The East China Sea Inner Shelf Of The Mud Area Deposition And Paleoenvironmental Evolution Since The Holocene

In this paper, based on a comprehensive survey of China's Coastal Sea Investigation and Research Project (908-01-CJ12). 927 surficial sediments, 4 section of suspended matters and 7 gravity cores from the inner shelf of the East China Sea were utilized by this research, on which sedimentary, geochemistry, mineralogy and isotopes analysis were conducted, and in site characteristics of suspended matters were observed by a LISST apparatus, combined with a CTD instrument.Researching on modern sedimentary environment of study area comprises investigation on the grain size, geochemical composition, clay mineral of surficial sediments and characteristics of the suspended matters. The result show that surface sediments are mostly transported from the north-east towards the south-west, they are controlled by The Yangtze River source material, coastal of Fujian and zhejiang, Taiwan warm current and so on. The study area can be divided into areas controlled by the Yangtze and Minjiang substances. factor analysis results showed that the study area is mainly affected by fine grained terrestrial chips, coarse grained terrestrial chips and marine autogeny, volcanism and marine chemistry.Based on the analysis of 7 sediment cores in the study area, the sedimentation and the evolution of the sediment environment since the Holocene were discussed. Geochronology results show that the sedimentation rate has been between 26.41-50.41cm/ka ever since the Holocene. Based on this fact, the intensity of the Fujian and Zhejiang costal current was reconstructed by sensitive grain size and clay mineral assemblage. Sensitive trace elements were applied to estimate redox environment. Organic carbon, biogenic silica and trace elements assemblage were used to infer the evolution of the paleoproductivity. The results show that the redox environment was leant to the oxygen enriched from 8400 aB.P. to 4000aB.P. in the study area, and the intensity of costal current was strong, paleoproductivity and upwelling were weak during that time; From 4200 aB.P. to 1300aB.P., the intensity of costal current , the redox environment, paleoproductivity and upwelling all presented a intense fluctuation; from 1300aB.P. up to now, the redox environment has been a lean oxygen-poor environment, and the costal current was weak, the paleoproductivity and the upwelling present a gradually strengthened trend. And the evolution of East Asia Monsoon could be deduced based on the mean fine grain size, the ratio of TiO₂/Al₂O₃ and (S+I)/K, 12 high values could be recognized corresponding to the contemporary cooling events during Holocene respectively, correlate well with the results of theδ18O curves of Dunde and GISP 2 and reveals the regional response to global climate change.