Petrography and geochemistry of the Paleocene sandstones from north of Birjand: Implications for provenance, tectonic setting and paleoclimate conditions

Introduction The relation between the tectonic setting, provenance and composition of siliciclastic deposits has been investigated by many researchers. The geochemistry of major and trace elements of siliciclastic deposits provides information about provenance, the paleoweathering conditions and tectonic setting of sedimentary basins. In terms of structural division, the study area is located in the Sistan Suture Zone (SSZ). The Paleocene- Eocene siliciclastic strata in the east of Iran have significant development, diversity and thickness lithologically. The studied section is located in the 17 kilometers of north of Birjand and 3 kilometers of east of Fariznuk village the most important way to reach the study area is the main road of Birjand- Mashhad. The Fariznuk section with Paleocene age is 113 meters in thickness and forms from three lithostratigraphic units consisting lower conglomerate, middle sandstone and upper carbonate units. The purpose of this study is to investigate the petrographic and geochemical properties of Fariznuk section in the north of Birjand in order to determine the provenance, tectonic setting and paleoweathering conditions. Materials and Methods In this study, 90 rock samples were collected from the studied sequence. The study of 35 sandstone samples components composition (modal analysis) is performed by using the point counting method of Gazi- Dickinson. Folk (1980) compositional classification of sandstones is used for studied samples. Geochemical analyses (major and some trace elements) are carried out by XRF method for 15 fine grain sandstone samples. Discussion of Results and Conclusions In the provenance studies, that are performed by petrographic methods, by using the compositional and textural evidences, the characteristics of provenance of sediments can be investigated. Fine to coarse grain sandstones of the studied sequence have angular to sub rounded grains with poorly to well sorting. Based on mineralogical composition these samples are litharenite (Q52.9, F7.3, RF39.8). The plutonic monocrystalline quartz in the studied sandstone samples confirms the presence of intrusive igneous rocks in the source area. While the existence of straight to weakly undolatory extinction in monocrystalline quartz together with metamorphic rock fragments are indicative the presence of metamorphic rocks with above igneous rocks in the source area. Also, the presence of volcanic rock fragments such as peridotite rock fragments from the