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Geology- year 2 > Sedimentary structures- Clastic and Lacustrine facies > Flashcards

Sedimentary structures- Clastic and Lacustrine facies Flashcards

1
Q

List 11 Primary Sedimentary Structures

A
  1. Planar bedding, laminations, varves
  2. Ripple Marks
  3. Cross-Bedding
  4. Graded Bedding
  5. Incised channels
  6. Flute channels
  7. Rills and Gullies
  8. Mud Cracks
  9. Raindrops
  10. Mud Volcanoes
  11. Trace Fossils
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2
Q

Planar bedding is separated by variations in?

A

color, composition, grain size with bedding surfaces parallel to bedding.

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3
Q

What is the depositional environment of a Planar Bed?

A
  • Deposition from high flow velocity

- settling from standing body of water with very low flow velocity (e.g.. lakes, varves)

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4
Q

What is hummocky cross bedding?

A

Is a distinctive sign of storms like hurricanes. Formed when piles of sand at least 1m high (called hummocks), are built up at the bottom of the sea floor. This results in a permanent new coat of sand covering the whole seafloor.

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5
Q

What are glacial varves?

A

Annual glacier laminations consisting of 1 dark layer (winter) and 1 light layer (summer)

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6
Q

How are asymmetrical ripple marks formed?

A

By unidirectional currents (asymmetrical)

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7
Q

How are symmetrical Ripple marks formed?

A

generated by multidirectional flows (currents, waves)

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8
Q

What is imbrication?

A

a stacking pattern of sediment particles that point to ancient currents.

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9
Q

How is imbrication formed?

A

by transporting (rolling) of disk shaped gravel class.

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10
Q

Cross bedding results from?

A

a change in current direction

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11
Q

Cross bedding is common in what depositional environments?

A

eolian, fluvial and marine sand bar deposits.

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12
Q

What is graded bedding?

A

fining upward sequence

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13
Q

graded bedding is a primary clue in the identification of?

A

deep water turbidites

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14
Q

Coarsening upwards sequence is indicative of what depositional environment?

A

Deltas

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15
Q

What are the 5 principles of stratigraphy?

A
  1. Principle of Uniformatarianism
  2. Principal of Original Horizontality
  3. Walter’s Law
  4. Law of superposition
  5. Law of faunal succession
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16
Q

What is a barchan dune?

A

an arc-shaped sand ridge, comprising of well sorted sand

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17
Q

What are secondary bedding plane marking are signs of what?

A

vigorous activity in sediments before they turned to rock

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18
Q

How are secondary bedding plane marking caused?

A

due to the alteration of primary depositional structures such as trace fossils, diagenetic, nodules, concretions and other features.

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19
Q

What are primary bedding plane markings related to and what are 4 examples?

A

to erosion and deposition of sediments.

  • Incised channels
  • Sole markings (flute casts)
  • Mud cracks
  • Rain drops
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20
Q

What are secondary primary bedding plane markings related to and what are 3 examples?

A

related to alteration of depositional fabric

  • Mud volcanoes and load casts
  • Trace fossils
  • Diagenetic- nodules, concretions, stylolites
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21
Q

Name 5 load casts

A 
sole marks
flute structures
flame structures
ball and pillow structures
mud cracks
rills and gullies
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22
Q

When is a ball and pillow structure formed?

A

is formed when a sudden load of sand deposits is laid down on a soft mud bed.

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23
Q

When is a pillar structure formed?

A

as fluid escapes from under-pressure sediments

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24
Q

What is a rill?

A

a narrow and shallow incision into the underlying structure

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25
Q

How are gullies formed?

A

gullies are small valleys formed by the development of rills

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26
Q

What are mud cracks a product of?

A

dessication and contraction of deposited muddy sediments

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27
Q

What is a trace fossil or ichnofossil?

A

a biogenic sedimentary structure, where preserved intact, are closely related tp the depositional setting

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28
Q

What are stromatolites?

A

layered bio-chemical accretionary structures formed in shallow water by trapping, binding and cementation of sedimentary grains by biofilms of microorganisms (especially blue-green algae)

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29
Q

Define walter’s law

A

whatever happens vertically, happens laterally!!!!!!!!!!!!

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30
Q

What is lithostratigraphy?

A

Correlation of sedimentary rocks based upon lithology

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31
Q

What are the units of lithostratigraphy?

A 
supergroup
group
formation
member
bed
32
Q

What is chronostratigraphy?

A

Correlation of sediments based upon relative or absolute age

33
Q

What are the units of chronostratigraphy?

A 
Eon
Era
Period
Epoch
Age
34
Q

What is biostratigraphy?

A

Correlation of sedimentary rocks based upon fossil content

35
Q

What are the units of biostratigraphy?

A

system
series
stage
zone

36
Q

Name 5 terrestrial systems and facies

A
  1. rivers
  2. deserts
  3. lakes
  4. downslope basins in mountains
  5. ice sheets/glaciers
37
Q

What are the 3 main terrestrial systems that we are focusing on in this class?

A
  1. fluvial
  2. eolian
  3. lacustrine
38
Q

What is the basic 3 fold sub division of terrestrial basins?

A
  1. Basins with thorough drainage are dominated by well established river systems.
  2. Basins with internal drainage (shallow, short lived, sabkhas, deserts)
  3. Basins with well developed lake environments.
39
Q

What are the 3 principal river types?

A
  1. Meandering river model
  2. Sandy braided stream model
  3. Anastomosing rivers
40
Q

In a meandering river system, sand deposition is normally restricted where?

A

to the main channel

41
Q

Does the channel floor in a meandering river have a coarse or fine layer?

A

Coarse…only moved at high velocities

42
Q

During normal discharge, how is sand moved through the system?

A
  1. dunes on the channel floor

2. ripples higher on the point bar

43
Q

Do meandering river fine upwards or coarse upwards?

A

fine upwards

44
Q

What are sandy braided rivers dominated by?

A

bars, channels, and sinuous crested dunes

45
Q

When does an anastomosing river occur?

A

when a river has multiple number of relatively stable channels.

46
Q

How are anastomosing rivers formed?

A

formed by high rates of vertical sediment accumulation/aggradation

47
Q

The occurrence of eolian deposits in the stratigraphic record is an indicator of what?

A

ancient climatic zones

48
Q

Eolian sequences are dominated by what kind of deposition?

A

dominated by cross-stratified sandstones reflecting migrating eolian bedforms developing during the lateral movement of sand dunes

49
Q

Are sediments commonly well sorted in a lacustrine sedimentary facies?

A

YES

50
Q

Do facies fine inward or outward in a lake?

A

fine inward toward the basin center

51
Q

lake sediments are predominantly fine or coarse sediments?

A

FINE

52
Q

What is a typical sequence that may be produced when a lake dries up?

A

coarsening upward sequence from laminated shales, marles and limestones to rippled and cross bedded sandstone and possibly conglomerates.

53
Q

What sedimentary facies typically shows varves?

A

LAKES

54
Q

How are varves produced?

A

by seasonal variation in sediment supply

55
Q

Lakes are typically ephemeral features, what does this mean?

A

only the largest lakes are likely to leave a significant sedimentary record.

56
Q

What 2 headings are lakes classified under?

A
  1. Hydrologically open lakes (outlet streams eg. glacial lakes)
  2. hydrologically closed lakes(inland drainage) (characterized by evaporate deposits eg. playa lakes)
57
Q

In a lake, where are the coarser clastics deposited?

A

close to shore and may display ripple marks and cross-bedding.

58
Q

What is generally found in the offshore region of a lake where clastics accumulation is reduced?

A

thin limestone and marls

59
Q

In a deeper part of a lake, what accumulates and why?

A

clays and silts accumulate from suspension at very slow rates

60
Q

In rare cases, tubidity currents may deposit what in the deeper part of a lake?

A

fining upwards sediment

61
Q

Are lakes a good place to find hydrocarbon?

A

not great, only found sometimes.

62
Q

Lake basins have many diverse origins created by the action of what 6 things?

A
  1. Glaciers
  2. Rivers
  3. Wind deflation
  4. Tectonics
  5. Volcanoes
  6. Meteor Impact
63
Q

What is a Tarn?

A

a small mountain lake, especially one that occupies an ice-gouged basin on the floor of a cirque.

64
Q

What are the margins of the sedimentation of a lake marked by?

A

alluvial fans and fluvial desiment

65
Q

What is the sedimentation in the center of a lake from?

A 
Finer sediments and 
turbidite cycles
cycles in  order from:
-Clastics and organics
-Limestones and Organics
-Evaporties and organics
66
Q

What sedimentary signature is a lake similar to?

A

A foreshortened marine setting

67
Q

A lake has what kind of shoreline?

A

narrow shores with beaches and deltas

68
Q

What does micritic mean?

A

oil

69
Q

Common ways lakes are formed?

A

glacial, flash flooding, wind deflation and mass wasting/man-made.

less common:
Tectonics (e.g. fault-bounded lakes; cratonic sags)
Volcanoes (crater lakes)
Meteor Impact (crater lakes)
Karsting (carbonate solution sinks)
70
Q

Great Lakes

A

Bodies of fresh water trapped on glacially scoured depressions on craton behind glacial moraines
Act as traps to clastic sediments
Climatic change is recorded in record of sediment fill
Water draw down encourages precipitates

71
Q

Caspian and the Aral Sea

A

Bodies of fresh to saline water trapped on craton behind major mountain chains
Tend to act as traps to clastics, carbonates and evaporitic sediments
Climatic change is recorded in the record of the sediment fill
Water draw down encourages evaporites

72
Q

Lake sedimentary facies

A

Sedimentary signature like that of a foreshortened marine setting
Narrow shores with beaches and deltas
Finer sediments and turbidites fill the lake center

73
Q

What kind of reservoir is the Daqing Oilfield?

A

Lower Cretaceous lacustrine-deltaic and fluvial sandstone

74
Q

what kind of source rock is in the Daqing oilfield

A

deep-water lacustrine shale and mudstone of early Cretaceous age

75
Q

Daqing Oilfield size?

A

It is 138 km long in north - south and 73 km wide in east - west, covering an exploration area of 72X104 km2 with 4103.37 km2 of oil-bearing area proven.

Geology- year 2 (7 decks)

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