.

- T.46N.

T.45M

Figure 22. Location and probable drainage conditions during growth of the Gribbenforest.

L A K E S U P E R I O R

woodtill

10,100 CW-154CD10,200 CM-359)10,230 CW-1414)10,250 CW-I541)

BuriedPoleosoL<not dated)

UPPER PENINSULAOF MICHIGAN

WISCONSIN

N

Locations of datable organics

formed during the Gribben interstadial

Figure 23. Locations and C14 dates of organic materials formed during the Gribben interstadial.

115

of trees must be more widespread than suggested by the Gribben area alone, as some

water-well logs in the Marquette County area describe wood encountered at 10-15 m

depth.

The arrival of Marquette ice is shown in Figure 24. A proglacial lake probably

formed at the ice front, flooding the area of the Gribben Basin. Because up to 3 m of

varved lacustrine silt and sand lie above the soil in which the forest grew, and the trees are

in situ within the sediments, it was estimated by Hughes (personal comm.) that the lake

must have been in place for at least 7-10 years. Sediments exhibit a general coarsening-

upward sequence, indicative of progressive filling of the lacustrine basin. Cross-bedding

in fluvial sediments overlying the varved silts and sands show a southward streamflow

direction.

Continued advance of the Marquette ice to its maximum extent is shown in Figure

25. Southward-oriented streamflow along the margin of the ice eroded the exposed

portions of trees at the upper surface of lacustrine sediments. Pointed tree tips terminate

in the coarse sand and gravel deposits. The tips are uniformly bent toward the south, in

the direction of streamflow. The meltwater also initially scoured the underlying lacustrine

deposits, and finally deposited 4-7 m of fluvial gravel and sand over the remnants of the

trees indicating continued filling of the lake basin. There is no till overlying the trees to

indicate that the ice advanced over the forest. The texture of sediments suggest high

competence streamflow.

As shown in Figure 26, the ice margin then retreated slightly and stabilized at the

position of the outer Marquette Moraine. At this time in neighboring areas, the Six Mile

116

Pre-Morquettesediments

Gribben forestS, downed trees

T.47N.

T.46N.

T.45N.

Figure 24. Arrival of the Marquette ice overrode much of the forest while a proglaciallake submerged the Gribben forest west of the ice margin. Up to 3 m of lacustrine silt andsand accumulated around the base of the trees.

117

Gnloloendiscoverysite

Jutwash channels

Pre-Marquettesediments

Outwash sandand gravel

Bedrock(with or without till;

SCALE

1I

Kilometers

Gribben forestS. downed trees

Goose Lake

T.47N.

T.46N,

T.45N,

Figure 25. The maximum extent of Marquette ice (Superior lobe). Competent proglacialstreams eroded the trees above the lacustrine deposits, leaving only pointed tipsprotruding into the coarse fluvial sediments and pointing in the direction of streamflow.

118

Dutwosh chonnels

Pre-MarquettesedimentsMarquette noraine(outer)Dutwash sanoand grave

Bedrock(with or without till;

Gribben forestclowned trees

Goose Lake

T.47N.

T.46N,

T.45N,

Figure 26. Formation of the outer Marquette moraine and the Sands outwash plain. Mostof the older deposits were buried under a blanket of fluvial sand and gravel.

119

moraine (Peterson, 1986) and Baraga plains outwash plain near L'anse, as well as the

Grand Marais I moraine (Drexler, 1981) and Kingston outwash plain near Munising were

formed. After a slight retreat of the ice from the outer Marquette moraine, the margin

stabilized at the position of the inner Marquette moraine (Figure 27). Because the inner

moraine is not as large as the outer moraine, it is interpreted that the ice did not occupy

that position for as long as it was present adjacent to the outer Marquette moraine (Flint,

1971).

The Marquette ice retreated from the inner Marquette moraine quickly, as no

younger moraines or ice-contact scarps were found in the up-ice direction. Figure 28

shows the Marquette moraines and the Sands outwash plain as they exist today. Drexler

(1981) traced an ice margin deposit younger than the inner Marquette moraine from the

Munising area to Marquette (called Grand Marais III), but no distinct landforms or

sediments were recognized in the present study area to show its position. Deposits lower

in elevation than the inner Marquette moraine (extreme northeast part of study area) are

predominantly post-Marquette lacustrine, eolian and fluvial deposits. Silt and fine sand

compose most of the features. The events that formed these deposits likely destroyed any

evidence of stillstand positions proximal to the inner Marquette moraine, if any existed.

There was substantial eastward drainage of meltwater through the

northeasternmost part of the study area as the Marquette ice retreated from the inner

moraine. For example, Hughes (1971) describes the eastward overflow of theDuluth

Lakes from the western Lake Superior basin. The western portion of the Chatham

channelways and the Au Train spillways are evidence of this eastward drainage.

120

MarqueIce

Jutwash channels

Pre—MarquettesedimentsBanquette noraine(outer & inner)Dutwash sandand gravelBedrock(with or without till)

Gribtoen forest& downed trees

SCALE

1 0 ]A

kilometersGoose Lake

T.47N.

T.46N.

T.45N,

Figure 27, Further retreat and stabilization of the Marquette ice resulted in the formationof the inner Marquette moraine and outwash terrace #8. Fluvial channels were incisedinto the crest of the outer moraine.

121

Elevation approx

Elevation approx

Post-MarquettesedimentsPre— MarquettesedimentsMarquette moraine(outer 8. inner)

Dutwash sand

Bedrock(with or without till)

Gribben forestdowned trees

Goose Lake

T.47N.

T.46N,

T.45N,

Figure 28. The post-Marquette physiography.

122

CORRELATION

Figure 29 and Table 4 show spatial and temporal correlations of moraines and ice-

contact positions of newly mapped segments throughout the current study area.

Correlations were made through interpretation of Landsat Multispectral Scanner (MSS)

imagery and the regional correlation of moraines and ice-contact positions described by

Attig et al. (1985). The numbers correspond to ice-marginal positions or moraines

constructed by the major lobes that transected the region. In the late Wisconsinan (about

13,000 YBP), the ice lobes advanced to their maximum extent in northwestern, northeast,

and east-central Wisconsin (Attig et al., 1985). This advance is called the Woodfordian

substage and the three lobes are named Wisconsin Valley, Langlade, and Green Bay, from

west-to-east, respectively. The lobes maintained their positions for a significant period of

time and constructed the large Harrison, Parrish, and Hancock moraines (Attig et al.,

1985). Positions of the ice margins during this period are shown by the numbers 3, 2 and

1 on Figure 29. Retreat from the terminal moraines of the Woodfordian advance resulted

in the deposition of several recessional moraines. For example, the Almond (also number

1 on Figure 29 because the post-Woodfordian ice re-advanced to nearly the same position

as the Woodfordian ice), Elderon (also number 1), and Bowler and Mountain moraines

(numbers 4 and 5 on Figure 29) were deposited during the post-Woodfordian by the

Green Bay lobe. The Summit Lake moraine was deposited at this time by the Langlade

lobe (also 2 on Figure 29). The Wisconsin Valley lobe retreated more quickly from its

terminal position than the other two lobes, and then stabilized to form a moraine well to

LakeSuperior

Regional Correlationof Moraines and

Ice-margin PositionsInterpreted Fron Landsat MSS imagery

1 Hancock. Alriond, Elderon

2 Parrish, Sunnlt Lake3 Harrison

4 Bowler

5 Mountain6 Early Athelstane

7 Late Athelstane

8 Crystal Foils9 Sagola & late Sagola

10 Vinegar

11 Marlnesco12 Va-tton

13 Saint Johns14 Republic15 Green HlUs

16 Ishpenlng

17 Six-Mile18 Marquette (Outer and Inner)

ICELOBES

Green Bay - 1,4,5,6,7,8,9,15Keweenaw - 10,11,12Langlade - 2 I MAPMichiganne - 13,14,16 fNUMBERSSuperior - 17,18Wisconsin Valley - 3

Moraines or ice contact Features(ticks point up-ice, dashed where inferred)

Drunllns or Flutes

Lakes

Figure 29. Regional correlation of moraines. Satellite imagery (Landsat Thematic Mapper (TM) and MultispectralScanner (MSS)) were used to correlate moraine segments within the study area to segments of known age in thesurrounding region (from Attig, et al., 1985). to

Years BP

c14

9,000

10,000

11,000

12,000

13,000

Advance

Marquette

Greatlakean

Port Huron

Ice lobes

West-central

Lake Superior

Six Mile

Watton

McDonald

Winegar

Central Lake

Superior

Lake Superior Lobe

Inner MarquetteOuter Marquette

LobesGreen Bay

Green Hills

Late Sagola

Sagola

Michigamme

Ishpeming

Republic

Saint Johns

East-central

Lake Superior

Grand Marais IQGrand Marais nGrand Marais I

?

Northeast

Wisconsin

Late Athelstane

Early Athelstane

Table 2. Regional (time) correlation of moraines in the Upper Peninsula and northeastern Wisconsin. 10

125

the northwest (outside the geographic limits of Figure 29). During this interval, portions

of the Green Bay lobe advanced slightly, into the area that was formerly occupied by the

Langlade lobe, and deposited the Crystal Falls moraine (8 on Figure 29). After a period of

further retreat, and a subsequent re-advance, the Early Athelstane and Sagola moraines (6

& 9 on Figure 29) were formed by the Green Bay lobe, while the Saint Johns moraine (13

on Figure 29) was deposited by the Michigamme lobe (the Langlade lobe of earlier

advances). To the west of the study area, the Winegar moraine (10 on Figure 29) was

deposited by the Keweenaw Bay lobe (formerly the Wisconsin Valley lobe). The time of

this advance was around 12,300-12,500 YBP (Peterson, 1986). Minor retreat of the

northern portion of the Green Bay lobe allowed deposition of the late Sagola moraine

slightly to the east of the Sagola moraine, while the Michigamme lobe deposited the

Republic moraine (14 on Figure 29), slightly to the northeast of the Saint Johns moraine.

These two moraines, the late Sagola and Republic, are the oldest moraines encountered in

the current study area. Retreat of Green Bay ice from the Green Bay lowland (just outside

the southeast corner of Figure 29) allowed growth of the Two Creeks forest. The

presence of the forest suggests a lengthy period of ice-free conditions. After probably a

couple hundred years, the ice re-advanced. Lobes that formed at this time were the

Keweenaw Bay Lobe in the west (Peterson, 1986), the smaller Michigamme Lobe (that

breached the Huron Mountains in the northeastern part of the study area), and the Green

Bay Lobe in the east (that also occupied the northern part of the Lake Michigan basin at

this time). The Green Bay lobe deposited the Middle Inlet till over the Two Creeks forest

south of present-day Green Bay, Wisconsin, and also formed the Late Athelstane moraine

126

(7 on Figure 29) at its terminal extent. Wood from the forest has been C14-dated at

11,850 YBP (Broeker and Farrand, 1963) and gives the date of burial. Thwaites (1943)

described the buried forest overridden by the Green Bay lobe and named the substage

"Valders". The stratigraphy here reflects an interstadial long enough for a mature Picea

forest to grow, as well as a significant re-advance of the ice that eventually overrode the

forest. Evenson et al. (1976) re-named the advance "Greatlakean" because of

questionable correlations of till sheets in eastern Wisconsin. The term Greatlakean is now

the preferred nomenclature for the advance. Farther north, sediments and landforms

found at the surface in the western part of the current study area are interpreted to have

been deposited at the ice front during the Greatlakean advance. The equivalent of the

Late Athelstane moraine within the present study area is herein named the Green Hills

moraine (15 on Figure 29). At this time, the Michigamme lobe formed the Ishpeming

moraine and ice-contact scarp (16 on Figure 29), and the Keweenaw Bay lobe formed the

Marinesco moraine (11 on Figure 29). It is generally believed that ice from this advance

reached its maximum extent about 11,850 YBP and began its retreat about 11,500 YBP.

Retreat from the terminal positions left several recessional moraines and ice-contact

features, the most significant probably being the Watton moraine (12 on Figure 29) of the

Keweenaw Bay lobe. Many ice-contact features and minor outwash surfaces formed by

the receding ice are recognized in the present study area and are shown by dashed line

segments on Figure 29. Retreat of all the lobes left the entire (modern) U.P. free of ice for

at least a few hundred years, enough time for drainage of Lake Agassiz through the Lake

Superior basin (Drexler et ai, 1983) to become established. Growth of the Gribben forest

127

near Marquette, Michigan (Hughes and Merry, 1978) and many others across the U.P.

occurred during this period. A final re-advance of the Marquette ice formed the Six-mile

moraine (17 on Figure 29) adjacent to the Keweenaw Bay lobe, and the Marquette

moraines (18 on Figure 29) adjacent to the Superior lobe.

CONCLUSIONS

From information derived through digital image processing techniques,

topographic map interpretation, and field and lab studies, glacial movements in the central

U.P. of Michigan were described. Three major advances of ice are recognized within the

study area. At about 13,000-12,500 YBP, during the Woodfordian advance of the

Laurentide ice sheet, and again during the Greatlakean advance (11,850 YBP), two

separate lobes transected the study area. About 10,000 years before present, the Superior

lobe advanced slightly south of the present-day Lake Superior shoreline in the Marquette

advance. In both of the older advances, the Green Bay lobe moved across the study area

initially from northeast-to-southwest, then fanned out toward the west. During both the

Woodfordian and Greatlakean advances, the Green Bay lobe passed over Paleozoic-aged

limestone and sandstone lithologies in the eastern part of the study area and terminated

over Archean granite bedrock in the west.

The Michigamme lobe transected the northern part of the region from northeast-

to-southwest. It passed over high-relief Precambrian metasedimentary rocks, which

impeded its forward motion. Thus, it did not extend as far south as the Green Bay lobe.

Because each of the ice masses passed over distinctly different bedrock types, lithologic

128

clasts in the till were used to differentiate sedimentary deposits and landforms of the lobes.

The Green Bay lobe sediments contain abundant limestone and sandstone lithologies.

Sediments of the Michigamme lobe contain little or none of these clasts, but are composed

of many different Proterozoic lithologies.

Landforms deposited as the ice retreated northeastward toward the Lake Superior

basin are well-preserved because the ice margin moved down the regional slope. There

were no re-advances that extended far enough to destroy older deposits. Thus, higher-

elevation moraines and outwash plains in the western part of the study area are evidence

of older, more vigorous advances. Within the study area, the ice margin(s) stabilized at,

or re-advanced to, a total of eight different positions in their retreat into the Lake Superior

basin.

At the confluence of the two lobes during almost the entire time they were

retreating, a nearly continuous interlobate deposit formed. The feature extends over 40

km west-to-east and is composed mainly of coarse-grained fluvial sediments and ablation

till. The feature is called the chain-of-Iakes interlobate deposit because of the numerous

lakes that occupy kettles in the feature along its entire course.

The final, significant re-advance of the Laurentide ice sheet into the study area was

first described by Hughes and Merry (1978) when they discovered the Gribben buried

forest southwest of Marquette, Michigan. The forest was re-examined in this study.

Hughes and Merry (1978) adopted the name Gribben interstadial for the ice-free period

during which the forest grew, and the name Marquette Stadial for the re-advance that

resulted in the death of the forest. Trees from the forest were dated at about 9,850 YBP

129

in their study. The Marquette advance resulted in deposition of the Marquette moraine(s)

and the Sands outwash plain. After retreat from the Marquette moraine, the Laurentide

ice sheet never again advanced into the Upper Peninsula of Michigan.

130

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