CONICET | Buscador de Institutos y Recursos Humanos

The Río Blanco Formation (Triassic, Cuyo Basin) is studied in the classic locality of Divisadero Largo. Based on the distribution of clastic sedimentary facies and geometry of lithosomes, four sections have been recognized in this unit. The lower section is composed of massive and bioturbated open lacustrine mudstones which are covered by progradational Gilbert-type deltaic lithosomes (medium¬ and large-scale cross-stratified sandstones with multiple reactivation surfaces), and mouth bars. A cyclic arrangement of channelized sandy-gravelly beds and massive mudstone intervals with abundant paleosol levels characterizes the second section, which is intepreted as a mixed-load high-sinuosity meandering fluvial system. The third and fourth sections are dominated by fine¬ grained, massive pyroclastics (tuffs, chonites), accumulated as lacustrine fall-out deposits and (subaerial) loessites. In the Río Blanco Formation two sequences (RB1 and RB2) were defined, each of them composed of a "high-base-level" and a "low-base-level" systems tract, related here to alternating periods of tectonic subsidence and quiescence. The fossiliferous stratum found in the first section of the Río Blanco Formation contains fossil plants belonging to Corystospermales, Czekanowskiales, Ginkgoales and Voltziales, as shrubs and trees. The identified taxa are: Dicroidium crassum (Menéndez) Petriella, Xylopteris elongata (Carruthers) Frenguelli, cf. Czekanowskia rigali Frenguelli, cf. Baiera cuyana Frenguelli, Heydiphyllum elongatum (Morris) Retallak and Cordaicarpus sp. Geinitz The characteristics of the plant remains suggest that the fossils underwent a short transportation and the parent communities grew in the levee deposit of the river. The riparian community could be a deciduous forest that reach the side of the river and was controlled by a template-warm climatic condition with a dry season.

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