GEOLOGIC MAP ILLUSTRATING THE STRATIGRAPHY AND STRUCTURAL GEOLOGY OF THE YORKVILLE, GEORGIA, 7.5-MINUTE QUADRANGLE

The Yorkville, Georgia 7.5 minute quadrangle was originally mapped as part of a project by the Georgia Geological Survey. Geologic mapping in this west Georgia area by Crawford was begun in the 1960's under the direction of Vernon J. Hurst. Areal distribution of lithologies and small-scale structures mapped at that time was the basis for designation of the Allatoona Fault (Hurst, 1970), since recognized as one of the major faults of the southeastern Piedmont/Blue Ridge. Subsequent mapping and refinement of the Valley and Ridge portion of the map was recently completed and digitally compiled with the Blue Ridge/Piedmont area of the quadrangle.

The northwestern corner of the quadrangle is underlain by rocks of the Valley and Ridge Province. In this area, detailed stratigraphic and structural mapping reveal a quasi-normal stratigraphic sequence, showing a complex stratigraphic and tectonic history. The Middle Ordovician Rockmart Slate is overlain by Mississippian Fort Payne Chert. This is the normal stratigraphy of the area. However, the Fort Payne Chert is structurally overlain by quartzite/quartzite breccia and phyllite of the Cambrian Chilhowee Group (Weisner and Wilson Ridge, respectively). The fault contact between the Chilhowee and Rockmart/Fort Payne is an imbricate thrust fault named the Springdale Church Fault. Along the trace of the Springdale Church Fault, rocks in the footwall are highly recrystallized and silicified, whereas rocks in the hanging wall are highly brecciated.

A major north-south trending structural feature is an important component of the Yorkville quadrangle geology. Referred to as the Mulberry Rock structure on the Geologic Map of the Atlanta 30' x 60' quadrangle, Georgia, by M.W. Higgins, T. J. Crawford, R. L. Atkins, and R. Crawford (USGS Map I-2602, 2003), this is one of several similar structures which we have mapped in the west Georgia and east Alabama area over the last 40 years. The size, structural complexity, and similarity in trend of these features and the spatial relationships between these and other major structural trends suggest that these features are an important component of Piedmont/Blue Ridge paleohistory, previously unrecognized. We will expand on this in a future paper.