The calcareous nannofossil species Neobiscutum romeinii, N. parvulum, and Cruciplacolithus primus, are considered in modern zonation schemes as index species for the lowermost Paleocene. Our studies, however, reveal that they are consistently present in upper Maastrichtian calcareous nannofossil zone CC26. The two Neobiscutum species were found several meters below the Cretaceous-Paleogene (K-P) boundary in cores from Brazos River (Texas) and Antioch Church (Alabama), and in outcrops at Geulhemmerberg (the Netherlands), El Kef (Tunisia), and Jebel Qurtasiyyat (Jordan). Except for the Jordanian record, the same applies to the occurrence of C. primus. These coccoliths are extremely small, ranging from 0.8 to 2.5μm for Neobiscutum and 1.5 to 3.5μm for C. primus, and they constitute less than 1% of the calcareous nannofossil association. This may explain why they were not consistently detected below the K-P boundary in earlier investigations. Since these species are not exclusively Paleocene indicators only their prominent acmes or, alternatively, the index species Biantholithus sparsus should be used to unambiguously identify the lowermost Paleocene. The geographic coverage in our study indicates that the late Maastrichtian appearances of N. romeinii, N. parvulum and C. primus are typical for marginal seas of the Northern Hemisphere.

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