Astronomical influence on climate change through the latest Maastrichtian: A high-resolution multiproxy cyclostratigraphic study at Gubbio (Italy).

Abstract:

A high-resolution multiproxy dataset is analyzed in the classic K-Pg section of Bottaccione near Gubbio (Italy), including magnetic susceptibility (MS), CaCO₃ content, δ¹⁸O and δ¹³C stable isotopes signatures. The stratigraphic interval covers the uppermost 7.2 m of the Maastrichtian. The proxy records provide insight on the paleoclimatological conditions of this interval, and make an evaluation of the potential imprint of astronomical climate forcing possible. Lithologic variations (MS and CaCO₃) are mainly reflecting the terrigenous influx (i.e. wind-blown dust) in the deep marine setting of Gubbio around the time of deposition. 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 Euro-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 controlled by 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 this tropical western Tethyan basin, both oceanic and terrestrial mechanisms depending on the precession amplitude modulated by eccentricity are proposed to explain the detected eccentricity periodicity in the δ¹³C record. The astronomical interpretation proposed in this study suggests that high eccentricity corresponds to relatively low δ¹³C and MS maxima values. Based on this phase relationship, an astronomical tuning of the Maastrichtian section is elaborated. The Maastrichtian part of magnetozone C29r has a duration of ~370 kyr. The duration of several biozones of the uppermost Maastrichtian is calculated. Tentative interpretations of the δ¹⁸O record and the astronomical interpretation of the MS record hint towards a warming event ~400 kyr prior to the K-Pg.