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Sedimentology > Week 9 > Flashcards

Week 9 Flashcards

1
Q

Pelagic sediment =

A

Mixture of non biogenic (clay), siliceous biogenic (radiolarians/diatoms), calcareous biogenic (nannofossils) and continental sediment which is organic rich

Accumulates due to settling of particles to floor of open ocean

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2
Q

Methods of downward transport

A

Aggregation

Brownian motion

Bacterial growth/mats

Caballing

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3
Q

What slows rate of fall?

A

Upwelling

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4
Q

Transport - aggregation

A

Without this the settling time of coccoliths = 30years
Actually 10-25 days due to formation of clumps

= differential settling rates

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5
Q

Transport - Brownian motion

A

Clumps collide and accelerate

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6
Q

Transport - bacterial growth/mats

A

= mucus = aggregation

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7
Q

Transport - caballing

A

Water = stratified due to density differences (salinity/T)

Two water masses of different salinity/T but same density (isobar) mix = higher density

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8
Q

Lateral movement

A
  1. THERMOHALINE CONVEYER BELT
    - affects ~8% ocean waters
    - ~1000 year turnover
  2. WIND DRIVEN EKMAN SPIRAL CURRENTS
    - water = stratified
    = pycnocline (density), thermocline (T), halocline (salinity)
    - each layer dragged different amount
    - = net transport 90’ to wind direction
    = CAN’T USE WIND CURRENTS TO PREDICT OCEAN CURRENT DIRECTION
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9
Q

Marine snow =

A

Aggregated coccolith plates/skeletal debris from microscopic animals
MUST be aggregated due to visibility on cm scale

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10
Q

Distribution: glacial/terrigenous/continental-margin

A

Near continents
Large continental shelves
Not even due to e.g. Bengal megafan (lots of river input)

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11
Q

Distribution: calcareous

A

= biological activity with some calcareous skeleton formation

In Atlantic NOT Pacific due to depth (CCD)
Not at poles due to cold T (dissolves)
Not at tropics as siliceous-dominated

N.B. Some areas produced but not preserved

LIKES OLIGOTROPHIC CONDITIONS

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12
Q

Distribution: siliceous

A

At poles due to cold T
At equator due to upwelling = nutrients

LIKES EUTROPHIC CONDITIONS

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13
Q

Distribution: Deep sea clay

A

Areas where too deep for calcareous and not enough nutrients for siliceous i.e. deep sea

V slow deposition rate 0.2mm/yr
Very fine material:
- volcanic
- cosmic dust

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14
Q

Tectites =

A

Small, glassy particles from space

Evenly distributed across globe but sampled in deep sea clay as signal not swamped (COMMON ISSUE)

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15
Q

Pelagic sediment thickness

A

Thicker near contents
Glacial/terrigenous/continental-margin most important in terms of volume
Deep sea clay = thin blanketing layer

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16
Q

Types of deep sea sediments

A

Terrigenous

Biogenic

Hydrogenous

Cosmogenous

17
Q

Terrigenous deep sea sediment

A

Erosion of land (river influx/aeolian dust)

Quartz sand/siliclastic mud

Continental margins/abyssal plains

18
Q

Biogenic deep sea sediment

A

Hard parts of marine organisms

Calcareous/siliceous ooze

Deep sea floor, mediated by CCD

19
Q

Hydrogenous (authigenic) deep sea sediment

A

Small component

(Bacterial mediated) precipitation of dissolved minerals

Manganese nodules/phosphorite deposits

MORs

20
Q

Cosmogenous deep sea sediment

A

Small component

Extraterrestrial dust

Tectite spheres/glassy nodules

Globally

21
Q

Pelagic ooze =

A

> =30% biogenic material

Can be siliceous/carbonate

N.B. biological productivity decreases with increasing distance from land

22
Q

Siliceous pelagic ooze

A

Radiolaria/diatoms

Cold seas
Dissolve at surface
High productivity seas
Lots of nutrient availability

23
Q

Carbonate pelagic ooze

A

Foraminifera/coccoliths

Warm
At depth
Low productivity seas
Little nutrient availability

24
Q

Palaeoreconstruction of pelagic oozes

A

Gives an idea of productivity and therefore how much material is from the continent

25
Q

Red clay indicates

A

No biogenic production

26
Q

Sapropel =

A

area of high fertility low depth

Usually cold water where nutrients dragged from depth

Can indicate climate changes
- wetter = more continental material washed in

= soft, black layers high in hydrocarbons

27
Q

CCD varies with space and time

A

Low T = shallow

More acidic = shallow e.g. terrestrial material = more organic = C
e.g. Atlantic

28
Q

Red clay

A

“Nothing else going on”

Very fine grained
Insoluble components
Hydrothermal minerals
~38% sea floor covered in it

29
Q

Rhythmite types (+ how to distinguish between)

A
  1. Turbidites
    - fining up sequence
  2. Tempestites
    - wavy beds at bottom
  3. Pelagic sediments
    - undisturbed beds
    - very laterally extensive
    - changes to CLIMATE (not tectonics) therefore in water column!!!
30
Q

Rhythmites =

A

Long // lines across outcrop

31
Q

Glacial dropstones, Heinrich events and ice-rafted debris

A

GLACIAL DROPSTONES:
Mark T isoclines within ocean = often aligned with boundaries between siliceous/carbonate ooze

Use cross-cutting relationships to date stones

Use deformation to determine lithification state of underlying sediment

Sedimentology (9 decks)

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