CYCLICAL INTERGROWTHS OF FERROMANGANESE AND PHOSPHATE MINERALS FROM THE CHARLESTON BUMP

The Charleston Bump is a large topographic feature situated along the edge of the continental shelf in the NW Atlantic, approximately 150 km southeast of Charleston, SC. Ferromanganese oxide/ hydroxide and phosphate minerals form opaque coatings on nodules. These were recovered from pavements as part of Johnson Sea-Link Submersible missions to study the Charleston Bump in 2001 and 2003. We focused on cyclical intergrowths of ferromanganese oxide/hydroxide and phosphate minerals indentified in the opaque coatings. These intergrowths were studied using reflected light microscopy and studied further using scanning electron microscopy with an EDAX system for element mapping and higher resolution study. The cyclical precipitation of ferromanganese oxide/hydroxide minerals and phosphate minerals may have been influenced by Gulf Stream dynamics. Episodes of high biologic activity and sedimentation associated with decreased O₂ levels would allow phospogenesis. Episodes of low biologic activity and sedimentation associated with increased O₂ levels would allow for ferromanganese oxide/hydroxide mineral precipitation.