La Paroi de Barrachin

The Barrachin wall has been exploited for backfill, wall construction and aggregate production. It offers a very nice outcrop that allows to reconstitute the history of the Domaine Briançonnais in the Triassic (around 230 million years and in the Jurassic). On the Barrachin wall, we first observe carbonate sedimentary rocks with alternating dark banks of limestone and light banks of dolomite. This sequence is repeated several times. Then, we can see sedimentary figures on the wall: bioturbations due to crustacean burrows, tempestites, "bird eyes" without forgetting the fossils of stromatolites and dasycladacées. These sedimentary figures and fossils are the proof of low water depth. Indeed, the fossils of blue-green algae which need light for photosynthesis indicate a shallow water (20 to 30 m deep basin). Thanks to the fossils, it has been possible to date certain terrains: they were deposited in the Triassic period. At that time, there was a shallow sea. Finally, deformations are visible, almost at the top we observe two normal faults, the deformation is brittle, it took place on the surface, it is contemporary of the sedimentation. A seismic fault overhangs them. But here, the deformation is soft. Indeed, it touched the mud during induration, agitated by an earthquake due to the activity of the normal faults at that time.

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