Paleoclimatic and paleogeographic signatures in the upper Triassic beds of Shemshak group in Central Alborz
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Abstract :
Late Triassic deposits of Shemshak Group in Emarat section at about 30 km south of Amol and Emamzadeh Hashem section and about 50km north east of Tehran in Central Alborz have been studied for some paleoclimatic and paleogeographic indicators. The data used in this study include: 10 point counting of sandstones, 13 main oxide analyses, 8 species of plant fossils and 4 genuses of palinomorphs. Lithological and geochemical data were restricted to the Late Triassic deposits. Important events of the Late Triassic such as: Late Norian and Middle Rhaetian droughts were revealed by the presence of gypsum beds. This study indicates that lithological signatures are clearly consistent with the mentioned global event and this tracer can be a good basis for controlling other age-related paleontological data. Comparison of the Alborz and Siberian plant fossils indicated that the study area did not have significant differences compared to more northern regions such as Siberia. The investigated palinomorphs indicated that most of them are hygrophytic and mesophytic and some of them had more well-known origin which belonged to some ferns. The point counting data revealed that the source area of the sediments experienced dry to semi-humid climates. This study also confirms that the Alborz region was part of Eurasia, due to the Eo-Cimmerian orogenic event based on recognized plant fossils.
