Materiales de edad maastrichtiense en la serie eocénica del flanco-SW del sinclinorio de Bizkaia (Arrigunaga, N. de Bilbao)

Abstract

A detailed study of the microfaune of a sedimentary series, belonging to the southern flank of the Biscay Synclinorium (N. Bilbao), has led us to evidence the presence of some Maastrichtian materials that are in tectonic relation with the Eocene age rocks. Lithologies of this series are very similar to those of the outcrops in the northern flank of the synclinorium. Fault directions observed between Maastrichtian and Eocene materials are concordant with the main tectonic structures previously described in this basin (Durango fault, Arratia fault, etc.). The analysis of the foraminiferal assemblages allows us to distinguish three big sections, with six different biozones. Some important gaps in the series are detected, one of them affected to a complete Eocene biozone. Consideration of the ostracode assemblages indicates a deep marine environment for these materials. A sample by sample analysis of those assemblages shows a progressive deepening from the Maastrichtian (outer shelf) to the middle Eocene times (bathyal, abyssal).