The Early Toarcian anoxic event in the westernmost Tethys (Subbetic): Paleogeographic and paleobiogeographic significance

A positive delta(13)C excursion reveals an oceanic anoxic event in the Subbetic, corresponding to the westernmost end of the Tethys during the Early Jurassic. This positive delta(13)C excursion exists in five stratigraphic sections consisting of Lower and Middle Toarcian pelagic sediments. The positive delta(13)C excursion in the Subbetic is located in the upper part of the Early Toarcian, serpentinus (approximate to falciferum) biozone, while in other Tethyan regions (Alps, Apennines, and Dinarides) it has been found in the lower part of the same biozone. The most significant positive delta(13)C excursion detected in the Subbetic is therefore about half a million years younger, although other relative peaks had been detected. This isotopic anomaly can be correlated with a maximum transgression that occurred earlier in the regions closer to the open sea of the Tethys ocean. Other features of the anoxic event (faunal crises and black-shale deposits), appear at different ages, related to the activity of the transgressive phenomenon that occurred through the Early Toarcian.