A SEDIMENTOLOGICAL CASE FOR ORNITHOGENIC GASTROLITHS AT THE GRAY FOSSIL SITE, EAST TENNESSEE

The Gray Fossil Site is a sinkhole lake deposit of Mio-Pliocene age within a Cambro-Ordovician carbonate terrain. This Site is noted for a diverse fauna of mammals, birds, reptiles, amphibians, fish, and much more. Microscopic examination of wet-screened residue from twenty-kilogram field collections have yielded rare polished, silica-rich, stones averaging three millimeters in size. Over six tonnes of field material have yielded about ten grams of polished stones (<1gm/500kg). About seventy percent of samples examined were barren; over twenty percent had one or two stones only; one sample, remarkably, had fifty-six polished stones. A Kolmogorov-Smirnov statistical analysis of stone roundness and sphericity shows a strong similarity between the "56 stone sample" and the scattered stones from multiple other samples. Roundness and sphericity measurements are compatible with published bird gizzard stone data. Average size is that for one kilogram weight birds, such as a large waterfowl (a faunal element at the GFS). One hundred eleven samples examined by the author were from the eighty-eight meter squares of the "Rhino Pit". A K-S analysis of bird megafossil and polished stone distribution in the "Rhino pit" shows a similar scatter pattern. Conventional sedimentological sources for polished stones such as wind, ice, and water are much less likely than avian gizzard-milling and aquatic dispersal.