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08 - Ocean Sediment oceanic crust(basalt nearly always...

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Unformatted text preview: Ocean Sediment oceanic crust (basalt) nearly always covered composition particles from land (volcanoes, rivers, dust, etc.) oceanic biological debris chemical processes in water Sediments record extraterrestrial (some) history organic + inorganic of Earth change! Almost all ocean floor is draped in sediment Accumulation rates vary! few cm/yr cm/thousand yrs Fig. 4-22, p. 115 by dust, gravel, silt, mud, etc... = SEDIMENT etc... Sediments provide a record of environmental change over time ocean sediment record = 180 million years only a small fraction of earth history but many older ocean rocks are now on land Seismic profile of layered ocean sediment over volcanic oceanic crust sediment size, type, origin, chemistry, What is a seismic profile? Kind of like sonar, but at lower frequency... distribution, thickness, etc... all reveal etc... something about the conditions at the time that they were formed Ocean sediments record Earth history Ex: Extinction of dinosaurs from asteroid impact core of ocean sediments from time of dinosaur extinction outcrop on land (Gubio, Italy) of uplifted ocean sedimentary rocks from same event / time! 1 Sediment classifications Size classification grain size determines energy needed to transport it bigger = more energy smaller = less energy (can remain suspended) mixture of sizes in a population = sorting well sorted = all one size poorly sorted = mixture of sizes So, sediment grain size can reveal history of fluid energy and transport... transport... Table 5-1, p. 132 Fig. 5-5, p. 132 Sediment classifications Source classification terrigenous : from land biogenous : from marine organisms hydrogenous : grow from seawater cosmogenous : extraterrestrial abundance Table 5-2, p. 133 2 Terrigenous sediments weathering erosion river transport wind transport dust volcanoes Terrigenous sediment transported in Mississippi River into Gulf of Mexico Mt. Pinetubo, Philippines: 1991 eruption ash transported in wind 100's of kilometers and deposited in the ocean 9 cm of ash 25 km from volcano terrigenous dust blowing off the NW coast of Africa into the Atlantic Ocean http://www.gsfc.nasa.gov/feature/2004/0116dust.html Ash layer in ocean seds from South China Sea (USGS) (6 cm thick) Biogenous sediment marine organisms body parts fecal pellets microorganisms most abundant in areas with nutrients & high biological productivity (continental margins, upwelling, etc.) form oil and gas Foraminifera skeletons found in sediment cores provide scientists a means to date cores. Fossils also contain information about ocean temperature, chemistry, currents, and surface winds. calcareous (made of Ca minerals) siliceous (made of Si minerals) 3 A living foraminifera, an amoeba-like amoebaamoeba-like organism that contributes to calcareous ooze Shell of a calcareous foraminifera calcareous coccolith, a form of planktonic algae coccolith, White Cliffs of Dover: made up of uplifted masses of coccolithiophores Calcium compensation depth (CCD) depth below which CaCO3 dissolves usually ~4,500 m above this level: warm water= CaCO precipitates (calcareous plants and animals in water and on seafloor) 3 below this level: cold water= CaCO3 dissolves (no calcareous ooze below this level) 4 Siliceous ooze: radiolarians, amoeba-like microorganisms siliceous ooze: diatom, single-celled algae most common at high latitudes Fecal pellet yes, it's poop from a small planktonic animal (e.g. foraminifera, radiolarians) ~ 80 microns long helps biogenous sediment bits settle to the ocean floor more quickly Enlargement of pellet's surface (2000x magnification) Fig. 5-17b, p. 143 Spatial distribution of sediment types neritic sediment : on continental shelf pelagaic sediment : in deep ocean Atlantic ocean avg thickness = 1km Pacific ocean avg thickness = 0.5 km Atlantic has more rivers, more "passive" tectonic passive" Pacific is bigger (more area to spread seds over), more active tectonic recycling- trenches recycling- setting Table 5-3, p. 137 5 Fig. 5-9, p. 136 Fig. 5-10, p. 137 6 ...
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