Programme: 2008 - 2009

© Craven & Pendle Geological Society

Indoor Meetings

Friday: 17 October
Environmental change in ancient and modern deserts. Nigel Mountney Ph.D., University of Leeds

Friday: 14 November
Arsenic in acid mine drainage environments and how to make it worse! Claire Corkhill MEarthSci (Hons)., University of Manchester

Friday: 12 December
Herbivory in Antarctic fossil forests: a modern day comparison. Claire McDonald BSc.(Hons), MSc., University of Leeds

Friday: 16 January
Mid-Jurassic geology of Ketton, Rutland
Peter del Strother MBE, Castle Cement

Friday: 13 February
Witnessing the birth of a new ocean in Afar, Ethiopia. Tim Wright Ph.D., University of Leeds

Friday: 13 March
Living with a lava dome: Mt Unzen, Japan. Hugh Tuffen Ph.D., University of Lancaster

Field Meetings

Sunday: 26 April
The Carboniferous sequence between Lothersdale and Cowling. Paul Kabrna & Jon Barber Ph.D., University of Leeds

Sunday: 17 May
The Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills. Paul Kabrna & Jon Barber Ph.D., University of Leeds

Saturday: 13 June
The geology of Horton and Ingleton Quarries. John Peate, Hansons Aggregates. Joint meeting with the Lancashire Group of the Geologists’ Association

Saturday: 11 July
Whitbarrow, the white hill: a walk through the Carboniferous Limestone of South Lakeland. Steve Webster

Sunday: 16 August
Triassic geology of Alderley Edge. David Turner, Jean Chicken & Paul Kabrna

Sunday: 6 September
Carboniferous rocks from Twiston to Foulridge. Paul Kabrna. Joint meeting with the Lancashire Group of the Geologists’ Association


Environmental change in ancient and modern deserts
Nigel Mountney, University of Leeds

Introduction

Approximately 30% of the present-day land surface of the Earth is characterised by arid desert conditions. The majority of desert environments are composed of a variety of contemporaneously active erosional and depositional geomorphic elements that each respond in a predictable manner to even relatively modest changes in controlling conditions, most notably climate. Predominantly erosional mountainous and badland regions occupy in excess of one-third of desert areas, whereas predominantly depositional regions composed of sand dunes, interdunes, sand sheets, playa lakes, sabkhas (salt flats), ephemeral and occasionally perennial rivers, and alluvial fans cover the remaining area. Where actively migrating sand dunes occur collectively, they form ‘sand seas’ or ‘ergs’, which cover approximately 20% of the surface area of the world’s major deserts. The erosion, transport, and deposition of sediment in deserts are dominated primarily by a variety of aeolian and fluvial processes, though chemical processes, such as salt precipitation, may be important locally.The competing processes that give rise to the varied range of landforms encountered within deserts are controlled by a variety of factors, most notably regional climate and tectonic setting. Together these factors govern key processes that operate in deserts that together dictate rates of weathering, the nature and rate of sediment supply, the availability of that sediment for transport and regional water table level. Desert processes and the resulting landforms that they give rise to are complex and vary both spatially and temporally, meaning that the geomorphological analysis of modern deserts and the geological analysis of their deposits in the longer term sedimentary record is a four-dimensional problem (3D-space plus time).Current research is assessing how arid climate aeolian, fluvial and lacustrine depositional systems accumulate through time and how they become preserved in the long-term rock record. Recent and ongoing studies have focussed on a range of both modern and ancient arid depositional desert systems, including the Namib Desert of Southwest Africa and the Permian Cedar Mesa Sandstone of Southeast Utah.

Namibia, South West Africa

Dunes in the Namib desert

Dunes and interdunes: Namib Desert

The Namib is a coastal desert in which aridity is promoted by cold offshore currents. Dunes of the Namib Sand Sea exhibit a broad range of morphologies and sizes and gradual spatial changes of dune type reflects adjustments in both the character of the prevailing wind and in the supply and availability of sand for aeolian transport. At the margins of the dune fields, evidence for ongoing competition between coeval aeolian, fluvial and lacustrine processes is widespread. Ephemeral fluvial stream channels show evidence for progressive diversion of their courses in response to dune growth across their path. In several places, dune-dammed streams terminate in a series of ephemeral playa lakes in which flood waters episodically accumulate for a few days each year before post-flood desiccation occurs following substrate infiltration and surface evaporation of the ponded water. A range of preserved sedimentary structures, including desiccation cracks, laminar calcrete profiles and a suite of biogenic structures, are evident in the older Namib Sand Sea succession. These testify to the repeated occurrence of various styles of aeolian, fluvial and lacustrine interaction and demonstrate the dynamic nature of this long-lived desert system.

Permian Mesa sandstone Formation, SE Utah

Cedar Mesa Sandstone

Permian Cedar Mesa Sandstone Formation of SE Utah. Photo by Nigel Mountney

One well exposed ancient example of a succession that records evidence for aeolian-fluvial-lacustrine interaction similar to that observed in the Namib Desert is the Permian Cedar Mesa Sandstone, which outcrops across much of southeastern Utah. This mixed aeolian-fluvial-lacustrine succession exhibits a systematic variation in preserved sedimentary architecture over a 30 km-wide belt from the Needles District of Canyonlands National Park to the Indian Creek area. In terms of palaeogeographic setting, this systematic spatial variation reflects a transition from a dry sand sea (erg) centre, through a water table-controlled aeolian dominated erg margin, to an outer erg margin subject to periodic fluvial incursion. The erg margin succession represents a wet aeolian system, accumulation of which was controlled by progressive water table rise coupled with ongoing dune migration and associated changes in the supply and availability of sediment for aeolian transport. Climatically-induced variation in the level of the water table relative to the depositional surface governed the nature of interdune sedimentary processes, and a range of dry, damp and wet (flooded) interdune elements is recognized. Variations in the geometry of these units reflect the original morphology and the migratory behaviour of spatially isolated dry interdune hollows in the erg centre, locally interconnected damp and/or wet interdune ponds in the aeolian-dominated erg margin and fully interconnected, fluvially-flooded interdune corridors in the outer erg margin. Relationships between aeolian dune and interdune units indicate that dry, damp and wet interdune sedimentation occurred synchronously with aeolian bedform migration. Temporal variations in the rates of water table rise and bedform migration within the system have been determined through analysis of the preserved stratigraphic architecture. From this, it has been possible to characterise the response of the desert system to changes in regional climate, whereby accumulation rates are shown to have increased during periods of rapidly rising water table, whereas sediment bypassing occurred in the aftermath of flood events in response to periods of elevated but temporarily static water table. During these flood periods, the outer margin of the dune field was subject to expansion of fluvially-flooded interdunes in front of non-climbing but migrating dunes, which resulted in the amalgamation of laterally adjacent interdunes and the generation of regionally extensive bypass (flood) surfaces.

Conclusions

The outcome of this work has been the development of a suite of models to explain how aeolian bedform topography controls fluvial incursions into sand-sea areas. These predictive models are being used for a variety of purposes. Firstly, they are helping to develop a better understanding of how deserts respond to environmental change over time and they are therefore important in helping to predict likely future desert response to ongoing climate change. This is important because desert fringe areas – which in places like the Sahel of sub-Saharan Africa support large human populations – are extremely sensitive to environmental change. Secondly, predictive models are being applied by the hydrocarbon industry for improved prediction of reservoir behaviour. Many of the UK’s remaining oil and gas fields will require the application of sophisticated sedimentological models if the true potential of their reserves is to be realised. Finally, these models are required to develop a better understanding of the character of aeolian and fluvial strata within the UK’s large subsurface saline aquifers that are currently being considered as possible sites for the long-term underground storage of captured carbon dioxide.

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Arsenic in acid mine drainage environments and how to make it worse!
Claire Corkhill, Manchester University

Introduction

Metalliferous and coal mining has left a global legacy of sites contaminated by acid waters and toxic metals generated by the breakdown of sulphide minerals. Particular problems are seen in parts of North and South America and in the UK. The release, transport and re-precipitation of contaminants are ultimately controlled by processes involving interactions between mineral surfaces and fluids and can be rapidly accelerated by the presence of microbial communities (called extremophiles) but are poorly understood in many cases.

This report focuses on minerals involved in mine waste systems involving arsenic and sulphur, with experimental studies of the oxidative breakdown reactions, in the presence or absence of bacteria, of arsenopyrite (FeAsS) and enargite (Cu3AsS4) to form iron and copper (oxy)hydroxides. The fate of arsenic in these minerals is investigated. This study makes use of experimental and computational resources and we focus here on surface investigations using XPS of the breakdown and precipitation reactions, contrasting bio and inorganically mediated systems.

Dunes in the Namib desert

Acid Mine Drainage of heavy metals including cadmium, lead, and arsenic, threatens waterways with toxic contamination. Photo by Claire Corkhill

My Research

Acid mine drainage (AMD) is a phenomenon that occurs when metal sulphide minerals breakdown when in contact with the atmosphere or oxygenated waters. These minerals degrade via oxygenation reactions and where groundwater is involved, the reactions lead to the generation of acidic solutions. This commonly occurs at metalliferous and coal mining sites where mine waste tailings, underground or open pit mine workings, ore stockpiles or spent heap leach piles are subject to the oxidative processes that cause acid mine drainage. This phenomenon can also occur when metal-bearing rocks (particularly containing iron sulphides) are exposed to atmospheric weathering without mining activity. This is termed acid rock drainage (ARD).

The fluids associated with AMD commonly exhibit low pH, usually ranging from 2-6.5, high Eh and elevated concentrations of elements and ions, especially iron, sulphate and H+ ions. The acidity of these fluids promotes the reactions with minerals in the host rocks which leads to the formation of new compounds. For example, initially formed Fe2+ from pyrite (FeS2) oxidation (equation 1) reacts to form Fe3+ (equation 2). This leads to the formation of iron oxyhydroxides which precipitate as an ochre solid (equations 3 and 4).

AMD Equations

Other metals are leached from the host rocks associated with the source of AMD such as manganese and aluminium, and heavy metals such as lead, cadmium and mercury are common. Arsenic is commonly released as the result of the oxidation of As-bearing sulphides including enargite (Cu3AsS4), orpiment (As2S3), realgar (AsS) and arsenopyrite (FeAsS), the most commonly occurring As-bearing sulphide mineral.

Influence of Fe – oxidising bacteria in AMD environments

The formation of acid mine drainage is promoted by the metabolic processes of acidophilic bacteria and archea. The most common Fe-oxidising bacteria in these environments is Leptospirillum ferrooxidans. This bacteria is a chemolithotroph which oxidises Fe2+, present in AMD waters and sulphide minerals to Fe3+. Other microorganisms such as Acidithiobacillus caldus are capable of oxidising sulphur and sulphide to sulphuric acid. The metabolic processes of these micro-organisms have been shown to increase sulphide mineral dissolution by ~260 %.

In the current study, the surfaces of arsenopyrite (FeAsS) and enargite (Cu3AsS4) were characterised after acidic (pH 1.8) oxidative dissolution in the presence of Leptospirillum ferrooxidans. The focus of the work has been on the chemical changes observed at the mineral surface, in particular those observed using X-ray photoelectron spectroscopy (XPS) and on changes in the chemistry of the coexisting aqueous phase. Biologically mediated oxidation of arsenopyrite and enargite (2.5g in 25ml) was seen to proceed to a greater extent than abiotic oxidation, although arsenopyrite oxidation was significantly greater than enargite oxidation. These dissolution reactions were associated with the release of ~917 ppm and ~179 ppm of arsenic. The formation of Fe(III)-oxyhydroxides, sulphate and arsenate was observed for arsenopyrite, thiosulphate and arsenate for enargite. Environmental Scanning Electron Microscopy (ESEM) revealed an extensive coating of an extracellular polymeric substance associated with the L. ferrooxidans cells on the arsenopyrite surface and bacterial leach pits suggest a direct biological oxidation mechanism. Although oxidation rates of enargite were greater in the presence of L. ferrooxidans, cells were not in contact with the surface, suggesting an indirect biological oxidation mechanism for this mineral. It has been found that cells of L. ferrooxidans are able to withstand up to several hundreds of ppm of arsenic.

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Herbivory in Antarctic fossil forests: a modern day comparison
Claire McDonald, Leeds University

Introduction

Today, most of continental Antarctica is permanently covered by snow or ice, with only a small proportion of ice-free terrestrial habitats. The majority of terrestrial habitats are covered in snow for most of the year with widely variable, unpredictable conditions, both short term and seasonally. Therefore, it is not surprising that there are only two insects known to be living in Antarctica, both flightless midges. They occur along the northwest coast of the Antarctic Peninsula where the conditions are warmer and wetter than elsewhere.

However, millions of years ago Antarctica was completely different with areas covered in diverse vegetation similar to the forests of New Zealand and southern South America. Such ecosystems support a large number of insect species, therefore, the same might have been true for Antarctica, but few insect body fossils have been found due to difficulty in preservation, with only small fragments recovered in most studies. Due to the rarity of insect body fossils from Antarctica it is possible to gain a better understanding of the insect fauna by examining indirect evidence of the insects’ presence. For example, the evidence of an insect’s behaviour preserved as fossils, known as trace fossils. There are three main categories of trace fossils that are shown on leaves: general chewing marks both marginal and non-marginal, leaf mines and galls. There is a large diversity of plants in the terrestrial fossil record and as insects are the major group of herbivores, the trace fossils provide a unique and direct record of the plant-insect interactions in the past. The trace fossils can indicate the type of insect that made the trace, at least to order, if not to family level, by the shape, size and position of the damage. This allows insect damage to be distinguished from other causes of damage such as mechanical damage or from other large herbivores.

There are several documentations of the vegetation of Antarctica for the past, especially during Cretaceous and Tertiary, but few mention the presence of insect traces. However, if temperate rainforests were once present in Antarctica, then the palaeoecological reconstruction would not be complete without considering the insect fauna that could have been present. Therefore, the main aim of the project is to identify the presences of insects in Antarctica in the past by examining fossil leaf collections from different localities from the Eocene. The trace fossils found will then be compared with modern ecosystems to identify the causal insects and the palaeoclimate they lived in.

Localities

The fossil leaves examined were collected from deposits on two islands off the Antarctic Peninsula, both Eocene in age. King George Island in the South Shetland Islands is situated at a latitude of 62°S, similar to that in the early Tertiary. Fossil leaves from several locations on King George Island were studied, such as Fossil Hill, Point Hennequin and Vatireal Peak.

Collections from Seymour Island were also examined. The sedimentary sequence exposed on Seymour Island is more than 2 km thick and represents the uppermost part of the infill of the James Ross Basin. The youngest beds, which outcrop on the northern part of the island, were grouped into the upper Palaeocene Cross Valley Formation and the Eocene, La Meseta formation and are placed together as the Seymour Island Group. All leaves belong to collections of the British Antarctic Survey.

Eocene Leaf

Fossil leaf from King George Island showing marginal leaf chewing
© Claire McDonald (University of Leeds)

Summary of Results

Insect body fossils from Antarctica are very rare, yet many collections of Eocene fossil leaves from Antarctica provide insect trace fossils, indicating that insects were an important component of the unique forests that once grew in south polar regions. These insect traces continue to provide an excellent opportunity to examine the palaeoecology of Antarctica. A database of all insect traces on the Antarctic fossil leaves was compiled and analysed in terms of the diversity of palaeoherbivory. The fossil leaves are diverse with several different plant families present such as Nothofagaceae and Cunoniaceae. The range of traces that were found includes (larval feeding traces inside the two leaf layers), leaf galls (protective chamber containing the larva or egg), and general leaf chewing.

To provide a greater understanding of ancient herbivore intensity and diversity in Antarctica, modern insect traces on Nothofagus leaves, and their associated insects were examined from the temperate forests in Chile, the modern day analogue of the Antarctic forests during the Eocene. Modern traces show a similar diversity of damage types to that seen in the Eocene, but the intensity of damage appears to be greater now. Results of an investigation into the herbivorous insect fauna of Nothofagus antarctica and Nothofagus pumilio are currently under analysis.

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Mid-Jurassic geology of Ketton, Rutland
Peter del Strother MBE., Castle Cement, Clitheroe

Introduction

Ketton has long been famous for an oolitic limestone, one of England’s finest building stones. Stone production continues but the very extensive quarry workings are mainly for cement production (Castle Cement Ltd) from the Lincolnshire Limestone and overlying clays. A new extension to the quarry has exposed a virtually continuous succession of the highly fossiliferous Middle Jurassic (approximately 170 million years old). These rocks were deposited in a shallow sea and at times under estuarine conditions.

Geology

There are extensive outcrops of Middle Jurassic strata in Ketton quarry. The section is continuously exposed from the Northampton Sand Ironstone to Kellaways Formation. A small exposure of the junction between the Lias and the Northampton Sand Ironstone can also be seen when the water table is low. The Collyweston facies of the Lower Lincolnshire Limestone is also exposed. The main formations follow (youngest first), including the superficial deposit of boulder clay:

Boulder clay
The boulder clay at Ketton contains derived fossils such as Gryphaea, belemnites and ammonites from the Jurassic. Ammonites from the chalk are also found. Cobbles of chalk and flint are common.

Kellaways Formation
Locally brought down by faulting, Kellaways Formation rests on the Cornbrash. The argillaceous lower member, the Kellaways Clay (about 3m) passes gradationally into the Kellaways Sand (about 5.5m). Belemnites and Gryphaea are quite common, but the exposure is reached via a small landslip and can be extremely boggy. This is currently the highest Jurassic horizon proved at Ketton.

Abbotsbury Cornbrash Formation
The Cornbrash is a massive limestone, weathering brown. The brachiopod, Obovothyris magnobovata at its base indicates Lower Cornbrash. The main part is Upper Cornbrash. Large oysters, Lopha marshii, can be seen on the top surface. Brachiopods and bivalves are common. The limestone is not oolitic.

The top surface of the Blisworth Clay has large Thalassinoides burrow systems at its contact with the Cornbrash. Pholadomya deltoidea can be found here.

Blisworth Clay Formation
The lower part contains ostracods and is taken to be marginal marine. The central part consists of bedded varicoloured clays and silts, at least one of which contains truncated rootlets.

Blisworth Limestone Formation
Within the confines of the quarry the Blisworth Limestone is variable both in thickness and in character. It is not oolitic. The oyster Praeexogyra hebridica is common. Also found are terebratulid and rhynchonellid brachiopods and fully marine bivalves such as Pholadomya lirata. The echinoid, Clypeus, can also occasionally be found.

The top is taken to be the prominent bed of cone-in-cone calcite.

Rutland Formation
This was formerly known as the Upper Estuarine Series. The Stamford Member at its base consists of quartz rich silts with conspicuous truncated rootlets. Some facies contain trilete megaspores.

The ‘rhythmic’ succession above the Stamford Member was interpreted by Bradshaw (1978) as a series of transgressive-progradational cycles across a coastal plain. Bradshaw was able to trace most of the rhythms from Oxfordshire to Lincolnshire, a distance of approximately 150 kilometres. The lowest rhythm contains Lingula as well as bivalves. Several truncated rootlet horizons are evident. There is an oyster bioherm near the top.

Rutland Formation

The Rutland Formation (previously Upper Estuarine Series). The arrows mark six ‘rhythms’ of sedimentation as defined by Bradshaw. Each rhythm is defined by an erosion surface at the base typically with truncated roots and immediately overlain by a shell bed. The shell bed above rhythm 1 contains brachipods as well as bivalves and is therefore evidence that marine conditions existed at the time of deposition of the shell bed. The presence of roots indicates deposition in a terrestrial environment but there are marine influences in more than one rhythm. Photo: © Peter del Strother (2009)

Lincolnshire Limestone Formation
Both Lower and Upper Lincolnshire Limestone are present, but the boundary between them is inconspicuous at Ketton. The junction between Lower and Upper Lincolnshire Limestone is several units below the plane between the horizontally bedded units and the cross sets, just above a unit rich in nerineid gastropods. It is not usually accessible. A number of hardgrounds are present. An oyster-encrusted bored hardground can usually be seen towards the north of the quarry about 1.5 metres below the topmost surface.

The lowest 0.5 m of the Lincolnshire Limestone consists of uncemented quartz sand. The next three metres or so consist of muddy limestone containing silt-sized quartz. This is the Collyweston facies from which the famous slate was mined at Collyweston. There is no slate quality material in the quarry, but locally signs of layering can be observed. Wood fragments are commonly found within these limestones and less commonly belemnites. There is evidence of burrowing, ripples and small-scale graded bedding including clasts of gastropods and calcareous worm tubes.

Further up the succession the siliceous content is minimal and below the highest hardground the limestone is strongly oolitic. In some areas there is no cement and the ooliths are ‘welded’ together to form the famous Ketton freestone.
Close to the freestone the rock is locally an oosparite with impressive coarse poikilotopic ferroan calcite cement (Emery 1988). Single calcite crystals up to about 4 cm long enclose the close-packed ooliths. On a bright sunny day the reflective fracture surfaces are easily seen.

The top 1.5 metres, above the hardground, weathers brown and is cross-bedded with an abundance of skeletal debris.

Secondary gypsum is found in the top 1 to 2 metres of the limestone. In some places it is fibrous.

There is a sharp lithological break at the top of the limestone and a significant time gap is reported, but there is no evidence of karstic erosion of the limestone.

Grantham Formation
Silts and clays of the Grantham Formation are exposed in a trial pit in the quarry floor. In this locality the quartz sand of the Lincolnshire Limestone overlies silts and fine sands with one or two horizons of truncated rootlets. The rootlets penetrate the top of the ironstone. The Grantham Formation was formerly known as the Lower Estuarine.

Northamptonshire Sand Formation
The ironstone is exposed in a trial pit in the quarry floor. A recent local chemical (oxide) analysis of the ironstone gave:- 21% SiO2 , 6% Al2O3 , 44% Fe2O3 , 10% CaO , with minor S, Mg, Na and K. The ironstone was opencast mined north and south of Ketton along strike, but the limestone and mudstone cover was too great to make such mining worthwhile at Ketton.

BGS did extensive work on the ironstones, and this is published in two memoirs dating from 1949 and 1951. Both memoirs refer to the greenish iron mineral as chamosite. It is now identified as berthierine. The term chamosite is restricted to true chlorite species. The structure of berthierine is similar to serpentine.

The local geological map, Sheet 157 Stamford, shows the areas of ironstone that have been opencast mined Ironstone working took place in Roman times. Domesday Book records the presence of iron forges at Corby in Edward the Confessor’s Time; (Edith Weston, not far from Ketton, is named after his wife). The Lincolnshire Limestone was used for fluxing, and the sands of the Lower Estuarine (now Grantham Formation) for refractories. Ore transport was almost entirely by rail. In 1942 a record output of 10.5 million tons was produced, and during the six years 1939 to 1945 the production provided considerably more than half the total British production of iron ore.

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Witnessing the birth of a new ocean in Afar, Ethiopia
Tim Wright, University of Leeds

The Afar Rift Consortium web site www.see.leeds.ac.uk/afar, compiled by Dr. Jacqueline Houghton of the University of Leeds is an excellent source of information.

Introduction

The Afar region covers the northeastern part of Ethiopia. The Afar depression, also known as the Danakil depression, forms the northern part of the region and is largely desert, whilst the Awash River valley forms the southern part of the area. The region is well known for its early hominid fossil finds including ‘Lucy’, an Australopithecus afarensis, discovered in 1974, who lived about 3.2 million years ago and more recently in the summer of 2007 the discovery of hominid remains 3.5 - 3.8 million years old.

Geology of the Afar region

Although the geological history of the region extends back into the Proterozoic (about 900 million years ago), a time when east and west Gondwana collided, the Afar region is currently dominated by the igneous rocks and structures associated with stretching and rupture of the continental crust over approximately the last 30 million years. As a consequence, the African continent is slowly splitting apart along the East African rift valley, a 3000 kilometres long series of deep basins and flanking mountain ranges. In the remote Afar depression the Earth’s outermost shell, usually a relatively rigid, 150 kilometre thick plate, has been stretched, thinned and heated to the point of breaking. Hot, partially melted rocks are rising up from the Earth’s mantle and are either erupting at the Earth’s surface or cooling just beneath it.

Tectonic Setting

The Red Sea is a narrow stretch of water separating Africa and Arabia. It’s one of Earth’s youngest oceans and is widening by an average of a metre during a human lifetime. But in the Afar Depression there has been a recent, violent, once-in-a-generation separation of tectonic plates that is synonymous with creating new oceans. The spectacular geological event began in late September 2005 when Ethiopian scientists detected exceptional earthquake activity, opening of surface fissures, and a small volcanic eruption in Afar. Remarkably, the tectonic plates had been relatively quiet for more than a century but in less than two weeks separated by nearly ten metres.

Afar rupture
Feleke Worku, a surveyor from the Ethiopian Mapping Agency, examines a ground rupture created during the September rifting event. Photograph © Tim Wright, University of Leeds.

As Ethiopia’s rift valley grows slowly wider, an international team of scientists led by Dr. Tim Wright are engaged in the study of seismic events in the remote Afar desert where the two mighty shelves of continental crust (the African and Arabian plates) meet and are tearing the landscape apart. For most of the time, this happens at around the same speed that human fingernails grow – about 16 millimetres a year. But the gradual build-up of underground pressure can lead to occasional bursts of cataclysmic activity. Ethiopia is the only place on the planet where you can see a continent splitting apart on dry land.

The Afar depression is so hot and dry that almost no vegetation covers the rocks at the surface hence satellite radar images are an ideal means to measure the way the Earth’s surface changes as faults move, and as molten rock moves up and along the fissures within the rift valley. However, when sudden large movements occur, often with devastating consequences as in September 2005, the impact on the landscape is dramatic; in this case a series of fissures opened along a 60 kilometre section of the Afar depression as the plate responded catastrophically to forces pulling it apart. There were 163 earthquakes recorded (magnitudes greater than 3.9) and a volcanic eruption occurred within the Afar rift. This event produced hundreds of deep crevices within a few weeks, and parts of the ground shifted eight metres, almost overnight. More than two billion cubic metres of rising molten magma had seeped into a crack between the African and Arabian tectonic plates, forcing them further apart. The rapidity and immense length of rupture are not unexpected, but have never before been measured directly. In the two years following the initial activity, more dramatic surface changes have continued to take place, and earthquakes continue to stir the region.

Summary

As the sides of the Ethiopian rift move apart, the gap between them is being plugged with molten rock, which then cools to form new land. Perhaps in one million year’s time the Red Sea could come flooding into the sinking region, re-shaping the map of Africa forever. “It’s very exciting because we’re witnessing the birth of a new ocean,” said Dr Wright. “In geological terms, a million years is the blink of an eye. We don’t precisely know what is going to happen, but we believe that it may turn parts of Northern Ethiopia and Eritrea into an island, before a much larger land mass – the horn of Africa – breaks off from the continent.”

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Living with a lava dome: Mount Unzen, Japan
Hugh Tuffen, University of Lancaster

Introduction

Mount Unzen is located on the Shimabara Peninsula, Nagasaki Prefecture, central Kyūshū, SW Japan. It is one of the most active volcanoes in Japan and was nominated as one of the Decade Volcanoes of the United Nation’s Decade of Natural Disaster Reduction since it represents an important type of dangerous volcano. In the last 30 years, Japan has witnessed an average of 3 volcanic eruptions as well as many more volcanic crises each year. Out of 50 deaths that occurred during this period, 44 were caused by the pyroclastic flows of Unzen volcano in 1991 (fatalities included French and American volcanologists). Previous historical activity was recorded in 1792 when Mayuyama (old lava dome), towering just behind the city of Shimabara, collapsed to the east following the summit eruption of Mount Unzen. A debris avalanche rushed into the island sea, generating a tsunami which resulted in 15000 fatalities. Precursory and associated strong shaking, and the avalanche, seriously damaged ancient Shimabara and the surrounding areas.

Unzen Volcano geology

Unzen volcano is an active composite andesitic-to-dacitic volcanic complex located in the western extremity of a large graben across Central Kyūshū where it forms the topographic highs on the peninsula. Almost all lava domes and eruptive centres are distributed within the “Unzen Graben”. The graben is bounded by E-W trending faults, such as the Chijiwa, Kanahama and Futsu. Unzen began phreatic eruptions in November 1990 at the summit craters after quiescence of 198 years.

The volcano complex can be divided into the Older and Younger Unzen volcanoes. Younger Unzen Volcano comprises Nodake, Myokendake, Fugendake and Mayuyama volcanoes and are characterized commonly by the formations of lava domes and their collapsed pyroclastic deposit. Fugendake volcano is built within the horseshoe-shaped scar of Myokendake where its eruption products are seen spread over the flank of Myokendake. Nodake volcano is an isolated volcanic centre adjacent to Myokendake. After intensive ash ejection in February 1991, a lava dome appeared on the eastern flank of Fugendake (1395m) in May 1991. The lava dome, named Heisei-Shinzan (1486m), gradually grew and yielded frequent pyroclastic flows until the eruptive activity ended in 1995. The initiation mechanisms of the pyroclastic flow on the 8th June, 1991 (Takarada,1993) began with a landslide which triggered the collapse of the lava dome. This was followed by an explosion in response to pressure reduction which produced the pyroclastic flow made up of fragmented materials of lava dome and basement.

Hugh Tuffen
Hugh Tuffen on Heisei-Shinzan (Unzen Volcano), Japan
Photo © Hugh Tuffen 2007

Unzen Scientific Drilling Programme

In order to understand the structure and growth history of the volcano and to clarify the eruption mechanisms of SiO2- rich viscous magmas, the Unzen Scientific Drilling Project (USDP), a six-year project consisting of two phases, was started in April 1999. In the first phase, two holes were drilled into the volcano’s flank (USDP-1 and -2). In the second phase, drilling penetrated the magma conduit that fed a lava dome at the summit. The detailed design and targets of the conduit drilling were determined in the first phase. The magma conduit, especially its upper part, is believed to be the site of effective degassing that is the major factor controlling eruption styles. The pressure-dependent nature of solubility of volatiles, principally water, accelerates vesiculation as magma approaches the surface and produces geophysical signals (earthquakes and inflation) in the shallow conduit region. Drilling into this region makes possible in situ observations and sampling of the still-hot conduit and wall rocks of the recent, well-observed eruption.

Summary

Geologists have long wanted to peer inside a volcano. Although we have good evidence from extinct and eroded volcanoes of their inner structure, we know little about the conditions in and near active volcanic conduits. Indeed, few features important to the study of geologic hazards have so much speculation but so little direct information available as the conduit of an active volcano. Early conclusions derived from the USDP-4 conduit hole:

1) Physical measurements and analysis of spot cores indicate that the conduit of the last eruption and its host rocks were successfully penetrated by USDP-4 at Unzen Volcano.

2) The conduit zone of the volcano is about 500m wide in a north-south direction and consists of multiple parallel dykes and veins of different ages intruded within a vent breccia. The conduit zone dykes are up to 40m thick.

3) The feeder dyke of the most recent eruption has cooled from 850˚C to less than 200˚C in nine years by effective hydrothermal circulation.

4) Degassing of ascending magma at the drilled depth probably occurred along cracks propagated by magma gas pressure ahead of the dyke and later along brecciated margins of the established conduit. It is likely that formation of cracks and the accompanying gas migrations are responsible for volcanic tremor events.

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Field Meetings

The Carboniferous sequence between Lothersdale and Cowling
Guides: Paul Kabrna & Jon Barber

Time / Date: 10:30 am, Sunday, 26th April

Meeting at: Raygill Quarry [SD 943455]: Raygill is located in the village of Lothersdale. It is well signposted from 3 miles away in all directions by brown tourist information signs. Postcode for Satellite Navigation is BD20 8HH. Packed lunch or perhaps the Hare & Hounds at Black Lane Ends.

Practical Details: Bring a packed lunch or pub lunch at the Hare & Hounds, Black Lane Ends on Skipton Old Road. During the day we will visit 7 localities in the area:
1) Raygill Quarry [SD 943455]
2) Dowshaw Delf [SD 935448]
3) Hawshaw Slack Delf [SD 948448]
4) Hawshaw Moor [SD 946446]
5) Stonehead Beck [SD 946437]
6) Knoll Hill [SD 960433]
7) Earl Crag [SD 985428]
8) The Hitching Stone [SD 986416]

Geological setting
The extensive Carboniferous sequence extends from Middle Mississippian (Visean) limestones to Lower Pennsylvanian (Bashkirian) around Laneshaw Reservoir. Over most of the area the beds dip steeply to the south-east which in turn are traversed by by two systems of faults; the main faults have a NW-SE direction, whilst a set having an E-W direction crosses the Lothersdale Anticline. The majority of the folds within the Craven Basin verge to the NW, although rare SE-verging folds (for example the Lothersdale Anticline) do exist. The main folds typically have a hinge length between 3 and 10 km and are non-cylindrical.

The glacial story is highlighted at Raygill Quarry and the Hitching Stone. In Raygill during the 1870's whilst quarrying, a pothole was revealed at the south side containg a cache of bones. This find was investigated by the Yorkshire Geological & Polytechnic Society (1880) with the site becoming famously known as the "Raygill Fissure". In contrast, the Hitching Stone is a remarkably large glacial erratic which dominates the moorland SE of Earl Crag.

The broad aim of the trip is to examine Carboniferous sequences beginning in Raygill Quarry where the core of the Lothersdale Anticline is exposed before moving into Dowshaw Delf to examine the Twiston Sandstone which here rest discordantly on an eroded surface of Embsay Limestone. Hawshaw Slack Delf is an outcrop of younger Pendleside Limestone which occurs throughout the Craven Basin and shows considerable variation in thickness and proportion of limestone to mudstone. The next outcrop on Hawshaw Moor is Pendle Grit which represents a sand-rich slope channel/fan complex deposited during the earliest phase of siliclastic input into the Craven Basin. Stonehead Beck is the European stratotype for the Mid-Carboniferous Boundary. Here Sabden Shales represent the time when the Craven Basin became anoxic and was filled with hemipelagic muds deposited in relatively deep water. Fully marine conditions are marked by marine bands dominated by a diagnostic thick-shelled ammonoid fauna. Knoll Hill offers a contrast to the Pendle Grit as these sandstones are of Kinderscoutian age and their mode of deposition is fluvial as opposed to marine! Earl Crag escarpment is another strand of the Kinderscout Grit and offers excellent views. Finally the Hitching Stone was probably positioned by the last glaciation (Devensian) of the area.

Maps
O.S. Sheet SD 84/94

References
Bray, Arthur 1927: The Carboniferous sequence between Lothersdale and Cowling (Colne). In Journal of the Manchester Geological Association. 1, 44 to 57.

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

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The Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills
Guides: Paul Kabrna & Jon Barber

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

Meeting at: Park in Great Ayton near the Tourist Information Office at [NZ 563107].

Practical Details: This is a gentle 12.5km route which uses numerous recognised paths and bridleways. Bring a packed lunch.

Geological setting
The day will include visiting outcrops of Lower and Middle Jurassic sedimentary sequences together with a look at the Tertiary Cleveland Dyke intrusion and the effects on the landscape of the late Quaternary glaciation of the area.

Roseberry Topping, a prominent landmark throughout the Cleveland Basin, is an erosional outlier, where the Middle Jurassic sandstone is detached from the main plateau. This Lower to Middle Jurassic sequence dips gently towards SSE.

The intrusion of the Cleveland Dyke some 59 million years ago has had a strong influence on the local landscape. The intruded dyke is considered to be part of the dyke swarm from the Mull volcanic centre and has been extensively quarried during the last 100 years.

Evidence for glaciation in the region is confined to the tills, glaciofluvial sands and gravels and lacustrine silts and clays on the lower slopes and in the valley bottoms. Glacial meltwater channels are also recognised.

Maps
O.S. 1:50 000 Sheet 93, Middlesbrough & Darlington.
O.S. 1:25 000 Outdoor Leisure Sheet 26, North York Moors, Western Area.
BGS 1:63 360 Sheet 34, Guisborough

Reference
1994: Senior, J., Rose, J. Jurassic, Tertiary and Quaternary around Great Ayton and Roseberry Topping, Cleveland Hills. In: Scrutton, C. (ed.), Yorkshire Rock and Landscape, Yorkshire Geological Society, Leeds, 110-118.

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The geology of Horton and Ingleton Quarries
Guide: John Peate, Hansons Aggregates

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

Meeting at: Ingleton Quarry. All visitors will need to wear hard hats, high visibility vests and stout footwear. Vests will be made available at the quarry. Ingleton Quarry where we meet is on the 1 mile NE of Ingleton along the Hawes road out of Ingleton (B6255).

Practical Details: Bring a packed lunch or take lunch en-route to Horton. Site tour at Horton Quarry takes place at 2pm.

Geological setting
The Ingleton Group succession typifies the style of clastic turbidite sedimentation characteristic of deep-water marine environments.In this case, deposition probably occurred in the middle or lower parts of a turbidite fan.This sequence has been recently re-surveyed by Jack Soper (2003) where special attention was paid to way-up evidence and cleavage/bedding relationships; hence, the established view that the sequence is isoclinally folded throughout is shown to be mistaken: only two large-scale folds dominate the outcrops with a common limb around 3000m thick.

The Ingletonian contains three lithofacies: thick bedded sandgrade turbidite greywackes commonly with delayed grading picked out by cleaved silty tops to the beds; thin bedded green siltstones, mudstones and sandstones with ripple cross lamination, flute casts, slump folds and intraformational breccias, interpreted as low volume turbidite deposits; and very coarse quartz-feldspar-lithic wackes, the 'Ingleton granite' of the quarrymen.

Horton Quarry in Horton in Ribblesdale began operating in 1888 when an enterprising Irishman saw an opportunity for a new lime works when the railway was built up in Ribblesdale. A huge extension was allowed in 1940 as its pure limestone was needed for a renewed steel industry. Quarrying of the Great Scar Limestone takes aggregate from the Gordale, Cove and Kilnsey limestones. The Cove Limestone continues to be the most valuable due to its purity, whilst the muddy Kilnsey Limestone is sold as low-value fill. If and when quarrying expands downwards into the Ingletonian greywackes the future of quarrying at Horton will be safeguarded for some time! It is currently permitted to extract 600,000 tonnes per annum.

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

References:
Johnson, E. 1994: Lower Palaeozoic rocks of the Craven Inliers. In Yorkshire Rocks and Landscape - A Field Guide by the Yorkshire Geological Society. Ed. Colin Scrutton

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Whitbarrow, the white hill: a walk through the Carboniferous Limestone of South Lakeland
Guide: Steve Webster

Time / Date: 10:30 am, Saturday, 11th July

Meeting at: Park on the private lane in front of Witherslack Hall, [SD 437859].

Practical Details: This is a full day excursion as the route is approximately 11km (7 miles) with frequent stops, though it can be shortened if appropriate. The hill is 215m and both ascent and descent follow very steep, rough footpaths, but on top the going is easy. Packed lunch, strong footwear and waterproofs are essential and there are no quick ways off if the weather turns poor.

Geological setting
Whitbarrow is a fault- bounded block of Carboniferous Limestone of Dinantian age, lying unconformably on slates and sandstones of Silurian age. The block is tilted towards the East and is capped by the Urswick limestone that falls away in steps, representing a series of marine cycles each lasting about half a million years. The main limestone masses were deposited in shallow, clear water seas that advanced across the eroded Lower Palaeozoic platform and the cycles have been interpreted as changes in eustatic sea level. The summit area contains the Hervey Nature reserve and is also a SSSI. The route up through the Chadian, Arundian, Holkerian and Asbian, allows us to examine five out of the six Lower Carboniferous limestones of the Southern Lakeland: namely the Martin, Red Hill, Dalton, Park and Urswick. Only the Gleaston beds of Brigantian age are absent as they have been eroded from the top. On a fine day the surrounding structural geology of the area can be observed as well as extensive views of Morecambe Bay and the Lakeland Fells. Devensian features in the form of Lake District erratics and wind blown loess from the Morecambe Bay will also be seen on the summit plateau.

Maps
Explorer OL7 1:25000 and BGS Sheet 49 1:50000

References
Whitbarrow- A geological walk looking at rocks, plants and landscapes. Murray Mitchell et al (Cumbria RIGS)

The geology of the Lake District. Frank Moseley, Yorkshire Geological Society (1978)

(both out of print)

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Triassic geology of Alderley Edge
Guides: David Turner, Jean Chicken and Paul Kabrna

Time / Date: 10:30 am, Sunday, 16th August

Meeting at: the Wizard car park (National Trust), Macclesfield Road, Alderley Edge. Grid Ref: SJ 859773. Turn left in Alderley Edge town. The NT car park is on the left just after the Wizard pub about a mile along the B5087 Macclesfield Road. There are two lay-by's on the approach to the National trust car park which presumably are free if you get there on time. Bear in mind that its at least a half mile walk to our meeting palce from the first lay-by you come to!

Practical Details: Cars will be left here for the day. Bring a packed lunch (although the cafe does serve up a mean egg & bacon teacake!). The day will involve walking over modestly rugged ground - total walking distance 3 miles. Collecting and use of a hammer is not permitted on NT property.

We will start with an optional trip down into the Wood Mine. This is run by the Derbyshire Caving Club who have a base and small museum at the NT Centre. Their website is www.DerbysCC.org.uk. The route should involve no more than stooping in some passages. Helmets and lamps are provided. There is a suggested contribution of £5 per person. After this we will also have the opportunity to examine the surface geology around Engine Vein mine which is now in a restricted area.

Geological setting
This is one of the classic locations for Triassic Sandstones which were laid down in semi-arid desert conditions interspersed with flash floods 230-180 mya. The day is intended to give the opportunity to interpret the sandstones, siltstones and conglomerates within the Sherwood Sandstone strata in various locations. This will include identifying aeolian (wind deposited) and fluvial (water deposited) sandstones, plus unconformities, disconformities and other features within the strata.

The Alderley Edge escarpment has been mined for nearly 4,000 years from the Bronze Age until the 20th Century. A Roman shaft of the 1st Century is located near Engine Vein mine. Some of the minerals mined include malachite, azurite, copper, galena, barytes and iron.

Maps
O.S. Sheets 1:50 000 Manchester (101)
O.S. 1:25000 SJ87/97 Macclesfield & Alderley Edge
Geological Survey Sheets 1:63360 or 1:50000 Stockport (98) Solid or Drift

References
Carlon, Chris (1979). Alderley Edge Mines. Sherratt, Manchester. p. 144 pages. ISBN 085427053X

Warrington, G. (1965). The Metalliferous Mining District of Alderley Edge, Cheshire. Mercian Geologist 1: pp 111–131.

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Carboniferous rocks from Twiston to Foulridge
Guide: Paul Kabrna

Time / Date: 10:30 am, Sunday, 6th September

Meeting at: the Witches Quarry in Twiston [SD 808444] midway between Lower Gate and Twiston Mill, about 2 km from Downham and just under 2 km from Rimington. Up to 10 cars can be parked in the quarry (open the farm gate and drive up the track into the quarry). The quarry is used by the local rock-climbing organisation who have negotiated access with the landowner. Ideally try to park on the roadside near the limekiln, or at least in a spot which doesn't inconvenience the local community of Lower Gate and the climbing fraternity.

Practical Details: The day will be spent driving from locality to locality. Parking may prove challenging so some walking to outcrops will be essential. After lunch we will ascend the hill behind the New Inn in Foulridge to Noyna Rocks so please bring appropriate footwear and outdoor clothing suitable for the vagaries of the British climate! Bring a packed lunch or bar snack at the Anchor pub in Salterforth.

Localities
STOP 1 [SD 808444] Bellman Limestone Member (Twiston: disused quarry)
STOP 2 [SD 838453] Rain Gill Limestone Member (Twiston: disused quarry)
STOP 3 [SD 887457] Pendleside Limestone Formation (Salterforth Railway Cutting)
Lunch
STOP 4 [SD 883447] Pendle Grit Formation (Park Close: disused quarry)
STOP 5 [SD 896427] Warley Wise Grit (Noyna Rocks: series of disused quarries)

Geological setting
The Mississippian sequence in the Bowland sub-Basin is very thick (over 6 km) and accumulated in an actively extending asymmetrical rift basin. Early Mississippian sedimentation began on a carbonate ramp (Stop 1: Bellman Limestone Member, Bowland High Group) which subsequently fractured and rifted into a series of intra-basinal highs and lows which resulted in a complete reorganisation of depositional style (Stop 2: Raingill Limestone Member; Hodder Mudstone Formation, Craven Group) from a carbonate ramp to a hemipelagic depositional regime.

By Mid Mississippian times the basin became progressively starved of sediment, culminating in the widespread deposition of pelagic cephalopod limestones (Hodderense Limestone Formation – not seen on this excursion). This was followed by an influx of turbidite limestones and minor sand bodies of the Pendleside Limestone (Stop 3: Pendleside Limestone Formation, Craven Group).

The Mid Mississippian to Late Mississippian transition was dominated by background deposition of hemipelagic mudstones comprising the Bowland Shales, largely dark, thinly intercalated, weakly calcareous, muddy silts and hemipelagic muds deposited in relatively deep, poorly oxygenated waters. Overlying the Upper Bowland Shales is the first major coarse grained siliciclastic input to the basin; the Pendleian aged Pendle Grit Formation turbidite system (Stop 4: Pendle Grit Formation, Pendleton Formation). A second influx of feldspathic sand, the Warley Wise Grit (Grassington Grit), was deposited on top of the Pendle Grit (Stop 5: Warley Wise Grit, Pendleton Formation). The influx of sand ended with a eustatic transgression at the beginning of Arnsbergian times as represented by the Cravenoceras cowlingense marine band.

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

References
Bisat, W. 1922. The Carboniferous Goniatites of the North of England and their zones. P.Y.G.S. 20, 40 - 124.

Earp, J. R., Magraw, D., Poole, E. G., Land, D. H. & Whiteman, A. J. 1961. Geology of the Country around Clitheroe and Nelson. Geological Survey of Great Britain Memoir, England & Wales, Sheet 68.

Kane, I. & Martinsen, O. J. 2007. Field Guide to the (Deepwater Pendle Grit Formation (Upper Carboniferous) of the Bowland / Craven Basin, Northern Engand, UK

Kabrna, P & Kane, I. 2008. Carboniferous geology of Pendle Hill.
Field guide for Liverpool Geological Society.

Miller, J. & Grayson, R. F. 1972. Origin and structure of Lower Viséan “reef" limestones near Clitheroe, Lancashire. Proceedings of the Yorkshire Geological Society, 38, 607-638.

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

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