Biostratigraphy and paleoenvironment of the Danian/Selandian (D/S) transition in the Southern Tethys: A case study from north Eastern Desert, Egypt

Abstract

In the present study, the sedimentary succession of the Danian/Selandian (D/S) transition exposed at Wadi El Maheer, north Eastern Desert, Egypt, has been subjected to quantitative high-resolution planktic and benthic foraminiferal analysis. The succession is here subdivided into six planktic foraminiferal biozones, documenting a case of continuous sedimentation during the D/S transition. The planktic foraminiferal biozones are: the Danian Praemurica inconstans (P1c), Praemurica uncinata (P2), Morozovella angulata (P3a) and Igorina albeari/Praemurica carinata (lower most part of P3b) biozones and the Selandian I. albeari (main part of P3b) and Globanomalina pseudomenardii (P4a) biozones. The D/S boundary is marked by a distinctive organic-rich phosphatic shale layer (∼25 cm thick) within the upper part of the Dakhla Formation, corresponding to the last appearance datum of P. carinata (El Naggar). The concerned organic-rich phosphatic shale layer reflects a deficiency in the marine oxygen content with bottom water rich in organic matter during its deposition. It is characterized by changes in both planktic and benthic foraminiferal fauna. Across the D/S boundary, the planktic foraminiferal taxa of the nonspinose praemuricids were gradually replaced by nonspinose morozovellids and acarininids, whereas the Danian outer neritic-upper bathyal benthic foraminiferal taxa were substituted by inner-middle neritic ones indicating shallowing at the D/S boundary. The Selandian deposits are marked by planktic and benthic foraminiferal genera of outer neritic-upper bathyal conditions. Oscillation in the mean sea level during the D/S transition was probably due to a true eustatic change rather than to a tectonic origin.