The Triassic carbonate rocks on the Avroman mountain, Halabja area, consist of massive gray-dark gray-colored detrital and biogenic limestones, that are stratigraphically represented by the Avroman formation in Iraq and Biston formation in Iran. This study focused on the tectonic setting and environmental conditions during the deposition of the formation using major and trace element and rare earth element (REE) analyses, along with their carbon and oxygen isotope data. The geochemical results are substantiated by field and petrographic studies, and extensive literature reviews. The study indicates that the limestones dominantly consist of CaO, followed by MgO, and minor quantities of SiO2 and Al2O3, suggesting a predominantly calcite mineral phase and absence of dolomitization. The negligible amounts of the latter two oxides is possibly due to the lack of siliciclastic input during limestone depostion. Among the trace elements, strontium reported the highest concentrations while displaying a negative correlation with CaO due to the low terrigenous fraction content. Other trace elements such as Ni, Cr, V, Sc, Rb, Ba, Cu, Pb, Zn, U, and Th occur in minor concentrations. The low concentration of uranium (0.0–4.0) and authigenic uranium (average total U − Th/3 value = 0.39), along with a positive value of Mn* indicate depostion from normal seawaters under oxic conditions. The enrichment of heavy REE (HREE) over the light REE (LREE), with negative Ce anomaly and slightly positive Eu and Y anomalies further indicate their precipitation from the seawaters. The negative correlation of ΣREE with Al2O3 FeO, TiO2, Cr Ni, and Sc, and a positive correlation with CaO and Y suggest extremely low contribution of terrigenous siliciclastic sediments and the absence of hydrothermal alterations during limestone precipitation. The δ18O and δ13C values for the four carbonate rocks from Avroman formation varied in the ranges − 3.53 to − 3.02‰ (average − 3.34‰) and 1.15–1.65 (average 1.39‰), respectively. The bivariate plot of δ18O and δ13C suggests that the majority of these carbonates are marine limestones. The Rb–Sr–Ba, La/Sc vs. Ti/Zr, and Sr/Rb vs. Sr/Ba plots categorize the Avroman limestones as carbonates of the continental margin with a tectonic setting relatively far away from igneous activities. Based on the above facts, a tectonic and paleogeographic model was constructed for the formation and was combined with the northeastern Arabian Plate margin, which bordered the Neo-Tethys ocean in the northwest during Triassic.
