Multi-isotopic study of the carbon and sulfur cycles in modern alkaline and stratified environments from Mexico and their microbialites

Started in January 2020

Defended the 15 september 2023

Supervisor: Christophe Thomazo

Funding: French national research agency (ANR)

Abstract

Stromatolites and, more generally, microbialites are organosedimentary structures formed under the influence of phylogenetically and functionally diverse microbial communities in interaction with abiotic factors. Fossil stromatolites represent the oldest undisputed evidence of life on Earth (~3.5 Ga). Yet, the specific identity and functions of associated microorganisms and the local environmental conditions resulting in their formation and long-term preservation in the geological sedimentary record are poorly understood. This PhD is part of an interdisciplinary ANR project at the geology-chemistry-biology interface to decipher microbialite formation process from the nanoscale to the macroscale. That is, identifying the present bacterial strains, understand if and how they favor mineral precipitation or dissolution, what mineralogy constitute the preserved microbialites, what/how chemical and environmental conditions influence their formation and overall, what chemical / isotopic signatures are preserved in the geological record and how we can relate it to the ancient sedimentary record. We will carry out the geochemical/isotopic aspect of this multidisciplinary project (using a combination of C, N and S stable isotopes signatures) in concert with metatranscriptomics functional information and detailed mineralogy to answer these questions.

Isotopic analyses in modern microbialites remain rare (available δ¹³C and δ¹⁸O data on microbialites and lake water are fragmentary and there is no data on δ¹⁵N and multiple sulfur isotopes Δ³⁴S, Δ³³S) and an effort to correlate spatial patterns of isotopic fractionations with the distribution of particular microbial lineages is lacking. Such combined data are essential to associate phylogenetic and/or functional guilds with isotopic signatures that can be meaningfully interpreted in the fossil record.

Therefore, we expect to pinpoint the most active members of microbialite communities from crater lakes in Mexico at different depths and sites using analyses of C, O, N and S isotopic signals in organic and mineral phases from the bulk to the nanoscale level. Moreover, we will analyze the waters and bottom sediments of these lakes in order to reach a global understanding of the complex biogeochemical relationships operating in these alkaline crater lakes. Eventually, we will try to relate these signatures to Archean microbialites that were sampled in the carbonate platform of Malmani (~2.5 Ga), Barberton Greenstone Belt, South Africa.

Keywords

microbialites, isotopic geochemistry, alkaline lakes, stromatolites, archean

Thesis advisory panel

Karim Benzerara
Vincent Busigny

Jury

Magali Ader, université de Paris Cité – reviewer
Yuichiro Ueno, Institut technologique de Tokyo – reviewer
Emmanuelle Vennin, université de Bourgogne – examiner
Nina Zeyen, université de Genève – examiner
David A. Fike, université de Washington à Saint Louis – examiner
Karim Benzerara, Sorbonne Université – invited
Christophe Thomazo, université de Bourgogne – supervisor

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Multi-isotopic study of the carbon and sulfur cycles in modern alkaline and stratified environments from Mexico and their microbialites

Started in January 2020

Defended the 15 september 2023

Supervisor: Christophe Thomazo

Funding: French national research agency (ANR)

 

Abstract

Stromatolites and, more generally, microbialites are organosedimentary structures formed under the influence of phylogenetically and functionally diverse microbial communities in interaction with abiotic factors. Fossil stromatolites represent the oldest undisputed evidence of life on Earth (~3.5 Ga). Yet, the specific identity and functions of associated microorganisms and the local environmental conditions resulting in their formation and long-term preservation in the geological sedimentary record are poorly understood. This PhD is part of an interdisciplinary ANR project at the geology-chemistry-biology interface to decipher microbialite formation process from the nanoscale to the macroscale. That is, identifying the present bacterial strains, understand if and how they favor mineral precipitation or dissolution, what mineralogy constitute the preserved microbialites, what/how chemical and environmental conditions influence their formation and overall, what chemical / isotopic signatures are preserved in the geological record and how we can relate it to the ancient sedimentary record. We will carry out the geochemical/isotopic aspect of this multidisciplinary project (using a combination of C, N and S stable isotopes signatures) in concert with metatranscriptomics functional information and detailed mineralogy to answer these questions.

Isotopic analyses in modern microbialites remain rare (available δ¹³C and δ¹⁸O data on microbialites and lake water are fragmentary and there is no data on δ¹⁵N and multiple sulfur isotopes Δ³⁴S, Δ³³S) and an effort to correlate spatial patterns of isotopic fractionations with the distribution of particular microbial lineages is lacking. Such combined data are essential to associate phylogenetic and/or functional guilds with isotopic signatures that can be meaningfully interpreted in the fossil record.

Therefore, we expect to pinpoint the most active members of microbialite communities from crater lakes in Mexico at different depths and sites using analyses of C, O, N and S isotopic signals in organic and mineral phases from the bulk to the nanoscale level. Moreover, we will analyze the waters and bottom sediments of these lakes in order to reach a global understanding of the complex biogeochemical relationships operating in these alkaline crater lakes. Eventually, we will try to relate these signatures to Archean microbialites that were sampled in the carbonate platform of Malmani (~2.5 Ga), Barberton Greenstone Belt, South Africa.

 

Keywords

microbialites, isotopic geochemistry, alkaline lakes, stromatolites, archean

 

Thesis advisory panel

Karim Benzerara
Vincent Busigny

 

Jury

Magali Ader, université de Paris Cité - reviewer
Yuichiro Ueno, Institut technologique de Tokyo - reviewer
Emmanuelle Vennin, université de Bourgogne - examiner
Nina Zeyen, université de Genève - examiner
David A. Fike, université de Washington à Saint Louis - examiner
Karim Benzerara, Sorbonne Université - invited
Christophe Thomazo, université de Bourgogne - supervisor

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