Flux and fate of small mountainous rivers derived sediments into the Taiwan Strait

High-resolution CHIRP sonar profiles across the Taiwan Strait reveal a large silt–sand-dominated deltaic clinoform, up to 50-m thick, overlying the postglacial transgressive sea floor across the southeastern, central, and northern strait. Delta-like configuration and internal depositional sequences indicate a northwestward progradation from western Taiwan, primarily from the Choshui (Zhuoshui) River. Grain-size and mineral data confirm the sediment's Taiwanese derivation. The CHIRP profiles, together with existing radiocarbon and geomagnetic dates, suggest that the clinoform has formed over the past 10 kyr. The estimated volume of 375 km3 of sediment (mainly sand and silt) suggests a mean annual accumulation of 60 × 106 t/yr. Presumably much of fine mud delivered by Taiwanese rivers has been washed away by the local currents, and escaped either northeastward into the Southern Okinawa Trough or southward into the South China Sea. Numerous shallow borings onshore over the central western Taiwan coastal plain reveal an additional 350 km3 of fluvial sediment that has accumulated over the past 10 kyr. The combined onshore–offshore Holocene accumulation, together with an unknown amount of finer sediment that escapes the system, indicates that the long-term sediment flux from Western Taiwanese rivers exceeds 100 × 106 t/yr, which is not different from the present-day combined annual discharges from the Choshui, Tsengwen, Ehrjen and Wu rivers into the Taiwan Strait.