General:
     Palynological investigation was carried on sixty samples from the Sarchahan Formation. All sample contain well-preserved and abundant chitinozoan taxa. A total of 9 genera (27 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, Plectoehitina saharica, Plcctochitina aff nodiflra, Plectochitina raphli, Plectochitina khosravii, Angochitina macclurei, Pterochitina deichia, Clathrochiti na all clathrata, Ancyrochitina covexa, Ancyrochiti na vikiensis, Cyathoch i tina carnpanulaeformis, and Conochitina algarada. Likewise, 9 out o127 chitinozoans are new species including Ancyrochitina iranensis, Ancyrochitina zagrosiensis, Ancyrochiti na wi nchesterae, Ancyrochitina faraghanensis, Ancyrochiti na zakeenensi s, Plectochitina zagrosiensis, Plectochitina kazhdurn iensis 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 Qalihah Formation in Saudi Arabia. On the other hand, the lithological and palaeontological data of Early Silurian sediments of Zagros basin of Iran arc quite similar to the Qalibah Formation of Saudi Arabia. l’his similarity suggests that the same environmental condition has been prevailed in northern and southern Persian Gulf during the Early Silurian. I3ascd on palacontological 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