نوع مقاله : مقاله پژوهشی
نویسندگان
1 استاد گروه زمین شناسی دانشگاه صنعتی شاهرود، شاهرود، ایران
2 دانشگاه صنعتی شاهرود
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
A complete stratigraphic succession of the Elika Formation (Early–Middle Triassic) and the Shemshak Group (Late Triassic–Middle Jurassic) is well exposed in northeastern Jajarm, in the Eastern Alborz structural zone. In this study, the upper part of the Elika Formation and the Shemirzad Formation of the Shemshak Group were investigated using stratigraphic and petrographic methods.
The upper part of the Elika Formation consists of approximately 80 m of medium- to thick-bedded dolomite and dolomitic limestone, which are mostly stromatolitic boundstone and lack fossils. These features indicate deposition in a tidal-flat environment. This formation disconformabaly overlies the Mobarak Formation.
The Shemirzad Formation is approximately 285 m thick and is predominantly composed of shale with interbeds of sandstone. Based on stratigraphic characteristics, it can be divided into several units. Marker beds include a middle sandstone layer rich in Calamites plant fossils and a fossiliferous limestone layer in the upper part. Petrographic analyses reveal that the predominant petrofacies of the Shahmirzad Formation are predominantly composed of siltstone, litharenite with clay matrix and cement, litharenite with carbonate cement, feldspathic litharenite with carbonate cement, feldspathic litharenite with siliceous cement, lithic arkose with carbonate cement, and lithic arkose with clay cement. litharenite represents one of the principal sandstone types associated with uplifted orogenic belts and deposition in foreland basins.
Key words, Jajarm, Shemshak Group, Elika Formation, Shahmirzad Formation, Petrofacies
کلیدواژهها [English]
)