Italy’s Dolomite Alps and strata

Italy’s Dolomite Alps strata and fossils

A section of the Southern Limestone Alps the Dolomites are known as the Pale Mountains because of their colour from the carbonate rock dolomite rock. They have multiple layers of different material including strata with marine fossils such as large clams.

Italy’s Dolomite Alps and strata

Beautiful Lake Misurina (Lago di Misurina), is nestled among northeastern Italy’s Dolomite Alps. Also known simply as the Dolomites, the mountain range is composed primarily of pale white-to-gray carbonate minerals, including limestone and the mineral dolomite, also called dolostone. Acclaimed for their beauty and geologic diversity, the peaks, valleys and lakes of the Dolomites have been declared a UNESCO World Heritage Site.

The mountains and the mineral dolomite circuitously derive their name from a French naturalist and his home village. During a 1789 visit to the Alps, Diedonnè-Silvain-Guy-Tancrede de Gvalet de Dolomieu was fascinated by the pale, limestone-like rock, and published a scientific letter about it in 1791.

Other naturalists and scientists followed, delving into the rock’s peculiar carbonate structure — which, they determined, had formed in shallow lagoons and tidal flats upon which fossils, bacterial mats and dolomite marls were deposited in thick sedimentary layers some 200 million years ago in the Tethys Sea, or Tethys Ocean. That rock was subsequently raised to alpine heights by the collisions of the African and Eurasian tectonic plates.
Lake Misurina in the Dolomite Alps

Dolomite. Dolomites. Dolomiti, Dolomiten. Dolomitis

Italy’s Dolomite Alps and strata

The Dolomites are legendary name to both mountaineers and geologists. The pink and beige mountains, with the characteristic layers, the free-standing towers with flat tables on the top, are on the UNESCO heritage list, and give dreamy eyes to those who study mountains, and to those who just climb them up or ski down.

Dieudonné Sylvain Guy Tancrède de Gratet de Dolomieu was born 1750 as the son of a French marquis in the Alps. After a military career, he spent most of his life studying the natural world, particularly geology and women. Dolomieu was interested in everything: volcanoes, minerals, and how the landscape changed with time. He believed the world was shaped through a series of ancient catastrophes, where water shaped the surface of the Earth.

But he did get something that few geologists do: He got both a mineral and whole mountain area named after him. During travels in what was then part of Austria, but now is part of northern Italy (more on that later!), he noted that the limestone in these mountains did not dissolve with bubbles and fizz when put into hydrochloric acid.

The forests lasted only a million years or so, before the sea once again rose and flooded the Cortina area. For the next ten million years, the sea laid down what was to become the signature rock of the Dolomites: the hard, layered dolomite, which makes up the magnificent cliff faces, which tower above the valleys. The dolomite is more than one kilometer thick, and its geological name is simply The Main Dolomite.

Limestones like this deposit in very shallow seas, where the tides may lay the land bare. Lots of light gives energy to the algae, which make fine particles of the mineral calcite, calcium carbonate. This limestone mud reacts with magnesium in the sea water, swaps half of its calcium atoms with magnesium and becomes dolomite.

How could the dolomite become so thick in a very shallow sea? It happened because the sea bottom sank in slowly, at the same pace the algae created rocks. By this lucky coincidence, the sea remained at around the same shallow depth for ten million years, building layer upon layer of rock.

Up close, the dolomite changes between thick layers of pure dolomite mud, often with large mussels called megalodonts, and layers with densely laminated mats of algae. It is the changes between these layers, which give the dolomites their characteristic cliff faces. The Dolomites: when the Alps were a tropical sea

Italy’s Dolomite Alps and strata

Italy’s Dolomite Alps and strata

Italy’s Dolomite Alps and strata

Italy’s Dolomite Alps and strata fossils