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LECTURE 2 WHAT IS A CONTINENTAL MARGIN?

CEE 598, GEOL 593 TURBIDITY CURRENTS: MORPHODYNAMICS AND DEPOSITS. LECTURE 2 WHAT IS A CONTINENTAL MARGIN?. EVERY CONTINENT IS SURROUNDED BY A MARGIN. The margin consists of a shelf (out to ~ 100 m), slope , and rise (which tapers off into deep water). continental plain (subaerial).

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LECTURE 2 WHAT IS A CONTINENTAL MARGIN?

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  1. CEE 598, GEOL 593 TURBIDITY CURRENTS: MORPHODYNAMICS AND DEPOSITS LECTURE 2 WHAT IS A CONTINENTAL MARGIN?

  2. EVERY CONTINENT IS SURROUNDED BY A MARGIN The margin consists of a shelf (out to ~ 100 m), slope, and rise (which tapers off into deep water). continental plain (subaerial) shoreline shelf slope rise

  3. THE POSITION OF THE SHORELINE VARIES WITH SEA LEVEL Interglacial high stand Glacial low stand http://www.teachingboxes.org/seaLevel/lessons/lesson4_SeaLevelCurveGraph.htm

  4. DURING THE LAST GLACIAL MAXIMUM, THE SHORELINE MOVED OUTWARD TOWARD THE SHELF-SLOPE BREAK Shoreline at low stand (lowest sea level elevation during glaciation) NASA World Wind

  5. SO SEA LEVEL FLUCTUATIONS STRONGLY AFFECT CONTINENTAL MARGINS continental plain (subaerial) shelf slope rise

  6. CONTINENTAL MARGINS COME IN TWO BASIC FLAVORS DEPENDING ON THE TECTONIC SETTING: ACTIVE AND PASSIVE MARGINS Passive margins tend to be broad, with extensive shelves. Active margins tend to be narrow, with constricted shelves. http://sio.ucsd.edu/png/science/

  7. CONTINENTAL PLATE TECTONICS http://www.geoware-online.com/GeowareMercatorMap.jpg

  8. MANTLE CIRCULATION DRIVES PLATE TECTONICS http://www.eoearth.org/media/draft/b/b5/Cross_section_of_the_earth,_tectonic_plates.gif

  9. SPREADING MARGIN: ATLANTIC OCEAN http://www.geoware-online.com/GeowareCentralNAtlanticMap.jpg

  10. PERU-CHILE MARGIN http://web1.hrhost.net/~huttonco/Other/Latinia/SAm_P&A750.jpg

  11. PERU-CHILE MARGIN http://astro.wsu.edu/worthey/earth/html/im-geology/peru-chile-trench.gif http://www.clas.ufl.edu/users/jmeert/sam.jpg

  12. CONTINENTAL MARGINS AROUND THE UNITED STATES Pratson and Haxby, 1997

  13. CONTINENTAL SLOPE OFF NEW JERSEY Dissected passive siliciclastic margin.

  14. CONTINENTAL SLOPE OFF GULF COAST FLORIDA Carbonate margin: life is the sediment factory.

  15. CONTINENTAL SLOPE, NORTHERN GULF OF MEXICO Here the continental slope is governed by salt tectonics.

  16. CONTINENTAL SLOPE OFF NORTHERN CALIFORNIA This is a characteristic active margin.

  17. CONTINENTAL SLOPE OFF OREGON Active margin with complicated tectonics.

  18. EACH MARGIN HAS ITS OWN SPECIFIC HISTORY AND ORIGIN EXAMPLE: SALT TECTONICS!

  19. THE NORTHERN CONTINENTAL SLOPE OF THE GULF OF MEXICO IS RIDDLED WITH DIAPIRICMINIBASINS

  20. HOW WAS THIS BASIN-AND-RIDGE TOPOGRAPHY CREATED?

  21. UNDERNEATH A LAYER OF SEDIMENT ~ 10 KM THICK IS A LAYER OF SALT ~ 1 KM THICK Salt tectonism: Salt is a Newtonian fluid with a very high viscosity! Overlying sediment (mud) ~ a Bingham fluid! Salt is lighter than mud! Salt flows up, sediment flows down. Result: minibasins on surface. Minibasins

  22. TURBIDITY CURRENTS HELP TO BOTH BUILD AND DISSECT CONTINENTAL MARGINS

  23. REFERENCE Pratson, L.F. & Haxby, W.F. ( 1997) Panoramas of the seafloor. Scientific American, 276(6), 82-87.

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