Today, the Tour de France peloton pushes their way to victory over a 163 kilometer-long stretch between Mâcon and Dijon. We ride through the riveting or more precisely rifting vineyards of the Bourgogne in the Bresse Graben, home of wine and mustard. Christian Prudhomme, the Tour de France director promises us this on the official website:
“Fans of medieval architecture enjoy the aerial images of Cluny Abbey and much more. The breakaway will set off with the ambition of holding off the peloton’s pursuit though the vineyards of the Côte Chalonnaise. However the sprinters should have the last word on the 800-meter straight into the prefecture of the Côte-d’Or”
The vineyards are in today’s blog but Christian seems to be missing something of great geological interest here. Perceptive observers see that the landscape type of this sixth stage of the Tour has the stage type “flat”. We have the Bresse Graben to thank for that. And wine and mustard as products to celebrate with.
This is a bit of rarity in the southeastern part of France, which hints at a peculiar plate tectonic history. Several million years ago, the general landmass of metropolitan France attempted to break (rift) away from the European continent. This attempt proved ultimately unsuccessful as France is still very much part of Europe. Still, this rifting event has had an important impact on the local landscape, European history and local (agri)culture. These are the exciting details we will explore below!
What is a graben
Rifting is a fundamental plate tectonic process that splits continents apart over the course of millions of years. This process involves the gradual stretching and thinning of the continental lithosphere (figure 2a). The process is driven by gigantic forces in the earth until an oceanic basin opens in between both continental fragments. Typical features in rift systems are normal faults. These are large fractures in the earth that allow downward motion of continental blocks to accommodate the overall stretching of the continent (figure 2a).
We call the resulting depressions between such faults grabens, from the German word for “ditch” or “trench”. These grabens are commonly filled up to a certain level with sediments to form distinct flat areas between the hilly “graben shoulders” that are uplifted during rifting and stand out in the landscape (figure 2b).
Scar tissue
When looking at the topographic map of Western Europe we can clearly see that rifting left its scars on the continent. A distinct series of roughly north-south oriented grabens with a flat topography marks the outline of the European Cenozoic Rift System. The Cenozoic is the period since the extinction of dinosaurs 66 millions years ago, until today.
Among these are the Upper and Lower Rhine Graben, but also the Bresse Graben. This is where we race today. Rifting in Western Europe was somewhat atypical because it was not driven by large-scale plate tectonic stretching of the continent. It was also not because of massive active upwelling of hot material from deep in the earth’s mantle below, as in most other rift systems. Instead, the European grabens formed as a response to Italy and Spain (both independent continental fragments in the past) moving northward to Europe since about 60 million years ago, on their way to create the Alps and Pyrenees.
It’s tectonics again
Initially, the impact of this northward motion was buffered by the closure of several small rift basins. But when Italy and Spain started to seriously collide with the main European continent some 35 million years ago, the Alpine and Pyrenean peaks rose to great heights. Simultaneously, this roughly north-south collision caused the region to the north of the Alps to be pushed sideways. The resulting east-west tension led to the opening of the various grabens of the rift system (figure 3c above). As such, France started to slowly move westward.
However, as soon as the major Alpine collision phase passed its peak around 25 million years ago, also the driving force behind the rifting in Western Europe faded. Thus, no new ocean opened and the general tectonic arrangement of the region we recognize today was established. Europe remained united. Even so, this does by no means signify that the region is geologically inactive. The various grabens still show signs of ongoing deformation. They see regular earthquake activity, exemplified by the 1356 earthquake that completely destroyed the Swiss town of Basel on the southern end of the Upper Rhine Graben.
Moreover, a quirk of the atypical rift setting in Western Europe likely caused disturbance deep in the mantle below. As a result, local rising hot material from great depths in the earth has caused intense “hot spot” volcanism. This is most famous in the Massif Central in France (stage 10 of 2024) and the Eiffel in Germany (figure 3b above). Some of the associated eruptions near the French town of Clermont-Ferrand occurred only about 8000 years ago. As you, that’s a blink of an eye in terms of geological time. Our planet is a quite dynamic one.
Graben shapes human history
Grabens often provide a landscape that is perfect for human habitation. The large rivers that generally run along their length provide ample water. The sediments deposited in their floodplains make for fertile agricultural terrain. Moreover, these plains and rivers make for easy transport and travel. The Bresse Graben is no different. Here, the Saône flows from the Vosges (the western graben shoulder of the Upper Rhine Graben to the north) southward along the length of the Bresse Graben, past Dijon and then Mâcon, as our spandex-clad heroes are racing in the opposite direction.
In Lyon, the Saône empties in the Rhône, which is sourced from the snowy Swiss Alps. The Rhône then continues further south along the Graben towards its delta near Marseille. This has been a key port city since its founding by Greek colonists around 600 BCE. Being one of the few pathways from the Mediterranean into northwest Europe, the Bresse Graben has always represented a crucial trading route. The resources of Gaul and Germania (present-day France, Benelux and Germany) to the north were exchanged for pottery and luxury goods from the sophisticated Greco-Roman world in the south. This was booming business back in those days. As Cicero writes, a merchant could sell an amphora of wine for a slave. Such was the love for wine in ancient Gaul.
Wine and mustard
The love for wine seems to have stuck until the present. After Julius Caesar’s conquest of Gaul in the 50’s BCE the locals eagerly adopted the art of winemaking. They swiftly became masters of their craft, eventually surpassing their teachers and conquerors from across the Alps. Many a modern-day Italians may deeply disagree though.
Today, the Bresse Graben is home to some of the best-known French wine regions such as Vallée du Rhône in the south, and Beaujolais as well as Bourgogne in the north. As Mr. Prudhomme points out on the Tour de France website, our riders will be passing by the Côte Chalonnaise. This is a small subdomain of the Bourgogne wine region. If they would care to make a pitstop at a café to enjoy down some well-deserved refreshments, as was a favorite practice during the pre-war editions of the Tour, they could test the excellent local Pinot Noir or Chardonnay.
Interestingly, these wine regions tend to be located on the graben shoulders rather than on the flatland in the graben itself. This is partially because the young sedimentary infill of the graben does not provide the ideal soil for quality wine. Secondly the hillsides of the uplifted graben shoulders provide better sunshine conditions for vines to grow and grapes to ripen.
Mustard and wine at the line
At the end of today’s 163 kilometer long race we reach Dijon, in the heart of Bourgogne. The name of this town is the namesake of the famous mustard that became a prominent fixture of the exuberant banquets the wealthy dukes of Bourgogne held at their medieval court.
Mustard itself seems to have been used as a foodstuff in India and Mesopotamia since as early as 3000 BCE. It may have been the Romans who introduced mustard in Gaul. Mustard turned out to grow well in the region. Once more, the locals ran with it and developed a culinary tradition that we know now around the world. Even so, make note that the product name “Moutarde de Dijon” itself is not protected. It merely indicates the use of the mustard recipe that was developed in Dijon.
In fact, the vast bulk of the mustard seeds used for mustard production in the region come from Canada, a somewhat shameful reality. But not all is lost! Efforts are currently made to revive French mustard seed cultivation. In Dijon, the weary cyclists have a perfect opportunity to revitalize themselves by testing the potent flavors of the “Moutarde de Bourgogne”, a protected product solely made from regional ingredients. This mustard goes very well together with a dish of fine pork and a glass of local Chardonnay, while looking out over the vineyard-covered hills as the sun is setting. All made possible by the peculiar tectonic history of the Bresse Graben! Thank you geology.
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