Prepared and Published with the Support of COUNTY ATLAS SERIES THE BLUE EARTH COUNTY BOARD OF COMMISSIONERS AND ATLAS C-26, PART A MINNESOTA GEOLOGICAL SURVEY the Minnesota ENVironment and Natural Resources Trust Fund Blue Earth County Harvey Thorleifson, Director as recommended by the LEGislatiVE-CitiZen Commission on Minnesota Resources Plate 2—Bedrock Geology NIC OLL ET COU NTY 7 Minnesota B BEDROCK GEOLOGY Ka 44°15' N. 285 300 R. 29 W. Kd m STRATIGRAPHIC COLUMN River 285 By 240 s 94° W. e i Lithostratigraphic r Composite natural gamma log 255 NICOLLET LE SUEUR COUNTY R. 26 W. COUNTY R. 25 W. e unit S 270 - e 315 Increasing count 330 Era m Lithology Kd e T. 109 N. sl Os 315 Julia R. Steenberg t Group, 0 100 s 24 Map symbol 19 y 300 300 24 24 Formation 270 lr 19 S API-G units Oo Thickness (in feet) 300 River 285 LIME JAMESTOWN 345 94°15' W. 255 Kd Wita Kd Creek 315 2012 315 )68 j Kd Lake j Dakota Kd 5-90 m.y.) Upper Formation Os Y 300 (99.6-93.5 T Duck Cretaceous 300 lr Morgan Os Lake N T. 109 N. CAMBRIA U 315 O 300 Minnesota 240 Ballantyne C LOCATION DIAGRAM Oo 300 Lake R 270 Madison MESOZOIC R. 28 W. U 31 Kd 300 31 Oo Unnamed Ka Os E Kd 30-90 36 31 Eagle Lake lr lr 36 315 36 U 36 S Cretaceous 300 ) 31 300 22 (112-93.5 m.y.) (112-93.5 Gilfillin 315 E Lower to Upper Lake L Judson Lake 315 300 lr 240 1 6 Y 6 240 Os Platteville Formation 255 315 T Opg 6 Madison 5-20 1 1 N 6 Glenwood Formation Ph 1 255 U sl 255 1 CORRELATION OF MAP UNITS O )60 Upper 315 315 C Lake A j (450 m.y.) 315 C ? E Kd Upper Cretaceous 285 14 Kd S Lithology Key 315 A St. Peter Osp W unconformity MESOZOIC Sandstone Mankato Mud Os 90-100 Lake Limestone Ka Lower to Upper Cretaceous? w j R. 27 W. Armstrong 300 )68 315 Lake Os 315 unconformity Lieberg Middle (458 m.y.) 315 Dolostone Lake Eagle Os T. 108 N. 300 300 Opg Lake Upper Ordovician n a Oo 255 Kd i c Sandy dolostone i sl v 255 o j 315 T. 108 N. Osp 169 Middle Ordovician d 255 j )83 r Ops Sandstone A 285 A' O Oo unconformity Very fine- to fine-grained Minneopa 300 Oo Oo Shakopee 300 300 Oo j 300 Os 300 300 315 Os Formation Creek 80-140 Fine- to medium-grained Kd 300 300 300 Y 315 300 Kd Born T unconformity 240 Kd N Lower Ordovician BUTTERNUT VALLEY MANKATO Lake U JUDSON SOUTH BEND Kd 300 LERAY Medium- to coarse-grained 300 315 O Oo j 300 285 C Kd N Oo 315 unconformity Kd 315 Lower (488-478 m.y.) Shaly Prairie du Chien Group W 31 300 j PALEOZOIC O 36 31 285 300 R Lily 270 Kd B Lake 300 36 31 31 Oneota 300 Oo36 31 300 300 36 36 sl sl Kd Dolomite Oo Siltstone Crystal 300 300Oo 60-100 Le Sueur Upper Cambrian Lake 300 270 315 lr Shale 300 1 6 6 1 6 Kd 1 Loon 1 6 unconformity 255 6 315 Lake Crystal Lake 300 1 w Chert 300 j Kd 315 Kd 300 e Oolites )60 lr Jordan River Oo Os 300 Kd 255 Middle Cambrian Sandstone j )66 St. Clair G Glauconite m 60-100 WATONWAN COUNTY WATONWAN Mills 255 Oo Lake Oo Oo unconformity Ph Phosphate grains 300 300 lr j Kd Le Sueur Phs Algal domes; stromatolites Blue j 300 unconformity MESOPROTEROZOIC j T. 107 N. LINCOLN 285 G Fossils (not used in limestone or GARDEN CITY Oo 315 dolostone units) Earth RAPIDAN DECORIA St. Lawrence C River MCPHERSON sl G Burrowed T. 107 N. Formation sl G 45-80 River PALEOZOIC Pebbles (gravel in unconsolidated units) j 315 G 300 G River Flat-pebble conglomerate Cobb G Garden Kd Rice Cross-bedded (festoon) Lake G City 285 300 River 300 285 300 315 MAP SYMBOLS Cross-bedded (planar to tangential) Lone Rock G lr G Upper Cambrian (501-488 m.y.) Formation Geologic contact—Approximately located. G Ripple cross-laminations Oo 100-130 31 36 31 300 Bedrock outcrop. 36 31 315 G 36 31 31 City Group Tunnel Dolomitic 36 Osp Location of geologic cross section. G 36 A A' 300 315 G G Calcareous 300 G Os Contact marks a major erosional surface 6 1 285 285 300 sl 6 285 1 6 1 6 300 Cobb Wonewoc 300 Watonwan 1 6 )83 1 w Facies change Maple Sandstone 315 50-80 River Good River 285 Kd Thunder 315 93°45' N. This gamma log is a compilation of five borehole Little Os geophysical logs collected from water wells in Blue 315 Pemberton G G 93°45' N. 800 Earth and Nicollet Counties; unique numbers 270341, sl 300 770449, 213694, 213696, and 209876. G G M Eau Claire 300 315 e G M 60-80 Formation G sl Severson315 300 Perch Lake F Kd Perch Lake T. 106 N. sl 300 Creek VERNON CENTER F sl LYRA BEAUFORD 285 MEDO 315 CERESCO T. 106 N. j M Oo Figure 1. Elevation of the stratigraphic lr 315 Vernon Cobb F tops of the Jordan and Wonewoc 285 j Center Kd 315 315 300 315 Sandstones in Blue Earth County, 315 River 800 F 800 315 315 showing the geologic structure of 750 Paleozoic bedrock. Contour interval is M Mt. Simon F 50 feet (15 meters), scale 1:450,000. In m 315 Sandstone 300 315 areas where some or all of the Jordan 31 Oo Cottonwood Middle Cambrian (504-501 m.y.) 36 31 36 31 Lake 700 and Wonewoc Sandstones are missing 650 approximately 150-350 315 36 31 36 36 31 650 because of erosion, the contours are 700 300 315 300 inferred from projection vertically 315 315 315 from other formation contacts, using 6 Kd 6 315 1 1 F 6 169 1 6 the estimated full thickness of the 1 6 1 900 Willow eroded formations, and shown with Mapleton Os 600 315 800 315 850 dashed line. The inferred traces of Creek 315 315 750 Ida Maple folds are shown. MESOPROTEROZOIC Lake Phs Perch (1200-900 M.Y. AGO) EXPLANATION thousands j 315 Knights Top of the Jordan Sandstone PLEASANT River sl Lake Osp 315 Os Top of the Wonewoc Sandstone Creek Blue 315 Osp Axial trace, syncline MOUND 315 SHELBY Oo STERLING MAPLETON DANVILLE MF 315 Axial trace, anticline T. 105 N. 315 )30 )30 Earth )30 T. 105 N. S N Amboy Rice 315 River Y 330 Lura T 315 N Lake U 315 Maple 315 O Kd 315 C Slough Y Kd Creek T N 330 N A Opg Big U W 315 )22 O N Os Cobb River C O 31 315 T 36 36 31 A A 31 36 31 C Hagar City Member 31 River E W 315 36 36 S Figure 2. Map of the first vertical derivative 315 Opg A MARTIN COUNTY R. 29 W. W F Oneota FARIBAULT COUNTY R. 28 W. magnetic anomaly data of Blue Earth County 94°15' W. R. 27 W. R. 26 W. Dolomite 94° W. R. 25 W. FARIBAULT COUNTY (Chandler and Lively, 2007). Lighter colors Digital base modified from the Minnesota Department of B' 800 Transportation BaseMap data; digital base annotation by indicate more magnetic. The structure contours GIS compilation by Julia Steenberg 750 the Minnesota Geological Survey. SCALE 1:100 000 of the stratigraphic top of the Wonewoc Sandstone Edited by Lori Robinson 775 M 1 0 1 2 3 4 5 MILES Elevation contours were derived from the U.S. Geological F 500 are overlain on this image showing a prominent Survey 30-meter Digital Elevation Model (DEM) by the anticline feature in the western portion of the map Blue Earth 1 0 1 2 3 4 5 6 7 8 KILOMETERS F siltstone Minnesota Geological Survey. area, based on the current well coverage. There is a Universal Transverse Mercator Projection, grid zone 15 550 Coon Valley subtle contrast in trends of the magnetic anomalies Member 1983 North American Datum CONTOUR INTERVAL 15 METERS Kasota ? from southwest–northeast in the southwestern sandstone ? 725 portion of the map area to southeast–northwest G G ORDOVICIAN 700 in the west-central part of the map area, possibly ? ? CAMBRIAN 600 reflecting a deep basement fold or fault structure. Jordan 650 This trend appears to coincide with the structural Sandstone cross section B-B' A A' grain of the Wonewoc Sandstone, suggesting that 1 meter 1,000 1,000 Paleozoic bedrock was displaced by reactivation unconsolidated Quaternary sediment Oo Oo Kd Oo unconsolidated Quaternary sediment Kd Os of the deep basement structural feature. Black 800 sl j Oo Os 800 Figure 3. Schematic stratigraphic section through the Late Cambrian Jordan Sandstone and the Oo line shows county boundary and pink lines show lr j Early Ordovician Oneota Dolomite depicting the stratigraphic relationships within the Hager City 600 w sl 600 structure contours. Inferred folds are also shown e and Coon Valley Members of the Oneota Dolomite from the Mankato area (N) to southeast Blue lr in black; scale 1:500,000. 400 m 400 Earth County (S). The Kasota sandstone, though equivalent in age to the lower part of the Coon ? w e Valley Member (Early Ordovician), was mapped as Jordan Sandstone (Late Cambrian) because 200 ? Archean and Paleoproterozoic rocks, undivided m 200 ? Phs the units cannot be distinguished from each other based on subsurface data.