EXCEPTIONAL FOSSIL PRESERVATION IN THE CONASAUGA FORMATION, MIDDLE CAMBRIAN OF WESTERN GEORGIA

Mudstones and siliceous concretions in the Conasauga Fm. (Middle Cambrian, Marjuman) in northwestern Georgia contain body and trace fossils showing some soft-tissue preservation. Identifiable, non-sclerotized taxa include components of a Burgess Shale-type biota, including algae, demosponges, priapulids, non-trilobite arthropods, and Naraoia. Exceptional preservation is also evident in preserved gills of a large ptychopariid trilobite, Glyphaspis capella, and hyolithids retaining helens and other delicate structures. Trace fossils include a string of oriented Haplophrentis tests in a siliceous concretion, interpreted as a priapulid coprolite. Several fossils show algal or bacterial overgrowths, suggesting that a partial cause of exceptional preservation is biological inhibition. Other specimens with fine details preserved show rims of altered mineralogy, indicating decompositional chemical alteration of clay minerals. Preservation of soft tissue is also attributed to the evident lack of infaunal bioturbation during and after deposition. The occurrence of lagerstätte preservation in the Conasauga Fm. has likely been overlooked due to the relatively poor resolution of fossils; nevertheless, this occurrence extends the geographic range of Burgess-type biota to the southeastern USA.