88 Structural Geology (Posters) I: Deformation Processes

BROXTON ROCKS- A GEOLOGICAL AND ECOLOGICAL ISLAND IN SOUTHERN GEORGIA

Paper number: 88-3
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The Broxton Rocks preserve, located in northern Coffee County, Georgia is owned by the Nature Conservancy. It occupies a portion of the Atlantic Coastal Plain where strata of Middle Miocene age dip gently eastward. “The Rocks” are erosional remnants of the Altamaha Formation, and exhibit outcrops that are less than six meters high, and contain numerous sub-vertical and vertical joints. Many of the joints have been widened by erosion and are large enough to walk through. Three fracture sets are dominant: 1) 095°-275°, 2) 015°-195°, and 3) 185°-355° (all +/-5°). The large fractures show the N-S joints are older than the E-W. Preferred orientations and relative ages correlate fracture sets previously studied on the Coastal Plain of Georgia and South Carolina. Rocky Creek, a first-order ephemeral stream, dissects part of the outcrop and flows in a rectilinear pattern from the knickpoint. Orientations of the stream channel mimic those of the fractures, but with a more dominant NW-SE trend (335°-155°).

Broxton Rocks also contains over 500 species of plants; some are very rare. Though the outcrops are dominated by longleaf pine (Pinus palustris) and numerous xeric species, the range of microclimates provided by the different joint sets is conducive to the growth of such unusual plants as filmy ferns (Trichomanes petersii), shoestring ferns (Vittaria lineata), and green-fly orchids (Epidendrum conopseum). Diverse animal species inhabit the varied landscape as well, including gopher tortoises (Gopherus polyphemus), indigo snakes (Drymarchon corais couperi), eastern woodrats (Neotoma floridana), flying squirrels (Glaucomys volans), and a variety of birds. Broxton Rocks exhibits both geology and natural communities that are unique in southern Georgia.