Calendar of Events: 2006

Programme: 2006 - 2007

Indoor Meetings

Friday: 27 October
Ordovician trilobites of Cincinnati, Ohio, USA. Dan Cooper, Cincinnati, Ohio, USA.

Friday: 24 November
Volcanic eruptions into Iceland's glaciers. Dave McGarvie Ph.D., Open University

Friday: 15 December
Members Presentations & Christmas 'Jacob's Join'.

Friday: 26 January
Causes and consequences of orogenesis: the Himalaya as a natural laboratory. Yani Najman Ph.D., Lancaster University

Friday: 23 February
The geology of asteroids. Professor Lionel Wilson, Lancaster University

Friday: 23 March
Virtual reality geology of the Suez rift. Paul Wilson Ph.D., Manchester University

Field Meetings for 2007

Sunday, 27^th May
Crummack Dale, Anticlines, Unconformities & the Norber Erratics.
David Turner

Sunday, 24^th June
The Sedgwick Trail at Sedbergh and the Taythes Inlier. Jean Chicken

Saturday, 28^th July
The position of the Whin Sill within the geological framework of Upper Teesdale.
Steve Webster

Saturday, 25^th August
The South Craven Fault at Settle. Paul Kabrna

Sunday, 23^rd September
Carboniferous geology around Dunsop Bridge in the Craven Basin. Paul Kabrna. This is a joint meeting with Huddersfield Geology Group.

www.isotelus.com Email: Dan Cooper

Introduction

The Ordovician System of Ohio is probably the most famous of the state’s Palaeozoic rock systems. The alternating shales and limestones of the upper part of this system crop out in south-western Ohio in the Cincinnati region and yield an incredible abundance and diversity of well-preserved fossils.

The most desirable fossils from Cincinnatian rocks seem to be trilobites. The remains of these arthropods are found in considerable abundance in some beds. The most common Cincinnatian trilobite, Flexicalymene, is best known from the Corryville Member of the Grant Lake Formation and from the middle part of the Waynesville Formation. Much less common are well-preserved specimens of Isotelus, Ohio’s official State Fossil

Trilobites

The first serious study of Ohio’s Ordovician rocks was undertaken by the first Geological Survey of Ohio in 1837-1838. At this time John Locke mapped portions of the southwestern corner of the state. Among Locke’s many discoveries were partial remains of a large specimen of Isotelus. Because of its size, Locke named the trilobite Isotelus maximus. He later changed the name to Isotelus megistos, but today Isotelus maximus is the accepted species name. Locke collected only the pygidium (tail) of the trilobite but, by proportional comparison, he estimated that the complete trilobite would have been about 21 inches in length.

Trilobites are an extinct class of the Phylum Arthropoda, which includes among its living members the horseshoe crab, crabs, lobsters, shrimp, scorpions, spiders, and insects. Trilobites first appeared in the fossil record about 542 million years ago and became extinct about 251 million years ago. They lived in marine environments, where they burrowed in sediment, crawled along the sea floor, or were free swimming. Most trilobites ate mud from the sea floor, whereas others filtered food directly from the water, scavenged, or were predators. They grew by periodically moulting their exoskeleton, a hard, outer shell similar in composition to fingernails. Thus, one trilobite could leave behind numerous fossil fragments representing shed exoskeletons. For defence against predators, some trilobites had sharp spines on their exoskeletons, and all had the ability to enroll, much like our hedghog.

Ohio's State Fossil

On 20th June, 1985, Ohio House Bill 145 designated the trilobite genus Isotelus as the official state invertebrate fossil of Ohio. Isotelus is a most suitable selection for the state fossil. Not only are specimens of this trilobite, or at least fragments, moderately abundant in the rocks exposed in southwestern Ohio, but they are represented by the Huffman Dam specimen, which is one of the largest complete trilobites ever collected. This giant specimen of Isotelus measures I4½ inches long by I0¼ inches wide. The Huffman Dam trilobite still occupies a prominent position in the palaeontological exhibits at the Smithsonian and is still one of the largest, complete trilobites of any kind ever collected.

Introduction

Iceland is the largest landmass exposed along the Mid-Ocean Ridge System. It has been constructed over the past 16 million years by basaltic to silicic volcanic activity occurring at the Mid-Atlantic Ridge. Large quantities of igneous material are produced in association with the Iceland hot spot, the centre of which is thought to be located beneath Vatnajökull ice cap. Although it is paradoxical that Iceland’s hottest region boasts its biggest ice cap, it is no coincidence: the ice sheet is huge and permanent, precisely because lava flowing from the mantle plume has built the mountains so high. Iceland is made of such paradoxes. Its mountains and valleys are sculpted primarily through the interplay of molten rock which builds volcanoes, and the glaciers’ solid water which ferociously erodes the landscape. The Icelandic people are continually confronted with a three-pronged pestilence of fire, flood, and ice.

Askja volcano

Askja

Askja (1516 m) is a large basaltic central volcano that forms the Dyngjufjöll massif which last erupted in 1961. It is truncated by three overlapping calderas, the largest of which is 8 km. A major explosive eruption on the SE caldera margin in 1875 was one of Iceland’s largest during historical time. It resulted in the formation of a smaller 4.5 km wide caldera, now filled by Öskjuvatn lake, that truncates the rim of the larger central caldera. The latest volcanic event in Dyngjufjöll occurred in 1961.

This volcano was visited by William Lord Watts in 1875 “… beneath us lay a pandemonium of steam and hideous sounds…the most hideous shrieks, groans, booming and screaming sounds rose from all parts of this terrible depression, the bottom of which was now utterly obscured. The sides of the crater were evidently falling in, and huge wide cracks, even where we stood, showed us that our position was not altogether a safe one. So we lit our pipes and waited until we could obtain a better view.”

Herðubreið

Herðubreið is a classic example of a “tuya” or flat-topped, steep-sided subglacial volcano. Icelandic tuyas are usually composed of pillow lavas at the base, followed by hyaloclastic breccias, capped by horizontal lava flows. For a tuya to form basalt lava is erupted into ~1.5 km of ice. The subglacial confinement prevents the lava from free flow away from the vent. In the case of Herðubreið, the subaerial basalt lavas quenched and fragmented when they reached a meltwater lake and formed breccias. Successive subaerial lava flows accumulated to make the characteristic lava cap. In Iceland these tuyas are the subglacial equivalents of basaltic shield volcanoes.

The Gjálp eruption in Vatnajökull (1996)

An eruption started beneath the Vatnajökull glacier in Central Iceland in the late evening of 30th September and lasted for 13 days. The eruption site which was discovered by aircraft was a subglacial basalt fissure eruption. Cauldron formation indicated that the glacier was being melted along a 4 km long fissure beneath the glacier. In fact the eruption took only 31 hours to melt through 600 metres of ice and 0.45 km³ of basalt melted 3 km³ of ice.

Meltwater from the eruption site drained into the Grímsvötn caldera, raising the ice shelf on the Grímsvötn caldera lake. The cauldrons widened and deepened and it is estimated that 0.3 km3 of water were added to the Grímsvötn lake in less than 24 hours. Meltwater escaped as a flood (jökulhlaup) 3 weeks after end of the eruption.

Grimsvötn (2004)

The subglacial Grimsvötn volcano, which is Iceland’s most frequently-erupting volcano, spectacularly erupted beneath the Vatnajökull ice cap between the 1st - 6th November, 2004. In the Grimsvötn caldera ice 150-250 m thick floats on a subglacial lake. The lake drained in November 2004, triggering a small subglacial eruption that eventually became ermergent. Clouds of ash and tephra were ejected beyond the vent (but not far). Preservation of eruptive material is generally poor because as soon as the eruption ceases, snow and ice rapidly cover the evidence.

Kerlingarfjöll

The volcano Kerlingarfjöll is the main feature in the chain of mountains and glaciers of the Kjolur area which covers about 150 km² area southeast of Hofsjökull. Subglacial rhyolite eruptions into thick ice at Kerlingarfjöll have produced steep-sided piles of fragmental material up to 300 m tall. Several edifices are capped with lava flows and these structures are therefore broadly equivalent to the ‘tuyas’ formed by subglacial basaltic eruptions. The pyroclastic material typically consists of massive, unconsolidated breccias containing blocks and lapilli of pumice within an ash matrix. Unlike the basaltic tuyas of Herðubreið, ponded water is present only during the initial phases of the eruption, and that the transition from explosive to effusive, lava cap producing, activity takes place in essentially ‘dry’ conditions.

Subglacial Rhyolite Tuyas

Öræfajökull

Eruptions of Öræfajökull have produced mafic and silicic magmas, and have taken place in both glacial and interglacial periods. Historically eruptions have been recorded in 1362 (rhyolite) and 1727 (basalt). The geology of the volcano records the differing response of magmas of contrasting composition to interaction with ice of variable thickness and gives insight into the development of a long-lived ice-covered stratovolcano. The southeast flank of Öræfajökull, is the first area of the volcano to have been mapped in detail. The oldest units comprise pillow lavas, hyaloclastite and jointed lava flows that were formed during subglacial basaltic eruptions involving abundant meltwater. Later a subglacial rhyolite eruption took place that was confined by ice to form a tephra pile over 200 m thick and that was subsequently intruded by dense rhyolite magma towards the end of the eruption.

Introduction

Among the most dramatic and visible creations of plate tectonic forces are the lofty Himalayas which stretch over 2900 km along the border between India and Tibet. This immense mountain range was formed by huge tectonic forces and sculpted by powerful denudation processes. Topographically, the belt has many superlatives: the highest rate of uplift (nearly 1 cm/year at Nanga Parbat), the highest relief (8848 m at Mt. Everest), and the highest concentration of glaciers outside of the polar regions. This last feature earned the Himalaya its name meaning in Sanskrit: «the abode of the snow».

Tethyan limestones in Tibet with Mt. Everest to the south © Yani Najman

Tethyan limestones in Tibet with Mt. Everest to the south
© Yani Najman Ph.D.

The Himalayas span six nations: Bhutan, China, India, Nepal, Pakistan and Afghanistan. It is the source of three of the world’s major river systems, the Indus Basin, the Ganga-Brahmaputra Basin and the Yangtze Basin supplying freshwater for more than one-fifth of the world population, and it also accounts for a quarter of the global sedimentation budget. An estimated 750 million people live in the watershed area of the Himalayan rivers which also includes Bangladesh.

Geological Setting

The Himalayas formed when the Tethys Ocean closed and India and Eurasia collided. This continent collision is continuing today and many aspects of the formation and evolution of the Tibetan Plateau remain unresolved. The mountain belt consists of six lithotectonic zones, separated by thrust and faults. From north to south, these belts and their representative rock types are as follows:

1. The Trans-Himalayan Zone batholiths which are interpreted as the Andean-type northern margin of the Tethys.

2. The Indus Suture Zone (the northern limit of the Himalaya) represents the line of collision between India and Eurasia. Here the rocks are predominantly marine sediments, ophiolites (pieces of oceanic plate that have been thrusted (obducted) onto the edge of continental plates), arc volcanics and mélange (a jumble of large blocks of varied lithologies of altered oceanic crustal material and blocks of continental slope sediments).

3. The Tibetan or Tethys Himalayan Zone is formed by strongly folded and weakly metamorphosed sedimentary rocks. In terms of age, they are Cambrian to Palaeocene sediments (the Tibetan Sedimentary Series) deposited on the Indian continental terrace.

4. The greater Himalaya (the backbone of the himalayan orogen which encompasses the areas with the highest topographical relief) is regionally metamorphosed Indian continental crust of mainly Proterozoic age.

5. The Lesser Himalaya is represented by non or weakly metamorphosed Indian continental crust ranging in age from Proterozoic to Palaeozoic and Palaeogene foreland basin sediments.

6. The Sub-Himalaya, which consists of foreland basin (foothills of the Himalayan Range), an area where the sedimentary record of material eroded from the mountain belt is preserved. The Foreland Basin provides a history of erosion, tectonism, and palaeodrainage in the orogen. A further sub-division of the early foreland basin into foredeep, forebulge and back-bulge depozones has been proposed.

Himalayan orogenic belt showing potential Himalayan source rocks for the sediments of the foredeep. MCT: Main Central Thrust; STDZ: South Tibetan Detachment Zone; MBT. Main Boundary Thrust; HFT = MFT: Main Frontal Thrust.

The collision process between India and Eurasia began at approximately 55 million years ago. The line of collision is the Indus-Tsangpo suture zone, which contains molasses, mélange, and ophiolitic material. The Indus River flows west along the line of suture zone and then cuts south over the Himalayas.

Timing of the surface uplift of the Tibetan Plateau has received much attention because of proposed links between high topography and change in regional and global climate such as monsoon intensification. A suggested late Miocene age of uplift assumes that east-west extensional faults and basins of late Miocene age in the southern part of the Tibetan Plateau developed in response to gravitational collapse of a thickened, high plateau.

The link between deep-seated tectonic processes and regional, if not global, environmental change is too tantalizing to ignore. In conclusion a variety of studies to test the interrelationship between Tibet’s growth and regional climate change and its impact on Tibet is the way forward.

The geology of Asteroids
Lionel Wilson, Lancaster University

Introduction

Asteroids are lumps of rocky debris that float around in the Solar System. Most asteroids are found in the main asteroid belt between Jupiter and Mars. Monitoring the trajectory of asteroids, especially those with the potential for colliding with Earth, is currently a serious global issue, however, there are other scientific benefits that may come from their study. Specifically, asteroids are relics of the formation of the Solar System some of which contain carbon-bearing compounds which may have delivered organic, life forming chemicals to the early Earth. Asteroids range in size from tiny dust particles to huge worlds nearly 1,000 km (600 miles) across. Most asteroids are oddly shaped. They aren’t spherical like planets, because their gravity is too low to pull them into a round form. (This only happens when asteroids are over 250 km in size.). Smaller ones are angular and shaped like potatoes and peanuts. The strangest looking asteroid so far is called ‘Kleopatra’, which looks like a 220 km long dog bone.

Asteroid classification

Astronomers often classify asteroids according to their chemical make up. Broadly-speaking their compositions can be deciphered by comparing their colours [seen through a telescope] with the characteristics of different types of meteorite.

There are three main classes:

1. Stony asteroids [S-Type]: These are the most common, although they come in various sub-classes. Asteroid 433 Eros is a stony asteroid that was recently photographed by the Near-Earth Asteroid Rendezvous (NEAR) mission. Some stony asteroids are bright, reflecting up to 40 percent of the sunlight that hits them (for example the large asteroid Vesta), while others are darker, reflecting only 10-15 percent of sunlight. Most meteorites are chips off stony asteroids.

2. Metallic asteroids [M-Type]: These are composed mostly of nickel-iron. Although they are bright like stony asteroids, these have slightly different colours. Radar echoes from these metallic asteroids are also strong, indicating that they are made of electrically conductive material (i.e. metal). Grouped with iron meteorites, these are pieces from the cores of fledgling planets destroyed by collisions when the Solar System formed.

3. Carbonaceous asteroids [C-Type]: These are dark and difficult to spot because they contain a great deal of carbon and tar-like substances. However, to scientists they are some of the most interesting targets. Only a handful of fragments of them – carbonaceous chondrite meteorites – have ever been found on Earth, the most recent falling in Canada in January 2000. The two moons of Mars, Phobos and Deimos, are actually carbonaceous asteroids, captured in a Martian orbit.

In the outer Solar System and the asteroids/minor planets tend to be redder in colour because they contain more organic material. They also contain a great deal of ice. Since some of the organic complement is actually alcohol, all the ingredients are available for a scotch on the rocks if you get the chance!

4 Vesta

4 Vesta is the second most massive object in the asteroid belt, with a mean diameter of about 530 km (around 330 miles) and an estimated mass 9% the mass of the entire asteroid belt. Its size and unusually bright surface make Vesta the brightest asteroid and the only one ever visible to the naked eye from Earth besides Ceres, which is visible under exceptional viewing conditions. Due to the availability of rock samples in the form of the HED meteorites (a grouping of achondrite meteorite types thought to have originated from the crust of the asteroid 4 Vesta), it has also been the most studied. HED meteorites are a grouping of achondrite (stony meteorite that is made of material similar to terrestrial basalts or plutonic rocks) meteorite types thought to have originated from the crust of the asteroid 4 Vesta.

For Vesta, there is a large collection of potential samples accessible to scientists, in the form of over 200 HED meteorites, giving insight into Vesta’s geologic history and structure. Vesta is thought to consist of a metallic iron-nickel core, an overlying rocky olivine mantle, with a surface crust. The most prominent surface feature is an enormous crater 460 km in diameter centred near the south pole. Its width is 80% of the entire diameter of Vesta. The floor of this crater is about 13 km below, and its rim rises 4-12 km above the surrounding terrain, with total surface relief of about 25 km. A central peak rises 18 km above the crater floor. It is estimated that the impact responsible excavated about 1% of the entire volume of Vesta, and it is likely that the Vesta family and V-type asteroids are the products of this collision. If this is the case, then the fact that 10 km fragments of the Vesta family and V-type asteroids have survived bombardment until the present indicates that the crater is only about 1 billion years old or younger.

The first space mission to Vesta will be NASA’s Dawn probe, which will enter orbit around the asteroid for nine months in 2010-2011.

Action plan for killer asteroids

A draft UN Treaty to determine what would have to be done if a giant asteroid was on a collision course with Earth is to be drawn up this year. The document is intended to set out global policies including who should be in charge of plans to deflect any object.

It is the brainchild of the Association of Space Explorers, a professional body for astronauts and cosmonauts. At the moment, NASA is monitoring 127 near-Earth objects (NEO) that have a possibility of colliding with Earth.

Asteroid mission concept unveiled

A NASA scientist has proposed using the replacement to the space shuttle to land on a near-Earth asteroid. The Crew Exploration Vehicle (CEV) is due to make its first flight in 2014, with the eventual aim of ferrying astronauts to and from the moon. The project is envisaged to include two or three crew members and last a total of 90 to 180 days. This mission is could help efforts to protect against an asteroid on course to hit Earth.

Introduction

The past decade has seen increasing research on the interaction between fault growth and stratigraphic architecture in extensional basins. The Rift Analogue Project (TRAP) which began in 2005 focuses on issues of normal fault development and stratigraphic / sedimentological response in rift basins. This innovative project forms a test bed for modern developments in digital outcrop mapping techniques and adopts novel approaches such as LIDAR high definition surveying, the latest in satellite remote sensing technology and includes the development of in-house geological interpretation and reservoir modelling software. The photograph below is taken by © Dr. Paul Wilson.

Geological Setting

The Suez rift, Sinai, Egypt, is the NW-SE-trending arm of the Cenozoic Red Sea rift system, formed in response to late Oligocene / early Miocene rifting of the African and Arabian plates (a rift system is a sedimentary basin that forms by heating and thinning of the crust and lithosphere at the time of rifting). It is 300 km long and up to 80 km wide, and is delineated on both margins by large-scale normal fault systems, which define classic half-graben-style tilted fault blocks, typically up to 20 km wide (a half-graben is a wedge-shaped basin in cross section that develops as the hanging-wall block above a normal fault slides down and rotates; the basin develops between the fault surface and the top surface of the rotated block). The study area is characterised by deeply incised wadis and a lack of vegetation which provides excellent 3D exposure of fault zones and stratigraphy.

The Wadi Nukhul half-graben is a well exposed example of a “rift initiation” depocenter (an area of maximum deposition). The segmented border fault system to the half-graben is exposed over 6 km and comprises distinct NW-SE and N-S striking elements. Displacement is at a maximum in the south and decreases northwards towards a well defined tip point and fault-tip monoclinal fold. Folds are evident parallel and perpendicular to the border fault. Fault perpendicular folds are associated with distinct fault segments, while folding parallel to the border fault is associated with a faulted monocline configuration. Photo below shows the working area of Wadi Nukhul. Taken by © Dr. Paul Wilson.

The thickness of the non-marine Abu Zenima Formation is controlled by the presence of palaeovalleys that existed prior to the onset of rifting, and by erosion of the uplifted footwall blocks of early active faults. In contrast, the thickness of the tidally-influenced Nukhul Formation is heavily influenced by the presence of folds related to the vertical and lateral evolution of the fault array. Deposits of the Nukhul Formation are attributed to linked offshore to shoreface and estuary depositional settings.

The offshore to shoreface deposits consist of variably bioturbated (bioturbation in this case is the mixing of sediment by benthic marine faunas) mudstones that pass gradationally upward to bioturbated bioclastic sandstones. The more landward estuary deposits can be separated into a tripartite division of estuary mouth, estuary funnel with bayhead delta, and upper estuary channel deposits. Estuarine processes generated a complex intercalation of lithologies, with both gradational and sharp facies transitions. In the estuary deposits, tidal ravinement surfaces are typically characterized by mudstones of the estuary-funnel association below, passing abruptly up to erosionally based estuary mouth sandstones. Maximum flooding surfaces are expressed by an abrupt erosional contact separating estuary-mouth sandstones below and estuary-funnel mudstones above.

Field Meetings

Crummack Dale: Anticlines, Unconformities & Norber Erratics
Leader: David Turner

Time & Date: 10:00 am, Sunday, 27^th May

Meeting at: Austwick, Grid Reference [769 686], at the bottom of Townhead Lane. (Limited parking may be possible at the junction with Thwaite Lane at Grid Reference [769 692] but it is also Bank Holiday Sunday.

Practical details: The excursion covers about 7 miles on paths and tracks with several stiles. Carry a packed lunch and be prepared for the vagaries of the Pennine weather. Boots are recommended for this excursion.

Geological setting: Glaciation in Crummack Dale has exposed the basement beds of Silurian strata which underlie most of the Yorkshire Dales. With the closure of the Iapetus Ocean (proto-Atlantic) at the beginning of the Devonian, the Ordovician and Silurian strata were folded and uplifted during the Acadian Orogeny. Erosion subsequently removed all the Devonian strata. Carboniferous limestone was laid down on the submerged landscape so that it lies unconformably on the inverted basement beds.

We will have the chance to look at examples of the unconformity and also at the surface outcrops of the Silurian anticlines where the Carboniferous limestone has been eroded by glaciation. We will walk amongst the famous Norber (Silurian) erratics and examine how they came to lie upon the later limestone strata. We will also examine the unusual purple and green striped Moughton Whetstone which occurs in one location along the unconformity.

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

Reference:
CPGS Resume No. 20 (2005) - The Norber Erratics (talk by Brian Parry).

JOHNSON, E. 1996: Lower Palaeozoic rocks of the Craven Inliers. In Scrutton, C. (ed.) Yorkshire Rocks and Landscape, a field guide. Yorkshire Geological Society, 30-41.

MURPHY, P. 2005: Exploring the Limestone Landscapes of the Three Peaks and Malham. BCRA Cave Studies Series: 15

The Sedgwick Trail at Sedbergh and the Taythes Inlier
Leader: Jean Chicken

Time & Date: 10:30 am, Sunday, 24^th June

Meeting at: Longstone Common, Sedbergh, Grid Reference [695 912]. The afternoon session will be in the River Rawthey valley some 5 km NE of Sedbergh along the A683.

Practical details: A well-marked 1.5 km trail on the A684 with easy to moderate walking. The afternoon session (although subject to change pending access rights) will be in the River Rawthey valley some 5 km NE of Sedbergh along the A683. It is advisable to bring a packed lunch and be prepared for inclement weather.

Geological setting:

MORNING: Besides seeing the Dent Fault, you will also be bale to observe the relationship between the Carboniferous rocks and the Silurian rocks. The trail is based on material supplied by R. B. Rickards of the Sedgwick Museum, Cambridge.

AFTERNOON: The Taythes Inlier is an area of upper Ordovician rock approximately 420-440 million years old surrounded by younger rocks. Two divisions of the Ordovician are represented: the Carodocian and Ashgillian Series. In fact the Ashgillian sections exposed here form part of a type or reference area. Good sections through the rocks are found in the incised stream valleys such as those of Ecker Secker Beck and Taythes Gill. These sections are important in providing evidence in the form of rock types and fossil content to help reconstruct the environment of the late Ordovician in this part of NW England. Fossil trilobites found in these rocks were first identified here making the Taythes Inlier their type locality.

O.S. Maps:
1:50 000 Landranger Series: Sheet 98

Reference:
DAY, A. 1989 The Palaeozoics of the Taythes Inlier, Cautley.
Proceedings of the North East Lancashire Group of the GA, 1989.

The position of the Whin Sill within the geological framework
of Upper Teesdale
Leader: Steve Webster

Time & Date: 10:30 am, Saturday, 28^th July

Meeting at: Bowlees Picnic Area [GR 908 281] about 6 km NW of Middleton in Teesdale on the B6282. Toilets available.

Practical details: Good footpaths throughout. Probably advisable to bring a packed lunch but we should be in the High Force area for lunchtime where snacks and lunches are available.

Geological setting: The River Tees leaves Cow Green Reservoir and cascades down almost the entire thickness of the whin Sill to form Cauldron Snout. Owing to major fault lines such as the Burtreeford Disturbance and the Teesdale fault the exposure of the sill is repeated several times. During the visit we will see at close hand its top margin where it has been injected into the sandstones of the Tyne Bottom Limestone Cyclothem to form the bed of the Tees at Low Force. Here too can be observed a raft of metamorphosed sandstone detached from the roof rock. Time permitting a stroll up the Bowlees beck will reveal cross bedding and channel fill sandstones of the Scar Limestone Cyclothem and the limestones of the succeeding Five Yards Limestone Cyclothem. At High Force we will see the bottom section of the sill exposed above the plunge pool where the Tees creates a magnificent waterfall.

O.S. Maps:
1:25000 Explorer OL31, North Pennines - Teesdale & Weardale

Reference:
SENIOR, J 1995: The geology and landscape of Upper Teesdale. Northumbrian Rocks And Landscape - A Field Guide. Yorkshire Geological Society. 2^nd edition, edited by Colin Scrutton. I.S.B.N. 0-9501656-4-6

The South Craven Fault at Settle
Leader: Paul Kabrna

Time & Date: 10:30 am, Saturday, 25^th August.

Meeting at: the road-side verge on High Hill Lane at the junction of Stockdale Lane [SD 836 632]. In the afternoon we will meet on the B6479 at Scar Top Garage on the Buck Haw Brow [SD 797 656].

Practical details: Boots and a waterproof are advised. Bring a packed lunch. Toilet stop available in Settle.

Geological setting: The Carboniferous palaeogeography was greatly influenced by structurally controlled blocks of Lower Palaeozoic basement which suffered extensional forces thus forming the half-graben of the Craven Basin. The Craven Faults, particularly the Middle Craven Fault defines the southern margin of the Askrigg Block The morning session examines the strata at the junction of the Askrigg Block and Craven Basin.

The afternoons session is based on Giggleswick Scar which marks the line of the South Craven Fault. There are a number of caves along the scars, and Kinsey Cave, which has only been superficially excavated, has yielded both Upper Palaeolithic artefacts and a few mammal remains of probable Devensian age. Currently the North Craven Historical Research Group have a project running on Giggleswick Scar which encompasses many different scientific disciplines.

O.S. Maps:
1:25000 Outdoor Leisure Map 10; Yorkshire Dales - Southern area.
1:25000 Outdoor Leisure Map 2; Yorkshire Dales - Western area.

References:
ARTHURTON, R. S. JOHNSON, E. W. & MUNDY, D. J. C. 1988: Geology of the country around Settle. Memoir of the British Geological Survey, Sheet 60, 147p.

MUNDY, D. J. C. & ARTHURTON, R.S. 1996: The Craven Fault Zone - Malham to Settle. In Scrutton, C. (ed.) Yorkshire Rocks and Landscape, a field guide. Yorkshire Geological Society, 30-41.