Palaeoenvironmental Evolution Recorded in the Villamartin Section (Spain) during the Coniacian-Santonian OAE 3: Comparison with the Olazagutia GSSP Section

The Coniacian-Santonian Ocean Anoxic Event 3 (OAE3) has long been considered to be local, diachronous and restricted to limited basins. However, some recent syntheses have suggested a global carbon isotopic perturbation with some correlatable isotopic events. Furthermore, the mechanisms leading to this perturbation are poorly understood, particularly in relation to the marine phosphorus cycle and climatic conditions in general. In order to investigate these issues further, a well-developed section will be studied: the Villamartin section (Spain). Compared to the official GSSP of Olazagutia, this section, located 150 km to the east, presents the advantage of a better biostratigraphic constraint (ammonites, inoceraminds, foraminifera, etc..). This study is based on mineralogy (bulk), geochemistry (stable isotopes, organic matter, phosphorus) to characterise changes in climate and primary productivity across the OAE3. The studied section from Villamartin is compared with the reference section from Olazagutia. Both sections, deposited under oxygenated conditions, record the δ13C patterns that characterise the Coniacian-Santonian OAE3 interval, in particular the positive carbon isotope excursions comprising the K2, Michel Dean and Bedwell isotopic events. Based on mineralogy, similar climatic changes are observed in both intervals. The climate shifted synchronously from relatively drier to warmer and wetter conditions above the Coniacian-Santonian boundary (C-S boundary) from the Michel Dean event to above the Bedwell event during the Early Santonian. Fluctuations in total phosphorus appear to have been mainly driven by changes in detrital input and consequently climate change.