Quantitative analysis and paleoenvironmental reconstruction of the middle Cenomanian deposits from southern Bellezma-Batna Mountains (northeastern Algeria)

Abstract

The middle Cenomanian deposits of the southern part of the Bellezma-Batna Mountains, northeastern Algeria, have been investigated to evaluate the response of Foraminifera to variations of paleo-bathymetry, oxygen, and salinity. The Djebel Azeb section, with a thickness of 40 m, is composed of a clay-marl mass interspersed with lumachellic limestone layers. It makes up the middle part of the ‘’Marnes de Smail’’ Formation. The Turrilites acutus Subzone of the upper part of the Acanthoceras rhotomagense Zone corresponds to the Aspidiscus cristatus Total Range Zone, and the Rotalipora cushmani Zone was recognized based on the study of ammonites, scleractinian and planktic foraminifera in this section. The statistical analysis of the foraminifera yielded only one assemblage of planktic foraminifera with globular chambers and trochospiral test belonging to the Cenomanian–Turonian; no association is typically restricted to the middle Cenomanian. The benthic foraminifera are poorly represented, belonging to the orders Textulariina, Lituolina, Trochamminina, Verneuilinina, Loftusiina, Orbitolinina, Miliolina, and Rotaliina. These foraminifera assemblages indicate that the bottom-water conditions during the middle Cenomanian were characterized by periodic changes in the oxygen and salinity. All planktic foraminifera species are opportunists related to poorly oxygenated, eutrophic conditions interspersed by a short interval of well-oxygenated environment with Planolites. The maximum abundance of Whiteinella and Muricohedbergella and the minimum amount of Planoheterohelix species within the Cenomanian of Djebel Azeb reflect dwindling palaeosalinity during this time, except for a slight increase in the middle of the section. Keywords: Foraminifera, corals, biostratigraphy, oxygen, salinity, Cretaceous.