پديد آورندگان :
خداشناس، ناهيد دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين‌شناسي، مشهد ، ايران , هادوي، فاطمه دانشگاه فردوسي مشهد - دانشكده علوم - گروه زمين‌شناسي، مشهد ، ايران , نطقي مقدم، مرضيه دانشگاه پيام‌نور - گروه زمين‌شناسي، تهران، ايران , خزاعي، احمدرضا دانشگاه بيرجند - دانشكده علوم - گروه زمين‌شناسي، بيرجند، ايران
كليدواژه :
زيست چينه نگاري , بغمشاه , نانوفسيل‌هاي آهكي , طبس
چكيده فارسي :
در اين پژوهش سازند بغمشاه در برش چينه‌شناسي خروان با هدف مطالعه نانوفسيل‌هاي آهكي مورد نمونه برداري قرار گرفته است. سازند بغمشاه با سنگ شناسي غالب شيل و مارن، در شمال طبس از رخنمون گسترده‌اي برخوردار است و در برش مورد مطالعه 239 متر ستبرا دارد. مطالعات ديرينه‌شناسي انجام شده در اين پژوهش به شناسايي 46 گونه متعلق به 26 جنس نانوفسيل آهكي با حفظ شدگي متوسط تا خوب انجاميده است. نظر به اهميت حضور گونه‌هاي شاخص و مجموعه گونه‌هاي همراه، زيست‌زون‌هاي CC1 تاCC5 از زون بندي (1977) Sissingh تعيين گرديد. بر پايه زيست‌زون‌هاي مشخص شده، سن سازند بغمشاه در برش مورد مطالعه بريازين پيشين تا هوتروين پسين پيشنهاد مي‌شود.
چكيده لاتين :
This research has studied calcareous nannofossils of the Baghamshah Formation in Tabas Block (eastern Iran). Calcareous nannofossils are one of the most important fossil groups for biostratigraphical analysis. The earliest paleontological studies on the Baghamshah Formation have focused on ammonites (e.g., Seyed-Emami et al. 1988, 1991, 1997, 2001, 2002; Wilmsen et al., 2009). Kallanxhi et al. (2016) have also considered this formation's ammonites and nannofossil contents. The current study is the first investigation of calcareous nannofossils of the Baghamshah Formation in the Kharvan section and aims to discuss the possibility of using the standard nannofossil zones for the Baghamshah Formation.
Materials and Methods
The Kharvan section with 239 meters thickness is located 40 km northeast of Tabas near the Kharvan village. The formation has lithologically consisted of green and gray shales and marls. Generally, 75 samples from the Baghamshah Formation have been taken. Samples were prepared via the smear slide method (Bown & Young, 1998). All nannofossils were photographed in both cross-polarized light (XPL) and (PPL) and identified using Perch-Nielsen (1985) and Bown & Young (1998).
Result and Discussion
46 species belonging to 26 genera were identified in the studied section. Amongst them, 38 species belong to 21 genera of nannoliths and coccoliths, and 8 species from 5 genera belong to Didemnid ascidian spicules. Didemnid ascidian spicules are organisms with soft bodies and rigid spicules, which carbonate-rich seawaters and coral reefs are suitable environments for their colonization (Varol, 2006). The most dominant genera from the Baghamshah Formation are Watznaueria and Nannoconus. Among the nannofossil species, Nannoconus steinmannii, Retecapsa angustiforata, Calcicalathina oblongata, Tubodiscus verenae, Lithraphidites bollii, Cruciellipsis cuvillieri, and Nannoconus abundans are index species, used for biozonation. The Biostratigraphic studies in the Baghamshah Formation is led to the identification of calcareous nannofossils biozones CC1 to CC5 of Sissingh (1977) in the Kharvan section. Determined biozones represent the age of the early Berriasian - late Hauterivian for the investigated strata in the Kharvan section
Conclusion
The nannofossil assemblages of the Baghamshah Formation in the Kharvan section have average to pretty good preservation. In this section, the presence of CC1 at the lower part of the Baghamshah Formation and the presence of CC5 at the upper part of the formation shows that the age of the Baghamshah Formation is Early Berriasian - Late Hauterivian in the Kharvan section.
