Microfacies and biostratigraphy based on calpionellids and calcareous dinoflagellate cysts across the Jurassic/Cretaceous boundary, western Neuquén Basin, Baños Morales and Lo Valdés formations, Río Volcán section, Central Chile

This study presents the first biostratigraphic analysis of calpionellids and calcareous dinoflagellate cysts in the Tithonian–Hauterivian Baños Morales and Lo Valdés Formations, which crop out in the Principal Cordillera of central Chile (34°S). Additionally, it provides a preliminary interpretation of the sedimentary environment based on microfacies analysis. The Baños Morales and Lo Valdés Formations form an ∼800 m thick succession of basinal marlstone, sandstone and limestone, shallow-water limestones and thick intercalations of lavas, which developed on the western margin of the Neuquén Basin. The Baños Morales and Lo Valdés Formations are characterized by an abundant fossil content, a remarkable stratigraphic continuity along several hundred meters, and include the Jurassic/Cretaceous boundary. The detailed study of its type section (Baños Morales town, Volcán river), allowed the identification of a moderately to poorly preserved association of seventeen calpionellid species and fifteen calcareous dinoflagellate cyst species and four subspecies. Six calpionellid biozones (Chitinoidella, Crassicollaria, Calpionella, Calpionellopsis, Calpionellites and Tintinnopsella) and eight calcareous dinoflagellate cyst biozones (Committosphaera pulla, Crustocadosina semiradiata, Colomisphaera tenuis, Colomisphaera fortis, Stomiosphaerina proxima, Stomiosphaera wanneri, Colomipshaera vogleri, and Colomisphaera conferta), already known from the Tethyan and Andean regions, have been identified, enabling a more precise stratigraphic calibration for the Baños Morales and Lo Valdés Formations, as well as their stratigraphic correlation with the stratigraphic units of Argentina and international time scales.