Análisis paleoambiental y registro paleontológico de la Formación Desencuentro (Mioceno Superior), Alto de San Nicolás, La Rioja, Argentina

GEORGIEFF, S.M., R. HERBST, G.I. ESTEBAN Y N. NASIF

AMEGHINIANA

Año: 2004 vol. 41 p. 45 - 56

0002-7014

The Alto de San Nicolás is a topographic high south of the Campo de Talampaya depression, where extensive Neogene rocks crop out (52°/18-6°). The Desencuentro Formation belongs to the upper section of the Alto de San Nicolás Group and has been recognized by satellite images and field control. A section of 1104 m has been surveyed and pelecypods, ostracods, charophytes, wood, and vertebrates not previously mentioned have been recorded. Part of them are very close to a notorious tuff layer dated 7.4±0.9 My. This continental sequence corresponds, from base to top, to an alluvial braided plain and aeolian fine sandstones (paleowind from NE), which becomes a sandy braided fluvial system (paleocurrent directions toward NE), followed by a sandy-silty fluvial plain that culminates with shallow lake deposits with invertebrates and charophytes. These deposits are covered by sandy braided river deposits (paleocurrents to the NW).  The fossil fauna and flora together with the sedimentological information indicate general temperate to warm climatic conditions with marked seasonality.