沉積學(xué)概論課件來自001緒論

用戶名：年月 社發(fā)李顯達(dá)攝達(dá)境內(nèi)河

積巖層或礦層形成的機(jī)制、作用過程、環(huán)境與背景，以及沉積作用的地史演化，沉積作用的功力學(xué)過程和沉積盆地分析等這樣一些很本性的理論問題，以及與這些問題密切相關(guān)的礦產(chǎn)頂測(cè)和環(huán)(1913.7.19-

例

外。 例 20世紀(jì)60年代以來，河流地貌學(xué)提出了一整套計(jì) 對(duì)古代湖泊沉積的研究，要求充分了解現(xiàn)代湖泊的水動(dòng)力條件和沉積物散布過程。這就涉及 例如具水象 如具水象例 儲(chǔ)層的孔隙度和滲透性與它生成時(shí)的沉積環(huán)境 牽和沉積物重力流、波浪和波理論、底型和流 用用ErosionandCertainmodesoftransportphysicallymodifyandphysicallyandchemicallysortparticlesenroute.SizesortingbysurfacewaterrunoffCurrentofagivenvelocitycangenerallycarryallnoncohesiveparticlessmallerthanacriticalsize;sincecurrentvelocitydropswithdecreasingslopesfrommountainstolowlands,itfollowsthatsedimentsevolvefrompoorlysortedandcoarse-grainednearsourcetowell-sortedandfinergrainedwithincreasingtransportErosionandChemicalsortingwithincreasingtransportdistanceislikeacontinuationofchemicalweatheringduringintermittenttimeswhenparticlesaretemporarilydepositedbeforefurthertransport;moststablemineralsaretransportedthefurthest.Texturesofparticlesaremodifiedbyabrasionduringwindorwatertransport.Closetosourceparticlesareangular;farfromsourceparticlesarerounded.CHAPTERFELIXM.EXNERANDTHEORIGINSOFFelixMariaExnerwasanAustrianresearcherwhowasactiveintheearlypartofthe20thCentury.Hismainareaofinterestwasmeteorology.Atsomepointhebecameinterestedintheformationofdunesinrivers(Exner,1920,1925;seealsoLeliavsky,1966).Inthecourseofhisresearchonthesubject,hederivedandemployedoneversionofthevariousstatementsofconservationofbedsedimentthatarenowreferredtoas“Exnerequations.”Inaddition,hemadeanimportantearlycontributionto1Dnonlinearwave

DunesintheMississippiRiver,NewOrleans,USAImagefromLUMCONwebDUNEDunesarerhythmicbedformsthatareoftenseenonthebedsofrivers.Theupstream(stoss)sideofadunehasagentleslope,whereasthedownstream(lee)sidehasasteepslope.Thischaracteristicasymmetryallowsthedeterminationofflowdirection.Intheimageontheright,theflowdirectionisfromtoptobottom.Dunesmigrateinthesamedirectionastheflow,i.e.downstream.

MagnifiedviewofpreviousDUNESINTHERHINEDELTA,THEImagecourtesyA.WilbersandA.DUNESINTHEDunesinachannelatSt.AnthonyFallsLaboratory,UniversityofMinnesota,USA

DunesinachannelatTsukubaUniversity,Japan.ImagecourtesyH.ANEXAMPLE:THEEASTPRAIRIERIVER,ALBERTA,Riverstraighteningwaspopularinthe1960’sand1970’s.Thegoalwasfloodprotection:thesteeperslopeofthestraightenedreachallowedhigherflowvelocities,andthusconveyanceofthesamedischargeatalowerdepth.Thisshort-termbenefitwasoftenoutweighedbythelong-termpatternofaggradationanddegradationinducedbystraightening.TheEastPrairieRiverprovidessuchanexample.SeeParkerandAndres(1976)formoredetails.Degradingupstream

EastPrairieRiver,Alberta,CanadaImagescourtesyD.AndresTHESTRAIGHTENEDWESTANDEASTPRAIRIERIVERS,ALBERTA,ImagefromEastPrairieWestPrairieEventuallytransportedparticlesanddissolvedionsreacha cewheretheycanbepermanentlydepositedandaccumulated.Thisissedimentation.Thesedimentaryrocksthatresultfromthisaccumulationarecontrolledbyandrecordthesedimentaryenvironmentwheretheyweredeposited.Weinterpretancientsedimentaryrocksbycomparisontomodernenvironmentswherewecanobserveongoingsedimentaryprocessesandrelatethemtothecomposition,texture,andstructureoftheresultingrocks.SedimentaryCharacterofbedding,fromsimplehorizontallaminaetocross-bedding,ripples,soft-sedimentdeformation,orbioturbated.Cross-beddingindicateshighandunidirectionalcurrentvelocity,oftenwindsinterrestrialsettings,formingsanddunelee-slopes.Ripplemarksrecordback-and-forthactionbywavesinMudcracksdemonstratedrying-outofathinlayerofsedimentfineenoughtohavesignificantcohesion.Definiteproofofterrestrialsettingorveryshallowwatermarginalmarine.Whataboutthisstructure?(Hint:itisnotthesurfaceoftheMoon)SedimentarySoft-sedimentdeformationindicatesslum compressionoflayersbeforecompletelithification.Bioturbationistheverticalmixingofsedimentarylayersbyburrowingorganisms.Evidenceofsuchactivitycanbe onbeddingsurfacesastracefossils.Indicativeofwaterdepth,availabilityofnutrientsandoxygen,etc.SedimentaryGradedBedding:sortingofparticlesizeswithinbedsindicatestimedependenceandhenceprocessofAnenvironmentinwhichaepisodesofhigh-energytransportgivewaytoperiodsoflow-energytransportgivesnormalgradedbeds:Alluvialsettings,withwanderingchannelsthatfillupandeoverbankdepositsContinentalslopeswithturbidityCarbonateMostcarbonaterocksarebiochemicalsediment,madeupofthebodypartsofcalciteoraragonite-precipitatingorganismsDeep-seacarbonateoozeismadeofforam ReefcarbonatesaremadeofcoralreefsStromatolitesareformedbycarbonateprecipitationbymicroorganismsSedimentaryenvironments:I.Fluvial(riversandstreamsofallkindsandAlluvialWesawalluvialfansonthefieldtrip.Theyformwheredrainagesexitmountainfrontsontosurroundinglowlands.Individualfansmaymergetoformapiedmontslope(likeInaridregionslikeCalifornia,sedimenttransportonalluvialfansisdominatedbydebrisflowslikemudslidesandlandslides,andbyperiodicstreamflowsthatdividethefanintochanneldeposits,overbankdeposits.Sortingispoor,butincreasesdownstream;grainsizedecreasesdownstream;sedimentsareoftenoxidizedandpoorinfossilsororganicmatter.Sedimentaryenvironments:RiverRiversareclassifiedintomeanderingorbraided,mostoften.Braidingisfavoredbyhighsedimentload,steepgradients,variablestreamflow,andunstablepoorlyvegetatedbanks.MeanderingisfavoredbytheSedimentaryenvironments:b.RiverMeanderingriversdevelopinafairlyregularpatternbychannelmigration,leavingapredictablesequenceofcyclic,fining-upwardsedimentarydeposits.Braidedriverdepositsaremorechaoticleavesomewhatrandomdeposits,sincechannelswanderrandomlyacrosstheflood Sedimentaryenvironments:II.DesertDesertsbasinsarebasicallyalluvial yas,andsanddunes.Theymaybedominatedbywindtransportorbyfluvialtransportrestrictedtorare,seasonalstormsandfloodsAlluvialfansaredebrisflowandstreamflowdeposits(asabove). yasaredryorseasonallakebedsdominatedbyevaporitesorfine-grainedandfinelylaminatedmudstonesandsiltstones.Sanddunesleavefascinatingcross-beddedtomassivesandstonedeposits.depositionofdustmakesthickdepositsofloess.Sedimentaryenvironments: eachwinter)areoftenp low-energylacustrinedepositionalenvironmentsascountableannuallayersorvarves.Sedimentaryenvironments:IV.Glacialandperi-Wesawsomeofthetypicalvalleyglacierdepositsonthefieldtrip.Butthereismoretotheglacialenvironmentthanmorainesandtills.Glaciersgeneratecharacteristicriverdeposits(frequentlybraided)andlakedeposits(frequentlyvarved)whentheyterminateonland,andcharacteristicmarinedepositswhentheyterminateintheocean(dropstones).Theymovelargeboulders,buttheyalsogeneratehugeamountsofveryfinerockflourthatendsupasmudorloess.Periglacialdeposits,likemostsedimentarysequences,haveseveralfacies:abasaltilldepositedinfrontoftheglacierisoverlainbymoraines,lakesediments,glacio-fluvialdeposits,andfinallyloess.Sedimentaryenvironments:MarginalMarineI.Deltaicenvironment:Deltasformwhereverriversemptyintoorlakes.Muchoftheclasticloadcarriedtothemouthoftheriverisdepositedinarestrictedareaatornearthecoast,formingadelta.Becausedeltasprogradeoutwards,theybuilddepositswithreversegrading,coarseningupwardsasthedeltamovespastagivenlocation. saffectingsedimentationinadeltaarefluvial,tidal,andwaves,anddifferentdeltasdis yeffectsofdominancebydifferent TheMississippideltaisBothtidesandwavesareweakintheGulfofMexico,sodistributionofsedimentisdominatedbytheriveritself,whichformslong,relativelystablechannels(lifespan~1000years)witheachchannelnarrowsupwardsuntilitpinchesSedimentaryenvironments:MarginalI.DeltaicFlowatthemouthofafluvial-dominateddeltaiscontrolledbytherelativedensityofriveroutflowandambientsea-water.Dependingonriversedimentloadandtemperature(andonoceansalinityandtemperature),theflowmaybe (riveroutflowdenser),or al(riveroutflowlessdense). alflowleadstoturbiditedepositsfromsediment-richflowsalongthe alflowleadstouniform,well-sortedsedimentssinceinthiscasesettlingiscontrolledbyflocculationoffineparticles.Sedimentaryenvironments:MarginalMarineTheGanges-Brahmaputradeltaistide-dominatedAlthoughtheriveroutflowishigherandmoresediment-ladenthantheMississippi,thetidalrangeislarge(about4meters).Thistypeofdeltabreaksupintosandbarsandchannelsorientedparalleltothetidalinflow-outflowdirection.Thereisalarge,intermittentlyexposed,tidalflat.TheSaoFranciscoriverinBrazilisWave-energyhereis100timesthatattheMississippi.Sedimentsreachingthemouthoftheriverarerapidlyreworkedandredistributedbylongshorecurrentstobuildbeaches,barriers,andlagoons,similartostretchesofcoastwherenoriverisSedimentaryenvironments:MarginalAnycontinentalmarginwherethereisnotarivermouthislikelytoformabeachwithasingleshorefaceorabeach-barrierisland-lagoonAbeachproducesadistinctivelyorderedsetofrecognizablefacies,fromdunesandsthroughthesurfzone,breakerzoneandintodeeperwater.Abarriercomplexhasalagoonandoftenaswampdepositbehindthebarrier.Sedimentaryenvironments:MarginalIfasimplebeachisprograding,i.e.buildingouttoseaanddepositingnear-shorefaciesontopofdistalfacies,itmightproduceastratigraphiccolumnlikethis,coarseningupwardsandhenceclearlydistinctfromanyriverflood orcontinentalslopeKeepinmindtherelationshipbetweenthe lsuccessionofenvironmentsatanyconstanttimeacrossabeachandtheverticalsuccessionofsedimentsshowninacolumnlikethisone.Sedimentaryenvironments:MarginalEstuarineAnestuaryisapartlyenclosedbodyofwateratthemouthofariver.Itmaybepartofadelta;itmaybethelagoonbehindabarrier-island.Generally,estuariesmusthaveaconnectiontotheopenoceanatleastathightide.Theyareenvironmentsofmixingbetweenseawaterandfreshwater.Example:SanFranciscoBayTidalAwide,flatareaoflandbetweenlow-tidelevelandhigh-tidelevelisatidalflat.Thesearecommonenvironmentsfordepositionofcarbonatesandevaporites.Theymaybeassociatedwithdeltas,beaches,orestuariesSedimentaryenvironments:NeriticThistermreferstodepthsbelowwave-baseandlowtide,andabovetheshelf-slopebreak.Attimesofsealevelhighstand,whenshallowseascoverthecontinental tforms,theneriticenvironmentmaypassasignificantfractionoftheearth’sarea.Theneriticenvironmentiswherecarbonatereefsarebuilt.Oceanic

Sedimentaryenvironments:Continentalslopedepositsarecharact