Project

Discipline

phosphate; Paleogene; PETM; CIE; Palaeo-environment; Palaeo-climate; oxygen isotopes; carbon isotopes

Lead
Lay summary
The aim of this project is to investigate the Paleogene phosphate sequences in order to trace thermal changes and perturbations in the carbon cycle in low latitude shallow deposits via geochemical analyses of sediments and vertebrate fossils. The obtained data are evaluated in terms of palaeo-environmental conditions, palaeo-oceanography and palaeo-climate. A widespread, extreme climatic warming appeared about 55 million years ago in the Paleogene (PETM - Paleocene-Eocene Thermal Maximum). One of the strongest signals describing this event is the large negative shift in the marine oxygen isotope record. The PETM is also associated with a negative 2.5-6 ‰ carbon isotope excursion (CIE), which is generally accepted to reflect the geologically rapid injection of a large mass of 12C-enriched carbon into the ocean/atmosphere system. The primary source of this carbon has been attributed to dissociation of methane hydrate released from seafloor sediments, further enhancing global warming. The PETM is the closest greenhouse period to modern time and in many ways it represents a natural experiment analogous to the modern anthropogenic situation, therefore the characteristics and mechanisms of this global event are under intensive study. Our project investigates Paleogene climatic and environmental conditions and the research is a follow-up of previous results from Tunisian phosphate beds that gave an interesting and in some ways unexpected result (Ounis et al., 2008). Here the marine phosphate remains reveal a large CIE at about 55Ma, but without any shift in the oxygen isotope values. The absence of any temperature anomaly in the Tunisian sections was initially interpreted as reflecting the low latitude position and the shallow, semi-closed condition of the basin. However, it is unclear whether this CIE really links to the PETM or it is rather a local signal of the region. The Tunisian layers are part of the giant Tethys-Caribbean phosphorite belt which deposited during the late Cretaceous-Eocene. It provides a good example of a widespread shallow marine environment at low latitude and many other regions can be sampled in order to test whether the observed isotope signal in Tunisia is unique or can be traced globally. If similar climate signal is widely recognized at other phosphorite localities, then the magnitude of the global warming at low latitude should be reconsidered, hence in a wider context the data might help to better understand modern climate changes as well.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

Number	Title	Start	Funding scheme

Objective: The aim of this project is to investigate the Paleogene phosphate sequences in North Africa in order to trace thermal changes and perturbations in the carbon cycle in these low latitude shallow deposits. The work will focus on the geochemical composition of vertebrate fossils and the obtained data will be evaluated in terms of palaeo-environmental conditions, palaeo-oceanography and palaeo-climate.Summary: A widespread, extreme climatic warming appeared about 55 million years ago in the Paleogene at the Paleocene/Eocene boundary (PETM - Paleocene-Eocene Thermal Maximum). One of the strongest signals describing this event is the large negative shift in the marine oxygen isotope record primarily preserved in carbonate fossils. The PETM is also associated with a negative 2.5-6 ‰ carbon isotope excursion (CIE), which is generally accepted to reflect the geologically rapid injection of a large mass of 12C-enriched carbon into the ocean/atmosphere system. The primary source of this carbon has been attributed to dissociation of methane hydrate released from seafloor sediments, further enhancing global warming. In many ways the PETM represents a natural experiment analogous to the modern anthropogenic situation, therefore the PETM has developed as a provocative geological case study in global changes, and the characteristics and mechanisms of this event are under intensive study. Several other short term thermal maximums coupled with negative CIE have been reported from early Eocene marine sediments (ETM2 and ETM3, Eocene Thermal Maximums), which demonstrate that the PETM was not a unique phenomenon.Recent studies in Tunisian Paleocene-Eocene phosphate layers indicate that marine phosphate remains also reflect the global CIE at the PETM, but without any shift in delta18O values (Ounis et al., 2008). The absence of any temperature anomaly in the Tunisian section has been initially interpreted as reflecting the low latitude position and the shallow, semi-closed condition of the basin. However, it is unclear whether this CIE really represents the P/E boundary in the area or whether it is rather a local signal restricted to the Gafsa Basin. The Tunisian layers are part of the giant Tethys-Caribbean phosphorite belt which was deposited during the late Cretaceous-Eocene and extends from the Caribbean in the west, through North Africa and the Middle East in the east. It provides a good example of a widespread shallow marine environment at low latitude and several localities can be sampled in order to test whether the observed isotope signal in Tunisia is unique or can be traced globally. If similar climate signal is widely recognized at other phosphorite localities, then the magnitude of the global warming at low latitude should be reconsidered, hence in a wider context the data might also help to better understand modern climate changes and can assist to constrain recent climate models.This project builds on our present data and has two main aims:1) Investigate in more detail the Tunisian phosphate deposits displaying multiple delta13C excursions to establish their relation to the global record and to local conditions. This would involve newly sampled sequences and would focus on both phosphatic units and the intercalated carbonate and marl layers. Analyses of the delta34S of sulphate incorporated in the fossils and delta13C of organic matter in the sediment will further support the interpretation of the CIEs and their relation to the global record. This first part of the proposal would be shared with a post-doctoral fellow, Anouar Ounis, invited from the University of Tunis El Manar. 2) Compare the obtained record with other phosphate deposits in North Africa in order to test the regional extent of the palaeo-climatic signals measured in part 1. The phosphate successions of Morocco are particularly interesting because besides the abundant marine vertebrate fossils, terrestrial remains occur as well, allowing investigation into the expression of climatic change in contemporaneous marine and terrestrial settings.Fossil bones and teeth from each of the successions will be studied for their structure, mineralogical compositions. Their trace element content will be determined in order to test the extent of early and late diagenetic interaction with the burial fluids and thus choose the best preserved fossils for the isotope studies. The trace element data can offer further knowledge about the palaeo-environmental condition and taphonomy. Beside the conventional isotope analyses, a detailed oxygen isotope study with ion microprobe is planned to be applied because it potentially allows in-situ measurement of isotope ratios with micron scale spatial resolution. This novel technology may reveal small variations in the delta18O record within individual fossils allowing greater confidence in the preserved signal.The chosen place to conduct this research is the University of Lausanne, which is ideally suited for such studies given the expertise present and its analytical facilities. Most of the analyses proposed, with the exception of the ion microprobe analyses, can be completed at Lausanne. For the ion microprobe measurements, it is planned to use the facilities at the University of Edinburgh. Several other collaborations, such as connections with the Tunisian phosphate company, the University of Tunis El Manar, the University of Southampton and National Museum of Natural History of Paris ensure that the project can be completed.