The brachiopod faunas from the Huaraco Formation (Andacollo Embayment): the transition of warm to cold sea currents along southwestern Gondwana

We present the first systematic descriptions of the brachiopod faunas from the Huaraco Formation in Andacollo, Neuquén Province, Argentina. This study analyzes two fossil-bearing horizons and briefly describes their sedimentary paleoenvironment. Additionally, a stratigraphic analysis was performed to determine the correct position of the fossil-bearing horizons in the stratigraphic column. The first fossil-bearing horizon crops out in the Cerro San Pedro, where the identified taxa are: Linipalus andacolloensis sp. nov., Neochonetes (Neochonetes) granulifer (Owen, 1852), Gonzalezius naranjoensis Taboada, 2004, Linispinus cf. L. crassus Lazarev, 2008 and Leiorhynchus sp. The second fossil-bearing horizon crops out at Cerro Minas, with the identified taxa being: Tivertonia jachalensis (Amos, 1960), Lanipustula patagoniensis Simanauskas, 1996, and Rhynchopora sp. These faunas, restricted to the Andacollo Embayment, allow us to establish new biostratigraphic units, the Linipalus-Neochonetes and Tivertonia-Lanipustula biozones, respectively. The first biozone is included in the Marginovatia-Maemia Chronozone, recognized in central-western Argentina, with an earliest late Bashkirian age. This, in turn, could indicate the southernmost extent reached by the warm sea currents of the First Pennsylvanian Transgression. On the other hand, the Tivertonia-Lanipustula Biozone, which characterizes the fauna of the second fossil-bearing horizon, has a Moscovian age. The co-occurrence of T. jachalensis and L. patagoniensis indicates that the cold sea currents displaced to the north reached the Andacollo Embayment, located approximately 60°S. The faunistic succession of brachiopods from the Andacollo Embayment enriches our understanding of the paleobiogeographic scenario of the southwestern margin of Gondwana, highlighting a transition between warm to cold sea currents.