Marine Sediments
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Why are sediments so important to
marine scientists?
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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
What is a sediment?
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Particles of organic or inorganic matter that
accumulate in a loose, unconsolidated form
Originate from weathering & erosion of rocks, from
volcanic eruptions, chemical processes in the water,
& from space
Examples: beach sand, muds of bays, the mix of silt
& tiny shells on continental margins, the fine clays of
the deep-ocean floors, oozes of abyssal plains, and
the nodules & coatings around hard objects on the
seafloor
How are sediments classified?
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By grain size
Classification
Grain Diameter
Clay
<0.004mm
Silt
0.004-0.0625mm
Sand
0.0625-2mm
Granule
2-4mm
Pebble
4-64mm
Cobble
64-256mm
Boulder
>256mm
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By origin
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Where do you think
sediment comes
from?
Where does sediment come from?
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Lithogenous/Terrigenous sediments come from
land, volcanic eruptions, & blown dust
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Biogenous sediments come from organisms
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Rivers, wind, ice and other geologic processes erode and
transport rocks and minerals into the sea
These particles make up most of the sediment near islands
and continents & ~45% of the sea floor
They come from the shells and exoskeletons of marine
organisms
They cover most of the area of the sea floor (~55%)
Where does sediment come from?
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Hydrogenous sediments come from chemical
reactions in the water
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Cosmogenous sediments come from space
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Sources may include minerals or chemicals that dissolve in
seawater, river runoff or hydrothermal vent water; often due
to bacteria
They make up less than 1% of seafloor sediments and tend
to form slowly
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Sources may include meteorites and cosmic dust
Least abundant of the four types of marine sediments
Make-up less than 1% of seafloor sediments
Can you name some common examples?
Lithogenous
?
Red Clay
?
Quartz
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Photos: USGS, USDA
Can you name some common examples?
Biogenous
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Plankton
? remnants silica or calcite
Cosmogeneous
Tektites
?
Photos: USGS
Do you think sediment is uniformly
distributed throughout the ocean?
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No!
Even though most sediment contains a mixture of
types, one type typically dominates depending where
you are in the ocean
Distribution: Biogenous sediment
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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 calcium
carbonate plankton skeletons
– siliceous ooze: composed mostly of silica
plankton skeletons
Distribution: Lithogenous (terrigenous)
sediment
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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
Sediment thickness in the deep ocean
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Sediment layering is not the same across all of
Earth’s ocean
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Do you think the Atlantic or Pacific ocean basin has
greater sediment thickness? Why?
Let’s look at a global map of ocean
thickness
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The Atlantic Ocean Basin has greater
sediment thickness
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Sediment thickness on the Pacific Ocean floor is
about half that of the Atlantic Ocean
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Rivers flowing into the Atlantic cover more land than
those flowing into the Pacific, so they bring more
sediment
Why study sediments?
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Sediments are historical records of ocean processes
(last 180 million years)
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They are economically important
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Paleoceanography: study of ocean’s past
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Building materials for roads and structures
Toothpaste
Paint
Swimming pool filters
In 2010, 39% of world’s crude oil & 35% of natural gas
Sand & gravel
Manganese & Iron deposits