Abstract

GALLI, Claudia Inés et al. Provenance of  the Payogastilla Group (Cenozoic), Calchaquí river, Salta Province. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.2, pp.261-276. ISSN 0004-4822.

Cenozoic deposits comprising the fluvial sediments of  Payogastilla Group (Middle Eocene-Late Miocene) were studied in the southern portion of  the Calchaquí Valley, Salta province.  The strata are well-exposed on both banks of  the Calchaquí river and comprise 5,400 m of  clastic deposits, defined,  from base  to  top, by Los Colorados, Angastaco, Palo Pintado and San Felipe  formations. Mineralogic, petrographic,  geochemical  and X-ray diffraction  analyses of   the  constituent  facies of  Los Colorados, Angastaco and Palo Pintado formations are described, including their provenance, derived from paleocurrent studies. The main sandstone facies component is characterized by quartz grains; other detrital components are potassium feldspar, altered plagioclase, perthite and abundant mica. The compacted and matrix supported conglomerate deposists exhibit clasts mostly of  pegmatite, granite, quartz, slate-clay, gneiss and migmatite. These data are associated with the results of  major and trace elements with a similar affiliation to the rocks of  the eastern edge of  the Puna (Eruptivo Oire Complex) and Sierras Pampeanas. X-ray difracction analysis of  clay samples from the Palo Pintado formation reveal illite and montmorillonite, which are interpreted to be of  detrital origin, while the saponite has been generated by weathering in a humid-temperate climate. Compositional characteristics and paleocurrent data suggest primary sediment contribution from the cumbres de Luracatao and sierra de Vázquez, as well as from the Runo and Durazno ranges, sierra de Quilmes and Cumbres Calchaquíes and, to a lesser extent, from the cerro Colorado, throughout the middle Eocene to late Miocene.

Keywords : Payogastilla Group; Petrographic analysis; Geochemistry and x-rays difracction.

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