Bioestratigrafía y geoquímica de alta resolución del Evento Anóxico Oceánico del Aptiense inferior (OAE1a) en el Subbético de Jaénsección de La Frontera

Abstract

The early Aptian Oceanic Anoxic Event was a time interval characterized by increased organic carbon accumulation in marine sediments, notable sedimentary and biotic changes, and abrupt carbonisotope excursions indicative of significant major palaeoenvironmental changes. Detailed bio- and chemostratigraphic studies (TOC, δ13C, biomarkers) carried out in La Frontera Section (south of Jaén) allowed us to recognize and characterize the local expression of the OAE1a in the Subbetic of Jaén. The succession consists of black shales (Carbonero Fm.) overlying marls and marly limestones (Carretero Fm.). A hiatus, uppermost Barremian-earliest Aptian, separates both lithostratigraphic units. An abrupt negative δ13Corg excursion followed by a pronounced positive excursion is recorded in the black shales of the Carbonero Fm. The beginning of this positive excursion (C4 segment), representing the onset of the OAE1a, is located in the upper part of Hayesites irregularis nannofossil zone and near to the top of the Globigerinelloides blowi planktonic foraminifera zone. The deposit of black shales previously to OAE 1a and the biomarker association confirm the importance of the local factors in the development of anoxic conditions before and during the OAE1a at this site.