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Oceanography > Marine Sedimentation > Flashcards

Marine Sedimentation Flashcards

1
Q

Ocean sediment

A

Various materials settled through the water column and accumulated on the ocean floor

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2
Q

Origin of lithegenous sediment

A
  • Weathering
  • Transportation
  • Deposition
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3
Q

Lithogenous sediment occurs as:

A
  • Neritic (nearshore) deposits
    e.g. beaches, continental shelves, turbidites, glacial rafted debris
  • Pelagic (deep ocean floor) deposits e.g. abyssal clay
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4
Q

Lithogenous sediment composition

A
  • majority= quartz (chemically stable and abundant)
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5
Q

Factors controlling sedimentation

A
  • Particle size
    -Turbulence of deposition environment
  • Rate of erosion
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6
Q

Terrigenous sediment

A

Sediments derived from erosion of rocks on land ( derived from terrestrial not marine environments ) and carried by rivers, wind and glaciers to the sea

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7
Q

What does average grain size reflect?

A

Energy of depositional environment

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8
Q

Lithogenous sediment texture over time…

A
  • Maturity increases
  • Degree of sorting increases
  • Clay content decreases
  • Rounding of and particles increases
  • Time increases
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9
Q

Hjulstrom’s diagram

A

Graphs relationship between particle size and energy for :
- Erosion
- Transportation
- Deposition

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10
Q

Shelf sedimentation is controlled by:

A

Tides, Waves and Currents
–> Influence of these factors decreases with water depth

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11
Q

Shoreline turbulence

A

Prevents small particles from settling
- Transports them seaward where they are deposited in deep water

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12
Q

Past fluctuation of sea level

A

Cause coarse (relict) sediment across the shelf (includes most areas where only fine sediments are deposited today)

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13
Q

What controls worldwide distribution of recent shelf sediments ?

A

Latitude and climate

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14
Q

What type of sediment dominates tropical shelves?

A

Calcareous biogenous sediments

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15
Q

What type of sediment dominates temperate shelves?

A

River-supplied sands and muds

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16
Q

What type of sediment dominate polar shelves?

A

Glacial till and ice rafter sediments

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17
Q

For a time frame of up to 1000 years:

A

Waves, currents and tides control sedimentation

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18
Q

For a time frame of up to 1,000,000 years:

A

Sea level lowered by glaciation controls sedimentation and causes rivers to deposit their sediments at the shelf edge onto the upper continental slope

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19
Q

For a time frame of up to 100,000,000 years:

A

Plate tectonics determine the type of margin that develops and controls sedimentation

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20
Q

How does hydrogenous sediment form?

A

Forms when dissolved materials come out of solution (precipitate)

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21
Q

Cause of precipitation:

A
  • Changes in temperature
  • Changes in pressure
  • Addition of chemically active fluids
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22
Q

Types of hydrogenous sediment:

A
  • Manganese nodules/crusts
  • Phosphates
  • Carbonates
  • Metal sulfides
  • Evaporite salts
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23
Q

What are hydrogenous desposits?

A

Chemical and biogeochemical precipitates that form on the sea floor. Including:
- ferromanganese nodules
- phosphorite

24
Q

Cosmogenous sediment

A

Composed of material derived from outer space (insignificant proportion of ocean debris)

25
Q

Two types of cosmogenous sediment

A
  1. Microscopic space dust
  2. Macroscopic meteor debris
26
Q

Methods of sampling deep sea sediments

A
  • Bottom dredges (wire bag) used to scrape up sediments
  • Grab samplers
  • Box corer ( up to 60cm sediment)
27
Q

Grab samplers

A

Take a ‘bite’ out of the sediment covering bottom (up to 50cm)

28
Q

Gravity Corer

A

This corer is a weighted tool with steel tubes attached, weighing from 100kg to 1000kg. It collects sediment samples with one to four-meter-long tubes fitted with a catcher. These tubes have a clear 63.5mm polycarbonate liner. To collect a sample, it’s lowered to the seabed on a wire, lowered into the sediment at a set speed, then raised to dismantle and remove the sample liner.

29
Q

Piston corer

A

The piston corer collects longer samples (90mm or 110mm diameter) than the gravity corer, using weighted steel tubes, a PVC liner, and piston mechanism.

30
Q

Collecting cores of ocean sediment

A
  • Specially designed ships collect cores by rotary drilling
    -Cores allow scientists to analyse ocean sediment
  • Sediment sequences of hundred of meters can be taken
31
Q

2 main sources of deep sea sedimentation

A
  • External - terrigenous material from the land
  • Internal - biogenous and hydrogenous from the sea
32
Q

Major pelagic sediments in the ocean?

A
  • Red clay
  • Biogenic oozes
33
Q

Origin of biogenous sediment

A
  • organisms producing hard parts when they die
  • Material rains down on ocean floor and accumulates as :
    -> macroscopic shells, bones,teeth
    -> Microscopic tests (shells)
34
Q

Biogenous ooze

A

Formed if biogenous sediment is formed of at least 30% test sediment

35
Q

2 main chemical compounds in microscopic biogenous tests

A
  • Silica (including opal)
    -> diatoms -> Radiolarians (protozoan)
  • Calcium carbonate or calcite (CaCO3)
    -> Coccolithophores (algae)
    -> Foraminifers (protazoan)
36
Q

Examples of silica- secreting organisms

A
  • Diatom
  • Radiolarian
37
Q

Siliceous ooze

A

Silica-secreting organisms accumulate to form siliceous ooze(>30% siliceous test material)

38
Q

Example of calcite- secreting microscopic organisms

A
  • Coccolithophores
  • Foraminifers
39
Q

Calcareous ooze

A

Calcite-secreting organisms accumulate to form calcareous ooze(>30% calcareous test material)

40
Q

Biogenous ooze –> rock

A

When biogenous ooze hardens and lithifies it can form:
- Diatomaceous earth (diatom-rich ooze)
- Chalk ( coccolith-rich ooze)

41
Q

What’s reflected in the distribution of sediments in the deep ocean?

A
  • Latitude
  • Distance from landmasses
  • CaCO3 compensation depth
42
Q

Glacial marine sediments

A

Occur in high latitudes

43
Q

Pelagic clays

A

Occur far from land and in deepest water

44
Q

Occur above the calcium carbonate composition depth

A

Calcareous oozes

45
Q

Distribution of biogenous ooze

A

Most found as pelagic deposits

46
Q

Factors affecting the distribution of biogenous ooze:

A
  • Productivity (amount of organisms in surface waters)
  • Destruction (dissolving at depth)
  • Dilution (mixing with lithogenous clays)
47
Q

Distribution of siliceous ooze

A
  • Silica slowly but steadily dissolves in seawater
  • Siliceous ooze found where it accumulates faster than it dissolves
48
Q

Distribution on calcareous ooze

A
  • Calcite dissolves beneath the calcite compensation depth (CCD) at 4.5 km
  • Calcareous ooze can be found below the CCD if it is buried and transported to deep water
49
Q

Deep- sea stratigraphy

A

Refers to the broad-scale layering of sediments that cover the basaltic crust

50
Q

The stratigraphy of the deep sea

A

Strongly influenced by sea floor spreading

51
Q

Stratigraphy of the Atlantic Basin

A

Contains a ‘two layer cake’ stratigraphy- a thick basal layer of carbonate ooze overlain by a thick layer of mud

52
Q

Stratigraphy of Pacific basin

A

‘four-layer cake’ stratigraphy
- Crosses the equator where the CCD is lowered to the ocean bottom

53
Q

Composition of red clay

A
  • Aeolian dust from land
  • Clay minerals -product of weathering
  • Volcanic ash
  • Minor biogenic material
54
Q

What ocean basin are red clays formed in ?

A

Central North Pacific Ocean

55
Q
A

Oceanography (23 decks)

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