Trends in temperature, salinity and productivity in the Vienna Basin (Austria) during the early and middle Miocene, based on foraminiferal ecology

Abstract

The Neogene Vienna Basin (VB) is a major hydrocarbon province with a long history of exploration accumulating extensive stratigraphic and structural information from numerous seismic and drilling programs. Based on the quantitative analysis of hundreds of foraminiferal samples from 52 drillings, we present the first continuous reconstruction of paleoenvironmental evolution of the VB from the early Miocene to the middle Miocene spanning 6.4 million years. Our analyses comprise reconstructions of sea surface temperature (SST), bottom water temperature (BWT), salinity, trophic levels, stress indicators, mode of life, feeding preferences and diversity indices (Fisher α, dominance and equitability) based on the transfer function for foraminifers of Hohenegger (2005, Palaeogeogr. Palaeoclimatol. Palaeoecol. 217, 115–130) and applied statistics (e.g. box plots and ternary diagrams). Bottom water temperatures indicate a cooling during the early and middle Badenian (Langhian), which seemingly contradicts the global warming of the Middle Miocene Climatic Optimum (MMCO) and a subsequent warming, which contrasts the expected trend following the cooling of the Middle Miocene Climatic Transition. Both trends are discussed as result of bathymetric evolution of the VB and intense upwelling during the early and middle Badenian. Repetitive alternations of Orbulina-rich assemblages, indicating a warm and stratified waterbody, with globigerinid-dominated assemblages, indicating upwelling and high productivity, are discussed in the light of a yet undescribed waxing and waning of upwelling intensity on a decadal to millennial scale. The applied formula for SST-calculations seems to underestimate real temperatures. Nevertheless, it reveals a distinct warming of about 3 °C from the early to the middle Miocene. In contrast to previous interpretations, we document normal marine conditions from the Ottnangian to the Sarmatian (middle Burdigalian to Serravallian) with a slight increase in salinity during the late Sarmatian.