Manganese Abnormity in Holocene Sediments of the Bohai Sea

ManganeseabnormityhasbeenobservedintheHolocenesedimentsofthemudareaofBohaiSea.Onthebasisofgrainsize,chemicalcomposition,heavymineralcontentandacceleratormassspectrometry(AMS)14Cdatingofforaminifer,relationshipsbetweenmanganeseabnormityandsedimentationrates,materialsource,hydrodynamicconditionsareprobed.ManganeseabnormityoccurredduringtheMiddleHolocenewhensealevelandsedimentationrateswerehigherthanthoseatpresent.Sedimentaryhiatuswasnotobservedwhenmaterialsourcesandhydrodynamicconditionswerequitesimilar.Comparedwiththeformerperiod,thelatterperiodshowedadecreaseinreductionenvironmentandaninclinationtowardoxidationenvironmentwithhighmanganesecontent,whereasprovenanceandhydrodynamicconditionsshowedonlyaslightchange.Fromtheaboveobservations,itcanbeconcludedthatcorrelationamongmanganeseabnormity,materialsource,andhydrodynamicconditionsisnotobvious.Redoxenvironmentseemstobethekeyfactorformanganeseenrichment,whichismainlyrelatedtomarineauthigenicprocess.