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In Wine List

May 2011 Trip

Mountain Building and Wine Making -The Geological Evolution of southern France

The geological processes that build mountains result in rock types and landscapes that can, in the right hands, provide the basis for the production of great wines. Such is the case on the flanks of the Alps and the Pyrenees in southern France. These two mountain chains have a similar geological history stretching back hundreds of millions of years, similarities in climate since at least the last ice age and two thousand years of wine-making since Roman times.

The mountains of the Alps and the Pyrenees were formed by the collision of the African and Spanish continental plates into the European plate to the north. Prior to this collision the Tethys Ocean occupied most of the area of the present day Mediterranean and its surrounding mountain belts. The Massif Central represents the old rocks of the European plate that would have formed a land area to the north of this ocean. At this time France was about 10 degrees north of the equator and basking in a hot dry environment with deserts and occasional rivers. The land areas accumulated conglomerates, sandstones, siltstones and mudstones which all have a rich red-brown colour from the oxidising climate. Nearby shallow seas accumulated limestones that were transformed to dolomites when they were buried within the Earth’s crust. Today these sediments are seen as 300-200 million year old red sandstones and dolomites to the east of the Massif Central and as a fringe around the Maures range of hills in Provence.

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Geological map of southern France showing distribution of rock types described in this website. Present day rivers and locations visited are also added

Following this phase, subsidence of the southern edge of the European plate allowed shallow tropical seas to flood over the region. These warm shallow seas promoted the growth of organisms with calcareous skeletons such as corals, algae and molluscs which accumulated on the seafloor to eventually form limestones. The surrounding deep water areas of Tethys accumulated mud (to form marls and shales) that are often to be seen forming layers of strata within the limestones.

These limestones and marls (blue on the map) were deposited during a phase of Mesozoic time, 200 to 65 m.y. (millions of years old) and are also known in France as the “Urgonian” strata. Today they are seen as folded and faulted strata within these two mountain belts to form spectacular limestone scenery of  Provence (Gorge du Verdon, Mont Ventoux and the Côte d’Azure) and Roussillon (Gorges de St Georges et Galamus, and the many limestone ridges capped by Cathar castles).

Mountains of Cretaceous limestone in the Fenouilledes south of Quillan. The Cathar castle of Puilaurens perches on a hill carved from near vertical beds of limestone. These would have originally been laid down more or less horizontally on the sea floor and have been upended in the Pyrenean orogeny:

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The collision of the African and Spanish plates into the European plate compressed and deformed the limestones and marls during the Alpine and Pyrenean mountain building episode that started around 125-130 m.y. so that the original horizontal layers on the sea floor have been upended, folded or even turned upside down. In addition to the compression and folding of the Mesozoic sediments of the Tethys Ocean, even older rocks that formed the landscape prior to the formation of Tethys were involved in the mountain building or orogenesis. These rocks, being buried deeper in the crust, referred to as the basement, were subjected to higher temperatures and pressure during the orogenesis. This led to their recrystallisation to form metamorphic rocks known as schists and gneisses which are found today in the central or core areas of the Alpine mountain chains (green on the map). In places the conditions were right for these basement rocks to melt, and then, because they were then hotter and lighter than the surrounding rocks, to move upwards through the crust to eventually crystallise as igneous rocks such as granite. Such granitic intrusions today form the spectacular mountains of Canigou in Roussillon and Les Maures above St Tropez and are marked in red on the map.

From this common history a similar pattern of rocks characterise this area of southern France. A central core of older metamorphic and granitic rocks, often forming the highest mountains, is surrounded on the flanks of the high mountains by folded limestones and marls of Mesozoic age as can be picked out on the geological map as the Alpine-Pyrenean chain swirls in an S-shaped swirl, curving southwards and southeastwards through the Alps, westwards through the Maures and then westwards on the basal curve of the S through to the Pyrenees. Originally these were a more or less continuous mountain chain that has since been eroded down and then flooded by the Golfe du Lion.

The next phase of the geological history of the area concerns the weathering and erosion of these newly formed mountains to form rock particles that are transported in rivers away from the mountains to the lower lying surrounding areas. Compression of the Tethyan rocks resulted in a thick deformed belt of relatively light rock. These lighter rocks float high in the Earth’s rigid crust and denser underlying molten layers to form mountains. The weight of this mountain chain causes a depression in the adjacent Earth’s crust which geologists call  foreland basins and these are found surrounding both the northern and southern flanks of the Alps and Pyrenees. These low-lying areas received the eroded debris from the mountains and are marked in yellow on the map as areas of youngest, or Cenozoic (65 m.y. to the present day) sediments.

The large river systems that today drain off the Alps (Rhône and Durance) and the Pyrenees (Aude, Gironde and the Adour) are long lived and can be traced back for millions of years through the Cenozoic history of the area. The rivers and earlier coastal areas accumulated kilometre thick piles of conglomerate (from pebbles) sandstone (from sand) and mudstone (from silt and mud) together with some limestones that formed in lakes and shallow marine areas. Today these foreland basins are still large areas of generally low relief land forming coastal plains around the southern part of the Rhône, from Montpellier to Narbonne, and the low relief countryside stretching from Carcassonne to Toulouse and Bordeaux.

As well as the foreland basins surrounding the mountains the region was subjected to an east-west stretching and fracturing of the Earth’s brittle crust to form another type of sedimentary basin; the Rhône rift valley. Here, a downfaulted block of crust forms the Rhône valley, floored by young (Cenozoic) sediments with older rocks forming rift shoulders. Basement metamorphic rocks form the western hills of the Cevennes whilst to the east are the folded Mesozoic limestones and shales of the Alps.

Although there are no active volcanoes in the area today the high heat flow associated with the Cenozoic deformation of these rocks resulted in molten rock (magma) rising to the surface to form volcanoes during the last 5 million years or so. Lava flows of basalt from these volcanoes form some of the youngest rocks in the area and cap the hills north of Bandol, a string of basaltic outcrops from Cap d’Agde, through Pézenas to the spectacular volcanic landscapes of Le Puy in the western Massif Central.     

 

Provence to Rousillon Vine Trail; May 2011

Bandol- Château Sainte-Anne

This area represents a cameo of the geology of southern France with most of the evolutionary stages of the Alps displayed in a small area. To the south lies the core of the Les Maures extension of the Pyrenees with schists and other metamorphic rocks outcropping around Toulon. These are overlain to the north by the conglomerates, dolomites, marls and shales of Triassic age before the landscape is dominated by Mesozoic limestones and marls around the village of Ste Anne d’Evenos.

The limestones here are part of a large Alpine fold so that the original horizontally layered rock has been up ended and overturned so the beds slope steeply to the south. Despite deformation of the rock and the graffiti, the original fossils that make up the rock (gastropods and clams of Cretaceous age) can still clearly be seen in the cut rock faces in the quarry.

Quarry in overturned Cretaceous limestones Ste Anne d’Evenos. The natural outcrop with the tilted bedding can be seen in the background and the saw-cut quarry facies with the graffiti follow the bedding:

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Cut surface of limestone in quarry at Ste Anne d’Avenos showing sliced sections through the fossil snails and clams that formed the limestone in the shallow warm seas of Cretaceous times:

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In the nearby village of Evenos the young volcanic larva flows can be seen resting more or less horizontally on the tilted limestones. The gas bubbles from the original lava flow are preserved as squashed out cavities within the basalt.

Boulder of Pliocene (2.5 to 5.3 m.y.) basalt in hilltop village of Evenos with holes formed from squashed gas bubbles in the original molten lava flow:

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Chateau Ste Anne lies within the north-south oriented valley of the river Reppe that cuts through the rocks that are oriented east-west in this area. The bedrock is made up of marls and sandy marls of Early Cretaceous age and these are overlain by pebbly alluvium that accumulated in the last ice age on an earlier river terrace of the Reppe. This valley faces north eastwards, which, together with the cooler air coming off the Alps to the north, provides a cooling influence to the chateau’s vineyards in this otherwise sun baked region. This results in lower alcohol levels in their wines whilst maintaining luxuriously strong flavours from the Mourvèdre, Grenache and Cinsault grapes in their reds and rosé and Clairette and Ugni Blanc in the white. The siting of vineyards where older river terraces lie close to well-drained bedrock is favoured in a number of different wine regions of France (Loire, Côte de Beaune and Languedoc-below).

 

Languedoc- Conte des Floris

From the Alpine rocks of Bandol we travelled west to the younger Cenozoic rocks of Pezenas in Languedoc. Here we visited Daniel Le Conte des Floris who, through careful research whilst working for the Revue du Vin de France, identified three different terroirs in the area around Pezenas in the Coteaux du Languedoc appellation. The three terroirs are defined by three different rock types and their associated thee different soils. From oldest to youngest these are:

  • Syrah growing on schists of Carboniferous age from nearby Faugères on the southern tip of the Massif Central producing his “Carbonifères”
  • Carignan growing on late Cenozoic basalt near Caux (producing his “Les Basaltiques”), from part of the chain of volcanoes that stretch from Agde on the coast to the Puy in the Massif Central.

Boulders of basalt outcropping in the vineyard at Caux:

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  • Grenache growing on river terraces of the Herault but with their roots reaching down into marls and sandy marls of the Cenozoic basin between the Pyrenees to the south and the Massif Central to the north. This produces his “Villafranchien” cuvee, the name here coming from Villafranchien times (about 1 – 3 m.y.) when the earlier Herault river was at a higher level and depositing pebbly sands derived from erosion of the Massif Central to the north.

 

White quartzite pebbles in the Villafranchien river terrace deposited by the ancestral Herault River flowing south from the Massif Central:

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There can be fewer examples of the close link between geology and wine as in the hands of Daniel Le Conte des Floris. His purchase of the vineyards was determined by the different rock types and because of its geological history this area of Languedoc is fortunate in having three very different rock types in close proximity.

The link between geology and wine gets transferred to the images on Daniel’s wine labels:

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All available at the Bar a Vin, Pezanas, and some at Vine Trail, Bristol

 

Roussillon- Cyril Fhal

North of the Pyrenees in the Roussillon area are two slices of ancient metamorphic rocks emplaced into Mesozoic limestones and shales. The larger Mouthoumet Massif of the Corbières between Sigean and Quillan and another forming the Fenouillede hills between the Agly and the Têt rivers. These slices of ancient rocks originate from the compressive forces that built the Pyrenees mountains. During compression the metamorphic basement and the Mesozoic sedimentary cover are folded to such an extent that the folds detach from their roots in the core of the mountain chain and slide laterally away from the core in what are known as thrust slices. This explains the repeated occurrence of metamorphic basement (green) and limestone (blue) on the geological map in Roussillon.

Cyril Fahl has a number of small plots in the Agly river valley that cuts mainly through gneisses that weather to form a thin red-brown soil. This provides the names on the labels Clos du Rouge Gorge. As with the Chateau Ste Anne vineyards many of Cyril’s also face north or north east and at heights of 200-300 metres provides a cooler setting than the baked valley of the Maury and Têt and coastal Rivesaltes.

The thin soils and dry climate ensure the vine roots penetrate deep down into these foliated rocks, particularly when this foliation is near vertical which encourages downward penetration of the roots. The accompanying photographs show the beauty of this part of France and the vines under Cyril’s care combined with his work in the cave seem to extract exceptional flavours in his wines. For more see Lionel’s tasting notes!

Planèzes, a few kilometres up the river Agly from Latour de France, nestles in a valley cut into ancient metamorphic gneisses from the core of the Pyrennean mountain chain:

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This road cut shows Grenache vines growing on a hillside with thin soil developed on weathered gneiss. The near vertical layering of the gneiss provides lines of weakness for the vine roots to penetrate far into this otherwise hard rock:

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Cyril Fhal explaining the intricacies of his biodynamic approach to viticulture to Nick and Lionel. Note the horse drawn ploughing in contours to suppress weeds and conserve the thin soils:

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Green manures (vetch, peas and oats) are planted in this new vineyard to suppress unwanted weeds and to provide nutrients to new vines to be planted in a year’s time. The vineyard has a mica schist bedrock capped by thin acidic soil. In the background the Col del Loup passes into Jurassic limestones and shales that dominate the landscape northwards, away from the mountains to the valley of the Maury:

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The Provence-Languedoc-Roussillon area of southern France produces some exceptional, but not widely known, wines. The three vineyards visited from each of these three areas demonstrate how in each case the vignerons have used the local geology, landscape and climate in combination with the right choice of grape varieties to produce some great wines.

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