Paleoenvironmental change in a precession-paced succession across the onset of the Messinian salinity crisis: Insight from element geochemistry and molecular fossils

The response of water column and sedimentary environments to the advent of the Messinian salinity crisis: insights from an onshore deep-water section (Govone, NW Italy)

“…The restriction of the Mediterranean leading to the MSC was associated with an intensification of water-column stratification (Roveri et al 2014) that persisted during the entire MSC event (Christeleit et al 2015;Simon & Meijer, 2017;García-Veigas et al 2018). The same evolution has been reconstructed for the Piedmont Basin (Dela Pierre et al 2011;Bernardi, 2013;Violanti et al 2013;Lozar et al 2018), especially by the study of the Pollenzo section, a section about 20 km SW from the Govone section (Natalicchio et al 2017(Natalicchio et al , 2019. For the Pollenzo section, the most compelling evidence of increasing water-column stratification after the MSC onset is the appearance of tetrahymanol.…”

“…The co-occurrence of tetrahymanol and isorenieratane in shales therefore supports pronounced water-column stratification at Environmental change at the onset of the Messinian salinity crisis 9 precession minima already before the onset of the MSC, occasionally accompained by photic zone euxinia. The lower contents of tetrahymanol and the lack of isorenieratane in the MSC shales apparently suggest the weakening of stratification, which is however in contrast with evidence from the neighbouring Pollenzo section (Natalicchio et al 2017(Natalicchio et al , 2019. This inconsistency could reflect unfavourable environmental conditions at precession minima for the producers of isorenieratene and tetrahymanol after the MSC onset in the distal part of the basin (Govone), rather than the weakening of water-column stratification.…”

“…These deposits, characterized by the repetition of shale and marl couplets, record progressively more restricted conditions heralding the onset of the MSC (Sturani, 1973;Sturani & Sampò, 1973). The lithological cyclicity was controlled by climate fluctuations driven by precession, with shales representing more humid conditions at precession minima and marls recording more arid conditions at precession maxima (Natalicchio et al 2019;Sabino et al 2020). At the basin margins, this unit is overlain by shale and gypsum couplets belonging to the PLG unit ( Fig.…”

“…The trophic relationship between autotrophic green sulphur bacteria and heterotrophic ciliates, already inferred for the MSC sediments of the Northern Apennines (Vena del Gesso Basin, Sinninghe Damsté et al 1995a), can potentially explain the trend of compound contents in the Govone section, where tetrahymanol peaks coincide with the presence of isorenieratane. Adverse conditions for green sulphur bacteria were most likely related to an intensified input of terrigenous material by rivers after the MSC onset, as evidenced by increasing contents of terrestrial plant waxes (Natalicchio et al 2019;Sabino et al 2020). Enhanced riverine runoff might have increased turbidity and input of oxygen in the upper water column, both deleterious factors for phototrophic green sulphur bacteria (Van Gemerden & Mas, 1995), in turn causing a decrease of the ciliate population.…”

“…The analysis of molecular fossils (lipid biomarkers) preserved in Messinian evaporites and their intermediate-to deep-water lateral equivalents provides fundamental information for the reconstruction of the Mediterranean hydrological cycle and palaeoenvironments (Vasiliev et al 2017;Natalicchio et al 2019;Sabino et al 2020). This approach is a valuable tool to unveil the conditions in the water column during the MSC.…”