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Earth history and life - 29202 > Mesozoic of the British Isles > Flashcards

Mesozoic of the British Isles Flashcards

1
Q

What systems was the Triassic initially dominated by?

A

Non-marine fluvial and aeolian systems (global warm period)

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2
Q

What did the increasing influence of marine conditions lead to in the Triassic?

A

Evaporites

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3
Q

What makes correlation difficult for the Permo-Trias boundary?

A

Lack of significant marine deposits (non-marine dominance till end Triassic)

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4
Q

What occurred in the Carnian (230 Ma)?

A

Ongoing breakup of Pangea

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5
Q

Why is the Carnian important?

A

Important rifting - with deposition of sherwood sandstone and sucession of Mercia mudstone

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6
Q

What conditions were sherwood sandstone deposited under?

A

Crustal extension

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7
Q

What conditions was the Mercia Mudstone deposited under?

A

Post-rift thermal subsidence

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8
Q

Where is the base of the Triassic taken from?

A

First pebble bed in the Triassic Sherwood sandstone

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9
Q

What are the rock groups of the Triassic? (old to young)

A

Sherwood sandstone
Mercia Mudstone
Penarth group

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10
Q

What does palynology prove?

A

Facies are diachronous

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11
Q

What is a suggestion of the mid-Triassic English midlands?

A

Marine influence

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12
Q

What does the Penarth group mark?

A

the beginning of the significant marine influence

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13
Q

What us early Triassic sedimentation like in the UK? (deposition of Sherwood sandstone)

A

Aeolian and fluvial

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14
Q

Where is a major source of the Sherwood sandstone?

A

Variscan Highlands transporting many well-rounded Quartzite clasts northwards

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15
Q

What are some examples of rock formations in the Sherwood sandstone?

A

Otter sandstone
Budleigh salterton pebble sands

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16
Q

What are the mudstones like in the mercia mudstones?

A

Red and green mudstones

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17
Q

What environment was the mercia mudstone produced in?

A

Restricted basins (salt assumulation)

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18
Q

Where is 90% of the UKs Halite located?

A

Cheshire basin.
Worth £¼ Billion p.a. to the U.K.
Currently producing about 6 Million tonnes p.a

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19
Q

What was the depositional environment of the Mercia Mudstone?

A

Less fluvial input.
Carbonate soils and marginal halites

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20
Q

What was the depositional environment of the Sherwood sandstone?

A

Fluvial input, braided rivers.
Coarse alluvial fans with anhydrite or carbonate rich soils.

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21
Q

What provides a biostratigraphic framework through the Jurassic?

A

Ammonites

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22
Q

What are ammonites good biomarkers?

A

Evolve rapidly
Planktonic (widespread distribution)

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23
Q

What marks the early Jurassic?

A

Global transgression

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24
Q

What caused significant changes to the sedimentary system throughout the Jurassic?

A

Fluctuating eustatic sea-level change, plate tectonics and local structural factors

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25
Q

What marks the end Jurassic?

A

significant global lowstand reflects global cooling

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26
Q

What was the early Jurassic palaeogeography?

A

Central Atlantic Magmatic Province
UK shallow shelf seas on northern Tethys

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27
Q

What is the basin structure of the Jurassic outcrop in the UK?

A

Basin and swell

28
Q

What are the swell (block) features of the UK Jurassic?

A

Mendips
Moreton
Market Weighton

29
Q

What might the highs and basins of the Jurassic swells in the UK have been like?

A

High - potentially emergent, Thinner and condensed
Basins - Thicker

30
Q

What was the early Jurassic lithostratigraphy like?

A

Almost exclusively marine (mud and shales)

31
Q

What is there evidence of near the top of the Early Jurassic?

A

Shallowing (sandstone and ironstone)

32
Q

What is found within the Blue liass formation and what does it show?

A

Ammonites, bivalves, crinoids, brachiopods, vertebrates, trace fossils
(well oxygenated environment)

33
Q

What is the jet rock of whitby mudstone an example of?

A

Ocean anoxic event

34
Q

What evidence is shown in the jet rock?

A

Perturbation of carbon cycle and ocean system

35
Q

What was the result of the oceanic anoxic event on the jet rock?

A

No benthos
Laminated sediments
Exceptional preservation of nekton/ plankton
Marked carbon isotope excursion (CIE)

36
Q

What is an example of the Toarcian and Aalenian in the UK?

A

Bridport Sands

37
Q

What are the Bridport sands?

A

Shallow marine, offshore shoal sands, on
top of which are the earliest beds of the Inferior Oolite

38
Q

What rock formation marks the Aalenian to the Bathonian?

A

Inferior Oolite of S England

39
Q

What is the Oxford clay?

A

Marine clay
Callovian to lower Oxfordian

40
Q

What are the characteristics of the Oxford clay?

A

Fine-grained, fissile, dark-grey shale, minor
mudstones/limestones
Rich in invertebrates (benthics)

41
Q

What is the economic importance of the Kimmeridge clay?

A

The source rock for much of our North Sea Oil

42
Q

What is displayed in the Kimmeridge clay?

A

Milnakovitch scale cyclicity

43
Q

How was the Kimmeridge clay deposited?

A

Under a stratified water column

44
Q

What marks the late Jurassic to earliest cretaceous?

A

Tithonian Portland Gp and Purbeck Gp

45
Q

What are the Tithonian Portland Gp and Purbeck Gp like?

A

Lagoonal limestone and shale with rich invertebrate and vertebrate and trace fossils
Gypsum and palaeosols

46
Q

What does the gypsum and palaeosols of the Tithonian Portland Gp and Purbeck Gp an indicator of?

A

Indicate climatic and environmental
conditions

47
Q

What was late cretaceous palaeogeography like?

A

Widening N. Atlantic & opening S. Atlantic
Tethys - Atlantic - Pacific connections
High sea levels - flooded continental margins

48
Q

Where can UK outcrops of the cretaceous be found?

A

Wessex and Hampshire basins, S England to East Anglia.
Weald Basin of SE England.
Cleveland Basin of the Yorkshire- Lincolnshire Coast.
East Antrim, NE Ireland

49
Q

What is the Berriasian like?

A

‘Purbeck’ marls & Lmst in the south
(alternating FW, brackish, marginal
marine); sands and marine clays to
the north

50
Q

What is Hauterivian like?

A

‘Wealden’ silts and clays in the
south (non-marine); marine marls,
clays & sands in north

51
Q

What is Aptian like?

A

Marine conditions return to the south
as Mn-Fe-rich sandstones (Greensands) & clays

52
Q

What is Albian like?

A

Marine clays and sands in the south
& east, iron-rich limestones in the
N Sea

53
Q

What occurred in the mid to upper Albian in the wessex basin?

A

Marine transgression (Gault clay and upper green sandstone)

54
Q

What happened in the weald basin between Lower Hauterivian to the Barremian?

A

Non marine - weald clay formation

55
Q

What is found in the weald clay formation?

A

Fluvial and mudflat/overbank
sediments; Main UK source of dinosaur
remains (Iguanodon); FW-Brackish
invertebrate fauna/flora.

56
Q

What are the characteristics of the Speeton clay?

A

Mid- to dark grey clay with horizons of concretions, glauconite and fossil
concentrations.

57
Q

What is the age of the speeton clay?

A

Earlt cretaceous

58
Q

How thick is the speeton clay at coastal exposure?

A

About 100 m

59
Q

What beds are present in the Speeton clay?

A

Bssal nodular beds (phosphatic nodules)

60
Q

What do organic rich shales in the Early Barremian indicate?

A

widespread anoxic event

61
Q

How will rocks be aligned in the Gault clay formation?

A

Grey calcareous clay, generally mid-late Albian, sandwiched between Lr & Ur
Greensands

62
Q

What is the late cretaceous dominated by?

A

Chalk

63
Q

What is the chalk of the late cretaceous like?

A

Pure limestone
Entirely planktonic/ biogenic

64
Q

What is the result of planktonic forms having evolved on the chalk?

A

fine-grained, pure low-magnesium calcite limestone (a biomicrite)

65
Q

What distinctive feature can be found in rhythmic black nodular layers?

A

Flint

66
Q

What are the characteristics of flint?

A

Hard, brittle, siliceous; early- diagenetic remobilization of biogenic silica (mainly sponge spicules, some radiolaria)

Earth history and life - 29202 (29 decks)

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