Programme: 2010 - 2011

© Craven & Pendle Geological Society

Indoor Meetings

Friday: 8 October
Permian mass extinction: evidence from around the world. Professor Paul Wignall, University of Leeds

Friday: 12 November
Hot Stuff in the Deep Sea: Present and Past Life at Hydrothermal Vents. Cris Little Ph.D., University of Leeds

Friday: 10 December
Mid Dinantian Ammonoids from the Craven Basin – new insights into a mysterious interval of Carboniferous time. Nick Riley MBE Ph.D., British Geological Survey

Friday: 14 January
Tsunami processes and response
Jeff Peakall Ph.D., University of Leeds

Friday: 11 February
Cave development in Caledonide marbles. Trevor Faulkner Ph.D., Limestone Research Group, GEES, University of Birmingham

Friday: 11 March
Victoria Cave: a half million year record of climate change. Tom Lord, Centre for North-West Regional Studies, University of Lancaster

Friday: 8 April
Members Evening
Geology of Anglesey
Paul Kabrna

Field Meetings

Saturday: 9 April
Waddington Fell Quarry & Ashnott Knoll
Guides: Paul Kabrna and Alan Whalley

Sunday: 8 May
Whitewell
Guide: Jean Chicken, Paul Kabrna and David Turner

Weekend: Friday-Sunday, 10-12 June
Geology of Anglesey
Guide: Paul Kabrna

Saturday: 16 July:
Glaciation and geomorphology around Kisdon, Upper Swaledale
Guide: Jon Barber Ph.D., University of Leeds. Joint meeting with the North eastern Geological Society.

Sunday:18 September
Carboniferous rocks around Gargrave and Skipton
Guide: Paul Kabrna


Permian mass extinction: evidence from around the world
Paul Wignall

Introduction

The study of mass extinctions was revolutionized in 1980 by the publication of evidence (an iridium-rich layer) that suggested the sudden extinction of dinosaurs at the end of the Cretaceous was linked to a giant meteorite impact. Since then the debate has widened to include flood basalt volcanism as another cause of mass extinctions. In fact most of the Earth’s extinction events coincide with flood basalt eruptions and so, not surprisingly, a lot of attention has been focused on trying to find the link between volcanism and environmental crisis.

The “Great Dying”

The End Permian extinction (about 251 million years ago) wiped out 95 percent of all marine species went extinct. This catastrophe was Earth’s worst mass extinction, killing 53 percent of marine families, 84 percent of marine genera, and an estimated 70 percent of land species (including plants, insects, and vertebrate animals.). This was the greatest crisis ever to be faced by life on Earth. Even conservative estimates of the extinction losses recognise that less than 10% of species survived. Almost unique amongst such extinction crises, the event affected the entire biosphere including groups that are normally resilient to such calamities including the insects and plants. Thus, the high-latitude forests of the southern hemisphere characterised by Glossopteris leaves went abruptly extinct. So severe was the effect on global plant communities that peat-forming conditions disappeared for several million years of the succeeding Early Triassic with the result that there is a unique “coal gap” at this time. In the oceans there is an equivalent “chert gap”. Chert is a siliceous rock made up of the tiny skeletons of radiolarians, the dominant fossil plankton group for much of the Phanerozoic. For hundreds of millions of years radiolarians rained down to the seabed where they formed a slowly accumulating siliceous ooze that over time hardened to form chert. This chert record temporarily disappears in the Early Triassic to be replaced by organic-rich shales: black shales.

PT Boundary in China

The international type section of the Permian/Triassic type section, Meishan, SE China. The rocks consist of alternating limestones and shales with a pale, rusty weathering ash band. The mass extinction is recorded in the limestone immediately above the hammer head, and below the ash band, whilst the Permian/Triassic boundary is just above the top of the hammer shaft at a level of a bedding plane within a limestone bed. Except for the ash band, these strata accumulated very slowly and record several 100 thousand years of deposition in a deep marine setting. Photo © Paul Wignall

The last two decades have seen a dramatic increase in studies on the end-Permian mass extinction. The Siberian Traps have emerged as by far the most popular “culprit”. The Traps are the remnants of a formerly vast expanse of flood basalts that erupted onto the West Siberian craton at precisely the same time as the mass extinction. Only half a million cubic kilometres of this lava currently remain but the original volume has been estimated as up to ten times this amount, making it the greatest manifestation of terrestrial volcanism known on Earth. The best link between this volcanism and the extinction comes from the timing; a link that is also strengthened by the fact that other similar flood basalt eruptions have coincided with other extinction events. However, the actual “kill mechanism” has proved elusive. How can giant lava flows in Siberia kill tropical reefs in South China? The Siberian eruption style is likely to have been dominated by fire fountains. These are great walls of ascending lava, which may have been several kilometres high, extruded from fissures tens to hundreds of kilometres in length. Whilst obviously impressive, this is not the most effective eruption style for injecting material into the stratosphere. Thus, typical effects of volcanism, such as cooling caused by stratospheric aerosols and dust need not necessarily have been as severe as expected from the scale of the volcanism. Nonetheless, most geologists link the Siberian eruptions and the end-Permian extinctions via a series of steps connected to the atmospheric effects of the eruptions. The two principal volcanic gases (other than harmless water vapour) are sulphur dioxide and carbon dioxide. The former generate clouds of sulphate aerosols and are rapidly removed from the atmosphere as acid rain. These effects operate over just a few years, a geological instant; whereas carbon dioxide’s well-known greenhouse effect is more pernicious and protracted. The observed stagnation of the world’s oceans and shift to black shale deposition has been linked to stagnation related to warming and this may form the ultimate link with volcanism and extinction.

Siberian Traps

Artists impression of the large outpourings of basalt that played a major part in the PT mass extinction

Problems still remain with this volcanic link: gas emissions are large but, when modelled, do not appear to be excessively so. More indirectly, almost-as-large volcanic eruptions at other times are not linked with extinctions which begs the question: what was so lethal about the Siberian eruptions? A possible solution to the extinction-volcanism impasse may come from consideration of the indirect effects of flood basalt eruptions. Such volcanism requires the passage of huge volumes of magma through the upper crust where it will have a baking effect on sedimentary rocks. Given the wrong kind of rocks some of the gases released by this sediment baking could be especially damaging. Thus, recent papers have highlighted the nature of the subsurface geology in western Siberia and the possibility that thermal metamorphism may have released lots of especially noxious gases such as methyl chloride. Such halocarbons affect the production of atmospheric ozone raising the possibility of an Earth without an ozone shield.

Summary

Like all mass extinction studies, there are plenty of other competing theories that do not involve volcanism. Inevitably these include giant meteorite impact but, despite several claims, substantive evidence is lacking. Even less plausible ideas invoking death from outer space include the transit of the Earth through an especially dense patch of dark matter and the effects of a nearby supernova. Imaginative as these ideas are, it remains likely that the great end-Permian mass extinction was caused by Earth-bound causes.

Back to top Back to Top


Hot Stuff in the Deep Sea: Present and Past Life at Hydrothermal Vents
Cris Little

Introduction

Research on the deep seafloor is a serious undertaking. Working on the mid-ocean ridges is even harder, because these are among the most geologically active areas on the planet. Here new ocean crust is being formed as lava erupts onto the seafloor, accompanied by strong earthquakes. Not only that, but the ridges are also sites of intense hydrothermal activity, with 370°C, highly acidic vent fluids gushing out of towering mineral chimneys on the seafloor. This challenging environment is the setting for our project to study fossilisation in deep-sea hydrothermal vents. Indeed, these challenges were confirmed when we lost an entire set of experimental devices to a major seafloor volcanic eruption early on in the experiment.

Brothers

A Black Smoker known as the Brothers (4 July 2008)
Credit: Photo © National Oceanic and Atmospheric Administration

Why are we interested in fossilisation at deep-sea hydrothermal vents?

The aim of the study was to better understand the evolutionary history of the extraordinary communities of animals that live only at hydrothermal vents. The most important compound in vent fluid is hydrogen sulphide, and many vent animals, including giant vestimentiferan tube worms, vent mussels and clams, depend for food on symbiotic bacteria that live by oxidising this sulphide. This dependence on geochemical rather than solar energy may have shielded vent communities from major environmental events, like the mass extinctions and global climate change that affected contemporary photosynthesis-based ecosystems. Thus, the evolutionary history of vent fauna is probably very different from that of other marine biotas. The only direct evidence for this history comes from the fossil record. But at present this is sparse, with only 25 examples known from the past 550 million years, and there are fundamental questions about why this is. For example, why do some ancient vent deposits contain fossils, while others in the same state of preservation don’t? There are also significant groups of animals, like crabs and shrimps, that are abundant at modern vents, but which do not appear in the vent fossil record. Why should this be? Is it a case of imperfect preservation, or were these groups not present at vent sites in the past?

To find out, we decided to investigate how modern deep-sea hydrothermal vent animals (vestimentiferan and polychaete tube worms, molluscs and crustaceans) become fossilised at vents. To do this we chose an area on the East Pacific Rise, 500 nautical miles south of Mexico, where scientists have studied vents for two decades. Unfortunately the deployment of our first fossilisation cages at two vent sites in May 2005 were destroyed by a major submarine volcanic event in the area late in 2005, in which an estimated 22 million cubic meters of lava erupted. Presumably our cages are still there, but covered by several metres of basalt! We deployed new sets of fossilisation cages at two different vent sites in November 2006 and December 2007, and recovered them after 373 days and 319 days, respectively.

Vestimentiferan worms

The giant tubeworm, Riftia pachyptila, from the hydrothermal vents at the East Pacific Rise at 2500 m depth. Each individual in the photo exceeds one meter in length.

Image source of Monika Bright, University of Vienna, Austria. http://oceanexplorer.noaa.gov/explorations/06mexico/
logs/may16/media/riftia_600.html

The results are very interesting, and go a long way towards answering many of our questions about fossilisation at hydrothermal vents. For example, we now know that fossilisation is very dependent on exactly where the remains are located around the vent. In our experiment, fossilisation by the growth of sulphide minerals on the biological materials (vestimentiferan tubes, periwinkle, mussel and clam shells) only occurred in the high-temperature areas of the vent sites, or where the vent changed over time — for example, where a diffuse flow vent turned into a black smoker during the experiment. Sulphide mineralisation did not generally occur at diffuse flow sites, although mollusc shells suffered considerable dissolution here, or at control areas away from active venting. The implication is that the fossils found in ancient vent deposits reflect only the parts of those communities that lived at the higher-temperature areas around the vents.

Results

We found that the mollusc shells and tubes acted as simple substrates for the growth of pyrite (iron sulphide) with mineralisation occurring on both shells and tubes. This is exactly what we might expect from the preservation of vent fossils in ancient vent deposits. We also discovered that the apparent bias towards the fossilisation of worm tubes and mollusc shells is a real phenomenon and reflects how well the various biological substrates resist chemical dissolution in the vent environment, which puts them under high pressure due to depth and exposes them to hot, acidic vent fluid. Thus, no shrimp carapaces remained in any of the ten cages, including those from the control sites away from active venting. Vestimentiferan tubes, by contrast, proved resistant enough to decay to become fossilised.

Conclusion

Our results are consistent with observations from ancient vent sites and let us better interpret the fossil record of vent communities. From this, we now know more of how vent fauna evolved, because we now understand how organisms are preserved in these environments, including the extremely rapid pathway to fossilisation — less than a year.

Credit: The text is taken from Hot stuff in the deep sea (Dr. Cris Little)
Planet Earth, Winter 2009, pp. 18 to 19
www.nerc.ac.uk/publications/planetearth/2009/winter/

Back to top Back to Top


Mid Dinantian Ammonoids from the Craven Basin – new insights into a mysterious interval of Carboniferous time
Nick Riley

Introduction

Ammonoids were first described by Phillips (1836) and subsequently by Bisat (1924, 1934, 1950, 1952) and Moore (1930 to 1952). The work of Bisat was particularly welcomed in coal-mining regions because his ammonoid zonation scheme significantly improved correlation of strata. Although ammonoid assemblages were referred to by Earp (1961) and Riley (1990a, 1990b, 1991), it was not until Riley (1996) in his Mid-Dinantian ammonoids from the Craven Basin, north-west England (Special Papers in Palaeontology 53, The Palaeontological Association) that a thorough account of their distribution and biostratigraphical framework was given. The ammonoid assemblages from the Bowland Sub-Basin of NW England, are the most prolific known, apart from those from the northern Urals of the Russian Federation (Kusina, 1973, 1974, 1980, 1983). The main genera described include Merocanites, Dzhaprakoceras, Ammonellipsites, Helicocyclus, Rotopericyclus, Beyrichoceratoides and Eonomismoceras.

Morphology

Ammonoids are shelled cephalopods related to squids, belemnites, octopuses, and cuttlefish, and more distantly to the nautiloids. The ammonoids all possessed an external shell, which is divided internally into chambers. The animal lived in the largest of the external chambers, and the internal chambers would have been filled with gas, making the animal buoyant in the water. They were a free swimming animals possessing a head with two well developed eyes and arms (or tentacles). It is generally accepted that the coiled ammonoids originated from a group of uncoiled cephalopods in early Devonian ammonoid species. The evolution of the coiled ammonoid conch from the uncoiled conch probably allowed an increase in manoeuvrability and maximum horizontal swimming speed.

The thin walls between the internal chambers of the shell are called the “septa”, and as the ammonoid grew it would move its body forward in the shell secreting septa behind it, thereby adding new chambers to the shell. The “sutures” (or suture lines) are visible as a series of narrow, wavy lines on the surface of the shell. The sutures appear where each septa contacts the wall of the outer shell. The design of the suture is one of the most diagnostic tools used in ammonoid identification. One explanation for this increasing extravagancy in suture pattern is that it leads to a higher strength of the shell.

Ammonoid distribution in the Bowland Sub-Basin

As alluded to before, ammonoids are the among the most satisfactory fossils for stratigraphic correlation because of their nektonic mode of life, potential for post-mortem distribution, and rapid evolution. The ammonoids associated with the Bowland Shale Group and younger strata are usually restricted to discrete marine black shale bands. By contrast, Mid-Dinantian ammonoids of the Clitheroe Limestone Formation and Hodder Mudstone Formation occur in a variety of lithologies in a totally marine sequence. Ammonoids are in fact rare in the Clitheroe Limestone Formation and are always associated with Waulsortian limestones. They first become abundant in the lower part of the Hodder Mudstone Formation, being most diverse in the Clitheroe Anticline where Helicocyclus and Michiganites are known. Their abundance reflects the change from carbonate ramp to a dysoxic hemipelagic environment. Despite their abundance, material preserved well enough for identification is sparse and limited to only a few localities where early diagenesis favoured uncrushed preservation.

Ammonoid

Ammonoid preserved in the Bellman Limestone Member, Clitheroe Limestone Formation, Late Tournaisian, Early Mississippian
(Photo: P. Kabrna, 2010)

Evolution of the family Goniatitidae (Morocco and Algeria)

The presence of Progoniatites and Winchelloceras means that the Ksar Bouhamed (Morocco) assemblage contains the stratigraphically oldest representatives of the families Goniatitidae and Girtyoceratidae. This is a remarkable fact since the Goniatitidae were thought to appear only in the Late Viséan, with little being known about their ancestry. The morphologically very similar Progoniatites and Goniatites are separated by a rather large timespan (latest Tournaisian to middle Viséan), from which no representatives of the family are known.

Progoniatites pilus

Progoniatites pilus n. sp. x2 Holotype MB.C. 18954.1
Type locality and horizon. Oued Temertasset, locality and sample MOU-E07 (Mouydir, South Algeria). Source (with permission): Dieter Korn et al. 2010 : Museum für Naturkunde Berlin, Invalidenstraße 43, 10115 Berlin, Germany.

This means that the Goniatitidae, one of the most common and geographically widespread families of the Late Viséan (Korn 1988, 1997) is a Lazarus taxon that suddenly reappeared after a long period of time and then became very diverse. The cause of the gap in the record may be explained by the relatively poor state of knowledge of the Early and Middle Viséan ammonoids, but also facies differences may play an important role. Late Tournaisian faunas are almost exclusively known from well-oxygenated limestone formations. However, too little is known about the ecology of Carboniferous ammonoids to explain the pattern of distribution within different facies belts. It is interesting that Progoniatites is not an endemic genus, known from North Africa, Central Europe, and the North Urals, and that Goniatites is also distributed almost globally.

The presence of Progoniatites in early Late Tournaisian ammonoid communities does not solve the riddle of the origin of the family Goniatitidae, as the ancestry of Goniatites now shifts to Progoniatites, of which no morphologically similar form is known from time-equivalents or stratigraphically older sedimentary rocks.

Back to top Back to Top


Tsunami processes and response
Jeff Peakall

What is a tsunami and why are they so destructive?
Tsunami is a Japanese word (tsu=harbour : nami=wave). They are fairly common in Japan and many thousands of Japanese have been killed by them in recent centuries. One way of describing a tsunami is a ‘gravity wave’ in the sea (or other body of water) produced by sudden displacement of the seafloor and the water column above it.

Tsunami Wave

The Great Wave off Kanagawa
Katsushika Hokusai (1760 – 1849)
Hokusai’s most famous print, the first in the series 36 Views of Mount Fuji

When compared to earthquakes, damaging tsunami waves propagate much further and can cause simultaneous catastrophic losses on opposite sides of ocean basins. Tsunami are formed by a number of different scenarios i.e., over 90% are triggered by earthquakes (most beneath the sea floor), however, only a small % of submarine quakes trigger tsunami (fortunately!). They can also be produced as a result of volcanic eruptions or even submarine landslides, mud flows or from dense pyroclastic flows entering the sea. Large asteroid/comet impacts are perhaps the most feared for obvious reasons. The incoming tsunami wave travels at high velocities and once it reaches its destination can have a high run-up height in excess of 20 m. There are commonly multiple waves making up a tsunami ‘wave train’. The behaviour of tsunami in the impact area is complex and strongly affected by local bathymetry and topography with inlets and bays generally being high-hazard areas.

Past, Recent and Future
Although tsunami are not common phenomena in Britain, historical accounts suggest that coastal areas of both Britain and mainland Europe, extending over areas which are now submerged, would have been inundated by a tsunami triggered by the Holocene Storegga Slide in the North Sea off Norway. This event would have had a catastrophic impact on the contemporary Mesolithic population, and separated cultures in Britain from those on the European mainland. An analysis of new and previously published radiocarbon dates indicates that from evidence in the United Kingdom, the event took place sometime around 7100 radiocarbon years BP.

The recent 26th December 2004 tsunami centred on Indonesia and Thailand was a very rare event with correspondingly large consequences. It affected as many as 11 countries and produced the largest life loss due to a tsunami (290332 deaths). There have been c.1000 tsunamis during the last century worldwide of which 13.5% caused significant damage and life loss. Where coastal populations continue to increase better foundation design and construction of buildings should be mandatory, even though this unlikely to ensure life safety in future tsunami.

Massive flank failures of island stratovolcanoes are extremely rare phenomena and none have occurred within recorded history. Recent studies have forecast the possibility of a mega tsunami event caused by massive slope failure of the Cumbre Vieja volcano on the island of La Palma in the Canary Islands. Geologists have observed a developing zone of weakness which appears to be giving rise to deformational instability on the volcano’s steep western flank. This is where a large-scale, gravitational collapse could occur with little or no precursory deformation. As early as 2001 it was postulated that a massive landslide, with a volume of up 500 cubic km, could be triggered by the next major eruption of Cumbre Vieja. The study concluded that the collapse of Cumbre Vieja’s western flank would generate a destructive mega tsunami which would strike both sides of the North and South Atlantic with waves of up to 50 m. Britain’s Atlantic coastline would be affected if such a catastrophe was to occur. In certain areas, the tsunami waves would travel as much as six to seven km inland, destroying everything in their path.

El durazno Crater

El Duraznero crater, Cumbre Vieja volcano, La Palma, Canary islands.
Photo © Hed Hickling

Deep-Ocean Assessment and Reporting of Tsunamis (DART)
The DART early warning system has a platform that lies on the seafloor monitoring seismic activity and sending signals to a buoy floating on the surface. The buoy then uses satellite communication to pass on the gathered information to tsunami warning centres. In the event of an earthquake it is designed to detect whether a tsunami will occur and pinpoint its height, location and when it will make landfall. However, there are occasional glitches in the system that need to be resolved. The National Weather Service in Seattle reported that a network of expensive tsunami detection buoys off the West Coast could offer better protection against devastating waves like the one that struck in the Indian Ocean - if they all worked. Of the six buoys placed throughout the Pacific Ocean, two near Alaska have been broken for 14 months. Scientists at the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska offered assurances that despite the breakdown, they can rely on information gathered by earthquake sensors and tide gauges.

Conclusion
Tsunami has the greatest destructive reach of any of our natural hazards. The threat is global and carries serious risk to chemical plants, fuel storage facilities and nuclear power generation plants. The situation is exacerbated by climate change triggered sea level rise. The question remains “Are governments doing enough to com

Back to top Back to Top


Cave development in Caledonide marbles
Trevor Faulkner

Geological background
Rocks of the metamorphic Caledonides derive their composition and structure from the Caledonian Orogeny. In Scandinavia, the remnant rocks of this orogeny occur along the Scandian mountain chain, 1800 km long with a width of 200–400 km. The author’s main study (Faulkner, 2005) was the speleogenesis of ~1000 marble caves in commonly steeply-foliated ‘stripe karst’ in ‘Central Scandinavia’ (Fig. 1).

Caledonide Marble Cave

Fig. 1 Waterfall at an amphibolite intrusion in vertically-foliated marble in Kvannlihola, Norway.

Karst speleogenesis in Central Scandinavia
The marble caves of the Central Scandinavian Caledonides were formed from open fractures that were created primarily by deglacial seismicity at the culmination of each of the many Quaternary glaciations that the region has experienced. Subsequent inundation by deglacial ice-dammed lakes enabled phreatic (ground water occurring below the water table) enlargement by dissolution, with passages either becoming relict during the following interglacial or else being entrenched by (mainly) vadose (water occurring above the water table) processes if recharged by streams that originated on the surface and flowed into cave systems. Because the distance of the contemporary fractures and therefore the cave passages from the nearest land surface is commonly constrained to be less than one-eighth of the depth of the local glaciated valley, the caves are rather epigean i.e. near surface in nature. This subsurface cave distance is of the same order of magnitude as the thickness of rock removed from valley walls and floors at each major glaciation. This suggests that, when viewed over several glacial cycles, caves are involved in a race to develop deeper during deglaciation and the following interglacial, before their upper levels are removed by erosion at the next glaciation. Indeed, relatively few cave passages in the study area can have survived from the previous, Eemian interglacial (Eemian = Ipswichian interglacial in the UK).

General model
A general model for cave development throughout these marble caves proposed that the prime control on the extent of karstification was the thickness of the local ice sheet at glacial maxima. This determined both the intensity of seismicity and the volume of water able to flow from deglacial ice-dammed lakes into the fractures and into any existing conduits. Caledonide marble caves in stripe karst outcrops should especially be considered as four-dimensional objects throughout their cmmonly intermittent existence. Mainly vadose caves are regarded as ‘half-cycle’ caves that developed primarily in the Holocene. Relict caves (primarily phreatic) and combination caves (with both phreatic and vadose elements) are commonly ‘single-cycle’ caves that developed their relict phreatic passages during Weichselian deglaciation, and only a few are ‘multi-cycle’ caves that have experienced several Pleistocene glacial cycles. The existing caves are more numerous and commonly larger than those that were present during previous interglacials.

Marble caves commonly experience a four-stage, cycle of development that is driven by the glacial cycle. The stages are as follows:

1. Rapid deglacial isostatic rebound that follows retreating ice margins causes seismicity and centimetre-scale movements, which form inception fractures to a maximum distance from the surface equal to one-eighth the depth of the local glacial valley.

2. Phreatic passages enlarge from inception fractures at high flow rates beneath deglacial ice-dammed lakes over periods up to ~2000 calendar years at relatively high wall-retreat rates, despite low temperatures and low PCO2 (carbon dioxide partial pressure).

3. Mainly vadose passages entrench at the lowest levels during interglacials at a rate constrained by the size of the local catchment area.

4. Glacial erosion removes whole caves or their upper and outer parts during the next glaciation (glacial removal), but valley-deepening in the range 15–55 m causes ever-deeper inception fractures at the first stage of the next cycle.

Relevance to Yorkshire
The Yorkshire Dales consist of a karst area with many caves formed in Carboniferous sedimentary limestones. This area has also been glaciated and deglaciated many times but there is still little understanding of how much the Dales were deepened by each successive glaciation.

Waltham reported the existence of two main groups of cave passages in Yorkshire: old, mainly phreatic relict passages and younger stream passages. It now seems possible that the upper relict passages were partly, enlarged under ice-dammed lakes at successive deglaciations and that the active vadose passages developed during the Holocene and earlier interglacials. Supporting evidence for deglacial ice-dammed lakes is the presence of high-level wind gaps and deep gorges through which south-flowing streams presently pass. These could have been partly formed by jökulhlaups when Yorkshire Dales ice-dammed lakes breached the lowering Devensian ice sheet to the south. The author has observed neotectonic movements both in caves and on the surface in the Craven area, suggesting that some cave passages may also have been initiated by tectonic inception.

References

Faulkner, TL. (2005): Cave inception and development in Caledonide metacarbonate rocks. Ph.D. thesis, University of Huddersfield.

Faulkner, T. (2010): Relationships between cave dimensions and local catchment areas in Central Scandinavia: implications for speleogenesis. Cave and Karst Science 36 (1) 11-20.

Back to top Back to Top


Victoria Cave: a half million year record of climate change
Tom Lord

Introduction
Victoria Cave [SD 8383 6504] was re-discovered north-east of Settle by Michael Horner in May 1837. Horner collected a number of Romano-British objects off the floor of the cave and showed them to his employer, Joseph Jackson. It was Jackson, in June 1837 on the coronation day of Queen Victoria, who subsequently explored the cave further and chose the name Victoria Cave. Jackson continued intermittent excavations of the cave for the next 30 years. In 1869 the Settle Cave Exploration Committee was formed, and in 1870 began large scale excavations at Victoria Cave. The Committee employed Joseph Jackson as site director for the excavation with William Boyd Dawkins acting as scientific director. Dawkins interpreted the cave as being first occupied in the Neolithic then following a hiatus being extensively re-used as a temporary shelter by wealthy Romano-British refugees at the end of the Romano-British period.

Since then it has become the most important historic cave in the British Isles. The cave is owned by Yorkshire Dales National Park Authority and not surprisingly has been designated a Scheduled Ancient Monument (SAM) and a Site of Special Scientific Interest (SSSI). The cave entrance is located along King’s Scar in a 17 m high cliff face of Gordale Limestone where four palaeokarstic surfaces, from 1.6 m to 8 m apart, are present.

Ice sheets occupied the region on several occasions during the Quaternary, however, the last glaciation during the late Devensian (c. 26000 - 10000 years BP) was so intense that it eradicated most of the evidence of earlier glacial events. Only within Victoria Cave are older deposits known along with a selection of mammalian faunas.

Victoria Cave

The photograph illustrates the early stages of the excavation of Victoria Cave in 1873. At this stage of the excavations, the glacial diamict (till or boulder clay) that underlies the scree is just coming into view to the left of the large upright wooden scale bar. The scientific interest of Victoria Cave attracted distinguished geologists’ of the time such as John Phillips, Charles Lyell, Adam Sedgwick, Dean William Buckland and Thomas Sopwith.

Richard Hill Tiddeman (1842-1917)
Tiddeman encouraged a further deep excavation in 1872, and in May 1872, the Settle Cave Exploration Committee discovered beneath the laminated clay an earlier bone bed with remains of Last Interglacial spotted hyaena and other extinct species. Further large scale excavations followed by way of an annual grant from the British Association for the Advancement of Science until 1878. The work under the direction of Richard Tiddeman is largely responsible for the present cave topography and the industrial scale spoil tip outside. Tiddeman’s excavations in Chamber A, and the previously unexcavated Chamber D created the present impressive entrance, and the broad, high entrance chamber. Inside the cave, Tiddeman’s excavations (1873-1879) cut the mine like passage linking the backs of Chamber A and B.

In presenting the Murchison Medal to Mr. Tiddeman in 1911, Professor Watts, the President of the Geological Society, said: “Ever since the beginning: of Mr. Tiddeman’s work for the Geological Survey on the borders of Yorkshire and Lancashire he has kept his eyes open to the observation of exceptional facts, and his mind employed in working out explanations for them. The excavation of the Victoria Cave, Settle, in which he took so active a part gave us valuable information on the history of the Pleistocene Mammalia: his work on the glaciation of north Lancashire still remains a model and a basis for glacial work all over the country.”

Recent Research
In 1937 examination of previously unexcavated areas at the back of the cave recovered faunal remains of the Hyaena Bone Bed encrusted by cave deposits. In the 1970s the cave was the focus of a program of AS U-Th cave dating. Although the results were limited by the precision and range of available techniques, the study provided the first direct ages for the last interglacial bone bed.

A team of scientists (Lundberg, J., Lord, T. & Murphy, P., 2010) revisited the site with three key aims in mind: a) to re-date all the important calcite horizons, b) to revisit sedimentological and stratigraphical relations in the field, c) to review the written documentation from the original field notes of the 1870s excavations. The sequence of laminated clays in Victoria Cave provides a record of continental ice expansion in this area during 4 glacial maxima. These laminated (varved) clay are interpreted to indicate glaciofluvial deposition in an lake environment caused by the ice advancing up the side of the glacial trough to the level of the cave where it was able to block the drainage.

Whilst laminated clays inside the cave have shed light on periods of maximum ice cover, the team turned their attention to cold but not glaciated periods of time (periglacial).The best evidence was collected outside the cave by using cosmogenic dating of glacial erratics. Using this technique, Vincent et al. 2010 suggested that the higher ground was deglaciated by ca. 18000 years and that scree accumulation in the region also dates to the period 18000 to 14000 and that the climate was cold, dry and windy. pre-Devensian ice ages are also considered to have undergone similar periglacial activity. The lack of periglacial deposits inside the cave when they were established outside suggest the cave entrance may have been blocked by scree. Sediment accumulation or scree outside the entrance would effectively limit access to the cave by larger faunas. The opening and closure of the cave entrance is probably a reflection of climatic cycles.

Conclusion
The dates reveal that cave formation began beyond the range of the dating technique (older than 600000 years ago). The sedimentary sequence is thus the longest of any cave in the region from early middle Pleistocene to Holocene. Having established a more accurate record of events dating back much longer than expected suggests that Victoria Cave may yet hold more secrets to uncover. The use of current and future high resolution techniques in dating will be an ever important tool in the elucidating the archaeological and geological history of the cave. It is even more important that Victoria Cave is preserved for future study.

The cliff face above the cave entrance is weathering and slowly deteriorating. There have been occasional small rock falls and there is some evidence that larger falls have occurred since the Victorian period excavations. The laminated clays are being eroded by rabbit and human activity and there had been a number of recent collapses. Of particular concern is the large block on the south side of the ancient rock fall, perched on an undercut block of laminated clay. It was considered that further collapses may occur in future. Rabbit burrowing has continued, particularly around the perched block, resulting in a considerable loss of these important and unique sediments and potentially contributing to the destabilisation of the block. Should this block fall it is likely to take with it further undisturbed sediments. Plans are afoot to control the rabbit population. Finally, though not totally unexpectedly, there is the thorny issue of visitor erosion The deposits are further suffering from the effects of mainly casual visitors to the cave. The occasionally wet nature of the cave surface and the steep angle of slopes creates further erosion as well as a severe though largely natural hazard.

Further Reading
Lord, T. C., O’Connor, T. P., Siebrandt, D. C., & Jacobi, R. M. (2007): People and large carnivores as biostratinomic agents in Late glacial cave assemblages.
Journal of Quaternary Science, V. 22, pp. 681-694.

Lundberg J., Lord T. C. & Murphy P. (2010): Thermal ionization mass spectrometer U-Th dates on Pleistocene speleothems from Victoria Cave, North Yorkshire, UK: Implications for paleoenvironment and stratigraphy over multiple glacial cycles.
Geosphere; August 2010; V. 6; No. 4; pp. 379-395.

Murphy. P. J.. & Lord. T. C. (2003): Victoria Cave, Yorkshire, UK: New thoughts on an old site. Cave and Karst Science, V. 30, No. 2, pp. 83-88.

Back to top Back to Top


Members Evening

Geology of Anglesey
Paul Kabrna

This overview of the geology of Anglesey will form the basis of what sort of geology will be seen during the week-end field excursion in June later this year.

The geology of Anglesey was privately mapped by Edward Greenly (1861-1951) in the early part of the century. Since then, other British geologists’ such as Shackleton (1909-2001), Wood (1934-2001), Horák and Gibbons, have made a significant addition to Greenly’s classic work. The root of almost all of the controversy since Greenly’s time has been the interpretation of the ‘old’ rocks on the island, i.e. Greenly’s Mona Complex which was considered to be entirely Precambrian in age. In 2004 Australian geologists used isotopic dating of detrital zircon collected from the South Stack Group on Holy Island. Their results confirmed that the ‘Mona Complex’ spans the late Precambrian (Neoproterozoic) to late Cambrian (750 and 500 million years ago); so not entirely Precambrian after all! High resolution techniques such as this continue to play a part in elucidating the age of Anglesey’s rock record.

Semipelite

Semipelitic Schist at South Stack
The photo shows what was probably a siltstone after being subjected to metamorphism. The deformation has produced a flat-lying crenulation cleavage, some small scale folds, and some isoclinal first minor folds.
Photo © P. Kabrna (2005)

The depositional environment of Anglesey’s ancient rocks is associated with oceanic plate subduction below an island arc system in the southern hemisphere. Geologists refer to the island arc as Avalonia. In such a tectonic setting you would expect to see (a) deep sea sediments being deformed and metamorphosed as they descend into the ocean trench; (b) intrusive and extrusive igneous rocks building up the island arc; (c) metamorphism of both sedimentary and igneous rocks adding considerably to the complexity of Anglesey’s geological history.

In fact, what makes Anglesey’s geology so fascinating is that all these three depositional environments of oceanic subduction are preserved in distinct fault-bounded slices trending NNE / SSW. These ‘slices’ have formed the basis of a conceptual framework based on ‘terranes’. There are three distinct terranes collectively known as the Monian Composite Terrane (originally termed the Mona Complex by Greenly). The three individual terranes are: the Monian Supergroup, the Coedana Complex, and the Aethwy Terrane. They are fault-bounded units with contrasting geological histories. The Monian Composite Terrane is overlain by Palaeozoic volcanic and sedimentary rocks.

Back to top Back to Top


FIELD EXCURSIONS

Waddington Fell Quarry and Ashnott Knoll
Guides: Paul Kabrna and Alan Whalley

Time and Date: 10:30 am, Saturday, 9 April 2011

Logistics: Park in the main car park at Waddington Fell Quarry. This is a public open day so a hard hat, high-viz jacket are not required. However, hiking-boots are essential (and wellingtons for Ashnott!). Carry packed lunch or alternatively visit the Parker Arms in Newton or the Moorcock in Waddington. At lunch we can discuss possible alternative parking for some members at SD [689 487] for access to the main wooded localities described below.

LOCALITIES

1. (AM) Waddington Fell Quarry [SD 718 477]: is located at the summit of Waddington Fell, 6 km to the north of Clitheroe and 3.5 km north of the of Waddington. This large quarry exposes a section through the lower part of the Warley Wise Grit (according to the original BGS mapping). This conclusion was based, to a large extent on the coarser nature of the sandstones. Field evidence confirms the age of the sandstone as Pendle Grit; the same age as sandstones at the Nick O' Pendle and Wiswell Quarry.

LUNCH

2. (PM) Ashnott Knoll, Bonstone Brook & Crag Beck SD [697 487]: Small amounts of lead found associated with Ashnott Knoll near Newton date back to the early 19th Century. There are traces of 5 shallow shafts and one adit into the knoll. Ashnott Knoll, which is one of the many Waulsortian mud-mounds in the Bowland Sub-Basin, is part of the Coplow limestone suite of mud-mounds scattered throughout the Bowland Sub-Basin.The end of the Waulsortian limestone phase coincides with the erosion and fragmentation of the carbonate ramp into a series of depositional ‘lows’ and ‘highs’ of which Ashnott Knoll is one of the more prominent 'high' point within the basin. The break-up of the basin also led to a complete reorganisation of depositional style with hemipelagic mudstones (Hodder Mudstone Formation) dominating. These mudstones are well exposed in stream sections in the wooded area to the west of Ashnott Knoll. At the confluence of Crag Beck and Bonstone Brook, the Dunbarella Bed is only 20 cm thick. Abundant bivalves such as Dunbarella and Pteronites occur in this bed. Other features to look out for: a) gravity slides (although perhaps not totally unexpected adjacent to a 'high''), b) starved turbidites, and c) slumping in the Rain Gill Limestone.

O.S. Maps
1: 25 000 sheet SD 64 / 74 Clitheroe and Chipping

References
Kane, I. A., Catterall, V., McCaffrey, W. D. and Martinsen, O. J. (2010): Submarine channel response to intra-basinal tectonics. American Association of Petroleum Geologists Bulletin, 94, pp. 189-219

Riley, N. J. 1995 Stratigraphy of the Worston Shale Group, Dinantian, Craven Basin, north-west England. PYGS Vol. 48, pp. 163-187

Back to top Back to Top


Whitewell
Guides: Jean Chicken, Paul Kabrna and David Turner

Time and Date: 10:30 am, Sunday, 8 May 2011

Logistics: Meet at the layby adjacent to Hall Hill Quarry, Whitewell [SD 667 467]. Carry packed lunch. The only facilities nearby are at the Whitewell Hotel. There is usually an ice-cream van at Burholme Bridge north of Whitewell (handy for the end of the trip)!

Cars will have to be moved around to fit the localities in, so where possible, please try to fill cars. As usual come prepared for any kind of weather. Boots are recommended.

Localities

1 Hall Hill Quarry [6675 4670]
2 Whitewell Gorge [6557 4655]
3 Ing Wood [6563 4486]

LUNCH

4 Leagram Knot [6390 4470]
5 Leagram Brook [6375 4450]
6 Calamine Mine [6442 4753]

Geological setting

Carboniferous Supergroup rocks underlie the entire Bowland Sub-Basin and crop out in a series of NE - SW trending folds which in turn are cut by faults trending NW - SE. The tectonic regime had a profound effect on deposition with limestones dominating the Bowland High Group and hemipelagic mudstones and turbidite limestones likewise dominating the Craven Group.

The area around the Whitewell Anticline (Loc. 1-3, 6) and the Throstle Nest Anticline (Loc. 4, 5) is an ideal setting for studying limestones of the Bowland High Group. All important members are present from the Chatburn limestone to the Bellman limestone and collectively mark the change from open shelf to deep water Waulsortian mud-mound development. The transition into the Craven Group deposits is marked by a basin-wide unconformity which represents the break-up of the basin into a series of 'highs' and 'lows'. The eroded surface of the fragmented basin was effectively smoothed over by deposition of the Limekiln Wood Limestone. This unit crops out at locality 3 and is considered to be one of best exposures of a boulder bed in the entire basin.

The Leagram Mudstone is a good example of hemipelagic mudstone deposition in the Craven Group. The main exposure is in a meander cliff on the east side of the brook. There are pronounced beds of wackestones throughout the sequence and with careful probing of the blocky mudstone, the ammonoid Merocanites may be found. The final locality at Dinkling Green, besides being a particular fine outcrop of Bellman limestone, is also an early site where zinc carbonate ore (smithsonite), better known as Calamine (De Rance 1873), was extracted from small pockets within the limestone.

O.S. Maps
1: 25 000 sheet SD 64 / 74 Clitheroe and Chipping

References
Aitkenhead, N., Bridge, D. McC., Riley, N. J. & Kimbell, S. F. (1992): Geology of the country around Garstang. British Geological Survey Memoir, England and Wales, Sheet 67

Riley, N.J. (1990): Stratigraphy of the Worston Shale Group, Dinantian, Craven Basin, north-west England. PYGS Vol. 48 , 163-187

Back to top Back to Top


Geology of Anglesey
Guide: Paul Kabrna

Time and Date: Friday to Sunday, 10-12 June 2011

Logistics: The Dinorben Arms Hotel in Amlwch and the Harbour Hotel in Cemaes are where the majority of the CPGS members are staying. Packed lunches will be required for both Saturday and Sunday. Be prepared for any inclement weather and as always have hiking boots with you.

Great care should be taken when walking along the coastal path which sometimes lies above sheer cliffs and can suffer from strong winds.

Itinerary
All NGRs lie within the 100 km grid square SH which is omitted in the text.

1. Friday: Lligwy Bay [492 873]; Parys Mountain [437 904]

2
. Saturday: Trwyn y Parc [374 937]; Llanbadrig [375 945]; Ogof Gynfor [378 947]

3
. Sunday: Llanddwyn Island [405 634]; Marquess of Anglesey Monument [536 716]

Nearby localities illustrating Anglesey’s rich industrial heritage are Porth Llanlleiana [3975 9505] and Porth Wen [4025 9470]. The former is the site where porcelain was produced from deposits of china clay found on Dinas Gynfor. Llanlleiana means Church of the Nuns and the works were built on the site of a convent.

In contrast, Porth Wen proved to be an ideal locality for the manufacture of silica bricks as quartzite is a siliceous rock, ideal for making refractory bricks for use in the steel industry. The bricks were then exported by sea from the works’ own harbour.

Silica Brickworks at Porth Wen

Porth Wen Brickworks

Silica bricks were manufactured for use in the steel industry in the In the late 19th century at Porth Wen. The silica was extracted from the abundant quartzitic sandstones of the Torllwyn Formation and exported by sea from the works’ own harbour. Photo © P. Kabrna (March 2011)

Site 1. LLIGWY BAY

Meet at 13.30 at Grid Ref. [492 873] Lligwy Bay Car Park (north side). From Amlwch follow the A5025 to Bryn Refail. Look out for a left turn down a single track road to Traeth Lligwy. The car park at the end of a road by the beach is pay and display (£2.50). No other facilities.

Lligwy Bay contains the only Old Red Sandstone (ORS) locality in North Wales and is well exposed in the northern part of the bay. At the opposite end there is carboniferous limestone and an intriguing feature known as the Lligwy Bay Disturbance.

Site 2. PARYS MOUNTAIN

Meet at Parys Mountain Copper Mine Trail [438 906]. From Amlwch drive to the A5025. At the roundabout [442 925] take the B5111 south for approximately 2 km. Look out for the brown signpost for ‘Copper Mine Trail’ and a car-park sign (P). There is a small interpretive display showing numbered trail posts, and a dispenser providing an information leaflet (£.0.25) at the car park. No other facilities.

Parys Mountain has been confirmed as a site of prehistoric mining, and there are also some indications of Roman activity. Extensive economic production of ore eventually resulted in the mine becoming (allegedly)the world’s largest copper mine in the 1780s. Until 1800 most mining was by open cast, but from 1810, Cornishmen opened up significant underground workings. By 1900 all significant mining activity had ceased.

Site 3. TRWYN Y PARC, LLANBADRIG, and OGOF GYNFOR

Meet at 09.45 at Cemaes car park [374 937] approached from a narrow road sign posted Gadlys Hotel. The narrow road leaves the A5025 1 km east of Cemaes Bay. The walk is about 2 miles and moderate. Cars could also be left at the Church of St. Patrick, Llanbadrig [375 945] for members who wish to avoid the walk back.

The walk from Cemaes to Ogof Gynfor highlights national and internationally important geological sites. At Trwyn Y Parc there are a number of 'Miocene pipes' in the Gwna Limestone, from which some of them have yielded Miocene fossil spores. In addition there are Precambrian stromatolites preserved in the very pure limestones of Gadlys Quarry. On the beach of Porth Padrig Ordovician strata are exposed along with the White Lady - a small sea stack made of white quartzite. The Llanbadrig peninsular is the informal type locality for the Gwna melange, a spectacualr and chaotic assemble of clasts from very small to very large! The cliff section at Ogof Gynfor is an important site for demonstrating the unconformity between Gwna rocks and Arenig Ordovician sandstones.

Site 4. LLANDDWYN ISLAND

Meet at 09.30 at the car park adjacent to Newborough beach at [405 634]. At Newborough turn down Church Street (opposite the post office) at the main cross-roads. There is a toll bar which will require £3 in coins. Distance from Amlwch to Newborough is about 34 km. Carry packed lunch. There are facilities at the car park.

Llanddwyn Island is a narrow tidal isthmus projecting south-west from the Anglesey coastline. The contrast of rock types with their distinctive colours and textures produces one of the most dramatic geological assemblages in the British Isles.

Llanddwyn means The church of St. Dwynwen. She is the Welsh patron saint of lovers, making her the Welsh equivalent of St. Valentine. Her feast day, the 25th January, is often celebrated by the Welsh with cards and flowers, just as 14th February is for St. Valentine. The island boasts two lighthouses. The older lighthouse, Tŵr Mawr has returned to service following the decommissioning of Tŵr Bach in 1975. Tŵr Bach featured prominently in the Demi Moore film ‘Half Light’ released in 2006.

The island records an entire plate tectonic event, from the creation of the ocean floor as a mid-ocean ridge, seen here as pillow lavas, through its journey across the ocean basin where it picked up sediments, to its burial and metamorphism as plates collided and the sediment sank down into a deep ocean trench i.e., we are looking at slices of ocean floor in an accretionary prism associated with a subduction zone (Kawai et al., 2008).

Site 5. MARQUESS OF ANGLESEY COLUMN

Meet in the free car park in Llanfairpwllgwyngyll (Llanfair PG) at [536 716]. The tourist Information centre is situated at James Pringle Weavers, 1 km away along Holyhead road (A5).

The 27 m tall column is composed of local fossiliferous limestone from Moelfre. It was built in 1816 in memory of Lord Paget, the Marquess of Anglesey of ‘Battle of Waterloo’ fame. From the top of the column there are good views of Plas Newydd, the stately home of the current Marquess of Anglesey and the Menai Strait. If you choose to climb the column there is a charge.

The blueschist exposed in the crags around the base of the column are Precambrian in age and as such are one of the oldest and quite probably the oldest assemblage of blueschists in the world.

O.S. Maps
1:25 000 Explorer 262 Anglesey West
1: 25 000 Explorer 263 Anglesey East

Further Reading
Bates, D. E. B., Davies, J. R. (1981): Anglesey. Geologists’ Association Guide No. 40, p. 31.

Conway, J., (2010): Rocks and landscapes of the Anglesey Coastal Footpath. ISBN 0-9546966-3-8 Available from The Old Watch House, Port Amlwch, Amlwch, Ynys Môn LL68 9DB Tel:01248 810287 or email geomon@btconnect.com

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, pp. 743–746

Greenly, E., (1919): The geology of Anglesey. Memoir of the Geological Survey of the U.K. [2 vols, 980 pp.]

Horák, J. M., & Evans, J. A. (2011): Early Neoproterozoic limestones from the Gwna group, Anglesey. Geol. Mag. 148 (1), pp. 78-88

Kabrna, P. (2005): Precambrian rocks of Anglesey. (Field Excursion Guide, CPGS)

Kawai, T., Windley, B. F., Terabayashi, M., Yamamoto, H., Isozaki, Y., Maruyama, S. (2008): Neoproterozoic glaciation in the mid-oceanic realm: An example from hemi-pelagic mudstones on Llanddwyn Island, Anglesey, UK. Gondwana Research 14, pp. 105-114

Oldham, T. (2006): The Caves and Mines of Anglesey.
p. 57. This book describes many smaller mines including the long forgotten coal mines at Berw.

Pointon, C. and Ixer, R. A. (1980): Parys Mountain mineral deposit, Anglesey, Wales: geology and ore mineralogy. Transactions of the Institution of Mining and Metallurgy, 89, B99-B109.

Tatham, D. et al. (2009). Field Excursion to Anglesey. Deformation, Rheology & Tectonics Conference, a joint venture between the universities of Liverpool and Manchester.

Treagus, J. (2008): Anglesey Geology - a field guide. ISBN 0-9546966-2-X

Walsh, P., Morawiecka, I. and Skawinska, K. (1996): A Miocene palynoflora preserved by karstic subsidence in Anglesey and the origin of the Menaian Surface. Geol. Mag. 133 (6), pp. 713-719. Cambridge University Press.

Web site
GeoMôn www.geomon.co.uk/

Back to top Back to Top


Glaciation and geomorphology around Kisdon, Upper Swaledale
Guide: Jon Barber
Joint meeting with the North Eastern Geological Society

Time and Date: 10:00 am, Saturday, 16 July 2011

Meeting at: Meet at the Resource and Heritage Centre in Keld, 10:00 am. Parking is available at the nearby farm at a cost of £2 per vehicle. Carry packed lunch but there is a pub with access to sandwiches. There is a section of approximately 50 metres where it could be fairly boggy so the usual stout footwear should be worn and be prepared for the vagaries of inclement summer weather.

Purpose: To examine landforms and sediments in the valleys and on the valley-side slopes around Kisdon, upper Swaledale noting the effects of glaciation and glacier wastage, and how the landscape was later modified by fluvial and slope-forming processes. The effects of 19th century mining activity will be noted also. The area is an SSSI and is located in the Yorkshire Dales National Park.

Background
The name Keld is taken from the Norse word kelda - meaning bog or mire.We will take the route to the east, out of the village and up Birk Hill where we will see to the north, the steeply incised valley carrying the River Swale, and to the south evidence of quarrying the Friarfold ore vein and the local rock for building stone. Evidence of lead mining is readily apparent and there are also several lime kilns in the area. At Birk Hill we follow a steep track upslope to the south to cross from the divide into the valley of the Skeb Skeugh. Here although equally dramatic the geomorphology is very different from that of the Swale. Shallow borehole data across the valley of the Skeb Skeugh show 2 m of peat overlying silty clay and gravel indicating a very different mode of development to that of the Swale valley less than 1 km to the north east. Landforms in this valley are reminiscent of those found in the glacially choked section of Wharfedale around Bolton Abbey and include glacial and interglacial features on the valley sides and a valley floor suggestive of Holocene wetland. We continue our walk along the high path on the western side of the Skeb Skeugh valley, noting some of the geomorphological features (including kames, eskers and rotational landslip before crossing back over the divide to the north west of Doctor Wood, to pick up the path alongside the engorged Swale back to Keld. This is a circular route of around 6 km. There are some short, steep sections to the path which some members may find challenging. Jim Rose really covered this area well in his paper 'Landform Development Around Kisdon, Upper Swaledale, Yorkshire'.

O.S. Maps
1:50 000 Sheet 98 Wensleydale & Upper Wharfedale
Outdoor Leisure Sheet 30 Yorkshire Dales, North and Central Areas

References
Raistrick, A. (1926): The glaciation of Wensleydale, Swaledale, and the adjoining parts of the Pennines. PYGS Vol. 20 pp. 366 - 410

Rose, J. (1980): Landform development around Kisdon, Upper Swaledale, Yorkshire. PYGS Vol. 43 , pp. 201-219

Back to top Back to Top


Carboniferous rocks around Gargrave and Skipton
Guide: Paul Kabrna

Time and Date: 10:30 am, Sunday, 18 September 2011

Logistics: Meet at Bell Busk. Turn right off A65 3.2 km west of Gargrave.
Drive 1.6 km north (under Railway Bridge), turn sharp right at first turning and park on verge by river bridge at [SD 905 564]. Twenty minute walk to Haw Crag (1.3 km by rough farm track with slight ascent). Carry packed lunch and be prepared for inclement weather. The longest walk is to Clints Rock Quarry which is 1.75 km from Rylstone car park adjacent to the B6265 at [SD 9692 5874].

Geological Setting
Carboniferous rocks on this excursion are from localities situated in the northern part of the Bowland Sub-Basin which early geologists such as R.G. Hudson referred to as the Craven Lowlands. Localities 1 and 2 are situated on the Eshton-Hetton Anticline whilst the remaining 3 localities are situated on the Skipton Anticline. Rocks to be seen include limestones, mudstones and sandstone from the Bowland High Group, Craven Group and the Millstone Grit Group. Observing the changes in depositional history during the day will enable us to see how the basin evolved during the Carboniferous Period. Fossils, sedimentary features and prominent geological structures seen at the localities will add greatly to the geological story of this part of the world.

Localities

1. Haw Crag Quarry [SD 9142 5637]: this has been an SSSI since 1954 primarily for its spectacular breccias and boulder bed. This is a key site for understanding carbonate environments.

2. Clints Rock Quarry [SD 9669 5751]: has been an SSSI since 1955 for its various limestone lithologies and includes 'Tiddeman's Breccia', a Pendleside Limestone conglomerate. This is one of the richest zaphrentoid coral localities in England.

3. Skipton Rock Quarry [SE 010 530]: this disused quarry exposes the Skipton Rock Fault, a reverse fault developed near the axis of the Skipton Anticline. The steeply dipping bioturbated Haw Bank Limestone outcropping by the fault is equivalent to the Chatburn Limestone in the Ribble Valley.

4. Hambleton Quarry [SE 058 535]: this disused quarry has been an SSSI since 1991. In the core of the minor fold the turbiditic Pendleside Limestone, formerly the Draughton Limestone, is represented by a spectacular breccia bed ('Tiddeman's Breccia'). The uppermost unit about 18 m thick, is the Bowland Shale Formation (formerly the Draughton Shales). Soft-sediment deformation is also a key feature of this quarry.

5. Whitshaw Bank Quarry [SE 0018 5483]: this is a small abandoned Pendle Grit quarry above Embsay reservoir. This locality exposes 30 m of coarse-grained, thickly bedded sandstones at the base of a channel complex. The site also offers good views over the Skipton Anticline.

Back to top Back to Top