A Lacustrine Record for the Cretaceous–Paleogene Boundary—Yacoraite Fm., (Northwest Argentina)

The Yacoraite Fm. (Salta rift basin, Argentina) consists of a mixed carbonate–siliciclastic lacus- trine succession, interbedded with volcanic ash layers and organised in four third-order stratigraphic sequences. It is one of the few sites in South America that encompass the Cretaceous–Paleogene (K–Pg) transition, the position of which remains debated. Here, samples were collected along a depocentral stratigraphic section that was previously dated by zircon and carbonate U-Pb geochronology. The consistency between zircon and carbonate U-Pb ages, together with an accurate petrographic analysis, allowed the selection of carbonates potentially preserving the original geochemical signature. Accord- ingly, C-O stable isotopes were analysed from microbialites, oncoids, ooids and lacustrine cements. The available depositional age model from zircon geochronology defined the stratigraphic interval, potentially including the K–Pg transition. Within this interval, carbonates provided negative δ13C values consistent with the negative C anomaly recorded in various K–Pg sites elsewhere. Additionally, spherical particles resembling spherulites related to meteorite impacts were found in two samples. Accordingly, the K–Pg transition could be placed at the top of the second stratigraphic sequence. These findings encourage further investigation of the Yacoraite Fm. to gain insights into the response of South American terrestrial settings to the K–Pg palaeoenvironmental crisis.