13a-ocean basin.ppt

1. Use of a diving bell, ca. 1752 in Britain — an early attempt at marine exploration

2. Ocean Basins • Bathymetry of ocean floors • Deep ocean basins • Continental margins

3. Key Concepts • Seafloor features result from a combination of: • Plate tectonic activity • Erosion and deposition processes • Deep sea floor is the ocean basin • Ocean-continent transition zone is called the continental margin • Sedimentation important process shaping architecture

4. Ocean Basins: Introduction • 71% of Earth’s surface is covered by oceans. • Little has been known about the deep sea until very recently • Methods of study: • Echo sounding and seismic profiling • Submarine diving • Dredging, coring, and drilling • Satellite measurements

5. Bathymetry • Echo Sounding • Multi-beam mapping • Satellite Altimetry

6. Echo Sounder and swath bathymetry

7. Multibeam Bathymetry • Ultra-high resolution, but labor-intensive

8. Bathymetry is topography

9. Satellite Altimetry • Principle: sea surface mirrors underlying topography because of gravitational effect • Lower resolution than multi-beam, but covers entire ocean

10. Deep Sea Trenches Mid-Ocean Ridges Continental Margins TOPEX-POSEIDON bathymetry Seamounts Abyssal Plains

11. Direct Access to Sea Floor Alvin submersible

12. Deep Ocean Drilling JOIDES Resolution

13. Continental margin Deep ocean basin

14. Deep-ocean Basins • More than 1/2 of Earth’s surface • All blanketed by sediment except youngest rocks at ridges • 2 main components: • Oceanic ridges • Abyssal plains

15. The Oceanic Crust • Rocks of the ocean floor differ from continents • Form by seafloor spreading • Mid-ocean ridges: • Largest topographic features on Earth • Divergent plate boundaries • Elevated due to heat • Rift valleys • East Pacific Rise • Mid-Atlantic Ridge

16. Ocean Basins and Abyssal Plains

17. Structure of Oceanic Crust

18. Ocean Crust composition • Balsaltic volcanism and gabbro intrusion • Pillow lavas • Hydrothermal vents (black smokers)

19. Seafloor Spreading Rate is 2-10 cm/yr • Mid-Atlantic Ridge is slow • East Pacific Rise is fast

20. Ocean Basins and Abyssal Plains

21. Ocean Basins and Abyssal Plains • Flat, featureless expanses of sediment-covered ocean floor • ~3700 to 5500 m depth • Older crust is cooler, subsides deeper • Pelagic sediment accumulates • Biogenic ooze: CaCO3 ooze, SiO2 ooze • Terrigenous fine-grained clays and silts

22. Biogenic Ooze • Calcareous or siliceous: • Radiolarians (SiO2) • Foraminifera (CaCO3) • Diatoms (SiO2) • Form cherts and chalks when lithified

23. Deep-ocean Trenches • Long, relatively narrow features • Deepest parts of ocean: up to 11,000 m deep! • Most are located in the Pacific Ocean • Convergent plate boundaries: • Sites where moving lithospheric plates plunge into the mantle --> subduction zones • Associated with island arc volcanoes

24. Continental Margins • Passive vs. Active Margins • Continental Shelf • Continental Slope • Continental Rise

25. Passive margins do not coincide with plate boundaries • Active margins do coincide with plate boundaries (convergent or transform) • Atlantic has mostly passive • Pacific has mostly active

26. Distribution of Continental Shelves and Slopes

27. Continental Slope surface: 5-25 degree slope • Dissected by submarine canyons • Transport sediment from shelves down slope to deep-sea fans

29. Turbidity Currents

30. Continental Rise • Apron of accumulated sediment at base of continental slope • Only on passive margins • 100 to 1000 km wide • Gradual slope (1/8 that of cont. slope)

31. Active Continental Margins • Continental slope descends abruptly into a deep-ocean trench -- subduction zone • Located primarily around the Pacific Ocean • Accumulations of deformed sediment and scraps of ocean crust form accretionary wedges

32. Active Continental Margins