Résumé
The origin of the global temperature decrease that initiated the last greenhouse-icehouse transition about 90 million years ago still remains debated. Among the potential processes driving long-term climate evolution over million-year timescales, this study investigates the possible impact of the uplift-weathering connection on the late Cretaceous atmospheric CO2 drawdown and associated cooling.We analysed a marine sediment record from the Demerara margin, using Nd and Hf isotopes in clay-size detrital fractions (ΔɛHf(t)clay) together with bulk and clay mineralogy and major element abundances to reconstruct the evolution of tectonic uplift and chemical weathering intensity in northeastern South America during the late Cretaceous. Our data indicate that silicate weathering intensified on the northeastern South American margin during the middle Campanian and the Maastrichtian, concomitant with an uplift phase of the Guiana craton. We propose that the tectonic pulse highlighted by apatite fission track data, argon/argon dating and primary silicate mineral evolution, was accompanied by an accelerated chemical weathering, which presumably acted as a sink for atmospheric CO2. By contrast, during the earlier late Turonian to early Campanian, period of relative tectonic quiescence, climate most likely acted as the main driver controlling the evolution of chemical weathering intensity. The main phase of enhanced weathering induced by the uplift of the northeastern South American margin occurred during the Campanian, thereby postdating the onset of global seawater temperature decrease (late Turonian). By inference, this regional event is unlikely to have triggered late Cretaceous cooling but it may have acted as an additional factor stabilizing colder climate conditions at that time.