RE-THINKING TRADITIONAL DEPOSITIONAL MODELS FOR A PASSIVE CONTINENTAL MARGIN: A CASE STUDY FROM THE EAST CHINA SEA

The traditional sequence stratigraphic model for passive continental margins predicts incision at the shelf-slope break and sedimentary bypass across the margin during the fall of relative sea level and lowstands. This trend is not observed in the shallow (<100 m), late Pleistocene strata on the East China Sea (ECS) continental margin where the stratigraphic framework has been established using an extensive, regional seismic and chirp sonar dataset. The ECS lowstand fluvial deposits prior to Oxygen Isotope Stage (OIS) 4 do not experience major incision or sedimentary bypass. Instead, strata are unincised and deposited across large portions of the margin. Furthermore, even though the most recent depositional sequences (OIS 4 to present) do exhibit well-formed incised valleys, the incision occurs on the central portion of the margin rather than at the shelf-slope break. The primary driver of ECS stratigraphy was Quaternary glacio-eustacy coupled with extreme geologic and oceanographic conditions that included an abundant sediment supply (Yellow and Yangtze Rivers) and a unique basin physiography (wide margin, low gradient, deep shelf-slope break). However, because the alteration of river discharge affects the flux of sediment to the fluvial and marginal marine environments, regional climate is a secondary variable that must also be considered. This is easily done for the ECS due to the well-constrained and globally correlated terrestrial record of alternating loess-paleosol sequences that record the effect of Asian monsoons during late Plesitocene glacials (loess) and interglacials (paleosols). Therefore, by placing the seismic stratigraphic framework of the ECS margin into both a global (Quaternary eustacy, global climate trends) and regional (shelf physiography, sediment input, monsoonal influence) context, this paper challenges traditional ideas of how depositional factors affect the formation and timing of sequence architecture in the stratigraphic record.