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Provenance of the Miocene Siliciclastic Sequence in Southern Israel: Isotope Geochemistry of the Hazeva Formation

Abstract

In the early Miocene, the central Negev region of Israel was progressively covered by a thick sedimentary section defined as Hazeva Formation. This formation was deposited during a critical time as the Dead Sea Rift Valley was formed. Changes and unconformities along the siliciclastic sequence imply that tectonic progression occurred during deposition. The sources contributing the sediments comprising the Hazeva Formation have not been studied in detail. Nevertheless, it is well demonstrated that a large drainage system crossed Israel toward the Mediterranean while depositing the Hazeva Fm., and continued into the Eastern Levant basin. In the present work, the isotopic systems of Sr, Nd and Pb which are commonly used for provenance research were applied for studying the Hazeva Fm. sediments. Each isotopic system was applied on three mineral phases: clays, heavy minerals (Zircon, Tourmaline Rutile), and apatite. Pb isotopic composition and εNd values, point to a dual source; the first recycled ancient Cambro-Ordovician sandstone and the second weathering products of juvenile crust of the Arabian Nubian Shield (ANS). All three phases indicate some contribution of out of the ANS source which was already incorporated in the Cambro-Ordovician sedimentary cover on top of the ANS. The lowest Member of the siliciclastic sequence (Gidron Mbr.) exhibits enriched εNd values with ancient Nd model ages of 1.4 Ga. The following Members (Zefa and Rotem Mbrs.) show a shift in the isotopic compositions towards more juvenile (ANS) values. Hence the Gidron-Zefa contact is a large erosional unconformity depicting change in the tectonic processes and sources that took place during the Miocene. Below the Gidron-Zefa contact, the major source of sediments to the Hazeva Formation's basin is recycled Cambro-Ordovician sandstone while above this contact, the sequence is comprised of recycled sandstone and ANS juvenile erosional products. Thus, the Gidron-Zefa contact actually marks the unroofing and exposing the ANS on the east margins of the Red Sea. Since in the course of this study the iso-geochemical properties of the Hazeva Formation and its members were established, they can serve as indicator for Miocene sedimentation in the Levan Basin.