Development of a NanoSIMS method for detecting trace elements in Paleoproterozoic microfossils

Abstract

We developed a method to detect trace elements directly from Precambrian fossiliferous organic matter using a high spatial resolution secondary ion mass spectrometer (NanoSIMS). Although the analysis of bio-essential trace elements is considered to be useful for identifying metabolic pathways of microorganisms, it has not been applied to fossiliferous organic matter due to technical limitations. In this study, we improved the conventional acid treatment method for sedimentary rocks and succeeded in separating microfossils from host rock while maintaining the original shape. The low sensitivity and the difficulty of peak separation from interference ions were improved by using an RF source in O- primary ion beam. As a result, we succeeded in detecting trace amounts of phosphorus (P), molybdenum (Mo), potassium (K), iron (Fe), and magnesium (Mg) directly from fossiliferous organic matter. These elements are cations used in various enzymatic reactions and in biological functions. The detected elements may be their residues. This method of in situ trace element analysis at the level of individual microfossils could be a new method that can contribute to constraining metabolic pathways in individual microorganisms at that time.