Abstract
The quantitative study of the planktonic Foraminifera (Globotruncanidae and Heterohelicidae) from the Cretaceous-Tertiary boundary type section of El Kef (NW Tunisia) reveals the succession of the classical biozones within the Late Campanian-Danian interval. Thanks to the application of the grade-dating method to the various taxa included within the Rosita fornicata anagenetic lineage, several numeric ages (from 74.45 to 66.60 Ma) are obtained. Those figures only have a relative value because they come from a chronologic scale which can be steadly modified. Sedimentation rates given by these new quantitative data are used to characterize the systems tracts belonging to five depositional sequences, SD1 to SD5, themselves more or less correlated to the 3rd order custatic cycles of 1987. Nevertheless, the thin evaporitic horizon (Iridium and Ni-rich magnetites peak), which marks the K/T boundary, must be regarded as a sequence boundary corresponding to a drastic fall of the sea level. This interpretation, principally founded on the presence of numerous reworked Globotruncanids at the base of the Danian marls already observed in European sections, suggests a modifications of the eustatic chart of 1987 with rejection of a cycle TA 1–2 straddling the K/T boundary.
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