Abstract

The Early–Middle Jurassic formations are regarded as important source rocks in the petroleum system of North Iraq. These formations contain papery shales between limestone and dolomite beds, and the major and trace elements of (early–middle) Jurassic shales in the Imbricated Zone, northern Iraq, were analyzed.In this study, the sediment provenance and tectonic setting were investigated, in addition to evaluating the conditions of paleok weathering in the source area.The elemental ratios in the Sehkaniyan and Sargelu shales, i.e., Al2O3/TiO2, Th/Sc, La/Th, Co/Th, (Gd/Yb)n, Eu/Eu*, and REE patterns, in addition to tectonic discrimination diagrams, indicated that they were derived from intermediate to felsic source rocks and deposited on an active collisional continental margin.REE patterns are characterized by significant LREE enrichment, negative Eu anomalies and relatively flat HREEs, which are typical of upper crustal rocks.The average Th/Sc ratios (0.52 and 0.67 for Sehkaniyan and Sargelu, respectively) of the studied samples are somewhat similar to those of upper crustal UCC 0.7 intermediate source rocks.The chemical index of alteration (CIA) (65 and 70 for Sehkaniyan and Sargelu, respectively) and the index of compositional variability (ICV) (1.02 and 1.46, respectively) represent immature compositions with the first cycle deposited in active tectonic settings.The Al2O3 - (CaO* + Na2O) - K2O (A‒CN‒K) triangular diagram of the shale suggested a moderate intensity of alteration (Figure 5).Owing to carbonate dilution, source–rock composition, sediment recycling, diagenetic alteration and tectonic activity, the intensity of weathering is moderate for both formations but increases from early to Middle Jurassic.