The biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin. This has particularly been the case with older Precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics; in some cases however, evidence has been preserved through very early mineralisation. Precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms. This study provides evidence from early Neoproterozoic columnar stromatolites in the Jiuliqiao Formation from the southeastern margin of the North China Platform for fossilized extracellular polymeric substances (EPS) and cyanobacteria, along with nanospheres which may represent permineralised viruses or viral-like particles. A similar chemical composition and colour along with their embedded and cross-cutting relationships with the matrix suggest they are syn-depositional products, and not modern artefacts or the result of sample preparation. The interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping, baffling and binding processes. The presence of virus-like particles and mineralized EPS with anhedral, fine-grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation. This study demonstrates the use of a high-definition scanning electron microscope to detect fossilized (calcified) filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis.
- Early Neoproterozoic
- Virus/coccoid bacteria