An independent test of planktic foraminiferal turnover across the Cretaceous/Paleogene (K/P) boundary at El Kef, Tunisia: Catastrophic mass extinction and possible survivorship

摘要

Planktic foraminiferal biostratigraphy and assemblage turnover across the Cretaceous/Paleogene (K/P) boundary at El Kef revealed the largest and most abrupt extinction event in the history of planktic foraminifera. Cretaceous assemblages were very abundant and diverse and included 67 stable identified species within the terminal Maastrichtian. The mass extinction was characterized by the disappearance of 6 (8.9%) species in the last 12 meters of the upper Maastrichtian and the extinction of 46 (68.7%) species at the K/P boundary as well as 15 (22.4%) possible survivors ranging into the lowermost Danian. The range of planktic foraminifera only based on six samples (equivalent to the previous El Kef blind sample test) showed an even more catastrophic extinction pattern, with only 1 species disappearing before the K/P boundary. The K/P debate is the result of several problems which include the "Signor-Lipps" effect, the possibility of reworking and the existence of hiatuses. However, irrespective of the different interpretations we conclude that there were no significant extinction nor quantitative changes before the K/P boundary and that most Cretaceous species suddenly became extinct at the K/P boundary. The El Kef section is one of the most continuous marine K/P boundary sections known and hiatuses have not been identified. Furthermore, possible Cretaceous survivors had a smaller size and lower absolute abundance in the lower Danian than in the upper Maastrichtian and the planktic foraminiferal evolutionary radiation began above the K/P boundary and not below. The same results have been found in other subtropical-temperate sections and may be sufficient proof for the existence of a catastrophic mass extinction at the K/P boundary. The planktic foraminiferal K/P extinction pattern is also very compatible with the catastrophic effects caused by the impact of a large extraterrestrial asteroid.