Slide 1Grain Size ClassificationSediments May Be Classified By Particle SizeSlide 4Poorly Sorted Well SortedSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13LithogenousSlide 15Slide 16Slide 17HydrogenousSlide 19Slide 20Rates of Sedimentation:Slide 22Slide 23Slide 24Slide 25Slide 26Slide 2711•Distribution of sedimentsDistribution of sediments•Seabed ResourcesSeabed ResourcesSediments are particles of organic or inorganic matter that accumulate in a loose, unconsolidated form. Record of geologic/oceanographic history•Types (Classification: size, location, source)Types (Classification: size, location, source)•Location or distribution of sedimentsLocation or distribution of sediments•Rates of Deposits/AccumulationRates of Deposits/AccumulationChapter 5 - SedimentsChapter 5 - Sediments22Large (L)Medium (M)Small (S)Grain Size Grain Size ClassificationClassification33Sediments May Be Classified By Particle SizeSediments May Be Classified By Particle SizeThe velocities of The velocities of currents required for currents required for erosion, transportation, erosion, transportation, and deposition and deposition (sedimentation) of (sedimentation) of sediment particles of sediment particles of different sizes.different sizes.To dislodge and carry a To dislodge and carry a particle of size A, the particle of size A, the speed of a current must speed of a current must exceed 20 centimeters exceed 20 centimeters per second (8 inches per second (8 inches per second). When the per second). When the current falls below 1 current falls below 1 centimeter per second centimeter per second (1/2 inch per second), (1/2 inch per second), the particle will be the particle will be deposited.deposited.44Sediment can be classified by particle size. Waves and currents generally transport smaller particles farther than larger particles.How far sediments go horizontally and how long it takes to get to bottom of sea depends on size. Shape is also important to how sediments go around and settle in the bottom. LMS55Poorly SortedPoorly SortedWell SortedWell Sortedwell sorted: uniform grain sizepoorly sorted: variable grain size66Bluff ErosionOffshore Glacially Deposited Sand Ridges, Relict Ebb ShoalsSources of Sand For Littoral Transport 2 mWave DominatedMixed EnergyGravelSandBarrier IslandCliff or Bluff Coast77Maximum Amount of Material Derived From Bluff Erosion•Historic estimates 81,100 yd3/yr to 132,100 yd3/yr•The bluffs at Montauk Point are receding at 1 ft/yr •This recession rate has been well documented due to endangerment of the historic Montauk Light House constructed in 1796.88•Littoral Transport reaches a maximum rate of 463,015 to 601,657 yd3/yr at Democrat Point (Fire Island Inlet)996 to 29 % of Longshore transport at Fire Island Inlet. 109,868 to 517,948 yd3/yr of sediment may be coming from offshore, (Schwab et al., 1999)1010Classification Based on LocationNeritic: near continental margins & islands Pelagic: deep sea floor1111Classification Based on Source & ChemistryType SourceTerrigenous pre-existing rock (or Lithogenous) all land derived materialBiogenous living organismsHydrogenous precipitation from sea waterCosmogenous space1212Marine Sediments Are Usually Combinations of Terrigenous (from rocks) and Biogenous (organic) DepositsThe sediment of The sediment of continental continental shelves is called shelves is called neriticneritic sediment, sediment, and contains and contains mostly mostly terrigenous terrigenous material.material.Sediments of the Sediments of the slope, rise, and slope, rise, and deep-ocean floors deep-ocean floors are are pelagicpelagic sediments, and sediments, and contain a greater contain a greater proportion of proportion of biogenous biogenous material.material.1313Sediment Thickness1414Lithogenous- From rocks, wood, waste sludge, volcanic stuff- From rocks, wood, waste sludge, volcanic stuff - Results from erosion by air & water Transported by - Results from erosion by air & water Transported by winds, water, ice and gravity. Also by glaciers and winds, water, ice and gravity. Also by glaciers and icebergsicebergs- Dominates the neritic sediments because it is the - Dominates the neritic sediments because it is the largest source for theselargest source for these¼ of all land derived sediments1515BiogenousOozes – sediment containing at least 30% biogenous material. Dominant on deep-ocean floor, 2 types of oozes: * Calcareous (CaCO3) oozes formed by organisms which contain calcium carbonate in their shells or skeletons – dominantpelagic sediment (cocolithophorids, pteropods, foraminifera)* Siliceous (SiO2) oozesformed by organisms that contain silica in their shells. The ocean is under-saturated with respect to Si, so it can dissolve everywhere. (photosynthetic organisms, Diatoms, Radiolaria)1616CCD (~4500 meters) depth where rate of dissolution of calcium carbonate is equals to its rate of accumulation Calcareous Oozes: Marine Snow1717Originate from chemical reactions with water that occur in the existing sediment. Hydrogenous sediments are often found in the form of nodules containing manganese and iron oxides. Hydrogenous sediments can be: Carbonates  direct depositionPhosphorites  abundant in continental shelf Salts  by evaporation Evaporites - salts that precipitate as evaporation occurs. Evaporites include many salts with economic importance. Evaporites currently form in the Gulf of California, the Red Sea, and the Persian GulfManganese nodules  Mn, Fe, Cu, Ni, Co. These are found in abyssal seafloor and continental margins, around ocean ridges and seamounts (but at higher concentrations than those found on land). The Co (cobalt) content is of strategic importance to US (used in aircraft’s manufacture).HydrogenousHydrogenous1818HydrogenousHydrogenousLithogenous (or terrigeneous) (abbyssal Lithogenous (or terrigeneous) (abbyssal clay, red clay Fe)clay, red clay Fe)1919Cosmogenous: Microtektites2020Map of distribution of sedimentThe general pattern of sediments on the ocean floor. Note the dominance of diatom oozes at high latitudes.What differences in the type and distribution of sediments do you note between the Atlantic Ocean and the Pacific Ocean?2121Rates of Sedimentation:Rates of Sedimentation: Neritic SedimentsNeritic SedimentsRivers 800,000 cm/1000 yearsRivers 800,000 cm/1000 yearsBays 500 cm/1000 yearsBays 500 cm/1000 yearsShelf 40 cm/1000