GEOLOGIC MAP OF THE PLAINVILLE AND SHANNON 7.5 MINUTE QUADRANGLES, FLOYD AND GORDON COUNTIES, NORTHWEST GEORGIA

Mapping was undertaken to elucidate relations between the Clinchport, Rome and Coosa faults north of the city of Rome. The trailing limb of the Clinchport thrust sheet carries a stratigraphy of Cambrian-Mississippian strata that outcrop in the Armuchee Ridges. Calbeck, Horn and Turkey mountains are ramp anticlines developed over a trailing imbricate fan of west-verging faults rising from the Clinchport decollement (possibly a duplex). On the east, the Armuchee ridges are bounded by the low-angle Rome thrust sheet consisting exclusively of Cambrian Conasauga lithologies. The Rome sheet is relatively thin, folded coaxially with the underlying Clinchport sheet and originally covered these folds. The Horn Mountain and Calbeck faults (informal names) both displace the Rome thrust sheet. The recognition and separation of Berry Limestone from Floyd Shale is critical to interpreting these structural relationships. By contrast with the sinuous trace of the Rome thrust, the Coosa fault is relatively straight and is not involved in the folding of the Armuchee Ridges. Within the map area the Coosa sheet carries a relatively homoclinal sequence of Cambrian Rome, Conasauga and Knox units. To the south, in the adjoining Rome North quadrangle, the Coosa fault truncates the Rome fault and rests on the Berry Limestone. From the above crosscutting relationships, the Rome fault predates the Clinchport fault and the Coosa postdates both the Rome and Clinchport sheets. The Rome fault cannot be interpreted as a splay off the Coosa. The Calbeck, Horn and Turkey Mountain faults transfer displacement from the Conasauga to a higher decollement in the Floyd Shale. This transfer is partly facilitated by the thrusting of incompetent Conasauga over Floyd Shale. While the Rome and Clinchport thrusts show forward progression, the Coosa fault appears out of sequence. South of Rome, the ‘Rome’ fault is described as out of sequence, but this is a different high-angle fault that truncates the typical flat-lying Rome fault as mapped in this area.