Orbital control of the anoxic events in the Hauterivian and Barremian stages
Résumé
Episodes of Environmental Changes (EECs) correspond to reinforced greenhouse
conditions associated to modifications of the carbon cycle that punctuated the Early
Cretaceous. From the latest Hauterivian to the Barremian, three EECs occurred (the
Faraoni, Mid-Barremian and Taxy events). Despite the δ13Ccarb shows various trends
during these events, they are all associated to short-lived geographic expansion of
organic-rich deposits in the western Tethys. We propose here an astronomical
calibration of the latest Hauterivian-earliest Aptian from the Subbetic Domain (SE
Spain) to better constrain the pacing of these events and understand their forcing
mechanisms. The sedimentary series studied are composed of orbitally-forced
hemipelagic marl-limestone alternations. Magnetic susceptibility was measured every 7
cm using a Kappabridge KLY-3. Spectral analyses revealed the pervasive presence of
the eccentricity cycles. Interpretations are notably validated by lithostratigraphic and
biostratigraphic correlations between the sections. The duration of the Barremian
Stage is calculated at 4.25 ± 0.17 Ma. Anchoring this duration to recently published
radio- astrochronological time scales, the base of the Barremian Stage is dated at 125.91
± 0.06 Ma and the top of the Barremian Stage at 121.67 ± 0.16 Ma. The EECs of the
latest Hauterivian and Barremian stages show a pacing of 2.34 Myr, suggesting a
control of the long eccentricity cycle on the expansion of oceanic anoxic conditions in
the Tethys through changes in humid/arid cycle, weathering, sea level and fertilization
of the sea surface.