JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2012 | Volume:27 | Issue:1 (46)|Papers Count:7

The Shurijeh Formation (Late Jurassic- Early Cretaceous) consists of siliciclastic facies in the southeastern and eastern parts of the Kopet- Dagh basin, whereas evaporate and carbonate strata are present in its facies succession toward central and western parts of the basin. In addition, various paleosols are identified in this formation that based on relative preference of pedogenic procecces, are classified into three classes including histosols, oxisols and calcisols. The Shurijeh Formation calcisols, based on mineralogical composition, are divided into calcretes and dolocretes and contain special macromorphology and micromorphology features. Based on macroscopic- microscopic properties (alpha and beta microfabrics), the Shurijeh calcretes are divided into pedogenic and non- pedogenic (ground water) types that are formed under different conditions. The Shurijeh Formation dolocretes, only found in one section (Esfidan section), and the mudstone host rocks, are probably non- pedogenic (ground water). Water table fluctuations with arid to semiarid climatic conditions are caused calsisols creation in the Shurijeh Formation.

A total of 104 surface samples were selected from the measured stratigraphic column (upper part of Padeha, Khoshyeilagh and Lower part of Mobarak formations) in the Mighan village. The samples were analyzed in the palynological Laboratory for palynomorph entities in order to determine the age relationships of the upper part of Padeha Formation and the whole Khoshyeilagh Formation as well as the lower part of Mobarak Formation. In addition to palynomorphs, brachiopod and foraminiferal taxa were investigated in this study. A total of 103 fauna and micro floral species was identified, belonging to 72 palynomorph species (46 genera). Out of 72 palynomorph taxa 32 species belong to miospore group, 38 species related to acritarch group, one chitinozoan and one scolecodont. Moreover, 5 micro faunal genera (10 species) and 21 macro faunal spcies (15 genera) were encountered. Based on stratigraphic distributions of palynomorphs, foraminifers and brachiopods taxa eight assemblage zones were established. The zone I occurs in the upper part of the Padeha Formation and suggests the early Frasnian. The zones of II to VII are present within the Khoshyeilagh Formation and reveals the Middle Frasnian to late Famennian. The zone VIII occurs in the basal part of Mobarak Formation and suggests Early Carboniferous (Tournaisian) for this part of Mobarak Formation. The presence of miospore species of Archaeoperisaccus opiparus in the upper part of Padeha Formation and miospore spcies of Vallatisporites pusillites, Retispora lepidophyta, Retusotriletes phillipsii and Hymenozonotriletes perplexa in the Khoshyeilagh Formation suggest a tropical latitude during the Late Devonian in the study area. On the other hand, based upon the continental elements vs. the marine elements (K=C.E./M.K.) is 1.587, suggesting a shallow marine environment, which is consistent with the sedimentological data. On the other hand, the presence acritarch taxa such as Deltotosoma intosum, Gorgonisphaeridium dicissum, Papulogobata annulata and Maranhites perplexus in the Devonian sediments were compared with those of Zagros, Central Iran, Algeria, Libya, Morocco and Western Australia suggesting broad similarity. This similarity reveals that all part of Iran has been part of Gondwana landmass during the Late Devonian.

The upper part of Dallan and Kangan formations (Permian-Triassic), are located in the Kuh-e Surmeh area in folded Zagros Basin with a thickness of 325 m overlying by Nar evaporite member and underlying by Dashtak Formation. Dominant lithology of these formations are limestone and dolomite. Our purpose in this study is to identify microfacieses, sedimentary environment and diagenetic proceses. To overcome this aim, thin sections petrographic studies, leaded to identify 12 microfacieses related to 4 facieses belt: tidal flat, lagoon, shoal and open marine. The observed microfacies patterns indicate a ramp carbonate platform as depositional environment. Based on petrographic studies, the important diagenetic processes in these formations consist of: micritization, dolomitization, cementation, stilolitization and chemical and physical compactions. Burial diagenesis is dominated diagenetic event. The observed porosities in this section are primary and secondary such as fenestral, vuggy, fracture, moldic, interparticle, intraparticle and channel.

Gavkhuni Playa Lake covers about 520 km2 and is located at the downstream of Zayandeh-roud River. This playa is composed of three main flats including mud, sand and salt flats. The muddy deposits mainly spread in Zayandeh-roud Delta and underly a saline sublayer. The fine grained sediments of Gavkhuni Playa Lake have potential for concentrations of heavy metals due to the climatic conditions, petrology and presence of lead and zinc ores in the drainage basin and the flowing of the river through the industrial and agricultural regions. Variations of characteristics are: calcium carbonate (35.5-73%), organic matters (2.53-17.12%), clay (6.45-60.88%), pH (6-8.53) and Eh (-334 -+ 47 mv). Calcium carbonate, pH and organic matters increase and clay and Eh decrease from north to south of the playa. Clay minerals of the muddy sediments in order of frequency include illite, chlorite, kaolinite and montmorionite, respectively and the amount of these minerals do not vary from north to south of the playa. Heavy metals concentrations in ppm are: Mn (395.5-1040), Sr (100.4-725.76), Ni (37-73.66), Cu (13.83-29.83) and Ag (3.03-4.76) in order of abundance. Ag, Ni and Sr concentrations are higher and Cu and Mn concentrations are lower than the mean concentrations of these elements in natural soils. Geoaccumulation index and enrichment factor show that the sediments are highly polluted only by Ag. Exchangable cation contents are much lower than the total concentrations. Organic matters have a more important role in the exchangeable concentration of the heavy metals relative to the type and content of clay minerals and their elevation leads to increase the exchangeable concentrations.

In order to micropaleontology, biozonation and age determination of Shurijeh Formation in west part of eastern Kopet Dagh, a stratigraphic section was selected and studied in south of Hamam Ghaleh. Shurijeh Formation with 953 m thickness in Hamam Ghaleh stratigraphic section consists of five lithological units which is different from other identified sections. These lithological units include lower terrigenous-evaporite unit, lower carbonate unit, middle terrigenous-evaporite unit, upper carbonate unit and upper terrigenous unit. A total of 402 samples were examined in this study. Three biozones were determined in studied deposits based on recognized microfossils and their stratigraphic range chart. In this study the Late Kimmeridgian? Hauterivian age was ascribed to Shurijeh Formation in Hamam Ghaleh stratigraphic section.

The Ghadir Member of the Nayband Formation is well-exposed in the Parvadeh mine area, southwest Tabas city, Central-East Iran. It contains abundant well-preserved plant macrofossils belonging to 24 taxa of various orders, such as Equisetales, Osmundales, Filicales, Peltaspermales, Bennettitales, Cycadales, and Coniferales. Based on the occurrence of Equisetites arenaceus, Scytophyllum persicum, Pterophyllum aequale, Pterophyllum bavieri, and Nilssoniopteris musafolia the Rhaetian age is suggested for this assemblage. Furthermore, Neocalamites cf. meriani, Weltrichia primaeva, and Carpolithes sp. are reported for the first time from this area. According to stratigraphic distribution of taxa, one biozone is recognized- Assemblage zone I. This assemblage of plant macrofossil remains suggests a humid tropical to subtropical climate for this period of time.