Analysis of organic biomarkers in single Precambrian oil-bearing fluid inclusions using ToF-SIMS

Organic biomarkers are valuable sources of information on the biodiversity and environment of early Earth. However, with organic biomarkers, especially in old samples, there are often problems of syngeneity and many of the most ancient biomarkers are suspected of being younger contamination. A type of sample where biomarkers are better constrained in the rock is oil-bearing fluid inclusions, especially if single inclusions can be analysed. However, most inclusions, including Precambrian oil-bearing fluid inclusions are so small (less than 10 mu m) that analyzing single ones with conventional techniques is not possible. Therefore, we have developed an approach employing time-of-flight secondary ion mass spectrometry (ToF-SIMS) to selectively open individual oil-bearing inclusions by C (sub 60) (super +) ion etching, and to subsequently analyse their content. Using this approach steranes and hopanes could be detected in single Ordovician oil-bearing inclusions (15-30 mu m) from the Siljan impact structure in Sweden. Now the developed approach has been applied on Precambrian samples. Four different oil-bearing fluid inclusions trapped in a 1.43 Ga sandstone from the Roper Superbasin in Australia were opened and analysed with ToF-SIMS. The ToF-SIMS spectra of the oil in the different inclusions were similar to each other indicating that the same oil was trapped in all inclusions. In addition, the ToF-SIMS spectra contained peaks that could be assigned to alkanes, cycloalkanes, aromatic moities, steranes and hopanes. With further development and if applied on other Precambrain samples this approach could help answering questions regarding early evolution of life on Earth.