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

http://www.dkimages.com/discover/previews/851/20117924.JPG

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/

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

Submarine Fans

• Submarine fans are found at mouths of canyons around the world.

http://www.indiana.edu/~g105lab/images/gaia_chapter_13/sfs026.gif

http://faculty.gg.uwyo.edu/heller/Sed%

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

• Like alluvial fans fans are fan shaped

• And “fine” in a proximal to distal direction

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

• The whole process is initiated as an underwater landslide.

http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg

• 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

• On the distal fan, the flow has a high water:sediment ratio

• and moves as a density current.

http://serc.carleton.edu/

http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg

• Density Currents• Our first quantitative

experience with density currents was in

• 1929 following the M 7.2 Grand Banks Earthquake

http://earthquakescanada.nrcan.gc.ca/historic_eq/20th/1929/1929_e.php http://www.benfieldhrc.org/activities/hrsr/h&rsr_2005

Estimated tsunami travel times (inhours) for waves generated by the 1929Grand Banks earthquake.

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

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

• Turbidite sequences can consist of 1000’s of individual beds

Upper Carboniferous (Namurian), Ireland. Note bed tabularity.

http://www.geoclastica.com/images/MisoaFm.jpg

• Turbidites are primarily

• distinguished on the basis of

• their graded nature.

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

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

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

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

Vertical Column

• And this is the best vertical section.