The Baixo Alentejo Flysch sequence corresponds to a thick succession of shales and graywacke, strongly tectonized, arranged in tight folds, intensely faulted and, sometimes, cut by quartz veins, belonging to three large metasedimentary formations. In Vale Fuzeiros, the Mira Formation (326-315 Ma) emerges, in which it is still possible to identify some sedimentary structures, such as drag marks and erosive structures, or have some conglomerates with clasts from the Piritosa Belt and goniatite fossils (Goniatites granosus). This formation constitutes the substrate of the Algarve Mesozoic formations east of S. Bartolomeu de Messines.

The rocks of this formation originated from episodes of sediment deposition (clays and sands), in a marine environment, associated with strong turbidity currents.