10 Years of GEO-LOGs Walton Hall Branch OUGS
Number 92, a Compendium of articles from past GEO-LOG issues December 2009
2009, that we could re-visit some of the geological Branch Organiser’s Bit events and locations that had been held in the field Hi Everybody, during the years 1995 to 2004 and re-print them for
Yes, it’s a bit different this time isn’t it. This is a one-off, our collective enjoyment. We were conscious that during the last few years we have several new special edition GEO-LOG that contains a compendium of members and therefore the reports will be new to articles from past GEO-LOGs and snippets of news from them. yesteryear. Hopefully, it will jog some memories, happy and sad, of times gone by. We hope you like it. I (Pauline) particularly recall the field trip to Anglesey back in 1995. This report mentions the names of two If you’ve been studying and taking exams this year, we branch members and Dr Richard Thorpe, who was a hope you got the results you wanted. Our timetable of events for next year is already in planning, with trips President of the Society in 1979-80, who in their absence were remembered on the beach at “oop north” to look at the Carboniferous of Northern
England, and more locally to Cambridge (The Newborough Warren. The national photographic competition is held in memory of Moyra Eldridge, Sedgwick Museum) and local exposures of the who had also been a Branch Organiser for Walton Jurassic and Cretaceous beneath our feet in Herts, Beds and Bucks. Hall.
A second item I selected from our archive, was a Have a Lovely Christmas, more ‘local’ field trip. As well as residential field-trips Tom in the UK and abroad, we do arrange one-day drips. PS – Please don’t forget to pay your subscription in I recall the day my husband accompanied me on a Walton Hall field trip to Milton Keynes where we January explored the building stones in the city centre. He A Message to all, from was amazed to see us on hands and knees with hand lenses, studying the stone, among the Pauline shoppers there. He’s recovered from this now and
Tom and I (Pauline Kirtley), have been discussing how perhaps would enjoy a day trip to Brixworth,
many field trip write-ups can be useful as a ‘geological’ Northants. Reading the field report of the area (the guide for an area that you may wish to visit in the second report) enables you to gain an insight into the future, even if you didn’t attend a OUGS field trip. varied rocks that were used to build Brixworth Since 1995, with electronic storage, our Branch now Church. has held copies of field-trip reports that we can review. As always, the committee is here to support its We thought, for this issue of the GEO-LOG, the last in branch members and to help promote an understanding and enjoyment of geology. We would I NSIDE T HIS M AILING always consider running field trips at a member’s 1 Branch Organiser’s Bit request … So perhaps, on reading some of these “historical” trip reports, you might want to ask us if we 1 A Message to all from Pauline could arrange a field trip there again. 2 Walton Hall Branch AGM Notice Have a Wonderful Christmas 2 Contents List Pauline Kirtley
3 10 Years of News and Trip Reports from GEO-LOG ougs.org/waltonhall
10 Years of GEO-LOGs 1
Notice of the 2010 Walton Hall Branch Annual General Meeting
To take place at 7.30 pm 4th February 2010, In the Seminar Room, Gass Building, Walton Hall Campus
AGENDA
1. Apologies for Absence 2. Minutes of the last AGM (printed in GEO-LOG July 2009) 3. Matters arising from the minutes 4. Officers’ Reports
• Branch Organizer’s Report • Treasurer’s Report • GEO-LOG Editor’s Report • Web Site Manager’s Report
5. Matters arising from the reports 6. Election of Officers 7. Any Other Business 8. Items from members
Committee 2009 - 2010:-
Tom Miller - Branch Organizer Tom Duff - Treasurer Terri Battrick – Webmaster Patricia Thomas - GEO-LOG Editor Terri Battrick – Librarian Pauline Kirtley John Stanbridge ______
10 Years of Past GEO-LOGs – The OUGS Walton Hall Branch Newsletter
A selection of news items and field trip reports published in our GEO-LOG, during the period 1995 to 2004. These are just a few. There are much, much more.
If you were with Walton Hall Branch throughout this period, you may remember these events and enjoy reminders of those times, and the people you shared them with.
Enjoy! Contents 1995 ...... 3 Anglesey Field Weekend ...... 3 A Visit to Brixworth Church and the Northampton Natural History Museum ...... 4 1996 ...... 5 A Weekend Visit to the Pembrokeshire Coast...... 5 A Visit to Barton Hills, Barton-le-Clay, Beds...... 6 1997 ...... 7 A Weekend Field Trip to North Norfolk to look at the Quaternary Geology...... 7 A Day Trip to Bradgate Park (Charnwood Forest) Leicestershire...... 9 1998 ...... 10 Return Visit to Ketton Quarry, Near Stamford ...... 10 1999 ...... 11 Field Trip to Hawaii ...... 11 North Devon Coast - From Millook Haven (Near Bude) to Ilfracombe ...... 13 2000 ...... 15 Visit to GEOU ‘Fossil Factory’ - OU Campus ...... 15 A Journey Through Namibia...... 17 2001 ...... 19 A 4-Day Field Trip to Cornwall ...... 19 2002 ...... 24 A Report of a Day Visit to the Isle of Sheppey...... 24 2003 ...... 25 A Report of a Day Visit to Old and Working Chalk Quarrys...... 25 2004 ...... 28 A Field Trip to the North Devon Coast...... 28
10 Years of GEO-LOGs 2 1995
The Richard Thorpe Memorial Prize 1995 Award S339: Understanding the Continents: Tectonic and Thermal Processes of the Lithosphere. In 1995, The Richard Thorpe Memorial Prize was awarded to Sue Russell, one of our own Branch Members. Sue received her award of books later that year at the Annual Symposium. Some Sad News John Daniels - Treasurer of the London Branch and known to many people who attended the S236 revision days at RHBNC, suffered a thrombosis in March 1995, from which sadly he did not recover. We will always remember John as a friend and colleague.
Some 1995 OUGS Statistics OUGS membership (nationally) stood at 1540 paid up members, of which 130 were new having joined within the last year. ______
Anglesey Field Weekend "A Mélange of Monian and Microplates" Led by John Durham and Ian Rigby March 3-5 1995
Anglesey has been a venue for OUGS field trips for over a decade, reflecting the appeal of its fascinating and complex geology, together with the peace and beauty of its countryside. Twentyeight of us gathered at the Harbour Hotel at Cemaes Bay over the weekend of March 3-5 1995, braving heavy snow to reach the island. Our trip was ably led by John Durham (PhD student at the OU) and Ian Rigby (part-time lecturer at Birkbeck College). Their itinerary encompassed the highlights of the Precambrian and early Cambrian features of Anglesey. The geology of Anglesey was originally mapped by Edward Greenly in the early part of the century and has been re-interpreted by others. The island contains some of the most important Precambrian rocks in the UK, subdivided into the Monian Supergroup, the Coedana complex and the Blueschist Belt (Fig. 1). These are overlain by Palaeozoic volcanic and sedimentary rocks.
On Saturday morning our first locality was the beach at Porth Nobla where a late Precambrian granite coexists with hornfels, part of the Coedana complex. We looked for a chilled margin at the junction to try to establish whether the granite was intruded into a pre-existing hornfels or if the intrusion caused the hornfels. We found no chilled margins of the granite, but we did find some evidence of finer-grained hornfels near the contact. To begin to reach any conclusion about this contact, more time and field evidence is required but a great deal of discussion did result at this location.
We drove on to Porth Cwyfan, Aberffraw where we examined the strongly foliated quartzose schists of the Central Shear Zone. Intrafolial folds indicate intense deformation during metamorphism, whilst boudinaged pods of hornblende schist and folding of the schistosity reveal subsequent extension and compression. The N-S compression shown by the folds is not the correct vergence for the Central Shear Zone of Anglesey - unless you appeal to transpression.
Near Llandrygarn Chapel we examined a gneiss with prominent porphyroblasts of feldspar which actually grew in a solid state, taking in surrounding rock as they expanded. Using a hand lens we saw tiny garnets produced during high temperature metamorphism. We were told that in thin section these are cracked indicating later medium temperature metamorphism, i.e. retrograde metamorphism.
10 Years of GEO-LOGs 3
After lunch we went on to Rhoscolyn on Holy Island where we saw the black and green serpentinites which have been used for ornamental purposes and reputedly provided a table top for Napoleon Bonaparte. The serpentinites, and the gabbros which appear to overlie them, provided our first view of the Monian Supergroup. In worsening weather we drove on to the classic exposure of blueschists in the woods beneath the Marquess of Anglesey's column near the Menai Straits. Within the foliated schists (which really do look blue) we were able to pick out the oval shaped areas of amphibole, epidote and quartz which have been interpreted as relict pillow lavas. The rocks therefore provide evidence for subduction and subsequent low temperature - high pressure metamorphism of ocean crust in the late Precambrian.
We saw more rocks of the Monian Supergroup at the final locality of the day - Newborough Warren Beach. We struggled across the sands, through heavy rain and driving wind, to reach Llanddwyn Island where we tried to work out which way up the tumbled piles of pillow lavas were. These pillow lavas, together with the gabbros and serpentinites we saw at Rhoscolyn, may represent fragments of oceanic crust and upper mantle - possibly portions of a dismembered ophiolite complex. The subaerial volcanic agglomerate we also saw at Llanddwyn Island is discontinuous with the submarine pillow lavas so the two are probably separated by a fault.
It was at Newborough Warren that Ian Rigby showed us a photograph taken here in 1987 and spoke in memory of the members no longer with us - Moyra Eldridge, Tony Richardson and Richard Thorpe. We spent a few moments remembering these and other OUGS members we have lost and appreciated Dot Hill's comment that it is as if they are still with us.
After an excellent evening meal, John and Ian gave us a synthesis of the current ideas on the tectonic history of Anglesey. Briefly, during the late Precambrian and early Cambrian, Anglesey lay on the south side of the Iapetus Ocean. The juxtapositioning of microplates within this setting would explain the complexity of what we now see - three major shear zones dividing a series of distinct terranes formed in a variety of tectonic settings. We also heard that this year's winner of the Richard Thorpe memorial prize for S339 is Sue Russell - particularly appropriate because Richard worked extensively on the geology of Anglesey. While modesty precludes Sue from commenting further at this point, Olwen and Pauline are delighted to add their congratulations to such a worthy winner.
Sunday morning was devoted to the famous Gwna group mélange. In bright sunshine we walked along the coast to Llanbadrig where we viewed the chaotic-looking and colourful assemblage of blocks and fragments of sandstone, limestone, quartzite, dolerite, serpentinite and jasper. It was noted by Greenly as "... really indescribable" and it is difficult to make any sense of it - it has recently been interpreted as a massive submarine rock slide. During our walk back to Camaes Bay we paused to examine a stromatolitic limestone, another part of the Gwna mélange.
The wind was getting stronger so we had to call off our proposed visit to South Stack - we'll be back! From all those on the weekend - thank you to both John and Ian for their excellent, thought-provoking and understandable guide around the outcrops and to the hotel staff who cheerfully put up with late meals, muddy boots and our drinking them out of several types of red wine.
By Olwen Williams-Thorpe, Pauline Catchpole and Sue Russell ______
A Visit to Brixworth Church and the Northampton Natural History Museum Led by Diana Smith June 1995
On 11 June, a small group of us from Walton Hall branch led by Di Smith visited the very old church at Brixworth, Northants.
Di told us that the oldest parts of Brixworth church were Roman/Saxon, built in approximately 750 AD (by Ethelbald of Mercia, for Boniface) and must have been of special significance in the spread of Christianity to the region at this time.
Of structural significance is the church's classic basilica shape (suggestive of build by French or Italian masons) and the barrel-vaulted, ring crypt which is one of only four in Europe. This is thought to be the fourth oldest church of this type in the country.
Di pointed out various stages in the build of the church and the stone assemblages used. The earliest parts were the base of the west tower and the nave, including the large Roman arches. These are of a mixed assemblage consisting of Blisworth limestone, Northampton sandstone, Triassic sandstone,
10 Years of GEO-LOGs 4 Charnian tuffs and slates, hornfels, markfieldite and granites from Leicestershire. There is evidence of re-use of stones from earlier buildings, in the form of heat damage (reddening) to individual stones here and there.
More recent and rebuilt parts (the lower windows, upper nave and 14th C. upper tower) show less variety of stone (Limestone, Northampton sandstone and tufa) and have more neatly butted masonry, with no mortar. There is much more we can say about Brixworth church, but we have limited space.
In the afternoon we visited the Northampton Natural History Museum, Geological Section, where we were invited to check out their compact but comprehensive collection of geological specimens, equipment and study material. This museum really is an excellent resource, right on our doorstep. They have a collection of some 5000 different sands all labeled with location and key features and held in neat storage racks. We spent hours there, totally engrossed.
Finally, we rounded off the day with a visit to William Smith's grave and monument in St. Peter's church, Northampton.
From Dot Hill, David and Elizabeth Maddocks, Sue Russell and Tom Miller
Thank you Diana, for an interesting and really enjoyable day. ______
1996
A Hearty Thanks to Mike At the WH Branch AGM, Mike Henty announced his desire to step down from the committee. Mike continues supporting the Branch to this day. Despite a recent bout of ill health, his support is as dynamic and motivated as ever.
And it was a welcome to Jenny Bennett Mike's stepping down paved the way for Jenny Bennett to stand on the Branch committee. Jenny joined us after stepping down from the National Committee, after several years as National Newsletter Editor.
OUGS National Membership in 1996 As we began 1996, the National Membership Secretary reported that the society membership stood at just 7 short of 2000 strong. ______
A Weekend Visit to the Pembrokeshire Coast Arranged by Elizabeth and David Maddocks "Sediments, Volcanics and Intrusives" 19-21 April 1996
The weekend in Pembrokeshire was advertised as “casual geology” which turned out to mean no professional geological leader to keep our attention fixed to the rocks, but a relaxed walk along the coast with as many stops to look at birds, plants and the scenery as to work out the geology.
The bird count included choughs, swallows, wheatears, kestrels, and an unconcerned ringed plover on the beach, not to mention the peregrine falcon (we think) with its nest on the cliff and a raven’s nest complete with several rather large baby ravens. Dave claimed to have seen a seal, and the horticulturalists found plenty to interest them on the ground, including the “first bluebell”.
As to geology we spent the first day walking from the Upper Cambrian Lingula Flags up the sequence to the Ordovician Llandeilo-Caradoc shales. We started with some rather attractive folds in the slates and quartzite, then moved on to identify the tuff horizons down in the bay, and finished in the next bay looking for, and finding Didymograptus graptolites and trilobites in the Caerhys shale.
Sunday was devoted to Ordovician igneous rocks further up the coast, beginning with a microtonalite intrusion - we found the contact with the mudstones as mentioned in the notes. We walked north along the cliff path, taking our turn at the sub-horizontal kink bands after another geological group, to find the rhyolite, the volcanic breccias and, with an eye of faith, a thin hyaloclastite horizon. The day ended with an impressive display of pillow lavas and pillow breccias, which was particularly appreciated by those who had been to Iceland.
10 Years of GEO-LOGs 5 For most of the weekend the weather was sunny and spring-like, although Sunday ended with the obligatory Welsh rain. Saturday evening was particularly clear, with a new moon, so we turned into astronomers and went out to look at an array of stars impossible to see in the town. The highlight was a spectacular view of the comet Hyukatake heading down towards the horizon with its tail streaming out behind.
The farmhouse we stayed in was comfortable, although the faulty fire alarm at 3 o’clock on Sunday morning came as rather a shock, and the welcome was friendly, particularly from the inseparable pony and goat often to be found investigating the cars. A generous supply of extremely good food kept us going for the weekend, and the rest of the week.
Patricia Thomas
Yes, several of us saw the seal, an Atlantic Grey Seal (says David) On the Monday morning ten of us gathered at St Justinian to catch the boat across to Ramsey Island, only to be told that the strong overnight winds had produced a swell too big for us to land safely. Out came the contingency plans and we drove a couple of miles round to Whitesand Bay. ______
A Visit to Barton Hills, Barton-le-Clay, Beds. Led by Dr Jill Eyers 4 July 1996
On that warm summer evening, a large group of us from WH branch gathered at St Nicholas' Church, Barton-le- Clay. Jill led us, far from the madding crowd, up into the Lower and Middle chalk of the Barton Hills. As we followed the path leading up into the hills, Jill encouraged us to continually look around at the path and surrounding country to recognise the changes in vegetation, gradient, soil, clay and chalk exposures along the way.
Our first stop was a spring producing crystal clear water, marking the base of the permeable middle chalk, resting on the less permeable lower chalk (clay chalk). The transition was quite distinct, marked by a sharp change of gradient and vegetation character. At the spring, a bottle of whisky appeared (Jill?) and a brief taste analysis of the spring water was carried out by those present (scotch on the impermeable rocks).
After clambering up the steep north scarp of the middle chalk (The Stairway) we reached the upper chalk and traversed the ridge, eastward, toward the top of Windy Hollow. On the ridge, looking North, we took in the fine view looking out over Windy Hollow across the flat Gault clay country towards Bedford. This was really enjoyable, and so close to home. From the ridge, the base of the middle chalk was easy to spot as a more competent horizon (some 3m or so in thickness) at the base of the scarp. This horizon was identified by Jill as the Melbourne Rock. A copy of Jill's hand sketch is given below.
We dropped down into Windy Hollow where Jill pointed out some classic indicators and features of past glaciation and generally colder times. Windy Hollow, it is supposed, is an example of a dry valley formed under conditions of sub-surface permafrost. The joints in the chalk were filled permanently by ice allowing surface water to run off as streams on the surface. A stream eroded the upper parts of Windy Hollow in a way which could not have occurred in a warmer climate. In warmer, post glacial times, the joints in the chalk would have thawed allowing sub-surface drainage to dry the valley out.
10 Years of GEO-LOGs 6 Further down Windy Hollow Jill pointed out small scarps in the chalk, and the fans of debris which make up the hummocky ground in the hollow. This, she said, might be due to a combination of freeze-thaw activity loosening the chalk, and solifluction transporting it in slumps down into the valley.
On the gentler slopes, the characteristic terracing caused by soil creep was clearly visible. According to Jill, this again might be caused by freeze-thaw action - not rabbits or sheep as some might suggest. The soil blanket is lifted by particle separation during freezing, directly away from the sloping rock surface beneath. During the subsequent thaw, the soil particles fall back vertically to a slightly lower level than before.
Our next stop was the pub in the village. Many thanks Jill for a pleasant reminder of all this interesting stuff so close to home.
Pauline Catchpole and Tom Miller ______
1997
In 1997, WH Branch organised several good field trips, including:
• A weekend in North Norfolk with Dr Jill Eyers and Dr Charles Turner • A day in Bradgate Park with Ian Rigby, and • A weekend in North The Forest of Dean, with Dr Clive Roberts
All well attended and thoroughly enjoyed…. ______
A Weekend Field Trip to North Norfolk to look at the Quaternary Geology "The Ice Age in Norfolk" Arranged by Susie Hall. Led by Drs Jill Eyers and Charles Turner 9-11 May 1997
This is a report on a memorable weekend spent by members of Walton Hall and East Anglian Branches in North Norfolk, on the coast and inland, investigating the Quaternary geology. The weekend was organised by Susie Hall, and led jointly by Dr Charles Turner and Dr Jill Eyers. In an earlier introductory talk (in April) Charles described the Quaternary history of the area. The warmth of late Tertiary times gave way to the first chills of the coming ice age(s) during the early Pleistocene (about 2.5 Ma ago) when the ericaceous heathland of the area was subjected to the alternating temperate and cold spells of the Beestonian stage. Throughout the Pleistocene there followed a succession of glacial and interglacial stages, which Charles outlined below.
Prevailing Stratigraphic Began Representation/Features in East Anglia Conditions Stage Name Interglacial Flandrian 10 ka ago Glacial Devensian 115 ka ago Last major glaciation, Blakeney ridge? Interglacial Ipswichian 130 ka ago Deposits at Ipswich, Cambridge Glacial Wolstonian Outwash gravels, Poorly known Interglacial Hoxnian Deposits at Hoxne, Nar Valley, Marks Tey Glacial Anglian 500 ka ago Lowestoft and Cromer Tills Interglacial Cromerian 750 ka ago Cromer Forest Beds Alternating Beestonian Significant gap in N. Norfolk stratigraphy 2.6 Ma ago Ericaceous heathland
Charles indicated that in East Anglia much of the Quaternary succession is missing, having been obliterated by later glaciations. Assembly of the stratigraphy has therefore been extremely difficult, requiring unorthodox methods such as detailed study of pollens in interglacial deposits and analyses of the oxygen isotope ratios in the foraminifera from the sea floor. So what did we actually see in Norfolk?
Saturday 10th May - West Runton
The first rock we looked at in Norfolk was Larvikite! There were huge blocks of it in the sea defences at Sheringham. We examined it briefly before setting off to the first location at West Runton. Moving on swiftly.
10 Years of GEO-LOGs 7 On the beach at West Runton we found ourselves facing cliffs of glacial till, overlying a thin horizon of very dark, complex material. Charles mentioned the effects of “glacial tectonics” to be seen here, and to westward of West Runton. We were looking at deposits of lower and middle Pleistocene age here; the Lowestoft Till of the Anglian glaciation resting as fallen blocks on the dark, organic layer of the Cromerian interglacial fresh water bed.
Moving east toward East Runton, the dark Cromer Forest Bed disappeared beneath the cliff base. Charles scooped out a small hole at the base of the cliff wall, about 1.5 m deep, to reveal a gravelly layer indicating a marine transgression overlying the dark Cromer Forest Bed. In the sand/clay till above the transgression horizon could be seen small “sand volcanoes” caused (suggests Charles) by compressional fluid movement.
At Goss Gap, a large collection of fossil fauna had been found, also a sizeable piece of erratic pink granite.
Further east, the cliff contained contorted, homogeneous bedded sands high up, overlying inhomogeneous tills which had flowed and distorted under loading. This is complex to the eye, affected both by ice compression and melting. These are the deformed Cromer Tills, which also contain huge rafts of chalk and Cromer Forest Bed. We were intrigued to see the vast blocks of homogeneous chalk “floated” on younger in-homogeneous tills beneath.
Sidestrand
After lunch at West Runton beach cafe, we drove east to Sidestrand. Here the huge chalk rafts were particularly impressive. Further along, the chalk blocks were overlain by cross-bedded pebble lag, lifted in-situ on top of the chalk blocks. Later, we drove further east to Happisburgh.
Happisburgh
At Happisburgh, walking SE along the beach, Charles pointed out an interesting contact of thinly bedded lacustrine clays with occasional ripple structures, overlying a thick bed of dark marine silts/clays. In the dark marine silts/clays there were shell fragments and small stones, unlayered and unsorted. Charles identified this as a marine till; from the North Sea floor (Cromer Till?). The thin layering in the lake clays were not varves, but were interpreted as subaquatically deposited turbidite cycles?
Sunday 11th May
Sunday was spent looking at landforms and periglacial surface features, at various sites near the coast and inland.
Blakeney
The first location was Wiveton Downs Gravel Pits just inland from Blakeney, on the Blakeney ridge. After an interesting drive out from Sheringham we all eventually assembled in the Downs car park on the top of the ridge. The Blakeney ridge, according to our field notes, is a NW-SE trending sinuous ridge of sand and gravels, about 3 km long and 100 m wide, and reaches a height of 15 m above the surrounding land.
Charles suggested that the ridge is probably a large esker of Devensian age, and took us to an excavated exposure of the Cannonshot Beds on the ridge, close to the car park. The Cannonshot Beds here are a clean pile of large, well rounded flint cobbles averaging 5 to 15 cm diameter. On examination, the cobbles are clean, clast supported and show considerable surface abrasion suggesting high energy transport to their present location. The sorting is good, but not good enough to suggest a beach environment of deposition. An interpretation of the cannonshot cobbles is that they were transported and abraded by occasional high speed “thrashing” through ice tunnels in/under a glacier, carried by melt water power. Many of the cobbles are almost perfect spheres - hence the name "Cannonshot Beds".
We walked some distance along the ridge comparing vegetational preferences on-ridge, and off-ridge on the calcareous marly drift. We could see a kettle hole (or kame?) in an adjacent field.
Telegraph Hill and Kelling Heath
Our second location was Telegraph Hill and the outwash plain of Kelling Heath. Telegraph Hill is interpreted as a terminal moraine, or perhaps a kame feature from a later (short) glaciation. The ericaceous vegetation on the hill indicates it to be a well drained, gravelly deposit.
East Walton
After lunch at the pub, we drove the 30 (or so) miles to East Walton near King’s Lynn. On Walton Common, East Walton, there are many shallow rimmed kettle holes of varying sizes from 10 m to 100 m diameter.
10 Years of GEO-LOGs 8
It is believed that these kettle holes are the result of melting out of ground ice lenses which formed where springs arose, during the last part of the Devensian cold stage.
In times past, the locals grew hemp/jute here, and used the hollows for soaking the fibres.
This was a splendid weekend enjoyed by everyone. Thanks to Charles’s and Jill’s willingness to share their knowledge, and the comprehensiveness of the field notes, we are all now much better equipped to appreciate the geology of the area.
Tom Miller and Dot Hill ______
A Day Trip to Bradgate Park (Charnwood Forest) Leicestershire Arranged and led by Ian Rigby 28 June 1997
Gerry and I decided to brave the continuing drizzle and rain of two weeks to visit an area we frequently drive past on the motorway; at last we get a closer look at rocks analogous to those stripy lumps in the cuttings near Leicester. After meeting at Leicester Forest services, our first locality was a disused quarry of Markfieldite, a granodiorite unique to the area, and dated at about 550 Ma (Ma = million years). This rock is used in British Rail car parks and between railway lines; note the pink feldspar - the colour is due to iron staining!
The rocks here are Cambrian and Pre-Cambrian in age. The geological periods are shown on the left.
At Beacon Hill Country Park outcrops of a fine grained massive rock, with a finely laminated bed above: a tuff deposited in water, now silicified to a very tough tuff! The rocks fine upwards - the cleavage shows a refraction pattern just like in a seismic profile (Snell’s Law....)! The cleavage to bedding indicated an anticline plunging to the south east.
After a brief shower the clouds lifted, the temperature rose and there were even patches of blue sky, three cheers for Dave Maddock’s magic helmet!
At Hunts Hill (Bradgate Park) our leader vanished into the bracken, muttering that the outcrop was there somewhere, after much crashing about backwards and forwards, it seemed he had located it - felsic agglomerate. The clasts were similar to the banded tuff of the previous locality in a less tough tuff; we were on the site of a Precambrian explosive eruption...
Further into the park cleavage to bedding relationships showed we were at the nose of the anticline plunge .. the deer on the level below marked the axis!!! The concentric rings on one outcrop (more tuff) was the fossil Charniodiscus Concentricus. The secondary cleavage was due to interlayer slip during folding, and there were even some neat little en echelon tension gashes between some beds.
Not too far away, past those strange circular ponds (meteorite craters? dinosaur hatching ponds, dew ponds, WW2 bomb holes?) an amazing oak tree was splitting apart more of the tuff. As well as larger clasts, there was slumping of the tuff (possibly a lahar deposit?) and on the other side of the exposure a bomb sag, but the bomb had been eroded away.
By now it was already 5pm, so Ian Rigby rounded off the day by summarising the story: The calcalkaline volcanics indicated the subduction of an ocean plate, with the Cadomian Ocean northwards beneath the Midlands craton. These Charnian deposits were folded and the intruded by the granodiorite; they now form an inlier surrounded by younger cover.
It was a full and very enjoyable day, with Ian Rigby explaining all the features clearly and a building up a fascinating story of the Precambrian Charnwood area. I look forward to his next field trip with us.
PS. The moral of the car parks is “take lots of change for the pay-and-display meters” Judith L Kelly
10 Years of GEO-LOGs 9
1998
Judith and Gerry Kelly introduced our youngest ever member to the February meeting, baby Christopher - borne early January this year.
Jenny Bennett was elected Branch Organiser for Walton Hall Branch.
Sarah and Steve Davis, who met each other through Walton Hall branch, were married on St Valentines Day this year, in Barton-le-Clay Village.
A big THANK YOU to David and Elizabeth, as they depart our region to live in Wiltshire. ______
Return Visit to Ketton Quarry, Near Stamford Led by Alan Dawn 23 May 1998
A group of approximately 20 people met with Alan at 10.00 am at the entrance to the geology trail, Pitstone Lane, Ketton - the site of the old Grange Quarry. Alan began by leading us around the geology trail, which gave us a preview (in miniature) of the strata we would examine in the main quarry.
Our first stop was to look at the Upper Lincolnshire Limestone and Alan explained this section as a back reef facies micritic mudstone - fine mud cemented with calcite. The main part of the upper Lincolnshire Limestone here is a pure oolite; massive, but in places cross-bedded. Parts of the quarry contain wholly uncemented "oolite sand", with much of the oolite being porous and only lightly cemented. This is the famous Ketton Freestone, often used for buildings, so named due to its lack of preference in cutting or working in any direction to make different shapes.
Figure 1 Ketton Quarry Section
Alan then explained, at the second location, the cyclic clays and shelly beds of the Rutland Formation which lie above the Lincolnshire Limestone (see left). After quarrying, these are used for making cement. It was in the foot of the clay beds, within the layer of ironstone nodules, that a Cetiosaur was found. This skeleton can now be seen in Leicester Museum.
The group then moved by car to Ketton Quarry itself. The ground was considerably drier than on our last visit and the sun shone on the almost lunar landscape of one of the largest working quarries in England.
The group discussed how the two-coloured appearance of the Blue Heart limestone - blue rag limestone - could have been formed. Alan explained how this oolitic limestone had become blue/grey in colour due to a primary (low-oxygen) breakdown of iron pyrite, but had later become yellow along joints where oxygen could reach to achieve a more complete oxidation of the iron. This was evident in the freshly broken blocks which showed the distinctive blue centres. Perhaps on first sight it was wrongly assumed that weathering had darkened the stone.
The upper quarry is in the Rutland Formation, previously known as the Upper Estuarine series. Here, Alan explained how changes in sea level, Earth movements, etc., affected the estuarine conditions to produce a sequence of transgressive-progradational cycles across a coastal plain. This section was particularly spectacular, with contrasting exposures, some clearly containing rootlets in the clays between the shell beds. The Blisworth Limestone, a fine- grained shelly limestone with marl interbeds, overlies this.
Overlying the Blisworth Limestone is the Blisworth Clay; the topmost part of which records a new marine transgression, the Cornbrash.
10 Years of GEO-LOGs 10 Of particular interest at Ketton are the series of spectacular faults, which have been exposed during quarrying. We saw evidence of a graben system the possible age and cause of which Alan discussed with us. The harder limestone strata above slid over thick beds of Liassic clay, creating a shallow anticline and extensional graben faults.
Alan had told us that recent quarrying had exposed a site of significant archaeological interest. Towards the end of the visit, he led us to an early Christian burial site of Roman age, which was currently under excavation. Here, we offered thanks and a gift to Alan and his wife Pauline, who had duly accompanied us. I was particularly grateful to Alan for leading us around Ketton Quarry again. His health has suffered recently, but he leads as busy a life as he can! As all agreed, Alan's enthusiasm for leading groups to Ketton never fails.
Finally, with Alan Dawn's choice of car parks, most cars will fail their next MOT's due to damaged exhaust pipes! The trip was so extensive and exhausting that eight people remained behind and will probably be featured in the next archaeological dig publication!
Pauline Catchpole ______
1999
Very Sad News - 30th October 1999
We were very sorry to announce the sudden death from a massive heart attack of Peter Francis in Paris on Saturday 30 October, at the age of 54. Peter was one of the leading UK volcanologists of his generation and is sadly missed.
Congratulations to the S260 Geology Course Multimedia Development Team!
Dave Rothery (Course Team Chair) and Glynda Easterbrook (Course Manager) went to Finland in November to represent the S260 Geology Course Team at the Final of the EUROPRIX 99 multimedia competition, for which the S260 CD-ROMs had been nominated. To our delight, S260 was chosen as the winner in the "Knowledge and Discovery" category, for which there were 118 entries from all over Europe. ______
Field Trip to Hawaii Led by Dr Peter Frances (OU) and Dr Dave Rothery (OU) February 1999
Aloha! Valentine’s Day 1999 was ten hours longer than usual due to the time difference between Great Britain and Honolulu where our party arrived late in the evening of Sunday, 14 February. We were greeted by our leaders, Peter Francis and Dave Rothery, and were garlanded with the traditional leis made of fresh flowers before being driven to our hotel in Waikiki.
Our geology programme started in a very gentle way on the Monday afternoon with a coach trip around the south- east of O’ahu to take in the features and sights of the Koolau shield volcano which was built up between 3 and 1.5 million years ago. The original shield shape has been incised by numerous valleys between which individual lava flows stand out. Half of the shield is missing as a result of massive landslides: bathymetric surveys in the early 1960s identified tongues of debris stretching over a hundred kilometres under the sea from O’ahu and the neighbouring island of Molokai.
10 Years of GEO-LOGs 11
Figure 1 The Hawaiian Island Chain
During our afternoon tour we visited Diamond Head tuff ring: we walked into the impressive crater which is about 1 kilometre in diameter and about 100 metres high for most of its rim; it rises to 232 metres on its south-western extremity. North-east trade winds must have been blowing strongly during the eruption to cause this asymmetry. The name Diamond Head came about because sailors who visited there thought that the calcite crystals they found were diamonds. We made several more stops and at one location found a large block of coral reef included in the tuff. We learnt that this block may be in place or may have been broken off during the Koko Crater eruption. The south- eastern end of O’ahu consists of the Koko rift vents which are some of the youngest in the Honolulu volcanic series. The deposits are the result of a phreatomagmatic eruption - these explosions are caused by the interaction of hot magma and water and occur when a vent opens in shallow water or in wet sediments.
Our first full day of geology took in Kapaa Quarry where we marvelled at the dykes (or dikes as Americans have it!) Erosion has removed the top 1 km of the Koolau volcano to expose the dyke swarm which has been intensively studied by Dr George Walker of the University of Hawaii. He estimated that in places the ratio of dykes to pre- existing rock reaches 2:1, there are about 7400 dykes with an aggregate width of 3-5 km. The thought that the body of the volcano had to be pushed apart 3-5 km to accommodate the dykes is mind-boggling and I think none of us had ever seen dykes like these before and probably never will again.
Figure 2 O’ahu Island
Our lunch stop that day was on the beach and most of the group took the advantage of a dip in the ocean - it’s hard work being on a field trip! Back on the geology trail we saw text-book examples of pahoehoe and a’a.
Wednesday was our last day on O’ahu and after a stop to look at post-erosional tephra we went to the University where we were to have two lectures. First, however, we were taken down in an elevator from the car park to view a massive lava exposure - this lava sits on a coral platform The first lecture by Steve Self gave us a comprehensive introduction to the volcanoes on Big Island - Kohala in its erosion stage, Hualalai in its post shield alkalic stage, Mauna Loa in the late shield stage, Mauna Kea in the post shield late stage and Kilauea which is still active, plus the embryonic island of Loihi which will emerge in about 60,000 years. Then we had a talk by Peter Mouginis-Mark about his work using remote sensing, mostly from satellites but also using more down to earth methods.
Our next destination was Big Island and with limited space it is only possible to mention a few of the highlights. The weather was perfect for our ascent of Mauna Kea. We were warned that to drive from sea level to just under 14,000 feet might cause problems and a few of us were quite content to wander around very slowly near the Observatory: however, the hardy majority walked up another couple of hundred feet to the summit. It was quite spectacular - the abundant scoria cones sprinkled with snow, with brilliant sunshine and blue sky, should give some amazing photographs. On the way up the mountain we had superb views of Mauna Loa. On our way back to Hilo we stopped off to clamber through a lava tube.
The following day we spent some time in a lava forest: it was an amazing sight - moulds of trees which had been engulfed by lavas from Mauna Ulu: fast flowing lava chilled enough to set around the trees, incinerated them and then drained away, leaving the moulds standing. Our lunch stop was in Mackenzie State Park where we had fine
10 Years of GEO-LOGs 12 views of the coastline: massive ledges are the cores of a’a flows; Dave Rothery found the seaward end of a large lava tube for us to look at. After lunch we went to look at a littoral cone which was formed when lava entered the sea and fragmented to form piles of debris: as this was the site of an abandoned quarry we were able to see some of the internal structure of the cone. The day ended with a walk over the lava from the eruption from the Puu Oo vent on the East Rift Zone of Kilauea, that buried the town of Kalapana in 1990. It was like walking on the illustrations in a geology textbook - superb examples of pahoehoe.
Figure 3 Hawaii Big Island
It was now Friday evening and we were all looking forward to moving to Kilauea Military Camp where we were to spend three nights on the crater rim. It started to rain very heavily at about 8 pm and over the next three days we had 12 ½ inches! I was unfortunate enough to be ill so missed one day in the field - but also avoided getting soaking wet. One of the memorable things apparently was eating packed lunches in the Thurston lava tube, the only place where it was dry - well, relatively dry. However, the stalwarts were rewarded with finding examples of Pele’s tears - solidified tear-shaped droplets of lava.
We were privileged to be able to go to the Hawaii Volcanic Observatory where several of the scientists told us about their work.
To enable continuous monitoring of the volcanoes there is a 65 station network on the island and radio telemetry is used to bring data to HVO. We heard from a gas geochemist about the monitoring of sulphur dioxide and the problems of "vog" - volcanic smog - affecting the Kona coast and stretching as far as other islands.
The real highlight of our stay there was the long walk over recent lava to the ocean entry: the previous evening we drove as far as we could and saw the glow in the distance as the lava emerged from its tube and dropped into the ocean, sending up plumes of steam; we could also see patches of red in the distance indicating skylights in the lava tube. The morning of our walk was dry and sunny and we all got very hot, not only from the brilliant sunshine but also the nearer we got to the ocean entry the warmer the lava over which we were walking. At the end of our trek we were rewarded by the spectacular view of the steam but, unfortunately, we did not see any "red stuff" as the lava was contained in a tube. The glassy surface of some of the lava looked golden and there were lovely examples of Pele’s hair - thin threads of golden glass spun as the tails of lava droplets fall.
Our final stay was on the west coast at Kailua Kona where we were able to enjoy a day of rest in the sunshine - this meant shopping, swimming, snorkelling, whale watching. We had a festive evening, starting with a cruise along the coast in a chartered boat - our leaders modelled the grass skirts they were given - and then we had a group dinner in a restaurant on the sea front.
Our final day took in the two older volcanoes Hualalai and Kohala: the highlight for the fit was a strenuous hike to find nodules of olivine and they came back very hot but with beautiful samples. We had a chance to see trachyte lava, relatively rare in Hawaii as it is confined to the post-shield alkalic stage.
How does one sum up a field trip like this? It was a fantastic experience and those of us who were lucky enough to participate are enormously grateful to Peter Francis and Dave Rothery for their excellent leadership and a big "thank you" to Dot for all the work she had done for a long time in making it all happen and to Linda who was her deputy and a great support out there.
Elizabeth Maddocks ______
North Devon Coast - From Millook Haven (Near Bude) to Ilfracombe Led by Ian Rigby 29-31 October 1999
This weekend field trip, led by Ian Rigby, was very well attended and will live long in our memories. We had a great time during that weekend. We visited the North Devon coast at four locations; Millook Haven, Bude, Hartland Quay and finally Ilfracombe. At these places, we looked at the Variscan folding and deformation, way up structures, and numerous small-scale sedimentary features. During Saturday evening we discussed the regional tectonics and the structural units left to us in these late Devonian and Carboniferous rocks.
Our accommodation at Hartland Quay was really interesting. The Hartland Quay Hotel is what remains of an old fishing port that once existed below the cliffs, south of Hartland Point. This is a really atmospheric little place. Our
10 Years of GEO-LOGs 13 first field location was Millook Haven, south of Bude. I'd been past there before (on the road), but I had no idea of the splendour in the cliffs to seaward of the road. After walking down the hill to the pebbly beach we were greeted with the sight of large zig-zag (chevron) folding in the cliffs. "Which way up is it?" was Ian's first question.
In short, Ian showed us no less than 5 ways of determining the way up of the beds shown in this photo:
1. Grain size grading (fining upwards on the "right way up" beds).
2. Flute Marks (on the sole of the "right way up" beds).
3. Compression lineation (bedding angle steeper than lineation angle = upside down).
4. Tension gashes (in the upturned beds, gashes wider at the top = upside down).
5. These are "S" forms (remember Zs & Ss of parasitic folds).
You can just see the tension gashes in this photo. Ian showed us that the vergence (compression field?) shown here was from the northwest. You can see the layer parallel slip faults in the right way up bit. My apologies Ian if I got this wrong!
Walking back towards the beach access, Ian pointed out some small-scale structures in the cliff, including a neat tip-line fold showing excellent cleavage development, and with a small fault displacing the lower limb.
Our second location on the Saturday was Bude. As we arrived in Bude, the weather turned really bad. It had not been good all morning, but this was steady rain and looked like setting in for the day. We ate lunch in the cars, then set out in the rain towards the beach. Out on the beach, the wind howled and the rain hammered down on us. We were all driven into a tight huddle under a low arch in the stone sea wall. We could see nothing. Ian shouted the main points of interest about the geology, above the roaring wind.
At last, the wind abated and the rain slowed, and we could wander out over the beach area. There were small- scale, hog's back periclines here (east-west orientation?) and tight but rounded folds with a different form and orientation to the chevrons at Millook Haven. There were several stratigraphic contrasts here, ranging from deeper sediments to rippled beach horizons, all within 100 metres or so. This was a really good stop, but was spoilt rather by the weather.
By the evening the weather had improved considerably. Some of us explored the Hartland Quay locality and then visited the lighthouse at Hartland Point before dinner. After dinner, Ian gave us a talk on the overall structural setting of the region. He referred to the following model (from Sanderson 1982).
10 Years of GEO-LOGs 14 According to the proposed model, the Variscan deformation of the region took place from late Devonian times to the end of the Carboniferous. It incorporated the Lizard obduction and significant crustal shortening (50%) throughout southwest England. A thin-skin model is preferred (with no deep root), but this makes the granites awkward to reconcile. Anyway, Ian described the main tectonic unit that we now have in the region, as a "Y" shaped synclinorium. This was thrust up from the southeast, and extends for 50km from northeast to southwest.
Tom Miller ______
2000
A Very Sad Year
Early in the year 2000 we were very sorry to learn from Linda McArdell, of the death of her husband, David.
Later, in September, we were again sorry to learn of the death of our branch member John Leadley. His quiet enthusiasm is sadly missed.
Also, in the same year, we gave a Hearty Thanks to Dr Peter Sheldon, whose term as President came to an end.
We welcomed Professor Bob Spicer to the Presidency of the Society, and also to Carol who we all met at the AGM at Shap Wells. ______
Visit to GEOU ‘Fossil Factory’ - OU Campus WITH WALTON HALL OUGS 19 February 2000
All of you who have taken OU Geology courses will be familiar with the fossil replicas that form part of the Home Kits. Far fewer of you will know where and how they are produced.
This trip originated over a year ago at Jenny Bennett’s house warming party in Hitchin. Dave Williams was chatting to me over a plate of goodies and fell victim to one of life’s most potent threats:- a committee member looking for possible site visits or lecturers. Being the kind man he is, Dave readily volunteered to take a party round the GEOU ‘fossil factory’.
The visit started with a very informal ‘lecture’ sitting round a table drinking tea/coffee and eating biscuits while David told us in fascinating detail (much of which I promised not to reveal) how he had found himself as General Manager of GEOU. Early evidence of his modelling skills came when was 8 years old and won a prize for the general structure and aesthetic beauty of a batch of rock cakes! Further fame followed at age 10 when, in one of his school reports, he was praised for his dexterity in modelling with powdered sawdust. And so, the die was cast (unintended pun). Interrupted only by a lifetime as a geologist, OU tutor, Course Leader, OUGS guide, etc. he moved inexorably towards his new career in the production of fossil replicas.
Apparently, in the early years of OU geology courses (S2.3., S236), there was fairly strong opposition to any ‘hands on’ element to the course with Home Kits being regarded as too expensive. However, sanity prevailed and an embryo HK was finally sanctioned. This included a basic but usable microscope (mass produced as a ‘one off’ enterprise by a very talented engineer called Mr Sato), rock specimens and fossil replicas.
At this stage, a fossil collector called Stuart Baldwin enters the story. Stuart had been collecting fossils for some 20 years and, most importantly, had researched, labelled and catalogued his collection. He decided to combine business with pleasure and started to produce good quality replicas for museums, universities, etc. Ian Gass and Chris Wilson chose Stuart Baldwin to be the official supplier for the OU and the rest is history. Quantities were large, with S102 requiring 5000 Kits each containing 12 fossil replicas!
In the mid-1990s, Stuart Baldwin decided to sell the business and invited offers from various organisations. Dave Williams recognised that since the OU was his major customer it made sense for the OU to purchase the business and produce its own fossil replicas. After much negotiation Dave persuaded his masters to purchase the business. For his sins, Dave was appointed as the General Manager of GEOU (Geological Enterprises Open University) - an educational charity and part of OU Educational Enterprises.
10 Years of GEO-LOGs 15 In mid 1995, Dave collected some 1600 fossil moulds from Stuart Baldwin and slowly established a workshop/store on the ground floor of the Earth Sciences block at Walton Hall. He had no formal business training and his ‘modelling’ experience was confined to the rock cakes and sawdust mentioned earlier - a steep learning curve if ever there was one!
It was decided that the OU would be supplied ‘at cost’ whilst supply to other organisations would be on a commercial basis. Customers include museums, schools, universities and private collectors in Britain, U.S.A., France, Germany, Australia, the Middle East and Japan. Total output runs at around 70,000 items each year, which includes some 30,000 fossils as part of 5000 disposable kits for S103. In addition to fossils, GEOU buys in items such as hand lenses and maps so they can supply complete Home Kits.
The range of fossil moulds was slowly expanding, as was the customer base and it soon became apparent that Stuart Baldwin’s original catalogue was in need of a major update. The cost of a new printed catalogue was prohibitive and it was decided to grasp the opportunities of new technology and create a database that could be searched via the Internet. With the able assistance of a certain John Colby, the database was established and now includes 1841 specimens each with Description, Period, Age, Cost, etc. Work is in hand to provide a picture of each specimen.
Finally, we come to the field trip! Dave showed us the tiny workshop where Stuart Baldwin’s original moulds are stored and the adjacent room where mass (re)-production takes place. It is difficult to grasp how so much gets done in so small a space.
The process looks deceptively simple but much practice is needed before true expertise is established. There are several stages:-
1. A silicone rubber Master Mould is taken of the original fossil (or a cast of a fossil). Protection of the original can present many problems. Single sided moulds are the simplest but three-dimensional specimens (a T Rex skull with teeth for example), present a much greater challenge and may require moulds to be taken of different parts of the fossil.
2. A Master Cast in plaster/resin is produced from this mould. For the simple, single-sided specimens, great care is needed to avoid air bubbles. For the complex, 3D-specimens many Masters of different parts of the original may be produced. Casts from these masters are assembled later to reproduce the original specimen.
3. Secondary Moulds are then produced from the Master Cast.
4. The Master Cast and Master Mould are stored carefully and not used in the mass production process.
5. Plaster/resin ‘copy’ casts are then produced, often in large numbers, from the Secondary Moulds.
6. The final appearance can be made more realistic by using coloured resin or dipping the white cast in various colouring agents. More specialist treatments include colourants that simulate bone or iron pyrite replacement. More dense plaster or resin may be used to give the replica the right weight.
We also visited the main store where the larger specimens are stored. This included what for me was the star of the show, a superb, boxed replica of a Pterosaur fossil complete with incredibly detailed feathers. The store is also home to the rock samples for the Home Kits and it is here that they are slabbed and then cut in small cubes; another huge but essential task.
Finally, we had plenty of time for some hands-on experience. Armed with moulds, resin, water and paintbrushes we all sat down to produce our own masterpieces. I find it fascinating to watch young children deep in concentration on any task but to see a group of adult students in the same situation is even better. I so wish I had taken a camera! We all left clutching our bivalve or micraster models each thinking they were the best ones ever made - I know mine was!
When I sat down to write these ‘field trip’ notes I thought they would occupy about ten lines. In the event, they include a potted history of the geological Home Kits which we all know and love and which have made geology courses so much easier to understand. They also reveal the very important part which Dave Williams (and many
10 Years of GEO-LOGs 16 other tutors) have played over the years in helping students and OUGS members to gain so much from their studies and interest. Sorry if this embarrasses you Dave but many thanks from us all.
John Stanbridge ______
A Journey Through Namibia With Elizabeth & David Maddocks May 2000
In May 2000 David and I travelled over 4,000 km to savour the wonders that this country has to offer in its geology and its wildlife. As David said in his talk following the Branch AGM this is a country of landscapes with geology like an open book.
Figure 1 Namibia Map
We picked up our little Toyota Corolla at Windhoek Airport and headed north to Etosha National Park. On the way, we visited Otjikoto Lake which is situated in 700 Ma dolomite and represents a karst lake which formed when the roof of part of a large cave system within the dolomite collapsed. As the floor of the cavity was lower than the groundwater level, a lake was formed. Otjikoto has very steep sides, it is 100m across and, at its shallowest is 55m deep. The full extent of the karst groundwater system is not known. It was extraordinary to come across something like this in such a dry country.
Figure 2 Otjikoto Lake
"Etosha" means "great white place" and exactly describes the seemingly endless plain of the Salt Pan. This is approximately 1200m above sea level and 4600 km2. Looking across the Pan in the heat it was difficult to believe that during the Gondwana Ice Ages a huge glacier scoured out this depression. The climatic change over millions of years meant that polar conditions were displaced by the hot arid desert. Originally, melting of the glacier formed a large lake. In good rainy seasons the shallow depression fills with water but evaporation in the burning Namibian sun leaves a hard salt crust. Along the southern edge of the Pan there are natural water holes which attract so many animals.
On our way towards the coast we visited several sites of geological interest. In the "Petrified Forest" we saw fossil tree trunks 30m in length. The perfectly preserved tree trunks with the smallest details and structures in bark and tree rings mirrored by silica indicate that these giant trees were deposited and immediately buried so that there was no time for the wood to decompose. The absence of roots and fossil soils, and the parallel alignment of trunks suggests that they were felled and transported in some catastrophic flood and deposited where they now rest. The trees have been identified as those which covered vast areas of Gondwana about 280 million years ago. We then visited Twyfelfontain, which means "doubtful spring": here water-bearing sandstone overlies a relatively impermeable layer of shale so groundwater can dam up along the shales to create a spring but this is very rare. The fine-grained aeolian sandstone has a very smooth flat surface on which stone-age bushmen carved images of animals and birds - a lovely example of geology and art coming together. To round off our mini field trip we looked at Burnt Mountain and the Organ Pipes. Burnt Mountain is a purplish-black rounded hill about 200 metres above the surrounding rock: about 125 million years ago huge amounts of lava were injected into adjacent shales and the resultant contact metamorphism resulted in the organic matter being vaporised, leaving a black compact rock. The shales are covered with purple shiny coatings due to the iron and manganese oxides that formed when Burnt Mountain was exposed to the atmosphere.
10 Years of GEO-LOGs 17
Figure 3 The Organ Pipes
The Organ Pipes are dolerite, which solidified into a group of homogeneously oriented columns with mostly hexagonal cross-sections - very similar to the basalt columns we are familiar with on Staffa. On our drive towards the coast we had the eerie view of fog rolling in from the sea: the cold Benguela Current causes an air inversion as cool winds from the southwest are pushed under the warm inland air. Our stay on the coast was primarily so that we could visit the Cape Cross Fur Seal Colony where we saw (and smelt) thousands and thousands of fur seals, but we also had a taste of the Namib when we took what is called the Welwitschia Scenic Drive. The Namib is a coastal desert stretching for 2,000 km, starting in the Cape Province of South Africa and extending northwards along the Atlantic coast of Namibia and up into southern Angola. However, it is very narrow and in Namibia reaches only up to 120 km inland before the Great Escarpment forms its eastern edge. During our scenic drive we had impressive views of the so-called "moonscape" of the Swakop valley. Sediments that were laid down 460 Ma ago and the granite rocks of the Damara Sequence had been deeply incised by the Swakop River. At one point we drove through a huge dolerite dyke formed about 125 Ma ago.Because of its resistance to weathering, the dark dolerite was clearly visible as a long ridge standing proud of the granite. The "welwitschia" is a dwarf coniferous tree unique to the Namib, the oldest one is over 1500 years old but is still less than a metre tall.
The long drive across the Namib to the south of the country was amazing: fabulous scenery with a variety of rock types - inselbergs, granites, sediments and schists - all weathering differently and giving rise to varied topography. Because there had been exceptional rain, there were grasses and flowers in what would normally be bare desert gravels. We drove through the Kuiseb Pass down into the deeply incised valley of the Kuiseb River: this represents the northern border of the Great Sand Sea of the southern Namib. We stopped at the Gaub Pass and looked at evidence of the torrential rain which fell earlier in the year which made the river flood over its banks - a rare occurrence - whole trees had been felled and were piled up by the river bridge.
One of the highlights of our holiday was the journey to Sossusvlei which means "gathering place of water in a hollow which is flooded during the rainy season". Rain comes rarely to this area but it had been very wet a few months before our visit and there was water in the vlei. Arriving early in the morning we had fantastic views of the star dunes (indicating variable wind directions) which looked red in the early light - the colour caused by the iron oxide coating on the sand grains.
Figure 4 Sossusvlei Dunes
Some of the dunes rise to 375m above the Tsauchab River and are amongst the highest in the world. Nearby is the Sesriem Canyon through which the Tsauchab flows. It was an easy walk through the canyon and we were able to see the geological history in the canyon walls: there was a distinct change from fine sandy layers to conglomerates, indicating dramatic changes in climatic conditions.
The final highlight was the visit to Fish River Canyon - second in size only to the Grand Canyon. It was awe- inspiring to look down at the river 549m below. The canyon is 161 km long by 27 km wide and it is possible for the very fit and hardy to walk a 90 km route through it, taking about five days.
Figure 5 Fish River Canyon
10 Years of GEO-LOGs 18 It all started about 350 Ma ago with graben formation. The Gondwana glaciation 300 Ma ago caused further development of the canyon and the breakup of Gondwana 120 Ma ago with the associated isostatic rebound allowed the river to erode down to its present depth. The oldest rocks exposed, belonging to the Namaqualand Metamorphic Complex, are older than 1,000 Ma. Those of you who saw David’s slides will have some appreciation of what it is like but even these do not do full justice to it.
Namibia is a country of superlatives: the oldest desert, the second largest canyon, the highest desert dunes. It has clearly visible rock formations and beautiful landscapes and is well worth a visit. by Elizabeth Maddocks ______
2001
In 2001, Jenny Bennett stood down as our Branch Organiser. Linda McArdell took over and saw the Branch continue in strength.
2001 brought, amongst other things, Foot and Mouth Disease
"Well, dare we say it, the numbers of new foot-and-mouth cases being detected seems to be abating, allbeit rather slowly. Lets hope the trend continues. Perhaps we might yet enjoy some time in the field this Summer. For the present, though, please continue to observe access restrictions, and minimise the risk of spreading the disease."
"GEOLOGY AT THE CELTIC FRINGE" - The Dublin Symposium was this year. Despite the Foot and Mouth Disease curtailing the field trips, the Dublin Symposium was one of the great ones to remember.... The fire alarm during preparations for the dinner. The "extended" address by the Guest Presenter. Splendid ______
A 4-Day Field Trip to Cornwall "To Study the Geology and Its Influence on the Economic Development of Cornwall Over Three Centuries" Led by Dr Dee Edwards and Prof. John Mather 5th-8th October 2001
In early October 2001, a group of OUGS members and friends, descended on the mining regions of Cornwall. A 4- day field visit ensued, led by Dee and John, and well supported by local experts Bruce Grant (RGS Cornwall) and Ivor Bowditch (Imerys). Also in the group were Drs Dave Williams and Peter Sheldon of the OU Dept of Earth Sciences. We were privileged indeed, to have so much knowledge and experience with us.
We stayed in the Atlantic Hotel, on the headland above Newquay. The accommodation was warm and comfortable. The food and wine were good, and the view from the hotel northward up the coast towards Trevose Head was a treat to the eye.
Friday, 5th October - Location 1 - Condurrow Mine
After a good breakfast in the hotel, and a brief introductory talk from John, we set off in our cars for the Camborne- Redruth district, in particular, Condurrow, which is a little to the south of Camborne. Here we were to visit the Condurrow Mine, which is a training mine used by the Camborne School of Mines. Our leader for this visit was Bruce Grant of the Royal Geological Society of Cornwall.
We assembled at the School of Mines depot site just outside Troon, and donned mining lamps handed out by Bruce. We walked for about a mile along an open path to the mine entrance, which was in a locked shed. Bruce unlocked the door and we assembled inside, around the top of the entrance shaft. We were each given a small ID tag to keep with us while we were in the mine. After descending two steep ladders we reached the first level at the top of the main stope.
Although only very low concentrations of radon gas could be measured in the mine, an air pump and trunking were used continuously to vent the mine while we were down there. Several horizontal levels had been built along the stope, at prograssively deeper depths.
10 Years of GEO-LOGs 19 Condurrow Mine is in the Carnmenellis granite and produced mainly copper at first, then tin later during its working life, from about 1700 to 1914. The main stope was sunk to around 2000 feet deep. We descended just two levels, to about 50 metres depth.
We were shown several items of mining equipment, including pneumatic rock drills and diamond-tipped cutters for taking cores and for making exploratory cuts to find new ore bodies. We were shown the complexities of sequenced-triggered blasting, for removal of rock from a working face. This was extremely interesting.
By mid-day we had returned to the surface again, and had handed in our ID tags. We trudged the mile or so back to the School of Mines depot, and with thoughts of lunch in mind we returned our lamps to the store. Just to the south of Carn Brea summit, there's a pub that sells HUGE Cornish pasties. It was quite busy when we got there, and sadly, there wasn’t enough Cornish pasties for everyone. But never mind, we ate well anyway, and without dallying for too long we set off for our second location - Wheal Jane Mine.
Friday, 5th October - Location 2 - Wheal Jane Mine, Tailings Dam
The weather had not been good all day (dull, overcast), but here at the Wheal Jane tailings dam it started to drizzle as we assembled by the cars. We were overlooking the settling lake that takes the poor quality mine waters (tailings) pumped from the Wheal Jane Mine. Here, John Mather explained, there had been a major pollution incident (1991/92) in which a large surge of metal-rich mine tailings had escaped from a plugged adit into the Carnon River. An "ochre" plume of low-pH, metal-rich contamination spread out across Falmouth Bay.
John told us that cleanup operations were continuing, and treatment processes were under development, and being trialled to find a longer term solution to the tailings problem. It seems that while mines such as Wheal Jane are working, there is a continuous need for removal of tailings from the workings. The tailings can be cleaned-up significantly by treatment with crushed limestone, which is trucked all the way from Derbyshire. The treatment takes place in the tailings dams. This raises the pH to a more environmentally acceptable level and removes the metal pollutant. However, this takes time and is enormously expensive. The costs must be met by the taxpayer.
After viewing the tailings dam and considering the effects on the environment (not insignificant in the Carnon Valley), we drove down to Bissoe Bridge over the Carnon River. Here there is a Pilot Treatment Plant that attempts to clean up a portion of the flow by a process of aeration/oxygenation and organic assimilation of the pollutant using tolerant water reeds. This treatment plant, for all its size, can handle perhaps 2% of the tailings flow. John explained that the treatment could work, in theory, but a practical realisation that could cope with the full tailings flow would probably be impossible to achieve. The final notion he left us to consider, was "is it all worth it?". The weather brightened-up. We finished off the day with a pleasant walk in the Carnon Valley to look at the County Adit (built in 1800s) near Twelveheads. It seems that mine drainage pollution is nothing new in this part of Cornwall.
Saturday, 6th October - Location 1 - West Penwith
Saturday morning the weather was very pleasant. We set off for the Penwith district in the far west. The plan was to drive all the way to St Just, near Cape Cornwall, get carry- out lunches in the supermarket and proceed in convoy to Botallack.
Figure 1 West Penwith
On arrival at Botallack, we walked a short way northward along the coastal path and then clambered down the slope to seaward to examine some very old surface workings. Here there had been some tin "floors" that had been worked out of the granite. All that remained were a few broad pillars of tourmaline, supporting the cave roofs. We clambered further down the slope towards Botallack Head and the Crown Engine House. This is where the metamorphic aureole on the edge of the Land's End granite is well exposed. We found sworling, folded patches of pelitic country rock, in amongst large, altered basalt bodies. Further down, beneath the engine house, traces of magnetite could be detected here and there, giving strong perturbations of the compass.
10 Years of GEO-LOGs 20 Returning back to the hill top, we came upon the remains of an Arsenic Calciner. See below.
Figure 2 Arsenic Calciner
The tin ore was roasted in arsenic calciners of this type, to remove the arsenic and surphides as vapours. The vapours condensed on the walls of the stone labyrinth, away from the fire. The resulting solids were removed occasionally from the walls of the labyrinth, to maintain the efficiency of the process.
After a short museum stop in Botallack, we returned to the cars and drove back to Cape Corwall to have our lunch. "Rather an eat here, let's take the short walk along the path to the beach and have lunch there" said John Mather. An hour's foot-slog later (well, it seamed like it), we made it down to the "beach" (Porth Ledden Cove) below Kenidjack Castle, and had lunch.
Saturday, 6th October - Location 2 - Cape Cornwall and Porth Ledden Cove
Exposed at the shoreline here is a spledid contact of the granite with the country rock. After lunch we spend a long time studying the contact, and features in the granite that spawned many very interesting conversations. There were many interesting inclusions and curious alignments of the large feldspar crystals in the granite, near to the contact.
Figure 3 Porth Ledden Cove
It was good to have so much knowledge and field expertise with us. Peter Sheldon found a dark inclusion in the granite that had had long feldspar crystals nucleate on it. These had grown out radially from it like small tree trunks. There was a great deal of tourmaline in the upper part of the granite, overlying the section that had the large feldspar crystals in it.
Further along the beach from the megacrystic granite we came upon large pegmatites and aplite structures. After a very satisfying afternoon in Porth Ledden Cove, we clambered up to the car park and rested with mugs of tea. This concluded our second day in the field. We drove back to Newquay.
Sunday, 7th October - Location 1 - Cligga Head
Sunday morning, the weather was bad. We set off in twos and threes in the pouring rain, westward towards Perranporth, and finally Cligga Head.
We parked the cars beside a large gliding club shed/hangar at the north end of the airfield and gathered in a huddle beside the hangar. Bruce Grant, who led us manfully that morning, gave us the plan of action. We were to walk out to the top of Cligga Head and examine some of the many features in the land that are due to the intense mineralisation in this region.
Here is a map showing the zones of mineralisation in the Cligga Head area. This map is taken from the field notes.
Figure 4 Mineralisation at Cligga Head
In walking out towards Cligga Head, Bruce showed us one of a number of sealed shafts. He explained that several exploratory boreholes had been sunk to try to locate the positions of older mine workings. The present requirement was to seal them for safety reasons.
Out at Cligga Head, we came upon a curious outcrop of granite that contained thin, sub-parallel dark veins and cracks. Bruce called these "greisening" alterations, which are the result of movement of chemically-laden
10 Years of GEO-LOGs 21 pressurised fluids along cracks in the rock. He presented a model of formation that involved the upwelling of the fluids beneath a flat, solid overlying cap. Sadly, the subtleties of his discussion were lost on most of us as the howling wind and driving rain prevented us from concentrating fully and hearing what was being said. Never mind Bruce, perhaps another day. Yes, on a different day this would have been a good site to visit.
Cold and soaked to the skin, we returned to the cars. A change of plan was called for. A rearrangement of the itinerary. Lunch, then an afternoon visit to the Eden Project.
Sunday, 7th October - Location 2 - The Eden Project (St Austell, Cornwall)
The weather on Sunday morning had been truly dreadful. Wind blown and soaked to the skin, we returned from Cligga Head and drove eastward to the Eden Project, located in the old Bodelva clay pit above St Austell. Walking down from the shuttle drop-off point, one is greeted with an overview of the two great "biomes" and interconnecting structure that is the Eden Project main exhibit. Man doesn't live by geology alone, so we had lunch first, then split into groups for a multi-pronged exploration of the Project. I chose to explore the smaller "Warm Temperate Biome" first. Here, the theme was the natural crop gardens of the Mediterranean, Californian and South African type habitats, halfway between wet green woodlands and the deserts. Here we were shown how fertile the deserts can be, with citrus, grapes and peppers, and also the oily and aromatic shrubs. There are those curious plants that have life strategies that not only survive fire, but also NEED it to burst open cones, trigger seed germination and kill competitors. We discovered how vitally important were the olive and the grapevine to the birth and development of human civilization.
Figure 5 The Eden Project
Next, I visited the Tropical Rainforest in the "Humid Tropics Biome". This is rather larger than the temperate biome, and contains some magnificent trees (See photo). It's hot up in the top of this area (35°C?). Here one can sample several tropical habitats including the oceanic islands, rainforest of Malaysia (this has a bamboo house), West African forest and tropical South American forest. Again, the themes are crops and cultivation in these areas, with production of rubber, timber, cocoa/chocolate, coffee, palms (including bananas) and rice.
The biomes are built of scaffolding with triple-skinned, hexagonal windows. Inside, the environments are temperature and humidity- controlled within fine limits by automatic window shutters and "misters". Generally, the message is the need for (1) Education, (2) Effective global stewardship for Sustainability, and (3) these can be achieved without great cost.
One day I shall return to the Eden Project, and continue those explorations. It's not finished yet. There is still some way to go.
Monday, 8th October - Location 1 - Roche Rock
Monday's weather was rather better. Dee took us up onto Roche Rock near Indian Queens, a lovely patch of original Cornish heathland that is now preserved as an SSSI. Roche rock is a quartz- tourmaline "schorl", the remnant of a pocket of boron-rich fluid on the cusp of the St Austell granite. See the photo (right) and geological map below (taken from Dee's field notes). This visit to Roche Rock was a precursor to our visit to the China Clay pit with Ivor Bowditch. The theme of course was kaolinisation, the formation of china clay. Dee explained "The western part of the St Austell granite has been extensively kaolinised, by deep weathering during a past geological time when the climate was hot and humid".
Figure 6 Roche Rock near Indian Queens
10 Years of GEO-LOGs 22
It seems that the character of the parent granite is of considerable importance to the quality of the china clay that might be extracted from it. Much of the younger granite in the western part of the St Austell granite is unusual because a lithium mica takes the place of the more usual biotite mica. This is important because the biotite tends to release iron oxide during kaolinisation, which discolours the china clay to a less desirable red or yellow. This is as shown in the geological map (below).
Figure 7 The St Austell Granite
Monday, 8th October - Location 2 - Imerys and the China Clay Industry
After taking lunch at the Wheal Martin visitor centre, we visited the Imerys China Clay works at St Austell. Susie Hall takes up the story…
At the Wheal Martin visitor centre we were met by an Imerys representative, Ivor Bowditch, who took us to a working clay pit. See below.
Figure 8 Imerys China Clay Works – Working Clay Pit
During our visit to the clay pit, Ivor explained the china clay formation, extraction and preparation processes as follows.
Kaolinite, or china clay, is a hydrated aluminium silicate. The alteration process from feldspar to kaolinite probably took place within the granite in several stages, through deep tropical weathering.
Quartz and mica within the decomposed granite remain relatively unaltered. China clay production can be distinguished by three stages.
Open-cast mining
After removal of the overburden, varying in depth between 1 and 15 metres, the pit face is fired at by a jet of water under gigantic pressure from a cannon known as a monitor. Clay is released, together with sand (quartz) and mica which has to be separated out in a series of processes, to be deposited on low-profile, landscaped tips. (Having seen the enormous scale of two or three of the Imerys clay pits, it becomes easy to understand how it is that the old whiteish quartz and mica spoil-hills dominate the landscape to the north west of St Austell.) After extraction of coarse sand, the clay slurry is sent by underground pipeline to the refiners. For every nine tonnes of waste rock and débris, there is one tonne of china clay.
Refining
Extraction of finer sand, mica and waste particles from the clay is highly automated and computerised, and takes place under a complex variety of processing techniques. The desired characteristics of china clay are whiteness and fine particle size. Over 60 different grades are achieved, the finest being less than two microns for the coating of paper.
Figure 9 Imerys China Clay Works – Drying the Clay
Drying
The water content of the liquid clay needs to be reduced to convert it into a solid material. Filtration is used for the
10 Years of GEO-LOGs 23 dewatering of the clay. The resulting moisture content is about 25%. Further drying to around 10% moisture content is attained by passing the clay through a thermal dryer fired by natural gas. For convenience of marketing, the clay is normally formed into pellets, ranging in size from 6 - 12 mm. See photo.
About three million tonnes of china clay are produced annually by French-based Imerys from the open-cast pits of Cornwall and Devon, the world’s largest producer. Nearly 3,000 people are employed in the UK. The early life of the industry was dominated by the market for ceramic products. Since about 1830, numerous markets emerged, the most important of which remains the paper industry, consuming 75% of output. 87% of Cornish china clay is exported from the local ports of Par and Fowey. Western Europe, particularly Scandinavia, is the main destination. China clay is second only to North Sea oil and gas in terms of raw material export. Thanks are due to Ivor Bowditch of Imerys for his most interesting tour.
After Roche Rock and the China Clay pits, we spent a rewarding afternoon studying the Devonian rocks in the coastal section from Trevone, northward towards Gunver Head. In this region there are two large blow holes. This section is an intricate succession of Middle to Upper Devonian mudstones and limestones that rest on a dolerite basement. This stretch of the Cornish coast is particularly beautiful and was thoroughly enjoyed by everyone.
Susie Hall and Tom Miller ______
2002
In 2002, John Barrett stood down as Treasurer. Tom Duff took over this position.
Tom Miller stood down as our Newsletter Editor. Judith Kelly took over temporarily and did a splendid job. Brian Cookson eventually took over in November.
Sam Aderson completed her PhD and left our Branch. She moved house to Nottingham.
OUGS 30th Anniversary Celebrations These started on Open Day with an informal party in the Walton Hall Cellar Bar.
Congratulations went to Lisa Duff, who got Highly Commended for her photograph "Sea Life Old and New" in the Moyra Eldridge Photographic Competition. ______
A Report of a Day Visit to the Isle of Sheppey led by Professor John Mather 20 April 2002
As a new OUGS member and never having been on a field trip before I wasn't sure what to expect, but the promise of studying coastal erosion and collecting fossils was too good an opportunity to miss.
The sun was shining but we still set off in our wellies with the promise of mud. We didn't have far to walk to the end of the path and our first observation of the continued effect of the sea eroding the coastline. Carefully we made our way along the top of the edge and stopped at the end of an arête to get a good view of toe erosion at work. John explained how the sea erodes away the toe of the cliff until a block slides down; behind this block, debris infills and, being clay, a small pond appears. This back-scarp area continues to fill (including the pond), the block keeps sliding, and the sea continues to erode at the toe of the landslip. Eventually the landslide is totally washed away, and the cliff becomes a steep slope again. With no support, another block starts to slide down and the 20 to 30 year cycle begins again. (I was impressed - I thought the sea just nibbled its way along!, but then I had only just started S260)
Isle of Sheppey - Collecting Fossils (Left to Right - Dot Hill, Julie Dorrill, Tom Miller and Professor John Mather)
10 Years of GEO-LOGs 24 We made our way down onto the landslip to get a closer look at the pond stage of the cycle. Whilst there 'we' found some septarian nodules (others found - I looked!) with some excellent calcite crystal formations. After making our descent down the landslip onto the beach, John gave us a quick talk through our handout sheets of the fossils we could hopefully find - pyritised wood, fruits and fossils. So off we went, fingers in the mud searching for fossils. Dot had brought some food bags and was kind enough to share so we could bag our finds. (A tip I took to summer school) There were abundant examples of pyritised wood, so the task was to find examples that showed details of bark or notches, or even to find seeds and berries.
A Few Fossils and Items of Interest
Next stop, lunch; but only after we made our climb up a muddy cliff. We were lucky it was dry, if it had been wet we would definitely have needed those wellies as proved by some fine examples of shoes that had been left stuck in the mud! Lunch was spent sitting outside in the sun (a fine treat in April) with some very generous portions. (Actually huge is probably a better description!).
Refuelled, we set off back to the beach a bit further along for some more fossil hunting. Back on our hands and knees, noses to the ground we set off on our quest. Only stopping when it was getting late and the tide was coming in.
How many times that day did I ask "Is this anything/What's this?" No one seemed to mind me asking and I along with others were rewarded with some great finds, sharks teeth, gastropods and even a small crab. To finish the day off, we went back to Linda's for tea and cake!
So, to all new members who haven't made the plunge to attend a meeting or a field trip, do it. I had a fantastic day, have attended some really interesting talks, members are friendly and all are keen to share a mutual interest. by Julie Dorrill ______
2003
In 2003, Brian Cookson formally took over as our Newsletter Editor.
We were sad to announce the death of Arthur Whitehouse. Arthur was our dearest and oldest member of the WH Branch. He passed away on 19th February 2003.
Saturday, 22 November, Walton Hall Branch hosted the AGM weekend at the Open University. This was followed by the Geoff Brown Memorial lecture, given by Hazel Rymer on “Predicting the Next Super-eruption”.
****Fossil Identified*** Remember the ammonite Linda McArdell found in the excavations outside her front door that summer. Well, it is an Amoeboceras seratum from the Amptill clay (that’s just above the Oxford clay). ______
A Report of a Day Visit to Old and Working Chalk Quarrys In Ashwell and Steeple Morden, N. Herts. "A Fossil amidst the Chalk and Flint - Recollections of the Walton Hall Branch Field Trip to Ashwell in Herts" Led by Chris Wood - 12 July 2003
WARNING! This account is by a septuagenarian 1st year Geology (S260) student. It may contain descriptions that will shock more advanced Level 4 students.
Prior to this year, chalk had only made an impression on me at two stages of my life. Since 1942, when I nervously attended my very first Chemistry lesson at my Protero-Grammar School in Sunderland, I have always remembered writing down in my virgin exercise book the words globigerinelloides, radiolarians, and foraminifera. I had only a vague idea they had something to do with chalk. (How is it that now, 62 years later I cannot remember even simple
10 Years of GEO-LOGs 25 words from my S260 Block books, like “a’a” for example, for more than 24 hours?). It turned out that my first chemistry teacher, “Baggy” Moore (so nicknamed because of the permanent shape of his trousers) was a keen amateur geologist. At that same first chemistry lesson, in spite of his trousers, he became my favourite master, by blasting a hole in the classroom ceiling whilst demonstrating what was meant by an exothermic reaction. That seemed much more exciting than Geology to an 11 year old boy, so I made the mistake of becoming a not very good chemist throughout my subsequent professional career.
My next skirmish with The Chalk came shortly after my marriage, when, not being able to afford to hire an excavator, I had to pickaxe a 2 metre deep driveway through the Chiltern stuff, to get to our newly constructed bungalow. My, how I cursed that calcium carbonate! Moreover our garden was, and still is, infested with flints and, although their shapes and origin were a constant source of curiosity to me, I hated them because they made it impossible to grow straight carrots. (In a fit of frenzy, one of our neighbours actually hand sieved his entire garden)
Earlier this year, as part of my initiation to geology, I invested £11 + postage on the BGS 1 : 50 000 geological map of my area. On first opening it I was excited to see the 'Line of Section' passed straight through our garden. But, on consulting the bottom of the sheet, all it said was 'Middle Chalk: hard white chalk with few(!!!) flints.' Boring stuff, chalk!
At least that was what I thought when I enlisted, this July, for the Walton Hall Branch trip to Ashwell, mainly for the company but partly out of curiosity. I was completely converted as soon as I saw our leader, Chris Wood. He had the twinkle of a real enthusiast in his eye, and chalk all over his trousers - just like Baggy Moore.
Cliff House Old Quarry (Susie Hall and Hayden study the Plenus Marls horizon)
In magnificent weather, we were rapidly transported from the meeting place to the lovely village of Ashwell, and backwards by more than 100M years, to examine two exposures of the local chalk, both seemingly in people's gardens. Chris was obviously on extremely good terms with the locals. He plunged us straight into the amazing complexities of the multiple strata of chalk, marl, flints, and fossils, which seem to be spread with remarkable consistency across the whole of Northern Europe and into Central Asia, not to mention Texas and Australia.
Disused Quarry at Ashwell (The Plenus Marls horizon, in close-up. View shows about 1 metre, top-to-bottom.)
So interesting, numerous, and complicated are these formations that since the 19th century leading geologists, showing typical brotherly love, have been constantly arguing about how the different layers should be named and distinguished.(Apparently some modern geologists are advocating the abolition of 'The Middle Chalk'. If only they had done that before I dug out my driveway!) An enjoyable lunch, with some good local ale, was followed by a brief inspection of the church of St Mary with its splendid 176ft (53.6m to three decimal places for the benefit of you OU tutors) tall tower, constructed from Totternhoe Stone- --part of the local Lower Chalk. The building blocks are suffering considerable erosion, but reveal some beautiful fossils (perhaps praying for the extinction of homo sapiens?).
Choosing Lunch at the "Bushel & Strike"
10 Years of GEO-LOGs 26
The Totternhoe Stone, used as building stone in Ashwell Church
This was followed by a visit to the sparkling source of the River Cam, which springs, amidst more geological controversy, from that same Totternhoe Stone. Next, by car to the huge Plantation Quarry, where we were able to wallow in fossils, and admire the separate layers of tabular and finger shaped flints, the latter having grown vertically in burrows in the chalk, exactly like inverted carrots. Our final brief visit was to Steeple Morden Station (working) Quarry, where the late afternoon sun's heat, bouncing off the chalk faces, finally got the better of me. Perhaps it was that lunch time beer.
Steeple Morden (Large Ammonite on show at the Plantation Quarry, found in February 1988)
It was my fourth encounter this year with the Walton Hall OUGS (2 lectures+2 field trips), and at each I have been greatly impressed by the friendly and helpful company, and by the high level of expertise of the speaker/leaders, and their ability to make their presentations so clear and interesting even to this complete beginner, and to stimulate me into looking further into those things I haven't fully understood.
Plantation Quarry Chris Woods compares flinty with flintless successions in the Holywell Nodular Chalk (overlying the finger flints).
Station Quarry Looking for fossil echinoids (Conulus Subrotundus)
So as not to disappoint you Level 4 students I can recommend two papers I have personally vetted as a result of this trip:
• Gale, A.S.(2,000). Late Cretacious to Early Tertiary pelagic deposits: deposition on greenhouse Earth. In: Geological History of Britain and Ireland (Eds. N. Woodcock & R. Strachan), pp356-373, Blackwell Science Ltd. [An excellent summary of how the relevant chalks, marls, flints and fossils are used to determine past variations in climate and sea levels.] • Clayton, C.J. (1986). The chemical environment of flint formation in Upper Cretacious chalks. In: The Scientific Study of Chalk and Flints. (Eds G.DeC. Sieverking & M.B. Hart), pp43-55. Cambridge University Press. [The definitive review of the formation of flint. Recommended by our field trip leader, Chris Wood] I don't want to fire off yet another geologist's controversy, but one final outcome of the trip is that, now, after suffering for more than 100 million years below the cabbage fields of Herts., a magnificent cluster of fossils on a chalky piece of tabular flint is now happily nestling on our mantelpiece beneath the beech trees of Bucks. Lucky chaps!
Alan Peacegood
10 Years of GEO-LOGs 27 2004
In 2004, Dot Hill and Brian Cookson chose to stand down from the branch committee. Jo Marsden joined the committee. Roger Beck took over as our Newsletter Editor.
"OU geologist on Time Team - the Riddle of the Wittenham Clumps!" Jill Eyers appeared on Time Team on 29 February as a result of her magnetometer survey of these for English Heritage catching TT’s interest.
Our Branch Organizer, Linda McArdell, graduated with an MSc in the summer of 2004.
Professor Chris Wilson retired from the OU at the end of September 2004. Chris was a founding member of the Faculty of Science and the Earth Science Department and was our President. ______
A Field Trip to the North Devon Coast "Evidence of Sea-Level Change preserved in the Pleistocene and Devonian sediments of North Devon" Led by Professor John Mather, Report by Tom Miller & David Maddocks 16-18 April 2004
A group of OUGS members and friends visited the north coast of Devon. We stayed in The Thatch and Billy Budd's hotels in the village of Croyde. The accommodation was friendly and comfortable. The food and wine were good and the weather forecast looked promising. A characteristically great weekend was to follow. It combined splendid locations with good technical geology.
The coast of North Devon and West Somerset from Barnstaple to Porlock is especially interesting in that it preserves a succession of raised Pleistocene beach deposits overlying a marine platform of Devonian/Carboniferous rocks (Saunton Sands to Baggy Point) and some important coastal geomorphology (the Valley of the Rocks, shingle ridge, etc.).
Saturday Location 1 - Saunton Sands
After breakfast in The Thatch (with no eggs!) and a brief introductory talk from John, we set off for Saunton Sands. The weather was excellent. The plan was to park below the Saunton Sands Hotel and walk the beach section from there westward to Down End, below Saunton Down. We set out across the wave -cut platform and reached our first point where the raised beach deposits could be seen resting on the platform.
The Group study the Raised Beach Deposit (Pleistocene) resting on the Wave-Cut Platform (Upper Devonian?)
Here, the beds of the wave-cut platform are dipping steeply and easily distinguishable from the sub-horizontally bedded younger raised beach deposits above. The wave-cut platform rocks are the Pilton Shale s, which are a transitional group joining the Upper Devonian and Lower Carboniferous systems in the region.
The Pilton Shales are hard and quite strongly folded. The Lower Cliff beach deposits (known as Sand Rock) are quite friable by comparison and contain small pebbles and shingle beds in a calcareous sandy matrix. The Sand Rock is controversial in age but is thought to date from the Ipswichian interglacial (125 ka), when a warmer spell, combined with a general eustatic high, raised the sea level above its present height.
John points out Shingle Beds and other Sedimentary Structures in the Sand Rock
The Sand Rock of the lower cliff has very even, laminar bedding, but is quite variable in thickness. There are occasional traces of plant rootlets on its upper surface, suggesting emergence and development of a land flora. The Sand Rock is superposed by a ‘Middle Cliff’ unit that contains much larger bedforms. These are interpreted (cautiously) as dune bedding (aeolian), ramped up against ancient cliffs (Pilton Shales) behind.
10 Years of GEO-LOGs 28 Dune Bedding in the Middle Cliff
Further along the beach we came across several points of interest including bands of crinoid debris in the Pilton Shales, indicating their environment of deposition as shallow marine. I was quite impressed with the discovery of ancient clusters of barnacles on blocks of the Pilton Shales. These are coming to light one by one as the Sand Rock is eroding away.
One of the most interesting features of this coastline is the line of erratic blocks and boulders that have come to rest on the marine platform. These rest on the Pilton Shales but are sealed in by the Sand Rock deposits. An estimate for the age of placement of these erratics is 450 ka BP, towards the end of the Anglian glaciation. Could they be drop-stones, or lag from eroded till? We discussed this at length but reached no firm conclusion.
A Porphyritic Microgranite erratic boulder sealed in by the Sand Rock, on the Pilton Shales
Sketch of the Saunton Sands / Saunton Down beach section
A fold in the Pilton Shales became visible in the section below Saunton Down. We looked at tension gashes and the axial plane cleavage with interest. This must have been Variscan front deformation. After this, we returned to the vehicles and drove to the National Trust car park on the north side of Croyde Bay.
Saturday Location 2 - Baggy Point
In the National Trust car park we stopped for lunch and considered the afternoon's activity. A walk up to Baggy Point, looking at further Pleistocene shoreline deposits and the Upper Devonian Baggy Sandstones.
We had, at times during the morning, glanced up at the Head (solifluction) deposits above the Middle Cliff but we did not look at them closely. After lunch, John led the group with some enthusiasm up the path towards Baggy Point to see the Head deposits more closely.
John Mather focuses attention on the glacial Head deposits. Baggy Point in the Background
Baggy point has a covering of glacial Head overlying the Baggy Sandstone beds beneath. The Head is a solifluction deposit and is thicker (banked up) on the flanks than on the top. It contains angular blocks of the Baggy Sandstone, orie ntated down-slope. Several periglacial ice distortion features can be seen in the thin Head deposits on the top of the headland, including ice wedges.
Up at Pencil Point we could see the Head deposits clearly banked up against the sandstone slope. Pencil Point gets its name from the curious way that the rock by the footpath crumbles into shards (like pencils). This is due to the nature of the jointing and the orientation of the pressure cleavage. John suggested that the curious interaction of bedding and cleavage here might give some clue as to the proximity of the axis of the fold we had looked at earlier in the Pilton Shales. One for the structural geologists in the group!
Head deposit, containing large angular blocks, banked up against the Baggy Sandstone
10 Years of GEO-LOGs 29 At Baggy Point there is a complex sequence of different sediments (sandstones and shales), recording many different environments (marine advances, retreats, lagoonal facies, freshwater deposits, etc.). We stood for a while here, enjoying the views to landward and seaward. We could see Lundy Island in the west, Pembroke on the horizon to the northwest and Morte Point to the north. North of Baggy Point, the raised beach and rock platform disappears, i.e. they are not present at Woolacombe and Morte Point. We made our way back to the vehicles and brought the day's excursion to a close. Tom Miller
Sunday Location 1 - Valley of the Rocks
Forecast overnight rain fell, true to plan, and was still falling as we drove across Exmoor but Lynton must have seen the OUGS coming as it stopped just as we arrived at the Exmoor National Park Picnic Area in the Valley of the Rocks.
The Valley of the Rocks is a dry valley extending southwards from Lynton for about 2 km or so, parallel with the coast, before ‘plunging over the cliff’ into the Bristol Channel at Wringcliffe Bay. At its northern end the East Lyn and West Lyn rivers meet, just before passing through Lynmouth into the sea. Each of these rivers has a steep channel in this vicinity and much erosion debris forms the Lynmouth delta that we see today. Although the Valley of the Rocks is 145 m above the Lyn rivers below, it seems logical to assume that they once flowed through it. There are two main theories as to how the present situation came about. One suggests that the North Devon coast slowly eroded back towards a bend in the river which was then able to discharge over a cliff waterfall into the sea and subsequently rapid erosion took place. The other theory is a glacial one. An ice dam across the mouth of the Lyn river would cause the water to back up and find a new course, through what is now the dry Valley of the Rocks. Certainly the ice front in glacial times is known to have been in this vicinity.
The Valley of the Rocks
The valley is eroded into the Lynton Beds, Devonian shallow-sea sediments formed mainly of sandstones, but with occasional thin beds of clays, silts and limestone. The latter contain brachiopod and crinoid fossil debris. In places there is slickenside evidence of beds moving over one another. Some of the valley is partly filled with Head, local erosion debris.
The seaward side of the valley is topped by a number of coastal tors, which at the same time are high points on the coastal cliff. Each is an outcrop of upstanding solid rock with conspicuous joints. It was whilst on the top of Castle Rock, one of these tors, admiring the rocks, plants, goats and birds, that we saw the big ye llow bird, the RAF Rescue helicopter, coming straight at us along the coast from the west. Just before Castle Rock it swerved inland up the dry valley, then turned on its side to go around the rock and through the tor gap back out over the sea. All this just feet off the ground and close enough to see the pimples on the pilot’s nose - and I thought it was the goats that kept the grass so short......
RAF Rescue helicopter
Sunday Location 2 - Porlock Weir
A delicious hot pasty lunch was taken en-route to Porlock Weir, our last location for the weekend. Here a substantial shingle ridge shields the salt marsh and habitation behind. The ridge has been starved of new pebbles for a couple of hundred years now so the sea occasionally breaks through. In the past these breaks have been repaired but the last break has been left to see how nature deals with the changing conditions. Just seaward of this ridge, and only visible on the lowest tides, is a submarine forest, the remains of oak and alder some 7,800 to 5,000 years old – evidence of sea level rise since the end of glaciation.
A not-so-easy walk along the shingle ridge towards Hurlstone Point allowed us to see the Hangman sandstone and much more of that unconsolidated gunge, the Head. Not surprisingly, there are regular landslips along this section of the coast. It had been cloudy but dry all day, reasonable field trip weather, and fortune had been with us. When I got home to Newbury it was raining and the rain gauge contained 31 mm that had fallen that day......
David Maddocks
10 Years of GEO-LOGs 30