RINGGOLD GAP, GEORGIA: A CLASSIC LOCALITY FOR ORDOVICIAN AND SILURIAN TRACE FOSSILS

The development of the interstate highway system created enormous exposures that rejuvenated stratigraphy in the Southeastern United States. Geologists and paleontologists quickly took advantage of one particularly informative roadcut at Ringgold Gap, cut for I-75 in 1970 through Taylor Ridge in northwest Georgia. The new cut afforded a complete, readily accessible exposure of the upper Catheys and Sequatchie Formations (Upper Ordovician) as well as the Red Mountain Formation (Silurian). As a result, Ringgold became a baseline for studies of Upper Ordovician and Silurian strata in northwest Georgia, including work on paleomagnetism, palynospores, paleoecology, and ichnology.

Trace fossil assemblages at Ringgold were first described in 1972 by Robert Frey and Timothy Chowns for an influential Georgia Geological Society field trip guidebook (no. 11). Graduate students Rindsberg and Martin extended this work in following years, with Rindsberg concentrating on taxonomy and Martin on ichnostratigraphy, and both on paleoecology. Discoveries of general interest resulted.

Shallowing-upward sequences in the Sequatchie and Red Mountain Formations demonstrated organismal responses to changes in sea level and basin dynamics. Probably the most significant discovery was that the Sequatchie Formation includes one of the oldest riverine-estuary sequences in the geologic record (Martin), as well as storm-dominated sequences and phosphatic hardgrounds that probably represent sequence boundaries. Similarly, the storm-bed ichnoassemblages of the Red Mountain Formation were among the first to be recognized. Paleoecologic discoveries included that several ichnogenera of burrows could be ascribed to trilobites, including Taenidium, the dominant burrow in redbed tidal-flat deposits (recognized by Seilacher on his visit in 1997), Phycodes, and Trichophycus. Isolated specimens of Paleodictyon may indicate that this trace originated in relatively shallow, quiet water, only later becoming restricted to bathyal and abyssal depths.

The completeness of exposure, abundance of fresh material, and ease of access (until the 1990s) enabled unusually complete understanding of trace fossils at Ringgold. This in turn was crucial to stratigraphic and paleoecologic analysis of these coastal to shallow-marine deposits.