Writers : Sohrabi,Sima ;Supervisor: S,Feyznia
Refference : M.Sc.Thesis- School of Earth Sciences, Tehran
Publishing Year : 1378

Abstract :

Abstract:
The Kopet - Dagh sedimentary basin in eastern north of Iran has fault contact with Tooran platform from the north and is bounded to the south by Binalood mountains. According to Berberian and King (1981), this zone becomes sedimentary after early Kimmerian orogenic event (It happened when the concurrence of Iran and Tooran finished thick sediments were gathered with various facies from Jurassic to Miocene without Dortant stratigraphic gap. These sediments were deformed under late Alpine orogenevents and formed various anticlines and synclines with northwest - southwest strike.
The main aim of this research is to view sedimentary environment of Tirgan formation in central part of Kopet - Dagh basin.
Type section of Tirgan formation in the 40th kilometer of Dargaz is 780 meters thick with the age of Neocomian - Aption.
The thickness of this formation is very different in different regions so that it is equal to 40 meters in the east of Kopet - Dagh basin in Mozdooran. The contact of these two formations (Shoorigeh and Sarcheshmeh) is sharp.
In some part pf Kopet - Dagh sedimentary basin, Tirgan formation is as reservoire rock of gas resources in the north of Iran. Mozdooran and Tirgan formations are also counted as kartsic formation in Kopet - Dagh basin and are valuable regarding to water resources. (from the Point of water resources).
In this research, Tirgan formation was studied in Radkan and Dadanloo (the thickness of 257 and 387 meters) in detailed.
150 hard samples and 10 soft samples were taken with average distance of 3.5 -4 meters and thin sections were taken from hard samples. Detailed Petrographic studies resulted in distinction of 13 microfacies.
They are as follows: 1-Calcimdstone. 2-Bioclastic wackstone. 3-Bioclastic packstone 4-Oolitihic packstone 5-Oolitihic grainstone 6- Oolitihic packstone 7- Mixed grainstone 9- Peletoid grainstone
10- Aggregate packstone 11- Aggregate, grainstone 12- Sandstone 13- Marl
On the bases of fossils contents and their vertical Position in stratigraphic sectionc. It was recognised that Microfacies 1.2 and 3 belong to open marine and lagoon and were placed (settled) in facies belt 2 and 7 of Wilson (1975).
Microfacies 4 belong to facies belt 6 of Wilson which is located between Oolitihic bars and open marin.
Microfa 5 and 6 belonged to facies belt 6 of Wilson show bar and beach.
Microfacies 7 and 8 belong to facies belt 7 and 8 of Wilson (1975).
Microfacies 9 were formed in Radkan sections which were in facies belt 8 of Wilson.
Microfacies 10 and 11 were seen in Dadanloo section which belonged facies belt 8 of Wilson and showed restricted platform environment.
Generally, sedimentation of Tirgan formation were formed in Tidal flat (supradital, intertidal) and subtidal environments. This basin was deepended with the passage of time so that shaly and Marly sediments of Sarcheshmeh formation were placed over Tirgan formation conformably and with variation of facies change into open marine environment.
According to these results, horizontal model of deposition of Tirgan formation
was drown.
Features, processes and important diagenetic environments in Tirgan formation are as follow: Micritization, Bioturbation, Geopetal fabric, Isopaques fibrous rim cements and early dolomitizatiom were distinguished in marine pheriatic. Early compaction Aragonitic shells winnowing were formed is under saturated fresh, water pheriatic zone.
Filling cavity and fractures by Spary cement, forming. syntaxial overgrowth drusy cement, Poikilolopic cement and Neomorphism happened in active saturated fresh water pheriatic zone.
Meniccus, pendent cement and vadose sitl were formed in fresh water vadose
zone.
Late compaction, Stylolitization, late dolomitization (Saddle dolomite) formation of Authigenic minerals and late fracture filling happened in burial environment. Cathodolominecence analyses, Electrone Microprob analyses were done in some thin sections. Cathodolominecance analyses demonstrated that cementation was occured in different phases. Fibrous cement deposited in environment.
For more detailed studies of diagenes marine and evestigation of environment of dolomite formation. isotopic investigation, Electroma croprop anlysis, SEM and cathodolominecance studies are needed. But according to Petrographic documents and staining by Alizarine red s and Potacium ferrocianore we can conclude that dolomitization in this formation in intertidal region lagoon region and also bar region which probably was the result of mechanism of rej7ux and seepage and dolomitization in burial diagenesis.

Subject List : Microfacies