Lake deposits as high-resolution archives of mid-Cretaceous equatorial climate variability: A combined approach including organic geochemistry and palynology

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The Cretaceous thermal maximum (KTM; Albian to Turonian) represents one of the best studied examples of greenhouse conditions in the geological record. The previously held view of an equable and stable mid-Cretaceous climate during this time of exceptional warmth is questioned by the occurrence of several short-term climatic perturbations (e.g. black shale events). Detailed information on Cretaceous climate fluctutations are mainly based on ¿ 18O studies from marine records of limited temporal resolution. This project will focus on continental lacustrine deposits (Araripe Basin, NE Brazil) to study equatorial climate variability during the onset of the KTM (Late Aptian to Albian) on a previously unobtained resolution. The existing biostratigraphic framework of the lacustrine succession will be refined by the use of chemostratigraphy based on ¿ 13C of land plant-derived biomarkers (long-chain n-alkanes) and fossil wood. Sequence-stratigraphic and palynofacies analysis of the lake deposits will provide detailed information on lake-level fluctuations. Additional information on changes in evaporation/precipitation and run-off patterns will be obtained from proxy data derived by organic and inorganic geochemical analyses (incl. C/N ration, Rock Eval, ¿ 13Corg, XRF scanning). The response of vegetation patterns to short- and long-term climate variability will be assessed by combining palynology and analyses of different land plant biomarkers. The proposed project will not only provide data on mid-Cretaceous environmental change on a unique resolution, it furthermore will significantly contribute to resolve the issue of the stability of warm climates.