The Ocean Floor and Its Sediments

1. The Ocean Floor and Its Sediments Chapter 16

2. Ocean Floor Features • Divided into 2 main regions • Continental margins • Ocean basins

3. Continental Margins • Continental Shelves: • Part of the continent that is underwater • Extends from the shoreline to the “shelf edge”

5. Continental Margins • Continental slopes • Begin at the shelf edge • Where water depth starts to increase rapidly • Crust changes from continental to oceanic

7. Continental Margins • Active Continental Margins • Shelf is narrow and bordered by an ocean trench • Shoreline is rugged with coastal mountains • Plate boundaries

8. 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

9. 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

10. 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)

12. 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

14. Ocean Basins • Abyssal Plains • Flattest areas of Earth’s surface • Made of sediment from continents • Common in Atlantic Ocean

16. 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

17. 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

19. 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