Paleozoic age of the Walden Creek Group, Ocoee Supergroup, in the western Blue Ridge, southern Appalachians: Implications for evolution of the Appalachian margin of Laurentia

摘要

In the foothills of the Great Smoky Mountains in Tennessee, low-grade metamorphic rocks of the Walden Creek Group, Ocoee Supergroup, contain a fossil assemblage composed of trilobites, bryozoans, ostracodes, pelmatozoans, algae, and agglutinated foraminifers, indicating a Silurian or younger age. The new paleontological data contradict older ideas on the Neoproterozoic age of the Walden Creek Group. The Walden Creek Group was not deposited in a continental rift basin preceding the opening of the Iapetus ocean but, possibly, in a pull-apart basin formed in a transtensional event during the Acadian orogeny. There is no field evidence indicating that the Walden Creek Group is separated from the lower units of the Ocoee Supergroup by a basin-wide unconformity and hiatus. A tentative geodynamic model is presented for the Ocoee Supergroup basin; the model is dependent on paleontological data indicating a Paleozoic age for the Walden Creek Group and concentrates on lithologic, petrographic, and basin characteristics. The model allows for the possibility that the entire Ocoee Supergroup was deposited in a Paleozoic transtensional basin.