Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "1. Evidence for the Northward Drift of Britain Through the Phanerozoic."— Presentation transcript:

1

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

3 Pre-Cambrian ~600 Ma Rondinia Supercontinent

4 Cambrian ~550 Ma

5 Early Ordovician ~490 Ma

6 Late Ordovician-Early Silurian ~ Ma

7 Mid-Devonian ~400 Ma Old Red Sandstone Continent

8 Pre-Cambrian ~ 850 Ma Carboniferous ~300 Ma Pangaea Supercontinent

9 Triassic ~237 Ma

10 Jurassic ~195 Ma

11 Tertiary ~65 Ma

12 What is the rate (mm/year) Southern Britain has moved northwards over the last 500Ma? 60°S to 55°N 1° = 111km

13 Explain how magnetic inclination preserved in rocks and apparent polar wandering curves provide evidence of changes in palaeolatitude. (25) Palaeomagnetism 1.Palaeomagnetism 2.Earth’s magnetic field 3.Magnetite in basalts 4.Erupt at surface & cool 5.Curie point 6.Align with magnetic field 7.Crystallisation 8.Magnetic inclination 9.Remnant magnetism 10.Palaeolatitude

14 PeriodAgeRocksMagnetic Inclination Palaeolatitude tan I = 2 tan L I = angle of inclination L = latitude Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Ice age deposits Crocodiles, lotus plant & laterites Chalk – Chilterns, North & South Downs Oolitic Lst - Cotswolds Desert sst - Eden Valley Carb lst – Pennines Coal - Wakefield 69º 61º 57º 50º 23º 0º0º 52º 42º 38º 31º 12º 0º0º tan I = tan L 2

15 “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

16 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)

17 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 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.

18 Permo-Triassic 290 – 208 MYA

19 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 (CaCO 3 ) – least soluble Gypsum/Anhydrite (CaSO 4 ) Halite (NaCl) Potassium salts Magnesium salts – most soluble Order of Precipitation

20 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:

21 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

22 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

23 “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

24 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/ExtensionEvaluation/Analysis of Evidence Conclusion:

25 Period/Age/LatitudeEvidenceClimateEvaluation 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 Uniformitarianism Coral species Cold 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 Downs Oolitic limestone – Cotswolds Land fossils – reptiles, dinosaurs Plant remains – Lotus flowers in Skye Red 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

26 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

27 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)


Download ppt "1. Evidence for the Northward Drift of Britain Through the Phanerozoic."

Similar presentations


Ads by Google