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Sedimentology and Stratigraphy > (S6) Glacial Environments > Flashcards

(S6) Glacial Environments Flashcards

1
Q

What is a “Nunatak”?

A

Protrusion of land above ice

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2
Q

What is an “Ice Shelf”?

A

Floating ice from an ice sheet

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3
Q

Where is the fastest flow in a valley confined glacier?

A

Center of the valley

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4
Q

What is the primary mode of transportation of sediment in a cold based glacier?

A

Sediment largely from valley fallen detritus carried on surface

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5
Q

What is the primary erosion and transportation regieme of a polythermal glacier?

A

PMP = glacial surges readily eroding bedrock which is released on retreat

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6
Q

What is the primary erosive regieme of a temperate glacier?

A

Abrasion, plucking, rock-flour and large blocks of bedrock

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7
Q

What is “supraglacial debris”?

A

Onto top from valley sides

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8
Q

How is basal debris formed?

A

Abrasion and plucking

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9
Q

What size of material is usually transported supraglacially?

A

Mostly coarse material from valley sides

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10
Q

What size of material is usually transported subglacially?

A

Large range from rock flour to larger rocks

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11
Q

How does internal deformation of a glacier effect basal debris?

A

May cause some basal debris to be brought up into the glacier body

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12
Q

How do englacial and subglacial channels affect the transport regieme of a glacier?

A

Sorting of sediments inside temperate glaciers

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13
Q

What is glacial till?

A

The direct deposit of (unconsolidated) rock by ice

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14
Q

What is tillite?

A

Till which has been consolidated

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15
Q

Where are melt-out tills found?

A

Front of glacier

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16
Q

Where are lodgement tills found?

A

Debris which has been plastered at the base of ice during movement

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17
Q

What are flow tills?

A

Accumulation of tills which have been reworked by gravity flows

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18
Q

What are the characteristics of sediment which has been transported by laminar flow in a glacier?

A

No mixing or sorting

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19
Q

What are the four main characteristics of glacially transported sediments?

A

No sorting, Angular, Material on top subject to weathering, Immature texture

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20
Q

Name one common and one uncommon lithology found in glacial deposits

A

Common: Lithic Fragments, Uncommon: Clays

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21
Q

What is an interesting feature about rock flour which is not common in all other sediment environments?

A

Retains it’s mineralogy as often not subject to chemical weathering

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22
Q

Rock flour does not ___ and therefore stays in ___ much longer

A

Flocculate, Suspension

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23
Q

What gives glacial melt its green colour?

A

Rock flour in suspension

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24
Q

Why are continental glacial deposits rarely preserved in the long-run?

A

Most modern glacial environments subject to erosion and thus are reworked and removed

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25
Q

What is the only thing commonly preserved from pre-quaternary glacial deposits?

A

Moraines

26
Q

What are the five forms of moraines?

A

Push moraines, Dump moraines, Lateral moraines, Medial moraines, Ice-cored moraines

27
Q

What are Push-Moraines?

A

Bull-dozer style

28
Q

What are Dump-Moraines?

A

Conveyor-belt type

29
Q

What are Ice-cored Moraines?

A

Moraines which may contain a core of ice which is insulated by debris

30
Q

How thick is a typical lodgement till?

A

10’s m’s thick

31
Q

How are ribbed moraines formed?

A

From the irregular ridges formed in lodgement tills

32
Q

How do drumlins form?

A

Deposition of lodgement till, reworked into elongate formations

33
Q

What are the typical dimensions of a drumlin?

A

Elongate axis towards flow - 10’s m wide, 10’s m to km long

34
Q

What is an esker?

A

Ridges elongate to the paleo-glacial flow - formed by deposition in subglacial rivers

35
Q

What are the typical dimensions of an esker?

A

m to 10’s m high, 10’s m to 100’s m wide

36
Q

What bedform/sedimentary structure may be seen in an esker?

A

Bars: x-bedded and horizontally stratified lenses

37
Q

How are esker bars distinguished from river bars?

A

Eskers: lack of bank sediment and internal deformation common due to collapse of ice around the tunnel

38
Q

What is a karne/karne terrace?

A

Mounds/ridges from the collapse of crevasses/lakes/edge of glacier

39
Q

What is a sandur?

A

Glacial outwash plain

40
Q

How do rivers tend to act on an glacial outwash plain?

A

Braided

41
Q

How can a glacial outwash plain be identified in the geological record?

A

Associated with features such as moraines

42
Q

What features does a Jokulhlaup deposit usually have?

A

Massive beds, combination of poorly sorted or cross-bedded and stratified

43
Q

What type of sedimentary reworking commonly occurs on the outwash plane?

A

Winnowing from aeolian and fluvial reworking

44
Q

What are ventifacts?

A

Clasts which are exposed at the surface and abraided by windblown sediments

45
Q

What is the main source of marine glacial deposits at the poles?

A

Basal debris

46
Q

What is a tide-water glacier?

A

A valley glacier which reaches a marine environment

47
Q

What is created by ice which is locally grounded on the sea floor?

A

Grooves and tunnel valleys

48
Q

What are tunnel valleys?

A

Eroded valleys on the sea floor by increased density/pressure

49
Q

What are ice-proximal glaciomarine sediments?

A

Detritus which is released from the bottom of the ice sheets forming till sheets on the sea floor

50
Q

What are ice-distal glaciomarine sediments?

A

Material which is dropped by icebergs

51
Q

How can dropstones be confused in the geological record?

A

Similar deposits may be carried by vegetation

52
Q

What happens to the finer material released from icebergs?

A

Deposited as mud as it is transported in suspension

53
Q

What is the general consensus on immediate glacial deposits and hydrocarbon potential? (4)

A

Bad: Lack of organic material, poorly sorted, little sandstone, may not be preserved in the geological record

54
Q

What are the typical lithologies associated with glacial deposits?

A

Conglomerate, sandstone, mudstone

55
Q

What element of glacial deposits may have some hydrocarbon potential?

A

Outwash plains which have been sorted could be a potential to store

56
Q

What would be expected of the mineralogies of glacial deposits?

A

Variable, compositionally immature

57
Q

What would be expected of the texture of glacial deposits?

A

Extremely poorly sorted in till, poorly sorted in fluvial glacial

58
Q

What would be expected of the bed geometry of glacial deposits?

A

Bedding absent to indistinct in many continental deposits - may be laminated in glacio marine

59
Q

What sedimentary structures would be expected in glacial deposits?

A

Usually none in tills, cross-bedding may be found in fluvioglacial

60
Q

What paleoflow would be expected in glacial deposits?

A

Clast orientation for ice flow

61
Q

What would be expected of the sedimentary colouring of glacial deposits?

A

Variable, not usually oxidised

62
Q

What facies would be expected to be associated to glacial deposits?

A

Fluvial facies, Shallow marine

Sedimentology and Stratigraphy (19 decks)

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