geotdf.bsky.social
At @GeoTdF.bsky.social we answer your questions on landscapes and geology cycling races | see Geo-Sports.org for more information!
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Eastern Albania is more mountainous, and consists of pieces of the former Greater Adria continent, pushed and piled up. And at the top lies one of the best preserved pieces of oceanic crust on land ('ophiolites') in the world: the Mirdita Ophiolite. But we'll stay west, and head for Italy next!
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This platform continues to the Greek Islands of Paxos, Lefkas, Kefallonia and Zakynthos. To the North and East of this platform was a deeper basin in which thin-layered limestones formed. You will see those, folded up and broken,in Albania. And later in Umbria and Marche, in northern Italy!
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The last intact remnant of Adria lies below the Adriatic Sea, and on the Karaburun Peninsula in southwest Albania, and in Puglia, where the Giro will ride its first meters in Italy this year. These intact remnants are shallow marine limestones of the Apulian Platform in the south.
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Greater Adria was pulled down into subduction zones: both to the west, below Italy, and east, below Albania (and Greece and the Balkan). The sedimentary rocks that formed at the margins of Adria were scraped off and pushed up, making the Apennines and the Albanides/Hellenides/Dinarides
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Yeah, we heard, very sad. But if we find some funding to make some clips, we'll throw them on our socials anyway ;)
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That continental edge was pushed below Corsica, 20 million years ago, and pulled back to the surface in the last 10 million years, when the Tyrrhenian Sea basin was formed.
The limestones became marbles, the marbles became gravel, and now it’s the peloton that is under high pressure! Enjoy!
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Marble is a metamorphic rock: it was originally a limestone that was buried to 25 km depth or so, and heated up to a few hundred degrees. In the case of Tuscany, these limestones formed as reefs on the edge of the Adria continent.
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So do we!
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😍🤯
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Where's that? Pillows are awesome.
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About 60 million years younger or so :) although peridotite doesn’t really have an age.
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The most spectacular rocks of the Semail Ophiolite are so-called 'pillow lavas'. These structures form when lava erupts below sea level: the lava quickly cools from the outside, but keeps flowing on the inside. Cut them, and you get a pile of pillows. Good for a rest day!
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In Oman, the Arabian continent went down into a subduction zone below oceanic crust, 80 million years ago, and scooped up the 'Semail' ophiolite. Along the race you see the magmatic rocks that formed at a spreading ridge, and rocks of the Earth's mantle that were below the ridge!
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An ophiolite is a piece of oceanic crust that is exposed above sea level. Oceanic crust forms at spreading ridges, and is normally many kilometers below sea level. But when subduction zones form in oceans, such as in the Philippines, oceanic crust may be uplifted and emerge.
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Hello!
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NW of Alula, the peloton will see dormant volcanoes of the Harat Uwayrid volcanic field of only 8-0.3 million years old. These are thought to relate to ‘plume’ volcanism, with calm basalt lava flows like on the Canary Islands! Familiar ground for those who trained on the #Teide !
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Sandstones of the next-younger Saq Formation is an Arabian lifesaver: these rocks are porous, and serve as the main aquifer (that is, a groundwater-bearing layer) of NW Arabia. These sandstones are rich in trace fossils: tracks in the sand made by ‘trilobites’that roamed the Cambrian sea floor!
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The Quweira Sandstonesare particularly resistant. These were were used for the famous settlements of Madain Saleh, not far from AlUla. This city was built in the 2nd century CE by the Nabateans, and has beautifully been preserved in the durable, hard rocks.
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There was a 'decent one' (M 4.5) last week!
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This causes earthquakes - mostly small ones, but in 1954 with a magnitude 5.4.
The faults that push up Mt Lofty slip on average half a mm per year. And with this ongoing uplift, the Tour Down Under gets a little harder every year 😃!
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But the ancient faults that cut these rocks were reactivated because the Australian plate is being squeezed between the Eurasia and the Pacific, and also interacting with India and Australia.
The squeezing popped up the Flinders ranges, and the epic Mount Lofty, and this process continues today.
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the Adelaide region forms a rare exception: it's shaking! Australia consists mostly of rocks of billions of years old, which formed when ancient continents collided and long-forgotten mountain belts formed. The rocks around Adelaide are up to 900 million years old, when life was only microbial.
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Welcome back! 🥳
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Eehm, that doesn’t look like DC…you sure you flew to the right Washington?
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Probably!
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Yes. Single gear, backpedal break, upright. The organization lends the riders a bike.