Juliette Dupeyron’s PhD
Multi-isotope study of the formation of iron sulfide in anoxic environments, analogous to Archean oceans
Iron sulfides are major minerals, present in the geological record since the Archean. Their iron and sulfur isotope compositions are widely used as tracers of ocean and atmospheric redox conditions. They reflect their formation mechanisms, which may involve sulfate-reducing or iron-reducing bacteria. These mechanisms as well as the associated isotopic fractionations have been mainly studied in the laboratory.
The objective of this thesis is to study the formation of iron sulfides and the associated isotopic fractionations of iron and sulfur in natural environments, two lakes analogous to the Archean oceans: Lake Pavin (France, anoxic and ferruginous) and Lake Cadagno (Switzerland, anoxic and sulfurous). These lakes have already been extensively studied and are therefore ideal natural laboratories.
To achieve this objective, the iron and sulfur isotopic compositions of the water column and sediments will be measured and compared, in order to identify each step of the formation mechanisms and to precisely associate isotopic fractionations. Samples will be studied by whole-rock isotopic analyses and in situ analyses. These in situ analyses will include mineralogical and isotopic characterization. The comparison of these two approaches at different spatial scales will allow to calibrate isotopic tracers for the interpretation of the Archean sedimentary rocks and to get into the details of the mechanisms of iron sulfide formation.