USING PALEONTOLOGY AND STRATIGRAPHY TO DETERMINE THE AGE OF A NW GEORGIA OUTCROP

This study focused on an exposure of limestone and shale on I-24W between mile marker 3 and 4 in northwest Georgia. The USGS lithology database indicates this exposure to be Silurian Red Mountain Formation, although strata and fauna are not consistent with other Silurian stratigraphic sequences in the area. This area has many thrust faults, making mapping and correlation more complex. This study evaluated stratigraphic and faunal evidence to determine if rocks at this exposure belonged to the lower and middle Ordovician Chickamauga Supergroup, upper Ordovician Sequatchie Formation, or the Silurian Red Mountain/Rockwood Formation, all cropping out nearby. The stratigraphy at the outcrop exhibits thin- to thick-bedded silt- and clay-rich limestone interbedded with medium- to thick-bedded shale and occasional oolitic hematite beds. The presence of a fossiliferous oolitic hematite layer is typically indicative of Silurian strata, however, these also are noted in Ordovician strata regionally. Hebertella sinuata brachiopods indicate a late Ordovician age for these strata. The outcrop also contains Prasopora, an Ordovician hemispherical bryozoan. Preliminary evaluation of the stratigraphic evidence most closely correlates with the Shellmound Member of the Sequatchie Formation.