A report from the Oligocene Qom Formation benthic foraminifera; northwest of the Sanandaj–Sirjan Zone; Western Iran

Abstract

The Posht Darband stratigraphic section of the Qom Formation is considered to undertake paleontological study in the northwest of Sanandaj–Sirjan Zone, Western Iran. Field observations demonstrate that the Qom Formation is composed of medium to thick-bedded limestone (as Member a ) and alternation of sandy limestone, sandstone and green marl (as Member b ). Based on paleontological studies the Assemblage Zone of Lepidocyclina–Operculina–Ditrupa has been recognized in the Qom Formation and there is a considerable correlation between the mentioned assemblage zone and the Zagros and European basins biozonation. Due to the lithofacies alternation of limestone to sandstone deposits in the upper portion of the Qom Formation, the abundance and variety of fauna in the Qom succession have drastically been decreased; whereas, no fossil have been found in the top of the Qom Formation. Hence, this interval of the of Qom deposits is considered as Barren Zone. Micropaleontological studies estimate the Rupelian-Chattian in age for the Qom Formation.