It was good to welcome Tom Argles, Senior Lecturer at the OU in CEPSAR (Centre for Earth,, Planetary, Space and Astronomical Research), who gave a lively and informative talk.
We started with a global elevation map to locate high mountain ranges and discuss why they are where they are. We then went specifically to a satellite image of the Himalaya – a range 2,500 km long but narrow, with an average elevation of 5000 m and crustal depth of up to 70+ km. Using the subduction depth of rocks as a clue to dating gives a date of around 50 My for the collision between India and the Eurasian land mass. Three geological units can be identified: a Tethyan sedimentary series, the granitic High Himalayan crystalline series with a metamorphic core and the much older Lesser Himalayan series.
To gain a good cross-section a field trip was organised from Bhutan through Sikkim to Nepal, which we followed, starting in the Siwaliks on the edge of the Gangetic plain, molasse conglomerate, with a view of the Brahmaputra. Thence into the Lesser Himalaya, consisting of ancient rocks (2 Ga) below the Main Central Thrust, containing Proterozoic quartzites, gneissic banding and tight foliation, and migmatites, with tea plantations on the steep slopes. The steepness makes for problems of travel in Sikkim, with flash floods and mudslides. From there, on into the heart of the mountains, the Greater Himalaya, with a view of Kanchenjunga.
Recent work in Sikkim suggests the rate of motion on the main central thrust is about 18mm/yr based on a north-south transect and monazite ages. The Lesser Himalayan series yields very varied ages, from 2.5 Ga to about 825 Ma in the west. Clues from Proterozoic palaeography suggest a link with the break-up of the supercontinent of Rodinia.
We finished with a ‘taste of fieldwork in Bhutan’, a record of his expedition with Clare Warren, also of the OU, trying to understand the mechanism of the building of the high peaks, while compiling a list of things not to do when trekking in remote mountains!
Chris is a Director of Wardell Armstong International, a firm specialising in mining geology and resource evaluation. The focus of the talk was gold mining in Butana, a desert area 200 km east of Khartoum. The problem at issue was how the Sudanese government could fill the hole in the country’s finances following the independence of South Sudan, where the oil and gas reserves are located and which prior to 2011 accounted for >90% of its revenue.
The alternative is gold, of which Sudan is the third largest producer in Africa: in 2012 50 metric tons with a value of US$2.5 billion were produced, but the production is inefficient and hampered by continued hostilities in the Darfur region. Of 125 mining companies currently active, only one, Hasai Mine, is a modern gold mine. In Butana the rest comes from artisanal mining, which is government approved, with 200,000 miners, maybe many more, working in small family units with children as young as 10, and living in camps in the desert. The camps are equipped with shops, cinema, mobile phones, satellite TV etc., but women are absent, presumably left at home on the Nile while the men earn a living.
Geologically the area is part of the Arabian-Nubian Shield with granites and meta-volcanics, and the gold is associated with quartz veins in the granites. Most veins are 10-75 cm thick, but they can reach 150 cm. It is associated with pyrites, chalcopyrite and arsenopyrite and limonite. The mining is elementary. The quartz is dug out by hand from unsupported pits, crushed with a pick or hammer, and then ground. Panning is done in a clay-lined pool, and the gold separated out by the addition of mercury to form an amalgam. This is then heated to drive off the mercury, which can be recovered by pressing through a muslin cloth.
There are no health and safety regulations; silicon dust is everywhere, and mercury is of course dangerous to handle. The resulting gold is sold to a government agent, who sells the mercury to the miners. There are no production records, and massive opportunities for fraud.
Meanwhile the tailings left behind have as much as 10 ppm gold and 25 ppm mercury, and the purpose of Chris’s visit was to explore the possibility of a mobile plant which could recover this gold with the use of sodium cyanide technology, less dangerous to the health of the miners if handled properly and if the Government can be persuaded of its safety.
Twenty two members of the OUGS visited Westminster Abbey to see the Sanctuary Pavement, led by Ruth Siddall, who had worked on the restoration. We are indebted to Ruth for arranging this rare viewing opportunity, and felt very privileged to be able to walk on the pavement in our thick socks and examine it in detail.
Ruth gave a brief introduction to the background of the Sanctuary Pavement. When Westminster Abbey was consecrated on 28/12/1065 King Edward the Confessor, who originally had it built, was too ill to attend and died about a week later. Westminster Abbey survived largely in its original form for two centuries until the middle of the 13th century, when King Henry III decided to rebuild the Abbey in the new Gothic style of architecture, the work commencing in 1245. Henry III moved the body of Edward the Confessor into a tomb behind the High Altar. This shrine survives and around it are buried a cluster of medieval kings and their consorts.
The Sanctuary pavement can be found west of the High Altar, in an area known as the Sacrarium. It was laid down in 1268 by order of Henry III. £50 was paid for the floor. The King's Council, his other advisors, and the country at large as represented intermittently in the then gradually emerging Parliament, were very unhappy with King Henry because of the extravagance.
The Sanctuary Pavement is of Cosmatesque style (Cosmati was the name of a 12th century AD family of Roman craftsmen). It consists of geometrical patterns with stones of different shapes and colours like a patchwork quilt: different shapes fitted together to make a pattern is referred to as ‘opus sectile’ (i.e.work in cut stone). In the medieval period symbolism played a key role in the decorative arts.
The Cosmati Pavement in Westminster Abbey © Ruth Siddall
It is said that the Pope’s blessing was needed for the Abbey to be built. Archbishop Wenlock met the Pope about 30 miles south of Rome. During the visit to Italy Archbishop Wenlock saw a particular floor in Rome. Archbishop Wenlock was so impressed with the floor he recommended to King Henry that Westminster Abbey needed to have a floor of similar design. Most of the stones are thought to have come from Roman-age sites, and some may have been taken from the neighbourhood of Rome itself, but there was also some use of material available in England, e.g. the substitution of Purbeck Green Marble for Carrara marble in the framework, which was better suited to local conditions and tastes.
The Sanctuary Pavement has a border with roundels and tombs enclosing areas of polychrome stonework (a quincunx within a quincunx). The decorative stones are marbles and porphyries with glass laid in a bed of mortar. The central roundel is made of alabaster and the pavement also includes purple porphyry, green serpentine and yellow limestone.
The original floor was laid in the 13th century (primary mix). It was restored in the 17th century (secondary mix) and restored again in the 18th century (tertiary mix). The eastern margin of the floor, adjacent to the Altar, was replaced by the architect George Gilbert Scott in the mid-19th century. He used a mixture of recycled and new stones. Sir George Gilbert Scott designed and installed the High Altar and its setting in the 19th Century.
Green and purple porphyry are the most abundant stone used (mostly in the primary mix). The word "Porphyry" comes from a Greek word, which originally meant "dark", but later acquired the new meaning of "purple", after a fish which provided purple dye, and which had a very similar name. It is applied to a trachytic andesite of purple and other dark hues, but with lighter phenocrysts, found on a mountain in the Eastern Desert of Egypt. This specific rock, "Imperial Porphyry", was highly prized in Roman and Byzantine times, as purple was the imperial colour.
A mixture of stones have been used in the Sanctuary Pavement including Purbeck marble, breccia (Breccia Corallina), alabaster (used in the centre roundel), Egyptian gabbro, white marble (largely Carrara marble) and Tadcaster limestone (a magnesium limestone from North Yorkshire).
Both opaque and transparent coloured glass has been used to enhance the ‘sparkle’. Six colours of transparent glass have been used: the colours include red, turquoise, cobalt blue and bluish white. They are chemically potassium-lime with the potassium coming from wood ash. The opaque glass is soda lime with the sodium coming from plant ash with tin oxide added to it. Lime mortar has been applied to the top of the floor.
The area in front of the High Altar contained three roundels in Imperial Porphyry. We were informed by a Latin inscription in the steps leading up to them, that they had been given to the church by Victor Alexander, Earl of Elgin, in token of his and his family's love for the place. This was not the Lord Elgin associated with the Parthenon marbles, but his grandson, the 9th Earl. However they had apparently been cut from Egyptian columns which had been brought home by his grandfather in segments from Byzantium (i.e. from Constantinople, present-day Istanbul, where the 7 Earl had been the British Ambassador).
The contemporary role of the Abbey was much in evidence as we left it, passing through the crowds of tourists and by more recent memorials, to walk along Victoria Street towards Westminster Cathedral.
On the way, we stopped at a number of the localities covered by Ruth in one of her building stones walks published on the internet.
At the Department of Business Innovation and Skills, we examined two facing stones, a black stone , probably Nero Zimbabwe, and a white-coloured rather unusual foliated quasi-granite from northern Norway, a trondhjemite sold under the name of "Polar Silver".
A little further on we stopped at a new set of offices, at No 39 Victoria Street, and looked at the floor in the reception area. The concierge kindly let us in to examine the floor more closely. It was a cream-coloured limestone with yellow-orange fossils, notably sponges and belemnites. Ruth said that it was similar to the Upper Jurassic limestone from Solnhofen in Germany, but came from the neighbourhood of Treuchtlingen, also in the Fränkische Alb.
At No 71 we stopped to look at a striking set of columns made out of an amphibolite-facies grey gneiss, probably resulting from the deformation of granite. Ruth said it probably came from China and is known as China Juparana. At No 75 we saw at the entrance arch to Artillery Mansions columns in grey- brown foliated granite. Ruth commented that the quarry was likely to have been near a fault zone, probably in Cornwall.
Striking grey gneiss columns at No. 71 Victoria Street, probably from China
At this point we crossed over the road to No 50, part of a complex of office buildings, and currently occupied by Transport for London. This was clad in a pink-brown charnockite from South Dakota, about 2,700 million years old, known as Dakota Mahogany.
Charnockites, we were told, are a granitic rock, but with pyroxenes and amphiboles, named after the tombstone of, and monument to, Job Charnock, the founder of Calcutta, which is made out of the material.
At the pub next door, the "Albert", we saw the lower panels in larvikite, the monzonite which displays the shimmering blue effect known as schillerisation, and which is frequently deployed at such localities. Higher up were panels of a Swedish red granite.
Crossing back, we walked over to Willcox Place, an area on the western side of the House of Fraser's Army and Navy store. This was paved in Chinese granites, a Chinese basalt, and a Chinese "Augen" gneiss.
On arrival at the piazza in front of Westminster Cathedral, Ruth gave us a brief introduction to the Cathedral itself. This had resulted from the conception of Cardinal Vaughan in the 19th century of a cathedral which could be built relatively quickly in terms of its structure (in order to meet the needs of the Archdiocese and the wider Catholic community), and decorated later, as resources became available. She mentioned the realisation of this concept by the architect Bentley, who designed the church in largely neo-Byzantine style, but with echoes of Northern Italian Romanesque, and had envisaged the use of at least 60 marbles and other decorative stones in its embellishment. In fact many more varieties had been added. She also mentioned the work of the stone-carver and merchant William Brindley, who provided much of the original stock of decorative stone for the Cathedral. Brindley had anticipated the increasing demand for marble and other decorative stones in the country, and had used his considerable geological knowledge to seek out the quarries from which the raw materials had been obtained in antiquity.
Ruth pointed out that a very full catalogue and description of the different varieties of stone had been provided by the Historian of the Cathedral, Patrick Rogers, in a book published in 2008 which was on sale in the Cathedral bookshop. This book specifies the location of some 129 varieties of stone by then identified, gives an account of the history use and sources of the most important varieties, and narrates the author's own experiences in visiting some of the quarries from which they were obtained.
Cosmatesque style panel on the pulpit at Westminster Cathedral
As it was inappropriate for Ruth to lead a fairly large group into the Cathedral, she indicated that she would leave us at this point. Having thanked Ruth for a most interesting and informative afternoon, we then made our way in smaller groups by ourselves to view the treasure store inside. Some of us bought copies of the Patrick Rogers book as our guide.
High up inside the Cathedral, much of the building remains as undecorated black-coated brick, notably the vaults of the nave, which produce a sharp contrast of austerity with the rich decoration below. Much of the mosaic and decorative stone work of the side chapels has apparently been added fairly recently. Apart from their specific religious themes, these side chapels illustrate the development of Roman Catholicism in England, from a very small persecuted sect in the aftermath of the Reformation, to the current large and very diverse group of Christians, which is probably now the most important religious denomination in the country in terms of the number of its practising, as opposed to nominal, members.
It seems likely from recent articles in the Cathedral magazine "Oremus" ("Let us pray"), that the work of cataloguing the decorative stones found there will continue. Like the Cathedral itself, it represents work in progress.
The following hyperlinks (to websites) may be of interest to the reader:
Leanne, a PhD student with the OU and the Natural Environment Research Council, talked to us about her research, undertaken to further our understanding of the phenomenon of the eruption of specific volcanoes and thus help to mitigate their effects on the population nearby. Problems include the definition of an eruption, the wide range of durations from hours to decades, the range of eruption types and the fact that the controls are poorly understood.
Her research includes the development of a model and the compilation of datasets of historical eruptions. If we can make forecasts and predictions, based on possible scenarios, future actions will be more firmly based, than, for example, in the case of the 2009 Italian earthquake.
The first example was Mount Etna, a highly active, well- documented volcano with 62 recorded eruptions, both effusive and explosive, with a median effusive duration of 34.5 days. Another problem for prediction, however, must inevitably be reporting bias, since the incidence of eruptions of all types appears to have increased between 1790 and 1990. Analysis of the data on long eruptions in the past can give the probability of an eruption exceeding a given length of time in the future.
We next looked at the Piton de la Fournaise in Reunion, which, from 1644 to 2011, has averaged two eruptions a year with durations ranging from 0.25 to 334 days, with a higher proportion on the shorter side.
Looking at the data we can forecast for Etna a likely duration of 20 days, with >86 days unlikely. Equivalent figures for the Piton de la Fournaise are 16 and 31.
Finally to Iceland and basaltic eruptions in a zone of axial rifting, with shorter eruptions inside the rift zone than outside. One theory suggests that in the external setting the conduits are larger than in the intraplate setting.
The research is ongoing, and potentially of great importance for the safety of the local inhabitants.
Twenty-three members of OUGS visited West Norwood Cemetery on the 5th April 2014. Colin Fenn who is a member of the Friends of West Norwood Cemetery (and was accompanied by some other Friends) told us about the history of the cemetery and about some of the famous people who are buried here and whose memorials we saw, while Diana told us about the stone used for the memorials.
Colin told us that West Norwood Cemetery was the second privately owned cemetery constructed around London to cater for the increased numbers of burials necessary as London doubled in size in the first part of the 19th century. In 1836 an Act of Parliament was passed for establishing the cemetery and a 40 acre site was purchased at what was then called Lower Norwood. William Tite was the company’s architect and director and set out rolling green fields, winding paths and high perimeter walls, battlemented piers and tall cast-iron railings and gates. Two Gothic chapels, styled after Kings College Chapel, Cambridge stood at the top of a hill. Tite reserved his own vault behind a carved stone vault in the catacombs (see later).
Norwood Cemetery Memorials
The cemetery was consecrated by the Bishop of Winchester in 1837 and the first burial took place soon after. A large area was left unconsecrated for burial of dissenters. Burial plots were leased for 75 years or in perpetuity with a subscription to a pooled fund to maintain the monuments. Provision was made for shared common graves for the poor.
The cemetery became renowned for the wealth and aspiration of those interred and people paid a lot of money for a prime position, and it became known as the ‘Millionaires’ Cemetery’. As we walked past the monuments we could see many of them were granite and Diana told us about the many types of granite which we could see.
Aberdeenshire Granites were important because the granites quarried there could be extracted in large pieces known as dimension stone and then worked on. In the 1830s Alexander Macdonald of Aberdeen developed a steam-driven polishing machine that enabled the slabs to be polished and dressed. He supplied many of the memorials at West Norwood and his name could be seen at the base of them. The granites (and experienced workmen) were exported abroad to Europe, America and Australasia.
The types of Aberdeen granite included:
As space started running out paths were closed or narrowed to fit in more burials. By 1965 the Cemetery Company was almost bankrupt and it was compulsorily purchased by the London Borough of Lambeth. Regardless of pre-existing burial rights and the original Acts of Parliament, Lambeth bulldozed 10 acres, graves were resold and new burials took place over ancient plots. The cemetery area was put within a conservation area in 1978 and in 1981 69 monuments were listed by English Heritage. But destruction continued until halted by the Archdeacon of Lambeth in 1994. Lambeth’s actions were judged to be illegal. Since then the cemetery has been run by a management committee and restoration and repair of some listed monuments has taken place.
Many are made from limestone such as Portland stone or marble, polished to a fine finish. Sometimes stone such as polished Purbeck stone are referred to as marble, but they are not marble in the geological sense. Diana told us to use our fingers as true marble will be much smoother. White stone such as Carrara marble was very popular with the Victorians as white was a symbol of purity. Also the use of carved ivy and stone urns etc. which were a symbol of death.
An example of a Portland stone memorial was that of James William Gilbart which is an exuberant Gothic ‘belfry’. It has medallions on the gable carved with the initials ‘JWG’ and a squirrel holding an acorn, which is a symbol of the savings movement. He founded the London and Westminster Bank and wrote the laws that set up building societies.
John Britton was a distinguished medieval antiquary whose memorial was a massive block of millstone from the Great Delta bank series from the Carboniferous, around 345-350 Ma. We could see bedding lines in the stone, formed by a moving delta system, a current day example is in the Mississippi area.
There was also a smaller memorial of millstone grit nearby which had inset photographs.
Millstone Grit Memorial
A disadvantage of sandstone is that it becomes case-hardened on the outside, as it dries out salts are drawn out and solidify as a skin which if damaged peels off.
The memorial for James Battersby Bailey was a massive Sandstone Celtic Cross. He was a surgeon, but his son Edward was a renowned geologist, a proponent of plate tectonics and director of the BGS from 1937 – 1945.
Celtic Cross Memorial (James Battersby Bailey)
Terracotta is one of the oldest building materials in the world, its iron content gives it its colour. It can be moulded and fired. Alkali allow the surface to be vitrified, it is fired at 1100°C and is cooled slowly for up to 14 days which gives it a very high durability.
We saw an early stone by Mary Seton Watts who was an artisan potter from Compton in Surrey. It was quite coarse.
The family vault of Sir Henry Doulton is a mausoleum constructed of red terracotta bricks, quoins and roof tiles, with a decorative iron grille door sitting within a hooded entrance. The pottery founded by his father initially made terracotta and salt-glazed stoneware sewer pipes. Henry expanded into decorative ware, figurines etc. and it became Royal Doulton in 1901.
Sir Henry Tate was a grocer who became a sugar refiner and introduced sugar cubes to Great Britain. His memorial is an ornate terracotta mausoleum with stylistic jigsaw type pieces and barrel edging.
Slate needs to be good quality otherwise weathering lifts off lamina. Good quality comes from Cumbria and takes lettering really well.
Larvikite is a type of igneous rock known as a monzonite from Norway. It contains virtually no quartz. It is very decorative and is used mainly for small pillars and scrolls. There are 4 types, Blue, Emerald Pearl, Grey and Imperial. Examples of Larvikite used for memorials in the cemetery are :
Serpentine is a rock that comes from Cornwall (amongst other places) and is used here mainly for decorative purposes.
Timber, Cast Iron and Bronze are also found.
The use of Emerging Stone where rough-hewn stone with a polished section that could be engraved became common at the turn of the century. Also polished black stone which is called Granite by the trade, but could be Gabbro from Aberdeen or from South Africa or Brazil. This takes lettering well and in the 1960s gold lettering was popular but this is now banned. The use of artificial stone, such as Coadestone, Pulhamite or Ransome’s artificial stone (an artificial sandstone) is now common.
Gideon Algernon Mantell was an English obstetrician, geologist and palaeontologist. He was an enthusiastic fossil collector and discovered 4 genera of dinosaurs including the iguanodon for which he is best known. His monument was restored with assistance from the Geologists’ Association which is acknowledged by an inscription on the side. The original cypress tree has been replaced by a Ginkgo tree (often called living fossils dating back 270 m years).
Robert Mallett’s monument is a high Celtic cross in Portland Stone. It has lost its polish and is very fossiliferous. He was known as the ‘father of seismology’ through his research into earthquakes. Amongst other things he also drilled an artesian well in Dublin for the Guinness Brewery.
The tomb of Baron Paul Julius de Reuter founder of the Reuter News Agency. It is a pedestal tomb with an urn in the Macdonald style in polished pink and grey granite. Adjacent is a highly polished granite disc for his two children.
Henry Grissell known as ‘Iron Henry’, whose company Regent’s Canal Iron Works made castings for bridges in England, Russia and Egypt. His family made gates and railings for Buckingham Palace, The Royal Exchange and The British Museum. His memorial is a cast-iron octagonal Gothic chest tomb. Its pilasters and colonnades carry angels and have blind Gothic windows with inscribed panels of pink granite. The tomb stands on a large rectangular granite platform with iron trapdoors at the rear to a deep vault with 13 shelves. The galvanised castings are still good but cream paintwork is badly deteriorated.
James Greathead whose memorial is a raised cross on a low marble slab invented Greathead’s Tunnelling Shield which was used to dig the tunnel under the Thames by Tower Bridge and the Blackwall Tunnel. The same type of shield is being used for Cross Rail today.
John Hughes amongst other things patented a number of inventions in armaments and armour plating. His company received an order from the Imperial Russian Government for plating a naval fortress. A town grew up around the factory called Hughesovka (Yuzovka). The town was renamed Stalino in 1924, then Donetsk in 1961. It is now part of the Ukraine.
William Knight's monument has recently been restored. He was a pioneer of gold and diamond extraction in South Africa. Seeing many diamonds on the surface he suggested digging deep with success, the area became the Kimberley diamond mines. Then he moved on to gold mining.
John Newlands was the first person to devise a periodic table of elements arranged in order of their relative atomic weights, and in 1865 published his ‘law of octaves’ which was ridiculed at the time. After Dimitri Mendeleev received the Davy medal for his later ‘discovery’ of the periodic table, Newlands fought for recognition for his work and received the Davy Medal in 1887.
Otto Berens was a Russian émigré who made a fortune selling fashionable fabrics and materials. His Mausoleum is a dramatic medieval Italianate structure of many different granites, marbles and limestones. It has a band of Minton encaustic tiles with alternate patterns of the Gothic letter ‘B’ and a bear holding a sword (the Berens Arms). Unfortunately it is in need of major repair. The undercarving of the roof is stuffed with Crinoid ossicles and a burst of coral.
Charles Alcock in his position as FA secretary founded the FA cup. He also became head of Surrey County Cricket Club. The lettering on his memorial has all been repaired. As marble erodes pegs on which letters are mounted are exposed and the letters fall out.
Mrs Beeton of cookery fame and Dr William Marsden who founded the hospital which later became the Royal Marsden are also buried here.
We also visited the Anglican catacombs created by Tite (who has a vault here) beneath the original Anglican Chapel which was pulled down in 1960 and replaced by a memorial garden.
A staircase led down to a central gallery of vaults with perpendicular aisles. Each aisle had 14 bays laid out as a series of high brick arches and piers. The central gallery which Colin showed us contains grand family vaults (we saw one belonging to Chaplin’s family) behind Gothic stone pillars and iron grilles now heavily rusted. Whole bays, part bays or individual compartments were set behind cast-iron gates armorial crests, stone panels or set with stone memorial tablets. A family vault would have cost ~ £300, a public vault about 4 guineas.
Some bays were left open and we could see exposed coffins and remains of mourner’s tributes. Colin told us there were 6 aisles, 4 full of coffins, 2 empty. There were ½ dozen lord Mayors of London down there as well as E Nesbit, the children’s author and a Chinese customs official.
The coffins would have been wood lined with lead and would have been delivered into the central gallery using a catafalque (hydraulic coffin lift) fitted in 1839 by Bramah and Robinson. The catacombs are no longer used. We could see water damage from the memorial garden above where stalactites were growing from the ceiling.
There is also a Greek Orthodox Necropolis at the Cemetery which we did not have time to see.
We thanked Colin and Diana for a most interesting morning and finished the day in the café across the road.
In writing this article reference was made to the guide ‘West Norwood Cemetery’s Monumental Architecture’ by Colin R Fenn and James Slattery-Kavanagh.
Framed by a comic reference to the last day of the Cretaceous, Paul gave us an enormous amount of information on the various impactors and their effects on our planet, how they formed, and the features of impact craters that differentiate them from the volcanic variety. Coming from the Asteroid Belt within the orbit of Jupiter, the Kuiper Belt, further out and the Oort Cloud, composed mostly of ice, they include asteroids on earth-crossing orbits, asteroid fragments from collisions, comets, cometary fragments together with planetesimals and their fragments, and date from the very beginnings of the Solar System.
Then followed a classification of meteorites with illustrations, such as the Brenham stony iron (US), the Hoba (Namibia) and Agpalik (Greenland) irons, a picture of Haley Bop comet impacting Jupiter, a detailed discussion of asteroid Eros, and a comparison of impact craters on the Moon with the volcanic structure of Vesuvius. This section ended with a table showing the results according to the size and energy of the impacting body.
A section on the Martian Alban Hills meteorite discussed the theory of panspermia and whether Earth was seeded by life from Mars, leading seamlessly into the formation of the Moon and the initiation of the Grand Bombardment early in the Earth’s history.
The Sunbury Astrobleme at 1.85 Ga produced the second- largest impact crater on Earth, when a 10 km asteroid melted the Mantle, resulting in huge deposits of nickel, copper, platinum and gold. The Ries crater at 16 Ma and the Triassic Rochechouart impact crater near Limoges were illustrated with photographs and diagrams, leading to a discussion of the Tunguska event in 1908, when an object of no more than 10,000 tons exploded 6-8 km above the Siberian surface. Not extensively researched until 1927, much uncertainty still surrounds the event: one body involved or two? A cometary impact?
Finally we returned to the end of the Cretaceous and the K/T boundary iridium anomaly with the Chicxulub crater in Yucatan. Was it this impact of a 10 km-wide asteroid (or comet?), or the volcanism of the Deccan Traps that was responsible for the extinction of the dinosaurs?
The summary nature of this note does little justice to the talk, but perhaps gives some idea of the range of reference. Paul had brought samples of meteorites to show their differing, and beautiful, structures.
The six full days in the field were led by Simon Drake of Birkbeck, University of London, and designed to provide an overview of the geology of Skye, (including some geological mapping) with the focus on Simon's PhD work on ignimbrites. This was a budget trip with the accommodation being hostel style to keep costs to a minimum. The intention was to attract some of the newer society members and get them involved with our trips. It did, and there was a nice mix of people.
This was our first full day in Skye and it was a washout. After briefly looking at a lava flow to the west of Loch Slapin near Strathaird, Simon decided it would be best to adopt a new plan. The original plan was to spend the whole day outdoors looking at rocks but, because the weather was so poor, we decided that it would be better to drive around the island looking at the most interesting parts (Figures 1 and 2). This was far from ideal, but it would be better than spending a day out in the field and getting absolutely drenched.
1. The Quiraing
2. Red paleosol and amygdaloidal basalt
First stop on the new plan was a chambered cairn near Broadford. Here, Palaeogene rhyolitic ash has been deposited directly on top of Cambro-Ordovician dolostone-- an unconformity of approximately 440 Ma. There are a lot of igneous intrusions on Skye, but relatively few extrusive examples. The eruptions are known to have been very big, and it is possible that the ash was deposited far away. Some believe that ash deposits found in Kent originated in Skye, although Simon thought this unlikely.
A quick glance at a geological map of Skye will show that almost all of the dykes are oriented NNW. This is because, when the plates attempted to separate during the British- Paleogene Igneous Province, they moved along a line that ran NNW-SSE. This combined with the dextral shear to create NNW-SSE weaknesses in the bedrock into which multiple dykes were able to intrude.
Next we went to the famous Kilt Rock (Figure 3). This is a microgabbro sill that has been intruded over Jurassic sediments, producing one of the UK's most recognisable geological features.
3. The Kilt Rock
We also visited Duntulm Sill, a rare example of a layered sill. The sub-horizontal black lines are pyroxene. The layer bases are mafic, which grade upwards to felsic rock. The change in colour is caused by the change from pyroxene to plagioclase. There are several theories about how layered sills form. Duntulm Castle sits atop the sill.
This was a good day, despite the weather. Simon made the most of it, and it was good to have a tour of the island at the beginning to whet our appetites.
On the second day, we took the mini-buses from Torrin to a lay-by on the Strathaird peninsula to try again to walk over the lava flows into Camasunary Bay – a walk we were unable to do the previous day due to the weather.
The path took us roughly north-west over the fairly bleak landscape towards the Black Cuillins. We initially walked over the Jurassic limestones of the Great Estuarine series, noting several basaltic dykes running north / south across our path. Somewhere south of Slat Bheinn a stream cut through, nicely exposing bedding planes in the Jurassic limestone. We stopped here for a little while to practice measuring dips and strikes. Just over the style next to this spot we moved onto a steeper incline – marking the boundary between the Jurassic and the flank of the Paleocene basalt plateau.
Simon chose us a lovely spot to stop for lunch – a large micro-gabbro dyke at about the highest point of our walk (Figure 4). This not only had commanding views over the Cuillins, but on a smaller scale it revealed some nice olivine crystals and also xenoliths of Torridonian arkosic sandstone.
4. Not sure it can get any better than lunch on a dyke
Continuing our journey, we then headed down into Camasumary Bay until we reached the shoreline. Our path had crossed the Camasunary–Skerryvore fault. This is a large normal fault running NNE-SSW. A section of the beach sat on the fault so we could see the Great Estuarine limestones to the east side of the beach, and uplifted Torridonian sedimentary rocks to the west.
After exploring the beach we headed back up the hill, some- what wearier due to the climb with backpacks slightly heavier from collected pebbles, and returned along the same path back to our awaiting transport.
We set out for Elgol (Figure 5) in warm sunshine to take the Bella Jane to Loch Coruisk (Figure 6) in the heart of the Cuillins, with the aim of examining the 58.9 million year old magma chamber, once 3 000 feet above sea level. We passed the “Bad Step” en route and admired the numerous seals basking on the rocks (Figure 7).
5. Classic view of the Cullins with deltaic sequences on the beach at Elgol
6. Loch Coruisk
7. Seal inspects rock
Once ashore we headed for the Loch, stopping on the way to look at the pyroxene-rich gabbro cross-cut by basaltic dykes, showing lots of chilled margins. Simon pointed out labradorite in the gabbro and the blue-green schiller effect caused by the refraction of calcium-rich plagioclase. The presence of chlorite and epidote testified to the alteration of pyroxenes by hydrothermal fluids.
We arrived at the loch after a short walk. I imagine everyone felt a sense of awe at being inside an ancient magma chamber and in such a spectacularly beautiful setting. It was magical. Sedimentary processes were evident everywhere, with lots of cross-stratification resulting from avalanching lava. Simon explained that convection currents in the magma chamber cause rhythmic layering, analogous to stratification caused by turbulence in rivers, resulting in pyroxene-rich and plagioclase-rich layers. The progression of fractional crystallisation could be seen in the different chemical compositions of the materials slumping down, with very dark pyroxene and olivine-rich gabbro which would have been the ultramafic sludge left on the side of the magma chamber, dark clumps of pyroxene and then clearly visible flows of lighter-coloured, more silica-rich fine grained gabbro. Pressure shadows could be seen, showing how the lava flow had been deflected round semi-solid plagioclase and solid clumps of pyroxene. There were also chatter marks in the gabbro, caused by ice movement as a glacier flowed over it at a later date.
Returning after lunch, the Bella Jane was overbooked so seven of us, including Simon, stayed behind and waited for the next boat in about two hours time!! Without hesitation we headed back to Loch Coruisk and tackled some boulder hopping to visit the Western shore of the loch. We were able to examine the basaltic dyke, approximately 100 m across and cross-cut by intrusions (dykes or sills?) of approximately 40-50 cms across, all brittlely faulted and fingered in. We remained mystified as to why the faulted offsets don’t continue into the country rock. Net veining was evident where criss-crossing fractures were infilled by foreign minerals.
We returned to the landing stage and were treated to an even more thrilling ride back, while we held on for grim death - and on to sedimentary rock...
Meanwhile, the rest of the group had been exploring the far side of Elgol beach where herring-bone cross-stratification, honeycomb weathering (Figures 8 and 9) and bioturbation can be seen in Jurassic deltaic sandstone. The weathering out of epidote had left big holes in the rocks (Figure 10). Distal rocks are organic rich and a sill is seen to be cut by a dyke on the beach.
8. Honeycomb weathering
9. Honeycomb weathering close up
10. Epidote nodules, deltaic sequence Elgol beach
The group re-assembled at the port and we had a short walk to a SSSI where Palaeogene sills had intruded into Jurassic organic shale, causing ductile deformation and tight folding of the country rock. There was also more net veining.
Those of us who had stayed behind at Loch Coruisk went to look at the Jurassic sandstone on Elgol beach, then it was back to Torrin having had another great day (arguably the best so far) on "The Winged Isle".
If water was ever in short supply it would not have been on this particular day on the Isle of Skye. With thanks to Anna Saich and her waterproof notebook out-classing my now not so waterproof Papier-Mâché agglomeration, I am able to recall some of the highlights of the day spent at Allt Nan Suidheachan, Kilchrist.
Our leader and expert in the field, hopefully now 'Dr' Simon Drake, spent his PhD working on the re-classification and re- mapping using distinct ignimbrite lithofacies to differentiate between the many, often wrongly classified, 'felsites' on Skye in order to improve the understanding of the volcanic evolution of the island.
Therefore, ignimbrites (Figure 11) formed the theme of this trip and as an amateur; I would say that I am now aware that they are not simply 'ash-flow tuffs' but products of pyroclastic density currents occurring over a range of grades. Many grades of ignimbrites were represented in the steep stream section we followed up the hill.
11. Ignimbrites at Allt Nan Suidheachan
Whilst ascending we stopped at various exposures in and around the stream to take note of the changing ignimbrite grades. From low-grade, low temperature fall deposits characterised by a non-welded texture up to the welded rheomorphic variety, demonstrating flow direction and formed by extreme heat, we saw a succession enabling a reconstruction of the eruption to be discussed. A particular highlight in the rheomorphic variety higher up the section, was the presence of chloritised fiammé. These deformed lenses of pumice within the ignimbrites were an indication of a distinct flow during formation.
Heading back down the hill the rain did not relent but we were treated to a view of the Torrin Marble Quarry (Figure 12) not far from our lodgings. This beautiful material is the metamorphic product of the Durness Limestone. Even the cows seemed to appreciate our presence that day, following us off the hill not at all hoping for a feed. The ensuing clothes drying bonanza back at the house was certainly a testament to a worthy day in the field.
12. View of Torrin Marble Quarry
We walked through heather and streams to Fionn Choire on the NW margin of the Cuillins. The rock exposures were poor, the map shows mostly basaltic lavas, including Hawaiite and some patches of intrusive microgabbro. The Cuillin rocks had been Uranium-Lead radiodated at 58.9 Ma but we were going to look at older high-grade extrusive pyroclastics, mostly in stream sections, dated 60.1 Ma. Simon had personally mapped and revised the ignimbrite lithofacies classification in 2010, following the new scheme reproduced in our notes. This was from the "Geological Society Memoir 27, Pyroclastic density currents and the sedimentation of ignimbrites", by Branney & Kokelaar in 2002. In addition, Simon had found welded ignimbrite xenoliths in the basalt lava flows at the margins of the Cuillins, which confirms that the ignimbrite had been erupted before the Cuillins lavas.
13. Ignimbrites, Fionn Choire
Fionn Choire has 4 of the 13 types of lithofacies although most exposures were about a metre across. The tuffs had both normal and reverse grading, but the Chapter 7 ‘Summary and Overview’ of the Geological Society Memoir says that current density cannot be deduced from this (Table 7.1 page 120). Previously, I had been taught that absence of grading meant the pyroclastic flow had suddenly weakened. Also that reverse grading occurred because the current was dense i.e. concentrated, making lighter large pumice float to the top. Laterally continuous tops and bases used to mean different flows with pauses between eruptions. Instead, Branney & Kokelaar say that there are so many variables that neither pyroclastic flow density, current flow-rate and stratification, nor current thickness can be deduced from the deposits.
Something that is still considered meaningful is degree of welding of the pyroclastic deposits. The Fairy Chimneys in White Valley, Turkey were crumbly and pumice-rich; I could pick out bits with my nail, which is why they formed 20 m pillars due to fast erosion. By contrast, the pyroclastics at Fionn Choire were rock-hard i.e. were formed at 1 000°C, which stuck the fragments together once they stopped moving. These strongly welded tuffs eroded slowly and were buried under peat, except where streams had cut down. So Simon correlated the volcanics by extensively logging the numerous stream sections and identified a thick sequence of 'Rheomorphic ignimbrite', one of the higher grades of the 13 new lithofacies categories. These rocks show refolded folds macroscopically. Banding within high grade ignimbrites is often pink or beige in colour, but this refolded texture was unusual (Figure 14). Simon’s notes (plus statistics from Wikipedia!) show 4 types of eruptions which generate pyroclastic density currents. They are firstly the sideways blast (Mt St Helens, USA 1980 killed 57) and secondly high column collapse (Mount Pinatubo, Philippines 1991 killed 847). Both types pull in a lot of air, which dilutes the pyroclastic flow. Both deposit unwelded fragments which may erode rapidly like the Fairy Chimneys; these are remnants of an extensive ash plain.
14. Rheomorphic lithofacies pyroclastic rock, Fionn Choire
By contrast, the early silicic Skye igneous rocks were thought to be produced by high temperature eruptions from a low eruption column; the resulting pyroclastic density currents were very hot. These are frequently termed 'boil-over events' and an example is the Mount Lamington eruption in Papua 1952, killed 3000. This type is very hot and deposits welded tuffs because it isn’t diluted by sucking in cold air. The fourth type is also hot, from the collapse of a high-silica dome e.g. Mont Pelee, Martinique 1902, killed 30,000. Stratovolcanoes generate all four of these types of pyroclastic density currents, so Skye might have been the site of a stratovolcano 60 million years ago.
Simon also found accretionary lapilli near Kilchrist, which is a separate lithofacies category in the Geological Society Memoire 27 2002. Accretionary lapilli are produced in ash clouds where they accrete and then fall into an underlying pyroclastic density current, where they continue to grow. They are quite distinct from ordinary lapilli, which are just volcanic fragments (it means 'little stones' in Italian) between 2-64 mm. Simon likes accretionary lapilli because they may provide a temporal record of the eruption. Ongoing research is suggesting that the various rims are chemically diverse, which may reflect different magma pulses that are pumped out of the vent into the pyroclastic density current. Wet muddy ash layers get plastered on to cores as the fragments tumble around in the eruption column.
We were all glad to have a bath or shower, get out of our muddy gear and rest after a tiring day.
The afternoon could hardly have been more different from the morning as we descended the 500 m from Fionn Choire to sea level, leaving behind the drizzle for glaring sunshine. We stopped by a local hostelry on the way to deposit our casualty from the morning so she might dry off along with one of our group who kindly volunteered to look after her – this was possibly a ruse for us all to stop back there on the way home.
We proceeded to Talisker Bay (Figure 15) for what might have been more sightseeing, were it not for the spectacular basalt colonnade of Preshal More we passed on the walk in.
15. Talisker Bay
Once on the foreshore round to the left of the beach, we spotted a lava tube in the cliff, it was a little too risky for most of us to climb up to inspect more closely, but it was nicely continued into the large sea stack opposite.
We were also treated to seeing pahoehoe preserved (Figure 16), and nearby a nice example of a'a. There were also plenty of amygdales on offer, in separate flow structures that made for plenty of discussion and head-scratching.
Sunny weather on Friday morning provided a great opportunity to practise our mapping skills. My last experience of mapping was in heavy rain and snow in the Forest of Dean so I was especially pleased to have good weather this time.
Armed with compass-clinos, mapping boards and coloured pencils we were ready to practice our field skills. We were provided with mapping slips on which to make our observations. Our mapping area was located to the south of Loch Cill Chriosd, in an area crossed by a dyke. Three different lithologies outcropped in the mapping area – dolostone (Figure 17), granite (part of the Eastern Red Hills granite) and the microgabbro dyke.
In addition to examining the outcrops we looked at differences in vegetation. A change from well drained grassy areas to heather marked the boundary between the dolostone and granite. With guidance from Simon were able to build up our maps. Discussion about the relationships between the different mapped lithologies followed.
The heat from the granite, and the later dyke, metamorphosed the dolostones. We were able to examine these metamorphosed dolostone in a small ‘Skye marble’ quarry (Figure 18).
18. Examining the outcrop in a small quarry
Here the dolostone was affected not just by the granite but also the dyke. This is one of few locations where mineralisation of the metamorphosed dolostones can be observed. We found examples of olive green forsterite (olivine) and darker green diopside (clinopyroxene) in the former quarry.
This was a great opportunity to get some hands on experience.
If Thursday had been a day of two halves, Friday proved that the same applied to the whole week. I had woken at first light, seen the sunny haze on the Cuillins out of the window and wondered if the people on the trip really knew how lucky we were. To be honest, this was the way I had planned the weather – get all the rain in at the beginning, and we finished off with Scottish sunshine at its most glorious. Entirely appropriate that we went to the sea again, and to the Lewisian gneiss that outcrops along the Sleat peninsula.
19. Ruins of Knock Castle atop a cliff of Lewisian
For some it was their first sight of the Lewisian, and I'm not sure it was the most representative outcrop, here it is heavily banded and rather easy to take in on a small scale. It was, however, a fascinating little locality with plenty of movement, and a stonking great bit of boudinage (Figure 20) – though there was much discussion about whether it really was boudinage, offers of what else it might be weren't really forthcoming.
20. Simon and an imbricate thrust stack
21. Gneiss with boudins
Another change from the beginning of the week – as we had arrived at the croft we stayed on there was much excited chatter about the wild rabbits. Day two we were graced with deer running past us during our lunchbreak, and yet later some of us were fortunate enough to spot a golden eagle. Yet here on the Lewisian was where a cry went out “Otter”. Many of us saw the otter run down into the sea, dive a couple of times, then proceed to munch its way through a crab. Feeling bad for some who had wandered off elsewhere, that was soon dispelled when they came back with big grins and tales of having seen pine martins. Not that wildlife has anything to do with Geology, but that is part of the allure of Skye, not quite knowing where to look and what to focus on, and the more time you spend here, the better it gets.
22. Knock Bay
From the outset I knew Simon would engage everyone with his knowledge of Skye's geology and enthusiasm for it, having no worries about the field aspect made the organiser's role that much easier. I would like to thank him, on behalf of the group, for making this trip so memorable.
I was truly inspired by the Skye trip. It was well paced so I never got overwhelmed, and found I had vastly improved my observation skills by the end of the week. The day after I got home, I went straight out on a self-trip using the Fife and Angus Guide - I skipped the last few but I found 90% of the stuff they wrote about.
Heidi Barnes (14); Jim Camp (3, 7 and 8); Danny Cheung (15 and 22); Sue Graham (6); Gavin Mair (2, 9, 12 and 16); Leslie Martin (18); Gosia Musur (4); Anna Saich (1, 1o, 11, 13, 17 and 21); and Alan Wilson (5, 19 and 20).
Many thanks go to all of our members who took part in the geoconservation day at Chalky Dell. Our thanks also go to members of the Harrow & Hillingdon Geological Society and the Amateur Geological Society as well as local Conservation Volunteers from Lesnes Abbey and Shooters Hill who joined us on the day. Our aim was to reveal the contact of the Thanet Sand with the Chalk near the top of the scree slope. We also wanted to cut steps up the scree so that the contact can be seen and to expose a section of the chalk nearer to the entrance gate. We achieved all 3 aims but will need to make the steps more durable on a future visit. The pictures below show what we achieved and include a picture of the bluebell woods in full bloom and a rhynchonellid brachiopod found in one of the Blackheath Flint pebbles by John Jarvis.
Site before work started
Lesnes Abbey Woods bluebells
Working at the pit face
Working at the pit face
John Jarvis's rhynchonellid
Chalk exposure beside path from entrance
Measuring thickness of Thanet Sand
The team on the steps
Crossbedding in Thanet on Bullhead Bed
Full section (arrows at base and top of Thanet)
Base of Thanet on Chalk
Gina, Professorial Research Assistant in the Department of Art and Archeology (SOAS) and originally an archaeologist, took her BSc at the OU after becoming interested in the different types of jade and their provenance. The two main types of jade: mutton fat jade or nephrite, which can be found in China and Japan, and jadeite, which is imported from Myanmar (formerly Burma). In China jade is yu, the royal gem.
The earliest jade we know about (7000 BP) is from the Hongshu culture of Inner Mongolia, and then Liangshu in the Yangtse River delta. Nephrite and jadeite are both metamorphic minerals, nephrite being hydrated and jadeite not. Jadeite is mostly green whereas nephrite ranges from white to brownish dark green. They are both very hard to work, with nephrite being tougher, and jadeite harder, and demand very fine engraving techniques, leading to the development of fibrosis, a form of silicosis, in the workers.
Because of its hardness and beauty, it was associated with immortality and used in burials, sometimes completely encasing the body of someone very high-born, but also in beads, weapons and tools.
We then had a technical description of nephrite and jadeite as solid solution minerals from the precipitation of fluids; the source rock is jadetite, 90% pyroxene. There are forty different rocks used as pseudo-jade, and only testing the chemical composition can distinguish true jade, as a lot of jade is dyed for the market.
Ophiolites, pushed on land as a result of back arc basins compressed in collision zones, are the main source of nephrites and we saw a map of nephrite and ophiolite locations. China itself is a 'hotch-potch' of different such terranes, while comparable work has recently been done by George Harlow in Central America in identifying sources, using caltodoluminescence,
But as she said, the subject of jade mineralogy is still at an early stage of research, and much work remains to be done, focusing on orogenic zones, testing artifacts and isotope analysis.
Over the last 20 years or so Brian Harvey researched and led geowalks for London Branch every year (in the early years there were 2 walks annually). For many members Brian’s walks were the highlight of the LOUGS field calendar. For a number of years the LOUGS committee have been hoping that the walks could be written up for future generations of OU students and last year Iain Fletcher took up the challenge and wrote up Brian’s Hog’s Back geowalk. We trialled it in May 2013 and it is now available to all on the LOUGS website: www.lougs.org.uk/localgeo/geowalks.htm.
This year was the turn of Brian’s Chilterns Geowalk to the Tring Gap and College Lake.
Iain opted to start and finish the 9 km-long round walk at the College Lake Nature Reserve where parking is more secure than Brian’s start point and there are facilities in the new eco Visitor Centre. The Reserve was once a chalk quarry working the Grey Chalk. I visited it in on an LOUGS trip in 1988 with Andy Gale, primarily to collect chalk fossils, when I remember it being a working quarry. On that occasion we inspected the spectacular cryoturbation features at the top of the quarry near the car park. We were also able to see the channel where mammal bones were found and because of their importance, this area of the quarry was already designated a geological SSSI.
When we visited with Brian in 2003, the distant working face of the quarry was already under water and the periglacial features, although still good, were not as sharp. Now in 2014 we were unable to see them. The sides of the quarry have become quite vegetated and the small ex-car park is now a restricted area. For those who came on the trip who would like to see what they missed, the cryoturbation is pictured on the Bucks Earth Heritage Group website: www.bucksgeology.org.uk/college_lake.html. It may be worth getting in touch with them to see if they can organise access and conserve both this section and a section in the chalk.
The new Visitor Centre has a lovely display of Quaternary Mammals and the little hut that displayed the chalk fossils on Brian’s trip is still there although the 10 intervening years have not done it any favours (Figure 1).
The VC cleverly incorporates strata of flints within the white-painted walls (Figure 2) – it is a pity that they could not add more about the chalk itself and the old quarry. The emphasis is on the Reserve and with an additional lake near the VC with hides dotted around the perimeter it is a really excellent venue for bird watchers, although Iain did spot a nice Scholoebachia ammonite by the side of the path.
After a short stretch along the road, the ancient Upper Icknield Way, the geowalk followed Brian’s route along the Grand Union Canal and crossing over the London to Birmingham Railway and Northfield Road, all 3 forms of transportation making use of the Tring Gap. We then climbed up through the woods onto Pitstone Hill. Trees had come down in last winter’s storms and we were able to examine the fresh roots to look for flints (Figure 3).
Rather to our surprise we didn’t find any as there were plenty on the path and the BGS indicated that the Middle Chalk topped the hill just above. Out in the open we visited a small exposure of Clay-with-flints, supposedly on top of the Middle Chalk. We found both rounded ‘Tertiary flints’ and un-weathered flints in the reddy-coloured matrix of the Clay-with-flints but the Middle Chalk below was no longer exposed and so we were unable to prove its existence by seeing in situ flints. From Pitstone Hill itself there was a magnificent view of the surrounding geology and we were able to reflect on the influence of geology on land use including the transport routes (Figure 4).
We await Iain’s description of Brian’s walk with anticipation and look forward to another gem in 2015. Thank you Iain.
Ruth introduced her core themes: supply of geomaterials, their availability, the cost of extraction etc; the importance of professional skills, other than technical and scientific: leadership, communication, management; and the transferability of these core skills. She took as her example a quarry in Croatia.
Before any quarry can be opened up, all these skills go into an assessment model, which typically considers archaeology, agriculture and soils, and aims to minimise dust, noise and vibration as much as possible. A mineral can only be mined where it naturally occurs and some adverse environmental effects cannot be eliminated, but following working the land should be restored and a new geology and landscape created, that should be beneficial to the environment and have natural- looking slopes.
For such an assessment, she then referred to key concepts such as modelling skill to identify a problem. Having made a field sketch, it was possible to define a problem, such as too narrow a shelf, or too steep a slope to make extraction possible and safe.
A cross section of a quarry in the UAE was used to emphasise the importance of field notes and sketching, facilitated by the use of an i-pad.
Working in a small firm showed the irrelevance of boundaries between technical studies, seismic etc, and the interaction between geology and engineering.
We then turned to the role of the commercial mediator, relating to the environmental impact of the quarry, its economic success and the social impact on the lives of those affected. We had a diagram of the sustainable development zone in the centre of three interlocking ellipses: bearable, equitable, viable, the main aim being to avoid danger to the workforce or the public.
There is sometimes opposition to quarries, and public hearings, being adversarial often make matters worse, so the solution is to engage the public from the beginning,
Ruth concluded by referring us the 2014 edition of: A Quarry Design Handbook, and giving us her email: email@example.com.
Our trip focussed on the exploration of the chalk of the Flamborough Head area of the Yorkshire coast, encompassing the geological processes that formed the sediments and those that created the range of tectonic structures which affect the fracture porosity and permeability of the chalk. Understanding the chalk is very important in engineering terms for many of the big projects that are being undertaken around Britain, the North Sea and into Europe. We were very privileged to have Rory Mortimore as our leader this weekend as he is one of the leading experts on all aspects of chalk geology and he had prepared a comprehensive set of notes for us.
Our first visit was Reighton Gap. After a slow stroll down to the beach we listened attentively to an extra safety talk – basically be very careful where you walk; sticky, plastic brown boulder clay can be hidden under the sands and the unwary can be caught and held fast. Rory had seen this happen to a member of a previous group and with the tide rising fast the rescue, though successful in the end, proved to be difficult.
We were given the outline of the geology that we were to see during the day and walked along the beach to see our first exposure. The first discussion was not about the chalk and its derivation but the glaciation that came later and affected the modern landscape. We looked at a small grey boulder of Carboniferous Limestone with Lithostrotion coral fossils (Figure 1).
1. Limestone with Carboniferous Lithostrotion fossils
This boulder was brought down by the glaciation in the area as was the till that we looked at next. The range of pebbles on the beach, the structure in the till (Figure 2) and the lineation of the long axis of the pebbles is the basis for evidence for the origination and the direction of travel of the ice sheets.
2. Structure in glacial till
The next feature that we looked at was the colour of the flints on the beach, these were much greyer than the very black flints that we are used to seeing in the south of the country. The differentiation in the colouration, caused by differential amounts of organic material in the sediment, is used as a diagnostic tool to determine the origin of the flints. The purer the chalk the blacker the flints. This can be used to inform geologists and civil engineers about the likely structure of the chalk in which they are working and could form the basis for discussion about building techniques and the hazards that they may encounter.
The next stop was to look at the structure of the sediments in situ in the cliffs. The first of these were the black marine clays of the Lower Cretaceous with tight isoclinal folding caused by later tectonic movements (Figure 3).
3. Marine clay with isoclinal folds
We moved along the beach towards Speeton cliffs up the section. We looked at younger, paler grey clays with belemnites and ammonites (Figure 4).
4. Fossil belemnites and imprints of ammonites
We saw clay pebbles with stylolites formed by pressure dissolution in the clay giving the pebbles the appearance of brains, somewhat solid, removed from a skull (Figure 5).
5. Clay pebble with stylolites
We then moved along the beach for our first look at the chalk. The Yorkshire chalk is much harder than the southern chalk and has different properties. This chalk is hard enough to remain as large pebbles on the beach and it has been used as building stone extensively in the local area. The clay minerals in the chalk are the basis of the stylolites that appear as delicate grey convoluted pencil marks along the face of the cliff (Figure 6).
6. Stylolites in chalk
These would not be found in the softer southern chalks. The periglacial freeze-thaw fractures are the conduit for the movement of minerals through the rock. We were treated to views of branching networks of thallasinoides focussed around animal burrows formed when the chalk was still soft and unlithified (Figure 7).
7. Flint thallasinoid burrows in chalk
There were also grey tabular flint veins which are stratigraphically consistent beds which are fractured with calcite veins. These are very useful markers for engineers and surveyors to inform them about the surrounding sedimentary structures.
The red chalk at the base of the cliff contains brachiopods in filled with crystals, very important as an analytical tool for geologists who can work on single minerals to build up a more comprehensive understanding of the chalk. These bands are one of the five phases of sedimentation of the chalk. The reddish clay (Figure 8) bands represent oxic and sub-oxic phases of deposition approximately 165 Ma. These occur at the base of the Ferriby chalk formation and lie directly on the Speeton clay at the top of the Albian. The Speeton clay is not found below the Humber.
8. White nodular chalk in reddish clay
Further up the succession in the Cenomanian and Turonian stage of sediment formation the chalks become progressively greyer and then white as the conditions of deposition become more anaerobic thus changing the communities of bacteria in the sediment. The Cenomanian stage extends in the cliff up as far as the black band which is a traceable marker bed between the Ferriby Chalk and the Welton Chalk, representing the base of the Turonian stage. The next key marker in the Speeton cliffs is the ledge of flint 5 m down from the top which is also traceable and represents the boundary between the Welton and the Burnham Chalk at the base of the Coniacian stage (Figure 9).
9. Prominent flint band boundary marker in the chalk cliffs
The final discussions of the morning were the origins of bioturbation highlighted by flint on a large boulder from higher up the succession, the formation of the pipes in-filled with calcite and glacial tills and the spectacular giant paramoudra flints from the sediments of the Turonian stage. Bioturbation can only take place as the animal community moves and feeds before the sediment has lithified. We are left with the traces as the sediment hardens into rock and chemicals in the sediment pick out the burrows and subsequently produce the spectacular patterns of flints that we see (Figure 10). The pipes that we saw were formed as water dissolves the calcite leaving a sinkhole and then redistributes the mineral on the side of the pipe which then fills with glacial till which then gets washed away leaving the original hole.
10. Flint burrows in chalk
The giant paramoudra flints are the most spectacular of all. They can form columns up to 5 m long and the ones that we saw on the shore were 30 to 50 cm across. They often retain a chalk core representing the original burrow and retain their shape as the flint grows around it. On some of the cross-sections it is possible to see what look like growth lines in concentric circles. Our discussion about the origin of these flints was very interesting and too long to include here but there is a lot of information to be found on the internet.
That was our first morning, the weather was kind to us and thanks to Rory’s planning the tides were too. We all felt that we deserved our lunch after the walking and the brain work too.
After lunch we went south and east to Flamborough Bay, starting in Great Thornwick Bay (Figure 11).
11. Tectonic ridges in Great Thornwick Bay
Here after tea and cake (some formed of piles of different coloured strata), we saw glacial till over the chalk, the till filling vertical pipes formed in the Devensian. Below the till was frost shattered chalk, over unweathered chalk. The local tectonic forces formed primary conjugate fractures (these can be reactivated to get oil to flow for extraction under the North Sea). The conjugate joints formed from early slipping in the chalk deposits, tectonically similar to southern England.
While there we also saw a seal, gannets, guillemots - and Vulcan Bomber. On the beach there are semi continuous lensoid flints and inoceramid fossils in the Welton Chalk. This is equivalent to the southern Newpit Chalk. Flints are only found here and in southern England when moving out of clay rich zones into cleaner chalks (e.g. into Zigzag chalk in south) as clay deposition is reduced, due to tectonic or tidal changes, or as the chalk deposition area moved further away from land.
Laminations and stylolites are seen in the northern chalk, which is more thinly bedded than that in southern England, and also the Ferriby chalk, due to the greater number of flint and marl seams. This can be wrongly classified as boreholes cutting heads tend to fracture chalk when going through flint, making the chalk appear more fractured, then recorded at a lower than actual strength, then leading to more expensive designs with piles much longer than needed.
The glacial and periglacial features are from the last ice age, the Devensian, and include till (diamicrite) on fragmented chalk. This formed in periglacial conditions by the action of freeze / thaw before and around ice fields and glaciers. More modern features are the caves along the side of bay: these are fracture controlled, with roofs supported by the flint bands. There are visible marker beds of clay seams, scattered fractured flints and marl seams and big flints. The sequence seen here can be traced south of the Wash as triple tabular flint, and is mappable as a landscape feature. This feature correlates cross country to the Grimes Graves in Norfolk, and represents the Turonian flint maximum.
After this we went on to North Sea Landings, and while some went to watch the last few of the nesting puffins from the cliff path, or drink tea, or eat ice creams, the rest went down the very steep road and launch ramp and into the bay. In the north cliff was a visible marl seam of green clay (the Ulceby Marl (Figures 13 and 14), a key marker in the Upper Turonian of Europe).
13. Ulceby Marl at North Landings
14. Rory standing in front of the Ulceby Marl
These marl seams correlate across North West Europe and form biostratigraphical boundaries, thus assisting both the mapping and understanding of the chalks. On the southern cliffs some were distracted by seeing a solitary puffin. Rory explained the principles of geophysical microresistivity logging; larger readings come from from less resistance from softer rocks. Once correlated with boreholes these logs can determine flint sizes and thus identify marker bands. The marls include ashfalls, and as these include radioactive isotopes they can also be logged using gamma signals. As they are instantaneous they can be used to date layers in the 90 Ma old rocks to within a few thousand years.
15. North Landing
North Landing (Figure 15) is located in a modern valley, with joints opened by stress release. The conjugate fracturing seen on the south side of the bay was caused by layers sliding between marl seams. The south side paramoudra flints (Figure 12) are from the same horizon as seen in cliff fall debris at Speeton this morning, and as they are denser than the surrounding chalk and they sank into the beds below.
12. Paramoudra flint
There was a visible pyrite centre and hole from softer fossil then a hard zone. Also in the flints were white patches eroded into cavities to form carious flint, in very laminated chalks containing oysters and sponges.
24. Oyster beds
Once we got back to the hotel, over tea, coffee or beer, Rory set out to summarise the day and explain the formation of flint.
Summary of today: in the morning at Speeton and Reighton we looked at the red and Ferriby chalk at the bottom of the Cretaceous – Speeton is Lower Cretaceous, and differing from the chalk of the Midlands, Southern England and north of the Humber due to the axis of sedimentation along the Market Weighton structure. In the afternoon, we went up section, to pass through the Welton and into the Burnham chalk. Starting at the Santonian Flamborough Beds we get progressively younger, these being correlated by ash beds and microfossils, to give a one metre accuracy between borehole and exposure logs. The chalks here experienced two phases of fracturing and two phases of uplift.
Formation of flint: The shapes of the flints reflect the sea floor burrows, and flint form by bacterial and chemical processes below the seabed. In decomposing buried organic matter, aerobic bacteria remove oxygen and form anaerobic conditions, and then sulphate reducing bacteria generate hydrogen sulphide gas which migrates upwards to mix with oxygen sinking from sea bed biological activity. These meet in the “mixing zone” – a local area of acid conditions which dissolves carbonates and precipitates silica. The only silica mobilised is that already present the mixing zone, and is precipitated around the outer walls of the burrows, thus the flints formed are larger in size than the original burrows.
Paramoudra flints form in the same way, but vertically around large trace fossils. Tabular flints are found in the northern chalk province, where the permeability and porosity are different to the southern chalks, and form around large areas of vertical burrow networks. Northern flints are different from southern, as they form in thinner layers, with narrower bands of flint closer together. Continuing sedimentation raises the mixing zone, and when a marl seam is deposited this seals the sea bed and flint formation ceases. The more the marl seams, the slower the flint formation as clays remove silica into themselves.
Flints form very early in the sedimentation process, thus the flint and chalk fracture at the same time. Sheet flints form on early fracture surfaces. Silica in chalk is in the form of opal CT, which is unstable, and when buried and heated to 40°C it undergoes a phase change to chalcedony (quartz silica), flint formation is a gravity driven process, parallel to, but below, the sea bed. Compare this to marls and hard beds which form on the sea bed. The silica comes from sponge spicules, but flint is formed chemically.
Northern flints are paler as there are more organics and impurities – colour is related to density which is related to the amount of impurities. The underside of horizontal flints have iron pyrites as the process started there, thus paramoudras have pyrites inside the centre, where flint formation started in them. It is thought that the paramoudra was a deep sea worm, which filtered fluids by pumping them through itself to feed, thus changing the local chemistry, porosity and permeability – providing the conditions for later flint formation. Often a vertical section of a paramoudra will show a central trace fossil, surrounded by flint, then chalk, then more flint, all in concentric layers.
Rory’s new book "Logging the Chalk" became available last month – a full guide to the features seen in chalk and how to log and understand them.
We set out from the hotel on a cold wet morning, suitably clad, but by the time we reached the Lighthouse car park at Flamborough Head the weather had cleared. We set off down the 100+ steps (Figures 16 and 17) and stopped at the viewing platform near the bottom where Rory gave us an overview of what we were about to see. The bay is controlled by a very big fault system coming through on both sides and in the middle of the bay and the beds are beautifully bent across the platform.
16. Folded section by steps to Selwick Bay
17. Steps to Selwick Bay
Here as on the previous day we have a lateral moraine, tills on top of the chalk which is washed down into sink holes with isolated blocks of chalk and caves developing as a result. There are a number of very interesting features which can’t be seen elsewhere in the UK. Where the big fault system comes on shore we have vertical bedding, a thrust system causing reverse faulting and ramp structures and in addition to all this we have lots of slump bedding in the chalk. This is all shown in the diagram ‘Selwicks Bay tectonic structures, modified from Starmer 1995’, which helps us to identify the range of structures present. Marker beds were found using fossils such as inoceramid fossils (Figure 19). There are not just vertical throws but strike-slip components as well. Using lithostratigraphy and biostratigraphy together one can work out the tectonics and date the events. The same fault systems go through the whole of the North Sea. This is a very important area for the oil industry as it is the only place where these systems can be studied.
19. Inoceramid fossils
We then went down to the beach starting at the Southern end. Here we could see beautifully rounded (indicating slow erosion) cliffs of relatively thinly bedded very white chalk with lots of thin marl seams (Figure 20).
20. Thin Marl seams
This is the Flamborough Chalk formation, in Southern England the equivalent would be the Newhaven formation which has marl seams and flints as well. Apart from 2 bands of white flints (Figure 21) in the basal Flamborough Chalk Formation there were no flints.
21. White flints
We then moved further round where a big frontal fault came in creating near vertical bedding and we saw some beautiful calcite crystals (Figure 22).
22. Calcite crystals
The rocks here had really suffered, cracked in all directions but there was a pattern of fracturing. The cracks went right through and we could see the flints going through which could be used to measure the displacement through the fault. The beds became progressively vertical turning up the structure, a classic example of a fault. There was dark colouration which is caused by hydrocarbons which have leaked along the fault zone, these would be permeability pathways for fluid flow in reservoir area of the North Sea. This would be of interest to the oil industry. We could see the flint band stepping up. Some of the fractures go very deep, down to the Trias and deeper. Pathways bring up deep circulating anoxic fluids. There were phases of tectonic movement, each migration would help the fluid up.
In the area just beyond the steps we could see rock sandwiched between 2 thrust planes, it was buckled up almost like soft sediment deformation with blocks of chalk folded in there. In this area we could see that House Martins were nesting in the cracks in the chalk and also Gannets were flying along the coast to and from the gannetry at Bempton Cliffs.
Rocks are folded and stacked on each other. These types of formations are a result of compressional tectonics, everything is being squeezed and sheared. Interestingly it is compressional along big strike-slip faults. The thrusts come on shore on splays off the strike-slip fault. This happens all the way under Southern Britain. This process only started in the Upper Cretaceous. Prior to this we had basin formations produced by tensional forces. There was a change in the stress field right across the globe, this was a major global event caused by plate tectonics associated with the break-up of the super continents. In this area this switch occurred in the Santonian in a period of only 2.5 Ma. We saw low-angle conjugate sheets typical of this formation.
By now the tide had receded and we were able to explore the beach area and the other side of the bay. We found stylolites on the surfaces of the fractures. Rocks which may have been slightly tensioned became strongly compressional and the switch of stress fields within the rocks created surfaces on which the stylolites could grow. We also saw more of the thin marl seams typical of this chalk formation which are marker beds which could be traced way outside these big structural zones. We also found areas where there were ‘slickensides’ and grooves, where there had been horizontal movement between rock layers. We found vertical cracks filled with calcite and big shell beds containing Inoceramid fossils (marker fossils) and other fossil remains including ammonites.
Further on we saw beautiful areas of slump bedding. Finally we visited Molk Cave (Figure 18) a rather spectacular structure formed as a result of erosion and the till falling down sink holes as described earlier.
18. Inside Molk Cave
We then returned across the bay and admired the beds bent across the platform which we could now see as the tide was out. We mounted the steps to the car park after a most interesting morning.
The old lighthouse at Flamborough—The original lighthouse is an octagonal chalk tower built in 1669 and is one of the oldest surviving lighthouses in England. It was designed to have a brushwood or coal fire burning on the top! It was restored in 1996 at a cost of £100,000 and 20 tons of chalk was used to replace the badly corroded North face.
“It’s going to be fun, this little bit!” — Rory
Paleo valley - walking southwest along the cliffs we could easily see a variety of deposits including chalk fragmented and tightly folded from tectonic activity, tightly folded, repeated areas of broken chalk going up the cliff, other materials including glacial till, and outwash gravels at top.
Rory posed the questions that industry in the North Sea would be interested in regarding these formations. What minerals are on the margins? How extensive are the fractures? He told us this is the only valley where all these deposits are visible, and he tries to convince industry reps to actually come see them to understand the structures.
Overall the whole valley is probably fault controlled, with two orientations related to the faulting from the Dowsing Fault system.
We walked further southwest with instructions to find fossils in order to date/age the sediments. Particularly to find a key index fossil Marsupites testudinarius. Members found: loose finds of Devil’s Toenails, echinoids (including Echinocorys elevata), sponges from the Flamborough sponge beds, belemnites in the cliffs, and cup-shaped pelagic Marsupites in the cliffs. The latter was proof of the difference in texture between the northern and southern chalks - the chalk was actually too hard to hammer out the fossil.
Finally we found a Marsupites testudinarius in the cliff. It has a reticulated structure like grooving. There is a clear shine from calcite in the cleavage planes. My notes fail me here, but I think Rory said this was a way to differential between echinoids and inoceramids when finding fossil fragments.
The question was posed as to why the chalk is less massive here than at previous sites? Cliffs contain more very thin marl beds with thin beds of chalk between them called “tile stones.” The more massive pure white chalks are only further above where there are no marls. There have been suggestions that the marl beds are from local dissolution. However, this makes no sense since the marl seams can be traced and retain their structure over large distances. During this period there was more volcanic ash, possibly North Sea activity, and magnetic field switching.
There was evidence of tight folding and lateral movement along marl seams, and even a Quaternary fault (Figure 25). So these faulting systems continue to be active. Visible on the current beach are a series of rolls and swells: tectonic rolling, part of a whole series of anticlines along the coast. We also saw some strata bound structures such as faults and marls within a bed.
25. Quaternary fault, Dane's Dyke
Rory set out to find visible sand - probably quaternary sand - which has been blown and reworked on the stretch of coast. A member finds it and goes to take same to see that it is indeed sand and not soil.
(At this point a member spotted the first peregrine falcon of the day!)
A summary of the In the sediment along the side of the valley. Within this cliff we could see the upward sequence of:
The change from raised beach to glacial till shows climate change and resulting sea level changes. The raised beach indicates a higher, warmer sea level than today, while the periglacial fragments still near the bottom of the cliff indicates a lower sea level.
As we moved further seaward along the cliffs, Rory showed us the distinction between true stylolites and marl that has buckled. Stylolites are very closely spaced relative to the chalk, with jagged or sharp contact. Marl has wider spacing between it and the chalk because it was in place before deformation and deformed with stylolitic action.
23. Styolite surface, Dane's Dyke
We ended the day with a grand sponge fossil hunt - three dimensional fossils that could be found along the platform. Rough pyramid “tubes” with a chalk middle. Finally stopping for a well-deserved ice cream after climbing back up to the Dane’s Dyke car park.
Rory Mortimore led, and Sue Vernon organised, an excellent weekend examining the chalk of the northern province in Yorkshire, which was enjoyed by all. Compared to southern England, the tectonic structures are striking and much more dramatic, the chalk is similar but different, and this weekend put the deposition of the chalk into a broader context. The area of cliffs around Flamborough are a good teaching section and well worth a visit.
Mortimore, R.N. (2014) Logging the Chalk, Caithness, Whittles Publishing, ISBN 978-1849950985 .
Photographs courtesy of: Denise Atkinson, Gill Hetherington, John Lonergan and Tina Mammoser.
There was a poor turnout for this family day to Barton. This trip was aimed at newer members of LOUGS with young families and unfortunately we were unable to attract them. Two families (general public) had booked up but in the end none of the children showed. Nevertheless, for those of us who made it, we had an absolutely glorious day. At Barton you cannot fail to find fossils – the cliff oozes them and we were delighted to see several independent families out collecting. The children were very excited about their finds and Iain was able to give them the unused handouts which pictured the most common species – mainly gastropods and bivalves. I was particularly pleased to be able to identify a piece of turtle bone one little girl had found – she had thought it might be something special and at first I thought it was just a mud pattern but it suddenly dawned me that it was a piece of Trionyx which has a finer ornament than most and is found at Barton. She was delighted. Our group did not manage to repeat the find but we ended up with a good spread of species with the most coveted specimens being the sharks’ teeth.
It is difficult to make sense of the cliffs at Barton because they are very slipped (Figure 1).
They are Middle Eocene in age (c. 40 Ma) and Iain showed us the excellent stratigraphic column and cliff section that can be found on Ian West’s website (see below). Our main guide as to where we were in the section came from the nodules that we could see within the slipped masses on the foreshore. Much of the cliff is completely tumbled but every now and again there is a section that has come down en masse and retained its original bedding. We started our walk along the beach from the car park at Highcliffe and the first of these beds we came to had large nodules at several horizons (Figure 2).
This is Bed C and is associated with many fine fossils. Further along, we found nodules that were clearly the septaria of Bed E (Figure 3, another bed known for good fossils).
Then we came to the distinctive indurated red beds of Bed G (Figure 4).
These are crammed with small, cemented fossils and because of their colour are very distinctive. My sample from an earlier trip ended up in Earthlab in the Natural History Museum! It was a good spot to stop for lunch.
We walked right up to the sea defences at the Barton end of the cliff. The extensive works to stabilise the cliffs had failed in places (Figure 5) and it is clear that geology wins in the end!
As the tide became lower the hunt for sharks’ teeth became more intense. One tooth was found amongst the shingle, but surprisingly the 3 others were found in the cliffs. We returned to the car park over the top of the landslip where better-preserved specimens were found but this is not recommended except in exceptionally dry weather; there is always danger of further slippage – these cliffs are constantly on the move.
Later, as we sat identifying our specimens over a cold drink in the café (Figure 6) several people came up to us with their own specimens to identify.
We referred them to the websites below and would also recommend them to anyone who is planning on a holiday on the south coast. You don’t need a leader, but it is best to find a falling tide if possible and just walk along the beach looking in the low cliff with a trowel and collecting bag. At the lowest point of the tide it is worth looking at the edge of the shingle patches for sharks’ teeth – they go down really well, particularly with younger collectors.
Ian West, from Southampton University has a brilliant website explaining the geology of much of the South Coast. There you will find details of the stratigraphy and a diagram of the cliffs detailing which beds are found where: www.southampton.ac.uk/~imw/barton.htm
Alan Moreton has made an excellent catalogue of the fossils that he is continually updating. His identifications are confirmed by experts: www.dmap.co.uk/fossils/
Ted Nield's talk, based on parts of his recently published book of the same title, drew heavily on his family ties to the mining industry and communities of 19th and 20th century Wales. He reminded us of our links to the land via both the agricultural and extractive industries upon which the quality of our lives, and more intimately the lives of our ancestors until very recent times, rest upon.
It is this essential link that brings our present and recent past together with the deep past of the Earth, when coal measures and iron ores were formed within the planet. The extraction of Earth's minerals by man leads to a transformation of the topography – natural landscapes undermined on the one hand and covered over by waste from the extractive industries.
Ted's family lived in Aberfan, and Ted presented the Aberfan disaster of 1966 as one of the themes of his talk. He explained the events that led to the creation of waste tip 7 and it being placed in an unstable position on top of a previous land slip and also above a spring-line which was hidden from view. The action of the spring water, and the unstable surface on which the spoil was placed, lead to the collapse of the tip. The people who, through simple ignorance, decided to place the tip in position "did not read the evidence of the past". So the recent past, the earlier collapsed tip; and the deep past, reflected in the geology; results in the disaster of 1966 – which is now our past.
The second theme of Ted's talk was what he described as the outsourcing of extractive industries from the UK to places such as India and China. In restoring the memorial to his grandfather in Aberfan cemetery, Ted discovered that it was easier and cheaper to import granite from China rather than locally mined Welsh granite. He suggested that it is developing countries nowadays that bear the brunt of environmental degradation and exploited labour in the extractive industries. The root cause being that transport was too cheap as against the cost of labour in places such as Wales.
In the same way that spoil heaps piled above Aberfan lead to the death of many children, Ted concluded that perhaps that there was a price to be paid for piling up "atmospheric carbon" in the atmosphere.
Dr Ted Nield is the editor of 'Geoscientist', the magazine of the Geological Society of London.
Underlands: A Journey through Britain's Lost Landscape By Ted Nield (Granta Books 251pp £20).
The aim of this field trip was to study the Lower Cretaceous greensands used as building stones in some historic West Sussex churches, and to visit Marehill quarry.
We started at Pulborough station, collecting those travelling by train, and then set off for the Marehill sand mines, an SSSI geological interest, but managed for bats and owned by the Sussex Wildlife Trust. This is the only mine in West Sussex, surprisingly, and is an outcrop quarry, linear and shallow. The mines follow the dip south underground, under the stronger ironstones which form the roof of the mines. These were initially used to quarry the Sandgate Formation of the Lower Greensand (Upper Aptian, 115 Ma).
Cross bedding and iron staining in Marehill sand mines
The good sandstone is two metres deep, orange-brown, cross- bedded, iron stained and friable. The sand is fine grained, coarsening upwards, and formed in winnowing areas of the sea bed, thus the finest material was removed. The end result is self-supporting sand, ideal for moulding item such as wheels, and was taken by train to the Midland foundries. Mining finished after the last war, and more recently the mines were used to grow mushrooms. These rocks are part of the Pulborough Sandrock Member, an homogenous, friable, well-sorted, locally cross bedded fine grained sand, buff or yellow when weathered (and grey when not). This was used locally as a building stone, as will be seen.
Inside the Marehill sand mines
We then moved onto the twelfth / thirteenth century Wiggonholt church. This is a single room, with rubble walls and Pulborough Stone sandstone ashlar quoins. The roof is Horsham Stone (slate), the walls principally various ironstones and Pulborough Stone. To add variety, we were shown Roman tile from a nearby villa, and some flints.
Studying the wall at Wiggonholt church
We then had lunch at the RSPB Pulborough Brooks, thoroughly recommended and with splendid views (and food!).
After lunch we went to Parham church, in the grounds of Parham House, a classic Elizabethan country house built in 1577. The site of the former medieval village has yet to be found, but the church dates from 1545, remodelled in 1820. The walls are mainly Pulborough Stone ashlar with malmstone in the rubble walls, some sections have walls of flint, the roofs are Horsham stone. The Victorian refurbishment used an oolitic limestone, similar to Bath stone.
Parham church with Horsham stone on the roof
Then on to Greatham church, on the high ground in the middle of the Pulborough Brooks. This is again one room, twelfth century with rubble walls and Pulborough stone ashlar quoins. The rubble walls include ironstone, perhaps the local equivalent of the ironstone layer roofing the Marehill sand mine – we brought along a small sample to compare these.
Greatham Church with ironstone in walls
We then went onto Stopham church, eleventh century with an impressive Norman nave and chancel (but some Saxon style doorways). The chancel is constructed of larger stones than the nave, suggesting the east end was rebuilt from an apsidal end. Pulborough Stone was used extensively as ashlar and dressed stonework, and also as rubble in the walls. Ironstone and chert are a major part of the walls, with oolitic limestone, similar to Bath stone, used in Victorian repairs. The roof is again Horsham stone, and the chancel floor is Sussex Marble (with gastropod fossils).
We ended the day by walking along by the river Arun, just north of the historic Stopham bridge, to look at probable quarry sites for the Pulborough stone used in the church. And then back to the station and a vote of thanks to David.
Pilborough stone quarry near Stopham bridge
It was an excellent day, well explained, and good to concentrate on a small area and a just a few stone types, and understand their origin and use. And this report was made much easier by using David’s excellent hand out.
We met Lesley Dunlop, our leader for the day, at the Church of St Peter and St Paul in Wadhurst. The church is built of local sandstone from the Wealden beds and has a fine Norman west end tower with a newly restored shingle spire. Most of the church walls and windows dated to the 13th and 14th century with evidence of later buttressing, raising of the chancel roof and modern restoration on the south aisle hood moulds of the nave windows. The restoration blocks were almost certainly sourced from the nearby Phillpott's Quarry using stone from the Ardingly Sandstone Member of the upper Lower Tunbridge Wells Sand Formation.
Before entering the church Lesley showed us a large slab of fossiliferous limestone immediately south of the porch. Unfortunately the pavement here was too worn to identify specific fossils, but it was agreed the stone was not the local "Sussex Marble", but a similar thin calcareous horizon probably found within the Wadhurst Clay Formation.
Our reason for meeting at this church was to view the impressive cast iron tomb slabs inset into the nave and chancel floors of which there were about 30. The earliest found dated to 1617 and they continued in use well into the 18th century and represent the largest collection of iron floor memorials in the country. The majority commemorated the lives of Wealden ironmasters who lived in and around Wadhurst. Each slab was produced by carving a piece of wood with the desired design and wording and impressing the wood firmly into a bed of fine sand to create a mould. Molten iron was then poured onto the sand. On some iron slabs marks could be seen caused by disruption within the sand formed during the manufacturing process.
Not to disturb the local ladies with their preparations for harvest festival we vacated the church and inspected a select sample of the local grave stones in the churchyard. There were a number of different stones in use during the 17th, 18th and 19th century, but the majority appeared to be of local sandstone, although the provenance and beds exploited was, at the time, anyone's guess. A box tomb south east of the porch, and of undecipherable date, was found to have a greensand cover. Measuring about one metre by two metres the stone cover also contained areas of chert, which stood proud from the greensand, indicating the relative hardness and durability of these two materials to local weathering. It was speculated that the stone was from the Lower Greensand Group and probably from the Hythe Formation. The stone bore little resemblance to the beds found in Kent and may therefore have been brought to Wadhurst from Surrey.
From Wadhurst we made our way by car to Eridge Rocks, an impressive exposure of Ardingly Sandstone that forms an 800 metre escarpment up to 10-12 metres in height. This location is very popular with climbers and some of the marks and pits on the rock face were thought to be attributable to the climbers' endeavours. By the time we reached the rock face the weather had changed for the worse and we found ourselves standing in heavy rain, whilst trying to make sense of the geology and geomorphology around us. We discussed the evidence for the environment of deposition of the massive sandstone beds and noted small-scale channels and cross- stratification. The evidence from these features indicated a palaeo-flow from north east to south west, which fitted in well with the perceived wisdom of braided channels draining north to south during the Lower Cretaceous from an upfaulted block of largely Palaeozoic rocks, known as the London Platform. Similarities were seen between the rocks at Eridge and those we had just viewed in the churchyard.
We also discussed the formation of honeycomb weathering on the sandstone faces. In places the weathering was very pronounced, but elsewhere, and in very similar looking rock, it was non-existent. Lesley thought the presence or absence of honeycomb weathering was due to subtle differences in the cement (silica, calcareous and/or iron) that bound the quartz grains. Had the weather conditions been more amenable we may have seen more of the escarpment, but with lunch coming-up and the weather having taken a turn for the worse, we made our way back to the cars.
Production of Iron in the Weald of Kent: From before 2000 years ago with peaks during the Roman occupation (43 – 410) and the Tudor to early Stuart times (1485 – 1603) until the industrial revolution. The area had the ingredients of iron rich beds in the Ashdown Sands strata, plentiful woodlands for production of charcoal and numerous streams for the water powered bellows supplying oxygen. Before, blast furnaces was the use of bloomery furnaces consisting of small stone and clay mounds forming ovens in which iron producing rocks, charcoal and oxygen are heated and poor quality iron pooled at the bottom. The introduction of the first blast furnace was in 1496. Originally, large stone structures where the raw materials are added at the top and the water powered bellows provides oxygen at the bottom. The lighter waste product, "slag", is tapped off from the furnace at a higher point than the iron at the bottom which flowed into a "sow" sand mould. The cooled sow shape of pig iron would be transported to a nearby forge for refining.
The afternoon started with us all meeting at the car park on the B2188 on Ashdown Forest. The rain was pouring, (one of the few occasions that the forecast was correct), but we were all prepared with our waterproofs.
It was pointed out that the forest was the source of needed charcoal and when this source became scarce, it was one of the reasons that the iron industry moved north. We walked (slipped?) down into a valley where Lesley showed the area that was once an iron producing furnace in the 1500 – 1600 centuries. We saw the red, iron rich stream that showed the remains of a dam that made the area into a pond supplying the water power.
Behind us was a steep bank where the furnace could have been placed with access at the top for the placing of the raw materials into the furnace. No building remains could be seen because it would be re-cycled for subsequent buildings in the area.
Limestone is a raw material in a blast furnace production of iron. The calcium in the limestone combines with unwanted silicates to form a purer iron. Maybe, the limestone was transported into the area from the thin Lower Greensand Beds surrounding the whole of the Weald.
Before a search for slag, there was a chat about the source of the iron rich beds that formed in the clay from sediments from the London Platform. It was noted, that the iron wasn't washed out as seen in the stream here, but chemically concentrated iron layered in clay seams. A walk across a past pond which had now in filled but extremely boggy we came to an area in search of slag. None was found here but a fine example was found in the stream.
Newbridge Furnace and Forge
Further into Ashdown Forest we were shown the site of the earliest blast furnace in 1496, built of stone. As many as 200 immigrants were employed from Northern France for their knowledge and expertise in this new iron production method. The geology of Northern France is the same as the Weald. Evidence of earlier bloomery type furnaces has been found here.
We were shown the earth workings of a mill stream and high bank. The stream flowing beside was a fine source of slag. Approximately, 3 cm angular, dark brown to black rock pieces with numerous holes and a bulbous appearance.
In the beautiful surroundings of Ashdown Forest we said our goodbyes. We had an enjoyable day about an interesting subject with surprising sites to enhance and see. I would like to give thanks to Yvonne and Lesley and to our friendly group.
Stewart, Senior Lecturer in the School of Environment and Technology, University of Brighton, aimed to introduce us to the global advances that have taken place in our understanding of silcretes and the formation of Sarsens andPuddingstones not only in southern Britain, but, as demonstrated by a world map, in numerous parts of the globe, and for the purposes of this lecture, particularly the Paris basin, southern Africa, and Australia, and illustrated with pictures of Stonehenge, 'streams' of sarsens in Wiltshire, landscapes in the Kalahari and New South Wales.
We started with definition: silcrete is a highly silicious indurated material >85% silica, formed at or near the Earth's surface by low-temperature physico-chemical processes. They can be classified according to fabric: grain-supported, floating, matrix or conglomeratic. Genetic classification divides them into fluvial, lacustrine. In-situ, capillary, pedogenic (soil-forming, from Greek pedon = ground)*, and detrital.
Earlier ideas (1980s) suggested the formation of a duricrust, a continuous carapace, formed in a subtropical climate with a stable, low-relief landscape in the Palaeogene. More recently a genetic classification has been developed in the context of basin evolution. Silcretes can be divided into pedogenic, and ground-water or drainage-line varieties. The pedogenic variety has a complex profile, with a columnar layer overlying a granular horizon, above clays, whereas the non-pedogenic has a simpler profile.
An example of the non-pedogenic variety in Botswana formed below the surface, dependent on ground-water flow above the valley. In the Paris Basin, there are pedogenic silcretes in an early Eocene palaeosurface, and groundwater silcretes in various sand formations. A tropical climate may not necessarily be implied.
Turning to the southern UK, we should abandon the search for uniformity. Pedogenic silcretes are found in the East Devon-West Dorset plateau, whereas in the East South Downs they are non-pedogenic. There are at least two phases of silcrete formation in the Palaeogene and the Neogene, and multiple layers are possible with depths of 5 m to 100 m. Many more detailed investigations are needed.
*Apologies to the more learned, but I had to look it up!
Having started the final presentation of S276 this autumn, I was really looking forward to the London OUGS Herne Bay field trip where new geology students are given an introduction to the subject. The day is spent by sandy cliffs along the beach from Beltinge to Reculver and manages to include observation skills, soft sedimentary rocks, hard igneous rocks, a few fossils, weathering and erosion and the use of natural resources.
After gathering in the Beltinge car park and paying our £3, we were given handouts with details of the local geology. We were also able to borrow hand lenses and grain size cards if we hadn't brought our own.
Our first activity was to collect pebbles of all shapes and sizes from the beach. We observed the range of material that we'd collected in just a few minutes and thought about the effect of the tide on shaping and sorting the pebbles.
Collecting pebbles on Beltinge Beach
For our second activity we went into Bishopstone Glen and, standing well back from the cliff itself, observed the strata visible in the cliff face. We were instructed in how to take notes (write down the date/time, precise location, and weather because you will not remember these details later) and how to make observations (texture, size, colour, order of the layers). Then those with hard hats approached the cliff face to verify some of our observations. The emphasis was on attention to detail and taking note of what you were seeing, not what you thought you should be seeing or trying to match the view to a diagram.
We then returned to the top of the beach to consider sea defences. This area near Herne Bay is prone to erosion and the council has invested in different types of sea defences such as concrete at the bottom of the cliffs and hard rocks at the top of the beach. We could see protected areas where there was housing and unprotected areas where there was not. We also took the opportunity to get up close to some hard rocks, specifically larvikite which had been brought in from Norway to form part of the sea defences and we used hand lenses to look at the crystals in the rocks and observed the different colours in the intrusions.
We walked up the hill to an area where we could see the highest strata at this site. Bits which disintegrated into handfuls of sand were chipped off and passed around. This was an opportunity to use the grade card from the S276 materials to compare grade size and density in two different soft rocks.
After a short drive to Reculver, some had lunch in the nearby pub while others picnicked in the ruins of the ancient church. After lunch, we gathered around the Millennium Cross and observed the weathering on the wind-facing side which has almost completely obliterated the lettering in just 14 years.
The Millennium Cross at Reculver (looking at differential erosion)
Then we walked around what remains of the wall of a Roman fort. We were able to identify some of the rock types, for example chert, and considered where the materials for the wall had come from (mainly local) and gone to (many were taken for later building projects such as the church). Similarly, the remains of the church within the walls of the fort provided the opportunity to examine the huge variety of stones, as well as Roman tiles, that were used in its construction.
Standing on the edge of the fort site we looked to the east where land had been reclaimed from the sea. Previously the area had been a channel, and as sea levels continue to rise, the sea wall will either need to be heavily fortified or the sea will be allowed to return. Looking to the north at an area where the Roman fort used to be and which is now underwater, we considered more sea defences. Here limestone rocks (some with small visible fossils) were piled up to protect the concrete wall that protects the site with the 12th century church towers.
We walked back down towards the beach where we could view older strata than we had in morning and an intriguing layer that turned out to be shells from a Roman rubbish pit. Finally, we gathered around a stone that had been brought from France to form part of the sea defences. This stone had a fossilised dinosaur footprint. We could see where the three- toed dinosaur had pressed its foot into the mud, the print had then been filled with sediment which formed the fossilised footprint when the surrounding, presumably softer, sediments had been removed.
Geoff Downer and the French dinosaur footprint
This was the end of the enjoyable and instructive introduction to geology in the field. I certainly learnt quite a lot and am looking forward to recalling things we covered on the day as I continue my S276 studies.
North from hotel along beach and flood alleviation in Swanage
The group emerged to an overcast but dry and mild day on Saturday after seeing and hearing about the Jurassic coastline from Alan Holiday the previous evening. His tour of the World Heritage site had shown us what to expect for the rest of the weekend.
After breakfast, we walked down the steps to the beach directly from the Grand Hotel. We then headed north, initially along the sea wall passing beach huts and then onto the beach proper. We were heading towards the cliffs of Ballard Point, which is the end of Ballard Down as it finishes in the sea.
Swanage is an east facing town that lies on Wealden Beds of sand and clay rocks, and we were heading northwards up the succession of lower greensand, gault, Upper greensand towards the chalk that makes up Ballard Down. The strata are gently dipping northwards, steepening as we walked further north.
The Wealden mix of sandstone, siltstones and clays was deposited in rivers and lakes between 120 and 139 million years ago in the tropics. This mix of porous/permeable then impermeable layers means that the cliffs are prone to mass movement giving rise to the dangerous landslips. As we walked past the relatively low cliffs we saw the considerable effect of wet winters over the last three years. Much material had been brought down along this coastline. Attempts to arrest this movement to help protect the Pines Hotel (Figure 1) could be seen along this stretch. Geotextile that covers the surface, the use of ground bolts and drainage pipes through the cliffs had been done but one wonders whether this has really helped. The drainage pipes had broken and the geotextile had been ripped. The building at the top of the picture (part of the Pines Hotel) also looked in a very precarious position.
1. The Pines Hotel above the landslip
It is debatable whether there should be hard engineering to protect this coast as it is a world heritage site and the coastline is a product of erosion. Obviously, where there are settlements and danger to human life such as in the Swanage area there can be attempts to mitigate this erosion. However, in the longer-term there is nothing that can be done to stop the effects of change and things are going to be lost. See http://jurassiccoast.org/ conserving-the-coast/coastal-erosion-and-coast- protection for examples of how the Jurassic coastline is being conserved in many places.
From this area of landslip we walked along the beach further, climbing over the wooden groynes. Toward Ballard Point we could see the effect of the 2000/1 winter with a large chalk scar in the cliffs (Figure 2).
2. Chalk scar in the cliffs
The immediate cliffs showed laminated sandstone cliffs (Figure 3) which had had iron oxide percolating down helping to cement them.
3. Laminations in the sandstone cliffs
The photograph (Figure 4) shows Liesegang bands in rocks. These had been produced by groundwater within the fluid-saturated rocks.
4. Liesegang bands
After walking some way along the beach we peered over a groyne to find we could go no further towards Ballard Point as the tide was higher than expected. Fortunately, there was a stepped incline up a gulley allowing us to climb up to the South West Path on the top of the cliffs. Just before reaching the summit there was an information board explaining the cliffs and helping people make the right decisions.
There was a slight whiff of oil by the board, indicating that the sandstone in the area contains disturbed oil – but nothing of significance. At the board were signs indicating the South West Path north to Old Harry’s Rocks or south to Swanage. Because we had been diverted prematurely, there was a change of plan: we would walk back to the hotel to pick up some cars and drive into Swanage where we would look at the flood alleviation scheme for the town.
Because Swanage lies in a dip between high land of stronger rocks to the north (the chalk of Nine Barrow Down) and south (limestone of the Purbeck beds), heavy falls of precipitation funnels floodwater through the town. It does not take long to get into the Swan Brook and its tributaries, which very quickly surcharges. In 1990 Swanage was flooded in the centre around the railway station and main road out (A351 – Victoria Avenue). The area was under seven feet of water, the town was closed to traffic and many people evacuated by boat.
This led Purbeck District Council and the Environment Agency to produce a flood alleviation plan in Swanage by catching water into suitable areas. The scheme was started in 1993 by building a channel underneath Victoria Avenue to an additional discharge point reducing flooding, with the whole scheme being completed in 1997.
We parked by King George’s Field in the centre of Swanage to look at the scheme. The short stream there rises and falls rapidly with heavy rainfall but we could see from the small bund we stood on how these bunds and railway line act as barriers to water allowing it to flood the field. A sluice gate is used to regulate the water and thus the flooding. The man-made channel with 60 m culvert was built under the town with the sluices that can be opened. A series of wide flood channels were built adjacent to Swan Brook’s original channel that can take the water away. Beyond there, we saw the further fields that could be used as reservoirs for the floodwater.
After completing Plan B, we went into the town, buying lunch of excellent looking pasties in the local bakers before taking it to eat by the coastal lookout station at Peveril Point.
We had our picnic lunches at Peveril Point, the tip of the headland enclosing Swanage Bay to the south. There was a Visitor Centre below the Coastal Watch tower, with poster displays about the ecology and environment of the area, including maps of the sea bed locally. This had been mapped by multi-beam sonar during the Dorset Integrated SeaBed Survey (DORIS) (Figure 5) and showed the variations in depth in false colour. It was striking how clearly the hard strata revealed the anticline east of Durlston Head, plunging to the east, and how linear side-steps of the strata showed up the faults. There was a sense in which more data on structural geology could be obtained from looking at these displays than from terrestrial geological maps.
5. DORIS bathymetry map off Durlston Head
The plan for the afternoon was to walk the whole section south to Durlston Head, examining the Purbeck succession of the Lower Cretaceous and the Upper Jurassic. Looking east from the Point, the lines of rocks running out to sea clearly showed a tight syncline (Figure 6).
6. Syncline off Peveril Point
The bed right at the core of the syncline, just above the surface of the sea, was the Purbeck Marble. This is not a metamorphic rock but a biosparite which occurs in different colours, red, green and blue, and it’s only called marble because it can take a smooth polish. This rock has been used for decorative interior columns in many local churches. Several metres out from the core of the syncline on both sides, outcrops of Broken Shell Limestone, or Burr, continued out to sea creating a strong surf line where the outgoing tide churned up the water. The surprising thing was that there should be a syncline here at all. The northerly dipping Wealden Beds which we had seen during the morning suggested that this should rather be an anticline. This is indeed the case, with an overturned anticline at the top of the Portlandian restoring the regional dip to the north. The observed syncline is just a small local feature due to the Alpine Orogeny and is not uncommon here, as seen dramatically in the Lulworth Crumple.
The Purbeck formation straddles the Tithonian (Upper Jurassic) and Beriasian (Lower Cretaceous), between 145 and 140 million years ago. The setting was an extensive lagoon system, in which salinity varied between brackish and hyper-saline. The climate would have been Mediterranean, warm with periods of very high rainfall. There was a limited range of species present, which varied over time with the changing conditions. The position of the Jurassic-Cretaceous boundary towards the bottom of the formation is not clear. At one time it was taken as the Cinder Bed (actually crushed oyster shells rather than cinders, but such is geological nomenclature!) but accurate dating is not possible due to the absence of suitable dating fossils such as ammonites in the lagoons. Nowadays, the J/K boundary, which is defined in Southern France, is thought to correlate better with the Soft Cockle gypsum bed lower down in the sequence.
Getting down to the beach was a bit of a scramble and some members of the group decided not to risk it. Once down at sea level we found a jumble of fallen slabs, among which were the Purbeck Marble and slabs from the Unio Bed with gastropods and bivalves as well as the eponymous mollusc Unio. The in-situ limestone beds in the cliff, separated by looser clays and shale bands, were very difficult to get to (Figure 7).
7. Difficult walking below Peveril Point
I found it quite difficult to make progress over the limestone slabs and occasional vertical scrambles from one level to another, and I thought of giving up a couple of times. Only the commitment to doing the write-up for the afternoon kept me going. At last, after one member had fallen on the loose, slippery rocks (fortunately no serious harm), Alan recognised that walking the complete section would be a bit too much considering the age of this group and the state of the tide, and decided to abandon the attempt. After short discussion back on the cliff top at Peveril Point an alternative plan was agreed. Plan C (plan B had been used during the morning) was to go and see some dinosaur footprints.
We then drove back through Swanage and Langton Matravers and parked where there was an excellent view north-east across the broad valley of the softer Wealden Beds to the chalk ridge running between Corfe Castle and Ballard Down, Alan pointing out the visible geological features. Walking through the small village of Acton we noticed some of the buildings roofed with tiles of neatly cut thin-bedded limestone and passed piles of quarried limestone slabs from the Purbeck formation. Trace fossils and fish teeth were identified in some of the slabs. Then after crossing a couple of fields we came to a large patch where quarrying had removed the upper beds to a depth between 2 and 3 metres and exposed the top of an anticline and a limestone bed on which many Sauropod footprints (Figure 8) were found.
8. Sauropod footprints in an inland quarry
Quarrying had been halted at this point to preserve the footprints, although they are still exposed to weathering. Only a few of the prints showed the distinctive three-toe dinosaur characteristic and it took a great deal of imagination to see any coherent tracks.
These prints were either direct impressions or possibly from a softer muddy layer above which had been compacted by the weight of the animal and pressed onto the harder layer beneath. In one place a long narrow trough was thought to be where the tail had dragged through the mud. This sediment would have had to be rapidly lithified to preserve the traces in stone.
Still with time left during the afternoon, it remained only to find a good country pub to round off the excursion in typical geologists' style. Alan knew a very suitable location, the Square and Compass down the road in Worth Matravers. There was an outstanding view to the south out over the English Channel which is obviously the main attraction of this pub for summer visitors. The wind was getting up by now, however, which made it uncomfortable to sit outside too long. A back room at this pub held a small local museum with quite a good collection of fossils from the Purbeck, Portland and Kimmeridge. There were numerous ammonites as well as Ichthyosaur and Pliosaur specimens. Local archeology also featured, with mesolithic flint tools, some Roman items, and relics from ships wrecked on this treacherous coast. The pub also did a good range of locally produced cider which rounded off the afternoon nicely.
Our destination on Sunday morning was the south facing Kimmeridge Bay, where low cliffs expose the core of a shallow anticline, and fringe a dark wave-cut platform, exposed at low tide, with the Clavell Tower, a folly, moved back from the receding cliff edge in recent years, standing above the eastern rim of the Bay on Hen Cliff (Figure 9).
9. Clavell Tower on Hen Head, Kimmeridge Bay
Our visit to the bay was preceded by a visit to Steve Etches' home in the village where he exhibits his diverse collection of invertebrate and vertebrate fossils, their original position in the bay sometimes observed and noted for many years, before they are painstakingly retrieved from the strata following the shifting of beach deposits or cliff falls. Frequent trips to the bay result in Steve’s return with enormous numbers of smaller intact fossils but also with some fragments which are pieced together over the years. Some larger specimens are back-achingly removed in huge slabs of strata to preserve them intact as far as possible whilst others have been found at inland Kimmeridgian exposures. Once in his workshop the patient cleaning, study, conservation and cataloguing of finds has greatly increased not only Steve’s understanding of locally changing conditions during the Kimmeridgian which makes future retrieval of complete and scientifically useful specimens more likely, but the collection provides a valuable resource for detailed scientific research. Steve was happy to share his fossil hunting experiences with us, focussing on the development of his collection, highlighting several of the huge number of rare and outstanding fossils on display. We could have spent far longer with this knowledgeable and enthusiastic collector amongst his amazing display of impressively conserved specimens, including no less than 4 holotypes as well as several rare three dimensional specimens. Each of us came away with a particular favourite fossil or group of specimens from the wide range of local Kimmeridge fossils, we had seen. These ranged from ammonite eggs; tiny bones; fish fragments including articulated ray, heads of sharks estimated to be 3 or 4 metres long in total, Coelacanth, almost whole fish with stomach contents, many jaws with teeth and without, fish scales of varying sizes; to gigantic bones of marine reptiles including ichthyosaurs and marine crocodile vertebrae some showing the predatory bites of pliosaurs; and even a rare dragonfly wing - too many to list in full (Figures 10, 11, 12 and 13). We all vowed to revisit Kimmeridge before too long and once this important fossil collection is permanently housed in the prestigious new museum being built in the village.
10. Some of Steve Etches' ammonite exhibits
11. Recent Icthyosaur find
12. Whole fossil fish with stomach contents
13. Steve Etches' Museum exhibits
Leaving our cars in the cliff-top car park of the private Smedmore Estate we walked along the low cliffs to the now famous ‘Nodding Donkey’, which sits over the core of the anticline. Layers of anoxic marine and swamp sediments were compressed during deep burial producing oil deposits. The source rock is probably the Lower Lias clay, oil being trapped in the reservoir rock, Cornbrash, below the cap rock in the anticlinal fold.
There is evidence of Kimmeridge oil shales being exploited from Neolithic times with finds of locally produced jewellery and even furniture manufactured between the Iron Age and the Roman period. More recently records show Kimmeridge shale was used as fuel for glassmaking and the production of Alum in 17th Century; as fuel by the ‘Bituminous Shale Co’ of Weymouth in 1848; to make fertiliser in Wareham in 1854 and as gas to light the streets of Paris in 1858. Adit mining in the cliffs produced up to 50 tonnes of oil per month. The present well is the oldest site continually producing oil in the UK and dates from 1959 although the importance of the site was recognised prior to World War II. Today approximately 65 barrels of oil are produced daily, taken by road to Wytch Farm, the nearby Poole Harbour site, for stabilisation before being piped to Hamble near Southampton for distribution.
A quick scramble down the cliff path brought us to the beach and wave-cut platform below where many of the fossils in Steve Etches' collection have been found. The gently dipping anticline was clearly visible at this point, younging to the east, and picked out by the differentially weathered alternate layers of clay, oil shales, bituminous and calcareous mudstone, coccolith limestone and dolomite in the cliff (Figure 14).
14. Kimmeridge Cliffs, Kimmeridge Bay
These bands are believed to show cyclic sedimentation related to Milankovitch cycles. One dolomite band stands out as the lighter Washing Ledge Stone Band dipping from the core of the anticline towards the western headland and eastwards from high in the cliff to beach level and forms a ledge which stretches centrally far into the bay at low water. The other, the Flat Stone Band, faulted and outcropping at the cliff base forms a ledge on the wave-cut platform further to the west. The surface of the Flat Stone Bed is far from flat with slabs rumpling and thrusting over each other. It is thought the beds were laid down and dolomitised soon after deposition, causing shrinkage but then dedolomitised later but being confined by pressure from above the bed was rumpled laterally. The darker richly fossiliferous mudstone and shale ledges are very slippery when wet but all heads were bent low as these are the areas where ammonites and other fossils can be seen exposed at low water. Many both large and small were seen on this occasion, but many more are also lost forever each year, by the constant scouring of sand and pebbles carried across the ledges by the tide, unless rescued for all by Steve Etches and other authorised collectors frequently seen in this well-known locality.
After lunch we went back toward Swanage to Studland Head. A short walk from the village, took us to the headland and to see the Old Harry Rocks. These are a collection of chalk sea stacks and arches (Figure 15), named after a pirate (Old Harry’s Wife was a stack that has eroded away).
15. Old Harry Rocks
The coast here is gradually eroding, significantly last winter, but generally steadily as the dip in the chalk is nearly horizontal. A cliff fall from earlier this year has exposed an old shear fault (Figure 16) with slickensides.
16. Old shear fault with slickensides at Old Harry
Alan sent us some photographs of Ballard’s Point (Figure 17), on the cliffs just south of here, where the chalk is locally vertical (south of this, near Swanage, the dip is gently south).
17. Four photographs of the strata on the seaward end of Ballard Down. Demonstrating how quickly the dip changes moving north.
We ended the weekend on the sunny cliff top, with a vote of thanks to Alan for an interesting and enjoyable weekend.
Dr Adrian Glover, a marine biologist, currently a Researcher in the Life Sciences Department of the Natural History Museum, delighted us with an enthusiastic and lively account of current developments in our knowledge of the strange colourless life forms at depths of 2,500 m, far removed from sunlight. I say ‘strange’, but what was really surprising was the abundance of life, and the similarity of many of these creatures to familiar surface- dwellers such as crabs, shrimps and barnacles!
The discovery of this life flourishing so abundantly round hydrothermal vents is relatively recent. It was only in 1872 that HMS Challenger confirmed the existence of the mid- Atlantic Ridge, and the volcanic nature of the rift valleys within mid-ocean ridges was not understood till the mid- twentieth century. In 1977 the Galapagos rift was explored with a submersible and the creatures filmed, but with no biologist involved.
At 5,000 m in the Caribbean, life is swarming round the vents. Species numbers are low, but with high abundance. Studying the ecology is hard, because of the difficulty of keeping deep-sea animals alive away from their native environment. Without access to light or photosynthesis, these animals graze on sulphide bacterial mats using strange, toothed jaws.
One of Adrian’s specialist fields is the evolution of giant tube worms or Vestimentiferans, related to Pogonophera, and to Osedax, feeding on whale bones. There are over 10,000 species of polychaete annelid worms, some of which can feed from hydrothermal vents using sulphide- eating bacteria. Related ecosystems using hydrogen sulphide or methane include crabs and mussels. One fundamental problem with the study of life forms in hydrothermal vents, is that each occurrence is unique, widely separated and with differing conditions, minerals and temperature.
The talk ended with a discussion of the possibility of mining to extract copper and other metals and minerals from hydrothermal vents, and recent developments in the field. Two different environments were discussed: that of Papua New Guinea in a vent field, and the mining of polymetallic nodules on the Central Pacific ocean floor.
A short question and answer session completed a lively and informative lecture.