Evaluating Biomarker Syngeneity of Permian-Triassic Sections from the Nanpanjiang Basin, South China

The end-Permian mass extinction is the largest mass extinction event. There has been growing interests in Permian-Triassic boundary sections in the Nanpanjiang basin, South China due to the exposure of fossil-rich sections in this region. In this study, we conducted, for the first time, an assessment on biomarker syngeneity with Permian-Triassic boundary samples from the Nanpanjiang Basin. Samples we selected cover both microbialite and micrite dominant facies from shallow water and black shale dominant facies of deep water origin. These geographically and lithologically diverse sections in the Nanpanjiang basin make us possible to conduct basinal scale biomarker syngeneity test.

In this study, we deployed micro-ablation technique to prepare samples in order to efficiently remove potential contamination. By using this technique, we separated rock samples into exterior and interior layers and special effort was made to compare the biomarker concentrations between exterior and interior layers. Various biomarker compound classes such as n-alkanes, hopanes, steranes, and carotenoids are detected in both exterior and interior of the sedimentary rocks from the examined sections. Absent of color for all extracts, we observed higher biomarker concentrations in the exterior than the interior layers. Strikingly, oleanane, which is a biomarker for angiosperm, was also detected in all layers despite of its emergence in Cretaceous. The presence of oleanane and concentration gradients between interior and exterior probably suggest that biomarker contamination has penetrated through the rock surface in the past time, negating the potential application of these samples for syngenetic organic geochemical analysis. Therefore, the Nanpanjiang Basin, South China is a critical region for studying the Permian-Triassic mass extinction event, unfortunately, it is unlikely a suitable candidate for biomarker study.