Geology of BHNP and N. Buckhead Area

by Scott Ranger

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Latitude/ Longitude
Lat    = 33 degrees, 51.9 minutes N
Long = 84 degrees,  22.8 minutes W

 

The entire BHNP property (and the bulk of the Nancy Creek watershed) is located in what is called the “Buttton Schist” formation. Here is it’s official description from the Geologic Map of Atlanta:

"Button schist (Permian? to Upper Ordovician?)—Gray to silvery, tan-weathering (±chlorite)-plagioclase-quartz-sericite button schist (Higgins, 1971) with C-S texture (Berthé and others, 1979); S-C mylonite of Lister and Snoke (1984) with fish-scale texture and locally displaying fish-flash (Simpson, 1986, p. 252); locally manganiferous; in many places including (±chlorite)-sericite-quartz-plagioclase phyllonite with mica-fish and fish-flash, and, locally, lenses and slivers of sheared chlorite-actinolite (±hornblende)-plagioclase and chlorite-actinolite-plagioclasehornblende amphibolites. Weathers to a red soil with buttons (mica porphyroclasts, mica-fish) scattered on the ground surface. Probably derived by shearing mostly of mixed unit (OZm). "
  
Higgins, M.W.,  T.J. Crawford, R.L. Atkins & R.F. Crawford. 2003. Geologic map of the Atlanta 30’x60’ quadrangle, Georgia. Scientific Investigations Map 2602, U.S. Geologic Survey. 

What it means is that this rock is highly metamorphosed, not from the Pangaean Orogeny, but from the effects of motion on the Brevard Fault Zone that runs right through Atlanta. When rock is subjected to long-term stress in faults it results in unique characters that are unmistakable to the trained eye. The primary one is of the rock being metamorphosed to the schist level and the schist having a “button” or “fish-scale” texture of the micas. 

Photo by Anne Stern: rock taken from nearby "Quarry" in N. Buckhead

Photo by Anne Stern: rock taken from nearby "Quarry" in N. Buckhead