Abstract
Provenance and tectonic setting of the Late Lower Cretaceous (Albian) sandstones in SW Iran have been interpreted on the basis of geochemistry (major and trace elements) of 35 samples from Iranian offshore oil fields (Soroosh, Nowrooz, Foroozan and Hendijan). Geochemically, trace-element concentrations, such as La, Th, Sc and Zr, and ratios, such as La/Sc, Th/Sc, La/Co, and Th/Co, of sandstones from Kazhdumi Formation at four localities indicate that they were derived from felsic source rocks and deposited in a passive continental margin. Most major and trace element contents of Kazhdumi sandstones are generally similar to upper continental crust (UCC) values. However, some samples are depleted in major and trace elements (such as K2O, Na2O, Sr and Ba) relative to UCC, which is mainly due to absence or smaller amount of Na-rich plagioclase and K-feldspar and also paucity of clay minerals, which is possibly due to intense weathering and recycling. Enrichments in Zr, negative Sr anomalies and Th/U ratios higher than 4 for Kazhdumi sandstones are further evidence for recycled sources. The study of paleoweathering conditions based on chemical index of weathering (CIW) indicates a moderate to intense weathering of first cycle sediments, or it may alternatively reflect recycling under semi-arid to semi-humid climate conditions in Kazhdumi sandstones. The results of this study suggest that the main source for the Kazhdumi sandstones is likely located in uplifted shoulders of a rifted basin (Neo-Tethys) in its post-rift stage (Arabian basement).
Highlights
The goal of provenance studies is to deduce the characteristics of sediment source areas
The major and trace element concentrations of Kazhdumi Formation at Soroosh, Nowrooz, Foroozan and Hendijan oil fields are listed in Appendix 1 and Appendix 2, respectively
Shales are higher in K2O, Fe2O3 and TiO2 contents than sandstones, which reflect their association with clay-sized phases [29] [30]
Summary
The goal of provenance studies is to deduce the characteristics of sediment source areas. Trace elements (e.g., Nb, Ni, V, Co, Y, La, Th, Sc and Zr) in clastic sedimentary rocks are considered to be immobile under conditions of weathering, diagenesis and moderate levels of metamorphism, and are commonly preserved in sedimentary rocks [12] [13]. Such trace elements might constitute well-established provenance and tectonic setting indicators [12] [14]. The objectives of this study are to evaluate the source area composition, tectonic setting and paleoweathering conditions during deposition of the Kazhdumi Formation. The data will help us to expand and improve models for the evolution of the Late Lower Cretaceous (Albian) siliciclastic rocks of the Middle East
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