نوع مقاله : علمی -پژوهشی
نویسندگان
1 گروه زمینشناسی، دانشکده علوم، دانشگاه اصفهان، اصفهان، ایران
2 دانشکده علوم طبیعی، دانشگاه پاول ژوزف سافاریک، اسلواکی
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Introduction Fossil vertebrates were first reported from Iran by Priem (1908), who reported on the fossil fishes from the Pabdeh Formation east of Ilam, in southwestern Iran. At the time, Priem (1908) considered these deposits to be Lower Cretaceous, but they are now known to be Eocene (Afsari et al. 2014). Several decades later, fish material from the same deposits was studied by Arambourg (1967), who had attributed the beds to the Oligocene. Since those studies, additional fish from the Pabdeh Formation have been described or revised (e.g. Haghipour and Brants 1971; Jafarian et al. 1999; Afsari et al. 2014; Davesne 2017) including members of the Scombridae, Carangidae, and Labridae. These support the revised Eocene age of the sediments. Recently, Mirzaei et al. (2016) reported a Pycnodontiform (a Neopterygian bony fish) tooth plate from the Albian–Cenomanian Sarvak Formation at Lorestan, southwest Iran. To our knowledge, this is the only Cretaceous vertebrate fossil from Iran, excluding the material we report here. The objectives of this paper are to describe and interpret the vertebrate-bearing horizons of the Dariyan Formation in order to determine the age of the vertebrate-bearing beds and to provide a preliminary report on the vertebrate assemblage present in this locality.Materials and MethodThe Sivand Section is located 80 km northeast of Shiraz, on the eastern flank of the Sivand Anticline at E 52° 51´ 27.70´´ and N 30° 4´ 54.88´´. The Fahlian, Gadvan, Dariyan, Kazhdumi, and Sarvak formations are exposed in this area. The thickness of the Dariyan Formation in the Sivand Section locality is about 287 ms. Dariyan Formation is mainly composed of cherty limestone, radiolaria-bearing limestones, Hedbergella-bearing marls, and thin-bedded micritic limestone layers. Vertebrates and ammonites occur mainly in the lower part of the Dariyan Formation. Among the bioclasts, fragments of bivalves, gastropods, and ammonites, Orbitalina foraminifera, and marine vertebrate debris can be observed. A section of sixty-five meters of the lower deposits of the Dariyan Formation was measured in detail in this region.Result and Discussion The samples, mainly slabs of micritic limestone with vertebrate fossils were collected, wrapped, packed and safely transferred to the Department of Geology lab., at University of Isfahan. Extra samples were systematically obtained from the special horizons for thin sections also a few washing samples in order to determine the precise age of the fossil bearing horizons of the Lower Dariyan Formation. Slabs of the vertebrate fossils were cleaned by special pneumatic air pen tool, photographed and studied in details for anatomical characteristics. Based on the succession of microfossil assemblages (Choffatella decipiens Range Zone, Radiolaria flood Range Zone, Globiogerinelloides blowi Range Zone, Mesorbitolina parva Range Zone), we propose that the Sivand fossiliferous deposits are Early Aptian (Bedoulian) through early Late Aptian (Early Gargasian) in age. Fossil vertebrates are preserved in the lower part of the formation.ConclusionsLaboratorial studies, Microscopic characteristics and the thin sections led to discrimination of five orders of fish fossils (Aspidorhynchiformes, Clupeiformes, Ichthyectiformes, Pycnodontioformes, and Semionotiformes) and a marine turtle fossil of genus Toxochelys, accompanied with 9 genera and 14 species of foraminifera were identified that represents early Aptian (Bedoulian) to the beginning of late Aptian (Early Gargasian) ages for the studied parts of the Dariyan Formation in Sivand section. The Sivand locality preserves the first known Early Cretaceous assemblage of marine vertebrates from southwestern Asia. The obtained samples of marine vertebrates also introduced from other regions of the world, including North America, Europe, Australia, Africa, China and Lebanon. The preservation of a diverse assemblage of fossil vertebrates, makes the Sivand locality of special significance for understanding the diversity of vertebrates in lower Cretaceous of South Asia.
کلیدواژهها [English]
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