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Geology of the Tour de France Profile picture
@geotdf
May 25 • 3 tweets • 2 min read Twitter logo Read on Twitter
Geo-#giroditalia2023 - Stage 18. The riders have entered the realm of the Eastern Alps and the Dolomites. Like in the west, the Eastern Alps are offscrapings of the European plate that subducted below Adria. But the Dolomites are offscrapings from Adria. Did both plates subduct? https://www.researchgate.ne...
The answer is yes, one after the other. The European continent was pulled down a few hundred km below Adria, but resists subduction. Africa and Europe convergence was since 10 million years ago accommodated by pushing Adria below the eastern Alps, 'reversing' subduction. https://agupubs.onlinelibra...
The riders will leave the Po Plain again, and then climb up the folded and broken up mess that once was Adrias northern slope. The sediments that formed on this slope were pushed southward, and make for some serious climbing. Let's see who will bend but not break today! Image

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More from @geotdf

Geology of the Tour de France Profile picture
May 23
Geo-#giroditalia2023 - Stage 16. After the peloton leaves the road west of lake Garda, they will climb through some of the most beautiful natural building stone of Italy: the Ammonitico Rosso. You'll have seen them on plenty of floors and walls: red limestone full of ammonites! https://www.alexstrekeisen....https://www.alexstrekeisen....https://geologyistheway.com...
In the Jurassic the 'Greater Adria' continent was broken up and formed shallow ridges and deeper basins. The basins trapped sediments from land, so the ridges only received 'pelagic' sediments: sediments that rain down from the water column, mostly living organisms. https://www.researchgate.ne...
These organisms were especially remains of plankton: foraminifera, algae, radiolaria, and many other microorganisms, together with bottom life. But in the Jurassic, the oceans were filled with famous shelled squids: belemnites and ammonites. The lattergive these rocks their name. https://res.cloudinary.com/...https://biojmlorca.blogia.c...
Read 4 tweets
Geology of the Tour de France Profile picture
May 19
Geo-#giroditalia2023 - Stage 13. Today, we recommend the entire peloton to join the grupetto and look around: the Giro organization prepared a fantastic geological excursion! The race will lead from Adria to the 'Penninic Front' of the Central Alps, a former subduction zone! https://www.sciencedirect.c...
The Alps are piled-up rock packages of a few km thick that were offscraped from the European plate that subducted below Adria. The riders will cross remnants of two oceanic basins (the blue colors) and a small continent (the 'Brianconnais', in orange). https://www.sciencedirect.c...
Before these remnants were folded up in the Alps, they covered an area of hundreds of kilometers wide, and we will ride in sequence from Adria to the Piemonte-Ligurian ocean, to the Briançonnais continent, to the Valais Ocean, and end on the slope of Europe! https://www.sciencedirect.c...
Read 4 tweets
Geology of the Tour de France Profile picture
May 18
Geo-#giroditalia2023 - Stage 12. The peloton is leaving the Apennines, will race over Adria again, and then enters the Alps today. The difference between these mountain belts is not just geographical: geologically, they're entirely different beasts! But it's a complex geometry! https://www.researchgate.ne...
As we saw last week, the Apennines formed because Adria, the continent that underlies the Adriatic Sea and that is part of the African Plate, subducted below Europe and its sediments were offscraped. In the Alps, however, it's the opposite: Europe subducted below Adria.
So for most of the day, the peloton races over the African Plate again, which in in the morning is a downgoing plate and in the afternoon an overriding plate. Sounds like an ancient Roman riddle, right? The transition is a geological mess called the 'Ligurian Knot' https://www.researchgate.ne...
Read 4 tweets
Geology of the Tour de France Profile picture
May 17
Geo-#giroditalia2023 - Stage 11. The peloton is going to race through an ocean today! We've reached the Ligurian 'ophiolites', the oceanic lithosphere remains below which the northern Apennines were offscraped and stacked up, which you may see as the black rocks along the race. https://www.sciencedirect.c...https://www.travelinggeolog...
Geologically, oceans, are not bodies of water, but the crust type that forms by magmatism at mid-ocean ridges. Continents continue into the sea as shelf and slope, and only then the ocean starts. The Apennines are shelf and slope rocks, the 'Ophiolites' are oceanic crust rocks. http://geoverse.co.uk/2000/...
The shelf and slope of the Northern Apennines became in the Jurassic separated from the shelf of Iberia and Corsica by an ocean: the Piemonte-Ligurian Tethys, that was connected to the Atlantic Ocean. This ocean opened between ~160-140 Ma ago. https://www.sciencedirect.c...
Read 5 tweets

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