Magnetic Properties And Their Paleoenvironmental And Paleoclimatic Implications Of ODP Site 1143 Sediments In The Southern South China Sea

The South China Sea (SCS) is the largest marginal sea in the West Pacific, and its abundant sediments give an insight into paleoclimate and paleoenvironment signals from global and regional scale. In this study, rock magnetic and environmental magnetic research were conducted on the core of the ODP Site 1143C sediments in the southern SCS, in order to reveal the long-term and short-term magnetic characteristic variations, and the controlling factors of magnetic characteristic and their paleoenvironment and paleoclimate implications.The rock magnetic results reflect that the fine-grained pseudo-single-domain magnetite is the dominant carriers, and only a small proportion of high-coercivity magnetic minerals (such as hematite) exist within the samples probably. The environmental magnetism results show that there is an abrupt change in magnetic records about 5.2 Ma occurred, probably due to the changes of terrigenous source and depositional environment. Before 5.2 Ma, magnetic minerals was diluted since the enrichment of a lot of clay minerals and carbonate within the sediments. Since then, the magnetic parameters appear to correlate with the East Asian summer monsoon (EASM). Stronger EASM condition possibly promote the growth of finer and more magnetite on the land, while weaker EASM condition form less fine-grain magnetite. Combined with the oxygen isotope analysis, the grain size and S-ratio of the magnetite displays the variations during glacial-interglacial cycle since 2 Ma. During glacial period, the magnetic mineral components indicate that coarser and high-coercivity magnetic minerals are increasing. On the other hand, finer and low-coercivity magnetic minerals are the predominated in the sediments during interglacial period. Variation of magnetic parameter assemblages at ODP1143C illustrated the effects influence by both climatic conditions and sea level fluctuation. The abnormal magnetic records at 3 Ma-2.6 Ma is presumably revealed the links between the responses of Northern Hemisphere glaciations to magnetic characteristics. The response of Mid-Pleistocene Transition (MPT) and Mid-Brunhes Event (MBE) to magnetic records are discussed.Spectral analyses of the magnetic parameters further show that 100 ka and 41 ka are dominant periodicities during the last 5 Ma in this site. Obliquity (41 ka) is the dominant periodicity at 2 Ma-1 Ma. After 1Ma, eccentricity (100 ka) becomes the dominant periodicity instead revealed by the magnetic parameters in the sediments.