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  • 1. Chapter 5Marine Sediments

2. Ocean sedimentVarious materials settle through the watercolumn and accumulate on the ocean floorLayers represent a record of Earth history,including:Movement of tectonic platesPast changes in climateAncient ocean circulation patternsCataclysmic events 3. Collecting ocean sedimentSpeciallydesigned shipscollect cores byrotary drillingCores allowscientists toanalyze oceansediment 4. The 4 main types of sediment1. Lithogenous = composed of fragments of pre-existing rock material2. Biogenous = composed of hard remains of once-living organisms3. Hydrogenous = formed when dissolved materials come out of solution (precipitate)4. Cosmogenous = derived from outer space 5. Origin of lithogenous sedimentForms by:Weathering =breakup of exposedrockTransportation =movement ofsedimentDeposition =settling and Sediment-transporting mediaaccumulation 6. Lithogenous sedimentcompositionMost lithogenoussediment iscomposed ofquartz, which is:AbundantChemically stableDurable 7. Lithogenous sediment textureTextureincludes:Grain sizeSortingRoundingMaturity 8. Distribution of lithogenoussedimentLithogenous sediment occurs as:Neritic (nearshore) depositsBeachesContinental shelvesTurbiditesGlacial-rafted debrisPelagic (deep ocean floor) depositsAbyssal clay 9. Origin of biogenous sedimentOrganisms that produce hard parts dieMaterial rains down on the ocean floor andaccumulates as:Macroscopic shells, bones, teethMicroscopic tests (shells)If comprised of at least 30% test material, calledbiogenous ooze 10. Biogenous sediment composition Microscopic biogenous tests are composed of 2 main chemical compounds:1. Silica (SiO2) including opal (SiO2 nH2O) Diatoms (algae) Radiolarians (protozoan)1. Calcium carbonate or calcite (CaCO3) Coccolithophores (algae) Foraminifers (protozoan) 11. Examples of silica-secretingmicroscopic organismsDiatomRadiolarian 12. Siliceous oozeSilica-secretingorganismsaccumulate to formsiliceous ooze(>30% siliceoustest material) 13. Examples of calcite-secretingmicroscopic organismsCoccolithophores Foraminifers 14. Calcareous oozeCalcite-secretingorganismsaccumulate to formcalcareous ooze(>30% calcareoustest material) 15. Biogenous ooze turns to rockWhen biogenousooze hardens andlithifies, can form:Diatomaceous earth(if composed ofdiatom-rich ooze)Chalk (if composedof coccolith-richChalk cliffs of southern Englandooze) 16. Distribution of biogenous oozeMost biogenous ooze found as pelagicdepositsFactors affecting the distribution ofbiogenous ooze:Productivity (amount of organisms in surfacewaters)Destruction (dissolving at depth)Dilution (mixing with lithogenous clays) 17. Distribution of siliceous oozeSilica slowly butsteadily dissolvesin seawaterSiliceous oozefound where itaccumulates fasterthan it dissolves 18. Distribution of calcareous oozeCalcite dissolvesbeneath the calcitecompensation depth(CCD) at 4.5 kmCalcareous ooze canbe found below theCCD if it is buriedand transported todeep water 19. Biogenous ooze asenvironmental indicatorSiliceous ooze Calcareous oozeSurface waterCoolWarmtemperatureMain locations Sea floor beneath Sea floor beneathfoundcool surfacewarm surface water in high water in low latitudes;latitudes; not too upwelling areas deep (CCD) 20. Origin of hydrogenous sediment Hydrogenous sediment forms when dissolved materials come out of solution (precipitate) Precipitation is caused by a change in conditions including: Changes in temperature Changes in pressure Addition of chemically active fluids 21. Types of hydrogenous sedimentMining Manganese nodules manganese Phosphates nodules Carbonates Metal sulfides Evaporite salts Evaporite salts 22. Cosmogenous sediment Cosmogenous sediment is composed of material derived from outer space Two main types:1. Microscopic space dust2. Macroscopic meteor debris Forms an insignificantMicroscopic cosmogenous proportion of ocean sedimentspherule 23. MixturesMost ocean sediment is a mixture ofsediment typesOne type of sediment usually dominates,allowing it to be classified as primarily:LithogenousBiogenousHydrogenousCosmogenous 24. Worldwide distribution of neritic and pelagic sediment 25. Ocean sediments as a resourceOcean sediments containmany important resources,including:PetroleumGas hydratesSand and gravelEvaporative saltsPhosphoriteManganese nodules and Offshore drilling rigcrusts 26. End of Chapter 5