Fossils of Iowa: Field Guide to Paleozoic Deposits

Fossils of Iowa: Field Guide to Paleozoic Deposits


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The Fossils of Iowa field guide is written primarily for amateurs in geological exploration and collecting. Robert Wolf provides a comprehensive coverage of more than 150 sites in Iowa and adjacent areas of Minnesota and Nebraska with the types of fossils that can be found and precise directions. Excellent illustrations by Carol Ann Ratcliff aide in identification. For an update in site conditions and geological names since the book was first published contact the author at

Product Details

ISBN-13: 9781504032919
Publisher: Open Road Integrated Media LLC
Publication date: 09/27/2016
Pages: 212
Sales rank: 861,917
Product dimensions: 5.40(w) x 8.40(h) x 0.60(d)

About the Author

Robert Charles Wolf is a self-taught geologist specializing in Paleozoic fossils of invertebrates, trace fossils, plant fossils, and vertebrates. He has been collecting for more than 40 years, a native of Iowa, and the author of Iowa’s State Parks. He is a newspaper correspondent and a freelance writer. Robert has donated collections of rocks and fossils to museums, schools, and colleges.

Read an Excerpt

Fossils of Iowa

Field Guide to Paleozoic Deposits

By Robert Charles Wolf, Carol Ann Ratcliff


Copyright © 2006 Robert Charles Wolf
All rights reserved.
ISBN: 978-1-5040-3278-0



For over 3 billion years life has inhabited the earth, but it was very primitive for most of this history. Dramatically, during the Cambrian Period, which began about 600 million years ago, more advanced life forms began to flourish. Three hundred million years later, thick forests and swamps covered parts of the continents, reptiles and amphibians roamed the forests, and insects filled the air. The Cambrian Period marked the beginning of the Paleozoic Era, which includes the Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian periods. The Paleozoic ended with the close of the Permian Period around 225 million years ago (a span of 375 million years).

Cambrian fossils from Iowa include burrows, trilobite fragments, and brachiopods. Burrows are very common and occur in several formations. Trilobite fragments are not very abundant and are usually only small pieces. Most of the brachiopods are inarticulates, but early orthids have been found. Cambrian fossils are more common in Minnesota and Wisconsin.

Fossils from the Ordovician Period in Iowa include a wide variety of marine organisms. Most orders of brachiopods can be found, but orthids and strophomenids are the most common. Other common fossils include echinoderm debris, nautiloids, gastropods, trilobites, corals, graptolites, pelecypods, and several others.

Iowa Silurian fossils include several types of brachiopods, the most conspicuous being the pentamerids. Stromatoporoids, a wide variety of corals, nautiloids, echinoderm debris, and other fossils can also be found.

The Devonian fossils from Iowa include many types of marine organisms. Spiriferid brachiopods, corals, echinoderms, stromatoporoids, and other fossils, including fish teeth, can be found. Some collecting sites exposing Devonian formations are quite famous for their well-preserved fossils.

Fossils from the Mississippian Period in Iowa include abundant brachiopods (of which the spiriferids are the most common), bryozoans, corals, pelecypods, fish teeth, gastropods, and echinoderm debris; several other forms can also be found. Iowa is famous for well-preserved Mississippian crinoid crowns. These occur mostly in the Hampton, Gilmore City, and Burlington formations.

Pennsylvanian fossils from Iowa include both flora and fauna. Abundant plant fossils occur in the Caseyville Formation and the Cherokee Group. Marine fossils are abundant mainly in the southwestern part of the state and include several types of brachiopods (mostly strophomenids, including productids and chonetids), pelecypods, gastropods, echinoderm debris, corals, bryozoans, fusulinids, nautiloids, trilobites, and several others.

During the latter half of the Paleozoic Era, beginning in the Devonian Period, North America, Europe, and parts of Africa and South America were joined into one continental mass. Seas frequently invaded the inner regions of the continent, and Iowa was flooded many times. In the Pennsylvanian and Permian periods, the rising and falling water levels of the seas were markedly rhythmic, forming cyclic deposits of alternating shales and limestones.

The Permian Period saw the rise of early, large reptiles that were the ancestors of mammals, and further advancements of marine and plant life occurred. However, by the start of the Mesozoic Era many life forms had become extinct, including several types of brachiopods, trilobites, eurypterids, blastoids, many types of crinoids and gastropods, and others. Most of the plants composing the Paleozoic forests soon became extinct also. There are no known Permian deposits in Iowa, but the system is well represented in some neighboring states, and the Permian System of Nebraska is briefly touched upon in this book.

This book is a field guide written for amateur fossil collectors and geology enthusiasts. Most of the Paleozoic deposits in Iowa are examined, beginning with the Cambrian Wonewoc Formation and ending with the Pennsylvanian Wabaunsee Group. Most of the sites listed are in Iowa and were examined firsthand unless otherwise noted. For collectors wishing information on additional exposures of the Paleozoic Era, the addresses of seven state geological surveys in the Midwest are given in the references. Several publications listing additional sites are also listed.

This book is not intended to be an introduction to fossil collecting. There are several excellent books serving that purpose. However, the need for personal safety equipment cannot be repeated enough. Some working quarries require such equipment for any visitor. The requirements include eye protection, hard hat, and steel-toed shoes. A sturdy pair of gloves is also recommended, and a compass not only will get you back to the main highway but will also direct you to your vehicle when hiking. A snakebite kit as well as boots are good precautions. Venomous snakes were encountered on a few field trips; one cannot be certain when or where they will be found, so always be prepared. Some sites in Nebraska are infested with scorpions, but none were encountered at any of the road cuts examined for this study. If stung by a scorpion, seek medical help promptly.

Suggestions on collecting are given throughout the text. The best time to visit a particular working quarry, where to obtain permission, special precautions, and other important points are included. When being permitted access to private property, try to make sure you do nothing to cause future collectors to be denied this privilege. Also, listen to the owners. They know the hazards of the area and can provide helpful hints as to where the best and safest exposures can be found. You may be required to sign a release form. An attempt to contact owners of the quarries described in this book was made, and replies are mentioned throughout the text.

In addition to being a field guide, this book is a faunal survey. In most cases when a fossil fauna is described, such terms as "few" or "abundant" are either substantiated or replaced with percentages. For example, the spiriferid brachiopod Spinocyrtia iowensis represents 63 percent of the fauna of the Solon Member of the Cedar Valley Formation at Vinton. However, since techniques vary, this collector will explain how these figures were derived.

1. Personal studies of the Mississippian and Pennsylvanian faunas in the Fort Dodge area have shown that at least one hour of collecting will pro vide a fairly accurate representation of the most abundant fossils. This was the time spent at most of the fossiliferous deposits examined for this book. Any specimens found through additional collecting were not con sidered when figuring the percentages. This one-hour survey varied slightly from highly fossiliferous shale to poorly fossiliferous limestone. If a deposit yielded no fossils after 15 to 30 minutes of searching, no further time was spent and the deposit was labeled nonfossiliferous. This does not necessarily mean that such a deposit is totally lacking in fossils, just that the casual collector is not likely to find many specimens with the unaided eye.

2. Loose specimens and fossiliferous slabs were collected for later identification and tabulation. When the rock was so dense that too much time would be spent in freeing specimens, those seen in the field were recorded and then extracted after the one-hour survey was completed. The deposits that warranted such an approach were few. The best ex ample of this situation occurs in the Wise Lake Member of the Galena Formation at Millville.

3. Educated guesses were made when dealing with numerous fossil fragments such as crinoid columns, bryozoans, and graptolites. In such cases only specimens over a certain size were counted; this size factor varied from fauna to fauna. In faunas made up of numerous small fragments, this collector used his own judgment in deciding what fraction should be used. Burrows represented a similar problem and were counted in the same manner. When burrows or fragmented fossils were few in number, each specimen was counted. Fusulinids and other small, unfragmented fossils presented a different problem. To remedy this situation, fossiliferous slabs were collected, and each specimen was counted later.

4. Every effort was made to examine all accessible parts of an exposure, trying not to concentrate merely on the most fossiliferous areas when making a faunal survey, unless there was a marked change in lithology.

5. Bulk samples were taken from some shales. These varied from 25 to 100 pounds. A bulk sample of at least 25 pounds should prove enlightening if the deposit is fossiliferous. Such a sample provides data on certain aspects of a fauna that are usually missed in the field, such as fragmentation of fossils; mortality rates based on numbers of immature forms; the smaller elements of a fauna, some of which can be extremely abundant; and specimens that are inconspicuous in the field. When collecting a bulk sample, small amounts of shale were taken from different areas of the same deposit at the same exposure, forming a composite. At home, the shale was rinsed with water through a sieve (mesh size 2 mm). The material remaining was removed and left to dry before the fossils were sorted by hand.

6. The faunal surveys included in the text are the findings of a typical amateur collector. They are included as an aid in identification for other collectors but do not necessarily reflect actual abundances. The references used most often in identifying fossils are given with each faunal list. When conflicts arose among references, Morre (1965) took precedence for brachiopods, Shimer and Shrock (1972) for others.

The localities of most sites are given as sections of townships. Iowa county maps and those issued by other states list townships and sections. Iowa maps are available for a nominal charge from the Iowa Department of Transportation, Office Supplies, Ames Storeroom, Ames, IA 50010.

Each township usually has 36 sections. Each section is 1 square mile (640 acres). An example of a site location is C/N½/SW¼/SE¼ sec. 10, T99N, R3W. This translates to the center of the northern half of the southwest quarter of the southeast quarter of section 10 in township 99 north, range 3 west. This particular township lies in the ninety-ninth tier north of a particular base line or latitude line and is the third township west of a particular principal meridian or longitude line. These figures appear on the margins of county maps.

Section 10 lies in the north-central area of a township. The section is subdivided by the example in this manner: the southeast quarter of section 10, the southwest quarter of that quarter, and the central part of the northern half of that quarter.

Most sites mentioned in this book include references given with the stratigraphic column listed for the site. These direct the reader to the original data sources. Very little information could be found for some sites, and in these cases the author had to measure and identify the exposures to the best of his ability. A description of the divisions of a stratigraphic column is given below.

Era — The largest division of a column. There were five such eras: the Archeozoic (the earliest time span extending back to the very creation of the earth), Proterozoic, Paleozoic (the subject of this book), Mesozoic, and Cenozoic (which includes the last 70 million years of geological history).

Period — Eras are divided into major systems of deposits called periods. At one time each period was thought to have ended rather abruptly, leaving a gap in the stratigraphic column before the next period began. Although in geological history major breaks or gaps are common, in which no new deposits were laid down for a considerable time and older deposits were eroded, they do not necessarily occur at the end of each period. The English River Formation of Iowa, for example, appears to be transitional, being deposited near the end of the Devonian Period and toward the beginning of the Mississippian.

Series — Periods are divided into series roughly corresponding to their lower (early), middle (mid), and upper (late) portions.

Group —Series are frequently split into associations of similar rock units (groups).

Formation — Groups in turn are usually composed of several formations, which are the primary units of a stratigraphic column. They are defined by lithology and stratigraphic position.

Member — Some formations are split into members based primarily on variations in lithology.

Iowa has abundantly fossiliferous deposits from the Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian periods. Faunas of the Cambrian and Permian periods can be found just outside Iowa's borders. This book, with its strong emphasis on prehistoric life, is intended to help the reader to better understand Paleozoic deposits in the state, assist in planning field trips, and aid in dating many exposures in this area that are not covered here.

As this book goes to print, geologists are actively revising and more precisely defining the stratigraphic column of Iowa. Some of the current work concerning the Paleozoic Era includes:

1. Revision of the Desmoinesian Series of the Pennsylvanian Period.

2. Research by Dr. Gilbert Klapper of the University of Iowa and Dr. James Barrick of Texas Tech University on a newly recognized Devonian Formation.

3. Preliminary reinterpretation of the Lower Mississippian in north-central Iowa (Glenister and Sixt 1982):

a. The Gilmore City Formation exposed at Gilmore City is now believed to be the equivalent of the Chapin Member of the Hampton Formation at Le Grand. The Chapin Member is laterally equivalent to the Starrs Cave Formation of southeastern Iowa, but the Chapin may actually be slightly older.

b. The limestone exposed in the Humboldt area is no longer considered to be part of the Gilmore City Formation, but is called the "Humboldt Oolite." It is equivalent to the Eagle City and Iowa Falls members of the Hampton Formation. Therefore, it is slightly younger than the Gilmore City Formation. The Humboldt Oolite is well exposed in the P & M Hodges Quarry north of Dakota City in Humboldt County (N½ sec. 32, T92N, R28W). The lower levels of the quarry carry an abundant and diverse gastropod-coral fauna, including the tabulate coral Syringopora. Permission and safety equipment are required. Contact Weaver Construction Company, Iowa Falls, IA 50126. Exposures of the Humboldt Oolite also occur along the Des Moines River in Humboldt.

c. The poorly fossiliferous limestone quarried in the Alden area in Hardin County is probably equivalent to the Humboldt Oolite.

4. The Wise Lake and Dunleith, once thought to be members of the Galena Formation, are now considered as separate formations. The Galena is no longer used as a formation name.

5. A recently discovered site: E½NW¼ sec. 22, T100N, R4W. Allamakee County. To reach the site take Highway 26 north from Lansing for about 9 miles to the bridge over the Upper Iowa River. Just south of the bridge turn left (west) onto a gravel road. Continue west and south for a fraction of a mile to two quarries on the east side. The Lodi Siltstone Member of the Saint Lawrence Formation, Cambrian Period, is exposed here. Fossils are particularly abundant in the southern quarry. Thin beds of burrows are common throughout the exposure, and the lower levels contain fairly abundant trilobite fragments between the burrow beds. Carefully split the rock as thinly as possible into one layer at a time, paying close attention to the layers immediately below the burrows. Cranidia, spines, thorax segments, and pygidia of the trilobite Dikelocephalus were found during three hours of collecting. Also found with the trilobite fragments were a dozen small inarticulate brachiopods believed to be Dicellomus, a few small specimens of the gastropod Proplina, and a small cranidium fragment probably of the trilobite Brassicephalus.

Two dense, tan colored, sandy dolomite rocks found on the floor of the southern quarry contained abundant brachiopods. They probably originated from the middle of the face but this could not be positively determined. Both contained a total of sixty specimens of the orthid brachiopod Finkelnburgia and a few possible specimens of the inarticulate brachiopod Lingulepis. However, the rock must be thoroughly broken up to find the specimens.


Precambrian and Cambrian Periods

Site 1. Location: sec. 11, T100N, R49W. Red quartzite (Sioux Quartzite) of the Precambrian Period crops out along the Big Sioux River in the extreme northwest corner of Iowa in the vicinity of the Gitchie Manitou State Preserve in Lyon County. This is the oldest exposed bedrock in the state. Collecting inside the preserve is not permitted. The age of this rock has been estimated to be about 1.5 billion years old.


Excerpted from Fossils of Iowa by Robert Charles Wolf, Carol Ann Ratcliff. Copyright © 2006 Robert Charles Wolf. Excerpted by permission of OPEN ROAD INTEGRATED MEDIA.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents


List of Plates,
1. Introduction,
2. Precambrian and Cambrian Periods,
3. Ordovician Period,
4. Silurian Period,
5. Devonian Period,
6. Mississippian Period,
7. Pennsylvanian Period: Desmoinesian and Morrowan Series,
8. Pennsylvanian Period: Missourian Series,
9. Pennsylvanian Period: Virgilian Series,
10. Permian Period,
About the Author,

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