HYDROGEOLOGIC MAP OF MINNESOTA BEDROCK HYDROGEOLOGY A Discussion to Accompany State Map Series Map S-2 Roman Kanivetsky and Matt Walton UNIVERSITY OF MINNESOTA MINNESOTA GEOLOGICAL SURVEY St. Paul • 1979 HYDROGEOLOGIC MAP OF MINNESOTA S-2 Bedrock Hydrogeology. 1978. R. Kanivetsky. Scale 1:500,000. Color. Sheet I (map), Sheet 2 (cross sections), with explanatory text. S-3 Quaternary Hydrogeology. 1979. R. Kanivetsky. Scale 1:500,000. Color. S-5 Bedrock Hydrogeology. In prep. R. Kanivetsky. Scale 1:3,168,000 (I inch=50 miles). Color. S-6 Quaternary Hydrogeology. In prep. R. Kimivetsky. Scale 1:3,168,000 (I inch = 50 miles). Color. S-7 Ground-water Resources. In prep. R. Kanivetsky. Scale 1:3,168,000. Color. S-8 Hydrogeochemistry of Quaternary Deposits. In prep. R. Kanivetsky. Scale I :3, 168,000. Color. S-9 Hydrogeochemistry of Bedrock Aquifers. In prep. R. Kanivetsky. CONTENTS Introduction. .. 1 Description of hydrogeologic units. .. 3 Cretaceous aquifer................................................................ 3 Cedar Valley-Maquoketa-Dubuque-Galena aquifer of Middle Devonian to late Middle Ordovician age ......................................................... 3 Red River-Winnipeg aquifer of Middle Ordovician age ................................ 4 Decorah-Platteville-Glenwood confining bed of Middle Ordovician age ................. 4 St. Peter aquifer of Middle Ordovician age .......................................... 4 Prairie du Chien-Jordan aquifer of Early Ordovician-Late Cambrian age ............... 5 St. Lawrence confining bed ........................................................ 5 Franconia-Ironton-Galesville aquifer of Late Cambrian age ........................... 5 Eau Claire confining bed of Late Cambrian age. .. 6 Mt. Simon-Hinckley-Fond du Lac aquifer of Late Cambrian-Proterozoic age ............ 6 Keweenawan Volcanic Rocks aquifer of Proterozoic age .............................. 6 Sioux Quartzite aquifer of Proterozoic age. .. 6 Proterozoic and Biwabik Iron-Formation aquifers of Proterozoic age ................... 7 Precambrian igneous and metamorphic rocks ........................................ 7 Potentiometric surfaces.................................................................. 8 Hydrogeologic parameters of bedrock aquifers in Minnesota ................................ 8 Definitions ...................................................................... 8 References ............................................................................ 10 ILLUSTRATION Figure 1 - Generalized stratigraphic column for southeastern Minnesota showing bedrock aquifers .............................................................. 2 TABLE Table 1 - Hydrogeologic parameters of aquifers in Minnesota ............................. 9 Published with the support of the Legislative Commission on Minnesota Resources. The University of Minnesota is committed to the polisY that all persons shall have equal access to its programs, facilities, and employment without regard to race, creed, color, sex, national origin, or handicap. HYDROGEOLOGIC MAP OF MINNESOTA BEDROCK HYDROGEOLOGY by Roman Kanivetsky and Matt Walton INTRODUCTION The Hydrogeologic Map of Minnesota is in and metamorphic rocks (p£im), which are gen­ fact a set of maps portraying different aspects of erally poor in water-bearing characteristics and the hydrogeology of the state, which is too com­ are not regarded as aquifers, although water is plex to represent on a single map. Map S-2, found locally, where these rocks are strongly Bedrock Hydrogeology, portrays the water-bear­ fractured. ing characteristics of the consolidated bedrock In using the bedrock hydrogeologic map to formations underlying the state. These forma­ evaluate the occurrence of ground water it must tions are important aquifers in some areas and of be borne in mind that in those areas underlain by limited value in others. Bedrock formations are well-stratified sedimentary formations (essen­ covered throughout most of the state with uncon­ tially the southeastern quadrant of the state), the solidated sedimentary deposits of glacial and flu­ aquifer shown at any given place on the map is vial origin, which are major sources of ground the aquifer at the bedrock surface, and it will be water in many areas. Their water-bearing char­ underlain by those aquifers in the stratigraphic acteristics are portrayed by Map S-3, Quater­ succession that lie below it, as is shown on the nary* Hydrogeology. Both maps need to be cross sections, Sheet 2. Figure I is a generalized consulted to evaluate the potential groundwater stratigraphic column for southeastern Minne­ sources in a given area. sota showing how the aquifers and confining The Bedrock Hydrogeologic Map (S-2) is beds correlate with geologic formations and giv­ derived from the Geologic Map of Minnesota, ing approximate maximum thicknesses of the Bedrock Geology, Map M-24 (33). On the Bed­ rock units. For a complete evaluation of ground­ rock Geologic Map rock units or formations are water occurrence in any given area, reference defined and classified according to geologic age, should also be made to the map of Quaternary mode of origin, structural continuity, and com­ Hydrogeology (S-3). position. On the Bedrock Hydrogeologic Map the Users should also be aware that these maps same rock units or formations are grouped into are on a scale of 1:500,000 or about 8 miles to the aquifers according to water-bearing characteris­ inch, and there are doubtless many areas where tics and hydraulic continuity. Aquifers consist of local ground-water occurrence and geology de­ one or more geologic formations that form an part from information shown on this scale. For hydraulically continuous unit, more or less iso­ example, dashed black lines on the map show the lated from overlying and underlying formations approximate locations of known preglacial val­ by confining beds or zones of rock that do not leys in bedrock that have been filled by Quater­ transmit water readily. Confining beds are not nary deposits so that no valley appears now at the shown on the map separately from the aquifers surface. In some places these valleys have cut for which they form a cap, but they are shown on through the bedrock aquifer shown on the map, the cross sections (sheet 2). Some aquifers, such and a narrow band of a lower aquifer that is not as the Proterozoic aquifer (p €p), are character­ shown at I :500,000 scale is present at the bedrock ized by sporadic zones of water-bearing rock with surface along the floor of the buried valley. Such little or no hydrologic continuity and uncertain conditions are known to exist for example in boundary conditions. Large areas of the state are buried valleys in parts of Minneapolis and St. underlain by Precambrian crystalline igneous Paul. There are undoubtedly other buried valleys that are not known and are not represented on the *Quaternary: the geologic period that includes both the Pleis­ tocene Epoch. or "lee Age," and the Holocene Epoch, or map. Where specific site conditions are impor­ "Recent," which spans the time from the Pleistocene to the tant, more detailed maps should be consulted if present. available, and test drilling should be considered. IAPPROXIMATY \ MAXIMUM HYDROGEOlOGIC ERA SYST EM GROUP FORMA TION GRAPHIC COLUMN THICKNES U ITS (FEET) Z <l Z o CEDAR VALLEY > w CEDAR VALLEY o MAQUOKETA- f--- DUBUQUE MAQUOKETA 70 GALENA f------ OU BUOUE 35 AQUIFER f------ GALE NA DECORAH 95 DECORAH­ Z f--- PLATTEVILLE­ <l PLATTEVILLE 35 GLENWOOD U CONFINING BED SYMBOLS :> GLENWOOO f---;e o o LIMESTONE 0: dolom itic ST. PETER o ST PETER <55 AQUIFER landy sholy u DOLOMITE o calcareous N sandy o sholy W 360 PRAIRIE du CHIEN SANDSTONE -.J JORDAN fine 10 very fine ONE OTA medium AQUIFER b: coorse ~: "" . ' ;~ Inoly JORDAN 110 SHALE K·. .. :·:~.· ~ Cher t ST. LAWRENCE 51 LAWRENCE 60 Ooliles CONFINING BED Dolomitic Silfy Benton!!. Glauconite Feldspothte ConQIom"olic Z Qua'lonobJe relationship <l a: Adopted from G.S. Austin (1969) CD ~ <l U MT. SIMON­ HINCKLEY FOND du LAC AQUIFER NOT AN AQUIFER Figure I - Generalized tratigraphic column for outhea tern Minne ota howing bedrock aquifer . Modified from Au tin (6). 2 DESCRIPTION OF HYDROGEOLOGIC Total dissolved solids in the water range from UNITS 500 parts per million (ppm) to 6,000 ppm. Most of the water in the aquifer is mineralized (more than Descriptions follow on the geology and water­ 1,000 ppm), with the most highly mineralized wa­ bearing characteristics of each of the hydrogeo­ ter concentrated in a narrow zone along the west­ logic units and other features shown on the map. ern border of the state ( 1,2,3,10,14,27,31,38, 42, 43). Only Cretaceous beds northeast of the Cretaceous Aquifer (K) Minnesota River contain water with less than 1,000 ppm dissolved solids (44). The Cretaceous aquifer comprises eroded remnants of sandy, silty and shaly beds deposited in a shallow sea which spread from the west Cedar Valley-Maquoketa-Dubuque-Galena across most of Minnesota in the Cretaceous Peri­ Aquifer of Middle Devonian to Late Middle od. Two large outliers, about 500 square miles Ordovician Age (Dcv+Omdg) (1,295 km2) and 100 square miles (259 km2) in The Paleozoic formations of Minnesota, area, occur south of the Biwabik Iron-Formation which include this aquifer, consist of almost hori­ (Mesabi range). The aquifer becomes nearly con­ zontal beds of limestone, dolomite, sandstone tinuous in large areas along the Red River and in and shale with very few known faults and minor the southwestern