Upper Carboniferous--Permian stratigraphy and fusulinids...

Introduction

Figure 1

[2] The area of investigation is situated nearby a small town Anarak, between the Dashte Kavir Desert in the north and the Kuh Rud Range in the south, and occurs within the Yazd block, one of the large, curved to the west submeridional fault blocks recognized in the structure of central Iran (Figure 1). The Carboniferous and Permian sediments were discovered there during the geological survey conducted in the 1970s by geologists from the USSR under the contract with the Iran government. Findings of brachiopods, bryozoans, cephalopods, and foraminifers permitted the recognition of the Visean-Namurian, the non-identified more precisely Carboniferous-Permian, and Lower and Upper Permian units. By analogy with the sections of eastern Iran [Stepanov, 1971; Stöklin, 1971], the Shishtu (Famennian-Namurian), Sardar (Carboniferous-lowermost Permian), and Jamal (Asselian-Upper Permian) formations were distinguished [Sharkovski et al., 1984]. We started a thorough investigation of the discussed section few years ago. In so doing a large stratigraphic hiatus was recorded within the Sardar Formation. Therefore it was subdivided into two separate units, namely, the Ghaleh (upper Serpukhovian?-Bashkirian) and Absheni (Moscovian) formations [Leven et al., 2006]. The Gzhelian sediments were also recognized and united together with the Asselian rocks in the Zaladou Formation. It was believed that the Kasimovian Stage is missing in the section [Leven and Gorgij, 2006]. Upward from the base the new dolomitic, presumably Sakmarian, Tighe-Maadanou Formation was distinguished. It is overlain by the Upper Permian Jamal Formation and is separated from it by a thin sandstone and shale sequence conventionally correlated with the Baghe-Vang Formation of eastern Iran, which is referred to the Bolorian Stage. The Anarak section is in general very similar to those from eastern Iran, namely, from the Ozbak-Kuh Mountains, Shirgesht, and Shotori. This permits the proposition of a single scheme for subdivision of the Carboniferous and Permian in central and eastern Iran, where these sediments are subdivided into three groups and several formations [Leven and Gorgij, 2005] (Table 1).

Figure 2

[3] All the above reported age determinations of stratigraphic units were inferred from foraminifers, mainly fusulinids that occur throughout the section. Their comprehensive descriptions were made only for the Bashkirian and Moscovian stages [Leven et al., 2006]. The first findings of the Gzhelian and Asselian fusulinids were also described [Leven and Gorgij, 2006]. This paper contains the characteristics of the Gzhelian (Kasimovian?)-Asselian part of the Anarak section referred to the Zaladou Formation, and of the encountered fusulinids twice collected by M. N. Gorgij. The samples numbered AC and P were collected initially, then followed by samples C. The relation of samples to the section is shown in Figure 2. Additionally, the samples PR, R, RL, Rup, and ML were derived from certain outcrops. Their precise relation to the section is not assured though its degree is rather high, which is indicated by the involved fusulinids. Over 800 oriented thin sections bearing fusulinids were produced from the samples. They were described by E. Ja. Leven. The thin sections are deposited in the Laboratory of Micropaleontology in the Geological Institute, Russian Academy of Sciences under the number 4781.