Jersey Shale Formation

The shales are the oldest rocks in the Island. You can see them in the west, across the centre and in the south of Jersey. They were formed by mud, silt and sand brought together on the sea floor about 600 million years ago. These sediments were transformed into rock by being pushed together, hardened and folded.

Over millions of years, the shale has been eroded away and given the shape of St Ouen’s Bay and St Aubin’s Bay.

The Jersey Shale Formation is part of the larger “Brioverian Supergroup”, which also includes rocks that can be seen outcropping in both the Baie de St Brieuc and La Manche regions of northern France.

Studies of the Jersey Shale Formation in the mid-80s concluded that these sediments were deposited in a subduction zone, where an ocean plate was being dragged down into the mantle underneath the neighbouring continent. The formation shows signs of having undergone deformation and low-grade regional metamorphism which geologists have associated with the Cadomian Orogeny and later mountain-building events.