How have stromatolites been used to subdivide some Precambrian rock sequences?

Stromatolites, which are layered structures formed by communities of microorganisms like blue-green algae, have been used to assist in the subdivision of Precambrian rock sequences through biostratigraphy.12

Because Precambrian sediments generally lack the abundant, rapidly evolving fossils found in later geologic periods, correlation is often difficult. However, stromatolites underwent sufficient evolutionary changes over time to allow researchers to identify distinct zones. For example, Russian biostratigraphers successfully utilized these evolutionary patterns to subdivide the Riphean sequence into four main zones across widely separated areas of former Soviet territory. Similar stromatolite-based stratigraphic divisions have also been recognized in regions including China, Australia, and the Norwegian islands of Spitsbergen.3

Despite these applications, stromatolite biostratigraphy remains limited in its overall scope. Consequently, geologists primarily rely on chronometric time scales and techniques such as zircon dating to correlate Precambrian rocks across different continents.3