Latest Tournaisian–late Viséan foraminiferal biozonation (MFZ8–MFZ14) of the Valiabad area, northwestern Alborz (Iran): geological implications

Abstract

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.

Mississippian lithofacies and foraminiferal biozonation of the Alborz Mountains, Iran: Implications for regional geology

“…The key sections are as follows: 1: Dozdehban: 2: Naserabad; 3: Valiabad; 4: Elika; 5: Khashachal; 6: Geirud; 7: Abnak; 8: Mobarakabad; 9: Mangol; 10: Jaban; 11: Sarbandan; 12: Arou; 13: Kahanag; 14: Tuyeh‐Darvar; 15: Gaduk; 16: Shahmirzad; 17: Peyghambaran; 18: Kiyasar; 19: Simeh Koh; 20: Abrendan; 21 Kalariz; 22: Labnesar; 23: Khoshyeilagh; 24: Bagherabad; 25: Qezelqaleh 26: Tilabad; 27: Kalate; 28: Nodeh‐Sud. (based on the data provided by Bozorgnia, ; Brenckle et al, ; Falahatgar et al, , ; Gaetani et al, ; Jenny, Jenny‐Deshusses, Stampfli, & Lys, ; Lys et al, ; Mosaddegh, ; Saeidi, Mosaddegh, & Babazadeh, ; Vachard, ; Zandkarimi, ; Zandkarimi et al, , 2017) [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…The Mobarak Formation of the north‐central Alborz has a relatively different lithology compared with that of type area, in south‐central Alborz. Consequently, it starts with thick‐ to very thick‐bedded limestone, followed by thin‐ to medium‐bedded occasionally sandy limestone and upper thick‐bedded fetid ooidal limestone alternating with the blackish shale (Figures and ; Mosaddegh, ; Zandkarimi et al, ; Zandkarimi, Vachard, Cózar, et al, ; Zandkarimi, Vachard, Najafian, et al, ).…”

“…Main lithology and formations of the Mississippian rocks and their underlying and overlying beds in the Alborz subzones, their relative names, and ages (compiled from Assereto, ; Bozorgnia, ; Brenckle et al, ; Falahatgar & Mosaddegh, ; Falahatgar et al, ; Jenny et al, ; Lys et al, ; Mosaddegh, ; Saeidi et al, ; Vachard, ; Zandkarimi, ; Zandkarimi et al, ; Zandkarimi, Vachard, Cózar, et al, ; Zandkarimi, Vachard, Najafian, et al, )…”

“…The Mobarak Formation was introduced by Assereto () in the Mobarakabad area, central Alborz, and comprises black fossiliferous limestone with subordinate black marl in the lower part. It has been widely studied and dated in central Alborz using brachiopods (Bahrammanesh, Angiolini, Antonelli, Aghababalou, & Gaetani, ; Gaetani, , , ; Qiao, Falahatgar, & Shen, ), conodonts (Ahmadzadeh Heravi, ; Habibi et al, ), and foraminifers (Bozorgnia, ; Devuyst & Kalvoda, ; Falahatgar, Vachard, & Sakha, ; Vachard, ; Zandkarimi, ; Zandkarimi, Najafian, Vachard, Bahrammanesh, & Vaziri, ; Zandkarimi, Vachard, Cózar, et al, ; Zandkarimi, Vachard, Najafian, Hamdi, & Mosaddegh, ). The Mississippian of the north‐eastern Alborz in addition to the Mobarak Formation contains relatively similar strata to the Dozdehban Formation, which was referred to as the “Bagherabad Formation” (Leven & Gorgij, ; Lys, Stampfli, & Jenny, ).…”

“…For a synthesis of the Mississippian foraminiferal zonation and Late Palaeozoic stratigraphy of Alborz, we have followed the works of Assereto (), Bozorgnia (), Stöcklin and Setudehnia (), Vachard (), Brenckle, Gaetani, Angiolini, and Bahrammanesh (), Falahatgar et al (), Zandkarimi et al (), Zandkarimi et al (), Zandkarimi, Vachard, Cózar, et al () and Zandkarimi, Vachard, Najafian, et al (), and several unpublished MSc and PhD theses (Bastami, ; Mosaddegh, ; Najafi, ; Payami‐e Rad, ; Zandkarimi, ) carried out on the Late Palaeozoic of Alborz, and for foraminiferal classification and correlation of zonation with well‐known Mississippian references, we have followed the works of Pirlet and Conil (), Vachard and Tahiri (), Vachard and Berkhli (), Hance, Hou, and Vachard (), Gibshman (, ), Gibshman, Kabanov, Alekseev, Goreva, and Moshkina (), Nikolaeva, Kulagina, Pazukhin, Kochetova, and Konvalova (2009), Kabanov, Alekseev, Gibshman, Gabdullin, and Bershov (), Vachard (), and various papers of Cózar and Somerville (, , , , ), Somerville (), Cózar, Somerville, and Burgess (, ), Cózar, Somerville, Aretz, and Herbig (); Cózar et al (), Cózar et al (), Cózar, Sanz‐López, and Blanco‐Ferrera (), and Cózar et al (). The microfacies and depositional interpretation follow the works of Dunham (), Read (), Burchette and Wright (), Mosaddegh (), and Flügel ().…”