Programme: 2007 - 2008

© Craven & Pendle Geological Society

Indoor Meetings

Friday: 19 October
Modelling ancient Earth climates. Alan Haywood Ph.D., Leeds University.

Friday: 16 November
Submarine channels: giants of the deep. Jeff Peakall Ph.D., Leeds University.

Friday: 14 December
Members Presentations.

Friday: 11 January
The end-Guadalupian mass extinction. Professor Paul Wignall, Leeds University.

Friday: 8 February
The last glacial stage (the Devensian) in NW England. Catherine Delaney Ph.D., Manchester Metropolitan University.

Friday: 7 March
The ebb and flow of the Yorkshire margin of the last British ice sheet. Mark D. Bateman Ph.D., Sheffield University.

Friday: 4 April
Rapid climate change and glacial growth in NW Scotland. Deborah McCormack BSc. MSc., Manchester University.

Field Meetings

Sunday: 18 May
Sheddon Valley and Great Bride Stones
David Turner & Paul Kabrna

Saturday: 14 June
The geology and glaciation around Clapham, Ingleborough
Paul Kabrna & Jon Barber

Saturday: 12 July
The Windermere Supergroup and Borrowdale Volcanics of Yewdale
Steve Webster

Sunday: 17 August
Carboniferous geology of upper Nidderdale
David Turner & Steve Birch

Saturday: 13 September
Pendle Hill: from Gerna Knoll to Little Mearley Clough (SSSI)
Paul Kabrna
Joint meeting with the Lancashire Group of the Geologists' Association.


Modelling ancient Earth climates
Alan Haywood, Leeds University

Introduction

At present we are living in an interglacial stage of the late Cenozoic ice age that began around 30 million years ago and has not yet ended. We know that global warming is happening now, even if we are not sure of the cause. Governments and scientists worry about its possible effects: heat waves, sea-level rise, coastal flooding, glaciers melting, diseases spreading, but what do we know of ancient global warming before the last ice age? And why should we want to know? In fact the problem is simple: we are right in the middle of it, so we can’t see the wood for the trees. We therefore need to consider palaeoclimates to try to find the best analogues in order to a) describe what might happen; b) to validate the models over a wide range of climatic situations; and c) to better understand all mechanisms which might influence climates warmer than today.

The Pliocene

The Pliocene era is the period in the geologic time scale that extends from 5.332 million to 1.806 million years before present. During the Pliocene era, three million years ago, the world was warmer than it is today. The degree of warming wasn’t uniform, and appears to have been greatest at the mid to high latitudes (30° to 90° north and south of the equator). If you’d taken a summer swim off the southern coast of Great Britain at this time, the waters would have felt almost Mediterranean.

We can tell the world was warmer from a range of fossil information. For example, tiny foraminifera (organisms a bit like an amoeba with a chalk shell) can be used to map out the surface temperature of the sea waters in which they lived. This is because different species, or assemblages of species, thrive at different temperatures. By comparing fossil foraminifera in seafloor samples from the Pliocene with foraminifera alive today, we can reconstruct how warm the surfaces of the oceans were. The technique suggests that the North Atlantic may have been up to 5°C warmer than it is now.

Why were mid and high latitudes so warm? There are two main ideas. One suggests that ocean circulation was stronger at this time, and that currents flowing from the tropics towards the poles carried more warm surface waters with them. The other explanation suggests that there was more carbon dioxide in the atmosphere, warming the world through a greenhouse effect.

The pattern of sea surface temperature change three million years ago gives a clue to the correct explanation. If Pliocene warmth was due only to the ocean currents, we would expect to see the tropics cooler and the higher latitudes warmer than they are today. This is indeed the pattern fossil foraminifera show But sophisticated numerical models of climate, known as general circulation models, and which are run on powerful super computers, suggest that both the tropics and the higher latitudes warmed. This result is now supported by new evidence which also suggests that sea surface temperatures were higher everywhere, including the tropics.

Tiny haptophyte algae (the best known being coccoliths that are a main constituent of chalk) that live near the sea surface produce carbon-based compounds which decay very slowly. These chemicals are incorporated into the seafloor mud. If you analyse a core taken from the seafloor, you can estimate sea surface temperatures when the algae were alive. These temperature estimates for the Pliocene sometimes disagree with those from foraminifera. They suggest that the sea surface was warmer in both the tropics and higher latitudes three million years ago—the same pattern of warming predicted by climate models. The pattern is also consistent with the greenhouse explanation, rather than the ocean currents idea, because carbon dioxide will cause warming at all latitudes.

Antarctica glaciation and global change

Around 34 million years ago, at the boundary between the EOCENE and OLIGOCENE epochs, the earth experienced a fundamental switch in its climate system from a “GREENHOUSE” state, where there were no significant polar ice sheets, to the current “ICEHOUSE” climate with a large, if variable, Antarctic ice cap.

So now there appears to be evidence that high levels of the greenhouse gas carbon dioxide were at least partly responsible for Earth's warmer climate three million years ago. Exploring the Pliocene world with advanced computer models, and investigating climate signals derived from fossils, is a good way to understand what Earth's climate may be like in the future, as a result of man-made greenhouse gas emissions.

Causes or coincidence

El Niño: Recent models suggest that El Niño–like conditions (an abnormal warming of surface ocean waters) may have contributed to Pliocene warming and that the termination of this state may have influenced northern hemisphere glaciation. However El Niño Southern Oscillation events are clearly expressed by the model. Sensitivity tests indicate that a prescribed permanent El Niño-like condition increases global mean annual surface temperatures by a maximum of 0.6°C. Tropical warming is in part, or wholly, compensated for by high-latitude cooling. Therefore, if the Pliocene were characterised by a permanent El Niño-like state, it is questionable that it provided a significant contribution to global warmth at that time and, therefore, it us uncertain that the termination of this state contributed significantly to the onset of northern hemisphere glaciation.

Panama Seaway: A variety of palaeontological data points to the fact that the final closure of the Panama Seaway and the onset of northern hemisphere glaciation happened at approximately the same time, during the Pliocene. It has been widely suggested that there is a causal link between the two events based on the fact that the closure of the seaway effectively cut off exchange of Atlantic Ocean water into the Pacific and vice-versa. It also strengthened the western boundary current in the northern Atlantic Ocean, the Gulf Stream (thus more northward heat transport) and initiated the development of the thermohaline 'oceanic conveyor belt' as we know it today — all processes necessary to 'feed' the growing ice sheets. However model results indicate that the closure of the Panama Seaway did not directly cause Northern Hemisphere Glaciation during the Pliocene.

Conclusion

The advantage of studying geological examples of global warming is that we can see the whole story played out in one take. We can work out how long it took and what its effects were — how much the sea level rose, how the atmosphere changed and how the plants and animals adapted (or died out). We can see the whole process on a 'panoramic' scale. Quantitative information derived from geological studies directly complements computer modelling of climate change. Worst of all, there is geological evidence that modern computer climate models seriously understate the magnitude of future climate change.

Furthermore, climate variations provided living conditions on Earth that ranged from 'snowball' to 'hot-house' climates. Such variations are also known to have triggered biological evolution as noted by a) the warming in the Cambrian (600 Ma) and b) the world-wide spreading of Homosapiens early in the Holocene (13 Ka).

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Submarine channels: giants of the deeps
Jeff Peakall, Leeds University

Introduction

Submarine channels (‘deep-sea rivers’) form troughs and valleys on the seafloor and behave in the most unusual way; improving our understanding of these systems is critical for improved oil and gas extraction. Because of their inaccessible location on the deep ocean floor, little is known about their dynamics and geomorphology, and existing conceptual models tend to consider submarine meanders as straightforward analogues of their fluvial counterparts. The channels on the seafloor, which are typically bounded by levees, can be kilometres wide and thousands of kilometres long. Also they provide significant conduits for sediment transfer from the continental shelf to the deep oceans, and are scoured by dense underwater flows (‘turbidity currents’) formed from muddy river floodwaters or underwater avalanches. These flows have formed meandering systems of a scale similar to or surpassing the greatest fluvial meanders on earth, and supply submarine fans, the largest sedimentary fans on Earth.

Over the last 75,000 years sediment from the Amazon River has created this 800 km long channel beneath the Atlantic. The image shows a 200 km long 4 km wide section of the channel with banks 100’s m high.

Credit: Amos and Peakall (2006) Savoye, IFREMER.

Sedimentary rocks formed from ancient seafloor deposits contain preserved seafloor channels, and these sandy deposits form some of the world’s major oil and gas reservoirs. The local Pendle Grit is a good example of an ancient sea-floor turbidite sand body. Recent research by our team at the University of Leeds has shown that flow and sedimentation in seafloor channels is dramatically and unexpectedly different, with the flow spiralling in the opposite direction to the flow of water in rivers, where the sediment eventually settles. However, perhaps the most spectacular difference is that the wiggleyness (‘sinuosity’) of submarine channels, seems to vary globally with latitude, with ones close to the equator spectacularly sinuous, and those towards the poles very straight. In contrast, wiggly rivers can be found anywhere on Earth, controlled in the main by slope. This observation of global variations overturns decades of thinking that sea-floor channels like their rivery cousins were primarily controlled by slope angles. Possible controls include climate, sediment supply, and Coriolis (due to the planet’s spin). If Coriolis is the control then Earth may have always shown this distribution, whilst if due to climate/sediment type then non-glacial periods may show a different pattern.

In the case of the Pendle Grits, these were formed in a glacial period, and at a time when Northern England was in the equatorial region, so in either case we can predict that channels were quite wiggly (unless slopes were so steep in the small Craven basin, that only straight channels could form). The existing model of Sims (1988) predicts almost straight, braided channels; this recent work of our team predicts wiggly, single thread channels. Fieldwork is just starting to see if these predictions are correct!

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The end-Guadalupian Mass Extinction
Paul Wignall, Leeds University

Introduction

All mass extinctions of the past 300 million years, and many of those before this time, coincide with large igneous province (LIPS) eruptions, but demonstrating a causal link has proved difficult. However, the connection is one of great relevance in earth sciences and the wider community because it allows the cause and consequence of high-amplitude climatic changes to be assessed. Many extinction scenarios involve a cascade of volcanically-driven environmental changes that include global warming from CO2 release and volcanic winters from pyroclastic eruptions. Such conflicting causes form the core of extinction debates that began in the early 1880’s. They have proved difficult to resolve. Many workers have implicated high-volume flood basalt eruptions of the Siberian Traps as a cause of the end-Permian mass extinction, whereas others “blame” the extensive Tuffaceous Series that underlies the basalts. It is difficult to test this link because the timing relationship relies on radiometric dating and its associated errors. Thus, the end-Permian mass extinction is best dated in its Chinese type section where data indicate an age of 252.6 MA. In contrast, dates for the Siberian Traps flood basalt eruptions indicate an age of 249.4 MA. Even allowing for problems when comparing two different radiometric systems, the resolution is still not sufficient to resolve which style of volcanism shows the closest temporal link with extinction. The ideal test occurs when the extinction and volcanism record can be examined in the same sections.

Emeishan Flood Basalts

The Emeishan Flood Basalts are the dark coloured rocks to the left of the roadside cutting. The basalt unconformably overlies the late Middle Permian Maokou limestone to the right. Photo taken at Ebian, Sichuan.
© Professor Paul Wignall (2007).

Fortunately, such a test is available in the form of the end-Guadalupian (Guadalupian-Lopingian) extinction / Emeishan volcanism link. Hitherto, there has been very little work on this Permian extinction event because it lies “in the shadow” of the great end-Permian mass extinction peak, and for a long time the Guadalupian extinction losses were incorporated into one protracted, late Permian phase of extinctions. Only in 1994 did two teams independently identify a separate mass extinction late in the Middle Permian followed by a phase of radiation and recovery prior to the end-Permian even.

The Guadalupian-Lopingian mass extinction (Mid-Late Permian boundary) has emerged as being a separate event constituting an estimated 70% minimum loss amongst marine species. This crisis is best known from shallow marine, equatorial carbonate settings and was particularly severe for brachiopods, corals, echinoderms (blastoids, echinoids, crinoids), reef-forming sponges and foraminifera (especially fusulinids). Intriguingly, at around the same time as the identification of this extinction event, a flood basalt province was discovered in SW China. This is the Emeishan Province and it was initially considered a contributory factor in the end-Permian crisis. However, improvements in dating indicated that there is a better temporal link with the Guadalupian event.

Although geologists are still in the early stages of establishing detailed extinction models for the crisis, initial results suggest that eustatic regression definitely played a significant part in the extinction of faunas. The evidence is just as compelling for both basaltic and acidic volcanism to have played its part in this extinction event. There remains a degree of uncertainty on the impact (if any) of global cooling and as for oceanic anoxia, the evidence suggests not.


The last glacial stage (the Devensian) in NW England
Catherine Delaney, Manchester Metropolitan University

The meeting commenced with Dr. Delaney presenting the ENI Geological Challenge Runner-up trophy and cheque to Paul Kabrna

Introduction

In 1837, a young Swiss naturalist Louis Agassiz announced to the world that the Earth had at one time been gripped by ice. Agassiz brought his land-ice theory to the meeting of the British Association in Glasgow in 1840. At the meeting his radical proposal faced intense criticism which lasted for the next two decades. However, by 1850, his doubters had changed their minds and the geological community began to accept the fact that Britain and Europe had been subjected to Arctic-like climates.

Today the term Quaternary (Desnoyers, 1829) is virtually identical in meaning to the term Pleistocene, although the Pleistocene (Lyell, 1839) is defined as having ended 10 000 radiocarbon years ago and is followed by the Holocene Series (which replaced ‘Recent’ in 1885) in which we still live.

The last Glaciation

The Devensian commenced c. 118000 BP, following a cooling of the climate. This took place following a series of warmer periods, where climate in Britain varied between conditions seen in southern Scandinavia today and somewhat colder conditions. Sea level varied between -60 and -12m O.D. as a result of expansion of ice sheets in North America. On land, the only physical evidence for conditions during the first part of the Devensian occurs in the Cheshire area, where sediments indicate that this period was marked by dominantly cool but non-glacial conditions, interrupted by one warmer period, the Chelford interstadial.

In recent years modern technology has enabled us to complete a clearer picture of what happened in the last ice age. By analysing a variety of ice cores, it is believed that the Devensian was characterised by considerable variability in temperature, ice volume and sea level.

Events on Land

The northwest of England contains extensive evidence for glaciation and sea-level change during the last glacial stage. On land extensive glacigenic deposits are associated with this main phase of glaciation. Erratic contents, till fabrics and drumlin orientations indicates the ice radiated outwards and extended southwards through Lancashire from local accumulation centres in the Lake District and western Pennines, while a major ice stream moved down the Irish Sea Basin from Scotland, penetrating south-eastwards into the Cheshire Plain. Ice also formed in the Welsh Mountains and moved eastwards to coalesce with the Irish Sea ice on the western side of the Cheshire Plain. Evidence from Chelford indicates that ice from the Irish Sea basin and Lancashire extended as far south as the Whitchurch end moraine.

The amateur geologist would immediately connect the Lake District with past glacial events. This is due to the magnificent erosional features associated with valley glaciers such as the bowl-shaped corries (cwms in Wales) and if filled with water are called tarns e.g Red Tarn on the east side Hellvellyn. Other spectacular features are the knife-edge ridges called arêtes (French for ridge).

View from Langdale Pike towards Windermere - a classic glaciated 'U'-shaped Valley

View from the Langdale Pikes, Lake District Source © Paul Kabrna: 1986

As the valley glacier advances, abrasion and plucking trunks the valley sides which leads to the formation of U-shaped valleys where streams into the valley can be left ‘hanging’. In lowland areas the affects of glaciers are noted by the less obvious depositional features such as moraines, kames, eskers and kettle holes not forgetting the enigmatic drumlins which locally are concentrated around Hellifield. Locally there are some excellent examples of erosional features called meltwater channels e.g. Cliviger Valley Gorge and the Nick O’ Pendle.

Conclusion

Sediments and landforms laid down during the deglaciation of the main Devensian ice sheet are prolific in the NW region. Mid-Devensian deposits are usually only seen in borehols. They indicate that much of the region outside the Lake District was dominated by cold, stadial conditions with a relatively arid climate. Only towards the Late Devensian, after 25,000 BP does ice cover the entire region. Ice moving from the Lake District and Western Pennines interacted with an ice stream in the Irish Sea basin along the western and southern fringes of the region. The sedimentary record is dominated by evidence of a warm-based, fast-moving, wet ice sheet during this period. While highland areas are dominated by erosion, in valleys and lowland areas much of the base of the ice sheet is likely to have been underlain by a deforming bed of water saturated sediment, which would have facilitated rapid ice flow and adjustment to changing mass balance and ice marginal conditions. This layer of basal sediment was easily sculpted by ice flow, resulting in the numerous drumlin formation charactistic of the NW region. Towards the ice margins, extensive tunnel valleys and meltwater channels indicates that considerable quantities of water were flushed from the system, depositing extensive outwash deposits beyond the ice margin. Where the two major ice sheets separated along the western fringes of the area, extensive proglacial lake sediments were deposited.

During deglaciation, initial recession appears to have been relatively steady, with a margin characterised by ice stagnation. However, towards the end of the main glaciation, recession became increasingly unsteady, and repeated oscillations of the ice margin occurred in the north. The later oscillations are associated with marine inundation into the Irish Sea Basin and then onland. A final re-advance of ice occurred in the Lake District, when small ice fields reformed on some plateaux. Some corrie glaciation may also have occurred in the Western Pennines.

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The ebb and flow of the Yorkshire margin of the last British ice sheet
Mark D. Bateman, Sheffield University

Introduction

During the Late Devensian icesheets surrounded Yorkshire on three sides and what wasn’t covered with ice was largely submerged under large pro-glacial lakes, e.g. Lake Humber. The nature and timing of the Late Devensian icesheet dynamics coming off the Dales/Pennine, down the Vale of York and down the present-day East Yorkshire coast has been the subject of considerable research over the years and is still the source of debate.

In the Vale of York maximal Late Devensian icesheet limits have been advocated both at the York-Escrick moraine complex and on a more southerly line around Wroot and Thorne in the Humberhead Levels. All this has huge implications for the formation and duration of the extensive pro-glacial Lake Humber, the largest single feature beyond the ice sheet in any model of Late Devensian Britain. The latter may have been a short-lived surge but remains disputed due to the dearth of glacial diamict found south of Escrick and arguments as to whether the gravels at Wroot-Thorne are glacio-fluvial in origin. Recent work from Ferrybridge found a buried glacial diamict with sandstone erratics which was interpreted as having been derived by Vale of York ice despite being around 20 km south of the Escrick moraine (Bateman et al. 2008). This has been luminescence dated as a glacial diamict between 23300 and 20500 years ago. Thus Vale of York ice may have extended beyond the York-Escrick moraine complex, then retreated and re-advanced to it.

Ice definitely came through the Humber gap as testified by the Horkstow moraine and deposits exposed on the Humber foreshore at North Ferriby. The two tills of the Holderness coastline (Skipsea and Withernsea), each with different erratic suites indicating both Lake District and Scandinavian origins, have been attributed to either to a ‘two tier’ glacier or to glacial surges from the North Sea. Both tills were deposited sometime between ca. 21900 and 15500 years BP. New work has found intact chironomidea in sands laid down between the two tills. The finding of these suggest that there must have been an ice-free period between the two tills and that they therefore must represent two glacial advances. Luminescence dating of the sand indicates this occurred around 16200 years ago.

What is clear is that more recent work has shown that ice can move and respond to climatic changes more rapidly than was previously thought. Thus ice on what is now the Holderness coastline and in the Vale of York may have been quite dynamic with more than one advance and retreat. What is also clear is that within the Late Devensian and in particular the Dimlington Stadial, ice may have existed in Yorkshire as late as around 16000 years ago. This fits not only with other re-advances at this time around Britain, e.g. in the Irish Sea basin (Killiard Point Re-advance) and in Scotland (Perth Re-advance), but also with ice re-advances in the neighbouring Fenno-scandinavian icesheet. All these ice-advances coincide with a recorded global climatic perturbation designated as Heinrich event 1. Thus the ice advances and retreats in Yorkshire may have been responding not just to regional conditions but to changes effecting the whole of the British Ice sheet.

References

Bateman, M.D., Buckland, P.C., Chase, B., Frederick, C.D. and Gaunt, G.D. (2008). The Late-Devensian pro-glacial Lake Humber: new evidence from littoral deposits at Ferrybridge, Yorkshire, England. Boreas, 37, 195-210.

Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A. and Bateman, M.D. (2004). Glacial map of Britain and GIS database. Boreas, 33, 359-375.

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Rapid climate change and glacial growth in NW Scotland
Deborah McCormack, Manchester University

Introduction

Home to the oldest rocks in the British Isles (Lewisian Gneisses) and some spectacular post-glacial scenery, the Wester Ross region of NW Scotland has been the focus of geological and geomorphological studies for hundreds of years. Within the past ~40 years, interest in the most recent glaciation (The Late Devensian) has been intensified with the realisation that the region is particularly sensitive to variations in the Gulf Stream. This surface current from the Gulf of Mexico brings warm, moisture-laden air to the shores of the NE European Margin, giving NW Scotland its characteristic warm, yet wet climate. Changes in the configuration in the oceanic conveyor however, have the ability to divert the Gulf Stream to the tropics, allowing the oceanic polar front to migrate to the south, and land ice to build up in the Northern Hemisphere. The signals from these “switches” are recorded in the onshore and offshore geomorphological and sedimentological records.

Huge till sheet, Torridon

NW Scotland

Sandstone erratic on quartzite
Photos: Deborah McCormack

Deglaciation and Readvance

At the Last Glacial Maximum (23.7-22.0 ka), northern Scotland was covered in an extensive ice sheet which progressed north westwards towards the edge of the continental shelf via ice streams through the mountainous areas. Sediment eroded from the mainland was deposited in the Sula Sgeir Fan, at the edge of the continental shelf. This was followed by a rapid deglaciation, interspersed with still stands and readvances.

The Wester-Ross Readvance (WRR), a regional event at 18-15.5 ka when ice originated from the mountains to the south east, is thought to be a response to Heinrich Event 1 (18-17 ka). The Loch Lomond Readvance (LLR) occurred during the Younger Dryas cooling event (12.5-11.5 ka) and is thought to differ from earlier glaciations, being topographically confined to localities such as Torridon and Applecross (Sissons, 1977). Evidence of readvances can be seen onshore as a complex array of glacial features which are particularly striking in the Torridon area. During the LLR, glaciers readvanced onto ground covered by till from late Devensian glaciations, resulting in the creation of unique erosional and depositional landforms. Erosional landforms include corries, striations and ice-scoured bedrock. Depositional landforms include boulder fields (including erratics), moraines and vast till sheets.

Methods

Mapping and interpretation have been carried out at 3 levels of detail: On foot, through the interpretation of aerial photographs and Digital Elevation Models (DEMs) and by using ground-based LiDAR (Light Detection and Ranging). LiDAR-derived Digital Elevation Models have been compiled for Coire Mhic Fhearchair, a north-facing corrie in the heart of Torridon. Striking 20cm-resolution imagery allows the viewer to travel around the virtual reality corrie to study the glacial landforms, and see bedrock features through the vegetation.

LiDAR work in NW Scotland

LiDAR reporting in Coire Mhic Fhearchair, NW Sotland is being hindered by too much Sun!
Photo: Deborah McCormack

The compilation of maps will aid the interpretation of the mode of retreat of the ice-sheet after the LGM, and valley/corrie glaciers following the LLR. In order to establish a chronology for the last deglaciation, cosmogenic isotope dating techniques will be employed. Cosomgenic ages are based on the fact that surfaces exposed to cosmic rays are re-set once eroded by a warm-based glacier, therefore a result will reveal the date at which a surface was finally deglaciated. There is however, some doubt as to whether all dates have been re-set, especially where cold-based, passive ice is concerned, but cosmogenics can still provide us with insights into the internal thermal dynamics of a glacier.

The Offshore Record

High-resolution sediment sequences in the Sula Sgeir Fan and offshore bathymetry can provide a full “source-to-sink” overview of the glacial system and associated retreat patterns. By analyzing sub-marine moraines and their relative positions, some perspective can be gained with regards to the mode and speed of retreat of the last ice sheet in NW Scotland.

Preliminary investigations support the “active” mode of retreat, interspersed with major readvances (WRR/LLR) and some minor oscillations which reflect the sensitivity of the area to changes in local and North Atlantic climate systems. The study of modern analogues can provide us with more information regarding the thermal dynamics and rate of retreat of both ice sheets, and smaller valley and corrie glaciers. This combined with the modelling of cryosphere-climate interactions could help us to understand the wider frame of events in the North Atlantic.

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Field Meetings

Sheddon Valley and Great Bride Stones
Guides: David Turner & Paul Kabrna

Time / Date: 10:30 am, Sunday, 18th May

Meeting at: the large car park next to the Sportsman’s Arms public house [SD 928 273]. Access to Great Bride Stones [SD 932 268] is a short walk along a by public footpath. The afternoon session begins at the car park beside the Long Causeway, Grid Reference [SD 892 291].

Practical Details: Bring a packed lunch. Boots and weatherproof clothing are advisable. The meeting should finish about 4 pm. The routes follow good footpaths making for easy walking.

Geological setting
MORNING:
Great Bride Stones formed from Kinderscout Grit outcrops as a 5 metre high rock face or scarp edge. The gritstone has been weathered and eroded, probably by wind, into unusual shaped blocks including a 4 metre high pedestal rock. The site demonstrates the coarse nature of Kinderscout Grit which forms the distinct moorland landscape of Upper Calderdale.

AFTERNOON:
The Sheddon Limestone Hushing Trail covers the remains of a unique pre-industrial lime burning industry which was not in a limestone area but in which men had discovered limestone boulders and pebbles. The trail follows the complete hushing process on the ground, beginning at the inlet channel.

Maps
OS 1:25,000 Explorer OL 21 South Pennines
BGS 1:50,000 Sheet 76 Rochdale

References
Titus Thornber 1992
Taking the Car for a Walk - No.2 The South Pennines (Walk No.10 pp 79 - 86)

Pomeroy, P. et al 1992
The Limestone Hushings of Sheddon.

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The geology and glaciation around Clapham, Ingleborough
Guides: Paul Kabrna & Jon Barber

Time / Date: 10:15 am, Saturday, 14th June

Meeting at: Clapham Car Park Yorkshire Dales National Park Authority Pay and Display [SD 7451669216].

Practical Details: Bring a packed lunch. From the car park we will walk up Clapdale for about 3 km. After this, it is intended that members will have the option of ascending Ingleborough, or visiting Ingleborough Cave, then returning to Clapham.

Geological setting
The oldest (Lower Palaeozoic) rocks outcrop in inliers on the upthrow (footwall) side of the North Craven Fault. These rocks are strongly folded and cleaved which is in marked contrast to the unconformably overlying Great Scar Limestone. This limestone which dominates the Yorkshire Dales was deposited 330 million years ago in warm shallow tropical sea over the Askrigg Block which supported an abundant shelly fauna.

Rivers from the north transported large quantities of mud, silt and sand into the area which resulted in the cessation of limestone deposition and therefore a loss of shelly faunas. Persistent incursions of marine seas at regular intervals produced a cyclical succession that is so characteristic of the Yoredale Group. Although these Yoredale rocks underlie the slopes of Ingleborough, they are largely concealed by glacial drift and peat. The top of Ingleborough is capped by much coarser feldspathic grits belonging to the Millstone Grit Group.

The final dominant geological processes are limestone dissolution (karst) and glaciation (caves, boulder clay, meltwater channels) that shaped the area.

O.S. Maps
1:25000 Outdoor Leisure 2: Yorkshire Dales - Western area.

Reference
ARTHURTON, R.S., JOHNSON, E.W.. & MUNDY, D. J. C. 1988: Geology of the country around Settle. Memoir of the British Geological Survey, Sheet 60.

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Windermere Supergroup and Borrowdale Volcanics, Yewdale
Guide: Steve Webster

Time / Date: 10:30 am, Saturday, 12th July

Meeting at: The trip will start from the main car park and toilets in Coniston. However, parking there is very expensive and it is worth trying the lane that leads towards Copper Mines Valley, just beyond the Ruskin Museum, which is free if you can find room.

Practical Details: Good footpaths and mostly gentle walking. Distance approximately 7 km. Packed lunch required.

Geological setting
Eroded remnants of rocks deposited during intense volcanic activity in the Ordovician form the high fells to the North and West of the valley. Of the 7 – 8000 metres of these resistant Borrowdale Volcanic Group rocks, only the top of the sequence is seen in Yewdale, as pyroclastic deposits in the form of welded tuffs. Unconformably overlying these are sedimentary mudstones, siltstones and sandstones of the Dent Group at the base of the Windermere Supergroup. They were laid down on the floor of a shallow sea at the end of the Ordovician, followed by rocks of Silurian age, the Stockdale Group and Brathay Formation, which are also seen on the walk. All the volcanic rocks and overlying sediments have a steep SE dip as a result of Early Devonian plate movements and continental collision at the end of the Caledonian Orogeny.

O.S. Maps
1:25,000 Explorer OL7, The English Lakes – South eastern area
BGS, England and Wales Sheet 38, 1:50,000, Ambleside

References
MITCHELL M & DEWEY. M, 2004
Geology, Scenery And History – A walk in Yewdale, northeast of Coniston.
Cumbria RIGS.

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Carboniferous geology of upper Nidderdale
Guides: David Turner & Steve Birch

Time / Date: 10:30 am, Sunday, 17th August

Meeting at: near Lofthouse in Upper Nidderdale at [GR 099735] (Map Exp 298). Go 200 metres past the turning to Lofthouse village and meet at a layby on the right-hand side.

Practical Details: Packed lunch required. We will be looking at three localities to examine the junction of the Carboniferous limestones and gritstones and see the thinning out of the Yoredale series. We will also be hunting for possible trilobite remains in shales near Scar House Reservoir, finishing with an optional trip to How Stean Gorge which also has a cafe.

Geological setting
This part of Nidderdale lies in the southeastern part of the Askrigg Block. The dale is located at the northern end of the main Millstone Grit outcrop of the Central Pennines, which extends southwards to Kinderscout. The varied geology makes this area special as there are abundant Carboniferous fossils, a variety of rock-types (limestones, shales and grits) and geological features such as outliers, inliers, faults and anticlines.

O.S. Maps
1:50 000 Sheet 99 Northallerton and Ripon
BGS 1:50 000 Sheet 51 Masham

Reference
Yorkshire Rocks and Landscape - A Field Guide Ed. Colin Scrutton
The Carboniferous rocks of upper Nidderdale: Chapter 5 pp. 58-65

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Pendle Hill: from Gerna Knoll to Little Mearley Clough
Guide: Paul Kabrna

Joint meeting with the Lancashire Group of the Geologists’ Association

Time / Date: 10:30 am, Saturday, 13th September

Meeting at: Downham’s main car park [SD: 785 442]. Please ensure that valuables are out of sight as the cars will be left here until the end of the trip.

Practical Details: The excursion is a circular route and you will need to carry a packed lunch and be prepared for inclement weather. Hiking boots are recommended (if not essential) because the day will be spent examining localities along the flanks of Pendle Hill, most of which are in stream sections.

Geological setting
The Craven Basin in Mississippian (Lower Carboniferous) times is characterised by rift basins, half-grabens and tilt blocks and Waulsortian Mudmounds. Gerna Hill, our first stop for the day, is an excellent example of a Waulsortian build-up as first described in the type locality in Belgium.

Pendle Hill is capped by sandstones of the Pendle Grit Formation (the type section being in Little Mearley Clough, which is a SSSI (a Site of Special Scientific Importance) and also the type section for the goniatite Tumulites pseudobilinguis. Below the Pendle Grit lies the Upper Bowland Shale Formation depicted by the steep gullies on the hillside. Goniatites and bivalves are the dominant faunas associated with these mudstones and shale sediments. The resistant Pendleside Sandstone marks the change in slope and transition into the Lower Bowland Shale Formation.

O.S. Maps
1: 25 000 sheet SD 64 / 74 Clitheroe and Chipping
Geol. Survey 1:63 360 Sheet 68 Solid Clitheroe

Reference
Riley, N.J. 1990: Stratigraphy of the Worston Shale Group (Dinantian), Craven Basin, north-west England.
Proceedings of the Yorkshire Geological Society, 48, 163-187.