Characteristic Physical and Biogenic Sedimentary Structures in Georgia Estuaries

Abstract

Estuaries of the Georgia coast possess a wide variety of sedimentary textures and physical and biogenic sedimentary structures. Sediment grain sizes range from fine mud to pebbles. Physical sedimentary structures include small- to large-scale sets of parallel-, ripple-, and cross-laminae. Biogenic structures include abundant burrows and bioturbations by many marine invertebrate organisms. Our studies of animals, sediments, and sedimentary structures in these estuaries indicate that (1) very fine-grained sediments tend to accumulate near the ocean, regardless of substantial sand sources far upstream; (2) Pleistocene sand outcrops are very important locally, especially near the ocean; (3) tests and shells generally are scarce; (4) ebb-current flow structures predominate over flood-current flow structures; (5) diversity and abundance of biogenic sedimentary structures decrease both landward and toward the deeper parts of estuarine channels; and (6) muds generally contain distinct burrows, whereas sands may contain both discrete burrows and more general bioturbation.