08 - Silica-rich Sediment Main sources High-productivity...

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Unformatted text preview: Silica-rich Sediment Main sources High-productivity regions High Preservation 95% of silica skeletons dissolve at surface Perhaps only 2% are buried Silica dissolves LESS at depth => deep, cold bottom has most sediment preservation Diatoms (one-celled algae) (one Radiolarians (one-celled animals) (one Upwelling zones, especially high latitudes siliceous ooze: diatom, single-celled algae most common at high latitudes Chert layers or nodules Siliceous ooze: radiolarians, amoeba-like microorganisms Carbonate-rich Sediment Main sources Important in Coccoliths (one-celled algae) (one Foraminifers (one-celled animals) (one Tropical regions (warm) Also true for Coral Reefs Shallow depths Chalk, Limestone Cementation with depth (pressure) and time calcareous coccolith, a form of planktonic algae coccolith, A living foraminifera, an amoeba-like amoebaamoeba-like organism that contributes to calcareous ooze 1 Carbonate-rich Sediment Dissolving CCD CaCO3 + H2O + CO2 <=> Ca + 2 HCO More dissolved CO2 (colder, deeper, or organic decay) "Carbonate Compensation Depth" Depth" Rate of Dissolving = Influx NO Carbonate in deeper depth "Snowline" effect Snowline" 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) Rise in CCD -- possibilities More CO2 in atmosphere Less life (less influx) Colder ocean waters plant calcareous coccolith diatoms animal foraminifera radiolarian Sediment thickness 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 setting passive" Pacific is bigger (more area to spread seds over), more active tectonic recycling- trenches recycling% ocean area % vol marine seds avg thickness siliceous Sedimentation Rates Deep-Sea average Deep Rapid deposition: 5-10 meters per million years Typical chalk or silica-rich rate silica Equatorial Carbonates = up to 100 m/myr Continental shelf = 10-20x Deep-sea rates 10Deep River deltas = up to 8 m/year! Faster burial or low-oxygen low = Better organic preservation = Future OIL-GAS sources OIL- "Red Clay" = only 1 m/myr Clay" Fig. 5-9, p. 136 2 Sediment types on ocean floor Resources of ocean rocks... rocks... what economic commodities are present in the ocean? biological resources physical resources result from deposition, precipitation, or accumulation of useful substances in the ocean or seabed ocean crust mineralization sedimentary accumulations take millions of years to form not an inexhaustible source! nonrenewable Fig. 5-10, p. 137 Let's define natural "resources" Let' resources" Let's "resources" things that are useful to "us"... us"... population & economic growth = need how are resources allocated? same resources on land, where they are production / distribution / consumption by individuals, governments, businesses more oil / gas / minerals easier to exploit- but as resources run out, exploitoceanic accumulations become more economically viable complicated "ownership" of marine ownership" minerals Global human population Physical oceanic resources hydrocarbon deposits petroleum natural gas methane hydrate sand and gravel salts metals magnesium and its compounds manganese nodules metallic sulfides Monday's lecture mineral deposits water 3 Methane Hydrates largest known hydrocarbon reservoir on Earth (2x all methane-laced ice crystals in continental slope methane in layers 200-500 m below the seafloor 200 only stable at specific temp/pressure not known how they formed exploitation would be costly and dangerous (Russia escape from seds likely played a major role in ancient The areas shown in blue are potential areas of an extended continental shelf beyond the 200 nautical mile limit (red) Exclusive Economic Zone fossil fuels) sediments (ice-like gas) (ice- has only commercial field- need better technology) field- climate change GHASTLI (Gas Hydrate and Sediment Test Laboratory Instrument) system, located at USGS laboratories in Woods Hole, MA Marine sand and gravel 2nd in $$ value only to oil and gas! >1 billion metric tons worth $500 million worlds largest mining operation- sand in the operationBahamas amount mined offshore in 1998... (couldn't find recent #s) 1998... (couldn' diamonds have been found in offshore gravel deposits in Australia and Africa sand is suction dredged from seafloor, built onto an artificial island, and CaCO3 is used in cement, glass, animal feed, reduction of soil acidity 4 Metal-rich Sediments Spreading centers Manganese nodules Hydrothermal vents spew Iron and Manganese Reddish-brown "fall-out" Reddishfall- out" Marine Mining in the Pacific: Science, Economics, and the Environment The 37th Annual Conference of the Underwater Mining Institute October 1520, 2007 University of Tokyo, Japan Baseball-sized concretions at sediment surface Baseball Mn-Fe, with Copper, Nickel, Cobalt Mn Debated economics, mining methods, and ownership Grow only 1 to 4 mm per million years! Growing lumps stay at surface Profitable marine mining industries are currently recovering seabed sand and gravel deposits in the coastal states. Potentially commercial marine mining ventures for seabed sulfide deposits of gold, silver, copper, zinc, and other metals are developing within domestic and international seabed areas. Ferromanganese oxide deposits are investigated primarily in the Pacific and Indian Oceans as future mineable deposits of nickel, cobalt, copper, and other metals. Methane hydrates composed of chemically stable deposits of methane gas bound within a matrix of water ice may form widespread deposits that represent potentially very large energy sources. All of these research and exploration programs are being supported by academic, industrial, and government establishments in many countries. Monday, October 09, 2006 Rising Cu, Mn, Zn Prices Make Case for Ocean Floor Mining Rising prices for copper, zinc, manganese and other important metals are causing some mineral experts to turn their attention to ocean floor mining. Although ocean floor mining is still not a highly commercialized venture, shrinking land-based resources combined with higher metal prices and advancing technology are making it more attractive. Black smoker deposits are rich in copper, manganese, nickel and gold. Manganese nodules are rich in manganese, nickel, copper and cobalt. Prices for these metals have shot up in the past few years as shown on the charts below. Instruments for Navigation, Exploration and Geological Sampling of the R/V Hakureimaru No. 2: Japan oil, gas, and metals national corp. Potential environmental impact?? "The emerging industry of deep-sea mineral mining on seamounts and around the hydrothermal vents, is a threat to unique ecosystems that have not yet been defined. Ocean noise from mining is projected to affect the migration of marine animals. Mineral prospecting is proceeding without any environmental restrictions on either exploratory or future extraction operations." 2/24/06: "We're on the brink of the era of deep ocean mining... advances in marine geology and deep ocean technology have combined to make it realistic to go more than two kms underwater for gold and other mineral treasures. It's a transformation that has evoked a knee-jerk reaction over the possible environmental impacts of this mining, which he believes could be less destructive than terrestrial mining... Presently, the world's first two neophyte marine mining companies, Nautilus Minerals and Neptune Minerals are actively exploring the possibility of mining deep sea floor deposits... Twenty years ago, most mining companies didn't want to hear about this possibility. They thought it was too difficult. But now some are seeing that it's a lot easier to go down through a couple of thousand m of water than through a couple of thousand m of rock... Presently the deepest undersea mines diamond mines off the coast of southern Africa are under just a few hundred m of water. But Dr. Scott points to the offshore oil and gas industry as an example of the possibility for change. The international oil and gas industry went offshore starting in the mid-1940s. Today, about a third of the world's oil comes from under the sea. There are producing wells in 1,500 m of water off the coast of Brazil, and there's drilling at 2,500 m depth in the Gulf of Mexico. 5 ...
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