Lithostratigraphy, petrography and geochemistry of sandstones in the Middle part of the Upper Red Formation at Toryan area, NW Zanjan

Document Type : Original Article

Authors

• Negar Kaboudmehri ¹
• Afshin Zohdi ²
• Hossein Kouhestani ³
• Mir Ali Asghar Mokhtari ³

¹ M.Sc. in Economic Geology, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran

² Assistant Professor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran

³ Associate Professor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran

10.22067/sed.facies.2022.71565.1004

Abstract

Toryan area is located in the Central Iranian zone, about 120 km northwest of Zanjan. In this area, the exposed rock units belong to the Upper Red Formation (URF). The thickness of the URF at Toryan is 1010 m, and consist of four main parts. These parts, from bottom to top, consist of: 1-alternation of gypsiferous (locally salt) green marls (300 m), 2-alternation of red marls and grey to red sandstones (275 m), 3-alternation of red and green marls intercalated with sandstone (210 m), and 4-green marls with interbedded green siltstones (225 m). Based on microscopic studies, average particle size of sandstones in the Toryan area is about 0.2 mm. These sandstones also display poor orientation, poor to moderate sorting, and mainly are angular to semi-angular. Based on component types and results of point counting, the studied sandstones contains 16% quartz (included mono and poly-crystalline with both straight and wavy extinction), different types of rock fragments (sedimentary, metamorphic and volcanic) and 10% feldspar (mainly ortoz). According to Folk (1980) classification, it can be stated that the studied sandstones are litharenite to feldspathic litharenite with calcite and evaporitic cements. Based on the main components and the results of petrographic, major and minor elements geochemical analyses, the tectonic setting of these sandstones is related to foreland and collision basins. These data represent an intermediate to felsic source rock for these sandstones, which were affected by semi-arid to arid climate.

Keywords

• Stratigraphy
• Geochemistry
• Tectonic setting
• Upper Red Formation
• Toryan
• Zanjan

Main Subjects

• Microfacies and Sedimentary Environments
• Geochemistry & Chemostratigraphy

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