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Home , Fort Atkinson Limestone, Maquoketa Formation, Princeton Sandstone, Quad Cities, Tradewater Formation, Washington Formation

Bedrock Geology of Scott County,

Introduction to the Bedrock Geology of Scott County, Iowa Title, Author, Agency, Contract and Acknowledgement Information LEGEND 90°52'30"W 90°45'0"W 90°37'30"W 90°30'0"W 90°22'30"W 90°15'0"W Scott County lies mostly within the Southern Iowa Drift landform region of eastern Iowa, an area of moderate topographic relief developed on eroded Illinoian and Pre-Illinoian glacial deposits, Wisconsinan loess, CAMANCHE and Paleozoic bedrock formations (Prior, 1991). Norton (1899) first described and mapped the and BEDROCK GEOLOGY OF CENOZOIC Paleozoic bedrock geology of the county and discussed the of the , and SCOTT COUNTY, IOWA B R04E strata that comprise the county’s bedrock units. Statewide bedrock geologic maps by Hershey (1969) and, R01E QUATERNARY SYSTEM most recently, by Witzke, Anderson, and Pope (2010) depict the increased understanding of the distribution of Iowa Geological and Water Survey R03E geologic units at the bedrock surface across this region, including Scott County. Open File Map OFM-11-04 Bedrock exposed at the land surface is restricted to small areas in the eastern, north-central, southern, and D D September 2011 Om northwestern portions of the county. All rock outcrops and quarries are located in close proximity to surface Sg Ss Ss U 41°45'0"N Qu – Undifferentiated unconsolidated sediment Consists of loamy soils developed in loess and glacial topographic lows coincident with the modern drainages of the Mississippi and Wapsipinicon rivers and their Om Ss prepared by D R02E Sh Qu till of variable thickness, and alluvial clay, silt, sand, and gravel. Maximum thickness can be up to 390 ft tributaries , Walnut Creek, McDonald Creek, and Dodges Creek. Throughout the remainder of the D C (119 m) in the western part of the county where Qu fills the deeply buried bedrock valley of the Cleona county bedrock is covered by moderately thick deposits of glacial sediments and bedrock formation distribution is H R05E Robert M. McKay, Huaibao Liu, Stephanie Tassier-Surine, and James Giglierano A MCCAUSLAND Channel. This unit is shown only on the cross-section and not on the map. known solely from water well drilling samples and rock cores. 41°45'0"N D A N The distribution of bedrock map units is dominantly influenced by the extremely gentle south to southwest Iowa Geological and Water Survey, Iowa City, Iowa DIXON dip of bedrock strata, approximately 12 feet per mile, in combination with the bedrock topography and the large- N Sh N Sg E scale unconformity between Pennsylvanian strata and older Devonian and Silurian formations. In the eastern part Sg L D Ss O PALEOZOIC of the county the topography of the bedrock surface is controlled by a network of -age bedrock valleys D and uplands. In the western and northern part of the county the bedrock surface is deeply incised by a major D E T80N bedrock valley called the Cleona Channel (Norton, 1899). The Cleona Channel is filled with Pre-Illinoian glacial T80N Ss L PENNSYLVANIAN SYSTEM tills and possibly represents a former channel of an ancestral . Sg C Ss Iowa Department of Natural Resources, Roger Lande, Director Prc D The oldest unit at the bedrock surface is the , a thick sequence of shale and dolomite. Prc - RACCOON CREEK GROUP (primarily Morrowan; locally includes Atokan-lower Desmoinesian Iowa Geological and Water Survey, Robert D. Libra, State Geologist NEW LIBERTY D The Maquoketa is not exposed in outcrop; it subcrops over a small area along the axis of the Cleona Channel and is Sg D Prc in upper part). Recognized only in eastern Iowa in Scott and Muscatine counties; covered by several hundred feet of Quaternary deposits. D includes in ascending order the “Caseyville” and Tradewater formations. Rests unconformably on older Prc Silurian strata comprise the largest area of the bedrock surface across the county. Witzke (1994) provides Supported in part by the U.S. Geological Survey map units in the county and fills paleovalleys and paleokarst developed in underlying Silurian and the best discussion of the Silurian stratigraphy for the county. The oldest Silurian map unit, the combined Cooperative Agreement Number G10AC00423 National Cooperative Geologic Mapping Program (STATEMAP) D Ss D Devonian carbonate rocks. Primary lithologies are: shale/mudstone, light to dark gray, partly silty to sandy; Hopkinton and Blanding formations, is restricted in subcrop to the deeper portions of the Cleona Channel. This LONG GROVE D DONAHUE Prc sandstone, very fine to medium-grained; siltstone, gray. Secondary lithologies are: carbonaceous unit, composed of cherty and moderately fossiliferous dolomite, is reached by the deeper Silurian water wells D Sg Sh shale/mudstone, gray to black; phosphatic black shale; , dense, partly fossiliferous, partly sandy; across the county. Witzke (ibid.), using drill cuttings, logs and core, provided a brief characterization of the (beds locally > 2 ft). Minor lithologies are: sandstone, coarse-grained to granular, partly Hopkinton and Blanding formations in Scott County and neighboring Clinton County. The Scotch Grove ACKNOWLEDGMENTS PRINCETON conglomeratic; mudstone, red to pink; limestone concretions (may be septarian); cone-in-cone limestone; Formation, primarily a moderately to abundantly -moldic dolomite, occurs across the county above the Ss New subsurface geologic data was partly generated by University of Iowa student Kyle Bracken who produced descriptive logs of Ss siderite/ironstone concretions and pellets; pyritic. Maximum thicknesses: 195 ft (59 m). Hopkinton-Blanding except where it is truncated within the Cleona Channel system. The Scotch Grove is an water well drilling samples. Thanks to Riverstone Group Inc., Linwood Mining and Minerals Corp., and LaFarge Corporation for D important aquifer, and its upper portion is quarried for construction aggregate. The Gower Formation overlies the access to and information about quarries in the county. Deborah Quade (IGWS) lent support with Quaternary field and office rs130 Prc Prc Scotch Grove Formation and is the most widespread surfacial bedrock map unit across the county. It is a laminated expertise; Jason Vogelgesang (IGWS) prepared well samples for stratigraphic logging; Ray Anderson and Brian Witzke (IGWS) provided valued information concerning the bedrock topography, geology, and Paleozoic stratigraphy of the area; and Bill Bunker and (Anamosa Member) to moderately fossilliferous (LeClaire Member) dolomite that attains maximum thickness in Sg Andy Asell (IGWS) provided GIS mapping technical help. D DEVONIAN SYSTEM Prc the eastern portion of the county at LeClaire. The LeClaire Member may be horizontally bedded but also may Prc Prc exhibit prominent “mounding” where fossiliferous beds may dip up to 45 degrees; horizontally bedded and Prc Dl - LIME CREEK FORMATION (Upper Devonian, upper ). The formation is comprised Prc T79N Dl laminated Anamosa Member may occur laterally to the mounded LeClaire Member. Construction aggregate is 67 MAYSVILLE Sg Sg ¤£ entirely of the Sweetland Creek Shale in the southwest portion of the county. Primary lithologies are light produced from several large quarries in the Gower Formation from the northern half of the county. green to brown shale and green siltstone containing an abundant and diverse fossil conodont fauna. Devonian strata of the Wapsipinicon Group, the Cedar Valley Group, and the Lime Creek Formation Prc Prc ELDRIDGE Prc Maximum thickness up to 12 ft (4 m). comprise Mid-Paleozoic bedrock map units across the southern half of the county. The Wapsipinicon Group T79N 41°37'30"N outcrops at numerous points in Davenport and Bettendorf along the Duck Creek drainage, and the group’s Dc – CEDAR VALLEY GROUP (Middle-Upper Devonian, middle -lower Frasnian). The group uppermost division, the Davenport Member, is named for those exposures. The group contains limestone, Dc includes in ascending order the Little Cedar, Coralville, and Lithograph City formations. Primary dolomite, and minor shale; is partly brecciated; and is underground mined at Buffalo where it is an important source D of high-calcium limestone, high-quality aggregate, and portland cement feedstock. Day (2006) and Witzke and Prc lithologies are: fossiliferous limestone, with an abundant and diverse invertebrate fauna, variably 41°37'30"N Bunker (2006) summarize the stratigraphy and paleontology of the Wapsipinicon Group in the area. The overlying D argillaceous, partly biostromal; and dolomite, partly fossil-moldic to vuggy, variably argillaceous. Cedar Valley Group is restricted to the southwest part of the county. Near the town of Buffalo a thick succession of D Maximum thickness of 85-90 ft (26-27 m) occurs in the southwest portion of the county near Buffalo. Prc fossiliferous Cedar Valley are quarried for portland cement production, and several investigations of the D D excellent exposures at the LaFarge Corporation quarry describe numerous aspects of the group (Day, 2006; Witzke Correlation of Map Units 80 Prc D Dw Dw - WAPSIPINICON GROUP (Middle Devonian, upper -middle Givetian). The group includes and Bunker, 2006). The youngest Devonian map unit is the Lime Creek Formation, a thin shale unit that lies Dw § LE CLAIRE ¨¦ in ascending order the Bertram, Otis, and Pinicon Ridge formations. Primary lithologies are: dolomite, Sg Prc unconformably above the Cedar Valley Group in the southwest corner of the county. In southeast Iowa, the Lime DURANT partly laminated, variably argillaceous, part fetid; and limestone, dense, “sublithographic,” partly laminated Creek is comprised entirely of the Sweetland Creek Shale. Bunker and Witzke (1992) discuss the regional Dw to intraclastic; dolomite, fossil-moldic to vuggy (lower Otis Fm). Secondary lithologies are: stratigraphy of the Lime Creek and Sweetland Creek, and Over (2006) provides a recent description of the type Sg Prc section in adjacent Muscatine County. STOCKTON limestone/dolomite breccia (evaporite collapse, upper Pinicon Ridge Fm); dolomitic shale and shaly M

R01E S

WALCOTT Prc Prc Pennsylvanian System strata of the Raccoon Creek Group comprise the youngest bedrock map unit in the E dolomite, gray to green-gray, partly silty-sandy; limestone, partly peloidal-oolitic to fossiliferous (Otis Fm). E

Dw I T78N county. Raccoon Creek strata rest unconformably on Silurian Scotch Grove and Gower formations, and all T R Minor lithologies are: chert and chalcedony nodules (Pinicon Ridge Fm); and sandstone, fine to medium AGE S MAP E with larger dolomite clasts (Bertram Fm). Maximum thicknesses of 112 ft (34 m). Devonian groups and formations. The lower portions of the Raccoon Creek Group fill paleokarst and paleovalleys Y STAGE S BETTENDORF Dw R05E developed on the underlying Silurian and Devonian carbonate rocks and contain, at certain localities, superb fossil (Ma) S UNIT Prc D plant assemblages (Leary, 1994). The name Raccoon Creek Group has recently been introduced into Iowa by Pope

and Anderson (2009) and Pope (2011); their revised nomenclature is employed by Witzke, Anderson, and Pope 6 QUATERNARY ¤£ 74 PANORAMA PARK Qu Dc Dw ¨¦§ SILURIAN SYSTEM (2010). The Raccoon Creek Group, comprised of the Caseyville and Tradewater formations, is dominated by shale, Pleistocene DAVENPORT mudstone, and sandstone with subordinate coal and minor limestone. Historic coal and clay production came from 2.58 D Dw Sg - GOWER FORMATION (Lower-?Upper Silurian, Wenlock-?Ludlow). The formation includes underground mines and surface pits within the Raccoon Creek group. major unconformity T78N D DD Sg D Prc Anamosa and LeClaire members; LeClaire Member can be a fossiliferous carbonate mound facies or a 307 Prc DD D References DD DD RIVERDALE horizontally stratified fossil-moldic facies. Erosionally beveled and truncated beneath Dw. Primary e

l D Desmoinesian

lithologies are: laminated to stromatolitic dolomite (Anamosa Mbr), part fetid/organic; dolomite mudstone, d Prc Bunker, B. J., and Witzke, B.J., 1992, An upper Middle through lower Upper Devonian lithostratigraphic and conodont N d

Prc A

280 i D dense, featureless. Secondary lithologies are: dolomite, fossiliferous to vuggy, moldic,; dolomite, partly biostratigraphic framework of the Midcontinent Carbonate Shelf area, Iowa, in Day, J. and Bunker, B. J. (eds.), The I Prc ¨¦§ N coarsely crystalline, vuggy, fossiliferous to sparsely fossiliferous, part crinoidal and coralline (LeClaire stratigraphy, paleontology, depositional and diagenetic history of the Middle-Upper Devonian Cedar Valley Group of M

A Atokan Central and eastern Iowa: Iowa Department of Natural Resources, Geological Survey Bureau, Guidebook Series No. Mbr). Minor lithologies are: chert; intraclastic dolomite. Maximum thickness occurs at LeClaire, 150 ft (46 312 V 16, p. 3-25. L

67 m); thins to the southwest to 70 ft (21 m) at Blue Grass. Y D ¤£ r Prc S 61 D D Day, J., 2006, Overview of the Middle-Upper Devonian sea-level history of the Wapsipinicon and Cedar Valley groups, with e

¤£ N R04E discussion of new conodont data from the subsurface Cedar Valley Group of southeastern Iowa, in Day, J., Luczaj, J., w Morrowan o Ss - SCOTCH GROVE FORMATION (Lower Silurian, upper Llandovery-lower Wenlock). The N

41°30'0"N L Ss and Anderson, R. (eds.), New perspectives and advances in the understanding of lower and middle Paleozoic epeiric E BLUE GRASS formation includes the Johns Creek Quarry, Welton, Buck Creek Quarry, Waubeek, and Palisades-Kepler carbonate depositional systems of the Iowa and basins: Iowa Geological Survey Guidebook Series No. 26, p.3- P members. The bulk of the formation is comprised of the finely fossil-moldic Welton Member. Carbonate 21. 318 mound facies of the Palisades-Kepler Member are replaced laterally by inter-mound strata of the Waubeek Hershey, H. G., 1969, Geologic map of Iowa, Iowa Geological Survey, scale 1:500,000 (out of print). major unconformity 41°30'0"N Member. Everywhere overlain by the Gower Formation. Primarily lithologies are: dolomite, porous, fossil- moldic to vuggy, part very crinoidal (includes Welton Mbr); dolomite, cherty to very cherty, dense (Buck Leary, R. L., 1994, Paleobotany of Pennsylvanian channel fills at Allied Quarry, in Bunker, B.J. (ed.), Paleozoic Stratigraphy 375 Creek Quarry Mbr). Secondary lithologies are: dolomite, sparsely fossil-moldic, dense, part vuggy of the Quad-Cities Region East-Central Iowa, : Geological Society of Iowa Guidebook 59, p. 85- (includes Waubeek Mbr); dolomite, coarsely crystalline, part very crinoidal (within Johns Creek Quarry 98. Dl Dw r T77N R03E and Palisades-Kepler mbrs); dolomite mudstone, dense. Minor lithologies are: dolomite, slightly Norton, W. H., 1899, Geology of Scott County: Iowa Geological Survey, Annual Report, v. 9, p. 389-520. e p Frasnian argillaceous; quartz druse, chalcedony, silicified . Maximum thicknesses of 150 ft (46 m). Over, D.J., 2006, Frasnian- boundary at the type Sweetland Creek Shale locality, in Day, J., Luczaj, J., and p

Anderson, R. (eds.), New perspectives and advances in the understanding of lower and middle Paleozoic epeiric U D D Sh – HOPKINTON AND BLANDING formations (Lower Silurian, ?, -upper carbonate depositional systems of the Iowa and Illinois basins: Iowa Geological Survey Guidebook Series No. 26, 385 N

Dl p.75-79. A Dc Sh I BUFFALO Llandovery. The Blanding Formation marks the base of the Silurian in the county and is overlain by the

N Dc D substantially thicker Hopkinton Formation. The map unit is at the bedrock surface only within the deeply Pope, J.P. and Anderson, R. A., 2009, Revision of stratigraphic nomenclature and reclassification of the Morrowan, Atokan,

22 O rs Desmoinesian, Missourian, and Virgilian stages in Iowa: Geological Society of America Abstracts with Programs, v. buried bedrock valley (Cleona Channel) in the northern and western part of county. Primary lithologies are: V Givetian

41, No. 2, p. 33. e E dolomite, fossil-moldic to vuggy, fine to coarse crystalline; dolomite, dense to porous, cherty to very l d A D cherty, nodular to bedded chert (especially Blanding Fm). Maximum map-unit thicknesses of 110 ft (35 m); Pope, J.P., 2011, Description of units, revision of stratigraphic nomenclature, and reclassification of the Morrowan, Atokan, d 390 i R02E Desmoinesian, Missourian, and Virgilian stages (Cherokee, Marmaton, Bronson, City, Lansing, Douglas, Dw

Hopkinton 95 ft (30 m); Blanding 15 ft (5 m). M Shawnee, and Wabaunsee groups) in Iowa: manuscript submitted and under review, Iowa Geological and Water Survey, 131p. 90°52'30"W 90°45'0"W 90°37'30"W 90°30'0"W 90°22'30"W Prior, J. C., 1991, Landforms of Iowa: University of Iowa Press, 153 p. Eifelian SYSTEM 395 Witzke, B. J., 1994, Silurian Stratigraphy in the Area, Iowa-Illinois, in Bunker, B.J. (ed.), Paleozoic Stratigraphy Om - MAQUOKETA FORMATION (Upper Ordovician; Richmondian [upper Katian]). The formation of the Quad-Cities Region East-Central Iowa, Northwestern Illinois: Geological Society of Iowa Guidebook 59, p. 3- 15. major unconformity Om includes in ascending order the Elgin, Clermont, Fort Atkinson, and Brainard members. The map unit is at 1:100,000 Witzke, B. J., and Bunker, B.J., 2006, Stratigraphy of the Wapsipinicon Group (Middle Devonian) in southeastern Iowa, in o

the bedrock surface only within the deeply buried bedrock valley (Cleona Channel) in the northern part of l

0 1 2 4 6 8 Day, J., Luczaj, J., and Anderson, R. (eds.), New perspectives and advances in the understanding of lower and middle d county. Primary lithologies are: shale, green-gray, variably dolomitic, mostly unfossiliferous; dolomite, u Miles Paleozoic epeiric carbonate depositional systems of the Iowa and Illinois basins: Iowa Geological Survey Guidebook L argillaceous, partly shaly, variably fossiliferous; dolomite, partly argillaceous, partly cherty. Secondary Series No. 26,, p.47-58. 423 r Kilometers e p

lithologies are: shale, brown to brown-gray, organic, partly graptolitic, partly finely laminated (lower n p

0 1 2 4 6 8 Witzke, B. J., and Bunker, B.J., 2006, Middle shelf facies of the Cedar Valley Group (Devonian) and their stratigraphic a i Sg

strata); interbedded dolomite and shale, partly fossiliferous. Minor lithologies are: dolomite, phosphatic, k relationships in eastern Iowa, in Day, J., Luczaj, J., and Anderson, R. (eds.), New perspectives and advances in the U c o

argillaceous (Elgin Mbr). Maximum thicknesses of 210 ft (64 m). understanding of lower and middle Paleozoic epeiric carbonate depositional systems of the Iowa and Illinois basins: l n

Iowa Geological Survey Guidebook Series No. 26, p.23-46. e W Witzke, B.J., Anderson, R.R. and Pope, J.P., 2010, Bedrock Geologic Map of Iowa, scale: 1:500,000: Iowa Geological and N 428 A Ss G EO LO G IC C R O SS-SE C TIO N A -B Water Survey, Open File Digital Map OFM-10-1 or printed Map Series, no. M-22. I R U

U IOWA CITY - CLINTON FAULT ZONE A normal, probably near vertical fault zone, trending through L I n

D S the northwest corner of the county with relative movement up on the north side and down on the south side. a i r r

Although not exposed, the fault has approximately 100-150 ft (30-45 m) of stratigraphic offset. e Sh

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e MUSCATINE 400 400 Map projection and coordinate system based on Universal Transverse Mercator (UTM) Zone 15, datum NAD83.

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v ( The map and cross section are based on interpretations of the best available information at the time of

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FREMONT PAGE TAYLOR RINGGOLD DECATUR WAYNE APPANOOSE DAVIS VAN BUREN Om LEE 200 200