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13a-ocean basin.ppt PowerPoint PPT Presentation

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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Use of a diving bell ca 1752 in britain an early attempt at marine exploration l.jpg

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

Ocean basins l.jpg

Ocean Basins

  • Bathymetry of ocean floors

  • Deep ocean basins

  • Continental margins

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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

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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

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  • Echo Sounding

  • Multi-beam mapping

  • Satellite Altimetry

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Echo Sounder and swath bathymetry

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Multibeam Bathymetry

  • Ultra-high resolution, but labor-intensive

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Bathymetry is topography

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Satellite Altimetry

  • Principle: sea surface mirrors underlying topography because of gravitational effect

  • Lower resolution than multi-beam, but covers entire ocean

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Deep Sea Trenches

Mid-Ocean Ridges

Continental Margins



Abyssal Plains

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Direct Access to Sea Floor

Alvin submersible

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Deep Ocean Drilling

JOIDES Resolution

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Continental marginDeep ocean basin

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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

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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

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Ocean Basins and Abyssal Plains

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Structure of Oceanic Crust

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Ocean Crust composition

  • Balsaltic volcanism and gabbro intrusion

  • Pillow lavas

  • Hydrothermal vents (black smokers)

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  • Seafloor Spreading Rate is 2-10 cm/yr

    • Mid-Atlantic Ridge is slow

    • East Pacific Rise is fast

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Ocean Basins and Abyssal Plains

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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

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Biogenic Ooze

  • Calcareous or siliceous:

    • Radiolarians (SiO2)

    • Foraminifera (CaCO3)

    • Diatoms (SiO2)

  • Form cherts and chalks when lithified

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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

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Continental Margins

  • Passive vs. Active Margins

  • Continental Shelf

  • Continental Slope

  • Continental Rise

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  • 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

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Distribution of Continental Shelves and Slopes

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  • Continental Slope surface: 5-25 degree slope

  • Dissected by submarine canyons

  • Transport sediment from shelves down slope to deep-sea fans

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Turbidity Currents

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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)

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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

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Active Continental Margins

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