Programme: 2012 - 2013

© Craven & Pendle Geological Society

Indoor Meetings

Friday: 14 October 2012
Dinosaur Tracking
Martin Whyte Ph.D., University of Sheffield

Friday: 26 November 2012
A Devonian desert in Orkney
Speaker: David Leather (CPGS)

14 December
Giant bedforms in the Millstone Grit
Speaker: Jochem Bijkerk MSc. BSc., University of Leeds

11 January
Geology of the Isle of Mull
Speaker: Lesley Collins (CPGS)

8 February
From glorified swimming worms: 500 million years of fish evolution
Speaker: Thomas Fletcher MSci., University of Leeds

8 March
Landslides in the Bowland Forest
Speaker: Alan Harrison

Field Meetings

Saturday, 18 May
Arnside
Guide: Paul Kabrna

Friday to Sunday, 21-23 June
Anglesey
Guide: Paul Kabrna

Saturday, 13 July
Ingleton Waterfalls
Guide: Paul Kabrna

Sunday, 4 August
Boston Spa - rocks and landscape
Guides: Karen Ashworth & Steve Birch

Saturday, 7 September
Ilkley & Otley
Guides: David Leather and Heather Craven


Dinosaur Tracking
Martin Whyte

Introduction
The Jurassic rocks of Yorkshire share sufficiently distinct characters to warrant recognition as a single depocenter. This area was generally known as the Yorkshire Basin, although more recently the term Cleveland Basin has been preferred. The Sheffield Dinosaur Track Research Group has been making a special study of the dinosaur footprints found in the Middle Jurassic rocks (Ravenscar Group) which are exposed along most of the east coast of Yorkshire from just south of Yons Nab to around Port Mulgrave in the north, a distance of approximately 55 km. Over twenty different vertebrate track types including those of sauropods and stegosaurs as well as bipedal theropods and ornithopods have now been identified from the Ravenscar Group. The dominantly non-marine Ravenscar Group (c. 240 m thick) consists in the main of shaly mud-stones, sandstones, siltstones, rare impure coals and ironstones that constitute three major non-marine units, the Saltwick, Cloughton and Scalby formations, which are 57 m, 85 m and 60 m thick respectively. The rocks of the Ravenscar Group is generally regarded as being a coastal plain and fluvial complex with occasional marine intercalations. This type of palaeoenvironmental setting supported a variety of dinosaurs.

Dinosaur Tracking
Tracks attributable to a sauropod dinosaur were first recorded on the Yorkshire coast by Whyte and Romano (1993) in fallen blocks from the Saltwick Formation, east of Whitby. The large sandstone track blocks (up to 3 m in length) were 1 m thick with a thin (c. 0.05 m thick) basal layer of sideritic siltstone. The tracks were preserved as natural casts on the undersides of the sandstone blocks. The largest track block included eight foot-falls within a single trackway, enabling a stride length of 0.95 m to be measured. At least five different groups of dinosaurs have been recognised from their tracks on the Yorkshire coast: large carnosaurs, large ornithopods, small ornithopods, coelurosaurian theropods and sauropods. Even swimming prints occur throughout the Ravenscar Group but are most characteristic of and most diverse in the Saltwick Formation.

In recording prints we have adopted the following terminology:
(a) surface prints: in which the rock splits cleanly along the surface on which the animal moved, to reveal the original footprint-bearing substrate and the infill as part and counterpart; (b) underprints: in which the rock splits along a surface intersecting with the print so that part of the original substrate adheres to the infill, or part of the infill adheres to the substrate (see fig. below). (c) transmitted prints: in which the rock splits along a surface which is entirely below the print and print-bearing surface so that both part and counterpart reveal only transmitted features.

The trackway of Deltapodus brodricki, was made by a quadrupedal stegosaurian dinosaur. This track type is most characteristic of the lower part of the Ravenscar Group. The animal here moved with a stride length of 1.0 m. The prints of the padded and tridactyl hind foot are 0.40m long and 0.34m wide and the crescentic front foot prints are 0,29m wide.

Tridactyl and other incomplete underprints showing claw marks.
Gristhorpe Member,Cloughton Formation, Yons Nab. Scale bar is 10 cm. (Source: Martin Whyte)

Conclusion
The studies of the dinosaur footprints are giving an insight into the character and behaviour of the dinosaur communities of the Yorkshire and of how they changed with time and with changes in the local palaeoenvironment. This is increasing our understanding of the environmental history of the local region and of the importance of dinosaurs as an environmental factor within it. In addition information is being gained on the palaeoecology and behaviour of particular dinosaur groups. Trackway information can also be used to shed light on dinosaur gaits and to estimate speeds of movement. The middle Jurassic was a time of diversification of the dinosaurs but in global terms skeletal remains are relatively scarce and thus footprint assemblages such as the Yorkshire material represent internationally significant repositories of information about these dinosaurs. Our reseach over the years suggests that the title 'megatracksite' to the Yorkshire sequence is justified and that the area qualifies as a site of global importance.

References
Romano, M. & Whyte, M.A. (2003): Jurassic dinosaur tracks and trackways of the ClevelandBasin, Yorkshire: preservation, diversity and distribution. PYGS, Vol. 54, Pt. 3, pp.185-215

Whyte, M. A., & Romano, M. (1994): Probable sauropod footprints from the Middle Jurassic of Yorkshire, England. Gaia 10:15–26.

Whyte, M. A., & Romano, M. (2001): Probable stegosaurian dinosaur tracks from the Saltwick Formation (Middle Jurassic) of Yorkshire, England. Proc. Geol. Assoc. 112:45–54.

Whyte, M. A.; Romano, M.; and Elvidge, D. J. (2007): Re-construction of Middle Jurassic dinosaur-dominated communities from the vertebrate ichnofauna of the Cleveland Basin of Yorkshire, UK. Ichnos 14:117–129

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A Devonian desert in Orkney
David Leather

By the Middle Devonian, about 285 million years ago, the Orkney area lay about 16° south of the Equator in the continent of Euramerica. A 2000km rift, known as the Orcadian Basin, had developed within the Caledonian Mountains between Greenland and Scandinavia, at the southern end of which Lake Orcadie formed in an inland desert basin.  An outlet occasionally opened to the present North Sea area.

Showing the position of Lake Orcadie at its maximum extent

In the island of Westray all the rocks outcropping along the coastline consist of Middle Devonian flagstones. They are mainly of the Rousay Flagstone Formation. Detailed stratigraphic logging (for example along the Stancro shore) show many repeated cycles of 10 or 15m in thickness. Each cycle has a fish bed of dark grey thinly laminated mudstone containing a variety of fossil fishes. This was a permanent lake deposit and the half-millimetre-thick laminations suggest annual ‘bedding’, a reflection of the climate with a wet and dry season. Thus a fish or lake bed of say 3m thick lasted for about 6,000 years whereas a full cycle went on for 100,000 years (Milankovich cycle) mostly without a permanent lake, and eventually river deposits.

Fossil fish include primitive armoured fish (Placoderms) such as Asterolepis orcadensis and Millerosteus minor. Lungfish such as Dipterus valenciennesii and spiny Acanthodians are also present as fragments and scales. The most interesting are the lobe-fins such as ‘Osteolepis’ which has two pairs of bony fins like primitive limbs and are the ancestors of all four legged animals. Primitive plants show spore cases not much different from the modern club moss and in the lake shallows blue-green algae grew on the lake bed building up calcareous algal mats or stromatolites. Footprints of a phyllopod were a rare find.

Above each fish bed, paler siltstones exhibit gypsum pseudomorphs indicating strong evaporation that led to widespread salt flats. Gypsum pseudomorphs are a common feature, particularly as star-shaped desert roses, covering large areas of flagstone. Further silts and muds show ripple marks and mudcracks of a lake which continually dried up with occasional flash floods. Towards the top of each cycle river channels cut into the desert surface leaving fluviatile sands.

Gypsum pseudomorphs indicate the drying out of the permanent lake to form salt flats

Along the shore on the hardest of the flagstones, glacial striae are to be seen beneath the orange-red boulder clay. Ice sheets brought boulders of Old Red Sandstone from the nearby island of Eday depositing them on Westray and colouring the glacial till. Occasionally I have found some interesting erratics including one of rhomb porphyry from Norway.

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Giant bedforms in the Millstone Grit
Jochem Bijkerk

The siliciclastic infill of the sub-basins of the Carboniferous Central Pennine Basin is enigmatic. The current research aims to resolve some of the questions posed by this succession based on a combination of fieldwork in the Craven-Bowland sub-basin and physical modelling at the Eurotank flume facility, Utrecht University, the Netherlands.

The Central Pennine Basin forms an extensional basin in post-rift phase during deposition of the Millstone Grit Group. The residual topography of the sub-basins (Craven-Bowland, Edale, Widmerpool, etc) is diachronously infilled by a thick succession of turbiditic deposits which is overlain by a large fluvio-deltaic cyclothem that develops giant bedforms. Within subsequent fluvio-deltaic cyclothems these giant bedforms do not form. This raises the question in what depositional setting these deposits form and why they form only in the initial fluvio-deltaic succession that enters a sub-basin.

Warley Wise Grit in Haracre Quarry, Farnhill, North Yorkshire

Several models have been proposed to explain the presence of these giant bedforms. These models range from a freely prograding Gilbert-style delta, bank-attached bars in large deltaic distributary channels, or Gilbert-style deltas that form within an incised valley, all of which have major implications for the basin fill history. The current model, based on the combination of physical modelling and fieldwork, suggests that these giant bedforms form within deeply incised valleys and also explains why they only form within this particular part of the succession. Furthermore, the physical modelling provides a generic insight in the controls on the infilling of basins.

Reference:
Aitkenhead, N. et al. (2002): British Regional Geology: The Pennines and adjacent areas. (Fourth edition) British Geological Survey.

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Geology of the Isle of Mull
Lesley Collins

The Isle of Mull and its islands have attracted geologists ever since the naturalist Joseph Banks ‘discovered’ Staffa and Fingals’ Cave in 1771.  In 1924, E Bailey opened his ground-breaking Geological Survey Memoir with the statement ‘that Mull includes the most complicated igneous centre yet accorded detailed examination anywhere in the world’.

The geology of Mull is very complex and is still subject to much debate and scientific investigation.  The story starts with the oldest rocks, of Archean age, exposed on the Isle of Iona. The rock suite is a metamorphic assemblage of mainly Lewisian Gneiss in which several tectonic cycles have been identified and includes the small but well known outcrop of Iona marble. Radiometric dates of 2000 Ma have been obtained from Iona but these are thought to relate to a metamorphic event and not the original formation date which may be much earlier. Along the east side of Iona, there is a 500m thick outcrop of altered Torridonian sedimentary rocks, thought to be part of the same suite as occurs on the Scottish mainland, although the correlation evidence is missing.

The Ross of Mull peninsula is dominated by a compact but complete sequence of Moinian metamorphic rocks, originally laid down in an offshore delta and subjected to several episodes of mountain-building and deep burial giving rise to high grade metamorphic rocks such as schists, pelites and gneisses. Ardalanish Bay is the best location on the island for seeing the Moine sequence and the preserved sedimentary structures in the highly metamorphosed rocks. Into this sequence, the Ross of Mull granite was intruded about 418 Ma, a very coarse pinky-red granite, giving rise to a distinctive pink landscape. The granite contains large xenoliths of the Moine rocks stoped from the roof of the granite magma chamber and incorporated into the melt whilst retaining the original rock characteristics. Several classic examples can be seen at Knockvologan Bay on the south coast of the Ross of Mull.

In the South East corner of Mull, the enigmatic Dalradian rocks outcrop in an exposed anticline, occupied by the lovely Loch Glennain. The exposures are small and the rocks have proved difficult to date, being heavily metamorphosed in the Caledonian Orogeny, but they seem to span from the late Pre-Cambrian through to Ordovician times.

The Moine rocks which form the basement underlying mainland Mull  were heavily eroded by the time the Mesozoic sediments were laid down. There are Triassic sandstones and conglomerates burying the Moinian landscape, best seen under the cliffs at Gribun on the west coast, followed by a marine sequence of Lower Jurassic rocks and a thin Cretaceous band. These rocks are only seen at the coast, poking out from underneath the later Tertiary lava flows. Carsaig Bay on the south coast is the best site at which to see the Mesozoic sediments and offers the chance of finding fossils such as Ammonites, Belemnites and Bivalves. The thin band of ‘Chalk’ on Mull is unlike the main Chalk sequence further south. It has been broken up and silicified and is now recognised as a re-deposited band, late Cretaceous or early Tertiary.

At the end of the Mesozoic, there was a period of uplift and erosion leaving a landscape of small hills and shallow valleys. About 60 Ma ago, igneous activity associated with the early stages of the opening of the North Atlantic started with massive outpourings of Basaltic lavas, burying the ancient landscape. Over 3000 ft of lavas flowed out from fissures, including the Staffa Formation, famous for its hexagonal columns and  Fingal’s Cave. Between the relatively thin lava flows, there were periods of weathering giving rise to the ‘red bole’ lateritic tops. Some sedimentary layers formed between the flows including the well-known leaf beds at Ardtun where exceptionally well preserved leaf fossils were found in the 19th Century. The lava flows give rise to a distinctive stepped landscape profile known as ‘trap’ country. The Staffa Formation also includes examples of trees completely submerged and preserved by the lava, the best known being McCulloch’s tree on the Ardmeanach Peninsula on the west coast.

There followed intense intrusive activity associated with the Mull Volcano, the Central Igneous Complex, with large granitic and gabbroic intrusions, and further surface lava flows most of which were subsequently eroded away. The intrusions on Mull show a complicated geochemical history, with the early intrusions being highly acidic, due to melting of the Lewisian and Moine basement rocks ‘contaminating’ the magma rising from the upper Mantle and changing the chemistry of the melt. The intrusions on Mull also show rare occurrences of magma mixing the best known example being the Loch Ba Ring Dyke where the acidic Felsite rock has layers of ultrabasic material mixed in. The final stage of igneous activity was the intrusion of the late Dyke swarm which cuts right through the Hebridean Igneous Province  and the north of England.

The igneous activity on Mull lasted no more than 5 Ma, ceasing with the start of rifting in the North Atlantic. There was no further geological activity after 55 Ma, resulting in substantial erosion of the Tertiary lava flows and exposure of the roots of the Mull volcano. The Ice Age left its dramatic effect on the island, forming u-shaped glacial valleys, depositing moraines and causing raised beach platforms around the coast. Mull is still rising isostatically, at a rate of 2 mm a year.

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From glorified swimming worms: 500 million years of fish evolution
Thomas Fletcher

Introduction
For convenience and referential ease ‘fishes’ persists as a term in biology, but its definition is far from clear. In fact there isn’t a defining feature which distinguishes them as a group from other vertebrates, for example fins are found in whales and dolphins (mammals) and gills are found in axolotls (an amphibian). As a result, finding the first fish is rather futile, as conflicting definitions can make classification quite subjective. Nevertheless, we do have candidates in the Cambrian (China’s Doushantou Formation) that fit a broad scientific consensus of what makes a fish, namely Haikouichthys and Myllokunmingia. They possessed well defined heads with eyes, blocks of muscle in a tail, a notochord (a stiff rod supporting the back), and gills. Despite their small size (just over an inch), it is likely that these early chordates (possessing a notochord) gave rise to the myriad vertebrate forms that followed (animals with backbones); including all fishes, amphibians, reptiles, birds, and mammals like ourselves.

The first uncontroversial fishes are the agnathans (literally ‘without jaws’), which include heavily armoured forms such as the osteostracan Cephalaspis (below), conodonts (often preserved as isolated teeth), the enigmatic thelodonts (Fig. 1), and the still-living hagfishes and lampreys. Despite their having thrived throughout the Palaeozoic, agnathans were pinched out by the gnathostomes; jawed fishes which dominated the Devonian and beyond.

Age of the Armoured Fishes
The Devonian was an acme for jawed fishes such as true sharks, acanthodians (spiny sharks), and early sarcopterygians; the tetrapod precursors. Arguably the most successful group however were the placoderms, which are found from the late Silurian until the very end of the Devonian, a period of ~90 million years. These ranged from small chimaera-like creatures that gave birth to live young, to the 10m long Dunkleosteus which cruised the ancient oceans armed with scissor like plates of bone in its huge (and very powerful) jaws. In fact Bothriolepis (Fig 1) - one of the most successful species of vertebrate ever to have lived – ended its reign along with all other placoderm fish during the Devonian/Carboniferous extinction, paving the way for other groups to occupy their ecological niches. Groups including the large Rhizodonts and a host of extraordinary sharks, such as the spiral toothed Helicoprion and the ‘ironing board shark’ Akmonistion.


Fig 1. Bothriolepis canadensis, an Upper Devonian placoderm fish from Quebec, Canada (H10438 Sedgwick, Cambridge).

It was only after the end-Permian mass extinction that the ocean’s fauna began to resemble what we’re familiar with today, and the ray-finned fishes rose to prominence, leaving other fish taxa in the minority for the next 200 million years.  

Convergence: similar solutions to similar problems
Modern fishes are a hugely diverse and successful group of organisms, which today make up over half the named species of vertebrate. What is perhaps more remarkable, is how predictable their diversity (or rather ‘disparity’) can be. In water there are constraints on shape depending on what kind of swimming the fish is adapted for. For example a long torpedo-like shape is perfect for speed, whereas a short, deep and thin body allows greater manoeuvrability, with the majority of species lying somewhere in the spectrum between these two extremes. There are a host of other modifications which contribute to the overall morphology (e.g. fins, overall size, mucus, musculature), and the swimming behaviour itself of course, but it is the scales which are the focus of my project.

Just as many modern sharks can manipulate the fine flow of a fluid with their scales, so too it seems can some of the earliest fossil fishes. Acanthodians (‘spiny-sharks’) and thelodonts have the characteristic riblets found on the scales of some of the faster swimming sharks, which is a well-studied method of drag-reduction. By detailing the occurrence of ribletted scales (Fig 2) as early as the Ordovician period, and proving experimentally that they are capable of reducing drag, I hope to demonstrate that not all ancient fishes were the cumbersome and slow-moving creatures depicted in older literature. If this hypothesis is correct, it means that fishes were utilising advanced fluid mechanics principles to swim quickly and efficiently through ancient seas over 460 million years ago.

 

Fig 2. Scale from a Silurian thelodont fish.

Useful References

  • Benton, M. J. 2005 Vertebrate Palaeontology. Oxford: Blackwell Science Ltd.
  • Helfman, G. S., Collette, B. B., Facey, D. E. & Bowen, B. W. 2009 The Diversity of Fishes: Biology, Evolution, and Ecology.West Sussex:Blackwell Publishing.

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Landslides in the Bowland Forest
Alan Harrison

A look at relict landslides of post Pleistocene age was undertaken first with a look at the large area of debris on the east side of Mellor Knoll and the lobe that nearly reaches Langden Brook on the slopes of Hareden Nab. Discussion of other sites such as Wolf Fell near Parlick and others followed. After this we moved on to the more recent ones that formed the main body of research.

During the January of 2005 a rain event on the 7th, 8th and 9th of the month left a trail of flooding from Carlisle, southwards to Penrith, Kendal and Preston and described by the Environment Agency as “the result of extreme weather the likes of which had not been seen for over 100 years”.

During a journey north through the Trough of Bowland, just past Sykes Farm, a brown stain was noticed high on the eastern fellside that extended down to Trough Brook overflowing the bank of same and extending past Sykes Farm. This sighting set in chain a plan to study as many as 25 similar events that had occurred at the same time in the surrounding fells.

Trough Event Scar

Permission was obtained to study the sites from United Utilities and work commenced in the summer of 2005. The sites were obvious from the bleached rock debris that had once been buried but was now scattered down the slopes. The question of what to study was not so simple. A back analysis to find the pore water pressure at the time of mobilisation was considered using the infinite slope model . (see below), or a similar method but the testing and collecting of soil samples would have been too expensive both in time and money and typical values derived from tables did not seem to fit the soil descriptions.

u = unit weight of water x depth of water in metres.  Φ = angle of internal friction.   β  = slope angle.  c = soil cohesion. Z = depth of soil. γ = unit weight of soil. F = factor of safety e.g. 1 means slope is liable to fail.

Infinite slope model, F = 1 when shearing forces and holding forces are equal.

Another line of enquiry was the rainfall data, supplied very generously by the Environment Agency. This was entered into a formula devised by Caine (1980) to predict, from the rainfall intensity and duration, if landslides were likely to occur. This proved remarkably accurate. See below:-

  1. Formula I = 14.82D -0.39 (Caine 1980) where
  2. I = rainfall intensity mm hour -1,
  3. D = duration in hours
  4. Bowland rainfall (24 hours) Factor = 14.7
  5. Bowland  rainfall (11 hours)    ,,    =  13.82
  6. Could be higher at altitude

The subject finally chosen to study was the run-out characteristics relative to the volume of the scar site, an area covered by many US and continental workers from pre WW 2 times when the great German geologist Albert Heim initiated research into this area. The survey was carried out using tape and metre rule for the scar site and a navigational GPS unit to trace the runouts using the 10 digit grid references obtained. The data was entered into Excel and analysed with the same. Many workers results were compared but the method that matched the Bowland data was by Corominas (1996) that obtained a factor -0.070 for earthflows, close to the Bowland data using the same formula at -0.073. This classified the Bowland slips as earthflows although the appearance would seem to indicate debris flows.

Bowland data using “angle of reach” R2 = 0.4581 and slope of – 0.0766, close to Corominas (1996).

The term angle of reach was coined by Heim and is essentially the tangent of the angle formed by the triangle made by the highest point of the scar site to the farthest point of the runout.

The work by Corominas (1996) was essentially an expansion of the work done by Scheidegger and Heim who all had the aim of predicting the runout distances in Alpine areas of all types of avalanches. The idea being that if a potential volume of debris could be identified and measured, property etc at risk could be given warning.  Many other people’s methods were looked at during this study that used rheology, numerical or empirical methods etc but the worker’s results  mentioned above compared most favorably with the Bowland data.

References
Caine, N. (1980): The rainfall intensity - duration control of shallow landslides and debris flows. Geografisker Annaler 62A (1,2), pp.23-27.

Corominas, J. (1996): The angle of reach as a mobility index for small and large landslides. Canadian Geotechnical Journal, Vol. 33, pp. 260-271.

Scheidegger, A.E. (1973): On the Prediction and the Reach and the Velocity of catastrophic landslides. Rock Mechanics, 5, pp.231-236.

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Field Trips

Limestones of Arnside
Paul Kabrna

Time / Date: 10:30 am, Saturday 18 May.

Meet at: 10:30 am at the Arnside shoreline parking area [SD 455 787] with additional parking adjacent to the Kent Viaduct [SD 458 790]. Public toilets near the Kent Viaduct [SD 458 789].

Logistics : approx. 8 km walking along public shoreline, cliff-top paths and sandbars. The return route has some easy uphill walking. Bring a packed lunch.

Background: Arnside is an AONB which is characterised by a landscape of low limestone hills and crags with intervening low-lying mosses and the expanse of Morecambe Bay dominating the western edges. The Limestone geology and coastal aspect of the area sustains a complex mosaic of habitats. There are many semi-natural ancient woodlands, wildflower-rich limestone grasslands, protected limestone pavements, deep peat mosses, coastal salt marshes and estuarine mudflats.

Geological Setting: The Carboniferous Limestone bedrock of the area was deposited during the Mississippian 359 million years ago (Ma) to 325 Ma when the region was located near the equator. At this time the area was dominated by shallow tropical seas, with varying sea levels and changing sedimentary conditions (giving periods of clear water then episodes of sediment-laden waters). There are three principal limestone formations of differing lithologies each demonstrating marked cyclicity: the Dalton Beds, the Park Limestone and the Urswick Limestone (Lower and Upper). Additionally the overlying and younger Gleaston Formation is exposed in a few places.

Map
1:25000 Explorer Map OL7. The English Lakes South-eastern area.

References
Dewey, M. (2008): Limestones of the Arnside area. Walk 9 in Exploring Lakeland Rocks & Landscape (Cumberland Geological Society).

Balderstone, M. & Dewey, M (2003): The Dinantian limestones of Far Arnside and Silverdale shoreline. Proceedings No. 31, Westmorland Geological Society.

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Anglesey
Paul Kabrna

Date: Friday, 21 June to Sunday, 23 June

Itinerary
All NGRs are in the 100 km grid square SH.

Friday (14.00 - 17.00)
Rhosneigr: [319 730]

Saturday (09.30 - 17.00)
Porth Dafarch: [234 800]
South Stack (Ynys Lawd): [212 818]
Rhoscolyn: [269 757]

Evening get-together at The Black Lion Inn: [319 865] Time: 20.00

Sunday (09.30 - 16.00)
Church Bay (Porth Swtan): [302 898]
Cemlyn Bay: [336 932]
Wylfa Head to Cemaes: [354 933]

Meet at: 1:45 pm, Friday afternoon at the High St. car park in Rhosneigr: Turn left at the clock tower into High St., then left again between Sandy’s Bistro and the Village Hall, and the car park is about a 100 m or so up on the left.

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

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

Map
1:25 000 Explorer 262 Anglesey West

References
Barber, A. J. & Max, M. D. (1979): A new look at the Mona Complex (Anglesey, North Wales). Journal of the Geological Society, London, 136, pp. 407–432

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

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

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

Maruyama, S., Kawai, T. and Windley, B. F. (2010): Ocean plate stratigraphy and its imbrication in an accretionary orogen: The Mona Complex, Anglesey-Lleyn, Wales, UK. in The Evolving Continents: Understanding Processes of Continental Growth edited by Kusky, T. M., Zhai, M. G. and Xiao, W., Geological Society London, Special Publications, 338, 55 -75.

Treagus, J. (2008): Anglesey Geology - a field guide. ISBN 0-9546966-2-X
Available from The Old Watch House, Port Amlwch, Amlwch, Ynys Môn LL68 9DB
Tel: 01248 810287 or email geomon@btconnect.com

Wood, M. (2012): The historical development of the term ‘Mélange’ and its relevance to the Precambrian geology of Anglesey and the Lleyn Peninsula in Wales, UK. Journal of Geography, Vol. 121, No. 1 (Japan).

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Ingleton Waterfalls
Paul Kabrna

Time / Date: 10:15 am, Saturday, 13th July 2013

Meeting at: 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 for each car. It is not a National Trust car park. Carry packed lunch.

Geological setting: The Ingleton Falls 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 Group. 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.

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.The Ingletonian is unfossiliferous and was traditionally thought to be of Precambrian age but the BGS has adopted an Ordovician age for these enigmatic rocks.

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 Dales National Park/Topic Series Geology by Albert Wilson

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

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Boston Spa - rocks and landscape
Karen Ashworth & Steve Birch

Time / Date: 10:30 am, Sunday, 4th August 2013

Meeting at: TBC

Practical Details: TBC

 


Ilkley Moor and Otley Chevin
David Leather and Heather Craven

Date: Saturday 8th September 2013

Meeting: 10.15am Cow and Calf car park, SE 1312 4669. Morning: to complete the last section of the Ilkley Moor Geology Trail (Ilkley Crags and Rocky Valley), missed out on Sunday 8 September 2012 trip to Ilkley Moor. In the afternoon to Otley Chevin and East Chevin Forest car park, SE 2121 4448, following the Chevin Geology Trail.

Practical details: The Cow and Calf car park is free and picnic lunch will be taken there before driving to Otley Chevin. Drinks are available at the Cow and Calf cp cafe and there are toilets for clients.

Geological setting:
The geology of the area is all in the Millstone Grit (Namurian) which lasted for about 5 million years, roughly from 320 to 315Ma. Out of a total thickness of about 1800m, about half way up the sequence is the Addingham Edge Grit and the two succeeding sandstones, the Long Ridge Sandstone and the Doubler Stones Sandstone. Each sandstone, together with the shales beneath (and an occasional coal seam above), represents a cycle and about 50 cycles have been documented in the five million years of the Millstone Grit. This fits in with the Milankovitch 100,000 year Cycle of Eccentricity, which caused the icecaps to alternately grow and melt which in turn resulted in big rises and falls in sea level and changes in sedimentation.

During Millstone Grit times a huge delta covered the area which is now the north of England (and out to the North Sea) which was on the equator with an equatorial climate. Ilkley and Otley were on the delta top where there were branching and meandering river channels, shifting sandbanks, lagoons swamps, tidal silts and deeper seas to the south. A large river from northern Caledonian mountains (Greenland) brought vast amounts of sediment.

Sedimentary structures include tidal laminites, sand volcanoes, current bedding and wave ripples. Fossil plant remains are Lepidodendron and Calamites. A thin coal seam and fossil soil outcrops above the Doubler Stones sandstone on Otley Chevin and the imprints of tree roots can be seen on the sandstone below. The dipping strata gives rise to scarp and dip slopes and some outstanding views. Effects of faulting can be seen above the Cow and Calf rocks.

The Wharfedale ice broke through into Airedale and there are good views of the Guiseley Gap. Sand and gravel pits on the valley floor around Otley are now flooded and form important conservation areas.

Maps: BGS Bradford sheet 69; O.S. Explorer 27, 1:25,000, Lower Wharfedale and Washburn Valley.

Leaflets: Ilkley Moor Geology Trail (Wharfedale Naturalists Society, 50p); Chevin Forest park Geology Trail (Friends of Chevin Forest, free).

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