Marine Sedimentation

Question 1

Ocean sediment

Answer 1

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

Question 2

Origin of lithegenous sediment

Answer 2

• Weathering
• Transportation
• Deposition

Question 3

Lithogenous sediment occurs as:

Answer 3

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

Question 4

Lithogenous sediment composition

Answer 4

• majority= quartz (chemically stable and abundant)

Question 5

Factors controlling sedimentation

Answer 5

• Particle size
  -Turbulence of deposition environment
• Rate of erosion

Question 6

Terrigenous sediment

Answer 6

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

Question 7

What does average grain size reflect?

Answer 7

Energy of depositional environment

Question 8

Lithogenous sediment texture over time…

Answer 8

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

Question 9

Hjulstrom’s diagram

Answer 9

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

Question 10

Shelf sedimentation is controlled by:

Answer 10

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

Question 11

Shoreline turbulence

Answer 11

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

Question 12

Past fluctuation of sea level

Answer 12

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

Question 13

What controls worldwide distribution of recent shelf sediments ?

Answer 13

Latitude and climate

Question 14

What type of sediment dominates tropical shelves?

Answer 14

Calcareous biogenous sediments

Question 15

What type of sediment dominates temperate shelves?

Answer 15

River-supplied sands and muds

Question 16

What type of sediment dominate polar shelves?

Answer 16

Glacial till and ice rafter sediments

Question 17

For a time frame of up to 1000 years:

Answer 17

Waves, currents and tides control sedimentation

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

How does hydrogenous sediment form?

Answer 20

Forms when dissolved materials come out of solution (precipitate)

Question 21

Cause of precipitation:

Answer 21

• Changes in temperature
• Changes in pressure
• Addition of chemically active fluids

Question 22

Types of hydrogenous sediment:

Answer 22

• Manganese nodules/crusts
• Phosphates
• Carbonates
• Metal sulfides
• Evaporite salts

Question 23

What are hydrogenous desposits?

Answer 23

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

Question 24

Cosmogenous sediment

Answer 24

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

Question 25

Two types of cosmogenous sediment

Answer 25

1. Microscopic space dust 2. Macroscopic meteor debris

Question 26

Methods of sampling deep sea sediments

Answer 26

- Bottom dredges (wire bag) used to scrape up sediments - Grab samplers - Box corer ( up to 60cm sediment)

Question 27

Grab samplers

Answer 27

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

Question 28

Gravity Corer

Answer 28

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.

Question 29

Piston corer

Answer 29

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

Question 30

Collecting cores of ocean sediment

Answer 30

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

Question 31

2 main sources of deep sea sedimentation

Answer 31

- External - terrigenous material from the land - Internal - biogenous and hydrogenous from the sea

Question 32

Major pelagic sediments in the ocean?

Answer 32

- Red clay - Biogenic oozes

Question 33

Origin of biogenous sediment

Answer 33

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

Question 34

Biogenous ooze

Answer 34

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

Question 35

2 main chemical compounds in microscopic biogenous tests

Answer 35

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

Question 36

Examples of silica- secreting organisms

Answer 36

- Diatom - Radiolarian

Question 37

Siliceous ooze

Answer 37

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

Question 38

Example of calcite- secreting microscopic organisms

Answer 38

- Coccolithophores - Foraminifers

Question 39

Calcareous ooze

Answer 39

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

Question 40

Biogenous ooze --> rock

Answer 40

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

Question 41

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

Answer 41

- Latitude - Distance from landmasses - CaCO3 compensation depth

Question 42

Glacial marine sediments

Answer 42

Occur in high latitudes

Question 43

Pelagic clays

Answer 43

Occur far from land and in deepest water

Question 44

Occur above the calcium carbonate composition depth

Answer 44

Calcareous oozes

Question 45

Distribution of biogenous ooze

Answer 45

Most found as pelagic deposits

Question 46

Factors affecting the distribution of biogenous ooze:

Answer 46

- Productivity (amount of organisms in surface waters) - Destruction (dissolving at depth) - Dilution (mixing with lithogenous clays)

Question 47

Distribution of siliceous ooze

Answer 47

- Silica slowly but steadily dissolves in seawater - Siliceous ooze found where it accumulates faster than it dissolves

Question 48

Distribution on calcareous ooze

Answer 48

- 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

Question 49

Deep- sea stratigraphy

Answer 49

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

Question 50

The stratigraphy of the deep sea

Answer 50

Strongly influenced by sea floor spreading

Question 51

Stratigraphy of the Atlantic Basin

Answer 51

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

Question 52

Stratigraphy of Pacific basin

Answer 52

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

Question 53

Composition of red clay

Answer 53

- Aeolian dust from land - Clay minerals -product of weathering - Volcanic ash - Minor biogenic material

Question 54

What ocean basin are red clays formed in ?

Answer 54

Central North Pacific Ocean