Fossil bacterial forms in Early Proterozoic dolomite at Kiihtelysvaara in eastern Finland

Microfossil-like tourmaline microlites in early Proterozoic nodular chert at Kiihtelysvaara, eastern Finland

“…Therefore, we used part of the original specimen and prepared a new HF-HC1 acid residue, which was mounted on epoxy and polished for analysis by electron microprobe. Figure 1 shows that the microfossil-like objects analysed from the new grain mount correspond to the description and figures in Tynni and Sarapää (1987). In figure 2 these objects are seen between crossed polarizers in the original grain mount (GSF-760) studied by Tynni and Sarapää (1987).…”

“…Microfossil-like objects discovered by Tynni and Sarapää (1987) occur in chert nodules within a dolomitic unit of the Viistola Formation (Pekkarinen and Lukkarinen 1991), which forms part of the early Proterozoic cover sequence deposited on the Archean platform. The geology of the area has been described by Pekkarinen (1979) and Pekkarinen and Lukkarinen (1991).…”

“…The drill core specimen (R310/185.50m) and thin sections studied by Tynni and Sarapää (1987) were kindly made available by the authors. Unfortunately the original thin sections and grain mount investigated by them did not contain any points suitable for microprobe analysis.…”

“…The most characteristic form of the objects is a 15-40 um long cylindrical rod containing abundant spiral chains or swarms of small dots less than 1 |im in diameter. Based on the morphology, Tynni and Sarapää (1987) suggested that the microfossil-like objects may be early sulphur bacteria resembling the extant Beggiatoa bacteria and named them Hyypiana jatulica n. gen., species R. Tynni. Given that our knowledge of the types of Proterozoic micro-organisms that existed is very limited, the suggestion of Tynni and Sarapää (1987) was reasonable. However, many inorganic objects effectively mimic biogenic morphologies and make identification difficult.…”

“…Here we apply petrographical and geochemical methods to show that the microfossil-like objects described by Tynni and Sarapää (1987) are, in fact, mineralogic pseudomicrofossils consisting of tourmaline microlites.…”