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  • 2. 4-1 Sediment in the Sea Classification of marine sediments can be based upon size or origin. • Size classification divides sediment by grain size into gravel, sand, silt and clay. – Mud is a mixture of silt and clay. • Origin classification divides sediment into five categories: terrigenous sediments, biogenic sediments, authigenic sediments, volcanogenic sediments and cosmogenic sediments.
  • 3. Pathways for Sediment to Reach the Ocean: 1) Fluvial Inputs--Rivers Discharge Sediment into the Ocean 2) Aeolian Inputs--Winds carry sediments from the continents into the ocean. 3) Biological Inputs--Marine organisms die and sink to the bottom. 4) Authigenic Inputs--Sediments that are formed in the oceans. Mainly metal rich materials near hydrothermal vents.
  • 4. Classification of Sediment by Source
  • 5. Factors that control sedimentation include particle size and the turbulence of the depositional • Terrigenous sediments strongly reflect their environment. 4-1 Sediment in the Sea source and are transported to the sea by wind, rivers and glaciers. • Rate of erosion is important in determining nature of sediments. • Average grain size reflects the energy of the depositional environment.
  • 6. Summary: General Distribution of Sediments in the Deep Sea 1) Near continental margins (500-1000 km), sediments tend to be dominated by terrigenous (lithogenic) material from the margins (turbidity currents and river derived material). 2) Away from margins and < 4000m, carbonate oozes dominate. 3) Away from margins and > 4000m, clays dominate (dominated by wind transport). 4) Away from margins, but under upwelling regions (high biological productivity), siliceous oozes dominate. 5) Near active mid-ocean spreading centers, metal rich sediment dominate.
  • 7. Sediment sorting can provide information about the depositional environment
  • 8. 1. Terrigenous sediments • most abundant • originate on the continents or islands • come from erosion, volcanic eruptions, and blown dust • the largest terrigenous deposits are near continental margins
  • 9. 2. Biogenous sediments • cover the greatest area of seabed • but their total volume is less than that of terrigenous sediments. • originate from the activity of animals and plants • over millions of years, can form oil and natural gas
  • 10. 3. Hydrogenous sediments • minerals that precipitate directly from water manganese nodules
  • 11. Hydrogenous (authigenic) Sediments: Hydrogenous sediments precipitate directly from seawater. Their formation is poorly understood, but it is thought to be associated with hydrothermal vent systems and mid-ocean ridge systems. Most common hydrogenous sediments are manganese nodules. Include evaporites and oolites.
  • 12. Manganese Nodules: Formed on concentric layers of manganese and iron oxides. Form very slowly (1-10 mm per million years). Found on large areas of the Pacific ocean. Recent interest in economic development.
  • 13.
  • 14. 4. Cosmogenous sediments • very rare • two main sources: 1) interplanetary (cosmic) dust 2) impacts by asteroids and comets
  • 15. Shelf Versus Basin Depths
  • 16. Sediments can provide information about the surrounding environment.
  • 17. Sediment grading usually reflects changes in the depositional environment with time. lower energy Higher energy “fining-upward’ event Each bed represents an individual depositional event.
  • 18. Marine sediments are usually combinations of terrigenous and biogenous deposits. Sediment patterns and composition can tell us about conditions in the overlying ocean • they preserve a record of past and present conditions
  • 19. General pattern of sediments on the ocean floor
  • 20.
  • 21. Key Points 1. Sediments vary greatly in appearance. 2. Sediments can be classified by particle size. 3. Sediments can be classified by source. 4. Neritic sediments overlie continental margins. 5. Pelagic sediments vary in composition and thickness. 6. Scientists use sensitive tools to study ocean sediments. 7. Marine sediments are economically important.