Nuevos aportes isotópicos para secuencias carbonáticas del Precámbrico superior (Formación Las Tienditas) del NO de Argentina: su implicancia en la evolución de la Cuenca Puncoviscana

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.