Variability Within Upper Offshore Facies

M. Paulsen

Large, undisturbed cores were collected adjacent to five of the barrier islands within the southeastern Atlantic Bight. Sampling was restricted to the narrow band of contemporary sedimentation within 16 km of the beach. X-radiography analyses of sediment texture, sedimentary structures, and bioturbation reveal significant variability within the upper offshore facies of a low-energy mesotidal nearshore environment.

Samples collected off southern Hilton Head and off southern Wassaw consist of bioturbated muddy fine-grained sand. The relative predominance of silt- and clay-size detritus within the cores taken north of the Savannah River inlet reflect the high quantities of suspended organic and particulate sediment flushing out the inlet mouth.

Cores taken south of the Savannah River inlet off southern Tybee consist of clean, medium to coarse-grained sand which is replaced by bioturbate silty fine-grained sand farther south along a transect normal to Williamson Island. Tybee Island has undergone continuous erosion during the 20th century. Samples taken from the nearshore in this area may reflect a deficit in the sediment budget or may reflect that increased tidal currents around Tybee Inlet prevent the deposition of fines. Interpretation of these cores is complicated by suspected contamination. Less than 2 km from our sampling stations is a dumping site for material dredged from the Savannah River navigational channel.

Two transects each were collected in the nearshore normal to Ossabaw and St. Catherines Islands. X-radiographs of these cores depict an interplay between bioturbate texture and physical sedimentary structures.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.