نشریه رخساره های رسوبی
سال چهارم شماره 1 (پیاپی 6، تابستان 1390)

Carboniferous corals of Sardar Formation, in Zeludu stratigraphic section (in Ozbak Kuh Mountains) was Studied. After selected of 50 specimens of coral fossils, from first band of corals, 9 species belong to 5 genera from rugosa and tabulata corals with Late Serpukhovian age were identified. These corals are included following species: Heritschioides pseudosolitarius, Heritschioides vepres, Heritschioides cf. vepres, Paraheritschiodes antoni antoni, Paraheritschiodes sp. 1., Paraheritschiodes sp. 2., Multithecopora sp., Orygmophyllum sp. and Durhamina sp. In addition to review of the ages of Heritschioides vepres, H. pseudosolitarius, H. cf. vepres and Praheritschiodes antoni antoni species, two genera including Orygmophyllum and Durhamina are reported for the first time from Iran. These fauna can be compared with corals of Ural region. Based on ecological evidences, corallites arrangement and dissepiments thickness, back-arc parts of a shallow carbonate platform of ramp type can be concluded for the paleoenvironment of our studied section.

Microfacies and depositional environments interpretation of Asmari and Jahrum were studied in boreholes 2, 10 and 11 in Gol- Khari oil field. Based on petrographic criteria, fauna assemblages, biofacies and sedimentary textures, 21 carbonate microfacies and 3 non- carbonate petrofacies were recognized. These microfacies were deposited in distinct depositional environments including tidal flat, lagoon, bar and open marine in a homocline carbonate ramp.

The Qom Formation in Ghohrud area, have been investigated in order to determine its biostratigraphy and palaeoecology. The thickness of Qom Formation is 325 meters at the study area and consists of thin, medium to thick bedded and massive limestons. They underline on Eocene volcanic with disconformably and its upper boundary is overlain by alluvium. Based on thin section studies 14 genera and 26 species of the benthic foraminifera was determined. The Assemblage of benthic foraminifera represents the Late Oligocene (Chattian) to Early Miocene (Aqitanian?) age. Large benthic foraminifera with thin hyaline wall such as large lepidocyclinidae and nummulitidae with symbiont bearing algae are present. This is due to increase in water depth, low energy, normal salinity and prevailing of a deeper open marine environment. In shallower open marine environment foraminifera’s wall (with hyaline wall) become thicker and smaller in size that represents decrease in water depth, and increase in light and energy. In this section in semi-restricted lagoon environment foraminifera with porcelaneous wall and foraminifera with hyaline wall are present together. In shallow water (restricted lagoon) foraminifera with porcelaneous wall such as Austrotirillina, Borellis, Miliolids and peneroplis are present, that reveals decrease of depth and increase light and salinity factors.

Kopet-Dagh basin is located in north and northeast of Iran. Khangiran Formation is one of the most important Formations of Paleogene deposits. For study of Khangiran Formation bivalves, Chehelkaman Syncline section has been selected. This section located in west of Sarakhs city, east of Kopet-Dagh basin. Lithology of this Formation in the Sarakhs region composed of marl, marly limestone and siltstone. In addition lithology of deposits with oyster shells consists of 50m olive green monotonous marl with large shells of oysters that are very well preserved. Based on this shells study, species of Sokolowia beldersaiensis and Sokolowia buhsii of Ostreidae family have been recognized. These shells indicate sub-tidal to shallow marine environments and euhaline waters and proposed Middle Eocene age (Bartonian stage) for these sediments. Furthermore, paleobiogeography survey of this bivalves indicate dependency of Khangiran Formation to Tethyan realm, that this realm limited to central Asian region and located between Transylvanian basin of Romania, in the west and Tarim basin of China in the east. Retreat of this sea in the Middle Eocene cause of oyster shells composed in the Bartonian stage. These shells indicate dependency of Kopet-Dagh basin to Turan Sea that this subject causes of strengthens of Urasian theory of Kopet-Dagh basin.

Sarcheshmeh Formation is one the Lower Cretaceous formations of the Kopet-Dagh Basin in the NE of Iran. An outcrop of this formation in the section of Daddanlou village was studied palynologically. The study section, 248 meters thick includs gray marl and gray shale, with interbeded limestone. Based on study of 135 slides of 27 samples taken from this formation showed the most of the samples contain palynomorphs (dinoflagellates). Additionally, three forms of Chorate, Cavate, and Proximate have been abserved. In this study 37 species belonging of 29 genera were indentified. Accroding to identified dinoflagellate, Aptian is determined for Sarcheshmeh Formation in Daddanlou section. The identified dinoflagellate studied section could be compare with part of Odontochitina operculata zone. Based on study of three main groups of palynological elements (phytoclasts, marine palynomorph and amorph organic matter) and results of statistical studies on protection factores of organic materiales such as rate of transparent SOM to opague SOM, rate of brown palynomaceral to opgue palynomaceral and rate of SOM to marine palynomorph indicates that rate precipitation and oxygen was different. Finally, based on index dinoflagellate, Sarcheshmeh Formation depositional environment had been varied from inner neritic to outer neritic.

Diagenetic processes in chalky-marl couplets of Ab-Deraz Formation are studied in Hamam-Qale and Padeha sections, which are located in east Kopet Dagh basin. Chalk units are composed of chalk-marl couplets with different diagenetic features. The common diagenetic processes in chalky and marly limestones are cementation, dissolution, compaction, aggrading neomorphism, pyritization, bioturbation and fracturing. The present of clay minerals and lack of grain framework in marly interbeds led to more dissolution and compaction, while the fewer amounts of clay minerals and abundance of grains in the chalky beds provide available condition for more cementation. Paragenetic sequence interpretation of Ab-Deraz Formation indicates that diagenetic processes have affected these sediments in marine, burial and uplift conditions.

The Upper Cretaceous thick bedded succession in Badamouyeh Mountain in Honooj area shows the Late Cenomanian-Santonian stages. Also, these deposits are well exposed in the south-west of Bibihayat and south of Cheshmah gaz village. In the studied section, Lower and Upper Honooj green marls (informal) with intercalation of Exogyroferous shaly limestone are overlain by thick bedded limestones and in turn cover the Jurassic shales and sandstones (probably Hojedk Formation) with disconformity. The presences of both platycopid and podocopid ostracods, high diverse assemblages of foraminifera and macrofossils in Honooj marls and also high diverse assemblages of benthonic foraminifera in upper limestone show a favorable condition during the deposition of the strata.

Calcareous nannofossils in boundary of Tirgan and Sarcheshmeh Formations at Qalezo section have been studied. This section is situated in the west of Kopet-Dagh Basin. In this study 35 nannoplankton species of 17 genera were identified. According to the first occurrence of index species and fossil assemblages two calcareous nannofossil biozones (CC7-CC8) of Sissingh (1997) have been recognized. Based on these biozones, age of this boundary is Late Aptian - Early Albian.