A paleoenvironmental analyses of benthic foraminifera from Upper Cretaceous – lower Paleocene oil shales of Jordan

This study is based on Maastrichtian and Danian oil shales of a cored well located in the Jafr Basin in central Jordan. Studied sedimentary rocks consist of alternations of monotonous bituminous marls, phosphatized marls, occasional dolomite, black chert, and limestone concretions. The main characteristics of these deposits are the high values of the total organic carbon (TOC) which fluctuate between 2.8 and 32.1 wt%. Benthic foraminifera were studied quantitatively in order to reconstruct environmental changes across the Maastrichtian and early Danian. Three clusters of benthic foraminifera, showing different assemblage compositions on the species level, were distinguished. Each of these assemblages is characterized by changes of diversity indices and abundances, indicating fluctuations of the bottom water oxygenation and organic matter fluxes. Water-depth preferences based on three associations and marker species of benthic foraminifera indicate an estimated paleodepth from middle to outer neritic (∼50–200 m) during the Maastrichtian and Danian. During the Maastrichtian, Anomalinoides praeacutus is the dominant benthic foraminifera species characterized by high abundances. A short decline of A. praeacutus, observed in calcareous nannofossil biozone UC18/19 (lower Maastrichtian), is compensated by an increase of Anomalinoides umboniferus. Abundance fluctuations of benthic foraminifera included in the Buliminacea (Sitella fabilis, Elhasaella alanwoodi, Neobulimina canadensis, Reussella aegyptiaca) are recorded from the assemblages. The taxonomic composition of the assemblages and the varying TOC values indicate low oxygen bottom-water conditions under high organic flux across the Maastrichtian. A moderate change is documented for the Danian, where A. praeacutus continues to dominate the assemblages, but Siphogenerinoides eleganta and Uvigerinella spp. are less common. These benthic associations along with a decrease of the TOC content suggest a gentle increase of the bottom water oxygenation with moderate organic fluxes.