Chapter 4 OCE1001 Marine Sediments Sediment eroded rock particles and fragments Deposit by settling through water column Oceanographers decipher Earth history through studying sediments Useful for providing clues to past geographic distributions of marine organisms movements of the ocean floor ocean circulation patterns climate changes on Earth and even global extinction events Lithified when sediment turns into rock and form sedimentary rock Mountains contain telltale marine fossils which indicate that these rocks originated on the ocean floor in the geologic past Mount Everest included Texture the size and shape of particles clues to sediment origins are found in the texture Paleoceanography study of how ocean atmosphere and land interactions have produced changed in ocean chemistry circulation biology and climate How are marine sediments collected and what historical events do they reveal Collecting Marine Sediments floor for analysis Dredge bucket like device used to scoop up sediment form the deep ocean Gravity corer hollow steel tube with heavy weight on top thrust into the sea floor to collect the first cores cylinders of sediment and rock depth of penetration was limited Rotary drilling performed by specially designed ships collect larger deeper cores Deep Sea Drilling Project used the Glomar Challenger its tall drilling rig resembling a steel tower to collect cores by drilling into the ocean floor in water up to 6000 meters deep o Scientists confirmed from these cores the age of the ocean floor increased progressively with distance from the mid ocean ridge sediment thickness increased progressively with distance from the mid ocean ridge Earth s magnetic filed polarity reversals were recorded in ocean floor rocks Ocean Drilling Program when the Deep Sea Drilling Project went international it became this o Used the JOIDES Resolution the new ship had a tall metal drilling rig to conduct rotary drilling pipe was 8200 meters long with a drill bit on the end and could drill 2100 meters deep into the Earth Integrated Ocean Drilling Program took over after the ODP used many ships to drill instead of just one o Used Chikyu can drill up to 7000 meters into the sea floor How do scientists study sediments Deep water cameras Clamshell samplers Piston corers Core libraries Seismic profilers Marine Sediment Classification Lithogenous or Terrigenous derived from rocks on land Classified by origin Biogenous derived from organisms Hydrogenous derived from water Cosmogenous derived from outer space Lithogenous Sediments Derived from pre existing rock material that originates on the continents or islands from erosion volcanic eruptions or blown dust Origin Begin as rocks on land until weathered down by water temperature and chemical effects When in smaller pieces they are eroded and transported It is transported by streams wind glaciers and gravity The greatest quantity is around continental margins Composition Discrete crystals minerals Quartz most abundant chemically stable durable mineral composed of silicon and oxygen in the form SiO2 same as glass It is resistant to abrasion to it is easily transported Courser sediments stay close to shore finer sediments go farther from shore Sediment Texture one of the most important properties of Lithogenous sediments Distribution Litho Sediments are ubiquitous found all over the ocean o Neritic deposits found on continental shelves and in shallow water near islands generally course grained o Pelagic deposits found in the deep ocean basins and are typically fine grained rivers bedding o Beach deposits quartz rich sand that is washed down to the coast by o Continental Shelf Deposits relict left behind sediments cover cont shelves from 3000 plus years ago the ice age changed the way sediments covered continental shelves o Tubidite Deposits composed of characteristic layering called graded o Glacial Deposits contain particles ranging from boulders to clays found in high latitude portions laid down during the most recent ice age by glaciers that melted ice rafting rock particles trapped in glaciers melt and are carried out to sea o Abyssal Clay clay particles carried by wind or ocean current Biogenous sediment Derived from the remains of hard parts of once living organisms Origin begins as the hard parts shells bones teeth of living organisms when they die they settle on the ocean floor and accumulate as biogenous sediment o Macroscopic large enough to be seen without a microscope o Microscopic particles so small you need a microscope includes ooze and tests Composition o Organisms that contribute algae and protozoans o Two most common chemical compounds calcium carbonate and silica Calcium Carbonate Coccolithophore photosynthetic algae coccoliths individual plates from dead organism rock chalk lithified coccolithrich ooze Distribution one of the most common types of pelagic deposits o Distribution depends on 3 fundamental processes Productivity the number of organisms present in the surface water above the ocean floor Destruction occurs when skeletal remains dissolve in seawater at depth Dilution occurs when the deposition of other sediments decreases the percentage of the biogenous sediment found in marine deposits o Carbonate Deposits Limestone rocks occur around tropical islands some deposits make caverns o Stromatolites lobate structures consisting of fine layers of carbonate that form in specific warm shallow water environments such as the high salinity tidal pools in Shark Bay Western Austrailia o Pelagic deposits Ooze is common on the deep ocean floor because there is little lithogenous sediment Siliceous ooze formed by organisms that contain silica in their shells Diatoms are one type of organism whose remains contribute to siliceous ooze contains 30 of the hard remains of silica secreting organisms Calcareous ooze formed by organisms such as foraminifera which contain calcium carbonate in their shells or skeletons contains 30 of the hard remains of calcareous secreting ooze o Lysocline when calcium carbonate is dissolved because the pressure of the deep ocean o Calcite Compensation Depth sediment does not usually contain much calcite because it readily dissolves by this depth Hydrogenous Sediment Usually the result of chemical reactions Hydrogenous sediments are often found in the form of nodules containing manganese and iron oxides Derived from the dissolved material in water Origin chemical reactions within seawater cause certain mineral
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