A brief overview about marine sediments
• Marine sediments contains clues/records of earth's history from origin.
• Marine sediments provides a variety of important resources.
• Marine sediments have a variety of origin.
What are marine sediments?
• They are eroded rock particles and fragments.
• They are transported to the ocean.
• Deposits by settling through water column.
• Oceanographers decipher earth history through studying sediments.
Paleoceanography and marine sediments
Paleoceanography: The study of how ocean atmosphere, and land interactions have produced changes in ocean chemistry, circulation, biology and climate.
• Marine sediments provides clues to the past changes.
Marine sediments classification
They are classified based on origin:
• Lithogenous: derived from land.
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• Biogenous: derived from organisms.
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• Hydrogenous or Authigenic: derived from water.
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Due to ocean water precipitation or ion exchange between ocean water and sediments, hydrogenous sediment forms. Examples include metal sulfides, evaporites.
• Cosmogenous: derived from outer space.
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For today's post we will focus on lithigenous sediments. While other sediments will be explained further.
Lithogenous sediments:
• Eroded rock fragments from the land.
• Also called terrigenous.
• Reflect composition of rock from which its derived.
• Produced by Weathering ( breaking of rocks into smaller pieces).
• Small particles are eroded and transported.
• Carried to the ocean, stream, wind, glaciers, gravity.
• Greatest quantity around continental margins.
Lithogenous sediments transport:
Water, wind.
Lithogenous sediments;
• it shows the composition of rocks of which it was derived from.
• Coarser sediments closer to shore.
• Finer sediments farther from shore.
• Mainly minerals- Quartz(si02)
**Grain size**
The grain size is proportional to energy of transportation and deposition.
Sediment texture:
• Grain size sorting: indicator of selectivity of transportation and deposition processes.
• Textural matural
increases maturity if
• clay content decreases
• sorting increases
• non-quartz minerals decreases
• Grains are more rounded (abraded)
Sediment Distribution
Neritic:
• Shallow-water deposits.
• Close to land.
• Dominantly deposited quickly.
Pelagic:
• Deeper-water deposits.
• Finer-grained sediments.
• Deposited slowly.
Neritic Lithogenous sediments
• Beach deposits:
Mainly wave-deposited quartz rich sand.
• Continental shelf deposits:
Relict sediments.
• Turbidite deposits:
Graded bedding.
• Glacial deposits:
- High latitude continental shelf.
- Currently forming ice rafting.
Pelagic deposits
• They are fine grained marine sediments, accumulated slowly on the deep ocean floor.
• Pelagic Lithogenous sediments are from:
- Volcanic ash (volcanic eruptions).
- Wind-blown dust.
- Fine grained material transported NY ocean currents.
• Abyssal clay: - At least 70% clay sized particles from continent.
- Red from oxidized iron (Fe).
- Abundant if other sediments are absent.
References
• Link
• Oxford geology dictionary
