COLOURFUL FLYSCH
The flysch is composed of four types of rock: lutites, marl and limestone in one layer, and sandstone in the other. They alternate to create a mosaic of colours, helping us to understand how the basin evolved between it opening and closing.
Black flysch
The black flysch is the oldest and is made up of black lutites and lots of intercalated turbidites, signalling instability during the opening up of the Bay of Biscay.
Calcareous flysch
Itzurun Beach is a perfect blend of limestone (harder) and marl (softer) formed on a calm seabed.
Red flysch
In Zumaia, the calcareous flysch has a reddish hue due to the higher iron content of the clay sediments.
Turbidites
Turbidites are usually yellow and contain layers that have been generated by movement. This flow generates elongated shapes at their sole, allowing us to reconstruct the direction of the currents.
Local sedimentation
Slow and gradual settling of fine sediments and the small shells of organisms on the seabed.
Lutites are formed from clayey sediments. Limestone contains a large amount of carbonate shells. Marl is a rock that is a mix of the two.
Turbidites
These are formed by large avalanches of water and sand that flow down submarine canyons to the deep seabed They travel at high speeds and cover the seabed with a layer of sand called turbidite.
Turbidites are more common in unstable environments.