In northern Iran, the late Cambrian trilobites have been documented largely from Furongian deposits exposed at Mila-Kuh, Shahmirzad, and some sections in western Alborz, whereas the available information on this group of fossils from the sections located in eastern Alborz is sparse. The major objective of the paper is a small trilobite assemblage, assignable to the Parabolina Fauna, which has been recovered for the first time from the Furongian (Cambrian Stage 10) Sah Member of the Mila Formation in the Tuyeh–Darvar section, eastern Alborz, northern Iran. This assemblage includes eight genera and species; two of them, Niobella darvarensis n. sp. and Macropyge (Promacropyge) sahensis n. sp., are new to science. The incursion of this fauna into Alborz probably occurred due to a significant drowning event and associated dark-gray shale deposition. While the generic composition of the assemblage is mostly cosmopolitan, it also contains a local endemic Alborsella; although some taxa exhibit a distinct sign of faunal links with South China and Tarim. On the other hand, Parabolina (Neoparabolina) frequens, which is common in olenid trilobite associations, is widespread mainly offshore in deposits from temperate Gondwana (Armorican terrane assemblage, Argentina) and Baltica of about that age.

A small trilobite assemblage, including Parabolina (Neoparabolina) frequens, assignable to the Parabolina Fauna, has been recovered from the Furongian (Cambrian Stage 10) Sah Member of the Mila Formation in the Tuyeh–-Darvar section, the eastern Alborz Mountains, north Iran. The assemblage includes eight genera and species; two of them, Niobella darvarensis n. sp. and Macropyge (Promacropyge) sahensis n. sp., are new to science. The incursion of a Parabolina fauna into Alborz is confined to a significant drowning event with associated dark-gray shale deposition, which most probably occurred in the lower part of the Cordylodus proavus conodont Zone. While the generic composition of the assemblage is mostly cosmopolitan with the exception of the endemic Alborsella, the occurrence of Indiligens, Macropyge (Promacropyge) sahensis n. sp., Agnostotes sp. aff. A. sulcatus, and Leiagnostus bexelli indicates faunal links with South China and Tarim. Parabolina (Neoparabolina) frequens is widespread mainly in offshore deposits from temperate Gondwana (Armorican terrane assemblage, Argentina) and Baltica of about that age.