Geologic Oceanography Sediments Geologic Oceanography

What are Sediments? Particles entering the ocean Accumulate Rapidly on continental margin (neritic) Slowly in the deep ocean (pelagic) Reflect ocean history

Types of Marine Sediments Sediment may be classified in two ways: By grain size By origin

Types of Marine Sediments Types of Marine Sediments by grain size: Boulder >256 mm Cobble 64 - 256 mm Pebble 4 - 64 mm Granule 2 - 4 mm Sand 1/16 - 2 mm Silt 1/256 - 1/16 mm Clay <1/256

Types of Marine Sediments Types of Marine Sediments by grain size: Small Large Move Low – moderate High Deposit Very quiet Low - moderate

High energy Low energy Low energy Still water Energy needed to move particle - Boulder - Cobble - Pebble - Gravel - Course sand - Medium sand - Fine sand - Silt - Clay - Boulder - Cobble - Pebble - Gravel - Course sand - Medium sand - Fine sand - Silt - Clay Energy needed to deposit particle Low energy Still water

Types of Marine Sediments Types of Marine Sediments by grain size:

Types of Marine Sediments Sediment can also be classified according to its source. Lithogenous Biogenous Hydrogenous / Chemical precipitates Cosmogenous

Types of Marine Sediments Lithogenous Sediments Sediments from terrestrial (land) sources Includes Sands and muds from continental margins Glacial deposits Clays

Types of Marine Sediments Lithogenous Sediments Red Clay Found in low productivity areas Low sedimentation rates Wind-blown sediment

Types of Marine Sediments Biogenous Sediments particles derived from hard parts and soft tissues of organisms Ooze = greater than 30% biogenous sediment Distribution related to: sediment supply rate of dissolution and sediment dilution

Biogenous Sediment Accumulation Thurman Essentials of Oceanography 6/e fig 4.15 Relationships among carbonate compensation depth, the mid-ocean ridge, sea floor spreading, productivity, and destruction allow calcareous ooze to be found below the CCD. Thurman Essentials of Oceanography 6/e fig 4.15

Types of Marine Sediments Biogenous Sediments Siliceous Oozes Fine-grained pelagic deposit Composition: 30% siliceous (SiO2) material of organic origin Diatoms (phytoplankton) and Radiolaria (zooplankton) Siliceous particles dissolve more slowly than calcareous particles siliceous ooze Fine-grained pelagic deposit of the deep-ocean floor with more than 30% siliceous material of organic origin. Radiolaria and diatom remains are the major constituents of the siliceous oozes, which tend to occur at depths in excess of 4500 m. A Dictionary of Earth Sciences, © Oxford University Press 1999 (www.xrefer.com)

Siliceous Oozes Thurman Essentials of Oceanography 6/e Siliceous ooze accumulates on the ocean floor beneath areas of high productivity, where the rate of accumulation of siliceous tests is greater than the rate at which silica is being dissolved.

Diatoms Composed of SiO2 Phytoplankton Base of food chain http://www.microscopy-uk.org.uk/micropolitan/marine/diatom/index.html

Radiolaria Composed of SiO2 Zooplankton Base of food chain http://www.microscopy-uk.org.uk/micropolitan/marine/radiolaria/index.html

Types of Marine Sediments Biogenous Sediments Calcareous Oozes Wide-spread in relatively shallow areas of the deep sea CaCO3 particles dissolve at “Carbonate Compensation Depth” = (CCD) Atlantic: ~ 4,000 m Pacific: ~ 500 - 1,500 m

Foraminifera Composed of calcium carbonate (CaCO3) Zooplankton

Types of Marine Sediments Hydrogenous sediments Minerals that crystallize directly from seawater Most common types include Manganese nodules Calcium carbonates Metal sulfides Evaporites © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Types of Marine Sediments Hydrogenous sediments Ferromanganese Nodules First discovered in 1868 on the Kara Sea (Russia) Characteristics small balls (lightly flattened) dark-brown and 5 - 10 cm in diameter Found at depths of 4,000 to 6,000 m Not clear how these nodules form http://www.ifremer.fr/drogm_uk/Realisation/Miner/Nod/texte/txt1_2.html

Distribution Of Manganese Nodules Thurman Essentials of Oceanography 6/e fig 4.23 This generalized map shows the distribution of manganese nodules on the sea floor. After Cronan, D. S. 1977. Deep sea nodules: Distribution and geochemistry, in Glasby, G. P., ed., Marine Manganese Deposits, Elsevier Scientific Publishing Co.

Sulfide Deposits EARTH: An Introduction to Physical Geology 7th ed / Tarbuck & Lutgens fig 21.25 Massive sulfide deposits can result from the circulation of seawater through the oceanic crust along active spreading centers. As seawater infiltrates the hot basaltic crust, it leaches sulfur, iron, copper, and other metals. The hot, enriched fluid returns to the seafloor near the ridge axis along faults and fractures. Some metal sulfides may be precipitated in these channels as the rising fluid begins to cool. When the hot liquid emerges from the seafloor and mixes with cold seawater, the sulfides precipitate to form massive deposits.

Types of Marine Sediments Hydrogenous sediments Evaporites Evaporation triggers deposition of chemical precipitates rock salt rock gypsum

Formation of Evaporites

Astronaut photo of the southwestern edge of the Zagros Mountains featuring salt domes (the white section in the middle and the bump on the left). Astronaut photo of the southwestern edge of the Zagros Mountains featuring salt domes (the white section in the middle and the bump on the left). Source http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17245 Date February 28, 2006 Author NASA Permission US government, public domain Source http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17245

Salt Ponds, S. San Francisco Bay http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=10263 http://www.nasa.gov/centers/ames/images/content/74814main_ACD03-0133-031.jpg (Earth Sciences and Image Analysis Laboratory at Johnson Space Center )

Death Valley, California Once a deep Pleistocene Lake (100 miles long 600 feet deep) Change in climate at end of ice age NASA images created by Jesse Allen, Earth Observatory, using data obtained courtesy of the MODIS Rapid Response team and the Goddard Earth Sciences DAAC.

Wieliczka Salt Mine, Poland Photo date 9/97; © by J.S. Aber http://academic.emporia.edu/aberjame/ice/lec14/wielicz.htm Great cathedral, a large chamber carved entirely within salt, including floor, walls, ceiling, and decorations. Chandeliers are made with salt crystals. Photo date 9/97; © by J.S. Aber http://academic.emporia.edu/aberjame/ice/lec14/wielicz.htm Closeup view of the cathedral's altar.

Wieliczka Salt Mine Virtual Tour http://www.kopalnia.pl St. Anthony’s Chapel, built between 1690-1710 St. John Chapel built ~1859

Types of Marine Sediments Organic Matter Oxidized Sediments Slow burial, organic matter will oxidize and produce water + carbon dioxide Find burrows = life = oxygen Oxidized mud = olive greenish gray Unoxidized Sediments Rapid burial, little time for oxidation Unoxidized mud = black

Types of Marine Sediments Organic Matter Weight of overlying sediment plus increase temperature - cook organic matter = petroleum Usually if black have lots of organic matter

Sediment distribution Sand Closer to shore, on margins of continents Brought to margins by by rivers Sand requires high energy to transport Waves rework sand along coast to form our beaches Some sand makes it to deep ocean through submarine canyons

Sediment distribution Clays & Silts Finer sediments are suspended in water Carried by the currents until they settle out of the water Found in deep ocean, low energy environments

Sediment distribution Where are sediments the thickest? Thickest in trenches—Accumulations may approach 10 kilometers Basins Pacific Ocean—About 600 meters or less Atlantic Ocean—From 500 to 1000 meters thick Thinnest along spreading centers Mud is the most common sediment on the deep-ocean floor

http://www.ngdc.noaa.gov/mgg/image/sedthick9.jpg

Sediment distribution Types of deep-ocean basin sediments Turbidites – deposits made by turbidity currents Oozes – deep-ocean sediment containing at least 30% biogenous material Hydrogenous sediments - originate from chemical reactions that occur in the existing sediment Evaporites - salts that precipitate as evaporation occurs © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Sediment distribution Rates Of Deposition Deep ocean 0.5-1.0cm/1000 yrs slow rates yet can get thick because oldest crust is 200 m.y. clays take 100 yrs to sink 3000 m

Studying Sediments How do scientists study sediments? Deep-water cameras Clamshell samplers Dredges Piston Corers Core libraries Seismic profilers © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Studying Sediments Dredges http://walrus.wr.usgs.gov/pubinfo/margeol2.html Rock samples being removed from a small rock dredge. Scientists inspect a just recovered dredge haul (below), which contains samples of volcanic basalt (above left) and a seafloor crust rich in manganese (above right).

Studying Sediments One method of studying sediments uses a clamshell sampler. The sampler can be used to obtain a relatively undisturbed sediment sample. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Van – Veen Mud Grab

Studying Sediments Grab Sampler Good for collecting soft sediment, sand or perhaps gravel. Low tech - basically just a weighted cage that is dragged along the sea floor. http://www.odp.usyd.edu.au/odp_CD/who/whoindex2.html#B

Studying Sediments Piston Corer Allows a cylinder of sediment to be taken for analysis to determine the age of the material, as well as the density, strength, molecular composition and radioactivity of the sediment. Used by research vessels such as the JOIDES Resolution © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Piston Corer

Drilling Ocean Cores EARTH: An Introduction to Physical Geology 7th ed / JOIDES Resolution can reenter holes years after initial drilling.

Corer This figure shows an examination of deep- ocean sediment cores. Long cylinders of sediment and rock called cores are cut in half and examined, revealing interesting aspects of Earth history. APT photo

Studying Sediments What can scientists learn by studying sediments? Historical information Location of natural resources, especially crude oil and natural gas © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Studying Sediments Based on data from core samples, scientists have determined the age of portions of the Pacific floor, measured in mega-annums, or millions of years. © 2002 Brooks/Cole, a division of Thomson Learning, Inc.

Seabed Resources Depletion of onshore resources - need alternatives Sand & Gravel Phosphorite Sulfur Coal Oil and Gas

How Much Do We Need?

EARTH: An Introduction to Physical Geology 7th ed / Tarbuck & Lutgens fig 21.2 The annual per capita consumption of nonmetallic and metallic mineral resources for the United States is nearly 10,000 kilograms (11 tons)! About 94 percent of the materials used are nonmetallic. (After U.S. Bureau of Mines)

Hydrocarbon Seeps Thurman Essentials of Oceanography 6/e fig 15.28a Hydrocarbon seeps on the continental slope of the Gulf of Mexico

Gas Hydrate Formed from a mixture of water and natural gas, usually methane. Occurs in the pore spaces of sediments http://woodshole.er.usgs.gov/project-pages/hydrates/index.html Gas Hydrate is an ice-like crystalline solid formed from a mixture of water and natural gas, usually methane. They occur in the pore spaces of sediments, and may form cements, nodes or layers. Gas Hydrate is found in sub-oceanic sediments in the polar regions (shallow water) and in continental slope sediments (deep water), where pressure and temperature conditions combine to make it stable. Natural Gas Hydrate contains highly concentrated methane, which is important both as an energy resource and as a factor in global climate change.

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