sign in sign up
<<
Home , Dunleith Formation, Leaf River (Illinois), Shakopee Dolomite

BEDROCK GEOLOGY OF OREGON QUADRANGLE Institute of Natural Resource Sustainability William W. Shilts, Executive Director OGLE COUNTY, STATEMAP Oregon-BG ILLINOIS STATE GEOLOGICAL SURVEY E. Donald McKay III, Director Mary J. Seid 2010

2 0 35 766 800 36 80 0 0 819 34 31 Op 70 Boat

33 10 E. R. 11 E. R. 32 815 75 800 72 Ramp 741 768 799 694

Og 0 0 32 0 75 80 80 676Q 0 850 75 694 72 700 Og BM 691 0 75 676Q Q 70 692 0 Parking T. 25 N. 704 80 792 8020 687 720 707 730 T. 24 N. Æ 692 T. 25 N. 748 718 692 0 696 Drag 75 800 823 720 697 T. 24 N. 704700 756 Æ Race Quarry Æ Track 0 70 75 0 0 70 800 730 750 0 75 70 0 Road 697 Side Op Park 0 700 2 800 75 5 5 0 3 75 709 70 1 687 0 4 6 741 682 704Æ 700 705 676 EXPLANATION 0 714 80 Rock 70 0 842 842 Quarry 0 70 709 850

0

75 0 70 Op Q Cahokia Formation Op 0 709 728 75 Peoria Silt Q 714 and 684 869 830 Quaternary 797 Equality Formation 735 700 Henry Formation 700 687 0 Roxana Silt 80 Quarry Glasford Formation S 115 756 702 k" 0 Æ 75 800 Og Unconformity 75 709 714 St. Peter 0 684 Og 70 70 0 8 0 7 784 Q 12 10 Quarry Guttenberg Formation 850 8 9 11 741 800 Road Q Æ 745 823 750 858 Side 850 682 0 756 80 Park 75 800 0 0 AЈ 85 Platteville Group 750 802 Op 0 Quimbys Mill Formation 760 735 80 Nachusa Formation 843 Q Mohawkian 750 C 106 Grand Detour Formation 0 k" 0 70 80 Og St. Peter Mifflin Formation 758 S 230 0 k" 837 861 830 70718 768 779 Pecatonica Formation 789 St.Peter BM 860 80 682 863 Unconformity 0 85 7560 0 75 C 185 Ancell Group k"St. Peter 800 2 0 C 54 Oa 75 k" Og Quimbys Ck"118 733 Mill Glenwood St. Peter Sandstone 761 C 125 85 802 0 k"

70 0 817 C 151 Pecatonica 0 80 85 Unconformity 0 k" 0 Pecato85nica C k" 216 75 85 838 75 0 Glenwood 782 S 72 0 18 BM 0 e" 13 17 Os 15 14 837 85 Ibexian 16 80 St. Peter 0 723 837 0 17 705 861 Units removed by faulting Op 0 817 80 Cambrian St. Croixan 75 Road _ 0 820 0 Side

75 0 Park 787 0 Power Plant 70 850 75 0 75 Cooling Towers Og Op 0 80 750 80 0 0 720 807 750 70270 691 801 879 791 842 S 1500 815 e k" Ç Mt. Simon 699 Quarry 0 89 0 700 80 800

0 85 0 750 Radio 85 848 Op Tower 710 840 828 85 0 0 20 70 23 832 24 19 0 21 80 0 835 20 782 70 835 850 871 700 22 807 887 858 750 681 0 80 850 Symbols 0 Og Op 70 715 ee e Strike and dip of bedding; number 3 40 85 e 704 o 0 indicates degree of dip 0 80 o 0 750 4 85 814 750 70 Horizontal bedding 850 0

0 748 817

75 2 764 825

800 794 871 876 G 745

Q 773 0 804 o 800

Golf 80 750 Vertical joint

Course | 0 CEM

 80 Op H |

800 G 55 | o 804

5 800 Inclined joint; box on down–dip side

o 784 H o| o3 0 843 10 7S5 850 199 12 0 e" 85 Ç Active quarry St. 687 871 o5 Peter 830 0 750 2 0 85 78 Æ Abandoned quarry 0

856 e 80 o 805 D Ä S 205 833 864 2 e0 o e" 70 U 750 29 850 o St. Peter 27 833 30 804 755 75 753 25

853 29 U 5 28 820 856 26 0 Op D 0 80

75 850 Drill Holes 801 0 Og 70 85

80 0 from which subsurface data were obtained 0 0

o 800 851

H

| Og

e 80 H

| o e" 0 Stratigraphic boring

G 750 S 250

5 k" 80

H 0 H | G 6

| 725 St.

| H 25 | 796 0 G e 10 80 o

H Peter

e e 85 e" 8 6 7 17 Water well | o G 80 0 o o 15 U o

e 892

o 11 16 o o 805 0 0 833 | oe 0 D o 75 85 827 15 892 75 804 855 792 0 800 e 21 80 U o U 0 Labels indicate samples (S) or core (C). D D C k" 125 Numeric label indicates total depth of boring in feet. Ç e 890 St. Peter 85 85 0 Unit label denotes formation at bottom. 0 Quarry 750 Radio850

Tower 85 Dot indicates location accurate within 100 feet. 3 0 e 850 800 o 800

85 850 819 75

0 þ Line Symbols

856 Og 845

0

ü

þ Q 0

^ 33 Oa ü 80 850 ^þ þü^ þþ 34 0 32 32 D 85 e 35 31 85 dashed where inferred, dotted where concealed U 0 Æ 36 o22 827 Picnic 0 2 89 0 80 Area 0 Contact 85 Statue 891 Campground 0 H Ä 85 850 0 809 64 846 80 Anticline

D o9 U G

85 12 Op U 0 D G o H G 864 866 Syncline; direction of plunge indicated by arrow D T. 24 N. 900 U 828 868 869 876 876 85 U 0 T. 23 N. 896 T. 24 N. 894 D Sub 878 Fault; U on upthrown side, D on downthrown side 93 "128 Station D T. 23 N. 0 U e 85 900 e 679Franconia 0 907 U 7 D Line of cross section 5 70 0 A AЈ 0 Fair 85 919 0

90

0 D 7 Grounds C 269 o  k"

U 88 Eau Claire 65 70 855 Note: Well and boring records are on file at the ISGS Geological Q 0 3 7 800 85 679 o   75 e o 0 Records Unit and are available online from the ISGS Web site. e 0 842 _ 900 906 Boat D 77 Op U Ramps BM 869 897 80 S 200 0 800 0 U 746 k" 90 874 D 869 750 750 Ironton 864 800 Q 743 900 745 89 4 85 0 o 0 13 o 873 D 0 886 886 U o S 283 90 738 Concrete U U k" D St.Peter S 1050 Dam 75 D Radio825 Ç 0 0 89 e" S 145 Æ Tower0 6 Sub e" 794 Quarry 5 Mt. 70 o 1 4 64 0 Galesville Station 0 5 Simon 1170 673 0 830 2 6 85 S k" 80 Oa S 234 Mt.Simon D e 0 717 e" U 814 75 Potosi 758 0 682 682 682 Q 728 75 Ä 0 e 0 80 Park Q Golf 64 850 Course e 850 750 70 S 215 763 743 o 702 0 e" e 2 771 800 699 St.Peter 750 75 797 R. 10 E. R. 11 E. R. 67 Q 0 S 307 0 e" 766 714 0 e 0 Potosi Oa 75 70 75 0 733 718 75 699 694 Q 0 e 700 0 Park 0 75 Athletic 75 Field 0 Os 80 709 0

700 0 70 70 0 Sewage 70 64 Disposal Quarry 738 737

723 717 707 702 705 694

67 723 722 756Æ o 70 0 0 75 0 D 0 12 70 Â Q U 64 8 70 11 7 Transmission Line 800 8 9 0 12 2 10 709 699 A

Base map compiled by Illinois State Geological Survey from digital data (Raster Feature SCALE 1:24,000 Geology based on field work by Mary J. Seid, 2009–2010. Separates) provided by the United States Geological Survey. Compiled from aerial photo- 1 1/ 2 0 1 MILE graphs taken 1977. Field checked 1981. Map edited 1983. Digital cartography by Jane E.J. Domier and Dawn Heckmann, Illinois State Geological 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET Survey. North American Datum of 1927 (NAD 27) 1 .5 0 1 KILOMETER Projection: Transverse Mercator 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 G09AC00197. 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 BASE MAP CONTOUR INTERVAL 10 FEET be interpreted as necessarily representing the official policies, either expressed or implied, NATIONAL GEODETIC VERTICAL DATUM OF 1929 of the U.S. Government. Recommended citation: Seid, M.J., 2010, Bedrock Geology of Oregon Quadrangle, Ogle County, Illinois: Illinois This map has not undergone the formal Illinois Geologic Quadrangle map review pro- 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 © 2010 University of Illinois Board of Trustees. All rights reserved. resources and priorities of the ISGS. 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 MA TR 1 German Valley NOR GNETIC Primary highway, Light-duty road, hard or UE NOR UE 2 Seward hard surface improved surface 3 Kishwaukee 4 5 Secondary highway,

4 Mount Morris TH hard surface Unimproved road For more information contact: 5 Stillman Valley T Institute of Natural Resource Sustainability 6 Grand Detour H Illinois State Geological Survey 6 7 8 7 Daysville 615 East Peabody Drive 8 Chana APPROXIMATE MEAN State Route Champaign, Illinois 61820-6964 DECLINATION, 2010 (217) 244-2414 http://www.isgs.illinois.edu

STATEMAP Oregon-BG Sheet 1 of 2 A Cahokia Formation, Peoria Silt, Equality Formation, Henry For- Öpikina and Streptelasma; Chondrites is a common trace in the H Pecatonica Formation Dolomite. Orange-brown, very fine-grained, beds; bedding surfaces vary from rough and hummocky to smooth and flat, THICKNESS mation, and Roxana Silt Sand, gravel, silt and clay. Sand is light gray middle of the unit. The characteristic feature of the Quimbys Mill is that it argillaceous and can be mottled with gray fine- to very fine-grained lime- show mud-cracks or ripplemarks, and are partly coated with films of green

OUP FORMATION GRAPHIC COLUMN

(feet) to brown-gray, coarse to fine grained, poorly sorted, ranges from weakly fractures with smooth, curved surfaces; it is called “the glassrock” in the stone. White chert is moderately abundant. The lower part of the Pecatoni- clay. The Shakopee contains thin beds of medium-grained, cross-bedded UNIT

GR

SERIES stratified to well stratified. Sand and clay occur as laminae or cross bed- Mississippi Valley zinc-lead mining district. In general, the top of the unit is ca contains abundant fine to medium well-rounded sand grains (St. Peter- sandstone, greenish gray shale, buff siltstone and bands and nodules of SYSTEM ded channels found on the floodplains and creeks. Gravels are angular to ferruginous and is capped by a prominent hardground omission surface. type). Phosphatic pellets are known to occur in the Pecatonica (Templeton sandy, oolitic chert. Algal stromatolite domes (Cryptozoon minnesotense)

Y sub-rounded, composed of chert, quartz and rock fragments of igneous, The basal contact is sharp but conformable with the Nachusa. 1951). The unit is mostly medium bedded but can be thick bedded in occur on the order of one foot wide in the region, but none were identified Cahokia Peoria Silt metamorphic and local sedimentary origin. Silt is brown and gray. Clay is places. are less abundant than in other Platteville formations. The in the study area. The only exposure of Shakopee within the study area Equality gray to yellow and intermixed with sand and silt layers. Unconformable with E Nachusa Formation Dolomite. Dolomite is yellow- to orange-brown, lower contact can be sharp or gradational and marks a widespread uncon- is a float exposure reported by Templeton (ca. 1940) in E ½ NE ¼ Sec. 8, OCENE 2–200 A

AND Henry units below. pure to argillaceous, mostly medium crystalline, mottled with light gray formity of low relief in the region. T23N, R10E; he reported another exposure just west of the quadrangle TERNAR

A Roxana Silt limestone. White or light brownish gray chert occurs in nodules or thin (Templeton ca. 1942) about 1700’ WL, 4000’ NL, Sec. 6, 23N, 10E. The HOLOCENE

QU Glasford PLEIST B Dunleith Formation Dolomite. Light gray on fresh surface, fine- to beds; chert is less abundant in the Nachusa than in the overlying Quimbys I Glenwood Formation Sandstone, shale, and shaly dolomite. Sand- Shakopee either rests conformably on the New Richmond and/or Oneota coarse-grained, crystalline; dark olive green or pale orange-tan on weath- Mill. Bedding appears massive but consists of medium to thick, tight beds stone is usually white to gray but is orange or blue in places, quartz Formations, neither of which is exposed in the study area, or is separated ered face. Massive beds comprise thin, wavy, indistinct bedding, and some where weathered. When identifying the Nachusa in the field, the fossil- arenite, very fine-grained with scattered coarse grains, well-rounded (St. from them by only a minor unconformity. beds are separated by thin, carbonaceous greenish shale partings. Moldic moldic porosity, fine- to medium-grained texture, and massively bedded Peter-type), thinly bedded, dolomitic in places, friable and poorly lithified. Dunleith 0–77 B porosity can occur on fresh faces; a pitted surface, or beehive weathering, appearance are key characteristics; it could be mistaken for the Galena Shale is reddish brown when weathered, blue- to green-gray when fresh, L Potosi Dolomite Dolomite, with interbedded shale, siltstone, and 0–100

Galena commonly occurs on weathered faces. Light gray to white chert occurs in Group dolomites in many cases. Fossils are generally moderately abun- fissile, wavy bedded in places. Shaly dolomite is light blue-green with yel- sandstone. Dolomite is highly variable in color, occurring as pink, buff, gray, flat slabs or lenses; the chert can be irregularly scattered throughout or dant in the lower part and include the tabulate coral Foerstephyllum and low mottles or streaks in thin to medium, tabular, blocky beds, and can ap- yellow, red, brown, purplish, or green, or any mottled combination of these Guttenberg 0–5 C form well-defined layers. A fewReceptaculites zones occur in this forma- the trace fossils Palaeophycus and Chondrites. The lower contact is grada- pear rubbly. In the lower 10 feet, 1mm diameter vertical tubes occur, which colors. It is very fine-grained but can be medium- to coarse-grained, dense tion but not in the Platteville Group; the occurrence of the calcareous algae tional to sharp but conformable with the Grand Detour below. results in tiny round pinhead-sized holes on weathered bedding surfaces. to porous, and very hard; bedding is massive when fresh, but weathers Quimbys Mill 15 D Receptaculites is useful to distinguish Galena dolomites from the Plat- The Glenwood is characterized by abrupt lateral changes in lithology, and into thin, irregular, discontinuous layers. Disseminated clay, silt, sand, Nachusa 15–25 E teville Group. When identifying the formations of the Galena Group in the F Grand Detour Formation Dolomite, limestone, and shale. Dolomite is in some places it is absent. It is very poorly exposed in the study area; the and glauconite are present in highly variable quantities; locally, it is mod- field, the crystalline texture is characteristic and is the key to telling it apart orange-brown when weathered, light brown when fresh; limestone is gray best exposure is in a St. Peter quarry about two miles southwest of Ore- erately glauconitic. Pyrite, white chert, and siliceous oolites occur spar-

ville from the formations of the Platteville Group. Several K-bentonite beds that when fresh and can have a distinctive dark blue-gray color. The Grand gon. The basal contact was observed in the same quarry face and showed ingly. Shales are green, pale gray, red, purple or brown; they are soft, silty, VICIAN

WKIAN Grand Detour 35–43 F are one-inch-thick or less have been identified from the Dunleith. Stylolites Detour varies vertically from fine- to medium-grained, from thick to thin a sharp angular unconformity with the St. Peter below. sandy, locally glauconitic, and rarely micaceous; beds are typically thin Platte 105–120 and hardground omission surfaces occur locally at the basal contact, but bedded, and from pure to argillaceous. Packages of thin beds can appear but can form layers up to 15 feet thick. Siltstones occur near the top of the

Mifflin 10–15 G ORDO MOHA the two formations otherwise appear to be conformable. massive. Shale is greenish gray, red-brown, or dark gray; it occurs gener- J St. Peter Sandstone Sandstone and chert. Sandstone is white to unit, are purple to green, glauconitic and thin. Sandstones are white to light Pecatonica 21–33 H ally in the upper part as wispy partings, but partings are not strong enough light gray when fresh, light yellow brown when weathered, quartz arenite, green and buff, are silty and dolomitic in places, and are dominantly fine to C Guttenberg Formation Dolomite and shale. Dolomite is orange and to cause the rock to cleave on those surfaces. The fauna is reported to be fine- to coarse-grained but mostly medium grained, well-rounded, frosted, medium grained. Grains vary from angular to well rounded, are unconsoli- Glenwood 10–35 I dense; shale is reddish brown or pale green and occurs as wavy, thin abundant and diverse, including the solitary rugose coral Streptelasma, the generally well-sorted, thinly to massively bedded, poorly cemented, and dated to hard, and occur in beds less than 5 feet thick. The heavy mineral partings. It is wavy bedded, is called “Oilrock” in the mining district, locally rhombiferan cystoids Coronocystis durandensis, the lithistid sponges An- friable. Bedding varies from thinly laminated rhythmic bedding to large suite of the Potosi includes garnet, zircon, tourmaline, and titanium. Fossils contains pea-sized vugs, and forms a re-entrant in weathered quarry or thaspidella and Zittelella, and the trace fossils Palaeophycus and Buthotre- cross bedding. It weathers to white sand and forms broad hills in most of appear to be absent. Small vugs lined with crystalline quartz are present to outcrop exposures. Small, white chert nodules and lenses are rare in the phis (Chondrites). Hundreds of horn corals can be concentrated on the its outcrop area; but where overlain by the Glenwood and Platteville Group abundant; this feature forms one of the most characteristic features of the area. Fossils are generally abundant; strophomenid brachiopods are the shaly horizons (Kolata, personal communication). Solution cavities at the dolomites, it is a bluff-former and contains small sapping alcoves. The up- formation. The nature of the basal contact is unknown. most conspicuous and ubiquitous, including the brachiopods Sowerbyella top of the unit were observed in the Steve Benesh and Sons Quarry (NW per 50 feet contains green streaks along bedding planes; the color seems

Ancell St. Peter J punctostriata and to a lesser extent Rafinesquina trentonensis. The Elkport Sec. 23, T24N, R10E); cavities were filled with greenish gray shale and to stain the exterior of the grains. The basal Kress Member is present in M Franconia Formation Sandstone, conglomerate, siltstone, and shale. 250–450 and Dickeyville K-bentonite Beds have been identified in the Guttenberg; large, jumbled blocks of dolomite. The shale content makes this a useful a City of Oregon water well (Sample Set 64615, Sec. 3, T23N, R10E); it Sandstone is light gray to greenish gray, very fine-grained to fine-grained, 240–425 the Dickeyville was sampled and analyzed on Thorpe farm, 2150’ WL, horizon for electric log correlation. The basal contact is conformable with contains 78 feet of chalky, white chert, which has been weathered to tripoli; subrounded, and bedding is thinly laminated; glauconite is abundant and 4350’SL, Sec. 2, T23N, R10E (Kolata et al. 1986). The Guttenberg can be the Mifflin and can contain a thin K-bentonite bed. it is oolitic in part, and contains sandy, reddish brown shale. The Kress forms thin bands. Conglomerate is composed of elongate clasts of the absent or extremely thinned from solution of the limestone within the for- Member is not present everywhere and was not observed in outcrop within sandstone, which are oriented at various angles to bedding, and the matrix Kress Member mation. The high shale content can make this a useful horizon for electric G Mifflin Formation Dolomite and limestone. Dolomite is orange and the study area. The St. Peter is penetrated, in some places, by white silici- is light gray, fine-grained sandstone; it is commonly known as the “flat-peb- Prairie log correlation. The lower contact is conformable with the Quimbys Mill. mottled with gray limestone. Limestone and dolomite are very fine-grained fied veins that cut at various angles to bedding; the veins were probably ble conglomerate”. (Kolata, personal communication).Siltstone is medium IBEXIAN du Shakopee 0–80 K to lithographic in thin, wavy beds separated by green or gray shale. The introduced from hydrothermal sources and seem to be present in close gray to brownish gray; it is interbedded with shale, which is olive gray to Chien D Quimbys Mill Formation Dolomite, shale, and chert. Dolomite is unit is the most shale-rich formation in the Platteville (Kolata personal com- proximity to inferred faults. The lower contact is sharp, unconformable, and medium gray, silty in places, commonly glauconitic, dolomitic, and thinly units removed by faulting (lower Ordovician–Upper Cambrian) mostly orange-brown, pure to argillaceous, lithographic; in thin, wavy, munication). The Mifflin is locally very fossiliferous and contains various scoured into several older formations as a result of pre-St. Peter uplift and laminated in planar to wavy beds. Many parts of the unit are stained with G smooth, and well-defined beds; and mottled with gray limestone in places. well-preserved bryozoans, brachiopods, bivalves, gastropods, ostracodes, erosion; the unconformity has considerable local relief. orange iron oxide. Horizontal burrows occur in many places throughout the Shale is olive gray, occurs in thin, wavy partings, and is more common and trilobite fragments. (Willman and Kolata 1978). In some places, the up- unit. Small vugs occur and are lined with pinkish brown siderite. The basal Potosi 25–62+ L at the top of the unit. Chert nodules and beds are common in core hole per part contains a prominent hardground omission surface and a 6-inch- K Shakopee Dolomite Dolomite, sandstone, shale, and chert. Dolo- contact is not exposed in the quadrangle, and the relation of the Franconia

OIXAN G G C-13651, ranging in color from light gray to yellowish gray to yellowish thick bed of shaly dolomite or limestone. The base is in sharp contact with mite is blue-gray when fresh, weathering to buff, whitish, red-brown, or to the underlying Ironton-Galesville interval is uncertain.

G brown or white. Unit contains fossil-moldic pores, has a chalky texture, and the Pecatonica and is marked by a thin, rusty-colored surface, which ap- gray-green, crystalline, fine- to medium-grained, pure to argillaceous, and CR . . G G

CAMBRIAN Franconia 85 M is burrowed along bedding planes. Fauna is not abundant but can include pears to represent submarine chemical erosion of the carbonate sea floor. breaks with a conchoidal to hackly fracture. It forms thin to thick lenticular ST G G

Introduction Geologists have argued that there may be a connection between the Sandwich and Plum Thrust faulting was reported by Bevan (1935a) in Oregon. He observed an abundant References River Fault Zones in the vicinity of the Oregon and Mount Morris 7.5-minute Quad- amount of St. Peter silicified fault breccia, an along strike trend of the breccia, and The Oregon 7.5-minute Quadrangle is located in north-central Illinois in the south- rangles. The northwest and northeast trending faults and shear zones within a three-mile repeats of the Franconia-Potosi interval. He concluded that a local thrust fault occurs Bevan, Arthur C., 1924, Surface geology of Oregon 15-minute quadrangle: Illinois central part of Ogle County, Illinois, about 20 miles southwest of Rockford, 40 miles radius of Oregon suggest a genetic relationship to the larger fault zones. However, the about 1500’ EL, 3300’ NL, Sec. 3, T23N, R10E. Templeton (1951, p. 30-37) discussed State Geological Survey, Map Room 4107 d5.1-179, 3 sheets. south of the Illinois-Wisconsin border, 90 miles northeast of the Quad Cities and 110 connections between these major structures has not been examined. Bevan’s conclusion in his report but proposed that St. Peter erosion and possibly fault- miles west of Chicago. It covers approximately a 55 square mile area that is bounded ing could explain the angular relationship between the Franconia and St. Peter at this Bevan, Arthur C., 1928, Large-scale map of Cambrian inlier: Illinois State Geological by 42° 00’ 00” and 42° 07’ 30” North latitude and 89° 15’ 00” and 89° 22’ 30” West Faulting within the Oregon Quadrangle locality. The writer concludes that the orientation of the fault plane can not be described Survey open files, Map Room 4107 d5.1-183, 4 sheets. longitude. The Oregon 7.5-minute Quadrangle occupies the southeast quarter of the Or- Faults within the quadrangle generally trend northwest, but some trend northeast. Frac- given the available outcrops and surface data. The fault that separates the Franconia and Bevan, Arthur C., 1935a, Cambrian inlier at Oregon, Illinois: Kansas Geological Soci- egon 15-minute Quadrangle. It is bordered by eight 7.5-minute quadrangles, clockwise tures and shear zones, as described by Templeton (1951), are high angle and have dis- St. Peter exposures here is believed to be a concealed, high-angle, dip-slip fault. ety Gudebook, 9th Annual Field Conference, p. 383–385. from top-left: German Valley, Seward, Kishwaukee, Stillman Valley, Chana, Daysville, placements of less than 50 feet. The faults outline a series of horsts and grabens, as in Grand Detour, and Mount Morris. It includes the townships of Oregon, Pine Rock, the Stronghold Fault that strikes northwestward through Secs. 28 and 33, T24N, R10E. Economic Resources Bevan, Arthur C., 1935b(?), Oregon Quadrangle: Illinois State Geological Survey Li- Rockvale, Marion, Leaf River, and Byron. The Rock River enters from the northeast Since many of the faults are on strike with the Sandwich Fault Zone, it is probable that brary, unpublished manuscript #2, 276 p., plus 32-page appendix and 71 figures. and flows southward through the center of the quadrangle. It lies within the Rock River faulting within the quadrangle is genetically related to movement along the Sandwich Oil and gas Hill Country of the Central Lowland Province. Agricultural, commercial, industrial, and Fault Zone. The dolomites and limestones of the Galena Group produce oil throughout the Illinois Bevan, Arthur C., 1939, Cambrian inlier in northern Illinois: American Association of residential developments currently drive the region’s economy. Basin. Oil and gas prospects are unlikely because the Galena (equivalent to Trenton Petroleum Geologists Bulletin, v. 23, no. 10, p. 1561–1564. Several small faults and numerous shear zones were documented by Templeton (1951) or Kimmswick) dolomites outcrop at the surface, and any oil has long since escaped. Bunker, B.J., G.A. Ludvigson, and B.J. Witzke, 1985, The Plum River Fault Zone and The Ancell Group is the uppermost bedrock in the southern part of the quadrangle, and but are not shown on this map. Descriptions of several faults and shear zones within the Probable source rocks above the Galena, the Ordovician Maquoketa and New the Structural and Stratigraphic Framework of Eastern : Iowa Geological Sur- successively, the Platteville Group and Galena Group cover the uplands in the northern quadrangle are found in Templeton’s field notes in the Map Room of the Illinois State Albany Shales, also are eroded at the surface. vey, Technical Information Series 13, 126 p. part of the quadrangle. Portions of this area were previously mapped by Bevan (1924) Geological Survey. and Templeton (1940) but remain unpublished. Sulfide deposits Freiburg, J.T., 2010, The timing, composition, and source of subsurface diagenetic Sandwich Fault Zone Sulfide deposits of the Mississippi Valley Type, including galena and sphalerite, have waters responsible for sulfide and carbonate mineralization in solution cavities of The field work for this map was completed in 2009 and 2010 by the author. The Illinois The Sandwich Fault Zone extends from Manhattan in Will County and continues to been found throughout the northern Illinois region (Freiburg 2010). However, the oc- the Ordovician Galena Group limestone, North Aurora, Illinois, USA: M.S. thesis, Water Well database and the Illinois State Geological Survey Geological Records Unit the northwest for about 85 miles, to near Oregon. The fault zone is about one-half to currence of sulfide deposits of commercial value near Oregon is unlikely. The only University of Illinois at Urbana-Champaign, 86 p. (https://www.ideals.illinois.edu/ were accessed for water well records. Drill cuttings or sample sets (SS) were examined two miles wide and is downthrown on the northeast side as much as 800 to 900 feet evidence of sphalerite in the Oregon Quadrangle was a small crystal found in a vug in handle/2142/16203) for subsurface data. Several rock cores within the quadrangle were examined at the the Franconia Formation at 55.2 feet depth in the borehole drilled for this study (Dirk- (Templeton and Willman 1952) at its midpoint in southeastern De Kalb County (Kolata Earthquakes in Illinois: 1795-2010: Illinois State Geolgical Survey, (http://www.isgs. ISGS Annex. sen #1) in Sec. 3, T23N, R10E. et al. 1978). Kolata et al. (1978) show the faulting in Oregon to be just to the north of illinois.edu/research/earthquake-hazards/pdf-files/earthquakes-il.pdf) Accessed Au- the northern terminus of the Sandwich Fault Zone. Just to the south of Oregon, in the gust 2, 2010. Stratigraphy Grand Detour 7.5-minute quadrangle, the Sandwich Fault Zone has between 0 to 300 Sand and Gravel feet of structural relief. The fault zone has undergone several movements throughout Unconsolidated sand and gravel deposits occur in thick, discontinuous pods within the Physiographic divisions of Illinois: Illinois State Geolgical Survey, (http://www.isgs.il- The bedrock formations that underlie the Oregon Quadrangle are Cambrian and Ordovi- geologic time, first in Devonian and then in late Paleozoic time; this later movement quadrangle. In Coon Creek (SW Sec. 21, T24N, R10E), the sand and gravel deposits are linois.edu/maps-data-pub/publications/pdf-files/physio-w-color-8x11.pdf) Accessed cian magnesian carbonates and siliciclastics. The sediments were all deposited in near- was a major event and was contemporaneous with the deformation of the La Salle Anti- being utilized on-site for golf course maintenance. On the west bank of a southward- August 2, 2010. shore or marine environments. The Cambrian rocks are all assigned to the St. Croixan clinorium. No quaternary movements have been documented. flowing tributary to Honey Creek (SE corner, Sec. 1, T23N, R10E), a large, abandoned Series. The Ordovician strata comprise the Ibexian (Ross 1993) and Mohawkian Series sand and gravel pit was examined. Sand and gravel deposits are extensive throughout Knappen, Russell S., 1926, Geology and mineral resources of the Dixon Quadrangle: Illinois State Geological Survey, Bulletin 49, 141 p., 2 plates, scale 1:62,500. (Thompson 1991), and they are further divided into the Prairie du Chien, Ancell, Plat- Plum River Fault Zone the area and will provide necessary resources for the future development of the region. teville, and Galena Groups. The Plum River Fault Zone trends east-west through Carroll and Ogle Counties, ex- Kolata, Dennis R., and T.C. Buschbach, 1976, Plum River Fault Zone of northwestern tending westward across the into Iowa. The fault zone is defined by a Pure quartz sand is mined for industrial use from the St. Peter Sandstone about three Illinois: Illinois State Geological Survey, Circular 491, 20 p. The Oregon Quadrangle contains one of the two reported outcrops in Illinois of the narrow belt of high-angle faults with a maximum of 270 feet of displacement, with the miles southwest of the city of Oregon in the adjacent Daysville Quadrangle. The sand- Franconia Formation, which is the oldest formation exposed in the quadrangle and in north side downthrown (Bunker et al. 1985). The displacement decreases eastward and stone is poorly cemented and friable because its clay content is low. The purity and Kolata, Dennis R., T.C. Buschbach, and Janis D. Treworgy, 1978, The Sandwich Fault the state. In most places, the Franconia Formation is overlain by the Potosi Dolomite; is 100 to 200 feet about nine miles north of Oregon. The fault system was mapped on thickness of the St. Peter Sandstone make it a viable resource for glass manufacturing Zone of northern Illinois: Illinois State Geological Survey, Circular 505, 26 p. the nature of the contact between the formations is unknown. Just to the east of the the basis of limited outcrop control along with borehole data (Kolata and Buschbach and enhanced recovery from hydrocarbon reservoirs. Rock River and the city of Oregon in Sec. 3, T23N, R10E, the Franconia is directly Kolata, Dennis R., Janis D. Treworgy, and T.C. Buschbach, 1983, Structure map of 1976). Although not numerous, there are outcrops showing fracture zones, faults, and the top of the Franconia Formation in northern Illinois, in D.R. Kolata, and A.M. overlain by the St. Peter Sandstone, from which it is separated by an angular unconfor- Stone cataclastically deformed rock in Illinois. Graese, Lithostratigraphy and Depositional Environments of the mity. The Cambrian Franconia Formation and Potosi Dolomite are mapped as a single Dolomite is extensively quarried from the Platteville and lower Galena Groups. The (Ordovician) in northern Illinois: Illinois State Geological Survey, Circular 528, 49 unit because outcrop control is poor and surface exposure is limited. dolomite is primarily used for road gravel, fill and aggregate, and was formerly quar- Strike-slip component of faulting p. Marshak et al. (2003) studied several examples of United States continental interior ried for dimension stone on the Stronghold property in SW Sec. 28, T24N, R10E. Three The stratigraphic interval between the Cambrian Potosi Dolomite and the Ordovician platform faulting, including the Sandwich and Plum River Fault Zones. They reexam- commercial quarries are active within the quadrangle—Thorpe Quarry (center of Sec. Kolata, Dennis R., 2010, Personal communication: Champaign, Illinois. St. Peter Sandstone has been locally thinned by pre-St. Peter warping and erosion. In ined the observations made by Templeton (1951) and interpreted the faults near Oregon 2, T23N, R10E), Martin Quarry (NE Sec. 32, T24N, R10E), and Steve Benesh and Sons Marshak, S., Nelson, W.J., and McBride, J.H., 2003, Phanerozoic strike-slip faulting in the southwestern quarter of the quadrangle, the St. Peter Sandstone overlies the Shako- as a subparallel, en echelon fault array dominated by dip-slip with a component of (NW Sec. 23, T24N, R10E). Nine small pits probably quarried stone for local uses; the continental interior platform of the United States: examples from the Laramide pee Dolomite; but in the remaining three-fourths of the quadrangle, the St. Peter scours strike-slip movements. these pits are unnamed and abandoned. All of the quarry exposures provided impor- down to formations as low as the Potosi Dolomite (Willman et al. 1975, p. 59). Locally, tant information about the stratigraphic relationships and structural features within the Orogen, Midcontinent, and Ancestral Rocky Mountains, in Storti, F., Holdsworth, R.E., and Slavini, F., eds., Intraplate Strike-slip Deformation Belts: Geological Soci- the St. Peter Sandstone overlies the Franconia Formation (in City of Oregon water well, Minor Structural Features quadrangle. ety of London Special Publication 120, p. 171–196. SS 64615, Sec. 3, T23N, R10E). Several minor faults and folds, which have short lateral extent, were recognized by Templeton (1951) by surface outcrops and well records. They are discussed herein and Natural Hazards Nelson, W.J., 1995, Structural Features in Illinois: Illinois State Geological Survey Bul- The St. Peter Sandstone and the overlying shales and sandy dolomites of the Glenwood are listed in alphabetical order. letin 100, 144 p. Formation compose the Ancell Group; the St. Peter and Glenwood are mapped as a Karst single unit. The St. Peter Sandstone covers the southern lowlands, lies under thick Qua- The Ashton Arch (Willman and Templeton 1951; Kolata et al. 1978; Templeton 1951) The Platteville and Galena Group dolomites lie at the surface in the majority of the Ross, R.J., Jr., Hintze, L.F., Ethington, R.L., Miller, J.F., Taylor, M.E., and Repetski, ternary sand and gravel deposits beneath the city of Oregon, and underlies State Route is a broad feature that lies on the southwestern (upthrown) block of the Sandwich Fault quadrangle beneath thin glacial drift or loess deposits. The dolomite is subjected to J.E., 1993, The Ibexian Series (Lower Ordovician), a replacement for “Canadian 64, which runs east to west through the quadrangle. The St. Peter underlies the main Zone. It trends roughly parallel to the fault zone and extends from southern Ogle Coun- weathering and erosion, which can cause sinkholes to form and lead to karstification. Series” in North American chronostratigraphy: U.S. Geological Survey Open-File tributary of the Rock River near Oregon and probably to at least as far north as Byron. ty to northeastern La Salle County. It reaches a structural high in Ogle County with a Sinkholes were discovered within the quadrangle in the Dunleith Formation. Report 93-598, 75 p. It is massive, extremely pure quartz sandstone and a major aquifer in the region. The maximum structural relief of about 500 feet. Farther to the southeast, it merges with the Templeton, J.S., 1939, The geology of part of the Woosung Quadrangle: Ph.D. disserta- Glenwood Formation is separated from the St. Peter by a sharp and angular unconfor- Earthquakes La Salle Anticlinorium in the center of Lee County. tion, University of Illinois, Urbana, 157 p. mity. Several dozens of joints, fractures, and faults occur within the quadrangle, but it is The Oregon Anticline was recognized by Bevan (1935b, 1939), Willman and Templeton believed that they are inactive. The connections of fault and fold zones to regional Templeton, J.S., ca. 1940, Draft geologic maps of the Oregon 15-minute quadrangle: Il- The dolomites and limestones of the Platteville Group are mapped as a single unit. (1951), and Kolata et al. (1978, 1983). It is a broad, low flexure located on the northeast seismicity in the northern Illinois region is poorly understood. Using the record of past linois State Geological Survey, Map Room 4107 d5.1-180, 4 sheets, 1:62,500. The thicknesses of the Pecatonica, Mifflin, Grand Detour, Nachusa, and Quimbys Mill (downthrown) side of the Sandwich Fault Zone, and it trends parallel to the axis of the seismicity, there is low seismic risk in the region. Templeton, J.S., ca. 1942, Field notes: Illinois State Geological Survey, Map Room. Formations range from 10 to 43 feet, which does not justify a mappable unit at the fault zone (Nelson 1995). The maximum structural relief on the Franconia Formation is 1:24,000 scale. The combined thicknesses of the five formations ranges from 105 to 200 to 300 feet. The Oregon Anticline is probably genetically related to the fault zone. Landslides Templeton, J.S., 1951, The geology and mineral resources of the Oregon Quadrangle: 120 feet, which constitutes a mappable unit. The glacial till and loess deposits range from 0 to 15-feet-thick in the study area. At the Illinois State Geological Survey, unpublished manuscript Ms. #3, 2 folders. The Mud Creek Fault Zone, named by Nelson (1995, p. 86) was observed by Temple- head of a small ravine (1800’ EL, 4250’ NL, Sec. 2, T23N, R10E), a slump scarp was Similarly, the dolomites of the Galena Group are mapped as one unit. The absence or ton and Willman (1952) in a small abandoned quarry just to the west of Oregon, in the observed in Quaternary deposits atop Platteville dolomites. Quaternary unconsolidated Templeton, J.S., and H.B. Willman, 1952, Central Northern Illinois: Guidebook for the thinness of the Guttenberg Formation in the Oregon area require that it be combined Mount Morris Quadrangle (NW SW SE Sec. 30, T24N, R10E). The fault and associated deposits (till and loess) are rich in clay and silt, and when saturated during periods of 16th Annual Field Conference of the Tri-State Geological Society: Illinois State with the overlying Dunleith Formation. monocline strike westward and have a cumulative displacement of 100 feet downthrown heavy and consistent rainfall, they can cause landslides. Geological Survey, Guidebook Series 2, 47 p. on the north. The exposure is now heavily vegetated and geologic relationships are no Thompson, T.L., 1991, Paleozoic succession in Missouri, Part 2, Ordovician System: Glacial and post-glacial deposits occur in the quadrangle. As this is a bedrock geologic longer visible. Acknowledgments Missouri Department of Natural Resources, Division of Geology and Land Survey, map, Quaternary unconsolidated sediments are not differentiated. Most of the area Report of Investigation 70, 282 p. was covered with ice during the Illinois glacial episode, and the southern part contains The Mud Creek Syncline (Templeton 1951, p. 55) trends northeastward through Mud I would like to thank the Martin, Thorpe, and Steve Benesh and Sons quarries for al- sediments from the Wisconsin glacial episode. Quaternary sediments are mapped only Creek for a distance of about 4.5 miles. It is about one-third to 1.5-miles wide. The lowing access and supporting this study. Special thanks go to UNIMIN Corporation for Willman, H.B., and J.S. Templeton, 1951, Cambrian and lower Ordovician exposures along Leaf River and Rock River where bedrock information is lacking. structural relief does not exceed 100 feet. permitting access to their silica quarries and for supporting our research. Dennis Kolata in northern Illinois: Transactions of the Illinois State Academy of Science, v. 44, p. was an invaluable resource and contributed his time and extensive knowledge of the 109-125; reprinted in 1952, Short Papers on Geologic Subjects: Illinois State Geo- Structural Geology The Silver Creek Anticline (Templeton 1951, p. 56) extends northwestward from the region. John Nelson provided helpful reviews of this report. Gregory Durant and Carl logical Survey, Circular 179, p. 109–125. center of the Oregon quadrangle (Sec. 21, T24N, R10E) through Silver Creek, to near Carman made valuable contributions to fieldwork. I thank Judy Knilans for her patience Willman, H.R., E. Atherton, T.C. Buschbach, C. Collinson, J.C. Frye, M.E. Hopkins, The Oregon Quadrangle is located near the terminations of two regional structural Leaf River. It is about nine miles long, with an average width of about one mile. The and permission to drill on her property. J.A. Lineback, and J.A. Simon, 1975, Handbook of Illinois stratigraphy: Illinois highs, the Wisconsin Arch and the Kankakee Arch, and lies just to the north of the Il- anticline is fairly symmetrical, has a structural relief of around 50 feet or less, and dips State Geological Survey, Bulletin 95, 261 p. linois Basin. The LaSalle Anticlinorium, a discrete zone of basement faults with drape- on the limbs do not exceed three degrees. This research was supported in part by the U.S. Geological Survey National Co- folds in Paleozoic sedimentary cover, trends north-south and extends southward from operative Geologic Mapping Program (STATEMAP) under USGS award number Willman, H.R., and D.R. Kolata, 1978, The Platteville and Galena Groups in northern the Sandwich Fault Zone. Northward from the Oregon Quadrangle, the regional dip is The Stronghold Dome (Templeton 1951, p. 38-45) is a small but high structural dome G09AC00197. The views and conclusions contained in this document are those of the Illinois: Illinois State Geological Survey, Circular 502, 75 p. to the north-northeast, away from the Sandwich Fault Zone. Southward from the quad- that has brought St. Peter Sandstone to the surface in an area chiefly underlain by Ga- author and should not be interpreted as necessarily representing the official policies, rangle, regional dips are to the southwest. There are two major regional fault zones that lena and Platteville dolomites. It trends north-south and is about one-half mile wide and either expressed or implied, of the U.S. Government. are recognized in the area, the Sandwich Fault Zone and the Plum River Fault Zone. one-third mile long. Much faulting occurs near the dome, with the major fault trends Several minor structural features were also recognized by Templeton (1951). striking about N59°W.

Southwest Northeast

A Woodland AЈ Creek Elevation Byron 255 City of Oregon (feet) #MW-20 Theatre Rock River Dirksen, #1 Spring Creek PEI #Angle 1000 Og Og 1000

Op Oa _ TD 185’ TD 106’ Opdc Oa TD 234’ TD 269’ _ _ 0 0 Horizontal scale: 1 inch = 2,000 feet Vertical scale: 1 inch = 1,000 feet Og Op Oa Opdc Prairie du Chein Group _ Cambrian Galena Group Platteville Group Ancell Group Vertical exaggeration: 2ϫ

STATEMAP Oregon-BG Sheet 2 of 2