The recognition of iron microbial mats in terrestrial environments is of great relevance for the search for extraterrestrial life, especially on mars where significant iron minerals were identified in the subsurface. Most researches focused on very ancient microbial mats (e.g. BIFs) since they formed on Earth at a time where similar conditions are supposed to have prevailed on Mars too. However, environmental proxies are often difficult to use for these deposits on Earth which, in addition, may be heavily transformed due to diagenesis or even metamorphism.Here we present modern and phanerozoic iron microbial mats occurrences illustrating the wide variety of environments in which they form, including many marine settings, ponds, creeks, caves, volcanoes, etc. Contrarily to their Precambrian counterparts, Modern and Phanerozoic deposits are usually less affected by diagenesis and the environmental conditions likely to be better constrained. Therefore, their investigation may help for the search for morphological and geochemical biosignatures (e.g. iron isotopes) in ancient iron microbial occurrences on Earth but also on other Planets. In particular, many of the case studies presented here show that microstromatolithe-like morphologies may be valuable targets for screening potential biosignatures in various rock types.
Laser-Induced Breakdown Spectroscopy (LIBS) is a fast in-situ analytical technique based on spectroscopic analysis of atomic emission in laser-induced plasmas. Geochemical mapping at macroscopic scale using LIBS was applied to a decimetric Zn-Pb ore sample from east Belgium, which consists of alternating sphalerite and galena bands. A range of elements was detected with no or minimal spectral correction, including elements of interest for beneficiation such as Ge, Ag and Ga (although the detection of gallium could not be confirmed), and remediation, especially As and Tl. The comparison between LIBS and Energy Dispersive Spectroscopy (EDS) analyses showed that LIBS intensities reliably relate to elemental concentration although differences in spot size and detection limits exist between both techniques. The elemental images of minor and trace elements (Fe, Cu, Ag, Cd, Sb, As, Tl, Ge, Ni and Ba) obtained with LIBS revealed with great detail the compositional heterogeneity of the ore, including growth zones that were not visible on the specimen. In addition, each mineral generation has a distinct trace-element composition, reflecting a geochemical sequence whose potential metallogenic significance at the district scale should be addressed in further work. Although qualitative and preliminary, the obtained LIBS dataset already produced a wealth of information that allowed to initiate discussion on some genetical and crystallochemical aspects. Above all, LIBS appears as a powerful tool for screening geochemically large samples for the selection of zones of particular interest for further analysis.
The Noqui peralkaline granite body (Matadi -Bas-Congo -DRC): a marker of 1.0 Ga lithospheric-scale triple junction updoming during long-lived Columbia breakup ..
The Azé cave (south Burgundy), from alteration to ghost-rock. The goal of this study was to gain a better understanding of the formation of the Azé Caves and the relationships which exist at this site between the surrounding rock and the sediments. A detailed study of the limestones from the Late Aalenian to the Early Bathonian which make up the surrounding rock shows that they contain considerable quantities of quartz and hundreds of ppm of manganese. Certain levels contain numerous siliceous cherts. From the Jurassic, the region underwent several phases of immersion. This period was also marked by a tectonic phase of weak amplitude. The faulting which occurred at this time allowed the circulation of meteoric water through the limestone leading to the dissolving of calcium carbonates and to phases of dolomitisation and dédolomitisation. As a result, "ghost rock" was created in the different stratigraphie units. However the hydrodynamism of these flows was weak and the alteration of the rock was isovolumic without evacuation of the alterite. During the Oligocene, the Méconnais region underwent a more severe tectonic phase. The structure of leaning blocks that we see today was put in place and the "ghost rock" was fractured by larger faults. As a result a hydrodynamic potential was created between the different sides of the massifs and the alterite was removed by water thus creating the caves. From that time on bacterial activity was able to develop on the walls of the cavities and in the residual alterite. The bacteria oxidised the manganese and iron contained in the limestone leading to the accumulation of manganese and iron oxide deposits in the limestone and on the walls, often in the form of structured encrustings. These bacteria were still active during certain periods of the Quaternary as shown by the discovery of deposits on bear bones. Under the effect of gravity, the least soluble limestone residues and the conglomerations of manganese formed by bacteria fell to the bottom of the caves or were carried away by flowing water. Depending on the hydrodynamic regime, these residues (clays, sands, gravels, pebbles) were to varying extents transported by water and were removed from or left behind in the caves. As a result, the sandy fractions of sediments deposited at the time of flows with the weakest hydrodynamism are mostly made up of these residues.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.