Integrated astrochronology of the Barremian Stage (Early Cretaceous) and its biostratigraphic subdivisions

摘要

The ages and durations of the stages in the Early Cretaceous commonly show discrepancies of several million years when the Geologic Time Scale (2020) from the International Commission of Stratigraphy (ICS) and recently published radio-astrochronologic data are compared. Here, we provide an astronomical time scale for the Barremian Stage and its subdivisions based on spectral analyses performed on magnetic susceptibility and calcium carbonate content series in two sections studied located in the Subbetic Domain of southeastern Spain. The sections are tied to Tethyan ammonite and calcareous nannofossil zones, allowing detailed correlations with other sections in the Subbetic Domain and other basins in the Tethyan Realm. Eccentricity cycles are observed throughout the series and can be correlated with the eccentricity cycles observed in other sections in the Subbetic Domain, showing that the results are reproducible. Based on the number of 405-kyr eccentricity cycles in the study interval, and considering uncertainties linked to variations in the sedimentation rates within an eccentricity cycle, the duration of the Barremian Stage is calculated at 4.58(-0.29)(+0.15) Myr. From the astronomical time scale proposed here, together with recently published radio-astrochronological studies, the base of the Barremian Stage is dated at 125.98 +/- 0.21 Ma and the top at 121.40 +/- 0.34 Ma. The age of the Barremian/Aptian boundary differs from the ICS Geologic Time Scale 2020 by 3.6 Myr, but fits with the age of the base of magnetochron M0r recently deduced from a synthesis of radiochronologic data. The episodes of environmental change of the late Hauterivian-Barremian show an average pacing of 2.2 Myr, suggesting an orbital control on the expansion of oceanic anoxic conditions in the Tethys.