The Open University Geological Society Wessex Branch Newsletter

Website http://ougs.org/wessex

July 2016

Branch Organiser’s Letter CONTENTS Dear All Branch Organiser’s Letter Page 1 I have just returned from the Exeter Symposium Lambourn Valley, Berks, 24 Apr 2016 Pages 2-3 and have learned “How the West Was Made”. It Mull trip, May 2016: , was wonderful to see so many of you from , Ardalanish and Gribun Pages 4-10 Wessex branch, I hope you enjoyed it as much as Minerals guide no. 20 – Stibnite Page 11 I did. We had some really interesting and Other organisations’ events Page 12 informative lectures. The field trips were Forthcoming Wessex Branch events Page 13 brilliant, including the boat trip to Brixham along the Red Beds coast. Exeter Events staff did us OUGS events listing Page 14 proud with accommodation, catering and lecture Wessex Branch committee Page 14 theatre. [Linda Morley’s photo shows Sheila receiving her own well-deserved bouquet. Ed.] Dorset. I have a lecture already confirmed by Thanks to all of you who helped so much before Dr Peter Skelton, recently retired from the OU, and during the symposium to make the event run Carbonate platforms of the Early Cretaceous so smoothly. A good time was had by all. I have 'miner's canaries' for perturbations of the global had some wonderful thanks from participants carbon cycle. Do look at his OpenLearn articles that are extended to all the helpers. http://www.open.edu/openlearn/profiles/pws4 I am looking for two more lectures on the A very big thank you to Rhiannon Rogers, whose thrjCretaceous so if you have ideas and contact work as treasurer for the Symposium is db jdetails please let me know. continuing. Also very many thanks to Hilary Barton who produced the brochure for us. Mark Barrett has booked 16 places at a gf hotel near Charnwood Forest for our Life in Wessex branch continues …. We r residential weekend 2nd-4th June 2017 are visiting working quarries in the I with leaders Keith Ambrose (recently Mendips in August. Places are limited so r retired from BGS) and Ian Williamson th at present there is a waiting list. On 25 e (ex BGS and Natural England). September we are helping Alan Holiday C Contact Mark for details at to clear a RIGS site in Abbotsbury, [email protected] and a chance to be really hands on. The book early if you’d like quarry was used for the extraction to stay at the hotel. of the Abbotsbury Iron Ore. In the afternoon Alan will lead Membership fees go up st a trip to other sites in Abbots- o on 1 January 2017 so bury to see exposures of Upper please ensure you change Cretaceous sediments lying your standing order and unconformably on Upper Jurassic ones. cancel the out-of-date one. The associate and full member’s fee is £22.00 plus £2.00 for th On 7 October we have a visit to Wytch Farm a family member. Joint members are £32.00. and Kimmeridge Bay with Giles Watts. The cut-off date for payment will be 31st Numbers are limited for this but we do still January 2017 so if you have not paid by then have some places so contact Jeremy. Do also your membership lapses. let him know if you are on the list but not now able to come. On 13th November we have a Best wishes visit with Alan Holiday to Bowleaze Cove near Sheila Alderman, Branch Organiser Wessex Weymouth as an introduction to Geology. Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Then next January we have our AGM and Tel. xxxxxxxxxxxxxx lecture day at the D’Urberville Centre in Wool, E-mail: [email protected]

Wessex Footnotes July 2016 Page 1 WESSEX OUGS FIELD TRIP TO LAMBOURN VALLEY, BERKS ON 24 APRIL 2016 Chalk Springs and Chalk Geomorphology Leader: Dr Lesley Dunlop Report by Bill Godenzie This trip to four locations near Lambourn in West Berkshire was led by Dr Lesley Dunlop who lectures at Northumbria University and is the Development Officer for the Berkshire Geoconservation Group (BGG). We viewed chalk quarries, an SSSI, springs and sinkholes. (For more information on these and other sites in Berkshire see http://berksgeoconservation.org.uk/index.php) The day started bright, clear and cold with rain forecast later in the day that never materialised. Lesley was joined by a group of a dozen keen geologists and two dogs, Badger and Jack. The first site visited, Fognam Quarry, has some of the best chalk exposure in southern England. This quarry was likely to have been used as a source of lime for agricultural purposes and is now a site of special scientific interest (SSSI). The chalk succession shown in the photo was laid down in the Upper Turonian (90Ma). These are split into three layers being the Top, Middle and Bottom Hardground Suites. The Top Hardground Suite starts just above the white hard hat worn by the geologist pictured. Each suite of beds has thin layers of marls, flints and manganese. These represent a change in the depositional environment. Ammonites (Subprionocyclus neptuni) have been found within these layers but none were found on this trip. However, bivalve fossils and Fognam Quarry, looking south - junction between the Middle shelly deposits were found and iron and Upper Chalk Photo by Lorraine Godenzie nodules were abundant. The interpretation of these finds was that the chalk was laid down in a shallow marine environment that was subjected to flux in sea level which accounts for the variance in depositional setting. It was noted that the general surrounding landscape had a number of asymmetric dry valleys shaped by water flow in glaciated times but subsequently run dry. It is not clear why the topology is not symmetrical but it is thought to be related to the differing exposure to the sun and the resulting flora which would have affected erosion rates. Lynch Wood Springs was the second site visited; this is a winterbourne (a stream that intermittently flows) feeding the river Lambourn. The flow is dependent on the rise and fall of the water table. On the day of our visit, water and gas bubbles could be seen gently (often sporadically) emerging from the bed of the spring. The bedrock is White Chalk overlaid by alluvial deposits. Springs in the area all emerge at similar levels and this implies that an impervious layer of clay stops the water finding escape routes through the chalk. Some of the Lambourn houses are constructed using local sarsens and red bricks made from the Lambeth General views of the spring, upwelling water and the group Formation that overlays the chalk. Photos by Lorraine Godenzie

Wessex Footnotes July 2016 Page 2 Snelsmore Common (100ha) was the third location visited, which featured a gravel plateau, bogs and dolines (a generic term for either a sink hole or swallow hole). This area is effectively a layer cake that is incised by rivers. The thickness of the gravel plateau (Quaternary), which varies in height by about 25m, is above clays (London Clay Formation) and sands (Reading Formation) that were both laid down in the Palaeogene. The flora changes between the gravels and the acidic clays. We were informed that further downstream the stream cut through to chalk and then descended into a sink hole. There are a number of swallow holes (depressions) in the landscape.

Snelsmore Common, looking east Photo by Lorraine Godenzie

Sketch by Bill Godenzie of the exposure at Owl Pit Quarry, Rushall Manor Farm

The last site of the day was Owl Pit Quarry at Rushall Manor Farm which shows an unconformity between the chalk and the overlying Lambeth Group. The sketch above shows how the chalk was laid down in a warm, shallow marine setting and subsequent uplift exposed the chalk that was eroded forming a karst landscape. Marine transgression resulted in clays being deposited in an estuarine environment and a later sea level fall led to red sands being deposited by meandering rivers. In summary, a most enjoyable day that provided an excellent overview of the best geology in West Berkshire.

Owl Pit Quarry at Rushall Manor Farm, looking north Photo by Lorraine Godenzie

Bill Godenzie

Wessex Footnotes July 2016 Page 3 WESSEX OUGS WEEK IN MULL, SCOTLAND: 15 – 20 MAY 2016 Leader: Ian Williamson

IONA (Sunday, 15 May 2016) Report by Marion Phillips and Gwenda Brewer

Iona is a small island off the west coast of the Peninsular in the Inner Hebrides. The small stretch of water that separates the two islands, the Sound of Iona, also marks a fundamental geological boundary. The Archaen Lewisian Complex (c 2,500- 3,000 Ma) underlies Mull and outcrops over the majority of Iona to the west. Originally they were sedimentary and igneous deposits but subsequently changed by many rock and tectonic cycles. The gneiss texture indicates high-grade regional metamorphism. The date given indicates the formation of the Lewisian gneiss and not the age of the deposits from which they originated, which were much older. As we walked to our first locality we discussed the possibility that the Sound of Iona could mark the position of the Moine Thrust, thus accounting for the dramatic difference in the rock types between the Isles of Mull and Iona. Our hike to the three localities visited took us across the beautiful island and enabled us to identify the topography with its low, well-rounded rocky knolls separated by boggy glens. We saw carpets of primroses, violets and orchids as well as sundews and Ian Williamson Photo by a member butterworts in flower in the boggy areas. We were also lucky enough to hear the of the group spring sounds of birds such as corncrakes, skylarks and cuckoos.

Locality 1: Port nam Mairtir (NM 285 237) Our first stop, on the eastern side of the island, was to view the low-grade regional interbedded fine- grained metasediments of sandstones and siltstones. These belong to the Iona Group which uncomformably overlay the Lewisian Complex (fig. 1). Cross-bedded channel cuttings were noted within the dark mudstones offering evidence of fluvial activity, Precambrian in age (fig. 2). In places boudinage and tension gashes were visible, indicating the rocks had been stretched. There was also quartz veining evident, likely to be as a result of low-grade regional thermal metamorphism from the Ross of Mull Granite intrusion, late Silurian-early Devonian in age (Caledonian Orogeny) (fig. 3).

Fig.2 Channel deposits Fig.1 Near vertical bedding of Photo by Gwenda Brewer Fig. 3 Tension gashes Iona Group vertical in centre of photo Photo by Gwenda Brewer Photo by Gwenda Brewer

In the past the rocks at this locality have been tentatively correlated with the Torridonian. However, recent research, using detrital minerals such as zircon to date the rocks, has caused controversy because it indicates that the rocks are much younger than previously thought (1,490Ma - 422Ma), linking them perhaps more closely to the Dalradian Grampian Group rather than the Torridonian. The present day beach sand contained feldspars and quartz thought to have been eroded from the Ross of Mull Granite. Shell fragments present contributed to the calcitic nature of the sediments.

Wessex Footnotes July 2016 Page 4 Locality 2: Iona Marble Quarry (NM2687 2182) This small narrow quarry (approximately 6-8 metres wide x 100 metres long) is in the south east of the island (fig. 4). The marble contained within it is a white metasomatise, metalimestone. These rocks stand out against the darker gneisses on either side, although both rock types form part of the Lewisian Complex. The marble is composed of calcite, sometimes with dark green and grey veins, and mottling where they contain quantities of tremolite and forsterite. In some freshly cut surfaces asbestos-like fibres were present (fig. 5). Some were showing a mild schistose fabric and others were talc bearing. There were many folds within the marble, which deforms more easily than other rock types present. An area of white quartzite at the edge of the quarry was cut by dark dykes off metadolerite (amphibolite), often showing chilled margins and shear boundaries between them. Both the dykes and the quartzite showed evidence of folding (fig. 6).

Fig. 5 Asbestos like edge to quartzite Total view ~25cm Photo by Gwenda Brewer Fig.4 Following cleft to Iona Marble Fig.6 Attenuated dyke Quarry with some industrial remains cutting quartzite Photo by a member of the group Photo by Gwenda Brewer

The rocks from this quarry have been quarried intermittently from medieval times until the First World War. The marble can be seen in the Iona Abbey Church in the form of the Communion Table and in a number of other churches in Southern Scotland and in Westminster Abbey. Walking to locality 3 a small outcrop of anorthosite was noted, a plagioclase-rich gneiss. In this instance it was thought to relate to the metamorphism seen at the Iona Marble Quarry.

Locality 3: Camas Cuil an-t-Saimh (NM 2655 2342) Our final locality of the day took us to another beach on the western coast. This area is dominated by more rocks of the Lewisian Complex. These were strikingly banded, streaked and foliated metagranitic (pink), intermediate and dark basic metadolerite (amphibolite) gneisses. The contact between these two rock types frequently showed a convoluted or feathery margin, indicating that the dykes were probably emplaced when the granite was still plastic (fig. 7). It appears that the granite has been cut by dolerite dykes prior to metamorphism. Sometimes a small chilled margin was also visible (fig. 8).

Fig. 7 Feathery edge of dyke Fig. 8 Chilled dyke on intrusion Photo by Gwenda Brewer Photo by Gwenda Brewer

Wessex Footnotes July 2016 Page 5 A further intrusion of pegmatite (quartzite and feldspar) was seen to cut across the metagranitic/ amphibolite gneiss. Finally veins of epidote (apple green) and quartz (white) also cut across the rocks, probably emplaced through hydrothermal deposition (low temperature, low pressure) (fig. 9). Also seen were garnets in a garnet-biotite granulite, evidence of a previous metamorphic phase (fig. 10).

Fig. 9 Veins of epidote-chlorite from Fig. 10 Evidence of several phases of retrograde metamorphism deformation Photo by Gwenda Brewer Photo by Gwenda Brewer

Behind the beach there is an extensive area of machair (fig. 11). This is a gaelic word for a low-lying fertile and grassy coastal plain which is typical of the Hebrides. The machair is formed because the alkaline, calcareous shell-rich sand is blown onto the land by the westerly winds. Islanders have used seaweed to fertilise the area so that many species of lime-loving plants grow well here in addition to lush grass for grazing. However this area on Iona is now mostly Fig. 11 Columbus Bay, with the machair sand and golf course used as a golf-course! Photo by Gwenda Brewer

Marion Phillips and Gwenda Brewer

CARSAIG BAY AND (Friday, 12 May 2016) Report by Con Gillen and Andy Mitchell We drove in four cars, and parked by the old Carsaig pier, where there is very limited parking. We set off in good sunshine, following the coast for an all-day hike to Carsaig Arches at Malcolm’s Point. From the pier, we followed the top footpath, westwards, and stopped to examine the view towards the headland. Ian pointed out the main geological features. At sea level we could see the flat beds of Scalpay Sandstone Formation (Lower Jurassic), which had formed on a shallow marine shelf; the sandstones are interbedded with some mudstone and shale units. The sedimentary rocks are cut by sills and dykes. On the shore at the point of Rubh’ a’ Chromain is a sill, actually a composite sheet, where felsite has intruded a thick basaltic sill; both units contain xenoliths. The cliffs that rise up to nearly 200 metres are made firstly of Cretaceous (Morven Greensand Formation) lying above the Jurassic, followed by a thin unit of brecciated Chalk (as we had seen at Jurassic on foreshore, cut by dyke Gribun), then overlain by the Beinn Iadain Mudstone (cliffs at top are lavas) Photo by Con Gillen Formation. This is mostly a degraded airfall tuff, and may represent a possible precursor to the lava flows at the base of the main Plateau Lava Formation.

Wessex Footnotes July 2016 Page 6 Ian explained that there is some controversy surrounding this tuff, as some geologists consider it could have been the precursor to all the volcanism. However, it does not seem to precede the Formation, and is likely only the first stage in the Plateau outpourings. Here we have some 300 metres of Staffa Formation, with the Plateau Formation above. The Jurassic rocks gradually dip down below the Staffa Formation, and the Plateau Formation covers the Staffa Formation. To the east the Staffa Formation reappears as peperite. What we have here is a small sub-basin in the Jurassic, covered by the Staffa Formation. Overall there is a gentle arch or dome, faulted in places, that would have formed a palaeo-high during the eruption of the Staffa Formation. Flows 1–9 are missing in Carsaig east bay. In the west of the bay there are many sills, formed mostly of high-temperature picritic basalt, many with xenoliths of Moine and Jurassic rocks, that had been heated close to melting point. Some of these contain sapphires as a result of very high-T thermal metamorphism. The Scalpay Sandstone that we examined on the beach (at NM 5337 2133) has large round concretions (or doggers) that formed during diagenesis (post-deposition); the pale yellowish sandstone has cross-bedding, and represents a deltaic facies. Fossils were fairly abundant, including gryphea, belemnites and some quite large ammonites (Liassic assemblage). Small spherical phosphatic nodules were abundant on the bedding planes of very dark fissile shale. Lamellibranch shells in the shale were usually replaced by rusty-coloured iron hydroxides. Two abandoned quarries were later seen at the base of cliffs of Scalpa Sandstone. Cliff faces exhibited honeycomb weathering and a series of Liassic fossils on black even-sized, slightly oval, dogger stones on the same level within the shale bedding plane Photo by Con Gillen sandstone. The sandstone was overlain by basaltic lava flows of the Central Group. Farther along, sills could be seen within the sandstone cut by inclined dykes across the cliff wall with some faulting evident.

We spent quite a lot of time looking at the thick, well- jointed sill (at NM 5340 2118). The sill cuts a dyke, and we could see small offshoots (apophyses) of both the dyke and the sill, going in several directions, and creating quite a complicated-looking (but fascinating) situation. Near the igneous bodies, the Jurassic rocks were baked, and the dykes and sills had clear chilled margins. Sill and dyke Photo by Andy Mitchell Continuing after a brief lunch stop on the beach, a formation known as Pulpit Rock was seen projecting from a partial cliff face – a flint conglomerate that had been formed from dissolved local chalk, showing cross bedding, fining upwards and a mixture of sands at the top. Under the flints was a lava flow – however, there was an interface made up of rounded basalt boulders suggesting a fluvial debris flow. The actual lava flow also had a thin sill intruded into it (lighter brown colouring). A second smaller flint exposure nearby marked the probable limit of the channel flow and the end of the flint. An outcrop in between two lava flows revealed another Pulpit Rock Photo by Andy Mitchell debris flow - fining upwards, becoming alluvial. Two huge boulders were seen nearby exhibiting a mixture of bedded lava flow, spatter, vugs and scoria – probably because close to a vent. After some 7km we reached Malcolm’s Point and the Carsaig Arches – an impressive feature of a dolerite sill over a basatic tuff, passing down into a conglomerate of about 4.5 metre thickness of rolled flint pebbles. Note the columnar cooling joints above the arch. Carsaig Arch Photo by Andy Mitchell

Con Gillen and Andy Mitchell

Wessex Footnotes July 2016 Page 7 ARDALANISH BAY (c. NM 37779 1874) (Tuesday, 17 May 2016) Report by Kelvin Huff

Ardalanish Bay is a nationally important SSSI and therefore a ‘no-hammer’ zone. It lies in the remote Ross of Mull, due south of our base at . We arrived at Ardalanish Bay under sombre skies with heavy rain forecast for later. The bay faces south and on the proverbial good day there are views of Jura and Colonsay. From our cars we followed a track down to the sea. Before it reaches the beach, the track crosses machair – one of the rarest coastal grassland habitats in Europe, found only in north and west Scotland and western Ireland. It occurs where shell sand has been blown inland from beaches and dunes and has mixed with the soil to form rich grasslands, creating spectacular displays of spring flowers and providing an environment that supports populations of breeding birds. Ian Williamson, our leader, knows the area intimately and gave us an overview of the geology before we moved on to the white sand of the bay and the beach exposures.

Geological overview Exposed here are rocks of the Moine Supergroup of Neo-proterozoic age (600-1000Ma.) The basinal sequence of these rocks includes metamorphosed sandstones, silts and mudstones (mostly psammites and pelites). These represent the Assapol Striped and Banded Formation of the Assapol Group. The sequence also includes numerous garnet amphibolite rocks which are the result of the metamorphosis of basaltic intrusions. These display prominent garnet porphyroblasts. Unfortunately, the garnets are not of gem quality! Four phases of regional deformation and at least two phases of regional metamorphism have been identified. This pre-Caledonian metamorphism is of medium (kyanite) grade. This regional metamorphism has then been thermally overprinted by the later intrusion of the Ross of Mull granite. The aim was then to move on to see the contact between the granite and the Moinian country rocks. The intrusion has a saucer-shaped roof with roof pendants of Moine rock and diorite dykes. Within the coastal outcrops on the western side of Ardalanish Bay, all stages of emplacement are preserved, from the impregnation of the Moine country rocks by granite sheets, to the spalling off and sinking of slabs and blocks of country rock into the granite magma (stoping). The earlier regional metamorphic assemblages in the Moine succession, which includes kyanite mineralogy, have been overprinted by the metamorphic aureole with the formation of andalusite (pink) and sillimanite. The bluish kyanite can be seen in kayanitic schists.

Locality 1: Ardalanish Bay Ian’s attention was drawn to a large isolated rock on the beach. On examination this proved to be a garnet amphibolite derived from the metamorphism of a basic intrusion into the Moine sequence. The presence of possible glacial striae was also noted.

Locality 2: Ardalanish Bay Sgeir Na Feannaige (NM3779 1874) We then walked eastwards across the beach towards Aird Dubh. The Moine metasedimentary sequence here comprised micaceous siltstones. We also observed paler bands of folded calc-silicate sediments with quartz veination and kink folds. Some relict sedimentary structures Garnet amphibolite were also seen, including ripple marks and cross-bedding. The effects Photo by Kelvin Huff of regional deformation were dramatically expressed as tight isoclinal fold structures, with closed fold features relatively common. The isoclinal folds were mostly NE trending. The whole area lies on a limb of the broad (Assapol) synform with fold closures and some evidence of boudinage and small garnets provided further evidence of the regional metamorphism and deformation.

Localities 3 and 4: Ardalanish Bay (east) We continued to traverse the beach and observed larger garnets in a metacalcareous sandstone with clear fold closures. Large “sweated Garnets in Moine meta- out” quartz nodules were seen close by as well as a coarse mica schist. sediments Photo by Kelvin Huff

Wessex Footnotes July 2016 Page 8 Localities 5 and 6: Aird Dubh (NM 3813 1845) The contact between the mica schists and a garnet-amphibolite was observed. The latter are probably metamorphosed dolerite sheets that intruded the sequence prior to the regional metamorphic event. The exposures displayed good evidence of boudinage affecting these mafic bodies. The heavy rain finally arrived at this point and my notes become progressively less legible and frequent! We continued working eastwards around the foot of Aird Dubh towards Eilean Nam Meann. We continued to examine the metasediments of the Moine sequence including a calc-silicate surface with biotite. This rock was originally muddy, carbonate-rich sediment. We also noticed some differentiation of lighter and darker minerals which had occurred during metamorphism. We saw a variety of Synclinal fold near Aird Dubh fold styles, from wide amplitude open folds to tighter and Photo by Kelvin Huff locally ptygmatic types. (Ptygmatic folds are chaotic, random and disconnected. They are typical of sedimentary slump folding, migmatites and decollement detachment zones.) Tight folds with tension gashes were common and in some examples we could see the development of cleavage in line with the axial plane, especially in the more pelitic units. Well- developed crenulations were noted on some fold surfaces. Crenulations form by the recrystallization of mica minerals during metamorphism, when an early planar fabric is overprinted by a later planar fabric. This confirmed more than Tight folding in Moine meta- one phase of metamorphism in this area. We also saw several sediments Photo by Kelvin Huff faults with associated fault breccias. Locality 7: Crag (Dun Fuinn) above the beach (NM 3754 1888) After a bit of scrambling we were able to see some effects of the thermal overprinting caused by the intrusion of the Ross of Mull granite. Four zones of increasing thermal effects inwards towards the granite contact are associated with metamorphic aureole. Dun Fuinn falls within Zone II. With a hand lens it was possible to see pale grey-blue bladed crystals of kyanite (formed by regional metamorphism) within a crag composed of schistose rocks. Some have undergone partial phase- change so they have been pseudomorphed by pink andalusite (formed by contact metamorphism). Locality 8: Ardalanish Bay, Carraig Mhor (NM 3678 1762) After a lunch stop some of the group worked their way westwards towards Carraig Mhor to study the contact between the Moine Supergroup and the eastern margin of the Ross of Mull granite, the latter being of Caledonian age (418 ± 5 Ma). For this section of the report I am indebted to Ian Williamson’s field guide notes which follow below. The roof-wall transition zone is exposed on the western side of Ardalanish Bay. This is a stoped floor zone at the base of the intrusion, which in places grades into a sub-horizontal (low dip to the east) step-wise sheeted complex of inter-fingering granite and country rock. These ‘roof pendants’ of the Moine gives a striped appearance to the exposure. This ‘contact envelope’ is gradational and occurs across 50-60 metres, from country rocks containing granite sheets concordant with the prominent foliation into ‘screens’ of Contact between Ross of Mull granite metasedimentary rocks. The marginal granite carries and Moine with diorite intrusion abundant rafts (some very large) and slab-like xenolithic Photo by Tony Loftus blocks. There are also later sheets of synplutonic porphyritic microgranodiorite. Assimilation of the metasedimentary material into the marginal granite resulted in the development of contaminated hybrid granite and localised ponding of fluids in the magma led to the crystallisation of pegmatite. A fantastic day’s geology, in spite of an overdose of Scottish ‘liquid sunshine’, wet clothes and the odd midge. At least we had a sumptuous evening banquet to sustain us for the next expedition!

Kelvin Huff

Wessex Footnotes July 2016 Page 9 GRIBUN (Wednesday, 18 May 2016) Report by Tony Loftus Gribun is a classic location for geology in Mull. Moine (1000-600Ma) metasediments, Permo- Triassic, Jurassic and Cretaceous beds are topped by Paleogene lavas. Glacial deposits including erratics occur near the shore. To the west lie Loch Na Keal and views of Staffa and the . We started by walking north (to NM 4560 3555) where the lavas of the Mull Plateau Formation (MPF) were well displayed and red laterite horizons were just visible high up. Landslips, promoted by the lavas being on top of weaker beds, were prominent. Whereas the early, high volume eruptions of the Staffa lavas produced typically columnar basalts, these later, lower volume lavas show less structure. The beds seen are end-on and different “fingers” of basalt can appear on the same level. More vesicular basalts provide a better substrate for lichen and so appear paler. Picritic (more primitive) lavas are higher in olivine and these weather to a browner colour. Meanwhile, down at ground level, the group found a stream and, reverting to childhood, immediately began to paddle about - to discover Cretaceous chalk boulders (Gribun Chalk Formation), Cretaceous Loch Aline White Sandstone and, in the stream wall, the familiar Jurassic Blue Lias. The Loch Aline Sandstone is renowned for its low iron content, making it suitable for production of high quality silicate glass. It was mined during World War 2 and uses included glass for submarine periscopes Moving south, low tide gave access to an area of Permo-Triassic rocks which indicated an arid environment with flash floods and playa lakes. Caliche deposits point to high evaporation rates drawing carbonates upwards to form a hard pan, while conglomerates of poorly rounded quartzite pebbles interbedded with lenses of finer material pointed flash floods and braided streams (fig. 1). The quartzite was presumed to be Moine in origin. Elsewhere green/brown sandstones indicated deposition in anoxic/aerobic conditions while mudcracks were extensive (fig. 2).

Fig. 1 Foreshore. Braided stream/flash Fig. 2 Mudcracks in Permo-Triassic flood deposits Photo by Tony Loftus (rucksack for scale) Photo by Tony Loftus Moving south required more of a scramble but was rewarded with an impressive angular unconformity: Permo-Triassic above Moine psammites (NM 4452 3367) (fig. 3). The upper beds showed evidence of a mudslide – a conglomerate, matrix- supported with some large clasts. The final location showed Paleogene lava intruded parallel to the Moine with a large deposit of the Permo-Triassic (paleovalley deposit?) above (fig. 4). Those still following the leader chose a slightly longer but bull-free return to the cars.

Fig. 3 Unconformity P-T strata above Fig. 4 Igneous Intrusion into Moine Neoproterozoic Moine Supergroup with P-T deposits above Photo by Ian Willliamson Photo by Tony Loftus Tony Loftus

Wessex Footnotes July 2016 Page 10 SIMPLE GUIDE TO MINERALS 20 - by Colin Morley

STIBNITE Sb2S3 Stibnite is also known sometimes as antimonite, which is not surprising considering that Sb is antimony and the S (as you probably know) is sulphur. It is an antimony sulphide and is the most important source of antimony. Antimony alloys are used for batteries, low friction metals, type- setting metal and cable sheathing; antimony compounds are also used to make flame-proofing materials, paints, ceramic enamels, glass and pottery. Stibnite ground up and mixed with fat has been used as eye liner since 3,000 BC. It is still used today as ‘kohl’ and was once well known as a remedy for hair loss – obviously a valuable mineral. It can be found in hydrothermal deposits, sometimes with galena. It is usually found in very small quantities worldwide from places like Arizona, China, Borneo, Germany and South America. Stibnite has a very metallic look. It is grey and sometimes it seems to have a hint of blue mineral with distinctive needle type structure (see the picture). Twinning is relatively common and the difference in the growth rates can lead to sweeping curves in acicular or bladed crystals.

It is an orthorhombic crystal structure and isn’t Specimen in the Sun City Rockhounds Club very hard, just 2 on the Mohs scale. For testing, Mineral Museum, Arizona, USA the streak is, unsurprisingly, a lead grey. Photo, with permission, by Colin Morley In the 1600s alchemists used this mineral as one of the steps to creating the ‘philosopher’s stone’ which could turn base metals into gold. Today it is even better, its metaphysical properties can transform your life and bring you what you most desire! Colin Morley

Jurassic Coast World FOSSILS OF THE JURASSIC COAST a new book by Sam Scriven Heritage Team receives

Sam Scriven is the Earth Science Manager prestigious award with the Jurassic Coast Team and leads an The Royal Geographical annual fossil-hunting trip for Wessex Branch Society has given its This new book has 220 pages with numerous Geographical Award to the full-colour photos and illustrations plus Jurassic Coast Team “for itineraries for various locations. It also outstanding collaborative work includes a large and detailed pull-out “Tree of to foster student and wider Life” diagram depicting the species that public engagement with the evolved during the Mesozoic. Price £14.95. ‘Jurassic’ coastline”. The http://jurassiccoast.org/product/6264/ award was presented in June.

Stepping Stones re-launched on-line Practical geology (and archaeology) for kids A recently-revised edition of Steve Drury’s Wessex Branch member Trevor Price, who is the Stepping Stones: The Making of Our Home World Community Learning Officer at the Dinosaur Isle

is now available on-line (for free!) at: Museum on the Isle of Wight, has recounted a fun (ie https://earthstep.wordpress.com/ messy!) project for kids which other members might Steve used to teach at the OU and, although not a like to try out in their own locality. It involves text book, Stepping Stones covers a certain collecting local clay, making objects from it and then amount of S276 material. It tells the story of the comparing them to pottery made by our ancestors. Earth, and life on it, from many different aspects. www.dinosaurisle.com/documents/CaseStudy2-2016.pdf

Wessex Footnotes July 2016 Page 11 OTHER LOCAL EVENTS – PLEASE CONTACT THE ORGANISERS DIRECT

DORSET GEOLOGISTS’ ASSOCIATION GROUP (DGAG) LULWORTH RANGE WALKS www.dorsetgeologistsassociation.com & TYNEHAM VILLAGE 23 July 2016 Chairman’s field trip and picnic, Portesham For information on opening times tel. 01929 404819 20 Aug 2016 A Mendips expedition (Andy Bradley & Alan Holiday) OPEN EVERY DAY OVER HOLIDAYS 15 Oct 2016 Holiday Rocks 30 July – 4 September 2016 OUGS members welcome but check beforehand that spaces are 18 December 2016 – 7 January 2017 available. Contact: Doreen Smith tel. xxxxxxxxxxxxx or e-mail OPEN EVERY WEEKEND EXCEPT: xxxxxxxxxxxxxxxxxxxxx 8-9 October 2016 19-20 November 2016 10-11 December 2016 DIGS: Dorset’s Important Geological Sites Group More details from Alan Holiday: xxxxxxxxxxxxxxxxxx http://www.dorsetrigs.org.uk If you would like to be kept informed of forthcoming BOURNEMOUTH NATURAL SCIENCE SOCIETY 39 Christchurch Road, Bournemouth BH1 3NS conservation sessions, please contact Alan, who will be happy http://www.bnss.org.uk to add your name to his e-mail circulation list. The Society covers all branches of natural science, including geology and palaeontology. It has an extensive, and very impressive, collection of fossils, RUSSELL SOCIETY, SOUTHERN BRANCH rocks and minerals which can be viewed on the http://www.russellsoc.org/ following dates (free entry, donations welcome): Gary Morse: xxxxxxxxxxxxxxx, tel. xxxxxxxxxxxxx Summer opening: 10am to 4pm on Mondays and Wednesdays from 18 July to 24 August 2016. For anyone interested in minerals, the Branch runs summer field trips plus winter lecture meetings on the second Thursday of the month at Open weekend: 8-9 Oct 2016 Wyvern Technical College, Fair Oak, Eastleigh, Hants. Forthcoming events include 17 Jul 2016 Fossils of the Jurassic Coast (lecture by Richard Edmonds) 21 July 2016 Imreys Clay Pit, Furzedown SOUTHAMPTON MINERAL & FOSSIL SOCIETY (field trip led by Ray Chapman) 18 Aug 2016 Worbarrow Bay http://www.sotonminfoss.org.uk (field trip led by Ray Chapman) Gary Morse: xxxxxxxxxxxxx, tel. xxxxxxxxxxxxx 7 Sept 2016 Bulgaria Revisited (minerals) The Society runs indoor meetings, field trips and other (lecture by Mike Brooke) activities relating to the collection of minerals and fossils, 15 Sept 2016 Bournemouth to Hengistbury Head and the sites where they are found. Monthly evening (field trip led by Ray Chapman) meetings are held at The Friends' Meeting House, 20 Sept 2016 Global warming and COP21 Ordnance Road, Southampton (guests welcome). (lecture by Brendan McNamara) 19 Jul 2016 Collection, Conservation & Curation (Gary YOUNG EXPLORERS’ CLUB (geology and more!) Morse) For children aged 7 to 12. £4 per child per meeting. 31 Jul 2016 Field trip to Plumpton Plain, East Sussex 16 Aug 2016 Swap and Sale evening http://www.bnss.org.uk/about/young-explorers 20 Sept 2016 Corals from Ancient Seas (Phil James) 20 Oct 2016 Kem Kem Dinosaurs (Dr Dave Martill)

DORSET BUILDINGS GROUP HAMPSHIRE MINERAL & FOSSIL SHOW The Group aims to promote the preservation of Dorset’s building traditions and so takes a practical interest in 10am – 4.30pm, Saturday, 3 September 2016 building stones and local geology. Winter lectures (held Lyndhurst Community Centre at Holt Village Hall, Dorset) plus summer outings. High Street, Lyndhurst, Hants SO43 7NY John and Sue Rowntree, xxxxxxxxxxxxxxxx http://www.sotonminfoss.org.uk/smfsshow.htm 26 Jul 2016 Guided tour of Wimborne (Ian Willis) 21 Aug 2016 Visit to new dig at Druce Farm 10-11 Sept 2016 Architectural Heritage Week display at Blandford Forum WINCHESTER SCIENCE FESTIVAL 4 July – 1 August 2016 Winchester Discovery Centre JURASSIC COAST SUMMER WALKS Jewry Street, Winchester S023 8SB A series of six guided walks in July and August. £5 each walk, must book. Check website for locations and dates. Festival weekend is 22 -24 July 2016 http://jurassiccoast.org/product/jurassic-coast- http://winchesterscifest.org/ summer-walks-series/

Wessex Footnotes July 2016 Page 12 WESSEX BRANCH EVENTS – DETAILS

Mendips quarries, Somerset Wednesday & Thursday, 17 & 18 August 2016 QUARRYING IN THE MENDIP HILLS, SOMERSET: THE TALE OF THREE QUARRIES with Dr Gillian Odolphie (limited to 10 members on each trip)

To book a place, contact: Jeremy Cranmer at [email protected] or tel. xxxxxxxxxxxxx

Gill Odolphie is the Manager of Field Study Centre of the Somerset Earth Science Centre Limited. This is a magnificent enterprise set up with the assistance of local quarrying companies to instruct on the geology and ecology of the Mendips Hills.

For safety reasons access to the locations is by minibus and Land Rover, hence each party is restricted to ten in number. We shall visit Whatley Quarry to see the extraction of Carboniferous Limestone, and then look at the iron deposits in Torr Works Quarry. Finally we will visit Moons Hill Quarry for the extraction of andesite which occurs in the core of the Mendip Anticline.

Access to each location is easy with walking of no more than a couple of hundred yards. As numbers are very limited it is likely that a waiting list will be operated.

Abbotsbury, Dorset Sunday, 25 September 2016

RIGS CONSERVATION: RED LANE, ABBOTSBURY with Alan Holiday To book a place, contact: Jeremy Cranmer at [email protected] or tel. xxxxxxxxxxxxx Alan Holiday taught geography and geology in Weymouth. He is now retired but spends much of his time leading field trips! Over the years he has been involved in a range of OUGS activities as well as now being Chairman of the Dorset GA Group and Dorset RIGS Group. In the morning we shall carry out some very necessary work at this disused quarry which is designated as a Regionally Important Geological Site. The quarry was used for the extraction of the Abbotsbury Iron Ore which is a unique deposit at the boundary of the Corallian and the Kimmeridge Clay and yields an iron-rich oolitic sandstone. The sediment is fossiliferous and has yielded fossil wood, bivalves, worms, ammonites and brachiopods, indicating a shallow-water nearshore environment, such as a subtidal barrier bar.

In the afternoon Alan will lead a trip to various other sites in Abbotsbury which display interesting and varied exposures consisting of Upper Cretaceous sediments lying unconformably on Upper Jurassic ones.

Isle of Purbeck, Dorset Friday, 7 October 2016

WYTCH FARM AND KIMMERIDGE OILFIELDS: PETROLEUM IN DORSET with Dr Giles Watts and Dr Suzie Baverstock (limited to 25 places) To book a place, contact: Jeremy Cranmer at [email protected] or tel. xxxxxxxxxxxxx With a billion barrels contained in three main reservoirs, Wytch Farm qualifies as one of Europe’s largest onshore oilfields and after 40 years it is still producing over 15,000 barrels of oil every day. Hidden amongst trees and heathland on the Isle of Purbeck it also remains a fine example of how the oil industry can operate discreetly and responsibly in a very beautiful and highly sensitive area. The tour will be conducted by Dr Suzie Baverstock, who is communications and external affairs team leader for Perenco, the current operator of Wytch Farm; and Giles Watts, who was senior Geophysicist at Wytch Farm from 1995 to 2000. We will visit the gathering station, a number of well sites and a high-point overlooking the whole field area. Perenco is kindly supplying a coach around the site and so numbers are limited to 25. In the afternoon we shall use our own transport to visit the “nodding donkey” which sits on the cliffs at Kimmeridge Bay and which has been producing oil from the Kimmeridge oilfield since 1961. We will also be able to see and discuss some of the structural elements which are key to understanding the petroleum geology and exploration potential of the area.

Wessex Footnotes July 2016 Page 13 THE OPEN UNIVERSITY GEOLOGICAL SOCIETY, WESSEX BRANCH – FORTHCOMING EVENTS This listing covers events in the Wessex area and general Society events. However, members can attend events organised by any OUGS branch - the full listing is at http://ougs.org/events/ Wessex Branch field trips Places are filled on a first come, first served basis. Non-members are welcome to attend events, but members will be given priority if places are short. Please contact the organiser to confirm details and to ensure there are spaces. Packed lunches, hard hats, strong footwear and waterproofs are usually required plus reflective clothing in working quarries. Please take note of the safety issues, which the leader will outline at the start of each trip. For day trips there is usually a charge of £2.50 per person to cover expenses. Events shown in italics are joint ones – please contact the host organizer as shown. Last-minute contact on the day, if you’re not coming or late: Jeremy’s mobile 07531 318314 ONCE YOU’VE SIGNED UP FOR A WESSEX DAY TRIP, JEREMY WILL E-MAIL THE HAND-OUT TO YOU A FEW DAYS BEFORE THE EVENT SO THAT YOU CAN READ IT IN ADVANCE. DATE EVENT LEADER(S) CONTACT Jeremy Cranmer Wednesday Moon’s Hill Quarry, Somerset Gill Odolphie [email protected] 17 Aug 2016 (limited to 10 members) tel. xxxxxxxxxxxxx Jeremy Cranmer Thursday Moon’s Hill Quarry, Somerset Gill Odolphie [email protected] 18 Aug 2016 (limited to 10 members) tel. xxxxxxxxxxxxx Jeremy Cranmer Sunday Conservation on a Dorset RIGS Alan Holiday [email protected] 25 Sep 2016 Red Lane, Abbotsbury tel. xxxxxxxxxxxxx Jeremy Cranmer Friday Kimmeridge and Wytch Farm Giles Watts [email protected] 7 October 2016 (limited to 25 people) tel. xxxxxxxxxxxxx London Branch AGM weekend with half- Yvonne Brett 28-30 Oct 2016 Di Smith day tours of Salisbury and Winchester xxxxxxxxxxxxx Beginning Geology at Bowleaze Cove Jeremy Cranmer Sunday Weymouth Alan Holiday [email protected] 13 Nov 2016 (suitable for those new to field geology) tel. xxxxxxxxxxxxx Saturday Wessex Branch AGM and lecture day Sheila Alderman Sheila Alderman 21 January 2017 Wool, Dorset [email protected]

INFORMATION ABOUT INSURANCE ON FIELD TRIPS AND EVENTS Each person attending a field meeting does so on the understanding that he/she attends at his/her own risk. The OUGS has Public Liability Insurance Cover for field and indoor meetings, but Personal Accident Cover and Personal Liability cover remain the responsibility and personal choice of the participant. There may be an element of appropriate cover included in house insurance or in travel insurance: although OUGS activities are not particularly dangerous, members are advised to check whether exclusions apply to activities in which they plan to participate in case they wish to arrange further cover. Annual travel insurance may be the best solution for any member who regularly attends field events: this again is a matter of personal choice. Please note however that all members participating in overseas events will be required to have travel insurance for the duration of the event: this is so that participants are covered for Medical, Repatriation and Personal Liability expenses. The Personal Accident element remains the personal choice of the member and again members are advised to check exclusions so that they can make an informed decision about the cover. Sheila Alderman, Branch organiser Jeremy Cranmer, Branch Day Events Organiser

Weekend in Charnwood The world-renowned area of Charnwood became famous for its Precambrian fossils after Charnia masoni was found there by 3 - 4 June 2017 Roger Mason. It has excellent volcanic and Triassic rocks too. Led by Keith Ambrose and Ian Williamson Further information from: Mark Barrett, [email protected]

WESSEX BRANCH COMMITTEE CONTRIBUTIONS TO THE

Branch Organiser Sheila Alderman [email protected] NEWSLETTER Treasurer Rhiannon Rogers [email protected] Day Trip Organiser Jeremy Cranmer [email protected] Is there anything you would like to tell or ask Newsletter Editor Hilary Barton [email protected] other members? All Residential Trips Mark Barrett [email protected] contributions welcome. Website Manager Colin Morley [email protected] Hilary Barton, Editor Librarian Jeremy Cranmer [email protected] [email protected] Ordinary members: Ian Hacker, Tony Loftus, Linda Morley, Marion Phillips, Jane Mead

Wessex Footnotes July 2016 Page 14