Environmental change and potential climate signal in the Burdigalian Upper Marine Molasse (North Alpine Foreland Basin)

• Foraminifera reveal Burdigalian environmental shifts and gradual shallowing. • Isotopes from planktonic foraminifera indicate warm surface waters (23–24 °C). • Isotopic offsets between foraminifera suggest water column stratification. • Erosive channel structures were likely formed by subtidal currents. • 405 kyr orbital cycle at 17.67 Ma may have influenced NAFB regional climate. The Oligocene–Miocene sediments of the North Alpine Foreland Basin (NAFB) provide a valuable continental archive for reconstructing paleoenvironmental change and exploring potential links to global climate cycles. This study focuses on middle Burdigalian deposits of the Upper Marine Molasse, specifically the widespread Neuhofen Formation (NH Fm.) at the Mitterdorf claypit (SE Germany), a key site for understanding regional environmental dynamics. We investigate paleoenvironmental shifts and the origin and timing of previously unexplored channel structures in the upper NH Fm. through detailed analysis of benthic and planktonic foraminiferal assemblages, along with oxygen and carbon stable isotope data. Eighteen samples were collected from two parallel vertical sections: one encompassing the sediment adjacent to a channel structure, and the other located within and beneath the sediment of the channel structure. Our results document a gradual shallowing of depositional environments from middle neritic (∼30–100 m) to inner neritic (∼0–30 m) conditions, under mostly warm surface-water temperatures of 23–24°C. Episodic freshwater influx, indicated by isotopic signatures and characteristic foraminiferal taxa, led to water-column stratification and elevated nutrient levels. Toward the top of the section, reduced isotopic offsets between benthic and planktonic foraminifera indicate weakened stratification in response to continued shallowing and potentially drier climatic conditions. The channel structures are interpreted as erosional unconformities, possibly formed by subtidal currents in a shallow marine setting. Integrating magnetostratigraphic age constraints from previous studies, our data support the interpretation that the global 405 kyr orbital eccentricity cycle around 17.67 Ma is recorded in the upper NH Fm., influencing regional climate conditions in the NAFB during the middle Burdigalian.