A Cenozoic calcareous nannofossil biozonation from low and middle latitudes: A synthesis

摘要

The need for an update of the calcareous nannofossil biozonations proposed by Martini (1971) and Bukry (1973,1975), more than 40 years ago, prompted us to develop two new biozonations published in 2012 and 2014, one for the Miocene through Pleistocene interval and one for the Paleogene interval (Backman et al., 2012; Agnini et al., 2014). These biozonations are here combined into a single Cenozoic biozonation from low and middle latitudes. A key strategy has been to employ a set of selected biohorizons for defining biozone boundaries, rather than aiming for obtaining the highest possible biostratigraphic resolution. This approach is aimed to find a balance between accuracy, applicability, and ease of communication and viability in practical geologic work. Each biozone boundary is defined with a single biohorizon. Subzones and auxiliary markers are avoided in order to maintain stability to the new biozonation. Combining the Paleogene and Neogene biozonations, a total of 38 Paleogene biozones and 31 Neogene-Pleistocene biozones are proposed: 11 Calcareous Nannofossil (CN) Paleocene biozones (CNP1-CNP11), 21 Eocene biozones (CNE1-CNE21), 6 Oligocene biozones (CNO1-CNO6), 20 Miocene biozones (CNM1-CNM20), and 11 Plio-Pleistocene biozones (CNPL1-CNPL11). Each of these 69 biozones contains one or several secondary biohorizons that are useful for biozone characterization. Age estimates are provided for all biozone boundary markers and the majority of the additional biohorizons. These estimates are derived from astronomically tuned cyclostratigraphies in the Pleistocene to middle Eocene (base of Chron C19n at 41.510Ma) interval and magnetostratigraphy in the early Paleogene, back to the Cretaceous-Paleogene boundary.