[en] Full text: Modern stromatolites and stromatolitic reefs, as analogues of the biotic Precambrian Earth which are still present on this planet, represent a significant resource for studying microbial ecology and evolution. Precambrian microfossils contain bacteria with similar morphology to oxygenic phototrophs of the phylum Cyanobacteria. The origin of our aerobic atmosphere coincides with paleontological evidence of vast stromatolitic reefs. Cyanobacterial mats, in conjunction with stromatolites, are also associated with the production of mineral sulphide deposits, inorganic carbon, and hydrocarbons of petroleum source rocks. Carbonate precipitation, in conjunction with trapping and binding of clastic sediment, by microorganisms is the primary process involved in stromatolite biogenesis. The morphology of the resulting geological structure is determined by both the physiological activity of the resident microbial community and the prevailing environmental conditions. The molecular biodiversity of stromatolite-associated microorganisms has not been previously studied and the nature of the phylogenetic relationships of these organisms is unknown. In summary, 'soft' rock samples and biota samples were collected from the microbial mats of stromatolites at Hamelin Pool, Shark Bay, Western Australia. The core samples were sectioned for SIMS analysis. The focus of this AINSE funded project was the unique columnar stromatolites, considered to be the modern analogues of the widespread and abundant Proterozoic stromatolites. A ten centimetre (cm) deep core was cross-sectioned and divided into four 2.5 cm sub-sections. Each sub-section was analysed for both positive and negative ions by SIMS spot analysis across the length of the facia. We estimated that this analysis transected stromatolite laminations dating back 100-200 years before present. A record of biological activity and environmental conditions may be recorded as the isotopic composition within these temporal laminations. Negative ions (O, S, C) was used as indicators of the relative biological mass and metabolism present. Certain positive ions (eg. Ca and Mg) was also performed to estimate the metabolic activity of extant microbial populations relative to surface SIMS profiles. Other positive ions, such as Si and various heavy metals, were also assayed during the SIMS spot analysis to determine if changes in pollutant concentrations could be archived in the stromatolite matrix. This work was also appropriate for detecting oxygen isotopic ratios which may vary with ocean temperature changes and its effect on the metabolism of stromatolite microbial communities