Palaeoenvironmental assessment and lithostratigraphic revision of the Carboniferous-Early Permian succession in the Sanandaj-Sirjan Block (Iran)

Abstract

An updated lithostratigraphy of the Carboniferous to Early Permian succession, exposed in the southeastern Sanandaj-Sirjan Block is presented. The succession includes the unnamed Mississippian strata, the Asad Abad Formation (new) and the Vazhnan Formation (revised). The unnamed Mississippian strata, are disconformably covered by the Asad Abad Formaition. The Asad Abad Formation (late Serpukhovian-Moscovian), is disconformably overlain by the Vazhnan Formation. The late Gzhelian-Asselian Vazhnan Formation is disconformably covered by the late Early–Middle Permian Surmaq Formation at the type and reference sections. According to facies and stratal patterns, continuity, lithology, sedimentary structures, and skeletal composition, most of the Early Carboniferous sediments were deposited on broad, low-gradient ramps during periods of relative tectonic stability and regional subsidence. In contrast, during much of the Middle Carboniferous to Early Permian, southeast and northwest parts of the Sanandaj-Sirjan Block were dominated by siliciclastic influx, whereas the central part of this basin was dominated by ramp type platforms and sediment gravity flow deposits. The mosaic-like pattern of deposition observed in stages of platform evolution during Middle Carboniferous to Early Permian suggests a compartmentalization of the depositional settings that could be linked to considerable differential subsidence of fault movements.