A plethora of hopanoid transformation products co-exist in a thermally immature Jurassic black shale II: Oxo- and thiohopanoids

• Hopanoic acids and thiohopanoids co-exist in a single Toarcian sediment sample. • Co-occurrence of oxo- and thiohopanoids requires habitat differentiation. • Identification of novel hop-17(21)-ene thiolanes. • Microbially mediated alkylation forms C 36 –C 38 hopane thiophenes. • C 33 dominance in 2α-methyl hopanoids may arise from nitrogen-cycling bacteria. Hopanoids are ubiquitous in sediments and sedimentary rocks and are commonly applied tools for paleoenvironment reconstruction. Biohopanoids during diagenesis transform to geohopanoids when they successively lose their structural diversity. Prior to elevated thermal maturity, where only hopanes and benzohopanes persist, a large variety of intermediate hopanoid transformation products can be intermittently abundant in immature sediments. We presented in a companion paper the highly diverse hopanoid hydrocarbon inventory in one immature black shale sample from the Toarcian Posidonia Shale at Hondelage, NW-Germany that was deposited under euxinic conditions. Here, the focus is on the plethora of oxo- and thiohopanoids co-existing in the same sample. The formation of hopanoic acids requires oxic conditions whereas thiohopanoid require sulfidic conditions. These contrasting requirements suggest spatial and temporal separation of hopanoic acid versus thiohopanoid formation prior to or after incorporation into the sediment. Hopanoic acids presumably form in the oxic upper water column with potential minor contributions from oxic microniches and/or seasonally induced brief suboxic events at the sediment/water interface. In contrast, thiohopanoids presumably originate within the sulfidic water column and/or the sediment. Persistent euxinic conditions during deposition of the Posidonia Shale at Hondelage favoured formation of a variety of thiohopanoids in a shallow marine setting below a salinity-stratified water column. Thiohopanoids include previously unidentified hop-17(21)-ene thiolanes and hopane thiophenes extending to C 38 . Since hopanoids extending past C 35 are absent for other hopanoid species, extended hopane thiophenes likely result from microbially mediated early diagenetic alkylation at the C35 position. Hopanoic acids as well as thiohopanoids occur as 2-methyl analogues and exhibit elevated abundances of C 33 homologues, which dominate in desmethyl hopanoids. Precursor organisms for 2-methyl hopanoids are most likely nitrogen cycle-affiliated α-proteobacteria and/or diazotrophic cyanobacteria.