Changes in calcareous nannoplankton assemblages around the Eocene-Oligocene climate transition in the Hungarian Palaeogene Basin (Central Paratethys)

Anita Nyerges,Ádám T Kocsis,József Pálfy

doi:10.1080/08912963.2019.1705295

Abstract

ABSTRACT The Eocene-Oligocene climate transition (EOT) is the last major greenhouse-icehouse climate state shift in Earth history, ending the warm, ice-free early Palaeogene world and ushering in the Antarctic glaciation. This study is focused on the Hungarian Palaeogene Basin within the Central Paratethys, aiming to characterise the effect of the global cooling event in the calcareous nannoplankton assemblages and to reconstruct the palaeoenvironmental evolution of the region. Calcareous nannoplankton biostratigraphy is focused on documenting the NP21 Zone. Hierarchical cluster analysis allowed us to distinguish five successive assemblages. Thereby defined phases are compared with recently published trends in δ18O values and foraminiferal changes. Taxa with a preference for oligotrophic and warm surface waters dominate the lowest assemblage. The next assemblage contains taxa that indicate oligotrophic conditions but temperate surface water at the onset of the EOT. Nannoplankton abundance drops to a minimum in the third phase, when taxa adapted to cool surface waters gradually became dominant. A gradual rebound of nannoplankton abundance is observed in the fourth phase, possibly reflecting regional climate change related to the uplifting Alpine chain. After the end of the EOT, the youngest assemblage includes mostly eurytopic taxa which could tolerate an increased rate of freshwater and terrestrial influx.

Highlights

The Eocene-Oligocene transition (EOT), the interval between 34 and 33.5 Ma (Pearson et al 2008), represents a major greenhouseicehouse climate switch in Earth history
Only six taxa were omitted and five rare taxa were included in further analyses, either for consideration of their last occurrences (LO) (Discoaster barbadiensis, D. saipanensis, D. tanii, Reticulofenestra reticulata) or their significant environmental preference (Helicosphaera euphratis)
This study revealed that the effect of a global cooling event is recognisable on the local calcareous nannoplankton assemblages across the EOT in the Hungarian Palaeogene Basin (HPB)

Summary

Introduction

The Eocene-Oligocene transition (EOT), the interval between 34 and 33.5 Ma (Pearson et al 2008), represents a major greenhouseicehouse climate switch in Earth history. The associated changes mark the end of the warm, ice-free early Palaeogene world and the onset of Antarctic glaciation (Zachos et al 1996). Biotic turnover has been recorded across multiple fossil groups as a response to the significant climate change (Zachos et al 1996; Pearson et al 2008; Villa et al 2008). A rich record of these changes has been explored from high-resolution analyses of deep-sea drill cores, with global δ18O, and Mg/Ca data proving a faithful archive of changes in palaeoclimate and the global carbon cycle (Zachos et al 2001; Villa et al 2008; Bohaty et al 2012; Inglis et al 2015)

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