The Valanginian "cold snap" and its impact on terrestrial environments - insights from plant biomarkers, stable isotopes and spore-pollen assemblages
Final Report Abstract
The Valanginian carbon isotope excursion (CIE) represents the first of several prominent and global δ13C anomalies, which characterize the early to mid-Cretaceous greenhouse world. In order to explain this positive CIE, multiple perturbations of marine ecosystems, climate and biogeochemical cycles have been proposed in the past. In this project, the response of terrestrial and marine environments to the changes associated with the CIE is investigated using biomarker data combined with spore-pollen records. A continuous 150 m thick section from the Vocontian Basin, SE France was chosen to study mid-latitude climate and the associated vegetation response at a high time resolution and has been compared in detail with a similar data-set from another mid-latitude site (Mid-Polish Trough, Poland). The establishment of an integrated stratigraphic framework including high-resolution δ13C chemostratigraphy facilitates the comparison of the novel biomarker and palynoflora records with existing marine-derived proxy data. Key findings of this study are the following. (1) Analysis of biomarker ratios across the CIE indicates rather stable oceanographic conditions and only minor changes in primary production, which contrasts with earlier scenarios involving high productivity and anoxia. (2) Spore-pollen records from the two studied midlatitude sites show very similar assemblages characterized by high abundances of nonsaccate conifer pollen and trilete spores. Stratigraphic trends in climate-sensitive indicators (spore-pollen ratio, Classopollis content) can be interpreted to reflect variations in moisture levels, most probably related to changes in overall rainfall patterns in the northwestern Tethyan realm. (3) Changes in organic matter composition from a marine towards a continental dominance across the CIE indicate significant variations in sea-level and/or continental input and highlight the importance of detailed organic matter inspection for the interpretations of paired carbonate-organic carbon stratigraphic trends (δ∆).
Publications
- (2012) No evidence for anoxia during the Valanginian carbon isotope event - an organicgeochemical from the Vocontian Basin, SE France. Global and Planetary Change, 92, 92-104
Kujau, A., Heimhofer, U., Ostertag-Henning, C., Gréselle, B., Mutterlose, J.
(See online at https://doi.org/10.1016/j.gloplacha.2012.04.007) - (2012): Climatic and environmental dynamics during the Valanginian carbon isotope event – Evidence from geochemistry and palynology, pp. 175. (PhD thesis Ruhr-University Bochum)
Kujau, A.
- No evidence for anoxia during the Valanginian carbon isotope event — An organic-geochemical study from the Vocontian Basin, SE France. Global and Planetary Change
Volumes 92–93, July 2012, Pages 92-104
Kujau, A., Heimhofer, U., Ostertag-Henning, C., Gréselle, B., Mutterlose, J.
(See online at https://doi.org/10.1016/j.gloplacha.2012.04.007) - (2013) Reconstructing Valanginian (Early Cretaceous) midlatitude vegetation and climate dynamics based on spore-pollen assemblages. Review of Palaeobotany and Palynology, 197, 50-69
Kujau, A., Heimhofer, U., Hochuli, P. A., Pauly, S., Morales, C., Adatte, T., Föllmi, K.B., Ploch, I., Mutterlose, J.
(See online at https://doi.org/10.1016/j.revpalbo.2013.05.003) - Palaeoclimate and palaeoenvironmental changes through the onset of the Valanginian carbon–isotope excursion: Evidence from the Polish Basin. Palaeogeography, Palaeoclimatology, Palaeoecology Volume 426, 15 May 2015, Pages 183-198
Morales, C., Kujau, A., Heimhofer, U., Mutterlose, J., Spangenberg, J. E., Adatte, T., Ploch, I., Föllmi, K. B.
(See online at https://doi.org/10.1016/j.palaeo.2015.03.013)
