Plate 2, Bedrock Geology Map (6.375Mb Application/Pdf)

Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-33, PART A MINNESOTA GEOLOGICAL SURVEY THE HOUSTON COUNTY BOARD OF COMMISSIONERS, AND Houston County Harvey Thorleifson, Director the Minnesota Legacy Amendment's Clean Water Fund Plate 2—Bedrock Geology

91° 22' 30" W. 91° 37' 30" W. 91° 30' W. LA CROSSE WINONA COUNTY R. 7 W. B R. 6 W. R. 5 W. R. 4 W. FILLMORE COUNTY COUNTY Looney Pine 300 Pine Creek lr ¤61 300 350 D Creek 2 350 1 300 6 1 6 U 1 6 BEDROCK GEOLOGY 6 Ops 76 Creek U ) U D 350 ¤14 Creek w 250 300 w D 300 Money 250 s 300 250 U 350 Mississippi Opo 200 D Silver La Crescent Opo e By FILLMORE COUNTY Blue 350 Ops j 300 300 Lake CORRELATION OF MAP UNITS s 350 Ops Pine Julia R. Steenberg j Creek lr Oc 350 Ops 350 Creek

Storer Day

MONEY CREEK 350HOUSTON 250 MOUND PRAIRIE LA CRESCENT )16 T. 104 N. Od Upper Ordovician T. 104 N. 2014 Root 250 350 M m Opg Creek River lr 300 Creek Target River 250 350 Silver Lake 300 w LOCATION DIAGRAM Os 300 350 Middle Ordovician 250 Creek 250 300 D 300 91° 15' W. M U 250 Root e Ops e 300 300 e River m River unconformity Creek 350 lr R Lower Ordovician o o 250 250 Root River t Opo Root M 300 R ive PALEOZOIC Ferndales r unconformity 31 w 36 31 w 36 31 36 31 36 31 e D lr 350 )16 250 )16 Mound j MAP SYMBOLS U 200

River Creek 350 250 300 s Geologic contact—Approximately located. Lithostratigraphic Creek Houston HOKAH WISCONSIN unit 6 1 6 Prairie 1 D6 U 1 Composite natural gamma log Root 250 )26 Fold—Axial trace of anticline, syncline. Fold limbs typically have Ops 1 6 Crystal Creek Hokah Upper Cambrian Era Lithology 350 350 300 300 Increasing count

43° 45' N. j )76 250 43° 45' N. lr F shallow dips and are inferred from subsurface data. Group, Creek Formation, Daley 300 300 Creek M 0 100

300 350 System-Series Fault—Faults are inferred from abrupt changes in the elevation of Map symbol Hydrostratigraphic properties unconformity Member API-G units Thickness (in feet) Swede )44 Bottom w 300 stratigraphic units from subsurface and outcrop data. Letters 300 350 350 Opo 350 Fork Opo w indicate relative vertical displacement: U—up, D—down. 300 Opo Lawrence e 350 Cummingsville Creek Lake Location of geologic cross section Oc Thompson Middle Cambrian A LA CROSSE A' Formation > 80 m Ops South Badger 250 Opo lr COUNTY Location of bedrock outcrop lr U 200 unconformity D Galena Group VERNON 300 Butterfield Ops Decorah 350 U COUNTY pC PRECAMBRIAN Od YUCATAN SHELDON UNION 350 Shale 30-35 T. 103 N. e 350 350 T. 103 N. Upper Ordovician 350 Beaver D Bridge Spring Platteville and Crystal 300 Opg 350 350 Glenwood Formations 30-35 s Branch Ph 300 350 Creek 350 j 300 Creek350 Creek 250 350 F Creek F Creek 300 St. Peter Os j Creek Brownsville Sandstone INTRODUCTION DESCRIPTION OF MAP UNITS 70-90

BROWNSVILLE Middle Odrovician 300 River The geologic map on this plate depicts the type, distribution, and structure of the bedrock Galena Group w w Indian Spring 350 250 e Root M Creek units in Houston County that are either exposed at the land surface or lie directly beneath w Sullivan oc Cummingsville Formation (Upper Ordovician)—Limestone interbedded with Wildcat 250 unconsolidated Quaternary sediments of variable thickness (see cross sections and Plate 3, shale. The limestone is yellowish-gray to yellowish-brown, shaley, fossiliferous, Fork Sheldon 36 31 31 36 31 M j 36 31 35 Surficial Geology). The map shows how the bedrock surface would appear if it were viewed from Shakopee and fine-grained with thin and crinkly bedding. The shale is green to gray and Formation Ops 350 Willow River an aerial perspective and the overlying Quaternary sediments were stripped away. The bedrock calcareous. Exposures weather to a serrated profile because of the alternating 90-120 Creek New Creek units near the land surface in Houston County consist of sedimentary rocks of Paleozoic age that Richmond 300 shale beds. Unit forms ledges where it caps small plateaus in southwest Houston lr lr 6 350 250 Ops 6 form distinguishable and mappable layers designated as formations. These units are commonly County. Thickness exceeds 80 feet (24 meters) locally. 1 6 U 1 6 1 2 South D exposed in bluffs, riverbanks, rock quarries, and roadcuts throughout the county. Some of these 350 Decorah Shale (Upper Ordovician)—Fossiliferous green-gray shale with thin LITHOLOGY KEY 350 )44 od Brownsville Beaver 350 formations are major reservoirs for the water supply in the county and a major source of aggregate Riceford interbeds of yellowish-gray fossiliferous limestone. Limestone beds are more

350 for construction materials. Opo abundant at the base. The maximum thickness ranges from 30 to 35 feet (9 to 11 Limestone )76 350

Ops 300 Ops The production of the map and associated products relied on several different data sources, meters). Creek

F including outcrops, water-well and scientific drilling records, drill cuttings, borehole geophysical Lower Ordovician opg Platteville and Glenwood Formations, undivided (Upper Ordovician)—The Dolostone Prairie du Chien Group Oneota 300 300 logs, and previously published geologic maps of Houston and adjacent counties (Mossler and Opo s Platteveille Formation is fossiliferous, thin- to medium-bedded, light gray to tan, Dolomite Hager City 170-200 East e Book, 1984; Olsen, 1988; Mossler, 1995; Runkel, 1996, 2001; Evans, 2003). The somewhat

350 Sandy dolostone Opo )26 finely crystalline limestone with thin gray shale partings. Quartz sand grains and irregular distribution and density of data can be seen on Plate 1, Data-Base Map, and this should dark phosphate clasts are present at the base. Unit forms ledges where it caps 300 Sandstone 200 be considered when assessing the reliability of the map at any particular location. Areas with a small plateaus in southwest Houston County. Maximum thickness ranges from 25 BLACK HAMMER CALEDONIA MAYVILLEj Very fine- to fine-grained T. 102 N. U Caledonia T. 102 N. high density of bedrock control points are more likely to have an accurate interpretation of the 300 350 to 30 feet (8 to 9 meters). The Glenwood Formation is sandy, green-gray shale. j 300 D 300 350 bedrock geology, whereas those areas with widely spaced control points may be less reliable and 43° 37' 30" N. North s 43° 37' 30" N. It contains dark phosphatic grains throughout. Thin, fine- to coarse-grained, Coon Fine- to medium-grained Valley G 350 inappropriate for site-specific needs. Characteristics of each formation are given in the stratigraphic quartzose sandstone lenses are common. The maximum thickness ranges from 3 350

350 column (Fig. 1) and in the description of map units. The accompanying bedrock geologic cross 350 Fork to 6 feet (1 to 2 meters). Medium- to coarse-grained Riceford Creek sections add the dimension of depth and illustrate the stratigraphic, structural, and topographic 300 West os St. Peter Sandstone (Upper and Middle Ordovician)—Mostly fine- to medium- Jordan 350 CROOKED CREEK Mississippi relationships of the bedrock units; as well as the variable thickness of the overlying Quaternary j Opo Crooked grained, poorly cemented, white to orange, quartzose sandstone. Sand grains are Sandstone 80-100 Shaly sediments. The geologic formations are thin in relation to their aerial extent and would only Os Crooked moderately- to well-rounded and well-sorted. The sandstone is structureless, and South be one-tenth as thick as shown on the cross sections if no vertical exaggeration were used. The Creek Os Opg 300 lr 350 Fork Creek less commonly, shows subtle cross stratification. The lower St. Peter Sandstone Siltstone U Creek exaggeration needed to show the thin rock formations gives the appearance of steeper slopes on D 250 River is more feldspathic and shaley, but this part of the formation is not exposed in the St. Lawrence 31 36 Ops 36 the bedrock unit contacts, the land surface, and bedrock topography. 31 31 36 31 s G Shale Ops 36 region. There is an unconformity at the basal contact with the Shakopee Formation Formation 60-70 350 With the exception of the Mt. Simon Sandstone, all of the Paleozoic units shown on this G Beaver (Smith and others, 1993). The uppermost surface is generally iron crusted and 350 M 31 Od plate can be seen at the land surface somewhere in Houston County. The sedimentary rocks G 300 burrowed. The St. Peter Sandstone is commonly exposed along hill slopes that Chert differ in their resistance to weathering and erosion, as indicated by the weathering profile on 350 Os lr WISCONSIN 6 1 are capped by the Platteville and Glenwood Formations. The maximum thickness 1 6 Winnebago 6 6 1 Reno Oolites 1 Ops 6 the lithology column of Figure 1. The units that cover the largest areas of the map are the most of the St. Peter Sandstone ranges from 70 to 90 feet (21 to 27 meters). PALEOZOIC G Clear resistant to weathering and generally form plateaus composed of carbonate rock (limestone and Lone Rock A 400 350 Creek Prairie du Chien Group lr G Glauconite 350 dolostone). The soft sandstone and shale formations are easily eroded and occur within the walls Formation 350 G 135-150 ops Shakopee Formation (Lower Ordovician)—Tan to gray dolostone, sandy dolostone, Ph Phosphate grains Opg Creek of valleys. Tomah 300 A' and sandstone divided into two members (Austin, 1971). The Willow River City Group Tunnel Opo Spring Od Upper Cambrian 400 The oldest known bedrock in the county, the Precambrian bedrock, lies unconformably beneath Birk- G Stromatolites 400 Opo w Member is composed of thin- to medium-bedded dolomite, sandy dolomite, and Grove 250 mose j 350 the Paleozoic sequence and is only shown on the cross sections. Little is known about these rocks G Od 350 thin quartz sandstone and minor shale beds. The dolostone and sandy dolostone Shells Oc 350 due to their deep burial. Geologic interpretations therefore rely significantly on aeromagnetic s beds contain an oomoldic texture as well as oolites and stromatolite fossils. Chert 350 350 and gravity data and are supplemented with borehole data where available. These data indicate Bioturbation U )44 300 350 )76 350 nodules are common. The Willow River Member is generally 60 to 80 feet (18

Creek D 350 e the hard, crystalline, Precambrian bedrock is likely Archean (about 3,600 to 2,500 million years to 24 meters) thick. The New Richmond Member represents the basal 15 to 40 Pebbles SPRING GROVE Os WILMINGTON WINNEBAGO JEFFERSON 200 old [Ma]) to Proterozoic (about 1,000 to 2,500 Ma) in age (Jirsa and others, 2012). Wonewoc T. 101 N. T. 101 N. w

feet (5 to 12 meters) of the Shakopee Formation. It is composed mainly of fine- Sandstone 110-130 Opg Intraclasts Riceford 350 The Paleozoic rocks of Houston County are characterized by relatively thin, widespread to medium-grained quartzose sandstone with low-angle cross bedding and can Od Hayshore Od )26 layers of sandstone, shale, and carbonate deposited in shallow seas during the Paleozoic era from 350 lr Lake be locally cemented by quartz or stained reddish-brown by hematite. There is Cross-bedded (planar) 250 M 350 about 500 to 450 million years ago. The Cambrian age formations are dominated by siliciclastic Opg s 350 Mud Lake an unconformity at the contact with the underlying Oneota Dolomite (Smith and F sedimentary rock including sandstone and siltstone with minor shale, such as the Jordan Sandstone Cross-bedded (trough) D others, 1993). The maximum thickness of the Shakopee Formation is 90 to 120 G U Opo and Lone Rock Formation. Carbonate rock occurs only as relatively thin layers in these units. feet (27 to 37 meters). Os 350 M G Cross-bedded (hummocky) Opg Os Os Winnebago Ordovician age formations, in contrast, are dominated by thicker units of carbonate rock with Bee opo Oneota Dolomite (Lower Ordovician)—The Oneota Dolomite is divided into two 250 Goose Lake less sandstone and shale, such as the Oneota Formation and the Platteville Formation. Dolomitic Os Creek 300 members. The Hager City Member is composed of medium to thick, irregular Eau Claire Creek e Ops Oc 300 350 300 350 COUNTY VERNON The Paleozoic strata lie on the eastern side of a broad cratonic depression known as the Formation Creek 115-150 Vugs 350 350 Ops tabular beds of dolostone and silty dolostone. The dolostone is light tan to light 31 Hollandale embayment (Austin, 1969). Strata generally dip less than one degree to the west G 31 Opg 36 Duck 31 36 350 gray and fine-grained crystalline, and may be intraclastic in the lowermost part. 36 31 36 31 Contact marks a major erosional surface Opo Eitzen Ops as part of the regional structural trend of the embayment. As a result, progressively younger FILLMORE COUNTY It contains white to gray chert nodules and calcite filled vugs throughout, though G 300 bedrock formations subcrop from eastern to western Houston County. Smaller scale structural 43° 30' N. they are more common in the upper and lowermost parts. The uppermost part 43° 30' N. WINNESHIEK COUNTY R. 7 W. ALLAMAKEE COUNTY B' R. 6 W. R. 5 W. R. 4 W. ALLAMAKEE COUNTY R. 3 W. features such as faults and folds are superimposed on this regional dip pattern and are recognized IOWA 91° 37' 30" W. IOWA 91° 15' W. may also be brecciated near the contact with the overlying Shakopee Formation. 91° 30' W. 91° 22' 30" W. by changes in the elevation of key bedrock contacts, as shown on Figure 2. A fault is recognized Digital base modified from the Minnesota Department of The upper and lower thirds of the Hager City Member contain stromatolitic and GIS compilation by R.S. Lively where changes in the elevation of a bedrock contact occur within a very short distance, generally Transportation BaseMap data; digital base annotation by Edited by Lori Robinson thrombolitic microbial textures. The intervening section consists of medium sized HYDROSTRATIGRAPHIC PROPERTIES KEY the Minnesota Geological Survey. 50 feet (15 meters) or more elevation change within a distance of 1,000 feet (305 meters). A fold SCALE 1:100 000 beds that are internally structureless or faintly laminated. The thickness of the is recognized where these elevation changes occur over a more gradual slope. The stratigraphic Relatively high permeability (aquifer) Elevation contours were derived from the U.S. Geological Survey 1 0 1 2 3 4 5 MILES Hager City Member is 145 to 160 feet (44 to 49 meters). The underlying Coon 30-meter Digital Elevation Model (DEM) by the Minnesota top of the Jordan Sandstone was contoured at 50-foot (15-meter) intervals to show the inferred Geological Survey. Valley Member consists of interbedded sandstone, sandy dolostone, dolostone, Relatively low permeability (except for fractures, aquitard) 1 0 1 2 3 4 5 6 7 8 KILOMETERS locations of the faults and folds in Houston County. Contours were drawn for 25-foot (8-meter) and minor shale. It commonly contains stromatolites, oolites, and an oomoldic Universal Transverse Mercator Projection, grid zone 15 intervals in many places to better constrain the location of the mapped faults and folds. The top 1983 North American Datum texture. The thickness of the Coon Valley Member is about 20 to 50 feet (6 to High permeability bedding fracture known to be common contour interval 50 METERS of the Jordan Sandstone was selected to portray these structures because it is a well-recognized Middle Cambrian 15 meters). There is an unconformity at the base with the contact of the Jordan Mt. Simon m and distinct contact, and has numerous control points including outcrops that expose the contact Sandstone that contains pebbles of Precambrian rocks up to two centimeters in Sandstone ~300-350 and water wells that penetrate it. However, there are areas where the 25-foot (8-meter) contours diameter (Runkel and others, 1999, 2007). The maximum thickness of the Oneota do not represent all water-well data points that are present. This is due to the vagaries associated Dolomite is 170 to 200 feet (52 to 61 meters). A A' with recognizing the top of the Jordan Sandstone versus the sandy Coon Valley Member of the 1,400 Unconsolidated Quaternary sediments Spring Grove Oc Cross section B–B' County Road 14 State Highway 26 _ Jordan Sandstone (Upper Cambrian)—Dominantly whitish-tan to orange, very fine- to Od lowermost Oneota Dolomite. j coarse-grained, quartzose, friable sandstone. Characterized by coarsening-upward 1,200 Os Opg Field evidence from outcrops for faulting include dipping beds (greater than 10°) and closely sequences of two interlayered facies (Runkel, 1994), which are not separated on the 1,000 Ops Ops Opo Unconsolidated spaced normal faults with progressive displacements of centimeters to decimeters. This suggests map. They are medium- to coarse-grained, commonly bioturbated, with trough or Figure 1. Generalized stratigraphic column depicting Opo j Quaternary sediments that displacement may occur along one major fault plane or over a cluster of closely spaced normal tabular cross stratification and a fine-grained, feldspathic, burrow-mottled facies the lithology, thickness, vertical succession, age, and 800 j s faults. Displacement along faults in Houston County is on the order of 25 to 200 feet (8 to 61 s lr with hummocky cross stratification. The maximum thickness of the formation is hydrostratigraphic properties for all units shown on the 600 U D lr w meters), sufficient in places to juxtapose two different formations along the fault contact (see 80 to 100 feet (24 to 30 meters). map. The gamma log is a compilation of the following w e cross sections). Blocks of bedrock that have dropped down alongside faults preserve remnants gamma logs: 239463, 231849, and 546911. Feet above sea level 400 _ St. Lawrence Formation (Upper Cambrian)—Mostly well-cemented, thin to medium s e of relatively young formations and uplifted blocks locally have brought older formations closer Precambrian rocks, pC m beds of tan to gray to pink siltstone, dolomitic siltstone, very fine-grained sandstone, undifferentiated 200 pC pC to the surface. There are no apparent changes in the thickness of any of the Paleozoic bedrock m pC and very thin shale. The very fine-grained sandstone is common in the upper 20 units near the folds or faults, which suggests that faulting and folding occurred after all of the feet (6 meters) of the unit. Glauconite is present throughout, but more common Paleozoic units were deposited and therefore affected the entire Paleozoic sequence. Most B in the lower 30 feet (9 meters) of the formation. Intraclastic beds are present near REFERENCES Houston State Highway 76 State Highway 44 Cross section A–A' B' faults trend in the northwest direction and several trend to the northeast. The trends observed in 1,400 the top and at the base of the unit. Small scale hummocky cross stratification and Opg Paleozoic strata are subparallel to structures in the underlying Precambrian bedrock, as inferred Austin, G.S., 1969, Paleozoic lithostratigraphic nomenclature for southeastern Minnesota: 1,200 Unconsolidated Os small and large diameter horizontal burrow traces can be found throughout the Minnesota Geological Survey Information Circular 6, 11 p. j Opo Quaternary sediments Ops Os from geophysical imagery. This implies that older Precambrian structures beneath the Paleozoic s formation. The contact with the underlying Lone Rock Formation is marked by 1,000 Opo rocks may have been reactivated locally after Paleozoic time or more recently, causing the fault ———1971, The stratigraphy and petrology of the Shakopee Formation, Minnesota: Iowa City, lr the base of an intraclastic conglomerate with rounded flat pebbles and cobbles j and fold structures in Houston County (Jirsa and others, 2012). University of Iowa, Ph.D. dissertation, 216 p. 800 w s of siltstone and sandstone. The maximum thickness is 60 to 70 feet (18 to 21 Evans, T.J., 2003, Geology of La Crosse County, Wisconsin: Wisconsin Geological and Natural e lr meters). 600 Hydrostratigraphy History Survey Bulletin 101, scale 1:100,000. w Tunnel City Group m Feet above sea level 400 U e The Paleozoic bedrock formations contain significant sources of ground water that provides Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2012, Karst conduit flow in the Cambrian _lr Lone Rock Formation (Upper Cambrian)—Formerly referred to as the Franconia D the water supply for Houston County. This map and associated products, such as the bedrock St. Lawrence confining unit, southeast Minnesota, USA: Carbonates Evaporites, v. 27, no. 200 Formation (Mossler, 2008). Fine-grained, glauconite-rich, feldspathic sandstone pC m 2, p. 167-172. Digital Elevation Models, provide a three-dimensional depiction of the rock properties that control and siltstone with interbedded green and gray shale and pink to tan, sandy, Jirsa, M.A., Boerboom, T.J., and Chandler, V.W., 2012, Geologic map of Minnesota Precambrian Vertical exaggeration = 10x flow in these water-bearing layers. Such rock properties are called hydrostratigraphic properties. glauconitic dolostone. It is composed of three members: in ascending order, the The hydrostratigraphic classification, shown by brown and blue colors on the hydrostratigraphic Birkmose, Tomah, and the Reno Members. The Birkmose Member is a glauconitic bedrock geology: Minnesota Geological Survey State Map S-22, scale 1:500,000. column of Figure 1, distinguishes layers that are dominated by relatively high permeability (easily sandstone with a well cemented, intraclastic, reddish-brown dolomite bed. The Luhmann, A.J., Covington, M.D., Peters, A.J., Alexander, S.C., Anger, C.T., Green, J.A., Runkel, transmitting water) material, versus layers dominated by lower permeability (relatively more Tomah Member consists of interbedded sandstone and shale with very little C.A., and Alexander, E.C., Jr., 2011, Classification of thermal patterns at karst springs and difficult to transmit water) material. This generalized characterization for Houston County is glauconite. The Reno Member is composed of bioturbated, glauconitic sandstone cave streams: Ground Water, v. 49, no. 3, p. 324-335. based on hydrogeologic reports by Runkel (1996), Paillet and others (2000), Runkel and others with thin beds of flat pebble conglomerate, especially in the upper 40 feet (12 Mossler, J.H., 1995, Bedrock geology, pl. 2 of Mossler, J.H., ed., Geologic atlas of Fillmore (2003, 2006a, b), Tipping and others (2006), Luhmann and others (2011), Green and others D U meters). Hummocky cross stratification is common throughout the formation. County, Minnesota: Minnesota Geological Survey County Atlas C-8, scale 1:100,000. (2012), and unpublished borehole and core data collected by Minnesota Geological Survey. The U D High-angle trough and planar cross stratification and extensive bioturbation are ———2008, Paleozoic stratigraphic nomenclature for Minnesota: Minnesota Geological Survey U high permeability layers are potential aquifers, able to yield economic quantities of water in most D D common in the upper half of the formation and in the lowest 15 feet (5 meters) of Report of Investigations 65, 76 p. places. The low permeability layers are potential aquitards that vertically retard flow, hydraulically the formation. Generally the Lone Rock Formation is coarser-grained and more Mossler, J.H., and Book, P.R., 1984, Bedrock geology, pl. 2 of Balaban, N.H., and Olsen, B.M., separating the aquifer layers from one another in many places, and protecting water resources poorly cemented than the St. Lawrence Formation. The Lone Rock Formation M in the underlying layers. High permeability bedding fractures are likely to be present, at least eds., Geologic atlas of Winona County, Minnesota: Minnesota Geological Survey County D conformably overlies the Wonewoc Sandstone. The maximum thickness of the Atlas C-2, scale 1:100,000. U locally, in all formations in Houston County, but are placed on the column where the hydrogeologic formation is 135 to 150 feet (41 to 46 meters). M reports cited above indicate they are most common. The relatively hard Precambrian, crystalline Olsen, B.M., 1988, Bedrock geology, pl. 2 of Balaban, N.H., eds., Geologic atlas of Olmsted Elevation (feet above sea level) _ Wonewoc Sandstone (Upper Cambrian)—Formerly referred to as the Ironton and

M bedrock does not supply water to Houston County largely because sufficient water resources are w County, Minnesota: Minnesota Geological Survey County Atlas C-3, scale 1:100,000. D Galesville Sandstones (Mossler, 2008). Fine- to very coarse-grained, weakly 1,150 available at shallower depths in the Paleozoic rocks. Paillet, F.L., Lundy, J., Tipping, R.G., Runkel, A.C., Reeves, L., and Green, J., 2000, Hydrogeologic U cemented, quartzose sandstone. The upper 40 feet (12 meters) are more poorly U characterization of six sites in southeastern Minnesota using borehole flowmeters and other D 1,125 In Houston County, most aquifers are layers dominated by coarse-grained sandstone such sorted than the lower part and contain coarser-grained sandstone grains and geophysical tools: U.S. Geological Survey Water-Resources Investigations Report 00-4142, 1,100 as the Jordan Sandstone and the Wonewoc Sandstone, in which water can be relatively easily abundant shale beds. White, brown, or black fossil shell fragments (phosphatic 33 p. U U transmitted in both horizontal and vertical directions through the pore spaces between sand grains, D 1,075 brachiopods) are locally common in the upper 10 to 15 feet (3 to 5 meters) of the D as well as through fractures. Other aquifers are composed mostly of carbonate rock (limestone or formation. A subtle disconformity exists within the formation and is locally capped Runkel, A.C., 1994, Deposition of the uppermost Cambrian (St. Croixan) Jordan Sandstone, and 1,050 dolostone) in which water is transmitted mostly through a relatively dense network of fractures, by a pebbly, coarse- to very coarse-gained sandstone bed that lies roughly in the the nature of the Cambrian-Ordovician boundary in the upper Mississippi valley: Geological Society of America Bulletin, v. 106, p. 492-506. F 1,025 such as the Shakopee Formation and upper part of the Oneota Dolomite. Layers designated as middle of the formation, though it is almost unrecognizable in the field (Runkel aquifers, including parts of the upper Mt. Simon and the lower Jordan Sandstones, can locally ———1996, Bedrock geology of Houston County, Minnesota: Minnesota Geological Survey F 1,000 and others, 1998). The lower 60 to 80 feet (18 to 24 meters) of the Wonewoc M contain low permeability strata that serve as small, internal aquitards. Sandstone is well to moderately sorted, fine- to medium-grained, quartz sandstone Open-File Report 96-4, 11 p., 3 pls., scale 1:100,000. M 975 Most layers designated as aquitards in the county have a much lower permeability in a vertical ———2001, Bedrock geology, pl. 2 of Runkel, A.C., ed., Geologic atlas of Wabasha County, U with minor shale, siltstone, and very fine-grained sandstone beds. It has trough D 950 direction than do aquifers. Examples in Houston County include the St. Lawrence and Eau Claire cross stratification and minor glauconite. The lower part locally intertongues Minnesota: Minnesota Geological Survey County Atlas C-14, scale 1:100,000. Formations. These rocks are composed mostly of very fine-grained sand and shale with small, F 925 with the feldspathic, very fine-grained, quartz sandstone of the underlying Eau Runkel, A.C., McKay, R.M., Miller, J.F., Palmer, A.R., and Taylor, J.F., 2007, High resolution poorly connected pore spaces. Carbonate rock with relatively sparse fractures such as the lower Claire Formation. The maximum thickness of the formation is 110 to 130 feet sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: The role 900 U part of the Oneota Dolomite are also aquitards. However, layers designated as aquitards with (34 to 40 meters). of special conditions of cratonic interiors in development of strata architecture: Geological D 875 very low permeability in a vertical direction, such as the St. Lawrence Formation, may contain _e Eau Claire Formation (Upper and Middle Cambrian)—Gray to greenish-gray to Society of America Bulletin, v. 199, p. 860-881. horizontal fractures that are conductive enough to yield large quantities of water. 850 purple shale, tan to gray siltstone, and very fine- to fine-grained sandstone. Gray to Runkel, A.C., McKay, R.M., and Palmer, A.R., 1998, Origin of a classic cratonic sheet sandstone: Horizontal as well as vertical fractures are also more common where bedrock layers are at 825 black fossil shell fragments are common (phosphatic brachiopods). The sandstone Stratigraphy across the Sauk II-Sauk III boundary in the upper Mississippi valley: Geological U or near the bedrock surface. As a result, aquitards in such conditions are likely to have higher is variably glauconitic. The formation coarsens upward, with sandstone becoming Society of America Bulletin, v. 110, p. 188-210. M 800 permeability compared to deeper conditions of burial and may have a diminished ability to retard D increasingly abundant. The upper 10 to 20 feet (3 to 6 meters) are mostly very Runkel, A.C., Miller, J.F., McKay, R.M., Shaw, T.H., and Bassett, D.J., 1999, Cambrian-Ordovician water flow to underlying aquifers. There is no precise boundary between shallow and deep conditions 775 fine-grained sandstone and siltstone. The maximum thickness ranges from 115 boundary strata in the central mid-continent of North America: Acta Universitatis Carolinae of burial, but in most areas of southeastern Minnesota about 50 feet (15 meters) of depth below 750 to 150 feet (35 to 46 meters). Geologica, v. 43, p. 17-20. U the bedrock surface is considered a best approximation (Runkel and others, 2006b). _ m Mt. Simon Sandstone (Middle Cambrian)—Not exposed in the county. Mostly white Runkel, A.C., Mossler, J.H., Tipping, R.G., and Bauer, E.J., 2006a, A hydrogeologic and mapping D Every reasonable effort has been made to ensure the accuracy of the factual data In addition to this hydrostratigraphic classification, the Minnesota Department of Natural to yellow, fine- to very coarse-grained, friable, quartzose sandstone. The top of the investigation of the St. Lawrence Formation in the Twin Cities Metropolitan Area: Minnesota on which this map interpretation is based; however, the Minnesota Geological Resources, as Part B of the Houston County atlas, will conduct a thorough hydrogeologic study M F Survey does not warrant or guarantee that there are no errors. Users may Mt. Simon Sandstone is marked locally by a thin iron stained sandstone that contains Geological Survey Open-File Report 06-4, 20 p. M of the ground water flow system, aquifer capacity, and aquifer sensitivity, which may or may not abundant black fossil shell fragments (phosphatic brachiopods). Variegated beds wish to verify critical information; sources include both the references listed Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Alexander, S.C., 2006b, Hydrostratigraphic D here and information on file at the offices of the Minnesota Geological Survey result in modifications or additions to this classification. Furthermore, designations of aquifers of feldspathic-rich shale, siltstone, and very fine-grained sandstone are common, U characterization of intergranular and secondary porosity in part of the Cambrian sandstone in St. Paul. In addition, effort has been made to ensure that the interpretation versus aquitards made here may not correspond precisely with those made for regulatory purposes particularly in the upper two-thirds of the formation. Pebble conglomerate or conforms to sound geologic and cartographic principles. No claim is made that aquifer system of the cratonic interior of North America: Improving predictability of Figure 2. Map of Houston County depicting the elevation of the stratigraphic top of the Jordan Sandstone showing by the Minnesota Department of Health. pebbly sandstone is common in the lower 50 feet (15 meters) of the formation, the interpretation shown is rigorously correct, however, and it should not be used hydrogeologic properties: Sedimentary Geology, v. 184, p. 281-304. the geologic fold and fault structures. Contour interval is 25 feet (8 meters). In areas where some or all of the Jordan especially in the lowest few feet. Limited subsurface data indicate that the Mt. to guide engineering-scale decisions without site-specific verification. Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., Green, J.A., Mossler, J.H., and Alexander, Sandstone is missing because of erosion the contours are inferred from vertical projection of lower formation contacts Simon Sandstone is 300 to 350 feet (91 to 107 meters) thick. S.C., 2003, Hydrogeology of the Paleozoic bedrock in southeastern Minnesota: Minnesota and the map is shaded. Scale is 1:250,000. Precambrian rocks, undifferentiated—Not exposed in the county; shown only on the pC Geological Survey Report of Investigations 61, 105 p., 2 pls. cross sections. Samples from deep water wells near La Crescent, and Winona and Lewiston to the north, penetrated the Mt. Simon Sandstone and intersected Smith, G.L., Byers, C.W., and Dott, R.H., Jr., 1993, Sequence stratigraphy of the lower Ordovician Precambrian rock. Drill core indicate that these rocks are granitic to tonalitic Prairie du Chien Group on the Wisconsin arch and in the Michigan basin: American Association gneiss of probable Proterozoic and Archean ages. Geophysical data indicate of Petroleum Geologists Bulletin, v. 77, p. 49-67. a broad range of metamorphic and igneous rock units are present beneath the Tipping, R.G., Runkel, A.C., Alexander, E.C., Jr., and Alexander, S.C., 2006, Evidence for hydraulic Paleozoic strata (Jirsa and others, 2012). heterogeneity and anisotropy in the mostly carbonate Prairie du Chien Group, southeastern Minnesota, USA: Sedimentary Geology, v. 184, p. 305-330.