September 2013
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Mercia Rocks OUGS West Midlands Branch Newsletter Issue No 4 (2013) September 2013 September’s field Trip to Gullet Quarries, Malvern Contents Branch Officers Branch Organiser’s report p 2 Next Field Trip Advert p 3 Branch Organiser – Sandra Morgan Field Trip Report:- Branch Secretary - Vacant Whitmans Hill and Gullet BranchBranch Organiser'sTreasurer- Susan Bit Jackson Quarries Malvern p 4 Newsletter Editor – Susan Jackson Wenlock Tabulate Corals p 7 Branch Committee Field Trip Programme 2013/14 p10 Patrick Joyce, Ian Kelly Other branches items p11 Other items p 12 If you would like to join the Random chippings from the committee please do get in touch Internet p 13 [email protected] Other Society Events p 15 1 [email protected] Branch Organiser’s Report Dear all, I hope that you had a good summer, and were able to enjoy the sunshine! In August the OUGS Symposium took place in Dublin, and participants were treated to some interesting lectures and excellent field trips. Next year’s Symposium will take place on 15-17 August in Canterbury with a theme of marine geology. Our September field trip to Whitman’s Hill Geological Reserve and Gullet Quarry was interesting and varied. Highlights included bentonite layers, pisolitic limestone, and fossils at Whitman’s Hill, and folded and shattered pre-Cambrian rocks at Gullet Quarry. Our thanks go to Susan Jackson for organising this field trip. See the full report in this newsletter. Also in September, I went with the OUGS Information Officer, Pauline Kirtley, to represent OUGS at the Science Revision Weekend at Yarnfield. Here we met many OU students, and succeeded in recruiting some of them to OUGS! Our next field trip takes place on Sunday 6 October. This will be at Ercall, organised and led by Ian Kelly. This location is geologically very interesting, and certainly worth a visit. Our last event of this year is a geological walk around the campus of Nottingham University followed by a visit to the British Geological Survey at Keyworth. This will take place on Wednesday 20 November. We are now putting together our programme for 2014: look out for the Day of Lectures on 15 February, and a Warwickshire field trip in March. Our branch AGM is scheduled for Saturday 18 January 2014 at Birmingham University. It is important that enough members attend, so do come if you can. There will be more information in our next newsletter. If you would like to get involved, as a committee member or in any other way, do contact me – volunteers are always welcome! Regards Sandra 2 [email protected] Next field trip Ercall Quarry field trip th 6 October 2013 The Ercall quarries are a group of quarries cut into the lower slopes of the Wrekin, primarily for roadstone, for which Ercall Quartzite was particularly prized. The site is perfect for beginners and the more experienced, with extrusive and intrusive continental and oceanic volcanics, a very visible strike/slip fault, igneous/sedimentary contact, a half billion year old beach, a great opportunity to do field sketches and lots to think about and discuss! The site is managed by the Shropshire Wildlife Trust, is well looked after and there is nothing too strenuous. Suitable footwear is highly recommended and hard hats are essential near the quarry face. The site is accessed in much the same way as The Wrekin nearby; exit the M54 motorway at J7 (last exit) or the last junction of the A5 from Shrewsbury before it becomes the M54. From there The Wrekin is signposted; follow this road until you reach The Wrekin, then follow the sign for the Buckatree Hotel. There is a small car park across the road from the hotel and the entrance is clearly visible. If this car park is full, head back towards the Wrekin and use the Forest Glen car park. We will be starting at about 10am and should to be finished by about 2.30pm. If the weather is fine we will be stopping for a break, so you may want to bring a packed lunch. If it’s very wet people may want to bash through it and go home. Any questions or queries or to book a place please email me [email protected] Contributions to the Newsletter are very welcome. The subject matter can be anything geological that you think other members would like to read. Items for inclusion in the next Newsletter, by email to: [email protected] by 1st December 2013 3 [email protected] Field Trip report Whitmans Hill and Gullet Quarries, Malvern Saturday 14th September 2013 Whitmans Hill Quarry We started our day at Storridge Village Hall car park to the north west of the Malvern Hills where we met our leader for the morning Margaret Rodway before making the short walk up to Whitmans Hill Quarry. The quarry forms part of a Geodiversity Discovery Venture funded by Natural England through DEFRA's Aggregates Levy Sustainability Fund Grant Scheme. In 1999 it was designated a RIGS for its educational value, interesting rock formations and the abundance of fossils. Later in 2005, a ten year lease was obtained by the Herefordshire and Worcestershire Earth Heritage Trust, and following the completion of extensive safety and face clearance works, the site is used as an educational and research resource. It also benefits from being within the Abberley and Malvern Hills European Geopark. Until 1988, the quarry was the site of limestone extraction, for use as local aggregate. The limestones and mudstones are Silurian (Wenlock) in age - about 425 million years old - and were formed at a time when this area was about 15 degrees south of the equator and the land was covered in warm, shallow seas, like the Seychelles or the Bahamas today. There are two main rock formations present; 12m of the Coalbrookdale Formation which forms the basal units and 25m of the Much Wenlock Formation which sits above. The boundary between the two units represents a rapid decrease in sea level in the area – shown by the red line on the sites graphic log. The Coalbrookdale Formation Rivers flowing from the east carried mud and silt which built up in the warm shallow sea eventually forming the mudstones of the Coalbrookdale Formation. Characterised by an olive-grey to dark blue- grey silty mudstones with occasional calcareous limestone nodules and impersistent nodular calcareous beds. Fossils are widespread and contain marine fauna such as brachiopods, trilobites, corals and bivalves. One of the feature in the quarry we looked at was an example of spheroidal ('onion skin') weathering in the siltstones of the Coalbrookdale Formation. This is the result of enhanced weathering and chemical reactions at joint intersections. At the bottom of the quarry track we were shown some ball-like structures from 10cm to over 2m in size T These balls are composed of calcareous cement and in many places exceed the bedding planes. Their composition makes them more resistant to weathering then 4 [email protected] the surrounding siltstones so they stand out. It is believed that these may have grown during the early phase of the rock’s formation as a soft sediment deformation structure The Much Wenlock Formation With the falling sea level a long period of mainly limestone was deposited and small reefs known as bioherms were formed on what were probably large carbonate platforms some distance from a landmass. These lens-shaped structures (about four metres across and diamond shaped in the rock face) are roughly in the centre of the quarry's east wall. They are similar to a modern-day patch reef, but are mainly made up of algae and stromatoporoids, unlike the corals which primarily comprise today's patch reefs. Towards the top of the formation the limestones are characterised by pale grey nodular to thinly bedded limestones. These nodular beds are know locally as the ‘Storridge Porridge’ and are found to have a nucleus of shelly material and were probably formed in slightly deeper water . Importantly at this site preserved within the limestone formation are a number of bentonite layers. During the Silurian sporadic volcanic eruptions where producing a great deal of volcanic ash. This ash sank to the seabed and it was altered chemically and preserved in the sediments. The quarry shows a total of nine bentonite layers varying in thickness. Current research has established the age of the bentonites using Zircon crystals which contain the radioactive element uranium which decays eventually to form lead. By working out the ratio of uranium to radiogenic lead in the zircon crystals they are able to confirm the age of the rocks in the quarry to around 425 million years. This is very similar to research currently being carried out at the Wrens Nest in Dudley where the layers are thinner, suggesting that Whitmans was near the volcanic source; whilst the location is unsure it is thought to be somewhere near Cheltenham or South Wales Crystals of apatite found in the bentonites can also tell us about the types of magma that came out of the volcanoes. Some of the older bentonites come from an acid magma whilst the younger ones at the top of Whitmans quarry are from less evolved magma with a more mafic/intermediate composition. This does suggest that different volcanoes many have been responsible for forming the different ash layers. After looking and discussing the various features found in the quarry we had the opportunity of indulging in a little fossil hunting. This was much enhanced by Alan Bates’s extensive knowledge of fossil types and a number of finds have made their way into our member’s collections.