OCNG 251: OceanographyOCNG 251: OceanographyTuesday, Nov. 11Tuesday, Nov. 11thth, 2008, 2008Defining Boundaries: 3) Marine SedimentsDefining Boundaries: 3) Marine Sediments1.1.ReviewReview2.2.Marine Sediments:Marine Sediments:a.a.IntroductionIntroductionb.b.Classification: Size Classification: Size vsvs. Origin. Originc.c.Factors that control sedimentationFactors that control sedimentationd.d.Sedimentation in the OceansSedimentation in the Oceansi.i.Shelf SedimentationShelf Sedimentationii.ii.Deep-Sea SedimentationDeep-Sea Sedimentatione.e.Global distributionGlobal distributionf.f.A Case Study: Puget Sound (WA)A Case Study: Puget Sound (WA)ReviewReviewDefining Boundaries: 3) Plate TectonicsDefining Boundaries: 3) Plate Tectonics1.1.Plate TectonicsPlate Tectonics!!Paleomagnetic signatures of oceanic crust.Paleomagnetic signatures of oceanic crust.!!Increased thickness (and age) of sediments away from mid-Increased thickness (and age) of sediments away from mid-ocean ridges.ocean ridges.!!Heat flow from the Earth interior to the crust decreases asHeat flow from the Earth interior to the crust decreases asthe distance from the ridge center and crustal age increase.the distance from the ridge center and crustal age increase.!!Age of the oceanic crust.Age of the oceanic crust.!!Shallow earthquakes (linked to ridges and faults)Shallow earthquakes (linked to ridges and faults)!!Deep earthquakes (linked to subduction zones and trenches).Deep earthquakes (linked to subduction zones and trenches).!!Balance of Earth volume!Balance of Earth volume!2.2.Formation of Oceans: From embryonic to suturingFormation of Oceans: From embryonic to suturing!!Pacific: Old Ocean (shrinking, 200 Ma)Pacific: Old Ocean (shrinking, 200 Ma)!!Atlantic, Indian, Arctic: New Oceans (growing, really?)Atlantic, Indian, Arctic: New Oceans (growing, really?)Defining Boundaries: 3) Marine SedimentsDefining Boundaries: 3) Marine SedimentsA.A. Introduction Introduction••Sediments are produced by the weathering (chemical andSediments are produced by the weathering (chemical andmechanical-physical break down) of rocks such as granitemechanical-physical break down) of rocks such as graniteand basalt into particles that are then moved by air, water,and basalt into particles that are then moved by air, water,and ice.and ice.••Sediments can also be formed from the accumulation ofSediments can also be formed from the accumulation ofshells or micro- and macro-debris of organisms.shells or micro- and macro-debris of organisms.••They can also come as a result of chemical precipitationThey can also come as a result of chemical precipitationreactionsreactions!!Sediments can therefore consist ofSediments can therefore consist of""Mineral particlesMineral particles""Fossil particlesFossil particlesDefining Boundaries: 3) Marine SedimentsDefining Boundaries: 3) Marine SedimentsA.A. Introduction Introduction!!Most erosion of rock occurs on land and most deposition ofMost erosion of rock occurs on land and most deposition ofsediments occur in the Oceans.sediments occur in the Oceans.##Net balance (erosion/deposition) would be to even outNet balance (erosion/deposition) would be to even outEarthEarth’’s surfaces surface##Tends towards equilibrium (i.e. thermodynamics)Tends towards equilibrium (i.e. thermodynamics)##Plate tectonics! (i.e. kinetics)Plate tectonics! (i.e. kinetics)Marine SedimentsMarine SedimentsB.B. Classification ClassificationSediments can be subdivided on the basis of:Sediments can be subdivided on the basis of:!!The size of the particles (The size of the particles (grain sizegrain size))SedimentTypeDiameter (mm)Gravel Boulder >256.0Cobble 64.0-256.0Pebble 4.0-64.0Granule 2.0-4.0Sand Very coarse 1.0-2.0Coarse 0.5-1.0Medium 0.25-0.50Fine 0.125-0.250Very fine 0.0625-0.125Silt 0.0039-0.0625MudClay 0.0002-0.0039Colloids <0.0002Marine SedimentsMarine SedimentsB.B. Classification Classification!!Their mode of formation (Their mode of formation (originorigin))••Terrigenous sedimentsTerrigenous sediments: Fine and coarse grains produced by: Fine and coarse grains produced byweathering and erosion of rocks on land (sands & muds).weathering and erosion of rocks on land (sands & muds).••Biogenous sedimentsBiogenous sediments: Fine and coarse grains that are derived: Fine and coarse grains that are derivedfrom the hard parts of organisms (shells, skeletal debris from the hard parts of organisms (shells, skeletal debris ––carbonates and silica)carbonates and silica)••Authigenic sedimentsAuthigenic sediments: Particles that are precipitated by chemical: Particles that are precipitated by chemicalreactions (diagenesis) in seawater near the sea floor or withinreactions (diagenesis) in seawater near the sea floor or withinsediments (phosphorites, ferromanganese nodules)sediments (phosphorites, ferromanganese nodules)••Volcanic sedimentsVolcanic sediments: Particles that are ejected from volcanoes (i.e.: Particles that are ejected from volcanoes (i.e.ash)ash)••Cosmogenous sedimentsCosmogenous sediments: Very tiny grains that originate from: Very tiny grains that originate frommeteorite shower and outer space material (mixed withmeteorite shower and outer space material (mixed withterrigenous and biogenic sediments)terrigenous and biogenic sediments)Marine SedimentsMarine SedimentsB.B. Classification Classification!!Both classifications are interrelated.Both classifications are interrelated.!!Sand & Mud, which are separated on basis of grain size, can beSand & Mud, which are separated on basis of grain size, can beterrigenous, biogenic, authigenic, cosmogenous, etcterrigenous, biogenic, authigenic, cosmogenous, etc……Hujlstrom’s diagram. Adapted from Pinet 2000C.C.Factors that controlFactors that controlsedimentationsedimentation!!Relationship between averageRelationship between averagegrain size and energy ofgrain size and energy ofbottom currentsbottom currents!!Erosion, Transport andErosion, Transport andDeposition (sedimentation)Deposition (sedimentation)depend on velocity of currentdepend on velocity of currentand grain sizeand grain size!!Settling rate of suspendedSettling rate of suspendedparticles varies with diameterparticles varies with diameter(Stokes Law)(Stokes Law)D.D. Sedimentation in the Oceans Sedimentation in the OceansTwo areas of sediment deposition on the basis of water depthTwo areas of sediment deposition on the basis of water depthi.i. Shelf sedimentationShelf