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Introductory field skills-33742 > Sea level change through geological time and other features relevant to fieldwork > Flashcards

Sea level change through geological time and other features relevant to fieldwork Flashcards

1
Q

What are the main sea level change principles?

A

Eustacy
Isostasy
Thermal expansion

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2
Q

What is eustacy?

A

Global change in amount of water in oceans due to climate and/or changing
basin geometry/volume due to tectonics changing the volume of water oceans can hold

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3
Q

What is isostacy?

A

Changes in relative height of the Earth’s crust due to loading (buoyancy,
subsidence)

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4
Q

What is thermal expansion?

A

changes in volume in relation to temperature change; warmer water has a
larger volume

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5
Q

What is regression?

A

sea levels fall and facies migrate seawards

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6
Q

What is transgession?

A

sea level rise facies migrate inland

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7
Q

What can regression and transgression identify?

A

when sea level has changed but not absolute height

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8
Q

What is a geological proxy?

A

natural recorder of direct measurement for environmental or climate variability

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9
Q

What are some examples of proxy data?

A

tree rings, ice cores, fossil pollen and spores, ocean sediments, corals and
historical data

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10
Q

Is there any reliable proxy for water depth?

A

only generalities and relative estimates

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11
Q

What is faunal proxy evidence?

A

fossil with eyes suggest organisms lived within photic zone

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12
Q

What is the photic zone?

A

depth light penetrates the water column

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13
Q

What are the problems with faunal evidence?

A

Fossil not ubiquitous
Eyes maybe not reserved
Photic zone depth varies (up to 200m)
Dont know eyes functional or relict
Was fossil in photic zone or transported

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14
Q

What can cause the photic zone to vary?

A

salinity, sediment levels/turbidity, biological
composition

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15
Q

What 2 ways can depositional water depth in the rock record be split?

A

proximal and Distal

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16
Q

What will proximal sediment composition be like?

A

High energy
Siliciclastic minerals
Coarse grain size
Rapid deposition
Frequent sedimentary structures

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17
Q

What will distal sediment composition be like?

A

Low energy
Mud dominated
Fine grain size
Slow deposition
Sedimentary structures less common

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18
Q

What will normal conditions be like for wave form and wave base?

A

Fair weather wave base (FWWB)

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19
Q

What can crest to crest length tell us above the waves?

A

depth of water displaced

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20
Q

What will conditions be like above FWWB in normal conditions?

A

water column and sediment affected by wave action and in coastal areas tides. May
also be influenced by currents

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21
Q

What will conditions be like below FWWB in normal conditions?

A

water column and sediment unaffected by affected by waves and tides, but may be
influenced by currents

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22
Q

What will the depth of the FWWB be?

A

varies between 5 and 15m

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23
Q

What does FWWB define in sedimentary environments?

A

upper shore face

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24
Q

What is SWB?

A

Storm Wave Base

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25
Q

What is the affect of larger wavs in SWB?

A

affect water column to a deeper level

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26
Q

How will SWB occur in relation to FWWB?

A

SWB will be below FWWB but not at same time

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27
Q

What is the depth of SWB?

A

15-40m but deeper in extreme events (hurricane, typhoon)

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28
Q

What does SWB define in depositional environments?

A

lower shore face

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29
Q

What will conditions be like above SWB?

A

water column and sediment: water interface affected by storm wave action agitating and re-working the sediment.

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30
Q

What will conditions be like below SWB?

A

water column and sediments not affected by storm wave action – currents may occur

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31
Q

What will be the cause for sedimentation below SWB?

A

current activity or from muddy sediment settling from suspension

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32
Q

What will the duration of background sedimentation for FWWB?

A

significantly longer longer than SWB

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33
Q

How will the water column be affected FWWB?

A

at this height not affected by wave or tidal action

34
Q

What sort of energy condition is FWWB?

A

low energy - no wave agitation

35
Q

What is the sedimentation rate of FWWB like?

A

very low- sediment as mud falling from suspension

36
Q

What might have a potential to introduce high energy conditions/ sediments?

A

perhaps current activity

37
Q

How would frequency of event sedimentation be described?

A

infrequent

38
Q

What is the duration of event sedimentation?

A

short duration

39
Q

How will the water column be affected in event sedimentation?

A

affected by wave action

40
Q

What will the energy conditions be like in event sedimentation?

A

high- mixing sediment and agitating sea floor if at this depth

41
Q

What will the sediment be like in event sedimentation?

A

coarse grained
poorly sorted
rapidly deposited

42
Q

What sediment structures are present in event sedimentation?

A

cross bedding
ripples
lenticular bedding

43
Q

What is the sedimentation rate be like event sedimentation?

A

high sedimentation rate

44
Q

What are the requirements with ripples?

A

Unconsolidated sand sized sediment particles
Current moving over the sediment (wind, water, ice)

45
Q

What is key observation of ripple shape in cross section?

A

symmetrical or asymmetrical

46
Q

What is key observation of ripple shape in plan view?

A

parallel
sinuous
bifurcating

47
Q

What is key observation of ripple wavelength?

A

distance crest-crest, or trough to trough

48
Q

What is key observation of ripple height/amplitude?

A

height from bottom of trough to top of crest

49
Q

What is key observation of ripple orientation?

A

orientation on ripple plane (plunge)

50
Q

What processes can exacerbate weathering?

A

Heating/cooling
Wetting/drying
Physical contact (abrasion) including wind and water transported debris
Biological weathering
Chemical weathering (often through water)

51
Q

What are the major physical properties of rock that affect susceptibility to weathering?

A

Composition
Hardness
Planes of weakness

52
Q

What are some examples of planes of weakness?

A

faults
fractures
joints
cleavage

53
Q

What is competent rock?

A

not easily broken or fragmented

54
Q

What are some examples of competent rock?

A

granite, gneiss, basalt, some sandstone, some limestone

55
Q

What can competent rock be used for?

A

building stone or aggregate

56
Q

What is incompetent rock?

A

easily broken or fragmented
susceptible to weathering

57
Q

what are some examples of incompetent rock?

A

mudrocks (mudstone, siltstone, claystone), some sandstones, some limestone

58
Q

What are some ways you can tell a rock has been weathered?

A

orange colours
honeycomb texture
joints and faults

59
Q

What will orange colour in rock suggest?

A

iron content oxidised

60
Q

What will honeycomb texture indicate with weathering?

A

heterogeneous calcium carbonate cement
careous weathering

61
Q

What will fresh rock surfaces allow for?

A

identification of original features grain/crystal size, shape and colour fabrics and textures within the rock

62
Q

What will weathered surfaces allow you to identify?

A

alteration products changes in mineralogy (shape, size, colour) additional fabrics within the rock

63
Q

When will baked and chilled margins occur?

A

when hot igneous body intruded into or extruded onto pre-existing and cooler rock strata

64
Q

What is a baked margin?

A

altered by contact metamorphism (hot rock affecting cold rock)

65
Q

What rock often present at baked margins?

A

hornfels

66
Q

What is a chilled margin?

A

when got intrusion cooled by country rock with smaller sized crystals

67
Q

What is sill?

A

igneous rocks intruded into existing strata

68
Q

What is lava flows?

A

igneous rocks extruded onto Earth’s surface

69
Q

What are ammonites?

A

linage of molluscs within class Cephalopoda

70
Q

What is distinctive about ammonites?

A

whorled shell with internal divisions into chambers

71
Q

Where are ammonites extensively found in fossil record?

A

Jurassic and cretaceous

72
Q

What are the positives of using ammonites?

A

Diverse and species/genera/families readily identified
Exclusively in marine rocks
Geographically widespread
Biostratigraphic applications (biozone 1Ma)

73
Q

What are trace fossils?

A

Physical evidence of fossil organisms in the absence of body fossils
Feeding, movement and habitation traces

74
Q

What is diagenesis?

A

Physical and chemical changes that occur in the transition of sediment to a sedimentary rock

75
Q

What are some examples of diagenesis?

A

Dewatering
Compaction
Dissolution
Cementation
Lithification

76
Q

What are diagenetic concretions (nodules) form?

A

Rounded mineral masses (typically calcium carbonate, iron carbonate or pyrite) that form after the host rock was deposited by diagenesis

76
Q

What can form if diagenetic concretions fracture?

A

fracture and recrystallise forming septarian nodules)

77
Q

What is taphonomy?

A

The science of death and decay; controls what and how organisms enter into the fossil record

78
Q

What are the key elements of taphonomy?

A

Life cycles of organisms
Physical transportation
Preservational biases
Mineralisation and geochemistry
Diagenesis
Decay zones and processes

79
Q
A

Introductory field skills-33742 (7 decks)

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