On the origin of 24-norcholestanes and their use as age-diagnostic biomarkers
On the origin of 24-norcholestanes and their use as age-diagnostic biomarkers
Geology (Boulder) (May 2007) 35 (5): 419-422
- alcohols
- algae
- Antarctica
- applications
- biochemistry
- biogeography
- biologic evolution
- biomarkers
- Cenozoic
- cooling
- Cretaceous
- diatoms
- Dinoflagellata
- DNA
- experimental studies
- fatty acids
- gas chromatograms
- geochemistry
- glacial environment
- glaciomarine environment
- ice sheets
- Jurassic
- laboratory studies
- lipids
- living taxa
- marine environment
- marine sediments
- mass spectra
- Mesozoic
- microfossils
- Miocene
- molecular biology
- Neogene
- Oligocene
- organic acids
- organic compounds
- Paleogene
- palynomorphs
- petroleum
- phylogeny
- Plantae
- RNA
- sediments
- spectra
- steroids
- sterols
- Tertiary
- Thalassiosira
- Gymnodinium
- Thalassiosira antarctica
- norcholestane
- norsterols
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- norcholesta-5,22-dien-3beta -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.