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Lesson 15: Sediments Geological Oceanography. Sediments are important to marine scientists. Did you know that ocean sediments hold clues about the earth? - PowerPoint PPT Presentation
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Lesson 15: Sediments
Geological Oceanography
Sediments are important to marine scientists
Did you know that ocean sediments hold clues about the earth?
They can provide information on earth’s past climate, the location of oil and natural gas resources, seafloor age, pollution patterns and many other processes
There are many types of sediments and we will learn different ways to classify them
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How are sediments classified?
By grain size By origin– Where do you think
sediment comes from?
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Classification Grain DiameterClay <0.004mm
Silt 0.004-0.0625mm
Sand 0.0625-2mm
Granule 2-4mm
Pebble 4-64mm
Cobble 64-256mm
Boulder >256mm
Where does sediment come from?
Lithogenous sediments come from land– Rivers, wind, ice and other geologic processes erode and
transport rocks and minerals into the sea– Also called “terrigenous,” these particles make up most of
the sediment near islands and continents
Biogenous sediments come from organisms– They come from the shells and exoskeletons of marine
organisms– They cover most of the area of the sea floor
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Where does sediment come from?
Hydrogenous sediments come from chemical reactions in the water
– Sources may include minerals or chemicals that dissolve in seawater, river runoff or hydrothermal vent water
– They make up less than 1% of seafloor sediments and tend to form slowly
Cosmogenous sediments come from space– Sources may include meteorites and cosmic dust– Least abundant of the four types of marine sediments
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Can you name some common examples?
Lithogenous
?
?
Quartz
Red Clay
Photos: USGS, USDA6
Can you name some common examples?
Biogenous
?Plankton remnants -silicasilica or calcitecalcite
Cosmogeneous
?Tektites
Photos: USGS7
Do you think sediment is uniformly distributed throughout the ocean?
No! Even though most sediment contains a mixture of
types, one type typically dominates depending where you are in the ocean
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Distribution: Biogenous sediment
The biogenic material in the ocean comes primarily from the breakdown of plankton skeletons
Deep ocean sediments are usually high in biogenic material Ooze is deep-ocean sediment that has more than 30%
biogenic material– calcareous ooze: composed mostly of calcareous ooze: composed mostly of calcium carbonate
plankton skeletons– siliceous ooze: composed mostly ofsiliceous ooze: composed mostly of silica plankton
skeletons
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Distribution: Lithogenous (terrigenous) sediment
Lithogenous sediments are generally found close to shore except for clay particles
Thus, sediments near the shore tend to be dominated by lithogenous material, while deep-ocean sediment tends to be dominated by biogenic material
Lithogenous clay particles are relatively light, so they can be carried further from shore by wind, forming pelagic red clay accumulations
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Sediment thickness in the deep ocean
Sediment layering is not the same across all of Earth’s ocean
Do you think the Atlantic or Pacific ocean basin has greater sediment thickness? Why?
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Let’s look at a global map of ocean thickness
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The Atlantic Ocean Basin has greater sediment thickness
Sediment thickness on the Pacific Ocean floor is about half that of the Atlantic Ocean
Rivers flowing into the Atlantic cover more land than those flowing into the Pacific, so they bring more sediment
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Exploring sediment distribution
In today’s activity, we will analyze maps of sediment distribution
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