A well-defined layer of about 70 cm thick stands out by its rounded instead of laminar inner shapes in the sandstone that outcrops at the foot of the ridge of Roca Tinyosa (Manresa), a few meters past La Gola del Bigaire by the shore of river Llobregat. This is really unusual because sediments deposit in flat layers, even if dragged by a turbulent flow.
The explanation of the phenomenon will be that the sediments of this specific layer were removed short after its deposition, when they were still a viscous mud, by the soft subsidence of a dry upper crust or newly arrived sediments. The result that is seen today, 40 million years later, is this layer with curious, rounded shapes, baroque into the flat pile of sedimentary rock.
[photo Florenci Vallès and Jordi Badia]