Magnetic susceptibility (MS) data were obtained from 11 sections of the Doushantuo (Edicaran) cap carbonate that directly overlies the Nantuo glacial diamictite in the southeastern margin of the Yangtze plat- form. The MS data revealed two regionally correlatable peaks at the bottom and top of the cap carbonate, sepa- rated by an interval of low values. The lower MS peak coincides with high percentage of insoluble siliciclastic residues that are compositionally identical to the matrix of the underlying diamictite, suggesting its origin con- trolled mainly by detrital components during the first phase of cap carbonate deposition at the end of the glacia- tion. The upper MS peak is associated with high clay content and iron sulfides, and can be interpreted as either derived from enhanced greenhouse weathering that could have brought more terrigenous components into the ocean, or the result of ocean anoxia at the late stage of cap carbonate deposition that could led to formation of abundant iron sulfides. The regionally consistent MS curves from the cap carbonates provided the first geo- physical record for the rapid climate change from icehouse to greenhouse conditions in the aftermath of the Neoproterozoic “snowball Earth” event.
Environmental magnetic measurements were carried out on the samples of street dust and topsoil,which were collected along the roadway in the urban and suburb of Beijing,including magnetic sus-ceptibility(χ),anhysteretic remanent magnetization(ARM),isothermal remanent magnetization(IRM)of all samples and temperature-dependence of magnetic susceptibilities and magnetic hysteresis pa-rameters of representative samples.Obvious differences exist between the samples of street dust and those of topsoil.Compared with topsoil samples,the concentration of magnetic particles and high-coercivity components in street dust samples are higher,and the magnetic grains are coarser.Both dust and topsoil samples are dominated by ferrimagnetic minerals,and iron particles are only detected in some dust samples.These results suggest that street dust samples reflect the characteris-tic of particles produced by industrial and traffic activities,and the magnetic property of topsoil sam-ples represents the characteristic of particles from both anthropogenic and natural sources.The dis-tribution of magnetic parameters is influenced by the environment where the samples are collected,like industry,traffic density and other road conditions.Hard isothermal remanent magnetization(HIRM)may be used as an indicator of particles produced by traffic activity.Dust storm samples collected on 17 and 18 April,2006 have different magnetic properties from street dust and natural particles,like loess and paleosol,which indicate that the dust storm might be mixed with anthropogenic particulates during transport and falling.
