Oxygen, carbon and strontium isotope records of Ediacaran carbonates in Central Iberia (Spain)

Carbon, oxygen and strontium isotope ratios were determined in the uppermost Neoproterozoic carbonate rocks at Pastores (SW Salamanca, Central Iberia). The low δ18O V-SMOW values (15–19‰) indicate an alteration of the whole stratigraphic series. However, the alteration process does not seem to have affected most of the δ13C and 87Sr/86Sr data. These data reveal that only one particular level of the carbonate section shows simultaneous relative increases in Mn/Sr and 87Sr/86Sr ratios, decreases in the δ18O and δ13C values, and covariations between 87Sr/86Sr and the other parameters. Despite this, most of the carbonate section lacks these covariations and its δ13C (−4.6 to −0.5‰) and 87Sr/86Sr (0.70845–0.70853) ratios probably reflect the seawater isotopic features at the time of sedimentation. The data for C and Sr isotopes at the Pastores carbonate section and the presence of Cloudina in platform carbonates together with an overlying major sub-Cambrian unconformity following a relative sea level fall are features comparable to those frequently shown by Proterozoic–Cambrian boundary series across the world. Thus, our results consistently support the notion that the carbonates at Pastores are equivalent to other carbonates deposited close to the Ediacaran/Cambrian boundary.