Trip to French Jura 2002
Text and Photos Lynn Everson
The story of our trip to the French Jura is one of limestone, water and wine. Elisabeth d’Eyrames put together a six-day programme of trips radiating from Arbois, her home town, which illustrated the interconnectedness of these three themes. Each trip had a new leader and so the week was one of immense variety. Elisabeth not only arranged the trips but also acted as translator for those amongst us whose French had got a bit rusty. And she arranged great evening meals and barbecues for the whole group in her garden. I imagine that at the end of the week she probably felt the need to hibernate for the rest of the year!
Since the Jura is the type region for the Jurassic, it should not be surprising to hear that 3 out of the 6 days were almost entirely devoted to exploring limestone.
Journey East West accross the structures of the Jura.
Our leader on the first day was the distinguished Prof. P Chauve, the author of a geological guide of the Jura. He is a specialist in the structural geology of limestone.
We started out at Le Cirque du Fer à Cheval near Reculée des Planches. Like so many of the terms we were introduced to, I don’t know the English word for ‘reculée’ (dead-end valley). A reculée forms when a limestone layer overlies a layer of marl. A stream will erode and remove the limestone, eating back an arena-shaped area in the upper layer so that cliffs surround the flat floor of underlying impermeable marl. Then the whole arena structure is known as a reculée.
For the rest of the day the professor took us on a journey across the short axis of the Jura. He started on the small scale, by leading us through a geological mapping exercise of the fault graben around a village called Montrond, near Champagnole. As we travelled further he showed us different tectonic styles and everlarger geological structures until we reached the grand finale overlooking the great kilometre-scale mega-cliffs of the Flumen Gorge at Roche Blanche. I seem to remember spontaneous applause breaking out as these came into view, but maybe it was just that I personally felt like applauding, for the sheer dramatic effect.
Mapping the graben at Montrond had another significance, apart from demonstrating how the smaller structures relate to the larger ones they are part of. It was an introduction to the concept of a 'faisceau’ (fasces or bundle in English), which was a word new to me that cropped up time and again throughout our wanderings. Rather than meaning a sedimentary facies, I think it would be better translated as a large-scale folded sedimentary complex. The down-faulted block of this graben at Montrond was part of the Faisceau of Syam. After the initial, extensional, graben-forming stage the block had been compressed and folded. Then a third event had seen the graben sliced through and offset laterally by a strike-slip fault.
The Jura region is roughly banana-shaped, surrounded by depressions. Our journey took us from northwest to south east across the short axis of the banana so that we encountered the three longitudinal sub units of the Jura region – the outermost 'faisceau’ (furthest from the centre of the orogeny), the middle plateau and the innermost folded subalpine high Jura.
From Montrond, we moved on to investigate a large fold structure in a road cutting by a tunnel near Sirod. This structure explained more about the formation of the Faisceau de Syam. We were told a story of faults that formed in the Oligocene and were reactivated in the opposite sense during the mid Pliocene by a second event that pushed the Jura over into the Plain of Bresse. I’m sorry to say that the details of this story escaped me, but I have to mention it as Annette has a good photo! Several of the geological sites had interpretation boards and an amusing one was to be found at ‘Le Chapeau de Gendarme’. The gendarme’s hat was the name for a local beauty spot, a cross section through an anticline in the shape of a hat, visible beside a waterfall. It seemed quite imposing as we stood close by, but at the end of the afternoon it looked very tiny and was only just visible when we viewed from Roche Blanche the grand sweep of the hillside of which it formed part.
Jurassic reef complex
On the second day, too, we concerned ourselves with limestone, but this was more ‘noses on the rocks’, upclose geology. Prof. Davaud of the University of Geneva had us crawling over limestone scree on the Prapont hillsides, along the Samine river valley near St. Germain de Joux, to inspect the reef and lagoonalperitidal carbonates from the upper Kimmeridgian and the lower Berriasian of the western Jura.
It seemed so strange to hear the names Kimmeridgian, Purbeckian, Oxfordian etc., so far from their English counterparts. We have become accustomed to vast geological timescales as they appear in the shallow vertical record, but often forget the enormity of the lateral extent of some formations. However, it appears that the English and French definitions of the terms do differ.
We looked for the development and eustatic control of an Upper Jurassic reef complex. Here were fine examples of transgressive cycles, maximum flooding surfaces and sequence boundaries; great for those of us who have studied S338 or it’s successor S369.
Rudists and more reef environment deposits
The hillside was composed of core reefs and flanks. The first reef we saw shallowed up into beach deposits. At the top of this reef, pore spaces caused by shrinkage and evidence for mixed brackish and salt water suggested emergence. Overlying this there was a black pebble conglomerate topped by microbial mats, the base of which is believed to represent the new sequence boundary (according to a study in our handouts by Dr. E. Fookes, University of Geneva). That afternoon we moved laterally from the reef facies into the lacustrine, coccolith mudstone. There were no other fossils preserved in life position, but there was up to 10% organic matter in some levels and it is the decomposition of this that had made the water anoxic. The environment of deposition for these muds has been interpreted as seasonal lacustrine brines that became oxic in winter, when there was less organic stuff entering the system.
This facies is likely to have been a protected lagoon, bordered all around by reefs, like in an atoll. We split open the rocks, looking for plant remains, which were dark brown and easy to see against the pale mudstone. There were occasional fish remains too. That night we stayed in a ski lodge called La Fauconière near Giron, in the high Jura, not far from Geneva. The day had been hot and sunny like the day before, 29 °C, and so the first thing I did when we arrived was to plunge into the hotel’s outdoor swimming pool. Bliss! No time to linger, though, as it was closing before dinner, in a few minutes time.
Then the third day dawned sunny and bright again. This time we were led by Christian Gourrat, a friend of Peter Skelton, so familiar to many of us from our OU studies. The first stop was beneath the Cirque Glaciale Fauconière, in the Oyonnax valley, where we searched for beautiful ammonites and other fossils that were plentiful in the bed of a stream.
After that we moved on to the entrance of a working quarry. There were 20 miles of tunnels in the quarry, but we stayed outside and inspected more corals and other reef fossils in the Upper Jurassic strata at the entrance. The limestone here was 99.99% pure calcium carbonate, with very little iron content and it used to be added to white bread, but is now used for toothpaste, paint, concrete, etc.
Then Christian took us to a small exposure of a reef in the woods near Marchon, a short drive from Oyonnax. He and Peter Skelton are researching the rudist bivalves that lived in the corals here. The shells of the rudists were not all the same shape – some had shells like ice-cream cones and some were twisted. However, the shape was not characteristic of different species. They were all oriented in the same direction and this gives an indication of the current direction. They were suspension feeders. The limestone here was peloidal, rather than oolitic.
We had lunch on the patio at Christian’s house in Marchon and drank wine and kir while munching our food. Then Christian showed us his workroom, which housed a superb collection of fossils of all sorts and sizes. He also demonstrated the stages in the preparation of fossils for study or display. These involved using a wooden chisel to hammer gently at the surface of the fossil to chip away the matrix and then using a pneumatic drill to expose the fine detail. I think that the final stage involved the use of a highly diluted hydrochloric acid solution – but please don’t try any of this unless you have confirmation from another source that it is correct, because I didn’t write it down and don’t remember the details, I’m afraid.
After this we took our leave of Christian and started our return journey to Arbois, stopping on the N78 at Pont de Poitte to gaze at the ‘marmites’ (cooking pots) in the bed of a river. These were depressions that had been excavated by water arriving in a fast narrow stream, then spreading out over a shallower area and expending its energy by stirring stones around in whirlpools, thereby excavating the pots. It was a beautiful scene, with people swimming in the shallow water and fishing and enjoying the sunshine.
Next was a stop near Montmorot to view a panorama above Lons-le-Saunier. We could see the main features of the tectonic style of part of the outer chain of the Jura (the Faisceau le Donien in Revermont). This stretches from Orgelet to Lons. During the Tertiary Period the faisceau was carried for 7km along a decollement surface over the crystalline basement towards the Plain of Bresse. In the group photo taken here you can see another new geological interpretation board that has been put in place by students at the local agricultural college.
Salines of Salins les Bains
Our last stop of the day was at the salt wells known as Les Salines in the town of Salins les Bains. Large drops of rain were starting to fall, forewarning us of the weather to follow over the next two days. We descended into the system of vaults where the pumps are housed. Inside Les Salines the temperature is only 14°C. Natural brine is pumped, using the power of an underground river called La Furieuse, from a depth of 246m up to a boiler house where it used to be evaporated to extract salt. The wells were in operation from the 6th century until 1962, when it was found to be too expensive to buy coal for the boilers.
The source of the brine is rainwater, which passes through the permeable layers in the limestone, dissolving the salt. Pressure brings the water back to near the surface, carrying 340g of salt in every litre. In the early days the brine was brought up from springs & wells by hand buckets, then horse, then paternoster. Now, a great wheel, turned by the river water drives a 5-horse power beam and pivot pump that that lifts 5,000 litres per hour.
The river water turning the wheel has only 30g salt per litre as the brine gets diluted on its way up. The water is no longer stored in the wells, though. Dilution of the water put back into the river means that there is no pollution from the wells. The salt would all end up in the river anyway. It’s all balanced.
There were 35 different boilers in the middle ages – big iron pans. Vapours from the boilers went back into the boiler room, making it very hot and humid. In the 18th century life expectancy for the workers was 35 years. Children used to heat rivets and crawled under boilers to take them for repairs.
In 1628 Salins les Bains was the 4th largest town in France and the wells were a walled town within a town because the salt was so valuable. It was needed to preserve food. For a first theft of salt in those days the thief was whipped. For a second offence, he was hung! In the past there were about 60,000 people in Salins, but now there are only 3,300. Our guide was a biochemist who could find no other work in the town. It is no longer known why there is such a large system of stone vaults. All evidence has been lost in fires and invasions. The building stone was quarried in Angoul, 17km away.
Wednesday and Thursday were devoted to karstic landscapes, the result of the powerful relationship between limestone forms and water. One day was spent looking at rivers, sink holes, springs, etc. and the other on investigating the caves that had been carved out in large part by the water running through them. The weather matched the geological themes perfectly; both days were wet.
A day of caving as tourists or speleologists
There were two choices for the group on the day that was designated for visiting caves. Either we could visit two easy access tourist caves, or we could be led by an experienced speleologist on an all-day trip of several kilometres, with lunch being taken underground. I opted for the latter. However, when ‘cave day’ dawned rainy and dark, I started imagining flash floods and being trapped in the dark, or drowning, and tried to pull out. My resolve wasn’t strong enough, though. I gave in to a little persuasion by the other, braver individuals and went along with the intrepid cavers after all.
Remi Limagne was our leader. He brought along an assistant who was also an experienced caver. She had had a very frightening experience herself in the very cave we were to visit, when rising floodwaters had trapped her and she had had to swim underwater to escape. But she didn’t tell us this until we were already deep in the cave and it was too late to change our minds. We were dependent on the leaders to show us the way out!
We were seven in all; the other OUGS members being Elisabeth d’Eyrames, Stuart Fairley, Jane Hickman and Mike Malloy. We donned Wellington boots, overalls and helmets to which we attached acetylene lamps. The lamps gave a wonderful all-round light, unlike the directed beams of electric torches, but some were rather troublesome to ignite and others leaked from the canister of acetylene and water attached to our waistbands. We also had to be careful not to burn our hands when descending ladders.
Whatever happened to Davy lamps and canaries?
The name of our cave was La Borne aux Cassots. Rather than a single cave, it was an inter-connected system of vast chambers, passageways and narrow tunnels. The latter had to be tackled on our knees or stomachs, wriggling along like worms! This was where having a small frame would have given a distinct advantage. I was a bit alarmed when in one climb along a narrow tunnel, I heard a voice announcing from behind that he was sorry but I was in danger of being burned on the bum by his lamp if I didn’t go a bit faster!
We saw some real geological wonders. There were underground rivers, walls that were fault planes and walls that were enormous bulging fold noses, whole caverns of sparkling gypsum crystals, fossilised wood in a ceiling, echoing chambers that had seemingly bottomless ravines where we could hear but not see the river flowing and narrow passages with fast rivulets that had carved out smooth ‘marmites’ (French for cooking pots), like those that we had seen previously in the riverbed at Pont de Poitte. There was also an awful lot of tillite mud and we were plastered in it by the time we emerged into the rainy afternoon. I was very relieved to see daylight though, and I personally have no plans to ever go caving again!
I am unable to report on the caves that the other half of the group chose to visit, Les Grottes des Moidons, but I was told that they were very large and spectacular and the brochure boasts of more than a million stalactites. Apparently, the public are not allowed to visit the gypsum caves or the bat caves of this system, though.
A day of hydrogeology
Thursday was another rainy day, very fitting for the subject of the day’s trips, namely hydrogeology. Jean-Pierre Mettetal, a hydrogeologist working for Directions Régionales de l’Environnement (DIREN), was our leader for the day. He told us that there were two karstic networks in the stratigraphic column, the Upper Jurassic and the Middle Jurassic, separated by Oxfordian-Argovian marls. The water for Arbois, where we were staying, is no longer obtained from the karstic network, for sanitary reasons, since there are bacteriological problems with karstic water, and the supply can be intermittent.
Our first stop was a viewpoint on the Middle Jurassic at Montfaucon Fort in the NW Jura, from where we would ordinarily have been able to see a tight loop in the River Doubs that encloses Besançon. Unfortunately, there was low cloud and little light today so our view was limited. However, we did see the River Doubs, and this river was to have greater significance later in the day, when we visited the Source (spring) of the River Loue.
Below us at the fort, the Doubs was flowing in a syncline but NW directed thrusts had complicated the geological succession and at Besançon the river flows through an eroded anticline that is part of the Besançon ‘faisceau’ in the Middle Jurassic. The meanders indicate that the river once flowed on a flat plain. When tectonics folded the strata into an anticline, the river kept to the same course as the original meander and cut down through the anticline in two places, exposing cliffs known as ‘cluses’ in French.
This is the ancient valley of the River Rhine. The Rhine once flowed south to the sea from this area, but then tectonics diverted it northwards. The Forest of Chaux in the plain of Bresse, to the west of the Jura, is the ancient Miocene delta of the River Rhine, prograding into the sea, as witnessed by the alluvial material originating in the Alps and Rhine radiolaria.
There is no surface water on the plateau between Besançon and Pontarlier and it used to be a real problem to provide water to the villages up there. In the 5th century the Romans built a 12 km long aqueduct on a gentle slope to Besançon. In the middle ages, the karstic water was abandoned, then, in the 19th century it was used again, but the water supply was in such a poor state that more than 3,000 people died of typhoid. Besançon is now supplied by a karstic aquifer of 100m depth in the Middle Jurassic strata below the Doubs valley. The water, of completely unknown origin, is of good quality, but nowadays it is treated by flocculation, oxidation, filtration and chlorine.
In 1984 Jean Pierre was asked by the authorities in Besançon to do a 2-year study of the springs and collecting basins and to protect the water. It is difficult to find out where the water collects from, as karstic systems are black boxes. The input is rain and the outputs are flows of water. Two methods of investigation are used – colouring the water and measuring the flow volumes.
The next stop was rather less salubrious; a natural marshy basin of glacial origin at Creux sous Roche that fills with rainwater and sewage effluent from the village of Mamirolle. It was empty of sewage when we walked through it, but the smell of ammonia and dense, waist-high stinging nettles, which were the chief vegetation, bore witness to the former contents. I don’t think our leader warned those who were wearing shorts about the nettles, and the experience must have been a very painful one for them (B******!).
The basin slowly fills up until the lake reaches a critical depth and then, suddenly and for unknown reasons, empties itself. They say the fish bump their heads on the bottom! Jean Pierre had brought us here to show us how drainage patterns are not constant. In 1910, a geologist had coloured the water and found that the lake discharged itself to the River Loue, in the south. However, Jean Pierre had carried out flow measurement studies in 1983/4 and discovered that the lake now drains into the Doubs, at the Acier spring, in the north.
The authorities once attempted to overcome the problem of the flooding by digging 15m deep holes, but this made the problem worse, so now it is a protected marshy area. In ten years time, the sewage will be taken to Besançon and treated there.
Our next stop was the Ravin du Puits Noir, or black well ravine, on the River Brême. This area is famous for being frequented and painted by Gustav Courbet, but we had come to visit the deep and mysterious black well and the strange river that flows in two directions alternately. At times of high, rapid rainfall, the river flows in one direction down into the well, but when there is continuous low rainfall on the plateau above, water fills the well from below and the river flows the other way.
After lunch at the pretty town of Ornans, on the River Loue, we visited the spectacular Source de la Loue, where the River Loue emerges from a dark cave in high Jurassic cliffs. It is the 8th largest spring in France.
The origin of the subterranean river was unknown until August 1901, when lightning hit the Pernod factory in Pontarlier more than 20km away and burned it down. To prevent the fire reaching the absinth, they emptied a million litres of the green liquid straight into the River Doubs (we had seen this river at Besançon, earlier in the day). The river turned white and smelled of aniseed.
Two days later, André Berthelot visited the Source de la Loue, on the other side of a high mountain ridge. He noticed a sudden change – the water had turned milky and a smell of aniseed filled the air! Free apéritif!
Nine years after that, the father of speleology, E.A.Martel, found a swallow hole in the bed of the river Doubs and carried out a colouring experiment. He poured a strong green pigment into the hole and 64 hours later the Source de la Loue turned green. This showed why the flow of the Doubs is reduced after Pontarlier. Thus the technique of using dye to trace ground water had been invented.
However, that was not the end of the story. When some mill owners along the Doubs, who had suffered from insufficient water, heard about the swallow holes, they started filling them with concrete to plug them. The inhabitants along the river Loue noticed a reduced flow, so a court battle ensued. The result was that the sealed sinks were allowed to remain, but it was forbidden to seal any more of them. However, such is the nature of erosion that eventually, in a few thousand years, the River Doubs will disappear entirely.
Our last stop of the day, on the return journey to Arbois, was to the Source of the River Lison, where the river emerges as a double-decker waterfall. It is situated between the Levier plateau and the Faisceau Salinois and the water level is very high. Up on the plateau, many little rivers disappear down potholes and there are dry valleys. A glacier once scraped the surface of the plateau. The Lison flows into the River Loue. Behind the spring here is one of the most extensively explored cave systems in the world, the Reseau du Verneau. It is world-renowned.
The last day, wine and soil
Our last day was gloriously sunny. The weather again seemed particularly fitting for the topics: vineyards and the soils derived from the rocks in the Jura.
Christian Barneou, a soil scientist, was our guide. First, he took us to the vineyards on an undulating plateau near Arbois, by a little village called Pupillin. We were on the Faisceau of Lons in the region of Revermont. The first thing that became apparent was that the soil beneath the vines was stuffed with belemnites. Yesterday’s rainwater had all dried up and they were liberally scattered in the dry earth around our feet.
The underlying rock alters very quickly indeed. We picked up rocks that just crumbled.
Where the limestone has been dissolved away, the clay which remains is more acidic and contains iron oxides. The soil layers that are not iron-rich dissolve and the calcite recrystallises elsewhere.
The colour of the soil was an indicator of the underlying rocks, typically marlstones. The marl is sometimes grey, green or red, according to the mineralisation. The plateau is very faulted and this has contributed to the chaotic, disturbed variety of the soils, or ‘terroirs’ as they are known in French. Savagnin, the most widely grown grape variety of the Jura region and used for the famous yellow wine, is best grown on Upper Triassic blue/grey marl.
Harder local rocks had been used for the construction of retaining walls beside roads. From these, we picked up gryphaea and ammonites of the lower Jurassic Lias. The walls are important to retain the earth and allow water to diffuse through and run downhill more slowly.
The permeability of the rocks is very important in soil development and retention. Where the rock is too impermeable, water runs off and erodes the soil. The porosity is also important, so that the soil acts as a reservoir for water and holds nutrients for the roots.
In the recent past, people used a lot of heavy machinery in the vineyards, which compacted the upper layer of the soil, so that the water didn’t permeate. We saw an example of a highly eroded vineyard where bad husbandry and neglect over 25 years had led to the formation of a veritable gully between the rows. There had been no grass around the vines and they had used insecticides. Nowadays the wiser viticulturists grow grass between the vines and use less damaging machines in order to protect the soils.
Insecticides and fertilizer are not generally used, as they give no character to the wine. Nitrogen gives bigger grapes and leaves but makes them more prone to disease. Only 5- 10% of the growers use chemical fertilizer. Vines are planted vertically down the slopes, to let the air circulate up the hill, as this also helps prevent diseases.
We took lunch in a wine cellar in Pupillin belonging to Jean Michel Petit. It was a great opportunity to sample the superb Arbois wines and learn from the experts about the special way each is created. We also tasted the local cheeses that compliment the individual wines.
There are five grape varieties grown in the region: Savagnin and Chardonnay for the white wines, Trousseau, Ploussard (or Poulsard) and Pinot Noir for the reds. There is even a name for the special bottle used for yellow wine, the Clavelin. This wine can be stored for over 50 years.
There are many speciality wines of the region. Yellow wine has already been mentioned. Straw wine is a dessert wine made from over-ripe grapes. After the harvest, the grapes are left on a straw bed or are suspended from the ceiling in a well-aired room to dehydrate until Christmas, when they are fermented. Macvin is a fortified wine made with ‘marc’, a liqueur distilled from grape skins. For more information on the wines of the Jura region, visit www.jura-vins.com.
Louis Pasteur lived and worked at Arbois and researched the mysteries of the fermentation of alcohol. The wine of Arbois was the first in the world to gain Appellation d’Origine Contrôlée, on May 15 1936 and there is a Wine Museum in the town.
After lunch we were taken to a vantage point from which we looked westwards out over the plain of Bresse. Beyond the plain was the Côte d’Or, where Burgundy wine is grown. It is an area that has the same karstic landscape.
We were also given a very comprehensive run-down on the creation of soils from rock. The following account is what I’ve put together from my field notes, but I can’t vouch for its veracity and will apologise to any real soil scientists out there for the gaffs I’ve probably made!
Soils are made from either hard rock or sands. The steps in their creation are thus:
- Disaggregation caused by biological, living organisms. These produce acid that dissolves the rock. The most fragile minerals will alter first and then the more resistant ones. It takes a few thousand years, depending on the hardness of the rock and the temperature for the first organic matter (mosses and lichens, then accumulation of other organic matter) to make the first soil.
- Dissolution of the organic and mineral material. This combines with the altered rock to form a new substrate and the new constituents will typically be as follow: a) crumbly and light like couscous, b) brown or yellow in colour, sticky aggregations, c) very close to the original rock type. Gravity continues the soil-making processes. Clay minerals migrate to the bottom layer. The upper layer is a lighter colour and poor in soluble minerals. Sand and silt stay in the top, organic rich layer that is around a metre in thickness.
- Acidification - during the final stage the soil becomes more and more acidic, so organic transformation cannot happen.
A young soil (10-15,000 years old) is not deep and is little differentiated i.e. the succession of beds are few or there is little difference between upper and lower layers. The lowest layer is structurally very close to the rock that it comes from.
Old, degraded, leached soils, known as podsols, are between 100,000 and 150,000 yrs old. They have very marked layering.
Climate, water, temperature or topography can stop the soil production at any time. On a slope, the soil falls down and always stays young. In a flat area there will be a thick layer and this is the only place where you can have an old soil, a palaeosol. A laterite has been stopped in the process of becoming a soil by huge amounts of oxides. During the last glaciation soil production stopped. If there hadn’t been such a climate change, the soil around Arbois would have become a laterite.
The flood area next to nearby Buvilly has ancient, 100,000 year-old soil that developed under a Mediterranean climate from altered marlstone. Other local villages that have the same soil and underlying geology as Arbois can also have their wines declared ‘Appellation d’Origine Contrôlée Arbois’.
For our last location that afternoon we were shown a rainwater measuring station in Arbois, where there were instruments for a project to measure the run-off from a vineyard. Up until 1980, the climate was semi-continental but since then there have been stronger rainfalls in the winter, which indicate that the climate is becoming more oceanic. The vine growers must be made aware of this, because they have to work the ground in winter and saturated soil is much more easily eroded by rain.
The soil in Arbois is not very well attached to the bedrock, so Christian thought that the houses which had been built next to the vineyard where the study was situated were in danger of being swept away. In 1921 there was a huge mudslide from there into the Cuisance River.
So this concludes my account of a very happy week spent immersed in the French landscape and culture. Would I like to go back? I certainly would!