The Ocean Floor and Its Sediments

Chapter 16

Ocean Floor Features

• Divided into 2 main regions–Continental margins–Ocean basins

Continental Margins

• Continental Shelves:– Part of the continent that is

underwater•Extends from the shoreline to the “shelf edge”

Continental Margins• Continental slopes

– Begin at the shelf edge– Where water depth starts to increase

rapidly– Crust changes from continental to

oceanic

Continental Margins• Active Continental Margins

– Shelf is narrow and bordered by an ocean trench

– Shoreline is rugged with coastal mountains

– Plate boundaries

Continental Margins• Passive continental margins

– Shelf is broad– No bordering trench or coastal mountains– Continental rises are only found at

passive margins– No plate boundaries

Continental Margins• Submarine

canyons– Start on

continental shelf– Continue all the

way to the end of the slope

– Sometimes formed by rivers emptying into the ocean

Continental Margins• Turbidity Currents

– “turbid” means muddy– Powerful currents that run like flash

floods down the continental slopes– Form when landslides of mud and sand

come down the slopes– Erosion!– Build fan-shaped deposits at the mouths

of the canyons (abyssal fans)

Continental Margins• Continental Rise

– Gently sloping region between continental slope and ocean basin

– Formed by deposition of sediment from land brought by turbidity currents

– Not found at active continental margins

Ocean Basins

• Abyssal Plains–Flattest areas of Earth’s surface

–Made of sediment from continents

–Common in Atlantic Ocean

Ocean Basins• Seamounts

– Cone-shaped mountain peaks that rise high above the deep ocean floor

– Often found in clusters or rows near plate boundaries

– Most abundant in Pacific– Volcanic origins

Ocean Basins• Guyots (GHEE-ohs)

–Flat topped seamounts–Thought to have been above water, where waves eroded the tops

–Then crust sank, and guyots are now underwater

Ocean Basins• Atolls

– Ring-shaped coral islands– Reef forms around volcanic island– Sea floor sinks, and mountain

drops lower– New coral grows on top of old

coral, so eventually the mountain is underwater with the ring of coral around where it used to be

– Lagoon in the center