557
IL6gui
991-D
uuide to the Geology of the
Pere Marquette State Park Area,
Jersey County
David L. Reinertsen
Jan is D. Treworgy
Field Trip Guidebook 1991 D, October 26, 1991
Department of Energy and Natural Resources
ILLINOIS STATE GEOLOGICAL SURVEY
Cover photo by J. D. Treworgy
Bluff of Mississippian strata along the Great River Road at Chautauqua, Jersey County, Illinois.
Geological Science Field Trips The Educational Extension Unit ot the Illinois State
Geological Survey conducts four free tours each year to acquaint the public with the rocks,
mineral resources, and landscapes of various regions of the state and the geological processes
that have led to their origin. Each field trip is an all-day excursion through one or more Illinois
counties. Frequent stops are made to explore interesting phenomena, explain the processes
that shape our environment, discuss principles of earth science, and collect rocks and fossils.
People of all ages and interests are welcome. The trips are especially helpful to teachers
preparing earth science units. Grade school students are welcome, but each must be
accompanied by a parent or guardian. High school science classes should be supervised by at
least one adult for each ten students.
A list of earlier field trip guide leaflets for planning class tours and private outings may be
obtained by contacting the Educational Extension Unit, Illinois State Geological Survey, Natural
Resources Building, 615 East Peabody Drive, Champaign, IL 61820. Telephone: (217) 244-
2407 or 333-7372.
) primed on recycled paper
Printed by the authority of the State of Illinois/1991/500
Guide to the Geology of the
Pere Marquette State Park Area,
Jersey County
David L. Reinertsen
Janis D. Treworgy
Field Trip Guidebook 1991 D, October 26, 1991
Department of Energy and Natural Resources
ILLINOIS STATE GEOLOGICAL SURVEY
615 E. Peabody Dr., Champaign, IL 61820
Digitized by the Internet Archive
in 2012 with funding from
University of Illinois Urbana-Champaign
http://archive.org/details/guidetogeologyof1991rein
CONTENTS
PERE MARQUETTE STATE PARK AREA
Overview
Definitions
Geologic History
Precambrian basement
Rifting in the early Paleozoic Era 3
Subsidence and deposition in the Paleozoic Era 3
Mesozoic and Cenozoic Eras 3
Glacial history 7
Stratigraphy 7
STRUCTURAL FEATURES 9
GEOMORPHOLOGY 10
Physiographic Provinces 1 1
Drainage 12
Relief 12
MINERAL RESOURCES 12
Mineral Production 12
Water Supply 13
Surface water 13
Groundwater 13
GUIDE TO THE ROUTE— STOPS 1 6
1 Glacial features of area 22
2 Limestone and shale exposures 22
3 Quarry exposure of dolomite 27
4 Lunch at Visitors Center 27
5 Pere Marquette State Park 29
A Trailside Museum 29
B-D Pleistocene deposits and landforms 29
E St. Louis Limestone breccia, upper St. Louis,
and possible Ste. Genevieve strata 29
F Salem Limestone and lower St. Louis 29
G Shelter House at McAdams Peak — landforms 31
H Twin Springs, Silurian, Devonian, and Mississippian Formations 31
I Kimmswick and Maquoketa (slumped) 31
RECOMMENDED READING 32
PLEISTOCENE GLACIATIONS IN ILLINOIS
DEPOSITIONAL HISTORY OF THE PENNSYLVANIAN ROCKS
FIGURES
Rock succession column iv
1 Generalized stratigraphic column for the field trip area 2
2 Location of some major structures in the Illinois region 3
3 Structural features of Illinois 4
4 Stylized north-south cross section of the structure of the Illinois Basin 5
5 Geologic map showing distribution of rock systems at the bedrock surface 6
6 Generalized map of glacial deposits in Illinois 8
7 Physiographic divisions of Illinois 11
8 Areal distribution, type, and water-yielding character of upper bedrock formations 14
9 Chautauqua West, near mileage 23 26
10 Cross section through Twin Springs showing Cap au Gres Faulted Flexure 30
Era
Period or System
and Thickness
a
\ Holocene
Age
(years ago)
General Types of Rocks
Quaternary
0-500'
8 8.
a> <
a o
L 10.000
Recent — alluvium in river volleys
Glaciol till, glacial outwosh, grovel, sand, silt,
lake deposits of clay and silt, loess and
sand dunes ; covers nearly all ot state
except northwest corner and southern tip
Pliocene
Tertiary
0-500'
Paleocene
Pennsylvanian
0-3,000'
("Coal Measures")
Mississippian
0-3,500'
Oevonion
0-1,500'
Silurian
0-1,000'
Ordovician
500-2.000'
Cambrian
1,500-3,000'
ARCHEOZOIC and
PROTEROZOIC
1.6 m
5.3 m.
36.6 m
57.8 m.
66.4 m.
f 144 m.
286 m.
320 m.
360 m.
408 m.
438 m.
505 m.
570 m.
Chert grovel, present in northern, southern,
ond western Illinois
.'.'SS.
Mostly micaceous sand with some silt ond clay;
present only in southern Illinois
Mostly clay, little sand; present only in southern
Illinois
Mostly sand, some thin beds of clay ond, locally,
grovel; present only in southern Illinois
Largely shale and sandstone with beds of coal,
limestone, and clay
Black ond groy shale at base; middle zone of
thick limestone that grades to siltstone,
chert, and shale, upper zone of interbedded
sandstone, shale, ond limestone
Thick limestone, minor sandstones ond sholes;
largely chert ond cherty limestone in southern
Illinois; black shale at top
Principally dolomite and limestone
Largely dolomite and limestone but contains
sandstone, shale, and siltstone formations
Chiefly sandstones with some dolomite and shale,
exposed only in small areas in north-central
Illinois
Igneous ond metamorphic rocks, known in
Illinois only from deep wells
Generalized geologic column showing succession of rocks in Illinois.
PERE MARQUETTE STATE PARK AREA
Overview
This guide will acquaint you with the geology, landscape, and mineral resources in the Pere
Marquette State Park area of Jersey County, Illinois. Pere Marquette State Park is about 75
miles southwest of Springfield, some 250 miles southwest of Chicago, and approximately 30
miles northwest of St. Louis. The area is characterized by gently rolling uplands that developed
on deposits left by two periods of continental glaciation during the last 300,000 years. The
area's surface continuity is broken where these glacial deposits are eroded by the Mississippi
and Illinois Rivers and their tributaries. Stone is the only mineral resource presently produced in
Jersey County.
This field trip will be somewhat of a departure from our normal field trip procedures. After
registration in the morning, you will leave the park and drive eastward to the first three stops,
where you will have the opportunity to collect fossils and perhaps a geode. In addition, you will
cross the uplands away from the major river valleys. You will then return to the park for lunch.
In the afternoon, you will be able to walk to several stops in the park where Survey geologists
will be stationed to describe the various strata and answer your questions. The best vantage
points for a superb view of the Illinois and parts of the Mississippi River Valleys entail about a
0.4-mile walk (each way).
Definitions
Bedrock is a general term for the solid rock that underlies soil or other unconsolidated,
nonindurated, surface material. The strata underlying Illinois are divided into formations. A
formation is a consistent body of rocks that has easily recognizable top and bottom boundaries,
is readily traceable in the field, and is sufficiently widespread to be represented on a map.
Many of the sedimentary formations have conformable contacts, that is, no significant
interruptions in deposition took place between them. In some instances, even though the
composition and appearance of the rocks change significantly at the contact between two
formations, the fossils in the rocks and the relationships between the rocks at the contact
indicate that deposition was essentially continuous. At other contacts, however, the lower
formation was subjected to weathering, and partial erosion occurred before the overlying
formation was deposited. The fossils and other evidence in the formations may indicate a
significant gap in time between deposition of the lower unit and the overlying unit. This type of
contact is called an unconformity. The unconformity is called a disconformity if the beds above
and below the unconformity are essentially parallel and an angular unconformity if the lower
beds have been tilted and eroded before the overlying beds were deposited. Figure 1 shows
several major unconformities (marked by a wavy line). Each unconformity represents a long
interval of time during which a considerable thickness of rock, present in nearby regions, was
either eroded or never deposited in parts of this area. Several smaller unconformities are also
present. They represent shorter time intervals and thus smaller gaps in the depositional record.
Geologic History
Precambrian basement The geology of the Pere Marquette State Park area, like the rest of
Illinois, has undergone many changes over several billion years of geologic time (see rock
succession column, facing page). The oldest rocks beneath us on the field trip belong to the
ancient Precambrian basement complex. We know relatively little about these rocks from direct
observations because they are not exposed at the surface anywhere in Illinois. Only about 35
drill holes have reached deep enough in Illinois for geologists to collect samples from
Precambrian rocks. From these samples, however, we know that these rocks consist mostly of
granitic igneous and possibly metamorphic, crystalline rocks about 1 .5 to 1 .0 billion years old.
These ancient rocks, which underwent deep weathering and erosion when they were part of
Earth's surface until about 0.6 billion years ago, formed a landscape that must have been quite
similar to the present-day Missouri Ozarks. The long time interval separating Precambrian
CENOZOIC
System
Series
Stage
Substage
Formation
Graphic Column
Thickness
(m)
Quaternary
Pleistocene
Holocene
Cahokia
Alluvium
■ ■
0-46
Wisconsinan
Wood-
fordian
Peoria /LJ
Loess /Henry
_._._._/.-.■.•.•.
0-23
0-15
Farmdalian
Robein Silt
__
0-3
Altonian
Roxana Silt
• • ■ • • •_
0-4
Sangamonian
imntuiifi
III inoian
Loveland ,n
Silt /Pearl
Z^-lr-l-/. •".•:■.'•:•:■
0-30
Glasford
-o- P"r» 1o'°,o?\
Yarmouthian
S 5 M IV Mm » f
Kansan
Banner
, - N 0 ^ .0 - V , , 0-
0-14
Tertiary
Pliocene
Grover Gravel
•<» ' O' o ■ o O . O O
0-9
PALEOZOIC
System
Megagroup
Series
Group
Subgroup
Formation
Graphic Column
Thickness
(ml
Pennsylvanian
Desmoinesian
Kewanee
Carbondale
=j — =?=S — ci ii
20-36
Spoon
0-26
Mississippian
Mammoth
Cave
Limestone
Valmeyeran
Ste. Genevieve
Ls.
O "J O 0 1 1 0 D
0-9
| O •• 0 | 0 0 | ■ 0 0 -|- .
St. Louis Ls.
I 1 1 1 A
52-73
■^j^^j^uj^-^:
Salem Ls.
. i ii
16-24
i i i i
Warsaw Sh.
i • / — ! —
15-24
i m s J _:_ J
M „
Keokuk Ls.
— I -r I a i
18-21
A A | A A 1 A
Burlington Ls.
* 1 A |*|
43-61
1 A 1 A A |
1 A | 'a |
1 A | A | | A
Fern Glen
1 1 1
0-9
-|A--A|-A-|A-Ar|-
Meppen Ls.
/ / /
0-6
/•/•/•/
Kinderhookian
Chouteau Ls.
1*1 1
6-21
1 1 1*1
Knobs
New Albany
Sh.
Hannibal Sh.
3-21
Horton Creek
—j. 1 _r
0-8
0 !-• o J_ 0 J 0
Devonian
Upper
Louisiana l_s.
| — T^"'
ft-1
Saverton Sh.
-^T- _
0-2
Sylamore Ss. ^
0-0.1
Hunton Ls.
Middle
Cedar Valley Ls.
Hoing Ss. Mbr.
0-12
1 1 1 1
■'.-". ' •' .' " ' .' '• ,' ,''', j, ' '..'.'
Silurian
Niagaran
Joliet
0-8
/ / / /
Alexandrian
Kankakee
/ / /
0-9
/ / / /
Edgewood
/ 1 / —
3-15
/ a— a/-^Z^^-^L^ -^ <£-0
Ordovician
Cincinnatian
Maquoketa Sh.
—
30-61
— — — —
Ottawa Ls.
Champlainian
Galena
Kimmswick
1 1 1 1
21-27
1 1 1
Decorah
1 — 1 1 — 1
9
. 1 I- ' T 1 T"
Platteville
Plattin
i — i i — i
30
i — i — i
i i — I I
Ancell
Joachim Dol.
/ / /
24
/ — / —/ - /
St. Peter Ss.
1 • •
46
Knox Dol
Canadian
Prairie du
Chian
"Shakopee Dol.
34
/— / - / -/
*Only upper part exposed
Figure 1 Generalized stratigraphic column for the field trip area.
crystalline rocks from Cambrian sediments, for which we have no rock record in Illinois, is
almost as long as all of recorded geologic time from the Cambrian to the present. Although
geologists in Illinois do not see Precambrian rocks, except as cuttings from drill holes, they can
determine some of the characteristics of the basement complex through the use of various
techniques.
Rifting in the early Paleozoic Era In southernmost Illinois, near what is now the
Kentucky-Illinois Fluorspar Mining District, evidence from gravity and magnetic field
measurements, surface mapping, and seismic exploration for oil indicates that rift valleys
formed. These valleys formed during a period when plate tectonic movements (slow global
deformation) were beginning to rip apart an ancient supercontinent in Early to Middle Cambrian
time, about 570 to 525 million years ago. In the Midcontinent region, these buried rift valleys
are referred to as the Rough Creek Graben and the Reelfoot Rift (fig. 2).
Subsidence and deposition in the Paleozoic Era During late Middle Cambrian time, some
525 million years ago, the rifting stopped and the surrounding hilly Precambrian landscape
began to slowly sink (subside) on a broad, regional scale. This permitted the invasion of a
shallow sea from the south and southwest. During the several hundred millions of years of the
remainder of the Paleozoic Era, what is now the Illinois region continued to receive sediments
that were deposited in shallow seas. As subsidence continued, these seas repeatedly covered
the area until at least 15,000 feet of sedimentary strata had accumulated in southern Illinois.
Subsidence decreased in magnitude northward, away from the rift, so the strata become thinner
northward. At times during the Paleozoic Era, the seas withdrew and the deposits were
subjected to weathering and erosion. As a result, there are some gaps in the sedimentary
record in Illinois.
Mesozoic and Cenozoic Eras Following the Paleozoic Era, during the Mesozoic Era, the
Pascola Arch (fig. 2) rose in southeastern Missouri and western Tennessee. It closed off the
southern end of the Illinois embayment and thus formed the Illinois Basin, separating it from
Figure 2 Locations of some of the major
structures in the Illinois region: (1) La Salle
Anticlinal Belt, (2) Illinois Basin, (3) Ozark
Dome, (4) Pascola Arch, (5) Nashville
Dome, (6) Cincinnati Arch, (7) Reelfoot Rift,
southwest to northeast, and Rough Creek
Graben, west to east.
-*-
Fault, downthrown
side indicated
Anticline
Syncline
Monocline
40 mi
=1
50 km
Figure 3 Structural features of Illinois (Treworgy 1981).
Chicago
Rockford
Figure 4 Stylized north-south cross section shows the structure of the Illinois Basin. The thickness of the
sedimentary rocks has been greatly exaggerated to show detail, and the younger, unconsolidated surface
deposits have been eliminated. The oldest rocks are Precambrian (Pre-C) granites. They form a depres-
sion filled with layers of sedimentary rocks of various ages: Cambrian (C), Ordovician (O), Silurian (S), De-
vonian (D), Mississippian (M), Pennsylvanian (P), Cretaceous (K), and Tertiary (T). Scale is approximate.
other basins to the south. The Illinois Basin is a broad downwarp covering much of Illinois,
southern Indiana, and western Kentucky (figs. 2, 3, and 4). The development of the Pascola
Arch in conjunction with the earlier subsidence of deeper parts of the region that would become
the Illinois Basin, gave the basin its present asymmetrical, spoon shape. The geologic map in
figure 5 shows the distribution of the rock systems of the various geologic time periods as they
occur at the bedrock surface; that is, as if all glacial, windblown, and surface materials were
removed.
The Pere Marquette State Park field trip area is located on the western flanks of the Illinois
Basin. Bedrock strata here are tilted slightly to the east and south toward the deeper part of the
basin located in Hamilton and White Counties about 140 miles away. Because tilting of the
bedrock layers occurred several times during the Paleozoic Era, dips of successive strata are
not always parallel to one another.
During the Mesozoic Era and part of the Cenozoic Era, before the start of glaciation 1 to 2
millions years ago, the ancient Illinois land surface was exposed to long, intense weathering
and erosion, which carved a series of deep valley systems into the gently tilted bedrock
formations. Later, the topography was flattened and filled in by the repeated advance and
melting of the glaciers, which scoured and scraped the old erosion surface, affecting all bedrock
except the Precambrian rocks. The glaciers finally melted away, leaving nonindurated deposits
into which the Modern Soil developed.
Pleistocene and
Pliocene not shown
MM TERITIARY
------- CRETACEOUS
E3
PENNSYLVANIAN
Bond and Mattoon Formations
Includes narrow belts of
older formations along
LaSalle Anticline
PENNSYLVANIAN
Carbondale and Modesto Formations
PENNSYLVANIAN
Caseyville, Abbott, and Spoon
Formations
MISSISSIPPIAN
Includes Devonian in
Hardin County
DEVONIAN
Includes Silurian in Douglas.
Champaign, and western
Rock Island Counties
SILURIAN
Includes Ordovician and Devonian in Calhoun
Greene, and Jersey Counties
ORDOVICIAN
CAMBRIAN
^ Des Plames Disturbance — Ordovician to Pennsylvanian
^- — Fault
40 60 M
-1— H
Figure 5 Geologic map of Illinois showing lateral distribution of rock systems at the bedrock surface.
Glacial history A brief general history of glaciation in North America and a description of the
deposits commonly left by glaciers is found in Pleistocene Glaciations in Illinois, a section at the
back of this guide.
Beginning about 1.6 million years ago, during the Pleistocene Epoch, massive ice sheets called
continental glaciers, flowed slowly southward from centers of snow and ice accumulation in
Canada. The last of these glaciers melted from northeastern Illinois about 13,500 years before
the present (B.P.). Although ice sheets covered parts of Illinois several times during the Pleis-
tocene Epoch, pre-IIIinoian drift deposits are known only from the deeper parts of the largest
bedrock valleys. During the lllinoian glaciation, around 270,000 years B.P., North American
continental glaciers reached their southernmost extent, advancing as far south as the northern
part of Johnson County, about 130 miles southeast of Pere Marquette State Park (fig. 6).
Until recently, glaciologists had assumed that ice thicknesses of 1 mile or more were
reasonable for these glaciers. However, the ice may have been only about 2,000 feet thick in
the Lake Michigan Basin and perhaps only 700 feet thick across much of the land surface
(Clark et al. 1988). These conclusions are the result of studying (1) the degree of consolidation
and compaction of rock and soil materials that must have been under the ice, (2) comparisons
between the inferred geometry and configuration of the ancient ice masses and those of
present-day glaciers and ice caps, (3) comparisons between the mechanics of ice-flow
observed in modern-day glaciers and ice caps and those inferred from detailed studies of the
ancient glacial deposits, and (4) the amount of rebound of the Lake Michigan Basin, which had
been depressed by the tremendous weight of the ice.
Although lllinoian glaciers probably formed morainic ridges similar to those of the later
Wisconsinan glaciers, lllinoian moraines are not nearly so prominent or apparently so
numerous. In addition, lllinoian moraines have been exposed to weathering and erosion for
thousands of years longer than their younger Wisconsinan counterparts. Scattered high hills in
this part of Illinois have been attributed to morainal remnants.
As mentioned previously, erosion had carved an extensive network of bedrock valleys deeply
into the irregular bedrock surface by the time glaciation began about 1.6 million years ago. As
glaciation began, however, the streams began to fill up with sediments because the flow or
volume of water was insufficient to carry increasing loads of materials. During times of
deglaciation, vast quantities of meltwater and sediments were released from the waning ice
front. No evidence, however, indicates that any pre-IIIinoian fills in the preglacial valleys were
ever completely flushed out of their channels by succeeding deglaciation meltwater torrents.
The topography of the bedrock surface through much of Illinois is largely hidden from view by
glacial deposits except along the major streams and in areas mantled by thin drift near the
glacial margins. This field trip is in an area where glacial drift is generally less than 25 feet thick
and does not completely mask the underlying bedrock surface configuration. Because of
erosion and the irregular bedrock surface, glacial drift is unevenly distributed across Jersey
County; it generally increases to the north and northwest along Otter Creek.
A cover of Woodfordian windblown silt, or loess (pronounced "luss"), covers the bedrock and
glacial drift in Jersey and neighboring counties. These fine-grained dust deposits are mainly of
Wisconsinan age and are more than 25 feet thick near the park, but they thin to less than 8
feet in eastern Jersey County. The fertile soils in the field trip area have developed in the loess
and the alluvial fill of the stream valleys.
Stratigraphy
The geologic column in figure 1 shows the succession of sedimentary rock strata, about 3,400
to 4,000 feet thick, that a drill bit might encounter in the field trip area. Here, these bedrock
strata range in age from about 490 million years old, the Ordovician Period, to about 300 million
I STEPHENSON H5iS|^0 '.^ BOONE i'jIliM^1 Y| L«KE ^
EXPLANATION
HOLOCENE AND WISCONSINANv
Alluvium, sand dunes,
and gravel terraces
WISCONSINAN
^p^3 Lake deposits
WOODFORDIAN
si Moraine
^x— /" Front of morainic system
Groundmoraine
ALTONIAN
Till plain
ILLINOIAN
ILLINOIAN
Till plain
DRIFTLESS
Moraine and ridged drift
Groundmoraine
Figure 6 Generalized map of glacial deposits in Illinois (modified from Willman and Frye 1970).
years old, the Pennsylvanian Period. The oldest rocks that you might see at the surface on this
field trip are Ordovician in age. Younger strata of Silurian, Devonian, Mississippian, and
Pennsylvanian ages (fig. 1) underlie all or parts of Jersey County and also occur at the surface
in places.
Pennsylvanian bedrock strata occur only in the northeastern part of the field trip area. These
rocks consist of sandstone, siltstone, shale, limestone, coal, and underclay that were deposited
as sediments in shallow seas and swamps about 330 to 300 million years ago. They are not
exposed at the surface. However, in the eastern part of Jersey County about 10 miles east of
Stop 1 , Pennsylvanian strata are nearly 200 feet thick. A description of these rocks and their
occurrence may be found in Depositional History of the Pennsylvanian Rocks (at the back of
the guidebook).
STRUCTURAL FEATURES
Pere Marquette State Park is located in the central Mississippi Valley area where strata dip
gently away from the Ozark Dome in southern Missouri to the east and northeast into the
Illinois Basin (figs. 2 and 3). The Ozark Dome was a low-lying landmass during late Cambrian
time and subsequently subsided and re-emerged at various times during the Paleozoic Era. It
has remained a prominent landform from Pennsylvanian time.
To the north of the Ozark Dome, two other major positive structures, the Lincoln Anticline and
the Mississippi River Arch, separate the Forest City Basin in northwestern Missouri and south-
western Iowa from the Illinois Basin on the east. The Mississippi River Arch is very broad and
flat; it trends northward and extends generally along the Mississippi River between Illinois and
Iowa. The Lincoln Anticline generally trends northwestward, roughly parallel to the Mississippi
River in northeastern Missouri from the Missouri-Iowa boundary to Madison County, Illinois.
The southeastern end of the Lincoln Anticline curves sharply eastward into Calhoun County,
Illinois, just to the west of the park; it has several smaller structures superimposed upon its
gently sloped northern flank. The southern flank of the fold in Illinois forms the steeply inclined,
faulted monocline known as the Cap au Gres Faulted Flexure (fig. 3).
The Cap au Gres Faulted Flexure derived its name from Cap au Gres bluff (French for
sandstone headland) in western Calhoun County. It is a narrow zone of strata that dips up to
90° southward and is penetrated by discontinuous, vertical faults. According to Rubey (1952),
the zone containing dips greater than 5° is about 1,000 to 1,475 feet wide. Strata ranging in
age from Ordovician to Mississippian are exposed at the surface within this narrow, deformed
zone. The structure extends east-southeastward for about 60 miles through Lincoln County in
Missouri, and southern Calhoun, Jersey, and northwestern Madison Counties in Illinois. It dies
out between Grafton and Alton beneath the broad alluvium-filled valley of the Mississippi River.
This flexure was recognized before 1870 and was originally thought to be a fault with a vertical
displacement of 650 to 800 feet or more. Some later workers thought that most of the structure
was a monocline. On the basis of his extensive field work in the area, Rubey ascribed the
greater part of the structural relief to folding and indicated that faults are less important than
previously thought. The extent and continuity of recognized faults are difficult to determine
because of limited exposures and the scarcity of subsurface data. From calculations on the dips
of strata, the distance between outcrops, and the thickness of a missing stratigraphic interval,
Rubey determined whether the presence of a fault was necessary to explain apparent
anomalies or whether folding would sufficiently explain the anomalies. He felt that faults account
for no more than one-third of the total structural relief at any locality. However, where faults do
occur, displacements of 5 to 450 feet have been observed. Although several theories have
been proposed to explain the nature and origin of the structure, Rubey concluded that the Cap
au Gres Faulted Flexure was caused by horizontal compressive forces acting within Earth's
crust. The best exposures of the Cap au Gres Faulted Flexure are in a series of outcrops in
Pere Marquette State Park along State Route (SR) 100; they will be discussed at Stop 5.
9
The Cap au Gres Faulted Flexure has undergone recurrent deformation throughout the
Paleozoic Era and in later times. Major movement along the Cap au Gres structure occurred in
middle or late Mississippian to early Pennsylvanian time. This movement is evidenced by an
angular unconformity where the Pennsylvanian Spoon Formation (Desmoinesian Series)
overlies steeply folded Mississippian St. Louis Limestone (Valmeyeran Series) and older strata
(Rubey 1952). If younger Mississippian strata (the Ste. Genevieve Limestone and Chesterian-
aged rocks) had been deposited across the area and been involved in the deformation, they
were removed by erosion before the Pennsylvanian strata were deposited. This movement of
the Cap au Gres Faulted Flexure is contemporaneous with other major tectonic events in the
Eastern Interior Region and coincides with the Alleghenian and Ouachita orogenies along the
eastern edge of the North American continent.
Later movements along the faulted flexure tilted Pennsylvanian strata. This left nearly 150 feet
of the Pennsylvanian Spoon and Carbondale Formations preserved on the south side of the
flexure and only patchy remnants of the two formations on the structurally high north side
(Rubey 1952). Still more recent movement along the Cap au Gres Faulted Flexure occurred in
the late Tertiary, coincident with or immediately following deposition of the Pliocene Grover
Gravel onto the flat, post-Pennsylvanian erosional surface (Willman et al. 1975). The gravel is
preserved on both the south and north sides of the flexure and has been displaced about 150
feet (Rubey 1952). This late Tertiary movement is reflected in the upland topography to the
west in Calhoun County.
There is no evidence for movement along the flexure since the Tertiary. Saint Louis University,
which has seismograph records from the downtown area since 1909, established a seismic
network in 1962. On the basis of these monitoring capabilities, university seismologists have
determined that the Cap au Gres Faulted Flexure is an area of "infrequent earthquakes" (R.
Heinrich, personal communication, 1979).
GEOMORPHOLOGY
Several interesting geomorphological features in the field trip area are attributable to the Cap
au Gres Faulted Flexure.
(1) The most dramatic feature is the abrupt change in direction of the courses of the Mississippi
and Illinois Rivers. The two rivers flow generally south-southeast, forming the west and east
boundaries of Calhoun County. Shortly after they cross the area of the flexure, they loop back
counterclockwise and flow east-southeast as one river, the Mississippi. Here, they are parallel
to and superimposed upon the Cap au Gres Faulted Flexure. About 5 miles (8 km) beyond
Alton at Wood River, the Mississippi again curves southward. Because water follows the path of
least resistance, it is reasonable to postulate that the courses of the Illinois and Mississippi
Rivers followed the relatively weak zone of deformation along the Cap au Gres Faulted Flexure.
(2) The reflection of the Cap au Gres Faulted Flexure in the upland topography in Calhoun
County has already been mentioned. You will be able to observe it from the shelter house at
McAdams Peak, Pere Marquette State Park, at Stop 5G.
(3) A third feature is the cuspate nature of the bluffs on the north side of the Mississippi River
about 2.5 to 6 miles east of Grafton, between Chautauqua and Lockhaven, where the
Mississippian Burlington and Keokuk Limestones occur. The steep bluffs have been eroded in
such a way that turret-like segments remain as protrusions, or cusps, whereas adjacent areas
have been weathered back in a crescent shape. The areas that have receded are concave
outward and have occasional zones that have been carved back so deeply that they form
shallow caves. Travertine deposits have been found at one locality in the bluffs near Elsah.
These features may have developed as subsurface solution cavities or caverns that were
formed by groundwater moving through the jointed zone of the Cap au Gres Faulted Flexure
before the Mississippi River eroded its valley and exposed them.
10
WISCONSIN , T|LL PLAINS \
.DRtFTLESS/ SECT|0N
vSECTION<
GREAT LAKE
SECTION
Chicago
I Lake
. Plain
LINCOLN"^, -p
HILLS W y^
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7> ^ \\ Oy
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^ -o iiS- Mt. Vernon Hill Country
HILLS SECTION LOW
PLATEAUS
COASTAL^ PROVINCE
PLAIN PROVINCE
Figure 7 Physiographic divisions of Illinois (Leighton et al. 1948).
Physiographic Provinces
A physiographic province is a region in which the relief and landforms differ markedly from
those in adjacent regions. The Pere Marquette field trip area is situated on the southwestern
boundary of the Till Plains Section of the Central Lowlands Province with the Lincoln Hills and
Salem Plateau Sections of the Ozark Plateaus Province (fig. 7). The present gross features of
the Till Plains Section and the Ozark Plateaus are determined largely by their preglacial
topography.
11
The Till Plains Section has seven divisions in Illinois and we encounter one of them on this field
trip — the Springfield Plain. The Springfield Plain on the east and northeast part of the field trip
area includes the outer portion of the level area of the lllinoian glacial drift. Although the plain
generally is flat in this part of the state, in some areas its surface is gently undulating with
modern shallowly entrenched drainage. Even though glacial deposits are somewhat thinner
than in the area covered by younger glaciers, the surface topography is essentially the result of
glacial deposition and subsequent erosion by streams.
The western edge of the field trip area is beyond the lllinoian drift border on the discontinuous
older Ozark Plateaus upland, which represents the eastern edge of an extensive upland in
southern Missouri and northern Arkansas. It includes the driftless and thinly drift-veneered
cuestas (pronounced "kwestas"— asymmetric ridges with a steep slope on one side and a
gentle slope on the other) on pre-Pennsylvanian rocks that are structurally and topographically
a part of the Ozark Dome.
The Lincoln Hills Section includes the partially drift-covered dissected plateau above the
junction of the Mississippi and Illinois Rivers. The principal physiographic feature in Illinois is a
maturely dissected central ridge, which forms the watershed between the two major rivers
throughout the length of the section. As noted previously, the eastern boundary follows the
lllinoian drift border. The southern boundary with the Salem Plateau is drawn along the Cap au
Gres flexure in southern Calhoun County. In Illinois, the upland central ridge is largely underlain
by Mississippian Valmeyeran limestones, of which the Burlington Limestone is most important
physiographically; its boundaries coincide quite closely with the Mississippian-Pennsylvanian
contact. The southern part is known as the Calhoun County Driftless Area, except for loess
deposits and a single high-channel filling of pre-lllinoian outwash gravel. Patchy remnants of
pre-lllinoian drift are found in the northern part of the section. The plateau surface is rugged
and broken by closely spaced valleys and ridges. Remnants of flat to gently rolling upland
representing the Calhoun Peneplain are present along the ridge crest. The Mississippi and
Illinois valleys are broad, deeply alluviated, terraced, and have precipitous walls. Most of the
minor valleys are narrow, V-shaped, and have steep gradients.
Drainage
The field trip area is drained on the west and south by the Illinois and Mississippi Rivers and
their tributaries. Only the lower portion of some of the largest tributaries have been somewhat
widened by alluvial deposits. Most of the small tributaries, as noted previously, have narrow, V-
shaped valleys with steep gradients.
Relief
The highest land surface on the field trip route is at Tucker Knob along the ridge road in Pere
Marquette State Park east of the Visitors Center, where the crest of a loess hill (and Indian
Mound?) is 892 feet mean sea level (msl) in elevation. The lowest elevation is approximately
419 feet msl in the pool above the Melvin Price Locks and Dam No. 26 across the Mississippi
River at Alton. The surface relief of the field trip route, calculated as the difference between the
highest and lowest elevations, is thus about 473 feet. Local relief near the bluffs can be as
much as 400 feet within less than 1 ,000 feet horizontally and range from about 200 to 300 feet
at the bluffs near Alton.
MINERAL RESOURCES
Mineral Production
Among the 102 counties of Illinois, Jersey County ranked 95th in 1989 for the total value of
minerals extracted, with stone being the commodity extracted. However, the total production of
stone is grouped with 14 other counties in District 4, where 28 companies have 33 operations.
The total production of stone for this district was 11,953,000 tons valued at $43,851,000
(Samson and Bhagwat, in preparation).
12
Ninety-eight counties in Illinois reported mineral production during 1989, the most recent year
for which complete records are now being published. The total value of all minerals extracted,
processed, and manufactured in Illinois during 1989 was $2,842,900,000, an increase of some
$35.3 million (1.2 percent) from 1988.
During 1989, the value of minerals extracted in Illinois was $2,550,900,000, an increase of 2.4
percent from 1988. Mineral fuels (coal, crude oil, and natural gas) made up 81.5 percent of the
total. Illinois ranked 17th among the 50 states in total production of nonfuel minerals, but
continued to lead all other states in production of fluorspar, industrial sand, and tripoli.
Water Supply
Surface water The Illinois and Mississippi Rivers are the principal sources of surface water in
Jersey County. Despite the vast quantities of water available from these rivers, there has been
relatively little withdrawn for use by cities, farms, and industries in western Illinois. Most of the
direct and indirect use of water by people in the area comes from the large reservoir of water
stored in the ground.
Groundwater Most of us generally do not think of groundwater as a mineral resource in
assessing the natural resource potential of an area. Yet, the availability of groundwater is
essential for orderly economic and community development. More than 48 percent of the state's
1 1 million citizens depend on groundwater for their water supply.
The source of groundwater in Illinois is precipitation that infiltrates the soil and percolates
downward into the groundwater system, which lies below the water table in the zone of
saturation. Groundwater is stored in and transmitted through saturated earth materials called
aquifers. An aquifer is a body of saturated earth materials of variable thickness that will yield
sufficient water to serve as a water supply for some use. The pores and other empty spaces in
the earth materials must be permeable, that is, they must be large enough and interconnected
so that water can overcome confining friction and move readily toward a point of discharge,
such as a well, spring, or seep. Generally, the water-yielding capacity of an aquifer can be
evaluated by constructing wells into it. The wells are then pumped to determine the quantity
and quality of groundwater available for use.
Because geologic conditions differ from place to place, groundwater is readily available in some
areas and extremely difficult to obtain in others. The variability of groundwater conditions in this
area is shown in figure 8. Bergstrom and Zeizel (1957) reported that water-yielding sand and
gravel deposits suitable for drilled wells are found mainly in the Illinois River valley and locally
in Otter and Macoupin Creeks. Sand is commonly encountered below 30 feet in the Illinois
Valley, and coarse sand usually below 50 feet.
Many farm wells in the eastern half of Jersey County obtain small supplies of groundwater from
fractures in Pennsylvanian shales within a depth of 180 feet (fig. 8). In wells drilled into
underlying Mississippian limestones, the Pennsylvanian rocks are commonly cased off to
prevent caving of the shales.
The Keokuk-Burlington Limestone is the source of private groundwater supplies in much of the
county, with wells ranging in depth from less than 50 feet in some of the hollows east of the
confluence of the Illinois and Mississippi Rivers to more than 350 feet on the upland east of
Jerseyville. At shallower depths in the eastern two-thirds of the county, the St. Louis-Salem
Limestone is sufficiently thick and creviced locally to yield water for farm wells.
Devonian-Silurian rocks, which are extensively exposed along the Illinois River bluffs above the
confluence with the Mississippi in the southwestern part of the county, locally yield water. The
Kimmswick-Joachim rocks, which occur about 150 feet below the base of the Silurian rocks in
the same area, commonly contain water unsuitable for domestic use.
13
Pennsylvonion
I 1 Moinly shale with fhin sand-
I I stone, limestone, and cool
beds Small groundwater sup-
plies obtained trom sandstone,
limestone, coal, or froctured shale
Pre-Pennsylvanian rocks, patterns shoded where
overloin by Pennsylvonion formations.
Mississippion
St Louis limestone -Worsaw shole. Limestone, water-
yielding where creviced. Shale not woter-yielding.
^
Keokuk -Burlington limestone. Creviced and woter-
yielding al most locations
Kinderhook shole Generally not water-yielding.
Devonion and Silunon
\X Limestone and dolomite Water-
yielding where creviced
Ordovician
Moquoketa shale, Kimmswick -Joachim dolomite, and
St. Peter sandstone. Groundwater conditions variable
L
—
Cap Au Gres
Faulted Flexure
V
20 Miles
Figure 8 Areal distribution, type, and water-yielding character of upper bedrock formations (modified from
Willman et al. 1967).
Groundwater from bedrock frequently is considerably more mineralized (salty) and is not
considered as important a source as is the supply from unconsolidated deposits. Although it is
not generally used, some of the moderately mineralized water from bedrock aquifers can be
given to livestock when more desirable quality water is in short supply.
Information on the distribution of earth materials and the contained groundwater is constantly
upgraded as new data are collected and compiled from drillers logs, test borings, and
geophysical studies conducted by the Illinois State Geological Survey.
14
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15
GUIDE TO THE ROUTE
Assemble in the parking lot of the Visitors Center, the first entrance north of the main entrance
to the lodge on SR 100, Pere Marquette State Park (NE NW SW SE Sec. 9, T6N, R13W, 3rd
P.M., Jersey County, Brussels 7.5-Minute Quadrangle [38090H5]*).
You must travel in the caravan. Please drive with your headlights on while in the caravan.
Drive safely but stay close to the car in front of you. Please obey all traffic signs unless the
road crossing is protected by an emergency vehicle with flashing lights and flags. When we
stop, park close to the car in front and turn off your lights.
Some stops on the field trip are on private property. The owners have graciously given us
permission to visit their lands on the day of the field trip only. Please conduct yourselves as
guests and obey all instructions from the trip leaders. So that we may be welcome to return on
future field trips, please do not litter or climb on fences. Leave all gates as you found them.
These simple rules of courtesy also apply to public property. If you plan to use this booklet for a
field trip with your students, youth group, or family, because of trespass laws and liability
constraints, you must get permission from property owners or their agents before entering
private property.
Miles Miles
to next from
point start
0.0 0.0 STOP: 1-way at exit from Visitors Center parking lot and SR 100. CAU-
TION: fast traffic. The highway curve limits your visibility from both
directions. TURN LEFT (southeast).
NOTE: you will pass some very interesting bedrock exposures between
the park and Stop 1 . Because of highway widening, most parking along
the roadway has become almost nonexistent. So we will be unable to
stop at these exposures as a group. Later, you may wish to retrace part
of the route, find parking for your own vehicle, and hike to the exposures
for a closer look at the rocks.
0.05+ 0.05+ To the left is the entrance to Pere Marquette State Park and the Lodge.
0.05 0.1+ To the left, the Lodge sits on the Pleistocene Brussels Terrace at an
elevation of about 470 feet mean sea level (msl). SR 100 crosses the
lower, younger Deer Plain Terrace at an elevation of about 435 feet msl.
0.45+ 0.6 Entrance to Pere Marquette State Park Campground and Ranger's Office
lies to the left. CONTINUE AHEAD (east).
0.2+ 0.8+ The house about 450 feet to the left (north) of SR 100 is on the Brussels
Terrace.
0.6+ 1 .45 Flat-lying Pennsylvanian Carbondale Formation shale and siltstone are
exposed in the roadcut on the left. We are on the south side of the Cap
au Gres Faulted Flexure here.
* The number in brackets [38090H5] after the topographic map name Is the code assigned to that map as part
of the National Mapping Program. The state is divided Into 1° blocks of latitude and longitude. The first two
numbers refer to the latitude of the southeast corner of the block; the next three numbers designate the
longitude. The blocks are divided into sixty-four 7.5-minute quadrangles; the letter refers to the east-west row
from the bottom, and the last digit refers to the north-south column from the right.
16
0.2 1 .65 The Brussels Terrace (elevation +460 feet msl) is well developed along
SR 100 for about the next mile.
0.15 1.8 The old barn and the house ahead on the left are constructed of Silurian
dolomite quarried in this area. Because the stone contains a small
amount of iron carbonate, it weathers to a soft tan.
0.5 2.3 Cross Deer Lick Hollow. The rock strata rise nearly 900 feet strati-
graphically in the next 0.75 mile from our position on the flank of the Cap
au Gres structure. Rubey (1952) reports that a group of small transverse
faults has broken directly across the Cap au Gres structure. Rocks on
the west side of the valley are offset so that they crop out about 200 feet
farther north and somewhat higher than those on the east side. The large
strike fault that cuts the flexure is offset about 300 feet horizontally, and
the rocks immediately south of it and west of the transverse fault group
are overturned so that they dip about 60°NNE.
0.05+ 2.35+ To the left is the oolitic Mississippian Ste. Genevieve Limestone that is
dipping southward at 40° to 45°. We are now slightly south of the crest of
the Cap au Gres Faulted Flexure. The strike (direction a bed takes as it
intersects the horizontal) of Mississippian strata, which crop out along the
left side of SR 100 for the next 0.7 mile, ranges from N70°W to N85°W
with dips ranging from 22°S to 75°S.
0.25+ 2.65 To the left, the cut for the bike path some 40 feet above SR 100 has
exposed Mississippian Burlington Limestone. These are the easternmost
exposures of the steeply dipping beds of the Cap au Gres Faulted
Flexure. Strata strike N78°W and dip 68°S. According to Collinson
(1957), the Burlington is about 100 feet lower topographically than the
base of the flat-lying Silurian about 500 farther north, but it is 300 feet
higher stratigraphically.
0.1 2.75 CAUTION: you are entering the congested area of the Brussels Ferry.
0.2 2.95 CAUTION: entrance to the free Brussels Ferry to Calhoun County lies to
the right. CONTINUE AHEAD (east).
0.45+ 3.4+ The entrance to the former River Science Center, operated by the Illinois
State Natural History Survey, is to the right.
0.15+ 3.6+ T-road from the left is from Graham Hollow. The ridge road in Pere
Marquette State Park ends a short distance to the north.
0.25 3.85+ To the left, the road swings around a large slump block of Silurian
dolomite several hundred feet long and 60 to 80 feet thick. The block has
pulled away from the joint-faced cliff behind it (lubricated by the underly-
ing Maquoketa shale) and rotated so that it dips back 40°N to 55°N.
Silurian Edgewood Dolomite is exposed in the slump block beneath the
fence, Kankakee Dolomite in the lower third above the fence, Joliet
Formation in the upper two-thirds, and 1 or 2 feet of Devonian Cedar
Valley Limestone at the top.
0.3 4.15+ The Maquoketa shale underlies the slope in front of the Silurian bluffs
800 feet to the left (north). The crest of the Lincoln Anticline plunges to
the east.
17
0.25 4.4+ The large stone cross to the left commemorates the first recorded
entrance of white men, Louis Joliet and Father Jacques Marquette, into
present-day Illinois. They had explored the Mississippi from Wisconsin
southward looking for a passage to the Pacific Ocean. They turned back
at the Arkansas River. On their return upstream in September of 1 673,
they camped near here after having entered the Illinois River Valley.
Father Marquette noted these facts in his journal of the trip.
0.15 4.6+ To the left is the entrance to the Illinois Youth Center Corrections Divi-
sion, Grafton facility.
0.1+ 4.75 Silurian dolomite occurs in the lower cliff to the left (north). The upper cliff
is mainly Mississippian Chouteau Limestone with the Meppen Limestone
in the reentrant near the top and nearly 30 feet of Burlington Limestone
at the top.
0.05 4.8 CAUTION: enter Grafton, known by local Indian tribes as "the gathering
of the waters." In Grafton, you will notice that many of the buildings and
chimneys are constructed of the Silurian dolomite, which weathers tan.
0.4+ 5.2+ The Mississippian rocks exposed at mileage 4.75 are exposed again in
the cliff about 250 feet to the left, but the Burlington Limestone appears
to be fairly thin.
0.1 5.3+ The mouth of Mason Hollow lies to the left.
0.15+ 5.5+ The lower cliff, nearly 400 feet to the left behind the stone church, is
Silurian dolomite separated from the upper cliff of Chouteau Limestone
by a slope developed on the lower Mississippian Hannibal Shale.
0.3 5.8 The 30 foot high cliff of Silurian dolomite, with the Kankakee Dolomite at
road level, dips very slightly to the south because this exposure is about
300 feet south of the crest of the Lincoln Anticline.
0.05+ 5.9 The Grafton Grade School is to the left.
0.1+ 6.0+ The house on the left has a garden wall and rock garden made of
geodes from the Mississippian Warsaw Shale.
0.1 6.1+ STOP: 4-way at SR 3 Junction. TURN LEFT (north) on SR 3.
0.1+ 6.25+ The road curves right (northeast) and begins its ascent of Jerseyville
Hollow, one of the longest and finest geologic sections in this part of the
state. Exposures are essentially continuous so that a complete section
from lower Silurian Edgewood dolomite up through Mississippian middle
Burlington Limestone can be studied. Some of the Silurian section is
repeated in the lower part of the hollow because of faulting. The following
section is exposed (from the top downward):
Mississippian System feet
Valmeyeran Series
Burlington Limestone 45
Fern Glen Limestone 20
Meppen Limestone 7
18
1.6+
12.65
0.05
12.7+
0.05+
12.8+
1.3+
14.1 +
0.9
15.0+
0.1
15.1 +
0.3
15.4+
Kinderhookian Series
Chouteau Limestone 50
Hannibal Shale 25
"Glen Park" Formation 1
Devonian System
Upper Devonian Series
Sylamore Sandstone 1/3
Middle Devonian Series
Cedar Valley Limestone 5
Silurian System
Niagaran Series
Joliet Dolomite 57
Alexandrian Series
Kankakee Dolomite 28
Edgewood Dolomite 20
Ordovician System
Cincinnatian Series
Maquoketa Formation (from shallow dug well)
Total 258 1/3
0.3+ 6.55+ Small abandoned roadside quarry in Silurian Edgewood Dolomite lies on
the right.
0.75+ 7.3+ Small cave in Hannibal Shale beneath 30 feet of exposed Chouteau
Limestone can be observed across the stream to the right.
0.1+ 7.45 Chouteau Limestone is well exposed in the roadcut on the right.
0.2 7.65 Cherty Burlington Limestone (tan) overlies Chouteau (gray). Burlington
occurs on both sides of the road for the next 0.2 mile.
0.95 8.6 Curve right (east): Otterville T-road intersects to the left on the curve.
CONTINUE AHEAD.
2.4+ 1 1 .0 Elsah T-road intersects from the right. CONTINUE AHEAD (east). Note
the gently rolling upland here. Bedrock is mantled with a thin veneer of
lllinoian glacial drift beneath Wisconsinan loess.
Salem Limestone is exposed in both sides of the roadcut.
Cross Mill Creek. Warsaw Shale is exposed near the creek bottom.
Crossroad, called Newbern to the left and Cemetery Road to the right.
CONTINUE AHEAD (east).
STOP: 1-way at T-junction with SR 109. TURN LEFT (north) on SR 109.
Prepare to turn left. Note the large hills ahead to the right and left.
TURN LEFT (west) at Dow crossroad (600N/1600E).
Begin ascent of glacial hill.
19
__ S a „ iSMffi* I
21
0.45 15.85+ Telephone transmission tower stands to the right near the crest of the
hill. To the left is the large water tank of the Jersey County Rural Water
Company.
0.15 16.05 PARK along the roadway. Please do not block the road as visibility is
somewhat restricted from the east.
STOP 1 We'll discuss the glacial features of the field trip area (S edge of SE SW SW SW
Sec. 28, T7N, R11W, 3rd P.M., Jersey County, Jerseyville South 7.5-Minute Quadrangle
[39090 A3]).
This hill, nearly 100 feet above the surrounding area, provides an excellent view of the country-
side and the opportunity to see similar hills to the north. All may be part of an old lllinoian end
moraine. The combined thickness of drift and loess in this hill is nearly 100 feet. Near the river
bluffs to the south and southwest, till has not been identified; but as noted earlier, the loess is
thick. The lllinoian glacial margin appears to have been about 8 or 9 miles to the west and
perhaps 6 miles to the south.
The hill and the immediate vicinity are underlain by the Pennsylvanian Colchester Coal
Member. Pennsylvanian strata extend north and east from here. These rocks were eroded
away between here and where the strata are exposed along SR 100 near the state park. The
erosion probably occurred long before glaciers advanced across the area. Overlying coals have
been mined north and east of this location in the past.
0.0 16.05 Leave Stop 1 and CONTINUE AHEAD (west).
0.35 16.4 TURN LEFT (south) at the crossroad (600N/1470E) west of the church.
This is the east side of the community of Dow.
0.5 16.9 STOP: 4-way at Joe Knight Road (550N/1470E) in Newburn. TURN
RIGHT (west).
0.05+ 16.95+ TURN LEFT (south) at T-intersection (550N/1465E).
0.45+ 17.45 PARK along the road before reaching SR 3. Please do NOT block the
driveway. CAUTION: walk south to SR 3 and then to the right (west)
along the shoulder of the road to Mill Creek.
STOP 2 We'll examine and discuss the Mississippian Salem Limestone and Warsaw Shale in
the roadcut and creek bank (SE SW SW SE Sec. 32, T7N, R1 1 W; and NE NE NE NW Sec. 4,
T6N, R11W, 3rd P.M., Jersey County, Elsah 7.5-Minute Quadrangle [38090H3]).
The Mississippian Salem Limestone exposed on both sides of the SR 3 roadcut on the west
side of Mill Creek is the same stone quarried in western Indiana and used for building
construction throughout the Midwest. The stone here is quite pure and 15 to 18 feet thick. This
is probably the best Salem exposure in the Grafton area. Locally, cavities are filled with calcite.
Below the Salem, the Warsaw shale is exposed down to stream level. In western Illinois, this
formation locally contains abundant geodes. Here the Warsaw contains geodes filled with a
variety of minerals. Minerals reported from this locality include quartz, chalcedony, calcite,
chalcopyrite, malachite, kaolinite, dolomite, and ankerite. Not enough specimens are available,
though, for you to collect representatives of each mineral. The origin of these geodes is
uncertain, but at least some geodes formed by mineral deposition in cavities left by fossils.
22
0.0
17.45
0.05-
17.45+
0.7
18.15+
0.3
18.45+
0.5+
19.0+
0.35+
19.4+
0.25
19.65+
0.2
19.85+
0.8
20.7+
Leave Stop 2 and CONTINUE AHEAD (south).
STOP: 2-way at SR 3 (500N/1465E). CAUTION: FAST TRAFFIC.
CONTINUE AHEAD (south) on Cemetery Road.
Shallow sinkhole occurs to the right.
T-road intersects from right. CONTINUE AHEAD (south).
Curve right (southwest) and descend hill.
Cross Mill Creek.
Cross small stream.
Cross the same small stream.
STOP: 1-way at T-intersection with Elsah Road. TURN LEFT (south) and
enter village of Elsah. This historic town began as a river town in the
1850s. Its 19th century charm has been well preserved. This is the first
entire community to be listed on the National Register of Historic Places.
0.25+ 20.95+ CAUTION: narrow bridge.
0.2+ 21.2 Access road to the left leads to Principia College, a Christian Science
liberal arts school with a beautiful campus overlooking the Missisippi
River.
0.2+ 21.4+ Bear right (southwest).
0.05+ 21 .45+ STOP: 1-way at intersection with SR 100, the McAdams Highway. TURN
RIGHT (northwest). For 3 miles east and west of Elsah, the bluffs are
predominatly Burlington Limestone. As discussed in the introduction,
unusual erosion of the bluffs has produced projecting buttes or cusps
and alternating hollows. Excellent exposures of Mississippian strata occur
in the 1 .5 miles of river bluff that separate Elsah and Chautauqua.
1 .45+ 22.95+ Entrance to the right leads to Chautauqua, a private community.
0.25 23.2 Chautauqua West geologic section (fig. 9). This location is special
because a distinct angular unconformity occurs between the Kinder-
hookian Chouteau Limestone and overlying Valmeyeran Meppen Lime-
stone. The Meppen attains its maximum thickness (20 feet) in Illinois
here.
0.75 23.95 Rock slide area: the lower slope developed on the Hannibal Shale. The
shale formed the slide plane down which a large segment of the over-
lying bluff slid after heavy rains in the spring of 1975. The bluff above the
shale includes the Chouteau, Meppen, Fern Glen, and Burlington Forma-
tions. Large slabs of the Chouteau, which were involved in the collapse,
are quite fossiliferous.
0.75+ 24.7+ Abandoned quarry in Silurian dolomite on the right.
23
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Burlington Limestone, 22 m (exposed)
Limestone, gray to very light gray, coarsely crystalline,
crinoidal; some beds of fine-grained, brownish-gray, dolo-
mitic limestone; beds and nodular masses of light gray to
white chert common; 1 m zone of brecciated chert; lower
portion argillaceous and gradational with Fern Glen.
m)
4
Brecciated chert zone
Fern Glen Formation, 5 m
Shale, very calcareous, green to buff, fossiliferous; lime-
stone, buff, coarsely crinoidal; much greenish gray chert;
fossils abundant, include brachiopods, corals, and crinoids;
grades vertically into overlying Burlington Limestone.
Meppen Limestone, 6 m
Dolomite, very calcareous, very fine-grained, buff, grading
to dolomitic limestone, medium-grained with coarse crinoid
fragments; massive; contains calcite-filled geodes (shown as
fi); conformably overlain by Fern Glen.
Chouteau Limestone, 1.5 m (exposed)
Limestone, light brownish-gray, medium- to coarse-grained
dense, fossiliferous; irregular bedding; gray chert nodules
and calcite-filled geodes (shown aso«»and 8 respectively)
present; angular unconformity with overlying Meppe
Limestone. /* The Great River Road
,*< S3 < <7 O A f><J3
Figure 9 Chautauqua West, near mileage 23. NWV4 NE% SE% Sec. 13, T6N, R12W, Jersey County, Illinois
(modified from Collinson et al. 1954).
26
0.15+ 24.9 Simms Hollow lies to the right. Prepare to turn right.
0.05+ 24.95+ CAUTION: TURN RIGHT and enter the abandoned quarry. PARK away
from the face. Wear your hard hat and safety goggles, if you have them.
Do not climb on the face. If you hammer on or near the face, check
the rocks directly above you— they might be loose!
You must be careful here! Take charge of your youngsters.
STOP 3 We'll examine Silurian dolomite exposed in the quarry (entrance: SE NW NE NE Sec.
15, T6N, R12W, 3rd P.M., Jersey County, Grafton 7.5-Minute Quadrangle [38090H4]).
The Silurian dolomite, about 100 feet thick here, is an excellent building stone that was used in
the construction of many local buildings. The stone is gray on fresh surfaces but weathers to a
light tan. In this vicinity, the Silurian yields complete, well-preserved trilobites, mostly Calymene.
In some places, the Devonian is present up to 5 to 10 feet at the top of the exposure, but it is
inaccessible. (If you wish to see the Devonian, see the Jerseyville Hollow section at mileage
6.25+.)
Elsewhere in the Illinois Basin, reefs that formed in Silurian rocks have been studied by ISGS
scientists (Whitaker 1988). Some reefs have been significant oil reservoirs and producers.
Conditions for the formation of reefs were better about 40 miles east of the field trip area.
0.1 25.05+ Leave Stop 3. STOP: 1-way at SR 100. USE EXTREME CAUTION
entering SR 100. The McAdams Highway narrows down to a 2-lane road
here.
0.1+ 25.2 CAUTION: enter Grafton.
0.35 25.55 STOP: 4-way at SR 3 Junction. CONTINUE AHEAD (west) on SR 100.
1 .3+ 26.85+ Leave Grafton.
1 .15+ 28.0+ T-road intersects from the right on the curve. This leads to the back
entrance to Pere Marquette State Park. CONTINUE AHEAD.
0.65+ 28.7+ To the left is the entrance to the Brussels Ferry. CONTINUE AHEAD.
2.85 31 .55+ To the right is the main entrance to Pere Marquette State Park.
CONTINUE AHEAD and prepare to TURN RIGHT.
0.1 31 .65+ Entrance to the parking lot of the Visitors Center.
STOP 4 LUNCH at the tables outside the Visitors Center or at one of the other picnic areas
close to SR 100. Please return to the parking lot in 1 hour.
Pere Marquette State Park is named for Father Jacques Marquette. The site, acquired in 1932,
is now Illinois' largest state park with nearly 7,996 acres. In addition to the Visitors Center and
Museum, there are many miles of hiking trails, bridle paths, campgrounds, and picnic areas.
About 18 prehistoric Indian village sites and a few burial mounds lie within the park.
27
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28
STOP 5 In Pere Marquette State Park, you'll be free during the afternoon to take a walking
tour at your own pace. Survey geologists will be available at special sites to discuss various
features, such as the Ordovician, Silurian, Devonian, and Mississippian strata, Cap au Gres
Faulted Flexure, and the landscape. Figure 10 shows how Stop 5 has been organized into a
series of substops, 5 A - 51, and where the geologists are leading the discussions.
■ 5A: Trailside Museum You may tour through the park museum, which houses collections
of fossils, artifacts, plants, and animals from the park and surrounding area.
■ 5B - 5D: Pleistocene deposits and landforms From the museum, you can look across to
the lodge. Take note of stops 5B, 5C, and 5D (fig. 10).
The lodge sits on the Brussels terrace (Stop 5B), which slopes down in front of the lodge to the
surface of the Deer Plain terrace (Stop 5C), crossed by the main highway. Just beyond, the
terrain drops about 10 feet to the floodplain level (Stop 5D), which is largely inundated by
backwater from the Melvin Price Locks and Dam at Alton.
Studies of the sedimentology and bathymetry (measuring water depth and charting bottom
topography) of the Illinois and Mississippi Rivers were conducted in Pool 26 above the locks
and dam at Alton by the Illinois State Water Survey, the Illinois State Geological Survey, and
the Illinois State Natural History Survey in the early 1980s. The Surveys were examining the
effects of boat traffic on habitats of the riverine ecosystem (Schnepper et al. 1981, Goodwin
and Masters 1983).
They found that, with few exceptions, bottom materials in the deeper parts of the channel,
where it has been dredged for navigation, are mainly sand. In shallower parts of the channel
bottom, silt is the major constituent of the sediments. Navigation traffic may contribute greatly to
the relative lack of clay and silt in the deeper parts of the channels. Bottom-dwelling organisms
such as clams, mussels, and worms (food source for fish, ducks, and early man) have difficulty
living in a sandy habitat. Creating wetlands along the valley bottoms, as some government
agencies are now doing, should improve bottom habitats outside the navigation channels. This
in turn will provide a better environment for fish and waterfowl.
■ 5E: St. Louis Limestone breccia, upper St. Louis, and possible Ste. Genevieve strata
The trail ascends a series of steps past a nearly complete section of the main St. Louis breccia.
The breccia, dipping 26°S, is composed mainly of angular fragments of fine-grained limestone
that is slightly argillaceous and silty. Some fragments are partly rounded, so the deposit is
called a conglomerate in some reports. The breccia is widely distributed from southeastern
Iowa through western Illinois and northeastern Missouri.
Overlying the breccia, about 70 feet of limestone are exposed along the trail. Apparently, the
beds above the breccia exhibit some type of cyclical deposition. The top 10 feet of the section
consists of very sandy coarsely oolitic limestone that may be Ste. Genevieve or it may repre-
sent a St. Louis-Ste. Genevieve transition zone.
In a zone about 10 feet above the breccia, Lithostrotion proliferum and Lithostrotionella cas-
telnaui are common, along with bryozoans and brachiopods. Spirifer littoni and Dictyoclostus
tenuicostus have been identified from beds immediately above the breccia, and Linoproductus
ovatus is common in the uppermost oolitic beds.
■ 5F: Salem Limestone and lower St. Louis The Salem Limestone is represented in the
section along this trail by a single long, narrow, rather steeply dipping outcrop of limestone on
the promontory just south of the Warsaw re-entrant. The outcrop, which consists of rounded,
broken fossil fragments and whole small fossils in a calcium carbonate matrix, extends to the
29
30
base of the bluff, where it includes some oolitic limestone. Beyond the Salem ridge is a more
prominent spur exposing the lower St. Louis limestone.
■ 5G: Shelter House at McAdams Peak— landforms From this point, you can look directly
west across the valley of the Illinois River toward peninsular Calhoun County, the crest of which
rises about 400 feet above the river. On the far side of the river, the Deer Plain terrace of late
Wisconsin age makes a low apron, about 1 mile wide, that slopes gently (15 to 20 feet per
mile) away from the base of the bluffs. Above it lies the Brussels terrace of lllinoian age; it can
be seen clearly behind the white barn in the middle of the large valley almost directly opposite
us. The valley, Greenbay Hollow, developed in the crest of the Lincoln Anticline.
About 1 mile north of Greenbay Hollow, nestled at the base of the first bold cliffs your eyes
encounter, is the village of Meppen for which the Mississippian Meppen Limestone is named.
The upland surface on both sides of the Illinois River in this region truncates the Lincoln
Anticline and is interpreted as a peneplain (a low, nearly featureless, almost plane land surface
formed through long, continued erosion) named the Calhoun peneplain by Rubey (1952, p.
102-104).
The steeply dipping beds of the Cap au Gres flexure, on which we're standing, cross the valley
and transect the opposite bluffs in the small conical hill on the left (south) side of Greenbay
Hollow. As we can see from this point, the upland surface of Calhoun County north of the
structure is about 175 feet higher than on the south side.
■ 5H: Twin Springs, Silurian, Devonian, and Mississippian formations The Silurian
reaches road level at Twin Springs, striking approximately east-west and dipping about 28
degrees south. The Twin Springs outcrop is cut by at least five faults. The best-exposed fault
planes also strike east-west, but dip north at about 65°, nearly perpendicular to the beds. The
main face is slightly oblique to both bedding and faults. The minor faults are exposed and the
throw of a couple of faults can be estimated visually from the obvious offsets. Drag on one of
the faults can be seen best behind and above the balance boulder, as approached from the left
along the ledge nearly halfway up the face. The planes of the two larger faults are not exposed.
Determining their throw depends upon identifying the stratigraphy of the rocks on either side.
■ 51: Kimmswick and Maquoketa (slumped) The oldest rocks exposed in Pere Marquette
Park belong to the middle Ordovician Kimmswick Formation, which crops out in three small
exposures along Highway 100 at the base of the bluff. At Florissant 18 miles southeast, the
formation produces oil at a depth of 1 ,000 feet. The Waterloo and Dupo production in Illinois
just southeast of St. Louis is also from the Kimmswick Limestone.
End of the trip to Pere Marquette State Park.
We look forward to seeing you at Cave in Rock in Hardin County on April
25, 1992, and at Galena in Jo Daviess County on May 16, 1992.
31
RECOMMENDED READING
Anonymous, 1989, Directory of coal mines in Illinois: Jersey County: Illinois State Geological
Survey, Coal Mines Directory, 4 p.
Atherton, E., 1971, Tectonic development of the Eastern Interior Region of the United States, in
Background Materials for Symposium on Future Petroleum Potential of NPC Region 9
(Illinois Basin, Cincinnati Arch, and northern part of the Mississippi Embayment): Illinois
State Geological Survey, Illinois Petroleum 96, p. 29-43.
Atherton, E., 1971, Structure (map) on top of Pre-cambrian basement, in H. M. Bristol, and T.
C. Buschbach, Structural Features of the Eastern Interior Region of the United States, in
Background Materials for Symposium on Future Petroleum Potential of NPC Region 9
(Illinois Basin, Cincinnati Arch, and northern part of the Mississippi Embayment): Illinois
State Geological Survey, Illinois Petroleum 96, p. 21-28.
Bergstrom, R. E., and A. J. Zeizel, 1957, Groundwater Geology in Western Illinois, South Part:
A Preliminary Geologic Report: Illinois State Geological Survey, Circular 232, 28 p.
Buschbach, T. C„ 1953, The Chouteau Formation of Illinois: Illinois State Geological Survey,
Circular 183 (Reprinted from Transactions of the Illinois Academy of Sciences, v. 45, 1953),
p. 108-115.
Clark, P. U., M. R. Greek, and M. J. Schneider, 1988, Surface morphology of the southern
margin of the Laurentide ice sheet from Illinois to Montana (Abstr.), in Program and
Abstracts of the Tenth Biennial Meeting: American Quaternary Association, University of
Massachusetts, Amherst, p. 60.
Clegg, K. E., 1965, The La Salle anticlinal belt and adjacent structures in east-central Illinois:
Transactions of the Illinois State Academy of Science, v. 58, no. 2, p. 82-94.
Collinson, C.W., 1957, Ordovician, Silurian, Devonian, and Mississippian Rocks of Western
Illinois: The Illinois Geological Society Field Trip Guide Book, 24 p.
Collinson, C. W., R. D. Norby, T. L. Thompson, and J. D. Baxter, 1979, Stratigraphy of the
Mississippian stratotype - Upper Mississippi valley, U.S.A.: Illinois State Geological Survey
(Ninth International Congress of Carboniferous Stratigraphy and Geology. Field Trip 8.)
108 p.
Collinson, C. W., and D. H. Swann, 1958, Mississippian rocks of western Illinois; field trip no. 3:
Geological Society of America Field Trip Guidebook St. Louis Meeting, 1958, p. 21-32.
Collinson, C. W., H. B. Willman, and D. H. Swann, 1954, Guide to the Structure and Paleozoic
Stratigraphy along the Lincoln Fold in Western Illinois: Illinois State Geological Survey,
Guidebook Ser. 3, 75 p.
Damberger, H. H., 1971, Coalification pattern of the Illinois Basin: Economic Geology, v. 66,
no. 3, p. 488-494.
Damberger, H. H., S. B. Bhagwat, J. D. Treworgy, D. J. Berggren, M. H. Bargh, and I. E.
Samson, 1984, Coal industry in Illinois: Illinois State Geological Survey Map; scale,
1:500,000; size, 30"x 50"; color.
Edmund, R. W., and R. C. Anderson, 1967, The Mississippi River Arch: eveidence from the
area around Rock Island, Illinois: Thirty-first Annual Tri-State Filed Conference, Augustana
College, 64 p.
32
Ekblaw, G. E., 1939, Pere Marquette State Park: Illinois State Geological Survey, Geological
Science Field Trip Guide Leaflet 1939D, 2 p.
Goodwin, J. H., and J. M. Masters, 1983, Sedimentology and Bathymetry of Pool 26,
Mississippi River: Illinois State Geological Survey, Environmental Geology Notes 103, 76 p.
Horberg, C. L, 1950, Bedrock Topography of Illinois: Illinois State Geological Survey, Bulletin
73, 1 1 1 p.
Leighton, M. M., G. E. Ekblaw, and C. L. Horberg, 1948, Physiographic Divisions of Illinois:
Illinois State Geological Survey, Report of Investigations 129, 19 p.
Leighton, M. M., and H. B. Willman, 1950, Loess Formation of the Mississippi Valley: Illinois
State Geological Survey, Report of Investigations 149 (reprinted from Journal of Geology, v.
58, no. 6, 1950).
Lineback, J. A., et al., 1979, Quaternary Deposits of Illinois: Illinois State Geological Survey
Map; scale, 1:500,000; size, 40"x 60"; color.
Piskin, K., and R. E. Bergstrom, 1975, Glacial Drift in Illinois: Illinois State Geological Survey,
Circular 490, 35 p.
Raasch, G. O., 1947, Grafton Area, Jersey County: Illinois State Geological Survey,
Geological Science Field Trip Guide Leaflet 1947B, 5 p.
Robertson, P., 1938, Some problems of the middle Mississippi River region during Pleistocene
time: Transactions of the St. Louis Academy of Science, v. 29, p. 169-240.
Rubey, W. W., 1952, Geology and Mineral Resources of the Hardin and Brussels Quadrangles
(in Illinois): United States Geological Survey, Professional Paper 218, 179 p.
Samson, I. E., and S. B. Bhagwat, In preparation, Illinois Mineral Industry in 1989 and Review
of Preliminary Production Data for 1990: Illinois State Geological Survey, Illinois Minerals.
Savage, T. E., 1926, Silurian rocks of Illinois: Bulletin of the Geological Society of America, v.
37, p. 513-534.
Schnepper, D., T. Hill, D. Hullinger, and R. Evans, 1981, Physical Characteristics of Bottom
Sediments in the Alton Pool, Illinois Waterway: Illinois State Water Survey, Contract Report
263, 41 p.
Smith, W. H., 1961, Strippable Coal Reserves of Illinois: Part 3 - Madison, Macoupin, Jersey,
Greene, Scott. Morgan, and Cass Counties: Illinois State Geological Survey, Circular 311,
40 p.
Treworgy, J. D., 1979, Structure and Paleozoic Stratigraphy of the Cap au Gres Faulted
Flexure in Western Illinois, in Geology of Western Illinois; 43rd Annual Tri-State Geological
Conference: Illinois State Geological Survey, Guidebook 14, p. 1-35.
Treworgy, J. D., 1981, Structural Features in Illinois: A Compendium: Illinois State Geological
Survey, Circular 519, 22 p.
Weller, S., 1906, Kinderhook faunal studies, IV; The fauna of the Glen Park limestone: St. Louis
Academy of Science Transactions, v. 16, p. 468.
33
Whitaker, S. T., 1988, Silurian Pinnacle Reef Distribution in Illinois: Model for Hydrocarbon
Exploration: Illinois State Geological Survey, Illinois Petroleum 130, 32 p.
Willman, H. B., and J. C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State
Geological Survey, Bulletin 94, 204 p.
Willman, H. B., et al., 1967, Geologic Map of Illinois: llliois State Geological Survey Map; scale,
1:500,000; size, 40"x 56"; color.
Willman, H. B., J. A. Simon, B. M. Lynch, and V. A. Langenheim, 1968, Bibliography and Index
of Illinois Geology through 1965: Illinois State Geological Survey, Bulletin 92, 373 p.
Willman, H. B., E. Atherton, T. C. Buschbach, C. Collinson, J. C. Frye, M. E. Hopkins, J. A.
Lineback, J. A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological
Survey, Bulletin 95, 261 p.
Wilson, G. M., and I. E. Odom, 1960, Grafton Area: Illinois State Geological Survey, Geological
Science Field Trip Guide Leaflet 1960B, 12 p.
Withers, L. J., R. Piskin, and J. D. Student, 1981, Ground water level changes and
demographic analyses of ground water in llinois: Illinois Environmental Protection Agency,
Division of Land/Noise Pollution Control, 41 p.
34
MISSISSIPPIAN DEPOSITION
(The following quotation is from Report of Investigations 216: Classification of
Genevievian and Chesterian. . .Rocks of Illinois [1965] by D. H. Swann, pp. 11-16.
One figure and short sections of the text are omitted.)
During the Mississippian Period, the Illinois Basin was a slowly subsiding
region with a vague north-south structural axis. It was flanked by structurally
neutral regions to the east and west, corresponding to the present Cincinnati and
Ozark Arches. These neighboring elements contributed insignificant amounts of sed-
ment to the basin. Instead, the basin was filled by locally precipitated carbonate
and by mud and sand eroded from highland areas far to the northeast in the eastern
part of the Canadian Shield and perhaps the northeastward extension of the Appala-
chians. This sediment was brought to the Illinois region by a major river system,
which it will be convenient to call the Michigan River (fig. 4) because it crossed
the present state of Michigan from north to south or northeast to southwest....
The Michigan River delivered much sediment to the Illinois region during
early Mississippian time. However, an advance of the sea midway in the Mississippian
Period prevented sand and mud from reaching the area during deposition of the
St. Louis Limestone. Genevievian time began v/ith the lowering of sea level and the
alternating deposition of shallow-water carbonate and clastic units in a pattern that
persisted throughout the rest of the Mississippian. About a fourth of the fill of
the basin during the late Mississippian was carbonate, another fourth was sand,
and the remainder was mud carried down by the Michigan River.
Thickness, facies, and crossbedding. .. indicate the existence of a regional
slope to the southwest, perpendicular to the prevailing north 65° west trend of the
shorelines. The Illinois Basin, although developing structurally during this time,
was not an embayment of the interior sea. Indeed, the mouth of the Michigan River
generally extended out into the sea as a bird-foot delta, and the shoreline across
the basin area may have been convex more often than concave.
....The shoreline was not static. Its position oscillated through a range of
perhaps 600 to 1000 or more miles. At times it was so far south that land condi-
tions existed throughout the present area of the Illinois Basin. At other times it
was so far north that there is no suggestion of near- shore environment in the sedi-
ments still preserved. This migration of the shoreline and of the accompanying
sedimentation belts determined the composition and position of Genevievian and
Chesterian rock bodies.
Lateral shifts in the course of the Michigan River also influenced the place-
ment of the rock bodies. At times the river brought its load of sediment to the
eastern edge of the basin, at times to the center, and at times to the western
edge. This lateral shifting occurred within a range of about 200 miles. The
Cincinnati and Ozark areas did not themselves provide sediments, but, rather, the
Michigan River tended to avoid those relatively positive areas in favor of the
down-warped basin axis.
Sedimentation belts during this time were not symmetrical with respect to the
mouth of the Michigan River. They were distorted by the position of the river
relative to the Ozark and Cincinnati shoal areas, but of greater importance was sea
current or drift to the northwest. This carried off most of the mud contributed by
the river, narrowing the shale belt east of the river mouth and broadening it west
of the mouth. Facies and isopach maps of individual units show several times as
much shale west of the locus of sand deposition as east of it. The facies maps
of the entire Chesterian. . . show maximum sandstone deposition in a northeast-south-
west belt that bisects the basin. The total thickness of limestone is greatest
along the southern border of the basin and is relatively constant along that
entire border. The proportion of limestone, however, is much higher at the
eastern end than along the rest of the southern border, because little mud was
carried southeastward against the prevailing sea current. Instead, the mud was
carried to the northwest and the highest proportion of shale is found in the
northwestern part of the basin.
Genevievian and Chesterian seas generally extended from the Illinois Basin
eastward across the Cincinnati Shoal area and the Appalachian Basin. Little
terrigeneous sediment reached the Cincinnati Shoal area from either the west or
the east, and the section consists of thin limestone units representing all or
most of the major cycles. The proportion of inorganically precipitated limestone
is relatively high and the waters over the shoal area were commonly hypersaline. . .
Erosion of the shoal area at times is indicated by the presence of conodonts
eroded from the St. Louis Limestone and redeposited in the lower part of the Gasper
Limestone at the southeast corner of the Illinois Basin...
The shoal area included regions somewhat east of the present Cincinnati
axis and extended from Ohio, and probably southeastern Indiana, through central
and east- central Kentucky and Tennessee into Alabama. . . .
Toward the west, the seaway was commonly continuous between the Illinois
Basin and central Iowa, although only the record of Genevievian and earliest Ches-
terian is still preserved. The seas generally extended from the Illinois and
Black Warrior regions into the Arkansas Valley region, and the presence of
Chesterian outliers high in the Ozarks indicates that at times the Ozark area was
covered. Although the sea was continuous into the Ouachita region, detailed
correlation of the Illinois sediments with the geosynclinal deposits of this area
is difficult.
Figure 4: Paleogeography at an inter-
mediate stage during
Chesterian sedimentation.
BRYOZOANS
TRILOBITE
CRINOIDS
BLASTOIDS
Phillipsio I x
Rhombopora I x
Archimedes Ix
BRACHIOPODS
Platycrmus \ x
Pentremites 2x
Pentremites 2/j x
CORALS
Or //to fetes I x
Schuchertella I x
Echinoconchus I x
DEPOSITIONAL HISTORY OF THE PENNSYLVANIAN ROCKS IN ILLINOIS
At the close of the Mississippian Period, about 310 million years ago, the sea withdrew from the Midcontinent
region. A long interval of erosion that took place early in Pennsylvanian time removed hundreds of feet of the
pre-Pennsylvanian strata, completely stripping them away and cutting into older rocks over large areas of the
Midwest. Ancient river systems cut deep channels into the bedrock surface. Later, but still during early
Pennsylvanian (Morrowan) time, the sea level started to rise; the corresponding rise in the base level of
deposition interrupted the erosion and led to filling the valleys in the erosion surface with fluvial, brackish,
and marine sands and muds.
Depositional conditions in the Illinois Basin during the Pennsylvanian Period were somewhat similar to
those of the preceding Chesterian (late Mississippian) time. A river system flowed southwestward across a
swampy lowland, carrying mud and sand from highlands to the northeast. This river system formed thin but
widespread deltas that coalesced into a vast coastal plain or lowland that prograded (built out) into the shallow
sea that covered much of present-day Illinois (see paleogeographic map, next page). As the lowland stood
only a few feet above sea level, slight changes in relative sea level caused great shifts in the position of the
shoreline.
During most of Pennsylvanian time, the Illinois Basin gradually subsided; a maximum of about 3000 feet
of Pennsylvanian sediments are preserved in the basin. The locations of the delta systems and the shoreline
of the resulting coastal plain shifted, probably because of worldwide sea level changes, coupled with variation
in the amounts of sediments provided by the river system and local changes in basin subsidence rates. These
frequent shifts in the coastline position caused the depositional conditions at any one locality in the basin to
alternate frequently between marine and nonmarine, producing a variety of lithologies in the Pennsylvanian
rocks (see lithology distribution chart).
Conditions at various places on the shallow sea floor favored the deposition of sand, lime mud, or mud.
Sand was deposited near the mouths of distributary channels, where it was reworked by waves and spread
out as thin sheets near the shore. Mud was deposited in quiet-water areas — in delta bays between dis-
tributaries, in lagoons behind barrier bars, and in deeper water beyond the nearshore zone of sand deposition.
Limestone was formed from the accumulation of limy parts of plants and animals laid down in areas where
only minor amounts of sand and mud were being deposited. The areas of sand, mud, and limy mud deposition
continually changed as the position of the shoreline changed and as the delta distributaries extended seaward
or shifted their positions laterally along the shore.
Nonmarine sand, mud, and lime mud were deposited on the coastal plain bordering the sea. The nonmarine
sand was deposited in delta distributary channels, in river channels, and on the broad floodplains of the rivers.
Some sand bodies 100 or more feet thick were deposited in channels that cut through the underlying rock
units. Mud was deposited mainly on floodplains. Some mud and freshwater lime mud were deposited locally
in fresh-water lakes and swamps.
Beneath the quiet water of extensive swamps that prevailed for long intervals on the emergent coastal
lowland, peat was formed by accumulation of plant material. Lush forest vegetation covered the region; it
thrived in the warm, moist Pennsylvanian-age climate. Although the origin of the underclays beneath the coal
is not precisely known, most evidence indicates that they were deposited in the swamps as slackwater mud
before the accumulation of much plant debris. The clay underwent modification to become the soil upon which
the lush vegetation grew in the swamps. Underclay frequently contains plant roots and rootlets that appear
to be in their original places. The vast swamps were the culmination of nonmarine deposition. Resubmergence
of the borderlands by the sea interrupted nonmarine deposition, and marine sediments were laid down over
the peat.
30 60 mi
Paleogeography of Illinois-Indiana region during Pennsylvanian time. The diagram shows a
Pennsylvanian river delta and the position of the shoreline and the sea at an instant of time during
the Pennsylvanian Period.
Pennsylvanian Cyclothems
The Pennsylvanian strata exhibit extraordinary variations in thickness and composition both laterally and
vertically because of the extremely varied environmental conditions under which they formed. Individual
sedimentary units are often only a few inches thick and rarely exceed 30 feet thick. Sandstones and shales
commonly grade laterally into each other, and shales sometimes interfinger and grade into limestones and
coals. The underclays, coals, black shales, and some limestones, however, display remarkable lateral continuity
for such thin units. Coal seams have been traced in mines, outcrops, and subsurface drill records over areas
comprising several states.
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=y Shale, gray, sandy at top; contains marine
fossils and ironstone concretions, especially
in lower part.
Limestone: contains marine fossils.
Shale, black, hard, fissile, "slaty"; contains
large black spheroidal concretions and
marine fossils.
Limestone: contains marine fossils.
Shale, gray; pyritic nodules and ironstone
concretions common at base: plant fossils
locally common at base; marine fossils rare.
Coal : locally contains clay or shale partings.
Underclay. mostly medium to light gray ex-
cept dark gray at top; upper part noncalcare-
ous. lower part calcareous.
Limestone, argillaceous; occurs in nodules
or discontinuous beds; usually nonfossilifer-
ous
Shale, gray, sandy
Sandstone, fine-grained, micaceous, and
siltstone. argillaceous: variable from massive
to thin-bedded: usually with an uneven lower
surface
The idealized cyclothem at left (after Willman and Payne, 1942) infers continuous, widespread distribution of individual cyclothem units,
at right the model of a typical cyclothem (after Baird and Shabica, 1980) shows the discontinuous nature of many units in a cyclothem.
The rapid and frequent changes in depositional environments during Pennsylvanian time produced regular
or cyclical alternations of sandstone, shale, limestone, and coal in response to the shifting shoreline. Each
series of alternations, called a cyclothem, consists of several marine and nonmarine rock units that record a
complete cycle of marine invasion and retreat. Geologists have determined, after extensive studies of the
Pennsylvanian strata in the Midwest, that an "ideally" complete cyclothem consists of ten sedimentary units
(see illustration above contrasting the model of an "ideal" cyclothem with a model showing the dynamic
relationships between the various members of a typical cyclothem).
Approximately 50 cyclothems have been described in the Illinois Basin but only a few contain all ten units
at any given location. Usually one or more are missing because conditions of deposition were more varied
than indicated by the "ideal" cyclothem. However, the order of units in each cyclothem is almost always the
same: a typical cyclothem includes a basal sandstone overlain by an underclay, coal, black sheety shale,
marine limestone, and gray marine shale. In general, the sandstone-underclay-coal-gray shale portion (the
lower six units) of each cyclothem is nonmarine: it was deposited as part of the coastal lowlands from which
the sea had withdrawn. However, some of the sandstones are entirely or partly marine. The units above the
coal and gray shale are marine sediments deposited when the sea advanced over the coastal plain.
Origin of Coal
It is generally accepted that the Pennsylvanian coals originated by the accumulation of vegetable matter,
usually in place, beneath the waters of extensive, shallow, fresh-to-brackish swamps. They represent the
last-formed deposits of the nonmarine portions of the cyclothems. The swamps occupied vast areas of the
coastal lowland, which bordered the shallow Pennsylvanian sea. A luxuriant growth of forest plants, many
quite different from the plants of today, flourished in the warm, humid Pennsylvanian climate. (Illinois at that
time was near the equator.) The deciduous trees and flowering plants that are common today had not yet
evolved. Instead, the jungle-like forests were dominated by giant ancestors of present-day club mosses,
horsetails, ferns, conifers, and cycads. The undergrowth also was well developed, consisting of many ferns,
fernlike plants, and small club mosses. Most of the plant fossils found in the coals and associated sedimentary
rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variations in the
climate (tropical). Many of the Pennsylvanian plants, such as the seed ferns, eventually became extinct.
Plant debris from the rapidly growing swamp forests — leaves, twigs, branches, and logs — accumulated
as thick mats of peat on the floors of the swamps. Normally, vegetable matter rapidly decays by oxidation,
forming water, nitrogen, and carbon dioxide. However, the cover of swamp water, which was probably stagnant
and low in oxygen, prevented oxidation, and any decay of the peat deposits was due primarily to bacterial action.
The periodic invasions of the Pennsylvanian sea across the coastal swamps killed the Pennsylvanian
forests, and the peat deposits were often buried by marine sediments. After the marine transgressions, peat
usually became saturated with sea water containing sulfates and other dissolved minerals. Even the marine
sediments being deposited on the top of the drowned peat contained various minerals in solution, including
sulfur, which further infiltrated the peat. As a result, the peat developed into a coal that is high in sulfur.
However, in a number of areas, nonmarine muds, silts, and sands from the river system on the coastal plain
covered the peat where flooding broke through levees or the river changed its coarse. Where these sediments
(unit 6 of the cyclothem) are more than 20 feet thick, we find that the coal is low in sulfur, whereas coal found
directly beneath marine rocks is high in sulfur. Although the seas did cover the areas where these nonmarine,
fluvial sediments covered the peat, the peat was protected from sulfur infiltration by the shielding effect of
these thick fluvial sediments.
Following burial, the peat deposits were gradually transformed into coal by slow physical and chemical
changes in which pressure (compaction by the enormous weight of overlying sedimentary layers), heat (also
due to deep burial), and time were the most important factors. Water and volatile substances (nitrogen,
hydrogen, and oxygen) were slowly driven off during the coal-forming ("coalification") process, and the peat
deposits were changed into coal.
Coals have been classified by ranks that are based on the degree of coalification. The commonly recognized
coals, in order of increasing rank, are (1) brown coal or lignite, (2) sub-bituminous, (3) bituminous, (4)
semibituminous, (5) semianthracite, and (6) anthracite. Each increase in rank is characterized by larger
amounts of fixed carbon and smaller amounts of oxygen and other volatiles. Hardness of coal also increases
with increasing rank. All Illinois coals are classified as bituminous.
Underclays occur beneath most of the coals in Illinois. Because underclays are generally unstratified
(unlayered), are leached to a bleached appearance, and generally contain plant roots, many geologists
consider that they represent the ancient soils on which the coal-forming plants grew.
The exact origin of the carbonaceous black shale that occurs above many coals is uncertain. Current
thinking suggests that the black shale actually represents the deepest part of the marine transgression.
Maximum transgression of the sea, coupled with upwelling of ocean water and accumulation of mud and
animal remains on an anaerobic ocean floor, led to the deposition of black organic mud over vast areas
stretching from Texas to Illinois. Deposition occurred in quiet-water areas where the very fine-grained iron-rich
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MISSISSIPPIAN TO ORDOVICIAN SYSTEMS
Generalized stratigraphic column of the Pennsylvanian in Illinois (1 inch approximately 250 feet)
mud and finely divided plant debris were washed in from the land. Most of the fossils found in black shale
represent planktonic (floating) and nektonic (swimming) forms — not benthonic (bottom-dwelling) forms. The
depauperate (dwarf) fossil forms sometimes found in black shale formerly were thought to have been forms
that were stunted by toxic conditions in the sulfide-rich, oxygen-deficient water of the lagoons. However, study
has shown that the "depauperate" fauna consists mostly of normal-size individuals of species that never grew
any larger.
References
Baird, G. C, and C. W. Shabica, 1980, The Mazon Creek depositional event; examination of Francis Creek
and analogous facies in the Midcontinent region: in Middle and late Pennsylvanian strata on margin of
Illinois Basin, Vermilion County, Illinois, Vermilion and Parke counties, Indiana (R. L. Langenheim, editor).
Annual Field Conference — Society of Economic Paleontologists and Mineralogists. Great Lakes Section,
No. 10, p. 79-92.
Heckel, P. H., 1977, Origin of phosphatic black shale facies in Pennsylvanian cyclothems of mid-continent
North America: American Association of Petroleum Geologist Bulletin, v. 61, p. 1045-1068.
Kosanke, R. M., J. A. Simon, H. R. Wanless, and H. B. Willman, 1960, Classification of the Pennsylvanian
strata of Illinois: Illinois State Geological Survey Report of Investigation 214, 84 p.
Simon, J. A., and M. E. Hopkins, 1973, Geology of Coal: Illinois State Geological Survey Reprint 1973-H, 28 p.
Willman, H. B., and J. N. Payne, 1942, Geology and mineral resources of the Marseilles, Ottawa, and Streator
Quadrangles: Illinois State Geological Survey Bulletin 66, 388 p.
Willman, H. B., et al., 1967, Geologic Map of Illinois: Illinois State Geological Survey map; scale, 1:500,000
(about 8 miles per inch).
Willman, H. B., E. Atherton, T C. Buschbach, C. W Collinson, J. C. Frye, M. E. Hopkins, J. A. Lineback, and
J. A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.
PLEISTOCENE GLACIATIONS IN ILLINOIS
Origin of the Glaciers
During the past million years or so, an interval of time called the Pleistocene Epoch, most of the northern
hemisphere above the 50th parallel has been repeatedly covered by glacial ice. The cooling of the earth's
surface, a prerequisite for glaciation, began at least 2 million years ago. On the basis of evidence found in
subpolar oceans of the world (temperature-dependent fossils and oxygen-isotope ratios), a recent proposal
has been made to recognize the beginning of the Pleistocene at 1 .6 million years ago. Ice sheets formed in
sub-arctic regions many times and spread outward until they covered the northern parts of Europe and North
America. In North America, early studies of the glacial deposits led to the model that four glaciations could
explain the observed distribution of glacial deposits. The deposits of a glaciation were separated from each
other by the evidence of intervals of time during which soils formed on the land surface. In order of occurrence
from the oldest to the youngest, they were given the names Nebraskan, Kansan, lllinoian, and Wisconsinan
Stages of the Pleistocene Epoch. Work in the last 30 years has shown that there were more than four
glaciations but the actual number and correlations at this time are not known. Estimates that are gaining
credibility suggest that there may have been about 14 glaciations in the last one million years. In Illinois,
estimates range from 4 to 8 based on buried soils and glacial deposits. For practical purposes, the previous
four glacial stage model is functional, but we now know that the older stages are complex and probably
contain more than one glaciation. Until we know more, all of the older glacial deposits, including the Nebraskan
and Kansan will be classified as pre-lllinoian. The limits and times of the ice movement in Illinois are illustrated
in the following pages by several figures.
The North American ice sheets developed when the mean annual tem-
perature was perhaps 4° to 7°C (7° to 1 3°F) cooler than it is now and
winter snows did not completely melt during the summers. Because the
time of cooler conditions lasted tens of thousands of years, thick masses
of snow and ice accumulated to form glaciers. As the ice thickened,
the great weight of the ice and snow caused them to flow outward at
their margins, often for hundreds of miles. As the ice sheets expanded,
the areas in which snow accumulated probably also increased in extent.
Tongues of ice, called lobes, flowed southward from the Canadian cen-
ters near Hudson Bay and converged in the central lowland between
the Appalachian and Rocky Mountains. There the glaciers made their
farthest advances to the south. The sketch below shows several centers
of flow, the general directions of flow from the centers, and the southern
extent of glaciation. Because Illinois lies entirely in the central lowland,
it has been invaded by glaciers from every center.
Effects of Glaciation
Pleistocene glaciers and the waters melting from them changed the landscapes they covered. The
glaciers scraped and smeared the landforms they overrode, leveling and filling many of the minor valleys and
even some of the larger ones. Moving ice carried colossal amounts of rock and earth, for much of what the
glaciers wore off the ground was kneaded into the moving ice and carried along, often for hundreds of miles.
The continual floods released by melting ice entrenched new drainageways, deepened old ones, and
then partly refilled both with sediments as great quantities of rock and earth were carried beyond the glacier
fronts. According to some estimates, the amount of water drawn from the sea and changed into ice during
a glaciation was enough to lower the sea level from 300 to 400 feet below present level. Consequently, the
melting of a continental ice sheet provided a tremendous volume of water that eroded and transported
sediments.
In most of Illinois, then, glacial and meltwater deposits buried the old rock-ribbed, low, hill-and-valley
terrain and created the flatter landforms of our prairies. The mantle of soil material and the buried deposits
of gravel, sand, and clay left by the glaciers over about 90 percent of the state have been of incalculable
value to Illinois residents.
Glacial Deposits
The deposits of earth and rock materials moved by a glacier and deposited in the area once covered
by the glacier are collectively called drift. Drift that is ice-laid is called till. Water-laid drift is called outwash .
Till is deposited when a glacier melts and the rock material it carries is dropped. Because this sediment
is not moved much by water, a till is unsorted, containing particles of different sizes and compositions. It is
also stratified (unlayered). A till may contain materials ranging in size from microscopic clay particles to large
boulders. Most tills in Illinois are pebbly clays with only a few boulders. For descriptive purposes, a mixture
of clay, silt, sand and boulders is called diamicton. This is a term used to describe a deposit that could be
interpreted as till or a mass wasting product.
Tills may be deposited as end moraines, the arc-shaped ridges that pile up along the glacier edges
where the flowing ice is melting as fast as it moves forward. Till also may be deposited as ground moraines,
or till plains, which are gently undulating sheets deposited when the ice front melts back, or retreats. Deposits
of till identify areas once covered by glaciers. Northeastern Illinois has many alternating ridges and plains,
which are the succession of end moraines and till plains deposited by the Wisconsinan glacier.
Sorted and stratified sediment deposited by water melting from the glacier is called outwash. Outwash
is bedded, or layered, because the flow of water that deposited it varied in gradient, volume, velocity, and
direction. As a meltwater stream washes the rock materials along, it sorts them by size — the fine sands, silts,
and clays are carried farther downstream than the coarser gravels and cobbles. Typical Pleistocene outwash
in Illinois is in multilayered beds of clays, silts, sands, and gravels that look much like modern stream deposits
in some places. In general, outwash tends to be coarser and less weathered, and alluvium is most often finer
than medium sand and contains variable amounts of weathered material.
Outwash deposits are found not only in the area covered by the ice field but sometimes far beyond it.
Meltwater streams ran off the top of the glacier, in crevices in the ice, and under the ice. In some places, the
cobble-gravel-sand filling of the bed of a stream that flowed in the ice is preserved as a sinuous ridge called
an esker. Some eskers in Illinois are made up of sandy to silty deposits and contain mass wasted diamicton
material. Cone-shaped mounds of coarse outwash, called kames, were formed where meltwater plunged
through crevasses in the ice or into ponds on the glacier.
The finest outwash sediments, the clays and silts, formed bedded deposits in the ponds and lakes that
filled glacier-dammed stream valleys, the sags of the till plains, and some low, moraine-diked till plains.
Meltwater streams that entered a lake rapidly lost speed and also quickly dropped the sands and gravels
they carried, forming deltas at the edge of the lake. Very fine sand and silts were commonly redistributed on
the lake bottom by wind-generated currents, and the clays, which stayed in suspension longest, slowly settled
out and accumulated with them.
Along the ice front, meltwater ran off in innumerable shifting and short-lived streams that laid down a
broad, flat blanket of outwash that formed an outwash plain. Outwash was also carried away from the glacier
in valleys cut by floods of meltwater. The Mississiippi, Illinois, and Ohio Rivers occupy valleys that were major
channels for meltwaters and were greatly widened and deepened during times of the greatest meltwater
floods. When the floods waned, these valleys were partly filled with outwash far beyond the ice margins.
Such outwash deposits, largely sand and gravel, are known as valley trains. Valley train deposits may be
both extensive and thick. For instance, the long valley train of the Mississippi Valley is locally as much as
200 feet thick.
Loess, Eolian Sand and Soils
One of the most widespread sediments resulting from glaciation was carried not by ice or water but by
wind. Loess is the name given to windblown deposits dominated by silt. Most of the silt was derived from
wind erosion of the valley trains. Wind action also sorted out eolian sand which commonly formed sand
dunes on the valley trains or on the adjacent uplands. In places, sand dunes have migrated up to 10 miles
away from the principle source of sand. Flat areas between dunes are generally underlain by eolian sheet
sand that is commonly reworked by water action. On uplands along the major valley trains, loess and eolian
sand are commonly interbedded. With increasing distance from the valleys, the eolian sand pinches out, often
within one mile.
Eolian deposition occurred when certain climatic conditions were met, probably in a seasonal pattern.
Deposition could have occurred in the fall, winter or spring season when low precipitation rates and low
temperatures caused meltwater floods to abate, exposing the surfaces of the valley trains and permitting
them to dry out. During Pleistocene time, as now, west winds prevailed, and the loess deposits are thickest
on the east sides of the source valleys. The loess thins rapidly away from the valleys but extends over almost
all the state.
Each Pleistocene glaciation was followed by an interglacial stage that began when the climate warmed
enough to melt the glaciers and their snowfields. During these warmer intervals, when the climate was similar
to that of today, drift and loess surfaces were exposed to weather and the activities of living things. Con-
sequently, over most of the glaciated terrain, soils developed on the Pleistocene deposits and altered their
composition, color, and texture. Such soils were generally destroyed by later glacial advances, but some
were buried. Those that survive serve as "key beds," or stratigraphic markers, and are evidence of the passage
of a long interval of time.
Glaciation in a Small Illinois Region
The following diagrams show how a continental ice sheet might have looked at various stages as it
moved across a small region in Illinois. They illustrate how it could change the old terrain and create a
landscape like the one we live on. To visualize how these glaciers looked, geologists study the landforms
and materials left in the glaciated regions and also the present-day mountain glaciers and polar ice caps.
The block of land in the diagrams is several miles wide and about 10 miles long. The vertical scale is
exaggerated — layers of material are drawn thicker and landforms higher than they ought to be so that they
can be easily seen.
.■■.'.■■..■'■■■■■..i. '-TJ-TrL-r-L-1d=cJr3=
1 . The Region Before Glaciation — Like most of Illinois, the region illustrated is underlain by almost flat-lying beds of
sedimentary rocks — layers of sandstone (■••■■•:). limestone ( ■ i ' ). and shale ( =s-=^). Millions of years of erosion
have planed down the bedrock (BR), creating a terrain of low uplands and shallow valleys. A residual soil weathered
from local rock debris covers the area but is too thin to be shown in the drawing. The streams illustrated here flow
westward and the one on the right flows into the other at a point beyond the diagram.
2. The Glacier Advances Southward — As the Glacier (G) spreads out from its ice snowfield accumulation center, it
scours (SC) the soil and rock surface and quarries (Q) — pushes and plucks up — chunks of bedrock. The materials are
mixed into the ice and make up the glacier's "load." Where roughnesses in the terrain slow or stop flow (F), the ice
"current" slides up over the blocked ice on innumerable shear planes (S). Shearing mixes the load very thoroughly. As
the glacier spreads, long cracks called "crevasses" (C) open parallel to the direction of ice flow. The glacier melts as it
flows forward, and its meltwater erodes the terrain in front of the ice, deepening (D) some old valleys before ice covers
them. Meltwater washes away some of the load freed by melting and deposits it on the outwash plain (OP). The advancing
glacier overrides its outwash and in places scours much of it up again. The glacier may be 5000 or so feet thick, and
tapers to the margin, which was probably in the range of several hundred feet above the old terrain. The ice front advances
perhaps as much as a third of a mile per year.
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3. The Glacier Deposits an End Moraine — After the glacier advances across the area, the climate warms and the
ice begins to melt as fast as it advances. The ice front (IF) is now stationary, or fluctuating in a narrow area, and the
glacier is depositing an end moraine.
As the top of the glacier melts, some of the sediment that is mixed in the ice accumulates on top of the glacier.
Some is carried by meltwater onto the sloping ice front (IF) and out onto the plain beyond. Some of the debris slips down
the ice front in a mudflow (FL). Meltwater runs through the ice in a crevasse (C). A supraglacial stream (SS) drains the
top of the ice, forming an outwash fan (OF). Moving ice has overridden an immobile part of the front on a shear plane
(S). All but the top of a block of ice (B) is buried by outwash (O).
Sediment from the melted ice of the previous advance (figure 2) remains as a till layer (T), part of which forms the
till plain (TP). A shallow, marshy lake (L) fills a low place in the plain. Although largely filled with drift, the valley (V)
remains a low spot in the terrain. As soon as the ice cover melts, meltwater drains down the valley, cutting it deeper.
Later, outwash partly refills the valley: the outwash deposit is called a valley train (VT). Wind blows dust (DT) off the dry
floodplain. The dust will form a loess deposit when it settles. Sand dunes (D) form on the south and east sides of streams.
4. The Region after Glaciation — As the climate warms further, the whole ice sheet melts, and glaciation ends. The
end moraine (EM) is a low, broad ridge between the outwash plain (OP) and till plains (TP). Run-off from rains cuts
stream valleys into its slopes. A stream goes through the end moraine along the channel cut by the meltwater that ran
out of the crevasse in the glacier.
Slopewash and vegetation are filling the shallow lake. The collapse of outwash into the cavity left by the ice block's
melting has made a kettle (K). The outwash that filled a tunnel draining under the glacier is preserved in an esker (E).
The hill of outwash left where meltwater dumped sand and gravel into a crevasse or other depression in the glacier or
at its edge is a kame (KM). A few feet of loess covers the entire area but cannot be shown at this scale.
TIME TABLE OF PLEISTOCENE GLACIATION
STAGE
SUBSTAGE
NATURE OF DEPOSITS
SPECIAL FEATURES
>
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cc
LU
O
HOLOCENE
(interglacial)
Years
Before Present
WISCONSINAN
(glacial)
SANGAMONIAN
(interglacial)
ILLINOIAN
(glacial)
YARMOUTHIAN
(interglacial)
KANSAN*
(glacial)
AFTONIAN*
(interglacial)
NEBRASKAN*
(glacial)
10,000 -
Valderan
- 1 1 ,000 -
Twocreekan
- 12,500 -
Woodfordian
- 25,000
Farmdalian
- 28,000 -
Altonian
75,000
125,000
Jubileean
Monican
Liman
300,000?
500,000?
700,000?
900,000?
1 ,600,000 or more
Soil, youthful profile
of weathering, lake
and river deposits,
dunes, peat
Outwash, lake deposits
Peat and alluvium
Drift, loess, dunes,
lake deposits
Soil, silt, and peat
Drift, loess
Soil, mature profile
of weathering
Drift, loess, outwash
Drift, loess, outwash
Drift, loess, outwash
Soil, mature profile
of weathering
Drift, loess
Soil, mature profile
of weathering
Drift (little known)
Outwash along
Mississippi Valley
Ice withdrawal, erosion
Glaciation; building of
many moraines as far
south as Shelbyville;
extensive valley trains,
outwash plains, and lakes
Ice withdrawal, weathering,
and erosion
Glaciation in Great Lakes
area, valley trains
along major rivers
Important stratigraphic marker
Glaciers from northeast
at maximum reached
Mississippi River and
nearly to southern tip
of Illinois
Important stratigraphic marker
Glaciers from northeast
and northwest covered
much of state
(hypothetical)
Glaciers from northwest
invaded western Illinois
'Old oversimplified concepts, now known to represent a series of glacial cycles.
Iinois State Geological Survey, 197
SEQUENCE OF GLACIATIONS AND INTERGLACIAL
DRAINAGE IN ILLINOIS
PRE-PLEISTOCENE PRE-ILLINOIAN
major drainage inferred glacial limits
YARMOUTHIAN
major drainage
LIMAN
glacial advance
MONICAN
glacial advance
JUBILEEAN
glacial advance
SANGAMON IAN
major drainage
ALTON IAN
glacial advance
WOODFORDIAN
glacial advance
WOODFORDIAN
Valparaiso ice and
Kankakee Flood
VALDERAN
drainage
(Modified from Willlman and Frye, "Pleistocene Stratigraphy of Illinois," ISGS Bull. 94, fig. 5, 1970.)
WOODFORDIAN MORAINES
H. B. Willman and John C. Frye
Le Roy Named moraine
ILLIANA Nomed moraimc system
Intermorainal area
30 M,i.»
40 Kilomdttt
|l I isols S I v I I ( ii i 0 I >i.n M Si h\ i \
QUATERNARY DEPOSITS OF ILLINOIS
Jerry A. Lineback
1981
Modified from Quaternary Deposits
of Illinois (1979) by Jerry A. Lineback
AGE
Holocene
and
'isconsinan
/isconsinan
and
lllinoian
lllinoian
-^-T_~J Cahokia Alluvium,
--T- ~* Parkland Sand, and
Henry Formation
combined; alluvium,
windblown sand, and
sand and gravel outwash
(isconsinan *X*I*J Peoria Loess and Roxana Silt combined;
windblown silt more >*_■
than 6 meters (20 ft) thick. '£>
Equality Formation; silt, clay, and
sand in glacial and slack-water lakes
Moraine
Ground
Wedron and Trafalgar
Formations combined;
glacial till with some
sand, gravel, and silt.
Winnebago and Glasford Formations
combined; glacial till with some sand,
gravel, and silt; age assignments of some
units is uncertain.
Glasford Formation; glacial till with some sand,
gravel, and silt.
Teneriffe Silt, Pearl Formation, and Hagarstown Member i
of the Glasford Formation combined; lake silt and clay,
outwash sand, gravel, and silt.
re-lllinoian LA/vl Wolf Creek Formation; glacial till with gravel, sand,
t-W3 and silt.
Bedrock.
ISGS 1981
ILLINOIS STATE GEOLOGICAL SURVEY GEOGRAM 5
Urbana, Illinois 61801 October 1975
ANCIENT DUST STORMS IN ILLINOIS
Myrna M. Killey
Fierce dust storms whirled across Illinois long before human beings were
here to record them. Where did all the dust come from? Geologists have carefully
put together clues from the earth itself to get the story. As the glaciers of the
Great Ice Age scraped and scoured their way southward across the landscape from
Canada, they moved colossal amounts of rock and earth. Much of the rock ground
from the surface was kneaded into the ice and carried along, often for hundreds
of miles. The glaciers acted as giant grist mills, grinding much of the rock and
earth to "flour" — very fine dust-sized particles.
During the warm seasons, water from the melting ice poured from the gla-
cier front, laden with this rock flour, called silt. In the cold months the melt-
water stopped flowing and the silt was left along the channels the water had fol-
lowed, where it dried out and became dust. Strong winds picked up the dust, swept
it from the floodplains, and carried it to adjacent uplands. There the forests
along the river valleys trapped the dust, which became part of the moist forest
soil. With each storm more material accumulated until the high bluffs adjacent to
major rivers were formed. The dust deposits are thicker along the eastern sides
of the valleys than they are on the western sides, a fact from which geologists
deduce that the prevailing winds of that time blew from west to east, the same
direction as those of today. From such clues geologists conclude that the geo-
logic processes of the past were much like those of today.
The deposits of windblown silt are called loess (rhymes with "bus").
Loess is found not only in the areas once covered by the glaciers but has been
blown into the nonglaciated areas. The glaciers, therefore, influenced the pres-
ent land surface well beyond the line of their farthest advance.
Loess has several interesting characteristics. Its texture is so fine
and uniform that it can easily be identified in roadcuts — and because it blankets
such a vast area many roads are cut through it. Even more noticeable is its ten-
dency to stand in vertical walls. These steep walls develop as the loess drains
and becomes tough, compact, and massive, much like a rock. Sometimes cracks de-
velop in the loess, just as they do in massive limestones and sandstones. Loess
makes good highway banks if it is cut vertically. A vertical cut permits maximum
drainage because little surface is exposed to rain, and rainwater tends to drain
straight down through it to the rock underneath. If the bank is cut at an angle
more water soaks in, which causes the loess to slump down. Along Illinois roads
the difference between a loess roadcut and one in ordinary glacial till is obvi-
ous. The loess has a very uniform texture, while the till is composed of a ran-
dom mixture of rock debris, from clay and silt through cobbles and boulders.
Many loess deposits are worth a close look. Through a 10-power hand
lens separate grains can be seen, among them many clear, glassy, quartz grains.
Some loess deposits contain numerous rounded, lumpy stones called concretions.
Their formation began when water percolating through the loess dissolved tiny
LOESS THICKNESS IN ILLINOIS;
■ More than 300 inches
Egsag 150-300 inches
Hg*SB?| 50-150 inches
I ~j Up lo 50 inches
I I Little or no loess
limestone grains. Some of the dissolved
minerals later became solid again,
gathering around a tiny nucleus or
along roots to form the lumpy masses. A
few such concretions are shaped roughly
like small dolls and, from this resem-
blance, are called "loess kindchen," a
German term meaning "loess children."
They may be partly hollow and contain
smaller lumps that make them rattle
when shaken.
Fossil snails can be found in some
loess deposits. The snails lived on the
river bluffs while the loess was being
deposited and were buried by the dust.
When they are abundant, they are used
to determine how old the loess is. The
age is found by measuring the amount of
radioactive carbon in the calcium car-
bonate of their shells.
Some of the early loess deposits
were covered by new layers of loess
following later glacial invasions. Many
thousands of years passed between the
major glacial periods, during which
time the climate was as warm as that of
today. During the warm intervals, the
surface of the loess and other glacial
deposits was exposed to weather. Soils
developed on most of the terrain, al-
tering the composition, color, and tex-
ture of the glacial material. During later advances of the ice, some of these
soils were destroyed, but in many places they are preserved under the younger
sediments. Such ancient buried soils can be used to determine when the materials
above and below them were laid down by the ice and what changes in climate took
place.
The blanket of loess deposited by the ancient dust storms forms the par-
ent material of the rich, deep soils that today are basic to the state's agricul-
ture. A soil made of loess crumbles easily and has great moisture-holding capaci-
ty. It also is free from rocks that might complicate cultivation. Those great
dust storms that swirled over the land many thousands of years ago thus endowed
Illinois with one of its greatest resources, its highly productive soil.
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