The 5th International Conference of Geobiology

Gammacerane, a C₃₀ triterpenoid biomarker traditionally interpreted as an indicator of water column stratification (Sinninghe Damsté et al., 1995) and closely linked to salinity variations (Tulipani et al., 2015), remains enigmatic due to the unexplained absence of its enrichment in high-salinity sedimentary environments. This multidisciplinary investigation of Miocene Nördlinger Ries lacustrine shales in southern Germany integrates mineralogical characterization and organic geochemical proxies (including total organic carbon [TOC], total sulfur [TS], biomarker signatures, kerogen elemental composition, and pyrolysis parameters) to elucidate the interplay between gammacerane preservation and microbial dynamics governed by hydrochemical conditions. Key findings reveal that although the paleolake evolved through mesosaline, hypersaline, mesosaline, and freshwater phases, gammacerane abundance exhibits no direct correlation with salinity gradients. Within the basal hypersaline anoxic interval, hydrochemically induced trophic collapse (manifested by diminished prokaryotic biomass) suppressed the metabolic activity of ciliates (primary gammacerane producers), concurrently reducing gammacerane biosynthesis and denitrification efficiency. The population decline of Gammaproteobacteria further impeded sulfate-reducing bacterial proliferation, as evidenced by coupled variations in organic sulfur content and pyrolysis Tmax values, thereby curtailing organosulfur compound formation. This study demonstrates that gammacerane preservation is governed not merely by stratification dynamics but predominantly by ecological feedbacks within microbial consortia, offering a revised framework for interpreting the geological significance and contextual constraints of gammacerane records in hypersaline lacustrine systems.

gammacerance,column stratification,hypersaline,sulfate-type lake,lacustrine basin