A New Low- to Middle-Latitude Biozonation and Revised Biochronology of Palaeogene Calcareous Nannofossils

Abstract

We present a new Palaeogene calcareous nannofossil biozonation that is integrated with the biostratigraphic frameworks of Martini and Bukry (Martini 1971; Bukry 1973, 1978; Okada and Bukry 1980). Age estimates are provided for all Palaeogene biohorizons. This new biostratigraphic scheme is derived from the biostratigraphic methodologies and data that we have generated over nearly three decades, studying calcareous nannofossils in Palaeogene marine sections and from deep-sea sediments, in low- and middle-latitude regions. Additional new data are also presented. The aim of our work has always been to pursue a detailed nannofossil biostratigraphy through the use of semiquantitative methods in combination with short sampling intervals. This strategy is aimed at capturing the details of the distribution and abundance behaviour of individual calcareous nannofossil taxa. A limited set of selected biohorizons has been chosen for establishing a relatively coarsely resolved biozonation that could guarantee ease of communication and applicability in practical geological work. Following the criteria used in a new Neogene biozonation recently published by Backman et al. (2012), we propose a new code system for the 36 biozones in the Palaeocene–Oligocene interval: Calcareous Nannofossil (CN) Palaeocene biozones 1–11, CNP1–CNP11; CN Eocene biozones 1–19, CNE1–CNE19; and CN Oligocene biozones 1–6, CNO1–CNO6. The average duration of the biozones is 0.9 Myr in the Palaeocene, ~1 Myr in the Eocene, and 1.9 Myr in the Oligocene. Age estimates are assigned to all biozone boundary markers and to numerous additional biohorizons. This biochronology has been derived from astronomically tuned cyclostratigraphies for the time interval from 23 to ~41 Ma (Pälike et al. 2006) and from the Geomagnetic Polarity Time Scale (GPTS) of Cande and Kent (1995) for ~41–65 Ma (to the K–Pg boundary). Emphasis is placed on the discussion about the reliability of those nannofossil biohorizons that have previously been been used or suggested for the definition/recognition of some Palaeogene stage boundaries.