PhD Offer in Geomicrobiology (Paris)

About the project

The Biomineralogy team of the Institute of Mineralogy, Physics of Matter and Cosmochemistry (IMPMC), in collaboration with CR2P and ESE, is looking for a PhD student to conduct a comparative study of Messinian fossil stromatolites and modern analogues from Sardinia, aiming toward a better understanding of paleogeobiological archives. The work will be performed within an interdisciplinary consortium in mineralogy, paleontology, and microbiology.

Context and scientific questions

Stromatolites are particularly emblematic geobiological materials since they are the oldest evidence of life-mineral interactions, dated at several billion years. They are found throughout Earth's history and have received strong attention for the information they provide about microbial paleobiodiversity and paleoenvironments. However, while this information is interpreted based on our knowledge about modern analogues, the latter remains very incomplete. Few modern stromatolites from coastal pond environments are known, where variations of physico-chemical conditions such as salinity are very strong.

This project aims to study mineralogical, geochemical, textural, and biological properties of modern coastal pond stromatolites recently discovered in Sardinia, from field- to nano-scale. They will be compared to fossil stromatolites from the Messinian (~6 Ma) which are abundant in the Mediterranean basin and whose coastal origin remains uncertain.

Key questions to be addressed:

• Are there mineralogical or geochemical signatures of a coastal environment recorded by the mineral part of such stromatolites?
• Which part of the microbial diversity populating these stromatolites is fossilized in the form of cells encrusted/replaced by minerals?
• Are cell ultrastructures preserved by early fossilization stages, and which of these traces can be identified in Messinian fossil stromatolites?
• What is the origin of laminae observed in these stromatolites?

Overall, Sardinian stromatolites may become a unique model of stromatolites subjected to severe environmental variations, particularly in salinity. Their comparison with Messinian fossil stromatolites will provide unique insight into this period of great interest for paleontologists.

Methodology and techniques

The student will use diverse techniques of petrology, mineralogy and geochemistry to characterize major and accessory mineral phases, their distribution and texture within stromatolites. In parallel, geochemical analyses of aqueous solutions surrounding stromatolites will be performed together with speciation calculations to determine the operating chemical equilibria. Spectroscopy (Raman, FTIR, visible fluorescence, synchrotron-based m-XRF) and/or microscopy (SEM, TEM, STXM) analyses will be conducted to identify potential mineral-microorganism assemblages and/or cells partly or totally replaced by minerals.

An optional component for candidates at the Earth science-biology interface is the characterization of initial microbial communities initiating microbialite formation using molecular biology tools (metabarcoding), in collaboration with colleagues at ESE in Orsay.

Candidate profile

The candidate should be able to learn how to use analytical tools. They will take charge of data acquisition and processing and should develop a critical view on their implications and limits.

Funding and start date

Funding will last for 3 years (standard PhD duration in France). The grant is provided by the DIM île de France "Matériaux anciens et patrimoniaux" and the employer will be the CNRS. The position will start as soon as September 1st, 2019, or at the latest on December 1, 2019, depending on the candidate's availability.

Application

Candidates should send their detailed CV and a motivation letter to Karim Benzerara (karim.benzerara@upmc.fr) and Jean-Paul Saint-Martin (jean-paul.saint-martin@mnhn.fr).