Mississippian

Burlington and Keokuk Limestones

Msl

Ms

Mw

Mbk

Om

Op

Ok

Od

St. Louis Limestone

Salem Limestone

Warsaw Shale

Maquoketa Formation

Plattin Limestone

Kimmswick Limestone

Decorah Formation

Unconformity

Ordovician

Valmeyeran

Mohawkian

Mfg

Unconformity

Cincinnatian

Fern Glen Formation

A A¢

503503

Line symbols are

solid where observed, dashed where inferred, dotted where concealed

Contact

Line of cross section

Syncline: direction of plunge indicated by arrows

Strike and dip of bedding: numberindicates degree of dip

Horizontal bedding

Water well:number indicates depth of boring (feet)

Oil well:number indicates depth of boring (feet)

Abandoned quarry

Data Type

Ord

ov

ician

un

differen

tiated O

u

Mbk &Mfg

Introduction Sand and GravelSand and gravel are available in the alluvial deposits of the

This map has been constructed by using several data sources. Field Mississippi River and talus from the toe of the bluff along the outcrops were the primary source of data for the upland areas above Mississippi River has been mined for construction fill material.the flood plain of the Mississippi River and boring records from the files of the Illinois State Geological Survey were the primary source Structural Geologyof data for the Mississippi River area. Only four borings reached bedrock in the Mississippi River bottomland area. Therefore the The major structural feature of the quadrangle is the Monroe City bedrock in the bottomland area has been projected and is subject to Syncline (Weller, 1939) which bisects the extreme northeast portion of change as new data is acquired. All Quaternary units have been the quadrangle. The Monroe City Syncline (Weller, 1939) is a gentle omitted from the map. northwesterly trending feature that parallels the west side of the

Valmeyer Anticline (Denny and Jacobson, in prep.). The bedrock dips The Kimmswick was formerly classified a subgroup of the Galena gently to the northeast throughout most of the quadrangle into the Group in Illinois. Missouri geologists recognize the Kimmswick as a Monroe City Syncline. Dips are generally less than 5 degrees. Formation and the type section is just across the Mississippi River near the town of Kimmswick Missouri. Nelson, Devera, and Masters References(1995) formally reclassified the Kimmswick subgroup as a formation “Kimmswick Limestone” for the southern Illinois region. Denny, F.B., and Jacobson, J. A., in prep., Geologic Map fo the

Valmeyer 7.5 Minute Quadrangle: Illinois State Geological Survey, Economic Geology IGQ Series, 1:24,000 scale.

Stone Nelson, W.J., Devera, J.A., Masters, J.M., 1995, Geology of the A few quarries once mined Mississippian limestones in the Jonesboro 15-Minute Quadrangle, southwestern Illinois; Illinois State quadrangle. Currently, none of these operations are active and they Geological Survey, Bulletin 101, 57 p.probably supplied a local supply of building and fill material.

Weller, J. M., 1939, Preliminary Geological Maps of the Pre-Oil Pennsylvanian Formations in Part of Southwestern Illinois: Illinois Two oil tests have been made in the quadrangle. Both of the wells State Geological Survey, Report of Investigations - NO.59, 15 p.drilled were dry holes.

Scale 1:24,0000

0

0 2,000 feet

2 kilometers

2 miles

NATIONAL GEODETIC VERTICAL DATUM OF 1929

Contour Interval 20 Feet

1 Herculaneum2 Valmeyer3 Waterloo4 Festus5 Renault6 Halifax7 Danby8 Bloomsdale

1 2 3

54

6 7 8

ADJOINING 7.5-MINUTE QUADRANGLES

7 8

Recommended CitationDenny, F.B. and Devera, J.A., 2002, Bedrock Geologic Map, Selma

Quadrangle (Illinois Portion), Monroe County, Illinois: Illinois State Geological Survey, Illinois Geological Quadrangle Map IGQ Selma-BG, 1:24,000.

George H. Ryan, Governor

Department of Natural ResourcesBrent Manning, DirectorILLINOIS STATE GEOLOGICAL SURVEYWilliam W. Shilts, ChiefIllinois Geologic Quadrangle Map: IGQ Selma-BG2002

MNGN

½

9 MILS1 40

30 MILS

UTM GRID AND 1996 MAGNETIC NORTHDECLINATION AT THE CENTER OF THE SHEET

ACKNOWLEDGMENTS

This map was significantly improved through review, suggestions, and comments by the following individuals: Dennis R. Kolata (ISGS) and Joseph A. Devera.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program.

BEDROCK GEOLOGIC MAP Selma Quadrangle (Illinois Portion),

Monroe County, Illinois

F. Brett Denny, and Joseph A. DeveraDraft #1 (August 08, 2002)Draft #1 (August 08, 2002)

For more information contact: ILLINOIS STATE GEOLOGICAL SURVEY 615 East Peabody Champaign Illinois 61820-6964 (217) 333-4747 http://www.isgs.uiuc.edu

Topographic Map produced by the United States Geological Survey

Selma QuadrangleBedrock Geologic Map

Monroe County, IllinoisIllinois Geological Quadrangle Map

IGQ Selma-BG, 1:24,000

A. St. Louis Limestone: limestone, siltstone, limestone Subsurface only (described from drill logs and reports).breccia, shale, and chert. Light gray to medium gray dense lime-mudstone with fossil wackestones. Part of the unit D. Burlington and Keokuk Limestone: limestone, chert, contains quartz sand and subangular limestone breccia clasts. siltstone, and shale. Light gray to white crinoidal grainstones Oolitic grainstones, greenish oncolitic packstones, peloidal dominate and are interbedded with nodular and bedded light grainstones, stromatolitic boundstones, and carbonate gray to black cherts. The cherts, which comprise at least 25 intraclastic conglomerates make up a highly variable mix of percent of the lowermost beds are white when weathered, and microfacies. Yellowish dolostone beds are also present in this some have bioclasts of crinoids and brachiopods. Sandy formation. Gray to dark gray chert occurs as nodules and limestones weather light brown, are cross-bedded, and contain stringers. Siltstones are calcareous and greenish. The shales brachiopod and crinoid molds. The unit is characterized by are greenish gray and reddish brown, calcareous, soft, and alternating layers of light gray to white crinoidal grainstones non-fissile. Acrocyathus floriformis, a colonial coral, occurs in with beds of argillaceous and sandy limestones. Large the upper part of the basal portion of this formation. A. spirifers are common along with crinoids, bryozoans, and floriformis is widespread near the base of the unit. The contact corals. Siltstones are dark gray with a greenish tint and are with the underlying unit is unconformable but difficult to calcareous. The unit is conformable with the underlying unit.identify due to lithologic similarities of the two units. The contact was placed 20 feet below the lower Acrocyathus E. Fern Glen Formation: limestone, siltstone, and shale. floriformis zone. Locally an erosional karstic surface can be Limestone is red to greenish gray, thin-bedded, and observed between these units. argillaceous; it contains small calcite geodes and crinoid

stems. Green and red shaly calcareous siltstones are B. Salem Limestone: limestone, dolomite, siltstone, and diagnostic. The cherts are greenish gray, nodular, and chert. Limestones are tan-brown to light gray and contain fossiliferous. The basal part is unconformable with the laminated tidallites, wackestones to grainstones composed of underlying formation.rounded and broken fossils and coated grains to gray lime-mudstones similar to the overlying St. Louis Limestone. F. Maquoketa Formation: dolostone, siltstone, mudstone. Bedding styles range from tabular to undulatory. Cross-beds This unit is poorly exposed and forms gentle hill slopes that are present in grainstone facies. The unit has a dirty gray- are well vegetated. The lower part of the formation is brown grainy appearance. The diagnostic character of this calcareous and grades upward into bluish green, thin formation is alternating beds of laminated, fine-grained calcareous siltstones interbedded with bluish gray mudstones. (calcisiltite) facies with coarse bioclastic, peloidal to oolitic The upper part is shaly buff-gray to greenish gray and has grains in shoaling-upward cycles. Dolomites are brown and interlaminated silts and shales. This unit is unconformable have moldic porosity. Cherts are light gray and may be with the underlying units. bioclastic and weather with a porous rind. Cherts occur between grainstones and laminated beds as elliptical nodules G. Kimmswick Limestone–Trenton Limestone in the containing concentric rings that spall off like egg shells when subsurface: limestone, dolostone, and minor shale. White to weathered. Siltstones are brown to light gray and thinly gray, coarsely crinoidal grainstone is the dominant facies in bedded, typically less than 1 inch thick. Oolitic beds are rare. this formation. Fossils include Receptaculites sp., Illaenus sp., The foraminifera, Fossil invertebrates include spiriferid and Isotelus gigas (trilobites), brachiopods, and gastropods that are productid brachiopods, rugose corals, conularids, and crinoids. commonly broken in the cross-bedded coarse bioclastics of the Ramose, fenestrate, encrusting, and bifoliate bryozoans are formation. Shales are calcareous and may contain pyrite. also present. The contact with the underlying unit is Cherts are not very common and are white with slight yellow gradational. tones. When cracked, the limestones have a faint petroliferous

odor. The basal contact is a distinct hardground omission C. Warsaw Shale: dolomitic limestone, siltstone, and surface.mudstone. Medium-gray, crinoidal, bryozoan wackestones and packstones that contain a few brachiopods. Dolomites are H. Decorah Formation: limestone and shale. Light gray-brown, thinly bedded, and contain chlorite-rich shale brownish to greenish limestone or lime mudstone interbedded clasts. The upper half of the unit is dominated by shaly with organic-rich reddish brown shales. The cherts are dark limestone and dolomite beds. The lower half contains bluish gray, and the dominant fossils are strophominid brachiopods.gray mudstones up to 20 feet thick interbedded with thin lime-mudstones. Conularids and gastropods occur in the shaly I. Plattin Limestone: limestone, dolostone, and shale. Light portion of this unit and brachiopods, spirifers, bryozoans, and brown to chocolate brown sublithographic limestone with echinoderms are very common in the limestones and alternating fossiliferous shales and sandy limestones near the dolomites. Siltstones are calcareous and fossiliferous and base. thinly bedded in the lower part. The basal contact is poorly exposed but thought to be sharp and conformable with the underlying carbonate beds.

GRAPHIC COLUMN

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fee

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DE

SC

RIP

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FORMATION

SE

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S

SY

ST

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Mis

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sip

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Va

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ran

Description

St. LouisLimestone

SalemLimestone

Warsaw Shale

Burlington-KeokukLimestones

MaquoketaFormation

KimmswickLimestone

DecorahFormation

PlattinLimestone

Ord

ovic

ian

Mo

ha

wkia

n

A

B

C

D

E

F

G

H

150 -200

120 -150

90 -110

100-150

+ 145

20-40

80-110

30-50

Cin

cin

na

tia

n

50-80

Fern GlenFormation

I

Acrocyathus floriformis Zone

MEMBER

OuMbk and Mfg

MwMs

Msl

MslMississippi River

400

200

800

600

Sea Level

Scale 1:24,000

2X Vertical Exaggeration

Elevation in feet

Looking northwest

400

200

800

600

Sea Level

Monroe City Syncline Monroe City Syncline Top of Bedrock

Quaternary Units

Bluff

Road

Railroad

A A’

Monroe C

ity

Syncline

Monroe C

ity

Syncline

A

A’3

5

file: selBG2.cdrexport file: selBG2.eps

195

45

38

58

105

60

665

43

490

64

MslMs

Mw

Ms

Msl

Ms

Ms

Mw

Ms

Mw MsMs

Mbk &Mfg

Ou