Biogeography of planktonic foraminifera and regional carbon isotope variations: productivity and water masses in late Cretaceous Europe
The first appearances of species of Marginotruncana (planktonic foraminifera) are found stratigraphically earlier in Boreal northwestern Germany than in the Tethys. Helvetoglobotruncana helvetica (Bolli) is rare in northwestern Germany and common in the Tethys. Its stratigraphic range is probably comparable between both areas. The biogeographic patterns are discussed with respect to influences of water depths (based on isotope evidence for the depth distribution of species of Hedbergella, Praeglobotruncana, and Rotalipora) and water temperatures. The regional variation of δ13C values of Cenomanian-Turonian pelagic carbonates was mapped for the European epicontinental basins and the southern European shelf (Helvetic zone of the Alps). The highest δ13C values (up to 5‰) were found in northwestern Germany and the eastern North Sea and are coincident with an upwelling zone numerically predicted by three independent climate models. Intermediate values in France and England (2–4‰) correspond to predicted weak upwelling. Lowest values occur in the Alpine Helvetic zone and the south German Regensburg area (1–2‰) and coincide with predicted absence of upwelling. The δ13C values are interpreted as indicators of increased biogenic productivity in the upwelling zone. Semiquantitative nannofossil data suggest abundance patterns influenced by latitude, neritic-oceanic gradients, and productivity. Observations agree with east-to-west wind-driven surface-current systems. Regional differences in nutrient supply and, subsequently, different primary productivity could have been a major factor controlling the evolution and the biogeographic distribution of planktonic foraminifera in Cenomanian-Turonian Europe.