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The 2 most common depositional systems along the coast of southern Oregon are the nonbarred nearshore and the longshore bar-rip channel systems. Detailed observation of these systems, largely by scuba diving, has led to delineation of facies of sedimentary structures and recognition of their genetic relation to physical processes operating in the high-energy coastal environment. A 3-dimensional analysis of the geometric interrelation of the facies within each system permits construction of progradational depositional models that can be used to identify deposits of similar origin in the stratigraphic record.
In the most simple depositional system, the nonbarred nearshore, the bottom profile extends smoothly seaward into deeper water. Progradation of the facies in this system will produce a distinctive vertical sequence. At the base lies fine sand of the offshore facies, which shows landward-dipping ripple lamination and scour-and-fill structure. The upper part of this facies is likely to contain lenses of crossbedded coarser sand in which foresets dip landward. The facies grades upward into predominantly cross-stratified beds formed by different facies of the surf zone. The upper crossbeds are likely to be gravelly and inclined seaward. They are overlain by planar-bedded swash facies.
Progradation of the longshore bar-rip channel system produces a different sequence. An erosion surface separates the offshore facies from overlying rip channel facies in which crossbedding dips seaward. Above the rip channel facies lies a gradational sequence of longshore trough facies, wave-current complex facies, and, at the top, swash facies. In an actual situation, the bar facies, in which cross-stratification dips onshore, may be preserved locally within the deposit.
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