Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-25, PART A MINNESOTA GEOLOGICAL SURVEY THE U.S. GEOLOGICAL SURVEY AS PART OF THE 2009 STATE GEOLOGIC MAPPING PROGRAM ELEMENT (STATEMAP) Nicollet County Harvey Thorleifson, Director OF THE NATIONAL COOPERATIVE GEOLOGIC MAPPING PROGRAM, THE NICOLLET COUNTY BOARD OF COMMISSIONERS, AND the Minnesota Environment and Natural Resources Trust Fund Plate 2—Bedrock Geology as recommended by the Legislative-Citizen Commission on Minnesota Resources

BROWN COUNTY 94°45' W. R. 33 W. R. 32 W. RENVILLE COUNTY SIBLEY COUNTY R. 31 W. 94°30' W. R. 30 W. 94°15' W. BEDROCK Geology 6300 R. 29 W. 1 315 R. 28 W. R. 27 W. 94° W.  315 300 R. 26 W. SIBLEY COUNTY Agr )4 mi 315 1 6 315 1 m Rice e 94°45' W. Kd Clear 1 6 6 Ami 300 6 Lake lr j Lake 315 1 LE SUEUR COUNTY 255 Kd 1 By 285 3 300 300 6  1 6  300 315 315 m 300 sl 300   Lafayette e w Little Ka Kd )22 300 315 John H. Mossler and V.W. Chandler 315 Ka )15 Amf lr 169 315 300 mi Rock 315 RIDGELY 225 Creek 2012 Amf mi 300 T. 111 N. ri 225 Creek sl Creek mi WEST NEWTON Ka NEW SWEDEN Sand LAKE PRAIRIE mi LAFAYETTE BERNADOTTE Lake Kd 300 T. 111 N.  Barney Fry R. 32 W. mi ri STRATIGRAPHIC COLUMN mi 300 j 300 Eight Mile  300 Digital base modified from 1990 Census TIGER/Line Files 25 300 mi 300 LITHOLOGY KEY of U.S. Bureau of the Census (source scale 1:100,000); Natural gamma log 30 300  300 System- county border files modified from Minnesota Department of e Ka Lithology mi Dolostone Series Increasing count Transportation files; digital base annotation by Minnesota  0 100 Geological Survey. Ami ni Group, Formation Era Lithostratigraphic units  Sandy Thickness (feet) 300 lr Map symbol API-G units Universal Transverse Mercator Projection, grid zone 15 Amf lr mi 300 Sandstone 1983 North American Datum mi 36 31 31 300 Very fine- to fine-grained 44°30' N. 300 w Dakota 36 31 300 36 )111 Kd 36 31 Fine- to medium-grained Formation 5-90 31 Upper R. 31 W. 36

 Cretaceous

mi 300 44°30' N. 300 m Medium- to coarse- (99.6-93.5 m.y.) grained Minnesota 6 300 1 Fritsche 1 1 6 Kd Shaly mi 6 Ka 300 1 300Creek 1 6 sl 6 )22 MESOZOIC Siltstone mi Kd 300 300 Unnamed Ka

300 MAP SYMBOLS 50-120 94°30' W. Shale Ag )15 Cretaceous?

Geologic contact—Approximately located. m.y.) (112-99.6  Lower to Upper BRIGHTON Erickson 300 sl A Lake Op lr Igneous rock Structural form line—Approximate structural fabric in Precambrian River 300 TRAVERSE  sl A' G Lower

rocks based on patterns in derivative-enhanced magnetic data. 270 Glauconite 300 Ordovician Prairie du 240 Op Bedrock outcrop 300 (488-  Algal domes; stromatolites Chien Group 35-45 Ka GRANBYKd sl 478 m.y.) Creek 255 LOCATION DIAGRAM B Kd e St. PeterKd Fossiliferous (not used in Heymans 300 300 Kd e 300 limestone or dolostone) T. 110 N. ak L Middle le Op 240 300 d Lake id 285 T. 110 N. Burrowed 300 M 300 Jordan 300  j j Pebbles Sandstone sl 70-90 300 Flat-pebble conglomerate 300  300 850 m Cross-bedded (festoon) 900 1°41' 285 850 850  A240g  Cross-bedded (planar to 750 Swan Lake lr Oakleaf COURTLAND OSHAWA tangential)

150 Lake 800 800 200  s 300 R. 26 W. 300 300 St. Lawrence 300 Kd Middle 300 Ka Ripple cross-laminations sl

Lake Formation 45-70 750 700 250 Calcareous 14 )99 550 G 36 300 31 R. 30 W. 31 300 36 Dolomitic G TRUE NORTH 31 450 31 36 Kd 300 Kd 300 300 MAGNETIC NORTH 36 Contact marks a major River G G 650 300Kd erosional surface  G 300 j 300 300  600 APPROXIMATE MEAN 6 Nicollet Seven Mile lr 1Kd G DECLINATION, 2010 255 6 )99 CORRELATION OF MAP UNITS 500 1 1 6 285 Courtland 1 350 j Kd 94° W. sl G 600 Creek lr 270 Kd Upper Cretaceous 110-130 650 e 300 300 Kd Upper Cambrian (501-488 m.y.) 850 400 unconformity G Figure 1. Elevation of the Precambrian surface; scale 1:300,000. BROWN COUNTY City Group Tunnel G Lone Rock Formation Nicollet Minnesota Lower to Upper Kd G Contour interval is 50 feet (15 meters). In eastern Nicollet County, 750   300 Ka MESOZOIC Kd w j Cretaceous? G 800 BLUE EARTH

Ka 300 from west of St. Peter and North Mankato to near Courtland and COUNTY 300 700 44°15' N. 300 unconformity Lafayette, contours are inferred from vertical projection of other w 44°15' N. Upper Cretaceous G 300 Kd Kr G formation contacts because of scarcity of data. Kd and earlier Kd 300 j

R. 29 W. 240 LE SUEUR unconformity Wonewoc Kd PALEOZOIC w NICOLLET BELGRADE COUNTY Sandstone T. 109 N. 300 60-70 SCALE 1:100 000 Kd Op Lower Ordovician 24 j 1 0 1 2 3 4 5 MILES 300  BLUE EARTH  lr lr Kd COUNTY unconformity  1 0 1 2 3 4 5 6 7 8 KILOMETERS j j T. 109 N. Creek G contour interval 15 METERS 285 169 30 sl  Eau Claire G G sl e G Formation G 75-85 sl Upper Cambrian PALEOZOIC lr G G 94°15' W. j 300 lr 255 unconformity 36 36 w

31 300  A Ka sl sl j Op A' 300 800 Ka 800 Kd e e R. 28 W. lr Middle Cambrian 1 14  m   j e w GIS compilation by R.S. Lively 6 1 400 m 400 Edited by Lori Robinson Op unconformity North Mankato Phf Mt. Simon m unconformity Sandstone

0 0 200-225 Ami T. 108 N.  Middle Cambrian (504-501 m.y.) A g Psc T. 108 N. Kd Ami unconformity -400 Phf -400 B' MESOPROTEROZOIC ri Elevation (feet above sea level) sl R. 27 W. ni -800 -800 MESOPROTEROZOIC- hf- B B' Pir MESOARCHEAN Ami 1,200 1,200 unconformity This gamma log is a compilation of three borehole geophysical logs collected from water wells in Nicollet County; unique numbers 209868, Op Kd Kd s 232487, and 529254. e Cross sections—The contact between glacial deposits and bedrock is based on bedrock 800 Kd sl j 800 Ka Ka topography contours shown on the map. Contacts for Paleozoic and Mesozoic units are based unconformity m lr on drillers' logs, water well cuttings, geophysical logs, and outcrops along the Minnesota PALEOPROTEROZOIC w  s mi e River in eastern and south-central Nicollet County. Position and dip of contacts for m 400 400 Mesoproterozoic, Paleoproterozoic, Neoarchean, and Mesoarchean rocks are based principally Pgd on two-dimensional modeling of gravity and magnetic data along profiles, sparse data from

well records, water well cuttings, geophysical logs, and outcrops along the Minnesota River Ag 0 0 in western Nicollet County. Due to vertical exaggeration (10x), features that appear to dip NEOARCHEAN steeply actually dip at moderate angles, generally 35° to 50°. Agr Ag Pgd Phf

Elevation (feet above sea level) -400 -400 Amf Pir MESOARCHEAN Psc Ami -800 -800 Vertical exaggeration = 10x Introduction rocks, typically at elevations between about 750 and 880 feet (229 and 268 meters). A thin interval of medium- to coarse-grained quartzose sandstone from a few abundant in the upper part of the sandstone. The upper part has inarticulate brachiopod County include the Franklin diabase dike, which has yielded a Pb-Pb age of 2,067 ± Chandler, V.W., McSwiggen, P.L., Morey, G.B., Hinze, W.J., and Anderson, R.R., 1989, Interpretation of They reach a maximum thickness of about 90 feet (27 meters) in the Courtland area inches to 6.5 feet (2 meters) thick that disconformably overlies the Jordan Sandstone valves. The basal part has more very coarse-grained to granular sandstone and there 1 Ma (Schmitz and others, 2006), and the gabbro-granophyre of the Cedar Mountain seismic reflection, gravity, and magnetic data across Middle Proterozoic Mid-Continent Rift System, This geologic map and cross sections depict the bedrock formations exposed at the land surface and west. and conformably underlies the Blue Earth Member contains an Ordovician-age fauna commonly is a quartzose conglomerate at the base. The Mt. Simon Sandstone has a Complex, which has yielded a K-Ar hornblende age of 1,750 Ma (Hanson, 1968). northwestern Wisconsin, eastern Minnesota, and central Iowa: American Association of Petroleum or lying beneath Quaternary deposits of variable thickness in Nicollet County. This map shows (Powell, 1935). It is considered to be a basal part of the Oneota Dolomite, equivalent maximum thickness of 200 to 225 feet (61 to 69 meters). The basal contact of the Mt. Geologists Bulletin, v. 73, p. 261-275. how the bedrock would appear if it were viewed from an aerial perspective after all the overlying Compared to patchy strata classified as Cretaceous farther east by North Mankato Pgd Proterozoic intermediate granitoid rocks (shown only on cross section B–B')—Inferred to the lower part of the Coon Valley Member of the Oneota Dolomite of southeastern Simon Sandstone with Precambrian formations is an unconformity. The Mt. Simon Grant, J.A., 1972, Minnesota River valley, southwestern Minnesota, in Sims, P.K., and Morey, G.B., eds., unconsolidated material was stripped away. Quaternary glacial till, lake sediments, outwash, and river and Judson (south of the Minnesota River in Blue Earth County), strata in western wholly from geophysical data. Rocks characterized by a subdued magnetic signature Minnesota (Runkel, 1994a; Runkel and others, 1999). Powell (1935) and Stauffer Sandstone overlies Mesoproterozoic Hinckley Sandstone, Paleoproterozoic Sioux Geology of Minnesota: A centennial volume: Minnesota Geological Survey, p. 177-198. alluvium cover the bedrock across most of the county. The unconsolidated deposits reach a maximum Nicollet County from the Courtland area and west can be assigned to the Cretaceous and a positive gravity signature. Inferred to be of Yavapai Orogeny affinity. and Thiel (1941) referred to this sandstone as the Kasota Sandstone because the Quartzite, and Neoarchean and Mesoarchean rocks, principally the Morton Gneiss thickness of about 450 feet (137 meters). Bedrock exposures are limited to the eastern and southern period with some confidence. The strata in western Nicollet Country are similar in Hanson, G.N., 1968, K-Ar ages for hornblende from granites and gneisses and for basaltic intrusives in Ordovician-age fauna it contained was substantially younger than the fauna in the and Fort Ridgely Granite (Southwick, 2002; cross sections A–A', B–B'). Archean Rocks parts of the county, along the Minnesota River and small tributaries. Therefore, bedrock geology lithic attributes and elevation to shale and sandstone from a clay pit near Courtland (Hu Minnesota: Minnesota Geological Survey Report of Investigations 8, 20 p. Jordan Sandstone. However, its lithic similarity to the Jordan Sandstone makes it must be generalized from available water well and engineering test boring records and geophysical and others, 2008) and to strata in Brown County near New Ulm and at Fort Ridgely in Western Nicollet County is underlain by rocks that are part of the Archean Minnesota River Holm, D.K., Schneider, D., and Chandler, V.W., 2007, Proterozoic tectonic and crustal evolution of the upper impractical to map as a unit separate from the Jordan Sandstone despite the presence MESOPROTEROZOIC ROCKS data. The production of this map and cross sections relied on information from a number of sources, extreme western Nicollet County (Pierce, 1961) that were dated by palynology. These Valley subprovince of southwestern Minnesota (Southwick, 2002). This subprovince is now thought Great Lakes region, North America: Precambrian Research, v. 157, p. 1-3. of a regional unconformity between them. Paleozoic bedrock in eastern Nicollet County lies on the edge of an eastward-thickening sequence including water-well and scientific drilling records (including holes drilled for this project as well as studies indicate a Late Cretaceous age for the unit. The outcrops that were the subject to have been emplaced by a series of accretionary and igneous events between ca. 3,500 Ma to 2,600 Holm, D.K., Schneider, D., and Coath, C.D., 1998, Age and deformation of Early Proterozoic quartzites in of Mesoproterozoic rocks of the Keweenawan Supergroup that was deposited in the Midcontinent Rift. holes drilled by the Minnesota Department of Natural Resources for their observation well network), of the palynological studies represent the easternmost extension of a large, nearly The Prairie du Chien Group is up to 40 feet (12 meters) thick in Nicollet County, Ma (Bickford and others, 2006), culminating with the emplacement of the Sacred Heart Granite and the southern Lake Superior region: Implications for extent of foreland deformation during final assembly The rift formed during a thermo-tectonic event 900 to 1,200 million years ago that involved extension of outcrop mapping, geophysical surveys, and previous geologic mapping of Nicollet and adjacent counties, continuous subcrop area of strata correlated with the Late Cretaceous Dakota Formation thinner than the maximum thicknesses observed elsewhere in southern Minnesota where related intrusions at 2,603 ± 1 Ma to 2,590 ± 1 Ma (Schmitz and others, 2006). of Laurentia: Geology, v. 26, p. 907-910. (Setterholm, 1990). The upper shale unit is interpreted to be the Woodbury Member it has not been subjected to pre-Quaternary period erosion as it has been everywhere the earth's crust in the area, with concurrent faulting, mafic volcanism, plutonism, and later deposition particularly mapping for the state bedrock geology map (Jirsa and others, 2010, 2011; see Plate 1, Neoarchean rocks Hu, S., Jarzen, D.M., and Dilcher, D.L., 2008, New species of angiosperm pollen from the Dakota Formation of the Dakota Formation and the lower sandy unit is interpreted to be the Nishnabotna in Nicollet County. The formation is present in the eastern part of the county mostly of a thick sequence of sedimentary rocks (Chandler and others, 1989). Although sedimentary rocks of Data-Base Map for the distribution of data). Some seismic data were collected specifically for this (Cenomanian, Upper Cretaceous) of Minnesota, U.S.A.: Palynology, v. 32, p. 17-26. Member of the Dakota Formation (Toth, 1996). The basal conglomerate is interpreted near North Mankato and St. Peter, where it is highly dissected and occurs as erosional the Midcontinent Rift extend beneath eastern Nicollet County, most of the rift-related igneous rocks ASouth Dakota, in Southwick, D.L., ed., Shorter contributions to the geology of the flanks it at a lower elevation (cross section B–B'). 2,595 to 2,603 Ma Sacred Heart Granite to the west in northern Redwood County rocks can be difficult, particularly on drillers' logs. The unit unconformably overlies Seven Mile Creek, and in nearby banks of the Minnesota River south of St. Peter. sandstone with grains that are angular to subrounded. The rock is mineralogically Sioux Quartzite (Early Proterozoic), southwestern Minnesota: Minnesota Geological Survey Report Buried stream channels incised into the bedrock surface combined with the east to southeasterly (Southwick, 2002). Granitic phases of the Morton Gneiss that might also correlate the Precambrian crystalline rocks and Paleozoic formations ranging in age from Middle The Jordan Sandstone is mined to the east in LeSueur County for silica sand that immature, containing appreciable amounts of feldspar grains and volcanic rock fragments of Investigations 32, p. 1-15. regional dip of the Paleozoic bedrock are the primary influences on the map distribution of bedrock with the Fort Ridgely Granite include an adamellite that yielded a U-Pb age of 2,600 to Late Cambrian and possibly Ordovician. Exposures of the unit along the Minnesota is used in various products including frac sand in the oil and gas industry. (Morey, 1977). It may be carbonate rich, especially in its upper part. The Solor Church Parham, W.E., 1970, Clay mineralogy and geology of Minnesota's kaolin clays: Minnesota Geological geologic units. In eastern Nicollet County, the principal units of the bedrock surface are Paleozoic units ± 0.4 Ma and an aplite dike that yielded a U-Pb age of 2,590 ± 1 Ma (Schmitz and River and small tributary streams from Courtland to New Ulm were described by Austin _ that become progressively older from east to west. In western Nicollet County, the Paleozoic units sl St. Lawrence Formation (Upper Cambrian)—Most of the formation is yellowish-gray Formation is thousands of feet thick like the Fond du Lac Formation; however, its Survey Special Publication SP-10, 142 p. (1970), who considered them to be Late Cretaceous in age and postdate the saprolith others, 2006). have been stripped off and the principal rock formations are Precambrian gneiss, granite, and quartzite. to grayish-orange-pink, dense to finely crystalline, silty dolostone. There is light thickness is extremely variable because of the faulting of Mesoproterozoic rocks. It Pierce, R.L., 1961, Lower Upper Cretaceous plant microfossils from Minnesota: Minnesota Geological (unit ). The unit has not produced biostratigraphically useful fossils but lithically Mesoarchean rocks Cretaceous sedimentary rocks were probably laid down across this bedrock surface as a continuous Kr greenish-gray, dolomitic siltstone in the uppermost part. is underlain by volcanic rocks, primarily basalt. The Solor Church Formation is not Survey Bulletin 42, 86 p. appears similar to McLeod County strata to the north that contain gymnospermous blanket, but because of subsequent erosion have been separated into scattered, discontinuous outliers. The St. Lawrence Formation is 45 to 70 feet (14 to 21 meters) thick where it is known to subcrop beneath Quaternary sediments in Nicollet County and therefore is Morton Gneiss—As described by Southwick (2002), this rock is generally quartzofeldspathic in Powell, L.H., 1935, A study of the Ozarkian faunas of southeastern Minnesota: St. Paul, Minn., St. Paul pollen and dinoflagellate cysts that are clearly Cretaceous and indicate a possible not shown on the bedrock geologic map. There is little evidence for faults in the Paleozoic and Mesozoic rocks in the county. In part this undissected by erosion. It subcrops extensively in the eastern part of the county and composition, and commonly includes tonalitic and granitic and granodioritic phases, Institute of Science Museum Bulletin 1, 80 p., 17 pls. Early to Late Cretaceous age (Ravn, 2009, unpub. data). outcrops along the Minnesota River valley just north and to the east of Judson in Blue may be due to the paucity of high quality subsurface data; however, the county is west of the western Franconia Formation are now sandstone with thin beds of grayish-green to dark gray shale. The sandstone is up to 30 friable to moderately cemented. The Wonewoc Sandstone is a maximum of 60 to 70 although the upper third of the formation has some features that are consistent with a shallow marine, amphibolite and feldspar-biotite schist. The magnetic signature of this unit is typically Geological Survey Bulletin 20, 261 p. assigned to the Tunnel City Group, which is subdivided into the Mazomanie Formation and the Lone feet (9 meters) thick. The sandstone generally is friable but has variable cementation feet (18 to 21 meters) thick. Contacts with formations above and below are gradational. tidally influenced environment (Ojakangas and Weber, 1984). subdued, although body margins may be associated with curvilinear magnetic highs. Toth, T.A., 1996, Stratigraphy, mineralogy, and geochemistry of upper Cretaceous deposits from the Minnesota by iron oxide and calcite. It is cross-bedded or structureless and differs from Paleozoic Rock Formation. The interval formerly referred to as the Ironton and Galesville Sandstones is now named Regional stratigraphic and paleontological study (Runkel and others, 1998) indicated < Sioux Quartzite—Pink to red to maroon and gray, very fine- to coarse-grained quartzite Unit is most commonly associated with positive gravity signatures. and Cottonwood River valleys, southwestern Minnesota: West Lafayette, Ind., Purdue University, Ph.D. quartz sandstone in that the grains are commonly subangular to angular. The sandstone the Wonewoc Sandstone. More detailed discussion of these revisions is given in Mossler (2008). s a regional unconformity occurs within the sandstone that approximates the contact and dark red to green-gray, hard, micaceous, siliceous shale. The quartzite is cross- dissertation, 199 p. contains clasts of kaolinite and thin layers of quartz and chert conglomerate. Claystone op Prairie du Chien Group (Lower Ordovician)—Predominantly light brown to grayish- between what were formerly referred to as the Galesville Sandstone and Ironton stratified and contains intercalated beds of mudstone and argillaceous orthoquartzite acknowledgements Zanko, L.M., Heine, J.J., and Setterholm, D.R., 2005, Geology of the Pre-Cretaceous weathering profile and has numerous leaf impressions and iron-rich concretions. Both the sandstone and the orange; thin- to thick-bedded dolostone. It commonly contains small, unfilled vugs. Sandstone; however, this unconformity generally cannot be distinguished in well in its lower part (Ojakangas and Weber, 1984). The upper part contains thin to thick Cretaceous strata of the Minnesota and Cottonwood River valleys, field trip 8, in Robinson, L., ed., shale contain dark gray to black lignitic material. The Dakota Formation has a thin The U.S. Geological Survey provided funding as part of the 2009 State Geologic Survey Mapping Meter-scale microbial mounds are common. The dolostone is sandy, glauconitic, and cuttings and geophysical logs. layers of conglomeratic orthoquartzite. It is cemented with authigenic quartz and Field trip guidebook for selected geology in Minnesota and Wisconsin: Minnesota Geological Survey basal conglomerate that is quartzose with abundant vein quartz and chert, and is dark Component (STATEMAP) of the National Geologic Mapping Program. Alan Knaeble located and contains some shale stringers near its base. This dolostone is principally equivalent _ Eau Claire Formation (Middle to Upper Cambrian)—Sandstone with minor shale and chert. There is a basal conglomerate west of the main outcrop area that contains clasts Guidebook 21, p. 144-153. reddish-brown to yellowish-gray in color. The matrix or cement of the conglomerate e described some of the bedrock exposures used in mapping the bedrock geology. to the Hager City Member of the Oneota Dolomite of the Prairie du Chien Group in siltstone. The sandstone is light gray to yellowish-gray and light brown, very fine- to of vein quartz, chert, iron-formation, and quartzite. Ojakangas and Weber (1984) Zanko, L.M., Oreskovich, J.A., Heine, J.J., Grant, J.A., Setterholm, D.R., and Hauck, S.A., 1998, Mapping is commonly highly ferruginous, which gives the conglomerate its dark brown color. southeastern Minnesota. However, thin remnants of the overlying Shakopee Formation fine-grained, and feldspathic. It is well indurated and cemented by feldspar overgrowths reported that 705 feet (215 meters) of Sioux Quartzite is exposed intermittently west of industrial clay potential in the Minnesota River valley: Natural Resources Research Institute, Report The chert pebbles contain fossils of Paleozoic, primarily Silurian and Devonian, age References of the Prairie du Chien Group may be present at some locations. and dolomite. Minor thin beds of pale olive to olive-gray shale and siltstone are Courtland, at and near the New Ulm Quartzite quarry. In addition, 62 feet (19 meters) of Investigations NRRI/RI-98/03, 53 p. (Andrews, 1958) that may be sourced from the east in Wisconsin. Sand grains and The Hager City Member is not quarried at present, as it has been in the past interbedded in the sandstone. The unit is very fossiliferous and contains numerous of basal conglomerate is exposed 1.25 to 1.5 miles (2 kilometers) west of the main Andrews, G.W., 1958, Windrow Formation of upper Mississippi valley region, a sedimentary and stratigraphic pebbles in the conglomerate are characterized by smooth, highly polished surfaces. at North Mankato and St. Peter, but it is mined extensively for building-stone and phosphatic brachiopod valves as well as hyolithids and trilobite fragments. It is exposures just north of New Ulm in Nicollet County (Ojakangas and Weber, 1984). study: Journal of Geology, v. 66, p. 597-624. It varies from less than a foot to several feet in thickness. aggregate products directly south across the Minnesota River in Blue Earth County. glauconitic, especially in its lower part. The contact with the underlying Mt. Simon The estimated total thickness from measured sections is 847 feet (258 meters). The Austin, G.S., 1970, Weathering of the Sioux Quartzite near New Ulm, Minnesota, as related to Cretaceous Mapped distribution of Cretaceous rocks is more speculative than for other map Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is Large (meter-scale) solution enhanced vertical joints and bedding plane fractures are Sandstone commonly is marked by a thin interval of rock with dark red-brown iron oxide thickness observed in a test well drilled at the New Ulm Quarry was 676 feet (206 climates: Journal of Sedimentary Petrology, v. 40, p. 184-193. based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may units; prediction of their subsurface distribution is rendered difficult by the presence particularly common in the Hager City Member. In exposures along the north bank stain. The basal contact with the Mt. Simon Sandstone is gradational and contains beds meters); however, the well did not reach the base of the Sioux Quartzite. Bickford, M.E., Wooden, J.L., and Bauer, R.L., 2006, SHRIMP study of zircons from early Archean rocks of wish to verify critical information; sources include both the references listed here and information on file at the offices of profound unconformities bounding these strata, and because information from water of the Minnesota River (T. 108 N., R. 27 W., secs. 11, 14) and nearby areas, these of medium- to coarse-grained sandstone typical of Mt. Simon Sandstone interbedded The Sioux Quartzite is quarried near Courtland for rock aggregate. the Minnesota River valley: Implications for the tectonic history of the Superior Province: Geological of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation well records alone is generally inadequate to confidently identify the strata as distinct conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously features are most commonly filled with gray to white shale and siltstone that appears with the very fine- to fine-grained sandstone of the Eau Claire Formation. The Eau Society of America Bulletin, v. 118, p. 94-108. from light colored Quaternary sand bodies or from in situ residuum developed on to be lithically similar to the underlying Blue Earth Member of the Oneota Dolomite Phanerozoic rocks. Local occurrences of yellow, gray, and white shale and may be siltstone that was squeezed up into the solution cavities. peridotite, pyroxenite, hornblendite, and hornblende- and mica-bearing diorite and The views and conclusions contained in this document are those of the authors and should not be interpreted as _m Mt. Simon Sandstone (Middle Cambrian)—Sandstone with minor thin siltstone and shale Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas C-13, 7 pls., necessarily representing the official policies, either expressed or implied, of the U.S. Government. This map is submitted and sandstone are mapped as Late Cretaceous in age in places where drilling records gabbro. Unit correlates with unit

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