Guide to the geology of the Decatur area, Macon and Christian counties

64 Pages·1991·3.4 MB·English

by  Reinertsen, David L

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1991-C
GUIDE TO THE GEOLOQY€>P
THE DECATUR AREA, MACON
AND CHRISTIAN COUNTIES
David L. Reinertsen
Field Trip Guide Leaflet 1991C, September 14, 1991
Department of Energy and Natural Resources
ILLINOIS STATE GEOLOGICAL SURVEY
Coverphoto byD. L. Reinertsen
Wisconsinan glacial deposits exposed along the north side of the Sangamon River at Stop 7.
GEOLOGICAL SCIENCE FIELD TRIPS The Educational Extension Unit of the Illinois State
Geological Survey conducts fourfree tours each yearto acquaintthe publicwiththe rocks, mineral
resources, and landscapes of Illinois. Each field trip is an all-day excursion through one or more
Illinoiscounties. Frequent stopsare madetoexplore interesting phenomena, explaintheprocesses
that shape our environment, discuss principles of earth science, and collect rocks and fossils.
People of all ages and interests arewelcome. The trips are especially helpfultoteachers preparing
earth science units. Grade school students are welcome, but each must be accompanied by a
parent or other responsible adult. High school classes should be supervised by at least one adult
for each ten students.
•CM
-o
A list of earlierfieldtripguide leafletsforplanning 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. Phone: [phone] or 333-7372.
prmtadonrtqrcMpi«M(
Printedbyauthorityolthe State ofIllinois/1991/500
GUIDE TO THE GEOLOGY OF
THE DECATUR AREA, MACON
AND CHRISTIAN COUNTIES
David L. Reinertsen
John M. Masters
Leon R. Follmer
Ardith K. Hansel
Philip C. Reed
Richard H. Howard
Stephen Whitaker
T.
Field Trip Guide Leaflet 1991C, September 14, 1991
ILLINOIS STATE GEOLOGICAL SURVEY
Morris W. Leighton, Chief
Natural Resources Building
615 E. Peabody Drive
Champaign, Illinois 61820
Digitized by the Internet Archive
in 2012 with funding from
University of Illinois Urbana-Champaign
http://archive.org/details/guidetogeolo1991rein
1
CONTENTS
GEOLOGIC FRAMEWORK OF THE DECATUR AREA
1
Bedrock 1
Stmctural and Depositional History 5
Glacial History 9
Physiography 10
Drainage 11
Relief 11
MINERAL PRODUCTION 11
Water Supply in the Field Trip Area 12
Surface water 12
Groundwater 12
GUIDE TO THE ROUTE—STOPS 16
1 Mueller Park, Decatur 16
2 Pavillion and Oriental Garden of Scovill Park 19
3 Vulcan Materials Company, Decatur sand and gravel operation 22
4 Lunch at the Griswold Conservation Area 27
5 Concrete marker commemorating Abraham Lincoln's work as a surveyor 29
6 Decatur Sand and Gravel Company pit 31
7 Lincoln Homestead State Park 33
8 Decatur Oil Field 37
9 Rock Springs Centerfor Environmental Discovery 39
REFERENCES 40
PLEISTOCENE GLACIATIONS IN ILLINOIS
GEOGRAM
2
FIGURES
Rock succession column Iv
1 Location of some major structures in the Illinois region 1
2 Unconsolidated deposits and bedrock in Springfield-Decatur region 2
3 Structural features of Illinois 4
4 Stylized north-south cross section of the structure of the Illinois Basin 6
5 Bedrock geology beneath surficial deposits 7
6 Generalized map of glacial deposits in Illinois 8
7 Physiographic divisions of Illinois 10
8 Groundwater conditions in and adjacent to the Springfield-Decatur region 13
9 Cross section showing nature of the unconsolidated deposits and the surficial 14
and bedrock topography of the Decatur area
10 Rock of the Pennsylvanian system directly underlie the unconsolidated deposits 18
in the Springfield-Decatur region
1 Rock identification key 20
12 Particle-size names in general use by the sand and gravel industry 22
13 Principal meridians and base lines of Illinois and surrounding states 30
14 Index map 30
15 Schematic diagram of a common type of oil production unit in Illinois 36
16 Approximate area (shaded) encompassed by the waterflood operation in 37
the Decatur Oil Field
17 Places where oil occurs in Illinois 38
PeriodorSystem Age
Era andThickness (yearsago) GeneralTypes of Rocks
\Holocene
Recent—alluvium in river valleys
Quaternary «c<c^ 10,000 Glociol till, glocial outwosh,grovel,sand,silt,
0-500' lake deposits of clay ond silt, loess and
^ o sand dunes ; covers nearly all of state
encept norttiwest corner ond southern tip
Pliocene - 51..63mm.. Cheorntdgwreavsetle,rnpreIlsleinntoisin northern, southern, '.v.>:^
36.6m.
Tertiory Mostly micaceous sond with some silt and cloy,
0-500' ^ present only in southern Illinois
- 57.8m,
Paleocene Mostly clay,little sand;present only in southern
-66.4m. Illinois
Mostlysand,somethinbedsofcloy and,locally,
r 144m. gravel;present only in southern Illinois
- 286m.
Pennsylvonion
0-3,000' Lorgely shale ond sandstone with bedsof coal,
limestone,and cloy
CCoalMeasures")
320m.
Block andgray shale at bose;middle zoneof
Mississippian thick limestone that grodes to siltstone,
0-3.500' chert,and shole, upper zone of interbedded
sandstone,shole,ond limestone
360m
Thick limestone,minor sandstones andshales,
Devonian
largely chert and cherty limestonein southern
0-1,500'
Illinois; block shaleat lop
408m.
zrzz:z
Silurian Principolly dolomite and limestone
0-1,000'
438m
Ordovician Largely dolomiteand limestone but contoins
500-2.000' sondstone,shale,ond siltstone formolions
505m
Combnan Chiefly sondstones with some dolomiteond shale,
,500-3,000' exposedonly in small areasin north-centrol
Illinois
570m
ARCHEOZOIC and Igneous and melomorphic rocks, knownin
PROTEROZOIC Illinois only from deep wells
Rock succession chart
—
GEOLOGIC FRAMEWORK OF THE DECATUR AREA
The geology, landscape, and mineral resources in parts of Macon and Christian Counties in
central Illinois are the focus of the Decatur geological field trip. Decatur is 38 miles east of
Springfield, about 180 miles south-southwest of Chicago, and slightly more than 115 miles
northeast of St. Louis.
Characterized by gently rolling uplands that developed from deposits left by two periods of
continental glaciation during the past 300,000 years, the area's surface continuity is broken
where the two sheets of glacial deposits meet and where they both are eroded by the
Sangamon River and its tributaries. Sand and gravel resources are abundant in the glacial
deposits. Other mineral resources produced from the bedrock underlying these counties include
coal, petroleum, and stone.
Bedrock
Rock units (beds), commonly solid and strongly cemented materials, underlie the relatively
loose (unconsolidated) glacial deposits at and near the surface of the earth. The geology of the
Macon-Christian counties area, like the rest of Illinois, has undergone many changes
throughout the several billion years of geologic time (see rock succession column, facing page).
The oldest rocks beneath the area of 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 Earth's surface anywhere in Illinois. Only about 30 drill holes have reached
deep enough in Illinois for geologists to collect samples from Precambrian rocks. From the
samples, however, we know that these ancient rocks consist of mostly 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 up to
nearly 0.6 billion years ago, formed a
landscape that must have been similar to
the present-day Missouri Ozarks.
You will note that the long interval for
which we have no rock record in Illinois
from the time Precambrian rocks were
formed until —Cambrian sediments
accumulated is almost as long as
recorded geologic time from the Cam-
brian to the present. Although geologists
seldom see Precambrian rocks, except as
cuttings from drill holes, they can
determine some basement complex char-
characteristics by using various tech-
niques. For example, evidence from
surface mapping, gravity and magnetic
field measurements, and seismic explora-
tion for oil in southernmost Illinois near
the Kentucky-Illinois Fluorspar Mining
District indicates that rift valleys similarto
those in east Africa formed during Early
and Middle Cambrian time (570 to 523
million years ago). At this time plate
tectonic movements (slow global deform-
ation) were beginning to rip apart an Figure 1 Location of some major structures in the
ancient Precambrian supercontinent. Illinois region: (1) La Salle Anticlinal Belt, (2) Illinois
Ttihneensterbeugriioendarrifet vcaalllleedysthinetRhoeumgihdcCorne-ek vsBiaolsuleitnhD,woe(ms3e)t,Otzo(a6n)rokrCtiDhnecoaimnsenta,,tia(n4A)drcPRhao,sucagonlhdaC(Ar7r)ecehRk,eeG(l5rf)aoboNteansR,hif-t,
Graben and the Reelfoot Rift (fig. 1). west to east.
,
thicker
bed- small
major in lime- sandstone.
from from
u Sangamon
O clay; aquifers reserves; creviced
supplies supplies
O and and permeable
(/) coal
gravel
bottom shale,
gravel, valleys large and E3
ground-waterand ground-water a
River
Sand, sand\rock\ Clay: fractured stone, 2
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Figure 2 Unconsolidated deposits and bedrock in the Springfield-Decatur region (Bergstrom et al. 1976).
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Figure 2 continued
Fault, downthrown
side indicated
—
-4 Anticline
Syncllne
Monocline
oo»
40mi
50km
FIgur* 3 Structural features of Illinois (Treworgy 1981]