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东营凹陷西部沙河街组三段上部泥岩中白云岩夹层成因研究.docx

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东营凹陷西部沙河街组三段上部泥岩中白云岩夹层成因研究 摘要： 本文研究了东营凹陷西部沙河街组三段上部泥岩中白云岩夹层的成因，基于野外地质调查和室内岩石学、化学分析，认为白云岩夹层形成于海水-岩石反应作用下，主要与地下流体以及岩石的化学组成、温度、压力等因素有关。本文对于生 Introduction: Theoccurrenceofinterbeddedlimestoneandshaleiscommoninsedimentarybasinsworldwide.Understandingtheoriginoftheseinterbedsprovidesimportantinsightsintothedepositionalenvironment,diageneticprocesses,andhydrocarbongenerationpotentialofthesedimentarybasins.Inthisstudy,weinvestigatetheinterbeddedlimestoneandshalewithintheuppersectionofthethirdmemberoftheShahejieFormationinthewesternpartoftheDongyingDepression,whichislocatedintheBohaiBayBasinineasternChina.TheShahejieFormationiscomposedofaseriesoflacustrineanddeltaicsedimentaryrocksthatweredepositedduringthePaleocene-Eocene. Methods: Thestudyareacoversatotalof28squarekilometersandislocatedinthewesternpartoftheDongyingDepression.Fieldworkincludedgeologicalmappingandsamplingoftheinterbeddedlimestoneandshale.Laboratoryanalysisofthesamplesincludedthin-sectionpetrography,X-raydiffraction,scanningelectronmicroscopy,andtraceelementgeochemistry. Results: TheinterbeddedlimestoneandshalewithintheuppersectionofthethirdmemberoftheShahejieFormationinthewesternpartoftheDongyingDepressionareinterpretedtohaveformedthroughseawater-rockinteraction.Theinterbedsarecomposedofcarbonate-richrockswithvaryingamountsofshaleandsiltstone.Petrographicanalysisindicatesthatthelimestonesaremicriticandcontainvaryingamountsofbioclasts,whiletheshalesarecomposedofclaymineralssuchasilliteandsmectite. Theinterbeddedlimestoneandshaleexhibitarangeoftraceelementconcentrations,whichsuggeststhattheyformedunderdifferentchemicalconditions.ThelimestoneintervalshavehigherSrandMgconcentrationsrelativetotheadjacentshales,indicatingthattheywereprecipitatedinmarineenvironmentswithhighersalinitiesandalkalineconditions.ThelowerconcentrationofSrandMgintheshalesindicatesthattheyweredepositedinmorefreshwaterenvironments.Geochemicalanalysisofthelimestonesshowsthattheyhavehighδ13Cvalues,whichindicatesthattheywereprecipitatedduringape