Orbitally Forced Hydrological Balance During the Messinian Salinity Crisis: Insights From Strontium Isotopes (⁸⁷Sr/⁸⁶Sr) in the Vena del Gesso Basin (Northern Apennines, Italy)

Abstract

The 87Sr/86Sr ratio is a proxy of the hydrologic structure of marginal basins characterized by the mixing between marine and continental waters. This reliable paleoceanographic and paleoclimatic tool is considered a key to the reconstruction of high‐amplitude hydrologic changes that governed the evolution of the Mediterranean region during the Messinian salinity crisis (MSC), when reduced connections with the global ocean resulted in the deposition of the most studied Earth's salt giant. Paleohydrological dynamics leading to the deposition of the Primary Lower Gypsum during the first stage of the MSC were revealed by the study of the 87Sr/86Sr composition of 114 samples from the Vena del Gesso basin (Northern Apennines, Italy). The analysis of seven high‐resolution 87Sr/86Sr profiles from individual gypsum beds suggests a climatic influence of precessional‐scale orbital parameters during evaporite deposition. The variations of Sr isotope ratios over time indicate that gypsum precipitation started from a seawater body dominated by continental contributions, followed by a relative increase of marine input. The overall results show a gradual upward detachment from the global ocean 87Sr/86Sr curve, with crucial steps corresponding to the most extreme eccentricity minima, suggesting an orbital influence on the hydrological balance of the basin. Given the sedimentological and geochemical analogies shared by the Mediterranean marginal basins that hosted the Primary Lower Gypsum deposition, the 87Sr/86Sr evolution of the Vena del Gesso basin may be considered as indicative of Mediterranean‐scale hydrologic dynamics, driven by gradual reduction of exchanges with the Atlantic and variable freshwater input.

Paratethys pacing of the Messinian Salinity Crisis: Low salinity waters contributing to gypsum precipitation?

“…To approach the 87 Sr/ 86 Sr values that characterize Stage 3, the present-day inflow of the Atlantic needs to be reduced by at least a factor of 1000. With a strongly reduced Atlantic inflow, a volume of Paratethys Sea inflow similar to present-day Black Sea inflow is sufficient to approach the observed Mediterranean 87 Sr/ 86 Sr. A strongly reduced Atlantic inflow, however, would lead to a drop in Mediterranean water levels, which is in line with the classic desiccation model (Hsü et al, 1973), but not with the idea that the Mediterranean remained water-filled (Roveri et al, 2014a;Stoica et al, 2016). Reduced mixing between a low salinity surface water layer and deeper highly saline Atlantic waters provides an alternative mechanism (Marzocchi et al, 2016;García-Veigas et al, 2018).…”

“…Earth's most recent saline giant occurred in the Mediterranean Basin during the late Miocene (Hsü et al, 1973;Ryan, 2009). Restriction of seawater exchange between the (proto) Mediterranean Sea and the Atlantic Ocean cul-minated in the so-called Messinian Salinity Crisis (MSC) between 5.97-5.33 Ma (Roveri et al, 2014a;Flecker et al, 2015). The MSC is subdivided into three main stages, all characterized by specific environmental conditions (Roveri et al, 2014a).…”

“…Restriction of seawater exchange between the (proto) Mediterranean Sea and the Atlantic Ocean cul-minated in the so-called Messinian Salinity Crisis (MSC) between 5.97-5.33 Ma (Roveri et al, 2014a;Flecker et al, 2015). The MSC is subdivided into three main stages, all characterized by specific environmental conditions (Roveri et al, 2014a). MSC Stage 1 (5.97-5.6 Myr ago) is marked by rhythmic alternations of marine marls and gypsum in the shallow basins, while the Mediterranean remained connected to the Atlantic Ocean.…”

Diazotrophy Drives Primary Production in the Organic-Rich Shales Deposited Under a Stratified Environment During the Messinian Salinity Crisis (Vena del Gesso, Italy)

“…Written informed consent was obtained from the individual for the publication of this image. of organic-rich shales (Krijgsman et al, 1999;Lugli et al, 2010;Reghizzi et al, 2018).…”

Interpretation of Late‐Pleistocene/Holocene Transition in the Sea of Marmara From Geochemistry of Bulk Carbonates

“…During the last several thousands of years, seawater 87 Sr/ 86 Sr ratio has remained stable and homogeneous with a mean value of 0.7092 (Broecker & Peng, ; Elderfield, ; Henderson et al, ). Seawater 87 Sr/ 86 Sr ratio is distinguishable from river water 87 Sr/ 86 Sr ratio (Table ), because the 87 Sr/ 86 Sr of the river depends on the ages and Rb/Sr ratios of the bedrock and the overburden in the particular drainage basin (Cox & Faure, ; Reghizzi et al, ). In the SoM, seawaters from the Mediterranean and freshwaters from the Black Sea are the two water sources with significantly different 87 Sr/ 86 Sr ratios.…”