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A PETROGRAPHIC INVESTIGATION

OF VERTICAL DEPOSITION WITHIN

THE MASON ESKER RELATIVE TO
ITS ORIGIN

Thesis fol H10 Degree 9! M. S.
MIG-IIGAN STATE COLLEGE
Mariwie Louise McCaIIum

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A PETROGRAPHIC INVESTIGATION OF
VERTICAL DEPOSITION WITHIN THE

MASON ESKER RELATIVE TO ITS ORIGIN

by

Marjorie Louise McCallum

A THESIS
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geology and Geography
1949

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Acknowledgements

The writer wishes to express thanks to
Dr. B. T. Sandefur, who suggested the problem
and gave freely of his time and assistance in
the laboratory.

Thanks are also due Dr. S. G. Bergquist.
and Dr. J. W. Trow, who assisted in the prepar-
ation of the manuscript, and Mr. F. V. Monaghan

who aided in constructing the maps and graphs.

31781?

Table of Contents

P380
IntPOduction ---- ............ do--- 1

Location ------------------------- 4

Laboratory Procedure ---- ------ ~-- 6
Splitting -~-------------—--- 6
Washing - ------------ -é------ 6
Sieving ------- --- ---------- - 7
Leaching -----e-------------- 10
Gravity Separation ~--------- 10
Mounting Slides --- ------- --- 12

Microscopic Investigation -------- 13
General --------------------- 13
Heavy Minerals -------------- 13
Mineral Descriptions ------ -- 16
Roundness and Sphericity ---- 20

Conclusions - ------ --------------- 23

’ K
in...
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Table
Table
Table
Table

Figure
.Figure
Figure
Figure
Figure
Figure
Figure
Figure

Figure

I :
II
III
IV

<0 a: -e es en .s on as .u

0.

List of Illustrations

Sorting, Skewness, and Kurtosis ------
Heavy Mineral Frequency-Size 100 ----
Heavy Mineral Frequency-Size 150 ----

Heavy Mineral Frequency-Size 200 ----

Areal Extent of the Mason Esker -----
Weight Percent Analysis of Sand -----
Generalized Cumulative Curve --------
Percent of Carbonate in Sand --- -----
Percent of Heavy Minerals in Sand ---
Roundness and Sphericity Values 9~---
Heavy Mineral Frequency-Size 100 ----
Heavy Mineral Frequency-Size 150 ----

Heavy Mineral Frequency-Size 200 ----

26
27
28

29

30
31
52
35
34
35
57
58
59

. ‘I

 

 

Introduction

The differences of opinion among glacial geologists
regarding the origin of eskers has prompted the writer
to undertake this investigation in an effort to discover
whether petrographic methods of study of sediments will
be of value in determining the origin of a particular
esker.

The general term esker is applied to a rather wide
variety of ridge-like accumulations of stratified glacial
drift. Although alike in having been formed during a
stage of deglaciation, they almost certainly have a number
of different origins.

The characteristic esker is a steep-sided, narrow-
crested and more or less sinuous ridge, which rises as
much as 150 feet above the surrounding country. In general,
the lateral slopes approximate the maximum.angle of
repose for gravel. In some localities the ridge is un-
interrupted for long distances, but in other places it
is discontinuous. An esker system, including all the
esker ridges attributable to a single glacial river or
drainage system, may be as much as 150 miles in length.
Sand and gravel are the chief constituents of most eskers
although silt and boulders are present in some.

A variety of hypotheses have been formulated to

account for the formation of eskers, although most

authorities are agreed that they were deposited by glacial
streams during some phase of deglaciation.

The chief proponent of the subglacial channel theory
is W.M. Davis.*

 

s Davis, W.M., The subglacial origin of certain eskers:
Boston Society of Natural History, Proceedings, vol. 25,
1893. pp. 477-499.

 

His explanation assumes a stagnant marginal zone of the
ice sheet. Water from basal and surface melting of the
ice flows into subglacial streams through crevasses. A
considerable amount of englacial and subglacial detrital
material is gathered into these streams. Some of this
material is deposited in the stream bed as a result of
overloading or through the sorting action of water. In
the event that the stream is diverted, the deposit will
be left in the abandoned tunnel. Protected by the sur-
rounding ice walls, it will gradually develop the lateral
slopes characteristic of eskers, and be left intact as
the mass of ice melts down by ablation.

Opposing Davis's subglacial channel theory is the

superglacial strewn theory, proposed by Crosby.*

* Crosby, W.O., The origin of eskers:.§pston society of
Eatural History, Proceedings, vol. 30, 1902. pp. 375-411.

 

Like Davis, however, he propesed that eskers were formed

 

 

near the marginal zone of a stagnant ice sheet. At the
outer border of the ice the gradient of a superglacial
stream.is controlled by a barrier of rock or till against
which the ice may temporarily terminate. This barrier
determines a base level below which the stream.cannot
cut by mere mechanical erosion. Thus a main stream,
accumulating the detritus of its tributaries, becomes
clogged and aggraded. As the ice thins and finally dis-
appears, the stream bed is gradually lowered in toto-
to the ground surface.

Still another possibility for the origin of eskers
is offered by Trowbridge.*

 

e Trowbridge, A.D., The formation of eskers: Scfence, n.s.

vol. 40, 1914. p. 145, abstract.

 

He suggested that eskers are in reality nothing more

than drawn-out kames. The term kame is applied to small
outwash cones built out from ice which later collapsed,
isolating the masses in irregular mounds. Since kames

are usually associated with interlobate moraines, while
eskers are related to ground moraines formed during
intervals of stagnation or retreat, he concluded that the
development of esker forms is dependent upon the rate of
recession of the ice front. Thus, streams discharging
from.the ice front build up small outwash cones at the

ice margin. As the ice retreats the cones form successive

segments of a serpentine-like ridge, called an esker.
A further explanation of eskers is suggested by
R.F. Flint,e ’

 

e Flint, R.F., Glacial Geology and the Pleistocene
E och, Appleton-Century Co., 1947. p. 153.

 

who notes that several glacial deposits which have been

described as eskers are actually crevasse fillings.
Undoubtedly several or all of these theories must

be employed to account for the large variety of esker

types found scattered over glaciated areas.

Location

The Mason esker, approximately twenty miles in
length, is one of the longest observed in Michigan. It
heads in a gravel pit at the corner of Main and Shepard
streets in southeastern Lansing, and extends southeast-
wardly through Holt and Mason. Its southern terminus is
obscured in the Charlotte morainic system southeast of
Mason. The ridge varies in height from.thirty to fifty
feet above the adjoining till plain, and often extends
thirty to forty feet below the water table, where it
widens as much as 400 feet. The esker has been described

at some length by Leverett,*

 

e Leverett, F., and Taylor, F.B., The Pleistocene of
Indiana and Michigan and the history of the Great Lakes:
U.S.G.S. Monograph as, 1915. pp. 209-211.

o-uh —~--- o—O—w

 

 

who writes:

"The esker, wherever opened, is
composed of stratified and more or less
perfectly assorted material. It gives
evidence of the action of a stream
which varied greatly in the rapidity
of flow in different places along a
given horizon, both longitudinally
and from side to side, as well as at
different horizons. The phenomena dis-
played are not unlike those found in
the beds of existing streams flowing
subaerially. The esker is evidently a
streamsbed deposit, though probably
deposited within ice walls."

The present investigation is limited to a single
vertical section through the Mason esker at a point
approximately mid-way between the northern and southern
termini. A recent cut, located Just east of the inter-
section of Aurelius and Miller roads in Lansing Township,

t
was selected as affording the best side for the sampling
of a complete and nearly vertical section. Samples were
collected from.the north face of the out. After the
slumped and weathered material had been scraped away,
channel samples approximately six inches wide were col-
lected from.top to bottom, beginning at the top of the
out, immediately below the deepest zone of soil develop-
ment. Each five foot sample was placed in a quart Jar,

covered, and labeled. Ten different samples, represent-

~ r1-

 

 

ing fifty feet of section, were collected.

Laboratory Procedure

Splitting

The field samples were numbered fromione to ten,
with sample one representing the first five feet from
the top, and so on. Approximately one half of the field
sample was taken for study, and the remainder retained
for reference. The samples were quartered by hand, using

the method described by Krumbein.*

 

* Krumbein, W.C., Manual of SedimentaryPetrography,

Appleton-Century Co., 1938. p. 44.

 

The sample was poured into a conical pile on a large sheet
of smooth paper and cut with a small spatula into four
quarters. Alternate quarters were retained and recombined.
Wherever necessary, the process was repeated until a
workable amount was obtained. This method was followed
whenever splitting of the sample was necessary.
Washing

The sample thus obtained was washed in a solution
of potassium.hydroxide to remove the clay particles. The
solution was decanted, taking care not to remove the fine
sands,until the water ran clear. The washed samples were

air dried and then passed through a twenty mesh sieve

to remove the gravel. Each sample was thus concentrated
to contain only the sand sizes.
Sieving

The sediment which passed through the twenty mesh
sieve was quartered to 100 gram samples and sieved in
the Ro-Tap automatic shaker for eight minutes. The shaker
was equipped with five sieves having 48, 65, 100, 150,
and 200 openings per square inch. A pan was placed at the
bottom to catch the material passing through the 200 mesh
sieve. The sands were thus separated into six grade
sizes, each of which was weighed and placed in properly
labeled vials. The mechanical composition of the ten
samples is shown in Figure 2. Grade sizes are designated
according to the mesh.of the various sieves.

The results of the weight percent analysis show a
decided difference from.sample to sample. Such changes
in curves may be expressed in terms of quartile devia-

tions. Krumbein e

* Krumbein, W.C., The use of quartile measures in describing
and comparing sediments: American Journal of Science, vol.

32, 1956. pp. 98-111.

-_

gives a good resume of the application of statistical
Inethods to description of sediments. Three attributes of
the normal curve are considered, namely, sorting, skewness

and kurtosis. Conventionally, the geometric measures of

these properties are used, as they yield results which
are independent of the size factors and units of measure-
ment.

Five values usually suffice for the computation of
the measures. They are the median, the first and third
quartiles, and the tenth and ninetieth percentiles. The
relationships of these values are shown in Figure 3.

Each is read directly from.the cumulative curve of the
size distribution. The median, M, is defined as that
diameter which.is larger than fifty percent of the diametas
in the distribution and smaller than the other fifty per-
cent. Its value corresponds to the point where the fifty
percent line crosses the cumulative curve. The first
quartile,Ql, is that diameter which has 25 percent of the
distribution larger than itself and 75 percent smaller
than itself. It corresponds to the frequency line of 25
percent. The third quartile, Q5, is that diameter which
has 25 percent of the distribution smaller than itself
and 75 percent larger than itself, and corresponds to the
75 percent frequency line. Accordingly, the tenth percen-
tile corresponds to the ten percent frequency and the
ninetieth percentile to the ninety percent frequency line.

Sorting is defined as the square root of the ratio

of the two quartiles and is found by the formula:

 

 

0n the basis of nearly two hundred analyses, Trask *

’—

e Trask, P.D., Origin and Environment of Source Sediments

ofggetroleum, Houston, Texas, 1952. pp. 67 ff.

 

found that a value of 'So' less than 2.5 indicates a
well sorted sediment, a value of about 3.0 a normally
sorted sediment, and a value greater than 4.5 a poorly
sorted sediment. The sorting values of the ten samples
from.the Mason esker are shown in Table I, and indicate
a well sorted sediment at each horizon.

Skewness is a measure of the extent of departure of
the median, or fifty percent frequency, from.the point
half way between the two quartiles. It is developed

from the formula:

I Q q'"
Sk 3 ‘—;§§—'
H

When the curve is symmetrical, skewness is equal to unity.
Values less than one indicate that the curve is skewed to
the left, or larger sizes, of the distribution. Values
greater than one indicate skewness to the right. Thus the
skewness values indicate whether the bulk of the sedi-
ment is composed of larger or smaller size grades. The
values for the Mason esker samples are shown on Table I.
The results indicate that the sediment is concentrated

in the larger sizes to a considerable degree.

Kurtosis is a measure of the degree of peakedness

10

of a curve. It rolves a comparison of the spread of the
central position of the curve to the spread of the curve

as a wh01e. Kurtosis is the ratio of the quartile deviation
to that part of the size range which lies between the

tenth percentile, P10, and the ninetieth percentile, P90.
Hence the formula:

Q1- Q3

QIPlo‘Pgo)

 

K:

The equation yields values which decrease with increasing
peakedness. The kurtosis values for the ten samples are
shown in Table I. They indicate a high degree of peaked-
ness for each sample.
Leaching

Each fraction of sand was digested in dilute hydro-
chloric acid to remove any carbonate, the presence of
which is objectionable in petrographic studies. The sme-
ples were then washed, dried, and reweighed. The amount
of carbonate present was computed from.the weight loss
in each sample. These results are shown in Figure 4.
Gravity Separation

Approximately two grams of each of the four smallest
size grades in the ten samples were placed in funnels
containing bromoform (Sp. Cr. 2.87 at 20°C.). Due to the
presence of dissolved alcohol, commercial bromoform is

usually low in specific gravity, often below that of

quartz. It is thus necessary to wash commercial bromoform

11

with water in order to raise the specific gravity suf-
ficiently to effect the separation of quartz and feld-
spar from.the heavier minerals. The method used was that

described by Ross.*

 

e Ross, 0.8., Methods of preparation of sedimentary
materials for study: Economic Geolggy, vol. 21, 1926.
pp. 454 ff.

 

A large volume of water was added to the bromofonm-
alcohol mixture in a two liter bottle. After vigorous
shaking the heavy bromoform.phase separated out and the
alcohol remained in the water phase. The water was then
decanted and the process repeated two or three times.
After the third decantation, the bromoformswater mixture
was poured into a separatory funnel. The bromoform was
then drawn off and run into a funnel fitted with several
thicknesses of filter paper, which served to absorb any
dispersed water which may have been present.

The stems of the funnels used for the gravity separa-
tion were fitted with short lengths of rubber tubing with
pinchecock attachments. Below each was another funnel,
fitted with filter paper, which in turn drained into a
beaker. The sand was placed in bromoform in the top
funnel, which was covered with a watch glass to prevent
evaporation. The sand was stirred occasionally with.a

glass rod to separate the individual grains and assure

 

12

a thorough separation of light and heavy minerals. Each
fraction was then allowed to pass onto a filter paper
in the funnel below. It was washed with alcohol, dried,
and weighed. The bromoform washings retained in the
beakers were combined and the bromoform was recovered as
described above. The weight percent of heavy minerals

in each sample is shown in figure 5.

Mounting7811des

Before mounting the mineral specimens on the slides,
the magnetite present in the heavy fraction was removed
with a small magnet.

A random sample from the heavy fraction of each of
the four smallest size grades was selected for mounting.
The two larger grades were discarded for this purpose,
as they were seen to contain a large proportion of broken
rock fragments. Only the one largest grade was discarded
in mounting the light minerals.

The samples were mounted in a synthetic resin having
a refractive index of 1.66. This medium was selected for
two reasons. First, the index of 1.66 divides the range
of indices of the heavy minerals into two more or less'
equal parts. Secondly, since the index of the resin, 1.66,
is much higher than that of quartz, 1.54-1.55, the clear
quartz grains mounted in this medium possess considerable
negative relief and thus show sharper outlines. This aided
in.making the projection tracings from.which the sphericity

13

and roundness results were obtained.
Microscopic Investigation

General

The macroscOpic study of this detrital sediment
consists of identifying and counting heavy minerals,
and determining the roundness and sphericity of the
quartz grains in the light mineral fraction. A polariz-
ing microscope was used as an aid in determining the
minerals present in each mounted sample. This type of
microscope permits obsgvation of the object by means of
plane polarized light as well as by ordinary light. The
slides were placed on a mechanical stage for counting
the heavies. By means of two thumb screws the object
slide could be moved in two directions for any given
distance. This permitted changing from one field to an-
other while counting without danger of overlapping.
Heavy Minerals

Of a total of twenty-two heavy minerals identified,
only seven were common to all slides. The three smallest
size grades for each of the ten samples were selected as
most convenient for identifying individual minerals. An
average of 300 grains per slide was counted, for a total
of 9000 grains in all. The results of the count were

converted to percentage frequency, and the figures are

l4

diown in Tables II, III, and IV. Cumulative histograms
were drawn for the ten most common constituents and are
shown in Figures 7, 8, and 9.

It may be interesting to note here some research

carried out by Dryden.e

 

*—

* Dryden, A.L., Accuracy in percentage representation of

heavy mineral frequencies: Natignal Acadggy:of Science

 

Proceedingg, vol. 17, 1951. pp. 255-258.

 

concerning the probable error made in counting only a
limited number of grains from.a random sample. He develop-
ed a formula which permitted the construction of curves
showing the probable error in frequency percentages for
counts ranging from 25 to 750 grains. Due to the nature
of the curve, accuracy is shown to increase very slowly
after a certain point. In most cases, a count of 500
individual grains per slide will yield satisfactory
results.

Since variations in frequencies of the minor con-
stituents of heavy mineral suites are often significant,
Hittenhouse s

a Rittenhouse, G., Curves for determining probable errors
in heavy mineral studies: National Research Couggil, 33
port of the Committee on Sedimentation, 1940. pp. 97-101.

 

constructed curves showing probable errors for mineral

 

 

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15

frequencies between 0.1 and 20 percent. The probable
error increases considerably for the frequency of the
rarer constituents. For example, with a frequency of
ten percent computed for a single mineral and a total
count of 500 grains, the observed frequency may deviate
1.5 percent from the actual or "true" frequency. However,,
with a computed frequency of only one percent and the
same 500 grain count, the deviation from the actual
frequency may be as much as 5.9 percent.

Since samples for this study were collected under
the same conditions and in one area only, it may be
assumed that such errors will be constant throughout the
investigation, and may safely be disregarded in inter-
preting the results. This probability of error is dis-
cussed here for the purpose of pointing out that the
mineral frequency percentages are only relative to the
number of grains counted, and do not represent absolute
values.

The general term "aggregate“ has been applied to
a large proportion of the material encountered on the
heavy mineral slides. Upon investigation under high
power, this material was found to be rock fragments
cemented by quartz and hematite. Such compound aggregates
are frequently encountered in the heavy fraction, and
often included in the counts, even though the individual

minerals are indistinguishable.

16

Mineral Descriptions

Following is a list of the minerals found in the
investigation of sediment taken from the Mason esker.
The identifying characteristics have been compiled from

several sources.e

 

* Dana, E.S., Descriptive Mineralogy, John Wiley and
Sons, Inc. 1914.

Johannsen, A., Essentials for the Micrgscopical Detep;
mination of Rock-forming_Minerals and Rocks, University
of Chicago Press, 1914.

Krumbein, W.C., op. cit. pp. 414 ff.

Milner, H.B., Sedimentary Petrographz, D. Van Nostrand
Co., 1929. pp. 97 ff.

AA

Hornblende: complex silicate of Ca,Na,Fe,A1,Mg

Crystal system : Monoclinic
Color : Var. Arfvedsonite- hlue-green
Var. Common hbl.- green to
‘ brown
Birefringence : .026-.027
Optic figure : biaxial negative
Elongation : positive
Pleochroism. : marked

Distinctive features : grains elongate, pris-
matic; color; pleochroism

Garnet: complex silicate of MgFe,Al,Mn,Cr

Crystal system.: Isometric

Color ° colorless,pink,red,orange
Distinctive features : isotropic; high relief;
conchoidal fracture; color.

Zircon: Zr02.3102

Crystal system : Tetragonal

17

Color : colorless to yellow
Birefringence : .055-.059

Optic figure : uniaxial positive
Elongation : positive

Distinctive features : crystal form: high
index; inclusions; parallel and complete
extinction.

Monazitg: (Ce,La,Nd,Pr)203.P205

Crystal system.: Monoclinic

Color : yellow,brown,red
Birefringence : .049-.05l

Optic figure : biaxial positive
Pleochroism. : faint

Distictive features : color between crossed
nicols same as in ordinary light; light yel-
low color: high relief.

Hypersthene: (Mg,Fe)SiO3

Crystal system : Orthorhombic
Color : pale pink and green
Birefringence : .009-.Ol6
Optic figure : biaxial negative

Elongation : positive

Pleochroism. : faint to marked

Distinctive features : high relief; low bi-
refringence: parallel extinction; pleochroism
pink to green.

Hematite: Fe203 (opaque)

Distinctive features : irregular powdery
aggregates; indian red by reflected light.

Leucoxene: composition uncertain: alteration product
of Ilmenite. (opaque)

Distinctive features : rounded grains, often
with unaltered core of Ilmenite; dead white
color in reflected light.

Epidote: Ca2(A1,Fe)3313012(OH)

Crystal system : Monoclinic

Color : greenish to lemon yellow
Birefringence : .028-.O5l

Optic figure : biaxial negative
Pleochroism. : distinct

18

Distinctive features : color: distinct pleo-
chroism; high index.

Topaz: 2(A1,F)O.8102

Crystal system : Orthorhombic
Color : colorless
Birefringence : .008

Optic figure biaxial positive
Distinctive features : irregular fractured
grains; basal grains common; high relief;
optic character.

Stfilfl‘OlitO: ZFOO e 5A1203e 43102eH20

Crystal system : Orthorhombic
Color : yellow,gold,brown
Birefringence : .010

Optic figure : biaxial negative
Pleochroism : marked

Distinctive features : irregular, somewhat
platy grains, determined by cleavage and
subconchoidal fracture: color: pleochroism

Rutile: T102

Crystal system : Tetragonal

Color : yellow,reddish brown,red
Birefringence : .287 A

Optic figure : uniaxial positive
Elongation : positive

Pleochroism : faint

Distinctive features : grains elongate, com-
monly prismatic: high relief reulting in broad
dark borders on grains; deep color: inclusions
common.

Titmito 3 CaO eTiOzeSiOz

 

Crystal system : Monoclinic

Color : pale yellow,light brown
Birefringence : .154

Optic figure : biaxial positive
Elongation : negative

Pleochroism : weak

Distinctive features : color; high index:
extreme birefringence; euhedral grains
Achipped and marked by conchoidal fracture;
negative elongation: lack of pleochroism.

19

Chlorite: complex hydrous silicate of Mg,A1,Fe

Crystal system Monoclinic (7)

Color : dirty yellow green to green
Birefringence : .OO5-.009

Optic figure : biaxial, negative and positive
Pleochroism. : marked in thin section only

Distinctive features : grains flat, rounded,
irregular cleavage flakes; pale green color;
weak birefringence; micaceous habit.

Zoisite: 4Ca0.5A1203.6Si02.H20

Crystal system : Orthorhombic

Color : colorless,rose,green,brown
Birefringence : .006

Optic figure : biaxial positive
Pleochroism : faint

Distinctive features : colorless grains; high
index; abnormal ultra-blue interference color.

Tourmaline:complex silicate of Na,Ca,A1, Fe,Mg,
with Li, Mn ,Cr,B,and OH

Crystal system.: Hexagonal

Color : yellow brown,dark brown,black
Birefringence : .019-.052

Optic figure : uniaxial negative

Elongation : negative

Pleochroism : strong

Distinctive features : color:p1eochroism;
negative figure: grains usually irregular
fractured pieces; east-west absorption.

Biotite: complex hydrous silicate of K,Mg,Fe,A1

Crystal system : Monoclinic

Color : brown,rarely green
Birefringence : .050-.064

Optic figure : biaxial negative
Pleochroism : marked in thin section only

Distinctive features : In flakes varying from
hexagonal to irregular: grains always yield
perfectly centered pseudo-uniaxial negative
cross; deep brown color; lack of pleochroism;
inclusions with halos.

§yanite: AlZSiO5
Crystal system.: Triclinic

20

Color . : colorless, pale blue
Birefringence : .016

Optic figure : biaxial negative
Elongation : positive
Pleochroism : faint

Distinctive features : Elongate grains of
marked rectangular outline: conspicuous cross-
cleavage; low birefringence; inclined extinction

Olivine: (Mg,Fe)2SiO4

Crystal system.: Orthorhombic
Color : colorless to pale yellow
Birefringence : .057

Optic figure biaxial positive
Distinctive features : fragments irregular;
colorless with bright interference colors;
clouded by decomposition products: rare ex-
cept in recent sediments.

Augite: complex silicate of Ca,Mg,Fe,Al

Crystal system : Monoclinic
Color : pale brownish grey
Birefringence : .018-.045

Optic figure . biaxial positive

Distinctive features : grains usually elong-
ate, worn cleavage fragments; high index; high
birefringence; high extinction angle; brown
color.

Apatite: Ca5(F,Cl)(PO4)5

Crystal system : Hexagonal

Color : colorless
Birefringence : .005-.005

Optic figure : uniaxial negative
Elongation : negative

Distinctive features : grains oval or nearly
circular; low birefringence.

Metals: includes - Magnetite: Fe304, Marcasite:
FeSz, and Pyrite: FeS2 “

Distinctive features : opaque in transmitted
light: metallic luster in reflected light.

Roundness and Sphericity

Roundness and sphericity are two factors of impor-

21

tance in the petrographic study of sediments. Wadell e

 

* Wadell,H., Volume,shape, and roundness of rock parti-

cles: Journal of Geology, vol. 40, 1952. pp. 445-451.

 

v—

apparently was one of the first investigators to distin-
guish between these two characteristics. He pointed out
that roundness is a measure of the sharpness of the
corners of grains, whereas shape is the measure of the
form of the grains independent of the sharpness of the
corners. Wadell used the sphere as a standard of reference
and employed the degree of sphericity as a measure of the
approach of the form of other solids to the sphere. He
also developed a method for measuring roundness and
sphericity of quartz grains, which proves to be very time
consuming. A more rapid and accurate method for measur-
ing sphericity by means of projecting images of quartz
grains was devised by Riley.*

 

* Riley, N.A., Projection sphericity: Journal of Sedi-

mentary Petrology, vol. 11, 1941. pp. 94-97.

 

Geology students at Michigan State College combined
the ideas of Wadell and Riley. Mr. G.T. Schmitt,*

 

e Schmitt, G.T., personal communication

a graduate assistant at Michigan State College, devoted

22

considerable time and effort investigating the problem,
and is partly responsible for the development of the
method used in this paper. He drew a concentric circle
protractor similar to the one used by Wadell, but on
white paper rather than on celluloid. By means of the
camera lucida the images of the quartz grains were pro-
jected to the concentric circle protractor which was
inclined at such an angle as to prevent distortion of
the images. It was then a simple matter to measure the
diameter of the inscribed and circumscribed circles
(sphericity) and the arc of the corners of each grain
(roundness) directly. The size grade 65 was found to
be the most desireable with which to work. About fifty
grains, with an average of ten corners each, were measured
for each slide.

Roundness values were computed from Wadell's *

fl

* Wadell, H., op. cit., p. 448.

 

formula:

(réR) : P , where

r is the radius of the corners

R is the radius of the inscribed circle
N is the number of corners measured

P is the total degree of roundness

For sphericity, the formula used by Riley e

 

s Riley, N.A., 0p. cit., p. 96.

 

25

is:

e, where

d is the diameter of the inscribed circle
D is the diameter of the circumscribed circle
5 is the sphericity of the grain
The roundness and sphericity values thus obtained were
averaged for each sample, and the results are shown in

Figure 6.

Conclusions

 

In examining the results of the mechanical and
petrographic analyses of the ten samples, representing
a fifty foot vertical section through the Mason esker,
it will be noted readily that each sample differs from
the other in all of the characteristics investigated.
All samples differ in their mechanical composition, as
shown by the size grade analyses. Accordingly, the total
weight percent of heavy minerals in each sample also
varies. The wide variations obserfed in the carbonate
content are undoubtedly due to the leaching action of
ground water.

An examination of the results of the heavy mineral
counts hinges on two outstanding differences. Aside from
their relative frequency, the suite of minerals found in
each sample is distinctive. Of the twenty-two minerals
identified, only seven are common to all slides. The

remaining fifteen minerals occur irregularly throughout

24

all the slides. Further, there is a wide divergence in
relative abundance of the seven minerals which are
present in all slides.

The roundness and sphericity averages show a similar
lack of consistency throughout each five feet of sample.

Thus, in all the characteristics investigated, the
various samples appear to be quite different from.each
other. This suggests that some sort of zoning or layer-
ing exists in the esker deposit from.,! top to bottom,
and the material in the deposit is consequently hetero-
geneous in character. All evidence tends to support the
theory that eskers are stream bed deposits, built up in
subsequent layers by simultaneous deposition throughout
their length. Whether these streams were subglacial or
superglacial cannot, of course, be determined from the
data available.

Regarding the hypothesis that eskers are in reality
"drawn-out kames", there is little in the results ob-
tained in this investigation to indicate that this is
true of the Mason esker. The origin of kames necessitates
(deposition in a very short interval of time. Consequently
the material encountered in a vertical section would be
expected to be somewhat homogeneous. However, since no
records exist of petrographic studies of kamic sediments,
few conclusive comparisons may be made in this instance.

Possibly a great deal of light might be shed on the

25

problem if similar studies of other glacial deposits
were carried out.

This investigation does show that petrographic
methods of studying and comparing detrital sediments
may very well aid in determining the mode of formation
of an individual esker, although studies of other types:.
of glacial sediments would be of great value for pur-

poses of comparison.

26

 

 

 

TABLE I
Sample Numbeg Sorting Skewness Kurtosis
l 1.46 .506 .291
2 1.52 .540 .285
5 1.52 .508 .290
4 1.51 .508 .292
5. 1.66 .506 .282
-6 1.55 .505 .284
7 1.66 .517 .269
8 1.64 .505 .272
9 1.54 .508 .269
10 1.65 .505 .252

SORTING, SKEWNESS, AND KURTOSIS

computed from cumulative curves
of size grades

IIIIIIIIVIII'I'IIIIII I

 

27

TABLE II

HEAVY MINERAL FREQUENCY - SIZE 100

1152.95.31
Metals
Aggregates
Hornblende
Arf‘sonite
Garnet
Ziroon
Monazite
Hypersthene
Hematite
Leucoxene
Epidoten
Topaz
Staurolite
Rutile
Chlorite
Zoisite
Spodumene
Tourmaline
Biotite
Kyanite
Olivine
Augite

total

112......1
22.2
22.2
10.6

6.2
19.6

0.9

 

100%

%

EQLME. EQLME

7.5 % 22.2 %
25.1 19.5
15.5 15.1
15.5 9.0

15.7 15.4

1.5 1.9
6.0 5.5
5.0 5.0
5.7 5.6
6.0
2.2 5.6
0.5
1.5 0.5

100% 100%

32a.é

17.5
16.7
18.4
14.5

12.2

0.6

0.6

 

100%

%

 

NO e E giglfi

 

20.7 7; 17.6
15.1 17.6
18.2 18.7
11.7 7.2
17.0 9.7
0.9
5.6 8.5
0.9 1.1
5.8 2.5
2.8 2.5
0.9 5.1
1.9 0.5
1.7
1.1
1.7
. 4.5

 

 

100% 100%

$21,

No. 7

M

29.6%;
18.7
15.0
7.5
14.5
0.6
6.9
0.6
5.1
1.2
'2.5
0.5

0.6

100%

No.J§

14.6
25.6
22.4
11.2
9.0
0.4
4.7
4.5

0.9

100%'

No.

5.4 %

51.4
22.7
8.5

6.0

1.5
4.1
5.8
1.5
5.8

100%

10

No.

5.8
55.7
22.5
10.7

6.1

1.5

0.6

5.9

5.2

1.9

 

100%

%

 

 

 

HEAVY MINERAL FREQUENCY - SIZE 150

Mineral
Metals
Aggregates
Hornblende
Arf'sonite
Garnet
Zircon
Monazite
Hypersthene
Hematite
Leucoxene
Epidote
Topaz
Staurolite
Rutile
Titanite
Chlorite
Zoisite
Spodumene
Tourmaline
Kyanite
Olivine
Augite

total

No. 1

27.8 %

20.0
12.5

10.6

0.5

100%

28

TABLE III

—’-w

11.5

10.0

5.0
5.0

2.2

0.4

1007

H9. 5

21.4

17.4

0.6

100%

%

No. 4

m

27.4 % 15.7 %

15.5
15.9

11.0

0.5

100%

No. 5

W

15.7

25.5

5.0
1.0

4.7

1.0

1.7

0.6

100%

No. 6

m

19.9 %

14.7
19.4
9.7

11.7

7.7
2.1
5.0
4.5

2.7

100%

No. 7

W

22.1
16.5
19.8
8.1
12.4
2.5
1.9
2.2

1.1

 

No. 8

10.6 %

19.5
19.6
18.4
10.2
0.4
5.4
'9.7
2.9
2.9

5.8

0.8

.5.8

0.5
0.5
10 .

No. 9

24.4
21.5
18.8
9.1
0.9
1.8
4.2
6.5
1.4

1.8

0.6
0.5

2.1

165%

10

NOW

15.9
14.0
9.6
8.9
5.1
1.5
4.6
1.9

2.7

0.4
1.2

0.8

 

 

HEAVY MINERAL FREQUENCY - SIZE 200

1419.93.91
Metals
Aggregates
Hornblende
Arf'sonite
Garnet
Zircon
Monazite
Hypersthene
Hematite
Leucoxene
Epidote
Topaz
Staurolite
Rutile
Titanite
Chlorite
Zoisite
Spodumene
‘Biotite
Kyanite
Augite
Apatite

total

No. 1

52.1
10.0
8.2
4.7

8.6

0.4

 

100%

%

29

TABLE

521.3

28.6
15.5
4.7
8.5
15.5

11.9

IV

0)’
/0

No. 5

25.9
9.2
14.4

14.8

No. 4

24.9 %

l

(.0
C51

0

1

OJ

.7

(0 O3
0 o
(\3 N

(I)
o
(J3

01 ()3 {\3
0
O

o
N)

No. 5

14.6 %

0.5

 

100%

No. 6

25.7 %

8.7
10.6
5.9
8.7
6.2
6.2
5.0
1.0
6.2
5.0

0.5

1.5
0.5
0.5
0.7
0.5
0.5

0.5

0.5

100%

No. 7

16.2
16.4
20.1
11.0
9.6
6.0
5.5
0.7
1.4
5.5
5.0
0.2
0.5
1.0
1.4
2.5
1.5
0.5

0.2

 

No. 8

18.9%

14.7
25.4
12.6
7.6
2.9
2.0
5.5
1.7
2.0

1.4

No. 9

m

28.0 %

6.8
14.7

12.1

8.0

6.5
5.7
4.8
2.0
2.8

2.8

0.5

1.1
0.8
2.8

0.2

100%

No. 10

30.5 %

5.2
9.5
8.6
9.4
9.4
1.4
1.9
5.8
2.5

2.5

0.4

2.5

0.4

100%

“

 

50

 

 

 

 

 

 

 

 

MICHIGAN

 

 
   
 
   

  

 

 

  

AURELIUS

 

 

 

LEGEND

E ESKER

 

 

FIGURE 1
AREAL EXTENT OF
LANS'NG THE MASON ESKER
\I: INGHAM COUNTY,M|CH'GAN
1
SCALE
( .0 I 2 ‘ 3U|L£3
bid
I'LL!“ '0‘ _\_

 

\ SECTION STUOIID

  
 
  

  

 

 

 

 

 

 

5 FIGURE 2

 

48

_s (V! sun

100%

90

80

70

60

50

4O

50

20

10

52

FIGURE 5

GENERALIZED CUMULATIVE CURVE 0F WEIGHT PERCENT

showing relationships of percentiles
quartiles and median as described in
the text

.......
l

v
.. .... “-4.

.....

.....

......

 

O4| | 02 I

Diameter in Millimeters

 

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54

FIGURE 5

 

 

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