On the origin of 24-norcholestanes and their use as age-diagnostic biomarkers
24-norcholestanes have been shown to be useful biomarkers to assess the age of sediments and petroleum, but until now, the biological sources of their precursors, i.e., 24-norsterols, were unclear. We have unambiguously identified relatively high concentrations of 24-norcholesta5,22-dies-3 beta-ol i...
| Published in: | Geology |
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| Main Authors: | , , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2007
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| Subjects: | |
| Online Access: | https://pure.uhi.ac.uk/en/publications/b02802c9-7127-4e92-88ab-a6842dba84c7 https://doi.org/10.1130/G23358A.1 |
| Summary: | 24-norcholestanes have been shown to be useful biomarkers to assess the age of sediments and petroleum, but until now, the biological sources of their precursors, i.e., 24-norsterols, were unclear. We have unambiguously identified relatively high concentrations of 24-norcholesta5,22-dies-3 beta-ol in the diatom Thalassiosira aff. antarctica (6%-10% of total sterols) and, in much lower concentrations, in the dinoflagellate Gymnodinium simplex (0.2% of total sterols). These identifications and other reports of 24-norsterols in dinoflagellates suggest that both diatom and dinoflagellate species are major sources for 24-norcholestanes in sediments and petroleum. The evolutionary history of these organisms suggests that observed increases of 24-norcholestane concentration in the Jurassic and the Cretaceous are related to dinoflagellate expansion, whereas an increase in the Oligocene-Miocene is likely caused by diatom expansion. Our results also explain the biogeographical distribution of 24-norcholestanes, i.e., high concentrations at high (paleo)latitudes are likely caused by diatoms, while low concentrations at lower (paleo)latitudes are likely caused by dinoflagellates. |
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