GMS Field Trip June 2025

GMS Field Trip
Geodes and Ordovician Fossils in Tennessee
Sunday, June 8, 2025

Who likes geodes? Fossils? Members got to collect both on this trip! Our first stop of the day was to collect geodes in a creek. The geodes in this area have a distinctive “rind”, i.e., the outer surface of a geode. Even for members who had never been there, it was easy to identify potential geodes by the rinds poking out of the gravel all around. These geodes are heavy, so you can’t weigh one in your hands to determine if it might be hollow and not a solid nodule. You must break it open to know for certain. The thick rind rarely has any sort of banding or color, so, unlike geodes from South America or the Western U.S., these geodes don’t look good when they are cut open. A natural break is much more aesthetically pleasing too, another good reason to break them open.

Charles explained and demonstrated his geode cracking technique with a hammer and chisel. Members who had never broken open a geode, including one of the juniors, started popping open beautiful geodes with ease. Occasionally, members found a geode that was already broken open. Already open geodes can have biological things like algae and tiny critters, so they must be cleaned.

In addition to geodes, the area has limestone karst. Karst is formed the dissolution the limestone by water. Small pieces break off and are mixed with the gravel. Some of these pieces are reminiscent of tiny canyons and other landscapes. They can be considered a type of “suiseki”, from the Japanese “sui” (pronounced swee”) meaning water, and “seki” (pronounced seckee) meaning stone. Members found several nice specimens. I found a beautiful little piece with many “valleys” and dark lines between layers. It is my favorite suiseki of all time from this location.

Because there is limestone in the area, there are fossils there too. I saw many little crinoid stems, a few brachiopods, a cephalopod in matrix, and one last-minute little coral. The coral was definitely elusive this year, as I saw only that one. The piece I found was different from those found in years past. Before, the coral we found was highly silicified. This one is mostly limestone, with only very small, silicified areas.

We took a relaxing break for lunch plus some rockhound chatter. We learned more about the rocks and fossils there, and a lot more about Jason and Nedra’s childhoods than perhaps we should have. Sufficiently refreshed, we caravanned to the second location of the day. There, we saw fossils everywhere! Members found fossil plates covered with beautifully preserved brachiopods, bryozoans, and teeny, tiny crinoid stems. Some plates had pyrite crystals inside bryozoan structures. There were a few cephalopods too, including the largest specimen we have ever seen there. It is approximately 6 inches wide, and if you extrapolate from the widest end to where the thinnest end would have been, it was probably originally more than a foot long, possibly longer, since we don’t know if the wide end is truly the end of the animal.

One day, about 485.4 to 443.8 million years ago, give or take a day or two, an arthropod was walking across the bottom of a sea. It stopped, fanned its legs in and out, stirring up the sediment so it could eat tiny things like plankton and algae as they floated out, or just to get comfortable. It left marks in the sediment that filled with finer sediment that ultimately helped preserve this one little moment in one little creature’s life. The marks are called Rusophycus, i.e., a trace fossil of the resting movements of an arthropod. In this case, the marks were most likely made by a trilobite, and they were the most exciting find of the day. Thankfully, Jason and Aaron recognized it as Rusophycus, so now we can add it to our knowledge of trilobites in that area. A trace fossil like this is distinguished from a body fossil by the fact that it preserves the activity or mere presence of an organism versus preservation of the organism itself. A body fossil in this case would be preservation of the trilobite itself, the one who rested on the sediment and moved its legs around.

What a great way to end a great trip! Members found so many interesting things to bring home, including fond memories of a fun day. Again, we are incredibly fortunate to have a member who allows us to park in the pasture (that she had just mowed for us!), helps us splash around in her creek, and who always regales us with her superb story-telling skills, wisdom, and geology expertise. She always makes every trip to the creek safe, fun, and educational. Thank you! Thank you! Thank you! Thanks as well to the fossil location property owner who lets us break and take rocks and fossils from their property. We also appreciate members who showed up on time, followed all of the directions and rules, and brought their favorite goodies to me to photograph for this report. Many thanks and kudos to Jason, Nedra, Aaron, Nate, and Madison who worked diligently to make the trip run smoothly, kept everyone safe, and were always on hand for specimen identification as well as any assistance needed.

Note: Specific location information is not included in this report to respect the privacy of property owners.

Lori Carter on behalf of Trip Lead Jason Leatherwood
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