Exceptional preservation of Mn-oxidizing microbes in cave stromatolites (El Soplao, Spain)

摘要: Abstract Many ferromanganese stromatolites of El Soplao Cave (N Spain) are characterized for the exceptional preservation and high diversity microbial fossils, probably representing best example described in deposits so far. The mainly formed by polymetallic Mn-rich oxides with subordinate variable amounts detrital material, consist both dendritic laminar microfacies. In microfacies, forms abundant relatively pure Mn-oxide rich whereas they scarce areas significant material. Microbial observed either cross section, completely embedded Mn-oxide-rich matrix, or three dimensions lining walls pores. Based on their morphology, we have separated most into six main morphotypes additional submorphotypes, which can be assigned to bacteria. Most coccoid, coccobacilus, filamentous forms. Therefore not diagnostic any particular bacterial group. However, ovoid cells morphotype B show cylindrical polar protuberances typical prosthecate alpha- Proteobacteria . On basis characteristic morphological features, submorphotypes genera: Hyphomicrobium , Pedomicrobium Caulobacter This ascription is supported well known Mn-oxidizing behavior common presence elsewhere. excellent partly related origin oxides, i.e. extracellular precipitation induced metabolism. Other factors contributing good low degree diagenetic alteration, accretion rates compared other deposits. generally diagenesis likely because remained stable at a rather temperature since were least 1 Ma ago. Still, some suffered alteration (partial dissolution replacement calcium carbonates Fe-rich oxides), obscuring even obliterating bioforms. case represents an how easily biogenic Mn altered, bioforms blurred, short geological time span spite being stable, alkaline, low-temperature setting. A implication that absence deposits, including rock varnish Precambrian iron formations, does disprove possible origin, chemical reactivity manganese makes them highly vulnerable diagenesis.