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 delta O-18 V-SMOW values (15-19 parts per thousand) indicate an alteration of the whole stratigraphic series. However, the alteration process does not seem to have affected most of the VC and Sr-87/Sr-86 data. These data reveal that only one particular level of the carbonate section shows simultaneous relative increases in Mn/Sr and Sr-87/Sr-86 ratios, decreases in the delta O-18 and VC values, and covariations between Sr-87/Sr-86 and the other parameters. Despite this, most of the carbonate section lacks these covariations and its VC (-4.6 to -0.5 parts per thousand) and Sr-87/Sr-16 (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. (c) 2006 Elsevier B.V. All rights reserved.