Sedimentary stratigraphic framework and palaeoenvironmental evolution of the northern outer shelf of East China Sea since MIS 6

Based on the newly collected high-resolution shallow seismic and lithological data of the Borehole SHD-1, the stratigraphic framework of the outer shelf of the northern East China Sea since MIS 6 was established with ages. Using the method of sequence stratigraphy newly proposed by Octavian Catuneanu (2005), it is observed that the strata since MIS 6 in the study area may be subdivided into transgressive, highstand, falling, regressive and lowstand system tracts. The shallow seismic profile data fit well with the stratigraphic pattern disclosed by drilling cores, upon which 7 reflective interfaces (D7—D1) were recognized and 7 seismic units (SU₇—SU₁) subdivided for the strata since late Pleistocene. The transgression and regression system tracts are observed in a rather regular pattern, corresponding well to sea level fluctuation. Both the seismic units SU₁ and SU₅ were transgressive deposits corresponding to MIS 1, MIS5, when neritic facies prevailed, and the places less than 100 m in water depth were dominated by tidal ridge deposits. Seismic unit SU₂, SU₄ and SU₆ correspond to MIS 2, MIS 4 and MIS 6 stage, respectively. They were deposited in regressive periods and dominated fluvial and deltaic facies sediments. The seismic unit SU₃ and SU₄ were the system tracts formed during the sea level falling periods, corresponding to late MIS 3 and MIS 4 respectively. MIS 4—MIS 3 are dominated by thick and widely distributed underwater deltaic deposits, but the size of the underwater deltas in MIS 4 was smaller than those in MIS 3. In conclusion, the study of sedimentary stratigraphy framework and sedimentary environment since MIS 6 may provide a good reference for sea level changes and palaeoenvironmental evolution of the East China Sea continental shelf in Late Quaternary.