The early Aptian oceanic anoxic event in the Maestrat Basin (NE Iberian Chain)

Resumen

High-resolution d13Ccarb curves are reported for three lower Aptian marine shallow-water sedimentary successions located in the Maestrat Basin (E Iberian Chain; E Spain). The resulting carbonisotope data show similar global d13Ccarb trends already observed in pelagic and marine shallow-water lower Aptian worldwide deposits by several other authors as well as the widely known d13Ccarb positive excursion corresponding to the onset of the oceanic anoxic event (OAE 1a). These global C-isotope anomalies allowed us to make an accurate geochemical correlation between the three studied Iberian sections. As suggested by numerous authors, the resulting correlation demonstrated the efficiency of the carbonate carbon-isotope geochemistry as a stratigraphic tool. In addition, a high-resolution ammonite biostratigraphy was carried out along the three studied outcrops allowing the recognition of three different ammonite biozones: Deshayesites weissi, Deshayesites deshayesi and Dufrenoyia furcata. This precise biostratigraphic analysis permitted us to constrain the OAE 1a interval inside the Roloboceras hambrovi horizon (Deshayesites weissi biozone)