Writers : Jalali, Ali; Supervisor: Seyed Ali Aghanabati
Refference : M.Sc.Thesis- Islamic Azad University North Tehran Branch
Publishing Year : 1386

Abstract :

This thesis investijates 3 stratigraphic sections of Lower Cretaceous sedimentary sequence in Northeast Iran (Kopeh-Dagh basin). The coordinates of these sections are: Bid-e-Sokhteh (northeast of Mashhad, geological map of Bazangan, scale 1:100.000) at 36,20,35 N, 60,20,36 E it subdivision to 3 members, Ab-e-Garm section (northeast of Mashhad, geological map of Chahchahe, scale 1:100.000) at 36,31,05 N, 60,04,52 E, it subdivision to 3 members and Geliyan section (south of Shirvan, geological map of Shirvan, scale 1:100.000) at 34,14,14 N, 57,54,12 E, it subdivision to 4 members, all these tree sections were examinated and sampled along NE-SW direction.
This study was aimed at investigation of the biofacies and lithofacies of Tirgan Formation and determination of the Lower and upper boundaries of the formation in these sections.
Filed and stratigraphic studies include that thickness of Tirgan Formation increases from east to west of Kopeh-Dagh basin. The thickness in Bid-e-Sokhteh near the Iran-Turkmenistan border, is only about 64 meters, while in Geliyan, which is the western most section, thickness is 167 meters. This evidence shows that the depth of this formation in the west is gradually replaced by the detrital facies.
The contact between red sandstone of Shurijeh Formation (Upper Jurasic-Neocomian) and light gray-brown limestone of Tirgan Formation (Lower Cretaceous, Aptian-Albian) is continuous and conform, the contact between Tirgan Formation and Sarcheshmeh Formation (Lower Cretaceous, Albian) is continuous and conform too.
Paleontoligical studies of this Thesis 40 genus and 20 species of Orbitolina and other kind of microfossils (from 200 samples were recognized), the hole assemblage confirms Aptian-Albian age for Tirgan Formation.
The following evidences of considered for determination of Aptian-Albian age for Tirgan Formation: existence of Dictyoconus aff. arabicus which belongs to this stage; existence of Pseudpchofatella sp. that belongs to this stage along with some index fossils of this stage Orbitolina debris, Iraqia cf. simplex, Orbitolina lenticularis,. ; existence of abundant of ooids in the basal part of Tirgan Formation is the other evidence for lower boundary of Tirgan Formation. And other evidence is sharp change from the red color of Shuridjeh Formation into grey oolithic limestone of Tirgan Formation.

Subject List : Biostratigraphy