《Organic Geochemistry》: Extended series of tricyclic terpanes in the Mesoproterozoic sediments

Analysis of Mesoproterozoic sediment extracts from the North China Craton by gas chromatography-mass spectrometry metastable reaction monitoring revealed an extended series of C18–C33 13a(nalkyl)-tricyclic terpanes. This discovery extends the previous known series to C33 with sixteen homologs. Because of the abundant presence of C22 and C27 homologs, and no isomeric peaks for the homologs > C24, it was confirmed that the side chain at the C-13 position is a long-chain n-alkyl group without a methyl substituent or an asymmetric carbon atom. The distribution of the extended tricyclic terpanes in the Mesoproterozoic sediments is mainly controlled by a primitive biological community, probably from certain specific bacteria and/or cyanobacteria. Their biological precursor was probably inhibited by highsalinity water conditions and not evolved during the deposition of the Gaoyuzhuang Formation.

Fig.1 Metastable reaction monitoring (MRM) chromatograms showing C18–C33 13a(n-alkyl)-tricyclic terpanes in the saturate fraction of the Xiamaling Formation.

Fig. 2 Proposed biosynthetic reaction schemes for the formation of two series of tricyclic terpanes