Caracterización bioestratigráfica mediante foraminíferos planctónicos de los términos basales del Flysch Calcáreo (Cretácico Superior) entre Andoain e Irun (Pirineos occidentales)

Abstract

The base of the Upper Cretaceous Calcareous Flysch along the NW margin of the Bortziriak Palaeozoic massif (NE margin of the Basque-Cantabrian Basin) has been dated differently by a number of authors. Thus, the aim of this work has been to carry out a detailed bios- tratigraphic study based on planktonic foraminifera of these basal deposits. The results of the biostratigraphic analysis yield a diachronic age for their base. On the one hand, a gene- ral hiatus from lower Cenomanian to upper Turonian is observed in the study area. Howe- ver, in the Txoritokieta anticline, the hiatus expands to late Campanian ages, reflecting a submarine paleohigh that was not covered at least until that period. On the other hand, resedimented upper Turonian-Coniacian breccia clasts indicate the erosion of previous stra- tigraphic units, which may locally extend the hiatus. In addition, several authors have pre- viously suggested the existence of limestones of middle to upper Cenomanian age in the Fagollaga area. This would demonstrate the sedimentation and subsequent erosion of sha- llow platform limestones during the sedimentation of the Calcareous Flysch. Finally, this study confirms the occurrence of a marine transgression during the Upper Cretaceous, which gradually flooded the Palaeozoic massif of Bortziriak.