Iowa Geology 2001
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IOWA GEOLOGY 2001 Number 26 1 IOWA GEOLOGY 2001 Iowa Department of Natural Resources Jeffrey R. Vonk, Director Geological Survey Bureau 109 Trowbridge Hall Iowa City, Iowa 52242-1319 (319) 335-1575 www.igsb.uiowa.edu Donald L. Koch State Geologist and Bureau Chief COVER The cool moist surface of a sandstone outcrop provides favorable habitat for a lush growth of liverworts (flat plants), mosses (dark green), and ferns in Clayton County. Throughout the state, geology and ecology combine to create natural areas of great beauty and scientific interest. Cover photo by Clay Smith ❖ Jean Cutler Prior Editor Patricia J. Lohmann Publication Designer ❖ Printed on Recycled Paper 2 This issue is dedicated to Donald L. Koch, retiring State Geologist of Iowa for 42 years a researcher of fossils, rock strata & groundwater; advisor to well drillers, aggregate & gas- storage companies; leader of the Geological Survey & supporter of informative publications for Iowans. The Age of Dinosaurs in Iowa 2 Monitoring Iowas Waters 8 Keeping Ahead of Groundwater Quality Questions 10 Baseflow: Where Groundwater Meets Surface Water 12 Topographic Relief Map of Iowa 14 The Geology of Pikes Peak State Park 16 Keokuk Water Works: Its Geological Foundations 22 Common Ground 28 1 The Age of Dinosaurs in Iowa Brian J. Witzke Did dinosaurs once live in Iowa? significant measure of good fortune. The simple and unqualified answer is Dinosaurs were the dominant land Yes, without a doubt! But the actual animals for about 170 million years of evidence for dinosaurs in Iowa is limited earth history, spanning the Late Triassic, to only a few fossils. Dinosaur fossils Jurassic, and Cretaceous periods. This have been found in several states ad- Age of Dinosaurs came to a close 65 joining Iowa (Nebraska, Minnesota, million years ago when a mass extinc- Missouri, South Dakota), and wander- tion ended the dinosaurs reign. (Almost ing dinosaurs would have been unim- all paleontologists consider birds to be peded by these artificial boundaries. descendents of small carnivorous dino- Fortuitous circumstances are saurs, so a segment of the dinosaur pedi- needed to preserve dinosaur remains in gree survived this extinction.) Sedimen- ancient sedimentary environments. Fol- tary deposits from the Age of Dinosaurs lowing the death of an animal, the cover extensive portions of Iowa and bones need to be buried within the sedi- have real potential to yield dinosaur ments and protected from chemical and fossils. The Jurassic Fort Dodge Forma- mechanical destruction. Many great tion was deposited at the same time as dinosaur discoveries are associated with strata in the American West that have sediments of ancient river systems, produced remarkable dinosaur fossils, where dinosaur bones may be preserved but no Jurassic dinosaur fossils have yet within floodplain and river channel de- been found in Iowa. The Cretaceous posits. The discovery of fossil bones is formations are more widespread in Iowa, aided by a careful understanding of a and these same formations have pro- regions geology (where to look), consid- duced dinosaur fossils at scattered lo- erable patience (keep looking), and a calities in the central United States. 2 Dinosaur Society Hadrosaur, by natural history and wildlife artist Karen Carr, courtesy of www.TheFernleaf.com Hadrosaurs, commonly known as duck-billed dinosaurs, occupied subtropical environments in the coastal lowlands of the central United States during the Cretaceous Period, about 100 million years ago. Iowas oldest Cretaceous sediments, in 1928 from the Missouri River bluffs the Dakota Formation, were deposited near Decatur, Nebraska. This locality in ancient river systems that drained lies only about one mile from the Iowa westward to an interior seaway during border. Although this fragmentary fossil the middle part of the Cretaceous pe- has not been assigned to a particular riod, about 95 to 100 million years ago, dinosaur species, its features are suffi- a time of global greenhouse warming. cient to identify it as a large ornithopod, Floodplains and coastal lowlands were a highly successful group of generally covered with lush subtropical vegetation bipedal plant-eating dinosaurs. The pro- at that time, providing suitable habitats portions of this leg bone, when com- for dinosaurs. The first dinosaur fossil pared with other ornithopods, indicate a found in the Dakota Formation, a por- dinosaur that was about 32 feet long. tion of a leg bone (femur), was collected This Dakota fossil likely represents an 3 The microscopic structure of a petrified dinosaur bone fragment from Guthrie County, Iowa, shows a once-porous network of vascular canals for blood vessels. (Enlarged 3-mm-wide view.) Brian Witzke early hadrosaur. Hadrosaurs are a well- cient river gravels of the Dakota Forma- known family of duck-billed ornith- tion in Guthrie County. The micro- opod dinosaurs that comprise the most scopic structure of this fragment (shown abundant and diverse group of Late above) revealed densely vascularized Cretaceous dinosaurs in North America. bone, indistinguishable from that seen Other dinosaur fossils have been in typical dinosaur bone. Although not uncovered from the Dakota Formation terribly impressive by itself, the Guthrie in nearby northern Kansas, eastern Ne- County discovery confirms that dinosaur braska, and Minnesota. A family of fossils indeed occur in the Dakota For- heavily armored ankylosaurian dino- mation of Iowa. saurs, the nodosaurids, is represented by The river deposits of the Dakota partial skeletons of a ten-foot-long crea- Formation were progressively flooded by ture known as Silvisaurus. Additional marine waters as a vast interior seaway hadrosaur bones have been found in encroached eastward later in the Creta- Minnesota. Three-toed fossil footprints ceous, and a succession of younger shale of ornithopod dinosaurs have been dis- and chalk deposits were laid down on covered recently in Dakota strata. the ancient sea bottom in western Iowa. In Iowa, a fragment of fossil bone These strata, named the Graneros, was found by the author in 1982 in an- Greenhorn, Carlile, and Niobrara for- 4 Dinosaur-bearing Cretaceous strata in Iowa and adjoining states Æ MN Dickinson Co. Æ SD Æ Plymouth Co. WS IL Decatur, NE Æ Guthrie Co. Æ MO Æ NE 050100miles KS Tertiary Cretaceous Precambrian Ogallala sand and silt Dakota sandstones and shales quartzites and igneous rocks Cretaceous Paleozoic Location of known marine shales and chalks undifferentiated dinosaur fossils mations, have yielded bones of large times linked with dinosaurs in the marine reptiles known as plesiosaurs publics imagination, plesiosaurs actually from several localities in Iowa. In nearby represent an unrelated group of extinct areas, these same formations have also marine reptiles. Long- and short-necked produced fossils of other extinct reptile plesiosaurs plied the waters of the Cre- groups including mosasaurs (giant sea taceous interior seaway with large lizards) and pterosaurs (large flying rep- paddle-like flippers in search of fish and tiles). Although plesiosaurs are some- other prey. The marine shales and 5 Fossil bone from the Dakota Formation in the Iowa area indicates that large ornithopod dinosaurs once inhabited the region. Reaching a length of 32 feet, these plant-eating giants browsed the lush subtropical forests and swamps. (Six-foot-tall human for scale.) chalks of this seaway also yield the re- derived from erosion of the Cretaceous mains of true dinosaurs. Dinosaurs cer- strata that underlie large areas of the tainly did not live at sea, but occasion- northern Great Plains. Reworked and ally a carcass would float out to sea, transported Cretaceous fossils, such as decay, and settle to the bottom. The plesiosaur bones and shark teeth, are discovery of dinosaur bones and teeth sometimes found in the glacial tills and (of hadrosaurs and ankylosaurs) in ma- associated gravel deposits in Iowa, espe- rine strata from nearby Minnesota, cially in the western part of the state. South Dakota, and Kansas certainly Two dinosaur bones can now be added raises the possibility of similar discover- to the list of Cretaceous fossils recov- ies in western Iowa. ered from glacially derived gravels in Long after extinction of the dino- Iowa, and to date these discoveries rep- saurs, huge continental glaciers ad- resent the best dinosaur fossils found in vanced and retreated across Iowa during the state. the Ice Age (the last 2.5 million Charlie Gillette of Dickinson years). These advancing glaciers incor- County picked up a dark-colored, 3-inch porated large volumes of rock and other fossil bone from a load of landscaping sediments as they moved across the con- gravel that came from a nearby gravel tinent. Much of the glacial material was pit. When his uncle Jack Neuzil, a re- 6 Fossil dinosaur vertebrae 3 and 4 inches long have been found in Dickinson (right) and Plymouth (far right) counties, Iowa, respectively. These specimens likely came from hadrosaurs. photos by Paul photos VanDorpe by Paul tired educator and dinosaur enthusiast, 1930s he picked up a fossil bone from a saw the bone he suspected that it could conveyer in a gravel pit near Akron in be a dinosaur vertebra. His suspicions Plymouth County, and the bone was were confirmed by a leading dinosaur kept on a shelf and occasionally used as paleontologist, and the discovery of a doorstop in the familys home. In re- Iowas first identifiable dinosaur bone sponse to a recent newspaper article was soon reported in the Des Moines about dinosaurs in Iowa, Mrs. Register (9/7/2000). The fossil is a tail Michaelson contacted the Geological vertebra from an unknown dinosaur, Survey Bureau and brought the bone in possibly a hadrosaur. for identification. It is a partially weath- Following this discovery, a second ered 4-inch dinosaur vertebra, likely dinosaur vertebra from Iowa has come from an hadrosaur. to light thanks to Doris Michaelson of Its only a matter of time before Bellevue.