It is a well-known fact that a glass of wine or a nice beer or two are needed upon return from the field, helping you to unwind and reflect on your efforts of the day. As you work your way through your glass of Tempranillo or bottle of Budvar (or even that 25 cent can of decent Pilsner that you found in the local supermarket) do you ever wonder about the geology behind the product you are drinking?

Image: The Côte d’Or limestone escarpment, which has been endowed with an optimal strike for wine production by the Alpine orogeny, is home to some of the finest vineyards in France.

Wine is grown in many countries around the world and some grapes will thrive in certain areas but cannot grow well enough in other areas for a number of reasons. Pinot noir is one such grape, being grown successfully in New Zealand (in the Central Otago region) and Chile (in the Casablanca and San Antonio regions). However the best pinot noir in the world comes from France in Burgundy, specifically from the Côte d’Or.

Côte d’Or is a Jurassic limestone escarpment that stretches from Dijon in the north to the river Dheune in the south. It overlooks the valley of the Saône to the east. The image above shows the escarpment near village of Meursault.

The eastern slope of the Côte d’Or is home to some of the greatest names in Burgundian wine; Romanée-Conti, Clos de Vougeot, Meursault and Montrachet are some of the top wine producing vineyards in the world. They are also producers of some of the most expensive wines in the world, a bottle of Domaine Leroy from Clos de Vougeot averages at almost €900 per bottle and in 2013, three bottles of the 1990 vintage Romanée-Conti were sold for $72,000.

Chardonnay, gamay and aligoté are also grown in this region but the escarpment is separated into two main areas: the Côte de Nuits to the north which produces red wine almost exclusively and the Côte de Beaune to the south which produces a mix of red and white wines.

The top wines grown in the region (Grand Cru) are all cultivated at an altitude of between 250m and 300m and are planted on slopes getting to a gradient of up to 20°.

They are grown on soils that have a stone content of between 5% and 20% due to the soils’ ability to keep heat and also for drainage reasons. This aspect of viticulture is

mirrored in Bordeaux where some of the top

wine is produced in the Graves and the Haut Medoc regions, both of which sit on gravelly soil. The Graves region is home to Sauternes and the Haut Medoc is home to Margaux.

In Burgundy, the strike and altitude of the scarp provides excellent drainage and aspect while the Jurassic limestone provides the soil that is rich in calcium carbonate. Many of the world’s top vineyards are set upon calcium carbonate rich soils. Geographically the region is far enough north to ensure the grapes ripen in most years, that being one of the main reasons why pinot noir is so hard to cultivate.

The Côte d’Or scarp was thrust up during the Alpine Orogeny. The area in red on the map represents Morvan, a mountainous massif formed during the Variscan Orogeny, representing the northerly extension of the Massif Central. As the Alpine Orogeny progressed, the sediment to the south-east was faulted up resulting in the roughly 30° strike of the Côte d’Or escarpment. The rocks to the south-east are fluvial in origin, mainly Oligocene, Pliocene and Quaternary in age deposited in the basin formed by the Alpine related faulting.

Further south in France is the Rhône valley. This wine region is neither as famous nor as historic as Burgundy but the geology of the area is quite interesting, especially when you consider the distribution of varietals This area too is split into two, the northern half home to appellations such as Crozes-Hermitage, Cornas and Côte- Rôtie, whereas the southern half is home to Châteauneuf-du-Pape and Gigondas and other less famous villages of the Côtes du Rhône.

Syrah (shiraz) is the only red grape grown in the northern half of the Rhône valley, some white varietals are also produced (viognier, marsanne and rousanne). This is in sharp contrast to the varietals produced in the southern area, where grenache, syrah, mourvèdre, carignan and cinsault dominate the vineyards. Because of this the wines from the north only consist of syrah (occasionally with some of the white mixed in) whereas the wines in the south can consist of up to thirteen different varietals.

One of the main reasons for the sharp differences in varietal growth in along the Rhône valley is the geology. The northern vineyards sit on granitic rocks that are part of the Central Massif (formed during the Variscian Orogeny) whereas the southern vineyards sit on much younger fluvial and calcareous sediment. The wines from the north are traditionally considered to be of higher quality (but also higher price) than those from the south. The high cost is largely due to the extremely steep south facing slopes of the crystalline rocks to the north, necessitating hand-harvesting. In the south, machines can be used to pick the grapes.

Of course not all vines are planted in areas dominated by a sedimentary environment as seen in the north of the Rhône valley and the granitic slopes at Hermitage in the Rhône valley are not the only wine region on igneous bedrock. There are plenty of wine regions around the world that have grapes growing on volcanic soil; Napa Valley, California is perhaps the best known of these. The Napa Valley is quite a small wine region but supports high diversity nonetheless.

The Napa Valley is found to the north of San Francisco, California. Fluvial clays and sands form the centre of the valley, deposited by the Napa Valley River. The river is flanked by low volcanic hills on either side. The minerals found in the volcanic soil enhance the flavours of the wine and the slopes provide excellent drainage. Rutherford is one of the top wine producing regions within the Napa Valley and the soil here is predominantly eroded volcanic runoff from the mountains to the immediate west.

The valley itself is a synform, the youngest sediments have been deposited in the centre of the valley by fluvial processes. The volcanic rocks are the next oldest and are Jurassic to Tertiary in age. Mt. Konocti to the north of the Napa Valley is a source of some of the volcanic rock in the area. The figure below shows the synform and what is immediately noticeable is the large variability in rock types found in the region. The mountain tops are ultra-mafic oceanic crust and the volcanics sit on top of the marine sediments.

This geology is the product of 150 million years worth of intense activity on the western coast of the United States. The combined effect of the coming together of the Pacific and N. American plates, the volcanism associated with such events and the migration north of the San Andreas Fault resulted in the compressional forces that formed the Coast Ranges. Around 3 million years ago plate motion shifted yet again, which caused massive folding in the region, the Mayacamas and Vacas ranges were uplifted with the Napa Valley sitting between these two.

Many famous and traditional wine regions of Europe were also established on volcanic soils. The Kaiserstuhl is a range of hills in south-west Germany that form part of the Upper Rhine Plain. The hills are volcanic in origin, alkaline lavas to be precise. These weather extremely quickly and the soil produced is very rich and excellent for growing wine, supporting fine wine in a climatically difficult area. The volcanism responsible for the Kaiserstuhl was associated with a major rift system. Rifting occurred during the early Cenozoic era and was triggered by the uplift associated with the Alpine orogeny as a dilation structure. Substantial crustal thinning led to the major extensional graben along which isolated volcanic activity is recorded. The volcanic activity peaked ca. 15 million years ago. The rift can be found between modern day France and Germany and has been filled in by the Upper Rhine Plain, roughly 350 km long and 50 km wide.

Since wine is grown on volcanic rocks of a more explosive nature too, it would be a crime not to mention Italian wine. With so many active and extinct volcanoes it comes as no surprise that a lot of the best Italian wine regions are sitting on top of volcanic bedrock. Mount Etna, whose vineyards withstood the phylloxera plague due to the high porosity of its ash-dominated soils, supports the unique Nerello varietals, whereas other Sicilian red wines are often made with the nero d’avola grape. On the mainland further north, in Basilicata and Campania, the Greek varietal Aglianico thrives, particularly on the slopes of the extinct volcano Monte Vulture. Southern Italian and Greek wine making have many aspects in common, including not only shared varietals but the preference to establish vineyards on volcanic soil.

A bottle of wine is thus not only a reflection of the winemaker’s skills and the climate but first and foremost of the geologic context of the vineyard.

Paul Guyett

M.Sc. student, Department of Geology, Trinity College Dublin

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