Abstract:
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. © 2006 Elsevier B.V. All rights reserved.
