LATE EDIACARAN TO EARLY CAMBRIAN FOSSILS OF THE LAURENTIAN IAPETUS MARGIN (SOUTHERN APPALACHIANS): CORRELATIONS AND IMPLICATIONS

The Chilhowee Group is a thick succession of sparsely fossiliferous clastic rocks recording rift-to-drift tectonics associated with origin of the Iapetus Ocean. Recent discoveries of trace fossils in the Chilhowee Group, integrated with a critical re-evaluation of previous reports of trace and body fossils from the unit, allow us to constrain a series of key events in the Ediacaran-Cambrian transition in the Southern Appalachians, by both refining the chronostratigraphy of the Chilhowee Group and relating units in the group to global patterns of sea level change. Regional occurrences include: (1) earliest marine incursions (late Ediacaran); (2) the Proterozoic-Phanerozoic boundary (upper Unicoi Formation); (3) early Cambrian (Fortunian) interaction of metazoans with microbial mats in shallow marine environments; (4) arrival of the Cambrian Agronomic Revolution in this part of Laurentia (Cambrian Stage 2); and (5) appearance of the familiar early Phanerozoic trace fossil record in the upper part of the Chilhowee (Cambrian Stage 3), before widespread development of carbonate platform/ramp deposits.

Taxa include Treptichnus, Archaeonassa, and tubular compression fossils (mid-Unicoi Fm.); Psammichnites, Helminthoidichnites and Planolites, (upper-Unicoi Fm.); Trichophycus-like, Psammichnites and isolated Diplocraterion parallelum (lower Hampton Fm.); Teichichnus, Diplocraterion, Syringomorpha, Rosselia associated the onset of the Cambrian Agronomic Revolution (mid-Hampton Fm.); abundant Diplocraterion parallelum in "pipestone rock" (lower-Erwin Fm.); Rusophycus cf. jordani, and previously reported ostracode Indiana tenneseeensis, and branchiopod Isoxis chilhoweensis, and multiple genera of acritarchs (lower-mid Erwin Fm.). Body fossils of trilobites (Olenellus cf. O. thompsoni) and hyolithids (Hyolithes americanus and H. communis) from the uppermost Erwin Fm. indicate the Bonnia-Olenellus Zone.