Quaternary transgressive and regressive depositional sequences in the East China Sea

摘要

Based on the interpretation more than 4000 km sparker single channel seismic profiles and the comparison with Borehole DZQ4 on the outer shelf of the East China Sea (ECS), the seismic sequences, sedimentary fades and pa-leo-sedimentary environment are studied to establish the chronology framework and discuss the Quaternary transgressive and regressive sequences of the ECS shelf as well as their response to glacio-eustatic sea-level changes. The sea level of the ECS fluctuated with global climate changes in the Quaternary. During the sea level rise, the Pacific tidal wave impacted actively on the ECS continental shelf and the reciprocating tidal currents in NW-SE direction formed tidal sand ridges, which represent large transgressive deposits visible on the seismic profiles. In response to sea level fall, the Yangtze River deltas prograded seaward and built massive subaqueous deltas to form regressive sequences on the seismic profiles. Alternative transgression and regression sequences were vertically distributed on the ECS shelf with the frequent eustacy in the Quaternary. The gentle slope of the ECS shelf makes it possible for the coastline to migrate hundreds of kilometers forth and back on the shelf because of tens of meters sea level changes, in the meanwhile, the Yangtze River discharged large amounts of sediments into the ECS resulting in large-scale subaqueous deltas and tidal sand ridges. There have developed 3 stages of tidal sand ridges and 4 stages of deltas on the ECS shelf since oxygen isotope stage 8.