The Magnetic Susceptibility Enhancement Mechanism of the Red Clay Sequence

Pedogenetic enhancement mechanism of magnetic susceptibility in loess/paleosol sequences of the Chinese Loess Plateau has been widely accepted.Magnetic susceptibility is used as a proxy of summer paleomonsoon intensity.The red clay underlying the loess/paleosol sequences is also aeolian deposit,however,its magnetic susceptibility enhancement mechanism has not been studied as intensively as that of the loess/paleosol sequences,and the reason why the strongly developed red clay gets low susceptibility is unclear.Studies were made on the magnetic mineralogy,magnetic concentration and magnetic grain size distribution of Jiaxian red clay.(1) The magnetic minerals of the red clay are magnetite,maghemite and hematite,similar with Quaternary loess/paleosol sequences;the average magnetic grain size is PSD;the strongly developed red clay contains much soft magnetic minerals(magnetite and maghemite) and the weakly developed red clay contains much hard magnetic minerals(hematite and goethite).(2) There is a positively linear relationship between χ,χfd and χARM,which implies that the red clay contains a lot of ultrafine ferrimagnetic grains(SP and SD).The grains produced during the pedogenesis process account for the susceptibility increase.(3) The values of χfd and χfd% of red clay are higher than the loess/paleosol sequences,which implies the red clay underwent a strong pedogenesis development process.The environment during the paleosol developed of red clay is similar with the loess/paleosol sequence of the Chinese Loess Plateau,different from that of the high latitude Alaska and Siberia.