كليدواژه :
بلمنيت , سازند بادامو , كرمان , توآرسين , باژوسين
چكيده لاتين :
Introduction
Belemnites are one of the most important groups of invertebrate fossils for biostratigraphical and paleoecological studies, particularly in the Jurassic system. The Badamu Formation is named after the village of Badamu and Kuh-e-Badamu (Badamu Mt) 24 km west of Kerman. This formation has been well known for many years because of its rich fauna, and its use in mapping the coal-bearing Jurassic deposits in the Kerman area (Seyed-Emami, 1967). The belemnites described in this paper have been collected from the Badamu Formation near the Cheshmeh Gaz village, about 60 km south of the Kerman. The Badamu Formation in Cheshmeh Gaz section has a thickness of approximately 52 meters and is predominantly composed of light-grey to cream limestones with shale intercalations in the middle part. Generally, a lower consisting of thin- to medium bedded marls with intercalations of limestones and an upper part of thick-bedded and cliff-forming limestone can be distinguished. The Badamu Formation is part of Shemshak group that was established in major parts of Central Iran ranges from the Late Triassic to Middle Jurassic (Aghanabati, 1977).
Materials and methods
The present material was collected by the senior author during several field works. From the Cheshmeh Gaz section, 68 specimens collected from marls and thin layers of yellow shaly limestone of this section. Well preserved specimens were cleaned, using a mild detergent and whenever necessary by using an ultrasonic vibrator and a preparation needle.
Discussion
After the closure of the Palaeotethys in the Late Triassic, the Iran Plate (Central and North Iran) occupied a position at the southern margin of Eurasia (Seyed-Emami et al., 2008). According to palaeogeographic maps of the Early Jurassic (Seyed-Emami et al., 2008) Central Iran occupied a fairly high latitudinal position at the northeastern margin of the Western Tethys. The faunal migration routes during the Early Jurassic and earliest Middle Jurassic followed most probably the epicontinental platforms at the southern margin of the Eurasian landmass (Seyed-Emami et al 2008). In this study, 7 genera and 17 species belemnites are reported from the Badamu Formation, in the Kerman area, for the first time. Based on identified belemnites, the age of corresponding strata is Toarcian-Middle Bajocian coinciding with Tenuicostatum- Humphriesianum ammonite zones. Belemnites study indicates an oceanic anoxic event at the beginning of Tenuicostatum biozone. The relative abundances at the genera level are Acrocoelites (%35), Pachybelemnopsis (%6), Parapassaloteuthis (%12), Holcobelus (%12), Homaloteuthis (% 6), Eocylandroteuthis (%12) and Passaloteuthis (%17). In the Cheshmeh Gaz section, the following belemnites genera are present Acrocoelites levidensis, Acrocoelites longiconus, Acrocoelites subtenuis, Acrocoelites triscissus, Acrocoelites trisulculosus, Acrocoelites vulgaris, Eocylindroteuthis corneliaschmittae, Eocylindroteuthis trautscholdi, Holcobelus tetramerus, Holcobelus trauthi, Homaloteuthis spinata, Pachybelemnopsis baculiformis, Parapassaloteuthis robusta, Parapassaloteuthis sp., Passaloteuthis bisulcata, Passaloteuthis laevigata and Passaloteuthis milleri. The similarity between Thissection belemnites with north-West Europe belemnites (Weis & Marriotti, 2008; Mariotti et al 2007; Mariotti et al 2010; Mariotti et al 2012; Dolye & Kelly, 1988; Iba et al 2014), can be state relation between mentioned sections on Toarcian to Bajocian sedimentary basins. Belemnites study indicates an oceanic anoxic event at the beginning of Tenuicostatum biozone. Based on Palaeoecological interpretation, the Badamu Formation in Central Iran was deposited in an open, shallow and warm environment with normal salinity.
Acknowledgments
I am greatly indebted to Prof. Alsen Peter (Geological Survey of Denmark and Greenland), Prof. Qiong Li (University of London) and Prof. Robert Weis (Museum national d'historie naturelle de Luxembourg) for their valuable comments on the identification of belemnites. I am deeply indebted to Prof. K. Seyed-Emami (University of Tehran) and Prof. N. Raisossadat (University of Birjand, Iran) for their guidance and constructive discussions.
