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BEDROCK GEOLOGY OF LEGEND BREMER COUNTY, Bedrock Geology of Bremer County, Iowa Iowa Geological and Water Survey CENOZOIC Open File Map OFM-10-0110 August 2010 SYSTEM 92°30'0"W 92°22'30"W 92°15'0"W 92°7'30"W prepared by

Qu – Undifferentiated unconsolidated sediment Consists of loamy soils developed in loess and glacial Robert M. McKay, Huaibao Liu, and James D. Giglierano till of variable thickness, and alluvial clay, silt, sand and gravel. Total thickness can be up to 90 m (300 ft) R11W Qu R14W R13W R12W in the eastern part of the county. Unit shown only on cross-section, not on map. Iowa Geological and Water Survey, Iowa City, Iowa

Dcv Om Dlc Dw Dw Dcv Sw Dw Dw Dlc PALEOZOIC Dlc D Sw D FREDERIKA Dcv SYSTEM Dw Dw Dcv 42°52'30"N 42°52'30"N Dcv Dlgc - Dolomite, , and Shale (Lithograph City Formation) Middle to Upper Devonian. Iowa Department of Natural Resources, Richard A. Leopold, Director Dlc Shb Dlc T Dlgc Iowa Geological and Water Survey, Robert D. Libra, State Geologist

9 Maximum thickness of this map unit is up to 15 m (45 ft), consisting of, in ascending order, Osage Springs Sw 3

N Dcv N Member which is dominated by dolomite and dolomitic limestone, in part argillaceous and fossiliferous; 3 9 Om T Shb Thunder Woman Shale Member which is characterized by grey shale, slightly dolomitic and silty; and Dcv Om Supported in part by the U.S. Geological Survey Shb SUMNER partial Idlewild Member which is characterized by interbeds of laminated lithographic and sublithographic Cooperative Agreement Number G09AC00190 93 rs188 rs limestone and dolomitic limestone with scattered to abundant and/or stromatoporoids. National Cooperative Geologic Mapping Program (STATEMAP) PLAINFIELD Dcv Shb Dcv Om Dcv Dcv - Limestone and Dolomite (Coralville Formation) Middle Devonian. Thickness of this formation varies between 0 and 10 m (0-32 ft), and is dominated by limestone, dolomitic limestone, and dolomite, in ACKNOWLEDGMENTS Dw Om part laminated and argillaceous; brachiopods and are usually abundant in the limestone facies.

Shb D Dw New subsurface geologic data was mostly generated by University of Iowa students Kyle Bracken and Sarah Byram who produced Dcv Dw Dlc - Dolomite and Limestone () Middle Devonian. The thickness of this formation Dlc descriptive logs of water well drill samples. Special thanks to Paul Niemann Construction, owner of the Denver-Foelske and the TRIPOLI ranges from 27 to 36 m (90-120 ft) in this quad. It is dominated by slightly argillaceous to argillaceous Tripoli quarries and BMC Aggregates, owner of the Frederika Quarry. Thomas Marshall of the Iowa Geological and Water Survey Dlc dolomite and dolomitic limestone, usually vuggy and partially laminated and/or cherty. This unit is (IGWS) provided additional descriptive logging of water wells. Michael Bounk (IGS) participated in part of the field work; Deborah Dlc Shb commonly fossiliferous and brachiopods are especially abundant in lower portion. Quade and Stephanie Tassier-Surine (IGWS) lent support with Quaternary field and office expertise; Jason Vogelgesang and Murray Dw Perdue (IGWS) prepared well samples for stratigraphic logging; Ray Anderson and Brian Witzke (IGS) provided valued information concerning the bedrock topography, geology and Devonian and of the area; and Bill Bunker, Chris Kahle and ¤£218 Shb D Om Dw - Dolomite, Limestone, Shale, and minor Sandstone (Wapsipinicon Group) Middle Devonian. This Andy Asell (IGWS) provided GIS mapping technical help. Dw Dw map unit usually contains the Pinicon Ridge Formation only, with a total thickness that varies between 6 Dlc and 12 m (18-40 ft) in the mapping area. It is dominated by laminated or brecciated, unfossiliferous Dlc 63 T

Dw ¤£ 9

2 limestone and dolomite that is sometimes sandy and cherty at its base.

N Shb Shb D N 2 Shb

9 Dw T Dlc SILURIAN SYSTEM

D D Om Shb Dw Shb – Dolomite with Chert (Hopkinton and Blanding formations) Lower Silurian. Total thickness up to Introduction to the Bedrock Geology of Bremer County, Iowa 42°45'0"N Shb Shb 20 m (65 ft). -moldic to vuggy dolomite, and cherty to very cherty with nodular to bedded chert in 42°45'0"N Dlc Dlgc the upper part of the Blanding. include corals, brachiopods and stromatoporoids. Bremer County lies totally within the Iowan Surface landform region of northeast Iowa, an area of subdued D topographic relief developed on eroded Pre-Illinoian glacial deposits, Wisconsinan loess, and Paleozoic bedrock D D Shb Shb formations (Prior, 1991). Norton (1906) first described and mapped the Quaternary and Paleozoic bedrock geology of the D D Sw – Limestone with Chert (Waucoma Formation) Lower Silurian. Total thickness up to 20 m (65 ft). DD Shb county, and discussed the stratigraphy of Devonian and Silurian strata that were exposed at the land surface. He also Sw This unit is a limestone facies that correlates with dolomite strata of the Blanding and lower Hopkinton noted the presence of strata at the bedrock surface in areas covered by thick glacial deposits. Statewide Dcv D WAVERLY Shb formations; it occurs in the northeast part of the county. Primary lithology is dense fossiliferous limestone, Dw bedrock geologic maps by Hershey (1969), and most recently, by Witzke, Anderson, and Pope (2010), depict the D Om and secondary lithologies are cherty to very cherty limestone to dolomitic limestone with silty to sandy D increased understanding of the complex distribution of geologic units at the bedrock surface across this region, including 3 dolomite locally at the base above the Maquoketa Formation. D rs D Bremer County. D Bedrock exposed at the land surface is restricted to the northern and western portions of the county and all rock rs116 READLYN Shb ORDOVICIAN SYSTEM D outcrops and quarries are located in close proximity to surface topographic lows coincident with the modern drainages of Shb Dlc D Dlc Dw D the Shell Rock River, the Cedar River and its tributaries Baskins Run and Quarter Section Run, and Crane Creek, and the D D Dlc Om – Shale and Dolomite (Maquoketa Formation) Upper Ordovician. Total thickness up to 78 m (250 ft). Dlc T Wapsipinicon River. Throughout the remainder of the county bedrock is covered by thick deposits of glacial sediments, Shb 9 Om D Dlc Interbedded green to gray dolomitic shale and shaly dolomite with minor limestone; variably cherty and

A 1 N Dlc Shb N 1 and bedrock formation distribution is known solely from water well cuttings samples.

9 D Dlc variably fossiliferous with brachiopods and graptolites; thin brown to brown-gray dolomitic shale layers D

T DD Dlc D Om Dw DD D occur in lower 10 m (33 ft). The distribution of bedrock map units is dominantly influenced by the extremely gentle southwest dip of bedrock D DD Dlc D D D DDD D D strata, approximately 15 to 20 feet per mile, in combination with the bedrock topography; gentle structural upwarp of D D Dw B Dlgc D D D Dw strata appears to superimpose a subtle contribution. In the eastern and southern portions of the county the topography of D D Dlc DENVER D D Drill Holes D DD Dlc the bedrock surface is controlled primarily by a complex network of buried pre- and Pleistocene age bedrock Dw Dlc Dw Dw D Dlc valleys and uplands. In the western and northern part of the county where the bedrock surface is elevated enough to D D D Bedrock Outcrops intersect modern drainages bedrock topography is influenced more strongly by the modern stream corridors. 218 Dlc Dcv ¤£ Dlgc Om D Dw The oldest bedrock mapped at the bedrock surface is the Maquoketa Formation, a thick sequence of shaly and D D JANESVILLE cherty dolomite and lesser dolomitic green, gray and brown shale. The Maquoketa is not exposed in outcrop due to it 281 R14W R13W R12W R11W rs occupying the deeper portions of bedrock valleys that are buried by thick glacial deposits. Correlation Chart Silurian strata of the combined Hopkinton and Blanding formations are exposed along Baskins Run, Quarter 42°37'30"N 42°37'30"N Section Run and Crane Creek and the Cedar River. The unit, composed of clean to cherty and moderately fossiliferous to extremely fossiliferous dolomite, is the major bedrock unit quarried in the county for construction aggregate. The area of 92°30'0"W 92°22'30"W 92°15'0"W 92°7'30"W the Loomis and Denver-Folske quarries along Baskins Run, and that of the Tripoli Quarry along the northern part of M S

E Location Map Crane Creek, has been the subject of several fieldtrips and investigations over the . (Dorheim and Koch, 1962; E I 1:100,000 T R S Bunker, Klapper and Witzke, 1983; Anderson, Smith, and Walters, 1992; and Walters, 1996). These quarries host the 0 1 2 4 6 8 10 AGE MAP E Miles Y STAGE best exposures of Silurian bedrock in the county and exposures at the Denver-Folske Quarry illustrate pre-Devonian S S (Ma) LYON UNIT OSCEOLA DICKINSON EMMET WORTH MITCHELL HOWARD WINNEBAGO WINNESHIEK ALLAMAKEE 0 1 2 4 6 8 10 KOSSUTH paleotopographic relief (Bremer County High) that influenced overlying Wapsipinicon Group sedimentation. The Tripoli SIOUX OBRIEN CLAY PALO ALTO CERRO Kilometers HANCOCK FLOYD CHICKASAW GORDO Quarry hosts a large pentamarid dominated biohermal buildup or mound that is unusual for the Hopkinton FAYETTE HUMBOLDT CLAYTON Qu PLYMOUTH BUENA BREMER QUATERNARY CHEROKEE POCAHONTAS FRANKLIN BUTLER VISTA WRIGHT Formation. The Waucoma Formation, a limestone facies of the Hopkinton/Blanding formations, is not exposed but is

2.58 BLACK BUCHANAN DELAWARE DUBUQUE WOODBURY WEBSTER HAWK IDA SAC CALHOUN HAMILTON HARDIN GRUNDY mapped beneath glacial deposits in the northeast corner of the county.

JACKSON JONES ± MONONA TAMA LINN CRAWFORD BENTON CARROLL GREENE BOONE STORY MARSHALL CLINTON The western third of the map area is dominated by the Devonian Wapsipinicon Group and the overlying

CEDAR HARRISON SHELBY GUTHRIE DALLAS JASPER POWESHIEK IOWA r POLK JOHNSON SCOTT Devonian Little Cedar Formation, Coralville Formation and Lithograph City Formation, all of which are carbonate AUDUBON

e MUSCATINE

p POTTAWATTAMIE CASS WASHINGTON ADAIR MADISON WARREN MARION MAHASKA KEOKUK formations of shallow marine origin within the well studied Cedar Valley Group of eastern Iowa (Bunker, Witzke and GEOLOGIC CROSS-SECTION A-B p LOUISA

U MILLS MONTGOMERY ADAMS UNION CLARKE LUCAS MONROE WAPELLO Day, 1986; Witzke, Bunker and Rogers, 1988; Bunker and Witzke, 1992; and Anderson, Smith and Walters, 1992). The JEFFERSON HENRY DES MOINES

385 FREMONT PAGE TAYLOR RINGGOLD DECATUR WAYNE APPANOOSE DAVIS VAN BUREN best exposures of these strata are along the valley walls of the Cedar River and its tributaries, the Denver Folske Quarry, N Dlgc LEE A

I and outcrops along the Shell Rock River. All of these units have been quarried in the past for construction aggregate, but Quarter Crane Dcv

Buck N A Cedar Baskins Wapsipinicon B are only secondary sources of crushed stone today. 1100 US 218 Section Creek Creek 1100 O Dlc V River e

Run l

River ( E

) 390 Denver f

Run d l

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D Dw d

e Shell Rock References i

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v 1000 1000

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Qu b Anderson, W., Smith, D., and Walters, J., 1992, Tropical seas to prairies a natural history field trip in Black Hawk and Bremer counties, Iowa, a n Qu

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Dw e e Geological Society of Iowa Guidebook 55, 60 p. o Dw

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900 v

s 900 395 t

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a a Dlc Shb

e Shb Bunker, B. J., Klapper, G., and Witzke, B.J., 1983, New stratigraphic interpretations of the Middle Devonian rocks of Winneshiek and Fayette counties,

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e northeastern Iowa, Geological Society of Iowa Guidebook 39, 38 p.

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e Bunker, B. J., Witzke, B.J., and Day, J.E., 1986, Upper Cedar Valley stratigraphy, North-Central Iowa, Lithograph City Formation, Geological Society

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Om Om v of Iowa Guidebook 44, 41 p. e

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l f 700 700 ) ( Bunker, B. J., and Witzke, B.J., 1992, An upper Middle through lower Upper Devonian lithostratigraphic and conodont biostratigraphic framework of n

a the Midcontinent Carbonate Shelf area, Iowa, Iowa Department of Natural Resources, Geological Survey Bureau, Guidebook Series No. 16, i N r p. 3-25 p. A 436 e

600 600 I v R o Dorheim, F. H. and. Koch, D.L., 1962, Unusual exposure of Silurian-Devonian unconformity in Loomis Quarry near Denver, Iowa: Proceedings of the d U

n Iowa Academy of Science, v. 69, p. 341-350. L I

a Shb Sw S 439 L Hershey, H. G., 1969, Geologic map of Iowa, Iowa Geological Survey, scale 1:500,000 (out of print). L Norton, W. H., 1906, Geology of Bremer County: Iowa Geological Survey, Annual Report, v. 16, p. 319-406. Prior, J. C., 1991, Landforms of Iowa, University of Iowa Press, 153 p. 445 Gamachian Walters, J., 1996, General and Environmental Geology of Cedar Falls/Waterloo and Surrounding Area, Northeast Iowa, Iowa Geological Survey Base map from Iowa DNR NRGIS Library (Bremer County GIS files) derived from USGS 1:100,000 scale DLGs, N n

A Guidebook 22, 115 p.

Census Bureau TIGER line files and IGS PLSS files. I a i t r C I

a Witzke, B. J., Bunker, B.J., and Rogers, F.S., 1988, Eifelian through Lower Frasnian stratigraphy and deposition in the Iowa area, central Midcontinent, Iowa Geological Survey digital cartographic file BremerCo_Bedrock10.mxd , version 8/20/10 (ArcGIS 9.3). e Om V n Map projection and coordinate system based on Universal Transverse Mercator (UTM) Zone 15, datum NAD83. p Richmondian U.S.A., in McMillan, N.J., Embry, A.F., and Glass, D.J., editors, Devonian of the World, Canadian Society of Petroleum Geologists, p. 221- n p O i

c 250. U Map and cross-sections are based on interpretations of the best available information at the time of mapping. 450 D n i Map interpretations are not a substitute for detailed site specific studies. R

C Witzke, B.J., Anderson, R.R. and Pope, J.P., 2010, Bedrock Geologic Map of Iowa, scale: 1:500,000, Iowa Geological and Water Survey, Open File O Maysvillian Digital Map OFM-10-1. Edenian