oa Exceptional Hopanoid Diversity in an Immature Black Shale: Aliphatic and Aromatic Hopanoids

Hopanes, hopenes and aromatic hopanoids are amongst the most widely applied biomarkers for palaeoenvironmental reconstruction, maturity assessment and source rock characterization. Their origin and diagenetic fate are important for our understanding of past environments. Here, we present the aliphatic saturated, unsaturated and aromatic hopanoids co-occurring in an immature black shale sample of Early Toarcian age. We identified >80 hopanoid structures in a single sediment sample and present their mass spectra, elution orders and characteristic mass fragmentograms of the different hopanoid species. We found pronounced differences in aromaticity, carbon number distribution and A-ring methylation pattern. The C24-C26 polyaromatic hopanoids for example do not exhibit A-ring methylation and are believed to originate from soil microbial biomass where extensive degradation can be invoked as explanation for the high aromaticity. The enhanced hydrological cycle prevailing during the early Toarcian, favours the transport of soil-derived hopanoids into the marine realm. Extended hopanoids within the aliphatic and aromatic fractions exhibit A-ring methylation. Here, the diaromatic 8(14)-secohopanes occur as both methylated at C2 and at C3. The remaining extended hopanoid species are only present as 2a-methyl analogues.