鶯-瓊盆地大型下切谷和海底重力流體系的沉積構(gòu)成和發(fā)育背景Abstract:

TheYing-QiongBasinislocatedinthewesternSouthChinaSea,whichisatypicalpassivecontinentalmarginbasin.Thelarge-scaleincisedvalleyandsubmarinegravityflowsysteminthisbasinhavebeenextensivelystudied.ThispaperprovidesacomprehensivediscussiononthesedimentarycompositionanddevelopmentbackgroundoftheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasin.Basedonthedataobtainedfromseismicdataanddrillingcores,wesummarizedthesedimentaryfeatures,depositionalenvironmentandcontrollingfactorsofthesegeologicalstructures.

Introduction:

TheYing-QiongBasinislocatedinthewesternSouthChinaSea,coveringanareaofabout50,000km2.DuetothetransgressionofthesealevelandthetectonicsubsidenceduringthelateOligoceneandMiocene,thebasinwasrapidlyfilledwiththicksediments.Thebasinischaracterizedbylarge-scaleincisedvalleyandsubmarinegravityflowsystemwhichhaveattractedalotofattentionfromgeologists.Thestudyofthesestructurescanprovideimportantinformationaboutpaleogeography,paleoclimate,andhydrocarbonreservoirsinthebasin.

Sedimentarycompositionoftheincisedvalley:

TheincisedvalleyintheYing-QiongBasinisalarge-scaleerosionalstructuredevelopedinthepaleo-hillofthepre-riftstrata.Theshapeofthevalleyisasymmetricalwithadepthofupto400mandawidthof2-6km.Theincisedvalleycanbedividedintothreeparts:theuppervalley,themiddlevalley,andthelowervalley.Thesedimentarycompositionoftheincisedvalleyiscomplexandvariesindifferentparts.

Intheuppervalley,thesedimentaryfaciesaremainlycomposedofconglomerates,sandstones,andsiltstones.Coarse-grainedsedimentsaredepositedinthemainchannel,whilefine-grainedsedimentsaredepositedinthelaterallevees.Themaindepositionalenvironmentisabraidedriversystem.

Inthemiddlevalley,thesedimentaryfaciesaremainlycomposedofsiltstonesandmudstones,whichindicatesameanderingriversystem.Thesedimentarystructureismainlyhorizontalbedding,withafewverticalbeddingandcross-bedding.

Inthelowervalley,thesedimentaryfaciesaremainlycomposedofmudstones,indicatingaquietanddeep-waterenvironment.Thesedimentarystructureismainlyparallelbedding.

Sedimentarycompositionofthesubmarinegravityflowsystem:

ThesubmarinegravityflowsystemisdevelopedintheslopeandbasinflooroftheYing-QiongBasin.Thesystemcanbedividedintotwoparts:thefandeltadepositionalsystemandthesubmarinefansystem.Thesedimentarycompositionofthesubmarinegravityflowsystemismainlycomposedofsandstones,siltstones,andmudstones.

Thefandeltadepositionalsystemiscomposedofsandstones,withathicknessofupto500m.Thesedimentarystructureismainlycomposedofcross-beddingandparallelbedding.ThefandeltadepositionalsystemisthemainhydrocarbonreservoirintheYing-QiongBasin.

Thesubmarinefansystemiscomposedofsiltstonesandmudstones,withathicknessofupto1000m.Thesedimentarystructureismainlycomposedofparallelbedding,laminated,andripplestructures.

Developmentbackgroundoftheincisedvalleyandthesubmarinegravityflowsystem:

ThedevelopmentoftheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasiniscloselyrelatedtothetectonicevolutionandsealevelchanges.Duringthetectonicsubsidenceperiod,thebasinwasfilledwiththicksediments,formingaplatform-likestructure.Duringthesealevelriseperiod,alargeamountofsedimentwasdepositedontheplatform,formingadelta.Duringthesubsequentsealevelfallperiod,therivercutthroughthedeltaandformedtheincisedvalley.

Thetimeoftheformationofthesubmarinegravityflowsystemisrelatedtothetectonicactivityinthebasin.Duringthetectonicsubsidenceperiod,theslopewassteepandunstable,andthefandeltadepositionalsystemwasdeveloped.Duringthelatetectonicsubsidenceperiod,theslopebecamegentleandstable,whichledtothedevelopmentofthesubmarinefansystem.

Conclusion:

Thelarge-scaleincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasinhavedifferentsedimentarycompositionsanddevelopmentbackgrounds.Theincisedvalleyismainlycomposedofconglomerates,sandstones,siltstones,andmudstones,whichrepresentdifferentdepositionalenvironments.Thesubmarinegravityflowsystemismainlycomposedofsandstones,siltstones,andmudstones,whicharerelatedtothetectonicevolutionandsealevelchangesinthebasin.Thestudyofthesedimentarycompositionanddevelopmentbackgroundofthesegeologicalstructurescanprovideimportantinformationforunderstandingthepaleogeography,paleoclimate,andhydrocarbonreservoirsinthebasin.Controlfactorsoftheincisedvalleyandthesubmarinegravityflowsystem:

ThedevelopmentoftheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasinisprimarilycontrolledbytectonicmovements,sealevelchanges,andsedimentsupply.

Tectonicmovements:

TheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasinaremainlycontrolledbythetectonicmovementsoftheSouthChinaSeabasin.DuringthelateOligoceneandMiocene,theYing-QiongBasinunderwentaphaseofrapidsubsidence,whichcreatedfavorableconditionsfortheformationoftheincisedvalleyandthesubmarinegravityflowsystem.Thetectonicmovementsofthebasinalsoplayedakeyroleinshapingthemorphologyoftheincisedvalleyanddeterminingthelocationandconfigurationofthesubmarinefansystem.

Sealevelchanges:

SealevelchangesalsoplayedacrucialroleintheformationoftheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasin.Duringthesealevelriseperiod,alargeamountofsedimentwasdepositedontheplatform,formingadelta.Duringthesubsequentsealevelfallperiod,therivercutthroughthedeltaandformedtheincisedvalley.Thesedimentarycompositionoftheincisedvalleyandthesubmarinegravityflowsystemisadirectreflectionofthesealevelchanges.

Sedimentsupply:

SedimentsupplyisanotherimportantfactorintheformationoftheincisedvalleyandthesubmarinegravityflowsystemintheYing-QiongBasin.Thesedimentsupplydeterminesthevolumeandtypeofsedimentdepositedinthebasin.Theincisedvalleyandthesubmarinegravityflowsystemwereformedduringaperiodofhighsedimentsupply,whichwastheresultofthetectonicsubsidenceinthebasin.

Implicationsforhydrocarbonexploration:

TheYing-QiongBasinisanimportanthydrocarbon-bearingbasinintheSouthChinaSea.Theformationoftheincisedvalleyandthesubmarinegravityflowsystemhasimportantimplicationsforhydrocarbonexplorationinthebasin.

ThefandeltadepositionalsysteminthesubmarinegravityflowsystemisthemainhydrocarbonreservoirintheYing-QiongBasin.Thedepositionandpreservationofhydrocarbonsinthefandeltadepositionalsystemarecloselyrelatedtothesedimentaryenvironmentanddepositionalhistory.Thestudyofthesedimentarycompositionanddepositiona