Physiography and Late Quaternary Sedimentation

Abstract

The East Sea (Japan Sea) is a semi-enclosed back-arc basin or marginal sea connecting with the Pacific Ocean through four shallow straits. There are three deep basins (the Ulleung, Japan and Yamato basins) separated by submarine topographic highs (the Korea Plateau, Oki Bank and Yamato Rise). The deep-water seafloor of the East Sea beyond the coastal and shelf regions is generally covered by fine-grained sediments which have been deposited by various pelagic and hemipelagic processes, such as pelagic settling, aeolian transport, and lateral transport by surface currents, river plumes, and mid- or bottom-water nepheloid layers. The oceanographic condition and pelagic and hemipelagic sedimentation pattern in the East Sea have undergone considerable variations due to Quaternary global climate changes, resulting in characteristic cyclic alternations of dark and light layers in the deep-water sediments. Along the margins of the East Sea, slope failures, mass movements and mass-flow deposits occur extensively in the uppermost (late Quaternary) sedimentary sequences. The slope failures and mass movements have been generated by various factors, such as earthquakes, sea-level changes, gas-hydrate dissociation and high sedimentation rate. The complex geomorphology of the eastern coast of Korea seems to have originated from the interaction of tectonic history of uplift, bedrock of panoramic lithologies and ages, and wave-dominated, micro-tidal hydrodynamic conditions. A number of sedimentary environments, such as beaches, lagoons, marine terraces, coastal dunes, river (or stream) mouth spits, rocky headlands and cliffs, can be found in the coastal land area. In the nearshore zone, submerged sand bars, channels (buried or active), tombolos and sea stacks are notable geomorphic features.