OICC Press Iranian Journal of Earth Sciences 2228-785X 2026 07 14 Facies analysis and depositional environment of the Upper Miocene-Pliocene deposits (Aghajari Formation) in the Afrineh syncline, southwest of Lorestan 10.57647/j.ijes.2025.17557 EN Mostafa Sedaghatnia Department of Geology, Faculty of Sciences, Bu–Ali Sina University, Hamedan, Iran Behrouz Rafiei Department of Geology, Faculty of Sciences, Bu–Ali Sina University, Hamedan, Iran https://orcid.org/0000-0002-5384-7462 Bizhan Yousefi Yegane Department of Geology, Faculty of Sciences, Lorestan University, Khorram Abad, Lorestan, Iran Journal Article 2026 07 14 The Aghajari Formation is found across the Zagros Folded Zone. The purpose of this research is to investigate the depositional environment of the Aghajari Formation (Upper Miocene-Pliocene) in southwest Lorestan. Seven stratigraphic sections were selected in the Afrineh syncline. The Aghajari Formation, more than 500 meters thick, consists of conglomerate (to a lesser extent), sandstone, siltstone, mudstone, and shale. Field investigations resulted in recognition of eighteen lithofacies, which comprise three conglomerate lithofacies (Gm, Gp, Gt), nine sandstone lithofacies (Sp, St, Sm, Sh, Sr, Sfl, Sl, Slr, Sr (Fl)), four mudstone lithofacies (Fm, Fl, Fcf, Fl(Sr)), a gray shale lithofacies rich in planktonic fauna, and a bioclastic grainstone facies. The Skolithos facies was also identified. In the sandstones, two petrofacies, chertarenite and calclitharenite, were recognized. The lower part of the Aghajari Formation was deposited in a meandering river environment. Along with sea transgression, these deposits were overlain by the tidal flat deposits, and marine facies were deposited at the end of the sequence. The bioclastic grainstone and the gray shale are associated with shallow and deeper marine environments, respectively. The changes in the depositional environment in the lower part of the Aghajari Formation were caused by the sea-level change. Following the deposition of marine shale, due to sea-level fall and regional tectonics, the studied sequences underwent a marine regression, resulting in the formation of fluvial deposits. The depositional environment changes occurred during the Miocene and Pliocene.