Magnetic minerals in sediments of the continental shelf are sensitive to environmental changes.Therefore,to determine the exact phases of magnetic minerals is the prerequisite to investigate the paleoenvironmental significances.In this study,a comprehensive rock magnetic investigation,coupled with mineralogical studies,was carried out on the long core NHH01(with a length of 125.64 m)from the central continental shelf of the South Yellow Sea.Single-domain greigite was identified as the dominant magnetic carrier in sediments between44.90 and 51.80 m,and terrigenous magnetite is the major magnetic phase in the adjacent layers.The existence of greigite unambiguously indicates an anoxic environment.We tentatively interpreted that such an environment could be formed by the fast sea level changes,long-existing of the cold eddies during warm stages,or in a lake which might be related to locally tectonic uplifting.Therefore,the occurrence of the thick-layer greigite could supply a new perspective to paleoenvironmental or even tectonic studies.
Jianxing LiuXuefa ShiShulan GeQingsong LiuZhengquan YaoGang Yang
Insoluble microparticles in ice cores are related closely to the transportation of eolian dust,and thus are important natural media to reconstruct climate change.In this study,we conducted a systematic mineral-magnetic investigation of insoluble microparticles in the Nojingkangsang ice core (29°2.1'N,90°11.88'E,5950 m) from the Southern Tibetan Plateau.Results indicate that the dominant magnetic mineral is magnetite,and its concentration has grown significantly since the 1980s,which coincides with trends in climate warming of the Tibetan Plateau.Influenced by regional warming,the glacial recession around Nojingkangsang shortens the distance between the dust source and glacial areas and thus increases the concentration of coarse-grained magnetic minerals in ice cores.However,the frequency of dust storms,associated with annual precipitation,could play only a regulatory role on the magnetic content over yearly (or seasonal) time scales.Therefore,using a new approach,the magnetic index of insoluble microparticles in ice cores of this region is seen as mainly reflecting trends in climate warming.
It is commonly accepted that the climate records in Chinese loess can be correlated well with that in marine s...
Chunsheng Jin,Qingsong Liu~* State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,PR China,100029
Aeolian dust, a primary terrigenous component of ocean sediments, has been widely used to reconstruct the paleoclimatic evolution because its transported distance, grain size and concentration are sensitive to climate changes. To further characterize the aeolian dust, the deposits at site Ocean Drilling Program (ODP) 882A in northwestern Pacific Ocean are divided into four grain-size fractions (<8, 8-16, 16-64, >64 μm) using the gravitative differentiation method. Detailed rock magnetism results show that magnetite and hematite are dominant magnetic minerals for the dust components. In addition, the aeolian dust (<8 μm) represented by the concentration of magnetic minerals increases sharply at 2.73 Ma, which corresponds to the onset of major glaciation in the Northern Hemisphere. In contrast, the ice-rafted detritus (IRD) (>64 μm) contributes little to the magnetic enhancement of the sediments at 2.73 Ma. These new results greatly improve our understanding of paleoenvironmental evolution during late Pliocene-early Pleistocene in this area.
