Record of the Valanginian climatic changes in the Tethysian domain
Defended on the 7th November 2008
Funding: ministry of research
Supervisors: Jean-François Deconinck and Jean-Pierre Garcia
Started in October 2004
The Valanginian is characterized by a δ13C positive incursion, outlining an increase in productivity that started in the Campylotoxus zone and reached its maximum in the Verrucosum zone. In order to detail the environmental changes and their chronology, this work focused on three basins located in the Tethysian domain: the Vocontian basin, the Betic basin, and the Lombardian basin. The method consisted in the study of clay assemblages, organic matter geochemistry, and paleotemperature reconstruction, based on isotopic composition analyses of belemnites. From the data gathered, a scenario is proposed. The environmental perturbations seem to begin in the Campylotoxus zone. The end of this zone is characterized by an increase in productivity and preservation of organic matter.This led to a significant cooling. Ice, permanent or not, appeared at higher paléolatitudes. Their formation triggered a sea-level fall at the Campylotoxus-Verrucosum transition, leading to higher kaolinite contents in the three domains studied. The setting-up of upwellings also contributed to organic productivity. A positive feedback loop seems to have maintained relatively cold conditions until the beginning of the Hauterivian. The production of organic matter has likely been initiated by the conjunction of several factors. There was probably an upwelling system at the beginning of the Valanginian. Also, the aerial volcanism recorded at the beginning of the Campylotoxus zone could have played a significant role in the organic production through the fertilization of oceans.
Valanginian, Betic basin, Lombardian basin, Vocontian basin, bentonite, clay minerals, organic matter, paleoenvironments, paleotemperatures