[32] The endemism of the fusulinid assemblage under consideration, which prevents correlation to those of well studied Permian sections of the Urals, East European platform, and Tethys, makes dating it difficult. In addition, the Khan Formation containing beds with fusulinids in its middle part is bounded by unconformities between Lower Carboniferous(?) and Triassic deposits. The position in the section does not allow assigning the formation more precisely than to the interval from Middle Carboniferous to Permian.
[33] The only indication of age of the assemblage is provided by its similarity with the Kalaktash assemblage of Central Pamirs. Sakmarian age of the latter assemblage was substantiated in [Leven, 1993] and there is no need to repeat the arguments herein. After the article came out new records that confirmed or contradicted its conclusions were published. The confirming data was derived from sections at the upper part of the Yarkhun River, northern Karakorum (Pakistan). There a fusulinid assemblage similar to the Kalaktash one occurs in deposits between beds with brachiopods (the Hunzina electa Zone), which according to Angiolini have Sakmarian age, and beds with fusulinids ( Pamirina, Pseudoreichelina, Chalaroschwagerina, Darvasites) typical of the Yakhtashian Stage [Gaetani et al., 1995]. The Yakhtashian Stage of the Tethyan scale is commonly considered to be equivalent of the Artinskian of the standard chronostratigraphic scale. If it is correct, the beds with the fusulinid assemblage studied have pre-Yakhtashian (pre-Artinskian), i.e., Sakmarian age. Because isochroneity of the lower boundaries of the Yakhtashian and Artinskian stages has not been proved yet, these beds may belong entirely or partly to the basal portion of the Artinskian Stage. This is indirectly supported by finds of Streptoghathodus aff. whitei in the Upper Pseudoshwagerina limestones of the Southern Alps [Forke, 2002]. The first occurrence of this conodont species is marked the Artinskian lower boundary. Previously the limestones were assigned to upper Asselian-Sarmarian. Presence characteristic for this limestone Zellia and Robustoschwagerina in the beds with the Kalaktash fusulinid assemblage was a serious argument for Sakmarian age of the beds. The cooccurrence of these fusulinids and Artinskian conodonts makes the argument less important because it appeared that Zellia passed from the Sakmarian deposits into Artinskian ones. The fact that Robustoschwagerina survived till the terminal Early Permian is well known. However in the Kalaktash section Zellia and Robustoschwagerina are accompanied by Sphaeroschwagerina, which has been recorded nowhere above the Sakmarian beds. In addition, the Sakmarian age of the Kalaktash assemblage is evidenced by the same type Eoparafusulina as in the lower Sakmarian deposits of Timan and by relatively primitive morphology of Pseudofusulina forms as compared with those of the Artinskian beds of the Urals.
[34] Bryozoan records cannot clarify this problem either. According to R. V. Gorjunova, the lower of two bryozoans assemblages of Unit 7 is Asselian-Sakmarian in age and the upper one is Artinskian. In view of their close proximity in the section, this large age interval seems doubtful. By the way, Artinskian age was also indicated by Gorjunova [1975] for Kalaktash bryozoans of Central Pamirs.
[35] With all reservations from the said above, we take the Sakmarian age for the Kalaktash assemblage and similar fusulinid assemblage of the Khan Formation.
[36] This conclusion somewhat contradicts the datings of F. Kahler mentioned above. However, one of two fusulinid species reproduced in his publication [Kahler, 1977] is identical of Eoparafusulina pamirensis of our material and the other may belong to new species Pseudofusulina gachalensis described below. So, the identifications of F. Kahler are most likely incorrect. As for the datings of A. Afghanabati, our conclusions make them more precise. It should be noted, however, that fusulinids listed by this author include Brevaxina, a genus of higher fusulinids, which is characteristic of the Bolorian Stage of the Lower Permian and found nowhere in older deposits. The presence of this genus in the Khan Formation does not agree with the suggested Sakmarian age. However our age assignment is related to the middle part of the formation only. As noted, the section lacks its upper part, which may contain Brevaxina. There is high probability that its identification may appear incorrect but now we are unable to check it.
[37] When describing Asselian fusulinids of Darvaz, Leven and Shcherbovich [1978] noticed differences in Asselian facies and faunas between the northern and southern regions of the Tethys. Correspondingly, the North Tethyan and South Tethyan biogeographic provinces have been established. The differences can be explained by location of the provinces in different climatic belts. The former province occurred within the tropical belt. The latter province stretched along the northern margin of Gondwana, crossing several climatic zones from subtropical in the northwest up to temperate-cold and cold in the southeast. This position brought about succession of biotas peculiar to certain climatic belts. Asselian fusulinids occupied the northwestern part of the province (the Mediterranean region, Turkey, Iran) but were not found in its southeastern part (Afghanistan, Karakorum and farther), where supposed Asselian deposits are represented by terrigenous facies with cool-water fauna of Gondwana-type (bivalves, Conularia, brachiopods, bryozoans).
[38] This paleobiogeographic pattern derived from analysis of the Asselian materials is in accordance with later data on the Sakmarian Stage [Leven, 1993] and distribution of Late Permian foraminifers [Ueno, 2003]. The Sakmarian Kalaktash-type fusulinids are absolutely different from coeval forms of the North Tethyan province. In the South Tethyan province they are known from sections of Oman [Angiolini et al., 2006], South Afghanistan [Leven, 1997], Central Pamirs [Leven, 1993], Eastern Hindukush (the Rosh-Gol section in the Mastuj River basin) [Gaeteni and Leven, 1993], northern Karakorum (upper part of the Yarkhun River) [Gaetani et al., 1995]. In the extreme southeast of the province the Kalaktash fusulinids are supposed to occur in the Tengchong and Baoshan tectonic blocks of southwestern China and in the Sibumasu block of western Indo-China. Monodiexodina, Eoparafusulina, and Pseudofusulina were found there. Their host beds are correlated to the Kalaktash deposits [Ueno, 2003] but well developed Monodiexodina indicate their younger age. Most likely these beds are related to the Artinskian (Yakhtashian) Stage because beds bearing similar Monodiexodina lie directly on beds with Kalaktash fusulinids in the Rosh-Gol section of East Hindukush [Gaetani et al., 1995]. In Karakorum and southeastern Pamirs the Monodiexodina beds are of Bolorian age.
[39] The initial Permian was characterized by temperature minimum and maximal Gondwana glaciation. This explains the fact that terrigenous sequences with glacial interbeds but not carbonates were accumulated over the area from Oman to SE Asia in the South Tethyan province. This also explains occurrence of cool-water fauna in the upper part of the terrigenous sequences. Appearance of carbonates in the sections coincides with the first occurrence of Kalaktash fusulinids. Both are evidently related to a climatic warming.
[40] The fusulinids appeared suddenly. They are not taxonomically diverse but very abundant. It is still unclear from where they migrated. Logically, as climate became warmer, they gradually moved to the southeast from the low-latitude northwestern areas of the South Tethyan province. The Asselian inhabitants may give rise to Sakmarian Kalaktash-type assemblage of fusulinids. This scenario supposes some transitional assemblages, which may occur in eastern Iran or southwestern Afghanistan. No such assemblages have been found. Asselian fusulinids are absent from southern Afghanistan but described from the Anarak (Central Iran) and Ozbak-Kuh (eastern Iran) sections [Leven and Gorgij, 2006; Leven and Taheri, 2003]. They cannot be considered endemic in relation to coeval warm-water fusulinids of the Urals, Alps, Fergana, and Darvaz. Their assemblage is composed of the same genera ( Pseudoschwagerina, Sphaeroschwagerina, Likharevites, Anderssonites, Ruzhenzevites, Rugosofusulina, Pseudofusulina) and species characteristic of the Asselian of the mentioned areas. Beside Pseudofusulina, none of the listed genera is a component of the Kalaktash assemblage. Single Sphaeroschwagerina were detected in the Kalaktash section of Central Pamirs. This is especially strange because the Khan section containing the fusulinid assemblage under consideration is located between the Anarak and Ozbak-Kuh sections relatively near (about 100 km) the latter section. The alien character of this assemblage probably stems from the position of the Khan section in the Posht-Badam tectonic block separated from the neighboring Yazd (the Anarak section) and Tabas (the Ozbak-Kuh section) blocks by the large fault (Figure 1). It should not excluded that the recent position of the blocks in Central and Eastern Iran is a consequence of complex tectonic evolution of the region. Initially they may be very far from each other. Special investigations are needed to judge more definitely.
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