Provenance, tectonic setting and source area-paleoweathering of sandstones of the Bahariya Formation in the Bahariya Oasis, Egypt: An implication to paleoclimate and paleogeography of the southern Neo-Tethys region during Early Cenomanian

The Lower Cenomanian Bahariya Formation forms the most prolific hydrocarbon reservoir in the Western Desert of Egypt, and represents a good example to illustrate the paleogeographical evolution of the southern Neo-Tethys region during the Early Cenomanian. It is also particularly important for its diverse vertebrate fauna including dipnoans, chelonians, crocodyliforms, squamates, plesiosaurs, decapod crustaceans and dinosaurs, which reflect sustained regional biostratigraphical and paleoenvironmental significance. It consists of fluvio-marine siliciclastic rocks (sandstones and mudrocks). A multidisciplinary approach of fieldwork, petrography and bulk-rock geochemistry of the sandstones of the Bahariya Formation was used to constrain their provenance, tectonic setting, source area-paleoweathering and paleoclimatic conditions within the Neo-Tethyan realm. Petrographically, the studied sandstones are mainly of quartz-arenite type with subordinate sub-arkose and sublithic ones. Quartz types, trace and rare earth element concentrations and ratios indicate the sandstones were sourced from felsic granitic rocks with a rare contribution of felsic gneisses. The modal analysis reflects that the sandstones are mainly of cratonic interior and quartzose recycled tectonic provenance. The chondrite-normalized REE distribution pattern of the Bahariya sandstones are characterized by enriched LREE and flat HREE similar to those of UCC with negative Eu/Eu* anomalies. Major and trace elements of the sandstones suggest their deposition on a Neo-Tethys passive continental margin related to the Early Cretaceous rifting. The weathering indices (CIA, CIW, PIA and ICV) and the Al2O3-(CaO+Na2O)-K2O diagram suggest moderate to severe chemical weathering in the source area under semi-humid to humid climatic conditions. In conclusions, the Bahariya sandstones could be sourced by a fluvial reworking of moderately- to intensively-weathered Precambrian granites and gneisses of the surrounding Gebel Uweinat Massive (at the southwest of the study area), and were deposited in a low-lying basin (Bahariya area) of a Neo-Tethys passive continental margin. In a broad interest, results of this study play an important role in reconstructing the paleoclimatic conditions and paleogeographical evolution of the southern Neo-Tethys region during the Early Cenomanian.