ToF-SIMS as a tool for analysing organic material in geological samples -Fluid inclusions and beyond

Abstract: In situ analysis of organic material in rocks has potential to answer questions in geochemistry, astro- and geobiology. Recently, successful studies which included in situ analyses of geological samples with time-of-flight secondary ion mass spectrometry (ToF-SIMS) were carried out. In this PhD project possibilities and limitations of ToF-SIMS analysis of organic material in geological samples will be further explored. The main objective of the project is to develop an approach for analysis of single oil-bearing fluid inclusions and most importantly the detection of biomarkers, such as hopanes and steranes, in these inclusions. Analysis of oil-bearing fluid inclusions is attractive as they may provide an uncontaminated source of Precambrian hopanes and steranes, which are key biomarkers for tracking the early evolution of life on Earth. Due to presence of several inclusion generations, single inclusion analysis is preferred in order to constrain biomarkers to specific inclusions. The small sample amount in oil-bearing fluid inclusions, however, usually makes it difficult to analyse single inclusions with standard technique gas chromatography mass spectrometry (GC-MS). ToF-SIMS with high sensitivity, high mass resolution, imaging and depth profiling capabilities provides an excellent tool for analysis of these types of samples. The development of the approach for analysis of single oil-bearing inclusions was done in a two-step process; i) a number of crude oils were analysed with ToF-SIMS and GC-MS to facilitate interpretation of ToF-SIMS spectra of these types of samples and, ii) a procedure that combines micrographs with ion etching and ToF-SIMS analysis was developed for analysis of inclusions. With this approach it was possible to detect hopanes and steranes in single oil-bearing fluid inclusions. The next step of the project will be to analyse inclusions in Precambrian rocks in search for hopanes and steranes. In addition to the Precambrian samples, the capabilities of ToF-SIMS in analysis of geological samples will be further explored with analysis of additional samples, including Martian meteorites and microbial mats from hot springs in Yellowstone National Park.