Chitinozoan Biostratigraphy and Palaeogeography of Lower Silurian strata Sarchahan Formation) in Zagros Basin, southern Iran

Palynological investigation was carried on sixty samples from the Sarchahan Formation. All sample contain well-preserved and abundant chitinozoan taxa. A total of ۹ genera (۲۷ species) were recognized in this study. Several critical chitinozoan species of Sarchahan Formation are common with contemporaneous chitinozoan assemblages from Saudi Arabia, Algeria, Libya and to less extent from northwestern Spain, Estonia, Florida, Paraguay, consisting of Plectochitina pseudoagglutinans, Plectochitina paraguayensis, Plectochitina saharica, Plectochitina aff nodifera, Plectochitina raphli, Plectochitina khosravii, Angochitina macclurei, Pterochitina deichia, Clathrochitina aff clathrata, Ancyrochitina covexa, Ancyrochitina vikiensis, Cyathochitina campanulaeformis, and Conochitina algarada. Likewise, ۹ out of ۲۷ chitinozoans are new species including Ancyrochitina iranensis, Ancyrochitina zagrosiensis, Ancyrochitina winchesterae, Ancyrochitina faraghanensis, Ancyrochitina zakeenensis,  Plectochitina zagrosiensis, Plectochitina kazhdumiensis and Cyathochitina sarchahanensis. Except for the new species, the rest of chitinozoan taxa of the Sarchahan Formation has been recorded from Qusaiba and Sharawra members of Qalibah Formation in Saudi Arabia. On the other hand, the lithological and palaeontological data of Early Silurian sediments of Zagros basin of Iran are quite similar to the Qalibah Formation of Saudi Arabia. This similarity suggests that the same environmental condition has been prevailed in northern and southern Persian Gulf during the Early Silurian. Based on palaeontological data, the Early Silurian is assignated to the Sarchahan Formation. Therefore, there is a hiatus between the Sarchahan (Early Silurian) and Zakeen (Early-Late Devonian) formations. This hiatus encompasses the Middle and Late Silurian strata, possibly corresponding to the Caledonian Orogeny.