Calcareous nannofossil assemblage changes from early to middle Eocene in the Levant margin of the Tethys, central Israel

Menahem Weinbaum-Hefetz,Chaim Benjamini

doi:10.1144/0262-821x11-017

Menahem Weinbaum-Hefetz, Chaim Benjamini

Open Access

https://doi.org/10.1144/0262-821x11-017

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Abstract

Abstract. Patterns of change in calcareous nannofossil assemblages during nannozones NP11 to NP16 on the southern Levant margin of the Tethys were observed from sections of early and middle Eocene age sediments of the Avedat Plateau, central Israel. A cooling process following the Early Eocene Climate Optimum (EECO) is supported by several events of biotic change over a 4 Ma interval. The rate of pelagic sedimentation varied from 7.5 at the EECO to 23.6 m Ma–1 at the cooling transition phase. Reduced numbers of discoasters mark the end of the oligotrophic regime within the NP13 nannozone, followed by an increase in nannofossil richness especially marked by Blackites and Chiasmolithus spp. In the middle part of the cooling process a prominent peak of reworked Paleocene taxa, up to 7% of total taxa, suggests that enhanced current activity caused re-sedimentation on the Levant margin slopes. When stability resumed in the upper part of the NP15–16 interval, Coccolithus-type placoliths became rare and Reticulofenestra-type forms became dominant. Calcareous nannoplankton response to this gradual cooling became irreversible in the late Palaeogene, but the change was, however, diachronous across the Tethys.

Highlights

The early Eocene was marked by conditions of extreme Cenozoic warmth including the Early Eocene Climate Optimum (EECO) (Zachos et al, 2008), with a lack of polar-ice, warm tropical climates (Pearson et al, 2009) and low latitudinal temperature gradients (Bijl et al, 2009)
The cooling trend terminating the EECO in NP14 is accompanied by a three-fold increase in sedimentation rate, and increased carbonate production continues to the NP14/NP15 boundary
The early Eocene of the Levant region was characterized by oligotrophic conditions, during the EECO

Summary

Introduction

The early Eocene was marked by conditions of extreme Cenozoic warmth including the Early Eocene Climate Optimum (EECO) (Zachos et al, 2008), with a lack of polar-ice, warm tropical climates (Pearson et al, 2009) and low latitudinal temperature gradients (Bijl et al, 2009). Some have suggested that stagnant warm saline waters formed in low latitudes, in the Tethyan realm (Kennett & Stott, 1990). These early Eocene conditions of extreme warmth ended prior to the Ypresian/Lutetian (early/middle Eocene) boundary with the initiation of cooling, especially at high latitudes (Bijl et al, 2009). Recent studies have stressed the sensitivity of coccolithophores to environmental change Many researchers noted their biotic response to the dramatic changes of the early Cenozoic Many researchers noted their biotic response to the dramatic changes of the early Cenozoic (e.g. Gibbs et al, 2006), the growing use of calcareous nannofossils as palaeoclimatic proxies. Agnini et al (2006) tracked the early/middle Eocene transition at Possagno, Italy, and emphasized the rise of clade Noelrhabdaceae as marking the development of a major part of the modern oceanic phytoplankton community during this interval. Agnini et al (2006) considered the Discoasteraceae acme event, coincident with the EECO, to represent a peak of oligotrophic opportunists during these conditions of extreme warmth. Tremolada & Bralower (2004) showed that the genus Chiasmolithus represents cooler and more nutrient-rich water

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