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Geology of the Tour de France Profile picture
@geotdf
May 26 • 3 tweets • 2 min read Twitter logo Read on Twitter
Geo-#giroditalia2023 - Stage 19. After weeks of rain and hardship, the peloton gets a nice day at a tropical beach. Unfortunately, it's located at 1900 m elevation, next to the Campolongo pass: the famous Sella Massif. This massif is a Triassic (245 million year old) atoll! https://commons.wikimedia.o...
The Sella Massif is a ring-shaped, high ridge made of reef limestones and dolomites. It formed on top of volcanic rocks of a volcanic island that is linked to a subduction zone on the northeast side of Greater Adria, and that led to breakup of the continent. https://peakvisor.com/range...Image
Atolls are best known from the Pacific Ocean, where they form on top of seamounts - underwater volcanoes that reach shallow water. Reefs then form on the crater rims, and grow upwards to compensate for the subsidence of the volcano. Enjoy a cocktail at the pass today gentlemen! Image

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More from @geotdf

Geology of the Tour de France Profile picture
May 27
Geo-#giroditalia2023 - Stage 20. If geology is predictive for cycling, the GC will go upside down today. The peloton has entered the biggest geological mess of this Giro: the junction region between the Alps, the Carpathians, and the Dinarides. No rock remains unturned. Image
At present, there is no active mountain building in the Carpathians: both sides of the mountains are part of Europe. Earthquake locations trace the active boundary between Adria (African Plate) and Eurasia from the southern Alps to the Dinarides, with Monte Lussari at the bend. https://gsw.silverchair-cdn...
But before ~10 million years ago, the Carpathians, the Alps, and the Dinarides were all subduction zones, and they in a 'Triple Junction'. With oceanic plates, like in Japan today, this makes for a reasonably orderly tectonic puzzle. But in NE Italy, the plates weren't oceanic... Image
Read 4 tweets
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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