Comprehensive sedimentary studies of mid-late Quaternary strata in the outer shelf of the East China Sea: Facies architecture, chronology, sediment sources, and depositional model

Abstract

The vast East China Sea (ECS) shelf provides a valuable opportunity for validating and refining stratigraphic and sedimentological principles. This research aims to investigate fundamental inquiries regarding facies architecture, chronology, sediment sources, and evolutionary processes of the shallow Quaternary strata of the outer ECS shelf using two deep boreholes, DH02 and DH03, in combination with a comprehensive collection of high-quality boreholes. By integrating sedimentological analyses and identification of benthic foraminifera assemblages, the interpretation of sedimentary facies from various boreholes were systematically reassessed. The facies were classified into four depositional systems: continental system (consisting of river and tidal river facies), estuary system (comprising tidal channel, intertidal, and subtidal flat facies), offshore system (distinguished by tidal ridge facies), and delta-inner shelf system (encompassing prodelta and inner shelf facies). Based on the revision of sedimentary facies, a latitudinal cross-section reveals three sedimentary cycles of the four depositional systems formed the approximately 100 m thick shallow strata. According to the borehole ages (radiocarbon and Optical Stimulation Luminescence), these three sedimentary cycles correspond to glacial eustacy since marine isotope stage 8. The clay mineral composition of borehole DH02 indicates that the Changjiang River likely played a significant role in supplying sediment to the ECS shelf during the mid to late Quaternary period. A spatiotemporal analysis of facies architecture reveals the existence of multiple depocenters, which were presumably influenced by the branching channels and/or channel diversions of the paleo-Changjiang River during this timeframe. A comparison of facies architectures with those of other global shelves indicates that similar sedimentary evolutionary processes are influenced by glacio-eustatism. The integration of findings related to facies architecture, sediment sources, and depocenters contributes to the development of a conceptual depositional model in response to glacio-eustatism.