Fossil Collecting at the Mazonia-Braidwood Fish and Wildlife Area

Welcome. The fossil-bearing ironstone concretions (or nodules) found at the Mazonia-Braidwood Fish and Wildlife Area are world famous. Paleontologists consider this fossil deposit to be one of the world’s most important fossil deposits. The plants and animals found in the nodules lived about 300 millions years ago (during a time known as the "Coal Age"). The fossils provide a wonderful glimpse of the plants and animals that lived during that time in what is now Illinois.

The area that is now the Mazonia-Braidwood SFWA was very different 300 millions years ago. The area was a mixture of low flat land, rivers, bays and sea. It was a massive delta building out into a shallow tropical sea. The land was covered with swamps (which would later form the coals mined in the area). The land and water teamed with life. When the plants and animals died, they were quickly buried at the bottom of the shallow bays. After they had been buried, ironstone nodules formed around the plants and animals, preserving them for us as Mazon Creek fossils.

These fossils are contained in concretions known as Mazon Creek Nodules. These are smooth, oval or round, generally rust-colored masses of rocks. They are formed in a layer of shale that covered the coal that was mined in the area. When the coal was mined, the shale and nodules (which was part of the overburden) were dumped into large spoil piles. As the nodules weather out of the piles, they can be collected.

The nodules contain a great variety of kinds of plant and animal fossils. Some of the kinds of plant fossils that are found in the nodules include fern fronds, bark of scale trees, and leaves of other coal age trees and shrubs. Animal fossils found in nodules include shrimp, worms, jellyfish, clams, and Tully Monsters. The Tully Monster, Illinois’ State Fossil, is known only from these spectacular deposits.

You cannot tell what may be in a nodule from looking at the outside, although some collectors with years of practice may be able to make a reasonable guess. In order to see the fossil, you need to break open the nodules. There are several ways to do this. Some people use a rock hammer to open nodules. Although this method is fast, it frequently causes nodules to break in a way that do not expose the entire fossil. Another common method used to open nodules is alternate freezing and thawing. Nodules are placed in a bucket of water. After they have soaked for several days (to get water into the nodule), the bucket and nodules are placed in the freezer. When the water has completely frozen, the bucket is removed from the freezer and the water is allowed to thaw. The freezing and thawing cycle is repeated. Between freezing, nodules that open should be removed and other nodules can be tapped (with a hammer or on a hard surface) to see if they will open. After about 10 cycles, allow the modules to dry completely. Then repeat the whole process. Most nodules that will open will do so in about 25 cycles or less. Other nodules can be opened with a hammer.

Sources of Information about Mazon Creek Fossils

If you would like to learn more about Mazon Creek fossils, or if you need help identifying your fossils, there are many sources of information on the subject. The following is a list of resources that may be of help to you.


The Mazon Creek Project

The Mazon Creek project is a mixture of amateur and professional paleontologists interested in education and scientific research on Mazon Creek fossils. The Project holds open houses, leads field trips, and provides information on the Mazon Creek fossils.

    Contact Information:

    The Mazon Creek Project

    Northeastern Illinois University

    Department of Earth Sciences

    5500 N. St. Louis Ave

    Chicago, IL 60625

    Phone 773-442-5759

Illinois State Museum

The Illinois State Museum can provide a variety of information concerning "Coal Age" fossils and the Mazon Creek deposits

    Contact Information:

    Dr. Richard Toomey

    Illinois State Museum

    1011 E. Ash St.

    Springfield, IL 62703

    Phone: 217-524-7908

    Email: toomey@museum.state.il.us

    www: http://www.museum.state.il.us/

Illinois State Geological Survey

                        The Illinois State Geological Survey can help with identification of fossils and with info on Mazon Creek

    Contact Information:

    Mr. Russel J. Jacobson

    Geologist and Acting Head, Coal Section

    Illinois State Geological Survey

    615 East Peabody Drive

    Champaign, IL 61820

    Phone: 217-244-2426

    Email: jacobson@isgs.uiuc.edu

    www: http://www.isgs.uiuc.edu/ 

Burpee Museum of Natural History

The Burpee Museum can provide help in identifying fossils and has a nice collection of Mazon Creek fossils on display.

    Contact Information:

    Mr. Michael D. Henderson

    Curator of Earth Science

    Burpee Museum of Natural H istory

    737 N. Main Street

    Rockford, IL 61103

    Phone: 815-965-3433

    Email: geocollections@burpee.org

    WWW:  http://www.burpee.org/ 

Bradley Unversity, Department of Geological Sciences

Dr. Foster at Bradley university is a paleontologist who studies the fossil animals of Mazon.

    Contact Information:

    Dr. Merril W. Foster

    Department of Geological Sciences

    Bradley University

    Peoria, Illinois 61625

    Phone: (309) 677-2352

    Email:  fossil@bradley.bradley.edu

    www:    http://www.bradley.edu/ 

Fossil Collecting Groups

Fossil collecting groups can often provide information on Mazon Creek fossils and on other fossil found in the state. One group that has been closely associated with Mazon Creek fossils is the Earth Science Club of Northern Illinois (ESCONI).

Contact Information:


Box 321

Downers Grove, IL 60515

Email: ESCONI@hotmail.colm

www: http://www.esconi.org


Illinois State Museum Online Exhibit on Mazon Creek Fossils http://www.museum.state.il.us/exhlibits/mazon_creek/

Illinois Geological Survey Tully Monster Geobit http://www.isgs.uiuc.edu/servs/pubs/geobits-pub/geobit5/geobit5.html


Earth Science Club of Northern Illinois, 1986, Keys to Identify Pennsylvanian Fossil Plants of the Mazon Creek Area (revised Edition). Downers Grove, IL. (P.O. Box 321, Downers Grove 60515): Earth Science Club of Northern Illinois, 60pp.

Earth Science Club of Northern Illinois, 1989, Keys to Identify Pennsylvanian Fossil Animals of the Mazon Creek Area (revised Edition). Downers Grove, IL. (P.O. Box 321, Downers Grove 60515): Earth Science Club of Northern Illinois, 125pp.

Andy A. Hay and Don Auler(Illustrator),Creature Corner , Downers Grove, IL. (P.O. Box 321, Downers Grove 60515): Earth Science Club of Northern Illinois, 78 Pages, 126 Black and White Drawings

R.E. Janssen, 1939, Leaves and stems from fossil forest. Illinois State Museum, Popular Science Series, I: 190pp (Revised 1979)

J.R. Jennings, 1990, Guide to Pennsylvanian Fossil Plants of Illinois, Illinois State Geological Survey, Educational Series, 13: 1-75.

C.W. Shabica and A.A. Hay (Editors). 1997, The Fossil Fauna of Mazon Creek, Chicago: Northeastern Illinois University, 309pp. ISBN 0-925065-21-8

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Last Updated 04/16/2003