LAUSR

Abstract The Early Ordovician conodont faunas from the Cerro La Chilca and Las Chacritas river sections (Central Precordillera) have been studied and compared to those of the well-known Talacasto section. The vertical distribution of the recovered upper Floian conodonts from Cerro La Chilca and Las Chacritas river sections is presented for the first time, recording the Oepikodus evae and O. intermedius zones, this distribution has been compared to the Talacasto section. The conodonts Bergstroemognathus hubeiensis An, and Microzarkodina n. sp. (sensu Pyle and Barnes) are recorded for the first time in the Precordillera, and these two species are described and illustrated herein. The occurrence of the B. hubeiensis and Microzarkodina n. sp. in the early Ordovician strata of the San Juan Formation, provides significant data related to the ties between Precordillera to Gondwana, peri-Gondwana, and Northwestern of the Midcontinent regions for this time interval, increasing the knowledge about the paleogeographic reconstruction of the western margin of Gondwana. The evidence of biogeographic connections between these regions let to suggest that those were in closer position than previous assumptions or at least that marine currents connected them during the late Lower Ordovician.