沉積學概論課件來自

NileRiverdelta,asseenfromEarthorbit.TheNileisanexampleofawave-dominateddeltathathastheclassicGreekdelta(Δ)shapeafterwhichriverdeltaswerenamed.三角洲沉積(Deltaic河流入海（湖）的河口區(qū)，水流TheconceptofadeltadatesbacktoHerodotus(c.400BC),whorecognizedthatthealluvial inatthemouthoftheNilehadtheformofthecapitalGreekletterΔ.ThefirststudyofancientdeltaswasthatofGilbert(1885),whodescribedPleistocenefresh-watergravellydeltasinLakeBonneville,Utah.Gilbertrecognizedabasicthreefoldsubdivisionofdeltadepositsintotopset,foreset,andbottomsetunits,aterminologythatremainsinusetothisday

三角洲的三層結構（據(jù)Small-scaledeltasystemprogradingintoPliocenelacustrinesuccession,withclearGilbertdeltatopset–foreset–bottomset(T–F–B)unit.StowDAV,2005,showingmarlstonealternationnearbase(pro-deltadeposits),andlargescalecross-stratificationincentreandupperview(Gilberttypeforesets,F,twounits).StowDAV,2005,Braid-deltachannelsandstoneswithlarge-scaleGilbertdeltaforesets(F)overbottomsets(B).StowDAV,2005,Detailofpro-deltasuccession,showingreversetonormalgrading(arrows)of StowDAV,2005,Barrell(1912)

“…adepositpartlysubaerialbuiltbyariverintooragainstabodyofwater.Theouterandlowerpartsarenecessarilyconstructedbelowwaterlevel,butitsupperandinnersurfacemustbelandmaintainedorreclaimedbytheriverbuildingfromthesea.Adelta,therefore,consistsofacombinationofterrestrialandmarine,oratleastlacustrinestrata,anddiffersfromothermodesofsedimentationinthisrespect” Ourunderstandingofmoderndeltasdevelopedrapidlyduringthelastfiftyyears,beginningwithworkontheMississippiDeltapublishedinthe1950sandearly1960s(e.g.,Shepardetal.,1960).Scruton(1960)recognizedthatdeltasareessentiallycyclicinnatureandconsistofaprogradational,“constructivephase”usuallyfollowedbyathinnerretrogradational“destructivephase”coincidingwithdeltaabandonment.Healsoillustratedavertical“deltaicsequence”(Scruton,1960)ofcoarsening-andsandierupwardfaciesrelatedtoprogradationofbottomset,foreset,andtopsetstrata.Deltasoccuratawidevarietyofscalesrangingfromcontinental-scaledepositionalsystems,suchasthemodernMississippidelta,withanareaofabout28,500km2,tocomponentsofotherdepositionalsystemssuchasbayheaddeltaswithinestuarineorlagoonalsystems.

Alargebodyofresearch,begunwithadventofseismicandsequencestratigraphy,emphasizestheevolutionofmodernandQuaternarydeltasinthecontextofrelativesea-levelchanges.representationshowsfaciesboundariesasundulatingbutapparentlysharp.Arrowsindicatedirectionofprogradation.Mostmoderndeltastudiesstillshowfaciescontactsinthismanner.Correctrepresentationoffaciesboundariesversustimelines.Bedboundariesaremorelikelytofollowthetimelines(FromGaniandBhattacharya,2005).Deltashavebeendefined“discreteshorelineprotuberancesformedwhereriversenteroceans,semi-enclosedseas,lakesorlagoonsandsupplysedimentsmorerapidlythantheycanberedistributedbybasinalprocesses”(Elliott,1986). alSuspendedmudsarecarriedoutintothereceivingbasinasabuoyantplume,resultinginlowerdepositionalslopes.Riverbedloadtypicallystopsmovingatthepointofflowexpansion,formingthemouthbar,whereassuspended-loadmudscontinuetobetransportedbasinward. aldeltasarethuscharacterizedbyadistinctseparationofthefrictioninducingsandybedloadfromthebuoyantsuspendedmuddyload.Dependingonplumestability,muddyplumesmayproducesubaqueousdistributarychannelswithwelldevelopedleveesthatmaycausethemouthbarandchanneltoformelongatebar-fingersands(Fisk,1961).Thedowndriftmarginsofmuddydeltasystemsarecommon,suchasthechenierinoftheLouisianacoast,whichliesdowndriftofthemightyMississippioutflow.TheCamaupeninsulaisalargelymuddyaccumulationthatformsthedowndriftwingoftheMekongdelta.Nearly50%ofmudtrappedinthemodernOrinicodeltainVenezuelaisactuallyderivedfromtheAmazon.TheAmazonmudsarethuscarriedalongtheshelfforadistanceofover1000km.MudfromthemodernPodeltahasalsobeentrackedforseveralhundredkilometerstothesouthalongtheAdriaticcoastLocationandbathymetricmapoftheBohaiSea(BS),NorthYellowSea(NYS),SouthYellowSea(SYS),andEast (ECS).TheYellowSeaWarmCurrent(YSWC)andtheYellowSeaCoastalColdCurrent(YSCCC).Shadedareasrepresentlocationofthe mudwedgeandothermudpatchesintheYSandECS.Waterdepthinmeters.J.P.Liu.,超密度三角洲（慣 控Infreshwaterlakes,sedimentconcentrationslessthan1kg/m3alconditionswhereassedimentconcentrationsgreaterthanthedensitycausedbydissolvedsaltinseawater(about35to45kg/m3)mayberequiredtogenerate alflowsinmarinesettings.alCretaceousDunveganFormation,Alberta,CanadaTheresultingdepositof flowiseitherafluidmud, sandygradedbed

sandstone,Utah,U.S.A等密度三角洲（摩 控 alsettingstheremaybeagreaterdegreeofmixingbetweentheriverandstandingbodyofwater.Thesesituationsarecommoninfresh-waterdeltasandcanalsooccurinmarinesettingswheretheamountofbedloadisLenaRiverdelta(RussianArctic)showsnumerousordersofbranchingwithmanytensofDeltascomprisethreemaingeomorphicenvironmentsofdeposition:thesubaerialdelta in(whereriverprocessesdominate),thedeltafront(thecoarser-grainedareawhereriverandbasinalprocessesin ct),andtheprodelta(primarilymuddy).平海平面River-dominatedLenaRiverdelta(RussianArctic)showsnumerousordersofbranchingwithmanytensofterminaldistributarychannels.2征。但較平原的 分流河口砂壩（微相 構造： 構造：水平層理為主。 尼西 MorphometricsubdivisionsoftheMahakamdelta,tan,Indonesia.Notethatmuddysubaqueousforesetisreferredtoasthe“deltafront”（注意 Pervasivelybioturbated,non-deltaicsandymudstone,CretaceousDunveganFormation,Scalebaris3ReadingandCollison(1996)的Postma(1990)Dalrympleetal.(1992)DeltatriangleofGalloway(1975)asextendedbyDalrympleetal.(1992)toreflectchangesinsedimentsupply(fromReadingandCollinson,1996).ReadingandCollinson的分類Classificationofshallow---marineshorelinesystemsbaseduponthelong---termmovementoftheshorelineandthekeydepositionalprocesses.ModifiedafterBoydetal.(1992).Fig.3.Faciesmodelsforshorefaceanddeltaicsystemshighlightingtheterminologyusedinthiswork.Obliquesa shoreline( Earth2007;fieldofviewisc.30kmwide).Theviewincludesshorefacesandwave-dominateddeltas.Obliquesa liteviewoftheBalizelobeoftheMississippi,amodernriver---dominateddelta( Earth2007;fieldofviewisc.30kmwide).Postma(1990)Typicalcoarsening-upwardfaciessuccessionsformedasaresultofprogradingdeltaiclobesandmouthbars.Mississippiexampleshowsacompositeofathickermouth-barsuccessionbelowandthemoreirregularbay-fillsuccessionsabove.Rhoneexample(left)showsprogradationofamouthbarforminganasymmetricalcoarsening-upwardsuccession,whereasRhoneexample(right)showstruncationbyadistributarychannel,andhasamoresymmetricalprofile.

yearsBPyears St.Bernard2800-years4600yearsBP

yearsBP

quemine750-500yearsBalize550ThelobesoftheMississippiRiverDeltathatformedoverthousandsofyearsduetodeltaicswitching.、、prodeltamudstonesoftheKavikFormation,PrudhoeBayField,Alaska,U.S.A

deformedsandstonebedoverlainbyparallel-laminatedtorippleddeltafronts ysinterpretedasdistaldeltafront,sedimentgravity-flowdeposits,CretaceousFerronsandstone,Utah,CoresandwelllogsfromthemodernMississippideltashowavarietyofupward-coarseningfaciessuccessions.Sharp-based,blockier-appearinglogpatterns(e.g.,profiles5and8)lieinthemoreproximalportionsofthedeltalobe.Interlobesuccession(profile1)isirregular.FromColemanandPrior(1982). SlopeinbasinInterdistributary-bayfillinariver-dominateddeltalobeintheDunveganFormation(Cretaceous,Alberta,Canada),showingthinirregularcyclesandoverallincreaseinproportionofnonmarinefaciesupwards.AfterBhattacharyaandWalker(1991).北部石炭紀（Elliott，1975）2Blockdiagramillustratingthehypothesizedthree-dimensionalfaciesarchitectureofanasymmetricdelta.Significantprodeltamudstonesareassociatedwithdowndriftportionofthedeltawheresandybarrier-barcomplexesoccurwithinlagoonalmudstonesandbayhead-deltadeposits.Theupdriftsideofthedeltacomprisesasandybeach-ridge in(fromBhattacharyaandGiosan,2003).Faciesphotosofwave-dominatedshorefaceoftheGallupSandstone,NewMexico,U.S.AClose-upofbasalsandstonesshowingpervasivebioturbation.Largemud-rimmedburrowisAsterosoma.SmallersandblebsinmudrimareChondrites.

Mud-pellet-linedOphiomorphaburrowsincross-beddedshorefacesandstonesinmiddlepartofcliff.Thesesuggestawave-dominatedshorefacecharacterizedbytheSkolithosichnofacies.Bidirectionalcrossbeddingintheuppershoreface.ToprowrepresentslowerfluvialdischargecomparedtobottomroToprowrepresentslowerfluvialdischargecomparedtobottomroAsymmetryindexrepresentstheratiooffluvialsedimentdischargetoalongshoresedimenttransportrate.Bifurcationisinhibitedinwave-dominateddeltasbecausetheriverisunabletoprogradeintothebasinasrapidly.Thiseffectivelyallowstherivertomaintainitsgrade,whichinturninhibitsavulsion.Wave-dominatedcoastlineassociatedwiththeParaíbadoSul,Braziliancoast.Podelta,Ebrodelta,Comparisonofdelta-frontsuccessionsinriver-dominated,wave-influenced,andwave-dominateddeltasintheUpperCretaceousDunveganFormation,Alberta,Canada.AfterBhattacharyaandWalker(1991).Theriver-dominatedsuccessionisthemostirregular.Basalmudstonesareincreasinglybioturbatedwithdecreasingfluvialinfluence.Environmentsa