Environmental conditions during the late Oligocene transgression in the North Alpine Foreland Basin (Eferding Formation, Egerian) - A multidisciplinary approach

The North Alpine Foreland Basin (NAFB) comprises one of the most complete sedimentary records of the Oligocene and Miocene, driven by global sea-level fluctuations, vast sedimentary influx and tectonic movement. The locality of Unterrudling near Eferding (Upper Austria) exposes the largest succession of sedimentary deposits from the late Oligocene in the eastern NAFB. Additionally, this section shows the facies transition from the shallow-water Linz-Melk Formation to the deep-water Eferding Formation. In this work, the fossil fauna and flora of the Eferding Formation as well as its lithology are re-evaluated using a multidisciplinary approach to gain new insights into the palaeoenvironment, palaeoclimate, and palaeoecology. A transgressive sequence is documented using sedimentological and ichnological data. Furthermore, a correlation to the late Chattian transgressive Ch-3 sequence is suggested. The impact of rising sea-level on marine biota is shown in detail by analysing various groups (Bivalvia, Echinodermata, Anthozoa, Foraminifera, Chondrichthyes and Osteichthyes), with several newly reported species for the Eferding Formation. Moreover, washed in plant material was analysed for the interpretation of the terrestrial climate indicating mainly humid subtropical conditions. Finally, the presence of phosphatic nodules indicates eutrophication on the shelf environment and the possibility of upwelling currents.

Automated summary

The study re-evaluated the fossil fauna and flora, as well as lithology of the Eferding Formation in Upper Austria. It showed the impact of sea-level fluctuations on marine biota and terrestrial climate, with the presence of phosphatic nodules indicating eutrophication in the coastal environment.