Astronomical calibration of the OAE1b, Col de Pré Guittard, Vocontian Basin, France

The Cretaceous period was punctuated by several episodes of widespread deoxygenation of the sea floor referred to as Oceanic Anoxic Events. The OAE1b around the Aptian - Albian boundary is characterized by a series of black shales deposits, namely Jacob, Kilian, Paquier and Leenhardt levels. They are well documented in the Vocontian Basin, and their equivalent have been observed in different basins across the globe. Disagreement of more than a million of years exist about the timing of these events, leaving vast uncertainties about the causes of these recurring environmental changes. In order to better understand the relation between the climate perturbation and anoxic events during the Aptian-Albian period, we have focused on high-resolution investigations of magnetic susceptibility of Col de Pré-Guittard section, Drôme, France (GSSP of the Albian Stage; Kennedy et al., 2017). This section in the Blue Marls Formation consists of monotonous dark-grey marlstones interrupted by limestone beds and organic-rich layers. Spectral analyses were conducted on a magnetic susceptibility signal sampled every 5 cm. From this, we detected the record of the eccentricity, obliquity and precession cycles. We used the 100-kyr eccentricity cycles to construct an orbital time scale and shows that the interval starting above the Jacob level and ending above the Leenhardt level contains 21 repetitions of the 100-kyr eccentricity in the magnetic susceptibility data, leading to a duration of ca. 2.1 Myr. This duration is significantly shorter than the duration of 4 Myr provided by the current geologic time scale (Gale et al., 2020) but agrees with the U-Pb ages anchored to a δ¹³C_org curve from the High Arctic (Herrle et al., 2015).

References:

Gale, A.S., Mutterlose, J., Batenburg, S., 2020. Chapter 27: The Cretaceous Period, in: Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M. (Eds.) Geologic Time Scale 2020. Elsevier BV, Amsterdam, The Netherlands, pp. 1023–1086.

Herrle, J., Schröder-Adams, C.J., Davis, W., Pugh, A.T., Galloway, J.M., Fath, J., 2015. Mid-Cretaceous High Arctic stratigraphy, climate, and Oceanic Anoxic Events. Geology 43, 403–406.

Kennedy, J.W., Gale, A.S., Huber, B.T., Petrizzo, M.R., Bown, P., Jenkyns, H.C., 2017. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Albian Stage, of the Cretaceous, the Col de Pré-Guittard section, Arnayon, Drôme, France. Episodes 40, 177–188.