Palaeoecology of a billion-year-old non-marine cyanobacterium from the Torridon Group and Nonesuch Formation.
A new chroococcalean cyanobacterium is described from approximately 1-billion-year-old non-marine deposits of the Torridonian Group of Scotland and the Nonesuch Formation of Michigan, USA. Individual cells of the new microfossil,Eohalothece lacustrinagen. et sp. nov., are associated with benthic microbial biofilms, but the majority of samples are recovered in palynological preparations in the form of large, apparently planktonic colonies, similar to extant species ofMicrocystis. In the Torridonian,Eohalotheceis associated with phosphatic nodules, and we have developed a novel hypothesis linkingEohalotheceto phosphate deposition in ancient freshwater settings. Extant cyanobacteria can be prolific producers of extracellular microcystins, which are non-ribosomal polypeptide phosphatase inhibitors. Microcystins may have promoted the retention and concentration of sedimentary organic phosphate prior to mineralization of francolite and nodule formation. This has a further implication that the Torridonian lakes were nitrogen limited as the release of microcystins is enhanced under such conditions today. The abundance and wide distribution ofEohalothece lacustrinaattests to the importance of cyanobacteria as oxygen-producing photoautotrophs in lacustrine ecosystems at the time of the Mesoproterozoic-Neoproterozoic transition.
Department of Earth and Environmental Sciences Weston Observatory of Boston College Weston MA 02493 USA.
Paul K
PK
Strother
Department of Animal and Plant Sciences The University of Sheffield Sheffield S10 2TN UK.
Charles H
CH
Wellman
Mesoproterozoic; Precambrian; lacustrine; microcystins; phosphogenesis