Univrsity of Tehran Press Geopersia 2228-7817 15 2 2025 11 29 Geochemical characteristics and paleogeographic analysis of the Late Cretaceous (Ilam Formation) in the Lorestan subzone, Zagros area, Iran - 253 271 100921 10.22059/geope.2025.389942.648804 EN Atefeh Yeganeh Moghadam Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran Asadollah Mahboubi Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran Mohammad Hossein Mahmoodigharaie Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran Reza Mousavi Harami Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran Journal Article 2025 02 04 The Ilam Formation in the Zagros basin, southwest Iran, is a rich petroleum reservoir rock that possesses considerable exploration potential. This study provides valuable insights into the paleoenvironmental and paleogeographic conditions of the Ilam Formation using sedimentological and geochemical analysis as well as sea-level changes during the Late Cretaceous time (Late Santonian-Late Campanian) in the Lorestan area. Based on petrographic analysis, four microfacies were identified in the studied area (Mehdi Abad section) in the Ilam Formation that were deposited in an outer ramp setting, from middle neritic to bathyal, in a homoclinal ramp. Sequence stratigraphic analysis led to detect two transgressive system tracts and one regressive system tract. In the current study, the paleogeochemical signatures, using redox-sensitive elements, show strong evidence of declining oxygen level during the Late Santonian and Late Campanian; however, increase of oxygen levels only observed during the Early Campanian time. The changes in oxic-anoxic conditions in the depositional basin during deposition of the Ilam Formation can be correlated with the final phase of the oceanic anoxic event in the Cretaceous. However, the closure event of the Neo-Tethys Ocean and subsequent changes in fault mechanisms and basin structure were causal mechanisms of oxic-anoxic conditions during this period. https://geopersia.ut.ac.ir/article_100921_d5b0e5e1abdc2044cce9b93bbc6c0ae0.pdf