Quaternary Magnetostratigraphy Recorded In The Sediments Of Core TJC-1 In The Western Bohai Sea

The Bohai Sea is considered as a typical area for Quaternary stratigraphy and sedimentary process due to its uniqueness in geographic,sedimentary and tectonic background,and there have been arguments regarding the buried depths of some important geologic events(e.g.Brunhes/Matuyama boundary)during Quaternary in Bohai.A 200.3-m-long sediment core TJC-1,obtained from the western Bohai Sea(38°43?55.72? N,118°57?09.75? E)with an average recovery of 79.8% at water depth of 26 m,was analyzed for palaeomagnetic characteristics to document the Quaternary magnetostratigraphy of the region.From the results of palaeomagnetic experiment of the core,it shows that the interval 0~71.48 m belongs to the Brunhes normal polarity epoch,and the interval 71.48~200.30 m belongs to the Matuyama reverse polarity epoch.It also shows that the deposition started at about 2.28 Ma B.P..Major polarity excursions,such as Blake(8.92~9.32 m)?Big Lost(51.02~51.32 m)etc.are identified in the Brunhes normal polarity epoch.And the major polarity excursions,such as Jaramillo(85.30~90.38 m)?Olduvai(154.76~169.38 m)and Reunion(185.04~188.34 m)are identified in the Matuyama reverse polarity epoch.Through an integrated analysis of sedimentary features and palaeomagnetic measurements of the core,we give a preliminary stratigraphic division: the interval 0~3 m belongs to Holocene Series and the interval 3~200.30 m belongs to Pleistocene Series.Furthermore,three sedimentary phases are identified on the basis of the paleomagnetic characteristics: phase I(0~0.781Ma)with a sedimentation rate of 82.236 m/Ma which indicates a stable tectonic period and climate controlled sedimentary process;phase II(0.781~1.068 Ma)with a sedimentation rate of 128.40 m/Ma;and phase III(1.068~2.28 Ma)with a sedimentation rate of 87.936 m/Ma.Stratigraphic correlation analysis among cores in western Bohai Sea and its adjacent areas is also carried out.Our results show that the buried depth of the B/M boundary in core TJC-1(71.48 m)is remarkably different from that of other cores(e.g.BC-1)in the area.This might be due to the differences of sedimentary thickness between identical geological units,which are in turn constrained by varied tectonic settings in the study area since Quaternary period.