Biogenic origin of manganese flowstones from Jaskinia Czarna Cave, Tatra Mts., Western Carpathians

Abstract

Biogeniczne pochodzenie polew manganowych w Jaskini Czarnej w Tatrach, Karpaty Zachodnie Flowstones composed mostly of amorphic manganese oxides occur in Jaskinia Czarna Cave in the contact zone between Middle Triassic carbonates and Upper Jurassic-Lower Cretaceous limestones on a substrate diagenetically enriched in Mn and Fe minerals. In the SEM micrographs, the flowstones display a dome-like structure, which is characterized by non-porous microfabric in the dome centres and porous microfabric in the outer parts of the domes, and in the inter-dome spaces. The filament elements of porous microfabric and co-occurring globular bodies are recognised as mineralized biogenic structures, probably bacterial or fungal in origin. The Mn/Fe ratio in the flowstones is 72.1:1, while in the substrate it is about 1.32:1. High concentration of Mn is caused by preferencial microbial precipitation. A very high rate of manganese oxide growth also suggests their microbially mediated precipitation.