The Carbonate Shelf Deposits of the Rooteh Formation in Estakhr Area (Eastern Alborz)

The Permian sedimentary succession of the Estakhr stratigraphic section (Eastern Alborz) is composed of the lower Permian Dorood and the middle Permian Rooteh formations. The succession disconformably covers Lower Carboniferous rocks (Mobarak Formation) through a fining upward basal conglomerate (considered as type-1 sequence boundary). The upper termination of the Permian deposits is hidden within the core of the Tooyeh antiform. Rooteh Formation in the studied section (108 m thick) is mainly carbonate in nature. Field and laboratory investigations have resulted in recognition of twelve major carbonate facies categorized into six facies associations. The carbonate facies associations, namely, have been: tidal flat facies association, lagoon facies association, back-reef shoal facies association, reefal facies association, fore-reef shoal facies association and mid-shelf facies association. The tidal flat facies were found: lime mudstone/bioclast mudstone, stromatolitic dolomudstone, peloid wackestone and intraclast wackestone/packstone. Lagoon facies association consists of oncoid wackestone/packstone facies. The oncoid coatings were created by cyanobacterian encrusters, mainly Girvanella. Oncoid grainstone/rudstones were formed in back-reef shoal assemblage (oncoid pavement), and coral boundstones have been shaped in the framework of the middle Permian carbonate reefs. Fusulinid grainstone and echinoderm grainstone belong to fore-reef shoal facies association. Mid-shelf facies association is composed of fusulinid packstone, echinoderm wackestone/packstone and bryozoan wackestone facies.Glacial motivated sea level fall in the late Carboniferous led to development of the erosive unconformity in the Carboniferous-Permian boundary in the region. The Carbonate facies of the middle Permian Rooteh formation, in Estakhr section, have been deposited in a carbonate shelf system which was established in the Paleothetys passive continental margin (north of Gondwanaland) due to sea level rise during the middle Permian. This rise is thought to be the result of the Permian deglaciation event. Carbonate shelf facies model is rarely reported from Permian successions of the Alborz mountainsystem.