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Earth history and life - 29202 > Pre-Cambrian of the British isles > Flashcards

Pre-Cambrian of the British isles Flashcards

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1
Q

Where do the majority of good pre-cambrian outcrops occur?

A

Scotland

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2
Q

How are the pre-cambrian deposits separated in scotland?

A

By a series of units (terranes) from the NW highlands to the southern highlands

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3
Q

What is the lithostatigraphical division of the UK in the precambrian?

A

Lewisian split into:
1. Scourian (older)
2. Laxfordian (yoiunger)

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4
Q

What are the typical Lewisian lithologies?

A

Foliated and banded gneiss

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5
Q

What is the history of the Lewisian?

A

Billion year time history so lots happened
With cross cutting dykes

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6
Q

What is the Hebridean terrane (scotland)?

A

Most north-west part of Scotland consisting of older basement lewisian and overlying Torridonian

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7
Q

What splits the Hebridean terrane and N.Highland terrane?

A

The Moine thrust

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8
Q

What are the lithologies of the N.Highland terrane?

A

Lewisian basement overlain by Moine

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9
Q

What happened in the Hebridean terrane between the Lewisian and the Torridonian?

A

Uplift and erosion in the Proterozoic

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10
Q

How many unconformities are there in the pre-cambrian?

A

3

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11
Q

Where are the unconformities in the precambrian sequence?

A
  1. Between Lewisian and Clachtoll
  2. Between Meall Dearg and Diabaig
  3. Between Diabaig and Applecross
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12
Q

What is the deposition of the diabaig evidence of?

A

Lacustrine deposition

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13
Q

What is lacustrine deposition?

A

finely layered fine grained sediments usually in lakes showing seasonal change in deposition

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14
Q

What event can be seen at similar horizons throughout the diabaig?

A

dropstones - thought to be due to a glacier coming into contact with water

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15
Q

What are dropstones?

A

are lumps found within the fine grained sediments

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16
Q

What additional layer is found overlying the Torridonian?

A

Eriboll (cambrian)

17
Q

What is characteristic about Moine rocks?

A

Sheath fold which leads to eye structures in rock

18
Q

What is the Grampian terrane?

A

Youngest in precambrian sequence

19
Q

What rock age makes up the Grampian terrane?

A

Dalradian

20
Q

What rock group in scotland holds evidence of multiple glaciations?

A

Argyll through tillite at its base

21
Q

How many levels of evidence for glaciations is in the Dalradian Terrane?

A

3 with Port Askaig being the first

22
Q

What are the 2 principle divisions of the Cambrian and pre-Cambrian in Anglesey?

A

Older- south stack - low grade metasediments
Younger- Gwna - sedimentary breccia

23
Q

What is the rock boundary for the Cambrian / pre-Cambrian at Wrekin?

A

Cambrian sandstone and pre-Cambrian separated by unconformity

24
Q

What evidence of volcanism in the late pre-Cambrian is there from Wrekin?

A

Rhyolites (effusive phase) and Granifiers

25
Q

What fossils are present in the charnian supergroup in charnwood?

A

Impressions of ediacaran fossils

26
Q

What are the stages of the wilson cycle?

A

Continental rifting
Seafloor spread
Ocean widens
Lithospheric subduction
Ocean base close
Ocean basin finally closed by continental collision
Continental rifting

27
Q

Why is there net erosion at uplifting zones?

A

due to lack of deposition which creates unconformity in rock record

28
Q

What is the oldest supercontinent in the pre-cambrian?

A

Columbia (Nuna)

29
Q

When was the Nuna supercontinent and how long did it last?

A

1.5 bn years ago and lasted 200 million years

30
Q

What was terrane like for Nuna supercontinent?

A

Terrane all agglomerated together

31
Q

What supercontinent was there after Columbia (Nuna)?

A

Rodina

32
Q

Where did Rodina form?

A

around the equator

33
Q

What partial supercontinent formation occurred after Rodina?

A

Pannotia (600 Ma)

Earth history and life - 29202 (29 decks)

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