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oa Exceptional Hopanoid Diversity in an Immature Black Shale: Coexistence of THIO- and OXO-Hopanoids
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IMOG 2025, Sep 2025, Volume 2025, p.1 - 2
Abstract
Despite their ubiquitous abundance in living organisms, functionalized hopanoids when under oxic conditions converted to hopanoic acids are seldomly reported from immature sediments despite their large abundances in different depositional environments. In contrast, thiohopanoids have mainly been reported from evaporitic settings and previously have not been reported from Toarcian black shales. Here, we present a suite of hopanoid thiolanes and thiophenes, hop-17(21)-enoic acids and hopanoic acids, all of these co-existing in a single sediment sample. We tentatively identified previously unreported hop-17(21)-ene thiolanes and a suite of hopane thiophenes extending to C38. All hopanoid species reported here also occur with A-ring methylation. For hopanoic acids both 3ß-methyl and 2a-methyl analogues are present whereas the other hopanoid species only exhibit 2a-methyl analogues only. Hopanoic acids and thiohopanoids both need contrasting environments for their formation. Hopanoic acids require the presence of oxygen to form, whereas thiohopanoids entail sulfidic conditions. Hence, either seasonal variations causing brief suboxic conditions, oxic microniches or spatial separation (e.g., hopanoic acid formation in the oxic part of the water column and thiohopanoid formation within the sulfidic sediment) can be invoked to explain their co-occurrence. Despite brackish surface waters, abundant organic sulfur compounds attest to sulfidic bottom water conditions.
