Análisis de procedencia de la Formación Falda Ciénaga (Ordovícico Medio, Puna Argentina) por petrografía sedimentaria, elementos trazas e isotopía de Nd

the objective of this paper is to provide a provenance study of the falda ciénaga formation and a paleotectonic scenario for the middle ordovician combining new data with published information from ordovician sedimentary successions of the puna, a highland in the northwestern part of argentina. the falda ciénaga formation oucrops between the salar de pocitos (24° 24' 59.5''s 66° 55' 18.0''w) and the sierra calalaste (26° 11' 52.5''s 67° 41' 02''w). the abundance of black shales containing pyrite, the absence of shallow water sedimentary structures and the lack of debris flows suggest that the falda ciénaga formation was deposited in a relatively deep basin. the material was deposited by turbidity currents in a depositional lobe, lobe fringe and basin plain environment (g？ttert, 1997; zimmermann et al., 1997). deposits in the northern region (salar de pocitos; fig. 1b) show different lithofacies to those to the south of salar de hombre muerto (fig. 1c). voluminous sandstones and greywackes outcrop in the northern area, while shale dominate in the southern outcrop region. furthermore, the succession in the north contains phyllograptus sp. (zimmermann et al., 1998) indicating a time lapse between upper arenigian and llanvirnian, whereas glossograptus sp. and glossograptus hieckinsis found in the southern outcrops (ace？olaza y toselli, 1971; this paper) suggests a llanvirnian age. further to the south, between salar de hombre muerto and antofagasta de la sierra (fig. 1b), the falda ciénaga formation is composed of massive turbidites and shales, rare siltstones and subordinate coarse-grained greywackes. the latter are interpreted as submarine channel deposits, as observed to the east of los nacimientos locality (fig. 1c). feldspathic to quartzitic arenites, medium to very-coarse grained greywackes and fine layers of pelites occur as lithotypes of the falda ciénaga formation. the composition of the sandstones changes between 65-78 % qt , 3-19 % f and 0-22 % l. the sedimen