SEDIMENTOLOGY OF POLISHED ALLIGATOR GASTROLITHS FROM THE GRAY FOSSIL SITE, TENNESSEE

The Gray Fossil Site is an early Pliocene sinkhole lake deposit within an early Ordovician karst carbonate terrain. This lagerstaette has yielded over one hundred species of both animal and plant fossils. Microscopic examination of water screened (1.7 mm) residue from twenty-kilogram (square meter) samples has yielded >1900 polished silica-rich stones averaging four millimeters in size (S=A+B/2), where A >/=B>/=C. 131 samples from TP 1-2004 (“Rhino Pit”) yielded 37 polished stones. No stone was larger than 7mm and there was a haphazard scatter of stones. In the adjacent pit, TP-2015 (“Ivory Target”), 79 samples yielded 44 stones of similar size and scatter. This totals 81 stones from 210 samples. In marked contrast, TP 1-2012 (“Tortoise Target”), 18 meters from the “Ivory Target”, has yielded 1834 stones from 112 samples (>16 /sample!). All these stones are within 5 m of a tightly clustered association of alligator skeletal elements. 26 samples have stones >10 mm. These and larger stones cluster closer to the alligator. Nine stones are polished, locally derived, oolitic chert, therefore polished within the paleo sinkhole. Nine alligator teeth and nine osteoderms were also found. Additionally, eleven bones (>6 mm) show a strong N-S orientation paralleling a north sloping concentration of gastroliths north of the “alligator cluster”.