ANALYSIS OF UPPERMOST CRETACEOUS LOWERMOST TERTIARY HEMIPELAGIC SUCCESSIONS IN THE BASQUE COUNTRY (WESTERN PYRENEES) - EVIDENCE FOR A SUDDEN EXTINCTION OF MORE THAN HALF PLANKTIC FORAMINIFER SPECIES AT THE K TBOUNDARY/

This paper summarises our current knowledge about 21 sections across t he WT boundary from the Basque Country (western Pyrenees), all of them comprising intermediate-deep basinal facies. This study allowed us to establish that Sopelana III and Bidart are the best sections for anal ysing the extinction of the planktic foraminifers at the K/T boundary. Detailed analyses of planktic foraminifers from four new sections all ow us to differentiate four biozones, one at the end of the Cretaceous and three at the beginning of the Tertiary. These analyses further sh ow that 63 Upper Maastrichtian planktic foraminifers species reached t he boundary where 33 species became extinct. The study also shows that some species decrease markedly in abundance in the last few metres of the Cretaceous prior to the extinction event which could be related t o environmental changes at the end of the Maastrichtian. More than 50 % of the planktic foraminifers, that is 33 species, became extinct at the end of the Cretaceous. However, most of the extinct species were r are and only about 20 % of the total Cretaceous assemblages are involv ed in the extinction event. The 30 surviving species, that is less tha n 50 % of the Cretaceous species, later disappear through the Pr. long iapertura and P. pseudobulloides biozones of the beginning of the Tert iary. Above the K/T boundary, samples are far poorer in planktic foram inifer specimens than those from the uppermost Maastrichtian and inclu de 16 Tertiary species. Moreover, together with this extinction event there are impact markers (iridium and Ni-rich spinels), as well as a h igh concentration of soot at the beginning of the Danian at the Sopela na III section. This strengthens the hypothesis of a causal link betwe en the impact and WT extinctions.