DIGITAL GEOLOGIC MAPS ILLUSTRATING THE STRATIGRAPHY AND STRUCTURAL GEOLOGY OF THE CAMBRIAN THROUGH MISSISSIPPIAN SYSTEMS IN A PART OF THE ROCKMART NORTH AND TAYLORSVILLE, GEORGIA, 7.5-MINUTE QUADRANGLES
The primary focus of this investigation was to determine the nature of the contact between the Rockmart Slate and the underlying formations. Although the Rockmart Slate appears to be in normal stratigraphic succession, detailed mapping and petrographic examination of the slate and underlying formations reveal the presence of a major thrust fault at the base of the Rockmart. Evidence for a faulted contact is inferred due to the local presence of fault breccia, local recrystallization of the underlying carbonates to marble, and the juxtaposition of the Rockmart and portions of the Lower Knox Group.
The location of fault breccias near the contact of the Rockmart and the underlying Newala Formation, was interpreted by Chowns (2004) as representing an unconformity surface between the Newala and overlying Lenoir Limestone and Rockmart Slate. However, detailed mapping of exposures at active and inactive quarries reveal the presence of Rockmart Slate matrix between limestone and dolostone clasts. Additionally, we think that large allochthonous bocks of Lenoir have piggy-backed on this detachment surface and are completely surrounded by slate. The allochthonous blocks of Lenoir have cleavage orientations nearly identical to the slate and differ from cleavage developed in thick limestones within the underlying Newala Formation.
In the north-central part of the Taylorsville quadrangle, the Rockmart Slate is well exposed on an isolated hill overlying lower lithologies of the lower Knox Group. This juxtaposition of Middle Ordovician Rockmart Slate on Lower Ordovician/Upper Cambrian lithologies further supports a major detachment at or near the base of the slate.