The Magnetic Parameters And Its Environmental Implications In Sediments Since Late Pleistocene From Dongsha Area, South China Sea

The study for marine sediments and its environmental significance of themagnetic characteristics in Environmental Magnetic Methods is increasing. But thesurvey of the magnetic characteristics of marine sediments and its environmentalsignificance in area containing gas hydrates is rarely reported. Detailed environmentalmagnetic measurements were carried out on973-3、973-4and973-5cores, whichwere obtained form the northern slope of the South China Sea region, includingmagnetic susceptibility, anhysteretic remanent magnetization, isothermal remanentmagnetization and κ-T curves. Through the Environmental Magnetic Methods, thepaper is intend to analyze the magnetic particles combined features of every core, toexplore the factors affecting the magnetic properties of sediments in gas hydrate zone.973-3、973-4and973-5cores are located on the northern continental slope, upperslope and deep basin of the South China Sea. Its deposition rate was high, and someintervals of every core suffered erosion of gravity flow deposits. All of the factorsproduce rich substances, and promote the burial of organic matter rapidly, which werenot sufficiently oxidized.The magnetic characteristics of973-3and973-5cores is similar to each other,their magnetic parameters, such as magnetic susceptibility, show the "high-low-high" trend from top to bottom. While the magnetic characteristics of973-4corepresent the "high-low-high-low" trend. Under normal circumstances, substancesand early reductive diagenesis are the two main factors that cause the features ofmagnetic parameters.Detailed analysis showed that the substances of973-3and973-5cores in the lowsegment of the magnetic susceptibility presented no significant changes. Although thesubstances of973-4core in the low segment of the magnetic susceptibility showedsome changes, it was not important. The results discover different effects of reductivediagenesis on the three cores. In the early reductive diagenesis, the original magneticminerals (magnetite) that come from land-based sources occured reductive dissolution,and the reductive dissolutions make the magnetic susceptibility decline. In the sulfate-reducing stage, dissolved sulfate is reduced to H2S, it reacted with Fe2+andgenerated greigite and pyrite.Also, Detailed analysis showed that there is some relationship between themagnetic characteristics of every core and methane eruption.