High resolution planktic foraminiferal biostratigraphy across the K/T boundary at Osinaga and Musquiz (Navarre, Pyrenees) allows us to recognise a small hiatus located just at the boundary. The hiatus affects the uppermost part of the P. hariaensis Bizone, the Cb. cretacea Biozone and the lo wermost part of the Pv. eugubina Biozone, being smaller at Osinaga than at Musquiz. Due to the hiatus the planktic foraminifera extintion model seems to be more catastrophic than in other more continuous sections