Russian Journal of Earth Sciences
Vol. 5, No. 5, October 2003
The origin of black shale-hosted Mn deposits in Paratethyan
basins: Constraints from geological events at the
Eocene/Oligocene boundary
I. M. Varentsov, N. G. Muzyliov, V. G. Nikolaev, and S. I. Stupin
Abstract
The giant, Phanerozoic largest Mn deposits of southern Ukraine and Georgia and the
Mn-rich strata of
Mangyshlak, northeastern Bulgaria, northwestern Turkey, Hungary, and Slovakia were
laid down synchronously at
the base of the Early Oligocene interval. Their formation was controlled by an optimum
combination of major
geological events. The collision of Eurasia and the Indian subcontinent in terminal
Eocene time boosted the
generation of new sea floor at the crests of the global system of mid-ocean ridges
with ensuing global transgression
and a huge input of hydrothermal components (Mn, Fe, SiO2, Ca, CO2, etc.). Meanwhile in the Paratethys, Early
Oligocene was a time of inception of and/or rapid subsidence in the marginal inland
basins that stored black shales
and vast amounts of dissolved Mn2+. Shelf settings provided the milieu for extensive Mn deposition due
to
transgressive incursions of dense oceanic waters that displaced the Mn-rich anoxic
ones.