Biostratigraphie et lithologie des s??ries serravallo-tortoniennes du massif du Dahra et du bassin du Ch??lif (Alg??rie). Implications sur la position de la limite serravallo-tortonienne

摘要

A lithological and biostratigraphical study was carried out on the Djebel Meni section (Dahra Mountain, Algeria) based upon 54 samples. According to the distribution of the main planktonic foraminifera species index we identified two subzones (Orbulina suturalis, O.a€ˉuniversa) attributed respectively to the Upper Langhian and Lower Serravallian stages and two biozones (Neogloboquadrina acostaensis, N.a€ˉhumerosa-N.a€ˉdutertrei) indicating a Tortonian age. These new data allow to reconsider the previous chronostratigraphic attributions and to point out the absence of the Upper Serravallian and of the base of the Tortonian. The transition features between the Serravallian and Tortonian deposits are better identified by comparisons with northern and southern margins of the Chelif basin. The precise age of the Tortonian transgression is specified.