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The impact of chemical weathering on the Late Cretaceous climatic cooling
Silke Voigt1, Sandra J. Huber1,2,3, Schlidt Vanessa1,3, Mathis Schickedanz1, H.-Michael Seitz1,3, Jacek Raddatz1,3,4, Jorit Kniest1,3,4, Alexa Fischer5, Oliver Friedrich5, Andrew S. Gale6, Philip Pogge von Strandmann7
1Goethe University Frankfurt, Germany; 2Landesmuseum Darmstadt, Germany; 3FIERCE, Goethe University Frankfurt, Germany; 4GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; 5Heidelberg University, Germany; 6University of Portsmouth; 7Gutenberg University Mainz, Germany
After the mid-Cretaceous hothouse, the Earth cooled severely by more than 10°C in the late Cretaceous largely under ice-free conditions. Causes of the cooling are still poorly constrained, mainly considered as result of reduced lithospheric outgassing after the climax of LIP-related volcanism or effects of ophiolite weathering. Possible interactions with changes in chemical weathering intensity based on changes in paleo-landscape and the terrestrial biosphere, instead, received little attention so far. Here, we present a new chalk-derived Li-isotope record for the Late Cretaceous and discuss its baseline and multi-million year-scale variability in terms of plate tectonic reorganization and paleo-landscape change. Rising and high δ7Li values in the Turonian-Santonian and the Maastrichtian contrast with lower δ7Li values in the Campanian. The pattern of the δ7Li record matches with results of paleo-landscape modelling showing an overall decrease in erosion rates together with variable fluxes of dissolved weathering solutes in the tropics and warm temperate zones based on budgets of sediment erosion and deposition. Rising δ7Li values in the Turonian-Coniacian and latest Campanian-Maastrichtian correspond to prominent cooling phases in concert with sea-level falls and the reorganization of fluvial catchments indicating rather incomplete weathering reactions by increased formation of clay minerals. We suggest that plate tectonic reorganization supported the conversion of terrestrial habitats and ecosystems through the spread and evolution of angiosperms. The higher productivity of flowering plants in terms of water usage together with the increased activity of ectomycorrhizal fungi intensified chemical weathering and contributed to the ongoing reduction of atmospheric CO2.
