Late Quaternary stratigraphy and evolution of a Korean tidal flat, Haenam Bay, Southeastern Yellow Sea, Korea

Sediment cores from a tidal flat in the southeastern Yellow Sea, Korea, contain two major depositional units, a Holocene unit (Unit I) and an underlying late Pleistocene unit (Unit II). Unit I (up to 15 m thick) is a middle to late Holocene, coarsening-upward transgressive deposit. Unit II (about 10 m thick) is interpreted as tidal-flat deposits from the last interglacial period (probably oxygen-isotope stage 5e), based on its many tide-influenced signatures such as laminated silt/clay, tidal rhythmites, fossil crab burrows, authigenic minerals (pyrite and halite), clay mineral composition and a dinoflagellate cyst assemblage comparable to that of Unit I. Units I and II are separated by a regional unconformity which is highlighted by a yellow ‘oxidized layer’ in uppermost Unit II. The layer contains abundant evidence of subaerial exposure, including a yellowish sediment color, semi-consolidation, desiccation cracks, cryoturbation structures, and high degree of magnetic susceptibility. Two major interglacial highstands (Units I and II) and one glacial lowstand (uppermost oxidized layer of Unit II) thus characterize coastal to nearshore tidal deposits along the eastern margin of the Yellow Sea (western Korea).