Contributions to the Geology of Pine County, Minnesota

MINNESOTA GEOLOGICAL SURVEY REPORT OF INVESTIGATIONS 60

CONTRIBUTIONS TO THE GEOLOGY OF PINE COUNTY, MINNESOTA

Terrence J. Boerboom, Project Manager

St. Paul, Minnesota 2002

iii This publication is accessible from the home page of the Minnesota Geological Survey (http://www.geo.umn.edu/mgs) as a PDF file readable with Acrobat Reader 4.0.

Recommended citation— Boerboom, T.J., Project Manager, 2002, Contributions to the geology of Pine County, Minnesota: Minnesota Geological Survey Report of Investigations 60, 91 p.

Cartography and other drafting by Philip Heywood

Edited by Lynn Swanson

Minnesota Geological Survey 2642 University Avenue West Saint Paul, Minnesota 55114-1057

Telephone: 612-627-4780 Fax: 612-627-4778 E-mail address: [email protected] Web site: http://www.geo.umn.edu/mgs

ISSN 0076-9177

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iv CONTRIBUTORS

E. Calvin Alexander, Jr. Professor, Department of Geology and Geophysics, University of Minnesota, Minneapolis

Scott C. Alexander Junior Scientist, Department of Geology and Geophysics, University of Minnesota, Minneapolis

Terrence J. Boerboom Scientist, Minnesota Geological Survey, St. Paul

Val W. Chandler Acting Director, Minnesota Geological Survey, St. Paul; adjunct faculty, Department of Geology and Geophysics, University of Minnesota, Minneapolis

Alan R. Knaeble Senior Scientist, Minnesota Geological Survey, St. Paul

R.S. Lively Information Technology Supervisor, Minnesota Geological Survey, St. Paul

C.J. Patterson Senior Scientist, Minnesota Geological Survey, St. Paul; adjunct faculty, Department of Geology and Geophysics, University of Minnesota, Minneapolis

Anthony C. Runkel Senior Scientist and Chief Geologist, Minnesota Geological Survey, St. Paul; adjunct faculty, Department of Geology and Geophysics, University of Minnesota, Minneapolis

Beverly L. Shade Director, Proyecto Espeleologico Purificacion, P.O. Box 8424, Austin, Texas, 78713

v INTRODUCTION This publication expands on information presented on the map plates of Part A of the Geologic Atlas of Pine County, Minnesota. The explanations given on those plates tend to be technical, and they include only that information necessary to read the maps. The papers included in this volume expand on the map explanations to help the user understand the geology and geologic framework of Pine County. The maps are intended only to provide general geologic information for use by (1) county residents; (2) resource managers and planners at various levels of government; (3) geologists, hydrologists, and others working in the county, and (4) those interested in learning about the geology of Pine County. Additional information is available in computerized data bases, such as the County Well Index, and in Arcview™ files that accompany Part A of the atlas. Because the maps in Part A of the atlas were constructed at a scale of 1:100,000, one must closely examine the data available for a given location before using them for detailed, site-specific studies, to determine the reliability of the geologic interpretations made for that area.

vi CONTENTS CHAPTER 1— Bedrock geology of Pine County, Minnesota, by Terrence J. Boerboom, Anthony C. Runkel, and Val W. Chandler Introduction ...... 1 Paleozoic bedrock ...... 1 Precambrian bedrock ...... 3 Paleoproterozoic and Archean rocks ...... 3 McGrath Gneiss (Archean) ...... 3 Denham Formation and related rocks (Paleoproterozoic) ...... 4 Volcanic and sedimentary rocks of the Midcontinent rift system (Mesoproterozoic) ...... 6 Volcanic rocks (Mesoproterozoic) ...... 8 Basalt outcrops at Pine City ...... 8 Basalt outcrops at the Kettle River east of Hinckley ...... 9 Other bedrock outcrops ...... 10 Sedimentary rocks (Mesoproterozoic) ...... 10 Fond du Lac Formation ...... 10 Unnamed sedimentary units overlying the St. Croix horst ...... 11 Hinckley Sandstone ...... 14 Summary ...... 18 History of copper exploration ...... 18 References ...... 18

CHAPTER 2— History of glaciation in Pine County, Minnesota by C.J. Patterson and A.R. Knaeble Introduction ...... 21 Preglacial landscape ...... 24 Bedrock distribution and buried bedrock topography ...... 24 Thickness of Quaternary sediments overlying bedrock ...... 25 History of glacial advances ...... 25 Late Wisconsin glacial activity ...... 26 Glacial activity of the Superior lobe ...... 28 Emerald phase ...... 28 St. Croix phase ...... 28 Glacial Lake Lind ...... 28 Automba phase ...... 28 Beroun phase ...... 30 Hinckley, North Hinckley, Grindstone, and Sandstone phases ...... 30 Askov, Lookout Tower, Kerrick, and upper and lower Split Rock phases ...... 33 Nickerson phase ...... 36 Glacial activity of the Grantsburg sublobe ...... 37 Pine City and West Rock phases ...... 37 Glacial Lake Grantsburg ...... 37 Late- and postglacial activity ...... 37 Glacial Lake Nemadji and the Kettle River ...... 37 Glacial Lake Duluth and the Brule and St. Croix Rivers ...... 38 Snake River and Cross Lake ...... 38 Wind erosion ...... 40 References ...... 40 vii CONTENTS continued CHAPTER 3— Investigation of stream-like magnetic anomalies in Pine County, Minnesota, by Val W. Chandler, Terrence J. Boerboom, and R.S. Lively Introduction ...... 43 General geology ...... 43 Aeromagnetic survey method ...... 43 Sandstone area ...... 45 Grindstone Lake area ...... 45 Sources of magnetic anomalies ...... 49 Model studies ...... 50 Conclusions ...... 52 References ...... 52

CHAPTER 4— Karst features in Pine County, Minnesota by Beverly L. Shade, Scott C. Alexander, and E. Calvin Alexander Introduction ...... 55 Karst features ...... 56 Background ...... 56 Global distribution of features ...... 56 Previous work ...... 56 Are the sinkholes in Pine County karst features? ...... 58 Observations ...... 59 Sinkholes ...... 59 Sinkhole D222 ...... 59 Sinkhole D144 ...... 60 Sinkhole D127 ...... 61 Sinkhole D355 ...... 64 Streamsinks ...... 64 Springs ...... 65 Caves ...... 65 Composite features ...... 65 Interpretation ...... 65 Sinkhole distribution relative to bedrock type ...... 65 Sinkhole distribution relative to depth to bedrock ...... 67 Sinkhole distribution relative to glacial features ...... 68 Sinkhole formation ...... 68 Collapse sinkholes ...... 68 Subsidence sinkholes ...... 68 Composite features ...... 69 What is not a sinkhole? ...... 69 Acknowledgments ...... 72 References ...... 72

viii CONTENTS continued

APPENDIX A— Geophysical and geologic logs of core recovered from five boreholes in Pine County, Minnesota ...... 73 Explanation ...... 73 Minnesota Geological Survey borehole log MGS-PCR1 ...... 74 Minnesota Geological Survey borehole log MGS-PCR2 ...... 76 Minnesota Geological Survey borehole log MGS-PCR3 ...... 78 Minnesota Geological Survey borehole log MGS-PCC1 ...... 79 Minnesota Geological Survey borehole log MGS-PCC2 ...... 81

APPENDIX B— Inventories of known karst features in Pine County, Minnesota ...... 83 Appendix Table B1. Pertinent information on 262 sinkholes in Pine County, Minnesota ...... 84 Appendix Table B2. Pertinent information on 24 streamsinks in Pine County, Minnesota ...... 90 Appendix Table B3. Pertinent information on 31 streamsinks in Pine County, Minnesota ...... 91

ix COUNTY ATLAS PLATES

The following is a listing of plates prepared for the Geologic Atlas of Pine County, Minnesota, Part A. The list includes short descriptions of the information contained on each plate, as well as suggestions as to how the various plates might be used for planning purposes. The use cited for each plate represents a single suggestion. It is left to atlas users to envision ways in which information from the various plates can be brought together to achieve their goals. 1 The Data-Base Map shows the location of factual data, for example, water-well logs, exploratory drill holes, and outcrops. Other information, such as well depth and stratigraphy, is directly accessible through Arcview� data files. The Data-Base Map can be used to evaluate the reliability of the geologic interpretations shown on other maps of the atlas. 2 The Bedrock Geology Map and Cross Sections shows the types of bedrock that are likely to be encountered in a given area, either beneath glacial materials or at the land surface, and the attitude of structural features like bedding and metamorphic foliation. Knowledge of the type of bedrock present below the land surface is essential when considering the likely quantity or quality of ground-water resources or the possibility of finding rock suitable for aggregate production. 3 Supplemental Data on Bedrock Geology and Geophysics shows the bedrock geology of some areas in the county where abundant outcrops permitted detailed mapping that could not be portrayed at the 1:100,000 scale of the geologic map on Plate 2. The plate also includes geophysical maps that were integral to interpreting the bedrock geology. The plate can be used by those who want to understand how geophysical information was used in the construction of Plates 2 and 6 (see description below), and for those interested in examining the geology of the areas portrayed in detail. For example, the understanding of materials encountered in drilling water wells can be better understood by examining similar rocks in outcrop. 4 The Surficial Geology plate shows the geology of the land surface. It can be used to gain general knowledge of the character of material at the surface—for example, sand-rich versus clay-rich material might be important in consideration of well-head protection areas. 5 Quaternary Stratigraphy shows the geology of Quaternary materials (unconsolidated sediment deposited by glacial activity) in cross sectional views. It is intended to demonstrate the types and distribution of the material present between the land surface and the underlying bedrock and can be used to understand the three- dimensional composition and distribution of glacial deposits, such as buried aquifers. 6 The Bedrock Topography, Depth to Bedrock, and Sinkhole Distribution maps on this plate show the "ups and downs" of the bedrock surface, the depth to bedrock at a given location, the distribution of mapped sinkholes, and cross sections of some excavated sinkholes. It can be used to ascertain the approximate depth to bedrock in a particular place, as, for example, an area where bedrock is covered by a thin layer of sandy till and contains sinkholes nearby; higher protection status may be required than for an area where the bedrock is covered by a thick, clay-rich glacial till. 7 The Geologic Endowment plate contains two maps that show places where one might find deposits of surficial aggregate (sand and gravel), accessible bedrock suitable for aggregate, and, possibly, dimension stone. The plate includes items of interest for mineral exploration, such as copper test pits, showings, and locations of mineral exploration drill holes. It also has a map showing the locations of potential sources of aggregate that may be developed in the future. Part B of the Geologic Atlas of Pine County, Minnesota, is published separately by the Minnesota Department of Natural Resources, Division of Waters. It will include plates that portray the hydrogeology and geologic sensitivity to pollution. This work necessarily follows the geologic mapping completed by the Minnesota Geological Survey for Part A of the atlas

x Chapter 1

BEDROCK GEOLOGY OF PINE COUNTY, MINNESOTA

By Terrence J. Boerboom, Anthony C. Runkel, and Val W. Chandler

INTRODUCTION basement. In particular, aeromagnetic data on Plate 3 of the Pine County geologic atlas (Boerboom and Chandler, The term bedrock refers to the rock that constitutes 2001) proved useful in distinguishing the major bedrock the earth's crust. In places, bedrock can be seen on the units and in interpreting the structural attributes of the surface in outcrop, but in nearly all of Pine County volcanic units in the eastern part of the county. bedrock is covered by unconsolidated sediment left behind by glacial processes (see Patterson and Knaeble, PALEOZOIC BEDROCK 2002; this volume). Most bedrock outcrops in Pine County are located along rivers that have eroded through Paleozoic rocks are present along the southern the glacial sediment and exposed the underlying bedrock. margin of the county, where they form scattered erosional However, in some areas the glacial cover is thin and remnants; the thickness of the remnants is generally 50 knobs of bedrock protrude through the glacial sediment or fewer feet. They are the northernmost known extent (Bauer, 2001; Data-base map, Plate 1 of the Pine County of Paleozoic strata that fill the Hollandale embayment geologic atlas). It was not possible to map every single of southeastern Minnesota. The distribution and outcrop in the time allotted, and, undoubtedly, there are thickness of the Paleozoic bedrock along the southern more outcrops present than shown on the data-base plate edge of the county is inferred entirely from drill-hole (Bauer, 2001). information and rare outcrops along the Snake and St. Most bedrock in Pine County is of Precambrian age Croix Rivers. The strata are invisible on aeromagnetic (about 2,550–1,000 Ma; Ma is an abbreviation for mega- and gravity geophysical maps because they are thin and annum—a period of one million years). Precambrian nonmagnetic. bedrock includes igneous and metamorphic crystalline Strata inferred to be of Paleozoic age in Pine County rocks, such as granite, schist, and basalt, as well as are composed chiefly of tan to white, friable, cross- sedimentary rocks, such as sandstone and siltstone. The stratified sandstone and subordinate interbeds of shale. Precambrian basement at the southern fringe of the county Medium- to coarse-grained sandstone is composed of is overlain by a thin veneer of Paleozoic-age sandstone greater than 98 percent moderately rounded to well and shale that constitute scattered erosional remnants rounded grains of quartz; finer grained sandstone and from a formerly continuous sheet of sedimentary strata. siltstone is feldspathic. Pebbles of vein quartz and pink The age of the Paleozoic rocks is about 510–450 Ma. quartzite as large as several centimeters in diameter are Bedrock geology is portrayed on Plate 2 (Boerboom, common. Red and green shale are present as thin laminae 2001a) of the Pine County geologic atlas and, in simplified separating cross-strata sets or are draped on foresets. form, on Figure 1. The geologic map shows the type of Fine-grained, disseminated glauconite and a mottled bedrock that is likely to be encountered in a given area, fabric are rare features of Paleozoic strata. either at the surface or, more commonly, beneath surficial The Paleozoic strata in Pine County cannot be glacial deposits. The map was constructed using data confidently assigned to individual lithostratigraphic units collected from bedrock outcrops, exploratory drill core, as have been mapped across much of the Hollandale cuttings samples, and interpretations of water-well logs embayment to the south. Several factors account for and geophysical data. Because most of the bedrock in the difficulty in applying the standard lithostratigraphic Pine County is covered by glacial sediment, interpretation nomenclature of Mossler (1987). Attributes typically of geophysical data played a key role in deciphering the used to recognize individual lithostratigraphic units lithologic and structural attributes of the Precambrian across much of the Hollandale embayment are obscured

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Figure 1. Simplified bedrock geologic map of Pine County showing the major subdivisions of bedrock by rock type, for example, sandstone, gneiss, and volcanic rock. The Archean and Paleoproterozoic rocks in the northwest corner of the county are part of the southern margin of the Penokean Orogen. The Keweenawan Supergroup rocks of Mesoproterozoic age are part of the Midcontinent rift system. Refer to the bedrock geologic map on Plate 2 of the Pine County geologic atlas (Boerboom, 2001a) for further information.

by facies changes that become pronounced north of the of Paleozoic strata in the extreme southern parts of Pine Twin Cities metropolitan area (Minneapolis and St. Paul). County include chips of very fine grained sandstone In addition, outcrops in Pine County and nearby areas are that appears most similar to the Dresbachian (Upper small and widely scattered, and subsurface information Cambrian) Eau Claire Formation. Quartzose sandstone is extremely limited. Furthermore, most outcrops and below the strata presumably is equivalent to the Mt. subcrops are dominated entirely by nonfossiliferous Simon Sandstone. Another set of well cuttings from quartzose sandstone that contains no attributes diagnostic Rush City Municipal Well 4 indicates that the Lower of individual stratigraphic units delineated to the south. Ordovician Shakopee Formation subcrops only three Limited information from three sites in Pine County miles south of Pine County. A core of mostly friable, fine- and nearby areas indicates that the outcrops and subcrops grained quartzose sandstone with a lowermost interval of shown as Paleozoic on the bedrock geologic map (Plate shale is generally similar to the Middle Ordovician St. 2) of the Pine County geologic atlas (Boerboom, 2001a) Peter Sandstone (sec. 11, T. 38 N., R. 20 W.). It contains probably include equivalents to units as old as the Late Cambrian Mt. Simon Sandstone, to as young as the Middle Ordovician St. Peter Sandstone. Well cuttings

2 pebbly sandstone and rare grains of Lower Ordovician faulted, and metamorphosed as a result of the Penokean Prairie du Chien dolostone. Orogeny, a period of crustal collision and mountain Upham (1888, p. 640) reported that white sandstone building that occurred about 1,880 Ma (Southwick and was quarried for dimension stone and used for the others, 1988). As a consequence of this collisional event, foundation of the courthouse in Grantsburg, Wisconsin. the Archean and Paleoproterozoic rocks in northwestern The quarry was reportedly operated by Mr. T.R. Rice, and Pine County have undergone at least one period of major it was located on the northeast bluff of the Snake River deformation and metamorphism, followed by a second, near its mouth, in the south half of the NE1/4 sec. 36, weaker deformation (Holm and others, 1998). Penokean T. 39 N., R. 20 W. There is a large outcrop of sandstone deformation has tilted the strata of the Denham Formation near the location given by Upham (1888), but no trace to a nearly vertical position. of a quarry was noted during the course of fieldwork for Thrust faults, a type of reverse fault in which the fault this project. plane dips at a shallow angle (in this case, to the south), are also a major component of the Penokean Orogen (the PRECAMBRIAN BEDROCK area affected by the Penokean Orogeny). Near Denham, The Precambrian basement of Pine County these low-angle reverse faults are inferred to have thrust (Fig. 1) includes rocks of Late Archean (2,550 Ma), a slice of the underlying McGrath Gneiss up into the Paleoproterozoic (about 2,100 Ma), and Mesoproterozoic Denham Formation. age (about 1,100 Ma). These rocks are the end product of varied geologic processes that through time included McGrath Gneiss (Archean) multiple episodes of igneous intrusion, sedimentation, The Archean McGrath Gneiss is the oldest rock in volcanism, and deformation (folding and faulting) Pine County; it has yielded a U-Pb zircon age of 2,550 ± accompanied by metamorphism. 14 Ma (Van Schmus and others, 2001), which reflects the The oldest rocks are located in the northwestern time at which the granite originally crystallized from a corner of the county, where they are locally well exposed magma. The McGrath was deformed and metamorphosed in outcrop. They include the Archean McGrath Gneiss during the Penokean Orogeny; the original coarse- and the Paleoproterozoic Denham Formation, as well as grained, porphyritic texture of the granite was variably unnamed metasedimentary rocks [the pelitic schist and recrystallized to the foliated, vaguely gneissic fabric metagraywacke unit (ps) on Plate 2; Boerboom 2001a], present in the rock today. both of Paleoproterozoic age. Mesoproterozoic volcanic The northernmost outcrops of the McGrath Gneiss and sedimentary rocks underlie the rest of Pine County; grade abruptly from the typical mineral assemblage of they are locally well exposed at the surface but generally quartz, orthoclase, plagioclase, and biotite to strongly are present in small and scattered outcrops. foliated, quartz- and sericite-rich schist containing large grains of relict orthoclase, but no plagioclase. The latter Paleoproterozoic and Archean Rocks assemblage, which is present near the overlying Denham The McGrath Gneiss, Denham Formation, and Formation, may be the product of metamorphism of an unnamed unit composed of pelitic schist and partially weathered granite, in which plagioclase feldspar metagraywacke are confined to the far northwestern had weathered to clay, but quartz and potassium feldspar corner of Pine County [Fig. 1 and Plates 2 (Boerboom, remained fresh. Studies of more recent weathered 2001a) and 3 (Boerboom and Chandler, 2001)] of the zones developed on Precambrian granitic rocks in Pine County geologic atlas. Compared to the volcanic southwestern Minnesota that are beneath sedimentary and sedimentary rocks mapped in the eastern portion rocks of Cretaceous age may provide an analogue of Pine County, these units have been much more (Setterholm and Morey, 1997). It has been demonstrated strongly deformed and metamorphosed. They lie at the that (1) plagioclase is one of the first minerals to alter to southern margin of the Penokean Orogen, a large area kaolinitic to illitic clay during the weathering process, of metamorphosed sedimentary and volcanic rocks and and (2) microcline feldspar and quartz are the minerals igneous intrusions that extends from near Moose Lake most resistant to weathering. Amphibolite-grade west to near Brainerd and south to St. Cloud. Collectively, metamorphism of a similarly weathered granite may have the rocks in the Penokean Orogen have been folded,

3 Figure 2. An outcrop of pillow basalt from the lowermost sequence in the Denham Formation, Pine County, Minnesota. The length of the hammer handle is 10 inches. led to the formation of the muscovite-rich assemblage isochron age of 2197 ± 39 Ma (Beck, 1988). Thus, the found in the upper part of the McGrath Gneiss. age of the Denham Formation is constrained to be 2550– 2,004 million years old. Denham Formation and Related Rocks The stratigraphic relationships and rock types of the (Paleoproterozoic) Denham are shown on Inset Map C on Plate 3 of the Pine The Denham Formation (Morey, 1978) is named after County geologic atlas (Boerboom and Chandler, 2001). the town of Denham in northwestern Pine County (Fig. 1). From bottom to top, the Denham Formation consists The formation consists of a heterogeneous but probably of fine-grained metamorphosed siltstone, dolomite- depositionally continuous sequence of pelitic to arenitic cemented arkosic arenite that contains scattered cobbles arkosic sedimentary rocks, pillow basalt, dolostone, and derived from the McGrath Gneiss, pillowed basalt flows, fragmental volcanic rocks. The strata were deposited shale, interbedded dolomitic arkose and dolostone, unconformably on the underlying McGrath Gneiss. Like coarsely fragmental basalt, and, at the top of the section, the underlying gneiss, rocks of the Denham Formation dolostone. The siltstone has been metamorphosed to fine- were metamorphosed to the amphibolite facies during grained biotite schist, the shale to coarse staurolite-garnet the Penokean Orogeny and have been recrystallized into schist, the volcanic rocks to amphibolite, and the dolostone schist, marble, and amphibolite. to marble. The original detrital grains in the arkosic rocks The Denham Formation lies unconformably atop are well preserved despite metamorphism, owing to the the McGrath Gneiss (2,550 Ma) and contains sediment abundance of dolomite between the framework grains derived from it (Boerboom, 2001c). The Denham and in the matrix. The dolomitic matrix may have absorbed overlying pelitic schist and metagraywacke unit (ps on most of the deformation and protected the quartz and Plate 2 of the Pine County geologic atlas; Boerboom, feldspar framework grains from deformation. Several 2001a) are probably related to the Mille Lacs Group drill holes located just to the east and northeast of the (Morey, 1978), which is cut by a granite 2,004 million outcrop area shown on Inset Map C in Plate 3 of the Pine years old (Van Schmus and others, 2001). Volcanic County geologic atlas (Boerboom and Chandler, 2001) rocks in the Denham Formation have provided a Sm-Nd penetrate as much as 500 feet of dolomitic marble.

4 Field and petrographic data suggest that the clastic corresponds to thinning of the overlying metasedimentary detritus (sand, silt, and clay) in the Denham Formation rocks. Furthermore, the upper fragmental volcanic unit was derived mostly from the weathered residuum nearly merges with the lower mafic volcanic unit to the developed on the underlying McGrath Gneiss. Like east, an arrangement that is consistent with the presence the upper outcrops of the McGrath Gneiss, which is of a volcanic edifice in that direction. The near mergence interpreted as metamorphosed saprolite, the arkosic parts of this upper fragmental and lower pillowed sequences of the Denham Formation lack plagioclase and contain implicates volcanic eruption into a shallow water setting, abundant detrital quartz and orthoclase feldspar. possibly shoaling into a subaerial, explosive volcano. Volcanic flow features are clearly visible in the two Outcrops of graywacke and argillite (map unit ps basalt units. The lower unit exhibits classic basalt flow in Plate 2 of the Pine County geologic atlas; Boerboom, sequences composed of a massive base that grades upward 2001a), metamorphosed to the staurolite facies, are (north) to amygdaloidal pillow basalt (Fig. 2), which located just northeast of the area of the Denham outcrops, is capped by fragmental basalt. The fragmental flow along the Soo Line trail. This metagraywacke is not tops and amygdaloidal pillows indicate that volcanism part of the Denham Formation proper, as described by occurred under relatively shallow water conditions. Morey (1978), but similar rocks intersected in drill holes Several lines of evidence suggest that the local show that the metagraywacke grades downwards into the source for these volcanic rocks lies just to the east of the marble unit of the Denham Formation. The transition is outcrop area shown on Inset Map C on Plate 3 (Boerboom marked by a horizon of graphitic argillite two to three feet and Chandler, 2001) of the Pine County geologic atlas. thick. Regional correlations suggest that this graywacke At the western part of the Denham outcrop area, the lower may be the eastern continuation of the Little Falls unit of basalt constitutes two individual flows. However, Formation (Morey, 1978). at the eastern limit of outcrop, this lower unit thickens; The strata at Denham and along the Soo Line trail as many as four individual flows were recognized within have been subject to two periods of deformation. The first it. The increase in thickness and number of flows deformation event, synchronous with the amphibolite-

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Figure 3. Equal area, lower hemisphere projections of structural elements of the Denham Formation and the overlying metagraywacke unit to the north. A, measured lineations; B, poles to measured foliations. Open diamonds represent the main early foliation, whch was refolded by a second deformation that produced only a weak foliation (crosses).

5 Canada

LAKE SUPERIOR

N. DAKOTA MINN.

WISC. S. DAKOTA LAKE MICHIGAN

MICH. NEBRASKA IOWA

ILINOIS

Figure 4. Aeromagnetic anomaly map of the north-central United States and adjacent areas of Canada, showing the approximate extent of the Midcontinent rift system. Modified from Hinze and others (1997).

grade metamorphism, produced the dominant foliation in The Mesoproterozoic volcanic and sedimentary rocks the schistose units, as well as a pronounced nearly east- that underlie most of eastern Pine County are part of the west stretching lineation (Fig. 3A). The early fabric was Midcontinent rift system, one of the largest continental later refolded by a second episode of deformation that rifts in the world (for example, Hinze and others, 1997; was coaxial with the first period. A weak, consistently Ojakangas and others, 1997). The Midcontinent rift is north-dipping foliation was produced by this second filled with basaltic lava flows and sedimentary rocks, all episode of deformation (Fig. 3B). of which are part of the Keweenawan Supergroup (Morey and Green, 1982). The extent of the Midcontinent Volcanic and Sedimentary Rocks rift system, the eastern arm of which extends from of the Midcontinent Rift System northern Lake Superior south to Kansas, is defined (Mesoproterozoic) by the pronounced positive gravity and aeromagnetic

6 A. About 1,110 million years ago, the North American continent began to separate Crustal along a 2,000-kilometer-long arc-shaped path through what is now the Lake Separation Superior area.

Rift valley

B. During the first 20 million years of the Midcontinent rift's history, layer after layer of lava was erupted into the ever- widening rift valley. By the time volcanic activity and crustal separation ended, hardened lavas had accumulated to a thickness of 20 kilometers (12.5 miles) in the Lake Superior area.

C. After volcanic activity and crustal separation ended, dense lavas caused the rift valley to continue to sag. Sediment (sand, gravel and silt) washed in, filling the valley and, ultimately, burying the lavas beneath many kilometers of sandstone.

D. Compression of the earth's crust reversed the movement along the earlier normal faults, forcing the previously deeply buried volcanic strata upward. Sub- sequent weathering and glaciation have eroded the sandstone in the central uplifted block (horst), resulting in the present-day distribution of bedrock types.

Figure 5. Development of the Midcontinent rift system in the northern midcontinent of North America. Stages A–C are modified from the Tettegouche State Park Interpretive Plaque of the Minnesota Department of Natural Resources. The Minnesota Geological Survey provided the geologic interpretation. Arrows on the diagrams above indicate the general direction of rock-body movement. geophysical anomalies (Fig. 4). The anomalies are of the earth's crust, deep-seated faults with normal produced by dense basaltic volcanic rocks that make up displacement formed along the rift margins. The faults the bulk of the rift fill. Geophysical anomalies are easily defined the edges of down-dropped crustal blocks, or traced, even where buried by younger sedimentary rocks grabens, that formed by subsidence of the central rift axis or by glacial deposits. as the crust was pulled apart. The early graben-bounding The rift formed in 1,109–1,087 Ma (Ojakangas and faults of the Midcontinent rift system acted as conduits others, 2001, and references therein) as the crust of the along which fluid molten rock, or magma, welled up from earth began to extend, or spread apart (Fig. 5A). To the mantle of the earth and was extruded onto the surface accommodate the extension and concomitant thinning as lava flows. A tremendous volume of volcanic rocks

7 filled in the rift via fissure eruptions as the crust subsided volcanic strata were tilted during both normal and reverse (Fig. 5B). After volcanism stopped, the central portion of stages of faulting. The tilting is especially prominent the rift continued to subside due to thermal subsidence, adjacent to the Douglas Fault, where the strata dip as producing a long, linear depression or basin that over much as 70 degrees east (Fig. 6). time filled with sediment washed in from the flanks of the rift by rivers and wind (Fig. 5C). In Pine County, these Volcanic Rocks (Mesoproterozoic) sedimentary rocks form a thick wedge of gently dipping The Mesoproterozoic volcanic rocks in Pine County sandstones that include the Fond du Lac Formation and are typical of basalts exposed around the rim of Lake the Hinckley Sandstones (located along the margins of the Superior, northern Wisconsin, and in the Taylors Falls  rift), and unnamed sedimentary rocks (unit msu on Plate area of Minnesota and Wisconsin. In Pine County, basalt 2 of the Pine County geologic atlas; Boerboom, 2001a) outcrops are irregular in distribution but are locally well on top of the St. Croix horst. Precise correlation of the exposed, for example, along the Snake River just east of latter unit to formally named Mesoproterozoic formations Pine City and along the Kettle River east of Hinckley. associated with the rift is uncertain, but the unnamed Until recently, all the basaltic volcanic rocks of the St.  sedimentary rock unit ( msu) is similar in lithology to the Croix horst were known as the Chengwatana Volcanic Fond du Lac Formation. Series, named for the exposures near Pine City at the old Following, and perhaps during, the final village of Chengwatana. Recent studies, including the sedimentation stage of rift development, the extensional production of the Pine County geologic atlas and work stress regime reversed to one of crustal compression, done by the U.S. Geological Survey (Cannon and others, possibly in response to crustal collision far to the east, in 2001) have shown that the St. Croix horst is composed the Grenville Orogen. The compressive event reactivated of several distinct volcanic units. As a result, the term the earlier rift-bounding normal faults as high-angle Chengwatana Volcanic Series is now restricted to that reverse faults, uplifting the central part of the rift (Fig. panel of volcanic rocks between the Pine and Douglas 5D). As shown in the cross sections on Plate 2 of the Pine Faults (see the simplified geologic map on Plate 3 of County geologic atlas (Boerboom, 2001a), the episode the geologic atlas; Boerboom and Chandler, 2001). The of reverse faulting squeezed the rift-filling volcanic Minong volcanic sequence, which underlies part of eastern rocks—once buried some 15 kilometers deep—up to a Pine County, is clearly differentiated on the basis of the higher level in the crust, forming the St. Croix horst. The attitude of volcanic layering and aeromagnetic mapping horst—an uplifted and fault-bounded sequence of volcanic (Boerboom and Chandler, 2001). A third, unnamed rocks—is a prominent feature of the Midcontinent rift volcanic unit that underlies northeastern Pine County is system south of Lake Superior. Because of the reverse shown as a separate unit on the basis of slightly divergent movement on the rift-bounding faults, volcanic rocks in aeromagnetic trends. Numerous reverse-polarity diabase the central horst are now juxtaposed against the flanking dikes are inferred from aeromagnetic data; however, they sedimentary rocks. Weathering, erosion, and glaciation were not seen owing to the spotty outcrop in the area. have eroded the bedrock to its present-day level. Other narrow diabase dikes of probable Keweenawan The western boundary of the uplifted central block of age that cut the Denham Formation in northwestern volcanic rocks (St. Croix horst), is marked by the Douglas Pine County were noted in outcrop (Inset Map C on Fault (Fig. 1). The position of the fault is well constrained Plate 3 of the geologic atlas; Boerboom and Chandler, by outcrop, water-well, and geophysical data, but other 2001), but they are not of sufficient width to show up on faults shown on Plate 2 of the geologic atlas (Boerboom, aeromagnetic maps. 2001a) that are located within the horst are less well determined, owing to the similarity of rock compositions BASALT OUTCROPS AT PINE CITY on either side. The volcanic rocks in the horst have Basalt flows and interflow conglomerates are well also been gently folded, probably in association with exposed along both banks of the Snake River starting just development of the reverse faults. In particular, the above the dam at Cross Lake and continuing downstream Bear Creek syncline (see Plate 2 of the geologic atlas; for about one mile (see Inset Map A on Plate 3 of the Boerboom, 2001a) exhibits the morphology of a growth Pine County geologic atlas; Boerboom and Chandler, fold that formed in front of a propagating thrust fault, 2001). The strata dip steeply (65 degrees) to the east, similar to modern examples in the Gulf of Suez, Egypt providing a good cross-sectional view of the basalt flows (Sharp and others, 2000). In addition to folding, blocks of

8 �� We��

Figure 6. Equal area, lower hemisphere projection of poles to planes of measured strike and dip of Keween- awan volcanic rocks in Pine County. Names listed in the explanation refer to the quadrangles in which the outcrops are present; number in parentheses is the number of measurements for each group. Plotted symbols represent average strike and dip for each locale.

and interflow conglomerates (Fig. 7). The flows show displaying traces of this activity was a water-filled pit, typical flow morphology, for example, massive bottoms presumably the remnants of a shaft, nearly one river and amygdaloidal tops. Some contain flow-top breccias mile downstream from the easternmost outcrop shown composed of angular pieces of scoriaceous basalt in a at this location. In addition, a water-well report from matrix of silt and fine sand. Six individual 30–50-feet the area near the observed remnants of the test shaft thick interflow conglomerates were mapped as part of notes the presence of native copper. Accounts of copper this sequence. The conglomerates contain (1) clasts of exploration and occurrences as summarized from early granophyric granite typical of Mesoproterozoic granite reports are given in Table 1. intrusions elsewhere in Minnesota and Wisconsin, (2) strongly porphyritic basalt containing tabular plagioclase BASALT OUTCROPS AT THE KETTLE RIVER EAST OF feldspar phenocrysts one to two centimeters in length, HINCKLEY (3) non- to weakly porphyritic basalt, and (4) rare Lake Basalt flows are well exposed along the banks of the Superior–type agates and felsite. The first two types of Kettle River east of Hinckley. They start at the Douglas clasts are volumetrically predominant, well rounded, Fault, located about three-quarters of a mile upstream of and commonly measure 30 or more centimeters in the Minnesota Highway 48 bridge, and continue more diameter. The conglomerates conformably overlie flow- or less without interruption downstream for about three top breccias and are capped by the massive base of the miles. Outcrops are also abundant on the banks of Pelkey overlying flow. Creek, which enters the Kettle River from the west (see Historical accounts report that numerous test shafts Inset Map B on Plate 3 of the Pine County geologic atlas; and pits for copper mineralization were excavated in this Boerboom and Chandler, 2001). The Douglas Fault is area from the late 1800s to early 1900s (see the bedrock not exposed at the land surface, but the fault trace forms a geologic map on Plate 2; Boerboom, 2001a) of the Pine sharp ravine occupied by Wilburn Creek, along which are County geologic atlas; see also the section below on outcrops of sandstone on the north bank and basalt on the the history of copper exploration. The only location

9 south bank. Both the basalt and sandstone are brecciated geologic atlas—contain similar lithologic attributes and and altered near the fault. may be the same or closely related. The Fond du Lac Historical accounts of copper exploration along Formation is overlain by the Hinckley Sandstone; both Pelkey Creek were verified by the presence of a rock dip gently to the southeast, except near the Douglas Fault, pile that presumably was excavated during that earlier where the strata dip variably to the north owing to fault exploration. Native copper and chalcocite noted in some perturbation. Taken together, these sandstones are two to of this material is present within veins of coarse prehnite three kilometers thick near the margins of the Saint Croix [see the bedrock endowment map (Boerboom, 2001b) on horst (Chandler and others 1989; Allen, 1994). They Plate 7 of the Pine County geologic atlas]. The Pelkey gradually thin to the west and northwest over a basement Creek occurrence is located on private property. of much older Archean to Paleoproterozoic igneous and metamorphic rocks, such as those exposed near Denham OTHER BEDROCK OUTCROPS (Fig. 1). Additional scattered outcrops of basalt were located and The sedimentary strata formed late in the development mapped across northeastern Pine County. Many of them of the Midcontinent rift system, following cessation of are located in parts of the Nemadji State Forest, which, volcanic activity. However, in Pine County the relative owing to the terrain, are nearly inaccessible. Although an timing of deposition of the sedimentary strata (Hinckley effort was made to map enough of the outcrop to ascertain Sandstone and Fond du Lac Formation) and reverse the distribution and structure of the volcanic rocks, there faulting are uncertain. Although these sedimentary rocks are undoubtedly many other small outcrops located along are now largely confined to the margins of the horst, a the creeks and streams in this part of the county that were thick package of sedimentary rocks similar to the Fond not located as part of this study. du Lac Formation (Boerboom and Chandler, 2001; unit msu on Plate 3 of the Pine County geologic atlas) is Sedimentary Rocks (Mesoproterozoic) preserved on top of the horst in southern Pine County. If Mesoproterozoic sedimentary rocks in Pine County the correlation of the rocks that are similar to the Fond du are divided into three groups, two of which—the Fond du Lac and the Fond du Lac Formation is correct, the Fond Lac Formation and the unnamed sedimentary rocks of unit du Lac may have spanned the entire rift prior to reverse Pmsu on Plate 2 (Boerboom, 2001a) of the Pine County movement of rift-bounding faults. Strata correlative

Sand- stone layer

Figure 7. Sandstone layer interbedded with interflow conglomerate in the Pine City basalt sequence, Pine County, Minnesota. The length of the visible part of the rock hammer near the center bottom of the photograph is 20 centimeters (8 inches). Photograph by T.J. Boerboom, Minnesota Geological Survey.

10 TOP Figure 8. Photograph of drill Sandstone core from the base of the Fond Siltstone du Lac Formation and the underlying basement rock (schist of Paleoproterozoic age), northwestern Pine County. Round cobbles in the bottom 1.5 feet of the Fond du Lac include clasts of Mesoproterozoic basalt, Paleoproterozoic marble and schist, and quartz. Dark bands higher in the core are silt-rich beds between sandy beds. The top of the core is in the upper left corner, the bottom is at lower right. Each row of core is about two feet long. Cobbles From diamond-drill core ML-54C (sec. 29, T. 45 N., R. 20 W.). Base of Fond du Lac Fm. BOTTOM with the Fond du Lac Formation (Orienta Sandstone) slope. This uniform dip indicates that faulting and crustal at Amnicon Falls in northern Wisconsin show evidence extension did not play a major role in the development of that deposition of the sandstone there was at least in part this portion of the western basin margin during the time coincident with the reverse faulting. This location was of deposition of the Fond du Lac Formation visited in conjunction with fieldwork for the geologic Archean and Paleoproterozoic basement beneath atlas of Pine County (Boerboom, 2001a), and evidence the Fond du Lac Formation was also intersected by the for faulting synchronous with deposition is preserved by exploratory core drilling in northwestern Pine County brecciated and redeposited sandstone clasts within the (Fig. 8). The upper part of these basement rocks are Orienta Sandstone adjacent to the fault. variably weathered, saprolitic Paleoproterozoic schist and Archean gneiss similar to that exposed in outcrops to FOND DU LAC FORMATION the east of the drill-core locations. Much of the detritus in The formation comprises predominantly arkosic to lithic the lower Fond du Lac Formation was derived from this sandstone (sandstone with a high proportion of feldspar weathered basement. and rock fragments) that is interbedded with siltstone Outcrops of arkosic, lithic sandstone that are and minor shale. In general, this unit is poorly exposed; interpreted to be upper Fond du Lac Formation are however, several drill-core and cuttings holes located in present near the Kettle River south of Sandstone. The northwestern Pine County and adjacent Carlton County sandstone is characterized by trough cross-beds that penetrate as many as 2150 feet of the Fond du Lac have conglomeratic bases containing clasts composed Formation. The basal one to three feet of the Fond du Lac predominantly of Mesoproterozoic volcanic rocks. in these cores is characterized by coarsely conglomeratic This mineralogically immature sandstone is overlain material, and it contains cobbles of material that include in sharp contact by quartzose sandstone interpreted as both the immediately underlying bedrock type and basal Hinckley Formation. The dip of the Fond du Lac Mesoproterozoic volcanic rocks. As determined from Formation strata in the outcrop area is generally shallow drill-core elevations, the base of the western part of the to the northeast, in contrast to the gently southeast dip of Fond du Lac Formation dips uniformly to the southeast at the overlying Hinckley Sandstone (Fig. 9). approximately four degrees; there are no abrupt changes in

11 Pine City 7.5-MINUTE QUAD. Pine City Pine City Pine City Pine City Hinckley and (or) Cedar Lake Lake Clayton

Schwartz (1949) Schwartz (1925)

Grout (1910, p. 471) Grout (1910, p. 471) Grout (1910, p. Upham (1888, p. 637) Upham (1888, p. 643) Upham (1888, p. 634) Upham (1888, p.

Upham (1888, p. 636–637) Upham (1888, p.

DESCRIPTION OF WORKINGS AND SOURCES DESCRIPTION OF WORKINGS OF INFORMATION "Search for copper in these rocks [below Chengwatana] was Adolph Munch, about three-fourths made several years ago by Mr. of a mile below Chengwatana, by several shafts little depth, upon each side of the river [Snake] and in its channel. During 1880 and 1881, further prospecting for copper was entered upon by the J. Bennett represented by Mr. Chengwatana Mining company, Smith, who has sunk shafts at three points on the north side of three-fourths of a mile, one and half miles river, east of Chengwatana. Smith "At the time of my observation here, October 17, 1881, Mr. was at work the shaft a mile east of Chengwatana, in an amyg- This had been daloidal bed, fifty feet in width, dipping 70°S. 75°E. excavated to a depth of 45 feet, below which further exploration has since been made with a diamond drill." where the "The most extensive work has been on the Snake River, exploration was carried down several hundred feet. In this and several other places, copper is found in quantities sufficient to keep up the enthusiasm of optimistic prospectors." mass of drift copper weighing eighty pounds is said to have "A been found by Scott La Prairie in the bed of Snake river a short distance below Chengwatana." "On Kettle River a recent shaft follows breccia, in which copper occurs as fine grains scattered in prehnite." Taylor N.C.D. Prospecting shaft dug by Mr. Abandoned copper mine shaft Abandoned copper mine shaft

YEARS 1880– 1881 1865

, Minnesota.

HOST ROCK Basalt and interflow conglomerate and zeolite amygdules mile down from the bridge east of Cross Lake. Contains calcite, laumontite, orthoclase, and native copper Numerous small masses of copper fill the irregular spaces in a vein of red laumonite, especially near the contact of the wall rock, a com- pact trap Glacial drift Basalt with prehnite veins and alteration rock (basalt) Trap

Amygdaloidal basalt with calcite Amygdaloidal basalt about one

DESCRIPTION OF LOCATION 0.75, 1, 1.5 mi downstream from Chengwatana on north side of river Snake River a short Bed of Snake River, distance below the Cheng- watana [Pine City] On the Kette River [Pelkey Creek?] exposed in north-east Trap bank, Kettle River

indicates years of exploration. Pertinent information on copper exploration prior to 1915 in Pine County

YEARS

TOWNSHIP (T.), RANGE (R.), AND RANGE (R.), (T.), TOWNSHIP secs. 25, 26, 27, 39 N, R 21 W T 40 N, R 20 W T 20 N, R 19 W T Table 1. Table The T.J. Boerboom. by enclosed by square brackets are clarifications Text range, section, and subdivisions of sections are given where known; question marks in parentheses, (?), indicate uncertainty. [Township, heading

SECTION (SEC.) SE1/4 sec. 24, 39 N, R 21 W T sec. 26, 39 N, R 21 W (?) T secs. 24, 25, 26, 27 (?), 39 N, R 21 W T 39 N, R 21 W T SE1/4 sec. 34 (?), center of SW1/4 1 2 7.5-MINUTE QUAD.

, p. 18–20, 23) , p. 1

Martin (1985, p. 139) and Martin (1985, p. 19) and Martin (1985, p. and Martin (1985, p. 19) Ileichen and Grimes (1908 p. 18–20, 23; also Martin, 1985, p. 19) also Martin, 1985, p. 18–20, 23; p.

Ileichen and Grimes (1908 Ojakangas and Matsch (1982, p. 140–141) Ojakangas and Matsch (1982, p.

DESCRIPTION OF WORKINGS AND SOURCES DESCRIPTION OF WORKINGS OF INFORMATION Businessman from Chisholm diamond drilling in secs. 19, 29, and sec. 26 SE1/4 and 35 NE1/4 copper from 1897 to 1902 "The Great Northern Copper Company is operating here." well, had to be abandoned because copper inhibited digging, Water and shown to M. Eng. sample was sawn off The Great Northern Copper Company reportedly mined native

1956 YEARS 1865

, Minnesota.

(1985, p. 19) (1985, p. 19) (1985, p.

Ileichen and Grimes Ileichen and Grimes Martin (1985, p. 139) Martin (1985, p.

, p. 18–20, 23) and Martin , p. 18–20, 23) and Martin , p. 1 1 (1908 (1908

HOST ROCK Soft blue clay-like substance which becomes very hard when dry, claimed to run 1.1% copper and 4 oz. Silver (in sections 19 and 29); rock type unknown. Drilling in sections 26 and 35 probably encountered basalt. Old copper mine shaft backfilled Transpor- by Minnesota Dept. of tation Sandstone maintenance garage in 1957, required periodic backfilling Apparently a fissure filled with quartzose material . random assays ran 0.17% copper and 0.2 oz. Silver." Ag Assay of qtz. Filling 0.25% oz. Native copper boulder 3 feet or more in diameter found at 10 feet depth in 1956 while digging well

DESCRIPTION OF LOCATION 48 Hwy. Trunk Roadbed of east of bridge near Hinckley, over Kettle River Just east of Hinckley on the east bank of the Kettle River Prospect a few feet north of Road Turpville bridge on the Pelkey Creek (?) John Fuery farm

. Pertinent information on copper exploration prior to 1915 in Pine County

continued

TOWNSHIP (T.), RANGE (R.), AND RANGE (R.), (T.), TOWNSHIP The editor of this volume was unable to locate a copy of, or a complete reference for, Ileichen and Grimes (1908). The following is the reference as it appears in Martin is the reference (1985): The following Ileichen and Grimes (1908). for, or a complete reference of, to locate a copy unable was The editor of this volume Table 1 Table SECTION (SEC.) secs. 19, SE1/4 sec. 26, and 29, 41 N, R 19 W T NW1/4 sec. 26, 41 N., R. 20 W T. sec. 26 41 N, R 20 W T sec. 26 (?), 41 N, R 20 W T sec. 34, 41 N, R 20 W (?) T SW1/4 NW1/4 sec. 22, 43 N, R 16 W T

1 Ileichen and Grimes, 1908, Keweenawan rock in Minnesota: Unpublished thesis, University of Minnesota, p. 7–23. 13 Unnamed sedimentary rocks overlying the St. HINCKLEY SANDSTONE Croix horst The Hinckley Sandstone is well known from the A thick interval of sedimentary strata is present on numerous cliff outcrops and inactive quarries in and near top of the St. Croix horst in southern Pine County and Banning State Park. The type section for the Hinckley farther south. The basin is recognized by its subdued Sandstone is in a small overgrown quarry just north of magnetic character, which obliterates the linear the Grindstone River at the City of Hinckley. The rock aeromagnetic anomalies of the underlying volcanic is typically tan to yellowish red in color and composed rocks. Aeromagnetic data (Boerboom and Chandler, of greater than 98 percent quartz. The thickness of the 2001) indicate that this unit thins to a feather edge along Hinckley Sandstone is not well established. It is at least the west margin and is thickest along the eastern margin, 100 feet thick (as measured in exposed areas), and water- where it lies in reverse-fault contact with volcanic rocks well data indicate it may be as thick as 500 feet. to the east. The strata along the eastern margin, must be The Hinckley Sandstone is well exposed in the stretch at least one kilometer thick to account for the complete of the Kettle River within Banning State Park. Outcrops eradication of the aeromagnetic anomalies in the on the west side of the river tend to form vertical cliffs underlying volcanic rocks. beyond quarried areas, whereas outcrops on the east side, A drill core obtained from the eastern edge of this although steep, tend to be more recessed, displaying large unit within the area of the subdued magnetic pattern blocks of sandstone that are commonly slumped and tilted shows that it is composed of arkosic lithic sandstone toward the river. This moderate difference in the outcrop and interbedded siltstone similar to the Fond du Lac configuration is likely a result of the gentle east–southeast Formation. The sandstone is locally cemented by iron dip of bedding in the sandstone, which enhances erosional carbonate, which in places constitutes as much as 30 undercutting, followed by slumping of the rock on the percent of the rock. eastern riverbank. Outcrops on the west bank of this stretch of the Kettle River contain numerous open fractures, some of

A B

Schmidt Equal Area Projection

Fond du Lac Formation (n = 15) Hinckley Sandstone (n = 25)

Figure 9. Planes of bedding in the Fond du Lac Formation in exposure east of Hinckley, and for the overlying Hinckley Sandstone across the entire area of Hinckley outcrop (diagram A, left) and (B, right) the orientations of 136 measured joints in the Hinckley Sandstone, Pine County, Minnesota.

14 A The thin-bedded facies of the Hinckley Sandstone is exposed in outcrop, where it forms thin layers between thick, trough-cross-bedded sandstone. The thin strata commonly contain ripple forms. Scale indicated by the 18-inch rock hammer (labeled).

Hammer

B Ripple-marked Hinckley Pencil Sandstone displays a dimpled surface that may be raindrop impressions or the product of biological activity on the exposed surface of the sand prior to burial. Scale indicated by pencil (labeled).

Figure 10. Exposures of Hinckley Sandstone in Pine County, Minnesota. Photographs by T.J. Boerboom, Minnesota Geological Survey. which are developed into small caves, such as Robinson's relatively straight and oriented north–south, an indication Ice Cave (also called the Bat Cave) and another smaller that the course may be controlled by fracture sets in the cave to the south within Robinson's Park. The caves are sandstone. located where two subparallel fractures are in proximity; Northwest of the Hinckley Fault (Boerboom, 2001a; see Shade and others (2002, this volume) for more Plate 2 of the Pine County geologic atlas), the Hinckley information on the relationship of the open fractures Sandstone exhibits both the fine- to medium-grained, and caves to the development of sinkholes. Fractures in well-sorted and well-rounded texture typical of the unit the Hinckley Sandstone were routinely measured during and a shallow dip to the southeast. Trough cross bedding the course of fieldwork. Although not exhaustive, the and large, low-angle cross beds that are visible in the measurements provide an approximation of the dominant cliff exposures in the park are thought to be the product fracture directions (Fig. 9B). The lack of measured of deposition by braided streams and wind-blown dunes, north–south fractures is unexpected given that much of respectively (Tryhorn and Ojakangas, 1972; Beaster and the Kettle River, Wolf Creek, and the buried drainage others, 2000). Thin intervals of fine-grained, ripple- channels (Chandler and others, 2002; this volume) are marked sandstone (Fig. 10) are scattered between the

15 1050 35

61 1000

Figure 11. Bedrock outcrop and 18 bedrock topography along the Kettle River Kettle River in the Sandstone area, Pine County. A valley 1100 cut into bedrock and filled with glacial sediment east of Sandstone crosses the Kettle 23 River valley, changing the meander pattern and valley width of the river northeast 1100 of Sandstone, where it exits southwest out of the buried

1050 drainage channel. 1100

1050 1000 EXPLANATION

18 1000 Bedrock topographic 1050 contour

River

Bedrock outcrop Sandstone

30 0 0 1 2 mi

0 1 2 3 km 35 T 61 UL FA

HINCKLEY

1000 950 PINE COUNTY 950

Area of Fig. 12

T UL FA

00 9 1050 DOUGLAS

1000

ettle

i v

16 ROCK TYPE MAP UNIT LITHOLOGY AGE

Unnamed sandstone zu Quartz-rich sandstone with minor Paleozoic conglomerate, shale (510–450 Ma) UNCONFORMITY Hinckley Sandstone mhn Quartz-rich sandstone

Fond du Lac mfl Formation Arkosic to lithic sandstone, siltstone, minor shale Unnamed msu sedimentary rocks Mesoproterozoic (about 1,100 Ma) UNCONFORMITY AND FAULT CONTACT Chengwatana Volcanic Group, Minong Volcanics,  mmv, mbu, Tholeitic basalt flows, minor interflow and unnamed  ncb, mcp conglomerate volcanic rocks UNCONFORMITY AND FAULT CONTACT Unnamed metamorphosed  ps Metamorphosed graywacke and slate sedimentary rocks Paleoproterozoic (about 2,100 Ma) Denham Formation  dam, dms, Metamorphosed clastic sedimentary rocks,  dmv mafic volcanic rocks, and marble

UNCONFORMITY McGrath Gneiss Amc Deformed and metamorphosed porphyritic Archean granite (2,550 Ma)

Figure 12. Lithology of major bedrock units in Pine County, Minnesota. Refer to Plate 2, Bedrock geologic map and sections (Boerboom, 2001a), of the Pine County geologic atlas for further information. thicker cross-bedded units. The layers are generally of bedding is more variable, probably owing to tectonic six to twelve inches thick, and they are apparently more disturbance related to faulting. permeable to ground water than the more thick bedded The stratigraphic relationship of quartzose sandstone units above and below. mapped as the Hinckley Formation and Paleozoic Southeast of the Hinckley Fault, the Hinckley quartzose sandstone to the south and east requires further Sandstone is slightly more coarse grained and feldspathic investigation (Fig. 12). The Hinckley Sandstone is than it is to the northwest, and it contains scattered, well- inferred to be Proterozoic in age and genetically related rounded cobbles of maroon quartzite. The strata dip more to underlying sedimentary rocks that fill the Midcontinent steeply (about ten degrees) southeast of the fault than on rift. It differs from so-called typical quartzose sandstone its northwest side (Fig. 11). In places, tributaries to the of Paleozoic age in southeastern Minnesota, chiefly owing Kettle River have eroded through the base of the Hinckley to its diagenetic attributes; in other words, the Hinckley is Sandstone into the underlying Fond du Lac Formation. relatively tightly cemented and more deeply tan to pink. This, together with the more immature mineralogy of The Hinckley also contains braided-stream and eolian the sandstone, indicates that the Hinckley Fault is a facies that are distinctly different from known Paleozoic reverse fault that has raised the basal part of the Hinckley facies farther south in Minnesota. In other respects, the Sandstone to a higher elevation. The Hinckley is in fault Hinckley is very similar to Cambrian sandstone to the east contact with basalt adjacent to the Douglas Fault. Here in north-central Wisconsin, where outcrops (1) contain a the sandstone shows evidence of brecciation, and the dip braided stream and eolian facies similar to those in the

17 Hinckley Sandstone, (2) are cemented with quartz to a in the Denham Formation, which, together with the wide similar degree, and (3) are locally similar in color. The variety of sedimentary rock types in the latter, suggest lowermost beds of the Wisconsin occurrences commonly deposition within a local rift basin. Subsequent crustal contain rounded cobbles of pink quartzite, as does the collision associated with the Penokean Orogeny about Hinckley Sandstone in Pine County. Furthermore, like 1.8 billion years ago deformed the strata of the Denham the Hinckley, these quartzose sandstones in Wisconsin are Formation into its present-day near vertical orientation. located a few tens of miles north of the principle body of Metamorphism associated with the deformation caused Paleozoic strata. However, the distribution of the strata widespread recrystallization and metamorphism of both in Wisconsin are more patchy and irregular in nature in the Denham Formation units and the underlying McGrath comparison to the Hinckley Sandstone, which in Pine Gneiss. Low-angle, south-dipping thrust faults also County has an elongate distribution parallel to the axis of played a role in the present-day distribution of bedrock in the Midcontinent rift. Investigations over the past several that area. years have demonstrated that the Cambrian sandstones in The Midcontinent rift system began to form about north-central Wisconsin are outlying remnants of landward 1.1 billion years ago through east–west crustal extension, facies deposited coevally with better known marine which caused thinning and normal down-dropped faulting strata to the south. This suggests a potentially similar of the crust. The faults acted as conduits for magma to relationship between the outcrops of Hinckley Sandstone work its way up from the mantle and erupt onto the in Pine County and the Paleozoic strata of the Hollandale surface as basaltic lava flows, which kept pace filling in embayment in southeastern Minnesota. However, the the subsiding graben to a thickness of several kilometers. Hinckley Sandstone is more or less continuous with, After volcanism ceased, the graben continued to sag, and very similar to, Keweenawan sandstone within the forming a long basin that acted as the center of deposition Bayfield Group of northern Wisconsin and Michigan, for the sedimentary strata, including the Fond du Lac which is confined to the margins of the rift basin and Formation and overlying Hinckley Sandstone. Shortly clearly affected by late reverse movement along the after or during deposition of the sedimentary strata, the Hinckley and Douglas Faults. The Hinckley Sandstone pre-existing normal faults were reactivated by crustal is here considered to be Precambrian in age, but this compression into reverse faults. The reverse movement assertion is somewhat tenuous owing to its similarities along the faults, particularly the Douglas Fault, raised with Paleozoic strata in western Wisconsin. If future formerly buried basaltic volcanic rocks to a higher studies can document that the Hinckley Sandstone is of elevation and juxtaposed them against the sedimentary Paleozoic rather than Precambrian age, then the timing fill located along the flanks of the uplifted horst. or duration of the reverse movement along the faults About 650 million years ago, after a long period of that bound the St. Croix horst would extend past the quiescence and crustal stability, sedimentary strata of Precambrian into the Paleozoic. Paleozoic age were deposited on top of the Precambrian rocks. Pine County is located at the northern edge of SUMMARY the main Paleozoic sedimentary basin, the Hollandale The oldest bedrock in Pine County is the 2,550 embayment, where the strata are quite thin and mostly Ma Archean McGrath Gneiss, which is part of a large eroded. Only scattered erosional remnants are preserved. body that extends westward as far as Mille Lacs Lake. See Figure 12 for a summary of the major rock units in The gneiss formed the continental base upon which the Pine County. Paleoproterozoic Denham Formation was deposited about two billion years ago. Information drawn from field and HISTORY OF COPPER EXPLORATION petrographic work indicates that the McGrath may have A summary of historical accounts concerning copper been weathered before or during the time of deposition exploration in Pine County is given in Table 1. The list of the overlying Denham Formation. Much of the clay, does not include more recent test pits and test drilling silt, sand, and pebbles that form the strata of the Denham performed in northwestern Pine County; for a summary of Formation were derived from the gneiss. Basaltic lava the latter, see Martin (1985). The approximate locations flows and explosive fragmental volcanism occurred of the copper pits and shafts listed in Table 1 are given on synchronously with deposition of the sedimentary units Plate 7 (Boerboom, 2001b) of the Pine County geologic atlas.

18 The following is an example of the written of ArcView to geologic mapping [extended abs.]: historical accounts available: Institute on Lake Superior Geology, 47th Annual At the time of my observation here, October 17, 1881, Meeting, Madison, Wisc., 2001, Proceedings, v. 47, pt. Mr. Smith was at work at the shaft a mile east of 1—Program and abstracts, p. 4–5. Chengwatana, in an amygdaloidal bed, fifty feet in width, Boerboom, T.J., and Chandler, V.W., 2001, Supplemental dipping 7° S. 75° E. This had been excavated to a depth of 45 feet, below which farther exploration has since data on bedrock geology and geophysics, Plate 3 in been made with a diamond drill. Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey (Upham, 1888) County Atlas Series C-13, Part A, various scales. The descriptions and locations given in Table 1 are Boerboom, T.J., and Jirsa, M.A., 2001, Stratigraphy either summarized or copied verbatim from the reports of the Paleoproterozoic Denham Formation—a referenced therein. continental margin assemblage of basalt, arkose, and dolomite [extended abs.]: Institute on Lake Superior REFERENCES Geology, 47th Annual Meeting, Madison, Wisc., 2001, Proceedings, v. 47, pt. 1—Program and abstracts, p. Allen, D.J., 1994, An integrated geophysical 6–7. investigation of the Midcontinent Rift System, western Cannon, W.F., Daniels, D.L., Nicholson, S.W., Phillips, Lake Superior, Minnesota and Wisconsin: Purdue, J., Woodruff, L.G., Chandler, V.W., Morey, G.B., Ind., Purdue University Ph.D. dissertation, 267 p. Boerboom, T.J., Wirth, K., and Mudrey, M.G., Jr., Bauer, E.J., 2001, Data-base map, Plate 1 in Boerboom, 2001, New map reveals origin and geology of North T.J., project manager, Geologic atlas of Pine County, American mid-continent rift: EOS, v. 82, no. 8, p. 97. Minnesota: Minnesota Geological Survey County Chandler, V.W., Boerboom, T.J., and Lively, R.S., 2002, Atlas Series C-13, Pt. A, scale 1:100,000. Investigation of stream-like magnetic anomalies in Beaster, K.F., Kohn, J.D., and Havholm, K.G., 2000, Pine County, Minnesota, in Boerboom, T.J., project Wind or water? Paleoenvironment of the Proterozoic manager, Contributions to the geology of Pine County, Hinckley Sandstone, northeastern Minnesota [abs.]: Minnesota: Minnnesota Geological Survey Report of Institute on Lake Superior Geology, 46th Annual Investigations 60, p. 1–20. Meeting, Thunder Bay, Ontario, 2002, Abstracts and Chandler, V.W., McSwiggen, P.L., Morey, G.B., Hinze, Programs, Pt. 1, p. 6–7. W.J., and Anderson, R.R., 1989, Interpretation of Beck, J.W., 1988, Implications for early Proterozoic seismic reflection, gravity, and magnetic data across tectonics and the origin of continental flood basalts, Middle Proterozoic Mid-Continent Rift System, based on combined trace element and neodymium/ northwestern Wisconsin, eastern Minnesota, and strontium isotopic studies of mafic igneous rocks of the central Iowa: American Association of Petroleum Penokean Lake Superior belt, Minnesota, Wisconsin, Geologists Bulletin, v. 73, no. 3, p. 261–275. and Michigan: Minneapolis, University of Minnesota Grout, F.F., 1910, Keweenawan copper deposits: Ph.D. dissertation, 273 p. Economic Geology, v. 5., no. 5, p. 471–476. Boerboom, T.J., 2001a, Bedrock geologic map and Hinze, W.J., Allen, D.J., Braile, L.W., and Mariano, sections, Plate 2 in Boerboom, T.J., project manager, John, 1997, The Midcontinent Rift System: A major Geologic atlas of Pine County, Minnesota: Minnesota Proterozoic continental rift, in Ojakangas, R.W., Geological Survey County Atlas Series C-13, Pt. A, Dickas, A.B., and Green, J.C., eds., Middle Proterozoic scale 1:100,000. to Cambrian rifting, central North America: Geological ———2001b, Bedrock endowment, on Plate 7, Geologic Society of America Special Paper 312, p. 7–35. Endowment, in Boerboom, T.J., project manager, Holm, D.K., Darrah, K.S., and Lux, D.R., 1998, Evidence Geologic atlas of Pine County, Minnesota: Minnesota for widespread ~1760 metamorphism and rapid crustal Geological Survey County Atlas Series C-13, Pt. A, stabilization of the Early Proterozoic (1870–1820 Ma) scale 1:200,000. Penokean Orogen, Minnesota: American Journal of Boerboom, T.J., 2001c, Redefined volcanic and Science, v. 298, p. 60–81. sedimentary stratigraphy of the northern St. Croix horst in Pine County, Minnesota, and the application

19 Martin, D.P., 1985, A compilation of occurrences, drill Minnesota: Implications for provenance studies: core, and testpits in the state of Minnesota: Minnesota Journal of Sedimentary Research, v. 67, no. 1, p. Department of Natural Resources, Division of Minerals 105–115. Report 231, 266 p. Shade, B.L., Alexander, S.C., and Alexander, E.C., Jr., Morey, G.B., 1978, Lower and Middle Precambrian 2002, Karst features in Pine County, Minnesota, in stratigraphic nomenclature for east-central Minnesota: Boerboom, T.J., project manager, Contributions to Minnesota Geological Survey Report of Investigations the geology of Pine County, Minnesota: Minnesota 21, 52 p. Geological Survey Report of Investigations 60, p. Morey, G.B., and Green, J.C., 1982, Status of the 55–72 [this volume]. Keweenawan as a stratigraphic unit in the Lake Sharp, I.R., Gawthorpe, R.L., Underhill, J.R., and Gupta, Superior region; geology and tectonics of the Lake S., 2000, Fault-propagation folding in extensional Superior Basin, in Wold, R.J., and Hinze, W.J., eds., settings: Examples of structural style and synrift Geology and tectonics of the Lake Superior basin: sedimentary response from the Suez rift, Sinai, Egypt: Geological Society of America Memoir 156, p. 15–26. Geological Society of America Bulletin, v. 112, no. 12, Mossler, J.H., 1987, Paleozoic lithostratigraphic p. 1877–1899. nomenclature for Minnesota: Minnesota Geological Southwick, D.L., Morey, G.B., and McSwiggen, Survey Report of Investigations 36, 36 p., 1 pl. (folded P.L., 1988, Geologic map (scale 1:250,000) of the insert). Penokean Orogen, central and eastern Minnesota, and Ojakangas, R.W., Dickas, A.B., and Green, J.C., 1997, accompanying text: Minnesota Geological Survey Introduction—Middle Proterozoic to Cambrian rifting, Report of Investigations 37, 25 p., accompanying map, central North America, in Ojakangas, R.W., Dickas, scale 1:250,000. A.B., and Green, J.C., eds., Middle Proterozoic to Tryhorn, A.D., and Ojakangas, R.W., 1972, Cambrian rifting, central North America: Geological Sedimentation and petrology of the Upper Precambrian Society of America Special Paper 312, p. 1–5. Hinckley Sandstone of east-central Minnesota, in Sims, Ojakangas, R.W., Morey, G.B., and Green, J.C., 2001, P.K., and Morey, G.B., eds., Geology of Minnesota: A The Mesoproterozoic Midcontinent rift system, Lake centennial volume: St. Paul, Minnesota Geological Superior region, USA: Sedimentary Geology, p. Survey, p. 431–435. 421–442 Upham, Warren, 1888, The geology of Pine County: Patterson, C.J., and Knaeble, A.R., 2002, History of Minnesota Geological and Natural History Survey glaciation, Chapter 2 in Boerboom, T.J., project Final Report, v. 2, 1882–1885, p. 629–645. manager, Contributions to the geology of Pine County, Van Schmus, W.R., MacNeill, L.C., Holm, D.K., and Minnesota: Minnesota Geological Survey Report of Boerboom, T.J., 2001, New U-Pb ages from Minnesota, Investigations 60, p. 21–41 (this volume). Michigan, and Wisconsin: Implications for Late Schwartz, G.M., 1925, A guidebook to Minnesota trunk Paleoproterozoic crustal stabilization [abs.]: Institute highway No. 1, Minnesota Geological Survey Bulletin on Lake Superior Geology, 47th Annual Meeting, 20, p. 52–56. Madison, Wisc., Program and abstracts, v. 47, Pt. 1, p. ———1949, Investigation of the possibility of the 100–101. occurrence of uranium in Minnesota, Report on contract no. AT (30-1) 565 between the Atomic Energy Commission and the University of Minnesota, 20 p.; Appendix, 217 p. Setterholm, D.R., 2001, Bedrock topography, on Plate 6 in Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas Series C-13, Part A, scale 1:200,000. Setterholm, D.R., and Morey, G.B., 1997, Rare earth elements in weathering profiles and sediments of

20 Chapter 2

HISTORY OF GLACIATION IN PINE COUNTY, MINNESOTA

By C.J. Patterson and Alan R. Knaeble

INTRODUCTION 96ϒ 94ϒ 92ϒ 90ϒ 0 100 mi The landscape of Pine County was shaped by the MANITOBA 0 150 km advance and wasting of two ice lobes during the most ONT ARIO recent glaciation. This glacial activity occurred from MINNESO TA 48ϒ about 25,000 14C years before present to about 10,000 14C years before present1. The bedrock of Pine County ior SUPERIORLOBE e Super is almost completely covered by sediment deposited by Lak PINE CO. glaciers, meltwater streams, and lakes during this cold MICH. WISC N. DAK. . period. The ice lobes originated in the Laurentide Ice 46ϒ S. D Sheet, which was located primarily north of Minnesota AK. in Canada (Fig. 1). The Superior lobe advanced into DES MOINES

Minnesota from the north–northeast and the Grantsburg GRANTSBURGSUBLOBE sublobe from the southwest. The latter was an offshoot LOBE of the south–southeast-trending Des Moines lobe; it 44ϒ moved in this direction because the land was lower to MINNESOTA IOWA the northeast. Modifications to the deposits during the last 10,000 years of relatively warm climate have been NEBR. WISC. ILL. minor, but the landscape appears very different today owing to the development of soils and vegetation. 42ϒ The northern regions of North America have been glaciated repeatedly during the last two million years.

Each time, glacial sediment left by the receding glaciers MISSOURI was recolonized and reoccupied by an assemblage of plants and animals that commonly was different from EXPLANATION that of the preceding glaciation. Pine County was Direction of glacial ice flow certainly affected by earlier glaciations, although it was Older margin of Superior ice sheet that was overridden by the Grantsburg the most recent glaciation—the Late Wisconsinan—that sublobe left the clearest and most complete geologic record and is Margin of the Des Moines lobe and responsible for the present-day, land-surface expression. Grantsburg sublobe Evidence of older glaciations is preserved locally in the subsurface sedimentary record. Figure 1. The location of Pine County in east-central This chapter describes the history of glaciation, Minnesota with respect to former ice lobes of the the resulting glacial stratigraphy, and the landscape Laurentide Ice Sheet, which covered the region preserved in Pine County. It is intended as a companion during the Quaternary Period. The Superior lobe to the surficial geology (Patterson and Knaeble, 2001) advanced into Minnesota through the Lake Superior and Quaternary stratigraphy (Knaeble and others, 2001) basin and was the first Late Wisconsinan ice mass plates of the Pine County geologic atlas (Boerboom, to enter what is now Pine County. The Granstburg sublobe was a later, northeast-trending offshoot of 1Carbon-14 (14C) dates diverge from calender dates due to the Des Moines lobe. variations in the rates of 14C production in the past.

21 PELITIC SCHIST FOND DU LAC

ND GRAYW .

1 W. R. 1 CO

BASALT (CHENG -- WATANA)

ϒ15'

T. 42 N.

H SA

0 10 mi

0 15 km

SILTSTONE, SHALE Figure 2. A Digital Elevation Model (DEM) of Pine County, Minnesota, showing Precambrian bedrock-geologic unit contacts (thinner black lines), faults (thicker black lines), lithology, and rock names. Scattered remnants of Paleozoic bedrock in the south are not shown on the figure. Bedrock geology in the county controls the relative elevation and shape of the land surface. The highland in the northwest is underlain by Archean crystalline rock. West-trending drumlins are superimposed on this bedrock highland, as are some younger, delicate, arcuate moraines. The southwest-trending low in the center of the county is underlain by the Fond du Lac and Hinckley sandstones. The Superior lobe was centered over the bedrock lowland underlain by sandstone; its moraines are generally perpendicular to the major bedrock contacts. This same area is where subglacial drainage features— tunnel valleys and eskers—are best developed. The ridged lowland in the northeast is underlain by folded and tilted layers of basalt; glacial landforms are not easily recognized here because glacial sediment is thin. 22 ��

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EXPLANATION 5 Superior-lobe moraines 9 Thrust moraine of the Beroun phase 1 Arcuate moraines and drumlins 6 Margin of the Askov phase (see also Fig. 8) 2 Area of outwash reworked by wind (see 7 Hummocky moraine of the Nickerson 10 Tunnel valley also Fig. 12) phase 11 Tunnel valley buried by sediment of the 3 Southwest-trending low 8. Ridges created by upturned edges of Grantsburg sublobe (see also Fig. 4) basalt (see also Fig. 9) 4 Grindstone Lake tunnel valley and nearby 12 Maximum northern extent of the moraine (see also Fig. 10) Grantsburg sublobe

Figure 3. A Digital Elevation Model (DEM) of Pine County, Minnesota, showing the location of significant Quaternary landforms, as well as figures that show greater detail of some features. 23 2001a), as well as a platform for discussion of stress. If very deep, the lake can become a barrier to observations made during mapping. further advance by creating a calving moat that, in order The last major reinterpretation of the Superior lobe to be crossed, requires a great increase in ice thickness. A in this region was recent model demonstrates that Lake Superior may have been deep enough to inhibit ice flow across it (Cutler and abetted by the availability of aerial photographs, which others, 2001). reveal subtle lineaments in the landforms barely visible in Glacial erosion may also permanently change the dense forest; of newly completed topographic maps, which document the topographic patterns suggested on bedrock drainage divides by reshaping the bedrock aerial photographs and which demonstrate how elevation surface. Bedrock may be ground away incrementally controls the position of the ice margin and the location by a glacier, or large slabs may be slid along by the of meltwater drainage features; and of radiocarbon dates, ice in places where the bedding planes of the bedrock which provide a chronological framework of suitable accuracy. (Wright and Watts, 1969). are favorably oriented. We reconstruct the shape of the ancient bedrock surface to understand the course of earlier Much of the reinterpretation presented here is based on rivers. This information also aids the interpretation of (1) a recent, high-resolution Digital Elevation Model paleoslopes, former drainage divides, and the locations (DEM) of Pine County (Figs. 2, 3); (2) new exposures of of stream-related deposits. For example, it would be surficial materials; (3) auger borings; and (4) Rotasonic™ necessary to reconstruct past watersheds to prospect for (rotary sonic) drill core. With each new view, we are able placer deposits or large aquifers in the subsurface. to decipher a little more of the complex glacial geology of this region. Bedrock Distribution and Buried Bedrock Topography PREGLACIAL LANDSCAPE The bedrock geologic map for Pine County (Plate It is helpful to visualize the preglacial landscape the 2; Boerboom, 2001b) shows the distribution of the types first ice advances encountered in order to predict two of bedrock buried beneath Quaternary sediment in Pine things: (1) the effect that topography and bedrock type County (see also Figure 2 for the location of bedrock had on glacial processes; and (2) the effect that glaciation faults and contacts). Bedrock was likely never exposed had in altering pre-existing, bedrock-controlled features as a continuous surface at any given time since the first like drainage channels and divides. Both bed relief and Pleistocene glaciation. Some channels in the bedrock slope affect the initial course of the ice—a glacier flows pre-date glaciation and probably formed in what was into a low in the landscape first. Even after an area is then an exposed bedrock landscape. Much of the bedrock inundated by ice, bed relief and slope affect processes was subjected to chemical weathering over the past tens beneath the glacier, including subglacial drainage, glacial to hundreds of millions of years. We do not know the erosion, and deposition. preglacial depth and extent of saprolith (chemically Bedrock slope also has an effect beyond the glacier weathered rock) development on the different bedrock margin. As a glacier advances up a bedrock slope, it can surfaces, but traces remain of what had been a more temporarily dam pre-existing drainage. This will result extensive weathered surface and saprolith has been in the formation of proglacial lakes that may affect the incorporated in glacial sediment. forward progress of the glacier through thermal and Different bedrock units have varying resistance to physical means. For example, a deep lake may represent chemical weathering and physical erosion that are that an unfrozen patch in otherwise permanently frozen are related to mineralogy, texture, and structure. Tectonic ground. Glacial Lake Lind, a proglacial lake (a lake that activity (Boerboom, 2002; this volume) and susceptibility formed in front of the ice margin) of the Superior lobe, is to chemical weathering are major controls on the elevation interpreted to have been deep enough for such a hole in of bedrock units. The Archean crystalline complex in the the permafrost to have developed (Johnson and others, northwest corner of the county is a bedrock high in the 1999). This would have affected the glacier, changing its subsurface, as well as a high in the present-day landscape dynamics depending on whether it was advancing over (Fig. 2), and it has probably been a high area throughout permafrost or thawed ground. Large lakes can also float much of geologic time. The crystalline rock is fairly a glacier margin. If the lake is shallow, this condition resistant to chemical weathering and erosion. Basalt in may facilitate an advance by reducing friction or shear

24 the eastern part of the county has a low-relief surface immediately north of Grindstone Lake represents one of expression that is dominated by features related to the the few places in the county that provided a record of what geometry of folded and dipping lava flows. Instability may be older glacial sediment (see graphic log PCR-1 in of many of the minerals in basalt at surface pressures and Appendix A at the end of the volume). Glacial sediment temperatures promotes a lowering of the bedrock surface is thick in the southern third of the county, owing to the through chemical weathering. Sandstones of the Fond du overlap of deposits of the Grantsburg sublobe of the Des Lac and Hinckley formations are even easier to erode, Moines lobe and deposits of the Superior lobe; both are and they currently form a low in the bedrock surface. Late Wisconsinan in age. Information drawn from bedrock outcrop, drill core, and Patterns of glacial erosion and deposition associated microscopic thin sections of rock samples (A.C. Runkel, with an ice lobe are somewhat predictable. Ice lobes Minn. Geol. Survey, verbal comm., 2000) indicate that can erode more deeply where they are thick and fast the Hinckley Sandstone is unevenly cemented, and the moving—that is, closer to the point at which they flow cement and grains have undergone several cycles of from the main ice sheet. A lobe decreases in erosive power chemical dissolution and precipitation. down-flow as the ice lobe thins and slows. Deposition Prior to glaciation, the sandstone terrane had a generally increases toward the glacier margin. The southerly slope and was probably lower in elevation deposits of the Grantsburg sublobe are thick in southern than the crystalline highland. The slope direction is Pine County because they represent the debris piled up indicated by the course of drainageways incised in the in the outermost moraines at and near the terminus of the bedrock beneath Quaternary sediment. Little is known lobe. In contrast, the deposits of the Superior lobe are of the composition of the fill in these valley; they may be thin over much of the county because the margin was far preglacial, but it is also possible that they are interglacial to the south, and Pine County was therefore in the zone (formed between glaciations) valleys. The drainageways of glacial erosion for much of the time it was glaciated. can be traced on the second vertical derivative The glacial sediment is also thin because the amount aeromagnetic map on Plate 3 of the Pine County geologic deposited depends on what the ice is carrying, which in atlas (Boerboom and Chandler, 2001), because gravel that turn depends on the erodibility of the rock that the glacier fills the valleys is more magnetic than the surrounding has moved across. Resistant rock, such as the basalt of bedrock (Chandler, and others, 2002). Drainage flowed Pine County, produced little glacial sediment in the form north to south from the Archean highland diagonally of till, ice-contact sediment, or outwash. across the sandstone; the bedrock slopes are interpreted to represent at least the slope before the last glaciation HISTORY OF GLACIAL ADVANCES (two million years old) and, possibly, the preglacial slope Minnesota was in a geographic position with respect (greater than two million years old). to the Laurentide Ice Sheet to have received sediment from two ice lobes, the sources of which were in very THICKNESS OF QUATERNARY different regions of the ice (Fig 1). During the Late SEDIMENTS OVERLYING BEDROCK Wisconsinan glaciation, the Superior lobe extended from Although the bedrock of the county was almost the eastern part of the Laurentide Ice Sheet, bringing completely buried by debris during repeated advances Canadian Shield rock types from as far away as Hudson of glaciers, the depth of burial is less than 50 feet in Bay, as well as rock from the Lake Superior basin. The much of the county. This is thin compared to other areas Des Moines lobe and its Grantsburg sublobe derived glaciated by the Superior lobe that are farther south sediment from the western part of the Laurentide Ice (see Plate 6, Depth to bedrock map of the Pine County Sheet from as far away as the Keewatin district of north– atlas; Setterholm, 2001). Most of the preserved glacial northwestern Canada, bringing rocks of Precambrian to sediment was deposited during the last glaciation. The Tertiary age to what is now Minnesota. evidence of older glaciations is mainly found in deep Ice sheets from earlier glaciations may have had bedrock valleys—for example, the buried valley in different configurations that would have brought in rocks which Grindstone Lake lies—and down-ice of bedrock from other parts of Canada. Such an interpretation is obstacles, where deposits were protected from erosion. offered on the basis of the source of the materials in A core taken from a rotary sonic drill hole in valley fill older tills that are preserved in the subsurface. The expectation—based on geologic mapping in counties to

25 the south and west—was to see glacial sediment derived can therefore assume that ice masses indicated by the from both the northwest and northeast in the subsurface previous three large isotopic excursions also reached the of Pine County. However, northwest-sourced glacial county, namely, MIS 6, 200,000–130,000 years B.P.; MIS sediment is rare in Pine County. The cross sections in 12, 475,000–423,000 years B.P.; and MIS 16, 660,000– Plate 5 (Quaternary Stratigraphy) of the Pine County 600,000 years B.P.). However, the Marine Isotope Age geologic atlas (Knaeble and others, 2001) show only very record does not specify exactly where the ice sheets were small areas of northwest-sourced glacial sediment (cross- located. It is possible that some smaller ice sheets of the section unit Qptg). All other preserved glacial sediment lesser isotopic excursions reached the area. Previous is from ice advances that originated in the northeast. workers in the area have noted the glacial sediment of at A frustration of working with glacial deposits older least four glaciations (Johnson and others, 1999). than the Late Wisconsinan is that there is currently no way to obtain quantitative ages, although we can approximate Late Wisconsin glacial activity age on the basis of stratigraphic position in the subsurface. It is tempting to assume that the advance of an We assume that the deposits get older with depth except in ice lobe like the Superior lobe represents a cooling of clear cases of ice thrusting, for example, the thrust feature the local climate. However, the relationship between in the moraine of the Beroun phase (feature 9 on Figure climate and ice-lobe advance is not so simple. Consider 3). There are no organic deposits or soil horizons in Pine the Granstburg sublobe and the Superior lobe. We know County to indicate interglacial periods, and no ubiquitous from stratigraphic relationships that the advances were datable layers, such as ash beds, that are suitable for not synchronous; they cannot both be responding to a isotopic dating. No method exists to link the terrestrial simple climate signal if the Superior lobe was receding deposits here in the Midcontinent of North America while the Granstburg sublobe was advancing. Cool with the well-dated ocean record of glacial episodes. climate and increased precipitation are the ultimate We know from marine oxygen-isotope records that four controls on the development of an ice sheet, but the lag glaciations that held large volumes of ice occurred in time between a climate signal and the response of the ice the last million years. Oxygen-isotope records show the lobe at the ice margin can be very long. The fluctuations volume of water missing from the oceans and stored on that are recorded at the margin of the ice lobes in Pine the land in ice sheets. The light isotope of oxygen (16O) County were probably a result of local ice dynamics in the is preferentially evaporated with respect to the heavy specific source area, or ice shed, of the lobe, rather than isotope (18O). Therefore, during glaciations, when the an unfiltered climate signal. In places, a warm climate evaporated water does not return quickly to the oceans but may cause a glacier to melt more quickly at the margin. is locked up in the ice sheets, the oceans become enriched It is equally likely that a warmer climate will produce in the heavy isotope. The isotopic composition of ocean more snow, causing a glacier to advance or create more water is recorded by the creatures that make their shells basal meltwater, also resulting in glacier advance We from ocean water and calcium (CaCO3) before falling to can document the asynchronous activity of the Superior the ocean floor to be added to the sediment. lobe and Grantsburg sublobe and have to conclude that The ocean sediment is cored to retrieve the record. climate is not a straightforward control on these ice-lobe The convention is to count back from our current fluctuations. interglacial period, Marine Isotope Stage 1, and note The activity of the Late Wisconsinan ice lobes every major excursion in isotope abundance, whether can be dated using radiocarbon methods where organic it shows an enrichment or depletion in 16O. A relative material is found in appropriate stratigraphic locations. depletion in 16O indicates a glacial period; a relative Unfortunately, no datable material was found during enrichment indicates an interglacial period. The first the course of this study. Nevertheless, the sequential glacial stage is Marine Isotope Stage (MIS) 2. All positions of the ice lobes and their relative positions previous glacial stages are even numbered; interglacial with respect to one another can be determined and used stages are odd numbered. There have been ten even- to develop the relative-dating framework and general numbered stages in the last 800,000 years. The first activity of the ice lobe. Following Wright (1972), we use glaciations began even a million years before that. The phase names to indicate the relative age of events within last of these glaciations—Marine Isotope Age (MIS) 2, a lobe. In this report, we recognize and name several the Late Wisconsinan, easily reached Pine County. We

26 LAKE

OSS

CR ublobe urg s limi ntsb t Gra

Esker

0 1 2 KILOMETERS

0 1/2 1 MILE

Figure 4. A tunnel valley of the Superior lobe runs north–south through Pine City in south-central Pine County, Minnesota. Contained within the tunnel valley is an esker partly buried by glacial sediment of the Grantsburg sublobe of the Des Moine lobe. The southwest-trending portion of Cross Lake lies within the tunnel valley, and an esker is preserved on the lake bottom (not visible on the figure). The tunnel and esker are preserved even where buried by thick glacial sediment deposited by the Grantsburg sublobe, a condition that requires no ice in the valley to protect these features during the advance of the Grantsburg sublobe. Modified from U.S. Geological Survey Pine City 7.5-minute topographic quadrangle map. 27 new phases of the Superior lobe and one new phase of the (Johnson, 1992; Johnson and others, 1999; Meyer, 1998) Grantsburg sublobe. (Fig. 5). The lake is no longer expressed in the surface sediment of Pine County, although deposits from it are GLACIAL ACTIVITY OF THE SUPERIOR LOBE near the surface in some of the strath (erosional) terraces EMERALD PHASE of the St. Croix River and exposed in cutbanks along the St. Croix River in St. Croix State Park near the lodge. The first Late Wisconsin activity of the Superior The lake sediment is a striking deposit of thinly bedded lobe, the Emerald phase (defined previously by Johnson red to pink clay and grayish silt (Fig. 6). The lamination and Savina, 1987; Johnson, 2000), was an advance 10–15 (fine layering) is interpreted as representing annual kilometers south of the widely recognized St. Croix deposition (varves); the varve chronology has been used phase. The deposits of this phase are not at the land to constrain the rate of Superior-lobe retreat to about 200 surface in Pine County. A sandy till, deeply buried by meters per year during the lake's existence (Johnson and younger glacial deposits in Pine County, may be a record others, 1999). The lake in Pine County was eventually of this phase. However, the till is difficult to distinguish filled in with sand from a delta prograding from the north. from overlying deposits of more recent lobe phases. Pink sands are directly beneath Granstburg-sublobe till Therefore, all sandy tills are lumped together in the cross in the southern part of the county (Fig. 7); the sands are sections on Plate 5, Quaternary Stratigraphy (Knaeble also exposed in cutbanks of the St. Croix River and its and others, 2001), of the Pine County geologic atlas. tributary gullies. ST. CROIX PHASE AUTOMBA PHASE The Superior lobe advanced far southward beyond The oldest deposits of the Superior lobe exposed at the the borders of Pine County (Fig. 1) to form the St. surface in Pine County are of the Automba phase, which Croix moraine at the time of the maximum of Marine is estimated to have occurred 17,000–15,000 14C yrs. Isotope Age (MIS) 2, about 20,000–18,500 14C yrs. B.P. (Wright and Watts, 1969). No ice marginal deposits B.P. (Clayton and Moran, 1982; Mickelson and others, of this phase are present within the borders of the county. 1983; Attig and others, 1985; Wright, 1972; Johnson, Textural analysis of samples from the sandy phases of the 2000). Johnson (2000) summarized the history of the drumlins in the northwest corner of the county (feature 1 name St. Croix moraine from its initial use by Berkey on Figure 3) and the sandy till of southern Pine County (1897) and Chamberlin (1905), to its later application show 62 percent sand, 26 percent silt, and 12 percent clay to a broader stagnation complex farther south (Leverett (see Table 1 in Knaeble and others, 2001). The analyses, and Sardeson, 1932; Wright, 1973). It is in the latter along with drumlin orientation and the extent of the sense of a stagnation complex that the term is used here. drumlin field, which is bounded by the moraine of the Deposits of the St. Croix phase were not recognized at Automba phase suggest that these features were created the surface in Pine County. They are buried, or were during the Automba phase of the Superior lobe. The eroded by, younger phases of the Superior lobe and drumlins are shallowly buried by till of later phases but Grantsburg sublobe. Buried tunnel valleys and eskers are still clearly visible. The till of this phase can have so of this phase (Fig. 4) are recognizable despite the cover much sand (83 percent) that it is difficult to distinguish it of younger sediment, because they probably were in part from glacial stream sediment, especially where exposures protected by ice during later phases. The tunnel-valley are shallow and there has been some alteration due to soil and esker features are correlated with this phase because formation. they terminate at the St. Croix moraine (Wright, 1973; The Automba phase was also one of tunnel-valley Patterson, 1994). They are similar in size to tunnel and esker formation, as inferred from the termination valleys that have not been buried by younger deposits of these features at the Automba margin outside of Pine (Wright, 1972; Patterson, 1994; Johnson, 2000). County. The tunnel valleys and eskers are best developed GLACIAL LAKE LIND in the area underlain by the Fond du Lac Sandstone, Glacial Lake Lind was a proglacial lake of the where the subglacial drainage was likely focused in this Superior lobe that developed as the ice retreated from relative topographic low. The well-developed drainage the St. Croix phase. It existed for more than 1000 years features are also related to sediment availability and and may have formed as early as 18,500 14C yrs. B.P. bedrock erodibility. Many smaller eskers east of this

28 Figure 5. Location of Glacial Lake Lind �� in southwestern Pine County, showing the area once covered by the lake. The � �

� former lake bed is not expressed at the land � � � � � surface; boundaries for it were determined �� by drilling and mapping exposures in surficial outcrops. In Pine County, red and �� gray laminated clay and silt are exposed in �� banks of the St. Croix River and in shallow �� gravel pits along terraces of the river. �� From Johnson and Hemstad (1998), and �� map D in Figure 1 of Plate 5 (Quaternary �� Stratigraphy) of the Pine County geologic

� � �

� �

� atlas (Knaeble and others, 2001). � ��

��

Figure 6. Varved lake sediment of Glacial Lake Lind, south-central Pine County, Minnesota. Reddish clay layers show in the photograph as very thin, dark horizontal lines; gray silt layers show as thicker, lighter layers. A single silt-and-clay layer, taken together. is called a varve couplet and represents deposits of a single year (Johnson and others, 1999). Glacial Lake Lind existed for more than 1000 years. Photograph by C.J. Patterson, Minnnesota Geological Survey.

29 Figure 7. An exposed section of Quaternary sediments showing pink fluvial sands �� that filled Glacial Lake �� Lind, southern Pine County, Minnesota. The sands are overlain by till of the Grantsburg sublobe of the Des �� Moines lobe. The pink to red �� sand is interpreted as fluvial and deltaic in origin (Johnson and others, 1999). The Granstburg sublobe overrode the sands, shearing small amounts of it into the till. In other respects, the contact �� with Grantsburg-sublobe till �� is sharp and distinct. Also visible is the deformed lake sediment between two layers of Grantsburg till. The lake sediment represents a local deposit, most likely restricted to a low between the next older moraine and the ice front. The trenching �� shovel is about two and a �� half feet long. Photograph by C.J. Patterson, Minnesota Geological Survey.

area are underlain by basalt. The Hinckley Sandstone until, finally, the pushing caused the folds to break along seems to have had minor eskers, as well as some drainage their hinges. A gravel pit in the feature exposed folds, through the bedrock. By far, the largest eskers and tunnel thrusts, and injection features that involved till, sand, valleys formed in the area underlain by the Fond du Lac and lake sediment. Till of this phase is sandy, similar to Sandstone. till of the Automba phase; it is included in the sandy till BEROUN PHASE average texture (62 percent sand, 26 percent silt, and 12 percent clay) given in the previous section on the Beroun The Beroun phase is the next youngest phase. It was phase. Discharges of water associated with this advance initially recognized by Leverett and Sardeson (1932), and left a bouldery lag deposit immediately down-ice of the later by Johnson and Mooers (1998) (Fig. 3). This distinct moraine. The lateral extension of the margin to the east readvance of the lobe created a clear thrust moraine (Fig. is unclear, owing to erosion associated with meltwater 8). It is easy to imagine a glacier bulldozing the sediment floods along the current courses of the Kettle and St. that lay in front of it, and it is not too much of a stretch to Croix Rivers. imagine the glacier, moving a bit more rapidly, actually buckling the sediment. This is the nature of the thrusted material in this moraine: it was buckled or folded, the folds were pushed even farther into a reclining position

30 Thrusted sediment of Beroun-phase moraine

0 1 2 KILOMETERS

0 1/2 1 MILE

Figure 8. A thrust moraine (outlined by the dashed line) south of the City of Beroun, south-central Pine County, Minnesota, that has pit exposures showing features associated with failure, namely, recumbent folds, thrust faults, and sand injection. The general direction of the thrust is indicated by the arrows. The topographic expression of the thrusted portion of this ice margin is limited to this area of Pokegama Township. Modified from the U.S. Geological Survey Beroun 7.5-minute (1:24,000 scale) topographic quadrangle map.

31 R. 17 W. R. 16 W.

T. 45 N.

T. 44 N.

T. 43 N.

�� Figure 9. Upturned edges of basalt flows �� in the northeasternmost (T. 45 N., R. 16 W.) and contiguous townships of Pine County, Minnesota, are visible in the Digital Elevation Model (DEM) above (the location map at left is a guide to identifying them on the image above). �� These features have been misinterpreted as

�

� � glacial landforms. Debris appears to have �

�

� � been deposited in narrow troughs within the stagnant ice that were coincident with

��

� the bedrock highs.

�

� �

LOCATION OF UPTURNED EDGES OF BASALT

32 Figure 10. Grindstone Lake in west-central Pine County, Minnesota, is an example of subglacial drainage in the form of a tunnel valley An esker runs along at least part of the lake bed, which is a remnant of an ice-confined Esker stream. North of the lake, the esker and tunnel valley Area of trend southwesterly; within the lake and slightly south sandstone of it, the features trend southerly. The dashed lines west outcrop and east of the lake indicate the limit of subglacial drainage. The lake has sandstone cropping out on the east side. Modified from the Giese and Kroschel U.S. Geological Survey 7.5-minute (1:24,000 scale) 80

60 topographic quadrangles. 20

120 HINCKLEY, NORTH HINCKLEY, GRINDSTONE, AND 80

SANDSTONE PHASES 140 Two phases of the Superior lobe near Hinckley were

40 named during this mapping project and represent a gradual

100 120 retreat from the Beroun phase. The margins—Hinckley 140 and North Hinckley—are subparallel and closely spaced

(feature 5 on Figure 3). Till of these phases is generally 100 80 sandy (included in average for sandy tills) and is similar to the till of the Automba phase. There are no distinct

40 subglacial landforms associated with these phases 120 other than eskers and tunnel valleys. The moraines are 80 discontinuous highlands that are more pronounced in the sandstone terrane but become difficult to trace in the basalt terrane. The ice margins are marked by water- 140 scoured surfaces immediately beyond the moraine that, Esker in lake bottom by the area eroded, indicate flow direction. No discrete 100 channels formed, only a planar scour, which suggests

60 localized, short-lived discharges of large volumes of water. Linear ridges that could be misidentified as ice 20 margins in the area underlain by basalt are actually shallowly buried edges of folded and dipping basalt flows, not ice-created marginal landforms (Fig. 9). The Grindstone phase has a similar appearance but possesses the remarkably deep Grindstone Lake tunnel valley terminating at its margin (Fig. 10). The esker within the Esker segments tunnel valley continues beyond the Grindstone margin; it is only the very deep tunnel that termininates here. During the course of this investigation, we determined through use of ship-borne seismic and radar that the esker trending southwest into Grindstone Lake continues south 0 1 2 KM across the bottom of this 153-foot-deep basin. Sandstone 0 1/2 1 MILE

33 CARLTON CO. . CARLTON CO.

93ϒ00' R. 21 W. SP R. 20 W. 92ϒ45' R. 19 W. R. 18 W. 92ϒ30' R. 17 W. R. 16 W. Nickerson

S. L I

R. T N R AITKIN CO AITKIN I O CK K E O N C ettle Sturgeon E R S K R K Lake I C KERRICK Sturgeon S T. 45 N. N T. 45 N. Lake O Denham N 23 Duquette Riv KE ICK er RR 35 46 R Kerrick E K Willow W River I C R R E O R O W er E O U T T Riv T K O K O T L ck U T. 44 N. Bruno T. 44 N. 61 – O 35 V K O Tamara O K O S V – L Rutledge O A K ϒ 46ϒ15' A S 46 15'

r Kingsdale

K TA ettle 23

. Lo . T T . WISCONSIN L MINNESO 18 Ri – Finlayson ve T. 43 N. A.–L. . T. 43 N. . r A

. 23 18 Askov

Cloverton AITKIN CO AITKIN DOUGLAS CO

. . NE TO DS Sandstone AN Y S E E L Grindstone SA NE K KANABEC CO Lake NDS T O N BURNETT CO O H. C G T N. N T. 42 N. R S I T. 42 N. I Lo N D E D H S TO N we I N Markville E r G R N TO Tamarack N R G S O R 61 ND River I S T O N E RI T H N D G Y H 35 E I N L C C K K L E Y H I N H IN C K L E Y N O R T H Y L E K T. 41 N. T. 41 N. C I N Hinckley 48 Cloverdale 48 H R. 16 W. 46ϒ00' 46ϒ00'

X RIVER OI 92ϒ30' CR R. 17 W. Kettle .

Brook 23 ST T. 40 N. T. 40 N. Park

R. 18 W.

Riv

er B Beroun E R O U 107 N 35 R. 19 W. 61 Henriette

T. 39 N. e T. 39 N.

Lak Snake ϒ egama 92 45' k

Po 0 10 mi Pine River City I N E C I T Y P RIVER 0 15 km River T R O C K OIX E S CR e W . Snak Y 35 T 361 70 ST T. 38 N. I C 70 T. 38 N. EXPLANATION 70 N E Names of ice phases are shown on the up-ice side of ice margins I Rock P TA 45ϒ45' Creek 45ϒ45' (thick black lines); unnamed phases show tick-marks on the up-ice . MINNESO side. Breaches in margin lines indicate where material has been KANABEC CO. WISC ISANTI CO. CHISAGO CO. R. 22 W. 93ϒ00' R. 21 W. R. 20 W. removed by the natural processes of erosion.

Figure 11. Former ice margins in Pine County, Minnesota, superimposed on the Digital Elevation Model for the county. The Nickerson, Beroun (Johnson and Mooers, 1998), and Split Rock (Wright and Watts, 1969) margins of the Superior lobe were previously recognized. All other names of ice margins were assigned during mapping for the Pine County geologic atlas. For the Grantsburg sublobe, Pine City is the name presently in use, whereas the West Rock margin was given its name during mapping. Modified from Figure 1 on the Surficial Geology plate (Patterson and Knaeble, 2001) of the Pine County geologic atlas.

34 is at the surface along the eastern shore of the lake but is lake has been referred to as an incipient Lake Duluth, buried in the west. or epi–Duluth (Phillips and Hill, 2001), and it preceded ASKOV, LOOKOUT TOWER, KERRICK, AND UPPER AND Glacial Lake Nemadji and Glacial Lake Duluth. Those LOWER SPLIT ROCK PHASES lakes were also proglacial lakes of the Superior lobe, but they postdate the Nickerson phase. The clayey tills are Younger phases of the Superior lobe document the thin and may be discontinuous. Clayey till thinly buries readvance of the ice lobe through a lake basin that must the well-developed eskers near Finlayson. have contained deposits of silt and clay, because the till The clayey till present within the limits of the Askov, of these younger phases is clayier than that of the older Lookout Tower, and Kerrick phases has in the past been phases (37 percent sand, 37 percent silt, 26 percent correlated with the Split Rock phase, with a minimum clay). The only way for the ice lobe to pick up clay as date of 13,500 14C yrs. B.P. (Wright and Watts, 1969; it retreated and advanced along the same trend was for Wright, 1972). We believe that the Askov, Lookout a deposit of clay to have accumulated in its path. The Tower, and Kerrick phases are distinct from the Split most likely scenario is that a proglacial lake trapped Rock phase (Fig. 11). No evidence was found to support and concentrated the clay. Glacial Lake Lind did not the correlation of the ice-marginal features near Split extend north of the margins of these phases (Johnson Rock Creek with the clayey till in the area of Finlayson. and others, 1999); therefore, the former lake must have The two segments of the formerly correlated ice margins been a separate lake that formed north of the bedrock were distinguished by referring to the one on the Archean divide near Sandstone (Wright and Watts, 1969). This

Figure 12. Sandstone blocks in a moraine ridge south of the City of Askov in central Pine County, Minnesota. The sandstone bedrock in this area is unevenly cemented. As the ice advanced to the Askov position, it pushed some of the loose blocks of sandstone to this position, forming a moraine that is atypical in composition; most moraines in Pine County are composed of glacial till. The trenching shovel near the middle right edge of the photograph is about two and a half feet long. Photograph by C.J. Patterson, Minnesota Geological Survey.

35 highland as Upper Split Rock (within feature 1 in Figure 3), and the one in the lowland as Lower Split Rock . The Superior two narrow and sharp moraines on the Archean highland 47ϒ Lobe originally were used to define the Split Rock phase ? MINN (Wright and Watts, 1969). The drumlins in Pine County WISC were also interpreted to be part of the Split Rock phase. However, they are older, because they extend beyond PINE CO. the moraine and are partly buried by the till associated with the advances. We interpret the drumlins to belong 46ϒ to the Automba phase and to have been partially buried by the Split Rock phase. The ice margin on the upland is not continuous across the county but separated by an Glacial Lake area of younger outwash. Till on the Archean highland Grantsburg is slightly siltier than that of the Askov, Lookout Tower,

WISC

Grantsburg MINN Kerrick, and Lower Split Rock phases, which also makes Sublobe correlation problematic. 45ϒ The moraine associated with the Askov phase (feature 6 on Figure 3) and underlain by the Hinckley 94ϒ 93ϒ 92ϒ Sandstone is unusual. It is difficult to trace in the area underlain by the Fond du Lac Sandstone (Fig. 2). The Figure 13. The location of Glacial Lake moraine is a very narrow and striking feature on the Granstburg. Both Glacial Lakes Lind Digital Elevation Model (DEM) (Fig. 3). In outcrop, and Grantsburg occupied a similar basin, it appears to be primarily composed of large blocks of referred to by Meyer (1998) as the Stacy sandstone (see photograph of moraine; Fig. 12). The ice Basin. Glacial Lake Granstburg developed advance may have gathered up loose blocks of sandstone because of the blockage of south-draining and piled them at the ice margin. The margin is also rivers at the time of the maximum advance unusual in that the sinkholes that have been identified of the Granstburg sublobe. It was a much in the county appear to be aligned with it [Shade and shorter lived lake than Glacial Lake Lind. others, 2001; Shade and others, 2002 (this volume)]. From Johnson and Hemstad (1998) and map One possible interpretation for this combination of I in Figure 1 of the Quaternary Stratigraphy features is that the ice advanced rather rapidly due to high plate (Plate 5; Knaeble and others, 2001) of subglacial water pressure. The subglacial water may the Pine County geologic atlas. have discharged through the fractures in the weathered bedrock along a path consistent with the hydraulic was gained by using former railroad beds and trails. The gradient—that is, downward and laterally beneath the ice, glacial sediment behind the moraine generally forms a then upward beyond the ice margin. This may have led to thin layer over the bedrock. The westward extension the excavation and (or) dissolution of weathered bedrock of the Kerrick phase is buried by younger outwash. We and, later, sinkhole development immediately beyond the interpret the western extension to be at the southern limit ice margin. of collapse features of this outwash plain. It is unclear if The Kerrick phase is marked by abundant outwash it can be correlated with any of the small moraines on the sediment that forms a southwest-trending plain along Archean highland to the northwest. the ice margin. Outwash may also have come from later NICKERSON PHASE phases. Some streams along the Kerrick margin in the After the Askov–Lookout Tower and Kerrick phases, northeast corner of the county appear to have been ice- the ice retreated and formed another proglacial lake. The supported as they are positive features on the landscape. till associated with the readvance of the Nickerson phase It is difficult to distinguish the positive relief of ice- contains even more clay (28 percent sand, 34 percent supported streams from the ridges of basalt in this region silt, 38 percent clay) than the Askov, Lookout Tower, because they are aligned. The area has few roads; access and Kerrick phases (26 percent clay). The Nickerson

36 phase occurred about 12,000 14C yrs. B.P. (Wright and of stability when the ice was at or near its maximum, which Watts, 1969). The clayey nature of the till produced was followed by a gradual retreat (rather than stagnation) a distinctive, finely hummocked area of stagnation through Pine County. Till of the Granstburg sublobe has topography along the northern border of the county an average texture of 43 percent sand, 33 percent silt, and (feature 7 in Figure 3; also Fig. 11). The pebble-poor 24 percent clay. It is easily identified by color (yellow till of the stagnation complex is in places difficult to brown where oxidized and gray where unoxidized) and distinguish from lake sediment. Outwash from this phase the presence of Cretaceous shale fragments. was deposited in a broad area south of Sturgeon Lake GLACIAL LAKE GRANSTBURG (mostly confined to the southwest quarter of T. 44 N., The Grantsburg sublobe was fronted by Glacial R. 19 W.), forming the Willow River outwash plain Lake Granstburg (Johnson and Hemstad, 1998; Meyer, (feature 3 on Figure 3) (Wright and Watts, 1969). 1998) (Fig. 13). The lake occupied the same basin as Meltwater also flowed into the lows between eskers the northern portion of Glacial Lake Lind. It existed of the Finlayson swarm and might have gone through for about 80–100 years (Johnson and Hemstad, 1998; Grindstone Lake to the south. Southwest of Sturgeon Johnson, 2000). Deposits of Glacial Lake Grantsburg are Lake, the outwash plain is characterized by low, irregular at the surface south of Hinckley in the southern part of sandy hills that we interpret as the product of reworking the county. Farming is made easier in the area because by wind at a later time (feature 2 on Figure 3). of the fine-grained, stone-free, calcareous nature of the soils, which formed in the Grantsburg lake sediment. The GLACIAL ACTIVITY OF THE GRANTSBURG SUBLOBE sediment is thick only in few places; elsewhere it thinly The timing of the advance of the Grantsburg sublobe drapes the pre-existing Superior-lobe topography. Sandy (Des Moines lobe) remains unresolved. Its advance to the near-shore deposits, which probably consist of reworked Pine City moraine postdates the St. Croix and Automba Superior lobe sands, are present in the northwestern and phases of the Superior lobe. Wright (1972) correlated it southeastern parts of the former lake basin. The lake with the Split Rock phase of the Superior lobe and linked was deepest and lake sediment thickest and most finely the two phases of the different lobes using a relationship grained (silt and clay) in southwestern Pine County, near involving what he interpreted as a delta created by the southwestern part of the basin. Superior-lobe meltwater in Glacial Lake Grantsburg near As the ice lobe oscillated near its maximum position, Hinckley. He estimated that it advanced prior to 12,000 water ponded between newly formed moraine ridges. 14C yrs. B.P., and as early as 16,000 14C yrs. B.P. We An outcrop of sediment in one of these minor moraines could neither confirm nor disprove this association and shows two till units separated by a weakly deformed lake found no new material to date. The lobe had to advance sediment (Fig. 7), an indication that water (1) ponded after Lake Lind filled with sand. That stratigraphic between the ridges, (2) deposited a continuous layer of relationship is easily established in outcrop. sediment, which was then advanced over, and (3) was PINE CITY AND WEST ROCK PHASES deformed but did not undergo sufficient strain to be Another unusual aspect of the Grantsburg sublobe obliterated. The moraines may represent small seasonal is the style of moraine building. Many of the moraines advances of winter ice during an overall period of in Minnesota are broad stagnation complexes. A single- recession. crested, well-formed morainic ridge is rare in Minnesota. The Granstburg sublobe did not create the tunnel The Des Moines lobe formed such a simple moraine valleys and eskers within its limit; it occupied two while at the Bemis phase in southwestern Minnesota. Superior-lobe tunnel valleys (features 10 and 11 on This moraine is much higher than those of the Granstburg Figure 3) that clearly extend beyond the Grantsburg sublobe, but in other respects it is similar in form. The margin. Subglacial drainage of the Superior lobe Grantsburg sublobe created two, closely spaced well- originally flowed to the south. Valleys may have been defined moraines: Pine City and West Rock moraines reoccupied by north-flowing subglacial meltwater of the (Figs. 3, 11). The West Rock was named during this Grantsburg sublobe (Meyer, 1993). Some Superior-lobe project. Large moraines of the Grantsburg sublobe are ice remained within the valleys while it was covered by paralleled by a series of smaller retreatal moraines to the Grantsburg sublobe, as indicated by the collapsed the south of the well-defined moraines (Fig. 3, 11). This nature of the Grantsburg-sublobe till overlying them and pattern of moraines indicates that there were two periods the exquisite preservation of the Superior-lobe esker.

37 Glacial Lakes drainage became restricted south of the broad outwash Nemadji and plain, and a new channel was cut through glacial sediment ϒ Duluth 47 and sandstone bedrock to form a bedrock-walled gorge. Moose Lake outlet Outwash north of the bedrock gorge is overlain in places

K by medium to fine, flat-bedded sand. This sand most ettle likely represents deposition by water that was backed up MINN WISC Brule as the Kettle River created its narrow channel through the

Riv PINE CO. outlet bedrock in what is now Banning State Park. A buried

er bedrock valley was exhumed and used downstream er 46ϒ of Banning State Park near Sandstone in central Pine Riv County. South of the area of shallow bedrock, the drainage again broadened, creating bar-shaped deposits of sand and gravel and streamlined erosional remnants of glacial sediment. Today, these are isolated highlands in a peaty, roadless wilderness. The St. Croix River valley

WISC MINN did not exist in its present form at this time, but its later Croix 45ϒ activity obscured the former course of the Kettle River downstream. The most likely course for the drainage of St. Glacial Lake Nemadji from the confluence with the St. 94ϒ 93ϒ 92ϒ Croix is along the perimeter of the Grantsburg sublobe Figure 14. Glacial Lakes Nemadji and Duluth moraine and into Wisconsin. occupied approximately the same area in what is In summary, the Kettle River has varied reaches now the Lake Superior basin of Minnesota and because it possesses a patchwork of valleys of different Wisconsin. The proglacial lake developed as age that were used during the draining of a large the Superior lobe retreated northeastward. It is proglacial lake. Its northernmost reach in Pine County referred to as Glacial Lake Nemadji for when it is developed in the sand and gravel of an outwash plain was at the highest level and drained out the Moose that is buried by slackwater sediment. The whitewater Lake outlet. The proglacial lake is called Glacial stretch of the Kettle River from Banning to Sandstone Lake Duluth for when it was at a lower level was cut into the rock at the time of the draining of the and draining out the Brule and St. Croix Rivers. proglacial lake; the valley south of Sandstone is, in part, Although the drainages appear to be confluent— an exhumed paleovalley that was reoccupied at this time. and the modern streams occupying them are, the Farther south, the former course of the river has been Kettle was created first, but lost most of its flow obscured by later events related to drainage of the same when the Brule outlet was created. lake through the St. Croix basin. GLACIAL LAKE DULUTH AND THE BRULE AND Late- and Post-glacial activity ST. CROIX RIVERS Glacial Lake Duluth was defined by N.H. Winchell GLACIAL LAKE NEMADJI AND THE KETTLE RIVER (1899) as the lower-level lake that drained out the Brule Glacial Lake Nemadji was defined by N.H. Winchell River (originally referred to as the Bois Brulé) and St. (1899) as the proglacial lake of the Superior lobe that Croix River (Fig. 14). The St. Croix River forms part drained through the Moose and Kettle Rivers (Winchell, of the eastern border of Pine County. It is characterized 1899; Leverett and Sardeson, 1932). Drainage of the by large bars formed on erosional (strath) terraces. The glacial lake breached the Nickerson moraine in Carlton strath terraces expose or shallowly bury a variety of County directly north of Pine County (Fig. 14). Once underlying geologic units, including till, lake sediment, through the moraine, the water crossed the Nickerson and bedrock. In places, the bars are large and sufficiently outwash plain diagonally and then spread out laterally gravelly to be economic aggregate deposits. Although the to form the broad, unpitted outwash surface south St. Croix River appears to be confluent with the Kettle, it of Sturgeon Lake in northwestern Pine County. The is unlikely that both rivers had large simultaneous flows.

38 Area of wind-blown sand

Blow-outs ont

Dune fr

0 1 2 KILOMETERS

0 1/2 1 MILE Figure 15. An area of glacial outwash that was reworked by wind located about one mile northeast of the City of Willow River, northwest Pine County. No well-expressed dune forms are evident in this atypical area of outwash, where the land surface has been altered to present a disorganized rolling topography. Several potential blow-outs—depressions eroded by the wind—are labeled. The highest area of sand is in the southeast along the banks of the Willow River. The wind direction was from the northwest, and the advancing dune front was most likely impeded by the river, causing the sand to pile up the highest in this position. Modified from U.S. Geological Survey Willow River 7.5-minute (1:24,000-scale) topographic map.

39 While the St. Croix River had its maximum flow, water ———2001b, Bedrock geologic map and sections, Plate backed up into its tributaries, which caused slackwater 2 in Boerboom, T.J., project manager, Geologic atlas sediment to be deposited within them, flattening the lower of Pine County, Minnesota: Minnesota Geological reaches of the tributary-river profiles. Later, after the St. Survey Geologic Atlas Series C-13, Part A, scale 1: Croix lost its maximum flow, its tributaries and gullies 100,000. deposited alluvial fans on the valley floor, and peat ———2002, Bedrock geology of Pine County, Minnesota, developed in areas of perched water table. in Boerboom, T.J., project manager, Contributions to SNAKE RIVER AND CROSS LAKE the geology of Pine County, Minnesota: Minnesota Geological Survey Report of Investigations 60, p. 1–20 The Snake River formed along the Pine City moraine (this volume). following drainage of Glacial Lake Grantsburg through Boerboom, T.J., and Chandler, V.W., 2001, Supplemental a now-obscured outlet (Johnson and Hemstad, 1998). data on bedrock geology and geophysics, Plate 3 in The river was receiving water from far to the north, an Boerboom, T.J., project manager, Geologic atlas of indication that it was not simply a glacial meltwater Pine County, Minnesota: Minnesota Geological Survey stream of the Grantsburg sublobe. The Snake River has County Atlas Series C-13, Part A, various scales. a low gradient, which gives it a complicated meander Chamberlin, R.T., 1905, The glacial features of the St. pattern, with numerous scroll bars and an uncommon Croix Dalles region: Journal of Geology, v. 18, p. crossing of a lake in Pine City. It is the obvious reason 542–548. for this lake being named Cross Lake. Chandler, V.W., Boerboom, T.J., and Lively, R.S., 2002, WIND EROSION Investigation of stream-like magnetic anomalies in There is a large expanse of windblown sand know Pine County, Minnesota, Chapter 3 in Boerboom, T.J., as the sand barrens in neighboring Wisconsin. Beneath project manager, Contributions to the geology of Pine the sand sheet, we found wind-polished and wind-faceted County, Minnesota: Minnesota Geological Survey stones called ventifacts. The only area of dune formation Report of Investigations 60, p. 43–53 (this volume). mapped in Pine County is south of Sturgeon Lake (Fig. Clayton, Lee, 1984, Pleistocene geology of the Superior 15), but the dunes there are not as well formed as those region, Wisconsin: Wisconsin Geological and Natural in the sand barrens of Wisconsin. Silty fine sand in History Survey Information Circular 46, 40 p., folded sinkholes in Pine County has been interepreted as loess or map. wind-blown sediment (B.L. Shade, Dept. of Geology and Clayton, Lee, and Moran, S.R., 1982, Chronology of Geophysics, Univ. of Minn., Minneapolis verbal comm., late Wisconsin glaciation in middle North America: 2002). Ventifacts were found at several shallowly buried Quaternary Science Reviews, v. 1, no. 1, p. 55–82. locations in Pine County, and they are interpreted to have Cutler, P.M., Mickelson, D.M., Colgan, P.M., MacAyeal, developed near the Superior-lobe ice margin in Late D.R., and Parizek, B.R., 2001, Influence of the Great Wisconsinan time. Some sand could have been reworked Lakes on the dynamics of the southern Laurentide ice during the warm period of the mid Holocene (Keen and sheet; numerical experiments: Geology, v. 29, no. 11, Shane, 1990). Predominant wind directions, as indicated p. 1039–1042. by the dunes, were from the northwest. Imbrie, John, and others, 1984, The orbital theory of Pleistocene climate; support from a revised REFERENCES chronology of the marine δ18O record, in Berger, Attig, J.W., Clayton, Lee, and Mickelson, D.M., 1985, A.L., Imbrie, J., Hays, J., Kukla, G., and Saltzman, Correlation of late Wisconsin glacial phases in the B., eds., Milankovitch and climate: Understanding the western Great Lakes area: Geological Society of response to astronomical forcing, Part 1: Dordrecht, America Bulletin, v. 96, p. 1585–1593. Netherlands, p. 269–305. Berkey, C.P., 1897, Geology of the St. Croix Dalles: Johnson, M.D., 1992, Glacial Lake Lind: A long- American Geologist, v. 20, p. 345–383. lived precursor to glacial Lake Granstburg in western Boerboom, T.J., 2001a, project manager, Geologic atlas Wisconsin and eastern Minnesota [abs.]: Geological of Pine County, Minnesota: Minnesota Geological Society of America Abstracts with Programs, v. 24, no. Survey County Atlas Series C-13, Part A, 7 pls., scales 6, p. 23. 1:100,000 and 1;200,000.

40 ———2000, Pleistocene geology of Polk County, of Porter, S.C., Late-Quaternary environments of the Wisconsin: Wisconsin Geological and Natural History United States: Longman, p. 3–37. Survey Bulletin 92, 70 p., 1 folded map, scale 1: Patterson, C.J., 1994, Tunnel-valley fans of the St. Croix 100,000. moraine, east-central Minnesota, U.S.A., in Warren, Johnson, M.D., Addis, K.L., Ferber, L.R., Hemstad, C.B., W.P., and Croot, D.G., eds., Formation and deformation Meyer, G.N., and Komai, L.T., 1999, Glacial Lake of glacial deposits: Rotterdam, Balkema, p. 69–87. Lind, Wisconsin and Minnesota: Geological Society Patterson, C.J., and Knaeble, A.R., 2001, Surficial of America Bulletin, v. 11, no. 9, p. 1371–1386. geology, Plate 4 in Boerboom, T.J., project manager, Johnson, M.D., and Hemstad, C.B., 1998, Glacial Lake Geologic atlas of Pine County, Minnesota: Minnesota Granstburg: A short-lived lake recording the advance Geological Survey County Atlas Series C-13, Part A, and retreat of the Granstburg sublobe, in Patterson, C.J., scale 1:100,000. and Wright, H.E., Jr., eds., Contributions to Quaternary Phillips B.A.M., and Hill, C.L., 2001, Deglaciation studies in Minnesota: Minnesota Geological Survey history and geomorphological character of the region Report of Investigations 49, p. 49–60. between the Agassiz and Superior basins, associated Johnson, M.D., and Mooers, H.D., 1998, Ice-margin with the 'Interlakes Composite' of Minnesota and positions of the Superior lobe during Late Wisconsinan Ontario, in Jackson, L., and Hinshelwood, A., eds., The deglaciation, in Patterson, C.J., and Wright, H.E., Jr., late palaeo-Indian Great Lakes: Geoarchaeological and eds., Contributions to Quaternary studies in Minnesota: archaeological studies of Late Pleistocene and Early Minnesota Geological Survey Report of Investigations Holocene occupation: Friends of the Pleistocene, 49, p. 7–14. Midwest Section, 47th Field Conference, Thunder Johnson, M.D., and Savina, Mary, 1987, The southern Bay, Ontario, June 1–3, 2001, Field guide, 24 pages in margin of the Superior lobe during the latter part of the a separately paged section. Wisconsin Glaciation exceeded the St. Croix moraine Setterholm, D.R., 2001, Depth to bedrock, on Plate 6 by 10 to 15 kilometers [abs.]: Geological Society of in Boerboom, T.J., project manager, Geologic atlas America Abstracts with Programs, v. 19, p. 206. of Pine County, Minnesota: Minnesota Geological Keen, K.L., and Shane, L.C.K., 1990, A continuous record Survey County Atlas Series C-13, Part A, scale of Holocene aeolian activity and vegetation change at 1:200,000. Ann Lake, east-central Minnesota: Geological Society Shade, B.L., Alexander, E.C., Jr., Alexander, S.C., and of America Bulletin, v. 102, p. 1646–1657. Martin, Samuel, 2001, Sinkhole distribution, on Plate Knaeble, A.R., Patterson, C.J., and Meyer, G.N., 2001, 6 in Boerboom, T.J., project manager, Geologic atlas Quaternary stratigraphy, Plate 5 in Boerboom, T.J., of Pine County, Minnesota: Minnesota Geological project manager, Geologic atlas of Pine County, Survey County Atlas Series C-13, Part A, scale 1: Minnesota: Minnesota Geological Survey County 200,000. Atlas Series C-13, Part A. Shade, B.L., Alexander, S.C., and Alexander, E.C., Leverett, Frank, and Sardeson, F.W., 1932, Quaternary Jr., 2002, Sinkhole distribution in Pine County, geology of Minnesota and parts of adjacent states: U.S. Minnesota, Chapter 4 in Boerboom, T.J., project Geological Survey Professional Paper 161, 149 p. manager, Contributions to the geology of Pine County, Meyer, G.N., 1993, Quaternary geologic map of Chisago Minnesota: Minnesota Geological Survey Report of County, Minnesota: Minnesota Geological Survey Investigations 60, p. 55–72 (this volume). Miscellaneous Map Series M-78, scale 1:100,000. Shakleton, N.J., and others, 1984, Oxygen isotope ———1998, Glacial lakes of the Stacy Basin, calibration of the onset of ice-rafting and history of in Patterson, C.J., and Wright, H.E.,Jr., eds., glaciation in the north Atlantic region: Nature, v. 307, Contributions to Quaternary studies in Minnesota: p. 216–219. Minnesota Geological Survey Report of Investigations Upham, Warren, 1888, The geology of Pine County: 49, p. 35–46. Minnesota Geological and Natural History Survey Mickelson, D.M., Clayton, L., Fullerton, D.S., Borns, Final Report v. 2, 1882–1885, p. 629–645; also map H.W., Jr., 1983, The Late Wisconsin glacial record of plate facing p. 629. the Laurentide ice sheet in the United States, in v. 1 Williams, F.F., Thunnell, R.C., Tappa, E., Rio, D., and Raffi, I., 1988, Chronology of the Pleistocene oxygen

41 Chapter 3

INVESTIGATION OF STREAM-LIKE MAGNETIC ANOMALIES IN PINE COUNTY, MINNESOTA

By Val W. Chandler, Terrence J. Boerboom, and R.S. Lively

INTRODUCTION age (Pleistocene Epoch). As described by Patterson and Knaeble (2002; this volume), more than one ice advance Mapping associated with the Pine County geologic moved into Pine County, but the bulk of the glacial atlas (Boerboom, 2001b) has documented the presence of deposits covering Pine County are related to the Superior several steep-sided channels that are deeply incised into lobe, which advanced from the northeast [see Plate 4, the bedrock beneath Pine County, particularly within the Surficial geology (Patterson and Knaeble, 2001) and Plate Hinckley Sandstone. The channels were probably part 5, Quaternary stratigraphy (Knaeble and others, 2001) of of an extensive preglacial drainage network. They are the Pine County geologic atlas (Boerboom, 2001b)]. now filled with unconsolidated sediment deposited by melting glacial ice and generally are not evident at the AEROMAGNETIC SURVEY METHOD land surface today. The channels are an important feature in Pine County; the contrast in hydrologic characteristics The magnetic survey method, whether conducted between the glacial fill and the adjacent bedrock walls from the air (aeromagnetic) or on the ground, uses very may strongly influence the movement of ground water precise measurements of the earth's magnetic field to in the subsurface. Also, the quality and quantity of investigate the geology beneath the land surface. Many ground water that is available from within the channel earth materials contain traces of a magnetic mineral fill is likely to be significantly different from that of the called magnetite, which causes small perturbations adjacent bedrock. (anomalies) in the earth's magnetic field. The anomalies Considering these effects on ground water, accurate are commonly quite small and not perceptible in everyday mapping of the buried valleys was an integral part of experience. Most geology-related anomalies range from a the geologic assessment. Drilling and geophysical data few to a few thousand nanoTeslas (abbreviated nT, which indicate that the valleys are 150–256 feet in depth, and is one billionth of a Tesla, the standard unit of magnetic approximately three-eighths of a mile in width. The field intensity). In comparison, the earth's magnetic difficulty arises because these narrow valleys cannot be field in Pine County has a background strength of about reliably traced using drill-hole data for any distance due 58,000 nT. A relationship exists between geology, to their uneven and commonly sparse distribution (Fig. magnetite content, and the expected anomaly signature. 1). However, as this chapter demonstrates, geophysical For example, the volcanic rocks that underlie eastern Pine exploration methods using aeromagnetic and seismic data County typically contain magnetite and, consequently, are provide an alternative way to trace buried bedrock valleys associated with large-amplitude and complex magnetic in western Pine County. anomaly signatures. In contrast, the sedimentary rocks (Fond du Lac Formation and Hinckley Sandstone) GENERAL GEOLOGY that underlie western Pine County contain virtually no magnetite and, where sufficiently thick, are associated Boerboom and others (2002; this volume) discuss the with a very subdued magnetic anomaly signature (Fig. 2). bedrock geology of Pine County; the reader is referred to Geophysicists and geologists commonly use magnetic the simplified bedrock geologic map therein for reference. data to help interpret the geology beneath the land Outcrops of bedrock are abundant in places along the surface. Indeed, the magnetic anomaly data were used Kettle River and its tributaries (Fig. 1), but much of the extensively to produce the bedrock geologic map for Pine remaining bedrock surface in Pine County is covered by County (Boerboom, 2001a; Boerboom and Chandler, glacial deposits that were laid down during the last ice

42 93ϒ00' 92ϒ45'

Sturgeon 23 Lake PCR-2 Duquette 35

61 r Rive Kerrick Willow Willow River

Riv er Bruno

Rutledge K

ettle 46ϒ15'

Riv Pine er

Creek

18 Finlayson

18 23 Askov

Crook

PCR-1 61 35 Grindstone Sandstone Creek Lake

Fork

East

Sand

Hinckley

K ettle 48

46ϒ00'

Riv

23 er

0 5 10 mi �� 0 5 10 15 km

EXPLANATION Drill holes. Seismic sounding location. Less than 150 ft to bedrock. �� Bedrock outcrops. 150 ft and greater to bedrock. Rotary-sonic core hole (PCR-1, PCR-2). 43 Figure 1 (previous page). Map of northwestern and north-central Pine County, Minnesota, showing the major sources of geologic information (well records, seismic soundings, and bedrock outcrops) that were used to map the geology. Refer to Plate 2 of the Pine County geologic atlas (Bedrock geologic map and sections; Boerboom, 2001a) for further information concerning the geologic units.

2001). Glacial deposits are commonly assumed to be SANDSTONE AREA nonmagnetic and therefore "transparent" to the magnetic Outcrops of Hinckley Sandstone along the Kettle survey method, but as described below, some glacial River, as shown on Plate 1, Data-base map (Bauer, deposits in western Pine County produce small but 2001) of the Pine County geologic atlas, yield important geologically significant magnetic anomalies. clues regarding the source of the stream-like magnetic The airborne-magnetic (aeromagnetic) data in Pine anomaly that crosses through the area (Fig. 3). West of County were acquired in 1979–1980 as part of a statewide the City of Askov, the magnetic anomaly coincides with high-resolution aeromagnetic surveying program an uncommonly straight north–south stretch of the Kettle (Chandler, 1991a, b). Surveying was conducted 500 feet River valley (Fig. 3). Here, the Kettle River meanders above ground along north–south lines spaced one-fourth through a flat-bottomed valley, and outcrops of bedrock mile (400 meters) apart . To facilitate the reduction of the are restricted to higher up on the bounding valley walls. data, east–west tie lines were flown 500 feet above ground To the south, near Banning State Park, the Kettle River surface at a spacing of 2.5 miles. A highly sensitive valley and the magnetic anomaly diverge; the Kettle instrument called a magnetometer was used to measure River valley bends to the southwest, and the magnetic variations in the earth's magnetic field at intervals of 250 anomaly bends to the southeast (Fig. 3). Southwest of feet (75 meters) along line. Several processing steps were this divergence, the valley of the Kettle River changes applied to the data, including removal of the background abruptly to a V-shaped gorge faced with cliffs showing magnetic field of the earth (the large field produced by extensive bedrock exposure, as well as rapids along the the core of the earth) and transformation of the flight-line valley bottom. This section of the river is interpreted as a data to a regular grid. The second vertical derivative of more recently formed stream channel cut by rapid erosion the gridded magnetic data was computed to enhance the from glacial meltwater. To the southeast, the magnetic magnetic anomaly signatures of near-surface geology anomaly intersects the wall of the modern valley at a (Fig. 2). Further details on the acquisition and preparation point where bedrock outcrops are conspicuously absent of the aeromagnetic data are given in Chandler (1991a), (Fig. 3). These observations are consistent with the and on Plate 3 (Boerboom and Chandler, 2001) of the Kettle River passing from a pre-existing and partially Pine County geologic atlas. filled bedrock valley to the north, to a more youthful, The thick nonmagnetic sandstones (Hinckley bedrock-lined valley to the southwest, whereas the and Fond du Lac) in western Pine County have a old bedrock valley extends to the southeast and south, smooth, subdued magnetic signature, which enhances completely concealed beneath glacial deposits. Farther identification of some rather weak (10–30 nT), narrow south, the channel-like magnetic anomaly swings back to magnetic highs that are most evident in Tps. 40–44 N., R. the southwest and cuts obliquely across the valley of the 20–21 W. (Fig. 2). These weak anomalies have narrow, modern Kettle River (Fig. 3). Here, there are no outcrops winding forms that are reminiscent of stream patterns, of sandstone over the area of the buried valley's axis, and although they commonly depart from modern streams the outcrops that are present follow the walls of the buried and valleys. channel more closely than the margins of the present-day The discussion that follows presents evidence that these Kettle River. stream-like anomalies actually reflect buried bedrock valleys. Two areas of interest exist: one near the city GRINDSTONE LAKE AREA of Sandstone, the other near Grindstone Lake, where Geological and geophysical data indicate that the relatively good geologic control exists for the bedrock stream-like magnetic anomaly in the Grindstone Lake area surface (Fig. 1). is related to a buried bedrock valley. Grindstone Lake is elongated coaxially with the magnetic anomaly and is as deep as 150 feet. In comparison, water well-data indicate

44 R. 21 W. R. 20 W. R. 19 W. R. 18 W. R. 17 W. R. 16 W. s on rock ti T. 45 N. PCR-2 a e rm n ozoic o to F ds cheanoter and ac L San Ar u y aleopr d e T. 44 N. P nd ckl o in 46ϒ15' F H Area of Figure 3. T. 43 N. PCR-1 Askov

Sandstone

T. 42 N. Area of Volcanic rocks, Figure 4. St. Croix Horst

Hinckley T. 41 N.

46ϒ00' R. 22 W. 92ϒ30'

T. 40 N. N

0 5 10 mi T. 39 N. Pine City 0 5 10 15 km 92ϒ45'

T. 38 N. 45ϒ45'

93ϒ00' Figure 2. Second vertical derivative of magnetic anomaly data of Pine County, Minnesota. The image also shows bedrock geologic contacts (thinner white lines) and faults (thicker white lines), as well as the locations of Figures 3 and 4. White arrows indicate the location of buried bedrock valleys, which were investigated during the project using seismic sounding techniques. Township and range numbers are shown along the left side and top, respectively, of the county outline; townships are delineated by white squares. Note the complex, large-amplitude magnetic anomaly signature characteristic of the volcanic rocks, in contrast to the subdued anomaly signature of the sedimentary rocks (for example, the Hinckley Sandstone). The north–south strips on the image are are of no geologic significance; they are artifacts of flight-line recovery and leveling. See also the simplified geologic map (Fig. 1) in Boerboom and others (2002; Chapter 1 of this volume).

45 Figure 3. Map showing �� the second vertical �� derivative of the magnetic data, bedrock outcrops, and the path of a buried bedrock valley in the area of �� Sandstone, west- central Pine County. North–south striping on the aeromagnetic image is an artifact of flight-line recovery and leveling.

��

� � ��

� � �� 4746 Figure 4. Map of the second vertical derivative magnetic

Aitkin County Tie line anomaly data in the Grindstone 1127-1 Lake area, west-central Pine County, Minnesota. Tie line 1129-0 is profiled in Figure 6 PCR-1 and tie line 1127-1 in Figure

Kanabec County 7. North–south striping on the aeromagnetic image is an artifact of flight-line recovery Grindstone and leveling. Lake Tie line 1129-0 EXPLANATION Drill holes. Less than 150 ft to bedrock. 150 ft and greater to bedrock. Rotary-sonic drill hole (PCR-1).

Seismic sounding location— A The letters A and B show the end points of the profile shown in Figure 5.

Trace of valley cut into bedrock and filled with glacial and postglacial B sediments.

��

0 2 mi

0 3 km

47 that the depth to bedrock of the Hinckley Sandstone (Fig. 5). Seismic refraction soundings at the north end of is commonly less than 45 feet below the land surface Grindstone Lake indicate a bedrock depth of greater than along the edges of the lake (Setterholm 2001b; Plate 6 240 feet along the axis of the magnetic anomaly (Fig. 4). of the Pine County geologic atlas). Thus, Grindstone A rotary-sonic drill hole was subsequently drilled at this Lake resides in an elongate bedrock depression, and the site (hole PCR-1; Figs. 1 and 4), which penetrated a 265- extension of the associated magnetic anomaly to the north foot thick sequence of glacial deposits before bottoming and south suggests that this bedrock depression continues out in Hinckley sandstone (see Appendix A at the end of as a buried valley beyond either end of the lake. this volume for stratigraphic log). The seismic refraction Seismic refraction sounding was used along the soundings confirm that the stream-like magnetic anomaly stream-like magnetic anomaly both north and south of in the Grindstone Lake area corresponds precisely with a Grindstone Lake to test for the presence of a buried buried bedrock valley. valley (Figs. 1 and 4). This sounding technique involves introducing a burst of energy into the ground, which SOURCES OF MAGNETIC ANOMALIES is achieved by striking a metal plate on the ground The stream-like magnetic anomalies in western Pine with a sledgehammer. Some of this energy encounters County clearly reflect buried bedrock valleys, but the underlying bedrock and is bent or refracted back to question remains as to why a valley filled with glacial the surface, where it is picked up by a series of highly deposits, which are typically assumed to be essentially sensitive detectors called geophones. The timing of this nonmagnetic, produces a magnetic anomaly. Pertinent returning energy, relative to that of the impact, can be factors are the arrival of Superior-lobe ice from the used to estimate the depth to bedrock. Seismic refraction northeast and the type of rocks that it would have crossed soundings south of Grindstone Lake indicate that bedrock and consequently incorporated before reaching western lies 50–100 feet below the land surface beneath areas Pine County. The rocks would include lavas and related that lie off the stream-like magnetic anomaly, whereas intrusions along the St. Croix horst, as well as similar the bedrock elevation drops off abruptly to depths in rocks along the shore of Lake Superior about 50 or excess of 200 feet in areas that overlap the anomaly more miles to the northeast. The lavas consist chiefly of

A B 1150 Less than 6,000 feet per second (unsaturated glacial deposits) Land surface 1100

1050

eet) 6,000 feet per second 8,000–10,000 (saturated glacial deposits) feet per 1000 second ation (f v Ele 950

10,000–15,000 feet per second 900 (Hinckley Sandstone)

850 -0.5 0 0.5 1.0 1.5 2.0 2.5 3.0 Distance (miles)

Figure 5. Interpretation of seismic refraction survey points (black dots) in the area of Grindstone Lake, west-central Dell Grove Township (T. 42 N., R. 21 W.), west-central Pine County, Minnesota.

48 ��

��

� ��

��

� ��

Figure 6. Model study of a segment of tie line 1129-0, which spans the southern part of Grindstone Lake (T. 42 N., R. 21 W.), west-central Pine County. Surface elevation and lake-bottom data were inferred from U.S. Geological Survey Kroschel 7.5-minute topographic quadrangle map. To remove a regional anomaly component, assumed to reflect deeply buried sources, a base level of 1052 nT and a gradient of +7.2 nT/(kilometers east) was removed from the observed total intensity data prior to modeling. The location of tie line 1129-0 is shown on Figure 4.

basalt, which typically contains as much as a few percent equate roughly to magnetite contents of a few tenths of magnetite. In addition, some ice may have passed over a percent by volume. The highest observed magnetic older, pre-rift rocks in northwestern Wisconsin, which susceptibilities appear to be associated with outwash would include magnetite-rich rocks like iron-formation (sand and gravel) deposits, although elevated magnetic (a source of iron ore) that contain greater than 10 percent susceptibilities also appear to be present in a till layer magnetite. Therefore, it is reasonable to suggest that the from hole PCR-2 (refer to graphic log in Appendix A at Superior-lobe glacial deposits in western Pine County the end of this volume). It is likely the elevated magnetic would be somewhat enriched in magnetite. susceptibilities in both till and outwash deposits reflect To gauge the magnetite content of Superior-lobe the contribution of finely disseminated magnetite grains deposits, magnetic susceptibility measurements were and clasts of magnetite-bearing igneous and metamorphic made on rotary-sonic cores of the glacial deposits from rocks. drill-holes PCR-1, PCR-2, and PCR-3 (Fig. 1; see Appendix A at the end of the volume for the graphic MODEL STUDIES logs) Magnetic susceptibility is a measure of how much Model studies are used to verify that glacial fill a material can be magnetized by induction in the earth's displaying magnetic properties similar to those observed magnetic field and is roughly proportional to the magnetite in drill holes PCR-1 and PCR-2 can account for the content of the material (Mooney and Bleifuss, 1953). observed magnetic anomalies associated with valleys cut The readings reveal that moderate (.00314–.00628 SI) into bedrock beneath western Pine County. The modeling magnetic susceptibility values are common for Superior- is focused on the Grindstone Lake area, owing to the lobe deposits. Using empirical relationships derived by constraints that drill hole PCR-1 provides with respect Mooney and Bleifuss (1953) from igneous rocks, the to valley depth and magnetic susceptibility. East–west observed susceptibilities of the glacial deposits would tie lines afford the best resolution for modeling of the

49 ��

��

� �

� ��

��

� ��

Figure 7. Model study of a segment of tie line 1127-1, which is located less than a mile north of Grindstone Lake, west- central Pine County, Minnesota. To remove a regional anomaly component, assumed to reflect deeply buried sources, a base level of 1049 nT and a gradient of +9.2 nT/(kilometers east) was removed from the observed total intensity data prior to modeling. The location of the tie line is shown on Figure 4.

bedrock valley anomalies; they transect the anomalies level, an excellent fit to the observed magnetic anomaly essentially at right angles and provide total magnetic data is achieved with an average magnetic susceptibility intensity values every 250 feet along line. Thus, of 0.003142 SI for the model, which agrees with the range modeling is conducted for segments of tie lines 1129-0 of average susceptibility values of drill hole PCR-1. The and 1127-1, located 1.4 miles south and 1.0 mile north of magnetic low between the two observed anomaly peaks drill hole PCR-1, respectively. Program SAKI (Webring, corresponds closely with thinning of the magnetic fill 1985), a profile modeling program that is based on two- caused by the surface depression that contains Grindstone dimensional (strike infinite) sources, is used for both Lake. This intervening magnetic low may reflect the lake models. A valley bottom elevation of 850 feet above mean bottom cutting out the magnetic outwash layers observed sea level, identical to that observed at drill hole PCR-1, at depths of 0–40 feet, 100–115 feet, and 150–185 feet in is assumed for both profiles, which in turn assumes drill hole PCR-1 (see Appendix A at end of volume). The that the ancient valley system was reasonably mature model also indicates that the eastern margin of the buried prior to burial and that longitudinal gradients were low. valley lies considerably to the east of the lake. Models are conducted with the assumption that the entire The model for tie line 1127-1 indicates a significant valley sequence has a uniform magnetic susceptibility. change in the nature of the valley fill north of Grindstone However, magnetic susceptibility data obtained from the Lake (Fig. 7). Assuming a valley bottom elevation of 850 drill cores show great variability among different types of feet, a good fit requires a model magnetic susceptibility glacial deposits, and their relative thicknesses may vary of 0.00581 SI, a value that is almost twice as high as the along the length of the valley. average value at drill hole PCR-1 and the modeled value The model for tie line 1129-0 (Fig. 6), which crosses along line 1129-0. This measurement may reflect an near the southern end of Grindstone Lake (Fig. 4), increase in proportional thickness of relatively magnetic indicates that magnetic susceptibilities similar to those outwash units at the expense of the less magnetic till observed in drill hole PCR-1 can easily account for the units. The model also suggests that the cross section observed magnetic anomaly expression. Using a valley of the valley is somewhat asymmetric, but caution is bottom assumed at an elevation of 850 feet above mean sea warranted: the magnetic anomaly may actually reflect

50 the distribution of magnetic materials within the valley other extreme, valleys that are cut into strongly magnetic sequence and, therefore, have little relationship to the rocks, such as the lavas in southeastern Pine County, are gross shape of the valley. Regardless, the models derived unlikely to show similar patterns because the weak signal for lines 1129-0 and 1127-1, as constrained by drill hole from the sediments is overwhelmed by strong amplitude PCR-1, indicate that significant variations in the valley anomalies in the bedrock. In this case, neither derivatives fill may be present over fairly short distances along the nor any other enhancement procedure is likely to isolate buried valleys. the subtle signatures associated with bedrock valleys.

CONCLUSIONS REFERENCES The stream-like magnetic anomalies in western Pine Allen, D.J., 1994, An integrated geophysical investigation County clearly reflect buried bedrock valleys. As such, of the Midcontinent rift system: western Lake Superior, the anomalies aided compilation of the Pine County Minnesota and Wisconsin: Purdue, Ind., Purdue Univer- geologic atlas maps (Boerboom, 2001b) that show sity, Ph.D. dissertation, 267 p. bedrock elevation and bedrock depth (Setterholm, 2001a, Bauer, E.J., 2001, Data-base map, Plate 1 in Boerboom, 2001b), especially in areas lacking drill-hole control. T.J., project manager, Geologic atlas of Pine County, Model studies lacking any independent control on depth Minnesota: Minnesota Geological Survey County Atlas or magnetic susceptibility are of limited value, owing to Series C-13, Part A, scale 1:100,000. ambiguities in deciphering thickness versus magnetic Boerboom, T.J., 2001a, Bedrock geologic map and susceptibility of a source that is probably the result of sections in Boerboom, T.J., project manager, Geologic complexities in the stratigraphy of the glacial materials atlas of Pine County, Minnesota: Minnesota Geological that fill the valleys. Modeling near drill hole PCR-1 in Survey County Atlas Series C-13, Part A, scale the Grindstone Lake area indicates that the fill sequence 1:100,000. changes significantly in average magnetic susceptibility, ———project manager, 2001b, Geologic atlas of Pine (and, presumably, stratigraphy) over short distances along County, Minnesota: Minnesota Geological Survey the valley. County Atlas Series C-13, Part A, scales 100,000 and Magnetic anomalies similar to the ones investigated 1:200,000. here might be used to trace buried valleys elsewhere Boerboom, T.J., and Chandler, V.W., 2001, Supplemental in the region, although the requirements are somewhat data on bedrock geology and geophysics, Plate 3 in restrictive. First, the valleys have to be cut into essentially Boerboom, T.J., project manager, Geologic atlas of nonmagnetic bedrock, and the glacial fill has to be Pine County, Minnesota: Minnesota Geological Survey somewhat enriched in magnetite. The latter requirement County Atlas Series C-13, Part A, various scales. would be most likely satisfied in areas where magnetite- Boerboom, T.J., Runkel, A.C., and Chandler, V.W., bearing igneous and metamorphic rocks are a reasonably 2002, Bedrock geology of Pine County, Minnesota, short distance in the former up-ice position, such as would in Boerboom, T.J., project manager, Contributions to exist for glacial deposits associated with the Superior and the geology of Pine County, Minnesota: Minnesota Rainy lobes of northern and east-central Minnesota. In Geological Survey Report of Investigations 60, p. contrast, glacial deposits of the Des Moines lobe of 1–20. northwestern and central Minnesota were largely derived Chandler, V. W., 1991a, Aeromagnetic anomaly map of from shale and carbonate bedrock to the northwest of Minnesota: Minnesota Geological Survey State Map Minnesota and, thereby, would be expected to be Series S-17, scale 1:500,000. magnetite deficient. In addition, the nonmagnetic rocks ———1991b, Shaded relief aeromagnetic anomaly map that host the buried valleys must be of sufficient thickness of Minnesota: Minnesota Geological Survey State Map to greatly smooth anomalies produced by the materials Series S-18, scale 1:1,000,000. that underlie them, which can be readily discriminated Chandler, V.W., McSwiggen, P.L., Morey, G.B., Hinze, from the short-wavelength signatures associated with W.J., and Anderson, R.R., 1989, Interpretation of the buried valleys. For example, geophysical studies in seismic reflection, gravity, and magnetic data across adjacent areas (Chandler and others, 1989; Allen, 1994) middle Proterozoic Mid-Continent rift system, indicate that the sandstones that host the buried valleys northwestern Wisconsin, eastern Minnesota, and central in western Pine County are 1500–9000 feet thick. At the

51 Iowa: AAPG Bulletin, v. 73, no. 3, p. 261–275. Knaeble, A.R., Patterson, C.J., and Meyer, G.N., 2001, Quaternary stratigraphy, Plate 5 in Boerboom, T.J., project manager, Geologic atlas of Pine County, Minne- sota: Minnesota Geological Survey County Atlas Series C-13, Part A. Mooney, H.M., and Bleifuss, R.L., 1953, Analysis of field results, pt. 2 of Magnetic susceptibility measurements in Minnesota: Geophysics, v. 18, no. 2, p. 383–393. Patterson, C.J., and Knaeble, A.L., 2001, Surficial geology, Plate 4 in Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas Series C-13, Part A, scale 1:100,000. ———2002, History of glaciation in Pine County, Minnesota, in Boerboom, T.J., project manager, Contri- butions to the geology of Pine County, Minnesota: Minnesota Geological Survey Report of Investigations 60, p. 21–41 (this volume). Setterholm, D.R., 2001a, Bedrock topography, on Plate 6 in Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas Series C-13, Part A, scale 1:200,000. ———2001b, Depth to bedrock, on Plate 6 in Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas Series C-13, Part A, scale 1:200,000. Webring, Michael, 1981, MINC: A gridding program based on minimum curvature: U.S. Geological Survey Open-File Report 81-1224, p. 43. ———1985, SAKI: A Fortran program for generalized linear inversion of gravity and magnetic profiles: U.S. Geological Survey Open-File Report 85-122, p. 110.

52 Chapter 4

KARST FEATURES IN PINE COUNTY, MINNESOTA

By Beverley L. Shade, Scott C. Alexander, and E. Calvin Alexander, Jr.

INTRODUCTION sinkholes in Pine County serve as the terminal sinks of perennial or ephemeral surface streams. Water that drains Sinkholes are closed depressions (holes) in the into sinkholes becomes ground water as soon as it reaches landscape that act as direct paths for surface water to the water table. The process may happen in seconds, and enter the subsurface. They form when shallowly buried it rarely takes longer than a few minutes. bedrock develops openings of sufficient size to allow The seasonal high water table is in or above some surface material to collapse or be washed downward of the sinkholes, and they are drowned during periods of into the openings. The openings may be the result of high water. It is unknown whether the drowned sinkholes solution or mechanical erosion. Although surface karst continue to accept water during these floods, or if the features are best known in areas underlain by carbonate flow reverses, and they act as springs, intensifying local bedrock, they can also form over quartzite or quartz floods. arenite sandstone (Wray, 1997). In central Pine County, The study began as a survey of the sinkholes in sinkholes have formed through the movement of surface Partridge Township (T. 43 N., R. 19 W.) near the center of material into an underlying system of open fractures in Pine County. The area of the search was later extended the Hinckley Sandstone. Such sinkholes range from less northeastward into Bruno Township (T. 44 N., R. 18 W.) than one meter to more than 100 meters in size. and southwestward into Sandstone Township (T. 42 N., Sinkholes present two challenges to environmental R. 20 W.). The full subcrop of the Hinckley Sandstone managers. They represent rapid and direct connections of has not been searched, and every sinkhole in the areas surface water to ground water, and they bypass the normal searched has not been located. Additional sinkholes cleansing processes of flow through the unsaturated undoubtedly exist. Sinkholes may also be discovered in zone. Water from shallow wells near sinkholes other areas of Pine County. The sharp boundary along commonly shows evidence of land-surface contaminants. the southeast side of the sinkhole array in the area of Sinkholes also raise stability concerns, particularly Partridge Township appears to be an actual boundary for water impoundment structures on the land surface of sinkhole occurrence (Shade and others, 2001; Plate 6 near sinkholes. These challenges can be minimized of the Pine County geologic atlas). The distribution of with careful planning, which recognizes the limitations sinkholes in other directions remains undefined. imposed by karst hydrogeology. This planning will focus Mapping shows that sinkholes tend to form in on areas near existing sinkholes. Karst conditions can clusters. East of the Kettle River in Banning State Park, exist, however, in areas without visible sinkholes, and a single linear array along a northeast-trending ridge many sinkholes remain unmapped. contains almost 20 percent of the 262 mapped sinkholes. In Pine County, sinkholes form when turbulent This group of sinkholes aligns with Robinson's Ice Cave surface water sinks through the unconsolidated deposits and adjacent small caves on the opposite, west side of the at the land surface and transports fine-grained sediment Kettle River. The caves are thought to have formed by into an underlying system of joints in the Hinckley the weathering and erosion of sandstone along a set of Sandstone, eventually causing the land surface to subside. fractures. The correlation of these caves with the linear Once formed, sinkholes are fed by surface runoff and can array of sinkholes to the northeast provides support for drain large volumes of water during spring snowmelt and after heavy rain. At times large whirlpools may form and water can be heard running underground. Several of the

53 the interpretation that sinkholes develop above buried that have "a specific type of fluid circulation capable of bedrock fractures. self-development and self-organization" (Klimchouk and The Hinckley Sandstone is a clean quartz sandstone. Ford, 2000). No carbonate grains or cements have been found in By focusing on the behavior of an entire system, sandstone samples from this area. Karst development in karst flow can be distinguished from porous-media flow. quartz rocks is a slow process because the solubility of In shallow systems, water carrying out the process of quartz at earth-surface temperatures and pressures is low. solution is routed quickly through landforms and into However, the Hinckley Sandstone is at least 450 million the subsurface, where it contributes to the function of an years old, and it is unlikely that the bedrock has ever integrated drainage system. been buried very deeply. Thus, the sandstone has been subjected at least intermittently to surface weathering GLOBAL DISTRIBUTION OF FEATURES processes since its deposition. Furthermore, Pleistocene Quartz karst features caused by solution processes glaciations in the study area have produced large volumes have been recognized on all continents and across a of unsaturated water during several periods in the past. wide spectrum of climates. Wray (1997) notes silicate The large volumes of water had the capacity to dissolve karst in Venezuela, Brazil, the United States, Morocco, and remove larger volumes of quartz than ground-water Chad, Niger, Nigeria, Zimbabwe, South Africa, Thailand, flows in nonglacial times. Australia, the United Kingdom, Poland, the former Czechoslovakia, and scattered sites in western Europe. KARST FEATURES Sites in northwestern New Mexico (Wright, 1964) and east-central Minnesota (this chapter; Shade and others, Background 2001) have also been noted. Caves with depths of nearly A fundamental management issue of ground water in 400 meters and lengths of several kilometers have been the Hinckley aquifer is the relative roles of porous media documented in quartz karst regions. demonstrating a and conduit and fracture flow. Surface contaminants local significance simply in regard to the pervasiveness move much faster and much farther in conduit and and scale of the phenomenon (Truluck, 1991; Wray, fracture flow systems than in porous media systems. 1997). The presence of sinkholes, caves, and sinking streams PREVIOUS WORK indicates karst conduit systems. A common assumption holds that karst phenomena are restricted to limestone Research on the genesis of quartz karst features has and dolostone, thereby excluding sandstones like the focused on sites in Venezuela and Australia. A variety Hinckley Sandstone from consideration of conduit and of karst features are present on large table mountains fracture flow. Karst on sandstone and quartzite rocks in the Roraima region of southeastern Venezuela and (those composed almost entirely of the mineral quartz) northwestern Brazil. Solution features include the are unfamiliar to many hydrogeologists and totally world's tallest waterfall (Salto el Angel), as well as caves unknown to most resource managers. However, this type that extend both vertically and horizontally. The Roraima of karst is well documented in the scientific literature and orthoquartzite is well cemented and made entirely of has been recognized in a variety of locations worldwide. quartz. Quartz-to-opal hydration (White and others, One aspect of this study addresses how sinkholes form on 1966), hydrothermal alteration of bedrock (Zawidzski sandstone and why they exist in central Pine County. and others, 1976), and meteoric precipitation augmented Recent research has emphasized the importance of a by alginic and amino acids (Chalcraft and Pye, 1984) systems approach to define karst on the basis of universal have all been suggested as driving mechanisms for the characteristics—one that does not require a specific type solution of bedrock in this area. of rock. One of these characteristics is the presence Several areas of sandstone karst have been studied of bedrock conduits. Conduits are high transmissivity in northwestern Australia. The Paleozoic Bungle Bungle features that connect recharge to discharge areas and are massif in the southeastern part of the Kimberleys is capable of transporting ground water rapidly in turbulent a tower-and-ridge terrain, whereas the Proterozoic flow. The critical size for transition from laminar to Cockburn Range to the northwest has mesa-and-scarp turbulent flow can be as small as one millimeter (Ford and morphology (Young, 1987). The difference in form Williams, 1989). Karst aquifers form parts of systems between the two ranges is probably due to differences in

54 Clear Lake 23 35 61 Bartels Long Lake Lake Bruno

Stevens Rutledge Lake

ettle 46ϒ15'

Fig. 6

Banning State Park Fig. 4

Creek

18 Riv Askov

er 23

35 Fig. 8 Sand 61 Fig. 2

Sandstone

92ϒ45'

Map 0 5 mi Sinkhole area 0 5 km PINE CO.

Figure 1. The general location of mapped sinkholes in north-central Pine County, Minnesota. Additional figures that show greater detail are also indicated (Figs. 2, 4, 6 and 8). The locations of sinkholes are provided in Appendix Table B1 at end of volume.

55 ��

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Figure 2. The distribution of sinkholes on the east bank of the Kettle River northeast of the City of Sandstone, Pine County, Minnesota. See Figure 1 for the location in Pine County of the area shown above and Figure 3 for a cross section of the excavation of sinkhole D222.

primary porosity at the onset of karstification. Extensive ARE THE SINKHOLES IN PINE COUNTY KARST FEATURES? etching of grains and optically continuous overgrowths The scientific literature documents that karst exists have been seen in scanning electron microscope (SEM) in sandstones and quartzites. Such features also exist images, where overgrowths and interstitial cements seem in Pine County, but mapping them is complicated more susceptible to solution (Young, 1988). because Pine County was completely covered by ice during the latest glaciation. When the ice melted, many closed depressions were created in the landscape with a

56 ��

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Figure 3. Stratigraphic cross section of sinkhole D222, as exposed by excavation, northeast of the City of Sandstone on the east bank of the Kettle River, Pine County, Minnesota. See Figures 1 and 2 for the location of this figure. The cross-cutting relationship of organic material within the throat of the sinkhole indicates the downward movement of surface materials. The expression of this karst feature is more pronounced in the subsurface than on the surface.

variety of sizes and scales. Some closed depressions are geometry of sediments. The sediment constitutes a sinkholes due entirely to karst processes. Some closed record of the sequence of events that produced the depressions are entirely due to glacial processes. Some surface features we see today, and it provides much useful closed depressions are composite features created through information, prompting us to ask more questions. both karst and glacial processes. Sinkhole D222 (Figs. 2 and 3) Observations Sinkhole D222 is located in the southwestern The investigation of karst features in Pine County portion of the study area (Fig. 1) near Hell's encompassed a range of activities. We began by Gate, Banning State Park (sec. 3, T. 42 N., locating karst features during fieldwork. The features R. 20 W.). A trench was oriented east–southeast— were assigned UTM coordinates through GPS (Global west-northwest across the sinkhole depression and Positioning System), and pertinent information was perpendicular to its overall trend of the sinkhole cluster. compiled on sinkholes, streamsinks, and springs It was excavated by hand to an average width of 0.7 (Tables B1, B2, and B3 in Appendix B at the end of this meters, and a depth of 1.5 to 2 meters; it did not reach volume). bedrock. The excavation revealed three sedimentary strata: (1) an organic-rich soil and layer of leaf litter, (2) SINKHOLES an eolian loess, and (3) a dark red till. Another deposit, a We conducted four excavations (Fig. 1) in Partridge gray material containing a high concentration of roots and Township (T. 43 N., R. 19 W.) and adjacent areas to sandstone blocks, crosscut the latter two strata (Fig. 3). understand how sinkholes form here and how they relate to The top 20 centimeters consisted of a black organic- local geology. The excavations provided the opportunity rich material composed of recent leaf litter and abundant to explore and map the three-dimensional subsurface shallow roots and larger tree roots. This layer was as

57 � � � �

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Figure 4. The distribution of sinkholes east of the Kettle River and south of Log Drive Creek, along the border of Finlayson and Partridge Townships, north-central Pine County, Minnesota. Sinkholes in this area are distinctly clustered. See Figure 1 for the location of the area above in Pine County. See Figure 5 for a stratigraphic cross section of sinkhole D144.

thick as 30 centimeters in the center of the depression. contained both locally derived sandstone (more angular) The dark organic layer was underlain by a tan layer of and glacial erratics (mostly basalt). The contact of the loess. The loess was silty to very fine sand. It lacked loess and till appeared to be unconformable. any significantly larger grains or rocks. It had a few tree The crosscutting material mentioned above was roots, but a thick tangle of roots from grass and small gray and organic rich, apparently an older version of the plants were concentrated in leaf litter. In total, the loess organic-rich duff. It was lighter in color than the modern was about three-quarters of one meter thick on the east leaf litter, and the organic material was less intact. This end of the transect, and greater than one meter thick on material also contained the highest concentration of roots the west end. and small amphibians (frogs and salamanders). The area The loess was underlain by dark red sand-rich till, also contained many large rocks, most of which were which was discontinuously separated from the loess by a large angular blocks of Hinckley Sandstone, although lag of fist-sized, well-rounded crystalline rocks. The till there was also a significant portion of well-rounded crystalline glacial erratics.

58 ��

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�� Figure 5. Stratigraphic cross section of sinkhole D144 as exposed by excavation, east of the Kettle River and south of Log Drive Creek, Pine County, Minnesota. The expression of this karst feature is more pronounced in the subsurface than on the land surface. Deposits in the throat of D144 display the same crosscutting relationship of organic material as was evident in sinkhole D222 (Fig. 3) an indication of the mechanism by which these sinkholes form.

Sinkhole D144 (Figs. 4 and 5) did not reach bedrock. Due to high amounts of rainfall at Sinkhole D144 was about 2.5 by 2 meters in diameter. the time, the local water table was encountered at a depth It was located north of D222 and directly east of the of about one to one and a half meters. Kettle River (sec. 13, Partridge Twp., T. 43 N., R. 19 W.; Figs. 1 and 4). The north–south trench across sinkhole Sinkhole D127 (Figs. 6 and 7) D144 was 4 meters long and had a maximum depth of Sinkhole D127 is located in the northeastern part of 1.75 meters. This sinkhole had only two sedimentary the study area (sec. 1 of Partridge Twp., T. 43 N., R. 19 layers, an organic-rich duff, and a dark red till. W.: Figs. 1 and 6). Unlike all other mapped sinkholes, The top stratum was a black, organic-rich material this was the site of a recent collapse—a 1.3 by 1.4 meter composed of recent leaf litter and abundant shallow roots, topsoil plug had dropped as much as 80 centimeters as well as larger tree roots. It was about 20 centimeters below the flat ground surface. The grass on the displaced thick outside of the sinkhole drain. The recent organic topsoil was still alive and the sides of the hole showed material filled the entire drain funnel and extended to the fresh dirt. The topsoil was undercut on the north and bottom of the excavation. west sides, so that the actual sinkhole had a diameter of 2 The organic duff was directly underlain by dark by 1.8 meters. This recent collapse is located 46 meters reddish brown sand-rich till. The till contains more clay east of a well-established stream sink (D126) that drains than sinkholes D222 and D355, both of which are south a swampy closed depression about 13 acres (0.05 km2) in of the glacial readvancement moraine. Sinkhole D144 is area (Fig. 6). Because these sinkholes are close together on the north side of the moraine. The till contained both and relatively far from other karst features, we assume locally derived rocks (more angular) and glacial erratics that the same fracture controls both. A trench oriented (mostly basalt), although there were not many large rocks north–south across this sinkhole is roughly perpendicular of any type. The Hinckley boulders were found inside or to the assumed orientation of an underlying joint. The close to the organic funnel. Excavation in this sinkhole three-meter long trench was excavated by hand to an average width of 1.7 meters and a depth of 2.5 meters.

59 ��

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Figure 6. The distribution of sinkholes in sections 11 and 12 of Partridge Township (T. 43 N., R. 19 W) directly southeast of the railroad tracks, north-central Pine County, Minnesota. Sinkholes in this area are distinctly clustered. See Figure 1 for the location in Pine County of the area shown above and Figure 7 for a cross section of the excavation of sinkhole D127.

60 ��

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Figure 7. Stratigraphic cross section of sinkhole D127, as exposed by excavation in sections 11 and 12 of Partridge Township (T. 43 N., R. 19 W), directly southeast of the railroad tracks, north-central Pine County, Minnesota. The vertical displacement of the mature, medium-grained sand unit is at least five meters farther down, into the underlying bedrock.

61 The excavation revealed six matrix sedimentary strata: municipal sewage lagoons (sec. 29, T. 43 N., (1) organic rich duff, (2) mixed sand and aeolian loess, R. 19 W.; Figs. 1 and 8). The closed area of this feature (3) mature reddish brown sand, (4) dark reddish brown was 10 by 12 meters; the main sinking point was a 1.5 by clay, (5) immature gravelly sand, and (6) dark red till. All 2 meters by 0.5 meter deep drain in the bottom of the main had been locally disturbed by the sinkhole collapse. depression. Two secondary drains were less than half a The top layer was a very dark grayish brown organic- meter across and less than one meter deep. With the aid rich material composed of dead grass, soil, and abundant of a backhoe, a trench oriented roughly north–south was roots; it ended at a well-defined A-horizon soil. This excavated across this feature to a length of 9.0 meters and layer was uniformly 20 centimeters thick across the a depth of 5.0 meters. The excavation reached bedrock entire excavation. The organic-rich layer overlies a 25- and encountered five sedimentary layers. centimeter thick layer of loess and sand. Few roots were The feature is located low in the landscape within a found in this light yellowish brown material. The sandy shallow stream bottom. The water table is fairly close to loess has gradational contacts with both the overlying and the surface; in fact, the seasonal high water level is above underlying strata. the ground surface. The till was wet, and the sidewalls of The sandy loess was underlain by 1.0 meter of dark the trench slumped continuously throughout excavation, brown sand. This sand is mature, uniform, and well making it difficult to construct a detailed cross section. sorted. There were no rocks and only a few small gravel The slumps also obscured the bedrock at the base of lenses. The sand bears a strong resemblance to lithified the trench, but we were able to observe two bedrock Hinckley Sandstone. fractures. The Hinckley-like sand was underlain by dark The top stratum was a black organic-rich material red clay that was an average of 15 centimeters thick, composed of recent dead grass and leaves, roots, and although its thickness and orientation was variable soil. It was about 25 centimeters thick across the within the excavation. The sand–clay contact appears sinkhole, and nearly 45 centimeters thick in the sinkhole to be unconformable. The clay layer was underlain by drain. The organic-rich material was underlain in places more sand, but this sand was immature and poorly sorted; by laminated fine silt and sand, which was as much as lenses of gravel or clay were common. The immature 1.0 meter thick. The rest of the excavation was in till sand was underlain by dark red, clay- and sand-rich, and gravel until reaching bedrock at a depth of about 5 rocky to gravelly till. The till contained both locally meters. Several large slabs of sandstone were lying on derived rocks and glacial erratics. The contact appears the bedrock surface. to be unconformable. The top of the till was very damp The excavation revealed several striking features the day after a short rainfall, whereas the overlying sands (Fig. 9). The first was the hourglass-shaped material were dry owing to the till being much less permeable than extending from below the primary drain, which is the sands. composed of leached organic material that cross cuts The sinkhole was excavated by hand (within safety other strata, like the funnel in the D222 excavation. This limits) without reaching bedrock. Two months later, hourglass persisted to about one and a half meters beneath we returned with the Minnesota Geological Survey's the drain, where it gained a significant amount of gravel truck-mounted Giddings Soil Probe™ to investigate the but remained gray in color, in contrast to the surrounding relationship of this collapse sinkhole to the underlying till, which was dark red. The shape of the gray gravel- bedrock. Bedrock outside of the sinkhole collapse area rich deposit was complex. Beneath the hourglass organic is about five meters below the land surface (Fig. 7). material it continued downward for another meter, taking Within the throat of the sinkhole, bedrock was deeper. It on a tail-like form higher to the south, thinning out, and formed an asymmetrical funnel in the rock surface, which then again becoming thicker about two meters to the extended to a depth of eight meters before narrowing into south. The gray material here reached almost to bedrock, a much smaller area, ostensibly a fissure. but by this depth the slump collapses interfered with our observations. In this second bulge, the drain gravel was Sinkhole D355 (Figs. 8 and 9) joined by another gravel stringer, this one carrying water. Sinkhole D355 is located south of the The current ground-water path is indicated on Figure town of Askov, near the southeastern end of the 9 by a black line with arrows. The lowest point in the

62 entire gray gravel deposit is located roughly above what The cross sections also show that the cave walls appeared to be a joint during excavation. are vertical and straight. They are formed by two near- parallel vertical joints in the sandstone. Near its entrance, Streamsinks the cave is as wide as seven meters, but it narrows to an Twenty-four streamsinks have been mapped in the impassible crack 63 meters from the entrance, where the study area (Table B2 in Appendix B at end of volume). fractures converge. The cave occupies the space between Streamsinks are the termination (sinking point) of the two main joints. If the orientation of these major streams. The streams may be either ephemeral or fractures is projected across the Kettle River, they line up continuously flowing. During dry periods, streamsinks with a dense linear cluster of sinkholes (the Hells' Gate can be difficult to distinguish from sinkholes. Additional sinkhole array). streamsinks exist in the area. The Big Sink south of The floor of the cave is entirely covered by sandstone Askov is a good example. A stream enters this large blocks that have fallen from the ceiling. Two observations closed depression (about 100 meters in diameter), but no can be made about the floor debris: (1) natural forces streams exit it. The stream has some natural reaches, but have removed much of the rock debris, creating the open in other places it has been turned into a county ditch. The space, and (2) a solid floor cannot be seen. In other original stream may have had only intermittent flow; it words, the depth of the debris pile is unknown; it may be now has almost continual flow and receives contributions as deep as the bedrock incision below the Kettle River. A from the Askov municipal sewage lagoons. number of sinkholes above the cave actively drain several wetlands between the valley wall and Minnesota State Springs Highway 23. Similar caves are found near the Robinson cave Springs are important karst features. They are that show the same structural control but are shorter natural outlets of the ground-water flow systems and and smaller than the main cave. Fourteen smaller return ground water to the surface. Thirty-one springs sandstone caves have been reported in the study area by were mapped in the study area (Table B3 in Appendix Matt Kramar (Minnesota Speleological Survey, personal B at end of volume). Not all springs have been located. commun. on cave locations, 2001). Many additional springs exist and remain to be found. Most springs are located along the Kettle River, which Composite features is an important base level control for the area containing karst features. Several types of springs exist. One type A final class of features have both glacial and karst produces young water and shows impact from human components. Where a karst system is developed in a activities. Another spring type produces old water that is glaciated landscape, it is inevitable that some features relatively unaffected by human activities. will have characteristics of both systems. In Pine County, such composite glacial karst features are typically large Caves closed basins of presumed glacial origin that drain internally to one or several specific sinkholes. Sinkholes There are several caves in the Hinckley Sandstone D126 and D327 are parts of two of these larger composite within the study area. The best known is Robinson's features (Fig. 6). Ice Cave (also called the Bat Cave), which is located in Banning State Park, due east of the City of Sandstone INTERPRETATION (Fig. 10). The plan view in the upper half of Figure 10 shows the horizontal shape of the cave. Labeled cross sections show the passage shape at various locations. Sinkhole Distribution Relative to Bedrock Type The profile view in the lower half of Figure 10 The Hinckley Sandstone underlies all of the mapped shows the vertical shape of the main cave passage, looking sinkholes, and all the sinkholes are northwest of the north. The profile also illustrates the very flat ceiling and Hinckley fault. Most sinkholes lie within five kilometers bedding plane effects. The ceiling in this cave is very of the fault. None have been mapped more than seven flat because sandstone blocks have fallen from it along kilometers from it (Shade and others, 2001; Plate 6 of the horizontal bedding surfaces. Pine County geologic atlas). ��

��

� ��

��

�

� ��

��

� �� Sinkhole � ��

Figure 8. The distribution of sinkholes south and east of the City of Askov (secs. 20, 29, and 30, T. 42 N., R. 19 W), about six miles northeast of the City of Sandstone, north-central Pine County, Minnesota. Sinkhole D355 and others are located less the 100 meters from municipal sewage lagoons. See Figure 1 for the location in Pine County of the area shown above and see Figure 9 for a cross section of the excavation of sinkhole D355.

64 ��

��

� ��

��

Figure 9. Stratigraphic cross section of sinkhole D355, as exposed by excavation in section 29, T. 42 N., R. 19 W., less than one mile south of the City of Askov, north-central Pine County, Minnesota. Dashed line indicates the extent of the excavation. Water was visibly moving through the soil into underlying bedrock fractures during the excavation.

The Hinckley Sandstone is thinner southeast of the sufficient size to allow surface material to collapse or be Hinckley fault, and the underlying Fond du Lac Formation washed downward into the openings. is closer to the surface. No sinkholes have been found Sinkholes located immediately northwest of the southeast of the Hinckley fault. The Hinckley Sandstone Hinckley fault appear to drain to wetlands located on is not as thick in this area and is somewhat feldspathic. the southeast side of the fault, where the landscape is Joints may not penetrate as deeply as they do northwest lower and wetter. On the west side of the sinkhole array, of the fault, where the sandstone is thicker. The Fond numerous springs along the Kettle River are probably fed du Lac has a higher content of clay and silt, sediments by flow related to the surrounding sinkholes. However, that are more likely to clog a developing fracture system. the connection of the feeder sinkholes to the springs In contrast, the Hinckley Sandstone northwest of the remains to be demonstrated, and the ground-water Hinckley fault is composed almost entirely of quartz, and, chemistry indicates the presence of multiple water types. hence, lacks clay or minerals that alter to clay. Karst development is commonly focused at the Sinkhole Distribution Relative to Depth to intersection of fractures and bedding planes. In outcrops Bedrock along the Kettle River, the Hinckley Sandstone contains The thickness and composition of Quaternary enlarged vertical joints, caves, and horizontal layers sediment are also important factors in determining where that have small conduits. If these features persist in the sinkholes are likely to form. Where such deposits are subsurface away from the valley, their presence would thin, surface water is able to move relatively quickly into provide ideal flow paths for the rapid movement of water the underlying bedrock. Areas of high transmissivity from the surface into the subsurface. Sinkholes form within the Quaternary section—for example, sand lenses, when shallowly buried bedrock develops openings of gravel lenses, or boulder concentrations—also permit

65 surface water to move downward rapidly. Areas of Sinkhole Formation thin, sandy, highly permeable Quaternary sediment that The sinkholes in Pine County formed when turbulent are underlain by fractured bedrock represent the most surface water sank through Quaternary sediment and favorable conditions for sinkhole development (Shade transported fine-grained sediment into an underlying and others, 2001; Plate 6 of the Pine County geologic system of open joints in the Hinckley Sandstone, which atlas). eventually caused the land surface to subside. Once In the area where sinkholes have been mapped, the formed, sinkholes are fed by surface runoff areas and Quaternary sediment is sandy and contains an abundance can drain large volumes of water during spring snowmelt of large boulders and slabs of locally derived Hinckley and after heavy rain, at which time large whirlpools Sandstone. In many places they are piled on top of one can form and water can be heard running underground. another in such a way that many large openings through Several sinkholes serve as terminal sinks of perennial which surface water can move rapidly are created These or ephemeral surface streams. Water that drains into conditions can promote periodic flushing of fine-grained sinkholes becomes ground water as soon as it reaches the sediment and the development and maintenance of water table. The process may transpire in seconds and sinkholes. Piles of boulders near joint openings may act rarely takes longer than a few minutes. as strainers, allowing fast moving water and its sediment The seasonal high water table is in or above some load to pass through at some points and blocking it at of the sinkholes, and they are drowned during periods of others. The process may prevent clay and other fine- high water. It is unknown whether the drowned sinkholes grained till transported by water from uniformly clogging continue to accept water during the floods or if the the joints. flow reverses and they act as springs, intensifying local floods. Sinkhole Distribution Relative to Glacial Our excavations indicate two modes of sinkhole Features formation: collapse and subsidence. The collapse The sinkholes generally lie along a glacial features are illustrated by the excavations of sinkholes readvancement moraine, but the causal relationship of D222 (Fig. 3), D144 (Fig. 5) and D127 (Fig. 7), and moraines and sinkhole distribution is uncertain. High subsidence features are illustrated by D355 (Fig. 9). volumes of unsaturated water from glacial discharge may have caused quartz and, therefore, bedrock solution to Collapse sinkholes proceed faster than at nonglacial-period rainfall levels. Sinkhole formation by collapse occurs when Discharge of glacial meltwater off the front of the infiltrating water moves material into open fractures in moraine at the end of the Wisconsinan glaciation may the sandstone bedrock, leaving a void in the dirt over also have flushed fine-grained sediment from joints in the the fracture. The process continues as the void enlarges underlying bedrock. Such open joints could subsequently and then collapses. The collapse may work its way act as subsurface conduits over which the sinkholes progressively to the surface in a series of failures, or could form. The movement of surface sediment into the the surface may collapse in a single catastrophic failure. underlying fractures and conduits is an ongoing process, D127 is a collapse sinkhole (Fig. 7). The area surrounding as demonstrated by the recent collapse of sinkhole D127 the sinkhole has relatively flat-lying sedimentary layers, (Fig. 7). which are consistent across the whole area, as verified A final point in the relationship of sinkholes and from soil borings. The sequence is only different within glaciation is that this area has been glaciated many the sinkhole. Furthermore, the sediments in the sinkhole times. The age of the conduits is unknown. Glacial are disrupted and mixed, indicating that they have been activity may not only keep the fracture system open by physically moved. Specifically, higher strata have been periodic flushing with meltwater, it would also add and moved downward, whereas lower strata are reduced or remove the Quaternary sediment in which the sinkholes completely missing. Collapse is the simplest explanation are developed. The sinkholes are ephemeral at a geologic for this geometry. Human activities or natural processes, time scale and possibly shift position through time. such as tree fall, would produce a different stratigraphy. Although the excavations of D144 and D222 were not as extensive as that of sinkhole D127, each follows

66 the same pattern: shallow sediments are being moved Our models, which are based on observations from downward into the subsurface. Sinkhole D144 probably sinkhole excavations, involve water moving into enlarged represents a more advanced stage of the process seen bedrock fractures as the driving mechanism of sinkhole in D127: the initial collapse created a sinkhole, which formation. Such fractures were observed in sinkhole continues to slowly move material downward. None D355 (Fig. 9), and in the Giddings Soil Probe borings of the original collapse features are left, owing to the in sinkhole D127 (Fig. 7). In sinkhole D127, bedrock ongoing activity of the sinkhole. The material in the was at a relatively uniform depth (about five meters) throat of the sinkhole was mostly relatively unweathered surrounding the collapse feature, both in the soil borings organic material, which indicates that the sinkhole is shown on Figure 7, and several other soil borings that are active. outside of the area of the figure. We made eight borings Sinkhole D222 is an even older version of this type in the area, in which the stratigraphy and depth to bedrock of sinkhole, in which the collapse funnel has stabilized was fairly uniform. Conditions differed only in the throat and an open hole (as wide as two inches in diameter) now of the collapse. In one boring, we reached a depth of 8.0 drains the sinkhole and continues to transport sediment. meters without hitting bedrock. The boring encountered Here, the organic material deeper in the original collapse only smaller rocks and the same mixed sand and till funnel has weathered to a paler gray, because this part of that typified the sinkhole funnel material. We stopped the sinkhole is inactive. at that depth because the soil probe became caught between rocks, not because we hit bedrock. Materials Subsidence sinkholes that are consistently seen at 1 meter to 1.5 meters in the In subsidence sinkholes, infiltrating water moves borings outside of the sinkhole have been moved at least material into open fractures in the sandstone bedrock, 7 meters farther in the subsurface in the sinkhole throat! and the unconsolidated material above is loose enough to Furthermore, this very deep area was small (narrow). Just continually settle, or only fine grains are removed out of a inches to the side we were not able to enter the fissure. high porosity deposit, such as very clean coarse gravel or Because the excavation and a set of soil auger holes were boulder pile. The excavation in sinkhole D355 (Fig. 9), oriented in a line perpendicular to a trend from D127 and about one mile south of Askov and immediately southeast the nearby streamsink D126 (Fig. 6), we would expect the of the sewage disposal ponds, provides the best example fissure to be narrow, and the elongate dimension to stretch of the process. This sinkhole is about 10 meters in between sinkholes D126 and D127. More sinkholes are diameter. Movement of material into the fractures affects present beyond sinkhole D127 in the woods to the east, the geometry of the sedimentary deposits. A cross-cutting the formation of which were ostensibly driven by the sinkhole funnel is directly below the drain and leads down same large fractures. to a distinct "channel" of gravel bearing organic material. We observed ground-water interflow moving through part Composite Features of the main gravel deposit, which has two distinct low The large-scale glacial and karst features that were points, both above bedrock fractures (Fig. 9). We infer discussed previously are presumed to be controlled by from the morphology of the gravel deposit below the many of the same features as the smaller sinkholes: sinkhole drain that when the sinkhole receives water, the (1) bedrock type, (2) depth to bedrock, (3) depth to the surface water follows the gravel connectivity to the same water table, and (4) variation in the underlying sediment. point that interflow water always travels, as indicated by However, the initial closed basins were created by the arrow-headed lines on Figure 9. The higher bulge glacial advance and recession. Many of the large closed of gravel directly below the sinkhole drain is interpreted drainages are evident on topographic maps of central to be an older flow path toward the joint that was briefly Pine County. They commonly align with moraines and examined. This gravel lens extends out of the plane of the direction in which a glacier moved. Depending on the the figure to the east beneath the auxiliary drains. It is type of sediment they constitute, they may hold water. A assumed that the water from the auxiliary drains reaches feature that holds water is more likely to form catastrophic the bedrock at this joint, to the east of the trench, in a collapse sinkholes or initiate soil-piping sinkholes. Large similar fashion. The presence of the large boulders like basins underlain by very permeable materials are more these near the bedrock surface may serve as filters.

67 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � MN58:C0001 � � � � � � � � � � � � � and CalvinAlexander � � � � � � � � � � � � � � Compass andSurveyTape by the Drafted by Bev Shade,August 2000 Robinson's Ice Cave (Bat Cave) Minnesota Speleological Survey August 2001: Bev Shade and CalvinAlexander Banning State Park, Pine County, Minnesota February 1980:Anne Kress, Ed Zawlocki, DavidTallman,

68 likely to leak into their surroundings fast enough not to initiate collapse features. �

� Several examples of composite glacial and karst �

� features are evident in Partridge Township (T. 43 N., � � R. 19 W.) (Fig. 6). Feature D126 is a sinkhole and � � � � � � � � streamsink at the edge of one of the large elongate basins � � � � �

� that are parallel to other glacial features. The basin is � � �

� presumed to be of glacial origin. A well-defined creek bed � in the lowest part of this basin leads down into a clean, washed boulder pile in the mouth of feature D126. The closure of this presumed glacial basin includes about 13 acres (0.05 km2). The water collected by a feature of this � � � size is capable of triggering sinkhole formation in an area � � � � � � �

� that already has shallow bedrock and extensive enlarged � � � � � � � � fractures. Nearby sinkholes form a roughly east–west � trend. The trend is presumably the surface expression of a bedrock fracture draining all of the sinkholes. � � �

� This type of composite feature is fairly common in � �

� the study area. A large closed basin (about 25 acres) of � �

� glacial origin is visibly drained by sinkhole D327 (Fig. 6). � �

� Several local residents have described large whirlpools � �

� forming over the sinkholes during snowmelt or after large � � rains. They also describe loud sounds of rushing water � � underground near the sinkholes. � � � � � � What is not a sinkhole? � � � What is a sinkhole? Ultimately, a sinkhole is a hole in the ground formed by karst processes that transmits water and material quickly below ground. It acts as a natural storm sewer. What is not a sinkhole? By the same criteria, a nonsinkhole is a hole in the ground made by other means, which does not act like a natural storm sewer. There are many karst sinkholes in central Pine County, but there are also many closed depressions that �

� are not sinkholes. Like sinkholes, these holes come in a

� variety of shapes and sizes. � Common examples are the holes left by fallen trees.

� Even if the fallen tree itself has decayed, a mound of dirt � � � � � �

� ripped up by the roots of the tree will remain. The mound profile view immediately above shows verticalthe configuration cave along the long axis, its cave showsof lookingThe north. � �

� � � � �

� of dirt is a good indication that the depression in not a � � � � � � � � sinkhole. The same can be applied to man-made holes. �

� Holes that are not formed by collapse or piping (the way

�

� � � � sinkholes form) must be formed by moving material Plan and profile view of Robinson's Ice Cave, on the west bank of the Kettle River in Robinson's Park, Pine County, Minnesota. The cave, � � � � � � � � � up and out of the hole. For efficiency, this material is commonly put as close as possible to the excavation.

� � � �

�

� Thus, man-made holes are characterized by nearby piles � � � � � � associatedplanviewandThe area.crosslargestthe sectionsthealsoknowncalledCave,whichfacingcaveinBatistheisthelateral pageshowthe on The cave.extentthe of clear structural control from two bedrock fractures, similar to the orientation of the Hell's Gate sinkhole array directly across the Kettle River.

Figure 10. of dirt. Glacial activity can create a variety of closed depressions over a wide range of scales that are not

69 sinkholes. Glaciers make closed depressions both Klimchouk, A.B., and Ford, D., 2000, Types of karst through deposition and erosion. The difference between and evolution of hydrogeologic setting, in Klimchouk, a purely glacial basin and a composite glacial and karst A.B., and others, eds., Speleogenesis: Evolution of feature can be hard to determine, especially when both karst aquifers: Huntsville, Ala., National Speleological exist in the same area. For example, feature D326 was Society, p. 45–53. originally mapped as a sinkhole within a glacial basin. Shade, B.L., Alexander, E.C., Jr., Alexander, S.C., and D326 is a large asymmetrical depression, about 250 Martin, Samuel, 2001, Sinkhole distribution, on Plate meters in diameter (Fig. 6). It is in an area that has both 6 in Boerboom, T.J., project manager, Geologic atlas of sinkholes and composite features. In the portions of the Pine County, Minnesota: Minnesota Geological Survey basin that were excavated, the stratigraphy was strikingly County Atlas Series C-13, Pt. A, scale 1:100,000. different from that in the other excavated sinkholes. It Truluck, T.F., 1991, Deepest and longest caves in Africa possessed no obvious drain points, no cross-cutting and southern Africa, and the deepest sandstone caves in relationships, and no movement of recent organic debris the world: South American Speleological Association down the funnel. The shape of the land surface there is Bulletin 32, p. 99–101. primarily controlled by a large pile of boulders, which White, W.B., 1988. Geomorphology and hydrology of forms a roughly north–south ridge on the east side of the karst terrains: New York, Oxford University Press, depression. Soil cover on top of the ridge was very thin. 464 p. Toward the center of the depression, the soil was much White, W.B., Jefferson, G.L., and Haman, J.F., 1966, thicker and plowing horizons were apparent. An irregular Quartzite karst in southeastern Venezuela: International surface of sandstone boulders underlaid the horizontal Journal of Speleology, v. 2, p. 309–314. sediments. Wray, R.A.L., 1997, A global review of solutional As stated in the section on composite features, weathering forms on quartz sandstones: Earth-Science karst sinkholes can develop in closed depressions of Reviews, v. 42, no. 3, p. 137–160. glacial origin. However, the development of this type of Wright, H.E., Jr., 1964, Origin of the lakes in the Chuska sinkhole depends on having shallow depth to bedrock and Mountains, northwestern New Mexico: Geological well-developed bedrock fractures. Sinkhole development Society of America Bulletin, v. 75, no. 7, p. 589–597. also depends on the composition of unconsolidated Young, R.W., 1987, Sandstone landforms of the tropical deposits on top of the bedrock. The deposits vary widely East Kimberley region, northwestern Australia: Journal in sediment type, even at the meter scale. Several closed of Geology, v. 95, p. 205–218. depressions (basins) of glacial origin (Fig. 6) are drained ———1988, Quartz etching and sandstone karst: by sinkholes or streamsinks (for example, D126 and Examples from the East Kimberleys, northwestern D327) in the area of Partridge Township (sec. 11, T. 43 Australia: Zeitshrift fuer Geomorphologie, v. 32, p. N., R. 14 W.) whereas others nearby are not. 409–423. Zawidzski, P., Urbani, F., and Koisar, B., 1976, ACKNOWLEDGMENTS Preliminary notes on the geology of the Sarisarinama Financial support for this project was provided by Plateau, Venezuela, and the origin of its caves: Boletain the Pine County Soil and Water Conservation District, de la Sociedad Venezolana de Espeleogaia 7, p. 29–37. and the University of Minnesota, Department of Geology and Geophysics. Banning State Park granted permits to investigate sinkholes within the park.

REFERENCES Chalcraft, D., and Pye, K., 1984, Humid tropical weathering of quartzite in southeastern Venezuela: Zeitschrift fur Geomorphologie, v. 28, p. 321–332. Ford, D.C., and Williams, P.W., 1989, Karst geomorphology and hydrology. London and Boston, Unwin Hyman, 601 p.

70 APPENDIX A

GEOPHYSICAL AND GEOLOGIC LOGS OF CORE

RECOVERED FROM FIVE BOREHOLES IN PINE COUNTY, MINNESOTA

EXPLANATION Township (T)–Range (R)–Section (Sec.)–subsection. See Appendix Figure A1 below for explanation.

Elevation—Land-surface elevations (in feet above sea level) are estimated (± 5 feet) from topographic contours on 1:24,000-scale quadrangle maps.

Map—U.S. Geological Survey 7.5-minute topographic quadrangle map.

MGS unique number—Unique numbers are assigned to wells that have have stratigraphic information.

Magnetic susceptibility—Magnetic susceptibility is measured in 0.001 SI units.

Gamma—Natural gamma radiation is measured in API gamma units.

Lithology—A graphic log showing the rock types found in the core.

Description—Summary descriptions made from physical examination of the core.

The location of drill holes is described by township number (T), range number (R), section number (S), and subdivisions of sections by quarters. The abbreviated T-R-S system used here reflects the fact that all B A townships in Pine County are north of a zero standard parallel, and west of a zero principal meridian, thus N and W are implied. The system used by the Minne- sota Geological Survey to subdivide a section (one square mile) assigns letters to the quarters of a section where A is the NE1/4, B is the NW1/4, C is the SW1/4, and D is the SE1/4. Each quarter is then subdivided into four more quarters using the letter system. In listing quarters, the largest subdivision is C D given first and each quarter of a quarter is given in sucession. In the example at left, the subdivisions of the section would read BCDAB.

Appendix Figure A1. Diagram to illustrate the process of locating a drill hole (bullet within a section by means of the abbreviated T-R-S system.

71 GIESE

SAND AND GRAVEL: Reddish brown, interbedded, moderately to well sorted sand; poorly sorted gravel. Outwash.

LOAM TILL: Faint reddish gray, unoxidized, dense, massive, uniform, calcareous; pebbles common; some small wood fragments; texture 39% sand, 40% silt, 21% clay (averages for 20 samples). Superior provenance till: Askov–Lookout Tower phase.

SAND AND SILT: Reddish brown, well sorted, fine to very fine sand interbedded with reddish brown silt layers; calcareous. Lake deposits.

LOAM TO SANDY LOAM TILL: Reddish brown, oxidized, dense, massive, noncalcareous; pebbles and cobbles common to abundant; inclusions of gray-green weathered basalt or saprolith common; texture 73% sand, 18% silt, 9% clay (averages for 10 samples). Superior provenance till: Grindstone or older phase.

SAND: Brown, well-sorted, medium to coarse, noncalcareous. Lake deposits or distal outwash. Continued on following page 72 Borehole MGS-PCR1 continued

0 Mag. Susc. (x 1000,SI) 12 0 Gamma 100 Lithology Description 150 SAND AND GRAVEL: Brownish gray, poorly sorted fine to coarse sand and fine to coarse gravel; noncalcareous. Outwash.

SANDY LOAM TILL: Brownish gray, unoxidized, dense, noncalcareous; pebbles common; texture 56% sand, 25% silt, 19% clay (averages for 2 samples). Superior provenance till: possibly pre-late Wisconsinan episode. SAND AND GRAVEL: Brown, poorly to moderately well sorted, fine to coarse sand with some fine to coarse gravel (gravel amounts vary), noncalcareous. Outwash.

SANDY LOAMY TILL: Dark brown, unoxidized, noncalcareous; some pebbles; texture 76% sand, 11% silt, 13% clay (one sample). Superior provenance till: possibly pre-late Wisconsinan episode. SAND AND GRAVEL: Yellow to red-brown, oxidized, poorly sorted to moderately well sorted, fine to coarse sand and fine to coarse gravel (some gravel in 225–256 ft; abundant gravel in 256–265 ft), noncalcareous. Outwash.

REWORKED SANDSTONE: Faint pinkish salmon, soft, very well sorted, very fine to fine, subrounded to rounded, quartz- rich; some scattered basalt grains. Reworked local sandstone.

SANDSTONE: Faint pinkish salmon, hard, very well sorted, very fine to fine, subrounded to rounded, quartz-rich. Hinckley Sandstone.

73 255282

SAND AND SILT: Brown, well-sorted, fine sand grading to silt, followed by brownish gray clayey silt; noncalcareous. Lake sediments. SAND AND GRAVEL: Brown, poorly sorted, fine to coarse sand and fine to coarse gravel; noncalareous; one-foot thick granite boulder at lower contact. Outwash. SANDY LOAM TILL: Reddish brown, oxidized, uniform (except for a 6-inch sand and gravel layer at 15 ft and a 6-inch silty fine sand layer at 20 ft); calcareous below 8.5 ft; pebbles common; texture 63% sand, 23% silt, 14% clay (averages for 5 samples). Superior provenance till (Sandstone or older phase).

SILTY SAND: Dark reddish brown, very well sorted, very fine sand; massive; calcareous; some thin till stringers and silt pods at upper contact; a few very thin red silty clay layers at 42 ft, and 1-ft thick silt and clayey silt layer at the lower contact. Lake deposits.

SILT LOAM TILL: Reddish brown, oxidized, calcareous; pebbles common; texture 17% sand, 62% silt, 21% clay (one sample). Superior provenance (undetermined phase). SAND AND GRAVEL: Reddish brown, poorly sorted, medium to coarse sand and fine to coarse gravel, slightly calcareous. Outwash. SANDY LOAM TILL: Reddish brown, partially oxidized, uniform, calcareous; pebbles and cobbles common; sand and gravel layer at 70.5–72 ft; texture 56% sand, 28% silt, 16% clay (averages for 11 samples). Superior provenance (Grindstone or older phase).

SAND AND GRAVEL: Reddish brown, moderately sorted, medium to coarse sand; some thin fine gravel layers, calcareous. Outwash. SANDY LOAM TILL: Reddish brown to gray, partially oxidized, calcareous; pebbles and cobbles abundant, a few large carbonate clasts; texture 51% sand, 32% silt, 17% clay (one sample). Superior provenance (Grindstone or older phase). SAND: Reddish brown, well-sorted, fine to coarse sand (coarsens with depth from fine to coarse); a little fine gravel at upper contact (116–117.5 ft); calcareous. Deltaic lake deposits.

Continued on following page

74 Borehole MGS-PCR2 continued

0 Mag. Susc. (x 1000,SI) 12 0 Gamma 100 Lithology Description 150

MIXED SANDY LOAM TILL AND WEATHERED SANDSTONE: Red, oxidized, dense, calcareous; pebbles predominantly Fond du Lac sandstone; a few basalt pebbles; texture 71% sand, 9% silt, 20% clay (one sample). Superior provenance (probably pre-Late Wisconsinan mixed with weathered sandstone fragments). SANDSTONE, SILTSTONE, AND SHALE: Red (some light gray layers), hard, fine sandstone with thin (1–3 in) layers of siltstone and shale. Fond du Lac formation.

75 SAND: Reddish brown, well-sorted, fine sand; cobble layer at base; noncalcareous. Outwash. SANDY TILL: Reddish brown, oxidized, noncalcareous; abundant pebbles; gray-green weathered zone at 7–8 ft; texture 82% sand, 8% silt, 10% clay (one sample). Superior provenance (Automba or older phase). SAND AND GRAVEL: Brown, poorly to moderately sorted, fine to coarse sand and some fine gravel; more gravel at base; noncalcareous. Outwash. SANDY TILL: Brown, oxidized, noncalcareous; abundant pebbles; texture 73% sand, 15% silt, 12% clay (one sample). Superior provenance (Automba or older phase). SAND AND GRAVEL: Reddish brown, poorly to well-sorted, fine to coarse sand and some fine gravel; 33–38 ft, fine to medium sand with no gravel; noncalcareous. Outwash. SANDY LOAM TILL: Reddish brown, oxidized, noncalcareous; abundant pebbles and cobbles; texture 57% sand, 24% silt, 19% clay (one sample). Superior provenance (Automba or older phase). SAND AND GRAVEL: Reddish brown, poorly to well sorted, fine to medium sand and some zones of fine gravel; increasing quartz near base; noncalcareous. Outwash. SANDSTONE: White, very well sorted, very fine, well-rounded, quartz-rich; 82.5–83.5 ft, 97–99.5 ft, fine to coarse with subangular to rounded quartz (chert) pebbles; 92–94 ft, red, silty fine sandstone with chert pebbles. St. Peter Sandstone.

SILTSTONE: Pink, red, green, and yellow; mottled, streaked, hard. Basal siltstone of the St. Peter Sandstone.

SANDSTONE: Dark red, hard; locally weathered; in places, floats of conglomeritic sandstone and other clasts in sandstone matrix. Basal St. Peter Sandstone

76 GLACIAL TILL: Red-brown, sandy, cobbly.

SAND.

GLACIAL TILL: Same as 0–23 ft.

GLACIAL TILL: Red brown to brown gray, sandy and silty till; a few pebbles.

SAND. GLACIAL TILL: Brownish gray; cobbles in places, for example, 47–78 ft.

GLACIAL TILL: Clay- and silt-rich; rare cobbles; zones of greasy red clay (lacustrine); more sand below 115 ft.

SAND: Presence of sand based on driller’s report but no sample recovery; a few cobbles near 149 ft depth.

Continued on following page 77 Borehole MGS-PCC1 continued

0 Mag. Susc. (x 1000,SI) 12 0 Gamma 100 Lithology Description 150

CLAY: Smooth, dark gray, very pure; possibly laucustrine.

SAND. GLACIAL TILL: Gray clay till; abundant cobbles at 6–12-inch intervals. CLAY: Tan brown, soft, watery; smooth drilling; few cuttings.

SAND: No cuttings; judged by ease of drilling.

SANDSTONE: Fine- to medium-grained; few cuttings; drilling mud turned red abruptly; sticky zone at 181–182 ft; possibly shale.

SANDSTONE: At start of drill core, lithic arkosic sandstone similar to Fond du Lac Fm.; dark red brown to light greenish tan; lithic; arkosic; shale rip-up clasts near base.

SILTSTONE: Interbedded siltstone and sandstone. SHALE: Dark red brown smooth shale grading to siltstone.

SANDSTONE: Brown, arkosic; some green shale chips.

SANDSTONE: Pale green to dark maroon brown: two-inch layer of siltstone at top; siltstone chips near 216 ft depth; scattered thin beds of sandy siltstone throughout.

78 ��

��

79 Appendix B

INVENTORIES OF KNOWN KARST FEATURES IN PINE COUNTY, MINNESOTA

80 Continued on following page

COMMENT ------Also B3 -- -- Also B4 -- -- Log Drive Creek—visible from road Log Drive Creek—visible from road ------Thienesson Thienesson Thienesson Thienesson—e Thienesson Thienesson—compound with D26 Thienesson—compound with D25 Thienesson—compound with D28 Thienesson—compound with D27 Thienesson—two collapses evident Thienesson Thienesson Thienesson Thienesson Ditch, east side Ditch, east side Ditch, east side -- Side of trail, small Askov south east of Woods Askov south east of Woods

SECTION 31 29 29 29 --- -- 36 31 30 13 13 ------21 20 20 20 20 20 20 20 20 20 20 20 20 20 14 14 14 30 13 29 29

TOWNSHIP Partridge Partridge Partridge Partridge Partridge Partridge Finlayson Partridge Partridge Finlayson Finlayson Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Finlayson Partridge Partridge

DATE 09/24/99 06/25/97 06/25/97 06/25/97 09/24/99 09/24/99 09/24/99 09/24/99 09/24/99 05/25/01 05/25/01 09/20/99 09/20/99 09/20/99 09/20/99 09/20/99 09/20/99 09/20/99 09/20/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/30/99 09/20/99 05/25/01 -- --

NAME Big Sinkhole -- -- Kroon Kroon Kroon -- Sahlen -- LDC2 LDC3 ------Field Stone -- -- Old Ford -- 25-26-27 25-26-27 25-26-27 ------LDC1 39-40 39-40 Truck

DEPTH (METERS) -- 1 ------1.5 1 ------1 3 2 3 1 4 4 4 2 1.5 1 1 0.5 1.5 ------0.5 -- --

DIMENSIONS (METERS) -- 6 x ------2 x 3 1.5 x 2 ------21 x 14 21 x 14 x 15 x 20 2 x 5 x 6 x 10 x 12 x 8 x 8 x 10 x 5 x 4 x ------1.5 x 1 -- --

UTM N (NAD83) 5113122 5114173 5114132 5114388 5114356 5114222 5113192 5112006 5113405 5117646 5117653 5119014 5118933 5118978 5118890 5119067 5119191 5119224 5119238 5115279 5115750 5115761 5115775 5115762 5115782 5115786 5115791 5115797 5115836 5115849 5115857 5115880 5115853 5117416 5117409 5117398 5113443 5117411 5114397 5114413

UTM E (NAD83) 516234 516998 516964 517540 517549 517440 514461 515420 515243 513285 513291 519564 519554 519660 519858 519788 519567 519897 518528 518745 518368 518346 518314 518292 518303 518298 518286 518274 518315 518345 518334 518320 518365 521610 521610 521612 516323 513274 518323 518294

UTM N (NAD27) 5112910 5113961 5113920 5114176 5114144 5114010 5112980 5111794 5113193 5117434 5117441 5118802 5118721 5118766 5118678 5118855 5118979 5119012 5119026 5115067 5115538 5115549 5115563 5115550 5115570 5115574 5115579 5115585 5115624 5115637 5115645 5115668 5115641 5117204 5117197 5117186 5113231 5117199 5114185 5114201

Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM E (NAD27) 516250 517014 516980 517556 517565 517456 514477 515436 515259 513301 513307 519580 519570 519676 519874 519804 519583 519913 518544 518761 518384 518362 518330 518308 518319 518314 518302 518290 518331 518361 518350 518336 518381 521626 521626 521628 516339 513290 518339 518310

Appendix Table B1. Table Appendix American Datum 1983); leaders (--), not determined.] American Datum 1927; NAD 83 is North American Datum (NAD27 is North Mercator; NAD, North Transverse [Abbreviations: UTM, Universal SINKHOLE NUMBER D001 D002 D003 D004 D005 D006 D007 D008 D009 D010 D011 D012 D013 D014 D015 D016 D017 D018 D019 D020 D021 D022 D023 0024 D025 D026 D027 D028 D029 0030 D031 D032 D033 D034 D035 D036 D037 D038 D039 81D040 road Continued on following page COMMENT Askov south east of Woods Askov south east of Woods Askov south east of Woods Askov south east of Woods Askov south east of Woods Askov south east of Woods Askov south east of Woods Askov south east of Woods Banning East ------Should be more sinks south of Al Jensen Shown by -- -- Seen from road -- In yard ------Foyt Foyt Anderman pasture, west field In Anderman pasture, west field In Near road—Anderman Sinks above Robinson Sinks above Robinson north of sewage ponds Woods north of sewage ponds Woods north of sewage ponds Woods East of sewage ponds Ken Nelsen Ken Nelsen Ken Nelsen Ken Nelsen Barnyard—filled Barnyard—filled Barnyard, filled Pasture—filled Banning park, south Banning park, south

SECTION 29 29 29 29 29 29 29 29 3 1 36 36 36 36 9 9 9 27 2 2 2 2 2 2 2 15 15 22 22 22 -- -- 29 29 29 29 29 29 29 29 18 18 18 18 26 26

TOWNSHIP Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Sandstone Partridge Norman Norman Norman Norman Partridge Partridge Partridge Bruno Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge -- -- Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge

DATE ------10/21/99 12/14/98 12/14/98 12/14/98 12/14/98 12/14/98 ------08/12/00 08/12/00 08/12/00 08/12/00 08/12/00 08/12/00 08/23/00 08/23/00 09/22/00 09/22/00 09/22/00 09/22/00 09/26/00 09/26/00 09/26/00 09/26/00 12/09/00 12/09/00 12/09/00 12/09/00 05/26/01 05/26/01

NAME (METERS) -- 42-43-44 42-43-44 42-43-44 ------Boulder drain U2 Beaver Sink Beaver Sink Beaver Sink Beaver Sink Beaver Sink ------61-62-63 61-62-63 61-62-63 64-65 64-65 -- Foyt Foyt Anderman Anderman Anderman ------1 of pair 2 of pair

DEPTH (METERS) ------1.5 2 2 1.5 1.5 1.5 1 ------1 1

DIMENSIONS ------3 x 4 3 x 4 20 x 10 10 x 10 x 7 18 x 5 2 x ------2 x 0.5 1.5 x 0.5

UTM N (NAD83) 5114435 5114481 5114516 5114544 5114564 5114522 5114579 5114434 5110577 5121274 5121283 5121314 5121314 5121313 5119037 5118922 5118997 5124455 5121119 5121058 5121087 5121001 5120959 5121027 5121232 5117995 5117710 5116236 5116332 5116417 5109929 5109852 5114261 5114271 5114340 5114156 5113914 5113939 5113966 5113827 5116585 5116610 5116562 5116450 5113787 5113790

UTM E (NAD83) 518270 518178 518194 518172 518101 518144 518240 518334 511512 523784 523803 523822 523827 523837 519394 519409 519294 529717 521644 521644 521668 521636 521655 521469 521214 520015 520042 520953 521016 520910 510611 510634 517080 517087 517285 517315 517679 517733 517745 517910 515223 515203 515224 515279 513234 513234

Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM N (NAD27) 5114223 5114269 5114304 5114332 5114352 5114310 5114367 5114222 5110365 5121062 5121071 5121102 5121102 5121101 5118825 5118710 5118785 5124243 5120907 5120846 5120875 5120789 5120747 5120815 5121020 5117783 5117498 5116024 5116120 5116205 5109717 5109640 5114049 5114059 5114128 5113944 5113702 5113727 5113754 5113615 5116373 5116398 5116350 5116238 5113575 5113578

continued.

UTM E (NAD27) 518286 518194 518210 518188 518117 518160 518256 518350 511528 523800 523819 523838 523843 523853 519410 519425 519310 529733 521660 521660 521684 521652 521671 521485 521230 520031 520058 520969 521032 520926 510627 510650 517096 517103 517301 517331 517695 517749 517761 517926 515239 515219 515240 515295 513250 513250

82 Appendix Table B1 Table Appendix American Datum 1983); leaders (--), not determined.] American Datum 1927; NAD 83 is North American Datum (NAD27 is North Mercator; NAD, North Transverse [Abbreviations: UTM, Universal SINKHOLE NUMBER D041 D042 D043 D044 D045 D046 D047 D048 D049 D050 D051 D052 D053 D054 D057 D058 D059 D060 D061 D062 D063 D064 D065 D066 D067 D068 D069 D070 D071 D072 D076 D077 D080 D081 D082 D083 D086 D087 D088 D089 D091 D092 D093 D094 D095 D096 Continued on following page COMMENT Banning park, south Banning park, south Banning park, south Campground, discovery sinkhole near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, near campground Banning West, Banning park, south Near rest stop Near rest stop Near rest stop lots of water Takes Banning East Banning East Banning East Banning East Banning East Steamsink near D127 Excavation 4 Petersen Spring area Petersen Spring area Petersen Spring area Petersen Spring area Petersen Spring—Anderman area Petersen Spring—Anderman area Petersen Spring—Anderman area Petersen Spring—Anderman area Petersen Spring—Anderman area Petersen Spring—Anderman area -- Petersen Spring area Log drive creek area Log drive creek area Log drive creek area Log drive creek area Log drive creek area Log drive creek area

SECTION 26 26 26 3 3 3 3 3 3 3 3 3 3 3 26 14 14 14 28 3 3 3 3 3 11 11 22 22 22 22 22 22 22 22 22 22 23 22 14 14 14 14 14 14

TOWNSHIP Partridge Partridge Partridge Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Partridge Finlayson Finlayson Finlayson Partridge Sandstone Sandstone Sandstone Sandstone Sandstone Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Finlayson Partridge Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson

DATE 05/26/01 05/26/01 05/26/01 ------05/26/01 05/17/00 05/17/00 05/22/00 08/15/00 11/21/00 11/21/00 11/21/00 11/21/00 11/21/00 08/15/01 08/15/01 ------08/30/01 08/30/01 08/30/01 08/30/01 08/30/01 08/30/01 -- 08/30/01 05/04/01 05/04/01 05/04/01 05/04/01 05/04/01 05/04/01

NAME 1 of pair 2 of pair solo 2 3 4 5 6 7 8 9 10 11 12 solo ------W2 W3 W4 W5 Af2 ------dig #3 --

DEPTH (METERS) 1 1 1 ------0.7 ------2.5 1 1 1 1 1 3 1 0.5 1 1 2 1.5 1.5 2 0.5 0.5 0.5 -- -- 0.4 1 1 1.5 0.75 0.5

DIMENSIONS (METERS) 2 x 2 x 3 x 4 ------12 3 x 1.5 ------12 x 15 4 x 4 x 4 x 4 x 4 x 5 x 2 x 1.5 20 x 10 45 x 15 15 x 10 x 15 x 20 25 x 10 40 x 10 x 10 x 10 x -- -- 0.8 x 1 2 x 3 5 x 4 x 2.5 x 3 6 x 4

UTM N (NAD83) 5113863 5113863 5113911 5111350 5111253 5111227 5111121 5111095 5111088 5111086 5111081 5111077 5111076 5110920 5113888 5117453 5117402 5117143 5114653 5110570 5110573 5110579 5110583 5110271 5119233 5119235 5115971 5115915 5115889 5115870 5115935 5116003 5116169 5116308 5116352 5116318 5116011 5116038 5116535 5116525 5116510 5116530 5116584 5116631

UTM E (NAD83) 513239 513243 513273 511358 511339 511345 511301 511248 511246 511243 511246 511245 511244 511236 513248 512709 512716 512744 518920 511525 511528 511534 511539 511367 521816 521773 521039 521014 520985 520962 521077 520950 520398 520438 520435 520414 512053 521081 513578 513594 513603 513625 513597 513624 Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM N (NAD27) 5113651 5113651 5113699 5111138 5111041 5111015 5110909 5110883 5110876 5110874 5110869 5110865 5110864 5110708 5113676 5117241 5117190 5116931 5114441 5110358 5110361 5110367 5110371 5110059 5119021 5119023 5115759 5115703 5115677 5115658 5115723 5115791 5115957 5116096 5116140 5116106 5115799 5115826 5116323 5116313 5116298 5116318 5116372 5116419

continued.

UTM E (NAD27) 513255 513259 513289 511374 511355 511361 511317 511264 511262 511259 511262 511261 511260 511252 513264 512725 512732 512760 518936 511541 511544 511550 511555 511383 521832 521789 521055 521030 521001 520978 521093 520966 520414 520454 520451 520430 512069 521097 513594 513610 513619 513641 513613 513640

See Petersen Spring See Petersen

Appendix Table B1 Table Appendix American Datum 1983); leaders (--), not determined.] American Datum 1927; NAD 83 is North American Datum (NAD27 is North Mercator; NAD, North Transverse [Abbreviations: UTM, Universal SINKHOLE NUMBER D097 D098 D099 D101 D102 D103 D104 D105 D106 D107 D108 D109 D110 D111 D112 D113 D116 D117 D118 D119 D120 D121 D122 D123 D125 D126 D127 D128 D129 D130 D131 D132 D133 D134 D135 D136 D137 D138 D139 D140 D141 D142 D143 D144 83D145 Continued on following page COMMENT Log drive creek area Log drive creek area Log drive creek area Log drive creek area East of D127—Zinkhan East of D127—Zinkhan East of D127—Zinkhan Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Excavation #1, Sept. 2000 Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Banning East Unmapped sinks to east? Cluster of 6 sinkholes Cluster Cluster—1 of 3 Banning East-—2 of 3 Banning East— 3 of Banning East

SECTION 14 14 14 14 11 11 11 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

TOWNSHIP Finlayson Finlayson Finlayson Finlayson Partridge Partridge Partridge Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone

DATE 05/04/01 05/04/01 05/04/01 05/04/01 010/19/01 010/19/01 010/19/01 11/20/99 9/30/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99 11/21/99

NAME (METERS) ------A B C D E E1 F G H I K L N O P Q R S T U1 V W1-dig #1 X Y Z AA AB AD AE AF2 AG AH AI AJ AK AL AL AL1 AM

DEPTH (METERS) 1 0.7 0.3 0.5 ------2 ------1.5 ------1 0.5 0.5 0.5 1 0.3 1 -- 1 1 0.5 0.5 1 0.8 1.5 0.5 0.4 1 0.3 0.7 0.5 -- 1.5 ------1.5

DIMENSIONS 4 x 6 x 6 x 2.5 x 2 ------12 x 8 ------6 x ------31 x 10 8 x 3 x 7 x 10 5 x 3 x 4 x 3 -- 5 x 5 x 4 4 x 4 x 8 x 7 x 15 x 4 6 x 5 x 4 x 6 x 8 x 4 x -- x 7 11 ------10 x 15

UTM N (NAD83) 5116611 5116637 5116633 5116365 5119228 5119261 5119266 5110628 5110630 5110670 5110667 5110824 5110834 5110847 5110863 5110868 5110866 5110682 5110637 5110452 5110420 5110455 5110491 5110551 5110569 5110556 5110571 5110574 5110575 5110570 5110381 5110383 5110410 5110340 5110271 5110270 5110271 5110314 5110341 5110319 5110280 5110264 5110231 5110248 5110224 5110245

UTM E (NAD83) 513637 513641 513843 513672 521874 521908 521943 511583 511596 511579 511578 511804 511778 511801 511799 511798 511803 511691 511638 511378 511368 511393 511420 511459 511473 511498 511508 511511 511530 511546 511361 511357 511339 511333 511328 511346 511359 511290 511239 511204 511172 511162 511088 511141 511115 511095 Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM N (NAD27) 5116399 5116425 5116421 5116153 5119016 5119049 5119054 5110416 5110418 5110458 5110455 5110612 5110622 5110635 5110651 5110656 5110654 5110470 5110425 5110240 5110208 5110243 5110279 5110339 5110357 5110344 5110359 5110362 5110363 5110358 5110169 5110171 5110198 5110128 5110059 5110058 5110059 5110102 5110129 5110107 5110068 5110052 5110019 5110036 5110012 5110033

continued.

UTM E (NAD27) 513653 513657 513859 513688 521890 521924 521959 511599 511612 511595 511594 511820 511794 511817 511815 511814 511819 511707 511654 511394 511384 511409 511436 511475 511489 511514 511524 511527 511546 511562 511377 511373 511355 511349 511344 511362 511375 511306 511255 511220 511188 511178 511104 511157 511131 511111

COMMENT Banning East Banning East Banning East Banning East Banning East Banning East Banning East—cluster of 2 Gate, NE Hell’s Gate, NE Hell’s Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek Log Drive Creek ------South of D314 ------[?] With D30, D331 Near Beaver Sink Near Beaver Sink Near Beaver Sink Road detours Road detours ------

Continued on following page

SECTION 3 3 3 3 3 3 3 3 35 14 14 13 13 13 13 13 13 13 19 19 19 15 15 10 10 10 15 -- 15 15 15 15 14 15 14 14 14 14 11 2 1 1 2 2 11 10 10

TOWNSHIP Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson Finlayson Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge

DATE 11/21/99 11/21/99 11/20/99 11/20/99 11/20/99 11/20/99 11/20/99 08/10/00 08/10/00 010/28/00 010/28/00 010/28/00 010/28/00 010/28/00 010/28/00 010/28/00 010/28/00 010/28/00 ------

NAME AM1 AN BA BB BC BD BE HR2 HR1 1 of 2 2 of ------Hole Triple LDC to Close ------Mailbox across road ------

DEPTH (METERS) -- 0.5 -- -- 2.5 -- 1 2 1.5 3 3 0.5 0.4 0.5 0.5 1 1.5 1.5 ------

DIMENSIONS (METERS) -- 6 x -- -- 5 x -- 2 x 18 x 8 8 x 5 20 x 10 18 x 10 2 x 2 x 20 x 15 2 x 1 1.5 x 1.5 x 16 x 10 ------

UTM N (NAD83) 5110241 5110207 5110251 5110255 5110239 5110218 5110206 5111337 5111686 5116440 5116471 5116539 5116522 5116488 5116540 5116565 5116566 5117181 5115135 5115223 5115223 5117952 5117954 5118045 5118078 5118058 5117241 5117372 5117348 5117343 5117327 5117305 5117192 5117137 5116891 5118023 5117723 5117652 5118109 5121189 5121144 5121098 5119663 5119699 5118558 5118613 5118606

UTM E (NAD83) 511110 511022 511238 511236 511229 511187 511179 511830 512087 513457 513454 513578 513604 513617 513620 513599 513600 513463 516011 515962 515901 521213 521174 521429 521435 521388 521539 521560 521547 521572 521541 521558 521627 521560 521707 521625 522652 522604 523189 523183 523213 523219 521822 521899 521676 521296 521513

Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM N (NAD27) 5110029 5109995 5110039 5110043 5110027 5110006 5109994 5111549 5111898 5116228 5116259 5116327 5116310 5116276 5116328 5116353 5116354 5116969 ------

continued.

UTM E (NAD27) 511126 511038 511254 511252 511245 511203 511195 511814 512071 513473 513470 513594 513620 513633 513636 513615 513616 513479 ------

COMMENT ------Filled ------North of road North of road ------Near cemetery Near cemetery Along county ditch/stream Along county ditch/stream Near streamsink/D5 Near road -- East of Ken Nelsen East of Ken Nelsen Excavation #2, Oct. 2000 near Banning West, campground ------

SECTION 11 11 11 22 22 16 16 10 32 6 -- 21 20 20 30 30 30 30 30 29 29 29 29 -- 29 29 29 3 23 23 15 14 15 9 9 16

TOWNSHIP Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Bruno Fleming -- Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge -- Partridge Partridge Partridge Sandstone Bruno Bruno Bruno Bruno Bruno Partridge Partridge Partridge

DATE ------_ ------12/09/00 12/09/00 12/09/00 12/09/00 12/09/00 09/24/99 09/24/99 09/24/99

NAME ------Oleson Oleson Oleson ------and streamsink

DEPTH (METERS) ------1 ------

DIMENSIONS (METERS) ------10 x 8 ------

UTM N (NAD83) 5118483 5118110 5118112 5116352 5116413 5116482 5116525 5118922 5121346 5121272 5115625 5114878 5114842 5114878 5113801 5113695 5114137 5114669 5114571 5114778 5114744 5114390 5113271 5113902 5113930 5114129 5114113 5111351 5125381 5125350 5126109 5126091 5126135 5119191 5119224 5117551

UTM E (NAD83) 521624 523189 523189 521355 520877 519794 519741 520258 526410 526327 519282 519052 518363 518302 516219 516312 516345 516146 516172 517483 517537 517565 517297 517718 517770 517677 517285 511333 531417 531429 531109 532545 531144 519867 519224 518747

Pertinent information on 262 sinkholes in Pine County Minnesota.

UTM N (NAD27) ------5125169 5125138 5125897 5125879 5125923 5118979 5119012 5117339

continued.

UTM E (NAD27) ------531433 531445 531125 532561 531160 519883 519240 518763

SECTION 31 29 29 36 16 28 3 16 26 26 26 30 29 30 19 19 10 1 36 --

TOWNSHIP Partridge Partridge Partridge Partridge Partridge Partridge Sandstone Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Partridge Norman Partridge

DATE 09/24/97 09/24/97 09/24/97 09/24/97 09/24/99 08/15/00 -- 09/24/99 05/26/01 05/26/01 05/26/01 -- 09/24/99 09/24/99 09/24/99 06/25/97 09/20/99 ------12/14/98 12/14/98 09/20/99

NAME Big Sinkhole -- Kroon Kroon -- Eklund Peterson Spring -- 2 of pair -- 1 of pair ------Big Sinkhole ------Beaver Sink Beaver Sink --

DEPTH (METERS) ------2.5 3 -- -- 1 0.7 1 1.5 ------

DIMENSIONS (METERS) ------12 x 15 5 x 5 -- -- 2 x 2 3 x 1.5 2 x 0.5 15 x 20 ------

UTM N UTM (NAD83) 5113122 5114165 5114389 5113192 5115826 5114653 5119233 5115774 5117551 5113863 5113888 5113787 5115935 5114356 5114222 5113405 5114132 -- -- 5115224 -- 5121274 5121283 5118978

UTM E UTM (NAD83) 516234 516980 517540 514461 518040 518920 521816 521582 518747 513243 513248 513234 521077 517549 517440 515243 516964 -- -- 515963 -- 523784 523803 519660

Pertinent information on 24 streamsinks in Pine County Minnesota.

UTM N UTM (NAD27) 5112910 5113953 5114177 5112980 5115614 5114441 5119021 5115562 5117339 5113651 5113676 5113575 5115723 5114144 5114010 5113193 5113920 5113231 5115135 -- 5118614 5121062 5121071 5118766

UTM E UTM (NAD27) 516250 516996 517556 514477 518056 518936 521832 521598 518763 513259 513264 513250 521093 517565 517456 515259 516980 516339 516011 -- 521296 523800 523819 519676

Appendix Table B2. Table Appendix American Datum 1983); American Datum 1927; NAD83 is North American Datum (NAD27 is North Mercator; NAD, North Transverse [Abbreviations: UTM, Universal leaders (--), not determined.] STREAM NO. SINK B001 B002 B003 B004 B005 B006 B007 B008 B009 B010 B011 B012 B013 B014 B015 B016 B017 B018 B019 B020 B021 B022 B023 B024

87 Appendix Table B3. Pertinent information on 31 springs in Pine County, Minnesota . [Abbreviations: UTM, Universal Transverse Mercator; NAD, North American Datum (NAD83 is North American Datum 1983); MPCA, Minnesota Pollution Control Agency).]

SPRING UTM E UTM N SPRING SPRING AQUIFER NAME (NAD83) (NAD83) TYPE NUMBER Partridge Creek Spring 521582 5115774 SP A01 Spring Gushing Orange Spring 510332 5106182 SP A02 Spring Spring A3 512702 5113817 SP A03 Spring Spring A4 512777 5113401 SP A04 Spring

Beaver Boil 512789 5117938 SP A05 Spring Ferrooxidans Rise 512967 5115217 SP A06 Spring Clear Spring 512859 5114231 SP A07 Spring Orange Mound Spring 512874 5114217 SP A08 Spring

No Charge Spring 513149 5113838 SP A09 Spring Mid Point Spring 513120 5113368 SP A10 Spring Gray Beaver Spring 513031 5112212 SP A11 Spring Orange Boil Spring 510763 5110007 SP A12 Spring

Frog Spring (Clear) 510828 5107073 SP A13 Spring Orange Scum Spring 510647 5106828 SP A14 Spring Hi Conductivity Spring 511096 5107233 SP A15 Spring Orange Seeps 510923 5106969 SP A16 Spring

Orange Seeps 511118 5107323 SP A17 Spring Hi Conduct. II 511124 5107370 SP A18 Spring Hike Spring 511179 5107389 SP A19 Spring Filip Spring 544121 5097159 SP A20 Spring

PSP-1 511165 5108509 SP A21 Spring PSP-2 511067 5109080 SP A22 Spring PSP-3 510855 5110065 SP A23 Spring PSP-6 533308 5088396 SP A24 Spring

PSP-4 533358 5088640 SP A25 Spring PSP-5 533306 5088612 SP A26 Spring KR 708 at Hwy 22 Location from MPCA SP A27 Spring KR 748 at Hwy 48 Location from MPCA SP A28 Spring

WL 727 at Hwy 27 Location from MPCA SP A29 Spring Banning Park 766 Location from MPCA SP A30 Spring Banning Park Low Bench Location from MPCA SP A31 Spring