Sr/Ca, Mg/Ca ratios and Sr and stable isotopes of biogenic carbonates from the Late Miocene Velona Basin (central Apennines, Italy) provide evidence of unusual non-marine Messinian conditions

The Sr/Ca and Mg/Ca ratios of fossil ostracod and mollusc shells from a Late Miocene (Early Messinian) lacustrine sequence in the Velona Basin (central Apennines, Italy) were used to calculate the Sr/Ca and Mg/Ca of waters in which these taxa lived. Sr/Ca of these waters were always higher than the Sr/Ca calculated for the Messinian seawater, despite the broad salinity ranges (fresh water-oligo/mesohaline) inferred from the paleontological analyses. The estimated Mg/Cawater from the Velona samples are below the Mg/Ca value for coeval seawater even though they represent relatively high values when compared with many non-marine waters. The salinity variations of the Velona lacustrine system, recorded by changes in faunal assemblages, are linked to variable inputs of Na–Cl from deep groundwaters and are not reflected in significant changes in Sr/Ca and Mg/Ca of the waters calculated from shell chemistry. The combination of δ18O signatures and Sr isotopic ratios from molluscs from the Velona Basin suggests a non-marine environment. During some episodes of the lake history, given the saline inputs, the waters in the lake would attain a large solute concentration (oligo to mesohaline), although they retained the meteoric δ18O signature. We compare the paleohydrochemical inferences from the studied sequence with other Messinian records, and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions.