16 LOESS HILLS: A National Natural CONTENTS Landmark Iowa Jean C. Prior Unusually thick deposits of wind-blown silt in western Iowa contribute to unique 2 STATE GEOLOGIST'S VIEWPOINT topographic forms which have been Geology Donald L. Koch recognized as nationally significant landscapes. Priority topics for investigation and funding include detailed geologic mapping, com- 1987 prehensive evaluation of groundwater 20 ALLUVIAL AQUIFERS: Northwest Iowa resources, assessment of industrial Summary minerals, and the potential for commercial Carol A. Thompson Geological Survey Bureau oil and gas. Studies of groundwater from sand and 123 North Capitol Street gravel deposits along river valleys in north· Iowa City, Iowa 52242 4 GROUNDWATER POLICY AND west Iowa reveal widespread nitrate con- GEOLOGY tamination as well as low concentrations of (319) 335-1575 Bernard E. Hoyer pesticides. Donald L. Koch The Iowa Groundwater Protection Strategy 1987, the fi rst report on an evolving ground· 22 REGIONAL FLOOD PATIERNS: The In- State Geologist and Bureau Chief water policy, recognizes the fundamental fluence of Topography role of geologic conditions in understanding Oscar G. Lara and James D. Giglierano contamination problems. Physical differences in terrain between Iowa Department of Natural Resources various regions of the state can be used to 8 GEODES: A Look At Iowa's State Rock improve estimates of flood magnitude and Brian J. Witzke frequency.
Spherically shaped rocks with hollow in· tenors lined with sparkling crystals may be 24 UNDERGROUND LIMESTONE MINING found 1n stream beds or weathering from Robert M. McKay and Michael J. Bounk Cover: shaley strata 1n southeastern Iowa. Some Iowa limestone producers have This thin-section view of a metamorphic rock (gneiss), as seen through shifted to underground operations in a petrographic microscope, shows interlocking mineral crystals of 10 MICROSCOPIC STUDIES OF ROCK response to geologic and market condi· white, gray, and black quartz with varicolored muscovite mica. The THIN-SECTIONS t1ons, and find problems as well as advan- tages to underground stone extraction. rock is from a cored sequence of uplifted Precambrian-age rocks near Greg A. Ludvigson Manson in northern Calhoun County. Thin-section studies provide im Colorful images of refracted light through portant information about the composition. origin, and history of Iowa's thin slices of rock are a valuable method for 27 FOSSIL AMPHIBIAN SITE: A Significant rock materials. Cross-polarized light, magnified 235x. determining the characteristics of Iowa's North American Find rock and mineral resources Robert M. McKay Cover photo by Greg A. Ludvigson Rare. well-preserved fossils of primitive am- Cover design by Patricia Lohmann 12 HISTORY OF THE UPPER MISSISSIPPI ph1bians and fish found in Iowa will aid VALLEY paleontologists studying the emergence of E. Arthur Bettis Ill vertebrates from water to the land.
A network of buried valleys and the distribu· Jean C. Prior ...... Editor tion of overlying glacial deposits provide 28 SELECTED SURVEY PUBLICATIONS evidence about the ancestry of the Patricia J. Lohmann .. . Publications Designer, Artist An annotated listing of reports published by Mississippi River in the Iowa-Illinois region. the Geological Survey Bureau 1n 1986 pro- Editor's Note.· Appreciation is expressed to Mary Pat Heitman for her vides a guide to completed geological in- secretanal assistance and to the individual authors for their vestigations and to sources of information cooperation. on the state's geology. STATE GEOLOGIST'S VIEWPOINT
ith each issue of Iowa Geology we conduct investigations. New techniques County on March 16, 1987. This is should be supported by state appropria W hope to broaden our readers' ac permit further study and understanding perhaps the most significant "geologic iions - these projects and programs quaintance with different aspects of the of our finite natural resources, and new event" in Iowa's history. The information represent an investment by the state in state's geology and hydrology. Past geologic concepts demand reexamina from this intended 15,000-foot test (near the acquisition of information that is issues have included articles on coal ex tion of long-held ideas and theories. ly three times as deep as the current critical to wise development, manage ploration; irrigation of croplands; mineral What areas of investigation remain to be depth record in Iowa) may confirm, deny, ment, and conservation of our natural resources; caves; water resource in addressed? What work remains to be or alter geologic interpretations about resources. Many projects require coor vestigations; topographic mapping; done? the Midcontinent Rift that presently are dination (and often participation) with hazardous-waste disposal; fossils; oil ex The current detail of geologic mapping based upon geophysical data (gravity, other state/federal agencies to assure ploration; and groundwater contamina is inadequate for much of the state. More magnetic, seismic). Whether or not oil or that all interests are considered, that tion. And yet we have hardly scratched accurate information is required for land gas is discovered, the drill-hole data will duplication of effort is avoided, and that the surface of interesting topics and use planning, environmental protection, add immensely to our knowledge about maximum use is made of each bit of in significant matters that could be brought and hazards control. Our groundwater the geologic framework of Iowa. formation derived from the project. to your attention. resources need further evaluation With all that geologic work to be done, Whether a project is large or small, or As you read this issue, you will relative to available supplies, the extent how do we prioritize and fund new proj whether the necessary tools and equip develop a new sense of our state's and type(s) of contamination, and , yes, ects, especially in light of a limited staff ment require high-altitude imagery or a geologic setting, from the megascopic to the impacts of a predictable drought. We and budget, and be responsive to the in microscope, the expertise of the GSB the microscopic. There are high-altitude need to further assess our supplies of in formation needs of taxpayers? Most new staff will assure a quality product. images of the Mississippi Valley and the dustrial minerals (limestone, clay, gravel, projects, once implemented, should be western Loess Hills; magnified details of etc.), particularly where urbanization two years or less in duration so that time crystal configurations; maps to estimate continues to limit extraction of these ly results are available to the user com flood characteristics; monitoring results com modi ties. munity. All expenses for a project must from sand and gravel aquifers; and And of course there is more to learn be fully considered so that no significant underground limestone mines. Thus, you about our state's potential for commer cost overruns occur. Federal funds will become further exposed to the wide cial oil and gas. Additional exploration should be sought for certain projects that Donald L. Koch range of our geological investigations - likely will occur in "shallow" sedimentary provide immediate, direct benefits to the State Geologist and Bureau Chief geographically across the state, vertical rocks of southeast and southwestern state or that otherwise mesh well with ly through the subsurface - at both Iowa, largely through the efforts of in the goals and responsibilities of the large and small scales. dividual operators and small companies. Geological Survey Bureau (GSB). Cer Just as geology itself is dynamic, so AMOCO Production Company started to tainly the longer term projects and on are the tools which geologists utilize to drill their M.G . Eischeid #1 test in Carroll going programs of basic data acquisition
2 3 ings have been chronicled in the press GROUNDWATER over the past five years. Today, the public is concerned. A Department of Natural Resources (DNR) POLICY sponsored public-opinion survey of 400 citizens, taken in the fall of 1986, re AND vealed that 86 percent of Iowans con sidered groundwater contamination as a GEOLOGY serious problem, and 83 percent be lieved more needed to be done to pro tect the resource. Sixty-three percent of Bernard E. Hoyer those who believed there was a problem volunteered ag-chemicals as the most significant source of that contamination. Documentation of water-quality prob Groundwater has always been important lems, combined with widespread media to Iowans, but it has never been regard coverage and the educational efforts of ed as a prominent, front-page issue. agricultural and other professional About 80 percent of the state's popula groups are responsible for developing tion utilizes this resource for their drink the public's awareness and concern for ing water supply, yet most are unaware Iowa's groundwater supplies. The of the geological conditions which supply General Assembly perceived this con water to their wells. Although the occur cern and mandated that the Environmen rence, availability, and quality of ground tal Protection Commission develop a water vary from one region of the state to groundwater protection plan for Iowa. another, its quantity and quality have This plan, the Iowa Groundwater Pro been accepted as inalterable products of tection Strategy 1987, is the state's first the earth, and its purity has been taken comprehensive attempt to design policy for granted. The only hazards to wells related to the protection of groundwater were thought to be associated with poor resources. The strategy was developed construction or improper placement, im by DNR staff, along with advisory com plying risks from local sources such as mittees drawn from government and in septic systems or barnyards. terested public groups. After approval by Findings of the past few years, the Environmental Protection Commis however, have revealed another side to sion in January 1987, the plan was sent the story. Gasoline has leaked into wells to the General Assembly. Legislation to and basements. Leachate from landfills implement the plan will be controversial, has moved off-site. Chemicals have but there is general agreement that been documented in wells near farm supply businesses. Hazardous sub stances from spills or waste-disposal Groundwater contamination occurs when sur sites have locally contaminated ground face drainage, carrying society's by-products, water and threatened public water sup infiltrates the soil and percolates downward to plies. Nitrate, long a problem of shallow recharge aquifers in deeper geologic materials. aquifers, has invaded deeper strata and Examples of conditions which are addressed in increased in concentration, a reflection the Iowa Groundwater Protection Strategy 1987 of two decades of intense agricultural ex include (from top to bottom) landfills where pansion. Minute residues of pesticides, waste is buried, watersheds which drain to especially commonly used herbicides, sinkholes, streams into which petroleum prod have leached through the soil and been ucts have leaked, application of farm chemi found in about 40 percent of wells thus cals to the land, and migration of leachate far sampled in Iowa. Many of these find- away from waste-disposal sites.
4 5 some form of groundwater legislation will curred. And even though only trace Strategy recommendations. There is em grams can encourage minimal-use areas be enacted. amounts of a particular contaminant are phasis on acquiring information about for grazing, wildlife, and recreation. An The plan establishes a goal of "non found, their detection serves as an early contaminants and their behavior in sur assessment of the health impacts of degradation," a concept which em warning system that the aquifer is face and subsurface environments. This drinking-water sources is needed, along phasizes no further deterioration of pres vulnerable. While water generally tends must include a strong monitoring pro with interagency cooperation, local in ent groundwater quality and, where to infiltrate rather slowly, the threat to gram for a wide variety of contaminants volvement, and an increase in public possible, improving water supplies to aquifers is greatest where recharge is in aquifers which supply municipalities awareness about causes of contamina previous quality levels. Prevention of the most direct. and private wells throughout the state. tion and practices that can be adopted to contamination is the key to groundwater Research at the Geological Survey The adoption of best-management prac protect their water supplies. protection. In addition, the public must Bureau is aimed at understanding the tices by farmers is recommended for Groundwater protection is a new issue. be confident that decision makers and various geological settings which provide minimizing the threat to groundwater The Protection Strategy 1987 sets the administrators have the best available in groundwater throughout the state, and posed by agricultural fertilizers and direction for a policy to deal with this formation for establishing sound policies includes the collection of water-quality pesticides. Uncontrolled, potentially issue. The Strategy recognizes that both and programs. This information and the data. This information about thickness, hazardous waste sites need to be the issue's origins and solutions lie with need for its acquisition, in turn, must be characteristics, and geographic distribu evaluated and possible clean-up pro society and its use and management of understood and supported by the public. tion of geological materials is combined cedures initiated. Construction standards the land. Geologic and hydrologic condi Reliable information on groundwater with conceptual models which predict designed to prevent and detect leakage tions which exist between the land sur quality and the geological characteristics changes in water quality with time and are needed for underground storage face and the point from which water is of the aquifers in which it occurs is a vital location. This geologic and hydrologic in tanks and for commercial chemical pumped from the ground are a vital link part of the strategy. formation is utilized to understand the storage and handling facilities. Site to understanding the present situation To a geologist, there is a certain movement of contaminants in the sub assessments are needed for landfills, and to guiding future policy develop "sameness" to all contaminant sources surface. Aquifers identified as most and alternative waste-management ment. Careful land management based and the threats they pose to ground susceptible to contamination are the techniques need to be developed. Ag on reliable information and on the sup water. Each potential contaminant has shallow sand and gravel deposits along drainage wells and abandoned wells can port of a well-informed public will assure chemical properties which enable it to stream valleys, sand and gravel lenses be made illegal. Financial assistance that Iowa's land supports those uses for react with soil, water, air, micro within the glacial drift which mantles may be used to promote both proper which it is best suited and protects those organisms, and sunlight. Each potential most of Iowa, and shallow bedrock plugging of these wells and adoption of groundwater resources which lie below contaminant also varies in how it is used , where the drift covering is less than 50 conservation measures in watersheds its surface. D the percentage lost to groundwater, the feet thick. Areas of the state containing that drain to sinkholes. Easement pro- accompanying health risk, and the sinkholes, abandoned wells, or recommended control mechanisms. But agricultural drainage wells run even the same sources of groundwater are higher risks because of the direct routing vulnerable to them all. of water from the land surface into the Contaminants move into our aquifers groundwater supply. along with the infiltrating waters which The Strategy is a starting point. It recharge them. Products in the air, on represents a first progress report on an the land, in the soil or buried beneath the evolving groundwater policy. It tries to soil are all potential contaminants. identify what is known and what is Groundwater starts as rainwater and unknown; it tries to respond to public soaks the topsoil. Continued rainfall and professional opinions, and to Iowa's allows percolating water to fill voids traditions and laws; and it tries to define around soil particles. Clay-rich soil slows what information is needed to guide movement and tends to direct the flow future policy decisions. Groundwater laterally; sand-rich soil speeds move policy needs to reflect politics, ment downward. Burrows and cracks in economics, hazard assessments, the soil conduct water downward at even monitoring results, and physical realities. faster rates. Such openings provide Geological considerations are a basic avenues for groundwater recharge part of the mechanism which should in through clay-rich glacial deposits as well fluence policy development and guide as through bedrock. Contaminants from forthcoming recommendations. the land surface are found only in Prevention, public education, and Understanding Iowa's geologic settings can provide valuable guidelines for selecting land manage aquifers where historic recharge has oc- reliable information punctuate all ment practices that effectively protect the land and underlying groundwater resources.
6 7 a variety of minerals, but quartz is domi GEODES: nant in most. Quartz is si licon dioxide, the primary mineral in ordinary sand. Beautiful transparent to white quartz A LOOK AT crystals cover the walls of many geode IOWA'S ST ATE ROCK cavities. These crystals become larger and fewer in number towards the center of the geode, and terminate in Brian J. Witzke characteristic pointed hexagonal pyramid shapes. Micro-crystalline quartz, or chalcedony, whose compo nent crystals are too small to be seen Iowa geodes have long been objects of with the naked eye, forms the outer curiosity, their sparkling interiors con shell in all " Keokuk geodes." taining some of the most beautiful Chalcedony layers also encrust the in crystals to be found anywhere in the terior walls of many geode cavities, Midwest. Although geodes are known covering the surfaces of the earlier from many localities around the world, generation quartz crystals in a variety of one of the most productive and famous colors, including white, gray, blue, collecting reg ions is encompassed yellow, and orange. Calcite is a common within a 35-mile radius of Keokuk, Iowa. and attractive calcium carbonate mineral Crystals of quartz reflect from the partially hollow interior of this 8-inch diameter geode from the Rock collectors commonly refer to in many geodes, which occurs in a Warsaw Shale of southeastern Iowa. geodes from this region as " Keokuk variety of crystal habits and colors. An geodes." In keeping with the world additional 17 minerals have been iden are derived from the Warsaw Formation , crystalline growths within their hollow in renowned status of the Iowa geodes, th e tified in "Keokuk geodes. " Some of the geodes also are known from other for teriors. The ultimate source of the Iowa General Assembly declared the more noteworthy include: kaolinite, a mations of Devonian and Mississippian mineralizing waters remains speculative. geode as the official "State Rock" in white clay mineral; dolomite in saddle age at scattered localities in eastern and Many common geode minerals, 1967. shaped crystals; pyrite or fool's gold, an central Iowa. especially quartz, are only weakly solu The word " geode" is derived from the iron sulfide; and sphalerite, a blackish The origins of geodes have vexed ble. Therefore, substantial volumes of Latin meaning " earthlike," a reference zinc sulfide. geologists for a considerable time, and water had to migrate through the lower to their rounded shape. Most Iowa Iowa's renowned " Keokuk geodes" many hypotheses have been put for Warsaw strata to precipitate the ob geodes are roughly spherical, often can be found in specific stream ward. The most recent geologic served minerals. lumpy or cauliflower-like in external drainages and excavations in parts of research, however, agrees on three Collecting geodes can be both fun form, with diameters typically ranging southeastern Iowa (especially Lee, general points: 1) Geode precursors and educational. Once you've located between about two and six inches. Henry, and Van Buren Counties), in were concretions (nodules formed by exposures of lower Warsaw strata or a However, specimens up to 30 inches cluding the area near Geode State Park. outward growth around some nucleus) geode-bearing stream course, all that's are known. The most prized geodes Most geodes are derived from strata of which grew within soft, unlithified sedi required is a little patience and a good have hollow interiors, although many the lower Warsaw Formation, a ment. 2) The outer shells of these con bricklayer's or rock hammer. A sharp geodes are solid objects in which crystal widespread rock unit of Mississippian cretions were replaced subsequently by blow with a hammer is usually sufficient growth has filled most or all of the in age. Muds deposited in a shallow sea chalcedony. 3) The interiors of the con to crack open individual geodes, expos terior volume. Although the distinction about 340 million years ago were cretions were dissolved, leaving a hollow ing their crystalline interiors to daylight may seem subtle, it is important to con primarily calcium carbonate and clay, space into which quartz crystals could for the first time. Remember that most trast geodes with other crystal-lined and were subsequently lith ified to form grow. The composition of the original geode-collecting localities are on private cavities, or "vugs. " Geodes differ from the shales, shaley dolomites, and concretions is unclear, though land, and permission must be secured vugs in possessing an outer mineral limestones that we see today. Fresh geologists propose they were either before entering. D layer which is more resistant to weather geodes can be dug out of exposures of limestone or anhydrite, a fairly soluble ing than the host rock. As such, com the lower Warsaw Formation, where calcium sulfate mineral related to Additional information is found in Horick, plete geodes commonly weather out of they are concentrated in certain layers. gypsum. P.J., 1974, The Minerals of Iowa: Iowa Geo/. rock exposures and accumulate in Where water and streamflow have erod The minerals now seen inside geodes Survey, Educ. Series 2, 88 p.; and Sinotte, stream bottoms. Crystal-lined vugs ed these strata, concentrations of were transported in groundwater solu S.R. , 1969, The Fabulous Keokuk Geodes: would not weather in such a manner. geodes may accumulate in stream chan tions and then precipitated as Wallace-Homestead Co. , Des Moines, 292 p. Geodes from the Keokuk area contain nels. Although the bulk of Iowa's geodes replacements of the geode walls or as
8 9 microscope, these refracted light rays with migrating groundwater. Probably pass through two opposing polarizing the most peculiar of these ancient fluids MICROSCOPIC filters, and appear as a characteristic in were the hot mineralizing brines that terference color against an opaque emplaced the veins of zinc and lead ores STUDIES background of unrefracted light. The col that were once mined in northeast Iowa, orful mosaics seen in petrographic im and now are believed to have migrated OF ROCK ages of thin sections (see cover) have a from a distant area of mountain building wonderful aesthetic appeal, but also are in Arkansas about 260 million years ago. THIN- SECTIONS a powerful tool for evaluating rocks in all Petrologic studies of many of the ma their aspects. The optical properties of jor rock units in Iowa have been com most rock-forming minerals are well pleted, and others are currently under Greg A. Ludvigson known , and experienced petrographers study. Correct geologic interpretations, usually are able to quickly identify the aided by petrographic analysis, of how mineral constituents of rocks in thin these interacting physical and chemical section view. processes have shaped the geology of Iowa are of fundamental importance to Geologists are often required to provide While the mineralogical composition of the Geological Survey's ability to pro detailed information about the physical a rock is of obvious importance, textural vide reliable information on the properties of Iowa's rock materials. relationships between separate mineral characteristics of Iowa's rock materials Petrology is a subdiscipline of geology grains and their arrangement within the and their associated groundwater and that is concerned with the composition, fabric of the rock are of equal impor mineral resources. The porosity and origin, and history of rocks. As might be tance to the geologist. These relation permeability of many sandstones, for ex expected, there are even further sub ships record evidence as to how the rock disciplines, as some geologists consider was formed and what has happened to it ample, makes them especially suitable for development as sources of ground themselves to be sedimentary, igneous, since. Petrologic research has shown water supplies. Shales, on the other or metamorphic petrologists, depending that different components of a rock's hand, with their tightly spaced grains, upon the principal rock groups they fabric may form at different times, and are not suitable aquifer materials study. All are allied, however, by a that major physical and chemical rel iance on the microscopic examination transformations may occur in rocks long because of their low permeability. In ad dition, the solubility of carbonate rocks, of thinly sliced sections of rock in order after their initial deposition. particularly where fractured or along cer to study and interpret these earth Precambrian-age igneous, metamor tain porous zones, makes them materials. This article describes the phic, and sedimentary rocks beneath desirable, high-yield groundwater practice of thin-section petrography, one Iowa's land surface date from 2.5 to 1.1 aquifers. of the most widely used procedures in billion years old , and record episodes of As more drillhole, petrographic thin the geological sciences. deposition and mountain-building defor Petrography was developed as a mation during the assembly of the North section, and other geologic data are ac cumulated, the accuracy of our picture of useful geologic technique in the early American continent. Over the last 550 the state's subsurface geology is steadily 1850's. As practiced today, optical million years , Iowa's rock record has refined . The results of long-term collec petrography is performed using thin sec originated exclusively from sedimentary tive efforts on the part of geoscientists tions that are sawed from hand-sized processes operating in terrestrial, rock samples, mounted on glass slides, coastal , or marine environments. These have contributed to a more complete and ground down to a thickness of 30 sedimentary rocks contain abundant understanding of the physical, chemical, and biological processes that have microns (about one-thousandth of an evidence of the biological activity of an shaped our state through time. And from inch). The polarizing microscope is the cient organisms, and petrographic a practical standpoint, these research standard instrument for petrographic studies have shown that some rocks are efforts have improved the ability of studies. It is specially designed to aid in composed totally of fossil remains. Survey geologists to anticipate and re the identification of translucent minerals Sedimentary rock strata in the midwest Greg Ludvigson by utilizing their unique crystallographic also have been offset along faults, frac spond to today's resource issues through better information on Iowa's earth properties. tured by regional stresses, and bent by The crystalline structure of many broad, gentle warping of the earth's Well-rounded quartz grains are cemented with materials. D minerals distorts, or refracts, the rays of crust. Additional characteristics and calcite crystals in this sandstone cored from a light that pass through them. When minerals have been imparted to these depth of 652 feet in western Sioux County. viewed through the petrographic rocks by their subsequent interaction Cross-polarized light, magnified 29x.
11 10 Three distinct groups of old glacial evident in eastern Iowa today; they ap Major valley entrenchment, on the HISTORY deposits (tills) have been documented in pear as broad , shallow swales crossing order of 100 feet or more in depth, took eastern Iowa and western Illinois. Two of the uplands. One of the unsolved place between about 100,000 and these groups are Pre-lllinoian age (more mysteries of this period is the location of 60,000 years ago. During that interval, OF THE UPPER than 500,000 years old); the other is the diversion channel south of the Iowa valleys were cut down to the level of their lllinoian. Deposits of the oldest group and Cedar Rivers. Possibly, the present bedrock floors. Most of the pre MISSISSIPPI have not been found east of the present Mississippi River flowed under or even Wisconsinan valley landscapes were Mississippi Valley north of the Princeton on top of the glacier south of the ice front altered as rivers adjusted to their new, VALLEY Channel. This suggests that the which blocked the Iowa-Cedar Valley. At lowered gradients. By about 35,000 ancestral Mississippi, along what is now the close of lllinoian glaciation, ice no years ago, a major period of valley filling the border of Iowa, Illinois, and Wiscon longer blocked the Princeton Channel was underway. Great thicknesses of E. Arthur Bettis Ill sin, came into being as a stream flowing and the drainage network reoccupied alluvial sand and gravel accumulated in along the eastern margin of the early essentially the same valleys it had tributary valleys, and probably in the glaciers that deposited these tills. previously. Mississippi Valley though they are not Deposits of the second group of tills are During the Sangamon Interglacial preserved because of later erosion. This Since its "discovery" by Marquette and found on both sides of the present period which followed, climatic condi period coincided with the discharge of Joliet in 1673, the Upper Mississippi Mississippi Valley; the. glaciers which tions similar to today's prevailed, and the glacial meltwater and outwash into the River valley has fascinated geologists in deposited them also flowed in a drainage network continued to develop. headwaters of the Mississippi during the terested in the landscape history of the southeasterly direction across Iowa and The ancestral Mississippi and its onset of the last or Wisconsinan glacia Upper Midwest. The first detailed into western and southwestern Illinois. At tributaries north of the Princeton Chan tion of the Upper Midwest. description of the geology and their maximum extent, a river draining nel area were in essentially their modern Between 25,000 and 21 ,000 years physiography of the lands drained by the the ice margin flowed in a southeasterly positions, but not as deeply entrenched ago, glacial ice advancing westward out Upper Mississippi system was made by direction through the Cordova and into the bedrock as their modern of the Lake Michigan Basin once again David Dale Owen in 1839 and 1852 Princeton Channels (see map), joined counterparts. Downstream of Clinton, blocked the Princeton Channel and following U.S. government-sponsored the bedrock valley which straddles the the ancestral Mississippi still flowed dammed the ancestral Mississippi. As expeditions to the area. Owen's reports central and lower reaches of the modern through the Princeton Channel and into lakes formed in the flooded valley, their touched off a series of investigations Illinois River, then flowed southwesterly the Illinois system. waters topped low divides and flowed aimed at documenting the region 's to join the ancestral Mississippi Valley in geologic deposits, inventorying their the St. Louis area. This drainage net economic minerals, and correlating the work persisted in eastern Iowa and west Upper Mississippi Valley strata with the central Illinois after these early glacial ANCESTRAL better known rocks to the east. Some of episodes. The modern Mississippi Valley AND MODERN these investigations focused on between the Princeton Channel and the MISSISSIPPI materials deposited during the St. Louis area was not in existence dur Pleistocene, or Ice Age. By the turn of ing Pre-lllinoian time. DRAINAGE the century, it was generally accepted The lllinoian glaciers, in contrast to SYSTEM that the Mississippi Valley between Iowa earlier events, advanced from the north and Illinois had been directly affected east out of the Lake Michigan region. As during at least three major periods of they pushed southwestward and crossed Pleistocene continental glaciation. the Princeton Channel, ice blocked the Studies of the buried bedrock surface ancestral Mississippi Valley and caused reveal the network of connecting valleys a series of lakes to form upstream of the Ancestral shown on the accompanying map. Re ice dam. As lake levels rose , water - valleys cent investigations have concluded that spilled over divides between the blocked these valleys, including the Mississippi, valleys and cut new channels along the Modern developed during the Pleistocene and advancing glacier's margin. At its max valleys are not pre-glacial in age. The distribu imum extent, the lllinoian glaciation ex tion of overlying glacial deposits provides tended west of the present Mississippi clues concerning their age relationships Valley into southeastern Iowa. Two diver and also gives us an inkling of the im sion channels which carried the pact that glaciers had on development of ancestral Mississippi's flow, the Goose the ancestral Mississippi. Lake Channel and Cleona Channel, are
12 13 northeast Iowa tributary valleys, while south of the Muscatine area its surface is about 10 feet above the Mississippi floodplain. A younger, prominent sandy terrace is found throughout the extent of the Mississippi in Iowa. Prairie du Chien, Guttenberg, and portions of Dubuque and Muscatine are built on th is outwash terrace, which accumulated after the Savanna Terrace during the waning stages of glacial meltwater input into the Mississippi system. During the last 9,500 years (Holocene), the Mississippi Valley has continued to evolve, but at a slower pace than during the late Wisconsinan. Minor downcut ting, lateral channel migration, and con struction of large, low-angle fluvial fans, or deltas, at the junction of large tribu taries have been the main processes. The most significant event in the late Holocene history of the Mississippi Valley was the authorization by Con gress in 1930 of the construction and maintenance of a 9-foot navigation chan nel to the St. Paul area. The lock and dam system built by the U.S. Army Corps of Engineers produced the series of pools and flooded bottomlands characteristic of the Upper Mississippi today. These areas provide unequalled habitat for migratory waterfowl and freshwater fisheries, in addition to a dependable avenue of commerce for the region. The long history of the Mississippi
Geological Survey Bureau Valley's development provides us with a perspective on the rapidly changing This color-infrared photo shows the city of Dubuque, Lock and Dam 11, and the Little Maquoketa entering the Upper Mississippi River at Peru Bottoms, a Savanna Terrace nature of landscape features as promi remnant. The Little Maquoketa formerly flowed southeasterly through Dubuque. Its abandoned channel, known as Gou/er Valley, may be traced in the photo. nent and seemingly permanent as the Mississippi Valley, as well as providing us with insights into the origin and southward. Soon a new channel, the length of the Iowa-Illinois border. deposits present in the main valley. Dur reasons for the present distribution of Port Byron Gorge (see map), formed by From that point until about 9,500 years ing these floods, fine-grained sediment geologic resources in the valley. This the merging of several separate valley ago, the valley acted as a conduit for the 1 was deposited in quiet backwaters pond perspective hopefully will allow us to bet segments. When the late Wisconsinan discharge of meltwater and outwash ed in the lower parts of tributary valleys. ter manage the valley's resources and glacier retreated eastward, Mississippi from late Wisconsinan glaciers in Iowa, J Today these backflooded deposits plan for their future. D River flow continued through the Port Minnesota, Wisconsin, and Illinois. On underlie the Savanna Terrace, a promi Byron Gorge rather than resuming its occasion, large floods, produced by the nent landform found in the lower few former course through the Princeton catastrophic drainage of large glacial miles of most Mississippi Valley Channel. The Mississippi Valley had at lakes in the headwater areas, rushed tributaries. This terrace rises up to 60 tained its modern position along the full down the valley and eroded the glacial feet above the modern floodplain in
14 15 of flood-spilled sediment. The winnowed The spine-leafed yucca blooming LOESS HILLS: silts were blown from the valley and along this steep sides/ope is one deposited downwind. The thickest and of the unusual prairie plants that coarsest deposits accumulated in thrives in the dry habitat among A NATIONAL western Iowa, immediately adjacent to the peaks and saddles of the NATURAL LANDMARK the great valley. The loess reached Loess Hills Nature Preserve in thicknesses of 100 feet or more as it Monona County. This classic buried the pre-existing land surface and association of topography and Jean C. Prior became the dominant element of the ter ecology is part of the recently rain in th is region. designated National Natural The loess was anchored first by co Landmark. niferous then deciduous forests, and eventually, as the post-glacial climate continued to warm, by the prairie. Kneaded by the deep root systems of prairie plants and associated organisms, watered and baked, frozen and thawed by seasonal climatic patterns during the last few thousand years, the upper several feet of these deposits were transformed into some of the world's most fertile soils. Today in western Iowa, extending north-south along the bluffs which border D Loess Hills Region the Missouri Valley, is a narrow band of • National Landmark Site rough , corrugated terrain covered with a ragged cloak of unkempt plants that seems out of place in the state's other Loess is one of the most common wise meticulously manicured landscape. geologic materials found on the land sur Last summer, nearly 10,000 acres of this face in the Midwest. This can also be land were selected by the U.S. Depart said for the lower Mississippi Valley, the ment of Interior, National Park Service LeRoy Pratt Palouse district of eastern Washington, as a nationally significant example of central and eastern Europe, the Ukraine landscapes dominated by loess. Visitors of southwestern Russia, and eastern to the Loess Hills of western Iowa have amine the special topographic forms that protection has been assisted by the China. The word itself is German in an opportunity to see, on a scale rarely subsequent erosion carved from the establishment of three state parks - origin, and as late as the 1860s was seen among the world's landforms, uniform, porous silt. It is the first place Stone, Preparation Canyon , and regarded as a " provincial" name for deposits of wind-blown silt that ac where today's west-bound, cross-country Waubonsie - and several smaller coun deposits along the Rhine Valley. Loess, cumulated in sufficient thicknesses to travellers can see a hint of the extensive ty conservation areas. A concerted effort glacial history, native grasslands, and have obscured the older relief and con native grassland habitats that once during the past 10 to 12 years by private productive agricultural regions are linked tributed their own distinctive signature to dominated the heartland east to the Ohio conservation organizations, college and together across the mid-latitudes of the the landscape. The Loess Hills region is border. Only scattered, stamp-sized rem university research projects, and the northern hemisphere. a place to appreciate the geologic pro nants remain east of Iowa's Loess Hills. state preserves and natural resources In Iowa, this wind-deposited sediment cess responsible for the parent material In a state dominated by agriculture, it programs has made valuable progress of silt-sized quartz grains was deposited which accounts for nearly 40 percent of is important to retain some reminders of toward the inventory, protection, and in over ice-free landscapes as continental our state's soil types. It is a place to see the geological and biological systems terpretation of this unusual natural area. glaciers melted to the north. The valley the steep faces of this deep, fine which made this land so productive. The The designation of portions of the of the Missouri River, which carried this textured geologic deposit whose form Loess Hills have protected themselves in Loess Hills as a National Natural Land glacial outwash, was the source of the elsewhere is usually lost against the the sense that their ruggedness and mark adds important federal recognition sediment. Its floodplain was wide, and its more bulky underpinnings of earlier ice steeply pitched slopes have kept them to these significant landscapes and braided river channel was clogged dur deposited materials or even older relatively isolated from the cropland habitats. The Landmarks Program in ing low-flow seasons with exposed bars bedrock foundations. It is a place to ex- which surrounds them on all sides. Their cludes select portions of America's land
16 17 and waters - an array of landforms, in western Iowa, prairie fires, which are geological features, habitats, and plant an important element in the maintenance and animal communities that constitute of this ecosystem, were suppressed. the best examples of the nation's natural Trees from the more moist and protected history. The objectives of this program backslopes and ravines have spread are four-fold: 1) to encourage preserva quickly into the grasslands, to the extent tion of sites which illustrate the that these " pioneering" woodlands have geological and ecological character of been proposed as a state forest. the United States; 2) to enhance the The Loess Hills are foremost a educational and scientific value of sites topographic form developed in thick preserved; 3) to strengthen the cultural deposits of coarse silt. While they appreciation of natural history; and 4) to originated as a wind-blown deposit be foster greater concern in the conserva tween 30,000 and 14,000 years ago, tion of the nation's natural heritage. The they are equally a product of fluvial ero designation does not affect land owner sion . The modern landscape is a product ship, nor does it restrict the use of the of several episodes of gully cutting and land. Landowners are encouraged, filling during the last 25,000 years. The however, to adopt sound conservation steep hillslopes and intricately dissected practices in the use, management, and terrain are related to both the extreme protection of the property in order to erodibility of the loess and yet its great preserve its significant qualities. apparent cohesiveness when dry, as well National Natural Landmark designa as the inherent cleavage planes that ex tion of the Loess Hills includes two tend vertically through the deposits. The separate tracts in the heart of the deep steepness of the topography, the loess country. The Turin site occupies a permeability of the loess, and high densi wedge-shaped parcel of 7,440 acres in ty of deeply incised drainageways con central Monona County between the tribute to strong contrasts in soil Missouri/Little Sioux Valley on the west moisture and temperature. These condi and the Maple River valley on the east tions produce specialized habitats for an and south. Approximately 30 percent of interesting variety of plant and animal the area consists of large, intercon communities. nected prairies, much of it included in This association of exceptionally thick the state-owned Loess Hills Wildlife Area loess, unique topography, and special and Loess Hills Nature Preserve. The ized habitats is a classic example of the second tract is the Little Sioux-Smith geologic-ecologic themes that the Na Lake site, a 2,980-acre parcel in northern tional Natural Landmarks Program Harrison County between the Soldier strives to recognize. No better example River valley and the Missouri/Little Sioux of these associated features exists within floodplain. This site is associated with a the tens of thousands of square miles of long history of scientific investigation of loess-covered landscapes in the the loess and associated Quaternary midwestern United States than in deposits, and also has considerable sup western Iowa's Loess Hills. D port among local landowners interested in protecting the hills. The Iowa Department of Natural Resources has recently launched a ma jor land-acquisition project to establish the Loess Hills Pioneer State Forest in Geological Survey Bureau Harrison and Monona Counties. Pioneer The rough-textured Loess Hills in southern Monona County contrast sharply with the cultivated is the right word. Prairie was the prevail Missouri Valley and the channelized Little Sioux River. Thick, wind-deposited loess was carved by ing vegetative cover on the Loess Hills erosion into intricate landscapes of alternating ridges and troughs. 100 years ago. As settlement took place
19 18 Feet Below Ground Level some pesticide contamination. Seven than 100 feet deep indicate that 40 to 70 Soil 0 ALLUVIAL percent have exceeded the recommend out of 16 of the alluvial monitoring wells ed maximum contaminant level (MCL) of in northwest Iowa have tested positive.
45 mg/I for nitrate (10 mg/I N03-N). Pesticides are currently found in low AQUIFERS: These high concentrations can cause concentrations, well below toxic levels. methemoglobinemia (blue baby). However, some evidence suggests that NORTHWEST IOWA In order to fully evaluate water quality pesticide concentrations are increasing, SUMMARY in northwest Iowa, 66 monitoring wells analogous to the rise in nitrate concen 10 were installed at 35 different locations trations that followed increased use of along the West Fork Des Moines, nitrogen fertilizers. WATER TABLE Carol A. Thompson Ocheyedan, Little Sioux, and Rock Stratification, or layering, of the Rivers. In addition, thirteen surfacewater pesticide occurrence within the aquifer sites are included. Samples are col is evident, as it is with nitrate; positive Sand and Gravel lected monthly or bi-monthly for nitrate occurrences are confined to the 20 (Alluvium) In Iowa, as well as other agricultural and bacteria. A subset of the wells have shallower wells. All surface-water regions of the country, concern about been analyzed for pesticides during the samples contain a variety of pesticides, the quality of drinking water is increas spring and summer months. although no multiple residues are pres ing. Several Iowa studies have Results of this nitrate monitoring have ent in any of the monitoring wells. In documented the existence of increased shown that although nitrate concentra contrast, work done on municipal concentrations of nitrate and other tions generally are not excessively high, systems utilizing the alluvium along the 30 agricultural chemicals in private and widespread contamination has occurred. Little Sioux River showed that 88 per public water supplies. Wells at depths Nitrate has been detected at 31 of the cent had measurable pesticide residues of less than 50 feet are particularly 35 well sites and at all surfacewater present regardless of depth. Perhaps susceptible to contamination from land sites. No single well or river, however, the heavier pumping of larger capacity surface activities. In northwest Iowa, has consistently exceeded the MCL. wells destroys the stratification and in most of the municipalities, irrigators, and Interestingly, the distribution of nitrate duces flow from nearby rivers. rural water-supply systems rely on within the aquifers is not uniform. Varia Pesticides have been found in ground 40 shallow alluvial (river valley) ground tions in concentration occur from well to water throughout the year, with some water sources. Many of these shallow well in addition to varying over time. types being more persistent than others. Clay sand and gravel aquifers are covered by Even with this variability some consis There is evidence that many herbicides sandy soils which present little impedi tent trends have been noted. Nitrate are persisting in the subsoil and then ment to the downward percolation of concentrations rise in response to moving into the groundwater during water and associated chemicals. The precipitation and snowmelt events and recharge events. 50 potential for increased water-quality prob fall as infiltration decreases. Thus, The occurrence of chemicals in Iowa's Nested wells placed to different depths within lems in the region is directly tied to nitrate levels in wells from the same groundwater today, even in low concen an aquifer enable vertical sampling of a site 's cropland management practices. In alluvial system show corresponding trations, is of concern because of the water quality characteristics. most northwest Iowa counties, from 60 trends, although they may differ in potential hazard to health through long to more than 80 percent of the land is in magnitude. Nitrate also has been found term exposure. Some initial studies sug corn and soybeans, row crops which to decrease with depth in all of the gest that elevated nitrate concentrations on human health is known. The long receive seasonal chemical applications. alluvial systems studied. This has impor may be associated with higher in term health impacts of these chemicals Alluvial valleys in particular, with their tant ramifications for the depths to which cidences of cardiovascular disease, birth are difficult to assess; epidemiological level terrain and fertile soils, are inten wells are drilled. Whether or not the con defects, and several forms of cancer. studies require an extended time frame sively cropped. tamination documented in the upper The persistence of low concentrations of for cause and effect to be shown. D Regional increases in nitrate levels in part of the aquifer will migrate over time pesticides also raises legitimate con groundwater have occurred in direct to lower parts of the aquifer is not yet cerns about chronic toxicity and related Additional information is found in Thomp relation to the increased use of nitrogen known. carcinogenic effects. With certain her son, C.A. , 1985, Alluvial Aquifers: Iowa fertilizers since the mid-1950s. Nitrate Studies by several agencies in Iowa bicides, the possibility also exists for Geology, v. 10, p. 8-11; and Hallberg, G.R., concentrations in public water supplies over the past six years have shown that combination with nitrogen compounds to 1986, Ag-Chemicals and Groundwater Quality: in northwest Iowa have risen steadily many commonly used pesticides also form other carcinogenic compounds. Iowa Geology, v. 11, p. 4-7. over the past thirty years. Data from the are being found in groundwater. Forty Since pesticides are just beginning to University of Iowa Hygienic Laboratory five percent (20/41) of alluvial wells occur in groundwater, several decades on samples from private water wells less sampled on a statewide basis showed of data will be needed before the impact
20 21 areas are not great enough to account along the bluffs that border the Missouri thirds of the recently glaciated Des REGIONAL for this difference in flood magnitude. Valley; it covers approximately the area Moines Lobe , and the flat-lying Missouri Th e physiographic differences, however, defined as the Loess Hills of western River floodplain. are pronounced. The bluffs along the Iowa. The rough, corrugated terrain of Region 5 has the lowest magnitude FLOOD Mississippi are steeply dissected with alternating, steep-sided waves and floods in the state. It covers the northern well developed drainage, while the area troughs is highly conducive to rapid sur portion of the Des Moines Lobe where PATTERNS: within the Des Moines Lobe is quite level face runoff. most of Iowa's natural lakes occur. The and not well drained. What separates Region 2 varies from rough to rolling nearly level topography, scattered lakes, THE INFLUENCE OF these areas as hydrologic reg ions is the topography and exhibits a well and undrained depressions have an at I TOPOGRAPHY drainage efficiency of their river basins. integrated drainage network. Runoff may tenuating effect on flood magnitude. Five hydrologic regions can be be rapid and flash flooding is common. The main purpose of regional analysis delineated in Iowa, which take into ac The bluffs along the Mississippi Valley of flood characteristics is to develop Oscar G. Lara* count the physiographic characteristics are typical of this landscape. It also in methods of estimating flood magnitudes of the land and available hydrologic data. cludes part of the Missouri-Mississippi and frequencies applicable to an entire James D. Giglierano On the map (lower right) these drainage divide, portions of the Iowa and region rather than to single stations hydrologic regions are shown as they Cedar river basins, the eastern border alone. Also, this study clearly establishes relate to the topographic rel ief of the area of the Loess Hills, and the upper the regional relationships between flood state. The shaded-relief map was basins of south-central Iowa streams. characteristics and topography. It is im Being able to estimate the magnitude generated by computer, using image Region 3 is described as gently rolling portant to recognize, however, that each and frequency of flooding is important to processing methods. Computations were terrain with fairly well-established region represents a predominant terrain those who live on, cultivate, build upon, performed on topographic data to add drainage systems. It covers most of the type, and that anomalous settings do oc or insure flood-prone property. The the effects of an artificial "sun" near the landform region known as the Iowan Ero cur. Further quantitative analysis of prediction of flooding characteristics, horizon. Illumination and shadowing sion Surface, as well as large portions of drainage basin shape, stream density, however, is usually based on records of from the low sun angle give a three the Southern Iowa Drift Plain and North and degree of slope will help refine this streamflow at scattered, individual gaug dimensional appearance to the valleys west Iowa Plains. regional approach to flood prediction. D ing stations. New culverts or bridges, for and ridges, and enhance the differences Region 4 is characterized by level ter example, must often be built at locations between regions. rain and poorly developed drainage. It ·oscar Lara is recently retired from the U.S. where no streamflow data exists. Even Region 1 extends north and south occupies approximately the southern two- Geological Survey in Iowa City. when records do exist, they may not represent the long-term distribution of floods at those sites. One way to better estimate flood REGIONAL magnitude and frequency is to study the contributing factors over a broad VARIATIONS geographic area. Regional analysis IN DRAINAGE takes into account the records for all sta EFFICIENCY tions in a hydrologically homogeneous area. This tends to reduce the errors associated with incomplete or non representative data, and thus may im High relief Most rapid prove the estimates of flood runoff characteristics at gauged as well as ungauged sites. • Records show that typically a one square-mile basin in the uplands along the Mississippi River has a potential for • producing a 100-year flood equal to 0 1,300 cubic feet per second (cfs), while a 100-year flood from a one square-mile basin on the Des Moines Lobe of north 8 central Iowa is about 180 cfs. The 1:---1 Low relief climatic differences between these two L....'.:_J Least runoff
22 23 UNDERGROUND LIMESTONE MINING
Robert M. McKay Michael J. Bounk
Counties producing limestone from • quarries
Active underground limestone Each year aggregate companies in Iowa • mines produce about 35 million tons of raw material from over 500 locations to sup ply a myriad of construction projects Most underground mines in Iowa are across the state. The bulk of this supply opened from the floors of existing quar is extracted from the familiar pits and ries. An entrance road or haulway is quarries where gravel deposits and driven into the quarry wall or floor de limestone bedrock are close to the land pending on whether the layers to be surface. But at ten locations across the mined are at the same level as the floor state (see map), where geologic and or deeper. The depth of the mining level market conditions permit, limestone for below the land surface may vary from 75 aggregate is extracted from underground to 400 feet. Once the entrance road or Bob McKay and Mike Bounk ramp has reached the proper level, the mines. The production of limestone aggregate from underground workings requires machinery to illuminate mine is ready to go into production. Though more costly than quarrying, the rock face and to hoist miners into position to clean drill holes and toad explosives for blasting A major element of the mining process the underground mining of limestone the rock. River Products Company, Columbus Junction Mine. can be both economical and necessary is breaking up the rock. This fragmenta in some areas of the state. Shallow rock tion is accomplished by detonating ex units, which were once acceptable, may plosives set in blastholes. The heading, front of the face, allowing the delayed rooms of mined out rock. This "room no longer meet newer engineering or rock face to be blasted, is typically charges to thrust material into and past and pillar" mining plan is often mapped standards for construction aggregate. In 40-feet wide by 20- to 25-feet high. A the initial blast opening. A typical opera out in advance with the help of engineer other instances, it is not economical to designed pattern of 40 to 50 horizontal tion can drill and blast up to five rounds ing firms specializing in underground strip both the overlying glacial deposits drill holes two inches wide by 12- to per day, loosening tons of rock in several developments. Secondary roof stabiliza and the poorer quality, shallow bedrock 14-feet deep, are bored into the rock different headings. The time-delayed ex tion, if necessary, usually involves in order to quarry. An operator must face by large portable drills. This con plosions not only increase blast efficien mechanical scaling of loose slabs of rock decide whether to cease production and figuration of holes is called a " round." In cy, but greatly reduce ground vibration. from the ceiling, and less frequently, move to an alternate location, if one ex a typical round, the holes are drilled at Front-end loaders then lift the rock into mechanical bolting of potentially loose ists, or to shift operations underground. an angle with the free face. Five hundred haul trucks which transport it to a rock ceiling rock to more sound rock above. Numerous factors are weighed to deter or more pounds of explosives may be crusher, usually outside the mine. In An occasional problem related to local mine the feasibility of such a production loaded in one round depending on the deep mines, such as the Kaser Corpora geologic conditions occurs when a room change. Is the needed quality rock pres size of the face. The detonation devices, tion's Durham Mine in Marion County, intersects a shale or sediment-filled cavi ent in sufficient thickness and at suitable or blasting caps, have set delay times so the primary crusher is inside the mine, ty in the limestone. The material in these depth? Are the market conditions that charges in the center of the face and crushed rock is moved via conveyor paleo-karst features usually extends satisfactory to warrant the added ex detonate first and the surrounding belt through an inclined tunnel to the sur above the ceiling, has little supporting pense of underground start-up and pro charges detonate two to several face where it is processed further. strength, and can collapse into the mine. duction? In the last decade several Iowa milliseconds later. Using this method, As the mine becomes larger, the A combination of roof bolts and support stone producers have opted to shift pro the explosives in the central angle-cut primary means of ceiling support are the ing wire mesh is sometimes used to duction underground. holes blast the rock into the open area in pillars of rock left in place between the stabilize this condition. At worst, that por-
24 25 tion of the mine may have to be closed Stripping unneeded overburden, a costly of 1986 preparations began for an ex off from further activity. Safety decisions inconvenience in surface operations, is FOSSIL cavation by the Geological Survey are usually determined by federal in eliminated. The land above the mine Bureau and the Field Museum, aided by spectors from the Mine Safety and can be utilized for other purposes AMPHIBIAN a grant from the National Geographic Health Administration, in consultation simultaneously with stone removal. Society. with the operator. Reclamation of disturbed land and its During the first two weeks of excava Controlling groundwater is another im associated costs are reduced. Noise and SITE: tion ten feet of rock overlying the main portant aspect of mining operations. dust pollution is generally contained bone-bearing horizon was carefully Water is usually present at some depth within the mine. Working conditions, A SIGNIFICANT removed by backhoe. A crew of four to below the surface; and once en while dark, are arguably more comfort NORTH AMERICAN FIND six people spent the remainder of the countered by mining, open crevices, able because mine air temperature summer in a painstaking effort to fractures, and solutional voids in the hovers around 50° F throughout the hot unearth and remove about 1,000 limestone may produce variable flows of summers and cold winters. Robert M. McKay specimens from the 1- to 2-foot thick groundwater. This inflow must be routed If geologic conditions are suitable and bone bed. Specimens include skeletal along drainage slopes and ditches to col proper planning has been done, large material from at least two extinct am lection places where it can be discharged portions of the mine workings may phibian groups (colosteids and an from the mine. Most operators eventually eventually be converted to usable In the spring of 1985, geologists working thracosaurs) , reptilian-like vertebrae, need to collect water in a sump, or low underground space. This space can be in Keokuk County discovered fossils of and fossil fish (sharks, acanthodians, spot, within the mine and pump it out utilized for warehouses, offices, in perhaps the oldest known four-footed palaeoniscoids, and rare lungfish [see from that point. On rare occasions, a dustrial production, agricultural product animals to walk the North American con photo] and crossopterygians). heading may intersect a fracture or void storage, and even recreational facilities, tinent (see Iowa Geology, 1986). These Interpretation of the bone-bearing St. which releases hundreds of gallons of such as tenn is courts. In Missouri, part are fossils of primitive amphibians, the Louis Formation indicates the environ water per minute. If the problem cannot of one mine has been converted into a earliest terrestrial vertebrates or ment of deposition was a sub-equatorial be remedied, a portion or all of the mine roller rink, and in Clayton County, Iowa, tetrapods. Dr. John Bolt, a specialist at lowland dotted with bodies of fresh or may be closed. an abandoned underground sandstone the Field Museum of Natural History in brackish water inhabited by a variety of Proper ventilation also must be main mine is now used as a storage facility. Chicago, enthusiastically examined the fish , tetrapods, and invertebrates. As the tained in any underground mine. Ex Underground mining in urban areas can preliminary collections, which contained Field Museum prepares and describes haust fumes from machinery must be be an attractive future alternative when abundant, well preserved amphibian the individual fossils, a more complete vented and fresh air introduced. Natural the stone producer must compete with and fish material. Paleontological finds picture of early land-dwelling vertebrates ventilation of level headings is adequate other land uses and increasing land ac of this type and geologic age (Mississip and their habitat on the North American when mine workings are not extensive. quisition costs. pian: 340 million years old) are ex continent will emerge. D Warm air, either from outside or within Throughout most of Iowa, production ceedingly rare worldwide. In the summer the mine, will flow along the ceiling while of limestone aggregate from surface cool air will move along the floor. As the quarries will undoubtedly remain the workings are extended, however, forced principal method of mining. Under ventilation becomes necessary. Fans ground mining, however, is an im move air from one or more exterior open portant and an increasingly common ings to the active part of the mine. As method of limestone production in the workings progress or become deeper, state. D the producer may have to drill large diameter vertical ventilation shafts from Editor's Note: Additional information on the surface to the mine level. Large economic mineral resource topics in past volume ventilation fans are installed issues of Iowa Geology include: Lead and Zinc which move air down, usually in colder Mining in the Dubuque Area (No. 9, 1984); weather, and can be reversed to move Gypsum Resources of Iowa (No. 10, 1985); air up during warmer humid weather. and Mining Iowa's Coal Deposits (No. 11 , Although operations of an under 1986). ground limestone mine are more expen sive and require some specialized
techniques to overcome inherent dif Bnan Witzke ficulties, there are also significant advan tages to underground stone extraction. Skeletal remains of the rare lungfish include skull plates and scattered ribs.
26 27 SELECTED SURVEY PUBLICATIONS ORGANIZATIONAL STRUCTURE
PUBLICATIONS OF THE IOWA GEOLOGICAL SURVEY GOVERNOR A revised and updated listing of publications was prepared in 1986. This brochure contains a com Te STRUCTURAL CONFIGURATION OF THE PRECAMBRIAN SURFACE OF IOWA Iowa Geological Survey Open-File Map Series 86-2 by R. R. Anderson (1986). This black and white, DIRECTED PROJECTS SECTION COORDINATION ANO INFORMATION DIVISION - Bernard E. Hoyer, Superviso< .... INFORMATION ANO EDLICATION BUREAU 1· 1,000,000 scale map is compiled from on-going studies and 1s available on a limited-edition basis. .... This interi m map displays the structural configuration of the Precambri an surface using a sea-level Matthew A. Culp James o. G;glierano PUBLICATIONS SECTION datum and a contour interval of 100 feet. Price $1.00, plus $.75 post/hand. He/eneG-be,g .... Mary R. Howes Patricia J. Lohman n John P. Linke t E. Anhur Bettis UNDERGROUND COAL MINES OF CENTERVILLE IOWA AND VICINITY; MINE-RELATED Timothy J, Kemmis .... ADMINISTRATIVE SERVICES DIVISION PROBLEMS AND SUBSIDENCE POTENTIAL Roben 0. Ubfa Geological Survey Bureau Open-File Report 86-2, 93 pages. by M.R. Howes, M.A. Culp, H. Greenberg, and P.E VanDorpe (1986). The location and extent of abandoned coal mines and known .... ADMINISTRATIVE SUPl'OOT BUREAU Anetta L Orelup occurrences of mine-related problems are documented. The report also covers local geology, mining Lois E. Bair history, and factors affecting subsidence. A detailed map and extensive appendices of compiled Mary Paf Heilman historical and physical data provide 1nformat1on for landuse planning. Available without charge. GEOLOGICAL ANO MINERAL RESOURCES SECTION Lucinda M Aohret Raymond R Ande1'0<1, Superviso, .... PALYNOSTRATIGRAPHY OF THE LOWER AND MIDDLE PENNSYLVANIAN COALS OF IOWA. Michael J. Bounk .... DATA PROCESSING BUREAU BiH J. Bunker Rle"8rdL Talcott Iowa Geological Survey Technical Paper # 7, 245 pages. by R.L. Ravn (1986). This monograph con Greg A. Ludv,gsor, Joost A. Korpel tains a thorough analysis of the stratigraphic distribution of plant microfossils (spores) preserved in the Robes '-A . McKay Patricia l Ring state's coal deposits, and includes formal descriptions of paleobotanical genera and species. Abundant Rooeo D Pyto Ca1hryn L. Scherer Brian J. Wit2ke Jot,n A. Schmidt plates. A primary reference for Pennsylvanian stratigraphic correlations in Iowa. Price: $10.00, plus $1.50 post./hand. GROUNDWATER RESOURCES OF HAMILTON COUNTY Iowa Geological Survey Open-File Report 86-40 WRD, 31 pages by C.A. Thompson (1986). This com WATER RESOURCES SECTION pilation of available data summarizes the distribution, accessibility, yield, and quality of surficial and rock Donivan L Gordon, SuperviS()( .... aquifers in Hamilton County Price: $1.00, plus $.50 post./hand D, Roger Bruner DarMn L. Evans GROUNDWATER RESOURCES OF IOWA COUNTY Paul J. Horick Jean C. Prio!' Iowa Geolog ical SuNey Open-File Report 86-84 WRD, 40 pages by P.E. VanDorpe (1986). This com Carol A. Thompson pilation of available data summarizes the distribution, accessibility, yield, and quality of surficial and rock Paul E. Van!lorpe aq uifers in Iowa County. Price: $1.00, plus $.50 post./hand. Vacant 28