Abstract:

:A59.4mlongXiashuLoessprofileinZhenjiangwasinvestigated.Magneticpropertiessuchashigh-temperaturemagnetic susceptibility(χ-T)curve,IRMacquisitioncurvesandhysteresisloopsofthisprofilewereanalyzedtoverifythemagneticsusceptibility changemechanism.Theresultsshowthat:1)magneticsusceptibilityvariesgreatlyinthewholeprofileandbetween6.4×10-8m3·kg-1 and186.3×10-8m3·kg-1.Inaddition,thelowerpart(24-59.4m)exhibitslowmagneticsusceptibilitywithanaverageof34.7×10-8m3· kg-1,whichismuchlowerthanthatoftheupperpartof126.1×10-8m3·kg-1;2)allof10representativesamplescanbedividedintotwo groups.Thefirstgroupischaracterizedbyhighmagneticsusceptibility.χ-Tcurvesexhibitobviouscuriepointofmagnetite;IRM acquisitioncurvestendtosaturateat300mT;thereversedemagnetizationcurverevealsacoercivityofremanenceof25-40mT; hysteresisloopsarethinandcloseat600-800mT.Thesefeaturesindicatethatsamplescontainhighabundanceofferrimagnetic minerals (e.g., magnetite, maghemite). The other group has lower magnetic susceptibility; χ-T curves show low initial magnetic susceptibility;IRMacquisitioncurvesarenotsaturatedevenat2.5T;andhaveacoercivityofremanenceof70-135mT.hysteresis loopsdisplayapronouncedwasp-waistedshape.Thesefeaturessuggestthatsamplescontainlittleferrimagneticmineralsandmassive high coercivity minerals (e.g., hematite, goethite), and possibly pyrite; 3) rock magnetic features suggest that the soil-forming environmentchangedwithtime,multi-stagewetenvironmentappearedbefore350kaandresultedinreducingenvironment,magnetite andmaghemiteweretransformedtoweakmagneticminerals,thereforemagneticsusceptibilitywasextremelylow.Thisphenomenonis ingoodagreementwithloessinSiberia;Xiashuloesswascontrolledbyoxidizingenvironmentsince350ka,whichisbeneficialtothe generationoffinemagnetiteandmaghemite,andissimilartotheloessontheChineseLoessPlateau.

Key words: XiashuLoess;Magneticsusceptibility;Rockmagnetism;Zhenjiang