Bedrock Geology

Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-34, PART A MINNESOTA GEOLOGICAL SURVEY THE WINONA COUNTY BOARD OF COMMISSIONERS, AND Winona County Harvey Thorleifson, Director the Minnesota Legacy Amendment's Clean Water Fund Plate 2—Bedrock Geology

92° W. 91° 52' 30" W. BUFFALO COUNTY R. 10 W. R. 9 W. WABASHA COUNTY 350 Trout 350 350 6 6 1 lr 1 River w 300 e Mississippi BEDROCK GEOLOGY Ops 300 m 250 Opo ¤61

350 300 350 Whitewater Creek 350 7 300 250 By Opo River 350 M w )25 WHITEWATER 250 MOUNT VERNON R. 8 W. Julia R. Steenberg s CORRELATION OF MAP UNITS T. 108 N. Creek j T. 108 N. Beaver Deering 300 Ops 300 Oc M 91° 45' W. 2014 Valley 22 Whitewater 200 200 WISCONSIN Od Upper Ordovician Creek e 200 350 Ops w 350 300 Opg 250 j 44° 7' 30" N. 44° 7' 30" N. LOCATION DIAGRAM Os River Middle Ordovician s s j 350 Speltz F 36 31 Ops 31 36 31 35 31 )74 Creek m WABASHA COUNTY unconformity MAP SYMBOLS Opo ROLLING 350 Lower Ordovician Garvin Opo Opo Geologic contact—Approximately located. 1 1 6 STONE unconformity 6 6 Brook 1 6 Fold—Axial trace of anticline, syncline. Fold limbs typically have shallow dips and are inferred from subsurface data. lr Creek Minnesota j F s 300 Straight300 PALEOZOIC )248 City M Fault—Faults are inferred from abrupt changes in the elevation of North Elba South w Creek 250 s stratigraphic units from subsurface and outcrop data. Letters 350 Fork Fork Rollingstone OLMSTED COUNTY )248 Upper Cambrian indicate relative vertical displacement: U—up, D—down. lr Location of geologic cross section lr R. 7 W. A A' Fork lr 350 unconformity Location of bedrock outcrop ¤61 350 w Bear F 350

Altura Creek Creek 200 T. 107 N. e Middle M T. 107 N. Ops Whitewater 350 Middle Cambrian 300 300 200 91° 37' 30" W m 250 ELBA NORTON HILLSDALE 350 )43 350 Goodview e WINONA B unconformity Fork

350 Rollingstone pC PRECAMBRIAN j U Brook Middle 300 River 350 D Lithostratigraphic 350 s 200 unit 300 Composite natural gamma log Ops Lake Era Lithology Garvin Group, Increasing count 350 Winona Gilmore Creek Os 300 Formation, Winona BUFFALO COUNTY 0 100

m System-Series Map symbol Hydrostratigraphic properties )74 Run Stockton ¤14 Member API-G units Thickness (in feet) 31 36 31 36 36 R. 6 W. 31 31 250 200 TREMPEALEAU COUNTY 36 31 Stockton w e Trout 91° 30' W. Cummingsville Oc

350 Formation > 70

250 Creek ¤61 6 River 1 6 1 6 6 lr ¤14 D 1 F 6

1 Galena Group U Whitewater Creek 1 Decorah 350 Opo Od U Shale 30-40 Peterson Valleylr D Upper Ordovician Creek Valley 300 300

44° N. 300 7 m 44° N. Platteville and Gilmore Opg

25-30 300 e Glenwood Formations Fork Creek Ph Creek D Os Os Burns 350 South U Lewiston Creek R. 5 W. Os West Valley Opo St. Peter Os Sandstone Garvin Brook w 70-90 LA CROSSE Os Creek Middle

Utica Burns 350 COUNTY Odrovician ST. CHARLES WILSON Homer HOMER RICHMOND T. 106 N. UTICA WARREN Creek w 300 350 T. 106 N. ¤14 250 Ops )43 East 350 M 350 D Little St. Charles 15 Opg 350 U Shakopee Trout 200 Ops

Creek Formation 300 j Willow River 90-120

Opg Valley Valley250 New LITHOLOGY KEY Richmond

D 400 250 Limestone U Creek 400 Ops 300 350 Trout 91° 22' 30" W. Opo Pleasant Rush 400 350 300 lr Cedar WISCONSIN Dolostone 90 400 ¦§ D Trout 90 U Big 31 ¦§ 36 31 400 36 31 Creek 36 31 36 31 300 j Run 400 36 31 D 350 Opo Sandy dolostone Oc Od 36 U 350 Lower Ordovician Oneota Sandstone Prairie du Chien Group Opo

A 400 Dolomite Hager City Witoka Dakota 350 Mississippi 160-180 Very fine- to fine-grained 6 Od 6 6 1 6 1 1 1 1 1 6 6 350 400 Creek Fine- to medium-grained Od 300 Ops A' e 350 j Creek ¦§90 250 Medium- to coarse-grained Dakota 350 300 Coon )74 w G Od U Creek 7 Valley 400 j River Ops Shaly D Ferguson Money U Opg Creek Os Creek Pine j s D 300 Pine F ¤61 Siltstone D R. 4 W. Jordan j Od )43 lr 350 U Dresbach Sandstone 80-100 350 Opg Creek PLEASANT HILL NEW HARTFORD T. 105 N. Shale SARATOGA FREMONT HART WISCOY 400 T. 105 N. Ahrensfeld 300 350 300 ¤14 m Opo Opo s St. Lawrence Chert U s G Os Creek Formation 60-70 250 D ¦§90 Oolites 350 400 j G 43° 52' 30" N. Money Gernander 400 D lr 43° 52' 30" N. Creek 250 350 Pine G G Glauconite D 300 350 U Opo 300 Hemingway Rush 300 Money Corey )76 Silver 250 DRESBACH Os Creek Reno Ph Phosphate grains U Creek 350 Ops LA CROSSE COUNTY PALEOZOIC G Opg 350Looney U Lone Rock Stromatolites Creek w D lr Creek Formation

Creek G 150-160 lr 300 300 300 300

Creek Creek Trout Creek Campbell 350 Shells 31 Creek 36 31 w 31

Run Tomah 36 31 36 31 36 36 31 36 City Group Tunnel Ops 31 e Upper Cambrian

OLMSTED COUNTY Os j Pine Creek 34 G Bioturbation Pine w Birk- mose G FILLMORE COUNTY R. 10 W. R. 4 W. HOUSTON R. 9 W. R. 8 W. FILLMORE HOUSTON COUNTY R. 7 W. B' R. 6 W. R. 5 W. Pebbles 92° W. 91° 52' 30" W. 91° 45' W.COUNTY 91° 37' 30" W. 91° 30' W. 91° 22' 30" W. COUNTY Intraclasts Digital base modified from the Minnesota Department of GIS compilation by R.S. Lively Transportation BaseMap data; digital base annotation by Edited by Lori Robinson Wonewoc Cross-bedded (planar) the Minnesota Geological Survey. SCALE 1:100 000 w Sandstone 100-120 Elevation contours were derived from the U.S. Geological Survey 1 0 1 2 3 4 5 MILES Cross-bedded (trough) 30-meter Digital Elevation Model (DEM) by the Minnesota Geological Survey. 1 0 1 2 3 4 5 6 7 8 KILOMETERS Cross-bedded (hummocky)

Universal Transverse Mercator Projection, grid zone 15 Dolomitic 1983 North American Datum contour interval 50 METERS G

G Vugs St. Charles Unconsolidated Quaternary sediments State Highway 6 State Highway 43 Cross section B–B' Witoka A' A Contact marks a major erosional surface 1,400 Od Dakota Eau Claire e Formation Oc 110-130 1,200 Os Opg Opo Ops G Ops Opo 1,000 j j s G s 800 lr HYDROSTRATIGRAPHIC PROPERTIES KEY lr w 600 Relatively high permeability (aquifer) w e e Feet above sea level 400 U D U D D U m Relatively low permeability (except for fractures, aquitard) 200 m pC pC High permeability bedding fracture known to be common

B Unconsolidated Quaternary sediments Cross section A–A' State Highway 76 B'

1,400 Middle Cambrian Mt. Simon Opo m 1,200 Sandstone Winona Opo j ~300-350 s 1,000 lr 800 w e 600 m Figure 1. Generalized stratigraphic column depicting Feet above sea level 400 the lithology, thickness, vertical succession, age, and 200 pC hydrostratigraphic properties for all units shown on the map. The gamma log is a compilation of the following Vertical exaggeration = 10x gamma logs: 239463, 231849, and 546911.

Precambrian rocks, pC INTRODUCTION Field evidence from outcrops for faulting include dipping beds (greater than 10º) and DESCRIPTION OF MAP UNITS coarsening-upward sequences of two interlayered facies (Runkel, 1994), which Precambrian rock. Drill core indicate that these rocks are a granitic to tonalitic undifferentiated closely spaced normal faults with progressive displacements of centimeters to decimeters. This are not separated on the map. They are medium- to coarse-grained, commonly gneiss of probable Proterozoic and Archean ages. Geophysical data indicate The geologic map on this plate depicts the type, distribution, and structure of the bedrock suggests that displacement may occur along one major fault plane or over a cluster of closely Galena Group bioturbated, with trough or tabular cross stratification and a fine-grained, a broad range of metamorphic and igneous rock units are present beneath the units in Winona County that are either exposed at the land surface or lie directly beneath spaced normal faults. Displacement along faults in Winona County is on the order of 25 to Oc Cummingsville Formation (Upper Ordovician)—Limestone interbedded with feldspathic, burrow-mottled facies with hummocky cross stratification. The Paleozoic strata (Jirsa and others, 2012). unconsolidated Quaternary sediments of variable thickness (see cross sections and Plate 3, 200 feet (8 to 61 meters), sufficient in places to juxtapose two different formations along the shale. The limestone is yellowish-gray to yellowish-brown, shaley, fossiliferous, maximum thickness of the formation is 80 to 100 feet (24 to 30 meters). Surficial Geology). The map shows how the bedrock surface would appear if it were viewed and fine-grained with thin and crinkly bedding. The shale is green to gray and fault contact (see cross sections). Blocks of bedrock that have dropped down alongside faults _ St. Lawrence Formation (Upper Cambrian)—Mostly well-cemented, thin to medium REFERENCES from an aerial perspective and the overlying Quaternary sediments were stripped away. The s preserve remnants of relatively young formations and uplifted blocks locally have brought calcareous. Exposures weather to a serrated profile because of the alternating beds of tan to gray to pink siltstone, dolomitic siltstone, very fine-grained bedrock units near the land surface in Winona County consist of sedimentary rocks of Paleozoic Austin, G.S., 1969, Paleozoic lithostratigraphic nomenclature for southeastern Minnesota: older formations closer to the surface. There are no apparent changes in the thickness of any shale beds. Unit forms ledges where it caps small plateaus in southwest Winona sandstone, and very thin shale. The very fine-grained sandstone is common in age that form distinguishable and mappable layers designated as formations. These units are Minnesota Geological Survey Information Circular 6, 11 p. of the Paleozoic bedrock units near the folds or faults, which suggests that faulting and folding County. Thickness exceeds 70 feet (21 meters) locally. the upper 20 feet (6 meters) of the unit. Glauconite is present throughout, but commonly exposed in bluffs, riverbanks, rock quarries, and roadcuts throughout the county. ———1971, The stratigraphy and petrology of the Shakopee Formation, Minnesota: Iowa occurred after all of the Paleozoic units were deposited and therefore affected the entire Paleozoic Od Decorah Shale (Upper Ordovician)—Fossiliferous green-gray shale with thin more common in the lower 30 feet (9 meters) of the formation. Intraclastic Some of these formations are major reservoirs for the water supply in the county and a major sequence. Most faults trend in the northwest direction and several trend to the northeast. The interbeds of yellowish-gray fossiliferous limestone. Limestone beds are more beds are present near the top and at the base of the unit. Small-scale hummocky City, University of Iowa, Ph.D. dissertation, 216 p. source of aggregate for construction materials. trends observed in Paleozoic strata are subparallel to structures in the underlying Precambrian abundant at the base. The maximum thickness ranges from 30 to 40 feet (9 to cross stratification and small and large diameter horizontal burrow traces can be Evans, T.J., 2003, Geology of La Crosse County, Wisconsin: Wisconsin Geological and Natural The production of the map and associated products relied on several different data sources, bedrock, as inferred from geophysical imagery. This implies that older Precambrian structures 12 meters). found throughout the formation. The contact with the underlying Lone Rock History Survey Bulletin 101, scale 1:100,000. including outcrops, water-well and scientific drilling records, drill cuttings, borehole geophysical beneath the Paleozoic rocks may have been reactivated locally after Paleozoic time or more Opg Platteville and Glenwood Formations, undivided (Upper Ordovician)—The Formation is marked by the base of an intraclastic conglomerate with rounded Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2012, Karst conduit flow in the Cambrian logs, and previously published geologic maps of Winona and adjacent counties (Mossler and recently, causing the fault and fold structures in Winona County (Jirsa and others, 2012). Platteville Formation is fossiliferous, thin- to medium-bedded, light gray to flat pebbles and cobbles of siltstone and sandstone. The maximum thickness St. Lawrence confining unit, southeast Minnesota, USA: Carbonates Evaporites, v. 27, Book, 1984; Olsen, 1988; Mossler, 1995; Runkel, 1996, 2001; Evans, 2003). The somewhat tan, finely crystalline limestone with thin gray shale partings. Quartz sand is 60 to 70 feet (18 to 21 meters). no. 2, p. 167-172. irregular distribution and density of data can be seen on Plate 1, Data-Base Map, and this should Hydrostratigraphy grains and dark phosphate clasts are present at the base. Unit forms ledges Tunnel City Group Jirsa, M.A., Boerboom, T.J., and Chandler, V.W., 2012, Geologic map of Minnesota Precambrian be considered when assessing the reliability of the map at any particular location. Areas with a where it caps small plateaus in southwest Winona County. Maximum thickness bedrock geology: Minnesota Geological Survey State Map S-22, scale 1:500,000. The Paleozoic bedrock formations contain significant sources of ground water that provides _lr Lone Rock Formation (Upper Cambrian)—Formerly referred to as the Franconia high density of bedrock control points are more likely to have an accurate interpretation of the ranges from 20 to 25 feet (6 to 8 meters). The Glenwood Formation is sandy, bedrock geology, whereas those areas with widely spaced control points may be less reliable the water supply for Winona County. This map and associated products, such as the bedrock Formation (Mossler, 2008). Fine-grained, glauconite-rich, feldspathic sandstone Luhmann, A.J., Covington, M.D., Peters, A.J., Alexander, S.C., Anger, C.T., Green, J.A., Runkel, Digital Elevation Models, provide a three-dimensional depiction of the rock properties that control green-gray shale. It contains dark phosphatic grains throughout. Thin, fine- and siltstone with interbedded green and gray shale and pink to tan, sandy, C.A., and Alexander, E.C., Jr., 2011, Classification of thermal patterns at karst springs and and inappropriate for site-specific needs. Characteristics of each formation are given in the to coarse-grained, quartzose sandstone lenses are common. The maximum stratigraphic column (Fig. 1) and in the description of map units. The accompanying bedrock flow in these water-bearing layers. Such rock properties are called hydrostratigraphic properties. glauconitic dolostone. It is composed of three members: in ascending order, cave streams: Ground Water, v. 49, no. 3, p. 324-335. Elevation (feet above sea level) thickness ranges from 3 to 6 feet (1 to 2 meters). 1,200 geologic cross sections add the dimension of depth and illustrate the stratigraphic, structural, and The hydrostratigraphic classification, shown by brown and blue colors on the hydrostratigraphic the Birkmose, Tomah, and the Reno Members. The Birkmose Member is a Mossler, J.H., 1995, Bedrock geology, pl. 2 of Mossler, J.H., ed., Geologic atlas of Fillmore M St. Peter Sandstone (Upper and Middle Ordovician)—Mostly fine- to medium- 1,175 topographic relationships of the bedrock units, as well as the variable thickness of the overlying column of Figure 1, distinguishes layers that are dominated by relatively high permeability (easily Os glauconitic sandstone with a well cemented, intraclastic, reddish-brown dolomite County, Minnesota: Minnesota Geological Survey County Atlas C-8, scale 1:100,000. grained, poorly cemented, white to orange, quartzose sandstone. Sand grains 1,150 Quaternary sediments. The geologic formations are thin in relation to their aerial extent and transmitting water) material, versus layers dominated by lower permeability (relatively more bed. The Tomah Member consists of interbedded sandstone and shale with very ———2008, Paleozoic stratigraphic nomenclature for Minnesota: Minnesota Geological Survey 1,125 are moderately- to well-rounded and well-sorted. The sandstone is generally M would only be one-tenth as thick as shown on the cross sections if no vertical exaggeration difficult to transmit water) material. This generalized characterization for Winona County is little glauconite. The Reno Member is composed of bioturbated, glauconitic Report of Investigations 65, 76 p. 1,100 based on hydrogeologic reports by Runkel (1996), Paillet and others (2000), Runkel and others structureless, and less commonly, shows subtle cross stratification. The lower sandstone with thin beds of flat pebble conglomerate, especially in the upper 1,075 were used. The exaggeration needed to show the thin rock formations gives the appearance of Mossler, J.H., and Book, P.R., 1984, Bedrock geology, pl. 2 of Balaban, N.H., and Olsen, B.M., F (2003, 2006a, b), Tipping and others (2006), Luhmann and others (2011), Green and others St. Peter Sandstone is more feldspathic and shaley, but this part of the formation 40 feet (12 meters). Hummocky cross stratification is common throughout 1,050 steeper slopes on the bedrock unit contacts, the land surface, and bedrock topography. eds., Geologic atlas of Winona County, Minnesota: Minnesota Geological Survey County (2012), and unpublished borehole and core data collected by Minnesota Geological Survey. is not exposed in the region. There is an unconformity at the basal contact with the formation. High-angle trough and planar cross stratification and extensive 1,025 With the exception of the Mt. Simon Sandstone, all of the Paleozoic units shown on this Atlas C-2, scale 1:100,000. 1,000 The high permeability layers are potential aquifers, able to yield economic quantities of water the Shakopee Formation (Smith and others, 1993). The uppermost surface is bioturbation are common in the upper half of the formation and in the lowest plate can be seen at the land surface somewhere in Winona County. Roadcuts such as those 975 in most places. The low permeability layers are potential aquitards that vertically retard flow, generally iron crusted and burrowed. The St. Peter Sandstone is commonly 15 feet (5 meters) of the formation. Generally the Lone Rock Formation is Olsen, B.M., 1988, Bedrock geology, pl. 2 of Balaban, N.H., eds., Geologic atlas of Olmsted along Interstate 90 west of Dakota, Garvin Heights Road, and State Highway 14 at Stockton M F 950 hydraulically separating the aquifer layers from one another in many places, and protecting exposed along hill slopes that are capped by the Platteville and Glenwood coarser-grained and more poorly cemented than the St. Lawrence Formation. County, Minnesota: Minnesota Geological Survey County Atlas C-3, scale 1:100,000. 925 Hill are some of the most complete sections of Paleozoic sedimentary strata found anywhere water resources in the underlying layers. High permeability bedding fractures are likely to Formations. The maximum thickness of the St. Peter Sandstone ranges from The Lone Rock Formation conformably overlies the Wonewoc Sandstone. The Paillet, F.L., Lundy, J., Tipping, R.G., Runkel, A.C., Reeves, L., and Green, J., 2000, U 900 in the state. The sedimentary rocks differ in their resistance to weathering and erosion, as D be present, at least locally, in all formations in Winona County, but are placed on the column 70 to 90 feet (21 to 27 meters). maximum thickness of the formation is 150 to 160 feet (46 to 49 meters). Hydrogeologic characterization of six sites in southeastern Minnesota using borehole 875 indicated by the weathering profile on the lithology column of Figure 1. The units that cover 850 where the hydrogeologic reports cited above indicate they are most common. The relatively Prairie du Chien Group flowmeters and other geophysical tools: U.S. Geological Survey Water-Resources the largest areas of the map are the most resistant to weathering, and generally form plateaus _w Wonewoc Sandstone (Upper Cambrian)—Formerly referred to as the Ironton and 825 hard Precambrian, crystalline bedrock does not supply water to Winona County largely because Investigations Report 00-4142, 33 p. D M 800 composed of carbonate rock (limestone and dolostone). The soft sandstone and shale formations Ops Shakopee Formation (Lower Ordovician)—Tan to gray dolostone, sandy dolostone, Galesville Sandstones (Mossler, 2008). Fine- to very coarse-grained, weakly U D U sufficient water resources are available at shallower depths in the Paleozoic rocks. and sandstone divided into two members (Austin, 1971). The Willow River cemented, quartzose sandstone. The upper 40 feet (12 meters) are more poorly Runkel, A.C., 1994, Deposition of the uppermost Cambrian (St. Croixan) Jordan Sandstone, U 775 are easily eroded and occur within the walls of valleys. 750 In Winona County, most aquifers are layers dominated by coarse-grained sandstone such Member is composed of thin- to medium-bedded dolomite, sandy dolomite, and sorted than the lower part and contain coarser-grained sandstone grains and and the nature of the Cambrian-Ordovician boundary in the upper Mississippi valley: The oldest known bedrock in the county, the Precambrian bedrock, lies unconformably D as the Jordan Sandstone and the Wonewoc Sandstone, in which water can be relatively easily thin quartz sandstone and minor shale beds. The dolostone and sandy dolostone abundant shale beds. White, brown, or black fossil shell fragments (phosphatic Geological Society of America Bulletin, v. 106, p. 492-506. M beneath the Paleozoic sequence and is only shown on the cross sections. Little is known about transmitted in both horizontal and vertical directions through the pore spaces between sand beds contain an oomoldic texture as well as oolites and stromatolite fossils. brachiopods) are locally common in the upper 10 to 15 feet (3 to 5 meters) ———1996, Bedrock geology of Houston County, Minnesota: Minnesota Geological Survey U D these rocks due to their deep burial. Geologic interpretations therefore rely significantly on D grains, as well as through fractures. Other aquifers are composed mostly of carbonate rock Chert nodules are common. The Willow River Member is generally 60 to 80 of the formation. A subtle disconformity exists within the formation and has Open-File Report 96-4, 11 p., 3 pls., scale 1:100,000. D aeromagnetic and gravity data and are supplemented with borehole data where available. U U (limestone or dolostone) in which water is transmitted mostly through a relatively dense network feet (18 to 24 meters) thick. The New Richmond Member represents the basal been noted to be locally capped by a pebbly, coarse- to very coarse-grained These data indicate the hard, crystalline, Precambrian bedrock is likely Archean (about 3,600 ———2001, Bedrock geology, pl. 2 of Runkel, A.C., ed., Geologic atlas of Wabasha County, of fractures, such as the Shakopee Formation and upper part of the Oneota Dolomite. Layers 15 to 40 feet (5 to 12 meters) of the Shakopee Formation. It is composed mainly sandstone bed that lies roughly in the middle of the formation, though it is Minnesota: Minnesota Geological Survey County Atlas C-14, scale 1:100,000. to 2,500 million years old [Ma]) to Proterozoic (about 1,000 to 2,500 Ma) in age (Jirsa and U D F U designated as aquifers, including parts of the upper Mt. Simon and the lower Jordan Sandstones, of fine- to medium-grained quartzose sandstone with low-angle cross bedding almost unrecognizable in the field (Runkel and others, 1998). The lower 60 D others, 2012). Runkel, A.C., McKay, R.M., Miller, J.F., Palmer, A.R., and Taylor, J.F., 2007, High resolution U D can locally contain low permeability strata that serve as small, internal aquitards. and can be locally cemented by quartz or stained reddish-brown by hematite. to 80 feet (18 to 24 meters) of the Wonewoc Sandstone is well to moderately The Paleozoic rocks of Winona County are characterized by relatively thin, widespread sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: D D Most layers designated as aquitards in the county have a much lower permeability in a The lowermost New Richmond Member may locally contain less than 10 feet sorted, fine- to medium-grained, quartz sandstone with minor shale, siltstone, U layers of sandstone, shale, and carbonate deposited in shallow seas during the Paleozoic era The role of special conditions of cratonic interiors in development of strata architecture: U D U vertical direction than do aquifers. Examples in Winona County include the St. Lawrence and Eau (3 meters) of oolitic sandy dolostone and sandstone beds known as the Prairie and very fine-grained sandstone beds. It has trough cross stratification and U from about 500 to 450 million years ago. The Cambrian age formations are dominated by Geological Society of America Bulletin, v. 199, p. 860-881. D Claire Formations. These rocks are composed mostly of very fine-grained sand and shale with Island facies and is present in the western part of Winona County. There is an minor glauconite. The lower part locally intertongues with the feldspathic, siliciclastic sedimentary rock including sandstone and siltstone with minor shale, such as the Runkel, A.C., McKay, R.M., and Palmer, A.R., 1998, Origin of a classic cratonic sheet small, poorly connected pore spaces. Carbonate rock with relatively sparse fractures such as the unconformity at the contact with the underlying Oneota Dolomite (Smith and very fine-grained, quartz sandstone of the underlying Eau Claire Formation. Figure 2. Map of Winona County depicting the elevation of the stratigraphic top of the Jordan Sandstone showing the geologic fold Jordan Sandstone and Lone Rock Formation. Carbonate rock occurs only as relatively thin sandstone: Stratigraphy across the Sauk II-Sauk III boundary in the upper Mississippi lower part of the Oneota Dolomite are also aquitards. However, layers designated as aquitards others, 1993). The maximum thickness of the Shakopee Formation is 90 to The maximum thickness of the Wonewoc Formation is 100 to 120 feet (30 to and fault structures. Contour interval is 25 feet (8 meters). In areas where some or all of the Jordan Sandstone is missing because of layers in these units. Ordovician age formations, in contrast, are dominated by thicker units of valley: Geological Society of America Bulletin, v. 110, p. 188-210. with very low permeability in a vertical direction, such as the St. Lawrence Formation, may 120 feet (27 to 37 meters). 37 meters). erosion the contours are inferred from vertical projection of lower formation contacts and the map is shaded. Scale is 1:350,000. carbonate rock with less sandstone and shale, such as the Oneota Dolomite and the Platteville Runkel, A.C., Miller, J.F., McKay, R.M., Shaw, T.H., and Bassett, D.J., 1999, Cambrian- contain horizontal fractures that are conductive enough to yield large quantities of water. Oneota Dolomite (Lower Ordovician)—The Oneota Dolomite is divided into two _ Eau Claire Formation (Upper and Middle Cambrian)—Gray to greenish-gray Formation. Opo e Ordovician boundary strata in the central mid-continent of North America: Acta Universitatis Horizontal as well as vertical fractures are also more common where bedrock layers are members. The Hager City Member is composed of medium to thick, irregular to purple shale, tan to gray siltstone, and very fine- to fine-grained sandstone. The Paleozoic strata lie on the eastern side of a broad cratonic depression known as the Carolinae Geologica, v. 43, p. 17-20. at or near the bedrock surface. As a result, aquitards in such conditions are likely to have tabular beds of dolostone and silty dolostone. The dolostone is light tan to light Gray to black fossil shell fragments are common (phosphatic brachiopods). Hollandale embayment (Austin, 1969). Strata generally dip less than one degree to the west as Runkel, A.C., Mossler, J.H., Tipping, R.G., and Bauer, E.J., 2006a, A hydrogeologic and higher permeability compared to deeper conditions of burial and may have a diminished ability gray and fine-grained crystalline, and may be intraclastic in the lowermost part. The sandstone is variably glauconitic. The formation coarsens upward, with part of the regional structural trend of the embayment. As a result, progressively younger bedrock mapping investigation of the St. Lawrence Formation in the Twin Cities Metropolitan Area: to retard water flow to underlying aquifers. There is no precise boundary between shallow It contains white to gray chert nodules and calcite filled vugs throughout, though sandstone becoming increasingly abundant. The upper 10 to 20 feet (3 to 6 formations subcrop from eastern to western Winona County. Smaller scale structural features Minnesota Geological Survey Open-File Report 06-4, 20 p. and deep conditions of burial, but in most areas of southeastern Minnesota about 50 feet (15 they are more common in the upper and lowermost parts. The uppermost part meters) are mostly very fine-grained sandstone and siltstone. The maximum such as faults and folds are superimposed on this regional dip pattern and are recognized by meters) of depth below the bedrock surface is considered a best approximation (Runkel and may also be brecciated near the contact with the overlying Shakopee Formation. thickness ranges from 110 to 130 feet (34 to 40 meters). Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Alexander, S.C., 2006b, Hydrostratigraphic changes in the elevation of key bedrock contacts, as shown on Figure 2. A fault is recognized characterization of intergranular and secondary porosity in part of the Cambrian sandstone others, 2006b). The upper and lower thirds of the Hager City Member contain stromatolitic _ Mt. Simon Sandstone (Middle Cambrian)—Not exposed in the county. Mostly white where changes in the elevation of a bedrock contact occur within a very short distance, m and thrombolitic microbial textures. The intervening section consists of beds to yellow, fine- to very coarse-grained, friable, quartzose sandstone. The top aquifer system of the cratonic interior of North America: Improving predictability of generally 50 feet (15 meters) or more elevation change within a distance of 1,000 feet (305 In addition to this hydrostratigraphic classification, the Minnesota Department of Natural of medium thickness that are internally structureless or faintly laminated. The of the Mt. Simon Sandstone is marked locally by a thin iron stained sandstone hydrogeologic properties: Sedimentary Geology, v. 184, p. 281-304. meters). A fold is recognized where these elevation changes occur over a more gradual slope. Resources, as Part B of the Winona County atlas, will conduct a thorough hydrogeologic study thickness of the Hager City Member is 145 to 160 feet (44 to 49 meters). The that contains abundant black fossil shell fragments (phosphatic brachiopods). Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., Green, J.A., Mossler, J.H., and Alexander, The stratigraphic top of the Jordan Sandstone was contoured at 50-foot (15-meter) intervals to of the ground water flow system, aquifer capacity, and aquifer sensitivity, which may or may underlying Coon Valley Member consists of interbedded sandstone, sandy Variegated beds of feldspathic-rich shale, siltstone, and very fine-grained S.C., 2003, Hydrogeology of the Paleozoic bedrock in southeastern Minnesota: Minnesota show the inferred locations of the faults and folds in Winona County. Contours were drawn for not result in modifications or additions to this classification. Furthermore, designations of dolostone, dolostone, and minor shale. It commonly contains stromatolites, sandstone are common, particularly in the upper two-thirds of the formation. Geological Survey Report of Investigations 61, 105 p., 2 pls. 25-foot (8-meter) intervals in many places to better constrain the location of the mapped faults aquifers versus aquitards made here may not correspond precisely with those made for regulatory oolites, and an oomoldic texture. The thickness of the Coon Valley Member is Pebble conglomerate or pebbly sandstone is common in the lower 50 feet (15 Smith, G.L., Byers, C.W., and Dott, R.H., Jr., 1993, Sequence stratigraphy of the lower and folds. The top of the Jordan Sandstone was selected to portray these structures because it purposes by the Minnesota Department of Health. about 15 to 50 feet (6 to 15 meters). There is an unconformity at the base with meters) of the formation, especially in the lowest few feet. Limited subsurface Ordovician Prairie du Chien Group on the Wisconsin arch and in the Michigan basin: is a well-recognized and distinct contact, and has numerous control points including outcrops the contact of the Jordan Sandstone that contains pebbles of Precambrian rocks up data indicate that the Mt. Simon Sandstone is as much as 300 to 350 feet (91 American Association of Petroleum Geologists Bulletin, v. 77, p. 49-67. that expose the contact and water wells that penetrate it. However, there are areas where the to two centimeters in diameter (Runkel and others, 1999, 2007). The maximum to 107 meters) thick. Tipping, R.G., Runkel, A.C., Alexander, E.C., Jr., and Alexander, S.C., 2006, Evidence for Every reasonable effort has been made to ensure the accuracy of the factual data on which this map 25-foot (8-meter) contours do not represent all water-well data points that are present. This interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that thickness of the Oneota Dolomite is 160 to 180 feet (49 to 55 meters). Precambrian rocks, undifferentiated—Not exposed in the county; shown only on hydraulic heterogeneity and anisotropy in the mostly carbonate Prairie du Chien Group, is due to the vagaries associated with recognizing the top of the Jordan Sandstone versus the pC there are no errors. Users may wish to verify critical information; sources include both the references listed _ Jordan Sandstone (Upper Cambrian)—Dominantly whitish-tan to orange, very sandy Coon Valley Member of the lowermost Oneota Dolomite. j the cross sections. Samples from deep water wells near Winona, Lewiston, and southeastern Minnesota, USA: Sedimentary Geology, v. 184, p. 305-330. here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort fine- to coarse-grained, quartzose, friable sandstone. Characterized by La Crescent to the south penetrated the Mt. Simon Sandstone and intersected has been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification.