Abstract

SURIANO, Julieta; ALONSO, M. Susana; LIMARINO, C. Oscar  and  TEDESCO, Ana M. Cuesta del Viento Formation (nov. nom.): A new lithostratigraphic unit in the evolution of  the Precordillera orogen. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.2, pp.246-260. ISSN 0004-4822.

In this paper is defined the Cuesta del Viento Formation, a new lithostratigraphic unit related to the Andean Orogeny in western  Precordillera.  This  unit  unconformably  covers  sandstones  and  mudstones  of   the  Puesto  La  Flecha  Formation (Oligocene?) and  low-grade metamorphic  rocks of   the Yerba Loca Formation  (Ordovician). Cuesta del Viento Formation (520 m thick) is mainly composed of  gray monomictic breccias and, to a lesser extent, of  mudstones, sandstones and polymictic conglomerates. According to previously ages the upper levels of  the Cuesta del Viento Formation were deposited during the Early Miocene. The sedimentological analysis of  the stratotype, that outcrops in the La Tranca valley, allowed to recognize five facies associations. Facies association 1 is almost entirely composed of  massive breccias which sometimes show chaotic stratification  interpreted as colluvial  fans dominated by gravity  flows. Facies association 2 corresponds  to stratified breccias that show lensoidal amalgamated beds and were deposited in multichannalized alluvial plains dominated by low-sinuosity channels. Facies association 3 is made up of  sandstones and polymictic conglomerates bearing granitic and volcanic clasts. It is very likely that the composition of  the clasts of  this last facies association represents the by pass of  sediments, by means of  braided rivers,  from  the neighboring Rodeo-Iglesia Basin  (from  the west). Mudstones and scarce conglomerates, which form facies association 4, would represent sedimentation in a shallow lake system that included fluvial mouth bar deposits. Finally, facies association 5 is mainly composed of  massive and laminated mudstones that sometimes show mudcracks, and a minor participation of  monomictic breccias. This stratigraphic interval was probably deposited in playa lake environments.

Keywords : Cuesta del Viento Formation; Tertiary; Precordillera; Provenance.

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