Paleoenvironmental evolution in the late Neogene Lower Chelif basin based on benthic foraminifera (North-western Algeria)

Abstract

The study of benthic foraminifera from the Messinian pre-evaporitic interval of Djebel Meni section (Northern west) allowed the reconstruction of surface and bottom-water conditions in the West Mediterranean during the interval that preceding the Messinian Salinity Crisis. Our data point out to three-steps paleoenvironmental evolution. During the first stagepresents an assemblage with high diversity of benthic foraminifera. This features materialized by the dominance of the oxyphilic taxa, a well-ventilated bottom-water conditions beside a considerable bathymetric and well exchanges of ocean water with and into Chelif basin. During that period, this interval is consideredasan outer shelf to slope environment. The second stage corresponds to the middle part of the section. It refersto moderate decrease of oxygen content which seems to be the main factor that leads to this stage, since the diversity of benthic foraminifera species decreases. Where the third stage witnessed rapid decrease in number of taxa corresponding to the upper part of the section with a common presence of barrens intervals of benthic foraminifera. This interval is dominated by the stress-tolerant taxa Bolivinaspp, Buliminaspp and Rectuvigerinasppgenus as dyoxic species with high salinity conditions. The interval refers to a oxygen depletion that probably caused by the restriction of Mediterranean water exchanges contributing to the stagnation of bottom water as shallowing environment referring to inner to middle shelf.