Armored Mud Balls from Cabretta and Sapelo Barrier Islands, Georgia

Abstract

ABSTRACT Armored mud balls similar to ones previously studied on marine and lacustrine shorelines are now forming on Sapelo and Cabretta Islands, Georgia. This report constitutes the first study of armored-mud-ball formation in a harrier-island environment. Small, 0.3-1.5-m-high sea cliffs of Pleistocene marsh deposits in the lower foreshore erode to form the mud-ball cores. During transport to the upper foreshore, beach sediment partially armors the surface of the mud cores. Predominance of sand-size armor and rootbound cores set these samples apart from earlier studies. Intermittent rolling in the swash zone on the gently sloping beach flattens the core and concentrates armor on opposing sides. No evenly armored, very highly spherical mud halls, common to fluvial environments, were found in his study area. Because several armored mud balls were found buried in sand on the backshore, it is likely that some will be preserved. Such lithified, armored mud balls may be especially useful in determining seaward facies of ancient barrier-island deposits.