Magnetic Properties Of The Sub-bottom Sediments On The Outer Continental Shelf Of The East China Sea And Implication On The Sea-level Fluctuation

The Late Quaternary relative sea level changes and associated stratigraphy varies from different regions in the coastal area and continental shelf of the eastern China, due to the global sea-level fluctuations and tectonic activities between Asia-Europe and Pacific plates. The Late Quaternary sea level curve of the eastern China does not coincide with the global change in terms of intensive marine transgression during MIS3. Meanwhile, most boreholes are obtained from the coastal area during the past decades, whereas little attention has been paid to continental shelf. The present study collected several vibrocores from the outer continental shelf of the East China Sea and carried out analyses including chronostratigraphy, magnetic properties and sedimentology, so as to demonstrate the sub-bottom strata of the outer continental shelf of the East China Sea, the distribution and the formation of the greigite, and further to reveal the Late Quaternary sea-level fluctuations and associated stratigraphy framework.The magnetic mineral, greigite (Fe₃S₄), is a useful indicator for the marine transgression. Previous studies showed the occurrence of greigite in the muddy sediments of depressions between sand ranges of the outer continental shelf of the East China Sea. Knowledge of its distribution in the strata and its relationship with the sea-level fluctuations is still quite limited. Previous studies indicate two possibilities of the formation of the greigite: 1) the seepage of seawater during the postglacial transgression provides sulfate and makes the reducing diagenetic conditions; 2) it may be precipitated as the authengenic mineral in marine or lacustrine sediments during the low sea-level stand of the Late Pleistocene. The present study obtained 6 vibrocores (1.5-2.5m deep, long vibrocore; B436, B437, B439, B459, B483, B484) from the Xihu depression and 4 vibrocores (0.3-0.5m deep, short vibrocore; ST9, ST13, ST15, ST23) at the- front of the Yangtze Shoal. The vibrocores were split for lithologic observation and sampled. Sediments were measured for U-series dating,...