1. Exit Choose to view chapter section with a click on the section heading. ►Continental-Shelf SedimentsContinental-Shelf Sediments ►Deep-Ocean SedimentsDeep-Ocean Sediments ►Sediments as Economic ResourcesSediments as Economic Resources Chapter Topic Menu

2. MenuPreviousNext 12 - 2 Sedimentation Processes on the Continental Shelf nTides, waves, and currents strongly affect continental- shelf sedimentation.  Waves are one of the most notable influences that keep particles from settling Continental-Shelf Sediments Chapter 12 Pages 12-16 & 12-17

3. MenuPreviousNext Recent and Relict Sediments nRecent sediments have accumulated since the sea level stabilized. They are found near the beach. nRelict sediments accumulated and were left stranded when the sea level was lower. These are found farther out on the continental shelf. 12 - 3

4. MenuPreviousNext 12 - 4 Continental-Shelf Sedimentation Rates nThe sedimentation rate on the continental shelf varies with region. nSedimentation on the shelf is more rapid than in the deep ocean.  At the mouths of large rivers, sedimentation can occur at a rate of one meter per thousand years nThe continental shelves undergo processes that produce lithogenous and biogenous sediments.  Continental-shelf sediments tend to have a mix of both biogenous and lithogenous materials. Continental-Shelf Sediments Chapter 12 Pages 12-17 to 12-19

5. MenuPreviousNext Continental-Shelf Sedimentation Rates nContinental-shelf sedimentation processes also affect the adjoining deep ocean.  Accumulating sediment on the continental shelf avalanches down the continental slopes. These are called turbidity currents. These deposits are called turbidites.  Turbidites consist of layers of lithogenous sand embedded with the more typical, fine deep-sea sediments. 12 - 5

6. MenuPreviousNext 12 - 6 Sedimentation Processes on the Deep-Ocean Bottom nSedimentation processes in the deep ocean vary regionally. nDeep-ocean sediments tend to be high in biogenous material.  Lithogenous sediments, except for clays, are rare.  Biogenetic sediments are primarily the remnants of plankton. nThe thickness of sediments in the deep ocean also varies with topography.  Sediments are thickest on the abyssal plains and thinnest or absent on the mid-ocean ridges and seamounts. Deep-Ocean Sediments Chapter 12 Pages 12-20 & 12-21

7. MenuPreviousNext 12 - 7 The Carbonate Compensation Depth nThe carbonate compensation depth is a point at which calcium carbonate dissolves as fast as it accumulates from above.  Above this depth calcareous (calcium carbonate) ooze dominates. Siliceous (silica) ooze dominates sediments below this depth due to the slow deep-sea dissolution of siliceous remains and high plankton productivity.  The slow dissolution of siliceous remains and high plankton productivity allow siliceous oozes to accumulate throughout the seafloor. Deep-Ocean Sediments Chapter 12 Pages 12-22 & 12-23

8. MenuPreviousNext The Carbonate Compensation Depth  The carbonate compensation depth varies with region due to temperature and water density. nIn the Atlantic and Pacific, it is around 4,500 meters (14,750 feet). nIn colder regions, the carbonate compensation depth is much shallower so siliceous oozes dominate biogenous sediments in polar regions. 12 - 8

9. MenuPreviousNext The Carbonate Compensation Depth 12 - 9

10. MenuPreviousNext 12 - 10 Fecal Pellets nScientists find that bottom composition is usually similar to the particle composition of the water above it. This is due to fecal pellets. nLarge planktonic organisms consume the calcareous or silicon organisms. These large organisms eliminate their waste as dense fecal pellets of multiple skeletal and shell remains compressed together. These dense fecal pellets sink quickly and form biogenous oozes. Deep-Ocean Sediments Chapter 12 Pages 12-23 & 12-24

11. MenuPreviousNext Mineral Nodules nFerromanganese nodules consist of iron and manganese found on over 50% of the Pacific floor. nPhosphorite nodules consist of phosphorite and other trace minerals found on the shallow banks and continental shelves.  Both forms of nodules are hydrogenous sediments produced by very slow chemical reactions.  Nodules grow at a rate of about 1 to 200 millimeters per million years.  Scientists believe that biological processes cause the chemical precipitation. 12 - 11

12. MenuPreviousNext 12 - 12 Petroleum and Natural Gas nWhat is the economic importance of ocean sediments?  Oil and natural gas found under the ocean contribute $125 billion in annual revenues.  More than a third of the world’s crude petroleum and a quarter of its natural gas come from sedimentary deposits on the continental shelf. Sediments as Economic Resources Chapter 12 Pages 12-25 to 12-27

13. MenuPreviousNext Other Sediments With Economic Importance nFerromanganese and phosphorite nodules have potential economic value. nMining metal sulfide deposits found at deep-sea hydrothermal vents could be economically feasible. nEvaporites are a source of calcium carbonate, calcium sulfate, gypsum and sodium chloride. nSand and gravel are an important resource for the construction industry. 12 - 13

14. MenuPreviousNext 12 - 14