New conodont records from the Rinconada Formation, eastern margin of the Argentine Precordillera: Tectono-stratigraphic implications

VOLDMAN, G.G.; ALBANESI, G.L.; ALONSO, J.L.; FERNÁNDEZ, L.P.; BANCHIG, A.L.; CARDÓ, R.; ORTEGA, G.; VALLAURE, M.

STRATIGRAPHY

MICROPALEONTOLOGY PRESS

Lugar: New York; Año: 2015 vol. 12 p. 79 - 83

1547-139X

INTRODUCTION The Rinconada Formation is a ca. 3750 m-thick mélange that records a period of instability in the Lower Paleozoic basin of the Argentine Precordillera; nevertheless, its origin and geological setting are a matter of debate (Heim, 1948; Amos, 1954; Peralta, 1993; Gosen et al., 1995; Peralta, 2013a). The mélange crops out along the eastern flank of the Villicum, Zonda and Pedernal ranges (Fig. 1) and is mainly made of mudstones, locally containing sandstone-mudstone alternations, conglomerates and up to km-scale blocks. The age of the formation is controversial because of the inherent reworked character of its components and the difficulty to detect autochthonous (coeval) fossils amongst the reworked material. In order to improve the understanding of the sedimentary history and the provenance of the mélange, we conducted an integrated study of the Rinconada Formation consisting of a systematic conodont sampling coupled with detailed structural and sedimentological studies. Twenty-four conodont samples obtained from carbonate-cemented sandstones, conglomerates and olistoliths were processed following standard laboratory techniques. All the conodont samples present a CAI around 3, which corresponds to burial temperatures of about 110-200 °C (Epstein et al., 1977), and commonly display sugary textures with scarce mineral overgrowths and common fractures. For the conodont zonation of the Precordillera and its global correlation, we followed the recent biostratigraphic schemes of Benedetto et al. (2007), Cooper and Sadler (2012), Albanesi et al. (2013) and Serra et al. (2015) (Fig. 2).