Évolution lithostratigraphique, paléoenvironnementale et séquentielle du Cénomanien-Turonien inférieur dans la région du Guir (Ouest algérien)

Abstract

The lithostratigraphy, paleoenvironment and sequence stratigraphy of the Cretaceous succession outcropping at the southern foot of the Saharan Atlas (south-western Algeria) are discussed in this work. Our current study focuses on the analysis of fif-teen sections distributed along to the northern and southern limits of the Guir Basin, between the Ben-Zireg to the East and the Meridja-Boukais axis to the West. In this area, three lithostratigraphic forma-tions were identified and interpreted from an environmental and a sequential points of view: 1 - The lower “Grès rouges” Formation attributed to the Lower Cenomanian, is dominated by fluvial or coastal detrital deposits; 2 - The middle “Marnes à gypse inférieures” Formation assigned to the Lower-Middle Cenomanian is characterized by littoral setting with some storm influences, especially towards the base; 3 - The upper “Calcaires de Sidi Mohamed Ben Bouziane” Formation of upper Cenomanian-early Turonian in age, is represents a laterally extensive, shallow carbonate platform environment. The three formations constitute an overall transgressive megasequence built of a number of transgressive-regressive minor sequences. The opening of the deposits towards the North is confirmed by the organization of the lithostratigraphic units and by the Tethyan paleobiogeographic affinity of the echinoids and bivalves, and especially the occurrence of Neolobites vibrayeanus ammonite.