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Coasts. Form of sediment is highly dependent on the effect of tides, wave activity and degree of clastic input from rivers.
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Coasts Form of sediment is highly dependent on the effect of tides, wave activity and degree of clastic input from rivers. Microtidal coasts: Usually stormed dominated. Coastal areas are dominated by sandy barrier island features, elongate parallel to the coast. Length of island increases with decreasing tide strength. Reworked rapidly during storms that cause breaks in islands and wash over into the tidal lagoon. Storms are capable of washing large volumes of sediments out on the shelf, producing sheets 5-10 cm thick and up to 50 km across. Inlets through island migrate rapidly due to daily current activity, 10s of m per years. Sediments fine rapidly offshore into shelf muds. Modern examples: Dutch coast Texas Gulf Coast, Carolinas.
Macrotidal coasts: No barrier islands but instead tidal flats. Sandy sediments develop wave ripple lamination, large scale dunes around river estuaries. Mud flat develop sandy ridges (Cheniers) where occasional storms activity sorts and reworks the flat sediment. Reworking by burrowing organisms is common. Current directions vary within the tidal zone resulting in sands with cross bedding showing flow in two opposite directions. “Tidal bundles” are formed in inter-tidal zones, due to settling of mud drapes over sandy dunes and ripples during the high tide. Spring and neap tides of varying strength can be traced through the strength of development of the tidal bundles. Shallow offshore is characterized by sand ridges running parallel to the tidal flow. Modern examples, English Channel, Bay of Fundy Canada, East China Sea.
