Facies analysis, sedimentary environment and sequence stratigraphy of the Khan Formation in the Kalmard Sub-Block, Central Iran: implications for Lower Permian palaeogeography

摘要

The Lower Permian Khan Formation in the Kalmard Sub-Block consists mainly of alternation of siliciclastic (conglomerate, sandstone, siltstone and shale) and carbonate rocks (limestones and dolostones), which were deposited in diverse coastal and shallow marine environments. The siliciclastic successions reflec several nearshore lithofacies, which constitute f ve major palaeoenviron-mental associations including proximal lower-middle shoreface, upper shoreface, foreshore, tidal inlet and washover fan/lagoon. The most abundant sedimentary structures in the Khan Formation sand-stones are horizontal lamination, planar and trough cross stratif cation, bidirectional plane bed, swaley and hummocky cross stratificati n. These successions were formed in a barrier island complex. Carbonate production in this formation is dominated by benthic foraminifera particularly fusulinids, brachiopods, mollusks, bryozoans, echinoderms, corals, Tubiphytes, ooids, intraclasts, and peloids. Based on fossil content, texture and sedimentary structures, 23 different facies types have been distinguished that accumulated in four facies associations. The majority of facies associations (FA1-FA4) were formed in tidal fat (FA1), lagoon (FA2), bioclastic shoal (FA3) and shallow open marine (FA4) which deposited on a homoclinal ramp including inner and middle ramp. On the basis of facies relationships and the recognition of key surfaces in the Khan Formation, four (in the Bakhshi and Bibisene sections) and three depositional sequences (in the Tangal-e-Shotoru and Randar sections) are recognized The stratigraphic architectures of the Khan Formation deposits are the result of the interplay between activity of the Kalmard Fault and relative sea-level changes. Palaeogeographic data show that during the deposition of the Khan Formation, the Kalmard Sub-Block was located in low latitudes in a warm and humid climate.