Oceanography Test Two (Marine Sediments)

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The thickest accumulations of sediments in the world are _________________.
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in the oceans.
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All but 8% of the world’s sediment is in the ocean in piles up to ___________.
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9 km thick.
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The thickest accumulations are on the ______________________.
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continental slopes and rises.
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These sediments on the continental margins form mostly from the weathering and erosion of rocks exposed at the Earth’s surface.
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TERRIGENOUS or LITHOGENOUS SEDIMENTS
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some marine sediments form from accumlations of the remains of dead marine organisms (___________), from extraterrestrial particles (_________) and from chemical reactions that cause solids to precipitate from sea water (___________).
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BIOGENOUS COSMOGENOUS HYDROGENOUS
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Sediments also differ as to ________________.
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texture, color, and composition.
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Texture
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The size, shape and sorting of grains in the sediment.
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All terrigenous sediments must be transported ___________ to be deposited in the ocean and most biogenic sediments are produced by organisms which _____________________________ and must, therefore, undergo transport to ________________.
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from land live near the sea surface reach the sea floor
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Only remains of bottom-dwelling organisms and hydrogenous sediments may be formed where __________________, and even these may be transported by bottom currents.
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they are deposited
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Sediment transportation is critical in determining _____________________________________.
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the type of sediment occurring in a particular area.
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The rate and manner in which sediment particles are transported to the sea, and the rate at which they sink to the sea floor, are controlled by their ______, so it is important to classify sediments according to ____________________.
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size particle grain size.
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Particle size tells us something about how much energy was necessary to carry that particle and, therefore, tells us something about ____________________________.
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the environment in which the particle was transported and deposited. (For example, fast-moving water indicates a higher-energy environment in which larger particles can be transported.)
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Sediment grains vary from ____________________________________.
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submicroscopic (1/4000mm) to boulder-sized (>256 mm in diameter).
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Classifying sediments according to grain size Gravel: Sand: Mud:
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> 2mm 1/16 mm < X < 2mm < 1/16 mm
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Grains larger than sand-size do occur along some high energy, rocky coasts, but the other size categories are by far ______________.
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more abundant.
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Big particles sink ______ than small ones.
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faster
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Really large particles such as large gravel sink so rapidly that they are rarely transported in suspension but mainly by _______________________________.
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being bounced and dragged along the bottom.
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Smaller grains can be kept in ____________________.
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by turbulent water motion.
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Rivers – Most terrigenous sediment (____) is carried to the sea by rivers, although the quantity of sediment carried by different rivers varies tremendously.
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85%
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Ice – Nearly _____ of terrigenous sediments are transported to the ocean in ice.
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10%
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Ice-rafting
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Ice bergs do the work of transporting sediments. These types of sediments are poorly sorted (i.e., showing a lot of variation in grain size) and the particles are angular.
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Wave energy also smooths and rounds the surfaces of grains ___________________________.
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by abrasion and by breaking off rough edges.
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Wind — A little less than ____ of terrigenous sediment is transported to the deep sea as wind-blown (Aeolian) dust, however in some portions of the deep sea the sediment is dominated by such terrigenous sediment.
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3% (especially in dry regions)
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______________________ are important sources of Aeolian dust.
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Arabia, Austrialia and North Africa
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Most of the terrigenous particles that arrive at the sea surface destined to become seafloor sediments _________________________.
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are very fine-grained.
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Particle Size (µm) Sinking Rate (cm/sec) Sinking Time 100 2.5 < 2 days 10 0.025 6 months 1 0.00025 51 years
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How long it should take particles of different sizes to sink to the bottom of a 4-km-deep column of seawater.
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The distribution patterns of sediments on the sea floor closely resemble the patterns of distribution of particles at ___________.
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the sea surface.
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Aeolian dust is found ______________________.
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downwind of arid regions on the seafloor.
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Biogenic sediment particles tend to occur on the sea floor directly _________________________________.
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under the areas where the contributing organisms are found in large numbers.
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Biopacking
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Process by which filter-feeders ingest small particles and package them into their feces.
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Turbidity Currents
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Not all terrigenous sediments that reach the seafloor sink from the sea surface. Huge quantities of sediment are carried along the bottom in turbid suspension by underwater avalanches known as turbidity currents.
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The majority of oceanic sediments are terrigenous because…
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of the severe conditions encountered on the continents exposed to the ravages of temperature and the atmosphere.
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Fine-grained terrigenous sediments (clays) make up ____ of oceanic sediments.
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20%
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Biogenic sediments
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Sediments in which the grains are formed by the action of a living organism. Shells, tests, and other hard parts secreted by organisms that fall to the bottom of the ocean and slowly accumulate.
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Ooze
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When the biogentic component makes up more then 30% of the sediment.
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Oozes composed of the hard parts of various organisms occur in the ________.
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deep ocean.
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Oozes dominate _____ of the deep ocean
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62%
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Hydrogenous sediments
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Sediments formed by chemical precipitation of the components dissolved in seawater. Very minor contributor to marine sediments.
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Evaporites
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Salt crystals that form when seawater evaporates. Can contribute to very thick piles of sedimentary rocks in arid, shallow-water marine environments
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Cosmogenous
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Extraterrestrially-derived sediments. Very, very minor from meteoritic debris.
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Estuaries
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Much of the sediment that reached the shelves in times of lower sea levels is now accumulating in drowned river systems
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Biogenic oozes accumulate very slowly in the deep ocean because…
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the surface waters of the central oceans are very poor in nutrients (mostly land-derived), such as nitrogen and phosphorus, that are required by the surface sea creatures. Therefore these waters are inhabited by only small populations which contribute very slowly to the development of deep ocean sediment.
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Two Major Types of oozes:
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Siliceous and Calcareous
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Siliceous oozes
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SiO2 oozes are made up of the tests of floating (planktonic) organisms that extract silica from seawater to make their hard parts. The most abundant of these are the diatoms (plants) and the radiolarians (animals).
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Siliceous oozes dominate ____ of deep ocean.
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14%
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Calcareous oozes
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CaCO3 made up of the tests of floating (planktonic) organisms that extract CaCO3 from seawater to make their hard parts. Coccolithophores (plants) and foraminifera (animals). Only depths less than 4-5 kilometers. (oozes) (tests will not accumulate).
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The carbon dioxide and water combine to form carbonic acid which dissolves the CaCO3.
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CaCO3 (s) + H2O (l) + CO2 (g) = Ca2+ (aq) + 2 HCO3- (aq)
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Calcareous oozes found mostly on the _______________.
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Oceanic ridges and plateaus.
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Abyssal or pelagic clays…
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are extremely fine-grained particles that have remained in suspension for great distances from the continents.
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Manganese nodules and Metal Sulfide deposits
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Very minor components of deep ocean dements but may someday become very important.
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General distribution of deep ocean sediments
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-Age and thickness of sediment increases away from ridges. -Terrigenous sediments dominate on the continental margins and in the highest latitudes where ice cover restricts biological productivity. -Siliceous oozes dominate in highly productive waters near the Equator in the central Pacific and north of Antarctica between 50 and 65o S. -Carbonate oozes dominate in temperate and tropical climates at depths less than 4-5 km. -Abyssal clays dominate deeper oceanic regions.
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The Deep Sea Drilling Project (DSDP)
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Was a major drilling project undertaken by the USA to investigate the sediments and rocks of the ocean basins and to uncover its history.

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