marine sediments and sedimentary rocks

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Marine Sediments and Sedimentary Rocks

Prof. Rosenheim EENS/EBIO 223

Introductory Oceanography

Interest in Marine Sediment

• Sediments reveal– Past climates– Ocean floor movements– Circulation patterns– Nutrient supplies– Ocean chemical history



Rock Cycle

1. Sediments deposited2. Lithification3. Burial, compression4. Deformation, melt5. Re-crystallization6. Tectonic uplift7. Weathering and further deposition

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Sedimentary Rock

• Deposited in horizontal layers

Strata (s. Stratum) –horizontal layers deposited on top of one another



Law of Superposition

Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.

Nicholas Steno



Retrieval of Ancient Marine Sediment

• Drilling ships needed to access oldest marine sediments under sea – R/V JOIDES Resolution

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Retrieval of Ancient Marine Sediment

• Drilling ships now can theoretically drill to mantle – R/V Chikyu is a riser drilling platform



Drill Ship Operations• Core through sediment layer

– Continuously pull core sections to the surface for analysis

• Find hole with sonar beacon– Ship uses thrusters for this purpose –

dynamic positioning• Rotary drill or Riser drill into

compacted, lithified layers below the sediment– Continuously bring core sections to

surface for analysis



Sediment Coring

• http://www.iodp.org/coring-procedure/

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Marine Sedimentation

• Lithogenous Sediment– Generated from pre-existing rock material

• Biogenous Sediment– Originating from living organisms

• Hydrogenous Sediment– Precipitated from dissolved material in water

• Cosmogenous Sediment– Sourced extraterrestrially



Sedimentation

• Energy dependent• Smallest grains in basins• Coarse grains nearer

coasts



From Sediment to Rock

• Lithification– Sediment compaction– Cementation

Figure: Dr. Bruce Railsback, UGA

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Sampling Lithified Marine Sediment

• http://www.iodp.org/deep-sea-drilling/2/• http://www.iodp.org/rotary-drilling/2/



Core Analysis

• Retrieve core• Non-destructive analysis• Split• Measure and analyze

– Sample (one half)– Archive (the other half)

• http://www.iodp.org/core-analyzing-process/2/



Sediment History

• What changes in sediment type ratios are there? (lithogenous vs. biogenous)

• How does biogenous sediment change through time? (biogenous)

• What evidence of impact sediments is apparent? (cosmogenous)

• How has ocean chemistry changed in the past? (hydrogenous and biogenous)

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Lithogenous Sediment

• Generated from pre-existing rock• Weathering, erosion, transport to ocean basin



Lithogenous Sediment Deposition• Neritic deposits – continental margins and

islands, dominated by lithogenoussediment

• Pelagic deposits – deep ocean basins



Lithogenous Sediment Sources

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Lithogenous Sediment Composition

• SiO2



Lithogenous Sediment Transport• Water

– Terrigenous sediment transported in rivers



Lithogenous Sediment Transport• Water

– Deposited in basins

photo: Lonnie Leithold

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Lithogenous Sediment Transport

• Air– Loess

• Wind blown dust• Finer material



Quartz Distributions – Wind Transport




• Ice– Calving ice sheets and

glaciers– Large, coarse fragments– Carried long distances by

icebergs

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• Ice-rafted debris




• Ice-rafted debris– High rates of glaciation




• Sea level change– Direct erosion of

vulnerable coastline– Transport out to sea and

deposition in basin

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• Volcanoes




• Tephra layers



Lithogenous Sediment Maturation

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Lithogenous Sediment Maturity



Turbidites – From Neritic to Pelagic




• Gravity transport – density current– underwater landslide

• Unique depositional record

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• Gravity transport – density current– underwater landslide

• Unique depositional record• High rate of speed




• Which ocean has the highest proportion of lithogenous sediments?




• Which ocean has the highest proportion of lithogenous sediments?

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Biogenous Sediment

• Sediment originating from living organisms– Foraminifera– Coccolithophorids– Radiolarians– Diatoms



Calcareous Biogenic Sediment

• Ca2+ + CO32- CaCO3 (s)



Calcareous Biogenous Sediment

• Calcareous Organisms– Foraminifera– Coccolithophorids– Pteropods

White cliffs of Dover (England) are made of chalk deposited in the Cretaceous Period. These cliffs are almost entirely made of coccoliths from ancient coccolithophorids.

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Coccoliths and Coccolithophorids



Coccoliths and CoccolithophoridsCoccoliths



Coccolithophorids

• Floating algae• Build coccoliths for protection and perhaps

light manipulation• Responsible for 25%CO2 sequestration by oceans every year

http://www.jochemnet.de/fiu/bot4404/BOT4404_16.html

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Coccolithophorids

• Dominant during Cretaceous Period– “creta” Latin for chalk

• Abundant in shallow inland seas• Warm and tropical



Pteropods

Swimming sea snails, some form tine snail-type calcareous shells. These form a small part of calcareous sediment.



Foraminifera

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ForaminiferaForaminifera are floating and benthic protists (first ones –Greek for early life forms) . They form complex calcareous shells (tests) and use a cellular “net” to trap food. Those living in the surface of the oceans are normally symbiotic with photosynthetic algae.



Foramifera

• Planktonic forams– Surface dwellers– Need and use light– Symbiosis– Tests fall to bottom

upon deathO.R. Anderson



Foramifera

• Benthic Forams– Dwell bottom

sediments– Leave shells mixed

with planktic species upon death

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Foraminifera Records

• Many species are geologically short-lived, making them useful for paleontologist to date rocks

• Also useful for paleoceanography– Assemblages tell of climate change and

extinctions– Test (or shell) chemistry tells of global climate

change



Foraminifera and Paleoceanography

• Cesare Emiliani –Father of Paleoceanography

• Sir Nicholas Shackleton – Emiliani’scounterweight




• Cesare Emiliani – isotopic change of oceans, recorded in foram tests, is related to temperature

• Sir Nicholas Shackleton – isotopic change of oceans is related to isotopic composition of oceans

• Answer – Both.

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Whereas temperature probably played a large role in the isotope composition of planktic foraminifera, Shackletonmeasured benthic species which also showed change. We know that the deep oceans are fairly resistant to temperature change. Deep benthic foraminifera showing isotope variations meant that the isotope composition of the water had changed in concert with the temperature. More ice meant heavier values in the oceans. Cold temperatures meant heavier values in the oceans. Benthics vs. planktics offered a solution to this argument.



Siliceous Biogenic Sediment

• Diatoms– Planktonic– Photosynthetic

• Radiolarians– Planktonic– Heterotrophic

• Siliceous Ooze



DiatomsPhotosynthic plankton with two halves (frustules). Like radiolarians, these collect in areas of high productivity.

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RadiolariansNoted for their beauty, are best preserved in areas of high productivity where they rain at a higher rate than dissolution.



Siliceous vs. Calcareous Ooze• Siliceous

deposits form in tropics and Antarctica –high productivity

• Calcareous deposits form where ocean chemistry allows preservation of delicate carbonate tests



Carbonate Compensation Depth

• Lysocline– Stability of CaCO3 is related to temperature and pH– Lower temperatures dissolve more CO2, making

water more acidic– CaCO3 tends to dissolve when temperatures are low

(i.e. deep water)• CCD

– Where dissolution of CaCO3 balances production and CaCO3 can no longer accumulate

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Siliceous vs. Calcareous Ooze

• Pacific is largely below present day CCD.

• Abyssal clay is undiluted here



Productivity and Preservation



Productivity and Preservation

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CCD and Lysocline



CCD and Lysocline



Sedimentation on the Ocean Floor

• Sediment grows thicker away from mid-ocean ridge (spreading center)

• Oldest (thickest) sediment found toward continental margins

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Biogenous Sediments in Neritic Zone

• Coral reefs– Calcium carbonate

skeletons– Fragments



Biogenous Sediments in Neritic Zone

• Mollusks– Calcium carbonate

skeletons– Shell hash



Hydrogenous Sediments

• Forming from within the water column– Precipitation from dissolved constituents of

seawater

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Whitings – Calcium Carbonate• Oceans can be supersaturated with

regards to calcium carbonate (surface)• Whitings



Why so blue?• Reflection of light through shallow waters

and white carbonate sands.– Biogenous– Hydrogenous



Manganese Nodules

• Manganese, iron, and other metals– 5 cm in diameter, layered– Nucleates around a pre-existing grain

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Ooids – Calcium Carbonate

• Round grains of layered calcium carbonate

• Formed by repeated agitation in shallow, supersaturated water



Ooids – Calcium Carbonate

• Make wonderful beach sand because of uniform spherical shape

• Lithified to oolite



Metal Sulfides – Black Smokers

• Precipitation of reduced chemicals in hydrothermal vent fluids

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Cosmogenous Sediments

• Derived from extraterrestrial sources– Spherules– Meteorite debris

• Tektites

• 300,000 tons of space debris reach Earth’s surface every year

• Macroscopic debris is more rare

Microscopic debris



Impact Debris

• Large impacts have been responsible for dramatically altering Earth’s conditions– Extinctions evidenced by impact

debris



Impact Debris

• Would the Permian extinction impact event (if there was one) be observable in ocean sediments?

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Key Concepts

• Sediment types and genesis• Transport and deposition• Preservation• Uses of sediment records• Sampling techniques

marine sediments and sedimentary rocks

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