Foraminiferal taphonomy, palaeoecology and palaeoceanography of the Eocene

The Eocene Epoch (˜34 to 55 Ma) of Earth history was characterised by warm temperatures, high partial pressures of carbon dioxide in the atmosphere (pCO2[atm]) and by small to non-existent continental ice sheets. Because we are currently heading toward a climate state characterised by warmer mean global temperatures and higher pCO2[atm], it is imperative to understand the nature and causes of climatic variability and carbon cycle behaviour during previous globally warm climates. The fossil tests of foraminifera are widely used for palaeoceanographic studies. Palaeoecological constraints are established here for diverse late middle Eocene planktic foraminiferal assemblages, which include many rare species and some previously undocumented morphotypes. The diversity of palaeoecologies highlights the potential for reconstructing the temporal evolution of upper ocean physical and chemical structures in the Palaeogene using a multiple species approach. In addition, an assessment is made of the microstructural preservation of Eocene foraminiferal tests, with the aim of developing a more quantitative estimate of the degree of diagenetic alteration in ancient foraminiferal calcite. This work has implications for the robustness of the geochemical proxy palaeoceanographic signals contained within their tests. The Eocene Epoch represents over one third of the entire Cenozoic Era. Yet virtually nothing is known of the magnitude and stability of Eocene warmth and carbon cycling on anything but a long-term (multi-million year) time-scale. This problem is addressed by using Eocene sedimentary sections recently recovered from Demerara Rise, offshore Surinam, during ODP Leg 207. A new early to middle Eocene benthic foraminiferal stable isotope stratigraphy (˜100 kyr resolution) from Demerara Rise is broadly consistent at the Myr time-scale with a composite record based on multiple sites (Zachos et al, 2001a). The overall form of a preliminary benthic foraminiferal middle Eocene Mg/Ca record is similar to the oxygen isotope record and in support of long-term middle Eocene cooling.