Asociaciones de foraminíferos y ostrácodos en el Cenomaniense de Leioa (Cuenca Vasca)

Abstract

The Leioa section is representative of deep Cenomanian sedimentation from the western area of the Basque Basin. Detailed analysis of the microfaunas of foraminifers (planktonic and benthic) and ostracodes, taking into account their diversity, type of assemblage (foraminifers: FB- 7 to FB-6; ostracodes: 0-1 to 0-7) and the presence of several benthic-free intervals (ISB), allow to distinguish seven paleoenvironmental episodes in the Cenomanian of this basin. Besides these faunal results, each phase is also characterized by its isotopic 5 ,3C and 8 wO trends. Thus the evolution of the series, that occurred within a bathyal paleoenvironment, can be described; the amount and quality of the nutrients seems to be one of the most important causes to explain the observed distribution of microfaunas. A large hipoxic interval, occurring along most of the Middle Cenomanian, produced many changes on the benthic biotas. A different response of the planktonic assemblages to paleoceanographic modifications was also recorded