MACROALGAL FOSSILS FROM THE ?PROTEROZOIC SANDSUCK FORMATION OF THE WALDEN CREEK GROUP, SOUTHEASTERN TENNESSEE

The depositional age of upper Proterozoic and lower Paleozoic strata in the western Blue Ridges remains contested, and this represents a major challenge in reconstructing the tectonic history of the southern Appalachians. The age of the Sandsuck Formation of the Walden Creek Group, for example, has been controversial, with estimates ranging from late Proterozoic to middle Paleozoic. Re-examination of previously reported soft-bodied metazoan fossils from the Sandsuck Formation in Starr Mountains of southeastern Tennessee revealed little anatomical information to affirm an animal interpretation because of their poor preservation. Here we report new macroalgal fossils from siltstones of the Sandsuck Formation at Ellis Branch east of Starr Mountain, southeastern Tennessee, in a fault block bounded to the east by the Alleghanian Maggies Mill fault and to the west by the Alleghanian Great Smoky Thrust. A well-preserved specimen is characterized by a dichotomously branching thallus with a possible holdfast. The fossils are preserved with carbonaceous remains and Raman spectroscopic analysis shows that the carbonaceous material experienced metamorphic temperatures up to ~300 degrees C, consistent with the geological history of the host rock. Scanning electron microscopic analysis indicates the possible preservation of cellular structures. The Sandsuck fossils are somewhat similar to, in overall morphology, Ediacaran macroalgae from the ~550 Ma Miaohe Member of the Doushantuo Formation in South China. Although macroalgal fossils are of limited biostratigraphic significance, the new fossils are consistent with a late Proterozoic age for the Sandsuck Formation.