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OCEANOGRAPHY
4.MarineSediments-part1
notesfromtextbook,integratedwithoriginalcontribu7ons
AlessandroGrippo,Ph.D.
DredgingoftheharborchannelinMarinadelRey,CA,2012©AlessandroGrippo
ChapterOverview
• MarinesedimentscontainarecordofEarthhistory
• Marinesedimentsprovideavarietyofimportantresources
• Marinesedimentshaveavarietyoforigins
whataresediments?
• therearethreekindofrocks– igneous(fromcoolingofmagma
orlava)– metamorphic(fromexposureto
hightemperaturesand/orpressures)
– sedimentary(fromcementa7onofrockfragmentsand/orprecipita7onfromasolu7on)
• allrockscanbeweathered,producingsediments– mechanicalweathering– chemicalweathering
mechanicalweathering– allphysicalprocessesthatbreakdownrocksinsmallerfragments
– fragmentsareiden7fiedbytheirsizeasgravel,sand,silt,andclay(siltandclaytogetheraredefinedasmud)
chemicalweathering:ac7onofoxygen
• allchemicalprocessesthatchangethecomposi7onofrocks
• twoagents:oxygenandacids
• theac7onofoxygenintheatmosphereandinwatercausesironmineralspresentinrocksto“rust”(ironoxides)
• 4Fe+3O2!2Fe2O3(hema7te)
chemicalweathering:ac7onofacids
• theac7onofacids“corrodes”rocksandturnsthemintoquartz,clayminerals,andionsinsolu7on
• Quartz– averycommon,resistantmineral– typicalcomponentofsandatthebeach
• ClayMinerals– averycommonbyproductofweathering– havespecialproper7es:theyareflat,theyabsorbwaterand
ions,they“swell”,• IonsinsoluKon
– anythingmineralthatcanbedissolvedinwater(Ca2+,Mg2+,Fe2+,Na+,K+,CO3
2-,etc.)
whatisnext?
• nowwehaveabunchofloosefragmentsatearth’ssurface,andionsinsolu7on
• theyarepickedup(eroded),movedaround(transported)andrese\ledsomewhereelse(deposi7on)by:– water(rivers)– wind– glaciers– directlybyrockfall/landslides
sand is picked up
then it is moved aroundby rivers, wind, waves;
it gets more weathered
it is then deposited(but it can also be picked up again)
it will get finally buriedby more recent sediment
the weight compacts the sand
water enters the pores
ions in solution are released (cement),turning the sand into a sandstone
EXAMPLEerosion
transportation
deposition
burialcompactioncementation
(lithification)}
andwhataboutionsinsolu7on?
• theyneedto“stayhydrated”(ionssurroundedbywatermolecules)
• ifthereisnotenoughwater,ionscrystallizeandformrocks(orcement,asseenbefore)
• maintypes:– carbonates(mostcommontype;limestone)– siliceousrocks(richinsilica;chert)– evaporites(formindryenvironments–notintheocean;halite,orrocksalt,gypsum)
MarineSediments• Intheend,manysedimentsareproducedonland
(lithogenoussediments)
• Whilesomeofthesearedepositedonland,mostarecarriedtotheocean(marinesediments)
• Someothertypesofsediments(biogenousandhydrogenous)areproduceddirectlyintheocean
• Whatevertypeofsedimentreachesorisproducedintheoceanwouldeventuallyse\lethroughthewatercolumn
• OceanographersdecipherEarthhistorythroughstudyingsediments
4.1–HowAreMarineSedimentsCollected,andWhatHistoricalEventsDoTheyReveal?
• Marinesedimentsoftodaycanbecollecteddirectlyfromtheoceanbo\om– difficulttogetto
• Marinesedimentsofthepastthathaveturnedintosedimentaryrockscanbefoundinlandoutcrops– easiertogettobutsca\eredsamples
collec7ngMarineSediments
• dredge• gravitycorer• rotarydrilling– NSFfundedaprogramforborrowingdrillingtechnologiesfromtheindustry
– Fouroceanographicins7tu7ons(Scripps,Rosens7el,WoodsHole,Lamont-Doherty)unitedtoformJOIDES(JointOceanographicIns7tu7onsforDeepEarthSampling)
– OtherschoolslaterjoinedJOIDES
collec7ngMarineSediments
• JOIDESprograms– DSDP(DeepSeaDrillingProject)
• 1966,GlomarChallenger,sampledto6000mofdepth• evidenceofspreading(ageofsediment,thicknessofsediments,magne7creversals)
– ODP(OceanDrillingProgram)• 1975,1983becameinterna7onal,underTexasA&M• broaderobjec7veofdrillingclosetoshelf• in1985,JOIDESResolu7onreplacedGlomarChallenger• newshipcandrillupto2100mbelowseafloor
GlomarChallenger&JOIDESResolu7on
• IODP(IntegratedOceanDrillingProgram)– 2003,thenin2013asIntegratedOceanDiscoveryProgram– mul7plevessels,includingChikyu– collec7onofsedimentscoresfromallovertheworld
Chikyu
• “PlanetEarth”• howdowedrill– (www.youtube.com/watch?v=yuu0QcnOVbo)
ThedrillingsystemofChikyu
Upperler:drillingpipesonthedeckofJOIDESResolu7on
Upperright:diamonddrillingbit(adrillingbitwouldnotgiveusacore,butrather“rockcusngs’,orfragments
Bo\omler:analysisofhalvedcoresonboardtheJOIDESResolu7on
EnvironmentalCondi7onsRevealedbyMarineSediments
• MarineSedimentspreservematerialsthatexistedintheoverlyingwatercolumns
• Thesematerialsarefunc7onofthecondi7onsoftheenvironment
• Analysisofcoresprovidesuswithinfoabout:– ancientseasurfacetemperature– abundanceofmarinelifeandmajorex7nc7onevents– atmosphericwindsandvolcanicerup7ons– oceancurrentpa\ernsandchangesinEarth’sclimate– movementoftectonicplates
Paleoceanography
• Thestudyofhowocean,atmosphere,andlandinterac7onshaveproducedchangesinoceanchemistry,circula7on,biology,andclimate
• Marinesedimentsprovidecluestopastchanges
Marinesedimentsalsoexistonland:turnedintorocks,andbroughtabovesealevelbyplatetectonics
TheseareturbiditesfromtheGreatFallsoftheMissouri,bythecityofGreatFalls,Montana(atthisloca7ontheexplorerLewisandClarkcouldnotproceedanyfurtherontheriver,andhadtostarttheirportageontheGreatPlains)
©AlessandroGrippo
MarineSedimentClassificaKon
• Classifiedbyorigin– Lithogenous–derivedfromland(lithos=rock)
• gravel,sand,silt,clay• ionsinsolu7on
– Biogenous–derivedfromorganisms• shells,reefs,animalandalgalstructures
– HydrogenousorAuthigenic–derivedfromwater• formingchemicallyintheocean
– Cosmogenous–derivedfromouterspace• cosmic“dust”
4.2–WhatAretheCharacterisKcsofLithogenousSediment?
• Erodedrockfragmentsfromland• Alsocalledterrigenous• Reflectcomposi7onofrockfromwhichderived• Producedbyweathering
– Breakingofrocksintosmallerpieces
• Par7clesareeroded,transported,deposited• Carriedtowardstheoceanby:
– Streams,Wind,Glaciers,Gravity
• Greatestquan7tyfoundaroundcon7nentalmargins– mostlyonshelves– alsoincon7nentalrisesortrenches
Composi7onandTexture• Reflectcomposi7onofrockfromwhichderived• Coarsersedimentsclosertoshore• Finersedimentsfartherfromshore• Mainlymineralquartz(SiO2)
• Grainsizepropor7onaltoenergyintheenvironmentofdeposi7on
• Grainsizesor7ng– Indica7onofselec7vityoftransporta7onanddeposi7onprocesses
• Texturalmaturity– Increasingmaturityif
• Claycontentdecreases• Sor7ngincreases• Non-quartzmineralsdecrease• Grainsaremorerounded(abraded)
Wheredowefindthesesedimentsinouroceans?
• Marinesedimentarydepositscanbefoundinvirtuallyallplacesontheoceanfloor,evenifsome7mesinveryminorpercentages.
• Thecanbecategorizedaseitherneri7corpelagic
• NeriKcDepositsarearefoundoncon7nentalshelvesandinshallowwatersaroundislands– usuallycoarse-grained(sands)
• PelagicDepositsarefoundindeep-oceanbasins– usuallyfine-grained(siltsandclays)
Neri7cDeposits• Beachdeposits– Grainsofallkindsbroughttothecoastbyrivers– Weatheringslowlymodifiesgraincomposi7onintoquartz-richsands
– Wavemo7oncausestransporta7on
SloughandbeachinGoleta,CA
©AlessandroGrippo
• Con7nentalshelfdeposits– Relictsediments:leroverasunderwaterformerbeachsediment
– formedduringthelast(oranyprevious)iceagepeak,thenfloodedduringtheinterglacial
– some7messhowingabovesealevelasbarrierislands
• Turbiditedeposits– SandsandmudsinCon7nentalRise– Gradedbedding
• Glacialdeposits– Highla7tudecon7nentalshelf– Currentlyformingbyiceraring(icebergscarryingrocksintoocean,calleddropstones)
Above:anicebergcarryingsedimenttotheoceaninPortageLake,ChugachNa7onalForest,ChugachMountains,Alaska.Photo©USGS
Right:adropstoneincross-sec7onalview,NamibiaPhoto©DavidL.Reid
bothimagesfrom:h\p://serc.carleton.edu/NAGTWorkshops/sedimentary/images/dropstones.html
PelagicDeposits
• Fine-grainedmaterial• Accumulatesslowlyondeepoceanfloor• Pelagiclithogenoussedimentfrom
– Volcanicash(volcanicerup7ons)– Wind-blowndust– Fine-grainedmaterialtransportedbydeep
oceancurrents
• AbyssalClay– Atleast70%claysizedpar7clesfrom
con7nents– Redfromoxidizediron(Fe)– Abundantifothersedimentsabsent
Rhythmicalterna7onsofdeep-marine(pelagic)biogenous(whitelimestones)andterrigenous(redabyssalclays)sediments
MidCretaceousPiobbicoCore,Pesaro-Urbino,Italy
©AlessandroGrippo
• endofpart1