O JHkm^ Msxsfk D. *< —< r Richard C. Anderson Augustana College David H. Ma one I Robert S. Nelson Illinois State University WayneT. Frankie Russell J. Jacobson >^ f?f\ VI Illinois State Geological Survd^i 'tit*** .'» Ml, A" -•*#£ -Sag-? ' . FieldTrip Guidebook 1999B May 22, 1999 -» '* Department of Natural Resources ILLINOIS STATE GEOLOGICAL SURVEY .-*• .* Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/guidetogeologyof1999ande Guide to the Geology of the Rock Island-Milan Area, Rock County Island Richard C. Anderson Augustana College David H. Malone Robert S. Nelson Illinois State University WayneT. Frankie Russell J. Jacobson Illinois State Geological Survey FieldTrip Guidebook 1999B May 22, 1999 Department of Natural Resources ILLINOIS STATE GEOLOGICAL SURVEY Natural Resources Building 615 East Peabody Drive Champaign, IL 61820-6964 Home page: http//www.isgs.uiuc.edu Coverphoto Collinson Brothers, Milan Quarry(photoby W.T. Frankie) Geological Science Field Trips The Geoscience Education and Outreach unit of the Illinois State Geological Survey (ISGS) conducts fourfree tours each year to acquaint the public with the rocks, mineral resources, and landscapes of various regions of the state and the geological processes that have formed them. Each trip is an all-day excursion through one or more Illinois counties. Frequent stops are made to explore interesting phenomena, explain the processes that shape our environ- ment, discuss principles of earth science, and collect rocks and fossils. People of all ages and inter- ests are welcome. The trips are especially helpful to teachers preparing earth science units. Grade school students are welcome, but each must be accompanied by a parent or guardian. High school science classes should be supervised by at least one adult for each ten students. A list of guidebooks of earlierfield trips, useful for planning class tours and private outings, can be obtained by contacting the Geoscience Education and Outreach Unit, Illinois State Geological Sur- vey, Natural Resources Building, 615 East Peabody Drive, Champaign, IL 61820-6964. Telephone: (217) 244-2427 or 333-4747. Two U.S. Geological Survey 7.5-Minute Topographic Quadrangle maps (Coal Valley and Milan) coverthis field trip area. Editorial Board Jonathan Goodwin, Chair Michael Barnhardt Anne Erdmann Brandon Curry David Larson Heinz Damberger Donald Mikulic William Roy ILLINOIS NttAPATIUWLRNAlQLi RESOURCE9 printedwith soybeaninkon recycledpaper Printedbyauthorityofthe State ofIllinois/1999/500 CONTENTS ROCK ISLAND-MILAN AREA 1 Geologic Setting 1 Stratigraphy 2 Silurian 4 Devonian 7 Pennsylvanian 8 Quaternary 9 GUIDE TO THE ROUTE 11 STOP DESCRIPTIONS 20 1 Borrow Pit of C. E. Peterson and Sons 20 2 Collinson Brothers, Milan Quarry 22 3 Moline Consumers, General Sand and Gravel Pit 22 4 Lunch: Sunset Park 23 5 Black Hawk State Historic Site 26 REFERENCES 37 GLOSSARY 39 SUPPLEMENTARY READING Period orSystem Age Era andThickness (years ago) General Types ofRocks Holocene Recent-alluvium in rivervalleys 10,000 0) 0) Qua0t-e50r0n'ary oo_eg Gllaacikaeldteilpl,osgliatcsiaolfocultaywaasnhd,sgilrta,vlelo,esssanadn,dssilat,nd dunes; coversnearlyallofstateexceptnorth- oj_tg westcomerandsoutherntip m 1.6 Pliocene •-356..36 mmiJ ChweersttegrrnaveIlll,inpoirsesentinnorthern, southernand Tertiary Mostlymicaceoussandwithsomesiltandclay; 0-500' presentlyonlyinsouthern Illinois m 57.8 Paleocene Mostlyclay, littlesand; presentonlyinsouthern 66.4 m Illinois ' Mostlysand, somethinbedsofclay, and, locally, 144 m- gravel, presentonlyinsouthern Illinois 286 m- Pennsylvanian 0-3,000' Largelyshaleandsandstonewith bedsofcoal, limestone, andclay ("Coal Measures") sss. 320 m Blackandgrayshaleatbase, middlezoneof Mississippian thicklimestonethatgradestosiltstone 0-3,500' chert, andshale; upperzoneofinterbedded sandstone, shale,andlimestone 360 m Thicklimestone, minorsandstonesandshales; I —I r- Devonian largelychertandcherrylimestoneinsouthern i ' i 0-1,500' Illinois; blackshaleattop 408 m Silurian Principallydolomiteand limestone 0-1,000' / / / /, / . 438 m Ordovician Largelydolomiteand limestonebutcontains / / 7 500-2,000' sandstone, shale, andsiltstoneformations 505 m Cambrian Chieflysandstoneswithsomedolomiteandshale; 1,500-3,000' exposedonlyinsmallareasin north-central Illinois 570 m Precambrian Igneousand metamorhpicrocks; known in Illinoisonlyfromdeepwells Generalized geologic column showing succession of rocks in Illinois. ROCK ISLAND-MILAN AREA The Rock Island, Illinois, area has been the destination for numerous geology field trips and geo- logic field conferences (for example, Edmunds and Anderson 1967, Anderson and others 1982). This field trip guidebook was developed largely from work published in these field guides. We wish to thankthe following for permission to entertheir property and help in developing this trip: Moline Consumers Inc., C. E. Peterson and Sons, Collinson Brothers, and the staff at Black Hawk State Historic Site. This guidebook is divided into four sections. The first section introduces the geology of Illinois and in particularthe Rock Island-Milan area. The second section is a road log forthe trip, and the third section provides detailed stop descriptions. The final section includes a glossary and supplemen- tary discussions of topics that are important to the field trip area. GEOLOGIC SETTING The oldest rocks present in the subsurface (termed basement rocks by geologists) of the field trip area include approximately 1.5-billion-year-old crystalline rocks of the Midcontinent Granite-Rhyolite Terrane (consisting mostly of granitic and rhyolitic igneous, and possibly metamorphic, crystalline rock). Very little is known about these basement rocks because they are not exposed anywhere in Illinois, and few (approximately 35) drill holes have penetrated deep enough to recover samples. From about 1.0 to 0.6 billion years ago, these rocks were exposed and deeply weathered into a landscape similarto that of the present Missouri Ozarks. The Illinois Basin is the major structural feature of Illinois. This broad elliptical cratonic basin began to develop as a failed arm of Precambrian rifting of North America (figs. 1 & 2). This rifting initially produced the Rough Creek Graben and the Reelfoot Rift in southernmost Illinois. These steep- walled tectonic valleys are filled with sand and gravel that was shed from the adjacent uplands. By the late Precambrian, the rifting had stopped, but the Illinois Basin remained an area of structural weakness prone to infilling of sediment throughout the Paleozoic Era. During the Paleozoic Era, strata accumulated in seas that covered Illinois and adjacent states. The shallow seas connected with the open ocean to the south during much of the Paleozoic, and the area of southern Illinois was an embayment. The southern part of Illinois and adjacent parts of Indi- ana and Kentucky sank more rapidly than areas to the north, which allowed a greaterthickness of sediment to accumulate there than elsewhere in Illinois. Where stresses built up in places, the rela- tively thin crust of the earth was periodically flexed and warped to produce both upward bends (anti- clines) and downward buckles (synclines). These movements, along with worldwide changes in sea level, produced repeated withdrawals (regressions) and invasions (transgressions) of ocean water across the slowly subsiding region. During the regressions, former sea floors were periodically ex- posed to erosion, removing some sediments from the rock record. During the Mesozoic Era, the rise of the Pascola Arch in southeastern Missouri and western Tennessee cut off the embayment and separated it from the open sea to the south. Development of the Pascola Arch, combined with the earliersinking of deeper parts of the area to the north, gave the basin its present asymmetrical, "spoon-shaped" configuration (fig. 3). Please note: although all present localities have only recently appeared within the geologictime frame, we use the present names of places and geologic features because they provide clear reference pointsfordescribing the ancient landscape. Rock Island County lies along the extreme northwestern margin of the Illinois Basin as de- fined by the occurrence of Pennsylvanian strata; immediately to the west is the Mississippi River Arch (fig. 2). The regional dip of Paleozoic strata is less than 1° toward the south and southeast. The Precambrian granite and rhyolite lie at a depth of about 4,000 feet beneath the surface in this region. These rocks are unconformably overlain by about 1,900 feet of sandstone and minor amounts of dolomite and shale (Cambrian Mt. Simon through Franconia Formations) fol- lowed by 1,800 feet of carbonate rocks, sand- stone, and shale (Cambrian Potosi through Devonian Cedar Valley formations) (see fig. 4). The Devonian rocks are unconformably overlain by varying thicknesses of Pennsylvanian shale, sandstone, and coal; and these units are subse- quently overlain by Quaternary glacial till, loess, and alluvium. This field trip will examine rocks and sediments that range in age from Silurian through Pleistocene (fig. 5). Rocks olderthan the Silurian are not exposed at the surface in the field trip area. STRATIGRAPHY Figure 1 Location ofsome ofthe majorstructures in Nearthe beginning of the Paleozoic Era, about the Illinois region. (1) La Salle Anticlinorium, (2) Illinois 570 million years ago, the rifting in and near BDaosmien,,((36))OCzinacriknnDaotimeA,rch(4,)(P7a)sRcooulaghArCcrhe,e(k5)GrNaasbhevni-lle southern Illinois stopped, and the hilly Precam- Reelfoot Rift, and (8) Wisconsin Arch. brian landscape began to slowly subside, allow- ing a shallow sea to invade from the south and southwest. During the several hundred million years of the Paleozoic Era, the area that is now southern Illinois continued to accumulate layers of sediment deposited on the bottom of the shallow seas that repeatedly covered it. The region continued to subside until at least 15,000 feet of strata were deposited. At times the seas withdrew and the deposits were weathered and eroded. As a re- sult, in Illinois there are gaps in the sedimentary record, which are called unconformities. The major gaps form boundaries that separate the Paleozoic rocks into foursuper sequences: Sauk, Tippeca- noe, Kaskaskia, and Absaroka. The major unconformities in the field trip area are shown on figure 4. Many of the sedimentary units, called formations, have conformable contacts; that is, no significant interruption in deposition occurred as one formation was succeeded by another (figs. 4 & 6). In some instances, even though the composition and appearance of the rocks change significantly at the contact between two formations, the fossils in the rocks and the relationships between the rocks at the contact indicate that deposition was virtually continuous. In contrast however, in some places the top of the lowerformation was at least partially eroded before deposition of the next formation began. In these instances, fossils and otherevidence in the two formations indicate that there is a significant age difference between the lower unit and the overlying unit. This type of contact is called an unconformity (fig. 6). If the beds above and below an unconformity are parallel, the unconformity is called a disconformity. However, if the lower beds were tilted and eroded priorto deposition of Anticline Syncline Monocline Fault,tickson F.C. FaultComplex downthrownside F.F. Faulted Flexure rMt. Crypto-explosiveor F.S. FaultSystem impactstructure F.Z. FaultZone Figure 2 Structural features of Illinois (modifiedfrom Buschbach and Kolata 1991) Chicago Rockford 100mi 00 km Figure 3 Stylized north-southcrosssection showsthestructureofthe Illinois Basin. Toshowdetail, thethicknessofthe sedimentaryrocks has been greatlyexaggerated andyounger, unconsolidated surfacedeposits have been eliminated. The oldest rocks are Precambrian (Pre--€) granites. Theyform adepressionfilledwith layers ofsedimentary rocksofvari- ousages: Cambrian (-G), Ordovician (O), Silurian (S), Devonian (D), Mississippian (M), Pennsylvanian (P), Cretaceous (K), and Tertiary (T). Scale is approximate. overlying beds, the contact between the lowertilted beds and the overlying flat-lying rocks is called an angular unconformity. Unconformities occurthroughout the Paleozoic rock record and are shown in the generalized stra- tigraphic column (located in the front of this guidebook) as wavy lines. In figure 4, the unconformities are labeled with a "U." Each unconformity represents an extended interval of time forwhich there is no rock record in this area. Silurian The oldest bedrock unit exposed at the surface in Rock Island County is the Silurian Racine Dolomite (fig. 4). We will examine the Racine Dolomite during the morning at the Collinson Brothers quarry in Milan, Illinois. Quarry operations have recently uncovered about 30 feet of the Racine. The unit ranges in colorfrom light yellow brown to light brownish or greenish gray and is as thick as 300 feet. The Racine Dolomite consists of numerous low oval reefs (bioherms) that vary in size from a few tens of feet to as much as % mile in diameter (Hinman 1968). Larger reefs are present in northeast- ern Illinois and northern Indiana. An idealized Silurian reef is shown in figure 7. The reef core con- sists of a mass of porous and fractured dolomite. The numerous fossils that are typically present in the bioherm cores include corals, stromatoporoids, crinoids, brachiopods, and molluscs. Corals and stromatoporoids were the most abundant organisms. The coral Favosites is particularly abundant.