Open University Geological Society (London Branch)
At each event we ask for a volunteer to record their experiences and impressions. These articles are published in our newsletter and eventually appear here as an archive of our activities. Note that these are only provided for reference, and are not endorsed by Event Leaders. Interpretations can change often and rapidly in Geology, any information stated should be verified from appropriate sources before being quoted.
Building Stones of the British Library • S260 Field trip to Herne Bay • Easter in Rhodes • Lower Thames Valley : Greenlands Pit and Lion Pit Tramway • Odiham and the Basingstoke Canal • Lizard Peninsula • Pegwell Bay, East Kent • Chalk coast of France
Building Stones of the British Library - Led by Eric Robinson
17 February 2005
A well wrapped-up group of us assembled on a cold afternoon outside the main entrance of the British Library for our talk about the building stones led by Eric Robinson. We started by marching across to the main gate so that we could get an overview of the building as a whole. Rising above the roof, on our right, we could see the elaborate architecture of St Pancras Station, and Eric explained some of the design issues - it would not have been appropriate to match the style of the station, but the colours of the building materials were chosen to complement it, hence the rich red-brown of the brickwork and silver grey roof tiles.
Eric firstly drew our attention to the white limestone slabs on top of the South Wall, just inside the main gate. These are Hauteville Limestone from the French Jura Mountains. Lower Cretaceous in age, they show plenty of evidence of the benthos of a warm shelf environment. The slab nearest the gate is the most bioturbated; in others we made out gastropods up to 15 cm long, bivalves and rudists. In all the slabs we could see stylolites, sutures caused by the pressure of deep burial.
We then turned to look up at the gate. Across the top are 8 large blocks of red Dumfriesshire sandstone from the Southern Uplands. These Permo Triassic sands were wind blown, some river sorted. We looked for bedding markings and Eric described the arrangement of the blocks as "patch and match." At ground level, we inspected an attractive reddish brown granite at the base of the outer wall. It has even-sized crystals of brick red feldspar, quartz, biotite mica and hornblende, giving it an overall homogeneous look. It is a Drammen granite from the Oslo Fiord in Norway and Eric said it came from the Royken Quarry. This granite is also used at the front of the Conference Centre and blends in with the redish brown scheme.
On the ground we examined the Hauteville Limestone slabs as we walked down the slope towards the Conference Centre. We noticed how the rain and dirt emphasised the markings on them: no need for Eric's bottle of water today. By the Conference Centre door Eric pointed out a slab that he said was Grade 1 listed. Was he joking? Probably not. It was teeming with evidence of fauna from the Tethyan Sea where it originated. We identified clusters of bivalves and rudists, gastropods and a sponge.
In the centre of the Courtyard is a circular, slightly sunken Quiet Area that did seem to be sheltered from the noise of the Euston Road. It is ringed by eight limestone pedestals, and on top of each is a large smooth stone with a crude human figure carved around it by Antony Gormley. As usual, Eric had the inside information - Gormley had wanted to use erratics from Scotland but they were not willing to part with them. Malmo in Sweden had been more accommodating.
As a result the pedestals are topped with eight Pre Cambrian, Baltic Shield erratics including dolerite, gabbro, gneiss, basalt and granite, all showing evidence of their original ancient craton having suffered stress before they were carried south to Malmo by glaciers. We could make out metamorphic textures and augen 'eyes.' Di climbed up to examine a granite at closer quarters, and confirmed the quartz crystals showed a blue-purple colour - evidence of internal fractures in this hard mineral. We mused on the significance of Gormley's work, the relationship between the figures he has carved and the ancient stones they embrace. Eric told us of a children's playground in Holland where erratics have been sited for children to scramble over. The stones have numbers relating to a map showing their place of origin. He thought we could make similar use of erratics here, and suggested Scunthorpe, where they are uncovered as the gravels are extracted.
It was too cold for musing further, so we made haste to get into the warmth of the Library. After announcing our presence at the Information Desk we looked first at the Portland Stone floor of the foyer. In the creamy coloured limestone we could clearly see the small white circular shapes of calcareous algae, known as pellets or biscuits. We saw evidence of bivalves and shell fragments of burrowing oysters, and could make out pathways in the sediments.
The wall blocks in the foyer are made of Italian Travertine. This is freshwater limestone deposited by springs cascading down the sides of volcanoes in the Tivoli Hills to the north of where Rome now stands. Because of its non-slip qualities, due to having numerous cavities, Travertine is frequently used as flooring. Some of us recognised it as 'MacDonaldstone.' The elongate cavities are the spaces left where the stems of reeds and rushes growing in the warm spring water have crumbled away during lithification. On the wall in the Library foyer the stone is used on its side, so that these features are horizontal. In one area the cavities have been filled to give a smooth face to take the lettering commemorating the opening of the building by HM the Queen on 25 June 1998. Eric referred to this as 'stocked' or 'plugged' Travertine.
On the landing above the foyer, the dark slabs of blue-grey limestone are teeming with fresh-water bivalve shells. This is lower Cretaceous, Purbeck limestone, most likely from the quarry at Worth Maltravers near Swanage. Eric explained that the dark colour represents a muddy, foul-smelling, sulphurised, stagnant environment, which obviously suited the bivalves, as their remains are abundant. We could also see long calcite veins, formed when the rock dried and cracked during its formation.
Eric's talk finished here. It had been a fascinating and thoroughly enjoyable two hours. For many of us it was our first visit to the new British Library building and we will be well aware of the geological aspects of it on further visits. I shall look forward to sitting in the Courtyard, surrounded by those ancient erratics, in warmer weather. As usual, Eric was full of anecdotes and stories, as well as his in-depth knowledge of all the materials used. Marilyn thanked him on our behalf.
S260 Field trip to Herne Bay
20 March 2005
I drove through the small village of Beltinge and nudged my car into the car park, wondering whether I had found the right place. I immediately saw that I had. Through the morning mist, I saw thirty or so people already there. All were well-wrapped against the biting north-easterly wind, and they all looked very well prepared for a geology field trip. Boots, rucksacks, and hard-hats were everywhere, and everyone looked like my image of what a professional geologist should be. I eyed my gleaming white hard-hat, which I had bought just the previous day, and wondered whether I should rub it into some gravel - give it a few battle scars so that I wouldn’t stand out as such a newbie. I quickly gave up on that idea though: there was far more to give me away than an overly shiny hat! I put aside my selfconsciousness, stepped out of the car and was immediately greeted by friendly faces.
Beltinge lies just outside the small town of Herne Bay. As a child, I had spent many a summer’s day on the beach there, and it was much as I remembered. This visit was going to be very different though. I might have seen it all before, but this time I was going to actually look, see it through a geologist’s eyes, and understand more about the forces that made this place.
Herne Bay lies just a few miles east of the Isle of Sheppey, exposed to the North Sea that erodes its soft, sandy cliffs. It is on the southern side of the London Basin, on the north-dipping slopes of a fold raised by the oncoming African plate. It is England’s crumple zone, but it is hard to see any of this from a casual observation – you need a more tutored eye than mine, but fortunately I was with a group of people with very tutored eyes.
We followed the path down onto the beach and Brian suggested we should have a look at the pebbles and see what we could see. Well, I saw pebbles - lots of them, in fact, different colours, shapes and sizes, and beneath them some sand. There’s this thing I had heard people talking about – something about “getting your eye in”. Obviously a lot of people had got their eye in very quickly, because where I saw pebbles, they were seeing weathered flint, mostly rounded, and instead of sand they were seeing fine, well-sorted angular quartz. Clearly, my “eye” most definitely wasn’t in at all. In fact, it seemed I had left it at home! Fortunately, there were people all around me eager to explain or just to point out things I missed. The cliffs slump and collapse under the force of the sea, but the sea quickly carries the debris away, leaving still steep-sided cliffs. The shallower sloping cliffs I could see to the west are artificial, sculpted by human hand and reduced to a stable slope, much less prone to catastrophic failure. The cliffs in our vicinity, however, were much steeper. Some of them have been left to the forces of nature, others are guarded by sea-defences, great blocks of rock that guard their base from the waves.
We moved on to look at some of these blocks. Even to my eye, these were obvious igneous impostors, clearly not raised and bred in the sedimentary south. These were black and crystalline monoliths, exhibiting crystals the size of the tip of my finger. These five-ton giants must have formed and cooled slowly at great depth, I think, otherwise how did the crystals grow so large? In fact, I am told, they come from Norway, where they are cut and prised out of the cliffs and shipped to wherever hard, unyielding weight is required.
We moved on, turning away from the shore to explore a deep cut into the cliffs. “So what do you make of that?” we were asked. It was a bit overwhelming – too much going on, too much detail to take in. How can make anything of a cliff? “Stand back”, I was advised, “take in the overall shape of the cliff, let the major features catch your eye…”, and sure enough, things did start coming into focus – distinct layers of yellowish material, layers of greyer material dotted by thousands of holes, then moving up, evidence of other layers. Somewhere at the top I knew there to be the London Clay, but I couldn’t see it from my position, or if I could, I couldn’t identify it as such. None of this stuff was really rock; it was rock in the making, waiting for cement and time and pressure to do its work.
Dee, one of the volunteers, was way ahead. She had already leaped over a stagnant looking stream and scrambled some way up the face of the cliff. She returned with a grin and a fossil shark tooth. Very soon, I was getting into the spirit of things too, leaping around, hand-lens at the ready, peering intently at each and every bit of stuff that looked in any way different from all the other bits of stuff. In all honesty, all I saw was wet, yellowish sand, and greyer, finer, more silty sand, but at least now I was checking the grain sizes and assessing roundness and sorting.
To finish the morning’s activities we climbed the cliff and finally came across an exposure of the promised London Clay, part of the same sheet that covers much of the London Basin. I grabbed some of it and moulded it in my hands. Clay for sure.
We left Beltinge and headed further east to Reculver, a place of many attractions, not the least of which was a warm, friendly pub where we quickly dispelled the chill from our limbs and talked over what we had seen in the morning. We somewhat reluctantly left the warmth of the pub at 2.15pm, back into the biting wind with the day still overcast but the mist mostly dispersed. We started by examining the walls of the two towers of the ruined Saxon church. But my “eye” had gone walkabout again – there was little I could identify, so I listened in others’ discoveries of Roman furnace slag (or was it breeze-block?!) and, well, truth be told, I can’t even remember what else, but the list seemed endless.
Finally, we wandered back along the beach, taking the opportunity to study concretions full of trace fossils, and more giant blocks – limestone, and to my eye, bland and virtually featureless, but on close inspection revealing all sorts of minerals and trace fossils. Then, finally, to my delight, I actually recognised something – so, okay, I missed the significance of the near alignment of some of the elongated crystals, but there, undoubtedly, was a hunk of granite. And the significance of the alignment of the quartz? This rock had solidified in a flowing melt, and the flow had aligned the quartz, whereas the unaligned mica ruled out metamorphosis. As this was explained to me, I could virtually see it in happen in front of my eyes, and I could map the clues in the rock to the processes that had formed it. Here, then, right at the end of our journey, I thought I had finally gotten my eye in. As we walked back to our cars I was feeling pretty pleased with myself - until Dee pointed out a large collection of fossil bivalves. I had walked right past them.
Easter in Rhodes
30 March - 8 April 2005
Wednesday 30th March
I am writing this part sitting in the sun on our balcony looking out to sea, whilst the red-rumped swallows and house martins swoop low over the wild flower meadow around our studios (inside the anti-goat fence). How far it seems from UK! If only the Greek jack hammers from the construction site up the hill would stop it would be perfect.
At 09:30, a very civilised hour to travel, the taxi arrived to take Gill and me to the airport, calling at Brian Harvey's house
to collect Diana Smith and him.
The flights were uneventful, all of our luggage made it through the transfer in Athens and Richard Bromley our leader for the
trip arrived just as the last one came off the conveyer belt in Rhodes - such timing!
After a longish drive in the dark we at last turned off south of Lindos onto a small driveway, up to some gates and across the grass to the studios. These ten bed sits are arranged five on the ground floor and five on the top. Each had an entrance at the back and a balcony or terrace at the front. Quickly we all selected our studios and did some basic unpacking before meeting in Studio 10, which was a common room. There we had a basic introduction to the facilities and talked about the days ahead with Richard and his wife Ulla. Much retsina was drunk before we bedded down for the night.
Thursday 31st March
Having arrived on Rhodes late Wednesday night and then driven in the dark for about an hour to reach our appartments a few minutes south of Lindos, it was a wonderful surprise to wake the following morning to the bleating of goats and sheep and find our apartments stood in a wildflower meadow which passed for a garden, high limestone cliffs on three sides, a view of St Nicholas Bay and an all-pervading smell of wild sage. Ominously the sky was grey and a chill wind blew but we were in high spirits.
After sorting some minor domestic issues with a little friendly bartering we hit the supermarket for such staples as yoghurt, honey, beer and wine then set off to look at some geology.
Our first stop, at the top of the small pass taking us out of St Nicholas Bay, was an introductory viewing of the Kolymbia limestone/Lindos Bay clay boundary which has been elevated during horst/graben tectonics. A mysterious volcanic ash horizon has also been identified between these two facies.
We descended the other side of the horst to a bay east of Pefka but rain intervened making the proposed descent over Lindos Bay clay treacherous. We duly retired to the apartments for an alfresco lunch on the balcony. The weather brightened so we returned in the afternoon and negotiated the descent very gingerly. Safely on Kolymbia limestone, which lies beneath the clay, we found it stuffed full of Thalassanoides trace fossils. Rather alarmingly we were warned not to stand or jump (some of us were trying to relieve our boots of their clay covering) on some metre wide depressions in the limestone. Rare fossils? Interesting infill in depressions? No, just the possibility the depression may collapse into a cave some 20m below us at sea level. We carefully approached one such vertical shaft and could see it had been used in the past as a means of transporting merchandise from boats to the cliff top. As to their formation – who knows. Theories abound but nothing conclusive.
Some of the party walked round to an adjacent bay for some successful fossiling. Paul Hetherington, being concerned for local wildlife, went to deposit some fishing line and hooks he’d found in a large communal refuse bin, spotted some movement, called us over and there lying on its back peering up at us and wiggling his feet around was a blonde hedgehog. Couldn’t leave it there so the writer climbed in, picked it up and passed it out to willing helpers then found it’s far easier getting into a refuse bin than out….
Proceeded to a beach south of Pefka – wonderful flora growing in the sand. Of geological interest was the beach rock dated
to approximately 420AD which appeared to overlie an algal reef which we were told was dated BC. The beachrock is believed to
have formed during a tropical pulse where high surface evaporation led to water being drawn up through sand covering the algal
reef, carbonate precipitation and formation of a hard calcite cement. Human footprints were visible in this rock as well as those
of a cow and possibly a pig.
Friday 1st April
Friday was the day for site seeing and paperwork. Yes, off to Rhodes town to sign and to pay for the cars. We left early in the morning to try and ensure that we would be able to park in Rhodes Town. As it happened, when we arrived in the narrow street where the car hire place was, we were directed to the car park of the Casino, which had plenty of room.
Soon we were seated in front of the café next door to the car hire shop and sipped our Greek coffee whilst Sue Vernon dealt with the paperwork and the money. Once this was out of the way, we were at liberty and split into smaller groups as the fancy took us. The group I was with (Gill, Brian, Di Smith and Ursula) made our way towards to the harbour side past the Muslim cemetery.
Mandraki harbour is the most northerly of Rhodes current three harbours, and the most attractive. The entrance is guarded by twin columns bearing statues of a stag on one side and a doe on the other, whilst a row of three medieval windmills complete the scene. The deer are said to represent a breed which was introduced to combat a plague of snakes – this must of worked as we saw no snakes on our visit.
We followed the line of the harbour from one column to the other, admiring the stones from which the quay and 15th century fortress of St Nicholas are constructed. After the making our way back to the town proper, we found our way into the dry moat surrounding the Old City Walls.
The old town moat is a fascinating place to visit, having only recently been restored from its previously derelict state, although plenty of evidence of Rhodes active military history remains. Stone cannon balls litter the moat and the effects of cannon fire can still be seen in the walls. There was plenty to see as we walked round, not only fortifications but also wild flowers, lizards, fossils, bird life and even the “Melina Mercouri” open-air theatre (named after the late Minister of Culture and film star).
Before we had completed our circuit of the walls we met Paddy and Di Clements who had entered by another gate into the moat. Soon we found ourselves back beside the water and eager for lunch. Purely by chance we wandered though a gate in the wall leading from the harbour and stumbled on a fish restaurant. The owner seemed to be the only one about, but offered us fish and Greek salad on the balcony in front of the restaurant. Before seating us, he urged us through the restaurant and into the kitchens, where he opened a drawer and offered us an enormous fish lying on ice – clearly too big even for the seven of us! Luckily Ursula was able to speak to him in Italian and he opened another drawer and drew out a merely big fish!
Soon we were armed with Mythos beers or retsina and then the fish arrived, grilled to perfection and served only with lemons
– unbelievably wonderful.
All too soon, it was time to make our way back to the cars and make the drive back to Lindos and the studios. I can thoroughly recommend Rhodes Town as a fascinating place to visit and I would love to go back.
Saturday 2nd April
This is the 4th day of our trip and the third out in the field – we did Rhodes town yesterday and found excellent rocks and fossils in the blocks used to build the old moat so it too could be called a day in the field. Today our first stop was Kallithea on the east coast just to the south of Rhodes town. The first notable point is the faded grandeur of the Spa built by the Italians during their occupation of the island between 1912 and 1943. It was once striking if not beautiful, unfortunately it is no more – only extensive renovation will return it back to what it once was.
Down on the beach we came to look at the rocks first studied by Richard and Ulla in the 1970’s. They are still stunning and amazing. The base rock is Jurassic with no bedding. They are draped with the Kolymbia Limestone. We came to see a surface in the Cape Arkhangelos facies of the Rhodes Formation. What a surface! It was covered by trace fossils with minute detail. They are Bichordites – a trace fossil of Echinocardium cordatum (hairy heart urchin) with burrows which show a backfilled structure with a single drain. There are some excellent photographs on the website but these cannot do justice to these brilliant fossils which show the traces of these animals that lived in the mid Pleistocene.
The rock itself is shallow marine deposit laid down in 20 to 40 metres of water. The Echinocardium cordatum (hairy heart urchin) were 10 – 15 cm across and approximately round in shape. It burrowed 20 cm down through the sediment. The trace that it left was caused by the sediment that it pushed behind it in waves, the drain tube through which it excreted its waste and, occasionally, a tube leading to the surface. We can see the trace because the mucus on the bottom of the burrow is different to the mucus on the top of the burrow which left the grains more strongly cemented on the base and more resistant to erosion.
The rocks with their clinoforms, trough cross stratification and tsunamiite deposits are signs of periods of rapid deposition in a high energy environment which was not always an easy place for the echinoderms to be. We were shown an echinoderm at the top of a vertical burrow where it was trapped as it was trying to escape the deluge of a large amount of sediment. There were other examples of trace fossils of shafts but none with the animal in situ. Further across the rocks to the South closer to the water there were other trace fossils in the form of Glycymeris burrows in life position some with shells to be seen.
This was a truly interesting place unfortunately soon to be spoilt by the building of a hotel right on the beach – something not at all interesting or attractive to look at. We were obviously something to note because a workman came over and asked to see our work permits, organised in advance by Richard, these were duly produced and we were allowed to go on our way.
Our next stop was approximately 50 km to the south near Ladiko. To get to Ladiko we had to drive through the notorious area of Faliraki – Greece uncovered and all that. We were there before the season so very little was open, and there were not many people around. The whole Island had the feel of a place in waiting, hotels were being spruced up, their swimming pools still empty, the shops were being repainted and restocked but not yet open and there were hundreds of shiny new hire cars in many pounds just waiting for their tourist drivers later in the season. Although the weather was not yet warm and the Sun not yet shining every day I think that we were there at just the right time – later might just be a bit too chaotic for my liking.
We did not stop in Ladiko but went on to a bay further round the coast called Anthony Quinn bay – so named after one of his famous films was made there. Here too was a place in waiting with a beach taverna also not open (not even the toilets). We came to find fossils. The rock is part of the Pliocene Kritika Formation below the Rhodes Formation which is evidence of a pulse of transgression and regression. This was once thought to be the Kolymbia now discounted because of the presence of Pinna fossils not found elsewhere in the Kolymbia and the presence of echinoids called Echinolampas which died out at the Pliocene/Pleistocene border. At the base of the formation are high magnesium rhodolites (algal growths) which would have been produced in 40 to 50 m of clear, warm, water. We went searching. We found yellow blobs which looked initially like tiny gastropods. We were just beginning to explain why you would get a perfectly spherical death assemblage of gastropods when Richard came and rescued us by explaining that it (not they) was indeed a rhodolite as they can grow in this lamellar form. Also on the beach we found a large algal reef and beach rock ripped up from the sea bed – these are 8000 year old tsunamiites draped over the top of the Kritika .
What we really came to see were the fossils in the cliffs. I am no fossil expert and have no head for heights so I have left this part of the report to Di Clements who was in her element clambering up cliffs finding and recognising a whole range of exciting fossils (see below). They were so good even Brian found some to get excited about.
Our third location of the day was further south to the coast east of Kolymbia to the type location for the Kolymbia Limestone. The basement topography is a shelf of Kolymbia Limestone which was probably laid down in 1000m depth of water indicated by the zoophycos found in the rocks. Above the Kolymbia Limestone is the Lindos Bay Clay and below it is Haraki Limestone with a kast surface which had been weathered and leached showing a false start to the major transgression of the time.
Here too we found trace fossils, this time of Heliocodromites mobilis – a spiral corkscrew made by a worm moving in a spiral motion. These burrows are seen as little stitches in the rock where the burrows have been filled in by iron pyrites. Unlike the first set of trace fossils these were made by a pognophore worm with no mouth and no digestion. It lived through a symbiotic relationship with sulphur bacteria hence the iron sulphide left behind in its burrows. This area of the coast was an excellent place to end a long and busy day during which we had seen a lot of Rhodes both places that we would like to revisit and some that we were all agreed would not be on our itinerary if we were to visit again. Thank you to Richard for sharing with us his enthusiasm for the trace fossils that give us such a good record of life as it was lived all those years ago.
Ladiko Sand fossils
Richard told us that the Ladiko Sand is only found in this one small bay. It is now thought to be older than his paper suggested (Hanken et al, 1996) with clasts of the underlying Kritika Formation included in the lower beds. He pointed out 4 distinct fossil horizons that we looked at. Most of the group started at the lowest layer and saw the mussels Mytilus galloprovincialis (very similar to the familiar Mytilus edulis that we so enjoy eating), as well as the bivalve Spisula, both typical of a near-shore environment.
The next horizon was by far the most fossiliferous. We lost 1 or 2 members at this stage (including Gill), who were either nervous about the climb or beginning to get hungry. The most exciting find was the small, conical bryozaon, Cupuladria. Bryozoans are tiny colonial animals that usually possess identical zooids where the soft parts are house. In this group the are differentiated so that ones at the base of the inverted cone provide a walking function. It is difficult to imagine how they decide in which direction to go!. We also found corals, barnacles and many different species of molluscs. The bivalve Barbatia and limpets were of particular note. Another gastropod, Gemmula, was often found with borings from a predatory naticid gastropod. The horizon was so rich in fossils that Sue collected a bulk sample for later sieving.
Onwards and upwards! By now Richard’s followers were down to 4 (including Brian!). First we came to a plant-rich layer and finally another layer of marine fossils but with slightly different fauna than below. The big Spondylus gaederopus with sponge borings was particularly noteworthy. There were also some excellent trace fossils, particularly the vertical, lined burrows Ophiamorpha nodosa probably made by crustaceans. After all this excitement we made a slow descent to join the others on the beach for a much-needed bite to eat.
Sunday 3rd April
The prospect pleases, even at 7am, real sheep’s yoghurt with Greek honey to accompany the caffeine fix; a precursor to Plio-Pleistocene sedimentation, matched by the fly-past of a long-legged buzzard. Having read Richard’s paper, which contained the discussion of the new type section for the Cape Archangelos Calcarenite (CAC), with a stunning picture of clinoforms, I volunteered to be the scribe for the day.
Richard had promised a stimulating journey, over rough terrain – unmade road out to Cape Archangelos Promontory, north of Lindos and sheltering behind Mount Prophet Elias. We bounced past silvery-grey olive orchards, admiring the sheep with their gambolling lambs, and the goats which can climb trees, that’s why some trees wear plastic sacking trunk covers! Sun shining brightly, we stopped to photograph and digitize the stunning clinoforms, prograding SW with truncated tops, the magic word for these structures is asymptotic. Above these structures is an abrasion platform, with the occasional cave, instigated during the Rhodes forced regression (a superb section for S369). This Plio-Pleistocene material sits on a blush-pinkish Jurassic Basement, formed of the Kritica Fm, easily visible against the azure sea, and overlain unconformably by the Kolymbia Limestone (late Pliocene), part of the Rhodes Fm, and the Lindos Bay Clay (LBC) (Plio-Pleistocene boundary).
We clambered back into the vehicles, and rumbled further down the track to park the cars, and despite the sun put on our waterproofs to stop wind-chill. We wandered along a horizontal canal-like quarry, exploited in Mediaeval times for the outbreak of castle building by the Knights of St John (Hospitallers). Reaching the end of the quarry, and clambering down the cliff, the wind calmed as we encountered a goat trough, more of which later, because the sun was not shining on it! Suddenly, the type section loomed above us. The path met the section at a lithological junction. Looking up, it was easy to see the interdigitating CAC and LBC at the base of the sweeping clinoforms. CAC was a mollusc-brachiopod packstone, interspersed with silty terrigenous intercalations.
Pulsing sedimentation was indicated in the repetitive cliff profile. There appeared to be about 6 approximately 50cm thick cycles, showing coarse to granule-sized tempestites, probably storm de- posits formed in shallow water, which comprise these off-shelf deposits. They incorporate detached balls of rhodolite (named for the red alga Rhodophyta), fragmented red algae, random pecten shells, and hints of cross-stratification. As sealevel vaccilated, energy levels decreased, the grain size fined, and bioturbation became abundant, to be truncated by the next storm episode.
Above these distal-shelf interfingerings of CAC and LBC, are the bases of the large scale sweeping asymptotic clinoforms, prograding units varying from 10cm to 1m in thickness, some dipping steeply at about 30° before flattening out at the base. Individual clinoforms show fining up structure with coarser pebble to gravel grade material, including clasts of the basement limestone, comminuted skeletal material, showing abrasion and rhodolites which can be seen easily because of their white, knobbly appearance. The clinoforms are between 20 and 30m high, whilst the lower, distal section is about 20m thick. Although the junction at the type section shows clear interfingering, in other parts of the island it becomes erosive, and clasts of the LBC are caught up in the CAC.
This rock succession shows clearly the progradation of marine carbonate sand shelf sediments into deeper water as sea level fell, with eventual exposure, captured in the overlying erosive surface. No large-scale, true karstic development occurred because the CAC is too permeable and ill consolidated, and rainfall was only about 75cm/year. Once we had seen the clinoforms at close quarters, it was quite easy to pick them up in other places round the island; they are truly spectacular, and part of a very interesting Plio-Pleistocene sedimentation story.
Whilst I was overdosing on the CACs, others were variously enjoying the sun, flowers, or, fossil gathering from the LBC below on a treacherous exposure, dry crumbly clay with few footholds! However, it was crammed with goodies. Many turritellids; worm tubes, both horn-shaped Ditrupa and serpulid; nuculid bivalves, easy to spot because their pearly interiors glistened in the sun; solitary ‘horn’ corals; Aporrhais paes-pelicani, a stunning gastropod, and a few Echinocyanus pusillus (flea-like echinoids!). The lack of brachiopods indicates that the water was probably less than 100m deep, deeper however, than that in which CAC formed.
Well satiated with sediments and fossils, we transferred our attention to the stone goat trough, now in the sun, and discovered a paradise! Chara, a khaki feathery alga, having calcite sporangia, and spiral ornamentation which evolves with time, hence, it is good for stratigraphic purposes. Hiding amongst its fronds were toadpoles (Bufo viridis), and ‘almost’ froglets! With the sun on out backs, we basked in admiration; then contemplated the silt at the base of the trough, probably a mix of Sahara sand brought in on the wind, Chara sporangia and toadpole coprolites!
Back to the cars, and lunch beckoned – but we had to stop just after reaching the metalled road, to mourn the ‘sad end to a great rock’! The CAC has been leached and reprecipitated to form a bleached ‘caliche’ or calcrete, indicating a period of exposure, so this may mark a sequence boundary.
In Archangelos village, we stopped to view the cemetery, another to add to my growing collection (possible slide show in there!). The deceased must have been very friendly; there was hardly room to pass between the white, bejewelled graves. Then, as it was after 2 o’clock, off to Kolymbia for a fish lunch in a bustling, busy restaurant with a wonderful selection. Our quartet decided on a starter each to share, and portions of ‘Fish A’! This we interpreted as ‘fish of the day’, and we chose our two glittering red snappers, which were then spirited off to the kitchen! A couple of Mythos beers and cheerful conversation, then the fish – fantastic! Suddenly, it was 4 o’clock, and time to return to base, but on the way out of the car park, I noticed that the wall was ‘galetted’, just like it is in the ‘carstone’ area at home, so that forms part of another set of slides!
A great day on some wonderful rocks, which tell a terrific story – thank you so much Richard!
Diana M Smith
Monday 4th April
Monday morning and we drove south under a clear blue sky, heading first for Asklipio Castle, built by the Knights of St John. The hamsters under the car bonnets slaved hard to take us up the steep hill and we parked below the towering white walls of the castle. From our vantage point on the ramparts – which had never had to face battle - we could see the karst landscape with a dry braided riverbed below, the time since the last major flood revealed by the ages of the bushes growing there. Wild plants and bushes flowered in abundance - quiet country in contrast to the tourist areas further north.
The village nestled white below with an old traditional domed church at its centre, the date 1060 above the door, part Byzantine but with aisles added by the Crusaders. The walls and vaulted ceilings were full of mosaics and wall paintings of Biblical stories and allegories in Byzantine profusion, recently restored in Oriental Gothic style but blackened by candle smoke. In the courtyard outside were patterns of dark grey and dark red pebbles gathered from the beach and sorted by local women.
Onwards to a road cutting on a low coastal plain beside a stunning blue sea near Katavia. Above deeply weathered Oligocene fleisch were Pleistocene paleosols full of plant roots and fossils - five types of land snail had enabled accurate dating - and paleodunes of what thin sections had revealed was ooid sand, the first found in the Mediterranean; sea level must have fallen and the sand blown in from the former sea bed to produce the carbonate dunes. Amongst them were many fossil footprints, a veritable trample ground of pygmy elephants such as are found in the Namibian desert today. Skeletons of elephant and sabre tooth tiger had been found nearby. Jurgen and his students had been investigating the road cutting and their numbered tags marked out the features and showed where they had measured, logged and photographed – fascinating to see this evidence of work in progress.
Our next stop was at the foot of a steep hill of soft pale grey rock marked by thin parallel subhorizontal lines of dark sediment. This was the Apolakkia formation, lacustrine Pliocene / Miocene (the authorities don’t agree) silts comprising three lithologies: black (when wet) and organic rich representing quiet periods; white sandy sediment washed in from the shores; and channels made by storms and filled with sand and animal fossils from the shore. More skeletons of elephant, deer and sabre tooth tiger nearby. At the top of the hill was a thin layer of yellowish travertine, the Monolithos formation. Down below and without too much difficulty we collected fossils of all three of the native snails – Theodoxus Hellenicus, Melanoides Tuberculata and Melanopsis Orientalis. On the way back to the cars we saw clumps of enigmatic eggshell-like material in the rocks. No one knows what these are and they are being analysed in Copenhagen as I write.
Now followed a long and “interesting” drive through the hills on dirt roads with great views of the coast and of the mountains. The hamsters under the bonnet were working hard, drivers of the non-automatic cars had to stir the box and keep it on the cam, and for some fuel was running low. At last we reached Messanagros and the most excellent Kafe Bar O’Mike, proudly recommended by Niell MacLean in the Sunday Times of 26th January 1992. Four ladies of mature years sitting in the sun by a white wall at the side of the street kindly made way for a table and we lunched hungrily on Mythos, retsina, salad, tzatziki and excellent omelettes and souvlaki rustled up by Mrs O’Mike, followed by Ouzo on the house. A very good time was had by all but a sobering-up walk around the white walled village was definitely indicated. We visited the white and blue church with its murals and icons and saw ancient terraces with olive groves and vineyards.
On the way downhill from Messanagros we stopped to inspect some fleisch and a spectacular upper Cretaceous turbidite sequence - deep basinal sedimentary fascies, sandstones from deep basins linked to the Alpine orogeny. Lots of trace fossils (ophiomorpha, paleodictyon) and erosional bases and tool marks. By this time the light was not good, the Ouzo was taking its toll of this scribe and we decided to go home and come back to examine the location properly next morning (though in fact we didn’t!).
Tuesday 5th April
Today we travelled to the Monolithos area to the west of the island, stoping as we neared Monolithos for an overview of the Monlithos Formation, consisting mainly of Travertine, overlying the lacustrine Apolonia Formation.
Our next stop was to climb the dizzy heights of Monolithos (one stone) Castle. This castle, built by the Knights of St. John, was never taken, and one could quite see why when viewing the sheer rock walls which surround it. The castle is built mainly of local stone, but in the steps we could see limestones containing marine fossils. There are no marine deposits in this area, so where did they come from? Ships ballast perhaps.
Moving on down to the cliffs we observed Travertine with vertical tubular structures which are interpreted as floating reed beds. There are modern analogues where floating reeds form internal air bubbles allowing them to float upright. Climbing further down the cliffs and on to the beach the reeds were seen to occur in random directions, indicating that they are preserved in life position. Other features were seen here, including a channel fill with a bioturbated base, Ramshorn Snails in dark fine grained sediment, and algal mats in fallen blocks. We were also shown an interesting example of red foraminifera, a modern protozoa, growing on timber on the shore.
After a quick stop at Siana to buy honey we moved on to the little village at Mesanagros for lunch. The proprietor of the restaurant kindly moved tables and chairs into the street for us, and we partook of an excellent meal entertained by the antics of one dog and many cats!
Some 3km down the road to Lachania we stopped at a roadside exposure of a Flysch deposit. At first glance this deposit appeared to be a typical AE sequence turbidite with massive fine sandstone units up to 1.5m thick interspersed with thinner pelitic units. Some trace fossils were seen, including vertical Ophiomorpha and some horizontal traces in the sandstones. However, further detailed inspection revealed that none of the bottom structures typical of the high speed flow of a turbidite could be seen on the base of the sandstone units, eg. load, flute and grove casts. There were also no dewatering structures such as flame structures often seen in turbidites, so perhaps this deposit should more properly be defined as a debris flow. These flows are thought to be derived from offshore deposits deposited by a deltaic river system flowing from land raised by Alpine compression during the Oligocene.
And so back to Lindos at the end of another interesting day.
Wednesday 6th April
Today was the day for the most fossiliferous place on the island: St. Paul’s Bay, just to the back of Lindos. But first a trip to the Akropolis and a magnificent lunch on the roof top at Timi’s Taverna.
Lindos is built into the hillside in a wonderful maze of narrow, winding, car-less streets bordered by small, low houses, many of the roof-tops now being utilised as restaurants. I remembered the black and white pebble mosaic streets from my previous visit over 10 years ago, but now many are replaced with paving blocks and you have to peep through halfopen doors to courtyards to see the mosaics. The walk up the hill to the Akropolis passes an array of tablecloths spread over the ‘basement’ Cretaceous, Limestone. Richard pointed out fissure fills of Pli/ Pleistocene St. Paul’s Bay Limestone which ex- tended as small pale pink dots to fill in the sponge borings marking the submerged palaeosurface of the ‘basement’.
The ‘Akropolis’ is a marvellous mix of ages and cultures. The original Doric Akropolis dating form 3-4 Century BC is in the process of renovation. Many of the original pillars had been replaced with new ones, probably from the Kleopolu Calcirudite, from the Pleistocene, Lindos Acropolis Formation, the youngest rock from this area. The project began in 2000 and was scheduled for completion within four years. This now being the fifth year is was un- clear how much more restoration will happen before the money runs out. According to the explanation board an earlier temple stood on the site which was ‘believed to be destroyed by fire’. We all thought it much more likely that it was destroyed by earth- quake in this unstable area on the edge of the Hel- lenic Trench dividing Europe from Africa. Surrounding the Akropolis is the Crusader Castle, abandoned when the Knights of St. John were ousted by the Ottomans in 1523. They, too, built with the Kleopolu Calcirudite. The walls also housed a small 13th Century Byzantine Church and a truly marvellous prow of a ship carved into the ‘basement’ limestone during the 2nd Century BC. Limestone and marble blocks littered the floor, each with 2 holes for feet in different poses. These were the plinths of ancient statues with chisel marks indicating that the statues themselves had been stolen, probably long ago.
The views from the top gave us a real feel for the local geology with the Cretaceous Limestone standing proud and the Plio/Pleistocene sediments filling local hollows in the karstic landscape. Across Lindos Bay is the type section of the Plio/Pleistocene Lindos Bay Clay with a channel of the contemporary St. Paul's Bay Limestone cutting through it. On the outer edge of the promotory were the younger Pleistocene rocks of the Lindos Akropolis Formation with type sections of all 3 rock-types including the ancient quarry for the Kleopolu Calcirudite (Hanken, Bromley & Miller, 1996). Behind the town to the west we could see the caves at the base of algal bioherms topping of Cape Arkhangelos Calcarenite, just as we had seen at Cape Arkhangelos. To the south lay St. Paul’s Bay, so-named as St. Paul was reported to have landed here. At the far end we could see how the infill onlapped the ‘basement’ limestone. We would have a closer look in the afternoon. The non-geologists amongst us thoroughly enjoyed looking down on the kestrels.
Lunch on the rooftop at Timi’s Taverna was very special. How glad we were that we had come today, the sunniest of all, rather than the scheduled 1st day with grey skis, rain and howling wind. Timi and Mary own the apartments that we are staying in.
Finally down to St. Paul’s Bay, a real melange of rock-types. The St. Paul’s Bay Limestone is slightly pink, filling fissures, as we had seen on our way up to the Akropolis, as well as being ‘plastered’ onto the sides of the steep slopes of the underlying Cretaceous Limestone. Elsewhere, loose blocks, predominantly composed of the branching coral Lophelia pertusa litter the foreshore. These blocks also contain large scaphopods, Antalis (Dentalium) dentalis and deep-water, thin-shelled oysters Arceste which today contain sulphur-eating symbiotic bacteria.
A particularly interesting area that we scrabbled over behind the little white church, is of the deep-water (probably Pliocene) lower Lindos Bay Clay with blocks of younger, shallower (probably Pleistocene) Lindos Bay Clay and St. Paul’s Bay Limestone embedded in it. Great care was needed to ensure that the observed fossils were from the intended rocktype and not just loose in the scree. The lower Lindos Bay Clay here is dominated by brachiopods – pretty Megerlia truncata with fine ribs and larger, smooth ‘glassy’ Glyphus vetreus, seldom found whole but often displaying the interior with their lophophore attachment structures. Less common is the species Terebratulina retusa. Tube ‘worms’ are also abundant. The block from the upper Lindos Bay Clay has fragments of branching corals Madrepora oculata – the race was on to find the biggest bit! - as well as small, solitary cup corals. Shells of the bivalves Barbatia and Nucula are also relatively numerous although of much smaller size than those seen at Cape Arkhangelos even though they seem to be the same species. Small conical gastropods, identified as Danilia otaviana, nestle within the branching corals in the block of St. Paul’s Bay Limestone.
In the low cliff at the back of the bay we met the overlying Cape Arkhangelos Limestone again, this time packed with various species of bryozoans to form a truly bryozoan limestone. Back towards the car park, at the back of the bathing beach, the appearance was much more as we had seen it on our first day at the little bay beyond Pefka, dominated by scallops but also containing bryozoans.
The Kolymbia Limestone was visible along the west side of the bay but not examined. So, in this one small bay we had most of the rock-types already viewed along the coastal strip of northeast Rhodes, neatly packed into this one spot: a fitting summary of Richard and Ulla’s work on the island over 30 years or so.
There was one more outcrop to examine on the way home, another fissure fill of the St. Paul’s Bay Limestone, this time with the largest of terbratulids, Terebratula grandis, familiar to me from the Pliocene Coralline Crag of Suffok, along with a shallow water coral Cladocora cespitosa. In one area the appearance of the limestone was quite different, made up almost entirely of shells of the mussel Mytilaster marioni nestled into each other. Richard thought that this might have been caused by the shaking motion of an earthquake. Unfortunately depth indicators of the fauna within these Rhodian limestones can be meaningless as frequent tectonic events shift material down the steep slopes of the ‘basement’ Cretaceous Limestone. Great care therefore needs to be taken with environmental interpretation with trace fossils often providing the best indicators. Lucky we had an expert on hand!
Thursday 7th April
Final day and where to go? Richard’s hoped for coffee stop was quickly vetoed and the three cars “Cabbage”, “Lettuce” and “Liquorice” (named for their colours) set off on a mystery tour.
On the road between Pifki and Lardros we stopped to ponder the juxtaposition of badly B.U. ophiolite, a severely bored basement limestone, and some badly weathered flysch. We never came to a positive conclusion as to what had happened.
Near Laerma we stopped at a church next to the monastery of St Michael which is notable for three things. An outdoor peal of bells, whose hammers were operated by huge solenoids, a wonderfully tranquil garden and the most persistent sales person who would undoubtedly become Alan Sugar’s apprentice if she had not taken a higher calling.
From here we took a scenic route (it was green on the map) to Profilia. This 10km dirt road took us 45 minutes to drive as the rocks I was most interested in were the ones that would destroy the sump or suspension of poor little Cabbage. When we arrived the struggle was well worth while as a new road into this hill village had cut into the most wonderful flysch we had seen. This sequence of sandstones, mudstones and breccias was some 30 metres above the road level and was thought to have originated in Turkey, some 40km north, and deposited into a deep sea.
Now the return to lunch at Timi’s in Lindos. The first road out had a “ROADWORKS” sign, the second lead us into a Farmyard so we took the third and after half a kilometre passengers decided to scout the road of foot. Given the “all clear”, we slowly inches our way passed another monastery and finally debouched onto another road under construction whose road bed was some 60cm lower that our track. Using off-road skills learned at Solihull and Eastnor Castle our resourceful organiser guided all three cars onto the next unmade road with little visible damage.
Lunch at Timi’s was half the size of the previous day’s, eaten on the same rooftop in the company of the same cats.
All the books I have referred to tell me that the Lesser Kestrel is a colonially breeding insectivore so the single nest and
the dangling tail spotted below an adult tells me that I will not be adding Falco naumanni to my life list just yet.
Friday 8th April
Sadly, even the best things come to an end and it was time to return home to the UK. First came the inevitable tasks of packing and tiding the studios before we piled into the cars for the trek back to Rhodes airport.
We stopped on the way to examine some ophiolite (oceanic crust material), but we soon arrived at the airport where we said goodbye to our faithful cars – I was quite sad to leave my little Matiz behind, it had done so well. After saying farewell to Richard & Ulla, we went through the airport formalities and onward to a trouble free flight to Athens, a longish wait and then the flight back to Heathrow.
I would like to convey my personal thanks to Sue Vernon for planning and organising such a successful and enjoyable trip.
References (placed in the LOUGS Library for anyone wanting further information):
Lower Thames Valley : Greenlands Pit and Lion Pit Tramway
16 April 2005
The group was very keen with many members arriving at Greenlands Pit, Purfleet well before 10 am for the 10:30 start. When we had all duly arrived and been given the handout to describe the day’s features, we walked through the gates to the former quarry and scrambled down a bank to the exposure, which was to be our morning’s study. Greenlands Pit is one of four quarries that make up the Purfleet Chalk Pits SSSI. We were standing near the edge of the Pleistocene sediments where they lie on chalk (unconformity), to study what was the edge of the ancestral River Thames with its sequence of cold and fossiliferous temperate climate deposits. These are preserved within an abandoned loop of the river.
Prior to the Anglian glaciation, the River Thames flowed through Essex to the north of its current course. It was joined by the Wey, Mole and Medway, entering the sea near Clacton. The Anglian glaciation was the most severe and occurred between about 480ka and 427ka. It was about 1,000 metres at its thickest and reached as far south as Finchley and Hornchurch (just 7km north of where we were standing). The Anglian ice sheet led to widespread local extinctions, carved out the Fen Basin, caused the breaching of the Channel and shunted the Thames southwards close to its current alignment.
Within the context of the Pleistocene climatic fluctuations that occurred from about 1.64 Ma1, Danielle explained the history of this site and how it related to Swanscombe across the river in North Kent. We were told how the Pleistocene is more complicated than previously thought, as pollen is not discriminatory and cannot determine separate interglacial periods, whilst it does give an indication of the palaeoecology of the horizon. Fossils have provided a better way to separate the interglacial periods. Palaeo-biological information gives an indication of change in cold and warm stages.
Barnfield Pit at Swanscombe became the first geological National Nature Reserve because fossils of early humans had been found, which is a very rare occurrence. Alvin Marston, a local dentist, found two pieces of skull in 1935 and 1937, with a third found in 1956 by John Wymer. Whilst there has also been debate over the age of this site, there is clear evidence of it being in the first post-Anglian interglacial. The mammalian evidence strongly suggests deciduous woodland and open grassland with a temperate climate. Although there are conflicting views based on looking at single types of evidence, the preferred correlation is with the first post-Anglian interglacial of OIS 11 (marine Oxygen Isotope Stage), about 428ka to 380ka.
During this period mammals such as deer, elephants, beaver and bears occurred. The sequence starts to see horses, voles and lemmings. Sea levels were rising but these were compensated by isostatic readjustment after the ice. There was movement of different peoples from the Low countries/German plain that did not have hand axes; whereas hand axes start to appear near the top of the sequence (from Spain, Italy and France) as it moves to OIS 10 (c370 ka).
OIS 11 is best analogy of the current interglacial, suggesting that we are now overdue for the next glacial period. As glaciations are controlled by Milankovitch cycle and OIS 11 has the same orbital configuration as today there maybe another 10,000 years of warmth.
Greenlands Pit, Purfleet
Greenlands Pit was a chalk quarry opened in the 1960s and we were standing on the Cobbetts Tey terrace, which has been dated to OIS 9 – the second of the four post-Anglian temperate periods at about 335ka to 300ka. As we were to see, it appears to represent a predominantly wooded habitat adjacent to the river.
The quarry has exposed richly fossiliferous shelly beds where temperate molluscs, ostracods and mammal bones were found. Danielle explained the debate that has occurred over the age of the deposits. Some concluded that these deposits were of the Hoxnian interglacial, post-Anglian glaciation, based on mollusc evidence. Others suggested the Ipswichian Interglacial, which is much younger, on the basis of evidence from pollen. The fossil and pollen information give a faithful reflection of the climate but provide little definitive evidence for dating. Some better dating can be obtained from human artefacts but the best evidence is obtained from the marineoxygen dating.
However, at this site it appeared that the Thames flowed from east to west, which added fuel to the idea that it was a tributary. In fact, it seems that the Thames was running as a reversed S, which was later abandoned and that we were standing on the very edge of channel. This was first recognised by Wooldridge and Linton in 1955 (Structure, Surface and Drainage in South East England). The fluvial deposits are very wide (up to 1 km wide) and the presence of the freshwater pearl mussel suggests that the water was up to 5 metres deep.
After this description of the site and its setting, the group began to look in detail at the sections, which were in front of us. (The photographs on the website show the general section that is better represented in the handout sketch.) We were all given the task of mapping the section’s lithology by grain size and making an interpretation. The group produced mixed results but did begin to understand the complexity of the section and that the only real way of understanding it was to undertake some detailed observations and draw the section. Diana Wrench made the find of the day – a flint artefact. The photographs of this can be seen on the website and John Jarvis took the piece home to make a detailed drawing from all angles: 1 See Table 9 of “Geology of London”, BGS 2004
The group saw the sequence from the first unit to base of gravel where there was a lot of chalk; with lenses of silt, sand and
clay. The build up to end of cold stage at end of interglacial could be seen with the Coombe rock (chalk broken up from cliff and
deposited; rounded pebbles; handful of artefacts, but only flakes – no hand axes).
The hand axe industry comes in the central gravel unit but there is no indication of temperature. It could be a mud-flat
deposit such as cold > temperate > cold > temperate cycle; but the decalcification means it is difficult to interpret here. At
the top of sequence the mid-Palaeolithic was found where Neanderthals evolved. This is the only site in UK and, therefore, making
it an important chronological-marker here.
After an excellent morning at Greenlands Pit we all went off to the Sandmartin pub, a modern building in orange brick with large windows and well landscaped gardens at Chafford Hundred, for our eagerly awaited lunch, which most of us had previously ordered at the beginning of the day.
Lion Pit Tramway, South Stifford
After lunch we travelled to Mill Lane to park the cars and walk into the site of the old tramway cutting that led from one of the many chalk quarries to riverside wharves. Field work in the early 20th Century went largely forgotten until the 1970s when the Nature Conservancy Council reviewed geological SSSIs. As at other sites, dating has been controversial depending on the evidence used. Here it is now generally recognised that we were looking at the Middle Palaeolithic of the penultimate interglacial OIS 7 (200ka) where mammoth, horse, large vole and humans (Levallois artefacts) all lived. The sequence here is in the Taplow/Mucking Formation.
The section observed on the east side of the cutting was about a 15m thick sequence of gravels, sands and silts that were banked up against a former chalk river cliff. Below the base of the section is coombe rock – angular chalk rubble formed by periglacial processes in the cold climate (at OIS 8). At the base of the section in the cutting there is cold climate gravel (OIS 8), which is the source of mid-Palaeolithic artefacts. The sequence upward exhibited alternate clayey, silty, fine and medium-fine sand with flint nodules followed by well-bedded sand with clay cross-cut bedding. A trench was dug in the 1980s when samples were collected from the next deposit – unoxidised brickearth, where compressed plant remains had been found.
Mammals have been found providing evidence of open conditions – grassland with sedges in temperate conditions of the mid to end of interglacial. Mammals have big effect – woolly mammoths (Ilford mammoth), horse, bison, Oryx, red deer, rhinoceros. Forest mammals were present but they were few in number. The large numbers of animals had a serious impact on vegetation. The woolly mammoth was well adapted to colder climate but required vast amounts of food (like elephants). Mammoths more adapted to temperate conditions (smaller, less woolly) had teeth that were adapted to harsh grass. It is good indicator fossil as they have evolved with distinctive teeth style to reflect the different environments.
Finally, it was noted that the large amount of development in the area is placing pressure on these important geological sites. It is imperative that consideration is taken, if the exposures are not to be lost through the indirect effects of human presence.
At the end of the afternoon, Danielle was thanked for leading such an interesting and informative field excursion. At lunch we had been offered, at a reduced rate, the Field Guide “The Quaternary Mammals of Southern and Eastern England” that Danielle had edited and written the chapters on the Lower Thames. She willingly signed copies for us at the end of the afternoon.
Postscript: Members may be interested to read about the upper part of a straight-tusked elephant (Palaeoloxodon antiquus) that was found in the Ebbsfleet Valley near Swanscombe during construction of the Channel Tunnel Rail Link, which exposed a 400ka Palaeolithic land surface. Further investigations are being undertaken at the NHM on this find, which lived in England during the warmer, interglacial periods of the last 1.8 million years and became extinct about 150ka. See the feature at: http://www.oxfordarch.co.uk/pages/ctrlele_feature.htm
Odiham and the Basingstoke Canal - Led by Brian Harvey
15 May 2005
Joy! The canal car park at Odiham is where I think it ought to be; I am early. The Southampton Ramblers are friendly and give me a programme in case I want to join them; the sun is shining. Geologists arrive.
Brian gave us a quick lesson at the canal side. We are at the Cretaceous/Tertiary boundary near the junction of the London Basin, the Weald and the Hampshire basin. The geology is complicated as the syncline of the London Basin plunges in the opposite direction to the anticline of the Weald (this is not allowed, S260 students please note!). Cretaceous chalk is exposed where Tertiary sediments have eroded. It youngs to the south-east whereas the Tertiary sediments to the north young to the north-east, indicating an unconformity between them. The new geological map shows low gravitational and magnetic anomalies so it is intriguing to speculate that there might be a granite intrusion far below, continuing the sequence in Cornwall.
The canal is a contour canal. Brian explained that it was built as an agricultural canal to transport lime and manure to the unproductive Tertiary deposits of north Hampshire. Planned in 1778 by the time it was finished in 1794 it had cost £27 000 more than the £126 000 estimate. Geology has decreed that it will always have water problems particularly as there is little scope for makeup during the winter months.
After a short walk east along the towpath during which we identified the flowers, insects and birds we climbed onto the parapet of Broad Oak Bridge. The sparkly blocks of stone on the four brick pillars at each end of the parapets are sarsen stones. Sarsen stones litter the countryside. Paul (Hetherington) even has two in his, nearby, garden. The silica grains are well cemented with silica cement and the orthoquartzite is hard and durable. Windsor Castle is made of dressed sarsen stones and it looks as good as new after nine centuries. Sometimes sarsen stones have root holes but otherwise they have no structure and are not a freestone.
Now think about it. If sarsens are on the surface they must be younger than their sur- rounds. The sediments here have not yet had time for complete lithification; indeed the clays have barely started the process. Sarsens are crystalline, unlike flint. So how have they lithified?
Further along the towpath we came to a bank of dark brownish clay from the London Clay Formation of the Thames Group. Clay has high porosity as it has such fine grains but the pores are also very small, capillary pores, so it is impermeable. This clay is eminently suitable for use as puddle to prevent water leaking from the canal but it must not be allowed to dry out. Brian appears to have spent much of his working life trying to mend the puddle bases of reservoirs, which have dried and cracked - not a straightforward problem.
We were all relieved to move on, as the insect life was rather hungry. As we continued along the towpath the narrow boat Quinquereme chugged slowly towards us. Now we were walking on the Bagshot Formation of the Bracklesham Group laid down during a marine incursion. Di Smith climbed the bank to demonstrate the free flowing, yellowish, medium-grained sand. We also saw coppiced trees that were used for hop poles. Surely it was nearly lunchtime.
We left the canal at Sprat's Hatch Bridge and paused to let geologist-shy horses cross. How kind of the owners to leave some granite setts by the path for us. The biotite stood out from the white feldspar and silica grains (3-4 mm). Di identified them as Portuguese or even Chinese.
Boundaries between beds are uncertain here as evidence is hidden in these fields. We were shown a virtual outcrop i.e. a filled in pit, visible when Brian and Di walked it out. The fresh clay surface was mottled and we were assured it was the Reading Formation. We also passed heaps of head i.e. geological rubbish. Highland cattle grazed peacefully.
The lakeside picnic spot confirmed that the wood we passed en route grows on Thames Group clay. The grass was lush and damp. The sun still shone and the water birds were busy on Dogmersfield Lake. Brian pointed out that London Clay was impossible to farm until land drains were installed.
After lunch we crossed the busy Farnham Road into woods. The footpath was soggy London Clay. Soon we came to every leader's nightmare: a diversion. Brian got lost last week when checking the walk but fortunately Di was here put him right. Anyway, when we came back to the road again we had to rejoin our route further on than planned. There were cracks in the Lambeth Group alluvium in this field but no sign of the river.
As we climbed to Odiham we passed a clear stream, just deep enough for ducks to swim, on a spring line. There water seeps out of the Bagshot Sands and flows down the impermeable London Clay. The soil is yellow in the field beside our path but at the top a footpath to the left is white with chalk so at some point we crossed the unconformity of the Cretaceous/ Tertiary boundary. A golden retriever was so excited to have so many people to herd that we forgot to look for the exact spot.
We followed a chalky path to a massive chalk pit possibly used as long ago as Caesar's time. The flint bands indicated Upper Chalk. The chalk is mainly only suitable for marling agricultural land but there is some hard ground where deposition slowed allowing bioturbation. We saw examples of such 'clunch' in the church.
In the churchyard we all dived into the early seventeenth century pest(ilence) house. If there is a sudden drop in LOUGS numbers it could be because germs are still lingering. Actually it felt quite cosy and welcoming.
Finally we looked at The Church of All Saints. This is a 'bitsa' building. The brick tower contrasts strangely with the flint walls but a brief inspection revealed Upper Greeensand, clunch, Oolitic Limestone and the odd brick in the walls as well. Harder wearing imported stone - with shells, has had to be used for the corners. If you visit Odiham be sure to look on the south outer wall for the trace of a heart urchin in one of the flints.
The Font is carved from a solid block of clunch. So many hands have stroked it over the last five hundred years the surface is almost oily. The chalk is exposed around the top rim where the ornately carved lime wood cover has been replaced carelessly.
As we wended our way back to the car park we admired the buildings of Odiham. Paul proposed a vote of thanks to Brian for giving us such an interesting day. I reflected on how confusing clays are. One last thought: Brian is convinced that somewhere near Windsor Castle there is a pit of sarsen chippings. If you happen across it don't forget to tell him.
Weekend to the Lizard Peninsula - Led by John Mather
28 May - 1 June 2005
Saturday 28th May (evening)
Our introduction to the geology of the Lizard Peninsula began on Saturday evening when our leader, John Mather, explained our programme for the next three days. We would see a variety of igneous and metamorphic rock types in this much studied and very complex area, interpretations of which have differed widely. Although it is now generally accepted that the Lizard complex is ophiolitic, some features are difficult to match up. But we would sort it out once and for all!!
Sunday 29th May (Morning)
On a very sunny Sunday morning, we set out for our first locality at Polurrian Cove on the north-west coast of the Lizard Peninsula. It was high tide when we reached the beach, but fortunately we were easily able to reach the most interesting exposures. On the south side of the cove, there were spectacular outcrops of dark blue banded hornblende schists, which it was decided could be metamorphosed gabbros or basalts. These outcrops were very clearly different from the dark blue slates on the north side of the cove which we looked at next. As we walked around the cove following John’s directions, we were soon able to note that separating these sections on the inside bend of the cove, the fault could be clearly seen as a zone of breccia, incorporating visible lumps of slate. The hornblende schists lie above the slate and the fault is therefore a reverse one. Much discussion followed regarding the origin and degree of metamorphism of these gabbros or basalt lavas at this boundary where the rocks of the Lizard complex are believed to have been thrust over the sediments to the north.
We left the beach to walk across the top of the cove, over the hornblende schists. Looking out towards Mullion island, there
were some who were convinced that they could see (with the aid of binoculars) the pillow lavas which are said to be evident there.
However, John was not convinced he could see anything more than “lumpy ground”!
Our next location, (which would have been the first of the day, but for the very high tide) further north along the coast, was only accessible via an interesting circuitous route through narrow, winding country lanes – two minutes if we were crows flying the same route! Here at Jangye Ryn, the Devonian country rocks showed clear evidence of classical knappe structures with tight folding and squeezing of the beds of alternating slate and greywacke (interpreted as turbidite formations) as they were pushed up to the north. Tension cracks vertical to the bedding were seen on many of the tight folds. Very interesting, quartz-filled S-shaped tension gashes were seen across many small faults, and on some of the slate surfaces there was evidence of earlier rip-up clasts.
Overlying this section at the top of the cliff were some very different horizontal beds of broken up gravels topped by finer material. John called on Jenny (Bennett) for an interpretation of these “young” rocks. Jenny explained that the sediments were of Pleistocene age formed by freeze/thaw action and solifluction in down-hill flows. During the Pleistocene, this area was affected by periods of extreme cold, comparable to central Europe and China today.
Sunday (Locality 3)
The final stop on Sunday was at Kynance Cove, down near the southern tip of the peninsula on the western side, and well onto the peridotite. This is the Cornwall of postcards and picture books, and we saw it in perfect weather at low tide. After descending the steep path from the car park we crossed the beach, picking our way over the towels of bathers and avoiding the sand-engineering projects of the children, to the rocky outcrops and a spectacular cave where, legend has it, a dragon used to live. The most common rock here is the fine-grain recrystallised peridotite known as tremolite serpentinite with the dark red and green banding and the distinctive “snake skin” appearance of weathered surfaces. Veins of green chlorite and yellow/green epidote were also seen, and some green glassy veins which were said to be a calcium silicate. There were also two large outcrops of granite, one on the beach and one higher up in the cliff, which appeared quite out of place among the dark mafic rocks. How this granite was emplaced is still a geological puzzle.
Returning to the top of the cliff beside the car park we had crossed a fault trending NNE-SSW and come onto a different type of serpentinite. This is bastite serpentinite, a coarser grained derivative of peridotite in which large shiny crystals of bastite could be seen glinting in the Sun. Bastite is a pseudomorph of enstatite orthopyroxene, and there was a lively discussion on whether enstatite in the original peridotite had been changed to bastite during serpentinisation, or whether it was the other way round. Bastite peridotite was considered to be the primary assemblage formed in the upper mantle, and the finer grained serpentinite formed later by recrystallisation at lower temperatures and pressures, a process that may still be going on.
Monday 30th May
Locality 4 – Church Cove, Landewednack
As we walked up from the sea to the abandoned quarry nearby, we passed a heavily weathered “grotty” exposure of the hornblende schist where quarry access had been cut through; a short distance further we reached the corner of the quarry where there was a contact between the hornblende schist and bastite serpentenite. We could identify the position of the fault contact by the strip of vegetation which had found a root hold on the fragmentary margin between clean exposures of the two rock types. Further on into the main part of the abandoned quarry and the bastite serpentenite had veins of talc wriggling through it. On the far side of the quarry from where we had entered the bastite serpentenite contained felsic gneiss intrusions with small lenses of augen gneiss characterised by being white with black blobs which the gneissic texture flowed around. It is most unusual for the dark minerals to form the augen (eyes) in this way since, rather than the other way round. Normally pale quartz or feldspar (being more resilient) form the augen with the darker minerals incorporated into the surrounding gneiss.
We also saw two black birds fly over us. There was much resort to binoculars, and some of the party identified these birds as having the characteristic red beaks and legs of the Cornish Chough. Others, however, remained unconvinced. The Cornish Chough is the national bird of Cornwall; its red beak and legs are purported to be stained so by the blood of King Arthur as his spirit took the form of a crow to journey to heaven and escape his savaged, dying body. In the past choughs had nested in several places on the Lizard, but having becomeen extinct in Cornwall in recent timesover the years, choughs have recently been reintroduced in this locality, and the party had been very much looking forward to seeing them.
By the derelict lifeboat station we examined a sequence of schists (predominantly mica schists but with some hornblende schists) and phyllites, which formed part of the Basal Unit of the Old Lizard Head Series of the Lizard complex. Offshore were some islets, the islets of the Man O'War reef. We were told that the islets were composed of the Man O'War gneiss, an intensively deformed rock with a much more basic composition then most gneisses. John explained that this gneiss was thought to come from the Southern shore of the Rheic ocean, the closure of which had led to the formation of the Lizard complex. The party then dispersed to take various refreshments and walk along the lane back to Lizard Town.
Some time later we embussed back at Lizard Town to go to Kennack Sands (locality 6) to examine the Kennack gneiss, a significantly later element of the complex, and its relationship with the serpentenite. As the bus could not get down to Kennack Sands, we parked at the village of Kuggar, and walked a kilometre or so down the small road to the shore.
Kennack Sands proved to contain a classic exposure, much used to train geology students to determine the sequence of rocks by
mapping the cross-cutting relationships. A cliff of bastite serpentenite is surrounded by banded gneiss, veins of which penetrate
into the serpentenite. The serpentenite is cut by a gabbro dyke which is cut by an epidiorite dyke, which in turn is cut across by
the banded gneiss. However while the gneiss appears to occur last in the sequence, it is not clear that it is a simple matter of
the intrusion of a later rock. The gneiss and the serpentenite are interlocked in a complex manner, and it is not entirely clear
how they came together. There is also controversy about the origins of the gneiss, whether it is derived from the hornblende
schists and other more felsic rocks in the Old Lizard Head Series, or whether it simply results from the fusion of various more
felsic or mafic magmas.
We saw that the serpentenite frequently had veins of talc and tremolite (asbestos) and round the corner from the main exposure we admired veins of "grossular" (ie "gooseberry") calcium garnet standing proud of weathered serpentenite. Further on, there was an offering for quaternary geologists in a solifluction deposit of Head, with very angular clasts, mostly matrix-supported.
As time was getting on, the party refreshed themselves with ice cream supplied at the vending huts by the beach, before walking
back up hill to the bus.
Helen Coombs and Richard Trounson
Tuesday 31st MayThe group assembled in full field trip gear including hard hats and with yellow hi-vis vests in our rucksacks, on a cloudy and rather overcast morning. The bus left about 10 minutes late due to the driver stopping to buy “The Sun” and we then proceeded to Porthallow on the eastern side of The Lizard peninsular, via typical Cornish roads - thin, windy with tall hedges at both sides. Encounters en route included a lorry, the post van and two lady joggers - various stopping and reversing ensued while the joggers passed us several times!
At Porthallow Cove we alighted and proceeded along the beach in a westerly direction examining the cliffs and the beach rocks and boulders. The cliffs revealed outcrops of Devonian slates with greywacke, followed by mica schist, then acid gneiss, followed by hornblende schist with talc and finally dunite serpentinite with more hornblende schist visible beyond this. Many different rocks were found on the beach including boulders of gabbros, serpentinite, etc. The confusion of rocks found here are a result of The Lizard boundary fault passing through Porthallow, although the exact line or lines of faulting were unclear. The serpentinite found on the beach included many specimens with unusually fine combinations of reds and greens and an “opal” type sheen, a number of these found their way into geologists’ rucksacks.
We then walked across the beach to the east side of the cove where the cliffs were formed of a grey igneous rock, apparently a sodic microgranite. We were told this eastern side of Porthallow Cove was formed of a breccia melange of limestone, quartzite, etc with blocks up to 30m in size, while there were also supposed to be pillow lavas - but none of this was very obvious.
Most of the party then proceeded up the coastal path, some of the steps proving rather large for those of a shorter disposition, until we were overlooking Nelly’s Cove. A section through the Quaternary deposits showed a raised beach with solifluction and frost shattering above. A kestrel was seen to land above this cross section.
The group then boarded the coach and proceeded to the West of England quarry at Porthoustock, a working gabbro quarry producing large quantities of roadstone, much of which was exported by ship from the deep-water port alongside the quarry. Before entering the quarry yellow hi-vis vests and hard hats were donned by everyone and we then proceeded along the upper road above the main working quarry, examining the rock face as we proceeded. This consisted of gabbro with many dykes of fine-grained basalt varying in thickness from a few inches to several feet. There was some discussion and difference of opinion on whether these dykes showed chilled margins. We followed the upper quarry road until we reached an old quarry on the seashore where a dyke swarm was seen. After this had been examined most people proceeded to the rocks along the shore to eat their picnic lunches.
After lunch we went onto the beach where the Quaternary deposits showed a fine raised beach, clearly laid down when sea level was several metres higher than at the present day. Angular pebbles above showed the effects of solifluction. Amongst the boulders seen on the beach were several composed largely of basalt but apparently showing small intrusions of gneiss within the basalt. We then proceeded back out of the quarry, stopping en route to view the hectic activity on the quarry floor, where quarried stone was being crushed, graded and removed in lorries.
As we finally left the quarry the long expected drizzle arrived. We therefore took the coach for the short journey down the hill to Porthoustock Cove where we proceeded up the coastal path to the east of the cove to have a look in the first of many large quarries, which were worked until shortly after World War Two. The remains of many concrete walls and buildings, tramways and a large concrete jetty for loading the rock onto ships showed these quarries to have been extremely extensive.
The rock here was found to be hornblende schist, composed of very fine grained metamorphosed lavas. By now the drizzle had set in and the air was distinctly chilly, and most people must have been glad they had not followed one of the ladies idea of wearing shorts! A buzzard was seen above the quarries while a lizard posed for its photograph. After a chilly 20 minutes or so we proceeded back to the coach to go to Coverack, our final site of the trip.
By the time we arrived at Coverack a steady drizzle had set in. The first steps to the beach were roped off and we therefore had to take the next steps to the beach where we headed eastwards, unfortunately encountering a stream running through very slippery rocks. While most people got through this slippery obstacle to go and examine the rocks along the beach, four of us retired to the local cafe where a hot chocolate and bacon sandwich was most welcome. By the time we had had a leisurely eat and drink and got to the beach the drizzle had stopped and the group were nearly back to their starting point, having observed outcrops of peridotite, gabbros and dunite serpentinite on the east side of the beach. Proceeding westwards towards the harbour we saw more gabbros and peridotite before coming across an outcrop of troctolite. This rock was red in colour with white spots and came from the Moho. As it was now nearly six o’clock we had to return to the coach and drive back to the hotel for dinner.
Another excellent dinner was enjoyed half an hour later than usual, after which Wilf presented John with a bottle of his favourite tipple, Laphroaig, and we all joined Wilf in thanking him for leading us on such an enjoyable and informative field trip over the previous three days. Thanks were also given to Wilf for his excellent organisation, to the two waitresses, and attempts were made to congratulate the chef but he turned out to be very shy and ran out of the back door of the hotel! Later in the evening some people made a surprise visit to the kitchen and managed to find the elusive chef, while Di Smith led several people in identifying the rock specimens collected during the day; serpentinite, troctolite, peridotite, gabbros, gneiss, schist, slates, etc - which are going to be used in a subsequent display to the Geologists Association. Most of us retired to the hotel bar for the rest of the evening, a good way to end a very successful and enjoyable field trip.
The geology of Pegwell Bay, East Kent
17 July 2005
Those who did not manage to get to Pegwell Bay missed a treat. On a glorious breezy, sunny day about twenty of us met just as the car park was being opened and gathered together as the leader, Peter Golding, put us in the picture. Peter is very well-placed to do this as English Nature, under their ‘face-lift’ programme for SSSIs, and Kent RIGS (Regionally Important Geological/ Geomorphological Sites) have recently been conserving this cliff section under his leadership.
Firstly the regional context: from where we were standing we were looking up the dip slope of the chalk (a dip of 8º is a lot in Kent!) which comes down in the Thames estuary. The chalk disappears under the Tertiary and reappears in Thanet. Originally the river Stour, the reason why Thanet is an island, drained to the north, part of the Thames and Medway system, but sea-level rise at the end of the Pleistocene, the Flandrian transgression, plus longshore drift, driving banks of shingle landwards, have resulted in its exit into Sandwich Bay. In AD43 the Romans landed at Richborough, as did Hengist and Horsa in 449, an event commemorated in 1949 by the donation of a replica Viking boat (though of course they weren’t Vikings; not for nothing is it called the Saxon shore!) Recently restored, it now stands proud and gleaming over the abandoned hoverport, the latter an object lesson in how quickly nature can undo the works of man.
We walked westwards along the degraded cliff line to the RIGS main cleared section, where we were invited to sketch what we saw. At the top is a deposit of brickearth (loess) with a line of black pebbles at the base. Beneath are Reculver silts, which have been extensively bioturbated and no bedding can be seen except in the prominent doggers, storm deposits lacking nutrients. Finally at the base of the cleared section greenish brown Pegwell Marls have been exposed.
Moving further west, at our second stop we examined the doggers more closely, and also saw columnar jointing, which together with the vertical position of many of the pebbles indicate frost action in the Ice Ages, though this part of the country was never covered by ice.
From here, we went back towards the east and beyond the steps from the ship we saw a solifluxion deposit of chalky material below the brick earth and above the silts and angular, frost-shattered flints. Our final site before lunch was in a trench in the lower Pegwell marl, which has a greenish tinge from the glauconite; quite large forams have been found here, but no shell beds.
We ate our lunch, still in sunshine, and were pleased to find samphire and wild fennel to supplement our diet!
Our next stop was the famous unconformity where the base of the Tertiary lies on top of an erosion surface on the chalk. Above the unconformity is a greenish sandy clayish bed with lots of glauconite and bull head flints. The clay associated with the flints is montmorillonite clay, made of volcanic ash about the date of the volcanoes in the Inner Hebrides at about 56My, right at the beginning of the Tertiary. The chalk under the unconformity is rubbly, perhaps the result of freeze-thaw.
Continuing eastwards towards our final section we saw dramatic involution and solifluxion with chalk and flint rising up into the Tertiary sediments, the result of repeated freeze and thaw. Pegwell Bay filled channel was the last cleaned site. The base of the channel has chalk clasts in a silty matrix below a solifluxion deposit, but the infill is Quaternary, with the lowest section about 88,000y by OSL dating, going up to 70,000y towards the top of the channel. Above is brick earth resting on an erosion surface at the top of a zone of involutions. We can perhaps imagine a cold and stony desert.
We walked on round the Chalk cliffs noticing numerous faults, a sponge bed showing as rusty patches, pyrite nodules, big burrow flints and late stage flints, later than the Chalk in which they are embedded.
Coming into Pegwell Cove by the sea wall, two big faults bring Whitaker’s Flint Bed to sea level and we were walking on a huge flat layer of flint and then on a chalk platform, an important site for rocky shore fauna. Across the bay the flint bed rises again. Our last marker was Bedwell’s Columnar Flint Bed with layered great flint masses, some with vertical burrows and a chalk core. It’s an interesting thought that our two or three kilometre walk along the beach covered perhaps a hundred million years from the brickearth to the Middle Chalk.
Our day ended with a walk round the headland to a steep exit from the shore through an artificial rock grotto to the top of the cliff, whence we made our way back to the starting point along a narrow path.
A really satisfying day with many thanks to Peter and also to Di, who had cleaned some of the sections!
Winter weekend : Chalk coast of France - Led by Prof. Rory Mortimer
28-30 October 2005
Day 1. Friday 28th October 2005
Rory joined the coach at the Dover ferryport and immediately the geology started!
But!! Even before we’d left Dover, lively discussion on the flint erupted:
The weekend was to be a traverse of French coastal geology to introduce some recent, stimulating ideas on the origin of chalk deposits in the Anglo-Paris Basin. This first day was designed to introduce key lithological and fossil marker beds that would be followed along the coast.
It was a smooth crossing, warm, sunny and spring-like to Calais, perfect for hanging over the stern rail instead of absorbing the handout we had just received! The simplified geological map we had been given showed Calais at the northern end of the chalk basin: we were to head south.
Passing the Sangatte terminal, Rory related how geologists had retrieved the Channel Tunnel construction programme using
microfossil analysis to speed the drilling machines through the chalk.
Rory continued the coach commentary, summarising the build-up to understanding “the beautiful chalk: God’s own rock” from the late 19th Century, but particularly the latter third of the 20th Century. Co-operation with the French had greatly advanced correlation of the Anglo-Paris Basin. We were to see and identify “familiar markers” from Sussex and Kent on the French coast.
The A16 was one of a number of autoroutes in the Paris Basin, constructed in the 80s and 90s which prompted investigation and produced much new data. Engineering of high-speed rail links and building nuclear power stations has produced better understanding of structural variations and tectonics in the chalk.
We climbed out of the Somme valley onto a plateau, where loess lies on top of the chalk. This is thought to have come from the Alps. It is unstable when wet and thus poses a very serious risk to engineering structures. A database has been compiled from many sources. This is part of multidisciplinary studies aimed at geohazards along coastlines and groundwater controlled floods.
At last we stopped (but no toilets) at a small town with a big, big problem! Ault is the most northerly of at least twenty
towns and villages with cliff-line recession due to chalk fracturing. The “shock” from waves breaking onto a wave-cut platform is
felt 20m into the base of the cliff, and rises and falls of the cliff have been correlated with the tides. Cracking and
fracturing are apparent from the beach. Loess tops the chalk with vacated houses on the cliff edge.
Leaving Ault, we passed through Le Treport. Rory pointed out that the rivers along the coast had exploited faults, and the
drainage was SE/NW. The largest fault, the Bray Fault ran through Dieppe, where we were now heading to our hotel..
Day 2. Saturday 29th October
On an overcast and misty morning, after shopping for lunch in the town, we joined the coach and drove out through the western
suburbs of Dieppe.
We then get back onto the coach for the drive to the Etretat area. We were able to appreciate the country behind the coast, dominated as Rory said by high plateaux pierced by valleys pointing in a SE - NW direction. This was farming country, which provided the basis for the rich cuisine of Normandy, and there were also numerous chateaux and other elegant residences on the route.
On the way Rory talked to us about various geological topics. He gave us an insight into the practical application of a
knowledge of the varied manifestations of the chalk in an engineering context. What appeared to be the initiated to be a fairly
uniform type of rock had greatly varying contents, porosities and densities, and these led to considerable differences of
behaviour in different conditions of moisture. This had significant consequences for building motorways, because in certain
conditions, particular horizons of the chalk could turn into a soft slurry. We were told of the use of huge drying machines for
making the chalk sufficiently firm to serve as a base for road construction.
As we passed through Fécamp, a favourite resort of cross-channel yachtsmen with its smart fish restaurants, discussion diverted
briefly from geology to the history of the local liqueur, Benedictine.
In geological terms, the section contained the upper levels of the Cenomanian and the beginnings of the Turonian. Rory drew our
attention to the extensive flint layers, much more extensive than in the main part of the Paris basin. Different sedimentary
processes operated in different parts of the basin. We were given an explanation of the difference between cherts and flints and
told, in particular, how purer chalk gave rise to denser and darker silica.
Having initially examined the cliffs to the west, we turned east along the beach to a suitable spot for lunch. On the way we examined an area of very variable stratigraphy, with channels down cutting into the Hard Grounds and big pipes at the top of the cliff, possibly tidal scour channels. We then enjoyed the sandwiches and other delicacies purchased that morning in Dieppe, in what was now bright sunshine.
Saturday afternoon 29th October 2005
The coast at Plage d’Antifer and Pointe de la Courtine
There was evidence of manganese (pink) colouring on flint, which suggested volcanic activity. It was here that Rory let us
loose for 20 minutes to look at the colours and sedimentology.
There was evidence of a lot of energy generated in the system – tidal scour channels – but Rory was sceptical since there was more energy involved than tides such as one-off events and then filled. It may have been the result of volcanism in the North Atlantic.
Moving further along the beach, the Tulliel hardground dropped out but huge mounds developed with sediment coming down big
fractures distorting things! We were reaching the upper Turonian and karst features.
When we reached the promontory we found that we could not get through. The sea had obviously been doing its erosion by washing
away the pebbles and steps that led up to way through. Some people had arrived from the other side and were managing to scramble
down but there were no toe-holds for us to go in the opposite direction. Therefore, we had to retrace our steps then to walk to
the top of the promontory.
After the evening meal we all took our places in the lounge to have a discourse with Rory:
Chichester is most active earthquake area of Britain, but very small ones. The Channel Tunnel project had to do a big seismic
study for its construction; Dover has been destroyed twice in historical times. And, all in an area that gives the Impression
of not being a seismic active area.
Tomorrow we will see spectacular karst structure – extraordinary structures! “It’s the totality – a total rock approach!”