use of a diving bell ca 1752 in britain an early attempt at marine exploration l.
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Use of a diving bell, ca. 1752 in Britain an early attempt at marine exploration ... Ocean-continent transition zone is called the continental margin ...

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ocean basins
Ocean Basins
  • Bathymetry of ocean floors
  • Deep ocean basins
  • Continental margins
key concepts
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
ocean basins introduction
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
  • Echo Sounding
  • Multi-beam mapping
  • Satellite Altimetry
multibeam bathymetry
Multibeam Bathymetry
  • Ultra-high resolution, but labor-intensive
satellite altimetry
Satellite Altimetry
  • Principle: sea surface mirrors underlying topography because of gravitational effect
  • Lower resolution than multi-beam, but covers entire ocean
topex poseidon bathymetry

Deep Sea Trenches

Mid-Ocean Ridges

Continental Margins



Abyssal Plains

deep ocean drilling
Deep Ocean Drilling

JOIDES Resolution

deep ocean basins
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
the oceanic crust
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
ocean crust composition
Ocean Crust composition
  • Balsaltic volcanism and gabbro intrusion
  • Pillow lavas
  • Hydrothermal vents (black smokers)

Seafloor Spreading Rate is 2-10 cm/yr

    • Mid-Atlantic Ridge is slow
    • East Pacific Rise is fast
ocean basins and abyssal plains21
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
biogenic ooze
Biogenic Ooze
  • Calcareous or siliceous:
    • Radiolarians (SiO2)
    • Foraminifera (CaCO3)
    • Diatoms (SiO2)
  • Form cherts and chalks when lithified
deep ocean trenches
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
continental margins
Continental Margins
  • Passive vs. Active Margins
  • Continental Shelf
  • Continental Slope
  • Continental Rise
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
Continental Slope surface: 5-25 degree slope
  • Dissected by submarine canyons
  • Transport sediment from shelves down slope to deep-sea fans
continental rise
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)
active continental margins
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