CEE 598 GEOL 593 TURBIDITY CURRENTS MORPHODYNAMICS AND
CEE 598, GEOL 593 TURBIDITY CURRENTS: MORPHODYNAMICS AND DEPOSITS LECTURE 2 WHAT IS A CONTINENTAL MARGIN? 1
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 shoreline (subaerial) shelf slope rise 2
THE POSITION OF THE SHORELINE VARIES WITH SEA LEVEL Interglacial high stand Glacial low stand http: //www. teachingboxes. org/sea. Level/lessons/lesson 4_Sea. Level. Curve. Graph. htm 3
DURING THE LAST GLACIAL MAXIMUM, THE SHORELINE MOVED OUTWARD TOWARD THE SHELF-SLOPE BREAK NASA World Wind Shoreline at low stand (lowest sea 4 level elevation during glaciation)
SO SEA LEVEL FLUCTUATIONS STRONGLY AFFECT CONTINENTAL MARGINS continental plain (subaerial) shelf slope rise 5
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/ 6
CONTINENTAL PLATE TECTONICS http: //www. geoware-online. com/Geoware. Mercator. Map. jpg 7
MANTLE CIRCULATION DRIVES PLATE TECTONICS 8 http: //www. eoearth. org/media/draft/b/b 5/Cross_section_of_the_earth, _tectonic_plates. gif
SPREADING MARGIN: ATLANTIC OCEAN http: //www. geowareonline. com/Geoware Central. NAtlantic. Map. jpg 9
PERU-CHILE MARGIN 10 http: //web 1. hrhost. net/~huttonco/Other/Latinia/SAm_P&A 750. jpg
PERU-CHILE MARGIN http: //astro. wsu. edu/worthey/earth/html/im-geology/peru-chiletrench. gif 11 http: //www. clas. ufl. edu/users/jmeert/sam. jpg
CONTINENTAL MARGINS AROUND THE UNITED STATES Pratson and Haxby, 1997 12
CONTINENTAL SLOPE OFF NEW JERSEY Dissected passive siliciclastic margin. 13
CONTINENTAL SLOPE OFF GULF COAST FLORIDA Carbonate margin: life is the sediment factory. 14
CONTINENTAL SLOPE, NORTHERN GULF OF MEXICO Here the continental slope is governed by salt tectonics. 15
CONTINENTAL SLOPE OFF NORTHERN CALIFORNIA This is a characteristic active margin. 16
CONTINENTAL SLOPE OFF OREGON Active margin with complicated tectonics. 17
EACH MARGIN HAS ITS OWN SPECIFIC HISTORY AND ORIGIN EXAMPLE: SALT TECTONICS! 18
THE NORTHERN CONTINENTAL SLOPE OF THE GULF OF MEXICO IS RIDDLED WITH DIAPIRIC MINIBASINS 19
HOW WAS THIS BASIN-AND-RIDGE TOPOGRAPHY CREATED? 20
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 21
TURBIDITY CURRENTS HELP TO BOTH BUILD AND DISSECT CONTINENTAL MARGINS 22
REFERENCE Pratson, L. F. & Haxby, W. F. ( 1997) Panoramas of the seafloor. Scientific American, 276(6), 82 -87. 23
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