Sedimentary Characteristics And Paleoenvironmental Records Of Core EC2005 In The Mud Area On The Inner Shelf Of The East China Sea

Based upon analysis of lithology, grain-size, AMS14C dating, clay and bulk minerals, geochemical compositions, rare earth elements (REE), total carbon (TC), total nitrogen (TN), total organic carbon (TOC) and magnetic susceptibility analysis for Core EC2005, located in the mud area off the Zhejiang-Fujian coast in the inner shelf of the East China Sea (ECS), the paleoenvironmental evolution, sea level change, formation of the Zhejiang-Fujian coastal current (ZFCC) and paleoclimatic change could be ascertained. The relationship among terrigenous mineral components, geochemical composition and grain-size distribution is also discussed.From the bottom 60.20 m to 41.00 m (17.3~13.1 ka BP), a lacustrine delta developed. The sea water arrived at the study area at 13.1 ka BP and a 41 m thick sediment formed from then on. From 12.3 ka BP, the study area was influenced by ZFCC, and Yangtze-derived materials had been transported southward from that time. Yangtze-derived materials played a dominant role from 10~9.8 ka BP while the sediments were mainly originated from the regional drainage area before. Since 7.3 ka BP, the sedimentary environment is dominated by the ZFCC, and the homogeneous mud sedimentation began to form. The important reason for material provenances change is sea level rise and the formation of coastal current.On the basis of environmentally sensitive grain-size population analysis of Core EC2005, a 700 a East Asian winter monsoon (EAWM) evolution between 5.9 and 5.2 ka BP was compared with the GRIPδ18O record. The good correlation suggested that inner relationship existed between the EAWM and the climatic changes disclosed by the GRIP ice core. The EAWM strengthened abruptly around 5500 a BP, which is corresponded to the worldwide cold event. The significant periodicities disclosed by power spectral analysis correspond to the solar activity such as the 62 and 11 a periodicities and the modern ENSO 3~8 a periodicity as 6 and 5 a. Theirfore, the EAWM evolution in the mid-Holocene and the 5500 a BP cold event may be influenced by solar and ENSO activities.The climatic warming from last deglaciation to the early Holocene in the inner shelf of the ECS has been worldwidely recorded, which may be the integrated results of orbital insolation forcing, the solar activities and the northward migration of intertropical convergence zone. Four rapid depositional periods such as 12.3~12.1 ka BP, 7.5~7.3 ka BP, 5.9~5.2 ka BP, and 1.5~1.3 ka BP disclosed by Core EC2005 well correspond to the worldwide Younger Dryas, 7.3 ka cold event, Neoglaciation or 5.5 ka cold event, and 1.4 ka ice rafted debris event, respectively. The worldwide 8.2 ka event is also well recorded in the core.The magnetic susceptibility variation is controlled by lithology, early diagenetic and human activity. The acute fluctuation since 3.6 ka BP may result from human activity. Variations of TOC, TN and TOC/TN in Core EC2005 are mainly controlled by lithology.A function model was built between grain-size and mineral components of terrigenous materials according to their inherent relationship. The mineral components show good correlation to geochemical compositions, suggesting the mineral constrains on the chemical elements in the sediments. The mineral constrains on the grain-size distribution and geochemical composition is crucial, whereas the grain-size distribution can only affect the geochemical composition via changes in mineral components.