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105_09-seafloor_part_2 - Continental Shelf Continental...

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Unformatted text preview: Continental Shelf Continental shelf and oceanic ridge system Continental Slope Submarine Canyon Submarine Submarine canyon – Origin during lower sea level – Submarine erosion – Slope change is at an average depth of 135 m where the continental slope begins – Much of the sedimentation in the world’s oceans takes place on the slope and rise Submarine Submarine erosion and deposition Abyssal Abyssal Fans – Underwater flows of sediment-laden water down canyons leaves fansedimentfanshaped sediment deposits Submarine erosion and deposition Turbidity Turbidity Currents and Submarine Fans – Fan-shaped deposits of graded beds Fan– Triggered by underwater earthquakes and landslides, or strong storms or floods 1 Submarine erosion and deposition deposition Passive Margins Pacific: active margin - trench, no rise – Includes continental shelf, slope, rise and extends to the abyssal plain at a depth of about 5 km (3.1 miles) Atlantic: passive margin - rise, no trench Passive Margins The Deep-Ocean Basin DeepContinental rise: Wedge Wedge of sediment between continental slope and deep seafloor Deposits Deposits made by – turbidity currents down flowing down the slope – Contour currents flowing along the along slope Abyssal Abyssal plains: flat featureless surfaces adjacent to the rise Active Margins Pacific: active margin - trench, no rise – Consists of continental shelf, slope & oceanic trench – Usually lacks a continental rise and abyssal plain – Usually associated with convergent plate boundaries Atlantic: passive margin - rise, no trench 2 Oceanic Trenches Oceanic trenches: long deep depressions parallel to a Oceanic continental margin or an island arc. Associated with subducting lithosphere. Oceanic Trenches South America Aleutian Islands The Deep-Ocean Basin Deep- The Deep-Ocean Basin DeepOceanic Oceanic Ridges – Telegraph Plateau (Atlantic) discovered in the late 1800s – 1925-27 discovery of a ridge in the center of the Atlantic 1925– Mid-Atlantic Ridge (MAR): 2,000 km wide, 2-2.5 km Mid2above seafloor – Part of 65,000 km long system of ridges – Mostly below sea level, but some are above: Iceland Iceland Azores Azores Easter Easter Island MidMid-ocean ridges: long mountain ranges where divergence occurs; shallow focus seismic activity 3 Equatorial Atlantic MidMid-oceanic ridge system Offset by fracture zones: Transform faults MidMid-Atlantic Ridge East Pacific Rise - Southeast Pacific Iceland Fracture Fracture Zones Fractures Fractures in the Seafloor – Offset ridges by transform faulting – Occur because of irregular rates of plate movement on Earth’s sphere – May extend for many kilometers from the ridge – We often see shallow focus earthquake activity here MidMid-Atlantic ridge 4 Iceland Iceland: Rifting at a divergent plate boundary The DeepThe Deep-Ocean Basin Oceanic Ridges Rift Rift along the center axis of the MAR – – – – 1-2 km deep, several km wide Shallow focus earthquakes Basalt volcanism High heat flow Hot Spot Trench Abyssal plains Ridge The Deep-Ocean Basin DeepAverage Average depth of 3.8 km Dark: Dark: sunlight penetrates only top 100 m No No plant life Temperatures Temperatures just above freezing Low Low biologic productivity – Exception: hydrothermal vent communities Hydrothermal vents Occur Occur along active rift zones 5 Hydrothermal vents Water Water percolates a kilometer down Heats Heats up Dissolves Dissolves minerals Boils Boils out hydrothermal vents Temperature Temperature up to 660 oC Hydrothermal vent communities Black Black Smokers – Hydrothermal vents spewing hot, metal-rich metalwater into colder seawater Hydrothermal vent communities Hydrothermal vent communities More than 400 species NEW TO SCIENCE discovered around hydrothermal vents Giant clams Seafood lover’s special: Hydrothermal vent communities Spider crabs Clams on the half-shell anyone? 6 Hydrothermal vent communities Tube Worm Riftia pachyptila Riftia Unique Unique animal No No mouth No No anus No No digestive tract Dependent Dependent upon bacteria living in its gut or “troposome” Gill Gill extracts sulfide, carbon dioxide & oxygen and blood delivers these to troposome In In return, bacteria provide nourishment for Riftia Seamounts and Guyots Seamounts: Seamounts: rise > 1 km above seafloor Guyot: Guyot: flat topped seamount (wave erosion) Hawaiian Islands Hawaii Maui 7 Kauai Hawaiian Islands 4.7 Ma 2.5 Ma 1.6 Ma 1.1 Ma 0 Ma Hot Spots 60 Ma HawaiiHawaii-Emperor Seamount chain 40 Ma 0 Ma Hot Spots of the World Sedimentation and Sediments on the Deep Seafloor Terrigenous Terrigenous – Land-derived Land– On rise and abyssal plain – Deposited by turbidity currents Pelagic Pelagic – Settles slowly through ocean water – Fine grained clay and skeletons of microscopic organisms 8 The Sea Floor Chapter 9 9 ...
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