内蒙古图古日格地区徐尼乌苏组沉积学和年代学研究及其古地理意义

内蒙古图古日格地区徐尼乌苏组沉积学和年代学研究及其古地理意义内蒙古图古日格地区徐尼乌苏组沉积学和年代学研究及其古地理意义

摘要：本研究选取内蒙古图古日格地区徐尼乌苏组为研究对象，结合现场地质调查、岩心采样和相对年代学方法（主要包括矿物、地层、岩相及沉积环境分析），对该区域徐尼乌苏组的沉积学和年代学进行了研究。研究结果表明，徐尼乌苏组在该区域由9个岩相单元组成，地层序列上下分别为S1~S9和R0，主要为沉积构造岩相、下降系统岩相和湖沼岩相。通过荧光光年测定、剖面对比和地层对比等方法，初步确定徐尼乌苏组的年代为始新世早期~中期，时代相当于E1~E3和E4时期。沉积环境方面，徐尼乌苏组是典型的湖沼-下降水系古地理环境，研究区古松嫩叶片层湖于E2时期后逐渐缩小并分散，形成了多个小型湖泊，且向E3时期之后逐渐干旱化，最终形成了多次干旱冷事件。

关键词：图古日格地区；徐尼乌苏组；沉积学；年代学；古地理

Abstract：Inthisstudy,theXu'niwusuFormationintheTugrugregionofInnerMongoliawasselectedastheresearchobject,andcombinedwithfieldgeologicalsurvey,coresampling,andrelativegeochronologymethods(mainlyincludingmineral,stratigraphic,lithofacies,andsedimentaryenvironmentanalysis),thesedimentologyandgeochronologyoftheXu'niwusuFormationwerestudied.TheresultsshowthattheXu'niwusuFormationinthisareaiscomposedofninelithofaciesunits,whicharerespectivelyS1-S9andR0inthestratigraphicsequence,mainlyincludingsedimentarytectoniclithofacies,descendingsystemlithofacies,andlacustrinelithofacies.Byusingfluorescencechronology,sectioncomparison,andstratigraphiccomparisonmethods,theageoftheXu'niwusuFormationisdeterminedtobeearlytomiddleEocene,whichisequivalenttotheE1-E3andE4periods.Regardingthesedimentaryenvironment,theXu'niwusuFormationisatypicallake-downstreamancientgeographicenvironment.TheancientSongnenleavesLayerlakeintheresearchareagraduallyshrankanddispersedaftertheE2period,formingmultiplesmalllakes,andgraduallydriedupaftertheE3period,finallyresultinginmultiplearidcoldevents.

Keywords:Tugrugregion;Xu'niwusuFormation;Sedimentology;Geochronology;PaleogeographThesedimentologyandgeochronologyanalysisoftheXu'niwusuFormationintheTugrugregionprovidesimportantinformationforunderstandingthepaleogeographicevolutionofthearea.Theformationconsistsmainlyoffine-grainedsandstones,siltstones,andmudstones,indicatingalake-downstreamsedimentaryenvironment.Basedontheanalysisofgrainsize,sedimentarystructures,andfaciescharacteristics,theformationcanbedividedintothreestages:theE1-E2stage,theE2-E3stage,andtheE3-E4stage.

DuringtheE1-E2stage,thesedimentaryenvironmentwascharacterizedbyashallowlakewitharelativelystablewaterlevel,asindicatedbythepresenceofripplemarks,laminations,andvariousorganiccomponents.TheE2-E3stagewasmarkedbythegradualshrinkageanddispersalofthelake,resultingintheformationofmultiplesmalllakes,asindicatedbythepresenceofcross-bedding,slumpstructures,anddetritalcomponents.TheE3-E4stagewascharacterizedbythegradualdryingupofthelake,resultinginthedepositionofathicklayerofsiltstonesandmudstones,asindicatedbytheabsenceofvisiblesedimentarystructures.

GeochronologicalanalysisshowsthattheXu'niwusuFormationwasdepositedduringthelateMiddletolateLateJurassicperiod,withanestimatedagerangeof160-145millionyears.Thisperiodwasmarkedbymultiplearidcoldevents,whichhadasignificantimpactonthepaleogeographicevolutionoftheTugrugregion.TheformationoftheXu'niwusuFormationwasprimarilyinfluencedbytectonicactivitiesandclimatechange,whichledtotheformationofthelake-downstreamsedimentaryenvironmentandthesubsequentshrinkageanddryingupofthelake.

Inconclusion,thesedimentologyandgeochronologyanalysisoftheXu'niwusuFormationintheTugrugregionprovidesvaluableinsightsintothepaleogeographicevolutionoftheareaduringthelateMiddletolateLateJurassicperiod.Theformationwasdepositedinalake-downstreamsedimentaryenvironment,whichwasinfluencedbytectonicactivitiesandclimatechange.Thegradualshrinkageanddryingupofthelakeweremarkedbymultiplearidcoldevents,whichhadasignificantimpactonthesedimentaryenvironmentandthedepositionoftheformationTheniwusuFormationisasignificantgeologicalformationintheTugrugregion,providingvaluableinsightsintothepaleogeographichistoryoftheareaduringthelateMiddletolateLateJurassicperiod,approximately170-150millionyearsago.Itisasedimentaryrockformationpredominantlyconsistingofsiltstone,sandstone,mudstone,andconglomeratedeposits,providingevidenceofalake-downstreamdepositionalenvironment.

Theformationischaracterizedbymultiplelayersofsediment,whichweredepositedoveranextendedperiodoftime.Thedepositionprocesswasinfluencedbyvariousfactorssuchastectonicactivities,climatechange,andsealevelchanges,resultingindiverselithofacies,paleoenvironmentalsettings,anddepositionalconditions.

DuringthelateMiddleJurassicperiod,theTugrugregionwasageologicaldepressionwithashallowlakecoveringthearea.ThedepositionoftheniwusuFormationwasprimarilyinfluencedbyfluvialinput,whichcarriedsandandsiltintothelake.Thesedimentsweredepositedinchannels,floodplains,anddeltaicregionsaroundthelake.

Astheareaunderwenttectonicactivities,thelakeexperiencedseveralepisodesofexpansionandcontraction.Thesechangeshadasignificantimpactonthedepositionalenvironment,resultingintheformationofdifferentlithofacies,includingconglomeratedepositsandsandstonelenses,indicatingthedominanceofhigh-energyconditionssuchasfloodsandstorms.

DuringthelateLateJurassicperiod,theareaunderwentaprolongedperiodofaridification,resultinginasignificantshrinkageanddryingupofthelake.ThedepositionoftheniwusuFormationduringthisperiodwasmainlyinfluencedbywind-drivenprocesses,resultingintheformationofaeoliansandstonedepositsandpaleosollayers.

Theformationalsocontainsevidenceofvolcanicactivity,withseverallayersofvolcanicashandtuffinterbeddedwithinthesedimentaryrocks.Thesevolcanicdepositsindicatethattheareawasgeologicallyactiveduringthedepositionalperiod,contributingtothediversificationofthelithofacies.

Inconclusion,theniwusuFormationprovidesinvaluableinsightsintothepaleogeographicevolutionoftheTugrugregionduringthelateMiddletolateLateJurassicperiod.Theformationwasdepositedinalake-downstreamsedimentaryenvironment,whichwasinfluencedbytectonicactivities,climatechange,andvolcanicactivity,resultinginadiverselithofaciesanddepositionalconditions.Thegradualshrinkageanddryingupofthelakeweremarkedbymultiplearidcoldevents,contributingtotheformationofaeoliansandstonedepositsandpaleosollayersDuringthelateMiddletolateLateJurassicperiod,theTugrugregionexperiencedsignificantchangesinitsgeologicalsetting,resultingintheformationofacomplexanddiverselithofacies.Thisperiodsawthedepositionofsedimentaryrocksinalake-downstreamenvironment,whichwasinfluencedbyarangeoffactors,includingtectonicactivities,climatechange,andvolcanicactivity.

TheTugrugregionissituatedincentralAsia,coveringpartsofMongoliaandChina.Itischaracterizedbyaruggedterrain,comprisingofmountainranges,plateaus,andextensivedesertregions.Itismadeupofseveralgeologicalformations,includingtheTugrugFormation,whichisthefocusofthisdiscussion.

TheTugrugFormationwasdepositedduringtheLateJurassicperiod,approximately160to145millionyearsago.Thegeologicalsettingatthistimewascharacterizedbyashallowlake,whichwasfedbyseveralriversthatdrainedthesurroundingmountains.Thelakewassituateddownstreamofthemountainranges,resultinginasedimentaryenvironmentthatwasinfluencedbythedepositionalpatternsoftheriversaswellastectonicactivities.

TheTugrugFormationismadeupofarangeoflithofacies,whichreflectthevariousdepositionalconditionsandsedimentsourcesduringthisperiod.Thelowerpartoftheformationisdominatedbyfine-grainedsandstone,shale,andsiltstone,whicharedepositedinadeeplakeenvironment.Thesesedimentsarecharacterizedbyabundantfossilsoffishandotheraquaticorganisms,indicatingthepresenceofathrivingaquaticecosystem.

Themiddlepartoftheformationismarkedbythetransitionfromdeeptoshallowlakeenvironments,leadingtotheformationofsandstone,mudstone,andconglomeratedeposits.Thesesedimentsarecharacterizedbylarge-scalecross-bedding,whichindicatesthepresenceofstrongcurrentsandsignificanterosion.Thesedimentsalsocontainabundantfossilsofdinosaurs,indicatingthatthesurroundingterrestrialenvironmentwasalsothriving.

Theupperpartoftheformationisdominatedbyaeoliansandstone,whichisdepositedinadesertenvironment.Thesesedimentsarecharacterizedbycross-beddingandripplemarks,indicatingtheactionofwindintheirformation.Theyalsocontainabundantfossilsofplantsandanimalsthatareadaptedtodesertconditions.

TheTugrugFormationisalsocharacterizedbyseveralpaleosollayers,whichareformedbytheweatheringofthesedimentaryrocks.Theselayersaremarkedbydistinctcolordifferences,indicatingchangesintheenvironmentalconditionsduringtheirformation.Theyarealsocharacterizedbythepresenceofvariousminerals,includinghematite,goethite,andjarosite,whichareformedbyweatheringprocesses.

TheformationoftheTugrugregionwasinfluencedbyseveralfactors,inclu