WELL-TRAVELED COCKLES - SHELL TRANSPORT DURING THE HOLOCENE TRANSGRESSION OF THE SOUTHERN NORTH-SEA

Radiocarbon dates from 34 shells of the intertidal bivalve Cerastoderm a edule demonstrate that shells were transported in both landward and seaward directions during the Holocene transgression of the southern N orth Sea. Old shells on the beaches of the East Frisian Islands of Ger many document landward transport and young shells in the German Bight and Dogger Bank document seaward transport. The area's sea-level curve and the shell ages were used to predict the original depth of each sp ecimen. The difference between a specimen's predicted age and its pres ent depth is a measure of depth displacement. Depth displacements rang ed from +35 to -37 m. Eight shells remained within 2.5 m of their orig inal depth and roughly equal proportions of the rest moved landward an d seaward. Specimens transported into deeper mater are a very small fr action of the shells at that depth, whereas specimens transported into shallow mater occur alongside abundant indigenous individuals of the same species. Rare fossils should not be used to estimate paleodepths.