BERRY LIMESTONE: AN INFORMAL FORMATION, INTRODUCED TO RATIONALIZE MISSISSIPPIAN STRATIGRAPHY IN THE FLOYD SYNCLINORIUM OF NORTHWEST GEORGIA

Geologic maps of Hayes (1902) and Butts (1948) show that most of the Mississippian System in Floyd and Chattooga counties, Georgia, consists of dark-gray silty shale assigned to the Floyd Shale. Cressler (1962) recognized the presence of a thick basal limestone associated with the Floyd, and recent detailed mapping shows this limestone, informally called the Berry Limestone, can be mapped nearly continuously through most of Floyd County and parts of Chattooga County. The Berry varies in thickness between about 150m on the campus of Berry College to more than 300m near Gore, Georgia. Coring near Gore indicates a motif of shallowing-upward parasequences commencing with shaly or cherty skeletal wackestones at the base, grading up into crinoidal packstones and ooid grainstones. Based on foraminiferal zonation (Rich, 1982; 1983), this limestone correlates with the Tuscumbia and Monteagle limestones of the Cumberland Plateau.

We suggest retaining the name Floyd to include clastic facies, both shales and sandstones that separate lower- from upper-Mississippian limestones, Berry and Bangor respectively. This usage removes the name Hartselle from the stratigraphic sequence as recommended by Thomas (1979).

Mapping of the Berry allows increased stratigraphic control that aids in the delineation of several structural features, in particular, thrust faults on the northwest limbs of Simms, Turkey and Lavender Mountain anticlines. Furthermore, Mississippian limestone (formerly mapped as Conasauga Group) extends much further north along the axis of the Horseleg Mountain anticline than previously mapped. This anticline is completely surrounded by imbricates of Conasauga shale that appear to be associated with the Rome Fault, except in one small area where the Rome Formation (Coosa Fault) rest directly on the Berry. This structural relationship suggests that the Rome Fault predates the Coosa Fault.