Middle–Late Jurassic pelagic microfacies and depositional evolution at the Alpine Tethys margin: The Niedzica-Podmajerz section, Pieniny Klippen Belt, Poland
Major geological and ecological transformations, linked to the progressive opening of the ocean basins, extensional tectonics, and changes in pelagic sedimentation occurred across the Tethys during the Bajocian–Tithonian interval. This study reconstructs supra-regional palaeoenvironmental changes, based on pelagic deposits from the Niedzica-Podmajerz section of the Pieniny Klippen Belt, representing the Alpine Tethyan domain. An integrated dataset, including carbon isotope stratigraphy, biostratigraphy, microfacies analysis, and CaCO3 content, provides insights into sedimentary evolution along a submarine slope. The succession reflects a long-term deepening trend, beginning with neritic crinoid-dominated deposition, followed by the accumulation of deeper-shelf sediments, rich in Bositra sp., juvenile ammonites, and gastropods, and continuing into basinal deposits, characterized by Globuligerina, radiolarian, and Saccocoma-filamentous and Globochaete-Saccocoma assemblages. This facies evolution parallels global phenomena, such as the transgression at the Middle–Late Jurassic transition, a carbonate production crisis, ocean acidification, climate changes and circulation changes, linked to the opening of the Atlantic-Tethys Seaway. Specific intervals of the studied section were assigned to the Oxfordian (Fibrata Zone), the Kimmeridgian (Parvula Acme, Moluccana, and Borzai zones), and the Lower Tithonian (Pulla Acme, Malmica, and Cieszynica zones), on the basis of calcareous dinoflagellate cyst analysis. These intervals correspond to key δ13C events: the Late Callovian–earliest Oxfordian and Kimmeridgian positive events and a minor negative shift near the Kimmeridgian-Tithonian boundary.
