Stage 7 | Sélestat – Le Markstein / Supercontinent assembly

As the riders ascend the Vosges today, they find themselves in times of geological turmoil. The rocks along the stage have seen the last stages of the formation of the supercontinent Pangea: we ride over the collision zone of rocks derived from the mega-continent Gondwanaland in the south, and the Euramerican continent to the north. The result was the formation of mountain ranges whose scars we now see in the Ardennes and Vosges, but that are now all over the globe, including for instance the American Appalachians or the northwestern parts of Morocco. The rocks that the Tour de France Femmes travels through today was located south of the equator and formed during the Carboniferous period (360 to 300 million years ago). Sea-level was higher, but the climate was not unlike today, with high temperatures on the equator and ice on both poles.

Carbonoferous rainforests: world's largest coal deposits

With global climate being more or less the same as today’s, it may not strike you as a surprise that the Carboniferous Tour-cyclist would have seen an environment in the Vosges that looks like Brazil today. The Carboniferous equatorial regions had no shortage of water, and the continents were covered in swamps and lush rainforests where plants, like ferns, could grow up to 40 meters tall. But the Carboniferous rain forests were the first of their kind: in earlier times, land plants had only just developed and were in short supply. Due to the lush greenery, the percentage of oxygen in the atmosphere rose from ~20% (about today’s values) to more than 30 %...and this allowed insects to grow larger and larger to rather scary proportions, the size of modern birds. And all these plants are still heating our modern world in more than one way. They created massive deposits of peat, which later turned into the world’s oldest and largest coal deposits. These are are still being mined in, for instance, the Ruhr area in Germany and in Pennsylvania in the US, heating our homes and, through CO2 release, global climate. The Carboniferous is named after this coal (Carbon).

Steep terrain

So look around today and imagine living 300 million years ago. Find yourself marvelling at the swamps and rainforest on the edge of a big mountain range. You would start the stage with a sweaty ride in the Brazilian Amazon, in a damp and green world. In the ponds you’d find major amphibians the size of crocodiles, or with funny hammerheads, armored fishes, early sharks of more than 6 meters long, and sea scorpions that looked a bit like horseshoe crabs. In the second halve of the stage, the ride starts climbing in the Vosges, the old and (now) eroded Hercynian mountain range. But if this was still the Carboniferous, the climbs would be longer, steeper, and full of active volcanoes: you would climb from the Amazon into the Andes mountains of Peru and Colombia. We expect a warm, wet, and exciting stage!

I study geodynamics, more specifically the interaction between the mantle and plate tectonic processes on the surface and on a very large scale. As we can not go into the mantle, my computer models are based on data from rocks all around the world that tell the story of plate tectonics. Check our complete team.

Erik van der Wiel