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Sedimentology and Stratigraphy > Depositional enviorments > Flashcards

Depositional enviorments Flashcards

1
Q

Name the three main depositional enviorments

A
  1. Continental enviorments
  2. Transitional enviorments
  3. Marine enviorments
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2
Q

Which sub-categories are in the continental enviorment?

4 punkter

A
  1. Glacial
  2. Aeolian (dessert)
  3. Lacustrine (lake)
  4. Fluvial (rivers and floodplain)

All continental environments

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3
Q

What is the difference between cold and temperate glacier?

Glacial environment

A
  1. Cold (polar) glaciers => Plastic flow, internal shearing.
  2. Temperate (mountain) glaciers => basal slip, determined by climatic setting. relatively faster flow
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4
Q

How can we recognize dropstones in ancient sedimentary sequences?

Glacial environment

A

Floating ice might melt and deposit dropstones, deforming the clay when hitting ocean mud ground.

Sediments deposited on top => half circle

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5
Q

Why is the Sahara an arid place?

Aeolian environment

A
  • Due to global wind patterns and water vapor (the monsoon).
  • Rainshadow (Atlas mountains)
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6
Q

Name the 2 different types of dunes and how they form?

Aeolian environment

A

2D dunes
- Straight
- Planar cross-bedding

3D dunes - requieres higher velocity
- Sinuous
- Through cross-bedding

Figure on drive

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7
Q

Name the 2-4 different types of rivers

River/floodplain environment

A

braided
Meandering
Anabranching (a “mix” of braided and meandering)
Straight

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8
Q

What does channel amalgamation and non-amalgamation refer to?

River/floodplain environment

A

In a cross section:

Amalgamated => sandbodies are connected. Braided rivers.

Non-amalgamated => sand-bodies are not connected. Meandering rivers

Difficult to tell braided and meandering apart only on deposit

Amalgamation = sammenlægning

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9
Q

What type of sediment will you encounter i a glacial environment?

Continental

A
  1. Fine grained till (and Tillites)
  2. Moraine (poorly sorted)
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10
Q

What type of sediment will you encounter i an Aeolian environment?

Continental

A

Only sand and silt!
- Well sorted
- Mainly quarts

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11
Q

What type of sediment will you encounter i a lacustrine environment?

continental

A

Sandstone
Mudstone
Fine-grained limestone
Evaporites

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12
Q

What type of sediment will you encounter i a river/floodplain environment?

Continental

A
  1. Conglomerate and sandstone
    => deposited by flowing water
  2. Mudstone (mostly clay)
    => deposited by still water in floodplain
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13
Q

What are calcretes nodules?

River/riverplains

A

Roots sucking out water > carbonate precipitation

???

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14
Q

Which sub-categories are in the transitional environment?

3 punkter

A
  1. Deltaic
  2. Estuary (lagoon)
  3. Littoral (clastic coast)

All transitional environments

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15
Q

Name the 3 different types of dominated deltas

Deltaic environment

A
  1. River-dominated (birdfoot, Missisippi)
  2. Wave-dominated
  3. Tide-dominated

(Nilen er i midten: The original delta (trekant))

Different shapes

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16
Q

The sedimentological record of a delta

A

???

Delta = coast progradating to sea

17
Q

Charecteristisc of delta deposits

A

???

18
Q

What is an Estuary (and a lagoon)?

Estuarine environment

A
  • Partly enclosed area protected from the full force of the ocean.
  • Recieve sediments from both fluvial and marine sources.

Lagoon: Shallow body of water partly seperated from larger body of water by a barrier.

Barrier can be bioconstructed reef, clastic beach materials or hard rock

19
Q

Name the two types of dominated estuarines.

Estuarine environment

A
  1. Tide dominated
  2. Wave dominated
20
Q

Name the two types of clastic coast

Littoral environment

A
  1. Dissipative coast
    => flat beach, sand, depositional
  2. Reflective coast
    => Steep beach w. berm, coarse sand and gravel, erosional

Berm = barrier. Marks the division between foreshore and backshore

21
Q

What is a beach berm?

Littoral environment

A

a small “barrier” that marks the division between foreshore and backshore area

22
Q

What is the three division/facies of the estuarine system?

Estuarine environment

A
  1. Bay head delta
  2. Central lagoon
  3. Estuarine mouth

The relative thickness of each will depend on the balance between fluvial and marine supply of sediment.

Thay may not all occour in a single vertical succession

23
Q

Charecteristisc of estuarine deposits

Estuarine environment

A

Mud, sand (maybe conglomerate)

24
Q

Charecteristisc of littoral deposits

Littoral environment

A
  • Sand and conglomerate
  • Well-sorted and well-rounded clasts
25
Q

Which sub-categories are in the marine environment?

4 punkter

A
  1. Shallow silici-clastic
  2. Shallow marine carbonate
  3. Pelagic (no movement)
  4. Deep clastic

All marine environments. Vi kender kun uddybende til dem med fed.

26
Q

Which prosseces causes the deposition of most clastic material in deep seas?

Deep clastic

A

Mass-flow processes
- Debris flows
- Density flows
- Turbidity currents

27
Q

What are the five divisions in an ideal turbidite (Bouma Sequence)?

Deep clastic

A

Upper flow regime:
a. Scoured base. Massiv rapid depostition, graded bedding.
b. Laminated sand

Lower flow regime:
c. Cross-laminated ripples
d. Laminated silt
e. Pelagic mud

Caused by turbidity currents. Overall decrease in energy (= grain size)

28
Q

Characteristics of deep clastic deposits?

A
  • Mud, sand and gravel
  • Turbidite!
  • Pelagic (free swimming/floating) organisms
29
Q

What is the difference between debris flows and turbidity currents?

Deep clastic

A

Debris flow:
- Dense and non-turbulent
- Low Reynold number

Turbidity currents - greater amount of sediment
- High suspended sediment load
- High Reynold number

30
Q

What is ooze?

Pelagic environment

A

Refers to a sediment composition with >30% microscopic remains.
- Diatoms
- Forarminifera
- Radiolara

Accumulates extremly slowly

31
Q

Which four factors are the composition of pelagic sediments controlled by?

Pelagic environment

A
  1. Distance from major landmasses
  2. Water detph (CCD, affects preservasion)
  3. Oceanic fertility (amount of biogenic organisms produced)
  4. Bottom currents (affects preservation)
32
Q

What is the calcite compensation depth (CCD)?

Marine

A

Depth where dissolution rate exceeds sedimentation rate and no calcite is presserved in the sediment.

The aragonite compensation depth is higher in the water collum due to higher solubility

Mordern oceans CCD is at a detph of 4 km depending on pressure and temp

33
Q

How does CCD affect pelagic sediments?

Pelagic environment

A

The distrubution of pelagic sediments.

Above CCD:
Calcareous ooze forms carbonate mudstone.

Bellow CCD:
Silicious ooze forms chert

34
Q

Characteristics of deep pelagic deposits?

A
  • Mostly limestone (some fine clays)
  • Calcite, aragonite, dolomite
35
Q

What are turbidity currents?

Deep clastic environment

A

Underwater currents flowing downslope due to a high suspended sediment load, resulting in a turbulent mass flow

Sedimentology and Stratigraphy (8 decks)

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