ocean deposits
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Marine Sediments
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Ocean sedimentVarious materials settle through the water column and accumulate on the ocean floorLayers represent a record of Earth history, including:
Movement of tectonic platesPast changes in climateAncient ocean circulation patternsCataclysmic events
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The 4 main types of sediment
1. Lithogenous = composed of fragments of pre-existing rock material
2. Biogenous = composed of hard remains of once-living organisms
3. Hydrogenous = formed when dissolved materials come out of solution (precipitate)
4. Cosmogenous = derived from outer space
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Origin of lithogenous sedimentForms by:
Weathering = breakup of exposed rockTransportation = movement of sedimentDeposition = settling and accumulation
Sediment-transporting media
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Lithogenous sediment composition
Most lithogenous sediment is composed of quartz, which is:
AbundantChemically stableDurable
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Lithogenous sediment textureTexture includes:
Grain sizeSortingRoundingMaturity
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Distribution of lithogenous sediment
Lithogenous sediment occurs as:Neritic (nearshore) deposits
BeachesContinental shelvesTurbiditesGlacial-rafted debris
Pelagic (deep ocean floor) depositsAbyssal clay
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Origin of biogenous sedimentOrganisms that produce hard parts dieMaterial rains down on the ocean floor and accumulates as:
Macroscopic shells, bones, teethMicroscopic tests (shells)
If comprised of at least 30% test material, called biogenous ooze
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Biogenous sediment compositionMicroscopic biogenous tests are composed of 2 main chemical compounds:
1. Silica (SiO2) including opal (SiO2 · nH2O)Diatoms (algae)Radiolarians (protozoan)
2. Calcium carbonate or calcite (CaCO3)Coccolithophores (algae)Foraminifers (protozoan)PteropodGlobigerina
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Examples of silica-secreting microscopic organisms
Diatom Radiolarian
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Siliceous oozeSilica-secreting organisms accumulate to form siliceous ooze (>30% siliceous test material)
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Examples of calcite-secreting microscopic organisms
Coccolithophores Foraminifers
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Calcareous oozeCalcite-secreting organisms accumulate to form calcareous ooze (>30% calcareous test material)
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Biogenous ooze turns to rockWhen biogenous ooze hardens and lithifies, can form:
Diatomaceous earth (if composed of diatom-rich ooze)Chalk (if composed of coccolith-rich ooze)
Chalk cliffs of southern England
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Distribution of biogenous oozeMost biogenous ooze found as pelagic depositsFactors affecting the distribution of biogenous ooze:
Productivity (amount of organisms in surface waters)Destruction (dissolving at depth)Dilution (mixing with lithogenous clays)
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Distribution of siliceous oozeSilica slowly but steadily dissolves in seawaterSiliceous ooze found where it accumulates faster than it dissolves
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Distribution of calcareous oozeCalcite dissolves beneath the calcite compensation depth (CCD) at 4.5 kmCalcareous ooze can be found below the CCD if it is buried and transported to deep water
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Biogenous ooze as environmental indicator
Siliceous ooze Calcareous oozeSurface water temperature
Cool Warm
Main locations found
Sea floor beneath cool surface water in high latitudes; upwelling areas
Sea floor beneath warm surface water in low latitudes; not too deep (CCD)
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Origin of hydrogenous sedimentHydrogenous sediment forms when dissolved materials come out of solution (precipitate)Precipitation is caused by a change in conditions including:
Changes in temperatureChanges in pressureAddition of chemically active fluids
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Types of hydrogenous sedimentManganese nodulesPhosphatesCarbonatesMetal sulfidesEvaporite salts
Mining manganese
nodules
Evaporite salts
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Cosmogenous sedimentCosmogenous sediment is composed of material derived from outer spaceTwo main types:
1. Microscopic space dust2. Macroscopic meteor debrisForms an insignificant proportion of ocean sediment
Microscopic cosmogenous
spherule
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MixturesMost ocean sediment is a mixture of sediment typesOne type of sediment usually dominates, allowing it to be classified as primarily:
LithogenousBiogenousHydrogenousCosmogenous
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Worldwide distribution of neritic and pelagic sediment
Figure 4-17
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Ocean sediments as a resourceOcean sediments contain many important resources, including:
PetroleumGas hydratesSand and gravelEvaporative saltsPhosphoriteManganese nodules and crusts
Offshore drilling rig