SABRINA TIMES OPEN UNIVERSITY GEOLOGICAL SOCIETY SEVERNSIDE BRANCH DECEMBER 2015 Branch Organisers Report Hello Severnside We enjoyed an excellent Day of Lectures in Cardiff of Saturday 28th November, with interesting talks about Dinosaurs in South Wales, including the latest find of the first terrestrial dinosaur to be discovered in South Wales; the Geology of Penarth; and the Evolution of very early life forms, particularly focused on Ediacaran fossils with examples from Newfoundland where the Branch visited in 2008. Lots of books were borrowed from the library and at the end of the afternoon, after a cup of tea, many of us enjoyed browsing two exhibitions in the galleries: William Smiths Maps and one about the new Welsh dinosaur. The paper writing up this find is due to be published very soon at which point its name will be made public. At present it is still a secret! Annual General Meeting I hope you all have the date of Saturday, 13th February 2016, in your diaries for the next Branch AGM? The agenda is elsewhere (page 14) in the Newsletter. It is important this year to have a good attendance as….. …. a New Branch Organiser is needed The Branch still needs a replacement Branch Organiser as I am standing down in February. I have outlined the duties in earlier Newsletters but am more than happy to discuss the post in person if you want contact me. I have really enjoyed my time representing the Branch and I am sure that my successor will get similar fun and support from everyone. If you would like to know more, please have a chat with me. The National AGM next year will be taking place in April in Scarborough. The programme is very interesting and it’s an opportunity to visit the north east and see some very different geology as well as meet old friends and enjoy two quality lectures. Please think about coming along. The Symposium in 2016 is being held in Exeter. Severnside is one of the three Branches responsible for organising this although Wessex is taking the lead this time. A good programme of speakers has already been advertised and we are open for bookings! Lots of information and the booking form can be found on the website - look under ‘Society Events’. There are additional events being organised before and after the main weekend if you would like to take a longer break in the area. I look forward to seeing you in the New Years and wish you all the best for Christmas Season. Best wishes Janet In this issue: Wye Valley 2 Cardiff Building Stones 4 MERRY CHRISTMAS AND A Events 9 HAPPY NEW YEAR Branch Library selection 12 TO ALL OUR READERS Contacts & Branch 13 Committee D25 Wye Valley 13th September 2015 Leader: Elliott Carter It was a lovely September morning as we stood by the side of the B4260 Wilton Road leading up into Ross. There was a good group of us come to be introduced to the geological history of the lower Wye Valley and to be shown how it has shaped the landscape. We were all strung out along the pavement looking at a road cutting which may have once been a quarry. It is now a Site of Special Scientific Interest (SSSI) and has been kept cleared of most vegetation and has a display board. Elliot described the depositional environment for this sandstone from the Brownstone Formation of the upper Lower Devonian. During this period subduction of the Iapetus Ocean created large mountain ranges behind the subduction zone. These shed erosion material into the area, carried south by large rivers. The cross bedding that we could see (Fig. 1) shows the variety of material brought by these changing braided river systems. The variety of Fig. 1 Wilton Road SSSI showing cross bedding pebbles embedded within the sandstone give an indication of the from a braided river system source of material and these have been mapped by JR Allen. A short drive brought us to a car park above the Biblins. From here we took a footpath through the woods and into King Arthur’s Quarry (Fig. 2). We were now up into the Carboniferous Gully Oolite. The oolite limestone was deposited in a shallow sea with little contamination from runoff. The seawater would have been saturated with calcium carbonate and, with small waves agitating the water, oolites were produced. This quarry has been used as a source of aggregate as the limestone has been altered by burial, warming and recrystallization producing a hard grey rock. It is now used by rock climbers. The alteration has destroyed many features in the limestone but some cross bedding was still discernible (Fig. 3). Fig. 2 Walking into King Arthur’s Quarry Fig. 3 Altered Gully Oolite, King Arthur’s Quarry, in which some cross bedding can still be seen. Further along the quarry wall a change in material had caused the quarrymen to leave a corner of rock. Elliot pointed out the encroachment of a band of sandstone in the upper level (Fig. 4) which would have contaminated the aggregate. This sandstone indicated a change in environment with sea level falling to bring the coastline closer and river borne sands into the area. Fig. 4 King Arthur’s Quarry showing change in depositional environment giving a sandstone feature 2 Wye Valley 13th September 2015 (contd.) Taking a footpath downhill we passed several short tunnels into the limestone which Elliot explained may have been carved by the River Wye when it created the valley it now occupies. In the process of down-cutting the river left benches and excavated the valley walls along lines of weakness. Natural England hold the PhD paper from the 1930’s which plotted the course of the Wye at different levels in the valley and it is available to be studied in their offices. The Cave known as Arthur’s Cave (he did get everywhere in the West of England and Wales) was probably constructed in the same way as there is evidence of a large fault which was a line of weakness (Fig. 5). This cave was excavated in the 19th Century by Rev. Symond and found to contain Prehistoric flint tools and animal remains! The path led down to the Seven Sisters Viewpoint where we had lunch overlooking the River Wye (Fig. 6). Here the river has cut a deep, steepsided valley through the resistant Carboniferous limestone and the Upper Devonian sandstone and conglomerates. Later we would look out from Symonds Yat Viewpoint to a different landscape (Fig. 7) where the river has taken a wide meander through the softer Sandstone of the Lower Fig. 5 King Arthur’s Cave Devonian. The overall pattern of developed as a result of water the Wye is of a series of looping action along a fault meanders that cross back and forth from the harder limestone to the softer sandstone ignoring the difference in resistance. This is a superimposed river pattern. The original meanders formed on a level, wide floodplain then as sea levels fell during the Ice Age the river cut down through the rock and the differences in resistance showed only in the width of the valleys. We continued on to the riverside near Biblins youth campsite where we Fig. 6 Wye Valley from Seven Sister’s viewpoint studied the cliff (Fig.8a). Once we found our way through the vegetation a closer inspection revealed the reason for the shiny surface to the rock. Rain water, saturated in calcium carbonate (CaCO3) from its passage through the limestone, had seeped out of the cliffs and the CaCO3 was precipitated out of solution and deposited on the surface of the rock as Tufa or flowstone giving some strange forms (Fig. 8b). Fig. 7 Wye Valley from Symonds Yat viewpoint Fig. 8a The Biblins – recent deposition of flowstone observed from path along Wye Fig. 8b Closer inspection of flowstone Elliot had given us a good introduction to the geology behind the impressive landscape of the Wye valley and had shown us how it had been Report by changed. Averil Leaver BSc (Hons) Geoscience 3 Cardiff Building Stones 25th October 2015 Leader: Linda Fowler Introduction This field trip to Cardiff was led by Linda Fowler, and explored the stones used in a number of buildings (old and new) in the Cardiff Bay waterfront area, which is situated in South Cardiff. We also walked along the Cardiff Bay Barrage to examine some in situ rocks in the tall cliff at Penarth Head. This report is based on Linda’s commentary during the day and her written notes. Most of the pre-lunch part of our outing is described in Leaflet 13 “Building Stones of Cardiff” produced by the Geologists’ Association - South Wales Group. A map of the Cardiff Bay area is shown in Fig. 1, and pinpoints the key parts of our route during the day. A more detailed view of the Waterfront area is shown in Fig. 2. This shows the route we took during the morning as we zig-zagged around various streets examining a variety of stone. Fig. 1 Map of Cardiff Bay We all met at the Havannah Street car park adjacent to the Wetlands area of Cardiff Bay. Once assembled, Linda explained the proposed itinerary for the day and gave a potted history of Cardiff over the last 200 years or so. Cardiff came to prominence with the building of docks and other infrastructure for export of the vast amounts of coal mined from the valleys of South Wales. The docks were built between 1830 and 1907, with the first one opening in 1839.