Foraminiferal and calcareous nannoplankton bioevents and changes at the Late Cretaceous–earliest Paleogene transition in the northern margin of Tethys (Hyżne section, Polish Carpathians)

Abstract

Foraminifera and calcareous nannoplankton from the Cretaceous–Paleogene (K-Pg) transition in the Hyżne section (Outer Carpathians, south-eastern Poland) show a relatively complete biostratigraphic record. Despite the absence of the Pa Zone in turbiditic deposits of the Polish Carpathians, the planktonic foraminiferal zones of the Late Cretaceous–Early Paleogene interval are well defined, including (1) the late Maastrichtian Abathomphalus mayaroensis Zone and its equivalents, (2) the earliest Danian Guembelitria cretacea second bloom Zone (P0 Zone), and (3) the top of the early Danian Parasubbotina cf. pseudobulloides (P1a) Zone. The foraminiferal events recorded in the studied section at the K-Pg transition are stratigraphically important. They include: (1) the interval with A. mayaroensis occurrence, (2) the interval with gradual disappearance of planktonic foraminifera from the most complex K-strategy forms, through the less specialized species to the large Heterohelicidae turnovers, and (3) the G. cretacea first and second blooms. Furthermore, the bloom of the opportunistic, benthic Bolivinita sp., the size reduction event, and the dissolution of the tests of the planktonic foraminifera are recorded. The K-Pg interval bioevents can be useful for better stratigraphic resolution of the flysch deposits of the Outer Carpathians. The nannoplankton event is represented by the appearance of Cruciplacolithus primus, which marks the onset of the return to more stable environmental conditions after the perturbations at the K-Pg boundary. The K-Pg boundary occurs within dark grey marly mudstones, above the upper boundary of the G. cretacea first bloom, and above the highest occurrence of the agglutinated foraminifera Goesella rugosa, at the top of the nannofossil CC 26 Zone, and below the deep-water agglutinated foraminifera (DWAF) dominance. The foraminiferal assemblages derive from different bathymetric zones corresponding to (1) the upper bathyal zone in the late Campanian (nannoplankton CC 22 Zone) and early late Maastrichtian (A. mayaroensis Zone), (2) the shelf margin in the latest late Maastrichtian (CC 26 nannoplankton Zone, G. cretacea first bloom), (3) the shelf margin in the earliest Danian (G. cretacea second bloom, NP1/2 Zone), and (4) the middle–lower bathyal depth, below a local foraminiferal lysocline and above CCD, in the latest early Danian (P. pseudobulloides Zone). As the foraminifera could have been redeposited by turbiditic currents, they do not necessarily show real bathymetric changes in the area of deposition. Such changes have not been observed in sedimentary features of the studied deposits. Foraminiferal and nannoplankton assemblages are typical of the “transitional zone” between the Tethyan and Boreal domains