The Permian-Triassic (P-Tr) boundary sections in the regions of Julfa (NW Iran) and Abadeh (Central Iran) have high potential for the study of the most dramatic extinction event in Earth’s history. As part of a multidisciplinary project, we have conducted high-resolution carbon isotope analysis of bulk carbonate rocks (δ13Ccarb), coupled with preliminary carbon isotope analysis of bulk organic matter (δ13Corg), and nitrogen isotope study of bulk sediment (δ15Nbulk), for three fossil-rich, pelagic P-Tr boundary sections in NW Iran (Ali Bashi, Aras Valley, and Zal) and one in the Baghuk Mountain area in Central Iran. The Permian-Triassic boundary sections in Iran display three characteristic rock units: (1) the Paratirolites Limestone (4 m thick) with the mass extinction horizon (P-Tr extinction event) at the top surface, (2) the Boundary Clay (0.5–2 m thick), and (3) the Elikah or Shahreza formations with the conodont P-Tr boundary near the base. The well-known negative δ13Ccarb excursion begins in the middle of the Paratirolites Limestone and culminates at the base of the Elikah and Shahreza formations; it is interrupted by a weak positive δ13Ccarb excursion within the Boundary Clay. The bulk δ13Corg values and time-equivalent bulk δ13Ccarb values show different trends. The δ13Corg curve reveals highly oscillating values throughout the entire section. A negative δ15Nbulk trend begins in the topmost part of the Paratirolites Limestone and culminates at the base of the Boundary Clay. The δ13Ccarb, δ13Corg, and δ15Nbulk isotope data, together with TOC and TN concentrations as well as Corg/Ntot ratios, provide evidence for significant environmental changes around the P-Tr boundary. The beginning of the negative δ13Ccarb excursion correlates well with the largely explosive Siberian Trap volcanism, and the δ13Ccarb peak at the top of the Paratirolites Limestone corresponds to the strong explosive felsic volcanism in southern China. The oscillation of the δ13Corg curve is attributed to a varying prominence of the input of marine and terrestrial organic matter, and/or the preservation mode of the organic matter. Corg/Ntot values and the δ15Nbulk signatures of the entire Paratirolites Limestone and of the base of the Elikah Formation reflect normal marine conditions controlled by biotic factors. In contrast, a dominance of abiotic factors appears to be recorded within the Boundary Clay, where the low TOC and Corg/Ntot ratios, the negative δ15N excursion, and the enhanced concentration of total nitrogen are observed. The low δ15N values within the Boundary Clay reflect the terrestrial origin of nitrogen and speak for an introduction of atmospheric nitrogen into the marine nitrogen cycle. We conclude that low Corg/ Ntot ratios within the Boundary Clay reflect the low organic matter accumulation ratios, coupled with a high content of inorganic nitrogen fixed within clay minerals. The enhanced TOC concentration and high Corg/Ntot ratios in the aftermath of the P-Tr mass extinction in the Elikah Formation may reflect a time of high primary organic productivity with elevated proportions of land-derived organic matter.The stable isotopes show that the environmental changes started in the Late Permian Paratirolites Limestone, below the actual P-Tr extinction event, and before the conodont P-Tr boundary.

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