نخستین گزارش کنودونت‌ها و ماهیان گوادالوپین از قاعده سازند دالان در برش گهکم، شمال بندرعباس (زاگرس بلند)

نهشته ‌های کربناتی قاعده سازند دالان در برش گهکم، شمال بندرعباس برای اولین بار با استفاده از کنودونت ‌ها مورد بررسی قرار گرفته است. گونه ‌های کنودونت sweetognathus iranicus, hindeodus wordensis و merrillina divergens همراه با آثار ماهیان استخوانی، پالئونیسکوئید و ‌هایبودونتید در سه لایه پایینی سازند دالان (pd1, pdx1, pdx2) یافته شده‌ اند. با توجه به گونه ‌های کنودونت به دست آمده و موقعیت چینه شناسی لایه ‌های قاعده ای سازند دالان، سن وردین برای آنها پیشنهاد می ‌گردد. مقایسه سازند دالان در برش گهکم با برش‌‌های سازند خوف در عمان نیز همین سن را برای لایه ‌های مورد اشاره ثابت می ‌کند. بررسی نشان می ‌دهد که قاعده سازند دالان در زاگرس از شمال باختری (زردکوه) به سوی جنوب خاوری جوانتر می ‌شود. مطالعه سنگ چینه نگاری نشان می ‌دهد که سازند دالان در منطقه شمال بندرعباس (برش گهکم) از دو عضو دالان زیرین و دالان بالایی تشکیل شده و عضو تبخیری نار در آن وجود ندارد..

First report of Guadalupian conodonts and fishes from the base of Dalan Formation in the Gahkum section, North of Bandar Abbas (High Zagros)

IntroductionPermian sequences of Zagros and Arabiab peninsula including Dalan Formation and its equivalent, Khuff Formation, are precisely investigated in order to hydrocarbon exploration. Type section of Dalan Formation is described by Szabo Kheradpir (1978) and composed of three members; Lower and Upper Dalan and Nar evaporite Member between them. Studied succession in the present paper is located in Gahkum anticline, southeast of High Zagros Zone, SE Iran. We should pass 134 km northward from Bandar Abbas to attain Sarchahan village and then 7.7 km eastward in order to access the section. Coordinates of section are: 28° 5’ 40.5&N, 55° 55’ 18.19&E.DiscussionNumerous researches have been conducted on the Dalan and Khuff formations in the MiddleEast. For example, Alsharhan Narin (1995) studied the sedimentary environment and stratigraphy of Permian sequences in the Arabian Peninsula. Angiolini et al. (1998; 2003) and Henderson Mei (2003) studied the paleogeography and paleoclimatology of North and southeast of Oman by using conodonts. Kolodka et al. (2011) studied the biostratigraphy and microfacies of Dalan Formation. Dalan Formation in the Gahkum section with 685m thickness conformably overlie the marine uppermost beds of Faraghan Formation and can be divided to Lower and Upper Dalan Members. No sign of Nar evaporate Member is seen between them. The absence of this member may be related to lateral facies changes of evaporite to carbonate. The Upper Dalan Member is disconfomably overlain by Middle to Late Triassic dolomites of KhanehKat Formation (Fakhari, 1995, Sabzehei, 1993). On the basis of foraminifer stratigraphy, Kolodka et al. (2011) proposed the age of Wordian for the base of Lower Dalan Member, and the present conodont species; Sweetognathus iranicus, Hindeodus wordensis and Merrillina divergens prove this age. On the other hand, the base of Khuff Formation (equivalent of Dalan Fm.) in the southeast and interior Oman has the age of Wordian (Angiolini et al., 1998; 2003). Conodonts are associated with microvertebrate remains such as skeletal particles, scales and teeth of paleoniscoids, hybodontiforms and osteichthyan fishes.ConclusionConodont studies in addition to the stratigraphic situation of the base of Dalan Formation in the Gahkum section show the age of Wordian. It seems that the base of Dalan Formation is diachronous and becomes younger from the northwest to the southeast of High Zagros. The absence of Nar evaporite Member between Lower and Upper Dalan carbonate members, may be related to the lateral facies changes. This is the first report of paleoniscoid, hybodontid and osteichthyan fish remains from the Permian strata of Zagros Mountains.Acknowledgment This paper is the result of project no. 95/200/168, so we appreciate Deputy of Research and Technology, University of Hormozgan for financial supports. Authors thank M.K. Kamali and F. AminNezhad who helped us in field and laboratory works.ReferencesAlsharhan, A.S., Nairn, A.E.M., 1995. Stratigraphy and Sedimentology of the Permian in the Arabian Basin and Adjacent areas: a Critical Review. In: Scholle, P.A., Peryt, T.M., UlmerScholle, D.S., (eds.), The Permian of Northern Pangea, SpringerVerlage, 2: 187–214.Angiolini, L.,  Nicora, A., Bucher, H., Vachard, D., Pillevuit, A., Platel, J.P., Roger, J., Baud, A., Broutin, J., Al Hashmi, A., Marcoux, J., 1998. Evidence of a Guadalupian Age for the Khuff Formation of Southeastern Oman: Preliminary Report. Rivista Italiana Di Paleontologia e Stratigrafia, 104 (3): 329340.Angiolini, L., Balini, M., Garzanti, E., Nicora, A., Tintori, A., Crasquin, S., Muttoni, G., 2003. Permian climatic and paleogeographic changes in Northern Gondwana: the Khuff Formation of Interior Oman. Palaeogeography, Palaeoclimatology, Palaeoecology, 191: 269300.Henderson, C.M., Mei, S.L., 2003. Stratigraphic versus environmental significance of Permian serrated conodonts around the Cisuralian Guadalupian boundary: New evidence from Oman. Palaeogeography, Palaeoclimatology, Palaeoecology, 191: 301328.Kolodka, C., Vennin, E., Vachard, D., Trocme, V., Goodarzi, M.H., 2011. Timing and progression of the endGuadalupian crisis in the Fars Province (Dalan Formation, KuhE Gakhum, Iran) constrained by foraminifers and other carbonate microfossils. Facies, 58 (1): 131–153.Sabzehei, 1993. Geological map of Haji Abad, scale 1/250000, Part G. Geological Survey of Iran.Szabo, F., Kheradpir, A., 1978. Permian and Triassic stratigraphy, Zagros Basin, South‐West Iran. Journal of Petroleum Geology, 1 (2): 57–82.