نوع مقاله : مقاله پژوهشی
نویسندگان
1 تهران - دانشگاه تهران - پردیس علوم - دانشکده زمین شناسی
2 استادیار پژوهشی، موسسه تحقسقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران.
3 دانشکده زمین‌شناسی، دانشکدگان علوم، دانشگاه تهران، تهران، ایران.
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
The palynofloras of Shemshak (upper part) and Dalichai (lower part) formations, Deh-Soufian, north of Semnan include 57 species of spores (34 genera), 25 species of pollen (13 genera), and 14 species of dinoflagellate cysts (8 genera). Based on the miospores, the Klukisporites variegatus-Striatella spp.-Contignisporites burgeri assemblage biozone is introduced. Co-occurrence of Contignisporites burgeri and Striatella seebergensis allows for the Bajocian-Bathonian boundary to be located 75m below the boundary of Shemshak-Dalichai rock units. The presence in the sequences below this chronostratigraphic horizon of Mendicodinium scabratum (Bajocian) supports this age assignment. The boundary of Shemshak and Dalichai (with basal sandstone) formations is discontinuous. While no significant change in composition of miospores is discernible in palynofloras retrieved from the above rock units, the relative abundance of such terrestrial palynomorphs varies drastically. This might be attributed to side effects of the mid-Cimmerian orogeny. It should be noted that 45m below boundary of the two rock units 24 miospore species exit whereas 11 different ones appear 20m above that boundary. Notable correspondence of the Iranian Middle Jurassic palynofloras across the Alborz Ranges signifies to a rather significant coastal vegetation similarity of the time in the area. Whereas both Gondwanan and Eurasian miospore key species occur in the palynofloras examined but those particularly endemic to the southern landmasses are missing from the palynofloras studied. Palynological evidence seemingly confirms location of the Alborz ranges on northeastern margin of the Neotethys Ocean in the Middle Jurassic. The available paleontological data (ammonites and dinoflagellate cysts) apparently support this interpretation.
کلیدواژه‌ها [English]
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