Five million years of life history record in an uppermost Cretaceous northern Tethyan marine succession, Eastern Carpathians (Romania): Microfossil content and palaeoenvironmental assessment

Abstract

New biostratigraphic investigations based on palynomorphs (mainly dinoflagellate cysts), foraminifera and calcareous nannoplankton recovered from eight geological sections indicate that the Hangu Formation near the Pluton-Pipirig area (Tarcău Nappe, Eastern Carpathians, Romania), previously assigned to the Senonian–Paleocene interval, includes only uppermost Cretaceous deposits. The palynological assemblages are moderately rich, with a total of 167 well-preserved taxa. The marine palynomorphs – essentially consisting of dinoflagellate cysts (dinocysts) – are dominated by peridinioid taxa, mainly recorded in upper Upper Campanian–lower Maastrichtian deposits, and by a high-diversity assemblage of gonyaulacoid taxa during the late Maastrichtian. Marine algae and dinogymnioid dinocysts were less common. The terrestrial palynoflora is dominated by fern spores and angiosperm pollen, with subordinate gymnosperm pollen. The foraminiferal assemblages include an assortment of well-preserved agglutinated forms, present mainly in the upper Maastrichtian deposits, whereas calcareous benthics and planktonic foraminifera are rare and poorly preserved. Calcareous nannoplankton assemblages are also rare, often represented by two taxa (Micula staurophora and Watznaueria barnesiae); certain important biostratigraphic markers were found to be reworked in the analyzed deposits. Age assignments for the studied sections were mainly provided by dinocysts, through the identification of significant marker taxa and comparisons with well-calibrated Campanian–Maastrichtian dinocyst assemblages from well-dated sections and stratotypes, located mostly in the Northern Hemisphere.Indices such as particulate organic matter (POM) composition, the relative abundance of dinocyst eco-groups, as well as agglutinated foraminiferal morphogroups, were used to reconstruct the depositional environments of the Hangu Formation from the studied area. The upper Upper Campanian–lower Maastrichtian deposits from the Pluton-Pipirig sections were mainly deposited in neritic marine conditions, although occasional redeposition of the sediments transported by turbidity currents towards deeper water settings is not excluded, either. The depositional environments evolve towards outer neritic to distal (bathyal) during the late Maastrichtian, as indicated by palynofacies constituents and by high frequencies of gonyaulacoid dinocysts and deep-water benthic foraminifera.