LITHOSTRATIGRAPHIC REDEFINITION OF THE CHOTA FORMATION IN THE BA-GUABASIN(NORTHEASTERNPERUVIANANDES)ANDITSIMPLICATIONSFORTHE CRETACEOUS–PALEOGENE BOUNDARY.
Chacaltana C.; Valdivia W.; Tejada-Medina L.; Batezelli A.; Sedorko D.; Reyes J.; Langer M.; Gamarra-Cuba M.; Ramirez-Ampuero A. · Serie Correlacion Geologica (2026) · DOI: 10.5281/zenodo.21534936
Resumen
A lithostratigraphic redefinition of the Chota Formation in the Bagua Basin, located between approximately 4° and 7° S in northeastern Peru, is proposed based on new geological and paleontological evidence supporting the recognition of two distinct lithostratigraphic units. The proposal is founded on newly documented fossil assemblages that enable the regional identification of a welldefined intraformational stratigraphic discontinuity. This discontinuity separates a lower detrital unit, composed predominantly of sandstones that become conglomeratic toward the top and containing Upper Cretaceous crocodilians and nonavian dinosaurs, from an upper unit consisting of detrital successions dominated by paleosols (Vertisols), calcareous sandstone beds yielding turtles and medium-sized placental mammals (Pyrotheria) of Paleocene–Eocene age, together with mudstones containing charophyte (Charophyta) and ostracod fossils. Although both successions display a characteristic reddishbrown coloration, they differ markedly in their lithological and paleontological attributes and are herein redefined as the Pongo de Rentema Formation and the Quebrada Seca Alta Formation, respectively. Collectively, these units record a stratigraphic interval spanning the Cretaceous–Paleogene (K–Pg) boundary and document major changes in the geological evolution of the Bagua Basin. Accordingly, the Chota Formation is abandoned in this basin, and the Pongo de Rentema and Quebrada Seca Alta formations are formally established as new lithostratigraphic units. Their distinctive lithological and paleontological characteristics allow recognition of two successive geological intervals corres-ponding to the Upper Cretaceous and the Paleogene.