GEOLOGIC MAP OF THE VALLEY AND RIDGE PART OF THE BENEDICT, GEORGIA, 7.5-MINUTE QUADRANGLE: STRUCTURAL RELATIONS OF THE ORDOVICIAN THROUGH MISSISSIPPIAN STRATIGRAPHY

Detailed geologic mapping of the Benedict, GA 7.5 minute quadrangle within the Valley and Ridge reveals a complex deformational history recorded in the foreland fold and thrust belt. Lithologies of the middle Ordovician Knox Group through lower Mississippian Fort Payne Chert/Floyd Shale show at least two different generations of folding and up to three thrusting events. The orientation of these structures allows interpretation of the different stress regimes in which the foreland stratigraphy deformed. The earliest generation of folding and thrusting is oriented nearly north-south reflecting east-west stresses; whereas, the later generation folding and thrusting is a result of more northeast-southwest directed stresses.

Early mapping by Cressler (1970), Hilton and Tull (2005), and Tull and Hilton (2007) indicate that the area displays a normal stratigraphic sequence with several regional unconformities. However, based on our observations through detailed mapping, we see a quasi-normal stratigraphic sequence with imbricate faults, as indicated by long linear ridges held up by Fort Payne Chert which are structurally overlain and stratigraphically underlain by middle Ordovician Rockmart Slate. Furthermore, fossiliferous, ferruginous sandstones previously interpreted as Frog Mountain by Cressler (1970), are observed to occur directly beneath the Fort Payne Chert and above the Rockmart Slate. Based on fossil occurrences and facies relationships, we interpret this portion of the stratigraphic section to be basal Fort Payne, equivalent to the Maury Shale northwest of the Rome Fault. Also, several imbricates are present within the Rockmart Slate as indicated by thin intervals of either fossiliferous Floyd Shale and Fort Payne Chert. These small imbrications are not mappable at 1:24,000-scale but are critical to understand the tectonic history of the area. The higher-angle imbricates are delineated by narrow ridges of Fort Payne Chert. These narrow ridges are locally overthrust by sub-horizontal strata that include the Rockmart Slate and Fort Payne Chert.