Accordingly to Carvalhido (2018) the Local Natural Monument of Canto Marinho preserves the occurrence of more than 700 salt pans dating from the Iron Age. The pans or bowls provide important paleoenvironmental information, namely on the relative position of the sea level during the Iron Age, which would be lower than the current one.

The sinks or bowls were sculpted in the rock through a chipping process with variable dimensions and shapes, taking advantage of the surfaces available in the rocks, being able to assume a sub-rectangular, trapezoidal or even semicircular shape. Regarding depth, it is estimated that they would be between 5 to 10 cm, with the purpose of containing a minimum amount of water that would allow easy and rapid evaporation (Almeida, 2009). As for the location, the salt pans would be above the high tide line, preventing it from flooding when it reached the maximum level. This fact leads us to see that the way they work, consisted of an indirect flooding system, according to which salt explorers would flood the pans with water they transported from the sea.

The pans or bowls can be seen along the coastal coast of Viana do Castelo, however in this place, there are several clusters of these findings because a schistous substrate is available, a rock more easily worked than granite, with greater thermal absorption and impermeability o that allowed greater evaporation efficiency.

Several of these findings are today submerged during the high tide, indicating that about four to five thousand years ago, during the Iron Age, the sea level would probably be about 1 to 2 meters below the position current. In this way, these relics are indicators of the position and evolution of the coastline along recent geological time.

References:

Carvalhido (2018). Livro de Pedra, Monumentos Naturais Locais de Viana do Castelo – Catálogo. Câmara Municipal de Viana do Castelo, 2ª edição.