Rare earth element signatures in the Messinian pre-evaporitic Calcare di Base formation (Northern Calabria, Italy): evidence of normal seawater deposition.

The Calcare di Base (CdB), a carbonate unit deposited at the base of the evaporitic succession, is a key to understanding the paleoenvironmental conditions before the Messinian Salinity Crisis. The concentration of rare earth elements and yttrium (REE+ Y) in the CdB, cropping out in the Rossano Basin, were measured with inductively coupled mass spectrometry (ICP-MS). The CdB shows coherent and reliable REE+Y patterns with typical characteristics of microbial carbonates: (1) enrichment in heavy REE (NdSN/YbSN = 0.52, SD = 0.09), (2) negative Ce and positive La anomalies, (3) marine Y/Ho ratios (57.08, SD = 3.07), (4) slightly positive Gd anomalies, and (5) tetrad effect especially in the La–Ce–Pr–Nd, and [Pm]–Sm–Eu–Gd tetrads. These features suggest that the CdB incorporated REEs in equilibrium with oxygenated seawater. They also corroborate the depositional model of Guido et al. in Palaeogeogr Palaeoclimatol Palaeoecol 255:265–283, (2007) that maintains carbonatogenesis occurred via heterotrophic microbial activity. The REE+Y signatures of the CdB support the interpretation that these sediments were deposited in normal marine condition and cannot belong to the evaporite succession.