Investigations of the Sedimentology and Stratigraphy of the

Sediments at the Cleo-Meyer Farm in Little Falls, MN

Lori McDonald

EAS 423 Fall

Dr. Kate Pound

Contents

Abstract..........................................................................................................................................5

Introduction....................................................................................................................................6

Location..........................................................................................................................................6

Previous Investigation....................................................................................................................8

Hypothesis....................................................................................................................................11

Materials and Methods................................................................................................................11

Results..........................................................................................................................................15

Grain Analysis...........................................................................................................................15

Sedimentology Interpretation..................................................................................................16

Stratigraphic Interpretation......................................................................................................17

Conclusions...................................................................................................................................23

Future Research............................................................................................................................24

References....................................................................................................................................25

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Abstract Surficial sediment in central Minnesota is dominated by glacial and glacio-fluvial deposits. These

sediments are associated with landscape features that record the advance and retreat of ice

lobes into Minnesota during the Pleistocene. Sedimentology is the study of the composition of

sediments such as sand, silt and clay and the processes that lead to their deposition.

Stratigraphy is the study of the arrangement of sedimentary layers in a given area. The

investigation of the sedimentology and stratigraphy of a glaciated area such as the Cleo-Meyer

farm near Little Falls Minnesota reveals the local glacial history. The outcrop area of the Cleo-

Meyer locality investigated is located in the Little Falls East quadrangle of the E ½ of the NE ¼ of

the NE ¼ of T40N R32W S27, with a base elevation of 1,250 feet above sea level. The largest

wall of the main gravel pit was the primary focus of this investigation. At this location, every

unique sedimentary layer was measured and recorded. Samples of each sedimentary layer were

gathered in the field and analyzed in the lab to determine the color, size distribution of the

grains, and relative percentages of sand silt and clay. The 1-2 millimeter grain size portions were

sorted into different lithologic categories. Once they were sorted, the grains were counted and

the relative percentage of each lithology represented was recorded. When combined, these

data allow for the stratigraphic correlation of the units present at each different location to its

corresponding till. The sediments present at the main section of the Cleo-Meyer location were

determined to be outwash and till deposits associated with either the St. Croix or the Wadena

moraines, with incorporated Superior lobe till and outwash material. These sediments were

deposited in sequence in a variety of different glacial processes associated with the ablation of

the ice lobes that once covered this area of Minnesota.

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Introduction The surficial geologic morphology of central Minnesota is dominated by glacial deposits

and glacially related processes; which has resulted in a glacially influenced and sculpted

landscape. (Hobbs, 2009) A provenance study is defined as the science that deals with the

description, classification, and origin of sedimentary rock. It is the study of modern sediments

such as sand, mud (silt) and clay, and the processes that result in their deposition. (Knaeble,

1996) Sedimentologists apply their understanding of modern processes to interpret geologic

history through observations of sedimentary rocks and sedimentary structures. In the area of

the Cleo-Meyer locality at the Little Falls East quadrangle of the E ½ of the NE ¼ of the NE ¼ of

T40N R32W S27, a provenance study was conducted on the glacial sediments that were found to

be present. The investigation of the sedimentology and stratigraphy of a glaciated area such as

the Cleo-Meyer farm near Little Falls Minnesota reveals the local glacial history of the area. It

also broadens our understanding of the different processes formerly present there that shaped

the land as we know it today.

Location The Cleo-Meyer pit is located in the Little Falls East quadrangle of the E ½ of the NE ¼ of the NE

¼ of T40N R32W S27, with a base elevation of 1,250 feet above sea level.

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Figure 1: Glacial sediments exposed at the Cleo-Meyer farm. Measured section of the study

area is 54 feet high from top of tape measure to the bottom (vertical line located in center of

photo). Left photo is original outcrop. Right photo has overlying color interpretation of the

stratigraphy of the different units observed there.

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Previous Investigation

Deposition of glacial material from the retreat of these massive ice sheets in differing

environmental conditions resulted in unique sedimentary deposits. These deposits are classified

according to the environment in which they were deposited. Some of the different

classifications of glacial sediments considered in this investigation include:

Glacial till

Glacial fluvial outwash

End moraines

All glacial deposits, including end moraines, have two distinct sedimentary types; glacial till, and

fluvial outwash.

Figure 2: Different glacial zones in which sediments are deposited.

Glacial Till: Till is material that is directly deposited by a glacial ice. Till includes a mixture of

undifferentiated material ranging from clay size to boulders. This is the usual composition of a

moraine. (Knaeble, 1996)

Glacial fluvial outwash: Fluvial and outwash sediments are deposited by water. These deposits

are usually stratified or sorted by the action of running water from the melting of a glacier. In

contrast to till, outwash displays layering that is a result from sorting and deposition by running

water. Crossbedding is a common sedimentary feature found in outwash. Till and outwash are

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generally found in close association to one another because outwash is formed by meltwater

streams as they wash out the ice margins. (Kaneble, 1998)

End Moraine: End moraines form along the outer edge of an ice sheet and mark the extent of

the ice advance. These features usually appear as massive linear mounds of till. In this area of

Central Minnesota, one of the best examples of an end moraine deposit is found at the Powder

Ridge ski area in Kimball. This is part of the St. Croix moraine located in central Minnesota.

Minnesota Historical Geology: The general surficial geologic history of Minnesota is

dominated by glacial events that occurred in the Pleistocene epoch, more specifically the

Wisconsin Age. During this time the Laurentide ice sheet covered much of northern America,

and Minnesota was located at the edge of the sheet. (Ojakangas, 1982)

Figure 3: Furthest extent of the Laurentide Ice Sheet advance

Glacial Advances: Throughout the Quaternary there were six major glacial ice advances, each

bringing with it a unique or “typical group” of sediments derived from the rocks and landforms

the ice sheets moved over as they advanced and retreated over different source areas.

Wisconsin age glaciation in Minnesota was dominated by four lobes that extended from the

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Laurentide Ice Sheet of Canada. Over the course of about 65,000 years, these lobes advanced

and retreated several times. During a glacial advance, a glacier will incorporate bedrock and

existing sediments from the local environment into the ice. Glacial ablation, or melting, deposits

the incorporated sedimentary material in various ways according to the location of the sediment

on the retreating glacier. Through investigation of the differences in the lithologies of the

glacial sediments throughout the state, the ice lobes that deposited the landform can be

identified.

Figure 4: One of the last glacial advances in Minnesota during the Wisconsin age. This image

shows the ice coverage of the Des Moines lobe and its sub-lobes.

The Rainy and Superior lobes reached their maximum extent approximately 20,500

years ago. (Norton, 1983) During the last advance of these lobes a coarse-textured till of basalts,

gabbro, granite, iron formation, red sandstone, slate, and greenstone was deposited. This

advance resulted in the St. Croix moraine which extended from Walker to St. Paul. (Norton,

1983) The surficial geologic units associated with the area of the Cleo-Meyer Farm include the

St. Croix moraine association, deposits associated with the Wadena lobe, and outwash

associated with St. Croix moraine. (Hobbs, 1983) The St. Croix moraine association is a till that is

mostly end moraine material. It is composed mostly of sand and gravel, with a sandy and stony

texture. The St. Croix Moraine also has units of parallel ridges that appear to be large scale

thrust features. (Knaeble, 1998) Near the moraine it locally includes calcareous drift

incorporated from the underlying Wadena lobe. The Superior lobe is also well known for its ice-

marginal thrust blocks in the St. Croix moraine in the Stearns County area. (Knaeble, 1997)

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Hypothesis

Because of the surficial units associated with the area investigated, it is hypothesized

that the sediments seen at the Cleo-Meyer farm will be consistent with the St. Croix Moraine

association, with Superior lobe thrusted material incorporated in it. Also, because of its relative

proximity to the Mississippi River, it is hypothesized that along with the St. Croix Moraine

association, there will be significant stream deposits found there that are either directly

associated with the Mississippi River, or one of its paleo-tributaries.

Materials and MethodsMaterials used in this investigation include:

Tape measure

Sample collection bags

Munsell Color chart

Sodium pyrophosphate

Glass beakers

Scale

Hydrometer

Graduated cylinders

Blender

Hot plate

0.63mm, 1mm, and 2mm mesh sieves

Ceramic dishes

Petrographic microscope

The study section was measured with a tape measure by placing it at the top middle of the

outcrop and pulling it down to the base. The entire section measures fifty-three feet high, with

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approximately a sixty-degree angle from bottom to top. Eleven unique sediment deposits were

observed at this location of the Cleo-Meyer gravel pit, each loosely consolidated to

unconsolidated. Each unique sedimentary layer was described and its characteristics recorded.

Samples were taken from each layer and brought back to the sediment lab for analysis. Dry

color was determined for each sample using the munsell color chart. Approximately 50 grams of

each sample was weighed out and placed into a clean glass beaker. A solution of 150ml sodium

pyrophosphate was added to each sample to disaggregate clay material present. After soaking

for 24 hours, the sediment and solution was stirred to remove air bubbles and allowed to settle.

Following this process, a hydrometer reading was taken for each sample using a graduated

cylinder containing 1,000ml of sodium pyrophosphate. After the sediment had settled, the

solution was transferred to a blender and was agitated approximately one minute to further

disaggregate any clay present. Each sample was then transferred into a large graduated

cylinder, and filled to 1,000ml with water. To determine satisfactory sediment to water ratio

had been achieved for the removal of clay particles, additional hydrometer readings were taken

at one hour intervals. At this stage the wet color is also recorded. The sediment was then

strained through a 0.063mm sieve and dried on a hot plate for approximately three hours. Once

dry, the 0.063mm, 1mm, and 2mm mesh sieves were used to separate grain sizes. Following

agitation, the contents of each sieve was transferred into separate envelopes which were

labeled, weighed, and recorded. Weight percentage was calculated and the 1-2mm size grains

are set aside for grain counting.

The 1-2mm fraction for each distinct layer was placed into a black tray. Individual sediment

grains were separated into a ceramic dish with 12 different partitions. The grains were

differentiated into color categories and sorted according to lithology using a petrographic

microscope. Grain assemblages for each layer were glued onto a numbered slide. They were

then analyzed, counted, and recorded. A grain count worksheet was used with this method to

determine percentages of each typical grain type represented in the 1-2mm analysis.

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Figure 6: Grain count worksheet used for classifying 1-2mm grains into Precambrian, Paleozoic,

and Cretaceous groups based upon individual grain lithology. This is used to determine

sediment provenance.

Figure 7: The Munsell soil color chart for color differentiation of soil and sediments.

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Table 1 : Descriptions and field notes of all the sedimentary units observed at the large pit at the Cleo-Meyer Farm.

Sample Thickness Field Description Dry Color Wet Color

CM 1-10b 52 – 53 ft Top layer. Sample taken to the north (off to the side) of the middle of the section. Dark reddish-brown silty particles mixed with coarse sand

7.5 YR5/6 7.5YR 6/8

CM 1-10a 52 – 53 ft Top layer. Sample taken from the middle of the section near the tape measure. Light tan, very fine sand to silty particles mixed with larger pebbles that have low sphericity, but are rounded.

10YR 6/4 10YR 7/8

CM1-9 48 – 52 ft Called “the holey layer” near the top of the outcrop. Medium grey. Made of very fine clay/ silty particles intermixed with fine slightly angular sand. Compacted, hard, very porous. Abundant holes in this layer made by birds or small animals.

10YR 6/3 2.5YR 5/4

CM 1-8 47 – 48 ft Darker brownish-red unconsolidated medium grained sand. Composed of more angular fragments.

7.5YR 4/4 7.5YR 6/8

CM 1-7 36 – 47 ft Light reddish-tan, medium to fine sand. Loose unconsolidated, horizontally bedded.

10YR 6/4 2.5Y 8/4

CM 1-6 35 – 36 ft Well compacted, red colored very fine sand. Medium to thin bedding with coarse laminae seen in the sandstone in the field.

10YR 5/6 7.5YR 5/6

CM 1-5 32 – 35 ft Very tightly compacted, not lithified, composed of very fine clay and silt particles. Cohesive clay-like texture, would stick together when squeezed. Alternating light and dark tan horizontal bands seen in outcrop. Called “the green layer” in the field because of small green plants/ moss growing out of it.

2.5Y 7/4 NA

CM 1-4 30 – 32 ft Very poorly sorted, thin conglomerate layer composed of very large pebble to cobble sized clasts in a medium to fine sandy matrix. Larger clasts are composed of rocks such as amygdaloidal basalt and rhyolite. Overall dark reddish-brown color.

7.5YR 5/4 NA

CM 1-3 4.4 – 30 ft Large massive very loosely to unconsolidated sand with large scale crossbedding features seen in the field. Medium to fine sand, well sorted. Dark reddish tan color. “ The big layer”

5YR 6/3 NA

CM 1-2 2 - 4.4 ft Fine-very fine sand, well compacted, slightly cohesive but easily broken up. Well defined thinly laminated crossbedding in outcrop. Sequence becomes more progressively coarse upwards.

10YR 5/4 10YR 6/8

CM 1-1 0 - 2 ft Bottom layer of the section. Coarse-very coarse sand with pebble sized grains incorporated that were rounded with low sphericity. Some crossbedding seen in outcrop.

10YR 6/4 10YR 8/4

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Results The 1-2mm grain size is considered to be very coarse sand. It provides critical information

on sediment provenance, and is very useful in distinguishing among till units and for

determination of ice-flow direction. The method used in this study for classifying individual sand

grains grouped them as precambrian, paleozoic, or cretaceous.

Grain Analysis Precambrian: Grains are grouped into light, red, and dark color categories. The light category

consists of granite, gneiss, quartz, and quartzite.

The red category includes iron, rhyolite, agate, arkose sandstone, and quartz arenite.

The dark category of the Precambrian encompasses dark mafic rocks and other dark igneous or

metamorphic rocks.

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Paleozoic: The Paleozoic grouping includes carbonate, chert, sandstone, and shale. The only

grains seen in this study for this category were cherts and Paleozoic sandstone

Cretaceous: Grains grouped as Cretaceous include grey shale, speckled shale, limestone,

inoceramous shells, pyrite, and lignite. No cretaceous sediments were observed in this study.

Sedimentology Interpretation Triangular Diagram Analysis: A triangular or ternary diagram is a graphical tool used to classify

different properties in geologic classification. In doing a triangular diagram analysis of each of

the layers investigated in the 1-2mm grain analysis, there are three different plots differentiating

Precambrian, Cretaceous, and Paleozoic rock types, comparing the sediments investigated with

known tills in the Central Minnesota region.

Figure 8: Different triangular diagrams used in soil and sediment analysis

Triangular diagram A differentiated total percentages of Precambrian versus Paleozoic and

Cretaceous grains. CM 1-1, CM 1-8, and CM 1-9 all were plotted on the diagram in the Shooks

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till range. CM 4-1 was plotted as First Red till. CM 1-10a and CM 1-10b were plotted in the

Wadena Till range.

Triangular diagram B and triangular diagram C compared different groupings within the

Precambrian category based upon relative percentages of granitic, quartz, and dark, red, or

sandstone grains present. In Triangular diagram B, the grain percentages plotted CM 1-1, CM 1-

9, and CM 1-10b in the range of the First Red till. CM 4-1 is plotted as Eagle Bend till, and CM 1-

10a is plotted in the range of Pierz till.

Triangular diagram C plotted CM 1-1 as St. Francis till and CM 4-1 as First Red till. CM 1-8

and CM 1-9 were plotted as being in the range of Wadena and Pierz till. CM 1-10a was plotted

as Eagle Bend till and CM 1-10b was plotted in the range of Sauk Center till.

Stratigraphic Interpretation CM 1-1: In investigating the physical structures of the layers in outcrop, the bottom layer of the

section is 2 ft thick. The larger are pebble sized, or about the size of a golf ball and are present

in a matrix of smaller sand sized material. This material was unsorted and a good example of

what we would expect from glacial till. The 1-2mm grain analysis showed that there were 99%

Precambrian grains, and 1% Paleozoic.

CM 1-2: The second layer from the bottom was also approximately 2 feet thick and is composed

of very fine sand with cross bedding laminations that can be seen in the middle of the section.

This stratum also seems to have a coarsening upwards sequence, with larger clasts towards the

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top of the sequence. There also appears to be some imbrications of the larger clasts seen in this

section. This section also had a 1-2mm grain analysis of 99% Precambrian grains, and1 %

Paleozoic. This section is interpreted as being related to a glacial outwash event.

CM 1-3: The third layer was the largest and most massive in the entire cross section. This

section is 25.5 feet thick, and is composed of very fine to medium sand particles. Because the

sand in this section was smaller than the 1-2mm fraction, a 1-2mm analysis was not conducted.

However, because of the large scale crossbedding and small scale laminations seen in the

sample, this layer was interpreted as being deposited by glacial meltwater as glacial outwash in

a large or more prolonged melting event, with water velocities at slower speeds to be able to

deposit smaller sized particles.

CM 1-4: The fourth layer is located directly on top of the massive cross bedded layer. It is a very

thin lens of pebble conglomerate. This very poorly sorted layer consisted of clasts that ranged

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from pebble (golf ball) size to very fine sand. The 1-2mm grain analysis of this layer showed

100% Precambrian grains, with a majority of them being associated with the superior till.

CM 1-5: The 5th layer in the section was nicknamed “the green layer” because it appeared to be

green when standing at a distance describing the section. However, when it was examined

more closely it was found to be composed of very fine clay particles that held enough moisture

for small green plants to be growing out of it. The clay in this layer is very thinly laminated and

is 3 ft in total thickness. The sediment in this layer was also too small to conduct a 1-2mm

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analysis.

CM 1-6: The sixth layer in the section was approximately 1 ft in thickness. Its composition is red

colored, very fine sand that is very thinly bedded in horizontal layers. The sediment in this

section also was too small to conduct a 1-2mm analysis, but because of the thin layering and red

color it is interpreted as being a glacial outwash from the rainy or superior lobes.

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CM 1-7: The seventh layer in the section is 9.5 feet thick and was composed of light reddish tan

medium to fine sand. This layer also displayed horizontal bedding features that can be

associated with glacial outwash deposits. A 1-2mm analysis could not be conducted due to

small grain size.

CM 1-8: The eighth layer in the section was composed of dark reddish brown medium to course

sand. It averages approximately a foot in thickness; however, there are abundant channel scour

and fill patterns seen in the section. Analysis of the 1-2mm grain portion revealed 100%

Precambrian sediment with most of the lithologies represented by typical rocks from the

superior lobe.

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CM 1-9: The ninth layer was approximately 3.5 feet thick and composed of mostly clay and silt

particles intermixed with fine to medium sized sand. This layer was nicknamed named “the

holey layer” because of the presence of bird and insect holes in it. The 1-2mm analysis revealed

that there were 98% Precambrian grains, with 2 % Paleozoic.

CM 1-10a/ CM 1-10b: The top layer in the section was divided into two different sections, one to

the right of the tape measure and one to the left. Section 10a was the section to the right of the

tape measure. It is composed of very poorly sorted till material with the largest clasts being

pebble (golf ball) sized. The 1-2mm analysis of this material showed that there were 99%

Precambrian sediments, with 1% Paleozoic. The top layer to the left of the tape measure was

labeled as section 10b. It is composed of dark reddish brown unsorted till material ranging from

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very fine silty particles to large pebble to cobble clasts. The 1-2mm grain analysis of this section

also revealed 99% Precambrian sediments, with 1% Paleozoic.

CM 1-10a

CM 1-10b

Conclusions The sediments present at the main section of the Cleo-Meyer location are outwash and till

deposits associated with the St. Croix and Wadena moraines. Each of the sedimentary layers

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that were able to be investigated were found to contain Precambrian material that originated

from the rainy and superior lobes. All of the 1-2mm grain analysis contained 99-100%

Precambrian sediments, with 1% or less Paleozoic sediments, and 0% percent cretaceous

sediment.

Comparing the results from triangular diagrams A, B, and C to the expected assemblages

associated with the St. Croix moraine found in the Geologic Atlas of Stearns County, the results

are inconclusive. None of the tills plotted on diagrams A, B, or C were plotted as the same till on

any of the consecutive diagrams. These results could have been skewed in many different ways.

One possible reason for the inconclusiveness of these diagrams is that these sediments were

deposited in conditions that were highly influenced by fluvial processes. Grains present in test

tills for the analysis done by the Stearns County geologic atlas could have been taken from sites

that were not as affected by these processes. Grains removed or dissolved in the presence of

moving water would skew the results of these diagrams, making their validity questionable.

Also, because the St. Croix moraine sediments in Stearns county commonly have been

associated with thrusted Superior Till sediments, that could have been another factor in the

weak triangular diagram results.

The percentages of 1-2mm grain lithologies present was consistent with a majority of

Wadena Lobe sediments, with some incorporated Superior lobe till and outwash. Typical St.

Croix end moraine sediment was largely unrepresented in this measured section. These

sediments were deposited in sequence in a variety of different fluvial glacial processes

associated with the ablation of the ice lobes that once covered this area of Minnesota.

Future Research Future research would include developing a more comprehensive classification scheme for

1-2mm grains. Many problems were encountered when trying to classify grains that did not fit

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into the current grain classification chart. Examples of problem grains were rose quartz, clear

quartz sandstone, tan to pink sandstone, and pink feldspar grains.

There is no clear current category that these grains can be classified into. Filtering these

results into categories that had the “best fit” could ultimately alter the results and

interpretations of the source of the sediment represented in the 1-2mm grain fraction.

References

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Danelski, T.C., Moe, S.A., Weeks, M.R., and Anderson, G.G., 1993, Ice-thrust Wadena drift in the southern St. Croix Moraine, Stearns Co., Minnesota; Geological Society of America, North-Central Section, 27th annual meeting: Abstracts with Programs - Geological Society of America, v. 25, p. 15-16.

Hobbs, H.C., 2005, The search for early Wisconsinan glaciation in Minnesota; Geological Society of America, North-Central Section, 39th annual meeting: Abstracts with Programs - Geological Society of America, v. 37, p. 89-90.

Hobbs, H.C., and Craddock, J.C.(., 1983, Structure and geomorphology of the St. Croix Moraine, Swanville area, Minnesota; North-central Section, the Geological Society of America, 17th annual meeting: Abstracts with Programs - Geological Society of America, v. 15, p. 251.

Johnson, M.D., and Savina, M., 1987, The late Wisconsin southern margin of the Superior Lobe was 10 to 15 kilometers south of the St. Croix Moraine; Geological Society of America, North-Central Section, 21st annual meeting: Abstracts with Programs - Geological Society of America, v. 19, p. 206.

Knaeble, A.R., 1998, Superior-Lobe glacial thrusting of sediment and bedrock along the St. Croix Moraine, Stearns County, Minnesota; Contributions to Quaternary studies in Minnesota: Minnesota Geological Survey, St. Paul, MN, United States (USA), Report 49, 15-26 p.

Knaeble, A.R., 1997, Glaciotectonic thrusting along the St. Croix Moraine, Stearns County, west-central Minnesota; 1997 abstracts with programs, The Geological Society of America, 31st annual North-Central Section: Abstracts with Programs - Geological Society of America, v. 29, p. 27.

Knaeble, A.R., 1996, Glaciotectonic thrusting along the St. Croix Moraine, Stearns County, Minnesota; Text supplement to the geologic atlas of Stearns County, Minnesota: County Atlas Series - Minnesota Geological Survey, v. C-10, p. 40-47.

Knaeble, A.R., and Meyer, G.N., 2006, Glacial landforms in central Minnesota; a perspective on the genesis and age of drumlins, moraines, and glacio-tectonic thrust ridges; Geological Society of America, North-Central Section, 40th annual meeting: Abstracts with Programs - Geological Society of America, v. 38, p. 70.

Metz, M.A., Meyer, D.P., Rogers, M.R., Thorne, R.E., and Anderson, G.G., 1994, The influence of basement block tectonics on ice thrust Wadena Drift in the southern St. Croix Moraine, Stearns Co., Minnesota; Geological Society of America, North-Central Section, 27th annual meeting: Abstracts with Programs - Geological Society of America, v. 26, p. 54-55.

Norton, A.R., and Craddock, J.C.(., 1983, Supraglacial and proglacial sedimentation associated with the Itasca and St. Croix moraine interlobate area, north-central Minnesota; North-central Section, the Geological Society of America, 17th annual meeting: Abstracts with Programs - Geological Society of America, v. 15, p. 251.

Ojakangas, R.W., and Matsch, C.L., 1982, Minnesota's geology: United States (USA), Univ. Minn. Press, Minneapolis, MN, United States (USA), .

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