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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