Bedrock Geology of the Cresco NE (Iowa) 7.5' Quadrangle 92°7'30"W 92°5'0"W 92°2'30"W 92°0'0"W

D LEGEND 43°30'0"N 43°30'0"N Owd Od Om D Owd Om CENOZOIC DD D

Owd Owd QUATERNARY SYSTEM D

D Qu – Undifferentiated unconsolidated sediment Consists of loamy soils developed in loess and glacial till of variable thickness, and alluvial Om Om D Qu Om clay, silt, sand and gravel. Unit shown on cross-section only, and not on map. D Od Om D Owd PALEOZOIC D D D D D D

Om DEVONIAN SYSTEM Dw Dc - Dolomite and Limestone (Cedar Valley Group) The lowest subdivision of this map unit, the Little Cedar Formation, occurs in the Om Owd Dc southwest corner of the quad and attains a thickness up to 12 m (40 ft). It is dominated by slightly argillaceous to argillaceous dolomite and dolomitic limestone, commonly fossiliferous and vuggy, and partially laminated. Dw

Om Dw Dw - Dolomite, Limestone, Shale, and minor Sandstone (Wapsipinicon Group) This map unit includes the Spillville Formation, up to 27 m Om (89 ft), overlain by the Pinicon Ridge Formation, up to 11 m (36 ft), for a maximum total thickness up to 38 m (125 ft). The Spillville Od D Formation is dominated by medium to thick bedded dolomite, with scattered to abundant fossil molds, and vugs commonly filled with calcite Om D crystals; basal portion is sandy or silty; a distinctive stromatolitic limestone facies occurs locally in the upper part. The Spillville is quarried for D Owd local aggregate and also hosts numerous small springs. The Pinicon Ridge Formation is dominated by shaly, laminated or brecciated, Owd D D D D D D D unfossiliferous limestone and dolomite. D Od D Dw D D D D D Owd ORDOVICIAN SYSTEM Om Owd Om Om Om - Shale, Limestone, and Dolostone (Maquoketa Formation) A nonresistant slope-forming map unit up to 40 m (131 ft) composed of variably cherty, interbedded argillaceous limestone, dolostone and grey and brown shale. Fragmentary trilobite and graptolite fossils are common in the basal Elgin Limestone Member, and chert nodules are notable in the middle Fort Atkinson Member. It forms an upper Om confining unit that bounds the karst system in the underlying Wise Lake and Dunleith formations, and may host sinkholes in its lower portion. Om D D Od D Owd Owd - Limestone and minor Shale (Wise Lake Formation and overlying Dubuque Formation) A prominent ledge and cliff-forming unit of Owd up to 31 m (102 ft) of limestone with notable thin interbedded shale in the upper 6 m. This map unit is the upper of two successive major Om D cavern and karst-forming bedrock units in the area. The Wise Lake Formation consists of 21 m (67 ft) of medium to thick-bedded relatively D Dw 43°27'30"N chert-free limestone, portions of which exhibit a distinctive bioturbated fabric; serves as a quarried aggregate source The Dubuque Formation Dw 43°27'30"N D consists of 10 m (34 ft) of crinoidal limestones and thin interbedded shale. Sinkholes are common to abundant within this map unit. Often mantled by 0 m to 2 m (0 –6 ft) of loess-derived and weathered bedrock-derived colluvium. Om Owd Owd Od Od - Limestone (Dunleith Formation) A prominent ledge and cliff-forming unit of up to 42 m (137 ft) of limestone with minor thin Dw Om interbedded shale. This is the lower of two successive major cavern and karst-forming bedrock units in the area. The formation consists of Dw fossiliferous limestone and argillaceous limestone with common chert nodules; it is commonly quarried for aggregate. Major springs occur near the base, and sinkholes and karst features are common. Frequently mantled by 0 m to 2 m (0 – 6 ft) of loess-derived and weathered D bedrock-derived colluvium. D

Drill Holes

D Om D Outcrops D

D B D Om Dw D

D D Dw Om

D D Od D DD D Adjacent 7.5' Quadrangles

Owd D Om Od Quadrangle Location D

LYON OSCEOLA DICKINSON EMMET D WINNEBAGO WORTH MITCHELL HOWARD GREENLEAFTON HARMONY CANTON_MN WINNESHIEK ALLAMAKEE KOSSUTH D SIOUX Om OBRIEN CLAY PALO ALTO HANCOCK CERRO GORDO FLOYD CHICKASAW

FAYETTE CLAYTON PLYMOUTH CHEROKEE HUMBOLDT BREMER BUENA VISTA POCAHONTAS WRIGHT FRANKLIN BUTLER D

BLACK HAWK BUCHANAN DELAWARE DUBUQUE WOODBURY IDA WEBSTER SAC CALHOUN HAMILTON HARDIN GRUNDY

D JACKSON D D JONES LINN MONONA CRAWFORD TAMA BENTON CRESCO_NW CRESCO_NE BLUFFTON CARROLL GREENE BOONE STORY MARSHALL CLINTON

Owd CEDAR HARRISON SHELBY AUDUBON GUTHRIE DALLAS POLK JASPER POWESHIEK IOWA JOHNSON SCOTT

MUSCATINE

POTTAWATTAMIE D CASS ADAIR MADISON WARREN MARION MAHASKA KEOKUK WASHINGTON Dw D 43°25'0"N LOUISA D MILLS MONTGOMERY ADAMS UNION CLARKE LUCAS MONROE WAPELLO JEFFERSON 43°25'0"N HENRY DES MOINES Dw FREMONT CRESCO_SW CRESCO_SE RIDGEWAY PAGE TAYLOR RINGGOLD DECATUR WAYNE APPANOOSE DAVIS VAN BUREN D D D LEE D D

Om D D D D

D Om Dw Base map from USGS Cresco NE 7.5' Digital Raster Graphic (IGS GIS file DRGB38.TIF) which was scanned from the Cresco NE 7.5' Topographic Quadrangle map, published by US Geological Survey in 1981 Topographic contours and land features based on 1975 aerial photography, field checked in 1977 D Land elevation contours (20' interval) based on NGVD 1929.

Iowa Geological Survey digital cartographic file Cresco_NEquad08_bedrock.mxd, version 8/18/08 (ArcGIS 9.2) D Map projection and coordinate system based on Universal Transverse Mercator (UTM) Zone 15, datum NAD83. Owd D The map and cross section are based on interpretations of the best available information at the time of Om D Dw mapping. Map interpretations are not a substitute for detailed site specific studies.

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D Dw Dw Dc Dw 43°22'30"N Dc 43°22'30"N GEOLOGIC MAPPING OF A THE UPPER IOWA RIVER WATERSHED:

92°7'30"W 92°5'0"W 92°2'30"W 92°0'0"W PHASE 4: Cresco NE 7.5’ Quadrangle 1:24,000 0 0.5 1 2 3 4 Iowa Geological Survey Miles Open File Map OFM-08-1 0 0.5 1 2 3 4 Kilometers August 2008 ± prepared by

GEOLOGIC CROSS-SECTION A-B Huaibao Liu, Robert M. McKay, Stephanie Tassier-Surine, and James D. Giglierano

Iowa Geological Survey, Iowa City, Iowa

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Dc Silver Minor Upper Iowa 1300 Qu Creek Creek River Valley 1300

Iowa Department of Natural Resources, Richard A. Leopold, Director Qu Iowa Geological Survey, Robert D. Libra, State Geologist Qu 1200 Qu 1200 Supported in part by the U.S. Geological Survey

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l Cooperative Agreement Number 07HQAG0087

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v National Cooperative Geologic Mapping Program (STATEMAP) v

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e e ACKNOWLEDGMENTS

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a We thank the staff of the Northeast Iowa RC & D for their efforts in helping to initiate this mapping project and for supporting our

o t work in the Upper Iowa River watershed. New subsurface geologic data was generated by the University of Iowa students Thomas

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e Marshall, Kelly Wilhelm and Gregory Stark who produced descriptive logs of water well drill samples. Luther College in Decorah f

( 1000 s 1000 actively participated in the project through subcontract 07-7380-01 for field mapping support. Luther College students Gabriel

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o Demuth and Carl Haakenstad were participants in field and office work in support of the mapping effort. Birgitta Meade of Luther i

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e College was instrumental in accurately locating and elevating water wells in the map area. Drilling in selected sites was provided a

v v under contract by Aquadrill, Inc. of Swisher, Iowa. Deborah Quade, Iowa Geological Survey (IGS) lent support with Quaternary field

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) and office expertise; Robert Rowden (IGS) participated in part of the field work; Amy Sabin (IGS) prepared well samples for E 900 900 stratigraphic logging; Brian Witzke (IGS) provided valued information concerning the Ordovician and Devonian stratigraphy of the area; and Andy Asell and Chris Kahle (IGS) provided GIS mapping technical help. Od

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