Environmental Magnetic Records Of Core Sediments In Xinghua In North Jiangsu Basin Since The Mid-Pleistocene

Closely linking the largest ocean and the biggest continent ,and under the control of the East Asian monsoon system, the North Jiangsu Basin is a most sensitive and an ideal region for global change research. Due to its complex evolution process, there is still a long way to go for the Quaternary research especially for the record since Pleistocene in this area. As an emerging edge discipline in 1970's, Environmental magnetism is widely applied in more and more fields for its particular merits- "cheapness, simplicity, convenience, non-destruction to samples, stable records of magnetism, etc.".However, magnetic characteristics of sediment are influenced by very complex factors, including sources, climate, transportation process, post depositional changes,etc.,there is no uniform pattern for the relationship between magnetic parameters and environment. How the magnetic susceptibility (MS) would respond to the paleoenvironment is worth researching in this land-sea interacting area. We choose the upper 82m part, which corresponds to the time period since mid-Pleistocene, from the ~740m length Xinghua Core 2 for environmental magnetism measurement, combining with lithology and granularity analysis, we try to analyse the magnetic characteristics in different facies and how they respond to paleoenvironment. Conclusions gained are as follows:(1) The relationship between MS and the grain size varies depending on the sedimentary facies. For the shallow lake and river sediments, MS is controlled by coarse component, i.e.,the particles bigger than 50um; for the river floodplain or lakeshore MS is related with fine particles especially those smaller than 15um.(2) Rock magnetic measurements carried out on the representative samples of the core show that almost all samples contain magnetite which is mainly derived from the terrigenous detrital minerals. For the sand, silty-clay and some brown clay samples, they have higher MS values, whose main magnetic carrier is magnetite, and some also contain a small amount of maghemite, goethite and lepidocrocite, and their magnetic domain status are MD or PSD; For samples with lower MS, most of them are clay with dark-grey or greyish black color and of PSD magnetic domain. Magnetite content reduces greatly, while the paramagnetic component increases. The low values of these samples may come from the dissolution, dilution by antimagnetic material of magnetite under reduction condition. There are even other low MS samples with Fe-Mn mottling contain goethite and hematite, reflecting the effect of secondary transformation on magnetism. (3) Overall, the MS and grain size have a positive correlation in the core, especially for sediments from river and shallow lake. The main peaks of MS correspond well with the marine oxygen isotope stages MIS19, 15,9,5,3, and the valley with MIS18, 16,14,12,10,8 ,which may reveal their response to global ice volume. However, under this positive correlation context ,there are still some stages in which MS and grain size are both of low level but counter-related in some smaller scale. According to lithology, they may be transformed after deposition.(4) MS is controlled by many factors such as source, paleoclimate, sedimentary facies, hydrodynamics, organic matter, redox conditions and so on. We must recognize the influencing factors and mechanism of MS changing before reconstructing the paleoenvironment.