GMS Field Trip December 2022

GMS Field Trip
Mississippian Marine Fossils and Geodes in Tennessee
Saturday, December 17, 2022

As the day of this trip drew nearer and nearer, Charles and I watched happily as the water level in the area went lower and lower. We were excited because the lower the water level, the more shoreline exposed, and the more shoreline exposed, the more fossils to be found. But then came the rain. We watched nervously as the water level went higher and higher and the temperature went lower and lower. Yet, all was well. The water level was fine and the cold did not affect the trip.

Charles arranged a special discount at a local hotel. There were so many of us that the hotel owner graciously allocated all of the rooms to GMS! There was a lovely outside patio with a fire pit and grill, so we started the fun a bit early by having a cookout the night before the trip. Members brought all kinds of goodies including chips and dip, baked beans, brownies, and blueberry cobber. We also had hotdogs and marshmallows to roast, plus some chocolate bars and graham crackers for making ‘smores. No comment on Charles’ grill lighting skills, but suffice it to say, we ultimately had some glowing charcoals perfect for roasting our dinner and for taking a little bit of the edge off of the crisp winds.

The next day, members were eager to get to the fossils. The area we visited is in the Fort Payne formation, where you can find a variety of Mississippian marine fossils that are about 323.2 to 358.9 million years old. At the first location, members had no trouble finding the rugose coral Lithostrotionella, easily identified by its hexagonal, colonial structures. One member had a bucket filled to the brim, but not with coral fossils – it was trash! Why? Because this location is on private property and Charles arranged with the owners to clean up trash in exchange for allowing us to collect there. As members collected coral fossils, they also picked up trash. We ended up carrying out a large garbage bag full!

At the second location, we found plenty of crinoid fossils, but it can be difficult to determine species. The crinoids Agaricocrinus and Eretmocrinus are well represented and can be identified by their elusive calyxes, which we will learn about below. Everyone got lots of crinoid fossils for themselves and for grab bags. And, although calyxes are difficult to find, several members were thrilled to bring home their first specimens! So, what are calyxes and why are they so hard to find? The answers lie in crinoid anatomy.

Although they may look like plants, crinoids are animals. And yes, the use of the present tense in the prior sentence is correct because, even though we tend to think of most fossilized creatures as extinct, there are still a few hundred species of living crinoids. They have their own class, Crinoidea, in the phylum Echinodermata, so their close relatives include starfish and sea urchins. Because of that, we often see a fivefold symmetry in the fossils. Some crinoids, often called “feather stars”, float through water. Others anchor to the bottom of the ocean and are often called “sea lilies” because their graceful forms give them a flower-like appearance.

The crinoid fossils we found originally consisted of calcium carbonate covered by a small amount of soft tissue. They had stalks made of columnal segments topped with a cup-like structure – the calyx. Arms with feathery structures called “pinnules” to filter water for food were connected to the calyx. There may have been root-like structures called “cirri” along the stalk and/or a structure called a "holdfast" at the bottom to help the crinoid anchor itself. The stalks could be several meters long, with the calyx comprising only a small portion of the animal. In fact, as of this writing, the longest fossilized stem found was 40 meters! Fossilized stalks tend to be broken into smaller pieces that we refer to more commonly as “stems”. Individual columnal segments can be found too. The stems can be so well-preserved that you can see individual columnal segments stacked and interlocked like poker chips, while calyxes may have been so delicate that they were crushed or broken before they had a chance to fossilize and even after they were fossilized. Considering all of these factors, it is easy to see why there are naturally more fossilized stems than calyxes.

In addition to crinoid stems and calyxes, we also found sedimentary rocks composed of crinoid fossils, some with crinoid stems sticking out. Rocks like these are called “encrinites” if they consist of more than fifty percent crinoid fossils. The crinoids in the encrinites we found are mostly highly silicified i.e., replaced with silica, and often have a subtle blue-gray color, so pieces that are not suitable as specimens may be suitable for lapidary material. Members found other fossils too, including horn corals, brachiopods, bryozoans, and even a blastoid, an extinct relative of crinoids.

We could have looked for crinoids all day, but there was more to see and do, so we took a break for lunch. Then, we headed to the third and final destination where we hiked through woods until we popped out onto the lakeshore. Some members practiced their geode breaking techniques while others collected small geodes and broken bits of geodes for grab bags. We also found many coral fossils there, but they are different from the corals we collected that morning. Some are hollow and lined with quartz crystals while some are mostly solid, silicified blue-gray like the encrinites at the second location. The corals can be identified as such by their external structures, but there are no fine details to help with species identification.

It was a wonderful trip and we all had so much fun together! The hotel was a big surprise and far beyond our expectations, so we must thank the hotel owners for the excellent accommodations. Many thanks to Charles for arranging the trip, and many thanks to everyone who attended.

Lori Carter
On behalf of Charles Carter, Field Trip Chair
e-mail: