Formación de una beachrock contemporánea en los depósitos de escoria antropogénica de la playa de Arrigunaga (Bizkaia, España)

Abstract The large, thick beachrock of Arrigunaga beach (Bizkaia, Spain) is unusual among beachrocks because (a) Its location, at 43ºN latitude; (b) substrate that was cemented, largely consisting on smelter slag mixed with natural sediment; (c) timing and amount dumping sea, millions tons waste dumped in the short interval AD 1902–1966; (d) sudden cessation (AD 1966), followed by immediate exhumation retrogradation (e) An aggressive engineering intervention 1999), supposedly aimed regeneration, imported bioclastic sands, resulting additional weak cementation residual blocks. Thickness identification internal clasts attest for a multiepisodic process least three main steps several CaCO 3 polymorphs precipitated from marine freshwaters. Evidence bacterial remains suggests biological activity helped to trigger cementation. C O isotopic values obtained cements confirm dominance freshwaters composition. Exact knowledge start finishing dates permits tightly constrain rapid cementation, which already evident since 1924, produced beachrock, as well its evolution towards current fast complete disappearance.