1 lecture 2 what is a continental margin? cee 598, geol 593 turbidity currents: morphodynamics and...
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LECTURE 2WHAT IS A CONTINENTAL MARGIN?
CEE 598, GEOL 593TURBIDITY CURRENTS: MORPHODYNAMICS AND DEPOSITS
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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).
shelf
slope
rise
continental plain (subaerial) shoreline
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THE POSITION OF THE SHORELINE VARIES WITH SEA LEVEL
http://www.teachingboxes.org/seaLevel/lessons/lesson4_SeaLevelCurveGraph.htm
Glacial low stand
Interglacial high stand
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DURING THE LAST GLACIAL MAXIMUM, THE SHORELINE
MOVED OUTWARD TOWARD THE SHELF-SLOPE BREAK
NASA World Wind
Shoreline at low stand (lowest sea level elevation during glaciation)
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shelf
slope
rise
continental plain (subaerial)
SO SEA LEVEL FLUCTUATIONS STRONGLY AFFECT CONTINENTAL MARGINS
6http://sio.ucsd.edu/png/science/
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.
7http://www.geoware-online.com/GeowareMercatorMap.jpg
CONTINENTAL PLATE TECTONICS
8http://www.eoearth.org/media/draft/b/b5/Cross_section_of_the_earth,_tectonic_plates.gif
MANTLE CIRCULATION DRIVES PLATE TECTONICS
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http://www.geoware-online.com/GeowareCentralNAtlanticMap.jpg
SPREADING MARGIN: ATLANTIC
OCEAN
11http://www.clas.ufl.edu/users/jmeert/sam.jpg
http://astro.wsu.edu/worthey/earth/html/im-geology/peru-chile-trench.gif
PERU-CHILE MARGIN
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CONTINENTAL SLOPE, NORTHERN GULF OF MEXICO
Here the continental slope is governed by salt tectonics.
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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 LAYER
SEDIMENT LAYER
SEAFLOOR
Salt flows up, sediment flows down.Result: minibasins on surface.
Minibasins
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