Browsing by Author "Hode, Tomas"

Steranes and hopanes are organic biomarkers used as indicators for the first appearance of eukaryotes and cyanobacteria on Earth. Oil-bearing fluid inclusions may provide a contamination-free source of Precambrian biomarkers, as the oil has been secluded from the environment since the formation of the inclusion. However, analysis of biomarkers in single oil-bearing fluid inclusions, which is often necessary due to the presence of different generations of inclusions, has not been possible due to the small size of most inclusions. Here, we have used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to monitor in real time the opening of individual inclusions trapped in hydrothermal veins of fluorite and calcite and containing oil from Ordovician source rocks. Opening of the inclusions was performed by using a focused C(60)+ ion beam and the in situ content was precisely analysed for C(27)-C(29) steranes and C(29)-C(32) hopanes using Bi(3)+ as primary ions. The capacity to unambiguously detect these biomarkers in the picoliter amount of crude oil from a single, normal-sized (15-30 mu m in diameter) inclusion makes the approach promising in the search of organic biomarkers for life's early evolution on Earth.

In this study, we show that time of flight-secondary ion mass spectrometry (ToF-SIMS) can be used to detect organic biomarkers, such as hopanes and steranes, in non-fractionated crude oils, without extraction and chemical preparation. Hopanes and steranes may provide valuable information on the history of life on early Earth, particularly if they are present in fluid inclusions in ancient rocks. Due to the presence of different generations of inclusions in even very small rock samples, it would be advantageous to find a method capable of detecting biomarkers in single oil rich fluid inclusions. The capability of ToF-SIMS for detailed chemical analysis of very small sample amounts makes it a potential technique for such analysis, and in this work this possibility is explored. The presence of hopanes and steranes in four different crude oils of different ages and stages of biodegradation was investigated using ToF-SIMS and GC-MS. By combining analyses of biomarker standards, crude oils and chromatographic oil fractions, specific peaks for the different biomarkers were identified in the ToF-SIMS spectra. The presence of these peaks in the spectra from the crude oil samples could be attributed to the biomarkers based on exact mass determination and by comparison with the spectra from the biomarker containing and biomarker lacking fractions, respectively. In addition, the results show that a significant biomarker signal may be obtained from a 10 m,2 oil sample, demonstrating the potential of ToF-SIMS for analysis of single oil bearing fluid inclusions, which in turn may contribute to a better understanding of the early history of life on Earth. (C) 2008 Elsevier Ltd. All rights reserved.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful method for the chemical analysis of solid surfaces. In this paper, the capabilities and limitations of this technique and the potential for its use in geochemical research are outlined. Using ToF-SIMS, the chemical composition of sample structures down to 10-100 mu m can be determined, without the need for pre-selection or labelling of the analysed substances. In addition, the lateral distribution of organic and inorganic compounds can be mapped in geochemical samples at a resolution in the micrometre range. The capabilities of the technique in geochemistry are illustrated by two examples. In the first example, it is shown that ToF-SIMS can be used to detect biomarkers in oil samples, making it a promising method for the analysis of biomarkers in fluid inclusions. In the second example, a number of specific lipid biomarkers were identified and mapped on the surface of a microbial mat cryosection surface. Post-measurement optical microscopy correlated the localisation of the lipids with the presence of methanotrophic archaea in the microbial mat.