Constraining the transport time of lithogenic sediments to the Okinawa Trough (East China Sea)

The transport time of siliciclastic sediments from their continental sites of formation to their final location of deposition on the seafloor is an important parameter bearing on land–sea interactions, climate variability and understanding of marine sediment record. 234U/238U activity ratios of the lithogenic fraction from late Quaternary sediment deposited in the Okinawa Trough, East China Sea, were reported in this study. On basis of 234U/238U activity ratios, the comminution ages and transport times were calculated using recoil loss factors (fα) derived from different equations based on grain size distribution. The transport times were longer (approximately 200 ± 100 kyr) for the Okinawa Trough sediments deposited between 27 and 14 ka, decreased gradually between 14 and 7 ka, and stayed relatively short (< 100 kyr) thereafter. Mineralogical, geochemical and isotopic evidences indicate that changes in sediment transport time correspond well with the shift of sediment provenance predominantly from Asia's interior prior to 14 ka to Taiwan Island after 7 ka. This study offers the first and robust constraint on time scale of sediment transport process in East Asia marginal sea, which is constrained by unique sediment source-to-sink transport pattern. The result illustrates the potential of this approach to decipher climate-related changes in the mode of supply of lithogenic sediment to marginal seas. It also highlights current difficulties in obtaining quantitative estimates of comminution age, mostly because of uncertainties in estimating the recoil loss factor.