Wessex Branch Newsletter
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The Open University Geological Society Wessex Branch Newsletter Website http://ougs.org/wessex December 2016 Branch Organiser’s Letter CONTENTS Branch Organiser’s Letter Page 1 Dear All Abbotsbury, 25 Sept 2016 Page 2 This feels very strange as it’s my final Branch Two Mendips quarries, 18 Aug 2016 Pages 3-4 Organiser’s letter! Thank you very much for Wytch Farm, 7 Oct 2016 Pages 5-6 your support to me over 20 years, as Events The Etches Collection, 22 Oct 2016 Pages 7-8 Organiser and then as Branch Organiser. Do look at the adverts on pages 6, 13 and 14 for Minerals guide no. 22 – Tugtupite Page 8 future events. I hope to see you at our AGM Staffa and Ardtun, 16 May 2016 Pages 9-10 and lecture day on the Cretaceous Greenhouse Wessex Branch committee Page 10 World, which is on Saturday 21st January 2017 Book review “Fossils of the Jurassic Coast” Page 11 in Wool (see page 11). Please let me know if Other organisations’ events Page 12 you plan to come so that we can cater accordingly. Forthcoming Wessex Branch events Page 13 WESSEX BRANCH REPORT 2016 OUGS events listing Page 14 Many thanks to the Wessex Committee and members for making us such a friendly and organising this, even though he could not come, enthusiastic group and to our leaders for and thanks to Ian Williamson for showing us opening our eyes to the wonderful geology such fantastic geology, including Fingal’s Cave! around us. 2016 has been highly successful, I’d also like to thank Mark’s wife Pauline who not only as a branch but also because of our helps Mark with the residential trips. record numbers at the Symposium in Exeter. I Thanks go to our Treasurer, Rhiannon Rogers, am pleased to be able to leave the branch in who not only continues to manage our branch such good hands when I stand down at the accounts with excellence but who also had the AGM in 2017. huge task of doing the accounts for the Exeter In 2016 we had an excellent AGM and Lecture symposium. Also thanks to Chris Crivelli for Day with the Theme of “Mull, Mountains and independently checking the sums. Our accounts Mars”. Thanks to our lecturers Ian Williamson, still appear to be healthy and our field trips and Tom Argles and Suzanne Schwenzer plus all events are well attended. Thanks to Hilary who contributed to the fantastic banquet. Barton for a brilliant Footnotes newsletter and to Colin Morley for updating the website and We had five trips led by Alan Holiday during putting so much of interest on it as news items. the year - to Vallis Vale on the Mendips in Also thanks to Colin for accepting the Somerset, Beer in Devon, Lyme Regis in nomination as Wessex Branch organiser, I am Dorset, Abbotsbury RIGs site in Dorset and sure Colin will be a brilliant Branch organiser Bowleaze Cove, Weymouth in Dorset. Many and I wish him well. thanks to Alan for all his support to Wessex OUGS over all the time I have been a member Best Wishes and before! We also visited Down Farm on Sheila Alderman, Branch Organiser Wessex Cranborne Chase, a Ball Clay works on Purbeck, 4 Yeovil Road, Montacute, Somerset TA15 6XG Lambourn Down in Berkshire, Moons Hill and Tel. xxxxxxxxxxxxxxxxxx Whatley Quarries on the Mendips and Wytch E-mail: [email protected] Farm and Kimmeridge in Purbeck. Thanks to our leaders Martin Green, Andrew Deeming, Janet Griffiths Lesley Dunlop, Jill Odolphie, Giles Watts and I am sad to say that Janet Griffiths lost her Suzie Baverstock. Also a very big thank you to fight with cancer on 18th November. She died Jeremy Cranmer for organising such a variety of peacefully in Christchurch Hospice with Ted at day field trips and for planning next year’s her side. Our thoughts go out to Ted and programme. Our residential week was in Mull their family. Sheila Alderman with Ian Williamson; thanks to Mark Barrett for Wessex Footnotes December 2016 Page 1 WESSEX OUGS FIELD TRIP TO ABBOTSBURY, 25 SEPTEMBER 2016 Leader: Alan Holiday Report by Sheila Alderman Alan Holiday and a group of seven intrepid OUGS Wessex members plus one DIGS enthusiast achieved an amazing transformation of the Dorset Regionally Important Geological Site at Red Lane Quarry in Abbotsbury, Dorset. Between us we were armed with a chain saw, rakes, loppers, secateurs, forks, scrapers, gardening gloves - and a lot of determination. Over the past 20 years I have visited the site many times to help with gradual clearance. It is a very impressive location and in such a beautiful part of the world. The group take a break Photo by Alan Holiday Job done! Photo by Colin Morley Alan told us about the geology of the area, which is summarised in an illustrated leaflet produced by Dorset RIGS and available as a .pdf file via http://www.dorsetrigs.org.uk/southwestrigs/abbotsbury/ The Abbotsbury Ironstone forms the earliest strata of the Kimmeridgian Stage in the Upper Jurassic Period. The outcrop is very limited in extent and only outcrops in the locality of the village of Abbotsbury. The deposit is thought to have formed in a marine near-shore environment saturated with iron salts, possibly a barrier bar where gentle wave action rolled the ooids around, building up concentric layers of iron minerals. Attempts to mine the deposits commercially in the 19th century failed as the ore contained too much silica and other undesirable impurities. Although the ironstone was found to be unsuitable for smelting, it was a useful building stone in local houses. Abbotsbury lies in the hollow of a syncline (U shaped fold). Corallian Group rocks (Sandsfoot Grit, Osmington Oolite) form the hills to the south of the village. The Abbotsbury Ironstone underlies the village itself and is seen at the surface on the north side of Chapel Hill to the south of the village, and the fields immediately to the north of the village. The outcrop ceases abruptly where it meets the Abbotsbury Fault. After a rest and lunch, Alan took us for a walk up Blind Lane to see the SSSI slightly higher up in the Jurassic Abbotsbury Ironstone sequence. Then to a tremendous view overlooking Abbotsbury. Making our way through the village, we identified various building stones, including the famous Ham Hill stone that is used in the “poshest” buildings from the Somerset quarry one mile from my home. We also identified a lot of Purbeck, Portland and Corallian building stones, plus a tiny piece of Forest Marble and various pieces of chert in the walls. Others less exhausted than me had a splendid walk up St Catherine’s Hill. Thanks to Alan Holiday for leading, Jeremy Cranmer View to The Fleet and Chesil Beach from Blind for organising the visit and participants for helping! Lane Photo by Colin Morley Sheila Alderman Wessex Footnotes December 2016 Page 2 WESSEX OUGS FIELD TRIP TO TWO MENDIPS QUARRIES, 18 AUGUST 2016 Torr Quarry and Moons Hill Quarry Leader: Dr Gill Odolphie (Manager, Somerset Earth Science Centre) Report by Andy Mitchell (Torr Quarry) and Helen Phythian (Moons Hill Quarry) This trip was so popular that Dr Gill Odolphie kindly offered to run it twice, on consecutive days. This report is from the second day, Thursday 18 August 2016. Many thanks to our leader Gill and also to Sean Johnson, Area Geologist with Aggregate Industries UK, who helped us at Torr Quarry. Introduction We assembled at the Somerset Earth Science Centre at 10.30. Two quarries were visited: Torr Quarry (Carboniferous Black Rock Limestone) in the morning and Moons Hill Quarry (Silurian andesite and other volcanics) in the afternoon. The field trip was completed by 16.00. It was a cloudy but dry day - and no mud to worry about! Torr Quarry (also known as Torr Works Quarry and Merehead Quarry) The rock here is Carboniferous Black Rock Limestone with varying levels of manganese and silica; it is therefore quarried for its rock strength, to make various concretes and road base material. It has been used on projects such as Crossrail and the Channel Tunnel. Some 5 million tonnes will be quarried this year. The quarry, which had its origin in Roman times, is situated on the southern limb of the Mendips Pericline – in what was a shallow estuarine depositional environment in the Carboniferous. In one small corner in the upper section of the quarry an unconformity could be seen, with Inferior Oolite (horizontal) overlying the Carboniferous rocks (~40inc). The quarry has a variable clay content within the limestone and some red Trias precipitation is evident in the upper levels. The quarry also has its own local mineralisation in the form of yeomanite (Pb2O(OH)Cl) and mendipite (Pb3Cl2O2). The quarry, which is operated by Aggregate Industries UK, is currently seven benches deep Field sketch of Torr Quarry Andy Mitchell and bounded by faulting. The 15m benches stand at a 73 wall angle. Plans are in hand to go deeper by another seven benches, though this presents issues for water drainage management. The reserves are currently estimated at 150 million tonnes, which would take production through to 2040. There was historically a 20% wastage but, due to recent washing techniques, old stored scalpings are now sold as road base materials. Moons Hill Quarry After a break for lunch at the Earth Science Centre, Dr Gill Odolphie gave us a talk on the history of the Centre. It was set up in 1997 by Hanson at Whatley Quarry to address the issue of public education (to explain why quarries are needed and why they have to be where they are) and as a hands-on resource for students.