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Shallow-marine and tidal-flat carbonate sediments form a seaward-prograding wedge (maximum 6 m thick) on the southwest coast of Andros Island. Sediments have been deposited in a large (85 × 25 km), arcuate embayment in Pleistocene limestone. Incursion of the sea over freshwater peat reached the inner, central margin of the embayment 5,000-7,000 years ago. Subsequent lateral progradation (maximum 30 km perpendicular to strike) of marine and tidal-flat sediments has occurred in several phases. 1. Continuous lateral progradation of a very shallow (less than 1 m), wide (3-5 km) subtidal platform adjacent to the shoreline. Sediments on the platform are poorly sorted, massive, fossiliferous, white-pellet muds with prominent filled burrows. 2. Development of 5 major shoreli es, roughly parallel and 2-5 km apart, during the past 5,000 years. Each new shoreline developed, presumably by storm action, onto the subtidal platform, and isolated a shallow linear lagoon. Abandoned shorelines form parallel bands of discrete to coalesced,
symmetrical, V-shaped hummocks. These vegetated ridges (up to 1 m high) are positions of former beach ridges and tidal-channel levees. Sediments in the hummocks are thin-bedded (3-15 cm), unlithified pellet sands with pronounced fenestral fabrics. Sloping flanks of the hummocks are composed of lithified crusts (up to 3 cm thick), commonly separated by unlithified sediment layers. 3. Initial infilling of the lagoons in the form of closely spaced, circular to ellipsoidal Carolina bays. Bay margins form by spit accretion of well-sorted pellet and skeletal sands. The bays themselves fill with poorly sorted, muddy pellet sands. 4. Bay sedimentation generates a mosaic of isolated small sand bodies within a muddy, pelletal, massive sediment. Vertical infilling of the lagoons in the form of l terally continuous, alternate thin beds of blue-green algae and pellet mud. (5) Capping of the sequence by laterally continuous, thin crusts of aragonite-dolomite.
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