We drove through rain leaving Atlanta, but found warm weather and sunny skies when we arrived at the CEMEX quarry located south of Perry, Georgia. All twenty seven members who had signed up for our trip showed up. We packed into Manager, Calvin Duncan’s office and received a safety talk, signed a safety release and were introduced to Warren Talton and Earl Dean, longtime CEMEX employees and fossil buffs who would accompany us to the quarry and help us to find some great fossils. Outfitted in hard hats and safety goggles we caravanned into the quarry. As we entered the quarry we could see a beautiful array of sedimentary formations in different colors lining the high walls of the quarry. We started collecting in the Tivola limestone.
This layer formed between 37 to 40 million years ago (mya) when the Atlantic Ocean and the Gulf of Mexico were connected through southern Georgia. The state of Florida was totally underwater and the coastline was located in the region where Macon now exists. The Trivola Limestone was a shallow marine enviroment with fairly high energy waves. The depth of the sea is estimated to have been between 10 to 30 meters. Sand dollars, carbonate bark, corals, bryozoans and bivales lived at this depth, and the waves broke many of their shells into pieces that formed a rock called coquina.
For a short time the seas retreated southward and the next layer up made of Fuller’s Earth, called the Twigs Clay Formation, was deposited. The Twigs Clay Formation is composed of river borne sediment deposited in an estuary containing some freshwater fossils. When sea level rose again to cover this area it formed the next layer, called the Sandersville Limestone or Ocmulgee Formation which was another marine environment similar to the Tivola.
One of our newest CCGMS members, Dr. John Anderson, who has studied the Sandersville Formation for over twenty years, suggested to our host that we explore a limestone layer near the top of the Sandersville Formation. They agreed and to everyone’s surprise (except John”s) an entirely new fossil rich horizon was found. This bed was filled with large gastropods, some fist-sized and the bivalves were so abundant that you had to watch where you walked to be sure you did not step on them. This level also contained scattered green “pellets” of glauconite clay (fossil “poop”) that is so rich in the element potassium that these pellets give precise radioactive dates of when the last sea covered this region.
The rather large, deep red layer at the top of the quarry wall is an old soil horizon resulting from thousands of years of erosion of these marine rocks, erosion that concentrated the iron as hematite. Each collecting site was unique.
The lower site had many fossils that were molds of the organism called “Turritella”, where the hollow interior of the shell had been filled with calcite and later the actual shell dissolved leaving behind only the internal filling that looks much like a cork screw.
The upper bed was also somewhat unusual because most of the fossil bivalves contained both halves of the shell. Everyone was delighted to find many fossils, and even our hosts were delighted with our trip as they found a new locality within the CEMEX quarry to show future fossil collectors.
(Thanks to John & Dion for their help on this article.)
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