SABRINA TIMES December 2016 OPEN UNIVERSITY GEOLOGICAL SOCIETY SEVERNSIDE BRANCH Branch Organisers Report Hello everyone, We had an excellent turn-out for our Day of Lectures on 3rd December at the YMCA Conference Centre in Newport. Everyone who came along enjoyed three excellent speakers on the diverse subjects of modern geophysical survey methods; the exploration of Precambrian oil in Oman; and Lichenometry in Norway. A new subject to many of us, we discovered that Lichenometry is the use of lichen to determine the age of exposed rock, and Hazel Trenbirth described the work done in dating the retreat of Norwegian glaciers using this technique. Peter Brabham described the variety of non-invasive techniques now widely used to build up a picture of what lies beneath the surface of a site requiring a detailed shallow survey. During his fascinating talk on oil exploration in Oman, Neil Frewin mentioned a museum that had recently opened at Kimmeridge in Dorset. It is called The Etches Collection, and it houses a large collection of Jurassic marine fossils discovered in the Kimmeridge Clay by Steve Etches over a 30-year period . The museum also features CGI screens on the ceiling that give visitors the impression of being underwater 150 million years ago in the company of extinct creatures. The Etches Collection is now on my list of places I must visit in 2017! You can explore the website at http://theetchescollection.org/home. If you attended the Day of Lectures, I would welcome any comments (good or bad) about this new venue. In the past we have been fortunate in being able to use a conference room at Cardiff Museum free of charge, which obviously reduces the cost of the event to members, but the Museum wanted to charge us quite a lot this year. Hence we had to shop around for a lower-cost venue, and eventually chose the YMCA Conference Centre in Newport. Perversely, at a very late stage Cardiff Museum decided to waive the hire charge for our AGM in February 2017! but we fully expect the Museum to charge us for future events held there, so any feedback on the Newport venue would be very helpful. Our last field trip of 2016 took place on 16th October in the Brecon Beacons, led by Dr John Davies. We were lucky with the weather and, with perfect timing, the sunny day turned to rain half an hour after the trip finished and we were all heading home. A summary of this very interesting and enjoyable trip can be found in the newsletter. I know that many of you will have enjoyed visiting various places both home and abroad during 2016, and will have undoubtedly taken some interesting geology-related photos. So please forget about social media and share your photos with other OUGS members by sending them, together with a few descriptive words, to our newsletter editor John de Caux at [email protected]. As always, any contribution to our newsletter is warmly welcomed! Finally, I hope to see you at our AGM on Saturday 11th February 2017 at Cardiff Museum, when we will be treated to a “behind the scenes” visit to examine the museum’s mineral collection. With my very best wishes for 2017, Norman Nimmo-Smith P.S. Please don’t forget about the new annual subscription rates – see inside this newsletter for details. , Inside this issue Brecon Beacons Field Trip 2 Day of Lectures 7 Philip Clark “Here’s one I made (25 years) Events 12 earlier” AGM Agenda 12 (see page 4) Contacts and Editorial 15 D30 Brecon Beacons October 16th 2016 Leader: Dr. John Davies Introduction A group of 17 OUGS members met in the Craig y Fro car park on the north flank of the Brecon Beacons, about 8 miles south-west of Brecon along the A470. In the company of our leader Dr John Davies, president of the South Wales Geological Association, the plan for the day was to explore the Old Red Sandstone (ORS) landscapes at a number of locations in the area. John has now retired from what was the Countryside Council for Wales. He is chairman of the Welsh Stone Forum and spends much of his time exploring Wales, mapping and co-relating the rocks that he finds. As shown in Fig. 1, we visited 5 different locations during the day. In John’s words, the day was to be a “coach tour” as we drove from site to site. By doing this he would be able to describe how the landscapes in this part of the Brecon Beacons were a result of its geological history and the different layers of the ORS sediments. Geological Context The ORS sediments were deposited during early stages of the Caledonian Orogeny, which in this area caused faulting rather than folding. Repeated tectonic movements caused these faults to remain active and large blocks to develop in the landscape (similar to Fig .1 Map showing locations visited in the Brecon Beacons those in Northern England, such as the Alston Block (map reproduced with permission of the Ordnance Survey) that some of us will have become familiar with on Summer Schools). These blocks were separated from each other by positive ridges caused by the major fault zones, in turn causing the sediments to vary in depth from one to another even when the source of the sediments was the same. There is much evidence for the sediments being deposited in various locations in a system of channels developed in a flat landscape. John’s belief is that, at the time these sediments were being laid down, the region was very similar in nature and size to what can be seen today in the Indus Valley (Fig. 2), with rivers flowing south-west along the south-eastern side of the rising mountain- front. Large amounts of sediment were transported by these meandering and braided river channels spread across the plains. Fluvial fining-upward cycles from sandstones to mudstones can be identified. Away from the main channels, flood-plain deposits include palaeosols with calcretes, and the sequence is followed by two marine incursions of the Upper ORS. Channels frequently commence with coarse bases containing debris eroded from previously deposited palaeosols, followed by massive sandstones and flaggy tops of finer material, passing up into mudstones and calcretes at the top of the cycles. Fig .2 The present-day Indus Valley (image courtesy of BBC) Naming of ORS rock layers (“stratigraphic nomenclature”) Many of our text books, and certainly the existing geology maps, all use nomenclature which is out-of-date and John provided us with details of the current names of the official formations, together with an explanation on how the old formations relate to them. The handouts that he provided demonstrate how it is possible to correlate formations right across the Anglo-Welsh basin from south Pembrokeshire in the west to Ross-on-Wye and Blakeney in the east, the sub- groups allowing the details of what were locally named members to be fitted into the big regional picture. 2 Brecon Beacons October 16th 2016 contd. John’s work has enabled him not only to correlate exposures across the whole of the Anglo-Welsh basin but also to identify additional formations not yet officially named by the ICS (see Note 1, page 6) due to their non-occurrence in Pembrokeshire. These are the Bryn Menyn Mudstone Member; Walford Mudstone Member; and Blaen Haffes Formation, all of which are within the upper half of the Cosheston Subgroup of the Daugleddau Group, previously known as the Brownstones. Fig. 3 shows John’s revised litho-stratigraphy for the ORS in the Anglo-Welsh basin, along with his new names for three of the units. See also Note 1 (page 6) Fig 3: A New Litho-Stratigraphy for the Old Red Sandstone of South Wales Location 1 Our journey started at the Craig-y-Fro car park on the A470, where John provided us with his handout and described the plan for the day. From the car park, John pointed out some Quaternary glacial features in the area. A small glacier had formed beneath the crags above the A470 road 11,000 years ago, and the road had been cut through mounds of moraine debris left behind when the ice melted. Across the road from the car park was a small disused quarry exposing rock of the Senni Formation. A waterfall running down the faces of the quarry kept Fig 4: Craig y Fro Quarry, with interbed- them clean. (Fig. 4). This quarry is a Site of Special Scientific Interest and is the ded sandstone and argillaceous rocks type location for two species of early plants (410Ma) found in the beds of the Senni Formation, namely Gosslingia breconensis Heard and Krithodeophyton Edwards. Apparently David Attenborough visited the quarry whilst filming his “Life on Earth” series, and used dynamite to expose fresh bedding planes in order to find some more plant fossils! On the north side of the quarry John pointed out a coarse pebble bed of the base of a cycle with finer-grained material lying above it, both of which exhibited cross-stratification (Fig. 5). The pebble bed contained calcrete and mud clasts; the latter had been washed out from the exposed surface to leave numerous holes. Fig 5: Craig y Fro quarry; pebble bed 3 Brecon Beacons October 16th 2016 contd. Location 2 We drove a short way along the A470, parking our cars in another layby, where John described the landscape scenery looking north down the Tarrell valley (Fig. 6).