Stratigraphic framework and evolution of the mid–late Quaternary (since marine isotope stage 8) deposits on the outer shelf of the East China Sea

Abstract

The East China Sea (ECS) is a vast river-dominated depositional basin because of its broad shelf and extensive river sediment supply. This study investigated the mid–late Quaternary stratigraphic framework and evolution of the outer ECS shelf based on a borehole core (DH02) and seismic profiles. Seven sedimentary facies were recognized in the core sediments according to lithology, grain-size composition, sediment structure, and microfossil assemblages, while eight unconformity-bounded major stratigraphic units were identified in the seismic profiles. Based on seismic–core correlations, dating data (radiocarbon and optically stimulated luminescence), and comparison between sedimentary cycles and sea-level curves, the 100 m thick strata below the seafloor were divided into three sequences corresponding to glacial–interglacial sea-level cycles of marine isotope stage (MIS) 1–2, MIS 3–6, and MIS 7–8 (Sq1–Sq3 from top to bottom). In particular, Sq1 is developing in the present sea-level highstand and consists mainly of deposits of transgressive systems tract (TST), including tide-influenced river, tidal flat, and tide-dominated estuarine facies. Sq2 and Sq3 consist mainly of prodelta and related inner-shelf facies of forced regressive systems tract (FRST) and transgressive deposits similar to those of Sq1. For all three sequences, a thin-sand sheet layer of open-shelf facies represents deposits of highstand systems tract (HST). Deposits of lowstand systems tract (LST) were typically represented by river facies. In addition, comprehensive analyses of seabed sand ridge distribution, core sediment characteristics, and ridge deposition mechanism suggest that the occurrence of a paleoestuary with transgression determined the development of a tidal sand ridge field. Based on all these results, a conceptual stratigraphic sequence model in association with the deposition of LST, TST, HST, and FRST was constructed. Overall, our stratigraphic framework, along with a comparison of the sequence stratigraphy to that of other shelves, suggested that glacial–interglacial sea-level fluctuations, huge amounts of river sediment supply, active subsidence, gentle shelf topography, and marine erosion processes (transgression and regression) controlled the mid–late Quaternary stratigraphic development of the ECS shelf.