Abstract:

focuses on the Cenomano-Turonian sediments observed in Thénièt El Manchar, the Bellezma-Batna Mountains, their evolution and the recognition of the main dating markers. The analysis (qualitative and quantitative) of the planktonic and benthic foraminifera and that of the ostracodes makes it possible to reconstitute the evolution of the paleo-environment and to estimate the variations of the relative paleo-depths. During the lower middle Cenomanian (Units IA, IB, IC and the lower part of ID), the microfaunistic associations are dominated by agglutinated benthic foraminifera testifying to a cold environment corresponding to the circalittoral deposits, in association with whole shells of ostracods indicating a weak hydrodynamism. In these deposits, the associations show a low to medium specific diversity and a more or less high faunistic richness, indicating trophic conditions and oxygenation considered normal. As for Unit ID (upper Cenomanian), it contains benthic foraminiferal biocenoses characteristic of warm and agitated seas. The return to deeper conditions, in the final terms of the Cenomanian and the beginning of the Turonian (Unit IIA), during a transgressive phase, is justified by the classical success of the events selected in North Africa, namely: The abundance of planktonic foraminifera, filaments and the drastic reduction of ostracofauna. These different elements open a reflection on the recorded paleo-environmental perturbations, the gradual disappearance of environmental stress and the return to relative normal conditions. These paleo-environmental interpretations agree with the data of the regional palaeogeographic context and highlight Tethysian features. Key words: sedimentology, geochemistry, paleo-environment, Cenomanian, Turonian, Batna, Algeria.