Sequence-stratigraphic evolution of the southwestern East China Sea since MIS 5: controls of sea-level change and tectonics

The southern East China Sea (ECS)’s inner shelf preserves a high-resolution record of Late Quaternary sequence evolution controlled by glacio-eustatic fluctuations, tectonic subsidence, and sediment supply. Based on integrated high-resolution seismic profiles and borehole core data, a sequence-stratigraphic framework spanning from the last interglacial period (Marine Isotope Stage (MIS) 5) to date is established, and the mechanisms controlling its evolution are evaluated. Three depositional sequences (Sq1–Sq3) are identified, recording successive transitions from terrestrial to shallow marine environments in response to relative sea-level changes. Quantitative analysis reveals a tectonic subsidence rate of ≥ ~0.81 m/kyr since MIS 5, which significantly enhanced accommodation space creation. This influence is particularly evident in Sq2, where an unusually thick lowstand systems tract (LST) characterised by aggradational fluvial-floodplain deposits developed during MIS 4–3. Sediment supply modulated spatial variability in sequence architecture, with inputs from the Minjiang, Yangtze, and western Taiwanese rivers being redistributed by alongshore currents and constrained by inherited topography, resulting in pronounced along-strike heterogeneity and localised depositional architectures. The results demonstrate that sequence development on tectonically active continental shelves is governed by the coupled effects of sea-level change, tectonic subsidence, and sediment supply, and may deviate from classical sequence-stratigraphic models.