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Submarine Canyons and Fans Submarine canyons: major conduits

Submarine Canyons and Fans Submarine canyons: major conduits of siliciclastic sediment from the continental shelf to the abyssal plain Submarine fans: accumulations of siliciclastic sediment from the shelf break onto the base of the continental slope.

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Submarine Canyons and Fans Submarine canyons: major conduits

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  1. Submarine Canyons and Fans • Submarine canyons: major conduits • of siliciclastic sediment from the continental shelf to the abyssal plain • Submarine fans: accumulations of • siliciclastic sediment from the shelf break onto the base of the continental slope http://www.dkimages.com/discover/previews/851/20117924.JPG

  2. Submarine Canyons (Basic Info) • Submarine canyons cut across continental shelves and slopes • Carry sediment to the deep ocean basins. • Many small submarine canyons and few large ones. • Large canyons associated with large coastal rivers. • Text from http://www.ocean.uni-bremen.de/EInfo/materialien/elemOc/top12-17/topic13.html http://www.geol.umd.edu/~jmerck/

  3. Submarine Canyons (Basic Info) • Submarine canyons formed, in part, by downcutting of coastal rivers during low sea level. • Later continued flow of water and sediment might lead to their further development • and extension into the deep sea. Text from http://www.ocean.uni-bremen.de/EInfo/materialien/elemOc/top12-17/topic13.html

  4. Submarine Fans • Submarine fans are found at mouths of canyons around the world. http://faculty.gg.uwyo.edu/heller/Sed% http://www.indiana.edu/~g105lab/images/gaia_chapter_13/sfs026.gif

  5. Submarine Fans (Basic Info) • Submarine fans divided into 3 zones • Proximal (upper) • Middle • Distal (lower) http://www.geol.umd.edu/~jmerck/geol100/lectures/31.html

  6. Like alluvial fans fans are fan shaped • And “fine” in a proximal to distal direction

  7. Submarine Fans: Transport Mechanisms • Sediment transport, in general can occur in one of 5 modes: • Traction • 1. Rolling • 2. Sliding • 3. Bouncing (saltation) • 4. Suspension • 5. Mass movement

  8. The whole process is initiated as an underwater landslide. http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg

  9. On the proximal fan, the slide has a low water:sediment ratio Debris flow facies http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg

  10. On the distal fan, the flow has a high water:sediment ratio • and moves as a density current. http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg http://serc.carleton.edu/

  11. Density Currents • Our first quantitative experience with density currents was in • 1929 following the M 7.2 Grand Banks Earthquake Estimated tsunami travel times (in hours) for waves generated by the 1929 Grand Banks earthquake. http://www.benfieldhrc.org/activities/hrsr/h&rsr_2005 http://earthquakescanada.nrcan.gc.ca/historic_eq/20th/1929/1929_e.php

  12. Grand Banks Earthquake • Density Currents • The earthquake triggered an underwater landslide/ density current as evidenced by a series of underwater telephone cable breaks. The last cable, 600 km south, broke 13 hours after the earthquake. Twenty-five years later, south of the earthquake site, a layer of sand was discovered on the sea floor, covering an area the size of the province of Quebec (shown above in light blue). And evidence of vast underwater landslides was found near the epicentre http://earthnet-geonet.ca/images/communities/earthquakemap.gif

  13. Turbidites • Turbidites are formed • as a result of waning • flow. • A classic Bouma sequence http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStrat%208/bouma.jpg

  14. Upper Carboniferous (Namurian), Ireland. Note bed tabularity. • Turbidite sequences can consist of 1000’s of individual beds http://www.geoclastica.com/images/MisoaFm.jpg

  15. Turbidites are primarily • distinguished on the basis of • their graded nature.

  16. Turbidites • The character of turbidites (e.g., the thickness and number of Bouma units varies with distance down the fan). http://csmres.jmu.edu/geollab/fichter/SedRx/subfan.html

  17. Knowledge of Submarine Fans • Almost all of our knowledge of submarine fans comes from ancient environments and geophysics. http://strata.geol.sc.edu/images/PosmentierKolla-elementsFan.gif

  18. Knowledge of Submarine Fans • Fan environments are 1000’s of meters below • ocean, they • apparently have features • that look very much like • those produced by • surface processes. http://strata.geol.sc.edu/images/PosmentierKolla-elementsFan.gif

  19. This is the best (and simplest) model we have of a submarine fan depositional facies

  20. Vertical Column • And this is the best vertical section.

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