1. Evidence for the Northward Drift of Britain Through the Phanerozoic

Pre-Cambrian ~600 Ma

Rondinia

Supercontinent

Cambrian ~550 Ma

Early Ordovician ~490 Ma

Late Ordovician-Early Silurian ~450-440 Ma

Mid-Devonian ~400 Ma

Old Red Sandstone Continent

Pre-Cambrian ~ 850 MaCarboniferous ~300 Ma

Pangaea

Supercontinent

Triassic ~237 Ma

Jurassic ~195 Ma

Tertiary ~65 Ma

What is the rate (mm/year) Southern Britain has moved northwards over the last 500Ma?

• 60°S to 55°N• 1° = 111km

Explain how magnetic inclination preserved in rocks and apparent polar wandering curves provide evidence of changes in palaeolatitude. (25)

Palaeomagnetism

1. Palaeomagnetism2. Earth’s magnetic field3. Magnetite in basalts4. Erupt at surface & cool5. Curie point6. Align with magnetic field7. Crystallisation8. Magnetic inclination9. Remnant magnetism10.Palaeolatitude

Period Age Rocks Magnetic Inclination

Palaeolatitude

tan I = 2 tan LI = angle of inclination

L = latitude

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

0

65

140

200

250

2

290

Ice age deposits

Crocodiles, lotus plant & laterites

Chalk – Chilterns, North & South DownsOolitic Lst - Cotswolds

Desert sst - Eden Valley

Desert sst - Eden Valley

Carb lst – PenninesCoal - Wakefield

69º

61º

57º

50º

50º

23º

0º

52º

42º

38º

31º

31º

12º

0º

tan I = tan L

2

“Palaeomagnetic data is a reliable indicator of palaeolatitude.”Evaluate this statement.

• igneous rocks with magnetite needed (very rare in sedimentary rocks)• doesn’t indicate which hemisphere

• assumes Earth’s magnetic field remained same over time (dipolar)• doesn’t tell lines of longitude

• remanent magnetism very weak so need lots of readings for average• re-melting/metamorphism destroys remanent magnetism

• inaccuracies caused by problems of radiometric dating of rocks

• very useful if backed up by study of sediments

Palaeomagnetic evidence suggests that during the Late Palaeozoic (Devonian, Carboniferous and Permian), Britain drifted across the equator.

a). Describe the evidence from sedimentary rocks and fossils which suggests an equatorial climate in Britain in the Late Palaeozoic.b). Describe and evaluate the palaeomagnetic evidence. (25)

With the aid of a labelled diagram, describe and account for the variation in heat flow across an ocean basin and an adjoining arc system.

(25)

• Read & dissect the question (doing words & key words)

Define meanings & give figures. Say what

you see!

Explain & give reasons for

How heat is transferred from inside the Earth to the outside

• Plan an outline & write out the essay question 1. Introduction

2. Main Body•Paragraph 1•Paragraph 2•Paragraph 3•Paragraph 4•Paragraph 5•Paragraph 6

3. Conclusion

• Use paragraphs as basic structuring unit in the essay

Topic sentence

• supporting evidence• supporting evidence• supporting evidence

Concluding sentence

Theme of paragraph & should link with concluding sentence of paragraph above.

Say what you are going to do by defining your version of the title. Show you have understood every significant word of it. Define key words.

Briefly summarise the essay by referring to the title

• Presentation

Each paragraph should be on a different aspect of the topic.Put the reader first.

Make it easy for them to read.

Clear & well presented.

Spelling & punctuation.

Permo-Triassic 290 – 208 MYA

Permo-Triassic 290 – 208 MYA

• evaporites/inter dune areas

• desiccation cracks

• playa lakes

• Zechstein Sea

A facies (a group of rocks and structures that indicate a particular environment. e.g. cross bedded desert sst, brecio-conglomerates, evaporites etc)

Burrells Quarry, Appleby, Vale of Eden

Pangaea 20ºN – semi-arid/desert

Hoff Quarry, near Appleby, Vale of Eden

Eden Shales, Vale of Eden

Desert sst

• Grain size – medium (fine)

• Grain sorting – very well sorted

• Grain Shape – well rounded

• Grain surface - quartz frosting

• quartz (sand)

• haematite cement

• barchan sand dunes

• cross bedding

Breccio-conglomerate “brockrams”

•wadis

• alluvial fans

• poorly sorted/angular to sub-rounded

• Carboniferous lst clasts

Calcite (CaCO3) – least solubleGypsum/Anhydrite (CaSO4)Halite (NaCl)Potassium saltsMagnesium salts – most soluble

Order of Precipitation

In Permo-Triassic times (~250 mya) Britain was about 20ºN of the equator in a latitude similar to that of present day North Africa. Consequently, Britain experienced a hot arid climate, which was very different from that of today. In this essay I will show how sedimentary structures, textures, fossils and mineralogy can be used as evidence to prove this.

1. Geological background/context of essay/definitions/set the scene

2. In this essay I will …. How/what going to do in essay

3. Outline content to be covered in essay

Describe the evidence from sedimentary rocks which shows that semi-arid and desert conditions existed in the British area during the Permo-Triassic period. (25)

Introduction:

In the Carboniferous period Britain was situated on the equator, and over the ensuing 300 million years has moved northwards to its present position of 50-60ºN of the equator. In this essay I will describe the evidence that proves this.

In the Carboniferous period Britain was situated on the equator, and over the ensuing 300 million years has moved northwards to its present position of 50-60ºN of the equator. In this essay I will describe how sedimentary and palaeomagnetic evidence can be used as evidence to proves this.

Describe the evidence for the northward drift of the British area from the beginning of the Carboniferous to the present day. (25)

Introduction:

Paragraphs:

4. Palaeomagnetism

1,2 & 3. Sedimentary rocks – Carboniferous, Permo-Triassic, Jurassic, Cretaceous, Tertiary & Quaternary

5. Fossils

During Late Palaeozoic times Britain moved from a tropical equatorial region in the Carboniferous (~350 mya) to a arid desert environment 20ºN of the equator in the Permian (~290 mya). In this essay I will show how palaeomagnetism, sedimentary rocks and fossils can be used as evidence to prove this.

Outline the evidence that Britain drifted north across the equator during the Late Palaeozoic. (25)

Introduction:

Paragraphs:

1. Palaeomagnetism

2. Sedimentary rocks – Carboniferous - limestones

4. Fossils

3. Sedimentary rocks – Permian – desert sst, brecio-conglomerates & evaporites

“Sedimentary rocks and palaeomagnetic data are reliable indicators of palaeolatitude.”

• Sedimentary rocks

• Palaeomagnetic data

Evaluate this statement.

• igneous rocks with magnetite needed (very rare in sedimentary rocks)• doesn’t indicate which hemisphere

• assumes Earth’s magnetic field remained same over time (dipolar)• doesn’t tell lines of longitude

• remanent magnetism very weak so need lots of readings for average• re-melting/metamorphism destroys remanent magnetism

• inaccuracies caused by problems of radiometric dating of rocks

• very useful if backed up by study of sediments

The rocks in Britain show evidence of climatic change throughout the Phanerozoic. Evaluate the evidence in the rock record for major climatic change in Great Britain from the Carboniferous to the present day. (25 marks)

Title:

Introduction:

Point ( Topic/first sentence) Evidence/Example/Extension Evaluation/Analysis of Evidence

1.

2.

3.

4.

5.

Conclusion:

Period/Age/Latitude Evidence Climate Evaluation

Carboniferous

0º Equator

Equatorial

300 Ma

Carboniferous lst – Pennines

Corals

Fossil soil

Coal – Wakefield, Yorkshire

Plant fossils - Lepidodendron

Amphibians

Tropical shallow seas

Tropical forest/swamps

UniformitarianismCoral speciesCold water lsts?

Indicates climate not latitude

Deciduous trees not evolved

Permo-Triassic

20º North

Desert

250 Ma

Desert sst (well sorted, well rounded, fine sand, haematite cement, frosted grains, cross bedding) – Eden Valley

Breccio-conglomerates

Mudcracks

Evaporites - Cheshire

Lack fossils

Beaconites (burrows) – Kingsand, Cornwall

Jurassic & Cretaceous

30º - 40º North

Tertiary

40º -60º North

Chalk – North & South DownsOolitic limestone – CotswoldsLand fossils – reptiles, dinosaurs Plant remains – Lotus flowers in SkyeRed laterite soils

Hot desert with dunes & wadis (flashflood canyons) leading out into alluvial fans.

Hypersaline conditions with playa lakes, inland seas & salt pans.

Tropical shallow seas

Tropical forest/swamps

Humid & sub-tropical

Principle of Uniformitarianism

Good evidence

Sedimentary facies – evidence needs to be taken as a whole

Implies high temp & tropical but mid latitude at time of high global temp

Implies sub-tropical but high latitude at time of high global temp

Why is it not possible to establish palaeo-longitude positions for Britain at different points through geological time?

• All places on same latitude will have similar climatic conditions

• Rock types do not vary with longitude

• Magnetic inclination is the same along every line of latitude

• Earth’s magnetic field is dipolar – aligned north to south due to spin of Earth

• One longitude could cross many climate types

Palaeomagnetic evidence suggests that during the Late Palaeozoic (Devonian, Carboniferous and Permian), Britain drifted across the equator.

a). Describe the evidence from sedimentary rocks and fossils which suggests an equatorial climate in Britain in the Late Palaeozoic.

b). Describe and evaluate the palaeomagnetic evidence.

(25)