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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. 
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.
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...
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!
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.
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!
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?
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.
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!
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!
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.
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.
Geo-#giroditalia2023 - Stage 14. After a refreshing dip into the Alps, the Peloton is quickly returning to the safe shores of Adria. When Adria was pushed over Europe to form the Alps, the Alps pushed back, deforming northern Adria and making the Southern Alps (Dolomites).
The riders will cross the 'Ivrea Body', which is a special geological region: it offers a rare glimpse into the deep Earth! The Alps jacked up northern Adria, and now we can see rocks of the mantle below that is normally at least 30 km deep, impossible to reach by drilling!
By the way, did you know that the northern Adria margin did not originally form next to the Alps region: in the supercontinent Pangea, the Po Plain was next to...Pau, in Southern France! So back then, today would have been a Pyrenean stage...had the Pyrenees already existed then.
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!
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).
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!
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!
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'
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.
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.
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.
