Microfacies and depositional environments from the Upper Cretaceous of Bourzal Formation (Zab Mounts, Biskra, Eastern Saharan Atlas, Algeria)

Abstract

The new introduced Upper Cretaceous (Cenomanian-Turonian) Bourzal Formation is about 235-m thick, made of carbonate, marl, and gypsum alternation, and is cropping in the section of the Zab Mounts (Biskra, eastern Algerian Saharan Atlas). It is subdivided into two informal units: (1) unit A, which is composed of 125 m thin to thick bedded limestone with interbedded marls and gypsum beds. (2) Unit B, consisting of 110 m fossiliferous marl–limestone-dolostone alternations. The field inspections, along with detailed microscopic examination, have led to the identification of eight microscopic standard facies, regrouped in three facies belts: tidal flat, lagoon, and shoal environments. They represent a homoclinal ramp (inner ramp), suggesting also changes in depositional depth.