Latitudinal temperature trends in the northern hemisphere during the Early Cretaceous (Valanginian–Hauterivian)

Abstract

We present the first detailed stable isotope record (δ13C, δ18O) for the Valanginian (Lower Cretaceous) of the southern Boreal Realm. The observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well-dated sections in northwest Germany. A major positive carbon isotope excursion (CIE) of ~ 2‰ in the early late Valanginian documents a perturbation of the carbon cycle. This positive CIE, which is well known as the ‘Weissert Event’ in the Tethys, is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes (35°, 39°, 65° North). These findings suggest that the environmental changes indicated by the CIE in the early late Valanginian are synchronous, thereby pointing to a global control. The combined oxygen isotope data sets show long-term fluctuations of up to 7 °C with a cooling in the late Valanginian for both the southern and the arctic part of the Boreal Realm, whilst Tethyan data document only a ca. 1 °C cooling. Based on a reliable bio- and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the Valanginian and supports the idea that a combination of regional and global factors caused such shifts.