Lithostratigraphic evolution, facies analysis and depositional environment of the Cenomanian-lower Turonian in the Guir area, Southwestern Algeria

Fifteen stratigraphic sections located in different parts of the Guir basin (Southwest Algeria) have been measured bed-by-bed and sampled in great detail, to study the stratigraphy, describe and interpret the facies and characterize the depositional environment of the Cenomanian-Turonian succession. Based on their stratigraphic ranges, lithofacies, regional distributions and depositional settings, the Cenomanian-Turonian succession is subdivided into three lithostratigraphic formations that are bounded by a regional scale discontinuity: the “Grès rouges” Formation attributed to the lower Cenomanian; the “Marnes à gypse inférieures” Formation assigned to the lower-middle Cenomanian and the “Calcaires de Sidi Mohamed Ben Bouziane” Formation placed in the upper Cenomanian-lower Turonian. Analyses of litho-, bio-, and microfacies resulted in the recognition of 25 facies types for this succession. These facies types have been grouped into seven facies associations (AF1 to AF7). The facies represented range from clastic, to evaporitic to carbonate, and were deposited in four major depositional environments: fluvial, siliciclastic costal, sabkha and homoclinal carbonate ramp settings. The main factors controlling depositional environments were eustatic sea-level fluctuations combined with environmental influences such as autochthonous carbonate productivity and siliciclastic supply.