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Chapt05_Sediments - Sediments of the Ocean Sediments of the...

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Unformatted text preview: Sediments of the Ocean Sediments of the Ocean Chapter 5 Sediments of the Oceans Sediments s s 1. 2. 3. Are particles of Are organic or inorganic matter that accumulates in a loose unconsolidated form form Originates from: Weathering Erosion Living organism 1. 2. 3. Volcanic eruptions Chemical process Outer space Why study Sediments Why s s s s s Sediments are the Sediments history book of the planet recording: planet Movement of plates Ocean currents Ancient climates and Ancient past ocean temperatures temperatures Mountain building and Mountain continental collision continental s s s s Evolution of life Volcanic eruptions Meteorite and asteroid Meteorite impacts impacts Sediments are also the Sediments waste products of both the continents and oceans. oceans. Weathering processes Weathering Mechanical weathering is the physical Mechanical breakdown of rock – biological sediments sediments s Chemical weathering is breakdown of Chemical rock by chemical processes rock s Igneous rock + water = what type of Igneous rock? rock? s Sedimentary s Erosion, Transportation, and Deposition and s s s Water delivers the vast Water majority of particulate and dissolved material to the sea. sea. Wind transports only a Wind small fraction of the sediment reaching the oceans oceans Glaciers: In polar regions, Glaciers: they deliver considerable quantities of coarse sediment. sediment. Sediment: Rounding & Sorting Sorting As material is transported, it is sorted by As size, since current velocity will set a maximum on the size of particle that can be transported. s Collisions between particles, particularly Collisions the larger ones, and with the bottom of a stream, will result in rounding of the particles. particles. s s All 4 particles types have 4 properties: All 1. Texture s 2. Porosity s 3. Permeability s 4. Composition s 1. TEXTURE 1. s s s s sizes of particles (Table 5-1) boulders, cobbles, pebbles, boulders, granules, sand, silt, clay, colloids. Silt + clay = mud) sorting (how much of each sorting size particle: all same size = well-sorted; mix of mud, gravel, sand = poorly sorted) gravel, Larger particles require more energy to Larger be moved (fig. 5.5) s The energy is supplied by moving water The or wind. s The faster the water or wind, the larger The size particle can be picked up. s 2. POROSITY 2. s s the spaces between the particles particles highest porosity highest occurs in clay occurs 3. PERMEABILITY 3. s s how inter-connected how the pores are the highest permeability highest is in sand; llowest is owest is in clay in 4. COMPOSITION 4. s s s A) Minerals (naturally-occurring, inorganic A) Minerals compounds with a specific chemical composition and a crystalline structure examples: halite, calcite, silicate minerals examples: minerals from rocks: basalt on the left basalt contains black silicate minerals; granite, on granite on the right, contains mostly white silicate minerals with a few black ones scattered through. s minerals from living organisms, calcite minerals calcite from corals from B) Non-minerals B) Non-minerals a. Organic: contains C (carbon) and H Organic contains (hydrogen), s Ex.:plant matter, algal matter (oil) Ex.:plant s s b. Inorganic: llacks the crystalline b. Inorganic acks structure (= glass) glass examples: volcanic ash; the silica (SiO2) examples: of diatom shells Classifying Sediments Classifying Terrigenous or Detrital Terrigenous s s s Detrital sediments consist of particles which Detrital arise from weathering on the continents; chemical sediments precipitate from seawater. seawater. Most sediments are a mixture of various Most components, but often one component is dominant dominant Sediment are classified according to this Sediment dominant component. dominant Lithogenous or Terrigenous (cont.) Terrigenous Rivers and volcanic eruptions are the Rivers main source main s Igneous rocks, sands, mud of the Igneous continental shelf continental s Volcanic Ash layers s Glacial Marine: sediment delivered to Glacial the oceans by glaciers and carried by icebergs. icebergs. s Biogenous Biogenous Biogenous, or biogenic, sediments are Biogenous, the remains of organisms; s most abundant, often the shells of most single cell organisms living in the surface waters. s Calcareous Oozes (consist of >30% Calcareous CaCO3 shells; eventually forms chalk or CaCO limestone) limestone) s s Foraminferal or Globigerina Oozes Foraminferal (protozoans). (protozoans). s Pteropod Oozes (swimming snails; Pteropod rare) rare) s Coccolith Oozes (algae) s Siliceous Oozes (consist of >30% SiO2 Siliceous SiO shells shells s Diatom Oozes (algae) s Radiolarian Oozes (protozoans) s Coral Reefs: reefs grow in shallow Coral water; carbonate skeletons of coral and cemented debris cemented Hydrogenous (Chemical) Hydrogenous Precipitated from the water s Evaporites are an important group of Evaporites hydrogenous deposits hydrogenous s Form when sea water evaporates s s Typical evaporite, It doesn't look like Typical table salt yet, because it has red clay and black organic matter in it and Manganese (Mn) nodules grow by Manganese precipitation of iron and manganese hydroxides from seawater (fig. 5.12) hydroxides s Require very low sedimentation rates. s Phosphate Nodules: grow by Phosphate precipitation from sediment precipitation s Cosmogenic Cosmogenic s s micrometeorites are micrometeorites an identifiable component in slowly accumulating sediments. sediments. Microtektites in the Microtektites shape of a drop can be observed on cosmogenic sediments (fig. 5.7) sediments Distribution of Marine Sediments Sediments Near-shore Deposition: coarsest Near-shore materials are deposited close to source and close to shore and s sediment on shelves tends to be sediment coarser (larger) in grain size (gravel, sand, and silt), while sediment in the deep areas tends to be finer (smaller) in grain size (silt and clay) s Turbidites Turbidites Turbidity Currents: play an important Turbidity role in transporting sediment to deep ocean ocean s Turbidity Currents are density currents: Turbidity a flowing mixture of sediment and water which is denser than surrounding water. s image of a turbidity current moving down the continental slope off California Like rivers, they seek lowest point. s Characteristics of Turbidite deposits: Characteristics graded bedding graded s Turbidity currents occur Turbidity catastrophically. catastrophically. s Associated features: submarine Associated canyons, fans, levees canyons, s Clays Clays Abyssal Clays (Brown Clays): In Abyssal general, these are very fine-grained products of continental weathering products s Gray clays: often distal ends of turbidity Gray currents. currents. s Red clays (contain hydrogenous Red component): wind-blown material is most important constituent. most s s s s calcareous oozes (carbonate) accumulates in shallower areas of the deep sea, along mid-ocean ridges, siliceous oozes accumulate in cold water accumulate areas (around Antarctica and off the coast of Alaska) and siliceous oozes accumulate where there is a accumulate source of rich nutrients (along the equator in the Pacific Ocean) the Calcite (calcareous) particles dissolve Calcite in deeper ocean water. s The pteropods go first, followed by the The forams, and, lastly, the coccoliths. s The water depth at which all of the The forams dissolve is called the lysocline. lysocline s s The water depth at which the coccoliths The dissolve is called the Calcium Compensation Depth, the CCD (fig. 5.9) red clay fills in the rest of the area s ''H' stands for 'hydrogenous', which is H' the same as 'authigenic'. s These occur where sedimentation rates These are very low (in red clay areas), and where deep ocean currents move swiftly (Cape of Good Hope, southern Africa; also between Florida and the Bahamas) s ...
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