Marine Provinces

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Chapter 4: Marine Provinces (slides created by M. Anderson, 2009)

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Marine Provinces

  1. 1. Introduction to Marine Provinces and the Ocean Floor<br />
  2. 2. 3 major provinces<br />Continental margins<br />Shallow-water areas close to shore<br />Deep-ocean basins<br />Deep-water areas farther from land<br />Mid-ocean ridge<br />Submarine mountain range<br />Ocean provinces<br />
  3. 3. Continental Margins<br />Zones separating the part of a continent above sea level from the deep‑sea floor. <br />The true geologic margin of a continent ‑ where continental crust changes to oceanic crust ‑ is somewhere beneath the continental slope. <br />
  4. 4. Passive Continental Margin<br />Passive Continental Margin ‑ Trailing end of a continental plate. <br />Posses broad continental shelves, a continental slope and rise. <br />Flat abyssal plains are adjacent to the rise. They lack the seismic and volcanic activity.<br />
  5. 5. Continental margins<br />Active<br />Associated with convergent or transform plate boundaries<br />Much tectonic activity<br />Convergent active margin<br />Oceanic-continental convergence<br />Where oceanic lithosphere is subducted. <br />Seismicity, a young Mt. range and andesitic volcanism. <br />The shelf is narrow and descends directly into a trench. <br />Example: western South America<br />
  6. 6. Continental margin features<br />Continental shelf<br />Shelf break<br />Continental slope<br />Continental rise<br />
  7. 7. Continental Shelf<br />Continental Shelf ‑ where the sea floor slopes very gently seaward. <br />It ends at a steep drop, the shelf ‑ slope break at @ 135m. <br />In the Pleistocene, sea level was much lower, @ 130m. <br />Much of the sediment on continental shelves accumulated in stream channels and floodplains. <br />Some glaciers extended onto the exposed shelves. <br />Affected by waves and tidal currents.<br />
  8. 8. Continental slope<br />Change in gradient from shelf <br />Average gradient 4o<br />Submarine canyonscut into slope by turbidity currents<br />Mixture of seawater and sediments<br />Move under influence of gravity<br />Erode canyons<br />Deposit sediments at base of slope<br />
  9. 9. Turbidity Currents<br />Turbidity Currents ; sediment‑ water mixture denser than normal seawater<br /> Flow down‑slope to the deep‑sea floor. <br />Coarsest particles are deposited first ‑ forming a graded bed. <br />Deposits accumulate as a series of overlapping submarine fans, forming a large part of the continental rise. <br />
  10. 10. Continental Rise<br />Continental rise ‑ gently sloping area from the slope to a trench. <br />Unaffected by surface processes and transport is controlled by gravity. Where most of the sediments are eventually deposited. Much of the sediment is transported by turbidity currents. <br />Deep ocean Basin ‑ seaward of the continental margin.<br />
  11. 11. Submarine Canyons<br />Deep, steep sided submarine canyons occur on continental shelves, but are best developed on the continental slopes. <br />Some Canyons can be traced across the shelf to associated streams on land. Some can not. <br />Strong currents move through these canyons and are probably responsible for their erosion.<br />Monterey Submarine Canyon<br />
  12. 12. Continental rise<br />Transition between continental crust and oceanic crust<br />Turbidite deposits<br />Graded bedding<br />Submarine fans<br />Distal end of submarine fans becomes flat abyssal plains<br />
  13. 13. Submarine fans<br />The product of turbidity currents in km water depth<br />Present/future targets of the oil industry once<br />shallower resources are exhausted<br />
  14. 14. Abyssal Plains<br />Flat abyssal plains are adjacent to the rise. They lack the seismic and volcanic activity.<br /> Abyssal Plains are the flattest, most featureless areas of Earth A result of sediment deposition.<br />Found adjacent to Continental rises.<br />Common in the Atlantic, rare in the Pacific.<br />Along active margins, sediments are trapped in an ocean trench so abyssal fans fail to develop.<br />
  15. 15. Abyssal plains<br />Very flat depositional surfaces from base of continental rise<br />Suspension settlingof very fine particles<br />Sediments cover ocean crust irregularities<br />Well-developed in Atlantic and Indian oceans<br />
  16. 16. Abyssal Hills / Plains<br />Abyssal hills ‑ average @ 250m high. <br />They are common on the sea floor and underlie thick sediments on the abyssal plains.<br />
  17. 17. Abyssal plains<br />Fig. 3.11<br />
  18. 18. Oceanic Trenches<br />Oceanic Trenches<br />Where lithospheric plates are consumed by subduction.<br />Long, narrow features restricted to active continental margins.<br />Oceanic trenches are the sites of greatest oceanic depth.<br />Marianas Trench : 11,000 m deep.<br />The crust here is cooler and slightly denser than elsewhere.<br />
  19. 19. Ocean Trenches<br />Trenches show a huge negative gravity anomaly; <br />The crust is held down and is not in equilibrium.<br />Seismic activity occurs at or near the trenches. <br />They have Benioff zones in which earthquake foci become progressively deeper in a landward direction. <br />Most intermediate and deep<br />earthquakes occur in such zones.<br />They are associated with volcanoes. (W. So. America)<br />
  20. 20. Seamounts<br />Emperor, Marshall and Hawaii seamounts<br />Seamounts are isolated volcanic mountains scattered across the ocean floor. <br />Most common in the Pacific Ocean, seamounts generally rise more than 1,000 meters above the sea floor, often forming islands.<br />
  21. 21. Seamounts<br />When the action of plate tectonics moves a seamount-formed island away from the mid-ocean ridge, the ocean crust sinks, pulling the island beneath the surface. <br />These submerged, often flat-topped, seamounts are called guyots.<br />
  22. 22. Volcanic peaks<br />Poke through sediment cover<br />Below sea level:<br />Seamounts, tablemounts, or guyotsat least 1 km (0.6 m) above sea floor<br />Abyssalhills orseaknollsare less than 1 km<br />Above sea level:<br />Volcanic islands<br />
  23. 23. Landward side of ocean trench<br />Island arc<br />Chain of islands, e.g., Japan, Hawaii, Aleutians<br />Continental arc<br />Volcanic mountain range, e.g., Andes Mountains<br />Volcanic arcs<br />
  24. 24. Andean Arc<br />As the South American continent moved west, in the Cretaceous Period (140mya) the Nazca plate subducted forming a trench.<br />By 130mya igneous activity began and a Volcanic arc was formed.<br />By 90 mya the trench had migrated west and a new volcanic arc formed along the west coast, while mountains to, now in the interior, ceased activity.<br />
  25. 25. Mid-ocean ridge <br />Longest mountain chain<br />On average, 2.5 km (1.5 miles) above surrounding sea floor<br />Wholly volcanic<br />Basaltic lava<br />Divergent plate boundary<br />Central rift valley, faults, and fissures<br />Seamounts<br />Pillow basalts<br />Hydrothermal vents<br />Deposits of metal sulfides<br />Unusual life forms<br />Fracture zones and transform faults<br />
  26. 26. Mid-ocean ridge features<br />Oceanic ridge<br />Prominent rift valley<br />Steep, rugged slopes<br />Example: Mid-Atlantic Ridge<br />Oceanic rise<br />Gentler, less rugged slopes<br />Example: East Pacific Rise<br />
  27. 27. Pillow lava / Pillow basalt<br />When lava flows enter the ocean, or when lava outpourings actually originate within an ocean basin, the flows outer zones quickly congeal.<br /> The lava within the flow is able to move forward by breaking through the hardened surface, when this occurs over and over.<br />The lava flow resembles large bed pillows stacked one upon another.<br />
  28. 28. Hydro‑thermal Vents<br />1970'S @ 2,500m in the Galapagos Rift in E. Pacific Ocean Basin hydro‑thermal vents were first observed. <br />ALVIN: Woods Hole Submersible<br />
  29. 29. Volcanic features of mid-ocean ridge<br />Hydrothermal vents<br />Heated subsurface seawater migrates through cracks in ocean crust<br />Warm-water vents <30oC or 86oF<br />White smokers >30oC <350oC or 662oF<br />Black smokers > 350oC <br />

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