Climate and paleoceanography controlled size variations of calcareous nannofossils during the Valanginian Weissert Event (Early Cretaceous)

Abstract

Abstract Strata of Valanginian age (Early Cretaceous, 139.8–132.9 Ma) record a 1.5‰ positive carbon isotope excursion (CIE), the Weissert Event. It coincides with volcanic activity of the Parana-Etendeka large igneous province. Unlike the Mesozoic Oceanic Anoxic Events (OAEs), no organic-rich deposits documenting widespread perturbation of the marine carbon-cycle are associated with the Weissert Event. To study the impact of paleoceanographic changes in the Valanginian on calcareous nannofossils, this study analyzes coccolith size data of three species (Biscutum constans, Watznaueria barnesiae, Zeugrhabdotus erectus) from northern Germany and the western North Atlantic. Further it presents a new Valanginian carbon isotope record of organic material (δ13Corg) from northern Germany. The dataset records the Weissert Event CIE in the late Valanginian. At both locations biometric analyses reveal size decreases of B. constans coccoliths during the Weissert Event. A size reduction of ~1 μm has been observed for northern Germany (37°N) and of 0.4 μm for the North Atlantic (23°N). The different magnitudes of size decrease possibly reflect the different paleogeographic positions of the sites and the paleoceanographic response to the late Valanginian climate variations. Proxy data support a link between a humid climate with increased weathering, and the observed coccolith size variations. This impacted nannoplankton communities either through the availability of light or by eutrophication and, possibly, nutrient limitation. In addition to increased terrigenous input, emissions of the Parana-Etendeka volcanism possibly acted fertilizing. Furthermore, widely dispersed volcanic emissions possibly caused increased concentrations of toxic trace metals in the surface ocean which affected marine primary producers.