Compositional study of the sediments from the Gruta del Indio, Rincón del Atuel, county of San Rafael, Mendoza.

Abstract

The infilling of the shelter is composed of three levels, all of them generated during intermittent fluvial action. The horizontal distribution of the infilling is sometimes disrupted by basaltic crumble from the roof of the shelter. The distribution of organic components is quite variable and it is controlled by the human and animal activity. They include: humus, coal, silicophytoliths and collophanite. Detrital grains are the most abundant and represent over 90 % of the whole samples analysed. They are clearly dominated by the light fraction. Volcanic lithoclasts, vitroclasts and calcic plagioclases are the more frequent constituents accompanied by scarce monocrystalline and polycrystalline quartz, potash feldspar, carbonate fragments and heavy minerals. A local sedimentary provenance is suggested on the basis of the clasts features. They are associated with roof's crumbles and the mixture with similar debris resulted from the erosion of the underlying deposits, and aloctonous fluvial and pyroclastic materials. The sediments may be included it the group of the para-tuff and the low mineralogical maturity observed suggests a dry and cold climate. However, micritic aggregates deposited on the surface are considerd to be the result of precipitation in situ of bicarbonated waters which indicates transient humid conditions. This interpretation is constrained for broken dripstones fragments.