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.
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.