Spanish and Tunisian Cretaceous/Tertiary boundary sections: A planktic foraminiferal biostratigraphic comparison and evolutionary events

Abstract

We performed a planktic foraminiferal biostratigraphic study of the most expanded and continuous sections of the Cretaceous/ Tertiary (KIT) boundary located in Spain and Tunisia in order to evaluate the continuity and thickness of the KIT boundary sec­ tions and establish the correlation among biozones and sections. It was important to test the extinction patterns of Maastrichtian planktic foraminifera and the evolution of Tertiary species in or­ der to determine the thickness of the different planktic foraminif­ eral biozones. We considered the four classical biozones: Abathomphalus mayaroensis Biozone (Cretaceous), Guembelitria cretacea Bio­ zone, Parvularugoglobigerina eugubina Biozone, and Parasub­ botina pseudobulloides Biozone (Tertiary). The bases of these biozones are placed at the first appearance of the eponymous species, except for the base of G. e retacea Biozone which is situ­ ated at the last appearance datum of A. mayaroensis, precisely at the KIT boundary. We distinguished Pv. eugubina (low-arched aperture) from Pv. longiapertura (high-arched aperture) and we realised the earlier appearance of the latter species. Since these morphospecies are considered synonyms by sorne authors, the Pv. longiapertura FAD has frequently been used to establish the base of the PO, which is not exactly equivalent to the Pv. eugu­ bina Biozone of Molina et al. ( 1998). In a comparative study of the sections, we established four quantitative stages in the planktic foraminiferal population in the lowermost part of the Danian. Initially, the planktic foraminifer­ al assemblages are dominated by Guembelitria. The lower part of the G. cretacea Biozone (=PO) is characterised by a major in­ crease of Guembelitria with a maximum peak in abundance. Parvularugoglobigerina and Globoconusa? proliferated across the boundary between the G. cretacea and Pv. eugubina Bio­ zones. Later, Chiloguembelina and Woodringina were the most abundant. Finally, they were replaced in abundance by Eoglob­ igerina, Parasubbotina, Praemurica, and Globanomalina in the lower Danian. These quantitative stages were initially observed and proposed for several Pyrenean sections (Zumaya, Osinaga, and Musquiz) by Arenillas et al. (1998). Furthermore, the partial or complete identification of these stages allows us to recognize and quantify the hiatus span across the KIT boundary, since these stages do not depend on problematic taxonomic assignments of species.