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记述产自西藏南部仲巴县的一个中国目前所知最年轻的菊石群，含2科4属6种，其中4新种。据菊石群面貌和它们所产出的层位可以划分出上、下两个组合带：上部Pachydiscus.cf. Hidakaensis-Libycoceras zhongbaense组合带；下部Manambolites cujiangdingensis-M.Pivaeteaui组合带。产菊石的曲贝亚组的下段和上段的中、下部(82F50及其以下层位)为晚Campanian期，上段上部(即82F52及其以上层位)为早Maastrichtian期。“,”ThispaperdealswithanammonoidfaunafoundinrnZhongbaCountysouthernXizang(Tibet),whichisthernyoungestammonoidfaunainageknowninChinaatprernsent.Thefaunainvolves2families,4generaand6rnspecies(including4newspecies).Basedonthefeaturesrnofammonoidfaunaandtheverticaldistribution,anupperrnandalowerassemblagezoneshavebeendistinguished:rnTheupperassemblageZonernPachydiscuscf.hidakaensis-Libycoceraszhongrnbaenseassemblagezone:only2genera,2speciesarernfoundandthelatterisanewspecies.BasedonthefactrnthattheformerspecieswasoriginallyyieldedinearlyrnMaastrichtianbedsinHokkaido,Japan,whilethelatterisrnsimilartoL.ismaelis,whoserangeisfromlateCampanirnantolateMaastrichtian,theageofthisassemblageisrernrnferredtoearlyMaastrichtian.rnThelowerassemblageZonernManambolitescujiangdingensis-M.pivaeteautiasrnsemblagezone:3genera,5speciesarefound.Inadditionrntothetwomarkerspeciesofthezone,theothersarernCoahuiliteszhongbaensissp.nov.,Libycocerastibetioumrnsp.nov.andL.zhongbaensesp.nov.BasedontheocrncurrenceofgenusManambolitesbeingrestictedtomiddlerntolateCampanian,especiallythepresenceofM.pirnvaeteauibeingonlyfoundinlateCampanianbothinrnMadagascarandTunisia,itisappropriatetoassignthisrnassemblagezonetolateCampanian.rnAgesofthebedsyieldingammonoidsaresuggestedasrnfollows:rnQubeiyaFormation:Themajorpartofthelowerrnmember,andlowerandmiddlepartofuppermembersrn(thebedsbelow82F50)canbeassignedtolateCampanirnan,whiletheupperpartoftheuppermember(82F52andrnrnthebedsabove)shouldbeearlyMaastrichtianinage.AsrnfortheoverlyingQuxiaFormationwithoutammonoidsitrnisinferredthatprobablyapartoftheearlyMaastrichtianrnandlateMaastrichtianareinvolvedbasedonthefindingsrnoflateMaastrichtianforaminifersandtheboundaryclayrnrnlayerwithiridiumanomaly,whichiscommonlyfoundatrnK-Tboundaryinmanyplacesthroughouttheworld.rnTheconsiderablepartoftheupperPadanaFormationrnunderlyingtheQubeiyaFormationisalsodeductedandrndatedasearlyCampanianinagealthoughnofossilevirndencehasbeenfound.