Age and genesis of the largest Phanerozoic Mn deposits in the Paratethys: Inferences from 40Ar/39Ar and U/Pb ages in NE Bulgaria and NW Turkey

The early Oligocene manganese (Mn) deposits around the Black Sea represent the second largest accumulation of Mn in the world (600 × 10 6 tons). Various hypotheses have been offered to explain the genesis of these deposits. However, very few can explain all the major characteristics of the Mn deposits, in particular: 1) their contemporaneity and short depositional time; 2) vast covered territory; 3) the source of the great volume of metals (Mn, Fe, P and Si) and 4) the mechanisms of metal precipitation and concentration. Most of the former hypotheses assume the source for the Mn is the local crystalline rocks, ignoring or misinterpreting the involvement of volcanic material. Here, we propose a volcanic-derived model sourced from a 33.2 ± 0.1 Ma supereruption from the Rhodope Massif, Bulgaria, which covers large areas of the Central, Southern and Eastern Europe with ash. The model is based on radioisotopic age data of the volcanic material from two of the Mn deposits, located on the western shore of the Black Sea. Our model implies that the Mn (along with other metals, Fe, P, Si) have been transported by the large amount of erupted dust and aerosols with absorbed soluble fluoride, chloride, and sulfate metals. The fast dissolution of gases and aerosols into restricted or shallow Paratethys sea basins produced anoxic-euxinic conditions, which in turn promoted high concentration and deposition of the Mn. Final structuring of the zonation of the deposits was the result of the restoration of the normal sea redox-stratification after the end of the volcanic influence. • The largest Phanerozoic Mn deposits are the result of a large Oligocene volcanic supereruption. • The volcanic gases and aerosols are the source of Mn and other metals. • The anoxic-euxinic conditions from the eruption create circumstances for the Mn deposition in Paratethys basins.