Astronomical calibration of the OAE1b from the Col de Pré-Guittard section (Aptian–Albian), Vocontian Basin, France

Abstract

A high-resolution spectral analysis was performed on magnetic susceptibility (MS) in the Col de Pré-Guittard section (CPG), Vocontian Basin, France to provide a new astronomical time scale of the Aptian–Albian transition and to explore the link between Milankovitch cycles and the occurrence of four laminated black shales events, namely Jacob, Kilian, Paquier and Leenhardt constituting the OAE 1b. The spectral analysis performed on the CPG section records the imprint of a strong predominance of the precession, and 100-kyr and 405-kyr eccentricity cycles. Based on the number of 405-kyr eccentricity cycles, the duration of the interval encompassing the Jacob to Leenhardt levels is calculated at 4.03 myr. The duration between Jacob, Kilian, Paquier and Leenhardt Events are respectively calculated at 1.55 myr, 1.62 myr, and 0.93 myr. The duration calculated for the occurrence of these events is not related to the Milankovitch cycles. However, these events are recorded near local maxima of the 405-kyr filter. Our results show that the 405-kyr eccentricity impacted the recurrence of anoxic levels in the Vocontian Basin, although additional factors, such as the emplacement of flood basalts or oceanic basaltic plateaus have contributed to the development of larger scale marine anoxia.