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Studies of charts, maps, and remote-sensing imagery of the world's shorelines, plus field studies of the shorelines of Chile, Europe, the Middle East, and most of North America, indicate that terrigenous clastic, coastal-plain shorelines vary systematically in response to changing hydrographic regime. Hydrographic regime is primarily a function of the interaction of wave-energy conditions (controlled by wave height) and tidal range. On coastal-plain shorelines that are wave dominated, deltas tend toward arcuate or cuspate shapes, with an abundance of beach ridges; whereas barrier islands are long and continuous, with abundant washover effects. On tide-dominated coastal-plain shorelines, deltas are multilobate, and barrier islands are supplanted by offshore, linear sand ri ges that trend obliquely or perpendicular to the strandline. Coastal-plain shorelines of mixed energy have complex delta systems and stunted barrier islands cut by numerous tidal inlets which are accompanied by large tidal deltas.
On modern coastal-plain shorelines, coastal environments at the entrance to shoreline embayments, or arcs, contain mostly wave-dominated features. The heads of the embayments, however, are usually tide dominated. As the balance between wave and tidal energy changes along the shoreline arc, delicate readjustments are made among such features as sediment-distribution patterns, relative abundance of washovers, nature and relative abundance of tidal deltas, and barrier-island morphology and stratigraphy.
These observations permit the construction of a spectrum of depositional models, ranging from purely wave-dominated to purely tide-dominated types, that may be applied to ancient depositional basins. Details of sandbody geometry, relative facies abundance, paleocurrent patterns, and other relevant stratigraphic conditions differ significantly among the different models.
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