by Dr. John Anderson
On a cold and blustery morning, Saturday November 13 to be exact, thirteen hearty souls met to excavate trilobites. Trilobites you ask? What is a trilobite? It is a marine creature that lived during the Paleozoic era and has been preserved in rock; the ones we were after were some of the oldest trilobites that lived on Earth during the Cambrian period, about 500 million years ago. Trilobites are related to modern crabs and lobsters; insects, isopods, and barnacles. Well to our hearty souls, they were venturing out near Resaca, Georgia with our Field trip leader, Dr. John (Anderson); Dr. Dion (Stewart) was there also, but he was there to collect fossils. The day was bright and sunny and the trilobites found in the Upper Conasauga Shale were plentiful. There were at least six different species of trilobites found as molds or casts, and often upon popping open the shale, both the trilobite mold and cast was found by our participants. I would estimate that about 100 trilobite specimens were collected that morning.
Why were the trilobites so abundant you ask? Well, trilobites like crabs and lobsters molt at least once a year, peeling themselves out of their old shell (carapace) so a new larger shell can be secreted to harden for a bigger and better more roomy existence. Under the right conditions, each of these old discarded shells could become preserved as a fossil. Some of the trilobites that were found were whole with an aureole of iron oxide (limonite) surrounding the whole trilobite. These whole specimens were most likely buried in the Cambrian mud alive, probably deep enough that they could not dig themselves out or maybe they burrowed into the mud to die. The iron oxide aureole is the organic goo (guts that have decomposed and oozed out into the surrounding mud) and the lack of oxygen in the mud caused by the decomposition of the goo facilitated the iron oxide to precipitate and create the oval or circular film around the trilobite fossil.
In addition to trilobites, Brachiopod molds, a sponge species Brooksella alernata, and hyolithid fossils were found. Several of the brachiopod molds had limonite crystals in the void left when the calcite shell of the brachiopod dissolved, thus the brachiopod soft body was most likely sealed inside the shell and facilitated the formation of limonite in the void.
Everyone had a great time on the field trip and expressed enthusiasm for attending the next CCGMS fossil trip.
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