Upload File

bedrock geology - university of minnesota

1
300 250 200 150 100 50 0 Thickness of Prairie du Chien Group rocks in feet CGF HFZ HUDSON-AFTON HORST CGFZ HF Figure 5. Color shaded map indicating the thickness of the Prairie du Chien Group where it exists below the St. Peter Sandstone. Blue colors represent areas where the Prairie du Chien Group is thinner and orange represents areas where it is thicker. There is progressive thinning toward the north, where it thins to 50 feet (15 meters) thick. Thicknesses reach nearly 300 feet (91 meters) in the southern part of the county except within the Hudson–Afton horst (HAH), where it thins to less than 50 feet (15 meters) in places. Small areas where the Prairie du Chien Group appears to thin abruptly are interpreted to represent areas of significant erosion during a hiatus marked by an unconformity prior to the deposition of the St. Peter Sandstone. CGF—Cottage Grove fault, CGFZ—Cottage Grove fault zone, HF—Hastings fault, HFZ—Hastings fault zone. Elevation of the top of the Jordan Sandstone in feet Less than 550 551-600 601-650 651-700 701-750 751-800 801-850 851-900 901-950 951-1,000 1,001-1,050 F F F M F F M F M M F F M F M F F M M F M F F F F Figure 4. Map of Washington County depicting the elevation of the stratigraphic top of the Jordan Sandstone showing the mapped fold axes (thin black lines) and faults (thick black lines). Colored intervals represent 50-foot (15-meter) elevation intervals; blue colors represent lower elevations, and orange represents higher elevations. Dashed lines depict the 25-foot (8-meter) contour intervals. In areas where the Jordan Sandstone is absent because of erosion, the map is not colored, and the contours are inferred from vertical projection of the contacts of stratigraphically lower formations. T. 32 N. T. 32 N. T. 31 N. T. 31 N. T. 30 N. T. 30 N. T. 29 N. T. 29 N. T. 28 N. T. 28 N. T. 27 N. T. 27 N. T. 26 N. R. 22 W. R. 22 W. R. 21 W. R. 21 W. R. 20 W. R. 20 W. R. 19 W. 92° 52' 30" W. 93° W. 44° 52' 30" N. 44° 45' N. 44° 45' N. 45° N. 45° 7' 30" N. 92° 45' W. 45° 15' N. 92° 45' W. 45° 15' N. 45° 7' 30" N. 45° N. 44° 52' 30" N. 93° W. 93° W. ANOKA COUNTY CHIS AGO COU NTY CHISAGO CO UNTY DAKOTA COUNTY ANOKA COUNTY WISCONSIN WISCONSIN DAKOTA COUNTY PIERCE COUNTY ST. CROIX COUNTY POLK COUNTY PIERCE COUNTY ST. CROIX COUNTY POLK COUNTY RAMSEY COUNTY RAMSEY COUNTY Forest Clear Lake Mud Lake Sylvan Lake Lake Nielsen Lake German Lake Lake Lake Sea Goose Fish Big Marine Lake Long Lake Lake Lake Sand Hay Square Lake Lake Terrapin Turtle Lake Lake Mud Lake Lake Oneka Lake Rice Egg Lake School Section Sunset Lake Lake Long Lake Round Lake Horseshoe White Rock Lake Lake Bald Eagle Lake Pine Tree Lake Mann Lake Fish Lake Long White Bear Lake Lake Long Lake Lake Olson Demontreville Clear Lake McDonald Lake Cloverdale Lake Lake Long Lily Lake Lake McKusick Lake Loon Silver Lake Louise Lake Lake Carnelian Little Lake Masterman Benz Lake Sunfish Lake Lake Point Eagle Lake Goose Lake Lake Tanners Lake Creek Battle Wilmes Margrafs Powers Lake Lake Colby Lake Lake Carver Lake La Baldwin Lake Conley Lake Lake Edith Lake Mooers Lake Big Carnelian Lake Lakes Twin Lake Jane Lake Elmo Bone Lake Hardwood Creek Creek Creek Hardwood Creek Creek Creek Creek River River St. Croix Mississippi Mississippi River River St. Croix River St. Croix Old Mill Stream Clearwater Silver Brown's Valley Valley Branch Trout Brook Brown's 6 31 1 1 31 36 6 6 6 6 6 6 6 36 36 36 1 1 1 1 31 31 31 31 36 35 36 36 31 31 31 31 6 6 6 6 1 1 2 2 35 36 36 36 6 6 6 6 1 1 1 25 31 31 31 31 4 2 ¤ 61 ¤ 61 ¤ 61 ) 36 ) 36 ¤ 10 ¤ 10 ¤ 10 ¤ 61 ¤ 8 § ¦ 35 § ¦ 494 § ¦ 694 § ¦ 94 § ¦ 494 ) 95 ) 95 ) 95 ) 95 ) 95 ) 97 ¤ 61 ) 97 ) 244 ) 5 ) 5 ) 95 ) 96 § ¦ 94 § ¦ 94 SCANDIA F OREST LAKE HUGO M AY GRANT S TILLWATER LAKE E LMO BAY T OWN WE ST LAKELAND L A K E L A N D AFTON WOODBUR Y DENMARK COTTAGE GROVE GREY CLOUD ISL AND St Paul Park Newport Cottage Grove Woodbury Lakeland Shores Beach St Croix Lake Point St Mary's Bayport Oak Park Heights Stillwater Marine St Croix On Forest Lake Hugo Dellwood Oakdale Pine Springs Mahtomedi 225 250 275 300 325 275 275 275 275 275 275 275 300 300 300 275 275 275 275 300 275 275 225 300 300 250 275 300 275 300 275 300 275 325 300 325 300 300 275 300 300 250 300 275 300 300 300 225 300 275 275 300 275 275 275 300 300 225 300 275 300 300 300 300 300 300 300 275 300 225 275 300 250 300 300 275 300 300 275 300 275 300 275 300 250 275 300 300 250 300 250 300 300 300 275 275 300 275 325 250 300 275 250 225 300 300 275 300 325 275 275 300 300 275 300 275 275 300 275 275 275 275 250 300 300 300 275 300 300 300 300 275 300 275 325 275 225 300 275 275 275 275 225 225 225 92° 52' 30" W. B' B A' C' C A F F F M F F M F M M F F M F M F F M M F M F F F F Ops j t Os Opg t Ops Os Os Opo t Opo Ops s s Opo Os Os j s j Ops Ops j Opg m e Os j Os Ops t Ops s w Od s Ops Opo t t Opo Od t Os Opo Ops Od Os Ops j j Ops Os Os Opo w s Os Opo Ops Os e Os s Opg Opg Os Ops Ops Os Opo j Os Opo Opo Os Os Os j j Os t s Opo s t t w Os j Opg Os j Os Os Os Os Opo Opo t t t Os Od j Opo Os e j Os j Os Ops Os t Os Os Opg j Os w j Os Ops j Os Ops Os Opo Ops t Os Opo Os s s s j s j Opo s w s w Opo j w s Ops Ops Os j s Ops Os w s Opg Os Os Opo Ops j Os j s j w Ops s Od t t Od Ops Ops Os Opo Ops w Os Opo Os Od s j Opo Os Ops s Opo Ops Os s Ops Opo Ops Os Opo Os Ops j Opg Os j j j COTTAGE GROVE FAULT FAULT HASTINGS t D U U D U D D U U D U U D D U D U D U U D U D D U D U D U U D U D U U D D U D U U U D U D U D U D U D U D U D U D U U D D U D D U DU D U D U D U D U D U D U D U BEDROCK GEOLOGY By Julia R. Steenberg and Andrew J. Retzler 2016 MINNESOTA GEOLOGICAL SURVEY Harvey Thorleifson, Director Prepared and Published with the Support of THE WASHINGTON COUNTY BOARD OF COMMISSIONERS, THE MINNESOTA DEPARTMENT OF NATURAL RESOURCES, DIVISION OF ECOLOGICAL AND WATER RESOURCES, AND THE MINNESOTA LEGACY AMENDMENT'S CLEAN WATER FUND Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification. COUNTY ATLAS SERIES ATLAS C-39, PART A Washington County Plate 2—Bedrock Geology contour Interval 25 MeterS 1 0 1 2 3 4 5 MILES 8 KILOMETERS SCALE 1:100 000 1 0 1 2 3 4 5 6 7 locatIon DIaGraM 0 200 400 600 800 1,000 COTTAGE GROVE FAULT ZONE HASTINGS FAULT Elevation (feet above sea level) Os Os Ops Ops Opg A A' D D D D U U U U Unconsolidated Quaternary sediments m e t w s j m e t w j Opo Opo Mpv Mss Mss HUDSON–AFTON HORST -200 -400 -600 Jamaica Avenue Manning Avenue Military Road s 0 200 400 600 800 1,200 1,000 B B' sediments Os Ops Ops Opg Os Elevation (feet above sea level) COTTAGE GROVE FAULT DU j s t w e m j s t w e m t e m Opo Opo Mpv Mss HUDSON–AFTON HORST -200 -400 -600 0 200 400 600 800 1,000 C C' Vertical exaggeration = 10x Elevation (feet above sea level) Unconsolidated Quaternary sediments Opo j s t w e m j s t w e m D U U Opo Od FALLS CREEK GRABEN Mbv -200 Forest Lake Manning Trail St. Croix Trail St. Croix River St. Croix River St. Croix River Dellwood Minnesota Highway 36 Lake Elmo Airport Interstate 94 Lakeland Mss Quaternary Unconsolidated INTRODUCTION The geologic map, cross sections, and stratigraphic column on this plate depict the type, distribution, and structure of the bedrock units in Washington County that are either exposed at the land surface or lie directly beneath unconsolidated Quaternary glacial sediments of variable thickness (see cross sections and Plates 3, 4, and 5, Surficial Geology, Quaternary Stratigraphy, Depth to Bedrock, and Bedrock Topography). The map shows how the bedrock surface would appear if it was viewed from an aerial perspective and the overlying Quaternary sediments were stripped away. The bedrock units near the land surface in Washington County consist of sedimentary rocks of Paleozoic age that form distinguishable and mappable layers designated as formations. These units are commonly exposed along the Mississippi and St. Croix River bluffs, within rock quarries, and along roadcuts within the county. Several of the Paleozoic bedrock formations are major reservoirs for water supply in Washington County and also provide a source of crushed carbonate rock and silica sand. Characteristics of each formation are given in the stratigraphic column (Fig. 1) and in the description of map units. The accompanying bedrock geologic cross sections add the dimension of depth and illustrate the stratigraphic, structural, and topographic relationships of the bedrock units, as well as the variable thickness of the overlying Quaternary sediments. Surfaces representative of the elevation of the tops of the mapped formations are also available as Digital Elevation Models (DEMs) for use in GIS programs. The geologic formations are thin in relation to their aerial extent, and would only be one-tenth as thick as shown on the cross sections if no vertical exaggeration were used. The exaggeration necessary to show the thin rock formations gives the appearance of steeper slopes on bedrock unit contacts, the land surface, and bedrock topography. Most of the Paleozoic units shown on this plate, with the exception of the Mt. Simon and Wonewoc Sandstones and Eau Claire Formation, can be seen at the land surface in places in Washington County. The sedimentary rocks differ in their resistance to weathering and erosion, as indicated by the weathering profile on the lithology column of Figure 1. The units that cover the largest areas of the map are the most resistant to weathering and generally form plateaus composed of carbonate rock (limestone and dolostone). The soft sandstone and shale formations are more easily eroded and commonly occur on bedrock plateau or valley walls. Production of the map and associated products relied on several data sources, including outcrops, water-well and scientific drilling records from the County Well Index, rock core, drill cutting samples, borehole geophysical logs, seismic soundings, geophysical images, and previously published geologic maps of Washington and adjacent counties (Mossler and Bloomgren, 1990; Mossler and Tipping, 2000; Mossler, 2005a, b, 2006a, b, c, d, 2013; Anderson, 2009). This map supersedes the previous bedrock geology map of Washington County (Mossler and Bloomgren, 1990). Significant improvements and modifications were made to the previous map based on additional water-well records, drill cuttings, borehole geophysics, and refined geophysical images. The Prairie du Chien Group is separated into the Oneota Dolomite and Shakopee Formation and the St. Lawrence Formation is mapped separately from the Tunnel City Group (previously the Franconia Formation). Faults and folds in the southeastern part of the county were mapped to reflect significant offset in the Paleozoic formations. This provides detail of the subsurface geologic conditions, which has implications for modeling groundwater flow. The different data sources and their irregular distribution and density can be seen on Plate 1, Data-Base Map, and these should be considered when assessing the reliability of the map at any particular location. Areas with a high density of bedrock control points are more likely to have an accurate interpretation of the bedrock geology, whereas those areas with widely spaced control points may be less reliable and inappropriate for site-specific needs. During production of this map, the records of over 14,000 located water wells existed within Washington County in the County Well Index and nearly 10,000 of those reached Paleozoic bedrock. Geologic interpretations of subsurface material described by drillers or gathered from other data sources were made by the authors and are represented in the County Well Index records. Every reasonable effort has been made for the geologic interpretations in the County Well Index to correspond to the map. Paleozoic bedrock lies on top of a thick sequence of Mesoproterozoic (approximately 1,100 million years, or Ma, ago) rocks of the Keweenawan Supergroup, associated with the Midcontinent Rift (see cross sections and Fig. 2). These rocks include sandstone, siltstone, and shale of the Hinckley Sandstone, Solor Church and Fond du Lac Formations (unit Mss), and volcanic rocks composed mostly of basalt including the Powder Mill (unit Mpv) and North Branch (unit Mbv) volcanic sequences. Due to their deep burial and limited subsurface data, the distribution of these individual units is less certain than the Paleozoic units. Therefore, the contact between the top of these units and the overlying base of Mt. Simon Sandstone is dashed in cross sections. No new mapping of these units was done for this project; instead a recent compilation map of the Precambrian bedrock geology of Minnesota is depicted (Fig. 2; Jirsa and others, 2012). The Paleozoic rocks of Washington County are characterized by relatively thin, widespread layers of sandstone, shale, and carbonate deposited in shallow seas during the Cambrian and Ordovician Periods of the Paleozoic Era, from about 500 to 450 million years ago. The older Cambrian-age formations are dominated by siliciclastic sedimentary rock including sandstone and siltstone with minor shale, such as the Jordan Sandstone and Mazomanie Formation (Tunnel City Group). Carbonate rock occurs only as relatively thin layers within these units. Ordovician-age formations, in contrast, are dominated by thicker units of carbonate rock with less sandstone and shale, such as the Prairie du Chien Group and the Platteville Formation. Where carbonate rock and silica-rich (quartzose) sandstone exist near the land surface (or within 50 feet [15 meters]), they are considered a valuable geologic resource. Carbonate rock products are crushed, sorted, and used as construction material for roads and buildings, and in concrete operations. The silica-rich sandstone is texturally mature and well-rounded, which makes it a sought after resource in the oil industry. It also has a wide variety of other uses including glassmaking, foundry operations, ceramics, filtration, and agriculture. However, viability of extraction is dependent on many other factors, including detailed geologic conditions at individual sites, proximity to bulk transportation, current land ownership and use, market prices, regulatory requirements, and many others. Figure 3 depicts where carbonate or quartzose sandrock is within 50 feet (15 meters) of the land surface and highlights the active quarry operations at the time this map was created. Across most of Washington County, bedrock units are slightly tilted (less than 1°) southwest towards the central Twin Cities metropolitan area, as part of the eastern margin of a shallow structural depression known as the Twin Cities basin. As a result, progressively younger bedrock formations subcrop from eastern to western Washington County. This general trend is locally interrupted by deep valleys that incise older formations, and by faults and folds. A fault is recognized where changes in the elevation of a bedrock contact occur within a very short distance, generally elevation changes of 50 feet (15 meters) or more within a distance of 1,000 feet (305 meters). A fold is inferred where these elevation changes indicate more gradual slopes. The stratigraphic top of the Jordan Sandstone was contoured at 25-foot (15-meter) intervals to show the inferred location of faults and folds in Washington County (Fig. 4). The top of the Jordan Sandstone was selected to portray these structures because it is a well-recognized and distinct contact, has numerous control points including outcrops that expose the contact, and has water wells that penetrate it. Displacement along faults in Washington County is on the order of 25 to 300 feet (8 to 91 meters), which is sufficient in places to juxtapose several different formations along the fault contact (see cross sections and Fig. 4). Bedrock that has dropped alongside a fault preserves relatively younger formations (shown with a D on the map) at the surface and bedrock that has been uplifted brings older formations closer to the surface (shown with a U on the map). Most faults trend in the northeast direction but several trend northwest. Several of the faults observed in Paleozoic strata are subparallel to faults in the underlying Mesoproterozoic Midcontinent Rift rocks, as inferred from geophysical imagery, and are therefore interpreted to represent reactivation of these older structures (Fig. 2). The aeromagnetic and gravity data show where a great thickness of dense and magnetic basalts have been brought near the surface in an inverted graben known as the Hudson–Afton horst (Sims and Zeitz, 1967; Cannon and others, 2001). Paleozoic rocks overlying the Hudson–Afton horst in Washington County are also uplifted relative to the rocks on either side, although the displacement is of a lesser magnitude than that in the underlying Mesoproterozoic bedrock (Fig. 4). Lower Ordovician Prairie du Chien Group rocks thin (less than 50 feet [15 meters]) within the uplifted horst and thicken along either side (less than 300 feet [91 meters]), suggesting displacement was occurring during Early to Middle Ordovician time (see cross section A–A' and Fig. 5). HYDROSTRATIGRAPHY The Paleozoic bedrock formations contain significant sources of groundwater, which provide the majority of the water supply for Washington County. This map and associated products, such as the bedrock unit DEMs, provide a three-dimensional depiction of the rock properties that control flow in these water-bearing layers. Such rock properties are called hydrostratigraphic properties. The hydrostratigraphic classification, shown by brown and blue colors on the hydrostratigraphic column of Figure 1, distinguishes layers that are dominated by relatively high permeability (easily transmitting water) material, versus layers dominated by lower permeability (relatively more difficult to transmit water) material. This generalized characterization for Washington County is based on hydrogeologic reports by Runkel (1996), Paillet and others (2000), Runkel and others (2003, 2006a, b, 2014a, b), Tipping and others (2006), Anderson and others (2011), Luhmann and others (2011), Green and others (2012), and unpublished borehole and core data collected by the Minnesota Geological Survey. The high permeability layers are potential aquifers, able to yield economic quantities of water in most places. The low permeability layers are potential aquitards that retard vertical flow, hydraulically separating the aquifer layers from one another in many places, and protecting water resources in the underlying layers from surface contamination. Fractures parallel to bedding that have been demonstrated to have high permeability are likely to be present, at least locally, in all formations in Washington County, but are placed on the column where the hydrogeologic reports cited above indicate they are most common. The locations of springs in Washington County most commonly occur within the lower Jordan Sandstone, St. Lawrence Formation, and upper Tunnel City Group, where high permeability bedding fractures are known to be common. The hydrogeologic properties of the Mesoproterozoic bedrock are poorly understood. It does not supply water to Washington County at least in part because sufficient water resources are available at shallower depths in the Paleozoic rocks. In Washington County, most aquifers are layers dominated by relatively coarse-grained sandstone, such as within the upper part of the Jordan Sandstone, in which water can be fairly easily transmitted in both horizontal and vertical directions through the pore spaces between sand grains, as well as through fractures. Other aquifers, such as the upper part of the Prairie du Chien Group, are composed mostly of carbonate rock in which water is transmitted through a relatively dense network of fractures and solution cavities. However, layers designated as aquifers can locally contain low permeability strata that serve as small, internal aquitards including parts of the upper Mt. Simon Sandstone and the lower Jordan Sandstone. Most layers designated as aquitards in the county have a much lower permeability in the vertical direction than do aquifers. Examples in Washington County include the lower Jordan Sandstone, St. Lawrence, and Eau Claire Formations, whose rocks are composed mostly of very fine-grained sandstone and shale with small, poorly connected pore spaces. Carbonate rock with relatively sparse fractures, such as the lower part of the Prairie du Chien Group (Oneota Dolomite), are also aquitards. However, layers designated as aquitards with very low permeability in the vertical direction may locally contain horizontal fractures that are conductive enough to yield large quantities of water, including the St. Lawrence Formation. Horizontal and vertical fractures are more common where bedrock layers are at or near the bedrock surface. As a result, aquitards in such conditions are likely to have higher permeability compared with more deeply buried portions of the same formation, and may have a diminished ability to retard water flow to underlying aquifers. There is no precise boundary between shallow and deep conditions of burial, but in most areas of southeastern Minnesota about 50 feet (15 meters) of depth below the bedrock surface is considered a best approximation (Runkel and others, 2006a). In addition to this hydrostratigraphic classification, the Minnesota Department of Natural Resources, as Part B of the Washington County atlas, will conduct a thorough hydrogeologic study of the groundwater flow system, aquifer capacity, and aquifer sensitivity, which may result in modifications to this classification. Furthermore, designations of aquifers versus aquitards made here may not correspond precisely with those made for regulatory purposes by the Minnesota Department of Health. DESCRIPTION OF MAP UNITS Od Decorah Shale (Upper Ordovician)—Dominantly grayish-green shale interbedded with thin beds of fossiliferous limestone. Fossiliferous, yellowish-brown limestone beds are most common at the base of the Decorah Shale, and are recognized as the basal Carimona Member (Mossler, 2008). The Decorah Shale is present as erosional remnants capping Platteville mesas in the southwestern part of the county. Though no exposures exist in the county, water well logs indicate the Decorah Shale has a maximum preserved thickness of 40 feet (12 meters). Opg Platteville and Glenwood Formations (Upper Ordovician)—The Platteville Formation is generally tan to gray, fossiliferous limestone and dolostone. The underlying Glenwood Formation is dominantly a green-gray, sandy shale. The Platteville Formation is the dominant uppermost bedrock unit across a large expanse of the southwestern part of the county. The combined thickness of the formations is 30 to 35 feet (9 to 11 meters). Platteville Formation—The Platteville Formation is 25 to 30 feet (8 to 9 meters) thick. It is composed of tan to gray limestone and dolostone. It is commonly burrowed, mottled, and fossiliferous. It contains fine- to coarse-grained quartz sand and phosphate grains in the lowermost 2 feet (0.6 meter). Glenwood Formation—The principal rock type of the Glenwood Formation is a grayish- green to brownish-gray, calcareous, sandy, and phosphatic shale. The Glenwood Formation is 3 to 7 feet (1 to 2 meters) thick. Os St. Peter Sandstone (Middle to Lower Ordovician)—The upper 100 to 140 feet (30 to 43 meters) of the St. Peter Sandstone is mostly a white to tan, fine- to medium-grained, friable quartzose sandstone. Bedding and structures are generally absent. It is exposed in patchy outcrops in the southern half of the county where glacial sediments are thin. The lowermost 10 to 40 feet (3 to 12 meters), referred to as the Pigs Eye Member, includes white to gray feldspathic shale and siltstone interbedded with coarser-grained sandstone similar to that of the Tonti Member. The Pigs Eye Member is not exposed in Washington County. The thickness of the St. Peter Sandstone varies from about 130 to 160 feet (40 to 49 meters). The basal contact of the formation with the underlying Shakopee Formation (unit Ops) is a major erosional unconformity (Smith and others, 1993). Prairie du Chien Group (Lower Ordovician)—Dominated by dolostone interlayered with lesser amounts of quartz sandstone. Outcrops are exposed along the tops of bluffs of the Mississippi and St. Croix River valleys; small patchy outcrops are also present in southeastern Washington County where the Quaternary sediments are thin. The Prairie du Chien Group is a significant source of rock aggregate in this part of the county. The Prairie du Chien Group is formally divided into two formations: the Shakopee Formation and underlying Oneota Dolomite. Geophysical logs and drill cuttings in the northern part of the county and within parts of the Hudson–Afton horst that span the St. Peter through the Jordan Sandstones are lacking and water well records are typically inadequate to distinguish the Oneota Dolomite from the Shakopee Formation and St. Peter Sandstone from the sandy upper Shakopee Formation. Therefore, the mapped distribution of these units is more speculative in these areas. The thickness of the Prairie du Chien Group beneath the St. Peter Sandstone varies greatly across Washington County, from less than 50 to nearly 300 feet (15 to 91 meters; Fig. 5). This is interpreted to be due to several factors, including syndepositional faulting along the Hudson–Afton horst, and erosion of the Shakopee Formation prior to deposition of the St. Peter Sandstone. This erosional surface is the unconformity that marks the contact between the Shakopee Formation and overlying St. Peter Sandstone. Ops Shakopee Formation (Lower Ordovician)—A heterolithic unit composed mainly of light brown, thin- to medium-bedded dolostone, sandy dolostone, sandstone, and shale. It contains oolites, intraclasts, fossilized microbial mounds, chert nodules, quartz sandstone, and green-gray shale partings. Thickness of the Shakopee Formation beneath the St. Peter Sandstone is quite variable within the area of the Hudson–Afton horst, ranging from almost absent to nearly 200 feet (61 meters) thick. It appears to be thickest in the most southeast part of the county, east of the Hastings fault, where it is nearly 200 feet (61 meters) thick. On the opposite side of the horst, on the west side of the Cottage Grove fault, it reaches thicknesses of 115 feet (35 meters) and appears to progressively thin towards the northwest. Based on a limited amount of drill cuttings and geophysical data within the Hudson–Afton horst, it appears that the Shakopee Formation thins to less than 50 feet (15 meters) and may even be absent beneath the St. Peter Sandstone at several locations (see cross section A–A'). Opo Oneota Dolomite (Lower Ordovician)—Predominantly a yellowish-gray to light brown, medium- to thick-bedded dolostone that generally lacks sedimentary features such as oolites and quartz sand characteristic of the Shakopee Formation, except in its lowermost part. The formation contains two members, the Hager City and the Coon Valley, but they are not mapped separately. The basal Coon Valley Member is a heterolithic unit composed of thinly bedded dolostone, sandy dolostone, and beds of fine- to coarse- grained, poorly sorted quartz sandstone. Thickness of the Coon Valley Member is quite variable, it is locally absent to 30 feet (9 meters) thick. There appears to be a slight trend in its thickness along the Hudson–Afton horst whereby it is thickest on the down dropped sides of the faults (20 to 30 feet [6 to 9 meters]) and thinner between the faults (10 to 15 feet [3 to 5 meters]). It also appears to be thin to absent towards the western edge of the county and within the central and northern parts of the county. The Hager City Member is primarily very finely crystalline dolostone, with microbial textures. Its thickness also shows a similar trend to the Coon Valley Member in being thicker along the down-dropped sides of the Hastings and Cottage Grove faults (50 to 70 feet [15 to 21 meters]) and thinner between them (40 to 50 feet [12 to 15 meters]). _j Jordan Sandstone (Upper Cambrian)—Dominantly white to yellow, very fine- to coarse- grained, friable quartz sandstone characterized by coarsening-upward sequences consisting of two interlayered facies (Runkel, 1994). They are medium- to coarse-grained, cross-stratified, generally friable, quartz sandstone; and very fine-grained, commonly bioturbated, feldspathic sandstone with lenses of siltstone and shale. The major part of the very fine-grained facies forms a regionally continuous interval that gradationally overlies the St. Lawrence Formation (unit _s), although there are lithologically similar intervals intercalated with the medium- to coarse-grained facies at higher stratigraphic intervals. An unconformity, locally marked by thin beds of quartz pebble conglomerate and silcrete-cemented sandstone clasts (Runkel and others, 1999, 2007), separates the Jordan Sandstone from the overlying Oneota Dolomite. The Jordan Sandstone is exposed along the Mississippi and St. Croix River bluffs and ranges in thickness from 80 to 100 feet (24 to 29 meters). In the northernmost part of the county near Scandia, it appears to thin to 65 to 70 feet (20 to 21 meters) thick. _s St. Lawrence Formation (Upper Cambrian)—The St. Lawrence Formation is principally light gray to yellowish-gray and pale yellowish-green, dolomitic, feldspathic siltstone with interbedded, very fine-grained sandstone and shale. Lenses and layers of light gray, finely crystalline, sandy dolostone occur locally, especially in the lowermost few feet of the formation (Runkel and others, 2006a). The formation is 35 to 45 feet (8 to 12 meters) thick. The upper contact with the Jordan Sandstone is conformable and gradational. The gradational nature of the contact in well cuttings and on natural gamma logs can make selecting a precise contact between these formations difficult. _t Tunnel City Group (Upper Cambrian)—The Tunnel City Group, formerly named the Franconia Formation (Berg, 1954), varies from about 160 to 180 feet (49 to 55 meters) in thickness across Washington County. It is formally divided into two formations: the Mazomanie and the Lone Rock Formations (Mossler, 2008). The Mazomanie Formation is dominantly white to yellowish-gray, fine- to medium-grained, cross-stratified, generally friable, quartz sandstone. Glauconitic grains typically are rare to absent and never exceed 5 percent (Berg, 1954). Some beds contain brown, intergranular dolomite cement. Skolithos burrows and sandstone intraclasts are common along discrete horizons. The Lone Rock Formation underlies the Mazomanie Formation and intertongues with it. It consists of pale yellowish-green, very fine- to fine-grained glauconitic, feldspathic sandstone and siltstone, with thin, greenish-gray shale partings. Thin beds with dolomitic intraclasts are common. In northeastern Washington County, individual tongues of Mazomanie Formation are as thick as 50 feet (15 meters), and the Mazomanie Formation as a whole can reach thicknesses of 100 feet (30 meters). The Mazomanie Formation thins to the south, where it is progressively replaced laterally by the Lone Rock Formation. As a result, in southern Washington County the Mazomanie Formation is less than 25 feet (8 meters) thick to absent. The upper contact of the Tunnel City Group with the St. Lawrence Formation is conformable. The contact is fairly sharp and the contrast between the siltstone and shale of the St. Lawrence Formation, and underlying fine- to medium-grained, quartzose sandstone in the Mazomanie Formation of the Tunnel City Group, is distinct and typically marked by an intraclastic conglomerate. _w Wonewoc Sandstone (Upper Cambrian)—This sandstone unit, formerly referred to as the Ironton-Galesville Sandstone, is composed mostly of fine- to coarse-grained, moderately to well sorted, light gray, cross-stratified, quartz sandstone (Mossler, 2008). White, brown, and black linguliform brachiopod shells are locally abundant. The upper part is the coarsest-grained; the lower part is finer-grained, better sorted, and progressively finer-grained toward its base. The very fine-grained sandstone in the lower part is feldspathic. The thickness of the formation is 45 to 75 feet (14 to 23 meters). The Wonewoc Sandstone is conformable with overlying and underlying formations; however, there is a subtle unconformity marked by a pebbly sandstone layer within the formation (Runkel and others, 1998). _e Eau Claire Formation (Middle to Upper Cambrian) —The formation is composed of yellowish-gray to pale olive-gray, fine- to very fine-grained, feldspathic sandstone, siltstone, and shale. White and brown linguliform brachiopod shells are common. The formation ranges from 80 to 100 feet (24 to 30 meters) in thickness. The contact with the Mt. Simon Sandstone is conformable. _m Mt. Simon Sandstone (Middle Cambrian)—The Mt. Simon Sandstone is pale yellowish- brown to grayish-orange-pink to light gray, medium- to coarse-grained, quartz sandstone. Interbeds of shale, siltstone, and very fine-grained feldspathic sandstone are common, particularly in its upper half (Mossler, 1992). Inarticulate brachiopod shells are locally common in the upper one-third of the formation. Thin beds of quartz-pebble conglomerate occur at several stratigraphic positions, and are especially abundant near the base of the formation. The Mt. Simon Sandstone unconformably overlies Mesoproterozoic rocks. Based on a limited number of full penetrations of the formation, it appears to have a maximum thickness of about 280 feet (85 meters). MESOPROTEROZOIC Keweenawan Supergroup Mss Sandstone, siltstone, and local conglomerate (shown on cross sections and Fig. 2)—Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solor Church Formations; deposited in eolian, fluvial, and lacustrine environments. Mbv North Branch volcanic sequence (shown on cross section C–C' and Fig. 2)—Part of the St. Croix horst. Mpv Powder Mill volcanic sequence (~1,099 Ma; shown on cross sections and Fig. 2)—Part of the St. Croix horst. REFERENCES Anderson, J.R., 2009, Bedrock geology of the Lake Elmo quadrangle, Ramsey and Washington Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-185, scale 1:24,000. Anderson, J.R., Runkel, A.C., Tipping, R.G., Barr, K., and Alexander, E.C., Jr., 2011, Hydrostratigraphy of a fractured urban aquitard: Geological Society of America Field Guide 24, p. 457-475. Berg, R.R., 1954, Franconia Formation of Minnesota and Wisconsin: Geological Society of America Bulletin, v. 66, p. 857-882. Cannon, W.F., Daniels, D.L., Nicholson, S.W., Phillips, J., Woodruff, L.G., Chandler, V.W., Morey, G.B., Boerboom, T.J., Wirth, K.R., and Mudrey, M.G., Jr., 2001, New map reveals origin and geology of North American Mid-continent Rift: Eos, v. 82, p. 97-101. Chandler, V.W., 1991, Aeromagnetic anomaly map of Minnesota: Minnesota Geological Survey State Map S-17, scale 1:500,000. Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2012, Karst conduit flow in the Cambrian St. Lawrence confining unit, southeast Minnesota, USA: Carbonates Evaporites, v. 27, no. 2, p. 167-172. Jirsa, M.A., Boerboom, T.J., and Chandler, V.W., 2012, Geologic map of Minnesota Precambrian bedrock geology: Minnesota Geological Survey State Map S-22, scale 1:500,000. Luhmann, A.J., Covington, M.D., Peters, A.J., Alexander, S.C., Anger, C.T., Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2011, Classification of thermal patterns at karst springs and cave streams: Ground Water, v. 49, no. 3, p. 324-335. Mossler, J.H., 1992, Sedimentary rocks of Dresbachian age (Late Cambrian), Hollandale embayment, southeastern Minnesota: Minnesota Geological Survey Report of Investigations 40, 71 p. ———2005a, Bedrock geology of the Hudson quadrangle, Washington County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-154, scale 1:24,000. ———2005b, Bedrock geology of the Stillwater quadrangle, Washington County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-153, scale 1:24,000. ———2006a, Bedrock geology of the Hastings quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-169, scale 1:24,000. ———2006b, Bedrock geology of the Prescott quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-167, scale 1:24,000. ———2006c, Bedrock geology of the St. Paul Park quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-166, scale 1:24,000. ———2006d, Bedrock geology of the Vermillion quadrangle, Dakota County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-168, scale 1:24,000. ———2008, Paleozoic stratigraphic nomenclature for Minnesota: Minnesota Geological Survey Report of Investigations 65, 76 p., 1 pl. ———2013, Bedrock geology of the Twin Cities ten-county metropolitan area, Minnesota: Minnesota Geological Survey Miscellaneous Map M-194, scale 1:125,000. Mossler, J.H., and Bloomgren, B.A., 1990, Bedrock geology, pl. 2 of Swanson, L., and Meyer, G.N., eds., Geologic atlas of Washington County, Minnesota: Minnesota Geological Survey County Atlas C-5, scale 1:100,000, 7 pls. Mossler, J.H., and Tipping, R.G., 2000, Bedrock geology and structure of the seven-county Twin Cities metropolitan area, Minnesota: Minnesota Geological Survey Miscellaneous Map M-104, scale 1:250,000. Paillet, F.L., Lundy, J., Tipping, R., Runkel, A.C., Reeves, L., and Green, J., 2000, Hydrogeologic characterization of six sites in southeastern Minnesota using borehole flowmeters and other geophysical tools: U.S. Geological Survey Water-Resources Investigations Report 00-4142, 33 p. Runkel, A.C., 1994, Deposition of the uppermost Cambrian (St. Croixan) Jordan Sandstone, and the nature of the Cambrian–Ordovician boundary in the upper Mississippi valley: Geological Society of America Bulletin, v. 106, p. 492-506. ———1996, Bedrock geology of Houston County, Minnesota: Minnesota Geological Survey Open-File Report 96-4, 11 p., 3 pls., scale 1:100,000. Runkel, A.C., McKay, R.M., Miller, J.F., Palmer, A.R., and Taylor, J.F., 2007, High resolution sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: The role of special conditions of cratonic interiors in development of stratal architecture: Geological Society of America Bulletin, v. 119, nos. 7/8, p. 860-881. Runkel, A.C., McKay, R.M., and Palmer, A.R., 1998, Origin of a classic cratonic sheet sandstone: Stratigraphy across the Sauk II–Sauk III boundary in the upper Mississippi valley: Geological Society of America Bulletin, v. 110, p. 188-210. Runkel, A.C., Miller, J.F., McKay, R.M., Shaw, T.H., and Bassett, D.J., 1999, Cambrian-Ordovician boundary strata in the central mid-continent of North America: Acta Universitatis Carolinae Geologica, v. 43, p. 17-20. Runkel, A.C., Mossler, J.H., Tipping, R.G., and Bauer, E.J., 2006a, A hydrogeologic and mapping investigation of the St. Lawrence Formation in the Twin Cities metropolitan area: Minnesota Geological Survey Open-File Report 06-4, 20 p. Runkel, A.C., Steenberg, J.R., Tipping, R.G., and Retzler, A.J., 2014a, Geologic controls on groundwater and surface water flow in southeastern Minnesota and its impact on nitrate concentrations in streams: Minnesota Geological Survey Open-File Report 14-2, 70 p. Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Alexander, S.C., 2006b, Hydrostratigraphic characterization of intergranular and secondary porosity in part of the Cambrian sandstone aquifer system of the cratonic interior of North America: Improving predictability of hydrogeologic properties: Sedimentary Geology, v. 184, p. 281-304. Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Green, J.A., 2003, Hydrogeology of the Paleozoic bedrock in southeastern Minnesota: Minnesota Geological Survey Report of Investigations 61, 105 p., 2 pls. Runkel, A.C., Tipping, R.G., Green, J.A., Jones, P.M., Meyer, J.R., Parker, B.L., Steenberg, J.A., and Retzler, A.J., 2014b, Hydrogeologic properties of the St. Lawrence aquitard, southeastern Minnesota: Minnesota Geological Survey Open-File Report 14-4, 56 p. Sims, P.K., and Zeitz, I., 1967, Aeromagnetic and inferred Precambrian paleogeographic map of east-central Minnesota and part of Wisconsin: U.S. Geological Survey Geophysical Investigations Map GP-563, 6 p., scale 1:250,000. Smith, G.L., Byers, C.W., and Dott, R.H., Jr., 1993, Sequence stratigraphy of the lower Ordovician Prairie du Chien Group on the Wisconsin arch and in the Michigan basin: American Association of Petroleum Geologists Bulletin, v. 77, p. 49-67. Tipping, R.G., Runkel, A.C., Alexander, E.C., Jr., and Alexander, S.C., 2006, Evidence for hydraulic heterogeneity and anisotropy in the mostly carbonate Prairie du Chien Group, southeastern Minnesota, USA: Sedimentary Geology, v. 184, p. 305-330. Carbonate rock within 50 feet of the land surface Quartzose sandrock within 50 feet of the land surface Active quarry Figure 3. Map showing where carbonate and quartzose sandrock are present within 50 feet (15 meters) of the land surface in Washington County. Brown represents quartzose sandrock (including the Jordan, Wonewoc, and St. Peter Sandstones) and beige represents carbonate rock (including the Platteville and Shakopee Formations and Oneota Dolomite). The active quarry operations in Washington County are shown in black. This figure was generated using the bedrock topographic surface and bedrock geology polygons, which are standard Geographic Information System (GIS) products of a county geologic atlas. Upper Ordovician Decorah Shale Platteville and Glenwood Formations St. Peter Sandstone Shakopee Formation Oneota Dolomite Middle Ordovician Jordan Sandstone St. Lawrence Formation Tunnel City Group Wonewoc Sandstone Eau Claire Formation Mt. Simon Sandstone Prairie du Chien Group Galena Group Hager City Coon Valley Lone Rock Formation m e w t Os Opg Od Lower Ordovician Upper Cambrian Middle Cambrian Mesoproterozoic and older rocks, undifferentiated 80-100 ~200-280 140-160 30-35 Ph G G G G G G G G G G G s j Opo Mazomanie Formation <40 50-80 90-120 85-100 35-45 160-180 50-60 Not Shown NOT EXPOSED IN WASHINGTON COUNTY Ops Pigs Eye Tonti Era System-Series Group, Formation, Member Lithology Lithostratigraphic unit Composite natural gamma log Hydrostratigraphic properties 0 100 Increasing count Map symbol Thickness (in feet) API-G units Relatively high permeability (aquifer) Relatively low permeability (except for fractures, aquitard) High permeability bedding fracture known to be common HYDROSTRATIGRAPHIC PROPERTIES KEY Chert Oolites Glauconite Stromatolites Shells Bioturbation Pebbles Intraclasts Cross-bedded (planar) Cross-bedded (trough) Cross-bedded (hummocky) Dolomitic Vugs Contact marks a major erosional surface Siltstone Shale LITHOLOGY KEY G Dolostone Sandstone Sandy dolostone Very fine- to fine-grained Medium- to coarse-grained Shaly Fine- to medium-grained Ph Phosphate grains Limestone PALEOZOIC Figure 1. Generalized stratigraphic column depicting the lithology, thickness, vertical succession, age, and hydrostratigraphic properties for all units shown on the map, as well as the schematic depiction of relative competence in outcrop where exposed. The gamma log is a compilation of the following borehole geophysical logs on file at the Minnesota Geological Survey: County Well Index unique numbers 783609, 777305, and 256005. GEOLOGIC ATLAS OF WASHINGTON COUNTY, MINNESOTA CGF CGFZ HF HFZ FCG HAH Mbv Mss Mpv ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( Mss Figure 2. Faults that displace Paleozoic bedrock in Washington County superimposed on a map of the first vertical derivative aeromagnetic data (Chandler, 1991) and the underlying Mesoproterozoic rock units (Jirsa and others, 2012). Paleozoic faults and fault zones where they cluster in the southern part of the map (CGF—Cottage Grove fault, CGFZ—Cottage Grove fault zone, HF—Hastings fault, HFZ—Hastings fault zone) are subparallel to strong, abrupt, linearly extensive contrasts in magnetic intensity in the underlying Mesoproterozoic rocks associated with the Midcontinent Rift. The aeromagnetic data display where a great thickness of magnetic Mesoproterozoic rift basalts (unit Mpv) have been brought near the surface in an inverted graben known as the Hudson–Afton horst (HAH), bounded by thrust faults, shown by black lines with teeth. Faults in the northeastern corner of the county that bound what is known as the Falls Creek Graben (FCG) are subparallel to foliation trends of underlying Mesoproterozoic lava flows (unit Mbv ). Due to their similar trends and close proximity, all Paleozoic faults are interpreted to have originated from reactivation of deep Mesoproterozoic structures. Abrupt thickness changes in the Prairie du Chien Group across the Hudson–Afton horst indicate that faults were reactivated during Early Paleozoic (Early to Middle Ordovician) time. Digital base modified from the Minnesota Department of Transportation BaseMap data; digital base annotation by the Minnesota Geological Survey. Elevation contours were derived from the U.S. Geological Survey 30-meter Digital el evation Model (DeM) by the Minnesota Geological Survey. universal transverse Mercator Projection, grid zone 15 1983 north american Datum GIS compilation by r.S. lively edited by lori robinson ©2016 by the regents of the university of Minnesota The University of Minnesota is an equal opportunity educator and employer A A' U D MAP SYMBOLS Geologic contact, approximatly located Geologic contact, inferred Fault —Faults are inferred from abrupt changes in the elevation of stratigraphic units from subsurface and outcrop data. Letters indicate relative vertical displacement: U—up, D—down. Dashed lines represent areas where it is inferred. Fold—Axial trace of anticline, syncline. Fold limbs typically have shallow dips and are inferred from subsurface data. Active quarry Bedrock outcrop Location of geologic cross section F M Cross sections—Every attempt has been made for the cross sections to match all geologic interpretations made from the County Well Index data. Symbology is the same as on the bedrock map. Only a small number of drill holes intersected Mesoproterozoic bedrock, thus the relief is generalized and inferred from the thickness of the Mt. Simon Sandstone. Dashed vertical lines represent Precambrian faults and the long dashed lines in C–C' represent volcanic flows inferred from geophysical imagery. m e w s j Od PALEOZOIC CORRELATION OF MAP UNITS unconformity t Opo Lower Ordovician unconformity Upper Cambrian Middle Cambrian MESOPROTEROZOIC unconformity Opg Os Middle Ordovician Upper Ordovician Ops unconformity Mss Mbv Mpv unconformity

Upload: others

Post on 04-Nov-2021

19 views

Category:

Documents


0 download

Report

TRANSCRIPT

Page 1: BEDROCK GEOlOGy - University of Minnesota

300

250

200

150

100

50

0

Thickness of Prairie du ChienGroup rocks in feet

CGF

HFZ

HUDS

ON-A

FTON

HOR

ST

CGFZ HF

Figure 5. Color shaded map indicating the thickness of the Prairie du Chien Group where it exists below the St. Peter Sandstone. Blue colors represent areas where the Prairie du Chien Group is thinner and orange represents areas where it is thicker. There is progressive thinning toward the north, where it thins to 50 feet (15 meters) thick. Thicknesses reach nearly 300 feet (91 meters) in the southern part of the county except within the Hudson–Afton horst (HAH), where it thins to less than 50 feet (15 meters) in places. Small areas where the Prairie du Chien Group appears to thin abruptly are interpreted to represent areas of significant erosion during a hiatus marked by an unconformity prior to the deposition of the St. Peter Sandstone. CGF—Cottage Grove fault, CGFZ—Cottage Grove fault zone, HF—Hastings fault, HFZ—Hastings fault zone.

Elevation of the top of the Jordan Sandstone in feet

Less than 550

551-600

601-650

651-700

701-750

751-800

801-850

851-900

901-950

951-1,000

1,001-1,050

FF

F

M

F

F

M

F

M

M

F

FM FM

FF

MM

F

M

F

F

F

F

Figure 4. Map of Washington County depicting the elevation of the stratigraphic top of the Jordan Sandstone showing the mapped fold axes (thin black lines) and faults (thick black lines). Colored intervals represent 50-foot (15-meter) elevation intervals; blue colors represent lower elevations, and orange represents higher elevations. Dashed lines depict the 25-foot (8-meter) contour intervals. In areas where the Jordan Sandstone is absent because of erosion, the map is not colored, and the contours are inferred from vertical projection of the contacts of stratigraphically lower formations.

T. 32 N.T. 32 N.

T. 31 N.T. 31 N.

T. 30 N. T. 30 N.

T. 29 N.T. 29 N.

T. 28 N. T. 28 N.

T. 27 N.T. 27 N.

T. 26 N.

R. 22 W.

R. 22 W.R. 21 W.

R. 21 W. R. 20 W.

R. 20 W.

R. 19 W.

92° 52' 30" W. 93° W.

44° 52' 30" N.

44° 45' N. 44° 45' N.

45° N.

45° 7' 30" N.

92° 45' W.

45° 15' N.

92° 45' W.

45° 15' N.

45° 7' 30" N.

45° N.

44° 52' 30" N.

93° W.

93° W.

ANO

KA C

OU

NTY

CHISAGO COUNTY CHISAGO COUNTY

DAKOTA COUNTY

ANO

KA C

OU

NTY

WIS

CO

NSI

N

WIS

CONS

IN

DAKOTACOUNTY

PIERCECOUNTY

ST. CROIXCOUNTY

POLKCOUNTY

PIERCECOUNTY

ST. CROIXCOUNTY

POLKCOUNTY

RAMSEYCOUNTY

RAMSEY COUNTY

Forest

Clear Lake

MudLake

SylvanLake

LakeNielsen

LakeGerman

Lake

Lake

Lake

Sea

Goose

Fish

Big Marine Lake

Long Lake

Lake

LakeSand

Hay

SquareLake

LakeTerrapin

TurtleLakeLake

Mud

Lake

Lake

OnekaLake

RiceEgg

Lake

SchoolSectionSunset

LakeLake

Long

LakeRound

LakeHorseshoe

WhiteRockLake

Lake

Bald Eagle

Lake

PineTree

LakeMann

LakeFish

LakeLong

White BearLake

LakeLong

Lake

LakeOlson

Demontreville

ClearLake

McDonaldLake

CloverdaleLake

LakeLong Lily

Lake

LakeMcKusick

LakeLoon

Silver

Lake

Louise Lake

LakeCarnelianLittle

LakeMasterman

BenzLake

SunfishLake

LakePoint

Eagle

LakeGoose

Lake

Lake

TannersLake

CreekBattle

Wilmes

Margrafs

Powers

Lake

Lake

ColbyLakeLake

Carver

LakeLa

BaldwinLake

ConleyLake

LakeEdith

LakeMooers

Lake

BigCarnelian

Lake

LakesTwin

LakeJane

LakeElmo

Bone

LakeHa

rdwo

odCr

eek

Creek

Creek

Hardwood

Creek Creek

Creek

Creek

River

River

St. Croix

Mississippi

Mississippi

River

RiverSt. Croix

RiverSt. Croix

Old M

ill Stream

Clearwater

Silver

Brown's

Valley

Valley

Branch

TroutBrook

Brown's

6

31

11

31 36

66

66

66

6

36

3636

11

11

31

31

3131

36

3536

3631

31

3131

66

6 6

1

1 2

2

3536

3636

6

6

6

6

1

1

1

25

31

31 31

31

4

2¤61

¤61

¤61

)36

)36

¤10

¤10

¤10

¤61

¤8

§¦35

§¦494

§¦694

§¦94

§¦494

)95

)95

)95

)95

)95

)97

¤61

)97

)244

)5

)5

)95

)96

§¦94

§¦94

SCANDIAFOREST LAKE

HUGO MAY

GRANTSTILLWATER

LAKE ELMO

BAYTOWN

WESTLAKELAND

LAKE

LAN

D

AFTONWOODBURY

DENMARK

COTTAGE GROVE

GREYCLOUDISLAND

St PaulPark

Newport

Cottage Grove

Woodbury

LakelandShores

BeachSt Croix

Lake

PointSt Mary's

Bayport

Oak Park Heights

Stillwater

MarineSt Croix

On

Forest Lake

Hugo

Dellwood

Oakdale

Pine Springs

Mahtomedi

225

250

275

300

325

275

275

275

275

275

275

275

300

300

300

275

275

275

275

300

275

275

225

300

300

250

275

300

275

300

275

300

275

325

300

325

300

300275

300

300

250

300

275

300

300

300

225

300

275

275

300

275

275

275

300

300

225

300

275

300

300

300

300

300

300

300

275

300

225

275

300

250

300

300

275

300

300

275

300

275

300

275

300

250

275

300

300

250

300

250

300

300

300

275

275

300

275

325

250

300

275

250

225

300

300

275

300

325

275

275

300

300

275

300

275

275

300

275

275

275

275

250

300

300

300

275

300

300

300

300

275

300

275

325

275

225

300

275

275

275275

225

225

225

92° 52' 30" W.

B'

B

A'

C'C

A

F

F

FM

F

F

M

F

M

M

F

F

MF

M

F

F

M

M

F

M

F

F

F

F

Ops

j

t

Os

Opg

t

Ops

Os

Os

Opo

t

Opo

Ops

s

s

Opo

Os

Os

j

s

j

Ops

Ops

j

Opg

m

e

Os

j

Os

Ops

t

Ops

s

w

Od

s

Ops

Opo

t

t

Opo

Od

t

Os

Opo

Ops

Od

Os

Ops

j

j

Ops

OsOs

Opo

w

s

Os

Opo

Ops

Os

e

Os

s

Opg

Opg

Os

Ops

Ops

Os

Opo

j

Os

Opo

Opo

Os

Os

Os

j

j

Os

t

s

Opo

s

t

t

w

Os

j

Opg

Os

j

Os

Os

Os

Os

Opo

Opo

t

t t

Os

Od

j

Opo

Os

e

j

Os

j

Os

Ops

Os

t

Os

Os

Opg

j

Os

w

j

Os

Ops

j

Os

Ops

Os

Opo

Ops

t

Os

Opo

Os

s

s

sj

s

j

Opo

s

w

s

w

Opo

j

w

s

Ops

Ops

Os

j

s

Ops

Os

w

s

Opg

Os

Os

Opo

Ops

j

Os

j

s

j

w

Ops

s

Od

t

t

Od

Ops

Ops

Os

Opo

Ops

w

Os

Opo

Os

Od

s

j

Opo

Os

Ops

s

Opo

Ops

Os

s

Ops

Opo

Ops

Os

Opo

Os

Ops

j

Opg

Os

jj

jCO

TTAG

E GRO

VE FA

ULT

FAU

LT

HAST

INGS

t

DU

UD

U D

DU

UDU

UD

DU

DU

DU U

DU

D

DU

DU

DU

UD

U

DU

UD

DU

DU

U

UDU

DU

DU

D U

DU

DU

DU

DU

UD

DU

D

DU

D U

DUDU

D UD

U

D U

DU

D U

BEDROCK GEOlOGy

By

Julia R. Steenberg and Andrew J. Retzler

2016

MINNESOTA GEOlOGICAl SURVEyHarvey Thorleifson, Director

Prepared and Published with the Support of THE WASHINGTON COUNTy BOARD OF COMMISSIONERS,

THE MINNESOTA DEPARTMENT OF NATURAl RESOURCES, DIVISION OF ECOlOGICAl AND WATER RESOURCES,AND THE MINNESOTA lEGACy AMENDMENT'S ClEAN WATER FUND

Every reasonable effort has been made to ensure the accuracy of the factual data on which this map interpretation is based; however, the Minnesota Geological Survey does not warrant or guarantee that there are no errors. Users may wish to verify critical information; sources include both the references listed here and information on file at the offices of the Minnesota Geological Survey in St. Paul. In addition, effort has been made to ensure that the interpretation conforms to sound geologic and cartographic principles. No claim is made that the interpretation shown is rigorously correct, however, and it should not be used to guide engineering-scale decisions without site-specific verification.

COUNTy ATlAS SERIESATlAS C-39, PART A

Washington County Plate 2—Bedrock Geology

contour Interval 25 MeterS

1 0 1 2 3 4 5 MILES

8 KILOMETERS

SCALE 1:100 000

1 0 1 2 3 4 5 6 7

locatIon DIaGraM

0

200

400

600

800

1,000

COTTAGE GROVEFAULT ZONE

HAS

TIN

GS

FAU

LT

Elev

atio

n (fe

et a

bove

sea

leve

l) Os

Os

Ops OpsOpg

A A'

DDDD

UUUU

UnconsolidatedQuaternary sediments

m

e

t

w

s

j

me

t

w

j

Opo Opo

MpvMss Mss

HUDSON–AFTON HORST

-200

-400

-600

Jamaica Avenue Manning AvenueMilitary Road

s

0

200

400

600

800

1,200

1,000

B B'

sedimentsOs

OpsOps

Opg

Os

Elev

atio

n (fe

et a

bove

sea

leve

l)

CO

TTAG

E G

RO

VE F

AULT

D U

j

st

we

m

j

s t

w e

m

tem

OpoOpo

MpvMss

HUDSON–AFTON HORST

-200

-400

-600

0

200

400

600

800

1,000C C'

Vertical exaggeration = 10x

Elev

atio

n (fe

et a

bove

sea

leve

l)

Unconsolidated Quaternary sedimentsOpo j

s t

w em

j

s t

wem

DU U

OpoOd

FALL

S C

REE

K G

RAB

EN

Mbv

-200

Forest Lake Manning Trail St. Croix TrailSt. Croix River

St. Croix River

St. Croix River

Dellwood Minnesota Highway 36 Lake Elmo Airport Interstate 94 Lakeland

Mss

QuaternaryUnconsolidated

INTRODUCTIONThe geologic map, cross sections, and stratigraphic column on this plate depict the type, distribution,

and structure of the bedrock units in Washington County that are either exposed at the land surface or lie directly beneath unconsolidated Quaternary glacial sediments of variable thickness (see cross sections and Plates 3, 4, and 5, Surficial Geology, Quaternary Stratigraphy, Depth to Bedrock, and Bedrock Topography). The map shows how the bedrock surface would appear if it was viewed from an aerial perspective and the overlying Quaternary sediments were stripped away. The bedrock units near the land surface in Washington County consist of sedimentary rocks of Paleozoic age that form distinguishable and mappable layers designated as formations. These units are commonly exposed along the Mississippi and St. Croix River bluffs, within rock quarries, and along roadcuts within the county. Several of the Paleozoic bedrock formations are major reservoirs for water supply in Washington County and also provide a source of crushed carbonate rock and silica sand.

Characteristics of each formation are given in the stratigraphic column (Fig. 1) and in the description of map units. The accompanying bedrock geologic cross sections add the dimension of depth and illustrate the stratigraphic, structural, and topographic relationships of the bedrock units, as well as the variable thickness of the overlying Quaternary sediments. Surfaces representative of the elevation of the tops of the mapped formations are also available as Digital Elevation Models (DEMs) for use in GIS programs. The geologic formations are thin in relation to their aerial extent, and would only be one-tenth as thick as shown on the cross sections if no vertical exaggeration were used. The exaggeration necessary to show the thin rock formations gives the appearance of steeper slopes on bedrock unit contacts, the land surface, and bedrock topography. Most of the Paleozoic units shown on this plate, with the exception of the Mt. Simon and Wonewoc Sandstones and Eau Claire Formation, can be seen at the land surface in places in Washington County. The sedimentary rocks differ in their resistance to weathering and erosion, as indicated by the weathering profile on the lithology column of Figure 1. The units that cover the largest areas of the map are the most resistant to weathering and generally form plateaus composed of carbonate rock (limestone and dolostone). The soft sandstone and shale formations are more easily eroded and commonly occur on bedrock plateau or valley walls.

Production of the map and associated products relied on several data sources, including outcrops, water-well and scientific drilling records from the County Well Index, rock core, drill cutting samples, borehole geophysical logs, seismic soundings, geophysical images, and previously published geologic maps of Washington and adjacent counties (Mossler and Bloomgren, 1990; Mossler and Tipping, 2000; Mossler, 2005a, b, 2006a, b, c, d, 2013; Anderson, 2009). This map supersedes the previous bedrock geology map of Washington County (Mossler and Bloomgren, 1990). Significant improvements and modifications were made to the previous map based on additional water-well records, drill cuttings, borehole geophysics, and refined geophysical images. The Prairie du Chien Group is separated into the Oneota Dolomite and Shakopee Formation and the St. Lawrence Formation is mapped separately from the Tunnel City Group (previously the Franconia Formation). Faults and folds in the southeastern part of the county were mapped to reflect significant offset in the Paleozoic formations. This provides detail of the subsurface geologic conditions, which has implications for modeling groundwater flow. The different data sources and their irregular distribution and density can be seen on Plate 1, Data-Base Map, and these should be considered when assessing the reliability of the map at any particular location. Areas with a high density of bedrock control points are more likely to have an accurate interpretation of the bedrock geology, whereas those areas with widely spaced control points may be less reliable and inappropriate for site-specific needs. During production of this map, the records of over 14,000 located water wells existed within Washington County in the County Well Index and nearly 10,000 of those reached Paleozoic bedrock. Geologic interpretations of subsurface material described by drillers or gathered from other data sources were made by the authors and are represented in the County Well Index records. Every reasonable effort has been made for the geologic interpretations in the County Well Index to correspond to the map.

Paleozoic bedrock lies on top of a thick sequence of Mesoproterozoic (approximately 1,100 million years, or Ma, ago) rocks of the Keweenawan Supergroup, associated with the Midcontinent Rift (see cross sections and Fig. 2). These rocks include sandstone, siltstone, and shale of the Hinckley Sandstone, Solor Church and Fond du Lac Formations (unit Mss), and volcanic rocks composed mostly of basalt including the Powder Mill (unit Mpv) and North Branch (unit Mbv) volcanic sequences. Due to their deep burial and limited subsurface data, the distribution of these individual units is less certain than the Paleozoic units. Therefore, the contact between the top of these units and the overlying base of Mt. Simon Sandstone is dashed in cross sections. No new mapping of these units was done for this project; instead a recent compilation map of the Precambrian bedrock geology of Minnesota is depicted (Fig. 2; Jirsa and others, 2012).

The Paleozoic rocks of Washington County are characterized by relatively thin, widespread layers of sandstone, shale, and carbonate deposited in shallow seas during the Cambrian and Ordovician Periods of the Paleozoic Era, from about 500 to 450 million years ago. The older Cambrian-age formations are dominated by siliciclastic sedimentary rock including sandstone and siltstone with minor shale, such as the Jordan Sandstone and Mazomanie Formation (Tunnel City Group). Carbonate rock occurs only as relatively thin layers within these units. Ordovician-age formations, in contrast, are dominated by thicker units of carbonate rock with less sandstone and shale, such as the Prairie du Chien Group and the Platteville Formation. Where carbonate rock and silica-rich (quartzose) sandstone exist near the land surface (or within 50 feet [15 meters]), they are considered a valuable geologic resource. Carbonate rock products are crushed, sorted, and used as construction material for roads and buildings, and in concrete operations. The silica-rich sandstone is texturally mature and well-rounded, which makes it a sought after resource in the oil industry. It also has a wide variety of other uses including glassmaking, foundry operations, ceramics, filtration, and agriculture. However, viability of extraction is dependent on many other factors, including detailed geologic conditions at individual sites, proximity to bulk transportation, current land ownership and use, market prices, regulatory requirements, and many others. Figure 3 depicts where carbonate or quartzose sandrock is within 50 feet (15 meters) of the land surface and highlights the active quarry operations at the time this map was created.

Across most of Washington County, bedrock units are slightly tilted (less than 1°) southwest towards the central Twin Cities metropolitan area, as part of the eastern margin of a shallow structural depression known as the Twin Cities basin. As a result, progressively younger bedrock formations subcrop from eastern to western Washington County. This general trend is locally interrupted by deep valleys that incise older formations, and by faults and folds. A fault is recognized where changes in the elevation of a bedrock contact occur within a very short distance, generally elevation changes of 50 feet (15 meters) or more within a distance of 1,000 feet (305 meters). A fold is inferred where these elevation changes indicate more gradual slopes. The stratigraphic top of the Jordan Sandstone was contoured at 25-foot (15-meter) intervals to show the inferred location of faults and folds in Washington County (Fig. 4). The top of the Jordan Sandstone was selected to portray these structures because it is a well-recognized and distinct contact, has numerous control points including outcrops that expose the contact, and has water wells that penetrate it. Displacement along faults in Washington County is on the order of 25 to 300 feet (8 to 91 meters), which is sufficient in places to juxtapose several different formations along the fault contact (see cross sections and Fig. 4). Bedrock that has dropped alongside a fault preserves relatively younger formations (shown with a D on the map) at the surface and bedrock that has been uplifted brings older formations closer to the surface (shown with a U on the map). Most faults trend in the northeast direction but several trend northwest.

Several of the faults observed in Paleozoic strata are subparallel to faults in the underlying Mesoproterozoic Midcontinent Rift rocks, as inferred from geophysical imagery, and are therefore interpreted to represent reactivation of these older structures (Fig. 2). The aeromagnetic and gravity data show where a great thickness of dense and magnetic basalts have been brought near the surface in an inverted graben known as the Hudson–Afton horst (Sims and Zeitz, 1967; Cannon and others, 2001). Paleozoic rocks overlying the Hudson–Afton horst in Washington County are also uplifted relative to the rocks on either side, although the displacement is of a lesser magnitude than that in the underlying Mesoproterozoic bedrock (Fig. 4). Lower Ordovician Prairie du Chien Group rocks thin (less than 50 feet [15 meters]) within the uplifted horst and thicken along either side (less than 300 feet [91 meters]), suggesting displacement was occurring during Early to Middle Ordovician time (see cross section A–A' and Fig. 5).

HyDROSTRATIGRAPHy

The Paleozoic bedrock formations contain significant sources of groundwater, which provide the majority of the water supply for Washington County. This map and associated products, such as the bedrock unit DEMs, provide a three-dimensional depiction of the rock properties that control flow in these water-bearing layers. Such rock properties are called hydrostratigraphic properties. The hydrostratigraphic classification, shown by brown and blue colors on the hydrostratigraphic column of Figure 1, distinguishes layers that are dominated by relatively high permeability (easily transmitting water) material, versus layers dominated by lower permeability (relatively more difficult to transmit water) material. This generalized characterization for Washington County is based on hydrogeologic reports by Runkel (1996), Paillet and others (2000), Runkel and others (2003, 2006a, b, 2014a, b), Tipping and others (2006), Anderson and others (2011), Luhmann and others (2011), Green and others (2012), and unpublished borehole and core data collected by the Minnesota Geological Survey. The high permeability layers are potential aquifers, able to yield economic quantities of water in most places. The low permeability layers are potential aquitards that retard vertical flow, hydraulically separating the aquifer layers from one another in many places, and protecting water resources in the underlying layers from surface contamination. Fractures parallel to bedding that have been demonstrated to have high permeability are likely to be present, at least locally, in all formations in Washington County, but are placed on the column where the hydrogeologic reports cited above indicate they are most common. The locations of springs in Washington County most commonly occur within the lower Jordan Sandstone, St. Lawrence Formation, and upper Tunnel City Group, where high permeability bedding fractures are known to be common. The hydrogeologic properties of the Mesoproterozoic bedrock are poorly understood. It does not supply water to Washington County at least in part because sufficient water resources are available at shallower depths in the Paleozoic rocks.

In Washington County, most aquifers are layers dominated by relatively coarse-grained sandstone, such as within the upper part of the Jordan Sandstone, in which water can be fairly easily transmitted in both horizontal and vertical directions through the pore spaces between sand grains, as well as through fractures. Other aquifers, such as the upper part of the Prairie du Chien Group, are composed mostly of carbonate rock in which water is transmitted through a relatively dense network of fractures and solution cavities. However, layers designated as aquifers can locally contain low permeability strata that serve as small, internal aquitards including parts of the upper Mt. Simon Sandstone and the lower Jordan Sandstone.

Most layers designated as aquitards in the county have a much lower permeability in the vertical direction than do aquifers. Examples in Washington County include the lower Jordan Sandstone, St. Lawrence, and Eau Claire Formations, whose rocks are composed mostly of very fine-grained sandstone and shale with small, poorly connected pore spaces. Carbonate rock with relatively sparse fractures, such as the lower part of the Prairie du Chien Group (Oneota Dolomite), are also aquitards. However, layers designated as aquitards with very low permeability in the vertical direction may locally contain horizontal fractures that are conductive enough to yield large quantities of water, including the St. Lawrence Formation.

Horizontal and vertical fractures are more common where bedrock layers are at or near the bedrock surface. As a result, aquitards in such conditions are likely to have higher permeability compared with more deeply buried portions of the same formation, and may have a diminished ability to retard water flow to underlying aquifers. There is no precise boundary between shallow and deep conditions of burial, but in most areas of southeastern Minnesota about 50 feet (15 meters) of depth below the bedrock surface is considered a best approximation (Runkel and others, 2006a).

In addition to this hydrostratigraphic classification, the Minnesota Department of Natural Resources, as Part B of the Washington County atlas, will conduct a thorough hydrogeologic study of the groundwater flow system, aquifer capacity, and aquifer sensitivity, which may result in modifications to this classification. Furthermore, designations of aquifers versus aquitards made here may not correspond precisely with those made for regulatory purposes by the Minnesota Department of Health.

DESCRIPTION OF MAP UNITS Od Decorah Shale (Upper Ordovician)—Dominantly grayish-green shale interbedded with thin

beds of fossiliferous limestone. Fossiliferous, yellowish-brown limestone beds are most common at the base of the Decorah Shale, and are recognized as the basal Carimona Member (Mossler, 2008). The Decorah Shale is present as erosional remnants capping Platteville mesas in the southwestern part of the county. Though no exposures exist in the county, water well logs indicate the Decorah Shale has a maximum preserved thickness of 40 feet (12 meters).

Opg Platteville and Glenwood Formations (Upper Ordovician)—The Platteville Formation is generally tan to gray, fossiliferous limestone and dolostone. The underlying Glenwood Formation is dominantly a green-gray, sandy shale. The Platteville Formation is the dominant uppermost bedrock unit across a large expanse of the southwestern part of the county. The combined thickness of the formations is 30 to 35 feet (9 to 11 meters).

Platteville Formation—The Platteville Formation is 25 to 30 feet (8 to 9 meters) thick. It is composed of tan to gray limestone and dolostone. It is commonly burrowed, mottled, and fossiliferous. It contains fine- to coarse-grained quartz sand and phosphate grains in the lowermost 2 feet (0.6 meter).

Glenwood Formation—The principal rock type of the Glenwood Formation is a grayish- green to brownish-gray, calcareous, sandy, and phosphatic shale. The Glenwood Formation is 3 to 7 feet (1 to 2 meters) thick.

Os St. Peter Sandstone (Middle to lower Ordovician)—The upper 100 to 140 feet (30 to 43 meters) of the St. Peter Sandstone is mostly a white to tan, fine- to medium-grained, friable quartzose sandstone. Bedding and structures are generally absent. It is exposed in patchy outcrops in the southern half of the county where glacial sediments are thin. The lowermost 10 to 40 feet (3 to 12 meters), referred to as the Pigs Eye Member, includes white to gray feldspathic shale and siltstone interbedded with coarser-grained sandstone similar to that of the Tonti Member. The Pigs Eye Member is not exposed in Washington County. The thickness of the St. Peter Sandstone varies from about 130 to 160 feet (40 to 49 meters). The basal contact of the formation with the underlying Shakopee Formation (unit Ops) is a major erosional unconformity (Smith and others, 1993).

Prairie du Chien Group (lower Ordovician)—Dominated by dolostone interlayered with lesser amounts of quartz sandstone. Outcrops are exposed along the tops of bluffs of the Mississippi and St. Croix River valleys; small patchy outcrops are also present in southeastern Washington County where the Quaternary sediments are thin. The Prairie du Chien Group is a significant source of rock aggregate in this part of the county. The Prairie du Chien Group is formally divided into two formations: the Shakopee Formation and underlying Oneota Dolomite. Geophysical logs and drill cuttings in the northern part of the county and within parts of the Hudson–Afton horst that span the St. Peter through the Jordan Sandstones are lacking and water well records are typically inadequate to

distinguish the Oneota Dolomite from the Shakopee Formation and St. Peter Sandstone from the sandy upper Shakopee Formation. Therefore, the mapped distribution of these units is more speculative in these areas. The thickness of the Prairie du Chien Group beneath the St. Peter Sandstone varies greatly across Washington County, from less than 50 to nearly 300 feet (15 to 91 meters; Fig. 5). This is interpreted to be due to several factors, including syndepositional faulting along the Hudson–Afton horst, and erosion of the Shakopee Formation prior to deposition of the St. Peter Sandstone. This erosional surface is the unconformity that marks the contact between the Shakopee Formation and overlying St. Peter Sandstone.

Ops Shakopee Formation (Lower Ordovician)—A heterolithic unit composed mainly of light brown, thin- to medium-bedded dolostone, sandy dolostone, sandstone, and shale. It contains oolites, intraclasts, fossilized microbial mounds, chert nodules, quartz sandstone, and green-gray shale partings. Thickness of the Shakopee Formation beneath the St. Peter Sandstone is quite variable within the area of the Hudson–Afton horst, ranging from almost absent to nearly 200 feet (61 meters) thick. It appears to be thickest in the most southeast part of the county, east of the Hastings fault, where it is nearly 200 feet (61 meters) thick. On the opposite side of the horst, on the west side of the Cottage Grove fault, it reaches thicknesses of 115 feet (35 meters) and appears to progressively thin towards the northwest. Based on a limited amount of drill cuttings and geophysical data within the Hudson–Afton horst, it appears that the Shakopee Formation thins to less than 50 feet (15 meters) and may even be absent beneath the St. Peter Sandstone at several locations (see cross section A–A').

Opo Oneota Dolomite (Lower Ordovician)—Predominantly a yellowish-gray to light brown, medium- to thick-bedded dolostone that generally lacks sedimentary features such as oolites and quartz sand characteristic of the Shakopee Formation, except in its lowermost part. The formation contains two members, the Hager City and the Coon Valley, but they are not mapped separately. The basal Coon Valley Member is a heterolithic unit composed of thinly bedded dolostone, sandy dolostone, and beds of fine- to coarse-grained, poorly sorted quartz sandstone. Thickness of the Coon Valley Member is quite variable, it is locally absent to 30 feet (9 meters) thick. There appears to be a slight trend in its thickness along the Hudson–Afton horst whereby it is thickest on the down dropped sides of the faults (20 to 30 feet [6 to 9 meters]) and thinner between the faults (10 to 15 feet [3 to 5 meters]). It also appears to be thin to absent towards the western edge of the county and within the central and northern parts of the county. The Hager City Member is primarily very finely crystalline dolostone, with microbial textures. Its thickness also shows a similar trend to the Coon Valley Member in being thicker along the down-dropped sides of the Hastings and Cottage Grove faults (50 to 70 feet [15 to 21 meters]) and thinner between them (40 to 50 feet [12 to 15 meters]).

_j Jordan Sandstone (Upper Cambrian)—Dominantly white to yellow, very fine- to coarse-grained, friable quartz sandstone characterized by coarsening-upward sequences consisting of two interlayered facies (Runkel, 1994). They are medium- to coarse-grained, cross-stratified, generally friable, quartz sandstone; and very fine-grained, commonly bioturbated, feldspathic sandstone with lenses of siltstone and shale. The major part of the very fine-grained facies forms a regionally continuous interval that gradationally overlies the St. Lawrence Formation (unit _s), although there are lithologically similar intervals intercalated with the medium- to coarse-grained facies at higher stratigraphic intervals. An unconformity, locally marked by thin beds of quartz pebble conglomerate and silcrete-cemented sandstone clasts (Runkel and others, 1999, 2007), separates the Jordan Sandstone from the overlying Oneota Dolomite. The Jordan Sandstone is exposed along the Mississippi and St. Croix River bluffs and ranges in thickness from 80 to 100 feet (24 to 29 meters). In the northernmost part of the county near Scandia, it appears to thin to 65 to 70 feet (20 to 21 meters) thick.

_s St. lawrence Formation (Upper Cambrian)—The St. Lawrence Formation is principally light gray to yellowish-gray and pale yellowish-green, dolomitic, feldspathic siltstone with interbedded, very fine-grained sandstone and shale. Lenses and layers of light gray, finely crystalline, sandy dolostone occur locally, especially in the lowermost few feet of the formation (Runkel and others, 2006a). The formation is 35 to 45 feet (8 to 12 meters) thick. The upper contact with the Jordan Sandstone is conformable and gradational. The gradational nature of the contact in well cuttings and on natural gamma logs can make selecting a precise contact between these formations difficult.

_t Tunnel City Group (Upper Cambrian)—The Tunnel City Group, formerly named the Franconia Formation (Berg, 1954), varies from about 160 to 180 feet (49 to 55 meters) in thickness across Washington County. It is formally divided into two formations: the Mazomanie and the Lone Rock Formations (Mossler, 2008). The Mazomanie Formation is dominantly white to yellowish-gray, fine- to medium-grained, cross-stratified, generally friable, quartz sandstone. Glauconitic grains typically are rare to absent and never exceed 5 percent (Berg, 1954). Some beds contain brown, intergranular dolomite cement. Skolithos burrows and sandstone intraclasts are common along discrete horizons. The Lone Rock Formation underlies the Mazomanie Formation and intertongues with it. It consists of pale yellowish-green, very fine- to fine-grained glauconitic, feldspathic sandstone and siltstone, with thin, greenish-gray shale partings. Thin beds with dolomitic intraclasts are common. In northeastern Washington County, individual tongues of Mazomanie Formation are as thick as 50 feet (15 meters), and the Mazomanie Formation as a whole can reach thicknesses of 100 feet (30 meters). The Mazomanie Formation thins to the south, where it is progressively replaced laterally by the Lone Rock Formation. As a result, in southern Washington County the Mazomanie Formation is less than 25 feet (8 meters) thick to absent. The upper contact of the Tunnel City Group with the St. Lawrence Formation is conformable. The contact is fairly sharp and the contrast between the siltstone and shale of the St. Lawrence Formation, and underlying fine- to medium-grained, quartzose sandstone in the Mazomanie Formation of the Tunnel City Group, is distinct and typically marked by an intraclastic conglomerate.

_w Wonewoc Sandstone (Upper Cambrian)—This sandstone unit, formerly referred to as the Ironton-Galesville Sandstone, is composed mostly of fine- to coarse-grained, moderately to well sorted, light gray, cross-stratified, quartz sandstone (Mossler, 2008). White, brown, and black linguliform brachiopod shells are locally abundant. The upper part is the coarsest-grained; the lower part is finer-grained, better sorted, and progressively finer-grained toward its base. The very fine-grained sandstone in the lower part is feldspathic. The thickness of the formation is 45 to 75 feet (14 to 23 meters). The Wonewoc Sandstone is conformable with overlying and underlying formations; however, there is a subtle unconformity marked by a pebbly sandstone layer within the formation (Runkel and others, 1998).

_e Eau Claire Formation (Middle to Upper Cambrian)—The formation is composed of yellowish-gray to pale olive-gray, fine- to very fine-grained, feldspathic sandstone, siltstone, and shale. White and brown linguliform brachiopod shells are common. The formation ranges from 80 to 100 feet (24 to 30 meters) in thickness. The contact with the Mt. Simon Sandstone is conformable.

_m Mt. Simon Sandstone (Middle Cambrian)—The Mt. Simon Sandstone is pale yellowish-brown to grayish-orange-pink to light gray, medium- to coarse-grained, quartz sandstone. Interbeds of shale, siltstone, and very fine-grained feldspathic sandstone are common, particularly in its upper half (Mossler, 1992). Inarticulate brachiopod shells are locally common in the upper one-third of the formation. Thin beds of quartz-pebble conglomerate occur at several stratigraphic positions, and are especially abundant near the base of the formation. The Mt. Simon Sandstone unconformably overlies Mesoproterozoic rocks. Based on a limited number of full penetrations of the formation, it appears to have a maximum thickness of about 280 feet (85 meters).

MESOPROTEROZOIC

Keweenawan Supergroup

Mss Sandstone, siltstone, and local conglomerate (shown on cross sections and Fig. 2)—Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solor Church Formations; deposited in eolian, fluvial, and lacustrine environments.

Mbv North Branch volcanic sequence (shown on cross section C–C' and Fig. 2)—Part of the St. Croix horst.

Mpv Powder Mill volcanic sequence (~1,099 Ma; shown on cross sections and Fig. 2)—Part of the St. Croix horst.

REFERENCESAnderson, J.R., 2009, Bedrock geology of the Lake Elmo quadrangle, Ramsey and Washington Counties,

Minnesota: Minnesota Geological Survey Miscellaneous Map M-185, scale 1:24,000.Anderson, J.R., Runkel, A.C., Tipping, R.G., Barr, K., and Alexander, E.C., Jr., 2011, Hydrostratigraphy of a

fractured urban aquitard: Geological Society of America Field Guide 24, p. 457-475.Berg, R.R., 1954, Franconia Formation of Minnesota and Wisconsin: Geological Society of America Bulletin,

v. 66, p. 857-882.Cannon, W.F., Daniels, D.L., Nicholson, S.W., Phillips, J., Woodruff, L.G., Chandler, V.W., Morey, G.B.,

Boerboom, T.J., Wirth, K.R., and Mudrey, M.G., Jr., 2001, New map reveals origin and geology of North American Mid-continent Rift: Eos, v. 82, p. 97-101.

Chandler, V.W., 1991, Aeromagnetic anomaly map of Minnesota: Minnesota Geological Survey State Map S-17, scale 1:500,000.

Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2012, Karst conduit flow in the Cambrian St. Lawrence confining unit, southeast Minnesota, USA: Carbonates Evaporites, v. 27, no. 2, p. 167-172.

Jirsa, M.A., Boerboom, T.J., and Chandler, V.W., 2012, Geologic map of Minnesota Precambrian bedrock geology: Minnesota Geological Survey State Map S-22, scale 1:500,000.

Luhmann, A.J., Covington, M.D., Peters, A.J., Alexander, S.C., Anger, C.T., Green, J.A., Runkel, A.C., and Alexander, E.C., Jr., 2011, Classification of thermal patterns at karst springs and cave streams: Ground Water, v. 49, no. 3, p. 324-335.

Mossler, J.H., 1992, Sedimentary rocks of Dresbachian age (Late Cambrian), Hollandale embayment, southeastern Minnesota: Minnesota Geological Survey Report of Investigations 40, 71 p.

———2005a, Bedrock geology of the Hudson quadrangle, Washington County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-154, scale 1:24,000.

———2005b, Bedrock geology of the Stillwater quadrangle, Washington County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-153, scale 1:24,000.

———2006a, Bedrock geology of the Hastings quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-169, scale 1:24,000.

———2006b, Bedrock geology of the Prescott quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-167, scale 1:24,000.

———2006c, Bedrock geology of the St. Paul Park quadrangle, Washington and Dakota Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-166, scale 1:24,000.

———2006d, Bedrock geology of the Vermillion quadrangle, Dakota County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-168, scale 1:24,000.

———2008, Paleozoic stratigraphic nomenclature for Minnesota: Minnesota Geological Survey Report of Investigations 65, 76 p., 1 pl.

———2013, Bedrock geology of the Twin Cities ten-county metropolitan area, Minnesota: Minnesota Geological Survey Miscellaneous Map M-194, scale 1:125,000.

Mossler, J.H., and Bloomgren, B.A., 1990, Bedrock geology, pl. 2 of Swanson, L., and Meyer, G.N., eds., Geologic atlas of Washington County, Minnesota: Minnesota Geological Survey County Atlas C-5, scale 1:100,000, 7 pls.

Mossler, J.H., and Tipping, R.G., 2000, Bedrock geology and structure of the seven-county Twin Cities metropolitan area, Minnesota: Minnesota Geological Survey Miscellaneous Map M-104, scale 1:250,000.

Paillet, F.L., Lundy, J., Tipping, R., Runkel, A.C., Reeves, L., and Green, J., 2000, Hydrogeologic characterization of six sites in southeastern Minnesota using borehole flowmeters and other geophysical tools: U.S. Geological Survey Water-Resources Investigations Report 00-4142, 33 p.

Runkel, A.C., 1994, Deposition of the uppermost Cambrian (St. Croixan) Jordan Sandstone, and the nature of the Cambrian–Ordovician boundary in the upper Mississippi valley: Geological Society of America Bulletin, v. 106, p. 492-506.

———1996, Bedrock geology of Houston County, Minnesota: Minnesota Geological Survey Open-File Report 96-4, 11 p., 3 pls., scale 1:100,000.

Runkel, A.C., McKay, R.M., Miller, J.F., Palmer, A.R., and Taylor, J.F., 2007, High resolution sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: The role of special conditions of cratonic interiors in development of stratal architecture: Geological Society of America Bulletin, v. 119, nos. 7/8, p. 860-881.

Runkel, A.C., McKay, R.M., and Palmer, A.R., 1998, Origin of a classic cratonic sheet sandstone: Stratigraphy across the Sauk II–Sauk III boundary in the upper Mississippi valley: Geological Society of America Bulletin, v. 110, p. 188-210.

Runkel, A.C., Miller, J.F., McKay, R.M., Shaw, T.H., and Bassett, D.J., 1999, Cambrian-Ordovician boundary strata in the central mid-continent of North America: Acta Universitatis Carolinae Geologica, v. 43, p. 17-20.

Runkel, A.C., Mossler, J.H., Tipping, R.G., and Bauer, E.J., 2006a, A hydrogeologic and mapping investigation of the St. Lawrence Formation in the Twin Cities metropolitan area: Minnesota Geological Survey Open-File Report 06-4, 20 p.

Runkel, A.C., Steenberg, J.R., Tipping, R.G., and Retzler, A.J., 2014a, Geologic controls on groundwater and surface water flow in southeastern Minnesota and its impact on nitrate concentrations in streams: Minnesota Geological Survey Open-File Report 14-2, 70 p.

Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Alexander, S.C., 2006b, Hydrostratigraphic characterization of intergranular and secondary porosity in part of the Cambrian sandstone aquifer system of the cratonic interior of North America: Improving predictability of hydrogeologic properties: Sedimentary Geology, v. 184, p. 281-304.

Runkel, A.C., Tipping, R.G., Alexander, E.C., Jr., and Green, J.A., 2003, Hydrogeology of the Paleozoic bedrock in southeastern Minnesota: Minnesota Geological Survey Report of Investigations 61, 105 p., 2 pls.

Runkel, A.C., Tipping, R.G., Green, J.A., Jones, P.M., Meyer, J.R., Parker, B.L., Steenberg, J.A., and Retzler, A.J., 2014b, Hydrogeologic properties of the St. Lawrence aquitard, southeastern Minnesota: Minnesota Geological Survey Open-File Report 14-4, 56 p.

Sims, P.K., and Zeitz, I., 1967, Aeromagnetic and inferred Precambrian paleogeographic map of east-central Minnesota and part of Wisconsin: U.S. Geological Survey Geophysical Investigations Map GP-563, 6 p., scale 1:250,000.

Smith, G.L., Byers, C.W., and Dott, R.H., Jr., 1993, Sequence stratigraphy of the lower Ordovician Prairie du Chien Group on the Wisconsin arch and in the Michigan basin: American Association of Petroleum Geologists Bulletin, v. 77, p. 49-67.

Tipping, R.G., Runkel, A.C., Alexander, E.C., Jr., and Alexander, S.C., 2006, Evidence for hydraulic heterogeneity and anisotropy in the mostly carbonate Prairie du Chien Group, southeastern Minnesota, USA: Sedimentary Geology, v. 184, p. 305-330.

Carbonate rock within 50feet of the land surface

Quartzose sandrock within 50 feet of the land surface

Active quarry

Figure 3. Map showing where carbonate and quartzose sandrock are present within 50 feet (15 meters) of the land surface in Washington County. Brown represents quartzose sandrock (including the Jordan, Wonewoc, and St. Peter Sandstones) and beige represents carbonate rock (including the Platteville and Shakopee Formations and Oneota Dolomite). The active quarry operations in Washington County are shown in black. This figure was generated using the bedrock topographic surface and bedrock geology polygons, which are standard Geographic Information System (GIS) products of a county geologic atlas.

Upp

er O

rdov

icia

n

Decorah Shale

Platteville and Glenwood Formations

St. Peter Sandstone

Shakopee Formation

Oneota Dolomite

M

iddl

e O

rdov

icia

n

JordanSandstone

St. LawrenceFormation

Tunn

el C

ity G

roup

WonewocSandstone

Eau ClaireFormation

Mt. SimonSandstone

Prai

rie d

u C

hien

Gro

upG

alen

a G

roup

Hager City

CoonValley

Lone RockFormation

m

e

w

t

Os

Opg

Od

Low

er O

rdov

icia

nU

pper

Cam

bria

nM

iddl

e C

ambr

ian

Mesoproterozoic and olderrocks, undifferentiated

80-1

00~2

00-2

8014

0-16

030

-35

Ph

G

GG

G

GG

G

G

G

G

G

s

j

Opo

Mazomanie Formation

<40

50-8

090

-120

85-1

0035

-45

160-

180

50-6

0

Not

Show

n

NO

T EX

POSE

D IN

WAS

HIN

GTO

N C

OU

NTY

Ops

Pigs Eye

Tonti

Era

Syst

em-S

erie

s

Group,Formation,

Member

Lithology

Lithostratigraphicunit

Composite natural gamma log

Hyd

rost

ratig

raph

ic

prop

ertie

s

0 100

Increasing count

Map

sym

bol

Thic

knes

s (in

feet

)

API-G units

Relatively high permeability (aquifer)

Relatively low permeability (except for fractures, aquitard)

High permeability bedding fracture known to be common

HYDROSTRATIGRAPHIC PROPERTIES KEY

Chert

Oolites

Glauconite

Stromatolites

Shells

Bioturbation

Pebbles

Intraclasts

Cross-bedded (planar)

Cross-bedded (trough)

Cross-bedded (hummocky)

Dolomitic

Vugs

Contact marks a major erosional surface

Siltstone

Shale

LITHOLOGY KEY

G

Dolostone

Sandstone

Sandy dolostone

Very fine- to fine-grained

Medium- to coarse-grained

Shaly

Fine- to medium-grained

Ph Phosphate grains

Limestone

PALE

OZO

IC

Figure 1. Generalized stratigraphic column depicting the lithology, thickness, vertical succession, age, and hydrostratigraphic properties for all units shown on the map, as well as the schematic depiction of relative competence in outcrop where exposed. The gamma log is a compilation of the following borehole geophysical logs on file at the Minnesota Geological Survey: County Well Index unique numbers 783609, 777305, and 256005.

GEOLOGIC ATLAS OF WASHINGTON COUNTY, MINNESOTA

CGF CGFZ

HFHFZ

FCG

HAH

Mbv

Mss

Mpv

(

(((

((

((

((

((

((

((

((

((

((

((

(

Mss

Figure 2. Faults that displace Paleozoic bedrock in Washington County superimposed on a map of the first vertical derivative aeromagnetic data (Chandler, 1991) and the underlying Mesoproterozoic rock units (Jirsa and others, 2012). Paleozoic faults and fault zones where they cluster in the southern part of the map (CGF—Cottage Grove fault, CGFZ—Cottage Grove fault zone, HF—Hastings fault, HFZ—Hastings fault zone) are subparallel to strong, abrupt, linearly extensive contrasts in magnetic intensity in the underlying Mesoproterozoic rocks associated with the Midcontinent Rift. The aeromagnetic data display where a great thickness of magnetic Mesoproterozoic rift basalts (unit Mpv) have been brought near the surface in an inverted graben known as the Hudson–Afton horst (HAH), bounded by thrust faults, shown by black lines with teeth. Faults in the northeastern corner of the county that bound what is known as the Falls Creek Graben (FCG) are subparallel to foliation trends of underlying Mesoproterozoic lava flows (unit Mbv). Due to their similar trends and close proximity, all Paleozoic faults are interpreted to have originated from reactivation of deep Mesoproterozoic structures. Abrupt thickness changes in the Prairie du Chien Group across the Hudson–Afton horst indicate that faults were reactivated during Early Paleozoic (Early to Middle Ordovician) time.

Digital base modified from the Minnesota Department of Transportation BaseMap data; digital base annotation by the Minnesota Geological Survey.

Elevation contours were derived from the U.S. Geological Survey 30-meter Digital elevation Model (DeM) by the Minnesota Geological Survey.

universal transverse Mercator Projection, grid zone 151983 north american Datum

GIS compilation by r.S. livelyedited by lori robinson

©2016 by the regents of the university of Minnesota

The University of Minnesota is an equal opportunity educator and employer

A A'

UD

MAP SYMBOLS

Geologic contact, approximatly located

Geologic contact, inferred

Fault—Faults are inferred from abrupt changes in the elevation of stratigraphic units from subsurface and outcrop data. Letters indicate relative vertical displacement: U—up, D—down. Dashed lines represent areas where it is inferred.

Fold—Axial trace of anticline, syncline. Fold limbs typically have shallow dips and are inferred from subsurface data.

Active quarry

Bedrock outcrop

Location of geologic cross section

F M

Cross sections—Every attempt has been made for the cross sections to match all geologic interpretations made from the County Well Index data. Symbology is the same as on the bedrock map. Only a small number of drill holes intersected Mesoproterozoic bedrock, thus the relief is generalized and inferred from the thickness of the Mt. Simon Sandstone. Dashed vertical lines represent Precambrian faults and the long dashed lines in C–C' represent volcanic flows inferred from geophysical imagery.

m

e

w

s

j

Od

PALEOZOIC

CORRELATION OF MAP UNITS

unconformity

t

OpoLower Ordovician

unconformity

Upper Cambrian

Middle Cambrian

MESOPROTEROZOIC

unconformity

Opg

Os Middle Ordovician

Upper Ordovician

Ops

unconformity

Mss

Mbv

Mpv

unconformity

Michigan’s Geology and Groundwater - Michigan …miwetlands.org/.../2017/10/Michigans-Geology-and-Groundwater.pdf · throughout geologic history ... § Bedrock geology varies across

River of History - Historic Saint Paul Corp › sites › default › files › 2 River_Ch_1.pdftial for site preservation. General Geology Bedrock Geology • Southeastern Minnesota,

British Columbia bedrock geologycmscontent.nrs.gov.bc.ca/geoscience/Publication... · Geology - Faults Geology - Basins Geology - Basins (transparent) Geology - Terranes Geology -

Bedrock Geology of the South Island Aggregates Stebbings Road

Forsmark site investigation – Bedrock geology – overview and

Bedrock geology and Quaternary sediments in the …Bedrock geology and Quaternary sediments in the Lista basin, S. Norway HANS HOLTEDAHL Holtedahl, H.: Bedrock geology and Quaternary

STRATIGRAPHY AND BEDROCK GEOLOGY OF …dec.vermont.gov/sites/dec/files/geo/specialbulletin/Mehrtens_1995...stratigraphy and bedrock geology of parts of the st. albans and georgia quadrangles,

Bedrock and Pleistocene Geology of Wayne County, Ohio

Index to Maps, Bedrock Geology, 1891 - 1991, Northern Sheet€¦ · Title: Index to Maps, Bedrock Geology, 1891 - 1991, Northern Sheet Author: Publication Services Section Created

Bedrock Geology and Bedrock Topography GIS of Ohio: New ... · geology and bedrock topography data sets form the framework for the new 1:500,000-scale bedrock geology and bedrock

Bedrock Geology C.C - Stanley ppt

Ordovician Karst of Southeast Minnesota Field Trip Guidebook · Figure 2 is a cross between the bedrock geology and depth to bedrock maps in southeast Minnesota. In the red areas,

Bedrock Geology of the Chepachet Quadrangle Providence

Bedrock Geology of Hardin County, Illinois

Bedrock Geology Virtual Tour - Maine.gov Geology Virtual Tour Maine Geological Survey Bedrock Exposures The Knife Edge of Mount Katahdin is a breathtaking bedrock exposure. oto

Bedrock Geology of Saline Mines Quadrangle - ISGS · Bedrock Geology of Saline Mines Quadrangle ... Ore bodies are of three types: (1) ... and other sedimentary structures

Bedrock Geology and Mineral Resources of the Knoxville 1

Appendix A - Geology of Minnesota

BEDROCK GEOLOGY OF THE SANTAN …repository.azgs.az.gov/sites/default/files/dlio/files/nid947/ofr... · BEDROCK GEOLOGY OF THE SANTAN MOUNTAINS,PINAL AND MARICOPA COUNTIES, ARIZONA

Bedrock Geology, Phantom Lake Section, Creighton, Saskatchewan€¦ · Bailey, K.A. (2005): Bedrock geology, Phantom Lake Section , Creighton, Saskatchewan (part of NTS 63K/12); 1:10

Overview of Indiana Bedrock Geology 6 - Bedrock geology.pdf · Department of Geological Sciences | Indiana University (c) 2012, P. David Polly Paleontology and Geology of Indiana

GEOTECHNICAL REPORT PROPOSED TRANSFER ...Bedrock Geology The 1955 bedrock geology map of the Chepachet quadrangle indicates that bedrock in the vicinity of the site consists of Ponaganset

Bedrock Geology of the Kassler Quadrangle Colorado · Bedrock Geology of the Kassler Quadrangle Colorado By GLENN R. SCOTT GEOLOGY OF THE KASSLER QUA.DRANGLE, JEFFERSON AND DOUGLAS

Bedrock Geology of Rhode Island - pubs.usgs.gov · Quincy Granite of northern Rhode Island were exposed by erosion before Penn ... Mr. Clifton N. Lovenberg, ... 6 BEDROCK GEOLOGY

5: BEDROCK GEOLOGY

Bedrock geology of northern and central Wintering Lake, Manitoba … › iem › geo › field › roa05pdfs › GS-05.pdf · 2014-06-09 · Böhm, C.O. 2005: Bedrock geology of northern

Bedrock Geology

Pre-Carboniferous Bedrock Geology of the ... - Nova Scotia

bedrock geology of barre area, the central; massachusetts

GEOLOGIC STRUCTURES “Architecture of bedrock” Structural Geology- –shapes, –arrangement, –interrelationships of bedrock –units & forces that cause them

Bedrock Geology Coastlines

THE BEDROCK GEOLOGY OF VARANGER PENINSULA, … · 2017-01-05 · 6 The bedrock geology of Varanger Peninsula, Finnmark, North Norway: an excursion guide BEDROCK GEOLOGY OF THE VARANGER

Bedrock geology of northern and central Wintering Lake ... · Bedrock geology of Wintering Lake The simplified bedrock geology of northern and central Wintering Lake, based on the

1993 12 Correlation of Bedrock Geology Indoor Radon--Where

Oskarshamn site investigation. Bedrock geology – · PDF fileTänd ett lager: P, R eller TR. Oskarshamn site investigation Bedrock geology – overview and excursion guide Carl-Henric