Writers : Ghavidel Sivaki,Mohammad
Refference : The 20th Symposium on geosciences;Tehran
Publishing Year : 1380

Abstract :

The Silurian strata in eastern Alborz Range is called Niur Formation. This formation is well-developed between the Esfaraien and Bojnourd road, approximately 35 km southeastern Bojnourd city(35 km southeastern Caspian Sea). The Niur Formation is 750 thick and in ascending stratigraphic order, it has been divided into Member I and Member Ii. The Member I is 500 m thick and consists mainly of black shales with subordinate thin- bedded limestones. The Member H is 250 m thick and comprises of white sandstones, changing into red shales towards upward. The lower and upper contacts of Niur Formation is conformable with underlying (Ghelli Fm.) and overlying (Padeha Fm.) formations. A total of 76 surface samples were treated for chitinozoans from this formation, in order to establish a chitinozoan biozonation and to determine the palaeogeographic relationships of eastern Alborz Range (Kopet_Dagh Region) to Zagros Basin of southern Iran as well as other parts of the world.

All samples of Member 1, contain well_preserved and abundant palynomorphs (acritarchs, chitinozoans, cryptospores and scolecodonts), but those of Member H are barren. Thirty_two chitinozoan species (6 genera) were recognized in this study, and arranged in four biozones. Biozone of Ancyrochitina mergo appears in the upper part of Ghelli Formation, suggesting the Ashgillian age. The biozones of Ancyrochitina laevaensis, Ancyrochitina ramosaspina / Angochitina aff longicollis and Plectochitina saharica occur through Member I of Niur Formation, that they suggest Early Silurian for this part of formation. Member II lacks of chitinozoans, but some samples contain cryptospores and a few acritarchs, indicating Wenlockian age. 115 chitinozoan.

Subject List : chitinozoa