Residual beachrock and coastal eolianite patches without anthropogenic components on the eastern coast of Cantabria (Spain)

Abstract

Isolated beachrocks appear as relict patches normally attached to protrusions of lower-upper Cretaceous limestones outcropping at Noja, Somo and Sonabia zones in the eastern coast of Cantabria (northern Spain). Additionally, remnant cemented dunes (eolianites) are present at different heights above present sea level. We concentrate on the petrographic features of first-generation cements, that are different in the lower foreshore and upper foreshore-backshore. δ¹³C and δ¹⁸O values measured in the cements of both beachrock and eolianite suggest mixing between marine and meteoric waters, generally with preponderance of the continental contribution. In all the studied examples, Coccus-type bacterial activity has been recognized, suggesting that it is the main trigger for the initiation of cementation. ¹⁴C dating shows that the different cementations studied did not occur in a single event at a specific age, since there is a notable variation, from the highest values of 8760 years BP to 2740 years BP, despite the beachrock patches being at the height of the current intertidal zone. In the non-cemented intertidal sands that form the current beaches there are also important variations, difficult to justify, from similar ages of 3050 years BP (Noja) and 3010 years BP (Somo) to a mere 390 years BP (Sonabia).