Open University Geological Society Journal Spring Edition 2007 Contents The Geoff Brown Memorial Lecture: Radioactivity from Lakes to Lavas: 1 Studies from Uranium series isotopes Dr Louise Thomas, Department of Earth Sciences, the Open University, Walton Hall, Milton Keynes Giant landslides, lava flow fields and the edge of the known world (1491): 5 an introduction to the geology of El Hierro, Canary Islands. Duncan Woodcock Field Observations in the Lower Ordovician rocks of the North Pembrokeshire coast 12 John Downes Walk along the Southern Strand: 17 London Branch field trip along the South Bank of the River Thames Diana Clements, J. Edwin Jarvis, Adrian Rundle A visit to the Belgian Ardennes 21 Gladys Dinnacombe Nisyros: A Greek Volcanic Island 25 David Rowe Scratching the Surface of New Zealand II: The North of South Island 28 Robin Lewando São Miguel on a Shoestring 36 Linda Fowler (ed) London Branch visit to Shetland 31 July - 7 August 2006 leader Allen Fraser 48 Maggie Morley, Gillian Hetherington, Peter Franklin, Bob Morley, Heather Rogers, Ursula Scott & Les Richmond Orkney 9-12 June 2006 54 Chris Arkwright, Linda Smith, Anne Lavelle & Gerry Shaw Thrombolites in danger - Lake Clifton, Yalgorup National Park, West Australia 59 M Rosemary Darby Intrigue at Belmont Hamlet 61 Rob Heslop Book reviews 4, 11, 16, 24, 27, 35, 47, 62 It is the responsibility of authors to obtain the necessary permission to reproduce any copyright material they wish to use in their article. The views expressed in this Journal are those of the individual author and do not represent those of the Open University Geological Society. In the opinion of the author the description of ven- ues are accurate at the time of going to press; the Open University Geological Society does not accept respon- sibility for access, safety considerations or adverse conditions encountered by those visiting the sites. Editor: Jane Clarke ISSN 0143-9472 OUGS Journal 28(1) © Copyright reserved email: [email protected] Spring Edition 2007 Cover illustration: Thin sections of several different habits of barite. Photographs: Jane Clarke. Botryoidal barite Acicular barite Poikilotopic barite Mag 538; ppl. Mag 549; xpl. Mag 530; xpl. Bladed barite (white) Botryoidal barite Spherulitic barite Mag 580; ppl. Mag 538; xpl Mag 584; xpl. Fasicular-optic barite Banded barite Banded barite Mag 549; xpl. Mag 538; xpl. Mag 538; ppl. Committee of the Open University Geological Society 2007 Executive Committee Members President: Dr Sandy Smith, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA Chairman: Joe Jennings Secretary: Polly Rhodes Treasurer: Bob Morley Membership Secretary: Stuart Bull Newsletter Editor: David Jones Information: Linda McArdell Events Officer: Glynis Sanderson Sales Manager: Lesley Laws Non-voting postholders Gift Aid: Ann Goundry Journal Editor: Jane Clarke Archivist/Review Officer: Jane Michael Minutes Secretary: Mike Jones OUSA Representative: Alasdair Farquharson OUSA Deputy Representative: Karen Scott Branch Organisers East Anglia: Andrew Fleming East Midlands: Don Cameron East Scotland: Anne Burgess Gogledd Cymru: Rachel Atherton Ireland: Phyllis Turkington London: Sue Vernon Mainland Europe: Annette Kimmich Northumbria: Annie Hedley North West: Jane Schollick Oxford: Sally Munnings Severnside: Janet Hiscott South East: Roger Baker South West: Gordon Neighbour Walton Hall: Michael Friday Wessex: Sheila Alderman West Midlands: Linda Tonkin West Scotland: Jacqueline Wiles Yorkshire: Amy Thomson Past Presidents of the OUGS 1973-4 Prof Ian Gass 1985-6 Dr Peter Skelton 1997-8 Dr Dee Edwards 1975-6 Dr Chris Wilson 1987-8 Mr Eric Skipsey 1999-0 Dr Peter Sheldon 1977-8 Mr John Wright 1989-90 Dr Sandy Smith 2001-2 Prof Bob Spicer 1979-80 Dr Richard Thorpe 1991-2 Dr David Williams 2003- 4 Prof Chris Wilson 1981-2 Dr Dennis Jackson 1993-4 Dr Dave Rothery 2005 - 6 Dr Angela Coe 1983-4 Prof Geoff Brown 1995-6 Dr Nigel Harris 2007 - Dr Sandy Smith Vice Presidents of the OUGS Dr Evelyn Brown Dr Michael Gagan Norma Rothwell The Geoff Brown Memorial Lecture: Radioactivity from Lakes to Lavas: Studies from Uranium series isotopes Dr Louise Thomas, Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA Introduction Henri Becquerel, the French physicist is attributed with the dis- Firstly thank you Joe (Jennings) for the introduction and second- covery of radioactivity in 1895, whilst he was experimenting with ly thank you to the OUGS for inviting me here today to give the uranium salts. Almost at the same time as the German physicist Geoff Brown Memorial lecture. I am honoured to do so. Wilhelm Rontgen discovered x-rays (one of his first pictures was of his wife’s hand, Figure 1), and soon after Marie Sklodowska- For those of you, who I’ve met (and I see lots of familiar faces in the Curie discovered and isolated radium. audience) during my twelve years at the Open University, whether on the fieldtrip to Tenerife or at one of the number of lectures I have In the early 1900s the research into radioactivity continued, given at regional branches, or at Walton Hall you will be surprised Ernest Rutherford amongst others had been studying radioactive to hear that this talk is not all volcanic, in fact that I have moved processes, and he suggested that it might be possible to date rocks more than a little way towards the dark side – soft rocks. This talk using radioactive minerals and within the next few years, urani- encompasses work that I have been involved in at the OU, where we um, thorium and radium isotopes were used to date minerals. are currently the NERC facility for Uranium Series. The age of the Earth was calculated to be in the billions of years, not millions. During a lecture to the Royal Institution on the heat I will start with the history of radioactivity, what types and uses, production of radioactivity and its effect on the heat of the Earth, what we have at the OU, then onto U-series, and how that works Rutherford was ill at ease to see Lord Kelvin in the audience. He and finish off with some applications, including hard rocks! This avoided a potential explosive conflict, by announcing that Lord talk covers a wide range of projects, many of which Peter van Kelvin had calculated the age of the Earth from its thermal histo- Calsteren, Mabs Gilmour and I have been involved with. ry, provided no new source of heat was found. Therefore, Lord History of Radioactivity Kelvin has in fact anticipated the discovery of radioactivity and the heat produced by this phenomenon. Lord Kelvin who had in During the mid to late 1800s, many physicists including William fact slept soundly through the rest of the talk, just beamed with Thompson, later known as Lord Kelvin, had been working on the pleasure (Source: Faure 1986). problem of the age of the Earth and the sun, using theories and estimates of cooling rates. Lord Kelvin concluded that the age of The occurrence of radium excesses was first found in volcanics the earth was probably around 20 - 40Ma. This was too long for from Vesuvius by Joly in 1909. The importance of U-Series dise- some and too short for others including Lyell’s theory of gradual quilibrium to the study of magmatic processes was only realised geological change and Darwin’s theory of evolution. T.C. around fifty years ago from work by Oversby and Gast and Chamberlin, a confessed agnostic in the audience added that there Allègre, and since that time the subject has been in continuous might be an as yet unknown source of energy. development on a whole range of rocks. Types of Radioactivity I have mentioned both radiation and radioactivity. What is the dif- ference? Radiation is the excess energy that is released as parti- cles or rays, during radioactive decay, whilst radioactivity is the property of an atom that describes spontaneous changes in its nucleus that create a different element. There are 3 main types of radiation: • Alpha (He nucleus) (stopping distance 1-3cm in air or stopped by paper) • Beta (electrons) (depends on energy but can travel several metres or stopped by perspex) • Gamma (X rays) (up to kms - most energetic, goes through everything!) Most alpha emitters occur naturally in the environment, for exam- ple, alpha particles are given off by uranium-238, and other mem- bers of the uranium decay series are present in varying amounts in nearly all rocks, soils and water. They are stopped by the dead layer of skin cells, however if they are ingested/inhaled then they can cause a lot of damage. Your home smoke detectors will have an alpha source – Americium 241. Alpha emitters were used as a cure Figure 1. Rontgen’s X-ray image of his wife’s hand with for aches and pains and as luminous paint on watches and compass wedding ring (source http://nobelprize.org) dials. OUGS Journal 28(1) 1 Spring Edition 2007 Beta particles are subatomic particles ejected from the nucleus of Written out for 230Th and normalised to 232Th and taking into con- some radioactive atoms. While beta particles are emitted by atoms sideration that 230Th is also radioactive and decays (to 226Ra) the that are radioactive, beta particles themselves are not radioactive. equation becomes: It is their energy, in the form of speed, which causes harm to liv- ing cells. They are used in a wide range of medical treatments. Gamma radiation is very high-energy ionizing radiation. Gamma rays and x-rays, like visible, infrared, and ultraviolet light, are part Also known as the ‘isochron equation’ and it requires a number of of the electromagnetic spectrum. While gamma rays and x-rays datapoints to calculate an age.