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Controls on the Morphodynamics and Stratigraphic Architecture of Compound Dunes and Point Bars on the Open-Coast Macrotidal Flat in Gyeonggi Bay, West Coast of Korea


Simple and compound dunes are developed on the intertidal tributary channel and channel bank of Yeochari macrotidal flat in Gyeonggi Bay, west coast of Korea. Dunes are asymmetrical with the majority of their steeper lee faces and master bedding surfaces dipping toward ebb current direction. Dunes consist of cross-bedded medium to coarse sands with a coarsening-up textural trend, which overlie channel bank comprised of sand flat and mud flat facies and channel point bars composed of various channel facies including fluid muds and channel lags. Four-year long morphodynamic observations revealed that simple dunes on the tributary channel migrate seaward as fast as 1.5–2 m per day. In contrast compound dunes on the southern channel bank migrate either landward or seaward at much slower rates of 2–3 m per month. Despite greater current speeds on the channel bank, smaller tidal asymmetry leads compound dunes to migrate relatively slowly. In the case of intense wave activity, however, compound dunes seem to migrate at a noticeable rate. Compound dunes continued to shift their location over point bars toward northern channel bank as tributary channel migrates back and forth. Concurrent migration of compound dunes and channels produced a complicated stratigraphic architecture consisting of fining-upward point-bar succession overlain by coarsening-up compound-dune succession with master bedding surfaces dipping nearly opposite to those of point-bar succession. Tidal asymmetry, wave intensity and migration of tributary channel are seen to exert an important control on the stratigraphic architecture of compound dunes and point bars in the intertidal environment.