Biostratigraphy of Late Devonian Deposits (Famennian) of Kuh-e-Kaftar section (Northeast Isfahan) based on conodont fauna

The main Paleozoic sequences of Isfahan Province cropped out in the northern part of Isfahan e. g: Soh and Natanz (Najhaf, Neqeleh, Varcamar, North Tar and west Kesheh section) (Zahedi, 1973; Adhamian, 2003, Ghobadipour et al. , 2013; Bahrami et al. , 2015); Zefreh, Chahriseh and Dizlu areas (Brice et al. , 2006; Gholamalian, 2003; Habibi et al. , 2013). Kuh-e-Kaftar section (Chahriseh area) is one of the most complete sequence of Upper Devonian deposits in north Isfahan (central Iran), which have been devoted many papers by different researchers on the fossils content of these deposits (Ghavidel-syooki, 2001; Hamedani, 1996; Brice and Kebriae, 2000; Djafarian, 2000; Mistian and Gholamalian, 2000; Mistian et al. , 2000; Yazdi et al. , 2000; Turner et al. , 2002؛ Safari and kangazian, 2003; Gholamalian, 2003, 2007; Webster et al. , 2007 and Hairapetian et al. , 2000). This paper focused on the Famennian deposits of Kuh-e-Kaaftar section to establish precise age of the lower and upper boundary of sequence, as well as the lithostratigraphic characteristics. Forty-four samples (3-4 kg each) were collected from Kuh-e-Kaftar section, the samples were processed with conventional acetic/formic acid technique. All collected samples were prolific and yielded more than 1613 conodont elements which helped in erecting the stratigraphic framework of biozonation of the Shishtu I subformation. Although the abundance of conodont elements is scarce, but the acceptable diversity and presence of Zonal index taxa let to establish the age framework of the studied interval. The state of preservation of the conodonts is generally excellent, where many specimens are complete without contamination. The color of conodonts is dark black (C. A. I. 4. 5- 5) in total elements of sampled section. All the studied conodont specimens are coded under acronym of EUIC and redeposit in the Department of Geology, University of Isfahan, I. R. Iran The studied deposits of Kuh-e-Kaftar section, which is located in southwest of Chah-riseh village 55 km northeast of Isfahan, comprises Famennian deposits equivalent to the Shishtu Formation (Shishtu I subfromation). The thickness of the studied and measured profile is about 110 meters, including 4 lithostratigraphic units (limestone, sandy limestone, marly limestone, shale and sandstone levels) including: bivalve, bryozoan, crinoids stems, brachiopod, trilobite, goniatite, conodonts and vertebrate micro-fauna. Alternation of medium bedded limestone and shale can be seen at the basal levels of the section. Basal level overlies on Frasnian stage sediments and underlines with an eroded surface (red clays) can be dated to Permian system. In order to establish the biostratigraphical framework for the Shishtu I subfromation, 44 samples were collected systematically and the examined samples contain 1613 conodont elements. Twenty conodont species and subspecies belong to eight genera have been identified as follows: Bispathodus aculeatus aculeatus, Bispathodus aculeatus plumulus, Bispathodus costatus, Bispathodus stabilis, Branmehla bohlenana, Icriodus cornutus, Icriodus sp. , Mehlina strigosa, Pandorinellina insita, Pelekysgnathus inclinatus, Polygnathus delicatulus, Polygnathus deplanatus, Polygnathus nodocostatus, Polygnathus brevilaminus, Polygnathus semicostatus, Polygnathus sp. , Neopolygnathus communis group, and Scaphignatus velifer velifer. The abundance and distribution of conodont elements as well as the sedimentary record suggest marine conditions of an inner shelf environment. The conodonts are related to the following conodont biozones as: Upper marginifera, Uppermost marginifera to Upper trachytera, Middle expansa, and Upper expansa zones. In terms of biofacies, the conodonts can be assigned to the icriodid–polygnatid, polygnatid– bispathodid and bispatodid–polygnatid biofacies. This study undertaken at the Department of Geology, Faculty of Science, University of Isfahan. The financial supports by the Vice Chancellor for Research and Technology, University of Isfahan highly appreciated.