استراکد‌های سازند چمن‌بید در برش قرونه (رشته کوه‌های بینالود)

سازند چمن ‌بید دربردارنده نهشته‌های ژوراسیک پهنه بینالود است. ضخامت این سازند در برش چینه شناسی قرونه واقع در شمال باختر شهر نیشابور، 715 متر و متشکل از شیل، مارن و سنگ آهک است که به طور پراکنده همراهانی نازک لایه از ماسه سنگ دارد. این سازند به طور همشیب بر روی توالی معادل با سازند کشف رود قرار گرفته و خود نیز توسط سنگ آهک‌های ضخیم و توده‌ای معادل با سازند مزدوران پوشیده می‌ شود. در این مطالعه برای اولین بار استراکد‌های سازند چمن‌بید در برش چینه شناسی یاد شده مورد بررسی قرار گرفته است. بر این اساس 59 گونه استراکد متعلق به 45 جنس مختلف شناسایی و عکس‌برداری گردید. استراکد‌های شناسایی شده با زیست‌ زون ‌های نانوفسیلی که پیش‌تر، از این برش معرفی شده بودند مقایسه گردید. این مقایسه گویای سن باژوسین پیشین بریازین پیشین برای توالی مورد مطالعه می‌باشد.

Ostracoda of Chaman-Bid Formation in Ghoroneh section (Binalud Mountains)

IntroductionThe Binaloud Mountains, with an almost easternwestern trend, is extended from the Jajarm area in the Northern Khorasan to the TorbateJam region. In the Binalud zone, Jurassic succession in many places covered Paleozoic rocks and metamorphic assemblages, known as Mashhad Phyllite. ChamanBid Formation is one of the most famous Jurassic deposits in the northeastern. The studied sequence in the Ghroneh section is located at 43 kilometers north of Neyshabur and northeast of Ghroneh village (580 45’ 36’’, 360 45’ 05’’), respectively contains siliciclastic rocks of Kashafrud Formation, shale, marl, limestone, and sandstone beds of ChamanBid Formation, and thick to massif limestones of the Mozduran Formation. Most paleontological studies on the ChamanBid Formation are done based on ammonites (Majidifard, 2003, 2008; Raoufian et al., 2011, 2014; Seyed Emami et al., 2013, 2018), palynomorphs (Mafi et al., 2014a,b), and more recently nannofossils by Amani et al. (2016). Based on calcareous nannofossils, the Early Bajocian–Early Berriasian age was suggested for the mentioned deposits in the Ghroneh section. In the present study, for the first time, ostracods of the ChamanBid Formation have been investigated. The present study introduces the ChamanBid Formation ostracods and compares this fauna within the calcareous nannofossils biozones.Methods and Results  The thickness of the ChamanBid Formation in the studied section is 715 meters and consists of shale, marl, and limestone, interbedded with some sandstone beds. Sixtyfour samples of the ChamanBid Formation with intervals of 10 to 15 meters were collected. 300 grams of each sample were soaked in water and hydrogen peroxide for 24 hours and washed in 30 and 60 mesh sieves. The residue was dried, and all ostracods in each sample were separated. The ostracods were studied with a Zeiss ZH55 microscope at 40x magnification and photographed in scanning electron microscopy (SEM) at the central laboratory of the Ferdowsi University of Mashhad.Results and ConclusionOstracoda is one of the most valuable crustaceans in paleontological and paleoecological studies. The remains of these small and microscopic crustaceans are widely distributed through Phanerozoic, and individuals belonging to this subgroup are characterized by their particular morphological and physical characteristics (Van Morkhoven, 1963). In the present study, 45 genera and 59 species of Ostracoda have been identified in the ChamanBid Formation in the studied section. Previous studies of Ostracoda have been compared with ammonite zones. The current study is important since there are no reports on Iran’s Jurassic ostracods. Therefore, introducing ostracods and determining their age range is a significant objective of this study; however, their preservation is relatively poor. The study of the ChamanBid Formation ostracods in the Ghroneh section led to identifying of 59 species belonging to 45 genera. For relative age dating in the present study, calcareous nannofossils have been used and identified ostracods correlated with them. These assemblages have been compared with 12 previously reported nannofossil zones from the Ghroneh section. Nannofossil zones (Amani et al., 2016) belong to NJ9 to Early CC1 and confirm the age of Early Bajocian to Berriasian for the discussed ostracod assemblages.References Amani, R., Hadavi, F., Ghaderi, A., Khodadadi, L., 2018. Biostratigraphy of the Chamanbid Formation in Ghoroneh section at the Binalud Mountains based on Calcareous Nannofossils. Sedimentary Facies, 10 (2): 193212.Mafi, A., GhasemiNejad, E., Ashouri, A.R., Vahidinia, M., 2014a. Dinoflagellate cysts from the Upper Bajocian–Lower Oxfordian of the Dalichai Formation in Binalud Mountains (NE Iran): their biostratigraphical and biogeographical significance. Arabian Journal of Geosciences, 7: 3683–3692.Mafi, A., GhasemiNejad, E., Ashouri, A.R., Vahidinia, M., 2014b. A note on the discovery of the suturocavate dinoflagellate cyst (Limbodinium absidatum) in the Middle East (Binalud Mountains, NE Iran). Journal of African Earth Sciences, 92: 2124.Majidifard, M.R., 2003. Biostratigraphy, lithostratigraphy, ammonite taxonomy and microfacies analysis of the Middle and upper Jurassic of Northeastern Iran. Ph.D. thesis, Julius Maximilians Universitat Wurzburg, 210 p.Majidifard, M.R., 2008. Stratigraphy and facies analysis of the Dailichai and Lar formations (MiddleUpper Jurassic) of NNE Iran. Beringeria, 39: 3 49.SeyedEmami, K., Schairer, G., Raoufian, A., Shafeizad, M., 2013. Middle and Late Jurassic ammonites from the Dalichai Formation west of Shahrud (East Alborz, North Iran). Neues Jahrbuch für Geologie und Paläontologie Abhandlungen Band, 267: 43 66.Van Morkhoven, F.P.C.M., 1963. PostPaleozoic Ostracoda. Their Morphology, Taxonomy and Economic Use. Elsevier Publication, Amesterdam, 478 p.Raoufian, A., Joly, B., SeyedEmami, K., Ashouri, A.R., Majidifard, M.R., Ameri, H., 2014. Phylloceratoidea du Jurassique moyen et supérieur du NordEst de l’Iran (Monts Binalud). Annales de Paléontologie, 100 (4): 311–325.Raoufian, A., SeyedEmami, K., Ashouri, A.R., Majidifard, M.R., Joly, B., 2011. Middle and Late Jurassic Phylloceratidae from the Binalud Mountains (Northeast Iran). Sedimentary Facies, 3 (2): 68–87. (in Persian).SeyedEmami, K., Raoufian, A., ZandMoghadam, H., 2018. Late Bajocian and Bathonian (Middle Jurassic) ammonites from the Dalichai Formation north of Damghan (Alborz, North Iran). Neues Jahrbuch für Geologie und Paläontologie, 288 (2):183–203.