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[MTT37-01] Simultaneous in situ analysis of C and N Isotope ratios in organic matter by SIMS: application for geological samples
Keywords:secondary ion mass spectrometry, nitrogen isotope, carbon isotope, geobiology, micro scale
The δ13C and δ15N values of 22 individual globules of organic matter in a carbonate rock from the 1.9 Ga Gunflint Formation, determined by the new procedure, were ranging –33.8 to -33.3‰ and +4.2 to 5.8‰, respectively. Mean values of them were consistent with bulk kerogen analysis within analytical precisions.
The ionization efficiency of 12C2– ions in carbonate is significantly lower than that of reduced organic matter. The difference in carbon bonding between these materials would be responsible for this difference (i.e., C-O and C-C). This suggests that measurement of 12C2– ions is highly advantageous for micrometre scale organic matter in a carbonate matrix.
Simultaneous analyses of carbon and nitrogen in the same nano-volume of organic matter in Precambrian sedimentary rocks will allow correlations with textures and mineralogical occurrences, which will provide more detailed constraints on environments and life on the early Earth. Furthermore, this method is applicability to research in modern biological studies such as: using δ13C and δ15N as a proxy of modern or ancient food chains; fossil-based study of paleo ecosystems; and paleoclimatology targeting organic matter in marine biocarbonates. This work will help to expand the range of analytical tools available for the study of stable isotopes as a biosignature.