Análisis integral (micropaleontología y sedimentologia) de un sondeo supramareal Holoceno en la ria de Gernika (Golfo de Vizcaya)

Abstract

The microfauna (foraminifers, ostracods) and sedimentology of a core from the supratidal polluted area of the Ria of Gernika (S of Bay of Biscay) have been analysed in this work. Four different episodes have been recognised in the last 6400 years in this area, based upon microfaunaI assemblages and sedimentological facies. The older one represents a subtidal palaeoenvironment with marine influences at the base of this core. A subsequent increase of the energy in a tidal palaeoenvironment is evidenced by the occurrence of rhythmic fades and estuarine characteristic microfaunaI assemblages. This level is correlated to transgressive pulsations previously described in the Bay of Biscay 3500 to 2500 y. BP. Third episode shows a progressive shallowing of the palaeoenvironment, with low-salinity and mixed waters in a supratidal marshy milieu. To the core top, a very fine sediment with abundant plant roots and very scarce microfauna indicate the present filling of this part of the estuary