ليتوستراتيگرافي و بيوستراتيگرافي نهشته هاي پرمين در برش مارسلان ، سنگرود(البرز غربي )

Lithostratigraphy and Biostratigraphy of the Permian Strata at Marselan Section, Sangrud, Western Alborz

The Upper Paleozoic strata widely crop out in the Marselan Valley, 28 km northeast of Loshan, north of Sangrud. The litho- and biostratigraphic study led to identification of 57 species (distributed among 37 genera) of foraminifera and 8 genera and species of algae. Three litho logic units (formations), seven litho zones and three assemblage zones are identified within the study interval. The rock units of the Permian system are in descending order as: a) Doroud Formation (Asselian- Sakmarian, thickness of 225 m), underlain disconformably by the middle Carboniferous (Bashkirian-Moskovian) Khashachal Formation, consists of red conglomerate, sandstone, shale, siltstone and buff oncoid limestone that can be divided in to three litho zones. b) Ruteh Formation (Murghabian, thickness of 364 m) mainly composed of cliff forming limestone that can be divided into two lithozones, unconformably overlying the Doroud Formation. c) Nessen Formation (early Djulfian, thickness of 140m) consists of marly limestone intercalated with shale (contains of two lithozones), unconformably underlain by the Ruteh Formation and overlain disconformably by Elika Formation of Early-Middle Triassic age. Thin beds of laterite-bauxite indicate an unconformity at the Permian-Triassic boundary. Also these beds reveal that the study area, with a humid warm temperature, was lying near lat. 30°S.