A buried palaeosol and late Pleistocene unconformity in coastal deposits of the eastern Yellow Sea, East Asia

摘要

Deep-drill core sampling with a high-resolution seismic survey was carried out to identify a Holocene-late Pleistocene boundary in the eastern coast of the Yellow Sea, East Asia. Analysis of core sections revealed the existence of an oxidized and desiccated sedimentary layer, lying directly below a Holocene horizon (Unit I) and being developed at the top of a late Pleistocene (Unit II), possibly last interglacial tidal deposit. The buried oxidized-sedimentary layer is characterized by semi-consolidated, yellowish sediments showing signs of desiccation and alteration such as periglacial cryogenic structures, lithified trace fossils, depletion of smectite, and high geochemical weathering index (Ba/Sr ratio). These features, together with radiocarbon ages, suggests that the layer, defined as a palaeosol developed in marine sediments, has formed as a result of prolonged subaerial exposure of Unit II sediments during the Wisconsinan sea-level lowstand, producing a regional unconformity (late Pleistocene unconformity). This unconformable bounding surface corresponds to a prominent near-surface reflector (R), which is observed in seismic profiles obtained across the drilled-core sections and further is traced ubiquitously across the Yellow Sea shelf. Consequently, the buried palaeosol layer associated with the seismic reflector presents a key horizon for the understanding of late Quaternary environmental changes and integrated stratigraphical correlation in the East Asian marginal seas.