The Amiran Formation with the age of Upper Maastrichtian - Paleocene is spread of in Lorestan region, Zagros sedimentary basin. The purpose of this research is to investigate the primary mineralogy and the type of diagenesis systems of the carbonate units of the Amiran Formation in southwest of Lorestan based on elemental geochemistry and lithological studies. In this regard, a stratigraphic section (Pirshamsoddin section) has been measured and sampled. The thickness of this section is 920 meters, which its carbonate part has a thickness of 45 meters. The lower boundary of this formation is gradual with Gurpi Formation and its upper boundary with Kashkan Formation is sharp. The diagenetic processes affecting carbonate rocks include cementation, crystallization, compaction, silicification, pyritization, and geopetal fabric. Based on lithological studies of carbonate rocks, the cements in this section are often related to marine diagenetic environments, deep burial, and shallow burial close to the surface diagenetic environments, as well as weakly atmospheric diagenesis. Moreover, biological components have been slightly affected by dissolution caused by meteoric diagenesis. Therefore, the dominant diagenesis system in the discussed sequence is a closed or slightly open diagenesis system. The high ratio of Sr to Mn element, low values of Fe and Mn elements and high ratio of Sr element in the studied samples and plotted of Sr/Ca values against Mn element indicate a dominant closed diagenesis system for the carbonates of the Amiran Formation. The elemental analysis results indicate that the primary mineralogy of aragonite for the Amiran Formation. In addition the high ratio of Sr/Mn and Sr/Na in the studied samples indicate a dominant closed diagenesis system in a weak and with the few exchange of water-to-rock ratio (W/R) for the carbonates of Amiran Formation.