Taphonomic Characteristics of Offshore Mollusk Shells, Sapelo Island, Georgia

Abstract

Detritalm ollusk valves from a small area on the offshore (palimpsest ) shelf near Sapelo Island were analyzed with respect to(1) proportions of new and old shells , (2) degree of encrustation or boring by subsequent organisms, and (3) general provenance of shell assemblages. Old shells predominated at both landward and seaward sites, whereas new shells predominated at intermediate sites; many new and most old shells were invested with encrustings (mainly bryozoans, serpulids) and/or borings (mainly sponges, barnacles). Valves of nearshore species were most abundant at landward sites, but valves of offshore species were somewhat more evenly distributed. These observations suggest that (1) nearshore and offshore components remain essentially in-situ, (2) old shells tend to be more intensely bored or encrusted than new shells, (3) proportions of old and new shells , and bored or encrusted shells , are governed principally by the duration of their exposure to physical and biological processes at the sediment-water interface, which is enhanced by extremely slow rates of deposition in this area, but that (4) such conclusions must be based upon the character of the total assemblage, not the condition of individual shells.