Geologic Atlas of Brown County, Minnesota
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Prepared and Published with the Support of COUNTY ATLAS SERIES THE BROWN COUNTY BOARD OF COMMISSIONERS, ATLAS C-37, PART A MINNESOTA GEOLOGICAL SURVEY the Minnesota Environment and Natural Resources Trust Fund Brown County Harvey Thorleifson, Director REDWOOD Minnesota COUNTY as recommended by the Legislative-CitiZen Commission on Minnesota Resources, Plate 3—Surficial Geology 255Qrk19 River AND the Minnesota Legacy Amendment'S Clean Water Fund 255 T. 112 N. Qf R. 33 W. Qa - Ql - - - - 31 - 270 - - - - RENVILLE - Qhl 34 - - - COUNTY - - - - - - - 300 NICOLLET 94° 45' W. Qc COUNTY 6 Qth Qrk Qhl 1 6 Lone Tree SURFICIAL GEOLOGY Lake 300 Qhl Qf By A' A 300 EDEN Qpo T. 111 N. R. 32 W. Howard C. Hobbs and Alan R. Knaeble 300 Creek Qc - Qa - - Spring - - - 2016 - - - - Ql 240 - - - 285 - LOCATION DIAGRAM - )4 Qf Minnesota Qpo - - Qhl Qpo - - - - - - 300 -- Qf River - Ql R. 31 W. - - - - 31 - - - 31 - 36 - 36 - 31 45° 22' 30" N. - 45° 22' 30" N. - Ql Qa - - Qc 240 - - - - - Qf - - - - - - - - - Qhl Ql 1 6 Qpo - 94° 30' W. - - - 6 1 - 315 6 - - 2 - - - Qf - - - - - - - - - - - - - - - Ql - - - - - - - - Ql - Qhl - - - - Ql - - B' - - - - Qhl - - CORRELATION OF MAP UNITS - - Evan - - - - Qhl - - - Qc - B 315 - Wind Stream Ice Lake Slope Bedrock Ql - - - 7 - - 255 - - Qsw deposits - deposits deposits deposits deposits - - - - - - Qpo - Qth )68 315 285 - Ql Ql - - - Qpo Qth - 270 - Holocene - - Qa Qf Qrk Qhl Qpo Qc - - Ql - - - Qa - MILFORD 300 T. 110 N. PRAIRIEVILLE HOME - 315 - - - - - Qsw Qt Ql - - - - - - - - Qc - - - - - - - 315 - Qth QUATERNARY - 14 - - ¤ - - - - - - - 240 - T. 110 N. Heiberg Member - Qi Qth Qwh Pleistocene - - - Qhl - New Ulm Formation 315 - Qpo - - Qhl - New Ulm Qs 315 - - - Qhl Dovray Member - - - 270 - 315 - Qtd Qwd - - - New Ulm Formation - Sleepy 300 240 - - - Eye - Qhl - - - Lake 300 - - 315 - - 315 - CRETACEOUS - Ku - - Qs QcRiver 255 - Ql - - Qwh - Qc - - - - -- 300 - - 36 31 Qs Qpo Minnesota 315 - Cottonwood 31 - Cottonwood Qt 36 31 300 36 31 Qa 95° W. Sleepy Eye - 285 Qt 315 - Qt R. 35 W. Cobden - River - - R. 34 W. - 34 MAP SYMBOLS - - 300 - Qt - - - - - - - Sleepy 315 - Qt - - Qwh Qwh Qth Ql - C' Geologic contact—Approximately located. ¤14 - Qs 255 - Eye Creek 6 1 6 - 1 300 - 6 6 Qth 1 Qhl 315 1 6 15 Broad, irregular trough—Interpreted to be a buried subglacial drainage channel (tunnel valley) - 6 ) 315 1 - Qhl Qwh 300 Qt Qwh Qc River or a preexisting drainage valley that was subsequently partially filled by sediment. When C - Qt Sleepy Qt Qsw - Qwh - 315 300 - Qs NICOLLET COUNTY 315 Qpo Qc Qf the ice melted, an irregular line of lakes and depressions was left behind where buried ice Qs Qs Qth Qwh 315 Qwh Qpo 4 Qwh 300 blocks had previously existed. Ticks point downslope. 315 ) Bachelor Qpo Qf 330 Qth Boise Qa Clear 315 Eye Qwh Qth Lake Esker—A narrow, sinuous ridge of predominantly sand and gravel, interpreted to have been Coal 300 Qth 12 - Lake Qth Qt Qhl Lake Qf - - - BLUE EARTH - -- - - - deposited by a meltwater stream in a tunnel under ice or in an ice-walled channel, primarily Qa 300 - Qs - Creek Qwh - 68 COUNTY 45° 15' N. 300 Qwh - ) identified by lidar imagery. Consists of fluvial sediment commonly covered by a cap of till. Qwh - 300 - Ku 315 - 45° 15' N. School - Qth - Cottonwood In many places the feature is difficult to differentiate from crevasse ridges. Arrowheads 315 - - Qs - - - - 270 Mine Zanders Qth Lake Qth - Qa 315 - D' Qwh - Springfield 258 315 Qs River Lake Qc point in the inferred direction of meltwater flow and sediment transport. Qt ) - Qt Little River T. 109 N. Qs Qth 315 General flow direction of a meltwater stream—The arrow points in the direction that glacial 330 Qth 285 ¤14 N COTTONWOOD - meltwater last flowed within the unit. Where shown in units and (washed till), ORTH STAR Qwh Qs LEAVENWORT - Qwh Qwd D BURNSTOWN H STARK SIGEL - Qt Creek 300 Qtd Qth Qs Qt - Qhl Qpo Qwh Qs - there may be thin sand and gravel deposits over the washed till. - - Qhl - Qwh- Qs 315 - Qwh River Qs - T. 109 N. Ice margin—Highly generalized inferred location of an ice margin based on topographic evidence - Qt - - - 300 - Ku Cottonwood Qa Qwh Qwh - and on the pattern of glacial meltwater flow. The presence of ice is required to explain why Qwh Qth - Qtd 315 Juni Ql water was diverted from flowing down the regional slope; inasmuch as the flow pattern was Qwd 315 330 Gilman Qth Lake Qwh extremely complex, these lines should be seen as representative of a sequence of unmapped Lake Qwh Qth - Qth Qs Qi ice margins (Fig. 5). Cottonwood - - - - - - - - - - Qwh - 315 315 - - - Qth 315 - Qth 330 - Ice-walled lake plain—Interpreted to be the approximate extent of sediment deposited in ice-walled - - River - Qs - Qth Qth - - - - - - - Qpo - Qs Qs - - Qs 36 31 36 31 31 36 Little lakes that formed on or in ice before the ice melted. Mapped in one place (T. 110 N., R. 31 - 330 Qhl 36 31 Qtd - 36 31 36 31 330 - Qwh - REDWOOD COUNTY - Altermatt Qwh W., secs. 27, 28, 33, 34) where slightly higher relief is vaguely visible on lidar imagery. - Qwd Cottonwood Qs - Lake Qwh 315 M 330 Qhl Crevasse ridge—Primarily sand and gravel deposited by meltwater in a crevasse in glacial ice. o 330 Qhl u Qtd - Q- td nd Qth 300 - - 330 330 - When the surrounding ice melted, sediments remained, forming a straight or slightly sinuous - Qa - - 6 - - 1 6 1 6 - 1 6 Qs 1 1 6 1 6 - ridge above the adjacent landscape. Deposits may contain lake sediment and in places till COUNTY Ql - Qth 330 330 330 - Creek Qs Qwh - may cap or be interlayered with sand and gravel. Ridges are commonly transverse to the Qpo 330 315 Qwh - - Qwd - E' - - Qpo - inferred ice-flow direction, concave up-ice, and visible on lidar imagery. 330 Qs - COTTONWOOD - - 315 - 315 - Precambrian bedrock, undivided—Granite, gneiss, and quartzite (see Plate 2, Bedrock Geology) . Qa Qs Qpo - 258 River - E ) Qhl These bedrock types are present throughout the entire county beneath either Cretaceous Qs Cottonwood - - 330 - Little - and Paleozoic bedrock or glacial deposits. They are exposed at the surface in only a few - - Qpo Qtd 315 Ql places, the most notable of which is in the Minnesota River valley at the northern tip of the - Qth Qa Qs - county. - - 300 - - Qpo - - - Qwd Qwd - Qwd - - - - T. 108 N. Qs Qth - Qpo Ql - - - - - 315 - - - - - - - - - - - - - Qpo - LA LINDEN M L - KE H STATELY U LIGAN - ALB ANSKA T. 108 N. BASHA - IN Hanska W Qwd - Qhl - Creek Qth - River - Omsrud - - - - - Lake - - - - - 315 - Linden - - - - Lake - - F' - 330 - - Qtd - - - - - - - 257 Qtd - ) RENVILLE Qs - - Lake - - - - 315 Mound - - - - - - - 3 - - Hanska - 345 4 - ) - Qh- l - - 345 - Qth Cottonwood - - Qpo - F' - Qwd - - 45° 7' 30" N. - - - - 45° 7' 30" N. - - - 315 - - - REDWOOD - Qtd - 345 Qtd - 1 - )15 Little - Qpo - - 315 Qhl 31 Qtd - Qhl Elevation (feet above mean sea level) 360 Qwd 31 36 31 36 31 36 Qs 31- 36 31 NICOLLET 36 - 36 High: 1,995 0 40 miles - - - 375 - - Qth Qpo BROWN 4 Comfrey Wood Qpo Qi Ql Lake Ql Ql 0 60 kilometers R. 35 W. R. 32 W. R. 31 W. R. 34 W. COTTONWOOD COUNTY WATONWAN COUNTY R. 33 W. R. 30 W. WATONWAN COUNTY Low: 682 95° W. 94° 45' W. 94° 30' W. BLUE EARTH GIS compilation by R.S. Lively 5 Glacial River Warren channel Digital base modified from the Minnesota Department of Edited by Lori Robinson Transportation BaseMap data; digital base annotation by SCALE 1:100 000 COUNTY BLUE EARTH the Minnesota Geological Survey. Villard 1 0 1 2 3 4 5 MILES Member Elevation contours were derived from the U.S. Geological Survey LAKE PEPIN WATERSHED 2 30-meter Digital Elevation Model (DEM) by the Minnesota 1 0 1 2 3 4 5 6 7 8 KILOMETERS SHEAR ZONE Geological Survey. Universal Transverse Mercator Projection, grid zone 15 contour INTERVAL 15 METERS Heiberg 1983 North American Datum Member INDEX TO PREVIOUS MAPPING Minnesota River INTRODUCTION now the town of Leavenworth, the meltwater flow left the line of the present day Cottonwood River Qt Terrace deposits—sand and gravel—Thin overbank fine-grained sand and silt overlying of the county (Plate 4, cross sections). In a number of places in west-central and BROWN COUNTY and flowed southeast across the course of the Little Cottonwood River and into the Lake Hanska channel sand and gravel. Deposits are commonly thin (less than 10 feet [3 meters] southwest Brown County, Dovray Member sediments may be interbedded with or This map portrays the primary sediment, its distribution, and its origin in the upper several meters channel (see broad, irregular trough in Map Symbols). thick) over till. The sand and gravel is outwash that may have been derived from overlie Heiberg Member till. This inverted or mixed stratigraphy is interpreted to Table 1. Physical characteristics of glacial deposits in the Brown County region (includes both surface and subsurface beneath the topsoil. Soils form in the uppermost geologic materials; thus a soil map provides clues deposits; see Plate 4, Quaternary Stratigraphy). When the ice margin retreated to the position shown in Figure 5D, a new channel formed parallel glacial meltwater of more than one ice lobe. The terrace is above the modern suggest that active Heiberg Member ice was incorporating Dovray Member stagnant to the material below in which it formed. The soil mapping units of Brown County (Christensen Glacial Lake to the ice margin, cutting a valley now occupied by Sleepy Eye Creek. A large flow continued floodplain because stream erosion later incised deeper into the valley. Mapped in ice and sediment.