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BEDROCK GEOLOGY OF MOUNT MORRIS QUADRANGLE

Prairie Research Institute OGLE COUNTY, STATEMAP Mount Morris-BG ILLINOIS STATE GEOLOGICAL SURVEY Mary J. Seid 2011 R. 9 E. R. 10 E. R.

198 ϫ 50 800 Op 7 487 e" 722 Q e" Op 850 715 Og BM ϫ 750 850 125 e" 702 727 S e" 715 ϫ700 ϫ Q e" 200 737 Æ 710 ϫ ϫ ϫ715 Q S 325 800 Op 774 750 ϫBM 886 ϫ e" 750 ϫ Q 750 Op

34 o 31 32 33 35 36 31 Op 1 779 AЈ ϫ 70 800 0 e"50 155 7 800 245 e" Q 786 ϫ 800 Q 750 165 T. 25 N.

165 265 170 190 e" 800 þ e" e" e" e"

285 265 165 799 764 691

ü e" 168 797 ϫ T. 24 N. e" ü ϫ ^þ 779 e" ϫ 165 ^ S 250 e" ϫ T. 25 N. þþ ϫ e" e e" 899 833 766 850 844 ϫ 150 ϫ 144 ϫ ϫ e" 700 T. 24 N. BM e" 800 825 900 180 200 145 ϫ 850 Se" e"195 e" ϫ858 Og Op 800 e" S 184 Op S e" 175 800 e" 835 800 ϫ 750 ϫ705

800 e" 200 700

255 220 330 e" 245 205 e" 850 Æ e" 2 e" 776 732 250 6 e" 5 SG 184 4 3 1 ϫ ϫ 6 e" 817 eÄ 822 800 e" ϫ 892 815 ϫ 238 855 114 ϫ 779 ϫ Æ e" ϫ 800 ϫ e"

85 0 800 Op 864 75 EXPLANATION ϫ 0 850

864 ϫ 830 8 850 ϫ 00 305 ϫ828 e" 225 900 e" 787 Q Cahokia Formation 850 ϫ ϫ817 820 800 Peoria Silt 902 891 ϫ871 840 ϫ Æ 873 ϫ90 ϫ 8 ϫ 889 846 ϫ 912 0 50 and 899 909 ϫ ϫ ϫ Quaternary Equality Formation ϫ ϫ 900 ϫ904 8 Roxana Silt 909 5 ϫ 343 0 S 280 e" 864 235e" e" e"135 ϫ Pearl Formation ϫ914 195 850 Æ e" 900 e" Glasford Formation Og 904 150 900 ϫ 850 900 Æ 9

00 Unconformity Q e"145 Q Æ 70

9 e" 820 Og

7 8 208 280 10 11 871 170 e"ϫ 12 820 7 Æ Wise Lake Formation

e" e" ϫ "e150 850 ϫ

906 S ϫ Q 909 þ ü 927 919 ϫ ϫ þ 902 ϫ914 ϫ ϫ e" 160 S 195 ^ ϫ e" 3 260 800 Guttenberg Formation e" 325 Æo e" e" 175 e" 215 900 ϫ799 Platteville Group ϫ761 Op 800 Quimbys Mill Formation 230 750 e" 750 Nachusa Formation Op ϫ Mohawkian 900 Grand Detour Formation 850 750 751 Mifflin Formation 900 820 897 853 ϫ ϫ 928 912 ϫ ϫ Pecatonica Formation 910 899 915 ϫ ϫ 290 886 904 ϫ 899 ϫ ϫ e" ϫ ϫ S 80 ϫ Unconformity e" 892 ϫ907 ϫ 800 900 Og Ancell Group e"339 e" 320 Oa e" 120 Se" 93 St. Peter Sandstone 800 ϫ815 900 Unconformity ϫ919 900 796 ϫ814 18 17 16 15 14 902 13 ϫ 932 917 ϫ 18 Os Ibexian 912 ϫ ϫ 899 ϫ871 ϫ ϫ894 ϫ BM 850 ϫ874 130 950 e" ϫ879 Æ 900 Og

Q 850 Æ 220 900 365 e" 900 208 e" e" 900 ϫ797 e 910 876 878 250 S ϫ 879 891 ϫ ϫ e" e" 275 Æ 876 ϫ ϫ 107 195 e" 858 ϫ858 ϫ e" ϫ k" 117 208 155 k" e" 850 850

800 U ϫ828 D 850 k" 330 Symbols 900 e" 95 ϫ881 e" 145 24 884 147 846 ϫ 19 20 21 e" 22 Og 23 851 ϫ830 ϫ 19 40 Strike and dip of bedding; number S 126 S 212 876 876 ϫ889 919 ϫ k" 848e" ϫ842 ϫ ϫ ϫ indicates degree of dip 891 ϫ822 ϫ ϫ D 850 Op U Se" 170 Horizontal bedding o12 200 CG U k" k" 335 900 Vertical joint D Se"348 e"165 k" 51 0 850 Inclined joint; box on down–dip side; number D 85 0 Q 874 85 U S 00 indicates degree of dip e"150 e" 919 879 902 9 ϫ 884 MT. 894 300 ϫ Æ ϫ ϫ 850 ϫ 897 825 ϫ ϫ MO 866 ϫ Oa ϫ ϫ 906 Æ RRIS ϫ Abandoned pit or quarry S 1353 900 STRUC k" 850 S 243 D 9 145 904 00 e" Og k" ϫ U 887 S k"1434 ϫ TURE 900 Op 0 Drill Holes D 0 Og 9 90 U S 1425 from which subsurface data were obtained 0 k"

850 85

290 320 0 837 36 914e" e" 832 837

ϫ 906 856 ϫ 335 ϫ ϫ e"

e" S 909 88 909 ϫ ϫ e" Stratigraphic boring

899 ϫ ϫe" o

814 846 856 ϫ e" 335 e 30 0

863 853 ϫ 85 ϫ 288 325 25 o 151 Â ϫ e" 7 ^ o ϫ 330 þ

ϫ e" e" ü e" 245 275 U 278 27 26 e" CLINE üþþ 315 N G 85 3 ^ e" e" 28 S e" 300 SY 8 5 e" Water well 0 Âo 78 e" 30 29 D e" Op 900 120 e" e" 125 þ 0 o

S 125 S 248 e" 300 e" Og EEK e" 2 5

k" 500 S 80 MUD CR oH7 5 e e" 0 7 o K o 8

D 85 REE FAULT

C 800 G 4 e"

800 10 D 9 o 750

85 U MU 27 25 Engineering boring

0 Oa o H 7

S 105 13 þ o

D 265 ü ^ Æ 28 U þ 828 9 Â ^ þ S 107 e" þ ü e" 9 ϫ ^ þ e" S 100 5 D 15 2 ü e"275 oo ^

S 65 o o Labels indicate samples (S), geophysical log (G), or core (C).

ü e" o þ

S U o 4 þþ e" e"

Æ 255 255 Se"305 5 50 290 850 SGC 125 e o Ä

e e" 305 e" k" Numeric label indicates total depth of boring in feet. e" 60 e" 851 2 3 Ä þ e" ü 264 4 4 þ o ϫ ^ 863 e" e" 899 ^ 919 o ϫ o

ü ϫ 130 899 100 o Dot indicates location accurate within 100 feet. 00 879 ϫ 65 o e" ϫ 150

þþ 8 838 ϫ860 ϫ e" 298 3 820 817 ϫ 8 906 o 4

ϫ ϫ 50 225 240 ϫ e" e" 2

e" e" S 245 o o S 234 160 e" þ U e" ^ü ^ þ þ D ü 8 90 0 850 0 þ 0 ϫ906 Line Symbols 255 e" 90 dashed where inferred, dotted where concealed 0 S 270 912e" Og ϫ 335 800 Og 920 e" ϫ ϫ928 ϫ927 Contact S 306 ϫ791 e"

31 32 S 105 33 31 240 34 35 36 94 S 85 G 320 800 e" 90 906 876 0 919 902 907 e" e" e" H G e" 85 e" 319 e" 909 912 ϫ ϫ ϫ Syncline; direction of plunge indicated by arrow 0 866 ϫ ϫ ϫ ϫ 210 ϫ833 ϫ e" 184 305 90 e" 0 Op S 86 170 S 267 Fault; unknown displacement ϫ833 e" e" e" ^ e Âü 88 U þþ 340 Fault; U on upthrown side, D on downthrown side

850 0 D

e" S0 335 9 e"

 9

Â86 879 00 Line of cross section

160 8 ϫ

 e 00 3 A AЈ

200e" Ä e" 36

245 Ä 11 S 85 S 155 C e" 853 874 T. 24 N. 150 e" e" 891 þü ϫ Ä Æ þ ϫ o 899 889

ee" ϫ ^ 76 909 ϫ ϫ 82 9 T. 23 N.

T. 24 N. 260 797 840 265 ϫ o 8 ϫ ϫ e" Note: Well and boring records are on file at the ISGS Geological

771 200 4 Âo 27 855 825 e" ϫ e" Â þ e o 848 ϫ o ϫ ^ü 275 o ϫ þ 5 o T. 23 N. e

^ þ e" 0 155 S 165 10 225 850 e" 8 e" Records Unit and are available online from the ISGS Web site. ü 80 e" e" e" e" 350 7 80060 295 þ 300 o e" e" 236 o

80 5 0 o 80 2 Ä 0 85

850 Æ o e Op 305 e" Og 850 Oa

ϫ833 Op

Og

e 919 897

e" 335 835 858 886 ϫ ϫ 405 þ ϫ e" 850 ^ü ϫ ϫ

^ þ þ 0 ü 75 8 275 00 þ 290 e" 260 e"

Ä e 0 e"

828 85 797 Oa

ϫ 800 Q ϫ 776 245e" ^þü S 270 Æ Æ ? ϫ o ^ þ e" Oa U

Æ ü o11o

871 Æ e 7 þþ ϫ 8 D GALE 50

823 810 833 Æ 245 ϫ ϫ ϫ o 1 Op Ä 265 o 200 e" 290 o e" e C 4 Os e" 82 e" Â REEK STR 199 254 e 282 e" e" 5 10 838 858 260 e" e" 210 S e ϫ ϫ 864 e" 906 e" 260 150 ϫ 868 29090 ϫ 320 230 6 e"5140 4 e" 3 e" BM ϫ e" 0900 1 6 e" ϫ833 2 80 884 0 UC 0 869 80 846 ϫ ϫe" 853 80 840e" 205 T 0 ϫ S 217 ϫ e" 265 ϫ URE Q 0 Æ 5 S 110 8 e" ? 0 Op 85 5 3 8 0 o Q S 183 298 e" 833 810 e" 853 850 820 S 812 830 ϫ ϫ ϫ 275

ϫ e" ϫ 764 ϫ 778 e" 192 ϫ 750 800 ϫ e e" 810

75 8 230 275 5 Oa 8 135 ϫ

e" 0 e" e" 230 50 Oa

A o e e" 205 e"

801

Ä

o ϫ e 0

12 1 S 75 þ 185

^ü 2 þ o e" 8

^ þ e Op Og U

ü 0

0 Æ þ D þ Og ü

Og ^ þ 205 Æ ^

850 e ü e"

þþ Op Op

e p U O 185

850 8 þ ^

0 ü

0 þ e"80 D

^ þ e 0 8 e

ü Ä 50

þ þ ^þü 850

^ þ þ

þ 851 ü 787 832

801 ^ þ ü 782 ϫ ? e" 833 817 þü^ ϫ 845 837 778 ϫ ^ þ þ ϫ 817 ϫ 95 ϫ ϫ ϫ ϫ ü o ϫ 250 800260 þ o o e ϫ 859 e" 8 87 233 850 ϫ e" 0 e 80 367

0 e" e"

800 0 3 þþ^ e" 98 þü^ S 115 e" S 450 3 e"175 üþ e" Og 7 8 e" 9 750 10 6 11 12 7 Oa e" 7 5 Æ Q 80 100 0 130 280 160 e" 0 0 e" 0 e" e" 273 80 80 R. 9 E. R. 10 E. R.

Base map compiled by Illinois State Geological Survey from digital data (2009 TIGER/Line SCALE 1:24,000 Geology based on field work by M. Seid, 2010–2011. Shapefiles) provided by the United States Census Bureau. 1 1/ 2 0 1 MILE Digital cartography by J. Domier and G. Woods, Illinois State Geological Survey. 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET North American Datum of 1983 (NAD 83) Projection: Transverse Mercator 1 .5 0 1 KILOMETER This research was supported in part by the U.S. Geological Survey National Cooperative 10,000-foot ticks: Illinois State Plane Coordinate system, west zone (Transverse Mercator) Geologic Mapping Program (STATEMAP) under USGS award number G10AC00418. The 1,000-meter ticks: Universal Transverse Mercator grid system, zone 16 views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, BASE MAP CONTOUR INTERVAL 10 FEET of the U.S. Government. Recommended citation: NATIONAL GEODETIC VERTICAL DATUM OF 1929 Seid, M.J., 2011, Bedrock Geology of Mount Morris Quadrangle, Ogle County, Illinois: Il- This map has not undergone the formal Illinois Geologic Quadrangle map review pro- linois State Geological Survey, USGS-STATEMAP contract report, 2 sheets, 1:24,000. cess. Whether or when this map will be formally reviewed and published depends on the resources and priorities of the ISGS. © 2011 University of Illinois Board of Trustees. All rights reserved. For permission information, contact the Illinois State Geological Survey. The Illinois State Geological Survey and the University of Illinois make no guarantee, expressed or implied, regarding the correctness of the interpretations presented in this document and accept no liability for the consequences of decisions made by others on the basis of the information presented here. The geologic interpretations are based on data that may vary with respect to accuracy of geographic location, the type and quantity of data available at each location, and the scientific and technical qualifications of the data sources. Maps or cross sections in this document are not meant to be enlarged.

2° ROAD CLASSIFICATION ADJOINING 1 2 3 QUADRANGLES NORT MAGNETIC 1 Forreston North NORTH TRUE Primary highway, Light-duty road, hard or 2 German Valley hard surface improved surface 3 Seward 4 5 Secondary highway, 4 Forreston South hard surface Unimproved road 5 Oregon

Prairie Research Institute H 6 Polo Illinois State Geological Survey 6 7 8 7 Grand Detour 615 East Peabody Drive 8 Daysville APPROXIMATE MEAN State Route Champaign, Illinois 61820-6964 DECLINATION, 2011 (217) 244-2414 http://www.isgs.illinois.edu

STATEMAP Mount Morris-BG Sheet 1 of 2 A Cahokia Formation, Peoria Silt, Equality Formation, Roxana Silt, Guttenberg interval. Guttenberg is exposed in the west bank of a west- this boundary. In the MM #1 core, dolomite recrystallization, steeply dip- GAMMA SCALE THICKNESS Pearl Formation, and Glasford Formation Sand, silt, gravel, clay, and southwestward flowing tributary to Pine Creek (100’WL, 3300’NL, Sec. ping fractures, and extensive burrowing occurs in a four-foot-thick section FORMATION

FORMATION GRAPHIC COLUMN (feet) ISGS MM #1 (feet) (feet) diamicton. Sand is tan to brown, fine to medium-grained, poorly sorted, 3, T. 23 N., R. 9 E.) and in the west bank of a southward flowing tributary in the middle of the formation. The lower one foot of the Pecatonica con-

GROUP

UNIT SYSTEM

GROUP

SERIES THICKNESS

SYSTEM friable, weakly to well-stratified, and occurs in floodplains and main to Pine Creek (1600’WL, 300’NL, Sec. 11, T. 23 N., R. 9 E.). The basal tains abundant fine to medium well-rounded sand grains (St. Peter-type) tributary valleys (Cahokia Formation). Silt is gray to brown, occurs as a contact is gradational with the Quimbys Mill below. and phosphatic grains (MM #1 core; Templeton 1951). Slightly pyritic in 0 HOLOCENE Cahokia, Peoria Silt, windblown sediment on hillslopes and as alluvium in floodplains (Cahokia basal one foot. Basal contact is sharp and scoured. QUATER- AND Equality, Roxana Silt, Fm. and Peoria Silt). Recent gravel occurs in the floodplains of major riv- E Quimbys Mill Formation Dolomudstone and chert. Light brown- NARY 0–40 A PLEISTO- Pearl, Glasford ers (Cahokia Fm.); older gravel and sand deposits occur on uplands and ish gray (2.5Y 6/2 wet) when fresh, yellow (2.5Y 7/6) when weathered, J Glenwood Formation Sandstone and shale. In the MM #1 core, 30’ CENE at high elevations in high in tributary valleys (Pearl Formation). Recent mottled with medium gray dolomudstone in places because of infilling of sandstone is white, quartz arenite, fine to medium grained, well rounded, 20.0

clay occurs in floodplains of major drainages (Cahokia Fm.); older clay burrows, abundant bands and smooth nodules of cherty dolomudstone, well sorted, frosted (St. Peter-type). Shale is greenish gray (5G 6/1 wet), QUATERNARY occurs above modern floodplain elevation but beneath the Cahokia Fm. bioturbated, becomes slightly shaly downward (MM #1 gamma log). Beds silty, occurs in uppermost one foot; the remainder of the interval is sand- Wise Lake at low elevations in the tributaries to major rivers. Diamicton is sandy and are thin and tabular. The characteristic feature of the Quimbys Mill is that stone with interstitial greenish gray clay. The Glenwood interval contains 0–70 B silty, tan to gray-brown, and discontinuously interstratified with sand and it fractures with smooth, curved surfaces; it is called “the glassrock” in the moderate pyrite. In outcrop, the greenish gray Harmony Hill Shale at the Wise Lake 24 40.0 Shell gravel. Base of the unit is unconformable on the Galena below. Mississippi Valley zinc-lead mining district. Fauna is not abundant but can top weathers to dusky red (2.5YR 3/2) and is fissile to wavy bedded. The casing 0–45 include Öpikina and Streptelasma; Chondrites is a common trace fossil Glenwood is characterized by abrupt lateral changes in lithology, and in Gastropod B Wise Lake Formation Dolomite. Light gray (10YR 7/2 wet) to light in the middle of the unit. In general, the top of the unit is ferruginous and some places it is absent. It is exposed in the south cutbank of an east Bentonite brownish gray (2.5Y 6/2) on fresh surface, weathers light yellowish brown is capped by a prominent hardground omission surface. Quimbys Mill is flowing tributary to Gale Creek (750’EL, 2800’SL, Sec. 1, T. 23 N., R. 9 60.0 Fisherites (10YR 6/4); pure grainstone, contains no chert, but locally contains exposed in the stream bed of a narrow east-southeast flowing tributary E.) and on the south bank of an eastward flowing portion of Gale Creek (Receptaculites) scattered light greenish gray clay (in ISGS corehole MM#1). Finely to to Pine Creek (1650’WL, 1000’SL, Sec. 2, T. 23 N., R. 9 E.) and on the (800’EL, 4050’N of the same section). The best exposure of Glenwood, medium crystalline, “sandy” texture, thin to medium bedded, bioturbated, northwest cutbank of a S 20° W flowing tributary to Pine Creek (200’EL, however, is in a St. Peter quarry about four miles southeast of Mt. Morris. 0–200 Galena knobby on weathered face. include the brachiopod Rafinesquina; 2000’SL, Sec. 4, T. 23 N., R. 9 E.). Very shaly at base; sharp but conform- The basal contact was observed in this quarry face and showed a sharp 80.0 Dunleith C gastropods Hormotoma and Liospira; coral Streptelasma; trilobite Il- able contact with the Nachusa below. angular unconformity with the St. Peter below, but in the MM #1 core, the laenus; and blue-green algae Fisherites (Receptaculites). A 2-inch thick basal Kingdom Sandstone Member is gradational with the St. Peter below. Hardground 125–130 shale (K-bentonite bed) at the base of the Wise Lake in the ISGS MM F Nachusa Formation Dolomudstone. Light brownish gray (10YR 6/2 omission surface #1 core probably correlates with the Dygerts Bentonite bed of Willman wet), relatively pure dolomite, some voids filled with very fine-grained K St. Peter Sandstone Sandstone and chert. Sandstone is white, and Kolata (1978) because no chert is present above this bentonite bed. crystalline dolomite, very thin very dark brown (10YR 2/2) shaly partings quartz arenite, fine to medium grained, well rounded, well sorted, frosted, 100.0 The Wise Lake occurs in the western part of the study area and on the occur sparsely, bioturbated, sparse fossil molds. Thin bedded, but bed- and well-indurated to friable. Cross bedded to thinly laminated within mas- 151

downdropped northeast side of the Mount Morris uplift. The upper 13 feet ding is indistinct in places. In the MM #1 core, four white chert beds occur sive beds. It weathers to white sand and forms broad hills in most of its Galena Guttenberg 0–4 D of the Victory School section (1750’EL, 700’SL, Sec. 32, T. 24 N., R. 9 E.) in the upper 9 feet of the unit; otherwise the unit is non-cherty. Chert is outcrop area; but where overlain by the Glenwood and Platteville Group Dunleith 127 of Willman and Kolata (1978) is Wise Lake. The basal contact is sharp but less abundant in the Nachusa than in the overlying Quimbys Mill. Fos- dolomites, it is a low bluff-former and contains small sapping alcoves. 120.0 conformable with the Dunleith. sils are generally moderately abundant in the lower part and include the The upper 30 feet contains green streaks along bedding planes; the color Quimbys Mill 10–12 E tabulate coral Foerstephyllum and the trace fossils Palaeophycus and seems to stain the exterior of the grains. The basal Kress Member is C Dunleith Formation Dolomite. In the MM #1 core, the upper part is Chondrites. The upper contact with the overlying Quimbys Mill is sharp present in a City of Oregon water well about two miles east of the study light yellowish brown (10YR 6/4 wet), finely to medium crystalline, “sandy” but conformable. The lower contact is gradational with the Grand Detour area (Sample Set 64615, Sec. 3, T. 23 N., R. 10 E.); it contains 78 feet 140.0 Nachusa 15–19 F texture, pure grainstone, intensely dolomitized, bioturbated, vuggy; it below. of chalky, white chert, which has been weathered to tripoli; it is oolitic in contains a few bedding-parallel shale partings and white to light gray part, and contains sandy, reddish brown shale. The Kress Member is not fossiliferous chert in nodules or 1-inch-thick beds. The lower part is light G Grand Detour Formation Dolomudstone and shale. In the MM #1 present everywhere and was not observed in outcrop within the study brownish gray (2.5Y 6/2 wet), contains thin wavy shaly partings, mul- core, dolomudstone is light brownish gray (10YR 6/2 wet); upper part is area. The St. Peter is penetrated, in some places, by thin (mm-scale) 160.0 tiple hardground surfaces, no chert, and is bioturbated. The lower part is more argillaceous than lower part (see MM #1 gamma log), and beds are white silicified “deformation band shear zones” (this type of strain localiza-

Grand Detour 34–42 G darker gray, more argillaceous, and less weathered than the upper part. In thin but indistinct. The upper part is identical to the Nachusa. The middle tion feature is discussed in Fossen et al. 2007) that cut at various angles MOHAWKIAN ORDOVICIAN outcrop, it appears massively bedded, but when examined closely, mas- part (Forreston or Stillman Member?) contains an intraformational con- to bedding. These cataclastic deformation bands are present in close sive beds are composed of several thin, wavy, indistinct beds, and some glomerate (collapse zone) where bedding is contorted, abundant pyrite proximity to inferred faults, and are identical to those observed in quartz 180.0 beds are separated by thin, carbonaceous greenish shale partings. The surrounds rounded dolomudstone clasts, and very thin very dark brown arenites in the Ste. Genevieve Fault Zone (southern Illinois) and Laramide Guttenberg 4 lower 36 feet of the Victory School section of Willman and Kolata (1978; shaly partings are common. A few feet above the collapse zone, bedding monoclines of the Colorado Plateau (Tindall and Davis 1999). The lower 1750’EL, 700’SL, Sec. 32, T. 24 N., R. 9 E.) as well as the bluffs of Pine dips 25°. The lower 13 feet is very cherty overall, bioturbated, contains contact is sharp, unconformable, and scoured into several older forma- Quimbys Mill 12

114–119 ORDOVICIAN Platteville Creek are Dunleith. Moldic porosity can occur on fresh faces; a pitted sur- few sparse fossil fragments, and dark brown shale partings become more tions as a result of pre-St. Peter uplift and erosion; the unconformity has 200.0 Mifflin 18 H face, or beehive weathering, commonly occurs on weathered faces. Light common downward. One foot from the base, sphalerite is present in a considerable local relief. gray to white chert occurs in flat slabs or lenses; the chert can be irregu- small vug. The fauna is reported to be abundant and diverse, including Nachusa 19 larly scattered throughout or form well-defined layers. A few Fisherites the solitary rugose coral Streptelasma, the rhombiferan cystoids Corono- L Shakopee Dolomite Dolomite, sandstone and shale. Dolomite is (Receptaculites) zones occur within the formation; the calcareous algae cystis durandensis, the lithistid sponges Anthaspidella and Zittelella, and light yellowish brown (10YR 6/4) on fresh surface, dark brown on weath- Fisherites is an index fossil of the Galena and does not occur in the Plat- the trace fossils Palaeophycus and Buthotrephis (Chondrites). Hundreds ered surface, very finely crystalline, hard, and breaks with a conchoidal 220.0 teville Group. Where Fisherites cannot be identified in the field or in core of horn corals can be concentrated on the shaly horizons (Kolata, person- to hackly fracture; contains moderately abundant sand (St. Peter-type), samples, the crystalline texture is characteristic and is the key to telling al communication). Lower contact is gradational with the Mifflin below. which is mostly medium grained with a few coarse grains, well-rounded, Grand Detour 34 Pecatonica 32 I it apart from the formations of the Platteville Group. Several K-bentonite and frosted. Thin, medium, and thick lenticular beds occur; bedding beds that are one-inch-thick or less have been identified from the Dunleith H Mifflin Formation Dolowackestone. In the MM #1 core, the Mifflin is surfaces vary from rough and hummocky to smooth and flat, show mud-

115 240.0 (Willman and Kolata 1978). Stylolites and hardground omission surfaces dolowackestone, mottled light brownish gray with medium gray, frequent cracks or ripple-marks, and are partly coated with films of green clay. occur locally at the basal contact, but the two formations otherwise ap- gray (10YR 5/1) wavy shale partings, bioturbated, contains fossiliferous Sandstone is brownish yellow (10YR 6/8) to bluish gray (5B 6/1), St. Platteville pear to be conformable. layers, thin to very thin wavy bedded, and mudcracks occur. The unit is Peter-type sandstone with dolomite or chert cement; bedding occurs in Harmony Hill Sh the most shale-rich formation in the Platteville (Kolata, personal com- various forms—indistinct, cross bedded, graded bedded, ripple-marked, Mifflin 18 260.0 Loughridge Ss D Guttenberg Formation Dolomite and shale. In the MM #1 core, dolo- munication). The Mifflin is locally very fossiliferous and contains various to stratified, thin bedded. Shale is light greenish gray (5G 7/1) to maroon, Daysville Dol 0–28 J mite is reddish brown (5YR 5/3), very fine grained, interbedded with dark well-preserved bryozoans, brachiopods, bivalves, gastropods, ostracodes, silty in part, and is thinly laminated. The unit is stained with manganese Kingdom Ss reddish brown (5YR 3/2) shale; it is very fossiliferous, and pyrite crystals and trilobite fragments. In the MM #1 core, the upper contact is marked by and iron in vugs and cracks. Algal stromatolite domes (Cryptozoon min- Glenwood in vugs are abundant in the lower 2 feet. In outcrop, the shale weathers a 1-inch-thick mature grainstone bed, but in some places, the upper part nesotense) occur on the order of one foot wide in the region, but none 280.0 to light gray to light greenish gray “gummy” clay, the shale bedding is very contains a prominent hardground omission surface and a 6-inch-thick bed were identified in the study area. Templeton (ISGS field notes) identified Pecatonica 32 wavy and contorted, coalesces into thick bands, and the interval contains of shaly dolomite or limestone. The basal contact is sharp and scoured low-spired, loosely-coiled gastropods, occasional pelecypods, and few

Ancell white “egg-like”, flat chert lenses. Fossils are generally abundant; stropho- with the Pecatonica below. brachiopods in the Gale Creek outcrop (location noted below). Only the 120–280 St. Peter K menid brachiopods are the most conspicuous and ubiquitous, including upper part of the formation is exposed in the quadrangle; an outcrop and the brachiopods Sowerbyella punctostriata and to a lesser extent Rafin- abandoned quarry exposes 35 feet of Shakopee (about 100’ southeast of 300.0

110–250 esquina trentonensis. The Elkport and Dickeyville K-bentonite Beds have I Pecatonica Formation Dolograinstone and dolomudstone. Light Oregon Trail Rd., 30’ northeast of Gale Creek, 1700’WL, 3700’NL, Sec. been identified in the Guttenberg (Kolata et al. 1986). The Guttenberg brownish gray dolograinstone mottled with dark brownish gray dolomud- 6, T. 23 N., R. 10 E.). The base of the formation is not exposed within the Glenwood 24 forms a re-entrant in weathered quarry or outcrop exposures; it can be stone, thin to very thin wavy bedded, less shaly and less fossiliferous than quadrangle, but stratigraphic relations in the adjacent Oregon Quadrangle

absent or extremely thinned from solution of the limestone within the for- the overlying Mifflin, bioturbated, vuggy. The top is marked by a pyritized (Seid 2010) suggest that the Shakopee either rests conformably on the 36+ 320.0 Prairie mation. The high shale content can make this a useful horizon for electric hardground omission surface (represents submarine chemical erosion of New Richmond and/or Oneota Formations or is separated from them by Ancell IBEXIAN du Shakopee 40+ L log correlation, but the MM #1 gamma log did not show a shale kick in the the carbonate sea floor), and fossil content decreases dramatically below only a minor unconformity (Templeton 1951). St. Peter 12+ Total Depth Chien 335 feet

Figure 1 Gamma log of ISGS MM #1 borehole.

Introduction Galena Groups. 1976, Bunker et al. 1985). Within the quadrangle, the bedrock is folded, broken, basement, like other major faults in the Midcontinent USA (Duchek et al. 2004, p. 1465–1484, doi: 10.1130/B25413.1. and sheared along several faults and folds in the study area—the Mount Morris McBride 1998, McBride and Nelson 1999). The stratigraphic relationships within Finney, S.C., and M.H. Nitecki, 1979, Fisherites n. gen. reticulatus (Owen, 1844), The Mount Morris 7.5-minute Quadrangle is located in north-central Illinois in The MM #1 core hole provided much information about the stratigraphy from structure; the Mud Creek fault and associated Mud Creek syncline; and the Gale the Oregon, Grand Detour and Mount Morris Quadrangles indicate tectonic activ- a new name for Receptaculites oweni Hall, 1861: Journal of Paleontology, the west-central part of Ogle County, Illinois, about 25 miles southwest of Rock- the Wise Lake Formation (Galena Group) down to the upper part of the St. Peter Creek structure. ity during the following times: 1) post-Shakopee, pre-St. Peter, 2) post-St. Peter, Vol. 53, No. 3, pp. 750–753. ford, 40 miles south of the Illinois-Wisconsin border, 85 miles northeast of the Sandstone (Ancell Group). pre-Glenwood, and 3) post-Galena, pre-Pleistocene. The structures in the study Flint, R.J., A.C. Bevan, and J.H. Bretz, 1931, Road materials resources of Ogle Quad Cities and 115 miles west of Chicago. It covers a 55 square mile area that Mount Morris Structure area are probably genetically related to multiple movements on the nearby Sand- County: Available from Illinois State Geological Survey Map Room, 4103.03 is bounded by 42° 00’ 00” and 42° 07’ 30” North latitude and 89° 22’ 30” and The oldest bedrock that outcrops at the surface in the quadrangle is the Shakopee Examination of water wells revealed an uplifted block or dome of St. Peter Sand- wich and Plum River fault zones. i5.4-2. 89° 30’ 00” West longitude. The Mount Morris 7.5-minute Quadrangle occupies Dolomite, which is assigned to the Prairie du Chien Group. Only the upper 35 stone in the town of Mount Morris. The structure is defined by four water wells the southwest quarter of the Oregon 15-minute Quadrangle. It is bordered by feet is exposed in the quadrangle, but it probably reaches a maximum thickness which reach St. Peter Sandstone just below surficial sediments. The wells require Future Research Questions Fossen, H., R.A. Schultz, Z.K. Shipton, and K. Mair, 2007, Deformation bands in eight 7.5-minute quadrangles, clockwise from top-left: Forreston North, German of 80 feet. The Shakopee is composed mainly of dolomite, but locally it contains that the uplifted block is elongated in the northwest-southeast direction. The Geologic mapping of the Mount Morris, Oregon, and Grand Detour quadrangles sandstone: a review, Journal of the Geological Society, v. 164, pp. 755–769. Valley, Seward, Oregon, Daysville, Grand Detour, Polo, and Forreston South. All sandstone, shale and chert. The only outcrop in the study area is an abandoned amount of displacement is between 100 and 250 feet, with the highest point in indicate that several fault-bounded blocks of upthrown older strata occur. In map Hansel, A.K., and W.H. Johnson, 1996, Wedron and Mason Groups: Lithostrati- of the stream drainages within the quadrangle flow toward the Rock River. The quarry 1,700 feet from the west line, and 3,700 feet from the north line of Sec. SW¼ NW¼ Sec. 27, T24N, R9E. This trend follows a small dome that Templeton view, the strike of these faults is oblique to the Sandwich and Plum River fault graphic reclassification of deposits of the Wisconsin Episode, Lake Michigan quadrangle lies within the Rock River Hill Country of the Central Lowland Prov- 6, T23N, R10E, where 35 feet of Shakopee is overlain by St. Peter Sandstone and Willman (1952) depicted along the axis of the Oregon Anticline. The Mount zones. The fault trends suggest that the upthrown blocks were uplifted as a result Lobe: Illinois State Geological Survey, Bulletin 104, 116 p. ince. Agricultural, commercial, industrial, and residential developments currently (Templeton 1942). About 200 feet to the south of the abandoned quarry, there is a Morris structure is in line with uplifted fault blocks of Shakopee (Prairie du of strike-slip motion on the Sandwich and Plum River structures. The faults and Kolata, D.R., 2011, Bedrock geology of Grand Detour Quadrangle, Ogle and drive the region’s economy. small Shakopee exposure on the east side of Gale Creek. The extent of the Shako- Chien) and a large outcrop area of thick St. Peter Sandstone (containing Devils folds in central and southern Ogle County therefore represent an en echelon array Lee Counties, Illinois: Illinois State Geological Survey, USGS-STATEMAP pee in the study area is poorly constrained, and the mapped occurrence to the east Backbone and Castle Rock State Park to the south in the Grand Detour Quad- of faults situated within a three-mile-wide step-over zone between the mapped contract report, 2 sheets, 1:24,000. Portions of this area were previously mapped by Bevan (1924) and Templeton in the Oregon Quadrangle is based solely on these two closely spaced exposures rangle, Kolata 2011). extent of the Sandwich and Plum River fault zones. Marshak et al. (2003, p. (1940) but remain unpublished. The bedrock geology of the adjacent Oregon and in the Mount Morris Quadrangle. The outcrop area of the Shakopee defines the 171) also proposed strike-slip movements on the Sandwich and Plum River fault Kolata, D.R., and T.C. Buschbach, 1976, Plum River Fault Zone of northwestern Grand Detour 7.5-minute quadrangles are published by Seid (2010) and Kolata northwesternmost extent of the Oregon Anticline (Bevan 1939) and is probably Mud Creek Fault zones, and Duchek et al. (2004) documented oblique-slip movement with as Illinois: Illinois State Geological Survey, Circular 491, 20 p. (2011). a pop-up structure related to the Sandwich Fault Zone (Kolata et al. 1978). The The Mud Creek fault zone (Templeton and Willman 1952) trends roughly east- much as 300 m of strike-slip displacement on another Midcontinent USA struc- Kolata, D.R., T.C. Buschbach, and J.D. Treworgy, 1978, The Sandwich Fault Zone contact between the Shakopee and the St. Peter Sandstone is an erosional uncon- west along Mud Creek, is roughly 1000’ wide and 3 miles long (from center ture, the Cottage Grove fault system. of northern Illinois: Illinois State Geological Survey, Circular 505, 26 p. Field work for this map was completed in 2010 and 2011 by the author. A total formity, except where it is uplifted by faulting. Sec. 25, T24N, R9E eastward to center Sec. 28, T24N, R10E The displacement Kolata, D.R., J.K. Frost, and W.D. Huff, 1986, K-bentonites of the Ordovician of about 200 field observations served as the basis for mapping geologic contacts is downthrown to the north about 30 to 50 feet. Faulted, brecciated and sheared However, in Ogle County, the geometry of the fault planes at depth (i.e. whether Decorah Subgroup, upper Mississippi Valley: Correlation by chemical finger- and recording structural data. Water well records were extremely helpful in areas The St. Peter Sandstone overlies the Shakopee. The contact at the base of the St. Dunleith (Galena) dolomites are exposed at many points along the length of Mud the faults are normal or reverse) is unclear. Further research should address the printing: Illinois State Geological Survey, Circular 537, 30 p. Peter is a major unconformity in Illinois. It separates the Sauk Sequence (below) Creek. The fault relationships were well exposed in 1946 (Templeton and Will- step-over zone between the Sandwich and Plum River fault zones in the subsur- of sparse outcrop data; the records were accessed from the Illinois Water Well Marshak, S., W.J. Nelson, and J.H. McBride, 2003, Phanerozoic strike-slip from the Tippecanoe Sequence (above) (Willman et al. 1975). Locally the St. man 1952) in a small quarry located 2750’WL, 1100’SL, Sec. 30, T24N, R10E. face (basement and overlying sediments). Geophysical imaging across the Mount database (http://isgs.illinois.edu/maps-data-pub/wwdb/launchims.shtml, ac- faulting in the continental interior platform of the United States: examples Peter Sandstone cuts deeply into Ibexian rocks, forming a very irregular erosional This exposure is now poorly exposed and on private property. Morris structure, the Mud Creek fault, the Gale Creek structure, the slice of cessed 6/1/11) and the Illinois State Geological Survey Geological Records Unit from the Laramide Orogen, Midcontinent, and Ancestral Rocky Mountains, surface. The Kress Member represents a thick accumulation of residual materials (Oregon Quadrangle, Sec. 3, T23N, R10E), and (ISGS GRU) in Champaign, Illinois. Drill cuttings or sample sets (SS) on file at in Storti, F., Holdsworth, R.E., and Slavini, F., eds., Intraplate Strike-slip at the base of the St. Peter. Mud Creek Syncline (new name) the Burlington Railroad faults (Grand Detour Quadrangle, Sec. 7, T23N, R10E) the ISGS were examined and provided subsurface data. Two hundred twenty-two Deformation Belts: Geological Society of London Special Publication 120, p. The Mud Creek syncline is a shallow N 80 to 85° W trending fold on the north- could be performed to address the subsurface geometry of faults and folds in this boreholes were utilized to map the bedrock, and 12 of those were located within 171–196. a 100 foot radius of confidence by field or plat (land ownership map) verification. The Platteville and Galena carbonates were “deposited in a stable, normal marine ern (downthrown) side of the Mud Creek fault. It runs approximately parallel to region. The presence of positive or negative flower structures could provide clues One new borehole was drilled through the Galena, Platteville, Glenwood, and St. environment characterized by relatively low depositional energy” (Willman and the fault zone and is characterized by Platteville and Galena dolomites dipping as to whether these faults were developed in a transpressional or transtensional McBride, J.H., 1998, Understanding basement tectonics of an interior cratonic Peter units (fig. 1, API #:121412600300, Core name: MM #1, Total depth of 335 Kolata 1978, p. 16). Although the Platteville is recognized at the Formation level about 20° on the steeper south flank and 5° on the gentler north flank. The fold is environment. If the sense of strike-slip motion could be determined, we could basin: southern Illinois Basin, USA: Tectonophysics, v. 293, p. 1–20. feet, located 260 feet from the east line, 1270 feet from the south line, Sec. 22, in Minnesota (Mossler 2008, Tipping and Runkel 2008), the most recent work in a doubly plunging syncline, with an eastward plunge in the Mount Morris Quad- better understand the kinematics of the en echelon fault array in the step-over McBride, J.H., and W.J. Nelson, 1999, Style and origin of mid- T24N, R9E, Latitude 42.0616° N, Longitude 89.43258° W, 881 feet elevation). A Illinois stratigraphy recognizes the Platteville and Galena at the Group level. The rangle and a westward plunge in the Oregon Quadrangle. The lowest point of the zone between the Sandwich and Plum River fault zones. deformation in the Illinois Basin, USA – Ancestral Rockies deformation?: continuous core for this hole is on file at the ISGS core library, and stratigraphic Platteville and Galena Groups in northern Illinois are further divided into many syncline is approximately located at the border between the quadrangles, and the Tectonophysics, v. 305, p. 275–286. descriptions and downhole geophysical logs are on file at the ISGS GRU. thin intervals at the Formation and Member levels (Willman and Kolata 1978). structural closure is roughly 50 feet. Economic Resources Mossler, J.H., 2008, Paleozoic stratigraphic nomenclature for Minnesota: Minne- sota Geological Survey Report of Investigations 65, 84 p. A thin layer of glacial deposits (0 to 40 feet thick) obscures the bedrock in most The Platteville Group is split into five formations, and four of the five formations Gale Creek Structure (new name) Sand and Gravel Ross, R.J., Jr., L.F. Hintze, R.L. Ethington, J.F. Miller, M.E. Taylor, and J.E. of the quadrangle, except for main tributary valleys to Rock River. Bedrock are split into several members. The lowest formation in the Platteville Group is The Gale Creek structure is defined by two closely-spaced outcrops of dipping There are no active sand and gravel pits in the study area, but sand and gravel of Repetski, 1993, The Ibexian Series (Lower Ordovician), a replacement for exposures occur in the South Fork of Leaf River, Coon Creek, Pine Creek, Gale the Pecatonica Formation, which is split into the Hennepin, Chana, Dane, New Shakopee in Gale Creek surrounded by St. Peter Sandstone. The Shakopee is the Quaternary Pearl Formation (Illinois episode of glaciation) has formerly been “Canadian Series” in North American chronostratigraphy: U.S. Geological Creek, Mud Creek, and Silver Creek. Quaternary Pearl and Cahokia formations Glarus, Medusa, and Oglesby Members, each attaining a thickness of 0 to 16 feet. uplifted about 130 to 180 feet, with the highest point near the center of the W½, mined at the surface from many pits within the quadrangle. Survey Open-File Report 93-598, 75 p. (Hansel and Johnson 1996) were mapped where the bedrock was deeper than 5 The overlying Mifflin Formation is not divided into members. Within the suc- Sec. 6, T23N, R10E. Faulting probably occurred after St. Peter deposition and is Seid, M.J., 2010, Bedrock geology of Oregon Quadrangle, Ogle County, Illi- feet. Abandoned pits and quarries were mapped where they were observed in the ceeding Grand Detour Formation are the Cowen, Stillman, and Forreston Mem- related to faults that cut the Ancell, Platteville, and Galena units about one mile Stone nois: Illinois State Geological Survey, USGS-STATEMAP contract report, 2 field, as shown in soil maps (Acker et al. 1980, Soil Survey Geographic Database, bers, which are each roughly 5 to 15 feet thick. The Nachusa Formation is divided southward in the Grand Detour Quadrangle. Field observations could not confirm One small long-abandoned quarry occurs in the Shakopee dolomite (1700’WL, sheets, 1:24,000. accessed in July 2011), and from a study of road resources in Ogle County (Flint into the Eldena, Elm, and Everett Members, which each reach a thickness of no or deny a fault bounding the uplifted and tilted Shakopee block. Therefore, the 3700’NL, Sec. 6, T23N, R10E). Three abandoned quarries occur in the Platteville et al. 1931). more than 10 feet. The uppermost Quimbys Mill Formation contains the Hazel author interprets the structure to be a faulted dome, with a concealed fault uplift- and Galena dolomites: Sec. 12, T24N, R9E (Dunleith Formation); Sec. 32, T24N, Soil Survey Staff, Natural Resources Conservation Service, United States De- Green, Shullsburg, and Strawbridge Members, and these range in thickness from ing the southwest flank. The map view geometry is depicted as an arcuate pod of R9E (Dunleith and Wise Lake Formations); Sec. 30, T24N, R10E (Quimbys Mill partment of Agriculture. Soil Survey Geographic (SSURGO) Database for Stratigraphy 0 to 9 feet. Shakopee in faulted contact with the St. Peter Sandstone, with a trend of N 50° and Dunleith Formations). None of the stone quarries were active during the time Ogle County, Illinois. Available online at http://soildatamart.nrcs.usda.gov . W. The structure is about 1¼ miles in length and occurs in Sec. 6, T23N, R10E, of mapping. Accessed July 22, 2011. The bedrock formations that occur at or near the surface within the Mount Morris The five formations within the Platteville Group are mapped as a single unit The Gale Creek structure occurs at approximately the northwestern extent of the Templeton, J.S., ca. 1940, Draft geologic maps of the Oregon 15-minute Quad- because the combined thicknesses of the formations (114 to119 feet) constitute a Oregon Anticline (Templeton 1951, Templeton and Willman 1952). Quadrangle are all Ordovician dolomites and siliciclastics. These strata are as- Acknowledgments rangle: Illinois State Geological Survey, Map Room 4107 d5.1-180, 4 sheets, signed to the Ibexian (Ross et al. 1993) and Mohawkian Series (Thompson 1991), mappable unit at the 1:24,000 scale. 1:62,500. Origin and Timing of Structures and they are further divided into the Prairie du Chien, Ancell, Platteville, and I thank the Village of Mt. Morris for permission to drill, Don Luman for prepara- The Galena Group is divided into three formations, and each formation is further The root of these structures can likely be traced downward into the Precambrian Templeton, J.S., ca. 1942, Unpublished fieldnotes: Available from Illinois State tion of the LiDAR basemap, Jane Domier for the cartographic preparation of the split into members. The Guttenberg Formation (fig. 2) is divided into the Gar- Geological Survey Library. map, Jack Aud and his drilling crew for good core recovery, and Dennis Kolata navillo and Glenhaven Members. The overlying Dunleith Formation is split into Templeton, J.S., 1951, The geology and mineral resources of the Oregon Quad- for helpful discussions on the geology of northern Illinois. the Buckhorn, St. James, Beecher, Eagle Point, Fairplay, Loves Park (contains rangle: Available from Illinois State Geological Survey Library, unpublished the Mortimer, Rivoli, Sherwood, and Wall sub-Members), and Wyota Members. manuscript Ms. #3, 2 folders. This research was supported in part by the U.S. Geological Survey National Co- The Wise Lake Formation contains the Sinsinawa and Stewartville Members. The operative Geologic Mapping Program (STATEMAP) under USGS award number Templeton, J.S., and H.B. Willman, 1952, Central Northern Illinois: Guidebook uppermost does not occur in the study area but is present G10AC00418. The views and conclusions contained in this document are those for the 16th Annual Field Conference of the Tri-State Geological Society: Il- less than one mile to the west of the western edge of the map area, as indicated by of the author and should not be interpreted as necessarily representing the official linois State Geological Survey, Guidebook Series 2, 47 p. well data. Fisherites (fig. 3, Finney and Nitecki 1979, old name: Receptaculites) policies, either expressed or implied, of the U.S. Government. Thompson, T.L., 1991, Paleozoic succession in Missouri, Part 2, Ordovician is an index fossil of the Galena Group (Trentonian, Middle Ordovician) in the System: Missouri Department of Natural Resources, Division of Geology and midwestern United States. References Land Survey, Report of Investigation 70, 282 p. The three formations within the Galena Group—Wise Lake, Dunleith, and Gut- Tindall, S.E., and G.H. Davis, 1999, Monocline development by oblique-slip tenberg—are mapped together for two reasons: 1) the lithologic character of each Acker, L.L., M.S. Hodges, G.T. Keller, and R. Rehner, 1980, Soil Survey of Ogle fault propagation folding: The East Kaibab monocline, Colorado Plateau, formation is so similar that an accurate contact could not be reasonably estimated County, Illinois: Illinois Agricultural Experiment Station and United States Utah: Journal of Structural Geology, v. 21, 1303–1320, doi:10.1016/S0191- in the field and 2) the author believes that their combined thicknesses constitutes Department of Agriculture, 242 p., 109 map sheets. 8141(99)00089-9. a mappable unit at the 1:24,000 scale. Bevan, A.C., 1924(?), Surface geology of Oregon 15-minute quadrangle: Illinois Tipping, R.G., and A.C. Runkel, 2008, Geologic investigations to support State Geological Survey, Map Room 4107 d5.1-179, 3 sheets. Ground-Water Management II, Rochester metropolitan area, Minnesota: Structural Geology Bevan, A.C., 1939, Cambrian inlier in northern Illinois: American Association of Minnesota Geological Survey Open-File Report 08-6, 15 p. Petroleum Geologists Bulletin, v. 23, no. 10, p. 1561–1564. Willman, H.B. and D.R. Kolata, 1978, The Platteville and Galena Groups in The Mount Morris Quadrangle is situated near the southeasternmost extent of the Bunker, B.J., G.A. Ludvigson, and B.J. Witzke, 1985, The Plum River Fault Zone northern Illinois: Illinois State Geological Survey, Circular 502, 75 p. Wisconsin Arch, the northwestermost projection of the LaSalle Anticlinorium, and the structural and stratigraphic framework of Eastern Iowa: Iowa Geo- Willman, H.B., E. Atherton, T.C. Buschbach, C. Collinson, J.C. Frye, M.E. Hop- Figure 2 View looking west of the dark reddish brown wispy shale in the Gutten- to the north of the Illinois Basin and to the south of the Michigan Basin. The Figure 3 Fisherites (old name: Receptaculites) fossil was found in a float block of logical Survey, Technical Information Series 13, 126 p. kins, J.A. Lineback, and J.A. Simon, 1975, Handbook of Illinois stratigraphy: berg Formation at stream level. The ledge above is dolomite of the Galena Group. regional dip of strata is west-southwest, with a few broad folds in the bedrock Galena Group dolomite on the west bank of Pine Creek (1750’WL, 2800‘NL, Sec. Duchek, A.B., J.H. McBride, W.J. Nelson, and H.E. Leetaru, 2004, The Cottage Illinois State Geological Survey, Bulletin 95, 261 p. This outcrop is located in the west bank of a southwest flowing tributary to Pine beneath Quaternary deposits (see cross section A–A9). The local bedrock struc- 4, T. 23 N., R. 9 E.). Fisherites is an index fossil of the Galena Group. A small Creek (100’ WL, 3300’ NL, elongate Sec. 3, T23N, R9E). Photo taken on Novem- ture is influenced by the Sandwich Fault Zone to the southeast (refer to Kolata et exposure of Galena occurs where the float was found. Photo taken on November Grove fault system (Illinois Basin): Late Paleozoic transpression along a Pre- ber 2, 2010. al. 1978) and the Plum River Fault Zone to the north (see Kolata and Buschbach 3, 2010. cambrian crustal boundary: Geological Society of America Bulletin, v. 116,

Southwest Northeast

Mt. Morris A structure AЈ Elevation (feet) Pine 1000 Creek Op Silver Creek 1000 Leaf River Kable #1 Kable 1,353 288 MM #1 335 248 319 195 130 320 Og 335 192 230 155 225 290 140 Q Oa 800 Og Og 175 800 Op Q Op Os Op Op 600 Oa 600 Oa Oa Oa 400 400

200 200 Well labels indicate total depth in feet. Horizontal scale: 1 inch = 2,000 feet Q Quaternary Og Galena Group Op Oa Ancell Group Os Platteville Group Shakopee Dolomite Vertical scale: 1 inch = 500 feet Vertical exaggeration: 4ϫ

STATEMAP Mount Morris-BG Sheet 2 of 2