The paleontological analysis of the fauna of ammonites collected in the marl-limestone series of the Pliensbachian and The Toarcian of the Es-Saffeh Mountains (Tiaret, western Algeria) brings new data to the Oceanic Anoxic Event of the lower Toarcian (T-OAE). During this time interval, hypoxia is characterized by a significant disturbance of the global carbon cycle marked by a negatve excursion of the isotope δ¹³C, δ¹⁸O and a increase in organic carbon content (TOC). Benthic life almost completely disappears and microfauna (foraminifera) is absent, it should however be pointed out that the few specimens of small size (swarf forms) collected in the marly levels and well identified (ammonites), attributed to the microshell forms; can be interpreted as a response to the conditions of the reducing environment during the Lower Toarcian, particularly at the end of the Polymorphum Zone and the beginning of the Levisoni Zone.