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Types of Marine Sediment - Keynote pdf
Abyssal Clays - Keynote pdf
Biogenous Oozes - Keynote pdf
Global Distribution of Marine Sediments - Keynote pdf and Graph


Marine Sediments

The characteristics of marine sediments provide oceanographers with information about how the ocean works. The currents, waves, chemistry, biota, temperature, pressure, and depth of the ocean are some of the factors that determine whether or not a particular type of sediment forms at a given locality.

The primary marine sediment characteristics that oceanographers examine are

Types of Marine Sediments

Marine sediments are divided into two basic categories:

  1. Continental margin sediments
  2. Deep-ocean basin sediments

Continental Margin Sediments

Characteristics of continental margin sediments:

Biogenous and hydrogenous sediments are common on continental shelf, slope, and rise; however these sediments constitute a relatively small percentage of the amount of continental margin sediments.
Biogenous and hydrogenous sediments are diluted by the rapid deposition rate of terrigenous particles (10's cm/1000 yr).

Most sedimentary particles and chemical constituents are transported to the ocean by rivers (stream runoff).

Deep-Ocean Basin Sediments

Characteristics of deep-ocean basin sediments:

In contrast, the characteristics of continental margin sediments are:

Deep-ocean basin sediments are divided into two basic categories:

  1. abyssal clays
  2. biogenous oozes

Abyssal Clays

Abyssal clays form in the deepest parts of the deep-ocean basin: the abyssal plains.
They are a fine-grained sediment, primarily clay-sized.

Most marine sediments are carried to the ocean by rivers and deposited in the nearshore environment: the continental margins.

Which mechanism would transport dust-sized particles into the middle of an ocean basin?
The primary transportation mechanisms for abyssal clay particles are

  1. wind (atmospheric currents)
  2. ocean currents

Microscopic particles can be transported 1000s of miles by ocean and atmospheric currents.

Abyssal clay particles are eroded from the continents, so their source is terrigenous.
Because abyssal clay particles are terrigenour, their composition is primarily Al silicate.
The deposition rate of abyssal clays is very slow, as low as 1 mm/1000 yr.

The primary particles sinking from the ocean's surface waters are biogenous, but by the time the sinking particles reach the deep ocean (4-6 km deep), abyssal clay particles are the most numerous.
Most biogenous particles dissolve before forming sediment in the deep-ocean basin, only 1-2% survive to form sediment.

Abyssal clays accumulate because nothing else is deposited in significant amounts on the deep abyssal plains.

Size - primarily fine-grained
Source - primarily terrigenous
Composition - primarily Al silicate
Deposition rate - relatively low

Biogenous Oozes

Scientists dredge up abyssal clays from the deep abyssal plain; however in other parts of the deep-ocean basin, a fine-grained, light-colored ooze is seen. This ooze is composed of the hard parts of microscopic organisms and is called a biogenous ooze.

The shells (tests) of these organisms are deposited in all sediments on the ocean, so one can ask, "When is a marine sediment a biogenous ooze?" A biogenous ooze is a sediment that contains > 30% by weight biogenous material. Note that these microscopic shells are light weight, so 30 wt% of the sediment means that biogenous material makes up most of the volume of the sediment.

Two types of biogenous oozes:

  1. calcareous (CaCO3)
  2. siliceous (SiO2)

Siliceous ooze types:

  1. diatom ooze - autotrophic
  2. radiolarian ooze - heterotrophic
  3. dinoflagellate ooze - autotrophic and heterotrophic

Calcareous ooze types:

The names of these organisms are important because they are the most numerous organisms in the ocean. In fact, there are so many of these creatures that after they die, their hard parts cover thousands of square kilometers of the sea floor. In contrast, one does not see sediments composed of whale bones or tuna bones, because these organisms are not as abundant.

Diatoms, radiolaria, coccolithopheres, and forams are the dominant life forms in the ocean.

Size - Primarily fine-grained
Source - Primarily biogenous
Composition - Siliceous and calcareous
Deposition rate - Relatively low

Global Distribution of Marine Sediments

The distribution of marine sediment is used to study marine processes, i.e. how the ocean works.

Distribution of Continental Margin Sediments

The basic pattern is terrigenous sediments forming the continental margins around the continents.
Most continental margin sediments are transported to the ocean by rivers.
A particular type of terrigenous sediment, glacial deposits, forms in the high latitudes, primarily around Antarctica.
Glacial sediments are transported by ice rafting.

Distribution of Deep-Ocean Basin Sediments

Draw and label the global distribution of marine sediments. - Graph

Relative amounts of deep-ocean sediments:

  1. calcareous ooze (48%)
  2. abyssal clays (38%)
  3. siliceous ooze (14%)

In the deep-ocean basin, the basic pattern of sedimentation is calcareous oozes forming in the shallowest part, the MOR, and abyssal clays forming in the deepest part, the abyssal plains.

Calcareous shells are the primary particles sinking in the deep-ocean basin.
However, calcareous particles dissolve in the deep ocean, so calcareous oozes primarily form on the MOR.
In the deepest parts, only the abyssal clay particles remain to form abyssal clays.

Where do siliceous oozes form?

Siliceous oozes form where silica-rich deep waters well up to the silica-poor surface zone.
These major open-ocean upwelling regions are in bands around the equator and around Antarctica.
Siliceous-shelled organisms grow in abundance in these regions.
After death, their microscopic tests sink to the sea floor forming siliceous oozes.

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