Chapter 5 - Sedimentology and Geochemistry of the Late Miocene–Pliocene Succession in the Fars Interior (SW Iran): Implications on Depositional and Tectonic Setting, Provenance and Paleoweathering in the Zagros Basin

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The Aghajari Formation, also called as Upper Fars, developed throughout the Zagros Basin during the Late Miocene–Pliocene. This paper presents the sedimentology, petrography, and geochemistry of the Fars Interior (SW Iran) section of the Aghajari Formation. The section shows the development of 11 lithofacies and six architectural elements. By combining the evidences from lithofacies analysis and architectural elements, the depositional setting of the Aghajari Formation is determined to be sandy meandering fluvial system. The paleocurrent direction determined by sedimentary structures (cross-bedding and imbrications) shows an NW–SE trend. Petrographic study revealed predomination of lithic arenite character. Model analysis suggested recycled orogen (quartzose and transitional recycled) tectonic provenance for these deposits. The sources of quartz are recognized to be low-grade and middle- to high-grade metamorphic rocks. In addition, quartz-rich (sedimentary) and granite/gneiss are determined as parent rocks for the Aghajari Formation deposits. The Aghajari Formation sandstones are characterized by low to moderate SiO2 contents, variable abundances of major element, and a fairly high proportion of ferromagnesian elements. Discrimination diagrams of sedimentary provenance, tectonic setting, and major and trace elements geochemistry, show that the Aghajari Formation sediments were derived from felsic and intermediate sources. The chemical index of alteration (53.8–65.8) showed moderate to highly weathered source rocks. The major and trace element geochemistry indicate an active continental margin for depositional setting of Aghajari Formation.