BOREAL EARLY TURONIAN CALCAREOUS NANNOFOSSILS FROM NEARSHORE SETTINGS-IMPLICATIONS FOR PALEOECOLOGY

Nutrients and sea-surface temperature were likely the most important paleoecological parameters that controlled the composition of Late Cretaceous calcareous nannofossil assemblages. The extinct nannofossil taxa Biscutum spp., Tranolithus orionatus and Zeugrhabdotus spp. are commonly thought to have preferred nutrient-rich surface waters. In order to test this hypothesis, calcareous nannofossils from two lower Turonian nearshore sections (Bochum, Herne; northwest Germany) were studied. These sections, which reflect a mesotrophic and perhaps cool paleoenvironment, contain well-preserved and highly diverse calcareous nannofossil assemblages yielding 92 species. Based on the first occurrences of Eprolithus eptapetalus, Quadrum gartneri, and Eiffellithus eximius, both sections have been assigned an early Turonian age. The most common taxa are Watznaueria barnesiae, Zeugrhabdotus spp., Biscutum constans, Prediscosphaera cretacea, and Tranolithus orionatus. In combination with previously published data from pelagic settings of the same area, these new findings allow the reconstruction of a nearshore-offshore transect. In proximal sections the abundances of B. constans and T. orionatus are higher than in coeval assemblages from distal localities. Zeugrhabdotus spp. shows no specific preference, whereas W. barnesiae is more common in open ocean settings. These findings suggest that B. constans and T. orionatus preferred more fertile and perhaps cooler nearshore habitats whereas W. barnesiae was adapted to oligotrophic and probably warmer paleoenvironments.