Stage 17 of the #GirodItalia passes along one of our favorite geo-landmarks of Italy, the Sella Pass, and the the famous Sella Massif! This massif is a Triassic (240 million year old) atoll! In the early to middle Triassic, the continental crust of (Greater) Adria continent broke up in two in the northeast, on the Balkan side. This was probably related to subduction processes that occurred in that region and that are now long-gone, but in any case, it was associated with formation of large volcanoes, also in the Dolomites. Once the volcanism went extinct, the region subsided and because it was close to the equator, limestone and dolomite deposition occurred. At the location of the Sella Massif, is a ring-shaped, high ridge made of reef limestones and dolomites formed, with in the center a flat area: a lagoon. The Sella Massif is an atoll! And it was uplifted, and eroded, but not much deformed, so you're looking pretty much at the original thing! 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. It wasn't quite that setting here in the Dolomites, that may have looked more like volcanoes on the modern eastern margin of Australia. But an atoll is an atoll, and you can still imagine the white beaches and palm trees! Enjoy a cocktail at the pass today gentlemen! @UniUtrecht @UniUtrechtPE @UUGeo @UUEarthSciences