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This study represents a cooperative effort by sedimentologists, zoologists, paleontologists, and mineralogists to determine what facies characteristics exist in a present-day sedimentary record. The results show that geologically recognizable subfacies can be established by primary physical and biogenic sedimentary structures.
The rather low energy of the Sapelo Island shoreline and the low dip of the beach surface, combined with a tidal range of 2.1 m, result in characteristic morphology, grain-size distribution, and types of sedimentary structures. Most beach features are controlled by wave activity, and obvious bioturbation is not abundant in the beach zone. The backshore and upper foreshore contain few species and few individuals. The lower foreshore has few species but numerous individuals.
At 100 m offshore (water depth, 1.5 m) there is a marked increase in the fine fraction; at the same place, biogenic sedimentary structures increase. Dominant sedimentary structures are ripple-laminated sand. Species of infaunal organisms are more abundant than in the beach but few individuals are present.
At a distance of 2,500 m offshore (water depth, 2.7 m) biogenic sedimentary structures become the dominant characteristic of the fine silty sand. The unreworked part of the substrate is characterized by parallel to subparallel laminated sand. These beds, referred to as "laminated-to-burrowed" are separated by erosional bedding planes.
Farther seaward at a distance of 5,500 m (water depth, 6 m) the substrate is almost completely reworked due to increased biogenic activity. This is the most densely populated zone in the beach-to-offshore sequence.
At a distance of 10 km seaward (water depth, 10.5 m) the substrate consists of clean, medium- to coarse-grained sands. Megaripples are the dominant physical sedimentary structure in the offshore area and few species and few individuals are found, but biogenic reworking by heart urchins is abundant.
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