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.
Recently discovered siderite globules from Upper Cretaceous cavity and fracture fillings in southern Belgium are described and interpreted with emphasis on the still unsolved problem of the carbonates in meteorite ALH84001, which enclose controversal evidence for ancient Martian life. The most interesting aspects of the carbonates described here are 1) their close association with fossil microbiota, 2) their environment, which is 100% sedimentary, subaerial and not hydrothermal and 3) their morphologies, some of which being similar to those in ALH84001. Although the question of the direct biological influence is not critical in this case, the biogenicity for the minerals will be discussed as a strong possibility and is not only inferred from the simple spatial (and temporal) association of the carbonates and the fossil microbiota. Morphological, textural and chemical data will be presented and interpreted as variations in fluid chemistry related to environmental changes. Although they may appear different from those in Martian meteorite and Spitzbergen xenoliths, the Cretaceous globules originated in subsurface environment which left evident traces of life in the form of fossil microbial/fungal mats. They are thus considered as an opportunity to investigate biosignatures in future research using the wide range of available techniques.
Conference Committee Involvement (2)
Instruments, Methods, and Missions for Astrobiology XI
12 August 2008 | San Diego, California, United States
Instruments, Methods, and Missions for Astrobiology VII
3 August 2003 | San Diego, California, United States
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