Abstract
A planktonic foraminiferal biostratigraphy of the relatively complete Cretaceous-Tertiary (K/T) boundary section at Bidart, south-west France, is given. With the exception of Rugoglobigerina hexacamerata Brönnimann and Guembelitria cretacea (Cushman), all Cretaceous planktonic foraminifera became extinct at the K/T boundary. Thanetian age strata are for the first time reported from Bidart, and a significant hiatus representing 350-750 kyr I is detected at the Danian/Thanetian boundary. Population changes within the Maastrichtian planktonic foraminiferal faunas are generally similar to those of other K/T boundary sections but large 'globotruncanids' increase in numbers close the boundary, rather than decrease as elsewhere. This change in faunal composition 2.5 m below the boundary correlates with changes in lithology (from grey to red micrite) and 87 Sr/ 86Sr ratio, an increase in δO 18 and a decrease in δ 13C. This evidence suggests that the palaeoceanography of the Bidart region changed from a Tethyan to a North Atlantic dominated setting towards the end of the Cretaceous.
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