Evolution of the Khoshyeilagh Formation platform during the Middle to Late Devonian in the Eastern-Alborz Mountains, NE Iran: Facies analysis, paleoenvironments and sequence stratigraphy

The Khoshyeilagh Formation in the eastern Alborz Mountains (north-east Iran) is Middle to Late Devonian post-rift succession. Facies analysis led to the recognition of five facies associations that are deposited in terrestrial (fluvial) and marine (carbonate ramp platform) environments. Its marine sediments are formed in inner ramp, mid-ramp, outer ramp, and basin sub-environments. Sequence stratigraphy of the Khoshyeilagh Formation is composed of five complete (and one incomplete) third-order depositional sequences with tectono-eustatic origins. Tectonic setting of the Khoshyeilagh Formation is an extensional post-rift or passive margin basin across the Paleo-Tethys Basin (northern rim of the Gondwana). This basin underwent various changes from Middle to Late Devonian and its ramp platform passed evolutionary stages from homoclinal type to distally steepened type. Depositional system of this basin is similar to mixed siliciclastic-carbonate system.