An examination of spherulitic dubiomicrofossils in Precambrian banded iron formations using the transmission electron microscope

The discovery of microfossils from the banded iron-formations of southern Ontario (Tyler and Barghoorn, 1954) has spurred many researchers to attribute a biogenic origin to a great variety of unusual structures in Precambrian BIFs. In particular, LaBerge (1973) has argued that jaspery and sideritic spherulites common to all major BIF deposits represent the fossilized remains of a unicellular blue-green algae of the Early Proterozoic, Eosphaera tyleri. Oehler (1976b), on the other hand, regards such structures as crystallization products of a viscous and impure silica gel. Examination of these 30-μm spherulites with a transmission electron microscope sheds doubt on both interpretations. Our analysis suggests that the jaspery spheres formed from the local recrystallization of the chert-hematite matrix after contact with an infiltrating fluid; thus, these structures are best viewed as diagenetic features. On the other hand, we discovered that the sideritic spheres contain cores of apatite; consequently, these spheres may have a biogenic origin, though the abundance of phosphate would indicate that they are not fossils of individual cells.