简介：

简介：AmarinestratigraphicsequenceacrossthePliocene/Pleistoceneboundaryhasbeenfoundinthenorth-erncontinentalshelfoftheSouthChinaSea.ThemarineQuaternarydepositsintheYinggehaiBasinmayex-ceed2,000minthickness,probablyprovidingthebestsectionforstudyingthelowerboundaryofthemarinePleistoceneinSouthChina.TheverticalsuccessionwithplanktonicforaminifersandnannofossilsrevealedinboreholesinthebasinhasbeenwellcorrelatedwiththatintheinternationalstratotypesectionofthePliocene/PleistoceneboundaryatVrica,Italy,resultingintheacquirementofabiostratigraphicboundaryat1.64Ma.Thisboundary,however,doesnotcoincidewithanyprominentlithologicalpalaeoenvironmentalchangesinthestudyareaandcanhardlybeusedingeologicalpractice.Thereare,incontrast,significantchangesatthelevelofLADofGloborotaliamulticameratasensulatolocatedbelowtheabove-mentionedboundary.Thepercentageofplanktonicforaminifersinthetotalpopulationandpreservationofforaminiferaltestsdisplaygreatchangesatthislevelcorrespondingtoaclearonlapontheseismicprofilesandindicatingadepositionalhiatusatca.2.0-2.5Ma.SincethelevelcanbewidelytracedinthePearlRiverMouthBasinandtheBeibuGulfBasinandwellcorrespondswiththemarkeddepositionalenvironmentalchangesrecordedinthewestPacificandotherregions,itisrecommendedthatthePlio/PleistoceneboundarybedrawnatthelevelofGr.multicameratasensulatoLAD,roughlyconcurrentwiththeGauss/Matuyamaturn.

简介：

简介：MicromorphologicalcharacteristicsoffourpaleosollevelsoftheManonga-WemberedepositsinCentralTanzaniaindicateperiodsofwetterclimateinthePliocenethanatpresent.Thestratigraphyofthestudiedsectionshowsaseriesoflacustrinecalcareousclaysedimentsalternatingwithgravel,sandandsilt.ThesedimentsarebelievedtohavebeendepositedintheManonga-Wemberepaleolakeenvironment.Paleosolsintercalatethesesedimentsandwereformedwhenstablelandscapesdevelopedonformerlakebedsduringregressionperiods.MicromorphologicalfeaturesofthepaleosolsindicatestrongclayilluviationofredtoyellowtypicclaycoatingandsomeFe-Mnhydoxidehypocoatingsinvoidsandchannels.Thegroundmassconsistsofeitheranaccumulationofbioturbatedyellowtoredclaycoatingfragmentsoranargillicredtoyellowgroundmassofclaymass.Suchanilluviationanditsassociatedgroundmassiscomparabletointenseclayilluviationfrontsthatarefoundinpresent-daycalcareoussedimentsofwarmandwetclimates.ThepaleosollevelsthereforerepresentwetterclimaticconditionsthantodayintheareaduringtheLowerPliocene.