WHAT IS A CONTINENTAL MARGIN?

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CEE 598, GEOL 593 TURBIDITY CURRENTS
MORPHODYNAMICS AND DEPOSITS
LECTURE 2 WHAT IS A CONTINENTAL MARGIN?
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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).
continental plain (subaerial)
shoreline
shelf
slope
rise
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THE POSITION OF THE SHORELINE VARIES WITH SEA
LEVEL
Interglacial high stand
Glacial low stand
http//www.teachingboxes.org/seaLevel/lessons/less
on4_SeaLevelCurveGraph.htm
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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
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SO SEA LEVEL FLUCTUATIONS STRONGLY AFFECT
CONTINENTAL MARGINS
continental plain (subaerial)
shelf
slope
rise
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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/
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CONTINENTAL PLATE TECTONICS
http//www.geoware-online.com/GeowareMercatorMap.j
pg
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MANTLE CIRCULATION DRIVES PLATE TECTONICS
http//www.eoearth.org/media/draft/b/b5/Cross_sect
ion_of_the_earth,_tectonic_plates.gif
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SPREADING MARGIN ATLANTIC OCEAN
http//www.geoware-online.com/GeowareCentralNAtlan
ticMap.jpg
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PERU-CHILE MARGIN
http//web1.hrhost.net/huttonco/Other/Latinia/SAm
_PA750.jpg
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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
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CONTINENTAL MARGINS AROUND THE UNITED STATES
Pratson and Haxby, 1997
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CONTINENTAL SLOPE OFF NEW JERSEY
Dissected passive siliciclastic margin.
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CONTINENTAL SLOPE OFF GULF COAST FLORIDA
Carbonate margin life is the sediment factory.
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CONTINENTAL SLOPE, NORTHERN GULF OF MEXICO
Here the continental slope is governed by salt
tectonics.
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CONTINENTAL SLOPE OFF NORTHERN CALIFORNIA
This is a characteristic active margin.
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CONTINENTAL SLOPE OFF OREGON
Active margin with complicated tectonics.
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EACH MARGIN HAS ITS OWN SPECIFIC HISTORY AND
ORIGIN EXAMPLE SALT TECTONICS!
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THE NORTHERN CONTINENTAL SLOPE OF THE GULF OF
MEXICO IS RIDDLED WITH DIAPIRIC MINIBASINS
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HOW WAS THIS BASIN-AND-RIDGE TOPOGRAPHY CREATED?
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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 flows up, sediment flows down. Result
minibasins on surface.
Minibasins
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TURBIDITY CURRENTS HELP TO BOTH BUILD AND DISSECT
CONTINENTAL MARGINS
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REFERENCE Pratson, L.F. Haxby, W.F. ( 1997)
Panoramas of the seafloor. Scientific American,
276(6), 82-87.