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Estuarine sand bodies assume complex morphologic characteristics in response to multidirectional tidal currents and wave action. Studies in 8 New England estuaries show, however, that the major forms are repetitive from estuary to estuary and that they display diagnostic suites of primary structures.
Sand accumulation around the seaward margin of the major inlets takes the form of ridge-and-runnel systems and recurved spits attached to the barrier beaches, large swash bars offshore, and submerged ebb-dominated sand sheets. Wave-generated flow over the intertidal bars creates an abundance of large-scale (up to 20 ft thick) planar cross-beds oriented landward.
Tidal deltas inside the inlets consist mainly of sand flats covered with flood-oriented sand waves-->20-ft wave lengths (^lgr). Margins of the deltas (ebb shields and ebb spits) contain predominantly ebb-oriented megaripples (^lgr = 2-20 ft) which produce festoon cross-bedding. In places, the deltas are cut by spillover lobes formed by ebb currents. Thus, zones of flood dominance are differentiated from zones of ebb dominance by distinct differences in scale and type of cross-bedding formed.
Major tidal channels are floored with large sand waves that may be ebb or flood oriented or bidirectional, depending on relation of bottom topography to current flow.
With respect to primary structures, a preserved regressive sequence of estuarine sand bodies would begin with large-scale, bimodal cross-bedding at the base that would grade upward into broad zones of flood-oriented, planar cross-beds interfingering with linear zones of small-scale, ebb-oriented festoon cross-beds. The sequence would be capped by burrowed sand (clam flats), mud (mud flats), and peat (salt marsh).
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