Proterozoic Mn-oxide precipitation by planktonic plant protists (acritarchs)

Microfossils of plant protists called acritarchs occur embedded in, mostly, authigenic chlorite cement in sandstones of the Visingsö Group (Upper Proterozoic; southern Sweden). These microfossils are commonly encrusted by a Mn-oxide layer. Similar Mn-oxide was not observed elsewhere in the sandstones, thus suggesting that certain acritarchs have played a role in the transfer and precipitation of Mn in ancient sedimentary environments. In the light of available information on the role of extant protists in biomineralization, possible mechanisms for the precipitation of Mnoxide in the Visingsö Group are discussed.