SILURIAN CONODONTS FROM THE RINCONADA FORMATION, ARGENTINE PRECORDILLERA

摘要

At the eastern margin of the Precordillera and close to the boundary with Sierras Pampeanas, the Rinconada Formation displays extensional faults, boudinaged sequences and scarce slump folds for which age is not well constrained. It represents a stacking of "broken formations" intercalated with scarce debris flows. A calcareous iron-rich sample from the upper levels of the Rinconada Formation yielded 134 conodont elements, including Dapsilodus obliquicostatus, Decoriconus fragilis, Oulodus sp., Pseudooneotodus beckmanni, P. b. bicornis and Wurmiella excavata together with ozarkodinids of the "Oz." bohemica-"Oz." snajdri lineage. The record of "Oz." aff. snajdri suggests a late Homerian-early Gorstian (late Wenlock-early Ludlow) minimum depositional age for the upper debris flows of the Rinconada Formation. The studied conodont fauna improves the biostratigraphic correlation of the Rinconada melange with other successions in the Precordillera and the world as well as provides clues on the tectonostratigraphic development of the SW Gondwanan foreland during Silurian times.