Palaeoenvironmental Reconstruction across the K/Pg Transition in Northern Patagonia (Argentina) Based on Benthic Foraminifera

Upper Maastrichtian to Danian benthic foraminiferal assemblages of the Jagüel Formation (eastern Neuquén Basin, Argentina) provide new insights into palaeoenvironmental evolution across the K/Pg (Cretaceous/Palaeogene) transition in northern Patagonia. The studied assemblages record the first Atlantic transgression that flooded northern Patagonia from the eastern coastal shelf towards the western volcanic arc, establishing shallow marine conditions during the Maastrichtian and Danian. Five benthic foraminiferal associations were defined based on species composition, and changes in the benthic fauna were evaluated to infer palaeoenvironmental changes across the K/Pg transition. The upper Maastrichtian associations (Tehuelchella caminosi, Gavelinella? neuquense – Planulina spp.) are characterized by low diversity, high endemism, and dominance of epifaunal morphogroups, suggesting stressed palaeoenvironmental conditions with limited organic matter at the seafloor. A mixed interval (Nonionella robusta – Anomalinoides spp. association) follows, marked by the co-occurrence of Maastrichtian and Danian species, interpreted as a within-habitat time-averaged deposit. The Danian associations (Cibicides spp. – Buliminella pseudoelegantissima, Valvalabamina sp. – Anomalinoides acutus) show higher diversity and are dominated by cosmopolitan neritic taxa of the Midway-type fauna, with mixed epifaunal and shallow infaunal morphogroups, indicating mesotrophic conditions and increased food availability. Endemism is the most distinctive feature of the foraminiferal assemblages at the K/Pg transition in northern Patagonia. Occurrence of endemic species in both Maastrichtian and Danian assemblages suggests that the Neuquén Basin occupied a relatively sheltered palaeogeographic position since the end of the Cretaceous. The presence of the stratigraphic hiatus encompassing Planktonic Foraminiferal Zones P0–Pα cannot be confirmed for the study section.