Morpho-sedimentary features and sediment dispersal systems of the southwest end of the Ryukyu Trench: a source-to-sink approach

The southwestern Ryukyu Trench near Taiwan is an ideal place for source-to-sink studies because of the short sediment transport route between the terrestrial sediment source in Taiwan and the marine sink in the Ryukyu Trench. Bathymetric and seismic reflection data and core samples from the area around the southwestern Ryukyu Trench were used to identify features of the trench–arc system, including submarine canyons, the trench wedge, bathymetric ridges, and forearc basins, which together form two distinct sediment dispersal systems: a longitudinal (trench-parallel) system and a transverse (trench-normal) system. The longitudinal sediment dispersal system carries sediments eroded from the Taiwan orogenic belt eastward, primarily along the Hualien Canyon and a channel–terminal fan system at its mouth, and deposits them in the southwestern end of the Ryukyu Trench. The transverse sediment dispersal system carries sediments eroded from the Ryukyu Islands downslope and deposits them in the Hoping, Nanao, East Nanao, and Hateruma forearc basins, behind the barrier formed by the E–W-trending Yaeyama Ridge on the trench-slope break. The presence of pyrrhotite, a characteristic component of sediments sourced from Taiwan, in a seafloor sample from the Ryukyu Trench and its absence in a sample from the East Nanao forearc basin support the view that the southwestern Ryukyu Trench is longitudinally fed by sediment derived from Taiwan, whereas the trench-slope forearc basins receive sediment transported transversely downslope from the Ryukyu Islands.