OCNG 251 Oceanography Tuesday Nov 11th 2008 Defining Boundaries 3 Marine Sediments 1 Review 2 Marine Sediments a Introduction b Classification Size vs Origin c Factors that control sedimentation d Sedimentation in the Oceans i Shelf Sedimentation ii Deep Sea Sedimentation e Global distribution f A Case Study Puget Sound WA Review Defining Boundaries 3 Plate Tectonics 1 Plate Tectonics Paleomagnetic signatures of oceanic crust Increased thickness and age of sediments away from midocean ridges Heat flow from the Earth interior to the crust decreases as the distance from the ridge center and crustal age increase Age of the oceanic crust Shallow earthquakes linked to ridges and faults Deep earthquakes linked to subduction zones and trenches Balance of Earth volume 2 Formation of Oceans From embryonic to suturing Pacific Old Ocean shrinking 200 Ma Atlantic Indian Arctic New Oceans growing really Defining Boundaries 3 Marine Sediments A Introduction Sediments are produced by the weathering chemical and mechanical physical break down of rocks such as granite and basalt into particles that are then moved by air water and ice Sediments can also be formed from the accumulation of shells or micro and macro debris of organisms They can also come as a result of chemical precipitation reactions Sediments can therefore consist of Mineral particles Fossil particles Defining Boundaries 3 Marine Sediments A Introduction Most erosion of rock occurs on land and most deposition of sediments occur in the Oceans Net balance erosion deposition would be to even out Earth Earth s surface Tends towards equilibrium i e thermodynamics Plate tectonics i e kinetics Marine Sediments B Classification Sediments can be subdivided on the basis of The size of the particles grain grain size size Sediment Gravel Type Boulder Cobble Pebble Granule Diameter mm 256 0 64 0 256 0 4 0 64 0 2 0 4 0 Sand Very coarse Coarse Medium Fine Very fine 1 0 2 0 0 5 1 0 0 25 0 50 0 125 0 250 0 0625 0 125 Silt 0 0039 0 0625 Clay 0 0002 0 0039 Mud Colloids Marine Sediments B Classification Their mode of formation origin origin Terrigenous sediments Fine and coarse grains produced by weathering and erosion of rocks on land sands muds Biogenous sediments Fine and coarse grains that are derived from the hard parts of organisms shells skeletal debris carbonates and silica Authigenic sediments Particles that are precipitated by chemical reactions diagenesis in seawater near the sea floor or within sediments phosphorites ferromanganese nodules Volcanic sediments Particles that are ejected from volcanoes i e ash Cosmogenous sediments Very tiny grains that originate from meteorite shower and outer space material mixed with terrigenous and biogenic sediments 0 0002 Marine Sediments B Classification Both classifications are interrelated Sand Mud which are separated on basis of grain size can be terrigenous biogenic authigenic cosmogenous etc etc C Factors that control sedimentation Relationship between average grain size and energy of bottom currents Erosion Transport and Deposition sedimentation depend on velocity of current and grain size Settling rate of suspended particles varies with diameter Stokes Law Hujlstrom s diagram Adapted from Pinet 2000 Marine Sediments D Sedimentation in the Oceans Two areas of sediment deposition on the basis of water depth i Shelf sedimentation sedimentation Shallow close to terrigenous sources ii Deep sea sedimentation sedimentation Deep abyssal plains Marine Sediments D Sedimentation in the Oceans Two major areas of sediment deposition on the basis of water depth i Two main sources External terrigenous terrigenous mud and sand Shelf sedimentation sedimentation theoretical equilibrium equilibrium Internal biogenic particles authigenic particles Source Pinet 2000 source USGC Marine Sediments i Shelf Sedimentation Sea level change Oscillation due to geological changes in the hydrological cycle Adapted from Garrison 2002 Adapted from Pinet 2000 Marine Sediments i Shelf Sedimentation Sea level change Oscillation due to geological changes in the hydrological cycle Adapted from Pinet 2000 Sea level change Marine Sediments i Shelf Sedimentation Sea level change transfer of terrigenous sediments back and forth between continental shelf and shelf break Modern deposits occur only on the 1st third of shelves and most deposits are relict in nature Present material not in equilibrium with present day conditions Robert A Rohde Global Warming Art project Adapted from Pinet 2000 Marine Sediments Adapted from Pinet 2000 Marine Sediments i Ice Rafting i Worldwide distribution of Shelf sediments Heterogeneous mix of terrigenous materials A regular pattern of sediment types occur based on latitude and climate 30 40 of sediments are recent 70 60 are relict Adapted from Pinet 2000 Adapted from Pinet 2000 Marine Sediments ii Deep Sea Sedimentation Two main sources External terrigenous mud and sand Internal biogenic particles authigenic particles Marine Sediments ii Deep Sea Sedimentation External sources terrigenous terrigenous mud and sand variable inputs Three categories Bulk emplacement Pelagic sediments Authigenic sediments Adapted from Pinet 2000 Marine Sediments ii Deep Sea Sedimentation Red clays clays Very fine grained particles of brownish color oxidized composed of clay minerals such as Kaolinite Kaolinite chlorite Illite and Montmorillonite Montmorillonite Dominant only when other sources are less abundant Some clay minerals show strong susceptibility to weathering and are altered due to chemical weathering Kaolinite formed in warm moist climate Chlorite formed in temperate and subpolar latitudes Adapted from Pinet 2000 Adapted from Pinet 2000 Marine Sediments ii Deep Sea Sedimentation Biogenic particles particles Usually hard parts shells or macro and microdebris Two main minerals CaCO3 and SiO2 CaCO3 Foraminifera Pteropods Coccolithophores 2HCO3 d Ca2 d CaCO3 s CO2 g H2O SiO2 Diatoms Radiolarian Biogenic oozes consist of 30 or more of skeletal debris of organisms 70 composed of inorganic mud particles Marine Sediments ii Deep Sea Sedimentation Marine Sediments Ferromanganese Nodules Authigenic particles particles Chemical precipitates that form at or near the sediment water interface or precipitate from seawater Ferromanganese nodules metals oxides Fe and Mn more that grow concentrically around nuclei 1 4 mm Ma Phosphorites precipitation of P205 up to 30 on continental shelves with very high primary productivity Adapted