Abstract

LOPEZ DE AZAREVICH, Vanina L. et al. New isotopic data for Late Precambrian carbonate sequences (Las Tienditas Formation) from NW argentina: implicitness in the evolution of the Puncoviscana Basin. Ser. correl. geol. [online]. 2010, vol.26, n.1, pp.27-48. ISSN 1666-9479.

The Puncoviscana basin registers four geodynamic episodes: a) Initial rifting related to breakup of Rodinia (800-750 Ma), b) Passive continental margin: formation of Puncoviscana sea and Volcan carbonates (750-580 Ma), (c) Active continental margin: development of Tilcarian magmatic arch and Las Tienditas-Tumbaya carbonates (580-550 Ma), (d) collision of Arequipa-Belén- Antofalla terrane: Tilcarian Orogeny with granitoids emplacement (550-525 Ma). Changing paleogeographic configuration and installation of new oceanic realm during the Neoproterozoic generate differences in nutrient distribution together with ice blocks transfer from the poles to equator. This process was related to restricted glacial sequences associated with Neoproterozoic cap carbonates, and wide variation of 13 C distribution in sea water that reflects high differences in isotopic curves. Although evolution of d¹⁸O and d¹³C in Las Tienditas Formation gives information about a post-Gaskier or Varanger deposition and paleoenvironmental conditions, detection of the Precambiran-Cambrian boundary is not so clear. Analysis suggests isotopic fractionation in the ocean-atmosphere boundary with fluctuations in nutrient supply, with d¹³C variation according to biologic productivity in the platform. Negative excursion of d¹³C to -2,16 ‰ PBD is associated with anoxic 13 C-depleted currents. Together with terrigenous material supply that produces an increment in the ⁸⁷Sr/⁸⁶Sr isotopic ratio.

Keywords : Geodynamic evolution; C-O-Sr isotopes; Las Tienditas Formation; Precambrian-Cambrian boundary; Northwest Argentina.

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