Marine sediment records and relative sea level change during late Pleistocene in the Changjiang delta area and adjacent continental shelf

摘要

Optically stimulated luminescence (OSL) dating and microfossil analysis were conducted on late Quaternary samples from two boreholes in the Changjiang delta area. Successions from 12 collected boreholes revealed lithology, stratigraphy and sedimentary facies of the Changjiang delta area and continental shelf of the East China Sea (ECS). These data were used to determine the chronology of two transgressions during marine isotope stage (MIS) 5 and MIS3, interpret the sedimentary facies and mechanisms of the distinctive transgression pattern, and reconstruct relative sea level of the study area during late MIS3. Fluvial gravelly sediment deposition prevailed with limited marine influence during MIS5, while muddy and sandy deposition occurs along with widespread coastal facies during mid-and late MIS3 in the Changjiang delta area. This suggests that the study area was dominated by high relief and local rivers developed with large freshwater and sediment discharge during MIS5. Therefore, marine micro-faunas may not have survived due to dominant freshwater process or strong erosion has scoured away the marine records of MISS. Tectonic subsidence is indicated to occur at a rate of ～1 m/ka since MIS5 and lower the Changjiang coastal area to be invaded by seawater during MIS3. The altitude of late MIS3 transgressive sediments decreases from the inner delta plain seaward gradually, reflecting differential tectonic subsidence of the study area. Abrupt sea level rise occurred, and relative sea level is proposed as -5 m during late MIS3.