The Pular Formation, northern Chile: Triassic or Paleozoic? Lacustrine or laggonal?

J.J. LATORRE, H. NIEMEYER, S. BALLENT, O.F. GALLEGO, D. POIRÉ, A. ZAMUNER, A.M. ZAVATTIERI

Mendoza

Congreso; Gondwana 12 Conference "Geological and Biological Heritage of Gondwana"; 2005

CONICET, CIG, ANPCYT, Academia Nacional de Ciencias de Córdoba, AGA, APA, AAS

The Pular Formation outcrops in Quebrada Pajonales (24º 21´ 32.4" S; 68º 33´ 56.4" W), Sierra de Almeida, northern Chile. This formation is approximately 350 m thick and includes conglomerates, sandstones, sandy tuffs, bituminous shales, limestones and minor poorly welded fragmental rhyolitic tuffs. Davidson et al. (1981) suggested a Triassic age for this formation, based on the presence of fossil plants close to the genus Yabeiella, as suggested by verbal communication of A. Troncoso. Nevertheless, Osorio and Rivano (1985) attributed to it a Lower Carboniferous age, based on the presence of ostracods assigned to the genus Chamishaella? sp. This different chronological assignment motivates the present revision of the Pular Formation. Fossil remains include plants, palynomorphs, fresh water ostracods and green algae, conchostracans, fish teeth and stromatolites. The presence of gondwanide elements such as, megafossil plants close to Pseudoctenis fissa Du toit, the polyplicate gnetalean pollen Equisetosporites sp., between other typical Triassic miospores genera and a conchostracan species that resembles Euestheria forbesi (Jones) Raymond, suggests a Triassic age. New paleontological and geochronological studies will contribute to a closer age determination and a further paleoenvironmental discussion.