Influence of global, regional, and local factors on the genesis of the Jurassic manganese ore formation in the Transdanubian Range, Hungary

Abstract

Economically important black shale-hosted manganese carbonate deposits occur in certain parts of the Transdanubian Range in Hungary. These ore deposits were formed in a short interval coinciding with the Early Toarcian global anoxic and mass extinction event that was associated with drastic perturbations of the oceanographic conditions. During the Early Jurassic the Transdanubian Range Unit was located between two ocean basins. Simultaneous opening of these two basins created an extensional regime resulting in a complex topography with tectonically-controlled small scale basins above an attenuated continental lithosphere. Sluggish circulation led to the development of layered water masses in certain parts of these basins, with oxygenated upper and oxygen-depleted lower reservoirs. This paleogeographic and paleoenvironmental setting favoured the microbially-mediated accumulation of manganese and iron.