Cherts are outstanding and widespread components of Ocean Plate Stratigraphy (OPS), occurring from the Archean to the present. Their composition reflects diverse depositional conditions that can be linked to contrasting and temporally changing processes associated with moving oceanic plates. In addition, they provide valuable insights into variations in seawater chemistry, temperature, and redox conditions of their depositional environments. This talk will present field and stratigraphic observations combined with elemental and isotopic (Sr–Si–C–O) data to unravel the origin and nature of chert successions in selected Neoproterozoic–Cambrian OPS sections. It will also address whether these rocks can serve as reliable geochemical proxies for variable processes on oceanic plates and for reconstructing past seawater chemistry.

In hydraulic stimulation experiments, such as those used in seismic and geothermal energy studies, monitoring dissolved reactive and noble gases in groundwater can provide key insights into fluid transport and redistribution. While tracers added to injection water reveal specific flow paths, dissolved gas monitoring in general captures a broader picture of how fluids are mobilized or redirected under pressure. At the Bedretto Underground Laboratory for Geosciences and Geoenergy (BULGG), we tested the geochemical response during an experiment designed to trigger a controlled magnitude-zero earthquake. High-pressure water (up to 20 MPa) was injected into borehole ST1, with krypton added as a tracer. A nearby borehole (ST2), 44 m away and discharging continuously, was equipped with a miniRuedi to measure dissolved He, Ar, Kr, N2, O2, and CO2 in real time, complemented by parallel radon monitoring with the Rad8. This setup enabled us to track both immediate gas responses to pressure and delayed tracer migration. Dissolved gas signals at ST2 revealed a clear response once injection began. N2 and Ar increased in terms of partial pressure, while relatively He partial pressures decreased, showing that injection resulted in mobilised or redirected younger, less radiogenic fluids toward ST2 well before the Kr tracer arrived. Radon activity increased only after tracer breakthrough, consistent with fracture opening and fluid movement under stress. These findings highlight dissolved gas monitoring as a sensitive tool for probing the behaviour of stress, fractures, and fluids, particularly in the context of hydraulic stimulation.

The management of natural hazards, the mitigation of climate change, and the need to meet growing global energy demands are pressing issues which are reshaping our approach to the Earth's subsurface. As we transition as a society towards renewable energies, it is now not only an environmental imperative but a matter of public safety to understand how geological systems host high-enthalpy fluids. The primary impediments of volcanic imaging and monitoring, as well as geothermal energy investment, are addressed here by Neural Network Nodal Ambient Noise Tomography (N3ANT). With near real-time prospects, N3ANT reduces geological uncertainty while minimising environmental and societal risks. This enhances our ability to respond dynamically to volcanic threats and to develop geothermal resources, thus bridging the gap between fundamental research and practical applications for sustainable management of Earth's resources and risk mitigation.

Rare earth elements (REE) are a group of 16 chemically similar elements with oceanic residence times of several hundred years. This duration is long enough for them to be transported across ocean basins without complete homogenization, before eventually being incorporated into authigenic phases within marine sediments and archives. The most widely used REE-based tracer is the radiogenic neodymium isotope composition, which provides insights into weathering, transport, and water mass mixing at Earth’s surface. However, the full suite of REE behaves geochemically coherently – almost like a single element – and thus encodes a far broader range of environmental information in their isotopic signatures and relative concentration patterns. In this presentation, I will explore these lesser-studied REE signals and demonstrate that they contain valuable information for reconstructing environmental and paleoceanographic processes. Finally, I will discuss how REE can be developed into a comprehensive compound geochemical proxy and highlight potential applications across other fields of Earth and environmental science.

Stromatolites are layered sedimentary structures formed under the influence of microbial communities and environmental factors. They constitute amongst the oldest known evidence of life on Earth – over 3.4 billion years old – and provide a unique fossil archive spanning nearly all of geological time. In this seminar, I will invite you on a journey through the Microbialite Collection of the Muséum national d’histoire naturelle (Paris), a unique archive to explore: • How do stromatolites record the oxygenation of Earth's atmosphere and oceans? • What can they tell us about the diversity of ancient surface environments? • Are the rhythmic laminations driven by biological processes… or by climate cycles? • Do these layered structures truly reflect biological activity? • And how can AI help distinguish biogenic from abiotic laminated rocks? At the intersection of geochemistry, palaeontology, and astrobiology, my research seeks to improve our understanding of how life has shaped the sedimentary record; with implications that extend beyond Earth’s history to the search for life on other planets.