Korte, Christoph3; Hesselbo, Stephen2; Ullmann, Clemens Vinzenz3; Ruhl, Micha3; Thibault, Nicolas Rudolph3
1 Geology, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet2 University of Exeter3 Geology, Department of Geosciences and Natural Resource Management, Faculty of Science, Københavns Universitet
The occurrence of ‘ice ages’ within the overall warm Jurassic Period has been the subject of much discussion and not a little controversy. Recently it has been suggested on the basis of occurrence of glendonites in circum-Arctic basins that cold episodes took place in the Jurassic (Price, 1999; Rogov and Zakharov, 2010). Here we present new high-resolution oxygen isotope datasets from marine calcitic fossils of different European basins that indicate strong temperature fluctuations during the Pliensbachian-Bajocian time span. The already reported cold Late Pliensbachian episode with at least three pronounced oxygen isotope ‘Ice Age’ cycles, and the subsequent well known Toarcian Oceanic Anoxic ‘supergreenhouse’ Event is followed by very warm seawater temperatures in the late Toarcian. Moreover, a very pronounced and effective cooling occurred during the latest Toarcian and early Aalenian (Early-Middle Jurassic Boundary Event) resulted in substantial expansion of Arctic climates to palaeolatitudes as low as 45° and in distinctly cooler seawater temperatures in lower latitude European seas. At least the extensive cooling at the Early-Middle Jurassic Boundary Event was most likely driven by substantial changes in oceanic current patterns which were initiated by a major tectonic uplift that prevented the transport of heat to Polar Regions.