Bacteria-like Ferruginous Structures in Carboniferous Limestones as Remains of Post-Variscan Hydrothermal Activity in Southern Poland

Structures resembling iron-related bacteria (IRB) have been found in the Mississippian limestones that form part of the carbonate platform in the Moravo-Silesian Basin that surrounds the Upper Silesian Block, an eastern margin of the Brunovistulicum. Microfacial, petrological, and geochemical analyses were used to determine the bacteria-like structures that are present in narrow zones unrelated to bedding. We present here the morphology and chemistry of the studied microstructures showing their similarities to IRB from the present-day Sphaerotilus-Leptothrix group, the Galionella group, and the Mariprofundus ferrooxydans species. We suggest that bacterial growth occurred in the originally empty micropores of microfossil skeletons and shells, between bioclasts or in secondary voids formed during the selective dissolution of micrite or smaller sparite crystals. Hydrothermal solutions, associated probably with the post-Variscan magmatism in this area, provided iron compounds for the growth of the IRB.