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, A.M.

Harrisonburg

Simposio; 12th International Symposium on the Ordovician System; 2015

IUGS UNESCO

The Rinconada Formation is a ca. 3750 m-thick mélange that records a period of instability in the LowerPaleozoic basin of the Argentine Precordillera; nevertheless, its origin and geological setting are a matterof debate (Heim, 1948; Amos, 1954; Peralta, 1993; Gosen et al., 1995; Peralta, 2013a). The mélangecrops out along the eastern flank of the Villicum, Zonda and Pedernal ranges (Fig. 1) and is mainly madeof mudstones, locally containing sandstone-mudstone alternations, conglomerates and up to km-scaleblocks. The age of the formation is controversial because of the inherent reworked character of itscomponents and the difficulty to detect autochthonous (coeval) fossils amongst the reworked material. Inorder to improve the understanding of the sedimentary history and the provenance of the mélange, weconducted an integrated study of the Rinconada Formation consisting of a systematic conodont samplingcoupled with detailed structural and sedimentological studies. Twenty-four conodont samples obtainedfrom carbonate-cemented sandstones, conglomerates and olistoliths were processed following standardlaboratory techniques. All the conodont samples present a CAI around 3, which corresponds to burialtemperatures of about 110-200 °C (Epstein et al., 1977), and commonly display sugary textures withscarce mineral overgrowths and common fractures. For the conodont zonation of the Precordillera and itsglobal correlation, we followed the recent biostratigraphic schemes of Benedetto et al. (2007), Cooperand Sadler (2012), Albanesi et al. (2013) and Serra et al. (2015)