Biofacies, Taphofacies, and Depositional Environments in the North of Neotethys Seaway (Qom Formation, Miocene, Central Iran)

Abstract

Abstract This research attempted to reconstruct the sedimentary environment and depositional sequences of the Qom Formation in Central Iran, using biofacies and taphofacies analyses. The Qom Formation in the Andabad area (3°48′12.6″ N, 47°59′28″ E) is 220 m in thickness. The thickness of the Qom Formation in the Nowbaran area (35°05′22.5″ N, 49°41′00″ E) was found to be 458 m. In both areas, the formation consists mainly of shale and limestone. The lower boundary between the Qom and Lower Red Formations is unconformable in both areas. In the Nowbaran area, the Qom Formation is covered by recent alluvial sediments. In the Andabad area, the Qom Formation is unconformably overlain by the Upper Red Formation. A total of 122 limestone and 15 shale rock samples were collected from the Andabad area, and 94 limestone and 24 shale rock samples were collected from the Nowbaran area. Analysis of the collected samples resulted in the recognition of nine biofacies, one terrigenous facies, and five taphofacies within the Qom Formation in both areas. Based on the vertical distributions of biofacies, the Qom Formation is deposited on an open shelf carbonate platform. This carbonate platform can be divided into three subenvironments: inner shelf (restricted and semirestricted lagoon), middle shelf, and outer shelf. Two third-order and one incomplete depositional sequences were identified in the Nowbaran area, but in the Andabad area, three third-order and one incomplete depositional sequences were distinguished.