NEWSLETTER, WINTER 2015 (40th ANNIVERSARY ISSUE) ----- 40 YEARS OF THE SOCIETY By Lesley Exton The inaugural meeting of the Geological Section of the Hertfordshire Natural History Society took place at St Albans College of Further Education on the 9th January 1975, chaired by Chris Wood. The proposed programme of lectures and field meetings was outlined and the election of officers took place. Chairman: Chris Wood; Secretary: Dr Roger Mason; Treasurer: John C. Whitcher and Field Secretary: Brian Palmer. The meeting heard with regret of the recent death of Dr Percy Evans, the leading authority on the geology of Hertfordshire who had been the proposed candidate for President of the society. It was suggested that the person subsequently nominated as President should deliver a lecture at the end of the year that would be known as the ‘Percy Evans Memorial Lecture’. Prof. John F. Kirkaldy subsequently became the 1st President of the Society (1975-6) and he delivered the first lecture of this series on the 8th January 1976. Subsequent Presidents served two years in office (occasionally three) with their lecture given at the end of their term. This next year will see the 39th lecture in this series by our current President, Dr John Catt, one of only two individuals to have served two terms (1977-80: 2013-5). The other being our current Chairman, Dr Haydon Bailey (1985-7: 2008-11). Prof. E.H. Brown delivered the very first lecture ‘The evolution of the landscape of S.E. England.’ Since then there have been at least 365 lectures, as well as a joint meeting with St Albans & Hertfordshire Archaeological & Architectural Society to celebrate the London Geological Society’s Bicentennial (2007), a Symposium on the Chalk of Hertfordshire (2009) and the Puddingstone Pow-wow (2010). At least 28 of the lectures have had associated field trips. Only 17 lectures have been cancelled, in the majority of cases (except when the lecture was cancelled due to adverse winter weather conditions) alternative speakers from within the membership have been successfully substituted. The first field meeting held in February 1975 was a tour round the Rugby Portland Cement Co. Quarry at Kensworth, followed by fossil collecting. We have returned to this quarry several times over the years and will be doing so again next year, twice! In total there have been 155 recorded field trips, with 40 in Hertfordshire, 21 in Bedfordshire, 21 in London, 17 in Kent, 12 in Buckinghamshire, 10 in Essex, and 10 in Wales. However, there aren’t many counties in England we haven’t visited at least once. In addition there have been 17 trips abroad, including Canada and Tunisia, with the remaining 15 trips to various countries in Europe. The Society changed its name to the Hertfordshire Geology Society (A section of Hertfordshire Natural History Society & Field Club) in 1984 and in 2003 it became an independent organisation. In 2012 the Hertfordshire RIGS Group became associated with the Society. The Society became a local group of the Geological Association in 2013 after being an affiliated member since 1991. 1 FAULD MINE, BRITISH GYPSUM (SAINT-GOBAIN) NEAR TUTBURY, BURTON UPON TRENT, STAFFORDSHIRE, SATURDAY 22nd MARCH 2014 By Nikki Edwards Photographs: Clive Maton Upon arrival, we were greeted with coffee and a full safety briefing from the mine manager Jim Daykin. Noel Worley (formerly Minerals and Estate manager at British Gypsum) then gave an illustrated talk on evaporate geology, depositional environments and the paleogeography of the Permian/Triassic. The deposits form part of the Mercia Mudstone Group with the Tutbury seams at the top of the Blue Anchor and the Westbury formation above the Sherwood sandstones. The whole formation is capped by glacial drift of Devensian and Anglian origin. The Mercia Mudstone was formed about 237 million years ago in the upper Triassic when the UK was just north of the equator, on the edge of the large sedimentary Needwood basin in the Tethys Ocean. The gypsum formed sub-aerially on mud flats or sabkhas along the water table, just below the surface where it was saturated with sea water. This was a period of intense evaporation, with hypersaline water being drawn through the muds below. At Fauld they are mining the Tutbury gypsum seam which is up to 3m thick. After the presentations we were kitted out with the necessary PPE and Self Rescuer (for carbon monoxide in case of fire) (Fig 1), and signed an indemnity form for radiation exposure. Uranium materials are concentrated around small black nodules of organic origin, B-particles caused Fe 3+ to Fe 2+ reduction so that they are surrounded by a pale aureole. Fig 1. The group before entering the mine. We entered the mine via an adit into an area of old workings where the tunnels twist and turn with many blocked off passages. The original miners (it started in the mid-nineteenth century with a 2 quarry then went into the hillside) just followed the seams, whereas the modern workings (now covering 13 sq km) are on a grid system with 75% of the gypsum extracted, the remainder left as pillars to support the operation. One of the most interesting features are the diapirs (Fig 2). These were caused first by the gypsum seams being buried to 2 to 3 km such that the temperature and pressure drove out the water and converted the deposits to anhydrite which take up 40% less volume. Subsequently as the cover was removed the stress was reduced so the addition of meteoric water converted the anhydrite back to gypsum and the lateral stress forced the gypsum into diapirs above the Tutbury seam up to 9m thick. The folded structures can clearly be seen in the roof of the mine workings. Fig 2. Part of a diapir in roof of tunnel. Fig 3. Alabaster in the tunnel. We also saw areas where the unique translucent quality of the gypsum showed that it reflects little light but glows when illuminated, due to having low light dispersion (Fig 3). This lead to its extraction as alabaster which was used extensively by the Victorians in churches for sculptured memorials. We were able to observe some fine examples of this craft in detail when we visited St Werburgh's church in nearby Hanbury at the end of the day (Fig 4). Originally the majority of the gypsum was used for plaster being either quarried or mined under limited cover e.g. where we were it was about 50m. The working part of the mine has over 100m cover, the increased pressure means it contains a much greater proportion of anhydrite and therefore sulphur. This is now all used in the production of Portland Cement (about 4%) where it acts to delay setting times. Fauld is centrally sited with many cement works within a 50 mile radius. On leaving the mine Noel lead us up the hill above the mine workings to an incredible view of The Fauld Crater, 250m across and about 30m deep (Fig 5). Although little known, it was the result of the largest non-nuclear explosion of the Second World War, when in November 1944 about 3500 tonnes of explosives detonated underground. The Peter Ford Mine to the east of the present mine was used from 1937 to store bombs. It developed into a site for both storage and maintenance of bombs, incendiaries and detonators for both RAF and US forces, separated from the working mine by blast doors. The accident occurred in the maintenance area where detonators were removed to replace the 3 contents of the bombs. The explosive force was channelled upwards forcing about 1.5m cu m of debris over 1000m into the air, wiping out the farm at the surface, causing damage to buildings in Hanbury and destroying a dam near the top of the hill used for water power which caused a major flood. In total 80 people were killed, about 30 of them Italian ex-POWs working in the plaster factory near the mine as Italy had changed sides by this date. The tragedy was compounded by the event being covered by the Official Secrets Act for 40 years, so families were not compensated for their loss and the story is not widely known (except by the locals). Geology was key to the event as the 40m of cover had been assumed to be a secure place to store such material. However as it consisted of glacial drift rather than lithified rock, the force did not go laterally to be contained by the blast doors, rather they ensured it to took the easiest route up through the glacial drift to the surface. Crater Rim Fig 4. Alabaster memorial in Hanbury church Fig 5. Fauld Crater This was a memorable trip and our thanks go to Noel Worley and Jim Daykin for their time and British Gypsum for the permission to visit the mine. BRYANTS LANE QUARRY, LEIGHTON BUZZARD, BEDFORDSHIRE, SATURDAY 9th AUGUST 2014 By/Photographs Lesley Exton There was a restriction on numbers for this trip, therefore it was a disappointment when four individuals dropped out a week before and then there were two no-shows on the day itself. However, those that did make it on a sunny morning in August met our leader Clive Rogers at Heath Inn car park and then made the short walk to the quarry entrance. There we waited while Clive ascertained where he was allowed to take us from the quarry worker who’d come to open up. On our walk in we stopped at a site that had been recommended by the worker as an area where ammonites had been found previously.