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

Abstract

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.

Palaeoenvironment, palaeogeography, and palaeoclimatology of the Mississippian carbonate ramp in the Alborz tectonostratigraphic zone: Implications for deciphering the controlling factors on ramp evolution

“…Alborz has been subdivided by several researchers (Stöcklin, 1974;Zanchi et al, 2009). However, none of the F I G U R E 2 Main lithology of the Mississippian rocks of Alborz subzones, their relative names, and ages (modified after Zandkarimi, Vachard, Najafian, Mosaddegh, & Ehteshami-Moinabadi, 2019) subdivisions are cited by other researchers, whereas the most referred subdivisions are those related to the geographical position, that is, western and central Alborz (Stöcklin & Nabavi, 1973) and eastern Alborz (Bozorgnia, 1973;Figure 1a; for more discussion, readers are referred to the discussion in Zandkarimi et al, 2019).…”

“…The main biozonation of the Mississippian rocks of Alborz has been carried out by using foraminifers which has been compared to the foraminiferal zonation of Belgian stratotypes (Bozorgnia, 1973;Brenckle et al, 2009;Falahatgar et al, 2015;Zandkarimi et al, 2016;Zandkarimi et al, 2019).…”

“…The Eoparastaffella Zone (MFZ8) is defined here by FO of primitive Eoparastaffella species, E. ovalis, E. rotunda, and E. interiecta, to the FO of E. simplex (Figures 5 and 6: panels 6,8,9). The zone records the maximum abundance and diversity of foraminifers in central Alborz (Bozorgnia, 1973;Vachard, 1996;Zandkarimi et al, 2016Zandkarimi et al, , 2019. The upper part of the zone is characterized by the joint occurrences of Lysella and Dainella.…”

The lower–middle Viséan boundary interval in the Palaeotethys: refinements for the foraminiferal zonal schemes

“…PhD thesis, University of Manchester,1981;Somerville, 2008) and in Asia (e.g. Hance et al 2011;Zandkarimi et al 2017Zandkarimi et al , 2018. Another important character within the Archaediscus is the progressive reduction of the microgranular layer during its evolution, which led to to consider the distinction between the genus Paraarchaediscus Orlova, 1955 (for those forms with welldeveloped microgranular layer) from Archaediscus Brady, 1873 (for those forms with reduced microgranular layer) valid.…”

“…The first occurrence of primitive Pojarkovella is at the same horizon as P. nibelis, and no difference exists. Zandkarimi et al (2017Zandkarimi et al ( , 2018 only recognized the MFZ11 and MFZ12 zones in northern Alborz, and they did not subdivide the former zone. The occurrence of Pojarkovella spp.…”