Lithostratigraphic analysis of the Turonian-Coniacian Bireno and Douleb carbonate Members in Jebels Berda and Chemsi, Gafsa basin, central-southern Atlas of Tunisia

The Turonian-Coniacian series of Bireno and Douleb Members (carbonate Members of the Aleg Formation) have been examined on their sedimentology, stratigraphy and faunistic contents to provide new insights into the paleoenvironment evolution and sea-level changes in the Gafsa basin. At this scale, both the Turonian-Coniacian series are mainly made of marls and limestones and locally include evaporites. In this paper, ostracods together with benthonic and planktonic foraminifers, collected from the Upper Cretaceous series of Berda and Chemsi mountains, are used to provide some chronostratigraphic precisions (age and limits) of these lithostratigraphic units. Accordingly, four lithostratigraphic units, belonging to the Aleg Formation, were recognized following an ascending order; the Annaba Member (Lower Turonian), the Bireno Member (Lower Turonian-Middle Turonian), the Lower Aleg Marls (Middle Turonian-Upper Turonian, Jebel Chemsi and Upper Turonian-Lower Coniacian, Jebel Berda) and the Douleb Member (Coniacian). These units are overlaid by the Upper Aleg marls Santonian in age. The recognized microfacies are interpreted as a shallow marine deposit of a lagoonal environment, shallowing upward from supratidal to subtidal settings with scattered rudistic patch reefs. The corresponding carbonate sediments were affected by several diagenetic stages starting at the sea floor (early diagenesis), continuing near the surface (meteoric diagenesis) and ending in the subsurface (burial diagenesis). (C) 2014 Elsevier Ltd. All rights reserved.