Chapter Overview Marine Sediments Marine Sediment Classification

CHAPTER 4Marine SedimentsPaleoceanography and MarineSediments• Paleoceanography – study of how ocean,atmosphere, and land interactions haveproduced changes in ocean chemistry,circulation, biology, and climate– Marine sediments provide clues to pastchanges.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Chapter Overview• Marine sediments contain a record ofEarth history.• Marine sediments provide a variety ofimportant resources.• Marine sediments have a variety of origins.Marine Sediment Classification• Classified by origin• Lithogenous – derived from land• Biogenous – derived from organisms• Hydrogenous or Authigenic – derivedfrom water• Cosmogenous – derived from outerspace© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Marine SedimentsMarineSediments• Eroded rock particlesand fragments– Transported to ocean• Deposit by settlingthrough watercolumn• Oceanographersdecipher Earthhistory throughstudying sediments.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Lithogenous Sediments• Eroded rock fragmentsfrom land• Also called terrigenous• Reflect composition ofrock from which derived• Produced byweathering– Breaking of rocksinto smaller piecesLithogenous Sediments• Reflect composition ofrock from which derived• Coarser sedimentscloser to shore• Finer sediments fartherfrom shore• Mainly mineral quartz(SiO 2 )© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Lithogenous Sediments• Small particles eroded and transported• Carried to ocean– Streams–Wind– Glaciers–Gravity• Greatest quantity around continentalmarginsLithogenous Quartz and WindTransport© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Lighogenous SedimentTransportGrain Size• Proportional to energy of transportation anddeposition© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Sediment Texture• Grain size sorting– Indication of selectivity of transportationand deposition processes• Textural maturity– Increasing maturity if• Clay content decreases• Sorting increases• Non-quartz minerals decrease• Grains are more rounded (abraded)Pelagic Deposits• Fine-grained material• Accumulates slowly on deep ocean floor• Pelagic lithogenous sediment from– Volcanic ash (volcanic eruptions)– Wind-blown dust– Fine-grained material transported by deepocean currents© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Sediment Distribution• Neritic– Shallow-water deposits– Close to land– Dominantly lithogenous– Typically deposited quickly• Pelagic– Deeper-water deposits– Finer-grained sediments– Deposited slowlyPelagic Deposits• Abyssal Clay– At least 70% clay sized particles fromcontinents– Red from oxidized iron (Fe)– Abundant if other sediments absent© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Neritic Lithogenous Sediments• Beach deposits– Mainly wave-deposited quartz-rich sands• Continental shelf deposits– Relict sediments• Turbidite deposits– Graded bedding• Glacial deposits– High latitude continental shelf– Currently forming by ice raftingBiogenous Sediment• Hard remains of once-living organisms• Two major types:– Macroscopic• Visible to naked eye• Shells, bones, teeth– Microscopic• Tiny shells or tests• Biogenic ooze• Mainly algae and protozoans© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Biogenous SedimentComposition• Two most common chemical compounds:– Calcium carbonate (CaCO 3 )– Silica (SiO 2 or SiO 2·nH 2 O)Calcium Carbonate in BiogenicSediments• Coccolithophores– Also callednannoplankton– Photosynthetic algae– Coccoliths – individualplates from deadorganism– Rock chalk• Lithified coccolithrichooze© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Silica in Biogenous Sediments•Diatoms– Photosyntheticalgae– Diatomaceousearth• Radiolarians– Protozoans– Use externalfoodCalcium Carbonate in BiogenicSediments• Foraminifera– Protozoans– Use externalfood– Calcareous ooze© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Silica in Biogenous Sediments• Tests from diatomsand radiolariansgenerate siliceousooze.• Siliceous ooze lithifiesinto diatomaceousearth.Distribution of BiogenousSediments• Depends on three processes:– Productivity– Destruction– Dilution© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Neritic Deposits• Dominated by lithogenous sediment, maycontain biogenous sediment• Carbonate Deposits– Carbonate minerals containing CO 3– Marine carbonates primarily limestone –CaCO 3– Most limestones contain fossil shells• Suggests biogenous origin– Ancient marine carbonates constitute 25% ofall sedimentary rocks on Earth.Calcareous Oozeand theCCD© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Carbonate Deposits• Stromatolites– Fine layers ofcarbonate– Warm, shallow-ocean,high salinity– CyanobacteriaCalcareous Ooze and the CCD• Scarce calcareous ooze below 5000 meters(16,400 feet) in modern ocean• Ancient calcareous oozes at greater depths ifmoved by sea floor spreading© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Calcareous Ooze and the CCD• CCD – Calcite compensation depth– Depth where CaCO 3 readily dissolves– Rate of supply = rate at which the shellsdissolve• Warm, shallow ocean saturated withcalcium carbonate• Cool, deep ocean undersaturated withcalcium carbonate– Lysocline – depth at which a significantamount of CaCO 3 begins to dissolve rapidly© 2011 Pearson Education, Inc.Sea Floor Spreading and SedimentAccumulation© 2011 Pearson Education, Inc.

Cosmogenous MarineSediments• Macroscopicmeteor debris• Microscopic ironnickeland silicatespherules (smallglobular masses)– Tektites– Space dust• Overall,insignificantproportion ofmarine sediments© 2011 Pearson Education, Inc.Pelagic and Neritic SedimentDistribution• Distribution controlled by– Proximity to sources of lithogenoussediments– Productivity of microscopic marineorganisms– Depth of water– Sea floor features© 2011 Pearson Education, Inc.Marine Sediment Mixtures• Usually mixture of different sediment types• Typically one sediment type dominates in different areasof the sea floor.Pelagic Sediment Types© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Pelagic and Neritic Sediment Distribution• Neritic sediments cover about ¼ of the sea floor.• Pelagic sediments cover about ¾ of the sea floor.Sea Floor Sediments RepresentSurface Ocean Conditions• Microscopic tests sinkslowly from surfaceocean to sea floor(10-50 years)• Tests could bemoved horizontally• Most biogenoustests clump togetherin fecal pellets– Fecal pellets largeenough to sinkquickly (10-15 days)© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.

Worldwide Marine Sediment ThicknessDistribution of ManganeseNodules© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Resources from MarineSediments• Energy resources– Petroleum• Mainly from continental shelves– Gas hydrates• Sand and gravel (including tin, gold, andso on)• Evaporative salts• Phosphorite• Manganese nodules and crusts© 2011 Pearson Education, Inc.End of CHAPTER 4Marine Sediments© 2011 Pearson Education, Inc.Mining Sea Salt© 2011 Pearson Education, Inc.