Cadomian Orogeny

The Cadomian orogeny was a big event that happened a very long time ago, between the Late Neoproterozoic and Early Cambrian, about 700 to 425 million years ago. It was named by a scientist named L. Bertrand in 1921, after the Latin name for the city of Caen in Normandy, France. This event changed the shape of the Earth’s surface by folding and lifting up rocks in parts of what is now Europe.

This orogeny happened when different pieces of land, called terranes, crashed into the northern edge of a huge ancient landmass named Gondwana. These terranes later moved away and became part of Baltica, which was an early version of Europe. Scientists have studied its remains in many places, including Europe, North Africa, the Arabian Peninsula, Jordan, Israel, and the Persian Gulf.

The Cadomian orogeny began with one of these terranes sliding down under Gondwana about 760 million years ago. This created volcanic mountains and basins that opened and closed over millions of years. The collisions happened in two main phases, starting in the east and moving westward, and they set the stage for the opening of a new ocean called the Rheic Ocean.

Cadomian geology in the Armorican Massif

The Armorican Massif has old rocks that formed the base before the Cadomian events. These rocks, called gneiss, are very ancient, dating back nearly 2,018 million years. They can be found in places like Guernsey and Normandy. Near Trégor, scientists have found even older gneiss rocks.

The Brioverian series includes many layers of rock that formed during the Cadomian time. These rocks are mostly made of mud, silt, and sand, with some mixtures of different materials. They were laid down in deep ocean areas. There were also volcanic eruptions adding more layers to these rocks. The rocks formed between 750 to 540 million years ago.

After the major mountain-building events, new layers of sediment covered the older, folded rocks. These newer layers include mixtures of stones and sand, showing how the land changed after the mountains formed.