Prepared and Published with the Support of COUNTY ATLAS SERIES THE DODGE COUNTY BOARD OF COMMISSIONERS, ATLAS C-50, PART A MINNESOTA GEOLOGICAL SURVEY Dodge County Harvey Thorleifson, Director THE MINNESOTA DEPARTMENT OF NATURAL RESOURCES, THE MINNESOTA ENVIRONMENT AND NATURAL RESOURCES TRUST FUND Plate 2—Bedrock Geology AS RECOMMENDED BY THE LEGISLATIVE-CITIZEN COMMISSION ON MINNESOTA RESOURCES, AND THE MINNESOTA LEGACY AMENDMENT'S CLEAN WATER FUND
RICE GOODHUE 93° W. 92° 52' 30" W. 92° 45' W. GOODHUE COUNTY COUNTY R. 18 W. R. 17 W. R. 16 W. COUNTY CORRELATION OF MAP UNITS 345 Od 330 STEELE 375 Ogs 345 Opg 360 330 Ogp 345 OLMSTED COUNTY Ogc 1 Kw 6 345 360 COUNTY Upper Cretaceous MESOZOIC 6 360 1 6 1 Ogp 330 unconformity Mi 375 unconformity A ddle Fork A' 375 Os Dlp BEDROCK GEOLOGY Od Middle Devonian Zum Ogs 315 Ops )57 360 bro Riv Ds er 330 Opg 330 unconformity By )56 Od Ogc Om Ogc 360 375 Ogc 360 Ogp Ogp 360 Od Odu Od ELLINGTON 375 CONCORD Andrew J. Retzler T. 108 N. MILTON T. 108 N. LOCATION DIAGRAM West Concord 345 Opg 360 Ogs 345 M Ogc Ogp Od Upper Ordovician 2019 390 390 Ogc Ogc 390 360 m Creek Lithostratigraphic Composite natural gamma log Milliken Creek Od
co unit
Milken Creek Increasing count to the right (API) ark M 44° 7' 30" N. Era 44° 7' 30" N. H Group, 0 A 100 Opg Formation, 0 C 100 Map symbol Lithology
Ogs System-Series Thickness (in feet) Member Hydrostratigraphic properties 0 B 100 it commonly is stained black or dark gray with manganese oxides on the 360 36 PALEOZOIC INTRODUCTION unconsolidated glacial sediment and water wells that penetrate bedrock tend to draw from 375 36 31 Os Middle Ordovician 31 36 31 Od Ostrander Fe higher carbonate aquifers in the Galena Group and above. outermost surface. Total thickness of the St. Peter Sandstone is about 110 Opg Windrow Kw Fe unconformity The geologic map, cross sections, and stratigraphic column on this plate depict the type, <110 Upper feet (34 meters). Formation Most layers designated as aquitards in the county have a much lower permeability in
MESOZOIC Iron Hill Cretaceous Fe A distribution, and structure of the bedrock units in Dodge County that are either exposed at Ogp Ops Prairie du Chien Group (Lower Ordovician)—Dominated by dolostone interlayered 6 390 the vertical direction than do aquifers. Examples in Dodge County include the Decorah 1 390 Little the land surface or lie beneath unconsolidated Quaternary sediments of variable thickness 6 1 Cedar Fe C unconformity Shale and Glenwood Formation, whose rocks are composed mostly of shale with small, with lesser amounts of quartzose sandstone. The Prairie du Chien Group is 1390 6 Lower Ordovician (see cross sections and Plate 3, Surficial Geology, Plate 4, Quaternary Stratigraphy, and Ogs Ogc Formation poorly connected pore spaces. Carbonate rock containing a relatively sparse network formally divided into two formations: the Shakopee Formation and underlying 375 Opo Plate 6, Bedrock Topography and Depth to Bedrock). The map shows how the bedrock 375 Dlp <77 Oneota Dolomite. It is commonly difficult to discern the contact between Little Cedar of fractures and/or interbedded with shale, such as the Maquoketa Formation, Dubuque Valley Group Valley Bassett surface would appear if it were viewed from an aerial perspective and the overlying Ogs unconformity Formation, or the lower part of the Prairie du Chien Group (Oneota Dolomite), are also the Shakopee Formation and Oneota Dolomite without high-quality drill Quaternary sediments were stripped away. The bedrock units nearest the land surface Middle Fork Zumbro Pinicon Ridge River 375 Fe Cj aquitards. However, layers designated as aquitards with very low permeability in the cuttings and borehole geophysical logs. Total thickness of the Prairie du Odu Ogc Os Formation in Dodge County consist of sedimentary rocks of Paleozoic and Mesozoic age that form 56 Ogs Middle Devonian Fe South Branch ) vertical direction may locally contain horizontal fractures that are conductive enough to Chien Group is about 300 feet (91 meters). 360 distinguishable and mappable layers designated as formations. Some of these units are Group Spillville Cs yield large quantities of water. 360 Ds B 60 Ops Shakopee Formation (Lower Ordovician)—A heterolithic unit composed Formation commonly exposed along small creeks and branches of the Zumbro River that flow eastward Wapsipinicon
Ogp EXPOSED IN DODGE COUNTY NOT Mantorville Ogp Ogp Upper Cambrian Horizontal and vertical fractures are more common where bedrock layers are at or near mostly of tan to gray, thin- to medium-bedded dolostone, sandy dolostone, 375 into neighboring Olmsted County, and within quarries generally concentrated within the 375 Clr 330 Od Maquoketa the bedrock surface. As a result, aquitards in such conditions are likely to have higher sandstone, and shale. It contains oolites, intraclasts, microbial mounds, CLAREMONT WASIOJA Om east-central portion of Dodge County. Several of the Paleozoic bedrock formations are MANTORVILLE Formation 30-55 chert nodules, quartzose sandstone, and green-gray shale partings. The T. 107 N. 390 T. 107 N. unconformity major reservoirs for water in the county, while others closer to the surface provide aggregate permeability compared with more deeply buried portions of the same formation, and may Om Ogs ek F Fe Cw Shakopee Formation is the oldest unit to subcrop in Dodge County, in the 390 re Dubuque and crushed stone materials. have a diminished ability to retard water flow to underlying aquifers. There is no precise Odu C 345 Odu 25 Formation Fe boundary between shallow and deep conditions of burial, but in most areas of southeastern northeastern corner of the county within the Middle Fork Zumbro River
375 Ce Characteristics of each formation are given in the stratigraphic column (Fig. 1) and in
r e t n e 57 Minnesota, about 50 feet (15 meters) of depth below the bedrock surface is considered a valley. Total thickness of the Shakopee Formation is about 180 feet (55 Ogc)345 C Creek Middle Cambrian the description of map units. The accompanying bedrock geologic cross sections add the 360 Cm best approximation (Runkel and others, 2006a, 2018). meters). Om 375 dimension of depth and illustrate the stratigraphic, structural, and topographic relationships Claremont Om e ek Stewartville ¤14 e Ogs r Ogs Oneota Dolomite (Lower Ordovician; shown only on cross sections)—The odg 375 ek 85 In addition to this hydrostratigraphic classification, the Minnesota Department of Natural Opo Odu D C re Thompkins Formation of the bedrock units, as well as the variable thickness of the overlying Quaternary sediments. C 390 Resources, as Part B of the Dodge County Atlas, will conduct a thorough hydrogeologic Oneota Dolomite is separated into two members, the Hager City and the 390 Odu Spring Ogp Projected onto these cross sections are the locations and approximate depths drilled Kw on Kasson Coon Valley. The Hager City Member is predominantly a yellowish-gray Odu 390 375 Uni k (shown as black lines) from available water-well data within a 1,640-foot (0.5 kilometer) study of the groundwater flow system, aquifer capacity, and aquifer sensitivity that may or B de Cree B' Casca may not result in modifications or additions to this classification. Furthermore, designations to light brown, medium- to thick-bedded dolostone that generally lacks Dodge Center 375 buffered area surrounding each cross-section line. Surfaces representing the elevation of Masten Prosser 36 Ogc Ogp of aquifers versus aquitards made here may not correspond precisely with those made for sedimentary features, such as oolites and quartz sand, characteristic of 31 36 390 Formation 40-45 the tops of the mapped formations are also available as Digital Elevation Models (DEMs) Ogs Om 31 36 31 for use in GIS programs. The geologic formations are thin in relation to their aerial regulatory purposes by the Minnesota Department of Health. the overlying Shakopee Formation. Thickness of the Hager City Member Kw Galena Group extent, and would only be one-tenth as thick as shown on the cross sections if no vertical varies from about 90 to 95 feet (27 to 29 meters). The basal Coon Valley Henslin Creek Upper Ordovician Cummingsville Member is a heterolithic unit composed of thinly bedded dolostone, sandy
14 Ogc 65 exaggeration were used. The exaggeration necessary to show the thin rock formations gives Om 6 Om ¤ Formation 1 1 dolostone, and beds of fine- to coarse-grained, poorly sorted quartzose 6 14 6 1 the appearance of steeper slopes on bedrock unit contacts, the land surface, and bedrock DESCRIPTION OF MAP UNITS Om Odu ¤ Ogs topography. About half of the units shown as first bedrock on this plate are exposed at sandstone. Thickness of the Coon Valley Member varies from about 25 to Odu MESOZOIC the land surface, with the exception of the Windrow Formation, Little Cedar Formation, 30 feet (8 to 9 meters). Total thickness of the Oneota Dolomite is about Decorah Windrow Formation (Upper Cretaceous)—The Windrow Formation 120 feet (37 meters). Od Pinicon Ridge Formation, Spillville Formation, Maquoketa Formation, Dubuque Formation, Kw Shale 44° N. 44° N. 45-60 and Prairie du Chien Group, which are buried by Quaternary sediments. Where exposed, unconformably overlies the Devonian and Ordovician carbonate units from Cj Jordan Sandstone (Upper Cambrian; shown only on cross sections)—Dominantly
390 the Bassett Member of the Little Cedar Formation down to the Stewartville white to yellow, medium- to coarse-grained, friable quartzose sandstone 360 the sedimentary rocks differ in their resistance to weathering and erosion, as depicted Platteville and Formation of the Galena Group and is divided into two members: the characterized by coarsening-upward sequences consisting of two interlayered Opg 30 graphically by the weathering profile on the lithology column of Figure 1. The carbonate Glenwood Formations Ph Odu Ogp rock (limestone and dolostone) units are the most resistant to weathering and therefore Ostrander and Iron Hill. The mapped extent of the Windrow Formation facies (Runkel, 1994). They are medium- to coarse-grained, cross-stratified, form widespread plateaus that cover the largest areas of the map. The soft sandstone and as shown on the map and cross sections is approximate and conservative generally friable, quartzose sandstone; and very fine-grained, commonly 375 LITHOLOGY KEY because it is difficult to verify its occurrence without high-quality water- bioturbated, feldspathic sandstone and lenses of siltstone and shale. The RIPLEY ASHLAND Odu CANISTEO 375 T. 106 N. shale units erode more easily and typically occur as thin veneers atop the carbonate rock T. 106 N. well records, drill cuttings, core samples, and/or borehole geophysical logs. major part of the very fine-grained facies forms a regionally continuous 390 360 Ogp Limestone plateaus or lie along valley walls. Om Production of the map and associated products relied on several different data The total thickness of the Windrow Formation can be as much as 110 feet interval that gradationally overlies the St. Lawrence Formation (unit Cs), St. Peter Os (34 meters). although there are lithologically similar intervals intercalated with the 405 Ogs Sandstone 110 Dolostone sources, including outcrops, water-well and scientific drilling records from the County 390 375 medium- to coarse-grained facies at higher stratigraphic intervals. An 375 Well Index (CWI) database, rock core, drill cutting samples, borehole geophysical logs, Ostrander Member—Yellowish-brown, orange-red, and grayish-white, very
Middle Odrovician unconformity, locally marked by thin beds of quartz pebble conglomerate )56 Sandy dolostone seismic soundings, geophysical imagery, and previously published geologic maps of friable, fine- to coarse-grained, rounded to sub-angular, quartzose sandstone Odu Sa and pebbly chert conglomerate with minor gray to black and orange, thinly- and silcrete-cemented sandstone clasts (Runkel and others, 2007), separates 390 lem Dodge County and adjacent counties (Mossler, 1995, 1998; Runkel, 1998; Tipping and Creek Sandstone the Jordan Sandstone from the overlying Oneota Dolomite of the Prairie Om 390 others, 2007; Steenberg, in press). Figure 2 shows a general overview of some of the laminated to massive, waxy clay and silty clay (Figs. 2G, H, I, K). The Ogs Very fine- to fine-grained characteristic Paleozoic bedrock outcrops in Dodge County and adjacent counties, as well sandstone is commonly micaceous and commonly contains thin beds or du Chien Group. Limited subsurface data in Dodge County indicate a total thickness ranging from about 85 to 100 feet (26 to 30 meters). A 405 Fine- to medium-grained as several examples of rotary-sonic drill core samples of the Mesozoic bedrock collected nodules of pyrite- or iron-cemented sand. Chert pebbles are commonly 31 36 representative total thickness of 100 feet (30 meters) was used in developing 36 31 36 for this project. This map supersedes a combined 1:100,000-scale bedrock geology map red-gray-white-black, very well-rounded, and polished. Many contain 31 the corresponding DEMs and in representing the Jordan Sandstone in cross Odu Medium- to coarse-grained of Steele, Dodge, Olmsted, and Winona Counties (Tipping and others, 2007). Significant silicified invertebrate fossil fragments of probable Devonian and Ordovician section. 390 Om improvements and modifications were made to the interpretations of the previous maps age. The Ostrander Member commonly overlies the Iron Hill Member, but
Mi based on additional water-well records, drill cuttings, rotary-sonic drill core, and borehole has also been previously described as lying directly atop Paleozoic strata Cs St. Lawrence Formation (Upper Cambrian; shown only on cross sections)— 1 6 390 1 Shaly 6 ddle 1 6 405 geophysical logs. These improvements include: generating model-ready top and bottom (Mossler, 1998). The Ostrander Member can be as much as about 85 feet Light gray to yellowish-gray and pale yellowish-green, dolomitic, feldspathic Ds 405 (26 meters) thick. siltstone with interbedded, very fine-grained sandstone and shale. Lenses Fork Siltstone bedrock surface DEMs for all of the bedrock units in Dodge County down to the Mt. Simon
360 and layers of light gray, finely crystalline, sandy dolostone occur locally, Om Zumbro RiverOm Shakopee Ops Sandstone, better defining the thicknesses and extents of the Galena Group formations Iron Hill Member—Orange and black, heavily oxidized, fine- to coarse- Od Formation 180 C M (particularly the Stewartville and Prosser Formations), better understanding of the lithology especially in the lowermost few feet of the formation (Runkel and others, Willow River Shale grained, pebbly, quartzose sandstone and siltstone intermixed with green, eda 375 2006a). Intraclastic beds are present near the top and base of the unit and Wes r Ogc and facies trends of the Dubuque and Maquoketa Formations, and delineating the extent white, tan, and red, pebbly, clay and silty clay as part of a weathering t Om Fork Riv glauconite is present throughout, but typically more concentrated in the 390 Chert and better characterizing the lithology of the patchy, Mesozoic-aged Windrow Formation residuum of the carbonate bedrock (Fig. 2J). The sandstone deposits are er Odu lowermost 30 feet (9 meters). The upper contact with the Jordan Sandstone Odu Ogs (Upper Cretaceous). Bedrock structure was also mapped in greater detail, revealing a commonly heavily mineralized and cemented with iron oxides. The base C Oolites Odu Dlp number of local folds superimposed on the regional dip of these strata. Collectively this is conformable and gradational, making it difficult to select a precise eda of the Iron Hill Member typically contains a heavily oxidized pebble or Ogp Lower Ordovician
Prairie du Chien Group New G contact between these formations even with well cuttings and/or borehole
r HAYFIELD M Glauconite provides a significantly improved depiction of the subsurface geologic characteristics, cobble lag that lies atop weathered Devonian or Ordovician carbonate strata.
v i R Richmond WESTFIELD VERNON T. 105 N. geophysical logs. The St. Lawrence Formation is the deepest penetrated T. 105 N. including hydrogeologic units, which has implications for modeling groundwater flow The Iron Hill Member can be as much as about 10 feet (3 meters) thick.
Hayfield Fe Iron staining/precipitate
r e ek Ds 30 bedrock unit by water wells in Dodge County. However, these wells do not 30 ) PALEOZOIC ) e and contaminant transport. r Ogc C Ph PALEOZOIC fully penetrate the entire unit. Limited subsurface data in Olmsted County 405 Phosphate grains The various data sources and their irregular distribution and density can be seen on Plate 390 and surrounding counties indicate a total thickness of about 60 feet (18 field Dlp Ds 1, Database Map. The spatial distribution and coverage of these data should be considered Bassett Member of the Little Cedar Formation and Pinicon Ridge Formation, Hay Om Stromatolites Dlp meters; Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). Ds Oneota Blooming Ds Ogs 43° 52' 30" N. Opo when assessing the reliability of the map at any particular location. Areas with a high undivided (Middle Devonian)—The Bassett Member of the Little Cedar 43° 52' 30" N. 390 )56 Om 120 390 Dolomite 390 r Hager City Shells Tunnel City Group (Upper Cambrian) Prairie River Ogs density of bedrock control points are more likely to have an accurate interpretation of the Formation and the Pinicon Ridge Formation are combined into a single map Ceda Ds 390 bedrock geology, whereas areas with widely spaced control points may be less reliable. Lone Rock Formation (Upper Cambrian; shown only on cross sections)— Eas Bioturbation unit with a full thickness of about 95 feet (29 meters) in Dodge County. Clr )30 t Odu Coon Valley G The bedrock surface DEMs supplementing this map were interpolated using the ESRI Description of this combined unit is based on a very limited number of Pale yellowish-green, very fine- to fine-grained, glauconitic, feldspathic Pebbles Fork Dlp ArcMap Topo to Raster tool and similarly inherit these biases in the data. Furthermore, wells with drill cuttings and borehole geophysical logs. sandstone and siltstone, with thin, greenish-gray shale partings. Pink and Dlp Kw 31 405 C' Jordan the accuracy of the DEMs is dependent upon the contour interval used when mapping the red dolostone beds are present near the base of the formation. The upper C Om 36 31 36 31 Cj 100 Intraclasts Bassett Member of the Little Cedar Formation—Light to medium gray, thick- 390 405 Om 36 Sandstone STEELE Sarge topographic surface of each unit and the errors inherited in the Topo to Raster interpolation contact with the St. Lawrence Formation is conformable and fairly sharp 218 405 ant Creek bedded dolostone. Total thickness of the Bassett Member varies between
COUNTY ¤ Ds 405 Cross-bedded (planar) method. For this map, the bedrock surface DEMs on average are accurate to within ± 12.5 because beds in the Lone Rock Formation are generally coarser-grained
COUNTY OLMSTED
COUNTY MOWER about 40 and 70 feet (12 to 21 meters; Mossler, 2008). One borehole and less well-cemented. The Lone Rock Formation is not penetrated by FREEBORN R. 18 W. R. 17 W. R. 16 W. Cross-bedded (trough) feet (3.8 meters). Significant efforts were made to ensure the accuracy of the bedrock geophysical log in Dodge County (CWI unique number 251204) indicates COUNTY 93° W. 92° 52' 30" W. 92° 45' W. surfaces; however, users should always refer to and consider the two-dimensional geologic a thickness of 67 feet (20 meters) for the Bassett Member. water wells in Dodge County; however, limited subsurface data in Olmsted St. Lawrence Cross-bedded (hummocky) map because it represents the most accurate and reliable representation of the uppermost County and surrounding counties indicate a total thickness of about 165 MOWER
Cs 60 COUNTY Digital base modified from the Minnesota Department of GIS compilation by A.J. Retzler Formation G Pinicon Ridge Formation—Composed mainly of light gray to yellowish-gray, SCALE 1:100 000 bedrock across the county. feet (50 meters; Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). Transportation BaseMap data; digital base annotation by Edited by Lori Robinson G Dolomitic silty or sandy dolostone with thin beds of dark gray and olive-gray shale Corey J. Betchwars. 1 0 1 2 3 4 5 MILES During production of this map, over 2,000 located water-well records and 1,050 Wonewoc Sandstone (Upper Cambrian; shown only on cross sections)—Fine- Elevation contours were derived from the U.S. Geological Survey and minor yellowish-gray limestone (Mossler, 1998, 2008). It can also Cw Vugs to coarse-grained, moderately- to well-sorted, light gray, cross-stratified, 30-meter Digital Elevation Model (DEM) by the Minnesota 1 0 1 2 3 4 5 6 7 8 KILOMETERS located engineering test and giddings soil probe borings existed within Dodge County in contain abundant chert nodules and sparry calcite- and quartz-filled vugs. Geological Survey. EXPOSED IN DODGE COUNTY NOT Contact marks a major the County Well Index (CWI) and the Minnesota Geological Survey's Quaternary Data quartzose sandstone (Mossler, 2008). White, brown, and black linguliform Universal Transverse Mercator Projection, grid zone 15 The upper and lower parts can contain more shaly dolostone and shale CONTOUR INTERVAL 15 METERS erosional surface Index (QDI) database. Nearly 1,230 of those reached Paleozoic and/or Mesozoic bedrock. brachiopod shells are locally abundant. The upper part is coarser-grained; 1983 North American Datum G (Mossler, 1998). Total thickness of the Pinicon Ridge Formation is about Geologic interpretations of subsurface material were made by the author based on material 30 feet (9 meters). the lower part is finer-grained, better sorted, and progressively finer-grained G descriptions by drillers or gathered from other data sources and are recorded in the CWI toward its base. The very fine-grained sandstone in the lower part is Spillville Formation (Middle Devonian)—Finely crystalline, light brown to Lone Rock and QDI databases. Ds feldspathic. The Wonewoc Sandstone is conformable with overlying and Upper Cambrian Clr Formation 165 HYDROSTRATIGRAPHIC PROPERTIES KEY grayish-orange dolostone with abundant fossil-moldic porosity and dog- G In Dodge County, Paleozoic- and Mesozoic-aged bedrock lie on top of a thick sequence underlying formations; however, there is a subtle unconformity marked by Relatively high permeability tooth, sparry calcite-filled vugs. The basal few feet are sandy to silty and of Mesoproterozoic rocks of the Keweenawan Supergroup associated with the Midcontinent a pebbly sandstone layer within the formation (Runkel and others, 1998).
Tunnel City Group Tunnel (aquifer) County may contain minor amounts of shale or shaly dolostone (Mossler, 1998). County Highway 5 Middle Fork Rift (Jirsa and others, 2012). These rocks include sandstone, siltstone, and shale of the The Wonewoc Sandstone was formerly referred to as the Ironton-Galesville A (140th Avenue) State Highway 56 State Highway 57 Highway 24 Zumbro River A' Relatively low permeability Description of the Spillville Formation in Dodge County is based on limited Ogp Sandstone. The Wonewoc Sandstone is not penetrated by water wells in Ogc Ogs (except for fractures, aquitard) Hinckley Sandstone, Solor Church, and Fond du Lac Formations. A deeply buried thrust drill cuttings, core samples, and borehole geophysical logs. Total thickness Dodge County; however, limited subsurface data in Olmsted County and 1,200 Unconsolidated Quaternary sediments Ogc Ogp Ogs High permeability bedding fault that offsets these rocks crosses the southwestern corner of Dodge County and trends of the Spillville Formation is about 60 feet (18 meters). surrounding counties indicate a total thickness of about 65 feet (20 meters; Wonewoc fractures known to be common northwest–southeast, as inferred by aerial geophysical imagery (Jirsa and others, 2012). 1,000 Cw 65 Om Maquoketa Formation (Upper Ordovician)—Dark gray-brown, silty and sandy Opg Sandstone The distribution, depth, and thickness of these Mesoproterozoic rocks is poorly constrained Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). Os Od Opg Os Od dolostone with light olive-gray shale and light gray-white, dolomite-cemented, 800 in Dodge County due to their deep burial and limited subsurface data. No new mapping Eau Claire Formation (Middle to Upper Cambrian; shown only on cross Ops Ops fine- to coarse-grained, quartzose sandstone with cross stratification. Sand- Ce G of these units or their associated faults was done for this project. sections)—Yellowish-gray to pale olive-gray, fine- to very fine-grained, 600 Opo Opo sized phosphate grains and some chert grains are abundant throughout. One Cj Cj G feldspathic sandstone, siltstone, and shale. White and brown linguliform The Paleozoic-aged rocks of Dodge County are characterized by relatively thin, possible hardground surface with rip-up clasts is present in core (DOR-2; 400 Cs Cs brachiopod shells are common. The contact with the underlying Mt. Simon Clr Clr widespread layers of sandstone, shale, and carbonate deposited in shallow seas during CWI unique number 340102) within a dark gray-brown dolostone bed. Sandstone is conformable and transitional, which is commonly apparent on 200 Cw Cw the Cambrian, Ordovician, and Devonian Periods of the Paleozoic Era, from about 500 Although the lithology of the Maquoketa Formation in Dodge County is Ce Ce natural gamma-ray logs. The Eau Claire Formation is not penetrated by to 375 million years ago. The older Cambrian formations are dominated by siliciclastic known only from poorly sampled drill cuttings and rotary-sonic core drilled 0 Cm Cm Eau Claire Ce 110 sedimentary rock, including sandstone and siltstone with minor shale, such as the Jordan water wells in Dodge County; however, limited subsurface data in Olmsted Formation G for this mapping effort, it appears to differ from neighboring Mower and Elevation (feet above mean sea level) County and surrounding counties indicate a total thickness of about 110 Sandstone and Tunnel City Group. Carbonate rock occurs only as relatively thin layers Olmsted Counties (Mossler, 1998; Steenberg, in press). In particular the Dodge Center City of Kasson/ Figure 1. Generalized stratigraphic column feet (34 meters; Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). B County Highway 1 U.S. Highway 14 Creek Dodge Center Union Spring Creek State Highway 57 Matsen Creek B' within these units. Ordovician and Devonian formations, in contrast, are dominated by presence of quartzose sandstone in Dodge County may be evidence of a G depicting the lithology, most common range Ogs thicker units of carbonate rock (such as the Prairie du Chien Group and the Galena Group), significant facies change that has previously gone unreported. Descriptions of Cm Mt. Simon Sandstone (Middle Cambrian; shown only on cross sections)—Pale Odu Odu Unconsolidated Quaternary sediments Odu Ogp in thickness, vertical succession, geologic age, with the exception of the St. Peter Sandstone and Decorah Shale. These carbonate rock yellowish-brown to grayish-orange-pink to light gray, medium- to coarse- 1,200 Kw G the Maquoketa Formation further south into Iowa note an increased presence Ogp Ogs and hydrostratigraphic properties for all units grained, quartzose sandstone. Interbeds of shale, siltstone, and very fine- Od units, most notably the upper Galena Group formations, are used as aggregate or crushed of phosphatic hardgrounds that may correlate with the hardground surface in 1,000 G shown on the map. One composite gamma Od Os Opg Ogc stone in a small number of quarries throughout Dodge County where bedrock is within 50 Dodge County noted above. The upper contact of the Maquoketa Formation grained, feldspathic sandstone are common, particularly in its upper half log of the Paleozoic bedrock units is shown 800 Opg Os Ogc Ops feet (15 meters) or less of the land surface (see Plate 6). Rock quarries are less abundant in with the overlying Spillville Formation is unconformable. Therefore, the (Mossler, 1992). Linguliform brachiopod shells are locally common in the Ops in black (A). Shown in magenta to the right upper one-third of the formation. Thin beds of quartz-pebble conglomerate Opo Dodge County than neighboring counties (such as Olmsted and Mower) due to the overall total thickness of the Maquoketa Formation can vary between about 35 600 (B, C) are two gamma logs of the Mesozoic Opo Cj widespread coverage of thicker Quaternary glacial sediments. The deepest bedrock unit and 55 feet (11 and 17 meters). A representative total thickness of 55 feet occur at several stratigraphic positions, and are especially abundant near the 400 Cj Middle Cambrian bedrock unit to illustrate the less diagnostic Cs penetrated by water wells in Dodge County is the St. Lawrence Formation. As such, the (17 meters) was used to develop the corresponding DEMs and to represent base of the formation. The Mt. Simon Sandstone unconformably overlies Cs Clr and more variable natural gamma radiation 200 Clr Cw thickness and general lithologic description of units underlying the St. Lawrence Formation the Maquoketa Formation in cross section. Additional high-quality drill Mesoproterozoic rocks. The Mt. Simon Sandstone is not penetrated by trends of this unit. The gamma logs illustrated Cw Ce Mt. Simon in Dodge County were inferred using geologic mapping efforts from neighboring counties cuttings, core samples, and natural gamma-ray logs are needed to better water wells in Dodge County; however, limited subsurface data in Olmsted 0 Ce Sandstone Cm 200 are from the following borehole geophysical Cm (Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). constrain and describe the Maquoketa Formation in Dodge County. County and surrounding counties indicate a total thickness of about 200 Cm logs on file at the Minnesota Geological feet (61 meters; Mossler, 1995, 1998; Runkel, 1998; Steenberg, in press). Elevation (feet above mean sea level) -200 The Paleozoic strata of Dodge County lie just east of the axial trace of a broad, cratonic Galena Group (Upper Ordovician) Survey: CWI unique numbers 251204, 340102, depression known as the Hollandale embayment. These stratigraphic layers are slightly Dubuque Formation (Upper Ordovician)—Light gray to yellowish-gray, Cedar River County Highway 5 State Highway 56 County Highway 9 County Highway 13 270th Avenue 603066, 809083, 223082, and 340101. tilted (less than 1°) southwest as part of the regional structural trend of the embayment. Odu C C' thin- to medium-bedded limestone and dolostone interbedded with light REFERENCES As a result, progressively younger bedrock formations subcrop from northeastern to Unconsolidated Quaternary sediments Dlp Ds Om Odu olive-gray to light gray, calcareous shale. Parts of the Dubuque Formation 1,200 Kw southwestern Dodge County. This general trend is locally interrupted by deep valleys Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2012, Karst conduit flow in the Cambrian Ds are fossiliferous with abundant crinoids and brachiopods and less common Ogs Ogp Ogc that incise older bedrock formations, and by local-scale folds. The stratigraphic top of St. Lawrence confining unit, southeast Minnesota, USA: Carbonates Evaporites, v. 1,000 Om Odu Ogs Ogp Ogc Od Precambrian rocks, undifferentiated bryozoans, trilobites, and bivalves. The Dubuque Formation appears to (not shown on map or cross-sections) the St. Peter Sandstone was contoured at 25-foot (8-meter) intervals to help constrain the 27, no. 2, p. 167-172. be more dolomitic and less shaly throughout Dodge County than has been 800 Od Os Opg location of local folds in Dodge County and to aid in the creation of the bedrock surface Jirsa, M.A., Boerboom, T.J., and Chandler, V.W., 2012, Geologic map of Minnesota— Opg Os described in nearby Olmsted, Mower, and Fillmore Counties (Sloan, 1987; Ops DEMs for each unit (Fig. 3). This unit was selected to portray these structures because its Precambrian bedrock geology: Minnesota Geological Survey State Map S-22, scale 600 Ops Mossler, 1998; Steenberg, in press). Description of the Dubuque Formation Opo upper contact is distinct and easily recognized by water-well drillers. It also provides a 1:500,000. in Dodge County is based on limited drill cuttings, core samples, and 400 Opo Cj fair amount of spatial coverage across Dodge County from the water wells that penetrate Cj borehole geophysical logs. Total thickness of the Dubuque Formation is Luhmann, A.J., Covington, M.D., Peters, A.J., Alexander, S.C., Anger, C.T., Green, J.A., Cs Clr Cs it, with the exception of the southwestern corner (Fig. 3). In general, folds were inferred 200 MAP SYMBOLS about 25 feet (8 meters). Runkel, A.C., and Alexander, E.C., Jr., 2011, Classification of thermal patterns at karst Clr Cw where changes in the elevation of the top of the St. Peter Sandstone indicate a gradual springs and cave streams: Ground Water, v. 49, no. 3, p. 324-335. 0 Ce Cw Geologic contact, approximately located change in slope greater than that of the regional, 1° structural trend. The axial trace of Ogs Stewartville Formation (Upper Ordovician)—Yellowish-gray and pale olive- Ce Cm gray dolostone and dolomitic limestone. Bedding is typically medium to Mossler, J.H., 1992, Sedimentary rocks of Dresbachian age (Late Cambrian), Hollandale -200 Fold—Axial trace of anticline, syncline. Fold limbs typically have shallow dips and most folds in Dodge County trend northeast–southwest, or roughly perpendicular to the Elevation (feet above mean sea level) Cm embayment, southeastern Minnesota: Minnesota Geological Survey Report of F M are inferred from subsurface data. thick near the base and thin and crinkly near the top. The Stewartville regional structural dip of the Paleozoic strata. Faults were not identified in Dodge County. Investigations RI-40, 71 p. Vertical exaggeration = 10x Formation typically displays a sugary, coarse-grained crystalline texture Location of geologic cross section The Mesozoic rocks of Dodge County are part of the Cretaceous Windrow Formation, A A' compared to the fine-grained, micritic texture more characteristic of the ———1995, Bedrock geology, pl. 2 of Hobbs, H.C., project manager, Geologic atlas of Rice which is dominated by variably thick, patchy, and poorly cemented siliciclastic sediments. Bedrock outcrop underlying Prosser Formation, and its beds are commonly highly burrow County, Minnesota: Minnesota Geological Survey County Atlas C-9, scale 1:100,000. The Windrow Formation lies unconformably atop the Ordovician and Devonian carbonate mottled. Differential weathering of this burrow mottled texture typically ———1998, Bedrock geology, pl. 2 of Mossler, J.H., project manager, Geologic atlas of rock units of the Paleozoic Era. It was deposited on the exposed Paleozoic carbonate bedrock gives the Stewartville Formation a "swiss cheese" appearance in outcrop Mower County, Minnesota: Minnesota Geological Survey County Atlas C-11, scale across a low, featureless plain during the Cretaceous Period when much of Minnesota was (Fig. 2F). The Stewartville Formation is typically fossiliferous in the lower 1:100,000. subaerial (Mossler, 2000). Some mapped Windrow Formation material is likely in-place A. B. C. and upper parts near its contact with the underlying Prosser Formation and ———2000, Contributions to the geology of Mower County, Minnesota: Minnesota ! ! ! ! ! ! ! ! !! ! weathering products of underlying Paleozoic bedrock, but other parts of the formation ! ! ! ! ! ! ! ! ! !! ! overlying Dubuque Formation. Fossils include brachiopods, gastropods, ! Geological Survey Report of Investigations RI-50, 109 p. ! ! ! ! ! ! ! ! ! ! ! are sediments deposited in streams and on floodplains. The distribution and thickness of ! !! ! Line of geologic cross section ! ! ! ! ! ! horn corals, crinoids, cephalopods, and receptaculitids, and are commonly ! ! ! ! ! ! ! ! ———2008, Paleozoic stratigraphic nomenclature for Minnesota: Minnesota Geological ! ! this unit is difficult to constrain without high-quality subsurface information such as drill A ! ! ! ! ! !! ! A' ! ! ! preserved as internal or external molds. Total thickness of the Stewartville ! !! ! Axial trace of fold ! !! ! ! Survey Report of Investigations RI-65, 76 p., 1 pl. ! ! ! cuttings or core. It can commonly be overlooked and misinterpreted to be unconsolidated ! !! ! !! ! ! ! Formation is about 85 feet (30 meters).
! ! !!
! ! ! Quaternary glacial sediment when using information from routine water-well drilling Paillet, F.L., Lundy, J., Tipping, R.G., Runkel, A.C., Reeves, L., and Green, J., 2000, ! ! Anticline ! ! ! M ! F ! ! ! ! ! Prosser Formation (Upper Ordovician)—Fine-grained, fossiliferous, ! ! !! Ogp !!! ! ! records. For these reasons, the Windrow Formation may have a significantly greater extent Hydrogeologic characterization of six sites in southeastern Minnesota using borehole ! ! ! ! ! ! ! ! !! ! ! ! yellowish-gray to grayish-brown limestone and dolomitic limestone (Fig. ! ! ! ! M Syncline than is shown on this map and corresponding cross sections. flowmeters and other geophysical tools: U.S. Geological Survey Water-Resources ! ! ! ! ! ! ! ! 2E). Bedding is typically thin to medium and flaggy, and fossils tend
! !! ! ! ! ! Investigations Report 00-4142, 33 p.
! ! ! M ! Water well penetrating the top ! ! to be concentrated in thin coquina layers. Fossils include brachiopods, ! ! ! ! of the St. Peter Sandstone HYDROSTRATIGRAPHY Runkel, A.C., 1994, Deposition of the uppermost Cambrian (St. Croixan) Jordan Sandstone, ! ! ! ! ! ! Figure 2. General overview of the characteristic Paleozoic bedrock outcrops in Dodge ! ! gastropods, bivalves, echinoderms, bryozoans, trilobites, horn corals, and !! ! ! and the nature of the Cambrian-Ordovician boundary in the upper Mississippi valley: ! !! Some of the Paleozoic bedrock formations include aquifers that are a significant County and adjacent counties, as well as several examples of rotary-sonic drill core ! ! ! Extent of partially to fully eroded cephalopods. The Prosser Formation contains chert nodules and is more ! ! ! ! Geological Society of America Bulletin, v. 106, p. 492-506. ! ! ! ! ! ! !! ! St. Peter Sandstone source of groundwater for Dodge County. About 90 percent of wells in the county draw samples of the Mesozoic bedrock collected for this project. ! ! ! ! ! ! micritic than the underlying Cummingsville Formation. It is progressively ! ! ! ! water from Paleozoic bedrock. This map and associated products, such as the bedrock ———1996, Bedrock geology of Houston County, Minnesota: Minnesota Geological ! !! more dolomitic to the southwest across Dodge County, making it more A. Small outcrop of the St. Peter Sandstone along Dodge County Road 24 (hammer ! ! ! !!! ! ! ! ! ! ! D. E. F. ! ! ! ! Elevation of the top of the St. Peter Survey Open-File Report 96-4, 11 p., 3 pls., scale 1:100,000. ! ! ! ! ! ! ! !! ! surface DEMs, provide a three-dimensional depiction of the rock properties that control difficult to distinguish from the overlying Stewartville Formation. Total !!! ! ! for scale). ! ! ! ! ! ! ! !!! ! ! ! ! !! !!!! ! !! ! ! ! ! Sandstone (in feet above mean sea level) ! ! ! !!! ! ! !! !! ! ! ! ! !! ! ! ! !! ! ! ! ! ! ! ! ! ! !!! !! ! ! flow in these water-bearing layers. Such rock properties are called hydrostratigraphic ———1998, Bedrock geology, pl. 2 of Setterholm, D.R., project manager, Geologic atlas ! ! !! !! ! ! thickness of the Prosser Formation is about 40 to 45 feet (12 to 14 meters). ! ! ! !! ! !!!! B. Small outcrop of the Platteville Formation lying just above and west of the St. Peter ! ! !! !!!! ! ! ! ! !!! !! !!!! ! ! !! ! ! ! ! ! ! ! F !!!! ! ! ! 1,051–1,075 ! ! ! !! ! !! ! ! ! properties. The hydrostratigraphic classification, shown by brown and blue colors on the of Goodhue County, Minnesota: Minnesota Geological Survey County Atlas C-12, ! !!!! ! !! ! !! ! !! !! Ogc Cummingsville Formation (Upper Ordovician)—Fossiliferous, yellowish-gray Sandstone outcrop pictured in (A) along Dodge County Road 24 (hammer for scale). ! ! !! ! !! ! ! ! ! ! ! ! !! ! ! ! ! ! hydrostratigraphic properties column of Figure 1, distinguishes layers that are dominated scale 1:100,000. ! ! ! ! ! ! ! limestone interbedded with green-gray, calcareous shale. The limestone is Here the Platteville Formation is a gray and light brown, thin-bedded, wavy limestone. ! !! ! !! ! ! ! ! ! 1,026–1,050 ! ! ! by relatively high-permeability (easily transmitting water) material, versus layers dominated !! ! ! Runkel, A.C., McKay, R.M., Miller, J.F., Palmer, A.R., and Taylor, J.F., 2007, High ! thin- to medium-bedded and commonly silty and/or shaly and crinkly. Fossils ! ! ! C. Another outcrop of the Platteville Formation showing light brown, medium-bedded B ! B' ! ! !!! ! !!!! by lower-permeability (relatively harder to transmit water) material. This generalized ! ! ! !! 1,001–1,025 resolution sequence stratigraphy of lower Paleozoic sheet sandstones in central North ! ! ! in abundance include bryozoans, crinoids, and brachiopods. Less common limestone along the South Branch of the Middle Fork Zumbro River in Dodge County ! ! characterization for Dodge County is based on hydrogeologic reports by Runkel (1996), America: The role of special conditions of cratonic interiors in development of stratal ! are trilobites, horn corals, cephalopods, and gastropods. The alternating (green pen for scale). 976–1,000 ! Paillet and others (2000), Runkel and others (2003, 2006a, b, 2018), Tipping and others beds of limestone and shale produce a characteristic, serrated weathering architecture: Geological Society of America Bulletin, v. 119, no. 7/8, p. 860-881. D. Cummingsville Formation outcrop along the South Branch of the Middle Fork ! ! !!! ! (2006), Luhmann and others (2011), Green and others (2012), and unpublished borehole ! 951–975 profile in outcrop (Fig. 2D). Chert nodules are locally abundant, particularly Runkel, A.C., McKay, R.M., and Palmer, A.R., 1998, Origin of a classic cratonic sheet Zumbro River in Dodge County showing its characteristic sawtooth weathering profile ! and core data collected by the Minnesota Geological Survey. The high-permeability layers !! ! I. ! in the upper half. Total thickness of the Cummingsville Formation is about sandstone: Stratigraphy across the Sauk II–Sauk III boundary in the upper Mississippi of interbedded limestone and shale (no scale; exposed cliff approximately 25 feet [8 ! are potential aquifers, able to yield economic quantities of water in most places. The low- ! ! 926–950 65 feet (20 meters). valley: Geological Society of America Bulletin, v. 110, p. 188-210. ! ! ! ! !! meters] tall). !!!!! permeability layers are potential aquitards that retard vertical flow, hydraulically separating !! ! !! Od Decorah Shale (Upper Ordovician)—Grayish-green shale containing thin Runkel, A.C., Mossler, J.H., Tipping, R.G., and Bauer, E.G., 2006a, A hydrogeologic and ! 901–925 E. Gray-tan, thin-bedded, flaggy limestone of the Prosser Formation just east of Dodge ! the aquifer layers from one another in many places, and protecting water resources in the ! ! beds of fossiliferous, blue-gray limestone. Fossils in abundance include mapping investigation of the St. Lawrence Formation in the Twin Cities metropolitan
County along Olmsted County Road 3 in Rock Dell Township (hammer for scale). ! ! ! underlying layers from surface contamination. Fractures parallel to bedding that have ! ! ! 876–900 bryozoans, crinoids, horn corals, and brachiopods. Less common are area: Minnesota Geological Survey Open-File Report 06-4, 20 p. been demonstrated to have high permeability are likely to be present, as least locally, in F. Tan-gray, medium-bedded, heavily burrowed dolostone of the Stewartville Formation ! ! ! trilobites, cephalopods, gastropods, and bivalves. Ferruginous ooids of a ! Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Alexander, S.C., 2006b, G. H. displaying its characteristic "swiss cheese" appearance exposed along U.S. Highway ! ! 851–875 all formations in Dodge County, but are placed on the column where the hydrogeologic brassy color are common in the upper half of the Decorah Shale, where Hydrostratigraphic characterization of intergranular and secondary porosity in part ! reports cited above indicate they are most common. Most karst and spring features in 63 near Rochester in Olmsted County (hammer for scale). they are cemented within thin limestone beds or disseminated throughout ! ! 826–850 of the Cambrian sandstone aquifer system of the cratonic interior of North America:
! Dodge County are concentrated in the Ordovician Galena Group carbonate formations where
G. Gray, very sandy clay interbedded with dark gray to black clay of the Ostrander M ! ! ! the shale. The Decorah Shale is exposed as outcrop along the South Branch ! ! Improving predictability of hydrogeologic properties: Sedimentary Geology, v. 184, ! ! ! ! M bedrock is within 50 feet (15 meters) or less of the land surface (see Plate 6). Bedrock !! ! Member, Windrow Formation (rotary-sonic hole: DOR-1; CWI unique number: 340101; ! 801–825 ! of the Middle Fork Zumbro River valley. It thickens rapidly from about p. 281-304. ! springs typically emanate from the Prosser and Cummingsville Formations, where high- ! ! ! depth interval: ~94.6 to 96.2 feet [28.8 to 29.3 meters]; up is to the left). ! ! 45 feet (14 meters) thick near the Dodge–Olmsted border to about 60 feet 776–800 permeability vertical and bed-parallel fractures are known to be common. Many springs Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Green, J.A., 2003, Hydrogeology H. Gray, pebbly, medium- to coarse-grained, quartzose sandstone of the Ostrander thick (18 meters) westward across Dodge County. emanating from the Cummingsville Formation tend to be focused approximately near its of the Paleozoic bedrock in southeastern Minnesota: Minnesota Geological Survey Member, Windrow Formation. Pebbles are well-polished chert (rotary-sonic hole: Platteville Formation and Glenwood Formation (Upper Ordovician)—The J. K. 751–775 middle. Sinkholes are generally concentrated in the Stewartville and Prosser Formations. Opg Report of Investigations RI-61, 105 p., 2 pls. DOR-1; CWI unique number: 340101; depth interval: ~116.5 to 118.5 feet [35.5 to Deeper into the subsurface, the hydrogeologic properties of much of the Upper to Middle carbonate of the Platteville Formation and underlying shale of the Glenwood Runkel, A.C., Tipping, R.G., Meyer, J.R., Steenberg, J.R., Retzler, A.J., Parker, B.L., Green, 36.1 meters]; up is to the left). C C' 726–750 Cambrian and Mesoproterozoic bedrock units are poorly understood, and these units do Formation are combined into a single map unit with a full thickness of J.A., Barry, J.D., and Jones, P.M., 2018, A multidisciplinary-based conceptual model I. Black, waxy, massive clay with silty laminations of the Ostrander Member, Windrow about 30 feet (9 meters). Miles 701–725 not supply water to Dodge County, at least in part, because sufficient water resources are of a fractured sedimentary bedrock aquitard: Improved prediction of aquitard integrity: Formation (rotary-sonic hole: DOR-2; CWI unique number: 340102; depth interval: 0 1.25 2.5 5 7.5 10 available at shallower depths within the unconsolidated Quaternary glacial sediment, St. Platteville Formation—Thin- to medium-bedded, tan to gray limestone and Hydrogeology Journal, v. 26, p. 2133-2159,
Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources include both the references listed here and information on file at the offices ©2019 by the Regents of the University of Minnesota ENVIRONMENT of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation AND NATURAL RESOURCES conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously The University of Minnesota is an equal opportunity educator and employer TRUST FUND correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification. GEOLOGIC ATLAS OF DODGE COUNTY, MINNESOTA