Raised Beaches in the Cantabrian Coast

Abstract

Raised beaches along the Cantabrian coast are related to erosion surfaces, locally known as rasas, affected by tectonic uplift. The higher surfaces, probably of Pliocene age, have a maximum relative height of 285 m above mean sea level (MSL). Generally, they have gentle seaward slopes and highly variable lateral and longitudinal distribution. They reach 20 km in maximum width in central Asturias, and the lower levels cover smaller areas. Two W-E-oriented zones may be differentiated along the coast: Burela-Nalón (107 km) and Nalón-France (365 km). Two or three levels of rasas were generated in the first sector, which gradually merge into one towards the west. In the Nalón-France zone, 12 levels have been recognised. These geomorphic surfaces are apparently slightly deformed, although some authors proposed that they are strongly faulted. Some aggradation and fluvial terraces, abrasion surfaces, as well aeolian sand deposits, can be correlated with rasa levels. Other old deposits disconnected from the rasas were generated associated with exposed and estuarine beaches and may include slope deposits less than 1.0 m thick. Most beach and aeolian dune deposits are siliciclastic, with a limited proportion of bioclastic sands and debris. Relevant pending issues to be resolved are the numerical age of the rasas and their possible correlation with erosion surfaces, eustatic changes and uplift, considering that neotectonic activity is thought to be low and localised. The most recent marine terraces have not been uplifted and are affected by a general recession due to sea-level rise.