Breakout Sessions

This workshop session will be organized in four main topics. Each participant will choose a workshop session. The objective is to establish a debate and a discussion moderated by the different participants of the workshop by exchanging their experience and their approach in the different thematics. In order to construct the session, a 2-slides PPT presentation is requested in order to determine the main topics developed during the session.

The day will end with a join session and a presentation of the main results and questions addressed in each workshop session.

Workshop 1

Experimental approaches and outlook: linking the field to the lab and the lab to the field

The experimental approach in interpreting microbialite fabrics and understand key mechanisms of their formation, two approaches are followed and often combined: field observations provide critical context, but include complex interactions of intrinsic and extrinsic factors, and laboratory studies are needed to help elucidate mechanisms but can be too simple and typically exclude interactions that are a critical part of the formation of the microbialite. In other words, there are pros and cons associated with both. This session will explore these benefits and drawbacks. Emerging field and lab approaches, experimental designs and computational modeling can advance our understanding rapidly; recent developments include/range from molecular techniques (omics, including bioinformatic databases), synchrotron-based XRF to advanced field methods, such as portable raman spectroscopy, high-resolution satellite imagery, and availability of field samples (e.g., drill cores). Finally , interdisciplinary experimental design can facilitate progress in microbialite research as well. Some questions for this session are: what are the emerging techniques used in microbialite research? What are the current limitations? How do we go about pertinent experimental design?

animated by Olivier Braissant, Anneleen. Foubert, Thibaut Duteil and Marlisa Brito

Workshop 2

Biomineralization vs. organomineralization and the role of intrinsic and extrinsic factors in shaping the microbialite systems/fabrics

The study of environmental conditions that control microbialite formation is critical for understanding the evolution of Earth. Both extrinsic factors (e.g., water chemistry, climate, tectonics, geological context, sediment supply, various physicochemical parameters (T, pCO2, pH, [Ca2+], [Mg2+]) and intrinsic factors (e.g., microbial metabolisms and their relative contribution to element cycling, microbial interactions, competition, community stability and succession, production and consumption of extracellular organic compounds) engage in microbialite formation. Combined field observations and experimental results are needed for a robust interpretation of various processes and mechanisms involved in the formation of microbialites. In light of new insights, it may be useful to revisit the terminology (and definitions) used in mineral precipitation. What are the major pathways of mineral precipitation and how do we define these? Which terms describe the processes best and what has recently changed, or needs to be modified, if anything? What do we need to focus on in future investigations to sharpen these definitions?

animated by Rutger de Wit, Raphaël Bourillot and Camille Thomas

Workshop 3

Microbialite fabrics from formation to diagenesis and preservation (or lack thereof) in the fossil record

Understanding the development, evolution and preservation of microbialites in space and time is crucial to unravel the factors controlling the formation. This topic focuses on the characterization and description of the main microbial fabrics and associated mineral phases, discussing their nomenclature and definitions. We will discuss mineralization mechanisms of ancient microbialites that may be inferred from comparison with their modern counterparts. Furthermore, we will explore the contribution of micro- to basin scale processes in the formation and development of microbial deposits. A few key questions include: how reviewing the sequence of precipitation mechanisms (paragenesis) can help in interpreting the transition between microbial mats and microbialites and how their transformation and preservation during early to late diagenesis is determined. Can the evolution of petrophysical characteristics in space and time will give insights in reservoir properties, e.g. for South Atlantic petroleum systems or future storage of CO2). Finally, all of these advances will lead to question what (physically, chemically and biologically) conditions are required to preserve microbialites in the fossil record.

animated by Elias Samankassou, Benjamin Brigaud and Mehdi Carmeille

Workshop 4

Into deep time: looking for microbialite biosignatures in the fossil record

Fossils microbialites in the form of stromatolitic limestones or silicified fossil microbial mats are arguably some of the oldest records of an active biosphere with field observations dating back to the Paleoarchean. The metabolic reactions associated with these early ecosystems are thus likely to have shaped the chemical evolution of the surficial environment with the most obvious effect the protracted oxygenation of the Earth’s oceans and atmosphere. However, numerous uncertainties remain on the exact nature of these early metabolisms and their trajectory and evolution through the geological times. Topics of interest include the evolution from anoxygenic to oxygenic photosynthesis, the diversification of heterotrophic lifestyles using the increasingly available electron acceptors (nitrate, sulfate, iron oxide…) that need to be better understood in order to build an integrated model of the deepest biosphere evolution. We will therefore encourage discussion around biosignatures preserved in the microbialites using state of the art techniques in geochemistry such as, but non-limited to, stable isotopes, organic matter characterization, chemical mappings using the geological record as well as laboratory experiments and study of modern analogues.

animated by Christophe Thomazo, Aurélien Virgone and Elodie Muller