Programme: 2003 - 2004

© Craven & Pendle Geological Society

Indoor Meetings

Friday, 17th October
Tertiary deep sea faunal communities associated with 'cold seeps'. Fiona Gill B.Sc.(Hons), University of Leeds

Friday, 14th November
The geology of La Palma, Canary Islands, Spain. Hed Hickling BA. MSc.

Friday, 12th December
Members Slides and Christmas Jacob's Join.

Friday, 23rd January
Triassic Salt of Cheshire and a 'pinch' of Miocene. Paul Kabrna

Friday, 20th February
Ice cold in Adel: urban and suburban glaciology in and around Leeds. Jon Barber B.Sc. (Hons), University of Leeds

Friday, 19th March
The volcanic geology of the Aeolian Islands. Alison Quarterman B.Sc.(Hons), Huddersfield Geology Group

Field Meetings 2004

Sunday, 16th May
The geology of the Ingleton Waterfalls
Paul Kabrna

Saturday, 26th June
Quarrying in the Millstone Grit Group around Stacksteads in the Rossendale Valley
Arthur Baldwin

Saturday, 21st August
Jurassic rocks of Runswick Bay, near Whitby
Will Watts

Saturday, 25th September
Almscliff Crag and Brimham Rocks
Paul Wignall and Bob Perris

Tertiary deep sea faunal communities associated with 'cold seeps'. 
Fiona Gill, University of Leeds

Modern hydrothermal vent and cold seep communities live in extremely challenging environments. For example, at vent sites the hydrothermal fluid that sustains the associated communities is hot (up to 400°C), highly acidic, anoxic and loaded with metals and hydrogen sulphide.

Cold seeps are also associated with passive and active continental margins where methane-rich and sometimes also sulphide-rich low temperature fluids are issuing onto the sea floor in deep water. Seep sites are thought to be long lived and are usually associated with carbonate deposits with distinctive carbon isotope values.

Living at cold seeps are communities of animals which are unlike almost all other marine communities because, a) they depend on geochemical rather than photosynthetic energy, b) their primary producers are bacteria which oxidise methane and sulphides for energy rather than plants that need sunlight, and c) they are dominated by animals that have symbiotic methane and/or sulphur-oxidising bacteria within their bodies. Ninety percent of cold seep species are not found in any other marine community and most of these species are restricted to individual seep sites. However, at higher taxonomic levels cold seeps share a number of genera and families with hydrothermal vent and other sulphide dependant communities, which suggests evolutionary connections through common ancestors.

There are many things we do not know about the origin of modern cold seep communities. For example, how did the high degree of endemism arise? Does this reflect long term evolutionary stasis in a geochemical-rich environment which is completely or at least partially divorced from environmental fluctuations affecting most other marine communities? Is the domination of modern cold seep communities by chemosymbiotic vestimentiferans and bivalves a relatively recent phenomenon? Are the biogeographic patterns seen in the modern seeps an artefact of poor sampling or do they have a historical basis? The answers to these questions may be sought for in the fossil record of cold seep communities.

The Tertiary has the best record of fossil cold seeps with numerous occurrences in Japan, the west coast of the USA, and Italy. These faunas are similar to modern seep communities in structure, being dominated by endosymbiotic bivalves. Notwithstanding, it is has proved difficult to reconstruct palaeobiogeographic distributions of Tertiary fossil cold seeps because of taxonomic problems and the previous lack of data from the Atlantic. Pertinent to these problems is a unique and very important collection of Miocene cold seep fossils from Cuba, Barbados, Trinidad and Venezuela in the Natural History Museum, Basle, Switzerland, and a subsidiary collection in the Southampton Oceanographic Institute (SOC). These poorly studied collections represent all of the known Caribbean cold seep faunas. The Caribbean is a region that has particular palaeobiogeographic significance, being a direct ocean link between the Pacific and the Atlantic prior to the raising of the Isthmus of Panama around 3Ma. ago. A study of these seep faunas offers an ideal opportunity to elucidate biogeographic and evolutionary links between the well known Pacific and Mediterranean Tertiary cold seep faunas, as well as giving insights into origin of the modern cold seep communities of the Caribbean and the Gulf of Mexico.

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The geology of La Palma, Canary Islands, Spain
Hed Hickling


El Duraznero crater / vent

The Canary Islands are an archipelago of oceanic volcanic islands lying off the north west coast of Africa, between the latitudes 270 N and 290 N. The most westerly of these islands are La Palma and El Hierro. Geologically, La Palma and El Hierro are the youngest members of the archipelago, their oldest sub aerial rocks being less than 2 million years (Ma) in age (Figure 1). Like the better known Canarian islands of La Gomera, Tenerife, Gran Canaria, Lanzarote and Fuertaventura, La Palma and El Hierro lie entirely upon Jurassic (~ 150 Ma) oceanic crust of the African plate.

La Palma is slightly larger than the Isle of Man, having a surface area of 706 km2. However, it is a very mountainous island, rising to over 2400m in the north (the Northern Shield) at the Roque de Los Muchachos on the rim of the Caldera de Taburiente, where many European astronomical observatories are to be found. The southern portion of the island is equally mountainous, being dominated by the north-south Cumbre Vieja ridge, which rises to nearly 2000m at the Deseada cone. Due to the relatively high annual rainfall, La Palma is much greener than the other Canarian islands, but this does not preclude the occurrence of excellent geological exposures around the coast, at altitude and within the Caldera de Taburiente. Mild temperatures throughout the year, combined with a weakly developed tourist industry, result in an unspoilt, friendly island suitable for those who want to get away from it all. That said, La Palma is criss-crossed by well-marked walking trails of all grades, from easy to very difficult.

La Palma is somewhat special, in that its rocks and structures allow the observer to trace the geological evolution of the oceanic volcanic island from its beginnings as a submarine seamount in the Pliocene (~ 4 Ma), through its growth as a sub aerial shield volcano in the early Pleistocene, to its present state as a rift-controlled, active volcanic edifice today. In terms of their chemistry, the La Palma intrusives, lavas and pyroclasts belong to the alkali basalt suite. Petrologically, the extrusive rocks consist of basanites, basalts (main rock type), tephrites, phonolites and trachytes.

The spectacular pillow lavas, sheeted dykes and plutonic rocks of the submarine seamount are superbly exposed in the Barranco de Las Angustias, within the Caldera de Taburiente. The latter feature is misnamed in that it is not a volcanic structure, but originated as a result of gravitational collapse of a section of the northern shield volcano and subsequent fluvial erosion at the margin of the collapse scar (see below).

By early Pleistocene times, the seamount had been uplifted, tilted and eroded and, up to 600m of breccias, agglomerates and sediments were deposited on top of the submarine intrusives and extrusives. By 1.4 Ma, sub aerial volcanic activity (effusive and mildly explosive) had built a steep-sided volcanic structure thought to have been up to 23 km in diameter and up to 3000m high above the seamount base. Today, the rocks of the Garafia volcano are only seen in the walls of the Caldera de Taburiente and in the deeply incised barrancos on the slopes of the northern shield.

Following the gravitational collapse of the south west sector of the Garafia volcano, further effusive and mildly explosive volcanic activity infilled the collapse scar and built up the Taburiente volcano, whose lavas flows and pyroclastic deposits covered those of the older Garafia volcano with a marked unconformity. These rocks are well exposed throughout the northern shield. It was probably at this time, that volcanism on La Palmy became focused on a rift system. By about 0.8 Ma, volcanism was concentrated along the southern rift, building up an unstable ridge or 'dorsale' known as the Cumbre Nueva. The Cumbre Nueva collapsed westwards about 0.56 Ma creating the Valle de Aridane. Further volcanic activity within the collapse scar produced the Bejenado volcano, while fluvial erosion at the contact between the collapse scar and the Bejenado volcanics produced the initial incision of the Barranco de Las Angustias and ultimately the formation of the Caldera de Taburiente.

After about 0.4 Ma, volcanic activity on and in the northern shield ceased. However, the source of volcanism migrated southwards and between 0.125 Ma and the present day, it has been focused on the Cumbre Vieja ridge, which continues as a submarine feature to the south of the island. In addition to many prehistoric eruptions along the Cumbre Vieja, there have been numerous eruptions since the island was settled in the 15th century, the most recent being that of the Teneguia volcano, near Fuencaliente, in 1971 (Figure 2). The magnificent Ruta de los Volcanes is a 20 km walk along the crest of the Cumbre Vieja, where most of the historical volcanic activity on La Palma has been concentrated.

In recent years, there has been much speculation on the likelihood of the gravitational collapse of the western portion of the Cumbre Vieja. Were this to occur, it has been argued, giant tsunamis would be generated that would inundate the Caribbean and the eastern shoreline of the USA. The scenario is undoubtedly a terrifying one, but it must be tempered with the knowledge that we are dealing with geological processes that are, as yet, incompletely understood and on a timescale vastly different to the human one.

Finally, the question arises, are the Canary Islands and other oceanic volcanic chains the products of the interactions of plate motions and mantle plumes? A few years ago, the answer would have been an unequivocal 'Yes'. Today, the plume (hotspot) model is the subject of a great deal of controversy and geologists are being required to look more critically at the evidence. As yet, a mantle plume has not been detected beneath the Canary Islands, but this is not to say that one does not exist. The jury are still out on this one!

References

Carracedo, J. C. et al 2001. Geology and volcanology of La Palma and El Hierro, Western Canaries. Estudios Geologicos 57, 175-273.

Carracedo, J. C. & Day, S 2002. Classic Geology in Europe 4: Canary Islands. Terra Publishing.

Carracedo, J. C. et al 2002. Cenozoic volcanism II: the Canary Islands. In The Geology of Spain Gibbons, W. & Moreno, T. (eds). The Geological Society London.

Scarth, A. & Tanguy, J – C. 2001. Volcanoes of Europe. Terra Publishing.

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Triassic Salt of Cheshire and a 'pinch' of Miocene
Paul Kabrna

Northwich (Circa 1920)

Introduction

Halite (rock salt) is a commodity many of us take for granted. It is so important to our lives that without it, life as we know it would not exist. As a member of the evaporite family (sulphates, carbonates etc.), it forms abundant and thick deposits throughout the geological record. The three well know uses are as table salt, as a raw material for the chemical industry, and as road salt. Rock salt is also a good capping deposit for trapping petroleum, and its ability to form salt domes (under burial conditions thick halite becomes 'plastic' and flows like toothpaste) makes it a particularly valuable to the petroleum industry.

Historical Overview

From the earliest times mankind has searched for sources of salt. It is an ancient industry that can be traced back to 5000 BC, to an inland spring near Krakow, Poland. Here in Cheshire natural brine springs were the first source of salt. The salt was produced by pouring brine over hot charcoal faggots and crystals of salt scraped off. This was thought to have occurred during the Iron Age (751 BC to AD 42). Great strides in salt production were made in Roman times (AD 43 - 409) due to the introduction of the 'open pan method of evaporation'. Rock salt itself was first found near Marbury (1670); quite by accident as miners were looking for coal! It was not until the 19th century that salt production expanded rapidly with Northwich becoming the centre of salt production. Not surprisingly the town motto is 'Sal Est Vita' which translated means 'Salt Is Life'.

Stratigraphy of Rock Salt

The Cheshire salt was deposited in the Triassic (247 - 206 MA) - a period of time marked by the rifting of Pangaea into the two supercontinents of Laurasia and Gondwanaland. It was a 'hot house' world and a critical time for life on land since the Earth had just been through the end Permian mass extinction event which wiped out 90- 95 per cent of all life on Earth.

For many years geologists' considered the Triassic in terms of Keuper, Muschelkalk and Bunter (Alberti 1834). This three-fold lithostratigraphical division of strata was replaced by a more useful chronological division based upon standard Alpine stage names. In Cheshire the Bunter is now regarded as the Sherwood Sandstone Group whereas the Muschelkalk and Keuper are now part of the Mercia Mudstone Group (1200 m). A key driving force for change was worldwide economic developments in underground exploration, notably for oil and gas and, to a lesser degree, for evaporites, water supply and underground gas storage.

The Cheshire halite comes from two distinct units within the Mercia Mudstone Group. The lower unit is the Northwich Halite Formation (283 m) and the upper one the Wilkesley Halite Formation (404 m). Both units contain beds of almost pure halite with others containing variable amounts of mudstone and siltstone. Halite crystals (hoppers and chevrons) help us to understand how the salt beds were formed i.e. sub aerial / subaquaeus deposition. Recent research at Keele University supports the idea that the rock salt beds were formed in an intertidal flat environment. The mechanism to create the vast deposits of salt is thought to have been repeated shallow marine incursions followed by periods of desiccation.

Cellular Embankment

Extraction of Rock Salt

There are three possible methods of working the salt; the pumping of 'wild-brine' from 'wet' rockhead, the development of artificial solution cavities in the salt beds, and the mining of rock salt. The uncontrolled pumping of 'wild' brine for many years led to catastrophic subsidence, particularly in Northwich. Around the Sandbach area, the appearance of linear subsidence hollows ('flashes') are a result of indiscriminate brine pumping.

The picture to the right is the 'Cellular Embankment' over the River Wheelock. The design supports the main-line Manchester to Crewe railway service.

Meadowbank Salt Mine in Winsford is still operational today. The salt is mined from the lower bed, the Northwich Halite Formation using the room and pillar method. Recently however, the government has given the go-ahead for the salt mine to become a dump for toxic waste (January 2004)!

In Northwich a geotechnical assessment of the old salt mines has been carried out. This work was commissioned by the local council to ascertain whether it is feasible to extend building in Northwich. The report suggested that failure of salt pillars could occur within the next 12 years. The proposed solution to the problem would be to inject the brine cavities below ground with grout (pulverised fuel ash) mixed with 3% in weight of cement. The grout would be mixed with the brine with the displaced brine being routed to a chemical plant for processing.

A 'pinch' of Miocene

The Wieliczka Salt Mine, located in southern Poland near the city of Krakow has been worked as a source of rock salt since the late 13th century. The salt deposit is 1 km wide, about 6 km long and more than 300 m thick, and consists of two units: a) the lower, bedded part (stratiform deposit) where the salt rocks are layered and form elongated structures similar to scales and asymmetrical folds; b) the upper part (boulder deposit) is developed as a coarse breccia mainly composed of salt clays (so-called zubers), with blocks of coarse-grained salts. The blocks are of irregular size and shape.

The mine has three specific uses: a) it's an active working mine; b) one of the chambers serves as a health sanitorium for the treatment of asthma & bronchial troubles amongst other things; c) it's an important tourist attraction (because it contains centuries-old salt carvings, it is therefore a site of 'outstanding universal value to mankind' under the World Heritage Convention in 1978). The mine was placed on the very first list of endangered World Heritage sites due to the serious threat of deterioration of the historic salt carvings within the mine. The salt carvings were created over many centuries by the miners and other sculptors, and represent an impressive body of art works within the hundreds of kilometres of mine passages.

The deterioration of the salt carvings is due to attack by water, much of which is transported through the air. Salt develops a liquid film on its surface and begins to dissolve when the relative humidity of the surrounding air reaches approximately 75%.

A U.S. specialist (Air Resources Laboratory) was called in to setup a dehumidification system which became operational in the spring of 1998. Conditions in the mine substantially improved from previous years. Due to the success of the system, the salt mine was removed from the list of endangered World Heritage sites in December 1998. It is the first site ever to be removed from the endangered list, thanks in part to the efforts of ARL scientists.

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Ice cold in Adel: urban and suburban glaciology in and around Leeds
Jon Barber, University of Leeds

Introduction

The southern and central Yorkshire Dales contain some of the most striking landforms and scenery in the British Isles. Much of this dramatic topography is a relict of glacial (and interglacial) events which occurred throughout the Pleistocene epoch (2 million - 10 000 years before present). The inferred margin of (at least) the last great ice-mass (Late Devensian) at its maximum extent, cuts across the southern Yorkshire Dales, leaving evidence of glaciation in Wharfedale and Airedale, but suggesting that Calderdale (the most southerly of the Yorkshire Dales) remained ice-free.

CPGS at Reeva Reservoir

Climatic fluctuation during the late Pleistocene and the associated changes in spatial extent of the Late Devensian (and possibly previous) ice-masses, trap both organic and non-organic (dateable) deposits between glacially derived material allowing the spatial extent of the Late Devensian ice-mass to be placed in a chronological framework. Study of ice-marginal (both end and lateral) landforms can support evidence suggesting that the Late Devensian ice mass was relatively flat in profile, allowing elevated areas proximal to the ice margin such as Rombalds (Ilkley) Moor to project through the ice as nunataks. All of the Yorkshire Dales (with the exception of Calderdale) exhibit several glacial re-advance features. Understanding the nature and timing of these events will help understand future climatic changes (and their effects) affecting the British Isles.

Study of the nature and form of glacial sediments may help to determine the thermal nature of the ice-mass. Frozen sediment structures suggest cold-based ice at the extreme margin of the Late Devensian ice. Whilst glacial material is abundant throughout most of Yorkshire, two different sources have been suggested evidenced by different erratic clast combinations. Whilst most of the ice to the west of the Pennines and in the Vale of York was sourced from the Lake District, the Pennines had a separate ice-centre based around the Mallerstang area.

Previous Research

Arthur Raistrick worked in the Dales in 1920s and 30s. Raistricks' theories suggested a Pennine ice source with valley glaciers dominating the landscape with high ground peaking through as rock 'nunataks'. All Dales valleys were glaciated except for Calderdale. He recognised two glaciations and two cold phases in the most recent glacial event. Raistrick believed that a large Pennine ice-centre drained via long, thin ribbon-like glaciers occupying the dales valleys whilst the interfluves remained ice-free.

W. 'Jim' Edwards was a BGS geologist who mapped the Leeds and Wakefield areas in 1940 –50. He was the first to note two river terraces on the lower Wharfe, Aire and Calder. He also suggested that glacial deposits around Leeds came from two discrete glacial periods, agreeing with Raistricks’ two phase Devensian model.

Current Glacial Chronology

The accepted chronology for glaciations in Yorkshire is that the last glacial (Devensian) had two cold phases separated by a brief warm period. Prior to this an interglacial event proved warm enough for Hippopotami to wallow in the River Aire. Prior to this warm period the Anglian glaciation was supposed to have covered the entire county in ice.

Key Questions

The focus of my research centred on the following:

a) Which deposits belonged to which glacial event?

b) How many glacial periods were there?

c) Were they ice sheets or valley glaciers?

d) Was there a different ice source for different glacials?

e) How much older is the older till?

f) How did the ice mass form, top down or bottom up?

In order to answer these questions I used a wide range of research techniques some of which include digging and drilling, field measurements and sampling, field mapping, air photos, borehole records, calcium carbonate content, and radiocarbon dating.

Conclusions

Radiocarbon dating has allowed a new chronological framework to be applied to glacial deposits in Yorkshire. Raistrick and Edwards' notion of a two phase Devensian glaciation must now be rejected and a new three glaciation model proposed.

Covering the entire area (with the exception of Calderdale) , the oldest glacial period evidenced in the Leeds area is probably the Anglian. Evidence of Lake District glacial erratics found in the dissected patches of till along with a distinct X-Ray Fluorescence (XRF) signature suggest deposition by a swollen lobe of ice occupying the Vale of York. Fragmented remnants of glacial till with igneous erratics occur at East Ardsley and at depth near Freizinghall, Bradford.

The more recent Wolstonian and Devensian glacial events were sourced from a Pennine ice centre. Most of the topographic expression of glacial activity belongs to the most recent glacial event (Devensian) which terminated around 13 000 years ago. Almost no topographic expression remains (but sedimentary evidence survives) from the older Wolstonian glacial that terminated around 130 000 years ago.

The Wolstonian and Devensian glacial periods are separated by an interglacial period (Ipswichian) with temperatures at least as warm as those of the present day. Evidence of warm temperatures exist at Oulton, Leeds, where a deep, reddened palaeosol developed on top of Wolstonian glacial deposits, and the numerous Hippopotami remains found in caves and river terraces.

Raistrick’s idea of long, thin valley glaciers separated by protruding nunataks is probably wrong. Evidence of ice passage around Great. Almscliff Crag (drift tail) and over Ilkley Moor (ice scratches at the Cow and Calf), suggest that ice covered most of the Pennine hills. The lack of glacial deposits on hills to the south of Bradford but the abundance of till in the Bradford basin itself, suggests that ice built up from the valley floors towards the southerly limit of the last glacial.

More modern analysis of the glacial and interglacial sedimentology found around the Yorkshire Dales has allowed a new chronological model of climate change to be proposed. This model broadly fits in with the chronology for the East Yorkshire coast proposed by Catt.

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The volcanic geology of the Aeolian Islands
Alison Quarterman, Huddersfield Geology Group

Introduction

The Aeolian Islands are located in the Tyrrhenian sea, just less than 40 kilometres from the northern coast of Sicily. The group of islands include Lipari, Vulcano, Salina, Stromboli, Filicudi, Alicudi and Panarea. There are also five small islets, Basiluzzo, Dattilo, Lisca Nera, Bottaro and Lisca Bianca. They are all of volcanic origin, separated from the Sicilian coast by waters of 200m deep. It appears that they have never been in contact with the Sicilian Island. Having been studied since at least the 18th century, the Aeolian Islands represent an outstanding record of volcanic island-building and destruction. The islands dramatically illustrate two of the types of eruption, Vulcanian and Strombolian, and so have featured prominently in the education of all geologists’ for over 200 years.

Fossa crater on Vulcano

Geological Setting

It is generally agreed that the Aeolian Islands form a volcanic island arc in the Tyrrhenian Sea. The island arc is a product of the collision of two plates: the African plate (or an adjacent microplate) which is being subducted beneath the Eurasian plate (or an adjacent microplate). The fragmented interaction between these two plates make the identification of actual plate boundaries quite difficult. Subduction still continues today and the regular volcanic activity is clear evidence of the deep-rooted activity below.

The complex geochemistry of the lavas (they range from calc-alkaline to potassic) suggest that the islands may have been formed from individual magma reservoirs. Hence a wide range of volcanic rocks can be studied; these include basalts, andesites, rhyolites and tuffs. With the notable exception of Stromboli and Vulcanello, silicic explosive magmas have dominated the recent eruptions of the Aeolian Islands. The complex and varied volcanic processes have combined to create spectacular landscapes incorporating steep cones, lava flows, and pyroclastic ash beds.

Faraglione – a pyroclastic cone very altered by fumarole activity

Vulcano and Vulcanello

Vulcano is the southernmost of the Aeolian Islands. It is a young island whose recent volcanic interest has centred on the Fossa Cone. All the lavas of Vulcano are potassic. The Fossa is essentially a trachyitic tuff cone that lies on a base of trachyte and leucite-tephrite lava flows. It has exuded a rhyolitic obsidian lava flow in the Pietre Cotte. Much of the ash of recent eruptions has been washed off the summit in lahars, exposing the older volcanic deposits. Fossa crater has had at least 7 major eruptions in the last 6000 years. Each cycle consists of volcanic breccia, followed by pyroclastic flows, then pumice and then a silicic lava flow, usually rhyolite or obsidian. There are numerous active fumaroles producing gases at about 150o C, with sulphur crystals. Vulcano needs constant monitoring because of the potential devastation of a sudden eruption like the one in 1888, on an island which has thousands of tourists visiting each day in the summer.

Vulcanello, similarly lies on the base of trachyte and leucite-tephrite lava flows. It has 3 cones, with pyroclastic flow deposits and lavas associated with each eruption. Vulcanello emerged from the sea in 183 BC and has been actively growing since then, with the last major eruption in 1550.

Lipari

The oldest rocks on Lipari (220,000 to 160,000 yrs) are exposed in the cliffs. Lipari has a complex volcanic history and has produced many types of igneous rocks, from basalts to rhyolites. The site of activity has migrated so the island has grown in size.

There is plenty of present day hydrothermal activity e.g. hot springs of San Calogero. This spa has hot pools fed by water at about 60o C and has been used for therapy since Roman times. Lipari Old Town, with its cathedral and geology museum, stands on an outcrop of rhyolite. In and around Lipari are many pyroclastic flows and ash deposits that are quarried. It is also a good place to see cliffs of welded tuffs.

The local towns folk have also exploited kaolin, a clay mineral produced by the breakdown of feldspar under hydrothermal conditions. There are many small quarries that have been used for centuries to produce clay for china and many other uses. There is a good disused kaolin quarry, Quattropani.

Porticello Pumice, Lipari

Monte Pilato crater is 1km x 200m and last erupted in 729 AD. The final eruption stage is the obsidian lava flow of Rocche Rosse. Nearby there are huge pumice quarries as typified by the one at Porticello. The pumice has been exploited at Porticello for centuries from mines and quarries and still employs 1600 workers. It is extracted in blocks and trimmed, then exported by ship. It has many industrial uses, such as cleaning, insulation and as a filler in soap and polishes. Pumice is the frothy lava produced by bubbles of gas produced as pressure is released on the silicic magma chamber. Bedded pumice is probably produced by explosive activity. The fragments fall back to the ground in layers.

Rocche Rosse Obsidian

Like pumice, obsidian has been worked extensively. It was originally worked for tools and blades from Neolithic times (at least 4000BC) and traded all around the Mediterranean, declining only as bronze began to replace obsidian for weapons. Obsidian is a very silicic rock, from a viscous and sticky magma characteristically weathers to a red brown colour, though the black glass is visible underneath.

Stromboli

Stromboli has been constantly active for the last 2000 years. It rises from the sea bed which is about 2 km deep, so the island represents the top of a large volcano. All the activity on Stromboli has been concentrated near the present summits so it is difficult to separate the stages of eruption over the last 100,000 years except by their chemistry. Present activity is concentrated on Sciara del Fuoco.

Strombolian volcanic activity is more or less continuous. For this to take place the magma has to be runny and flow easily from the vents. Lava flows result from lava fountains, which can be up to 200 m high. For there to be continuous activity the magma must be basaltic in composition, as silicic magma is very viscous and sticky. Spindle-shaped volcanic bombs are commonly produced as the lava cools as it flies through the air after being ejected by a lava fountain.

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Field Meetings

The geology of the Ingleton Waterfalls
Leader: Paul Kabrna

Time / Date: 10:15 am, Sunday, 16th May 2004

Meeting at: Giggleswick Scar lay-by opposite Scar Top Garage at Grid Ref: (796 657) to view the South Craven Fault. From here we will move on to Ingleton’s Broadwood car park at Grid Ref: (693 733) on the west side of the River Twiss.

Practical Details: The Broadwood car park provides a convenient starting and finishing point for picturesque walks up the valleys of the Rivers Twiss and Doe. Access has been aided by the provision of levelled paths and concrete steps past the waterfalls. There is a charge of £6 for each car. It is not a National Trust car park. Carry packed lunch.

Geological setting: Giggleswick Scar is a classic fault-line scarp formed by the South Craven Fault. The scar is Dinantian Great Scar Limestone and the lower ground is Namurian Millstone Grit. Although tree and scree cover reduce the sharpness of the fault line, it is still one of the most impressive fault scarps in the UK.

Ingleton Glens Waterfall walk provides a geological itinerary of first rate importance. It includes crossing three major faults, volcanic dykes, excellent outcrops of the regions oldest rocks, and one of the most famous examples of an unconformity in Britain. The inlier exposes Ordovician (Precambrian?) strata which are seen to be unconformably overlain by the Carboniferous Great Scar Limestone. The youngest rocks however are the red beds exposed in the banks of the River Greta. They are of Westphalian A age and are an indicator of Ingleton’s past coal mining industry.

Late Devensian glaciation (c.26000 - 10000 years BP) covered the area with a south and south-easterly moving ice sheet whose origin was in the Northern Pennines, Howgill Fells and the Lake District.

O.S. Maps: Outdoor Leisure 2 : Yorkshire Dales (Western area) 1:25 000

Reference:
Yorkshire Rocks and Landscape - A Field Guide by the Yorkshire Geological Society : 1994

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Quarrying in the Millstone Grit Group around Stacksteads in the Rossendale Valley
Leader: Arthur Baldwin

Time / Date: 10:30am, Saturday, 26th June 2004

Meeting at: The public car park in Stacksteads opposite the Rose ‘n Bowl public house; Grid Reference (SD 854 217)

Practical Details: Lee Quarry is accessible on foot. The quarry is about half a mile south of Stacksteads, near Bacup via the main incline from Glen Street off the A671. Carry packed lunch.

Geological setting: The rocks belong to the Namurian Series, in particularly the Millstone Grit Group. The quarries of this area expose a repetitive association of rock types caused by the repeated advance of sandy deltas into a deep water basin that occupied this part of the world in the late Carboniferous. The combination of rich trace-fossil assemblages and good sedimentary features makes this area of great importance to studies of late Carboniferous environments and palaeogeography. Lee Quarry has been extensively quarried for Haslingden Flagstone.

Stone quarrying has had a major impact on Rossendale’s landscape. Lee Quarry is one example. It was worked from 1820 until the end of the 20th Century when it was acquired by Lancashire County Council as part of the Rossendale Quarries Strategy. In the past as one quarry became exhausted, little or no attempt was made to restore the site to its former glory. With the aid of government funding, Rossendale Quarries Strategy was developed to reclaim disused quarries for the benefit of wildlife, geology and archaeology. In order to make the site safe, improvement to drainage and soil-stabilisation have been put in place.

O.S. Maps:
O.S. 1:25 000 Sheet 690 Rawtenstall & Hebden Bridge
O.S. 1:50 000 Sheet 103. Blackburn & Burnley
BGS 1:50 000 Sheet 76, Rossendale (solid edition)

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Jurassic rocks of Runswick Bay, near Whitby
Leader: Will Watts

Time / Date: 10:00 am, Saturday, 21st August 2004

Meeting at: right-hand slipway at Runswick Bay Grid Ref: [NZ 809 160]

Practical Details: There is a large public car park beside the start point. Packed lunch will be needed as will boots and clothing appropriate to the weather (including suncream / hats if sunny!).

Geological setting: In the late Lower Jurassic eustatic change in sea level led to increased water depths in the Yorkshire Basin. This began a prolonged period of mud deposition. The rocks exposed in Runswick Bay belong mainly to the Early Jurassic Whitby Mudstone which forms the upper part of the Lias. Caves in the cliffs show where the mineral jet was dug from the main jet rock band. Jet is a type of compressed fossilised wood, very light in weight, is easily carved and takes a high polish. Although mining of jet ceased about 1920, jet can still be found washed up on the beaches. The underlying grey shale with its calcareous concretions, is also exposed here.

At the south-eastern end of the bay lies the headland of Kettle Ness where the chemical alum was extracted from the cliffs in large quarries from the Alum Shale. Alum was used in the tanning of leather, as a mordant (fixer) in dyeing, and in the manufacture of parchment and candles. On the western side of Kettleness, the Cleveland Ironstone is seen on the foreshore below Whitby Mudstone.

Last but not least expect to find some ‘half decent fossils’!

O.S. Maps: O.S. 1:50 000 Sheet 94 Whitby

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Almscliff Crag & Brimham Rocks
Leaders: Paul Wignall and Bob Perris

Time / Date: 10:30 am, Saturday, 25th September 2004

Meeting at: Roadside parking is possible adjacent to Almscliff Crag at Grid Ref: (SE 265 491).

Practical Details: Almscliff Crag: From the A658 Harrogate-Otley road, take the sign posted road uphill to North Rigton. At the west end of the village, turn into Crag Lane and continue past Almscliff Crag and park along the roadside. Carry packed lunch if required. A pub stop will be available.

Brimham Rocks: Located 4 miles east of Pateley Bridge of the B6265. The area is owned by the National Trust.

Geological setting: Almscliff Crag - The lower reaches of the Wharfe Valley between Otley and Wetherby are characterised by a broad plain. The E-W running hills that flank this valley reveal, in a series of sporadic outcrops, a series of Millstone Grit (Namurian, Upper Carboniferous) sandstones dipping generally southwards. The resilient sandstones of the Kinderscout Grit Group form a major ridge running for 30 km unbroken between Otley and Ilkley, on the south side of the Wharfe Valley. In contrast, the northern ridge, formed of the Almscliff Grit has very few natural exposures except for Almscliff Crag which stands out like a sore thumb from the otherwise gentle slope. The reasons behind this exposure essentially relate to the fact that the sandstone greatly increases its thickness for around 150 m along strike at this location.

Almscliff Crag is also an important geomorphological site for studies of tor formation, rock weathering and landscape evolution. It is one of the most massive gritstone tors in the Pennines. The crag is a good site to study the association between unweathered and weathered bedrock and how this ties in with periglacial processes and glacial erosion caused by the late Devensian ice sheet.

Brimham Rocks - Similarly to Almscliff Crag, Brimham Rocks is a collective name for a large group of tors on Brimham Moor. They form a spectacular landmark in the Nidderdale District. Brimham Rocks are typically pebbly, cross-bedded fluvial sandstones of Lower Brimham Grit (Kinderscout Grit).

Tors, particularly in this region, are associated with Millstone Grit escarpments. They are thought to have become isolated from retreating scarp edges when the climate was intensely cold. This may have occurred during the main late Devensian glaciation (as at Almscliff Crag) or during the following Loch Lomond interstadial.

Geomorphological setting: Tors are residual masses of rock rising above their surroundings surrounded by free faces. They have been described from many climatic regions in the world and have been linked to the UK with resistant rocks such as granite in upland areas such as Dartmoor. Gritstone tors are a common feature in the Pennines, both on hill-tops and scarp edges.

The origin of tors has been the subject of considerable debate for many years. There are currently two major theories regarding their formation, the first of which involves a two-stage model of weathering then mass-wasting whilst the second requires a single cycle of development. Linton (1955), working on Dartmoor, proposed a hypothesis based upon firstly a period of deep sub-surface chemical weathering of rock under sub-tropical conditions (thus Tertiary in age), controlled by structure as water percolated along lines of weakness such as joints. This weathering produced a mantle of rotted rock (saprolite) surrounding 'corestones' of relatively fresh rock. Later removal (in stage two) of the weathered mantle took place in the Quaternary, accomplished by meltwater and solifluction processes.

Palmer et al (1956 onwards) disagreed with Linton's hypothesis, arguing that a single cycle of Periglacial activity, involving frost-shattering and subsequent removal of weathered products by solifluction produced tors as part of an assemblage of periglacial landforms. Palmer's work was mainly in the Pennines where tors are mainly of the scarp-edge type whereas Linton's work involved mainly summit tors on Dartmoor. It may thus be the case that tors are polygenetic in origin.

Almscliff Crag is a summit-type tor and shows evidence of corestones surrounded by a variable thickness of weathered rock (grus). Linton cited this Crag as a good example of a tor emerging from beneath an extensive weathered mantle, comparable in origin to Dartmoor tors; an explanation disputed by Palmer! A possible clue to the origin of grus was explored by Wilson (1980), who examined the surface texture of grains from gritstone grus at Blackstone Edge. Using a scanning electron microscope, he showed that the grus at Blackstone Edge developed in two phases; chemical followed by mechanical weathering but without evidence of prolonged chemical decay as envisaged by Linton.

Brimham Rocks are an excellent example of scarp-edge tors, initially interpreted circa 1869 as sea stacks! Of particular interest at Brimham are the shapes of the corestones, many of which rest in situ on narrow pedestals, reminiscent of residual rock landforms in desert areas as he role of aeolian action has therefore been involved in theories of tor development here.

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