Evolución sedimentaria del polder Anbeko (Reserva de Urdaibai, Golfo de Vizcaya) durante el Holoceno

Abstract

The sedimentology and micropaleontological content (benthic foraminifera) of a core located in the Anbeko polder of the Urdaibai estuary (Southern Bay of Biscay) have been analysed in order to characterize the holocene evolution of this polder. Based upon sedimentology and micropalaeontological assemblages, four units have been identified in this core. During the first phase this area was under marine conditions, with a a maximum marine influence around 5000 years BP. The pulsation described during the Atlantic-Subboreal transition of the Holocene is then registered in this core. Sedimentological facies of the second unit indicate a decrease of energy in this environment, where outer estuarine foraminifera dominated the assemblages. The third phase indicates the progressive filling of the estuary, with the appearance of a vegetated marsh, as evidenced by the total dominance of agglutinated foraminifera. This marsh, which is progressively isolated from the tidal influence, was anthropologically transformed into a polder during the 1 8th. century