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.

库姆组的 Posht Darband 地层剖面被认为在伊朗西部 Sanandaj-Sirjan 区西北部进行古生物学研究。现场观测表明，库姆组由中厚层石灰岩（如“a”段）和砂质石灰岩、砂岩和绿色泥灰岩交替（如“b”段）组成。根据古生物研究的组合带Lepidocyclina -盒果藤属- Ditrupa在 Qom 地层中已经得到认可，并且在上述组合带与 Zagros 和欧洲盆地生物带之间存在相当大的相关性。由于库姆组上部石灰岩与砂岩沉积的岩相交替，库姆层序中动物群的丰度和种类急剧减少；而在库姆组顶部没有发现化石。因此，库姆矿床的这一区间被认为是贫瘠地带。微古生物学研究估计了库姆地层的 Rupelian-Chattian 年龄。