Abstract
Abstract. The aim of the study was the biostratigraphical evaluation of Padeha Formation based on conodont accumulation in Yazdanshahr. The section under study is located north of Yazdanshahr in northwestern Zarand County in Kerman, central Iran. After investigating several sections of the Padeha formation in the Kerman area, one fossiliferous section was chosen for study. In terms of lithology, the section is composed mainly of red-colored clastic and evaporative rock with carbonate intercalations. The conodont accumulations indicate two local biozones: the Zieglerodina remscheidensis and Pandorinellina steinhornensis assemblage zones and the Eugenathodontidae-Icriodus assemblage zone. Based on the abundance of Spathognathodontidae and similarities to global biozones, these biozones were found to be of the Late Silurian (Early Pridoli) age. No evidence of the Icriodus genus (especially woschmidti or postwoschmidti species) was observed in this assemblage. The latter biozones manifest the appearance of Eugenathodontidae in the Early Devonian; therefore, a sedimentary hiatus exists within the Late Silurian to the start of Early Devonian (Late Pridoli to Pragian). The sediment was deposited in a depositional environment ranging from lagoons to shallow waters (inner carbonate platform). The Yazdanshahr section was the most complete of the Padeha formation because conodonts were found in the lower, middle and upper parts of the section. This function will allow researchers to correlate their sections with these findings based on stratigraphic principles.
Introduction
Devonian deposits in Iran were first reported on a geological map prepared by the National Iranian Oil Company. Located near Gush-Kamar in the Ozbak-Kuh mountains, the type section was studied by Ruttner et al. (1968) , Stocklin (1971) and Stocklin et al. (1965 . Late Silurian-Early Devonian sediment has been studied in Kerman province in Iran and reported according to stratigraphic principles (Huckriede et al., 1962) . Most Geologically speaking, Iran is divided into five structural units: the Zagros, Alborz, Sanandaj-Sirjan, Eastern Iran and Central Iran (Stocklin et al., 1965; Stocklin, 1968; Stocklin and Nabavi, 1971; Stocklin and Setudehnia, 1991; Heydari et al., 2008) . In terms of structure, Central Iran is composed of five blocks: the Lut, Tabas, Kalmard, Posht-Badam, Anar and Dehshir (Alavi, 1991; Heydari et al., 2008 ; Fig. 1 ). Devonian sediment has been described in the Jeirud Formation in the Central Alborz (Assereto, 1963) , the Khoshyeilagh formation in the northeastern Alborz (Bozorgnia, 1973) , the Moli and Ilanqareh Formation (unofficial name) in West Azerbaijan and Maku (western Nasehi (Ruttner et al., 1968) . The type section of the Padeha formation is named after the village of Padeha in the Ozbak-Kuh mountains (Eastern Iran). Lithologically characterized by red sandstone, dolomite and gypsum at Ozbak-Kuh (eastern Central Iran), the Padeha formation overlies the fossiliferous carbonates of the Niur formation and underlies the Sibzar dolomites. This formation formed in the Early Devonian and exhibits shallow facies related to the Caledonian orogeny (Ruttner et al., 1968; Stocklin, 1971 ). The Padeha formation was deposited in an inner platform and extends across all of the Central Iran basin. Based on its stratigraphic position, this formation has been aged back to the Early Devonian.
Introduction
Devonian deposits in Iran (Pedeha, Sibzar, etc.) are not well known and a large deal of uncertainty is associated with them. In general, Early Paleozoic Devonian deposits in Iran precipitated in separate geological units. Few studies have been done on the effect of sea level at the time the Late Silurian and Early Devonian rock formed. Evidence indicates the effect of Caledonian movement (Ruttner et al., 1968; Stocklin, 1971) . Sea transgression covered most of Iran in the Middle and Late Devonian. In the present research, an attempt is made to determine the age of the sediment based on conodont accumulation.
Methodology and study area
The structural units of Iran were investigated and the Kalmard block was selected for study. The study area is located about 18 km from Zarand and 70 km to the northeast of Kerman. The measured section was delimited as 31º3′55′′N and 30º2′40′′N latitude and 56º17′ 5′′E and 56º15′10′′E longitude (Fig. 1) . Field sampling and length measurements were undertaken systematically wherever a change in the lithology was identified to carefully investigate the biostratigraphy of the study area. If needed, more than one sample (+4 kg) was taken from the corresponding bedding. The samples were studied carefully after undergoing the following preparation steps: crushing (to dimensions of 3 cm), acid treatment (10% acetic acid), washing, sieving (75, 125, 250 and 710 mesh), picking (with a needle) and photography. These radical changes in thickness can be attributed to horst and graben basins from the Caledonian and Hercynian epirogenic phases in Central Iran (Soffel and Forster, 1980; Weddige, 1984) . The presence of gypsum as evaporative facies in the section base along with carbonate intercalations containing Spathognathodontidae indicate a lagoon on an inner carbonate platform (Table 1 ) (Sweet, 1988; Flugel, 2010) . The presence of evaporative facies in the Late Silurian can be attributed to the Ardenian orogeny. The Early Devonian red-colored clastic facies with carbonate intercalations can be attributed to the Earian orogeny.
Discussion

Lithostratigraphy of Yazdanshahr section
The study area is located in the northern Shabjereh mountains near Khorramabad (northeastern Kerman, Central Iran; 
Biozonation of Yazdanshahr section
The conodont collections in this section contain 15 genus, 20 species and 5 subspecies were identified (Fig. 3) . Together, these identify two biozones as follows:
Biozonation of Yazdanshahr section
1. Zieglerodina remscheidensis, Pandorinellina steinhornensis assemblage zone. As such, the age of this biozones is Pridoli.
Eugenathodontidae-Icriodus assemblage zone
The elements collected in this part are related to Eugenathodontidae and include the followings genus: (1975, 1991) It is difficult to identify the contact between the Silurian and Devonian. The studied section exhibit a stratigraphic hiatus between the Late Pridoli and Early Pragian. Lochkovian deposits have not been observed in Iran; therefore, Central Iran was exposed out of water.
Conclusion
The studied section indicates that the Padeha Formation has two members across this area. The lower part (evaporative deposits with carbonate intercalations) has been aged back to the Late Silurian, while the upper part of Padeha Formation (clastic deposits Within this time window, present-day Iran formed on the northern margin of the Gondwana Supercontinent, which later divided into separate structural units under the effect of Caledonian epirogenic movement (from faulting and formation of horst and graben basins). In the Late Silurian and Early Devonian, sea transgression and regression occurred, respectively. Note that the transgression at this time extended to limited parts of Iran. The evidence presented herein confirms the hypothesis of a horst and graben basin along the paleo faults in Central Iran in the Early Paleozoic.

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