The Mobarak Formation in the Valiabad area (northwestern Alborz, Iran) is composed of bioclastic, oolitic and sandy limestone interbedded with black shale, and is disconformably underlain and overlain by the Cambrian Lalun and Permian Dorud formations, respectively. In this study, 104 foraminiferal species belonging to 12 families and 33 genera were determined. Among them, six genera and nine species are reported for the first time in Iran. Analysis of the foraminiferal assemblages has identified eight local biozones, which can be correlated with the MFZ8 to MFZ14 zones of the Viséan stratotypes in Belgium. The Valiabad equivalents of these biozones are essentially characterized by (1) Eoparastaffella ex gr. rotunda‐‘florigena’–Lysella cf. gadukensis; (2) Eoparastaffella simplex–Lapparentidiscus bokanensis; (3) Ammarchaediscus; (4) Uralodiscus–Glomodiscus; (5) Glomodiscus–Archaediscus; (6) Pojarkovella–Mstinia fallax; (7) Mstinia bulloides–Pseudoendothyra; and (8) Howchinia gibba–Howchinia bradyana–Tubispirodiscus attenuatus. Consequently, the Valiabad section appears to be one of the most complete Viséan sections in Iran. Some taxonomic precisions are provided about the principal taxa. Biogeographically, (1) the MFZ8–MFZ11 biozones are extended to all the shelves of the Palaeotethys (from Ireland to South China) and Urals oceans; nevertheless, due to the complete evolution of archaediscoids, they seem more related to the Perigondwanan assemblages from Sinai and Taurus (including the Antalya Nappes); (2) the MFZ12 assemblage appears relatively endemic; and (3) the impoverished assemblages of the biozones MFZ13‐14 have marked affinities with the Kazakhstan Block. It is currently impossible to indicate precisely if these variations are related with a drift of the Alborz region to the north, or to a change of oceanic currents. Moreover, the double affinity highlights the narrowness of the Palaeotethys in Iran during the Viséan. Copyright © 2014 John Wiley & Sons, Ltd.

The Mississippian rocks at 5 sections, Kalariz, Peyghambaran, Jaban, Naserabad, and Dozdehban, have been measured and sampled in a SE–NW direction across the Alborz Mountains. Foraminiferal zones recognized in those sections, as well as a revision of other foraminiferal assemblage previously published from the Alborz Mountains, allow to recognize 12 biozones: 5 in the Tournaisian: Unilocular (MFZ1–MFZ2? interval), Septabrunsiina krainica (MFZ3–MFZ5 interval), Eotextularia diversa (MFZ6), Darjella monilis (MFZ7), and primitive Eoparastaffella (MFZ8); 5 Viséan biozones: Eoparastaffella simplex (MFZ9), primitive archaediscids (MFZ10), Uralodiscus rotundus (MFZ11), Pojarkovella–Koskinotextularia (MFZ12), Neoarchaediscus (Upper Mikhailovian), Howchinia gibba–Archaediscus/Paraarchaediscus at angulatus‐tenuis stage–Neoarchaediscus akchimensis (Venevian substage); and 2 Serpukhovian biozones: Biseriella parva–Climacammina (Tarusian–Steshevian substages) and Turrispiroides multivolutus–Brenckleina–Eostaffellina protvae (Protvian substage) for the Mississippian rocks of Alborz. Analysis of foraminiferal assemblages indicates a noticeable age difference of the Mississippian rocks between the northern and southern flanks of Alborz. Accordingly, south‐eastern and east‐central Alborz (Kalariz, Peyghambaran, and Jaban sections) display complete Tournaisian deposits (MFZ1–MFZ8), whereas northern Alborz contains the strata dated from Late Tournaisian to Late Serpukhovian (MFZ8–MFZ16). The sedimentological studies also reveal sharp facies variations following the mentioned age variation. Previously, the age variations of these rocks were attributed to various events, such as the Mississippian glaciation phases. However, the age, facies, and thickness variations of lithostratigraphic units in the Alborz are not specific to the Mississippian and are reported during the entire Palaeozoic and even Mesozoic and Cenozoic. They can rather be attributed to the inherited basement and syn‐sedimentary E–W‐trending faults.

No abstract

No abstract