Programme: 2004 - 2005
© Craven & Pendle Geological Society
Friday, 22nd October
Gems Paul kabrna
Friday, 19th November
Life in the Precambrian - Evidence from Down Under. John Nudds Ph.D., University of Manchester
Friday, 10th December
Anatomy of a crisis: the Montserrat volcanic emergency 1995-99. Peter Kokelaar Ph.D., University of Liverpool
Friday, 14th January
Lower Jurassic of Tibet. Paul Wignall Ph.D., University of Leeds
Friday, 11th February
The Norber Erratics. Brian Parry BSc.; Huddersfield University
Friday, 11th March
The geology of Nova Scotia, Canada. Alison Quarterman BSc.(Hons), Huddersfield Geology Group
Friday, 8th April
Members slides and displays
Field Meetings for 2005
Saturday, 30th April
Coplow and Bellman Quarry, Clitheroe Paul Kabrna & Ben King (Castle Cement)
Sunday, 22nd May
Upper Namurian and Lower Westphalian of Cheesden Valley
Paul Wignall, University of Leeds
Saturday, 18th June
The Skiddaw Group: gabbros, greisens and metamorphic aureoles
Paul Kabrna & Hed Hickling
Saturday, 6th August
Early Dinantian and early Namurian of Worston and Whalley
Saturday & Sunday 17th/18th September
The geology of Anglesey
Gem deposits are a very important group of mineral deposits. They form in a variety of geological environments and occur in rocks of all ages. In addition they have been a part of human history for over 20 000 years.
Minerals have both geological significance and cultural value in as much as they are the building blocks of rocks and a source of metal, building material, cosmetics and of course jewellery.
Gems are likely to form inside magma chambers where there is enough time to cool slowly and allow large crystals to grow. In lavas, vesicles (gas bubbles) in the rock sometimes make ideal havens for gems to form. Zircon, topaz and ruby are good examples of magmatic gems.
Diamonds are formed deep in the mantle (100 km to 200 km). They find their way to the surface in kimberlite magmas. These kimberlite magmas that carry diamonds to the surface are often much younger than the diamonds they transport (the kimberlite magma simply acts as a conveyer belt!). Dates suggest that their formation was restricted to the first few billion years of Earth history.
Gems are frequently associated with metamorphic rocks. Two typical environments of formation include: a) Plate boundaries which are characterised by high temperature and high pressures e.g. jadeite (jade) and b) Regionally metamorphosed rocks (mountain ranges) that are buried and changed in response to increases in pressure and temperature. Minerals found in these rocks might include gems such as garnet and cordierite (in gem terms Iolite).
The formation of gems by hydrothermal processes is not dissimilar to formation of gems from water near the Earth’s surface. The solutions involve rain water and / or water derived from cooling magma bodies. Gems crystallise from solution in cracks. As a result, ‘veins’ of minerals fill these pre-existing cracks. Minerals such as beryl, emerald, tourmaline need unusual elements, and some of these, like beryllium (for beryl) or boron (for tourmaline) are derived from cooling molten rock (magma).
Pegmatites are unusual magma bodies. As the main magma body cools, water originally present in low concentrations becomes concentrated in the molten rock because it does not get incorporated into most minerals that crystallise. Consequently, the last, uncrystallised fraction is water rich. It is also rich in other weird elements that also do not like to go into ordinary minerals. When this water-rich magma is expelled in the final stages of crystallisation of the magma, it solidifies to form a pegmatite.
Alluvial gem deposits were probably the first source of gems. After rock is brought to the surface, gems may be released from the rock by weathering. The minerals that survive unchanged may be washed into streams where they are concentrated by river / ocean processes. A good example is gold.
Early jewellery was made from organic materials such as Mother of Pearl and bone. Crystalline gems were probably first gathered in stream beds where the running water separated them out from the other stream gravels.
Enhancement of a gem often starts with basic cutting and polishing, but subjecting a gem to heat or radiation also produces desirable effects. Enhancement can go too far; some of these methods (if detected) actually decrease the value of a gem. Some gemstones may be beautiful on their own, but many must be cut and polished into a finished gem to be truly valuable. A gems brilliance (sparkle), fire, (reflected colours of the rainbow), lustre, colour, and resistance to scratching are require the artistry and skill of a gem-cutter.
Thus a gemstones value is based on the four C’s: Colour (some more desirable than others); Clarity (flaws, cracks / inclusions reduce the value); Cut (rely on the skill of a good gem-cutter; and Carat Weight (although bigger is not always better). In addition rarity and supply must play a part!
There are gemstones assigned to the Seasons e.g. Autumn with Sapphire, Planets e.g. Mars with Ruby, Days of the Week e.g. Saturday with Amethyst and Birthstones e.g. January with Garnet; February with Amethyst.
If you are born in January your birthstone is garnet. According to the Talmud, Noah’s ark was illuminated by a brilliant garnet. The ancient Greeks also attributed light giving properties to this glowing gem, which they called the “lamp stone,” believing that it enabled its wearer to see in the dark. Cabochon garnets are known as carbuncles, which means “glowing coal.” One superstition states that dragons’ eyes were made of carbuncles.
If you are born in February, then your birthstone is amethyst. Grape-hued amethyst is frequently associated with the god Bacchus, who is said to have created it. According to the legend, Bacchus, in a fit pique, threatened a young girl who worshipped the goddess, Diana. Diana intervened, turning the girl (whose name was Amethyst) to clear stone. Afterwards, a remorseful Bacchus poured wine over the stone maiden, turning her glowing purple.
Amethyst is the traditional gem worn by the Catholic Church hierarchy. Paradoxically, it is known as Bacchus’ stone and as the Bishop’s stone. In the latter context, it was said to strengthen faith and aid prayer.
Gemstones and crystals are thought in some circles to possess healing properties. The theory is that gemstones supposedly carry vibrational energy i.e they behave like vibrating tuning forks. Used correctly they can ‘apparently’ activate dormant energy fields in the body which crystal healers use to good effect.
Crystal skulls are of ancient origin (5,000 & 36,000 years old). They are linked with the Mayan and Aztec civilizations and were noted to have remarkable magical and healing properties. One such crystal skull was loaned to Hewlett-Packard Laboratories for extensive study in 1970 and produced totally unexpected results. Why so remarkable then? Because they are made of clear quartz crystal which has been ‘carved against grain’ and should have shattered! To add to the enigma, HP could find no microscopic scratches on the crystal which would indicate it had been carved with metal instruments. To quote one HP technician - “The damned thing simply shouldn’t be.”
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Life in the Precambrian - Evidence from Down Under
John Nudds, University of Manchester
Earth history is dominated by the Precambrian - a vast passage of time in which the planet was ruled by bacteria. In the early days the Precambrian was thought to be devoid of fossils and therefore of little interest to collectors. All that has changed and now there is much interest specifically in the late Precambrian because of the spectacular remains of soft-bodied organisms that were first discovered by Reginald C Sprigg in South Australia in 1946.
The locality in the Flinders Ranges is known today as the Ediacaran. The strange Ediacaran fauna record the rise of multi-cellular organisms. The international importance of this has been recognised in the construction of a new geological period - the Ediacaran Period (established in March 2004) - the first period to be defined since 1891. The name “Ediacara” comes from an Aboriginal language expression meaning “veinlike spring of water” -- the “spring,” perhaps, from which complex animals have arisen.
Living stromatolite systems though uncommon on earth, can be seen at Shark Bay, Hamelin Pool in Western Australia where they were first discovered in 1956. Microbial communities of cyanobacteria bind fine sediment grains into layers which grow into dome and pillar structures called stromatolites. These “living fossils” are able to survive here because the water is twice as saline as normal sea water. The stromatolites are mainly of Holocene age (research in 1991 puts the oldest stromatolites at 1 250 years to 3 000 years BP).
The oldest stromatolites in the world occur in the North Pole - Marble Bar area of Pilbara. They have been dated using Uranium-Lead geochronology to about three and a half billion years old (give or take 3 million years!). In the outcrops studied there was some discussion as to whether they were stromatolites or perhaps tectonic folding.
Having ‘survived’ an overnight stay in a 5 star “Donga” at Nanutarra Roadhouse, a three day journey to Duck Creek proved very rewarding. The outcrops of well-bedded dolomites and ironstones finally yielded some amazing 2 billion year old fossilised domed stromatolites. This part of the survey concluded at Hancock Gorge in the Karijina National Park.
The Ediacaran Fauna
The excursion to the Ediacara Hills in the Flinders Ranges, north of Adelaide, South Australia began at the Prairie Hotel at Parachilna (famous for its ‘ferral food’ menu and the Leigh Creek Coal Train - the longest train in the world, 2.85km long with 161 wagons which rattles by every evening). The centre piece of the ranges is Wilpena Pound, a spoon-shaped syncline ringed by the Rawnsley Quartzite. The Ediacaran Member is positioned between the Upper Rawnsley Quartzite and the Lower Rawnsley Quartzite / Chace Quartzite Members. Access to these localities is via the Brachina Geological Trail.
Also along the trail is the Trezona Formation in Enorama Creek where superb fossil stromatolites can be seen. Above this horizon lies the Elatina Tillite - evidence of low latitude glaciation near the end of the Precambrian.
The Precambrian was subjected to periods of glaciation unlike anything the Quaternary had to offer. The entire surface of the earth was believed to have been covered with ice. This is commonly known as “Snowball Earth”.
The Ediacara Member lies within the prominent orange Rawnsley Quartzite which lies above the red Bonney Sandstone. The fossils remain one of the greatest enigmas within evolutionary palaeobiology. Glaessner (1984) considered these fossils the ancestors of all the animals in the geological column (the Cambrian is the first period of time where abundant fossils can be found). Many palaeontologists’ believe that the Ediacaran organisms were unique and met their end at the close of the Precambrian. Ediacaran forms once thought to be “jellyfish” by Glaessner (1984) have been reinterpreted as the attachment discs of fernlike fronds. As you can see things are not entirely ‘cut and dried’!
In conclusion you may like to consider the evolutionary implications as highlighted in Stephen Jay Gould’s “Wonderful Life” published in 1989. “Suppose we could replay life’s tape from the Late Precambrian times, and that the flat quilts of Ediacara won on their second attempt, while metazoans were eliminated. Could life have ever moved to consciousness along this alternate pathway of Ediacara anatomy? Probably not . . . . If Ediacara had won the replay, then I doubt that animal life would ever have gained much complexity, or attained anything close to self-consciousness. The developmental program of Ediacaran creatures might have foreclosed the evolution of internal organs, and animal life would then have remained permanently in the rut of sheets and pancakes. . . . If on the other hand, Ediacara survivors had been able to evolve internal complexity later on, then the pathways from this radically different starting point would have produced a world worthy of science fiction at its best”.
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Anatomy of a crisis: the Montserrat volcanic emergency 1995-99
Peter Kokelaar, University of Liverpool
Montserrat is one of the Caribbean islands situated in the Lesser Antilles. It is a small island, 16.5 x 10 kilometres (about 100 km²). Its rugged hills mark four volcanic centres. These and other volcanic centres on other Lesser Antilles islands form an island-arc created by the Atlantic plate being subducted beneath a much smaller Caribbean plate.
The Main Event
Soufrière Hills Volcano which is only 5 kms east of the capital Plymouth is one of Montserrat’s main volcanic centres. It gained centre stage in July 1995 by producing a spectacular series of eruptions. Over a four year period the several major phases of activity devastated large areas of southern Montserrat, eventually requiring the evacuation of the population from the capital city Plymouth and surrounding areas.
The eruption of the Soufrière Hills volcano was to many vulcanologists was not entirely unexpected. Earthquakes in the mid 1930’s, mid 1960’s and as recently as 1992 had set the scene by forcing magma up through the volcano at very high pressure. The series of eruptions began when heated groundwater exploded from the side of an old lava dome within English’s Crater. The explosive release of heated groundwater (a ‘phreatic explosion’), formed these craters in the old dome (Castle Peak dome).
Montserrat’s volcanoes are mainly made up of andesite lavas that commonly produce steep lava domes. In the case of Soufrière Hills the lava dome complex is not a classic symmetrical cone shape as is commonly associated with volcanoes, because the erupted lava is very viscous and sticky. As viscous lava is not very fluid, when it is extruded it cannot flow away from the vent easily. Instead it piles up on the vent forming a large dome shaped mass of material. Violent but short-lived Vulcanian explosions have been associated with the growth of the viscous lava dome at the Soufriere Hills volcano. Each explosion ejects a slug of ash and rocks at initial speeds of hundreds of metres per second. A huge amount of loose ash and mud debris has been deposited on the flanks of the volcano. Much of the remaining vegetation is killed by the effects of ash. When there is heavy rainfall, this debris gets washed down the main valleys giving rise to mudflows. This hazard will continue until vegetation becomes re-established.
The volcanic activity is being closely monitored by an international team of vulcanologists. The first response to the crisis was provided by the Seismic Research Unit (SRU) at the University of the West Indies in Trinidad, which had maintained a seismic network on the island. Their team was later supplemented, at the request of the government of Montserrat, by scientists from the U.S. Geological Survey (USGS), the Guadeloupe Volcano Observatory, and the United Kingdom. The Montserrat Volcanic Observatory continues to monitor volcanic activity in order to provide timely warnings of future eruptions and to collect data for hazard and risk assessment.
What went wrong?
The main reason for the lack of preparedness in Montserrat in 1995 was a breakdown in communications between the Seismic Research Unit and the Government of Montserrat. Contributory factors can be found on both sides. All of the information indicating that an eruption was imminent was available and all of it had in fact been communicated to the authorities in Montserrat. Unfortunately the way in which the information was communicated conveyed no sense of urgency whatsoever. It was contained in the routine quarterly report of the Seismic Research Unit for the third quarter of 1994. No attempt seems to have been made at person-to-person contact with either the Governor or Chief Minister.
The geologists’ who continue to monitor Montserrat can’t predict the exact time of an explosion or even say how likely it is to explode. It’s all kind of relative. However, they can monitor the volcano’s behaviour (earthquakes, phreatic activity and magma dome distortions) in order to make an educated guess. Sometimes they warn that it might explode and they issue an alert, calling for people near the troubled area to leave immediately. Sometimes they are wrong, but when they are right these warnings have saved the lives of many people living around active volcanoes.
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Lower Jurassic of Tibet
Paul Wignall, University of Leeds
Before embarking on the road to Tibet a brief overview of the Lower Jurassic of the East Yorkshire coast is in order.
The Lower Jurassic rocks of the Yorkshire coast were deposited in open marine conditions in what was then the Cleveland Basin. The rocks form a sequence of dominantly mud-grade sediments reaching about 420 metres in thickness in North Yorkshire. The cyclic variety of sedimentary facies is probably due to a combination of global sea level rise and fall and local earth movements.
Many beds have a sharp erosive base, a shelly channel-floor lag deposit and are usually overlain by sands showing planar cross-stratification (typically representative of shallow-water storm events). Throughout you can see spectacular sedimentary structures and well preserved invertebrate faunas and trace fossils e.g. Rhizocorallium - these are burrows excavated by shrimp-like crustaceans. Besides the ammonites, there are bivalves, belemnites and scaphopods. The ammonite fauna goes extinct at a level that is well displayed on the beach at Runswick Bay by a thinly laminated bed known as the Sulphur Band.
How does this compare to Tibet!
Introduction to Tibet
The Tibet Plateau began to take shape 200 million years ago when the Himalayas and Tibet were uplifted by the collision between the Eurasian continent and the India sub-continent. It is the highest plateau in the world with an average altitude of 4 500 metres (14 763 feet) and a crust thickness of 70 kilometres. It has the two highest mountains in the world in Mt. Everest at 8,850 m (29,035 feet) and Mt. K2 at 8,611 metres (28,250 feet) and the largest canyon in the world at the Yalung Tsangpu (Brahmaputra). The plateau is still geologically active with frequent earthquakes and regular glacier movements.
The geological processes that formed the Tibetan Plateau are not fully understood with popular opinion being divided by the following:
• Basement Reactivation
Crust is thickened by the faulting and subsequent movement of large masses of rock, which are stacked one on top of another. In this type of model you would expect to find major compressional deformation of the rocks.
• Continental Subduction
The Indian continental crust is consumed beneath the Tibetan Plateau thus causing uplift. It is nevertheless difficult to imagine how the buoyant Indian crust could be kept deep enough to get far beneath the plateau before bobbing to the surface. Perhaps the great speed at which India is collided into Eurasia allowed this to happen.
• Continental Injection
In this process Indian crust beneath Tibet melts (magma). Granitic melts then rise into the overlying Eurasian plate thus transferring heat into the base of the Tibetan Plateau. The addition of light granitic material at the bottom of the Eurasian crust acts like a hot air balloon causing the increase in the height of the Plateau.
This is a view of the Kyoto Limestone in the Nien Valley, looking down a steep slope at the Lhasa-Kathmandu highway. Thin-bedded facies at the right record the deepening event referred to in the text.
Lower Jurassic of Tibet
The southern fringe of Tibet is composed of sedimentary rocks that formed on the northern margin of the Gondwanan continent. They thus record marine deposition on the southern margin of the Tethyan Ocean. Most of this record is dominated by clastic deposition (sandstones, shales) but in the early Jurassic a distinctive limestone was formed, known as the Kioto Limestone. This is mostly a shallow-water deposit and is full of distinctive shallow-water fossils. These include the unusual lithiotid bivalves whose large, thick shells often formed small patch reefs on the seafloor.
The lithiotids and many other fossil types disappear within the Kioto limestone. This appears to be associated with a deepening event because the limestones become finer, darker and thinner bedded. It is possible that this deepening / extinction is the same event as that seen in the Early Jurassic of the Yorkshire Coast. Here the shallow-water conditions recorded by the Staithes and Cleveland Ironstone formations are replaced by the deep water conditions of the Grey Shales and Jet Rock. Proof of this contention could be had if the Tibetan sections contained the same ammonites as those seen in Yorkshire, but unfortunately the Tibetan rocks contain no ammonites at all. Attempts to date the Tibetan rocks have therefore relied on their chemical attributes, particularly the ratios of carbon isotopes. Preliminary results have shown, somewhat surprisingly, that the Tibetan deepening event occurred several million years after that seen in Yorkshire.
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One part of the study area for my Ph.D. is Crummack Dale, north Yorkshire just south east of Ingleborough. It is a classic area for the study of glacial geomorphology and karst. My interest however lies in the assemblage of perched glacial erratics resting on Carboniferous Limestone. These erratics are commonly known as the Norber erratics (SD 770 704) and their origin has attracted a great deal of scientific debate and speculation over many years. They have been described by Howson (1850), Phillips (1855), Hughes (1886), Daykins (1872), Tiddeman et al (1890), Kendall & Wroot (1924), Dunham (1950), Brumhead (1979), Waltham (1987), and Arthurton et al (1988). Interestingly enough these authors have widely different opinions on where these erratics came from. Some support a local origin of about 1 kilometre, others further a field such as Ribblesdale, Chapel-Le-Dale, the Howgills, the Lake District and even Northumberland!
The locality of the Norber erratics is situated in one of the Lower Palaeozoic Craven Inliers (an area where pre-Carboniferous basement rocks outcrop at the surface surrounded by younger sub-horizontal Carboniferous limestone) found on the southern margin of the Askrigg Block just north of the North Craven Fault. The junction between the basement rocks and the Carboniferous limestone is an unconformity. In this region the unconformity is a classic angular unconformity as seen in Crummack Dale itself, Thornton Force in Chapel Le Dale, and at Combs Quarry in Foredale (SD 800 701).
The actual Norber erratics are large, angular greywacke / siltstone (turbidites) belonging to the Silurian Austwick Formation. Here at Norber some of the erratic blocks stand on pedestals of limestone. The story behind the pedestals is a focus of future research during my Ph.D. study.
The erratic blocks were recorded by mapping, although there shear weight in number forced a reassessment of which erratics ought to be recorded. Eventually I opted for mapping perched blocks of half a metre upwards. Care was taken during this process because there are limestone erratic boulders scattered around the study area.
On further inspection of the erratics it was noted that there huge size (in some cases) and their overall angularity suggested that they may not have travelled very from the source. Another interesting aspect to the distribution of the erratics was there overall tendency to cluster and occur in specific areas of Crummack Dale. This suggested that the forces which transported these blocks probably originated from an ice sheet as opposed to a valley glacier. If a valley glacier had been responsible for their transportation I would have expected a more wavy distribution following the winding course of the valley glaciers as it drifted down towards the Ribble Valley.
The study of glacial striae on the limestone pavement and on the limestone pedestals provided conclusive proof as to the direction the ice moved during the late Devensian. A key technique to recording glacial stria was to wet the surfaces that you are looking at!
The evidence appears to suggest that the erratics must have been plucked from a local source of Austwick Formation. The key now was to find a local outcrop of rock that was of sufficient size for the ice to have successfully plucked these blocks away. The enclosed map shows the ideal spot from which the erratics must have come from. Case closed for now!
The Norber erratics are a classic example of an erratic train caused by glacial erosion and transport by the Yorkshire Dales ice sheet. Furthermore, there use as an indicator of the rate of surface lowering of the surrounding limestone pavements and pedestals is still shrouded in doubt.
The province of Nova Scotia is conveniently divided by a fault into two geological zones both of which are fundamentally different to one another.The northern zone, which includes Cape Breton and the northern mainland Nova Scotia, is known as the Avalon Zone. The are to the south is the Meguma Zone. The geology of the the two zones is different because the Avalon Zone was part of Laurasia whilst the Meguma Zone was a part of Gondwanaland. Thye were separated by the Iapetus Ocean eventualy coming together when Pangea was formed.
The oldest rocks of Nova Scotia can be found at the north-eastern tip of the province. They are Precambrian in age and are dated as aprroximately 1.4 billion years old. They are complex rocks having been subjected to a number of orogenies and to further complicate things have been intruded by granite, diorite and anorthosite.
During the Cambrian Period the three areas in the Avalon Zone; Cape Breton Island, Antigonish Highlands, and Cobequid Highlands, were subjected to intense periods of volcanic activity. However the Meguma Zone lay seaward of a large continental landmass, believed to have been North Africa. Large volumes of sediment were transported from the continental shelf of the landmass to the depositional area of the Meguma Group by turbidity flows.
The Cambrian Period was charactised by intense periods of volcanic activity especially in the Avalon Zone. The Meguma Zone on the other hand saw large volumes of sediment transported from the Continental shelf by mass turbidity flows. This pattern was to continue into the Ordovician Period.
Silurian rocks in Nova Scotia are remarkable for their differences. The oldest Palaeozoic rocks are early marine Silurian siltstones with graptolite fossils. In the Cape Breton Highlands, there are thick sequences of sedimentary and volcanic rocks that were later strongly deformed and metamorphosed. On Ingonish Island a small section of felsic and mafic volcanic rocks were deposited during the Silurian Period. The fossil record so far has been patchy. However the seas of the Silurian Period were warm, shallow and pulsating with life.
From the Middle Devonian Nova Scotia was in one piece due to the coming together of the continetal land masses to form Pangae.The mountain building episode driving the continents was the Acadian Orogeny.
Subsidence in the Lower Carboniferous produced a new branch of the sea, often shallow and with relatively poor circulation to deeper water. There was significant evaporation of sea water which led to the precipitation of thick layers of limestone, salt, gypsum and anhydrite, all important minerals that are mined today from the Windsor Group.
The warm climate of the Upper Carboniferous Period, encouraged the growth of large trees which could reach heights of 30 metres as found at Joggins. The fossil cliffs of Joggins are a world-class palaeontological site located near the head of the Bay of Fundy. Joggins is well known for a diverse selection of plant-life and amphibian fauna, e.g. Arthropleura trackways and some of the world’s first reptiles.
At the opening of the Permian Period, Nova Scotia occupied a central position on the Pangean supercontinent. The Permian Period was quiet tectonically, with only erosion of pre-existing rocks occurring. Except for a few small exposures of Cretaceous clays and sandstones, the early Jurassic rocks were the last known rocks deposited onshore in Nova Scotia before the Pleistocene glaciations. Offshore on the continental shelf, thick Jurassic deposits record the breakup of Pangea and the development of the Atlantic Ocean margin.
There were more than 16 glaciations during the Quaternary Period, starting at the beginning of the Pleistocene Epoch with each glaciation lasting about 100 000 years. Halifax is built amongst drumlins and the spectacular exposures of rocks seen throughout Nova Scotia are frequently scoured and polished by the glaciers whose direction can easily be determined by the numerous striae found on the rock surfaces.
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Time & Date: 10:30 am, Saturday, 30th April 2005
Meeting at: the lay-by entrance to Bellman Quarry at Grid Reference [SD 756 428]. Lunch at the Black Horse or bring packed lunch.
Practical details: Coplow and Bellman Quarries are the property of Castle Cement (Ribblesdale) Limited, Clitheroe, Lancashire BB7 4QF. Before visiting either of these sites it is necessary to obtain permission from Castle Cement. Salthill Quarry is a SSSI. Wellington boots, safety glasses and hard hat are necessary on this visit.
Geological setting: the Lower Carboniferous rocks of the Clitheroe district are well known and have been described in a diverse literature (Earp et al 1961, Miller & Grayson 1970, Lees & Miller 1985, Riley 1996). The mud mounds (formerly knoll reefs) form small hills which have been quarried for limestone since the 17th Century. The quarries are internationally famous for having been described by the Scottish amateur palaeontologist James Wright who published the seminal work “Monograph of the British Carboniferous Crinoidea”, 1950 - 1960. Also, the quarries were frequently visited by the late Stanley Westhead who wrote in 1979 “It is true to say that nowhere else in England have Carboniferous crinoids been found in such large numbers and also in such variety of genera and species [as around Clitheroe]”.
During the visit we should expect to see crinoids, blastoids, corals, brachiopods, and bryozoans. Also we shall look for evidence of mud mounds comparing them with the classic mud mounds of Salthill Quarry. If time permits we will take a short visit to Salthill Quarry Point 1 and Point 6.
1:50 000 sheet 103 Blackburn and Burnley
1: 25 000 sheet SD 64 / 74 (Clitheroe and Chipping).
Geol. Survey 1:63 360 Sheet 68 Solid Clitheroe.
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Time & Date: 10:30 am, Sunday, 22nd May 2005
Meeting at: the Owd Betts pub on the A680, 4½ kilometres S.E. of Edenfield at 10.30 am. Carry packed lunch (or pub lunch at Owd Betts) and as usual be adequately prepared for the vagaries of Pennine weather. Finish about 4 pm.
Geological setting: British geologists have been at the forefront of scientific work in the Upper Carboniferous, particularly in biostratigraphy in the Pennines. This is a classic area for Namurian studies because of the extensive exposures of Millstone Grit and Coal Measure deposits. Cheesden Valley is a particularly important site and offers considerable incentive for conservation.
The Namurian rocks exposed in Cheesden Valley are characterised by mainly northerly derived deltaic deposits filling a shallow marine basin, and the Coal Measures (Lower Westphalian) by fluvio-deltaic deposition. Separating the sandstone bodies are shale beds, some of which contain goniatites (ammonoids) amongst other fossils. The goniatites have been extensively used for correlating rock outcrops - an aspect of biostratigraphy first put in place by W.S. Bisat (1924). The ammonoid-bearing strata are commonly referred to as marine bands. There occurrence marks a period of time in earth history where the land was flooded by the sea.
O.S. 1:50.000 Sheet 109
O.S. 1:25 000 SD 81/91
Geol. Surv. 1:63 360 Sheet 76. Rochdale Solid & Drift.
Wignall, P.B. 1988. A Geological Guide to the marine and deltaic sediments of the Silesian of Deeply Dale, North Bury. The Amateur Geologist XII, pp. 25-30.
Wignall, P.B. 1986. A guide to the geology of Turf Moor, Rossendale. The Amateur Geologist XII/1
1927: The Geology of the Rossendale Anticline. Memoir Geol. Survey of England.
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Time & Date: 10:30 am, Saturday, 18th June 2005
Meeting at: the car park adjacent to the Blencathra Centre at Grid Reference [NY 302 257]. Turn off into Threlkeld village and take the road sign posted ‘Blease Road leading to Blencathra’. Follow this track to the car park just beyond the Blencathra Centre.
Practical details: Nearest public toilets are at the Lakeside Car Park, Keswick (5 km away).
Geological setting: The Lower Palaeozoic rocks of the Lake District record the rifting of ancient continents during the closure of the Iapetus Ocean. This seaway separated Gondwana (south) and Laurentia (north). Large volumes of granitic magma (Eskdale and Ennerdale) were generated in response to subduction of the Iapetus oceanic crust. At a later date the Shap and Skiddaw granites were emplaced around the margins of the batholith. However, on this excursion, we will look at the more unusual mafic (gabbro) plutonic intrusion that makes up part of the Carrock Fell Intrusion complex. The superb exposure of these rocks and depth of erosion in the Lake District allow a view into the depths of the magmatic system rarely seen in modern examples.
Metamorphic Aureole: (am). The route along Glenderaterra Beck demonstrates clearly the effect that the intruded Skiddaw Granite has had on the Skiddaw Group of mudstones and greywackes. As you get nearer to the outcropping Skiddaw Granite in Sinen Gill, the effects of the thermal metamorphism become more pronounced. The Skiddaw Granite was emplaced in either late Silurian or early Devonian occurring towards the end of the Caledonian Orogeny. There is extensive mineralisation with lead and copper bearing veins. For the intrepid field geologist with an interest in minerals, a visit to Glenderaterra Mine for collecting may be possible if time permits.
Greisens: (pm). The next stop is alongside the Caldew River at the confluence with Grainsgill Beck. The alteration (contact metamorphism) of the Skiddaw slates together with the rather curious alteration of the roof of the Skiddaw granite into greisen are clearly seen in the beck. There may be time for a look on the disused mine workings and tips at the confluence of Grainsgill Beck and Brandy Ghyll. Several mineral veins (now a protected site) had once been mined, but the remaining spoil heaps are now severely depleted by collectors. If your lucky you can still find wolframite, apatite and arsenopyrite.
Gabbros: (pm). The third part of the excursion will focus on the Mosedale Gabbros which represent the oldest part (Lower Ordovician) of the Carrock Fell Intrusion complex and indeed the largest layered intrusion in England.
O.S. 1: 25 000 Outdoor Leisure Map, English Lakes, North Western Area
1: 50 000 Sheet 89 or 90
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Time & Date: 10:15 am, Saturday, 6th August 2005
Meeting at: the lay-by on the A59 Chatburn road cutting Grid Reference [SD 773 438]. After lunch meet at Grid Reference [SD 733 358] (roadside parking).
Geological setting: the Craven Basin in early Dinantian times is characterised by rift basins, half-grabens and tilt blocks and Waulsortian Mudmounds. Worsaw Hill, Warren Hill and Crow Hill are excellent examples of these phenomena, first described in the type locality in Belgium. Worsaw Hill may be an opportunity to see depositional dips as first described by Miller & Grayson in Salthill Quarry in 1970. In the afternoon we shall ascend Whalley Nab to search out the two millstone grit grindstone wheels. On the top of the Nab there are outcrops of Pendle Grit and Warley Wise Grit.
Our return to the car will be via Butler Clough where exposures of the fossiliferous Bowland shales contain the bivalves Posidonia, Posidonomya, and Caneyella, and the zonal goniatite, Cravenoceras malhamense, which appears near the top of the E1C1 bed. In good weather, Whalley Nab is an excellent view point over the Craven Basin.
1:50 000 sheet 103 Blackburn and Burnley
1: 25 000 sheet SD 64 / 74 (Clitheroe and Chipping).
Geol. Survey 1:63 360 Sheet 68 Solid Clitheroe.
Bisat,W. 1922. The Carboniferous Goniatites of the North of England and their zones. P.Y.G.S. 20, 40 - 124.
Earp, J. R., Magraw, D., Poole, E. G., Land, D. H. & Whiteman, A. J. 1961. Geology of the Country around Clitheroe and Nelson. Geological Survey of Great Britain Memoir, England & Wales, Sheet 68.
Miller, J. & Grayson, R. F. 1972. Origin and structure of Lower Viséan “reef limestones near Clitheroe, Lancashire. Proceedings of the Yorkshire Geological Society, 38, 607-638.
Riley, N. J. 1990. Stratigraphy of the Worston Shale Group (Dinantian), Craven Basin, northwest England. Proceedings of the Yorkshire Geological Society, 48, 163-187.
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Acknowledgements: the excursion to Anglesey will draw upon the excellent work of Wes Gibbons Ph.D. and Jana Horák Ph.D. and also the Wales RIGS Group who have produce a colourful account of the geology of the Rhoscolyn Anticline.
Time & Date: Saturday, 17th and Sunday 18th September 2005
Meeting at: 09.30 am at South Stack, Holy Island: Explorer 262 Grid Reference [211 818] or Grid Reference [SH 203 823]. Please note that there will be an opportunity for a pub lunch on both days.
Localities: Saturday: South Stack, Cae'r Sais, Rhoscolyn (all on Holy Island); Sunday: Gwalchmai, Llanddwyn Island, Marquess of Anglesey's Column
Practical details: Accommodation is best booked in advance. B&B’s and Hotels can be found at www.islandofchoice.com or telephone directly to the Tourist Information Centres of Holyhead 01407 762622 e-mail firstname.lastname@example.org or Llanfairpwll (James Pringle Weavers) 01248 713177 e-mail email@example.com
Geological setting: Anglesey or Anglesea (Welsh: Ynys Môn pronounced “Uh-niss Morn”), is an island and county off the northwest coast of Wales. There are an amazing variety of rock types and geological structures, superbly exposed along the coastline which for the most part is fairly easy to access.
The geology was originally mapped by Edward Greenly in the early part of the century and subsequently re-interpreted by others (Gibbons, Horák, Shackleton). Since Greenly et al, it has become clear that Anglesey contains some of the most important Precambrian rocks in the UK. They have been subdivided into the Monian Supergroup, the Coedana Complex and the Blueschist Belt. These ancient rocks are overlain by younger Palaeozoic volcanic and sedimentary rocks.
In order to better understand the tectonic setting, the rocks on Anglesey are conveniently grouped into crustal units called ‘terranes’. The geological terranes must not be confused with ‘terrain’ which is a physiographic feature.
One of the localities that we shall visit is Rhoscolyn which is designated a Site of Special Scientific Interest. It is one of the most visited geological localities in Great Britain. There are easily accessible coastal exposures of deformed sedimentary rocks that show spectacular cascades of folds, some of which are superimposed on one another. The most famous exposures lie in the core of the Rhoscolyn Anticline, a huge, arch-shaped fold exposed in the cliffs. The nearest rocks in the UK that come even close to matching such splendid exposures are those in the highlands of Scotland.
Within an easy drive of Holy Island, the famous ‘Monian’ rocks of Anglesey preserve the internationally known Gwna Melánge (the first melánge ever described), and some of the oldest blueschists on Earth. In addition there are well exposed Ordovician, Silurian, Devonian and Carboniferous sediments, some of which are richly fossiliferous, not to mention Parys Mountain, once the largest copper mine in Europe.
Even for those not especially involved in geology, the huge variety of different rocks on Anglesey makes for varied and beautiful scenery, especially great for coastal walking and wildlife spotting.
1:25 000 Explorer 262 Anglesey West
1: 25 000 Explorer 263 Anglesey East.
Barber, A.J. & Max, M.D. 1979. A new look at the Mona Complex (Anglesey, North Wales). Journal of the Geological Society, London, 136, 407–432
Carney, J.N., Horák, J.M., Pharaoh, T.C., Gibbons, W., Wilson, D., Barclay, W.J., Bevins, R.E., Cope, J.C.W. & Ford, T.D. 2000. Precambrian Rocks of England and Wales. Geological Conservation Review Series, Joint Nature Conservation Committee, Peterborough, 20.
Collins, S.A. and Buchan, C. 2004. Provenance and age constraints of the South Stack Group, Anglesey, UK: U-Pb SIMS detrital zircon data. Journal of the Geological Society, London, 161, 743–746
Dallmeyer, R.D. & Gibbons, W. 1987. The age of blueschist metamorphism in Anglesey, North Wales: evidence from 40Ar/39Ar mineral ages of the Penmynydd Schists. Journal of the Geological Society, London, 144, 843–850
Gibbons, W., Horák, J.M. 1990. Contrasting metamorphic terranes in northwest Wales. In: D'Lemos, R.S., Strachan, R.A. & Topley, C.G. (eds) The Cadomian Orogeny. The Geological Society, London, Special Publications, 51, 315–328.
Gibbons, W., Tietzsch-Tyler, D., Horák, J.M. & Murphy, F.C. 1994. Precambrian rocks in Anglesey, southwest Llyn and southeast Ireland. In: Gibbons, W. & Harris, A.L. (eds) A revised correlation of Precambrian rocks in the British Isles. Geological Society, London, Special Reports, 22, 75–83.
Gibbons, W., Horák, J.M. 1990. Contrasting metamorphic terranes in northwest Wales. In: D'Lemos, R.S., Strachan, R.A. & Topley, C.G. (eds) The Cadomian Orogeny. Geological Society, London, Special Publications, 51, 401–423.
Gibbons, W., Horák, J. M. 1996. The evolution of the Neoproterozoic Avalonian subduction system: Evidence from the British Isles. In: Nance, R.D. & Thompson, M.D. (eds) Avalonian and related peri-Gondwanan terranes of the circum-Atlantic. Geological Society of America Special Papers, 304, 269–280.
Greenly, E., 1919. The geology of Anglesey. Memoir of the Geological Survey of the U.K. [2 vols].
Horák, J.M., 1993. The Late Precambrian Coedana & Sarn Complexes. PhD thesis, University of Wales, Cardiff.
Shackleton, R.M., 1975. Precambrian rocks of North Wales. In: Harris, A.L.,
Shackleton, R.M., Watson, J., Downie, C., Harland, W.B. & Moorbath, S. (eds) A correlation of Precambrian rocks in the British Isles. Geological Society, London Special Reports, 6, 76–82.
Tietzsch-Tyler, D. & Phillips, E.R. 1989. Correlation of the Monian Supergroup in NW Anglesey with the Cahore Group in SE Ireland. Journal of the Geological Society, London, 146, 417–418
Treagus, J. E., Treagus, S.H. Droop, G.T.R. 2003. -Superposed deformations and their hybrid effects on the Rhoscolyn Anticline unravelled. London, Journal of the Geological Society, London, 160, 117–136
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