Ferromanganese concretions in Tasmanian lakes

Abstract

Discoid ferromanganese concretions on pebble nuclei, resembling those found elsewhere in the world. occur in a number of Tasmanian lakes. Those from the now-flooded Lake Pedder had distinctive Mn/Fe ratios. The genesis of concretions is a subject of debate, but the botrpoidai nature of the oxide rims and the occurrence of globular encrustations of gelatinous cyanobacteria and bacteria on pebbles suggest microorganisms are responsible.