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104 Cards in this Set

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What is the range of sediment diameters?
1 μm to 10 cm
Are most sediments macroscopic or microscopic?
microscopic
What is the range of sedimentation rates?
1 mm per millenium to 1 meter per year
What are sediments consisting of only one size of particle called?
well-sorted
What are the five grain sizes, from biggest to smallest?
boulders, gravel, sand, silt, and clay
What does mud consist of?
silt and clay
What are the four types of sediment, classified by origin?
lithogenous (lithosphere), biogenous (life), hydrogenous (dissolved chemicals), and cosmogenous (meteorites)
What parts do biogenous sediments usually come from?
hard parts of plankton as well as mollusk shells, fish bones and whale and shark teeth
What are sediments with a high proportion of lithogenous particles called?
terrigenous
What are six mechanisms for bringing lithogenous sediments to the ocean?
freshwater runoff, glaciers, waves, winds, landslides, and pollution
Where are the largest particles carried by rivers deposited?
near the coast, on land
Where do most rivers drain?
into estuaries
Why do most rivers draining into subduction zones not carry as much sediment?
The mountain ranges created by subduction are relatively close, limiting available land to drain.
What is sediment in water called?
suspended
What percentage of lithogenous sediment is brought by rivers?
90%
What percentage of river sediment loads comes from Asia?
80%
What is the only major river that discharges directly into an ocean?
the Amazon, into the central Atlantic
What mechanism can deposit boulders into the ocean?
glaciers
What sediment can make lakes appear milky?
glacial flour, finely ground particles, deposited in lakes or fjords with long residence times
How do waves sort sediment?
Waves take smaller sediments farther out to sea.
What causes the one-directional flux of dust from the air to the water?
Suspended sediment in the ocean cannot be easily resuspended in the atmosphere.
How can large particles be suspended in the atmosphere?
volcanoes
What are two effects volcanic ash in the upper atmosphere can have?
Volcanic ash can reduce the albedo of Earth in general, and also reduce the concentration of ozone in the ozone layer.
Name four recent and major volcanic eruptions, their years, and their locations.
1991 Mount Pinatubo (Phillipines)
1980 Mount St. Helens (Washington state)
1883 Krakatau (Indonesia)
1815 Tambora (Indonesia)
How do phytoplankton contribute to biogenous sediment if they are eaten so often?
The phytoplankton's hard parts are not digested, and are packed into fecal pellets, which then sink to the seafloor rather quickly.
What are dead bodies of larger organisms and fecal pellets of smaller ones collectively called?
detritus
What are the two types of marine organism hard parts?
calcareous (CaCO3) and siliceous (opal SiO2)
What two major factors determine the rate of accumulation of biogenous sediment?
the rate of production of these particles and the rate of dissolution or decomposition
What is the dominant marine plant form in high latitude areas of coastal upwelling?
diatoms
What organisms have small calcareous plates and make up the white chalk cliffs of Dover, England?
coccolithophores
Is silica saturated in seawater?
No, it dissolves.
Where is silica dissolution the fastest?
at the surface
What kingdom are coccolithophores in?
Plantae (not really; they are photosynthetic though)
What zooplankton have calcareous shells?
foraminiferans and pteropods
What is an example of an animal with siliceous hard parts?
a radiolarian
Where are radiolarians abundant?
tropical waters, near the equator
How do fecal pellets make it easier for biogenous particles to accumulate on the ocean floor?
Fecal pellets protect particles from dissolving in the ocean until the organic matter in them disintegrates.
What are diatom hard parts called?
frustules
Where is calcium carbonate dissolution the fastest?
at the ocean floor
What are the two types of calcium carbonate shell, and what are examples of animals with each?
calcite (foraminifera) and aragonite (pteropods)
Which form of calcium carbonate dissolves better in seawater?
aragonite
What is the CCD?
carbonate compensation depth, where the dissolution and deposition rates of CaCO3 are equal
What effect does an increase in dissolved CO2 have on calcium carbonate solubility?
It lowers the pH, increasing solubility.
Why does older deep water have a larger concentration of CO2 than younger water?
Respiration at depth creates more CO2 over time.
At what depth is the CCD in the Atlantic and Pacific?
4 km in the Atlantic, 2.5 km in the S Pacific, and 1 km in the N Pacific
What are the five major hydrogenous sediment types?
hydrothermal minerals, manganese nodules, phosphorite nodules/crusts, carbonates, and evaporites
How are hydrothermal minerals deposited?
Hot anoxic water containing lots of metal sulfides is emitted from hydrothermal vents and mixes with dissolved oxygen, which precipitates many insoluble metal oxides.
When were hydrothermal vents discovered?
the late 1970s
How big are manganese nodules?
Many are larger than potatoes.
What are the primary constituents of manganese nodules?
30% MnO2, 20% iron oxides
What makes manganese nodules commercially attractive?
They contain small percentages of useful metals, such as Cu, Ni, and Co.
What forms the center of manganese nodules?
large sediments, like a shark's tooth
What is phosphorite defined as?
a mineral with up to 30% P
What chemical condition does phosphorite nodule formation require?
low dissolved oxygen, like under upwelling areas where detritus depletes the oxygen
How do phosphorite nodules form?
We don't know, but they only accumulate on the underside of objects (crusts).
Why aren't phosphorite nodules commercially useful?
We already have plenty of phosphorus on land.
Was CaCO3 precipitation more or less common in the past?
more common
What chemical conditions favor carbonate precipitation?
high temperatures, low dissolved CO2 => high pH (high primary productivity helps this)
Where are manganese nodules most common?
the North Pacific between 10 and 20 degrees latitude, and the central south Pacific
What is an example of a location where carbonate does precipitate?
the Bahamas
What are white CaCO3-coated suspended particles called?
ooliths
What is the order of evaporite deposition?
CaCO3 and MgCO3, then CaSO4, then NaCl
What three marginal seas have evaporites?
The Dead Sea, Red Sea, and Persian Gulf
Why do scientists think the Mediterranean has been evaporated to dryness in the past?
There are several deep layers of evaporite sediments under the floor of the sea.
What are the two types of meteorites?
stony and iron-rich
What do stony meteorites form?
silicate spherules, which look just like lithogenous sediments
What do iron-rich meteorites form?
.2-.3 mm diameter spherules, which are often magnetic
What two factors determine if a particle is suspended or deposited?
its size and the current (or river) velocity
What mechanism primarily resuspends particles deposited by rivers?
waves
How do large sediment particles reach the abyssal plain?
via turbidity currents, avalanches of rock that can go up to 70 km/hr
What are deposits formed from turbidity currents called?
turbidites
Why is the Atlantic much flatter than the Pacific?
The Pacific has trenches that trap turbidite deposits, which flatten out the Atlantic
How was the speed of a turbidity current first measured?
An earthquake triggered a turbidity current in 1929 off Nova Scotia which snapped five telephone cables on the seafloor, so they could figure out the speed based on the times at which the cables were snapped.
Where do turbidity currents most often flow?
down submarine canyons
Which sedimentation rates vary locally most?
lithogenous sediments
What is the definition of an ooze?
at least 30% biogenous
What is the order of most common sediment inputs?
lithogenous, biogenous, hydrogenous, cosmogenous
Where are most lithogenous sediments found?
close to land, on the continental margins
What and where are the slowest sedimentation rates?
1 mm per millenium, deep oceans far from land
What are relict sediments?
sediments deposited under a different set of ocean conditions than today's, such as a lower sea level
Where are continental margin sediments not dominated by lithogenous particles?
near coral reefs and where CaCO3 precipitates
What particles are deposited in the deep ocean away from land?
fine quartz grains and clay minerals, called deep sea clays
Where in the deep seafloor do radiolarian oozes dominate?
in a band around the Equator, where high productivity and the CCD allow siliceous oozes to accumulate, but not as much in the Atlantic because there is more lithogenous sediment and a deep CCD
Where do diatom oozes dominate?
upwelling areas away from the Equator, mostly around 60º
What are transitional areas between diatom areas and deep sea clays called?
deep sea muds
What dilutes the enormous biogenous inputs to polar areas?
glacial debris from glaciers or icebergs
What are three marginal seas dominated by terrigenous sediments from rivers?
the Arabian Sea, Bay of Bengal and Gulf of Mexico
Where do calcareous sediments accumulate?
above the CCD, such as seamounts and oceanic plateaus
What is the only place known to have hydrothermal sediments dominate?
the central basin of the Red Sea
About how far back in time do oceanic sediments go?
170 million years, which is the age of the oldest remaining oceanic crust
What is the study of sediment layers called?
stratigraphy
What is the mixing of the upper layers of sediment by benthic organisms called?
bioturbation
What are two ways the sediment record can be messed up?
increased current speeds can erode already deposited sediment, and benthic organisms can mix the upper layers of sediment
What are three ways sediment can be dated?
radioactively (using radioisotope decay), magnetically (using magnetic field reversals), and biologically (using extinct species)
What is diagenesis?
physical/chemical changes occuring in sediment after deposition
What do most diagenetic changes involve?
pore/interstitial water trapped in between sediment grains
What happens to chemicals dissolved in pore waters?
They diffuse out of the sediment and sometimes into the overlying ocean.
What happens to dissolved oxygen in pore waters?
It decomposes organic matter and is replaced by oxygen from nitrate and sulfate reduction.
What impact does the reduction of sulfates to sulfides have on pore waters?
Iron, manganese and more are dissolved as sulfides and escape the sediment, only to be redeposited once they reach the oxygen in the ocean water.
How are diagenetic processes important to life?
Nutrients such as nitrates, phosphates and silicates aren't stored as sediments because they are oxidized and escape through the pore waters.
What happens to calcareous sediments falling on the mid-ocean ridge?
The mid-ocean ridge is above the CCD, so they do not break down, and get buried beneath other sediments, which prevents them from dissolving once they are lowered below the CCD.
What do oxygen-18 concentrations tell us about Earth's past climate?
When the climate was colder, O-16, which evaporates more easily than O-18, was moved to ice and the oxygen in CaCO3 had a higher percentage of O-18 in it.
What does a high O-16 to O-18 isotope ratio in sediments mean for temperature and sea level?
The water was warmer (because of differing chemical reactivities and evaporation rates), and thus sea level was higher.
What are the two leading theories of dinosaur extinction?
Lots of volcanic activity and/or a meteorite impact caused dust to enter the atmosphere, block the sun, lower temperatures, and kill the dinosaurs.