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Detection of hopanes and steranes in single oil-bearing fluid inclusions using ToF-SIMS
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
SP Sveriges Tekniska Forskningsinstitut.
SP Sveriges Tekniska Forskningsinstitut.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
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2009 (English)In: IMOG 24th International Meeting of Organic Geochemistry, Book of Abstract, www.imog2009.org, 2009, 6- p.Conference paper, Published paper (Other academic)
Abstract [en]

Hopanes and steranes are key biomarkers when tracking early evolution of life on Earth. A potential contamination-free source of Precambrian biomarkers is oil-bearing fluid inclusions as the oil has been secluded from the environment since the formation of the inclusion. Due to presence of often several generations of inclusions it can be problematic to assign the biomarkers to specific inclusions. It has, however, because of the small size of inclusions (5-30 µm), not been possible to analyse single oil-bearing fluid inclusions. We present here an approach employing time-of-flight secondary ion mass spectrometry (ToF-SIMS) to selectively open individual oil inclusions in situ by ion etching, and precisely analyse their picoliter content for steranes and hopanes.

A number of oil-bearing inclusions from hydrothermal veins in the Siljan impact structure in south-central Sweden were analysed. The approach used for analysis of a single inclusion consisted of the following steps i) localization of suitable inclusion in double polished thin section with optical microscopy, ii) opening of inclusion by ion etching with C60+ gun inside the ToF-SIMS instrument while recording in real-time the opening of the inclusion and, iii) analysis of the exposed inclusion contents with ToF-SIMS. The micrographs and the ToF-SIMS ion images collected before, during and after analysis ensured the correct inclusion had been analysed. ToF-SIMS spectra reconstructed from analysis times and 2D regions of interest with increased organic ion signal showed a large number of organic peaks (up to m/z 500) that are characteristic for a crude oil. Comparison of the reconstructed spectra with those of a Siljan seep oil, which has previously been analysed with ToF-SIMS, showed a high degree of resemblance, as expected from the geological interpretation of the origin on the oils. All major characteristic peaks for several hopanes and steranes were detected in the mass spectra from the single fluid inclusion (Fig. 1). The agreement with respect to mass accuracy (< 50 ppm), fragment pattern and isotope distributions between these peaks and those observed in spectra from standard samples and from hopanes and steranes in the Siljan seep oil, provide strong evidence for the presence of hopanes and steranes in the analysed single fluid inclusions. The results thus demonstrate that the approach presented here has the capability to detect specific biomarkers in individual single oil inclusions.

It is to our knowledge the first time hopanes and steranes have been detected in single oil-bearing fluid inclusins and the next step will be to analyse single oil-bearing fluid inclusions in Precambrian rocks with ToF-SIMS in search for organic biomarkers. Detection of hopanes and steranes in such an inclusion could help to answer questions regarding early evolution of life on Earth, including the first appearance of the eukaryotes on Earth.

Place, publisher, year, edition, pages
2009. 6- p.
National Category
Natural Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-33660OAI: oai:DiVA.org:su-33660DiVA: diva2:283318
Conference
IMOG 24th International Meeting of Organic Geochemistry
Projects
Fluid inclusions, biomarkers, ToF-SIMS, oil
Available from: 2009-12-23 Created: 2009-12-23 Last updated: 2012-06-19Bibliographically approved

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