Coastal Sediments and Patterns of Bioturbation, Eastern Buzzards Bay, Massachusetts

Abstract

ABSTRACT Coastal sequences of eastern Buzzards Bay exhibit characteristic suites of physical and biogenic sedimentary structures related to energy gradients, geomorphology, and distributions of palimpsest glacial debris. In beach-to-offshore sequences, unbioturbated planar- to ripple-laminated or cross-bedded pebbly sands of the foreshore and shoreface give way abruptly to thoroughly bioturbated, poorly sorted sediments of the offshore zone. Preserved biogenic sedimentary structures first appear at water depths of 1 to 2 m (below MLW) and bioturbation of sediments is complete at depths of 2 to 4 m offshore. The seaward shift from physical to biogenic structures is a pivotal point almost equally discernible among modern and ancient beach-to-offshore deposits. Sequences in harbors and embayments intergrade with those of such allied environments as salt marsh estuaries, tidal flats, and the offshore zone. Tidal creek deposits within salt marshes range from sparsely bioturbated cross-bedded sand to completely bioturbated impure sand. Most streamside marsh deposits consist of thoroughly bioturbated root-bound muddy sand or sandy mud. Collectively these bay-marsh sequences are reminiscent of, albeit at a much smaller scale than, estuarine sequences of the Georgia Bight.