Stratigraphie du Jurassique supérieur du djebel Bechtout au Nord-Ouest de tiaret (Bordure sud-tellienne, Algérie); Comparaison avec le Bou Rheddou

Abstract

The study of the Upper Jurassic of the Bechtout Mountain (Southern Tellian border) allows us to distinguish five formations and to precise their age assignment owing to new collections of ammonites. Previous stratigraphic assignments are modified. Stratigraphic and sedimentologic data give evidence that each of the five Bechtout formations can be correlated with those encountered in the Bou Rheddou Mountain. As in the Bou Rheddou, first beds with ammonites are Middle Oxfordian in age. The Oxfordian «Ammonitico rosso facies begins in the Transversarium Zone up to the Planula Zone. The uppermost formation (Calcaires médians du Bou Rheddou) that begins in the Upper Oxfordian (Planula Zone) is essentially Kimmeridgian what causes us to exclude the time range Portlandian-Lower Cretaceous previously assumed.