Abstract

CIOCCILI, Patricia L et al. Stratigraphy of the Vinchina basin (Tertiary), Sierras Pampeanas, La Rioja province. Rev. Asoc. Geol. Argent. [online]. 2010, vol.66, n.1-2, pp.146-155. ISSN 0004-4822.

The Vinchina Basin, in the northwest of the La Rioja Province, conforms one of the Cenozoic depocenters of the broken-foreland in the Andean Sierras Pampeanas- Famatina-Precordillera-Cordillera Frontal segment. The beginning of the basin fill corresponds to a thin sequence of ephemeral fluvial to lacustrine systems assigned to Puesto La Flecha Formation (Paleocene-Early Eocene). This unit is covered by aeolian deposits of the Vallecito Formation (Eocene). The Vinchina Formation (Oligocene- Early Miocene) rests on the Vallecito Formation by means of an erosional unconformity and is dominated by sandy-shale and sandy-gravel fluvial system deposits of semiarid climate conditions. The Vinchina Formation. is composed of two members; the lower one is made up of sandstones and shales while the upper one is dominated by sandstones and conglomerates. The upper member rests on a low angle erosional surface draped by several conglomeratic levels (progressive unconformities). The Toro Negro Formation (Miocene- Early Pliocene) covers by means of an erosional unconformity the Vinchina Formation. The lower member of the Toro Negro Formation is dominated by sandy-shales deposits with low proportion of conglomerates corresponding to the sedimentation in anastomosed fluvial systems. The upper member that rests on the lower member through an erosional surface is composed of conglomeratic deposits corresponding to braided fluvial systems and stream-flow dominated piedmont. Finally, alluvial fan deposits of the El Corral Formation (Pliocene) appear. This new stratigraphic chart for the Vinchina Basin permits the correlation with the Tertiary outcrops of the La Troya Basin and to propose an initial stage of common evolution and a latter stage of independent sedimentation (broken foreland).

Keywords : Broken-foreland; Vinchina Basin; Tertiary; Stratigraphy.

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