Citation:
Abstract:
A comprehensive study of the lithological, sedimentological and palaeontological characteristics of deposits belonging to the middle Turonian to Coniacian age in the Bellezma-Batna Mountains was carried out in order to establish a new biostratigraphic framework and interpret the evolution of the palaeoenvironment and sea-level fluctuation during this period. The studied sequences, exposed at Chaabet (Djebel Boukezzez) and Chihat, are mostly composed of marls and limestones. They are mainly composed of three formations: the Marly Limestone of the Chaabet Formation, the Upper Limestone of the Berriche Formation and the Marls of the Chaabet Formation. Biostratigraphic interpretations were based mainly on planktic and benthic foraminifera (H. helvetica, Marginotruncana cf. sigali, Discorbis turnicus, Nezzazatinella picardi HENSON), ostracods (Ovocytheridea sp., Brachycythere ekpo), and rudists Vaccinites praegiganteus, from the lower limestone member at both the Chaabet and Chihat sections, which is considered as a good indicator of the Upper Turonian age. Fourteen types of microfacies were identified and grouped into three facies assemblages- outer, middle, and inner ramp—based on sedimentological and palaeontological features. Sequence stratigraphic analysis establishes five sedimentary sequences that mark successive cycles of transgression and regression. A significant rise in sea level during the middle Turonian led to deep open marine conditions, followed by a regression in the late Turonian and early Coniacian that led to progressively shallower environments. These fluctuations reflect the combined effects of eustatic changes and regional tectonic movements.