APPLIED SEDIMENTOLOGY
Year:2018 | Volume:6 | Issue:11 |Papers Count:7

The Pesteliegh Formation (Lower Paleocene) is composed of 94/5 m of sandstone, shale and evaporate units in the Chahchahe section. Shale samples show that major oxides such as SiO2, Al2O3, Na2O, P2O5 and trace elements like Sr, Ba, Nb and Ce are depleted relative to Upper Continental Crust (UCC) while, U and CaO enriched. The diagram of TiO2 versus Al2O3 and Zr versus Al2O3 suggest an intermediate igneous rock as possible source rock for shale of the Pesteliegh Formation. The diagram of K2O/Na2O versus SiO2 and ternary diagram of Th/Co/Zr, La/Th/Sc, Th/Sc/Zr show a continental arc islands as tectonic setting for this Formation. The CIA index values reveal poor to moderate degree for intensity of weathering and arid to semi-arid as paleo-climate in the studied area. In the other hand, the U/Th and Ni/Co indexes indicate oxidant condition in depositional environment. The beginning of Paleocene was along with tectonic activity and regression of sea level in most parts of the word and well the Kopet-Dagh Basin in Iran. These occurrences were most important factor for deposition of siliciclastic sediments of the Pesteliegh Formation. Due to regression, the thickness of this formation decrease, from south east toward north west in Kopet-Dagh Basin.

Asmari Formation (Oligocene-Miocene) is the most famous carbonate reservoir that ever known in the world. It is the main hydrocarbon reservoir in Iran and also the major oil production in Dezful Embayment. In this study, in order to understand the reservoir quality controlling factors of this Formation, detailed petrography studies were carried out in Ghale Naar oil field. This formation in the Ghal’ e Naar oil field is composed of grain-supported bioclastic-pelloidal (foraminiferal-algal) faciese and nine sedimentary facies have been identified based on eight hundred microscopic thin section studies from core and cutting samples in this oil field. These facies are related to the lagoon, shoal, nummulitic bank and open marine sub-environments of a homoclinal ramp carbonate system. The results of this study showed that the diagenetic processes like dissolution and dolomitization are related to the grain supported shoal microfacies and nummulitic shoal. Dissolution along with dolomitization are factors that increase reservoir quality and cementation and compaction are the most important factors in reducing the quality of reservoir in Asmari Formation.

Diverse and well-preserved palynofloras dominated, by land-derived palynomorphs (miospores) in association with marine entities such as dinoflagellate cysts, scolecodonts, foraminiferal test linings, and acritarchs (sensu lato) occur in surface samples of the Dalichai Formation, at the Pol Dokhtar stratigraphic section, central Alborz. Stratigraphic distribution of the dinocysts at the Pol Dokhtar stratigraphic section lead to the introduction of three successive biozones i. e., Cribroperidinium crispum Total Range Biozone (late Bajocian), Dichadogonyaulax sellwoodii Interval Biozone(Bathonian to early Callovian), Ctenididinium continuum Interval Biozone (early to middle Callovian) and Subzone a (early to middle Bathonian). Furthermore, presence of such index late Bajocian species of dinoflagellate cysts as Meiourogonyaulax valensii, Cribroperidinium crispumin association withCarpatodinium predae(early to middle Bathonian) and Ctenidodinium combazii (Bathonian to early Callovian) suggests a Middle Jurassic (late Bajocian-Callovian) age for the host strata. Quantitative analysis of the palynological and palynofacies elements indicates low sedimentation rate in a relatively deep, low-oxygenated marine environment with decrease of the depth.

Basal Anhydrite is the main evaporite unit presents at the lowermost part of the Asmari Formation (Oligo-Miocene) which its geochemical characteristics have not been studied yet. In this study, seven outcrops, including Bangestan, Safid, Asmari and Anaran anticlines from the Zagros sedimentary basin were selected and their geochemical characteristics and depositional conditions were determined. The mineralogical (XRD, BSE-EDX) and elemental analysis (ICP-OES) were performed. The petrography and mineralogy studies show that the secondary gypsum with alabastrine texture was produced by hydration of anhydrite during exhumation. In order to perform geochemical analysis, four outcrops (Bulfares, Putu, Geletorsh and Anaran) were selected. Based on elemental analysis, calcium and sulphur are the most important elements that found as gypsum. The highest amounts of elements strontium, magnesium and sodium and the lowest amount of iron were found in the Bulfares section, which indicates the effects of diagenetic and biological processes and shallow depositional environment. The amounts of strontium, magnesium and sodium elements decrease and the amount of iron increases toward Geletorsh section (north part of the basin), which indicates deepening of the basin in this area. Putu and Anaran sections show variable elemental changes that demonstrate the area is mostly affected by hydrological conditions. The concentration of lithium is low in the studied sections, which can be attributed to excess evaporation.

The Khan Sormeh deposit is located at western Isfahan, within the Lower Cretaceous carbonate rocks (K3 unit) which belongs to Malayer-Esfahan Metallogenic Province (MEMP). Galena, sphalerite and pyrite occurs as the main sulfide minerals in the study area and mostly were distinguished with dolomitization, sulfidation and silicic alterations. Based on petrographic evidence, at least four types of dolomite are recognized at carbonate host rocks, including: grey fine-grain dolomite (Rd1), brown-red medium-grain dolomite (Rd2), coarse-grain saddle dolomite (Sd) and vein and veinlet late dolomite (Vd). The CaCO3 and MgCO3 content of dolomites are varies between 58. 5 to 61. 3 wt% and 37. 6 to 40. 2 wt%, respectively. The highest and lowest molar ratio of Ca/Mg are distinguished in fine-grain dolomite (AV. 1. 65) and vein-type dolomite (AV. 1. 1), respectively. Also, total REE content (∑ REE) of dolomite are varies between 5. 8 to 13. 9 ppm, which this variation have high content in fine-grain and saddle dolomites relative to medium-grain and vein-type dolomites. REE distribution in various dolomites is shown the fine-grain dolomite is very similar pattern to Lower Cretaceous host rock. Moreover, LREE enrichment (especially La) of the saddle and vein-type dolomites shows this dolomites occurs in high water rock ratio and its belong to sulfide mineralization in the Khan Sormeh deposit.

The Siahrudbar bauxitic horizon is located in ~25 km southwest of Aliabad Katoul, Golestan Province, north of Iran. This deposit is stratiform and were developed along the boundary of the Elika and Shemshak formations. Petrographic observations along with the results of XRD analyses of the ore samples revealed that diaspore, hematite, and kaolinite are the major constituent minerals which are accompanied by lesser amounts of chamosite, anatase, boehmite, goethite, rutile, calcite, muscovite, clinochlore, and quartz. These minerals display various textures including pelitomorphic, granular, pseudo-porphyry, fluidal, pseudo-breccia, dumbbell-shaped grains, and clastic fragments, indicating allogenic origin. Based upon quantitative values of minerals, the Siahrudbar deposit consists of two types of ores, (1) the clayey bauxite and (2) the bauxitic clay. These ores were formed during deferrugenization and desilication processes from the clay minerals. The geochemical data of less mobile elements indicate that the Siahrudbar deposit is of karst bauxite type and generated from the weathering of igneous (basaltic-andesitic) rocks. Furthermore, the Eu anomaly values together with the ratios of TiO2/Al2O3 and Sm/Nd revealed that the Siahrudbar bauxitic deposit was formed in a continental margin tectonic setting.

In this study, in order to investigate the effect of the physical and chemical properties of carbonate rocks on the development of karst forms, carbonate rock units of the Sarvak Formation have been studied in the anticline of the Rag-Henna (south of Isfahan). This formation consists of a thick sequence of carbonate deposits, and karst geomorphological phenomena such as carneys, dissolution cavities, ponors and karst springs are well visible. The Sarvak Formation is composed of 8 sedimentary that are deposited in tidal, lagoon, barrier and open sea environments. According to the results of chemical analysis, the percentage of calcium oxide in the studied samples is more than 40% and monirim oxide is at most 1. 27%. Also, by conducting geotechnical experiments, the porosity of carbonate samples was determined. Diagenic processes affecting the porosity of the Sarvak Formation in the region include compression, cementation, dissolution, fracture and dolomitization. The lacquer supporting luminosities of the lagoon division have better porosity due to the effect of their dissolution and fracture, and more variation in the karst forms of this microfacies is observed. Therefore, determination of porosity and the evaluation of diagenesis processes on carbonate rocks can be a useful tool for separating the zones from the point of view of their ability to develop.