This is Mazon Monday post #138. What's your favorite Mazon Creek fossil? Tell us at email:[email protected]. Thanks!
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Jim and Sylvia Konecny were very active in ESCONI for many years. They held various board positions over the years with Jim serving as president in 1966. They were prolific fossil collectors, who donated a significant collection to the Field Museum back in 2019. Their collection spanned many time periods but had an emphasis on Mazon Creek. Here's a few photos of them in 1993 leading tours of their collection after they moved to Arizona.
They wrote quite a few articles for fossil enthusiast magazines, Earth Science, the ESCONI newsletter, and Fossil News. The following article appeared in the October 2009 edition of Fossil News. Jim wrote the article and Sylvia did the artwork.
It's interesting to note that their collecting spanned the era of plenty, where concretions were easy to obtain and a hammer was the tool of choice. Currently, concretions are much more scarce and using the freeze/thaw method improves the odds of getting a good split. You can read more about how freeze/thaw in Mazon Monday #27. The explanation of how concretions form is still very relevant. However, applying varnish is not recommended as it can compromise the quality of the specimen and is very hard to remove.
Preparing Mazon Creek Nodules for Display
The fossils of the Mazon Creek area have been known for about 150 years. These beautifully-preserved plants and animals come neatly packaged in their own containers. These containers are known as concretions or nodules. A brief introduction on the formation of these nodules is in order. The ground in which these plants and animals are buried must contain certain chemicals, basically iron and pyrite, for the formation of these nodules to take place. After the organism falls to the ground, it is covered by silt from flood waters (Figs. 1a & lb).
The decomposing, buried organism immediately chemicals in the ground towards the organism, Figs 1c & 1d. This combined action and reaction creates a type of gel equidistantly surrounding the organism. Over time, load pressure hardens this gel into stone. We have our nodule or siderite concretion, Figs. 1e & 1f. This process has been replicated in a laboratory and it was found that any organic substance (slime, feces, mucous, etc.) can initiate the process.
For anyone interested in a more detailed and tech- nical description of the formation of Mazon Creek and Mazon Creek-type concretions, I recommend the references cited at the end of this article.
The organism within the nodule creates a plane of weakness through the center of the nodule. In order to expose the organism, the nodule must be split open. For this, the plane of weakness can be exploited. There are two methods by which this can be accomplished. One, the original method, is to place the nodule on edge on a hard rock (1.e. granite, limestone, etc.) and strike it with a rock ham- mer (Fig. 2). Usually one blow will not be sufficient, and several blows are required. The nodule should split along this plane. There are times when this plane of weakness is not constant throughout the nodule and it will not split fully along this line. It may run off on a tangent and only part of the organism will be exposed. In this case, a little work with a chisel is required to expose the entire organism. This requires great care and only experience will tell you to place the chisel. If the nodule breaks into several pieces, use your favorite glue to mend it.
The second way to split the nodules is the 'freeze-thaw' method. This method was developed by Larry Osterberger in the early 1970s. Occasionally nodules are found in the field already split open. This has been accomplished by various weathering agents. Larry decided to replicate this process by placing the nodules in a bucket and filling the bucket with water, then leaving it outside over the winter to freeze and thaw naturally. Of course, this can only be done in northern climates where the nighttime temperatures drop to well below freezing and rise to above freezing during the day. For those living in a mild climate, the same thing can be accomplished by placing the nodules in a pot of water and putting this into the freezer overnight, and then placing it outside during the daytime. This process may have to be repeated as many as twenty to twenty- five times-maybe even more. Be patient.
Occasionally the split faces of the nodules, especially those found already split open, may have a light grey coating covering them, thereby obscuring the details of the plant or animal. This coating is probably residue from dirty water and can easily be removed by placing the nodule into a weak acid solution of 1 part muriatic acid to 4 parts water. After about 30 to 60 seconds, brush lightly with a soft toothbrush and place into a container of clear water. A few seconds in the clear water is all that is needed to neutralize the action of the acid. If you have sensitive skin, you should wear rubber gloves when working with acid. This is especially important if Most of the time, the plant or animal is found you have a small cut or abrasion on your hand.
There is another kind of coating that is frequently encountered. This is a rather hard, white substance which is an aluminum clay known as kaolin or kaolinite. I have not found a chemical that will dissolve it. A brisk brushing will usually re-move it if the kaolin is soft enough. All of the nodules are not of the same hardness, and some are soft enough that brushing will leave brush-marks, thereby ruining the specimen. I like to experiment by first brushing a clear portion on the split face using various hardnesses of brushes. If the kaolin is hard, and brushing will not remove it, and if the nodule is hard, one can try gently scraping with a dental tool. However, extreme caution must be used so as not to scratch the surface. There are times when one must be content with leaving the kaolin in place. There are also times when the kaolin is merely outlining the fossil, as in Fig. 3. This actually enhances the specimen, so it is wise to leave it in place.
Most of the time, the plant or animal is found preserved in a slightly darker or lighter shade than the surrounding matrix. This contrast is exactly what we want for optimum display (Fig. 4). However, there are times when the fossil is almost, or exactly, the same shade as the surrounding matrix and is difficult to discern (Fig. 5). In order to make the organism a contrasting shade, I mix a solution of 1 part dull varnish to 1 part turpentine. I use Pratt & Lambert brand dull varnish, but I imagine that any brand of dull varnish will do. It must be a dull varnish-satin finish will not work properly. Using a fine artist's brush, I coat only the impression with this solution- not any part of the matrix. This darkens the plant or animal without dark- ening the background, thus obtaining the contrast that we want to make the fossil more attractive (Fig. 6). For this reason, it is imperative that you use a dull varnish, since any amount of glossiness will obscure fine detail. Care must be taken not to get any of the mixture on the matrix. It can be a tedious procedure when working with specimens that have very fine, thin, and small structures, but the result is rewarding, as shown in Fig. 7. As can be seen in Fig. 6, I like to use a magnifying glass with a strong light when doing this coating. For those of you who may be leery of using the turpentine/varnish solution for fear that it might ruin the fossil for future research study, I have found that ordinary paint and varnish remover will remove the coating without doing any harm to the fossil. I also wish to stress the importance of using a good grade of artist's brush (such as camel's hair). Do not use a cheap watercolor brush. Also, when you see that the bristles of the brush are starting to separate, discard it and use a new brush.
Your specimen is now ready for display. If you exhibit your fossils in a case where they are laid flat in a horizontal position, there is nothing left to do but attach your label. I like to display my Mazon hanging them in a frame on the wall, Fig. 8. There are seven frames in our display room ranging in size from 32" x 36" to 48" x 48". In order to hang the nodules, some sort of hanger must be fastened to the back of the nodule. I use a thin canvas material and cut it into strips about 1/2" wide and about 4" long (shorter for smaller specimens). One end of these strips is then looped through a small brass (about 3/4" diameter) ring and is folded over about an inch. This is then sewed to hold the ring in place. Now it is glued to the back of the nodule (Fig. 9). I like to use 'Mighty Tacky' and coat the entire back of the strip and also the back of the nodule. After the glue is dry, it is ready to be hung in the frame. I use round-head screws in the frame because the ridge on the head prevents the ring from slipping off (see Fig. 10). In the Fig. 10 photo, the rings on the backs of several nodules are visible so that the way the nodules are hanging can clearly be seen. Also visible are the ID tagsluse. Each tag has the fossil name and loca- tion. In the Mazon Creek area there are actually 16 separate locations where nodules can be found, hence the need for the ID tags showing locations. The backs of the nodules have an ID number written on them in India ink.
No doubt there are collectors who have different ways of preparing and displaying their Mazon Creek material. However, in the 40+ years that I have been working with Mazon Creek fossils, I have found this to be the best method for me.
References
Woodland, Bertram G. and Richard C. Stenstrom, 1979. The occurrence and origin of siderite concretions in the Francis Creek Shale (Pennsyl- vanian) of northeastern Illinois. In Mazon Creek Fossils, Matthew H. Nitecki (ed).
Zangerl, Rainer, Bertram G. Woodland, E. S. Richardson, Jr. and D. L. Zachry, Jr., 1969. Early diagenetic phenomena in the Fayettville Black Shale (Mississippian) of Arkansas. In Sedimentary Geology v. 3.
These images were generously provided by ESCONI member Ralph Jewell. Thanks, Ralph!
