Astrobiology Workshop, Macquarie University July 12-13 2001

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The Tinto river geomicrobial system: a valid analogue for the Archean BIF's

David Fernandez-Remolar (Centro de Astrobiologia, Madrid)

Fe-driven systems dominated the Archean oceanic biogeochemistry of the primordial Earth. On the contrary, they are rare on the modern Earth. Their global influence in the Terrestrial system is so low that is difficult to establish reference systems for understanding by modern environments the interaction between ironstone formation pattern and the hypothetical microbial communities. The Tinto River Basin (Huelva region, South Spain), a modern system supported by the iron hydrochemistry, shelters a diverse microbial community that is maintained by biolixiviation processes on metal sulfide ores of the Pyritic Belt. The microbial bioleaching of the metallic sulfide have two different effects in the hydrochemistry: extreme pH lowering (1.3 to 3) and ferric iron solution (<20 gr/l). In these conditions, the water reservoir is dominated by sulfur, ferric iron and silicon; common elemental association in the Banded Iron Formations. The high microbial activity induces the generation of a great diversity of stromatolitic-like structures as well. Moreover, the Tinto River Basin records Tertiary and Quaternary iron lithostratigraphical units that allow observing the preservational patterns in fossils and structures, as well as the biogeochemical transformations in ironstones by determination of the different diagenetic stages through the stratigraphical succesion of the three different iron levels. This work deals the Tinto River system as a feasible natural and modern reference for enlightening the processes that were involved in the genesis of the Banded Iron Formations. On the first hand, the main variables that constitute the Tinto River geomicrobial system will be described; on the second, a comparison between the Archean and the Tinto River system will be discussed.