Interhemispheric time scale for the Hauterivian and its implications for the carbon cycle in the Berriasian-Barremian times

Abstract

Discrepancies in the ages and durations of the Berriasian to Barremian stages still exist between geological data and the proposed geological time scale 2016 (Ogg et al., 2016; Lena et al., 2018). The Hauterivian Stage suffers from these discrepancies as its duration is proposed at 3.92 myr (Ogg et al., 2016), while astrochronology in the Tethyan area (SE France and SE Spain) led to a duration of 5.9 ± 0.4 myr (Martinez et al., 2015). In order to reconcile these durations, we investigated the Agrio Formation in the Neuquén Basin (Argentina). A total of 2,200 samples were collected every 0.25 cm and measured in magnetic susceptibility with a Kappabridge KLY-2. From spectral analyses realised on these MS signals, it appears that the 100-kyr eccentricity is continuously recorded throughout the Agrio Formation, allowing duration calculations. In addition, a new U-Pb age measured on zircons was provided in the upper part of the Agrio Formation using the CA-ID-TIMS method. Thus, four U-Pb ages are now available in the Agrio Formation measured with the U-Pb CA-ID-TIMS (Aguirre-Urreta et al., 2015, 2017). Notably, the astrochronological durations fit with three of the U-Pb ages. A fourth age appears 300 kyr elder than suggested by astrochronology, which may be due to protracted crystallization of zircons in the magmatic chamber. This new data in the Agrio Formation, together with correlations to the Tethyan area, highlights a revision to the duration of the Hauterivian Stage of 5.22 ± 0.11 myr starting at 131.29 ± 0.25 Ma and ending at 126.07 ± 0.25 Ma. The previous overestimate of the duration of the Hauterivian Stage was likely due to distortion of the 405-kyr eccentricity in the sedimentary record, as recent studies document (Laurin et al., 2017; Martinez, 2018). Thanks to these revised ages and previous astsochronological frameworks, we were able to revise the ages and durations of stages from the Late Berriasian to the Barremian-Aptian boundary. A synthesis of δ13C measured on belemnites (Martinez and Dera, 2015) indicate a clear 2.4-myr cycle in the carbon cycle record which fit with the main paleoceanographic events. Higher amplitudes of this cycle are notably observed during major volcanic episodes, suggesting that acceleration of the hydraulic cycle lead to a reinforcement of the long-Milankovitch cycles.