SamenvattingThe classical stratigraphic sections of Gubbio (Italy) provide a unique opportunity to study Jurassic to Miocene paleoclimatology. In this thesis, a high-resolution multi-proxy dataset is studied that contains magnetic susceptibility, CaCO3-content, oxygen and carbon stable isotopes. The stratigraphic interval consists of the uppermost 7.2 meters of the Maastrichtian (latest Cretaceous), the Cretaceous - Paleogene boundary (K-Pg boundary), and the lowermost 14 meters of the Danian (earliest Paleogene). The collected proxy records provide insight in the paleoclimatological conditions of this interval, and make it possible to evaluate the potential imprint of astronomical climate forcing in these records. Lithologic variations, represented by the magnetic susceptibility and CaCO3-content proxies are mainly caused by dust input at the deep marine setting of Gubbio around the time of the Cretaceous - Paleogene asteroid or comet impact. The availability and transport of this dust is hypothesized to be a function of the vegetation cover on large source areas in the African and/or Asian continents. This vegetation cover would be susceptible to changes in the monsoonal circulation intensity and patterns. The monsoon and the Intertropical Convergence Zone (ITZC) are determined by insolation, which in turn is depended on the precession and obliquity. A vegetation-cover-threshold mechanism is proposed to explain eccentricity related periodicities in the MS record. Together with the dust influx in the paleo-Mediterranean, both oceanic and terrestrial mechanisms depending on the precession amplitude modulated by eccentricity are proposed to explain the detected eccentricity periodicity in the ?13C record. The astronomical interpretation made in this study suggests that high eccentricity corresponds to relatively low ?13C and MS maxima (? CaCO3 minima) - and vice versa. Based on this phase relationship an astronomical tuning of the BOT section is presented. The Cretaceous part of magnetozone C29r has an estimated duration of 370 kyr. The duration of several biozones of the uppermost Maastrichtian is calculated. Tentative interpretations of the ?18O record and the astronomical interpretation of the MS record hint towards a warming event some ~400 kyr prior to the K-Pg.
Several aspects make an astronomical tuning of the Danian interval of this study more challenging. Firstly, the sedimentation rates are not constant. Secondly, the Eugubina limestone and DAN-C2 hyperthermal event in the first meter of the Danian are not well enough understood. Thirdly, there is the possibility that the astronomical forcing was not fully recorded in the COH sediments because of the large climatic perturbations after the K-Pg. For these reasons no conclusive tuning for this section is proposed in the framework of this thesis.
|30 jun 2014
|Philippe Claeys (Promotor)