Comparison of sedimentary processes on adjacent passive and active continental margins offshore of SW Taiwan based on echo character studies

Echo character recorded on Chirp sub-bottom sonar data from offshore of SW Taiwan was analysed to examine and compare the sedimentary processes of adjacent passive and active continental margin settings. Seafloor echoes in the study area are classified into four types: (1) distinct echoes, (2) indistinct echoes, (3) hyperbolic echoes and (4) irregular echoes. Based on the mapped distribution of the echo types, the sedimentary processes offshore of SW Taiwan are different in the two tectonic settings. On the passive South China Sea (SCS) margin, slope failure is the main process on the upper continental slope, whereas turbidite deposits accumulate in the lower continental slope. In contrast, the submarine Taiwan orogenic wedge is characterized by fill-and-spill processes in intraslope basins on the upper slope, and mass-transport deposits are observed in the canyons and on the lower Kaoping slope. This difference is largely caused by the huge influx of terrigenous sediments into the submarine Taiwan orogenic wedge compared with the passive SCS continental margin. In the latter, loading and movement of the Taiwan orogenic wedge has had a significant effect on the seafloor morphology and has triggered retrogressive failures. Gas hydrate dissociation may have enhanced the slope failure processes at some locations.