Introducing the newly-established “Varkan Member” in SW Kashan as the oldest member of the Qom Formation


Department of Ecology, Institute of science, High technology and environmental science, Graduate University of advanced Technology, Kerman, Iran;


The Qom Formation, (Oligocene-early Miocene in age) consists of thick successions of marine marls, limestones, gypsum, and siliciclastics. It is deposited in the Sanandaj–Sirjan fore-arc basin, Urumieh-Dokhtar Magmatic Arc (Intra-arc basin), and Central Iran back-arc basin and it was subdivided into 11 members to date. "Unnamed member" which is identified by Nummulites intermedius and Eulepidina cf. dilatata and attributed to Rupelian, was introduced as the oldest member of the Qom Formation. Recent studies by the current author subdivided the Rupelian stage into “early Rupelian” and “late Rupelian”, based on the first appearances of lepidocyclinids in the latter one. Accordingly, the "unnamed member" is late Rupelian in age. Besides, the early Rupelian strata are characterized by the presence of Nummulites without lepidocyclinids, reported merely from southwestern and southern Kashan. The basal deposits of the Qom Formation sections in SW and S Kashan (composed of marl, limestone and marl limestone) are distinctly different from the “unnamed” member (alternation of silty marl, sandstone and limestone), “a” member (basal limestone) and “b” member (sandy marl) of the Qom Formation, in terms of lithology. Therefore, the mentioned deposits are introduced as a new member and named the "Verkan Member". Accordingly, the number of the Qom Formation members has increased to 12 and the “Varkan Member” (with 108-m thickness in the Varkan section and early Rupelian in age) is introduced as the oldest member of Qom Formation. The “Verkan Member” is present in the Varkan (SW Kashan), Vidoja (SW Kashan) and Ghohroud (S Kashan) sections.


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