Palaeoenvironmental reconstruction of the Karpatian-Badenian (Late Burdigalian-Early Langhian) transition in the Central Paratethys. A case study from theWagna Section (Austria)

The Karpatian-Badenian (Burdigalian-Langhian, Early-Middle Miocene) transition is a key interval in the evolution of the Paratethys and the proto-Mediterranean Sea. We present here, based on the Wagna section (Styrian Basin, Central Paratethys), a study of a quantitative analysis of the microfossils (foraminifera and calcareous nannofossils) and a statistical treatment of data to reconstruct the palaeoenvironmental condition during this time. During the Karpatian, relatively deep water, cool conditions with a relatively high nutrient input prevailed in the Styrian Basin, as suggested by the high abundance of cool-water foraminifera and calcareous nannofossils. The Badenian was generally warmer, with a lower availability of nutrients, and was characterized by carbonate units and patch reefs and associated microfossil assemblages (e.g., Eponides spp.). Riverine plumes brought fresh water into the Styrian Basins during the Badenian and induced high productivity and the proliferation of species highly tolerant of low salinity such as Ammonia tepida. The passage from calcareous nannofossil Zone NN4 to NN5 is characterized by a reorganization of water masses and the transition from cooler and nutrient-rich to warmer and nutrient-poorer waters. Based on the microfossil abundance trends we interpret the planktonic foraminiferal species Globigerina tarchanensis as preferring cooler nutrient-rich waters and Reticulofenestra minuta as preferring warmer and nutrient-poor waters. The application of cluster analysis based on the Bray-Curtis Similarity and non-metric MultiDimensional Scaling (nMDS) adds important information to that obtained only from microfossil abundance curves, enabling identification of cryptic trends and correlation with sequence stratigraphy. This method may even complement biostratigraphic interpretation and support age attribution in the Paratethyan area, where marker species are missing.