Download Marine Sediments

OCEANOGRAPHY
4.MarineSediments-part1
notesfromtextbook,integratedwithoriginalcontribu7ons
AlessandroGrippo,Ph.D.
DredgingoftheharborchannelinMarinadelRey,CA,2012
©AlessandroGrippo
ChapterOverview
•  Marinesedimentscontainarecordof
Earthhistory
•  Marinesedimentsprovideavarietyof
importantresources
•  Marinesedimentshaveavarietyoforigins
whataresediments?
•  therearethreekindofrocks
–  igneous(fromcoolingofmagma
orlava)
–  metamorphic(fromexposureto
hightemperaturesand/or
pressures)
–  sedimentary(fromcementa7on
ofrockfragmentsand/or
precipita7onfromasolu7on)
•  allrockscanbeweathered,
producingsediments
–  mechanicalweathering
–  chemicalweathering
mechanicalweathering
–  allphysicalprocesses
thatbreakdown
rocksinsmaller
fragments
–  fragmentsare
iden7fiedbytheirsize
asgravel,sand,silt,
andclay(siltandclay
togetheraredefined
asmud)
chemicalweathering:ac7onofoxygen
•  allchemicalprocessesthat
changethecomposi7onof
rocks
•  twoagents:oxygenandacids
•  theac7onofoxygeninthe
atmosphereandinwater
causesironmineralspresentin
rocksto“rust”(ironoxides)
•  4Fe+3O2!2Fe2O3(hema7te)
chemicalweathering:ac7onofacids
•  theac7onofacids“corrodes”rocksandturnstheminto
quartz,clayminerals,andionsinsolu7on
•  Quartz
–  averycommon,resistantmineral
–  typicalcomponentofsandatthebeach
•  ClayMinerals
–  averycommonbyproductofweathering
–  havespecialproper7es:theyareflat,theyabsorbwaterand
ions,they“swell”,
•  IonsinsoluKon
–  anythingmineralthatcanbedissolvedinwater(Ca2+,Mg2+,
Fe2+,Na+,K+,CO32-,etc.)
whatisnext?
•  nowwehaveabunchofloosefragmentsat
earth’ssurface,andionsinsolu7on
•  theyarepickedup(eroded),movedaround
(transported)andrese\ledsomewhereelse
(deposi7on)by:
–  water(rivers)
–  wind
–  glaciers
–  directlybyrockfall/landslides
EXAMPLE
erosion
sand is picked up
transportation
then it is moved around
by rivers, wind, waves;
it gets more weathered
deposition
it is then deposited
(but it can also be picked up again)
}
burial
compaction
cementation
(lithification)
it will get finally buried
by more recent sediment
the weight compacts the sand
water enters the pores
ions in solution are released (cement),
turning the sand into a sandstone
andwhataboutionsinsolu7on?
•  theyneedto“stayhydrated”(ionssurrounded
bywatermolecules)
•  ifthereisnotenoughwater,ionscrystallize
andformrocks(orcement,asseenbefore)
•  maintypes:
–  carbonates(mostcommontype;limestone)
–  siliceousrocks(richinsilica;chert)
–  evaporites(formindryenvironments–notinthe
ocean;halite,orrocksalt,gypsum)
MarineSediments
•  Intheend,manysedimentsareproducedonland
(lithogenoussediments)
•  Whilesomeofthesearedepositedonland,mostare
carriedtotheocean(marinesediments)
•  Someothertypesofsediments(biogenousand
hydrogenous)areproduceddirectlyintheocean
•  Whatevertypeofsedimentreachesorisproducedinthe
oceanwouldeventuallyse\lethroughthewatercolumn
•  OceanographersdecipherEarthhistorythroughstudying
sediments
4.1–HowAreMarineSedimentsCollected,
andWhatHistoricalEventsDoTheyReveal?
•  Marinesedimentsoftodaycanbecollected
directlyfromtheoceanbo\om
–  difficulttogetto
•  Marinesedimentsofthepastthathaveturned
intosedimentaryrockscanbefoundinland
outcrops
–  easiertogettobutsca\eredsamples
collec7ngMarineSediments
•  dredge
•  gravitycorer
•  rotarydrilling
–  NSFfundedaprogramforborrowingdrilling
technologiesfromtheindustry
–  Fouroceanographicins7tu7ons(Scripps,Rosens7el,
WoodsHole,Lamont-Doherty)unitedtoformJOIDES
(JointOceanographicIns7tu7onsforDeepEarth
Sampling)
–  OtherschoolslaterjoinedJOIDES
collec7ngMarineSediments
•  JOIDESprograms
–  DSDP(DeepSeaDrillingProject)
•  1966,GlomarChallenger,sampledto6000mofdepth
•  evidenceofspreading(ageofsediment,thicknessof
sediments,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:drillingpipesonthedeck
ofJOIDESResolu7on
Upperright:diamonddrillingbit(a
drillingbitwouldnotgiveusacore,
butrather“rockcusngs’,or
fragments
Bo\omler:analysisofhalvedcores
onboardtheJOIDESResolu7on
EnvironmentalCondi7ons
RevealedbyMarineSediments
•  MarineSedimentspreservematerialsthatexistedin
theoverlyingwatercolumns
•  Thesematerialsarefunc7onofthecondi7onsofthe
environment
•  Analysisofcoresprovidesuswithinfoabout:
–  ancientseasurfacetemperature
–  abundanceofmarinelifeandmajorex7nc7onevents
–  atmosphericwindsandvolcanicerup7ons
–  oceancurrentpa\ernsandchangesinEarth’sclimate
–  movementoftectonicplates
Paleoceanography
•  Thestudyofhowocean,atmosphere,and
landinterac7onshaveproducedchangesin
oceanchemistry,circula7on,biology,and
climate
•  Marinesedimentsprovidecluestopast
changes
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–WhatAretheCharacterisKcs
ofLithogenousSediment?
•  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?
•  Marinesedimentarydepositscanbefoundinvirtually
allplacesontheoceanfloor,evenifsome7mesinvery
minorpercentages.
•  Thecanbecategorizedaseitherneri7corpelagic
•  NeriKcDepositsarearefoundoncon7nentalshelves
andinshallowwatersaroundislands
–  usuallycoarse-grained(sands)
•  PelagicDepositsarefoundindeep-oceanbasins
–  usuallyfine-grained(siltsandclays)
Neri7cDeposits
•  Beachdeposits
–  Grainsofallkindsbroughttothecoastbyrivers
–  Weatheringslowlymodifiesgraincomposi7oninto
quartz-richsands
–  Wavemo7oncausestransporta7on
SloughandbeachinGoleta,CA
©AlessandroGrippo
•  Con7nentalshelfdeposits
–  Relictsediments:leroverasunderwaterformer
beachsediment
–  formedduringthelast(oranyprevious)iceage
peak,thenfloodedduringtheinterglacial
–  some7messhowingabovesealevelasbarrier
islands
•  Turbiditedeposits
– SandsandmudsinCon7nentalRise
– Gradedbedding
•  Glacialdeposits
– Highla7tudecon7nentalshelf
– Currentlyformingbyiceraring(icebergs
carryingrocksintoocean,calleddropstones)
Above:anicebergcarryingsedimenttotheoceaninPortageLake,
ChugachNa7onalForest,ChugachMountains,Alaska.
Photo©USGS
Right:adropstoneincross-sec7onalview,Namibia
Photo©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)and
terrigenous(redabyssalclays)sediments
MidCretaceous
PiobbicoCore,Pesaro-Urbino,Italy
©AlessandroGrippo
•  endofpart1