Encountered plant macrofossils of Shemshak Formation in Ghoznavi - Fasian area, along Shahrud - Azadshahr road (Eastern Alborz), Northern Iran: Regional stratigraphic implications and Palaeoclimatic condition

نوع مقاله : بدون عنوان

نویسنده

• نجفی حاجی پور نجفی حاجی پور

10.22067/sed.facies.v2i1.1439

چکیده

The Shemshak Formation is well-exposed in northern Ghoznavi – Farsian area which is located along Shahrud – Azadshahr road. The thickness of this formation in the studied area is about 1200 meters and consists of sandstones, siltstones and shales with a few coal seams interbeds. The Shemshak Formation disconforably rests on the Elika Formation and it is overlain by the Farsian Formation. In this area, most parts of this formation contain plant fossil including leaves stems and reproductive organs. The identified mega fossils consist of 25 species (12genera) such as Baiera gracilis, Baiera muensteroana, Cladophlebis cf. nebbensis, Cladophlebis denticulate, Cladophlebis raciborski, Clathropteris meniscoides, Ctenozamites iranica, Cycadatites sp., Dictyophyllum sp., Nilssonia cf. acuminate, Nilssonia feriziensis, Nilssonia tenuinervus, Nilssoniopteris vittata, Otozamites eichwaldi, Peterophyllum bavieri, Podozamaites lanceolatus, Pterophyllum braunianum, Pterophyllum tietzei and Scyhtophyllum persicum. The above mentioned plant mega fossils belongs to various plant orders such as Bennetitales, Coniferales, Cycadales, Filicales, Ginkgoales, incertae sides ferns and Peltaspermales. Based on the above- mentioned plant fossil taxa, a Late Triassic (Rhetiain) – Middle Jurassic age is suggested for the Shemshak Formation. Based on identified thermophitic plants, such as Dictyophyllum, Otozomites, Pterophyllum and Zamites, it is interpreted that a humid- subtropical climate has been prevailed during deposition of Shemshak Formation in the studied area.

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