فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و ششم شماره 2 (پیاپی 79، تابستان 1399)

The Zakeen Formation is one of the possible gas reservoirs in the Zagros sedimentary basin. In this paper, the cyclostratigraphic study of the upper part of the Zakeen Formation was performed by using evolutionary spectral analysis methods. The Multi-Tapper Method (MTM) periodogram is one of the evolutionary spectral analysis methods used in this study to identify and prove the frequency ratios of Milankovitch cycles in the studied sediment sequences. In this study, using the introduced methodology, the frequency ratios of the Milankovitch cycles in the upper part of the Zakeen Formation was identified for the first time, and their existence was confirmed. Besides, the spectral powers of spectral gamma-ray (SGR) and density (RHOB) series, in evolutionary Fast Fourier Transform (FFT) and Wavelet Transform (WT) Scalograms, in 2SK-1 and 2SKD-1 wells of Salman gas field show strong astronomical signals of the Milankovitch cycles (E, e, O, P). After investigating the cyclostratigraphy of the upper part of the Zakeen Formation in the studied wells, by using new methods of evolutionary correlation coefficient and evolutionary significance levels, comparison of sediment accumulation rate variations of the Zakeen Formation was performed in the studied wells.

In this study, the Tiz Kuh Formation of Aptian age in the Pol-e-Zoghal section (south of Chalus) with a thickness of 113 m was evaluated for depositional environment, sequence stratigraphy, and elemental geochemistry. The Tiz Kuh Formation in this section with disconformity lies on the Lower Cretaceous volcanic unit and associated disconformity of the Upper Cretaceous volcanic subdivision. According to calcimetric studies, the Tiz Kuh Formation in this section is composed of limestone and argillaceous limestone. Field and laboratory investigations led to the identification of eight microfacies belonging to 3 sub-environments of lagoon, shoal, and shallow open marine. Gradual microfacies changes and the absence of large barrier reefs, oncoids, pisoids, aggregate grains, and slump structure along with the presence of dasycladeceae family algae (e.g. Terquemella sp. and Bakalovaella elitzae.) and gymnocodiaceae (Permocalculus sp.) confirm the existence of a ramp-type carbonate platform. This evidence may indicate warm marine shallow very saline environment; These conditions highlight the shallow sedimentary and aragonitic environment. Sequence stratigraphic studies in this section identified three third order sedimentary sequences associated with the HST and TST with SB1 and SB2 sequence boundaries depositional sequence. In this study, sedimentary depth resulted in variation of orbitolinid shape The results of the geochemical analysis, of major and minor elements, Sr / Na values of more than one, Sr / Mn values (mean 7) and plotting of Sr / Ca values against Mn indicate that the primary mineralogy was aragonite and have been affected by non-marine diagenesis in a closed to slightly open diagenetic systems. Variation of elements along the stratigraphic section shows that the amount of Sr in the upper part decreases as the Mn content increases; These conditions indicate the greater impact of meteoric diagenesis on the upper part.

The upper Yakhtashian to Bolorian Bagh-e Vang Formation was studied in two stratigraphic sections in north Tabas, east-central Iran. The examination of fusulinids and small foraminifers of the Bagh-e Vang Formation in two studied sections led to the identification of the new fusulinid and small foraminifer genera and species which are recovered from the upper Yakhtashian and Bolorian strata of Iran for the first time. Based on identified fusulinids, three biozones including upper Yakhtashian Pamirina darvasica-Sakmarella spp., lower Bolorian Chalaroschwagerina vulgarisiformis and upper Bolorian Misellina  termieri in the Bagh-e Vang section and two biozones containing lower Bolorian Misellina (Brevaxina) dyhrenfurthi-Chalaroschwagerina vulgarisiformis and upper Bolorian Misellina cf. termieri in the Shesh Angosht section were recognized. Paleomagnetic data and time of volcanic activities in Cimmerian microplates along with fusulinid appearance in Late Paleozoic reveal that the Neotethys opening in these blocks did not happen at the same time and in the northern blocks (like Iran, south and central Afghanistan and southeast Pamir) was faster than those in the southern blocks (like Qiangtang and Baoshan blocks). The reason for the occurrence of warm water subtropic to tropic palaeoequatorial fusulinid fauna of verbeekinds and neoschwagerinids during the Bolorian in Cimmerian microplates is not only because of the northward drift of its blocks but also factors such as global warming in the Bolorian and warm water oceanic currents were effective.

The Fahliyan Formation is a member of the Khami Group with Neocomian–Barremian age. In two surface sections in the Izeh Zone and two wells of the southern Dezful Embayment, it includes 12 microfacies deposited on four facies belts as tidal flat, inner ramp (lagoon, Lithocodium–algal mounds and bioclastic–peloidal shoals), middle ramp and outer ramp. A homoclinal ramp model is proposed as its depositional environment. Important diagenetic alterations are dissolution, micritization, compaction, dolomitization, silicification, pyritization, cementation and fracturing. They represent marine, meteoric and shallow to deep burial diagenetic realms. Sequence stratigraphic analysis resulted in the recognition of four depositional sequences that seem to be third-order sequences, according to their relative ages (biozones), thickness and correlation with neighboring areas. Reservoir quality evaluation indicates coupled imprints of facies characteristics and diagenetic alterations on reservoir properties of this formation. Important reservoir units are formed in Lithocodium–algal mounds/patch-reefs (in the Garangan Field) and high-energy facies of shoal setting (in the Gachsaran Field). They include primary pore types such as intra- and interparticle pores and mainly concentrated in highstand systems tracts (HSTs) of depositional sequences. Some secondary pores are also present that include dissolution vugs and molds. In addition, middle ramp facies provide some reservoir units in the transgressive systems tracts (TSTs). No macroscopic pores are recorded in these facies and micropores are responsible for high reservoir quality.

Hormuz Island at the entrance of the Persian Gulf and Oman Sea is a symbol of Iranian diapirism and the Hormuz series. In considering the location of the island and the development plans for Hormuz Island, it is important to know the composition and characteristics of the island's coastal sediments. This study was conducted to study the sedimentary, mineralogical, and geochemical properties of the coastal sediments of this island. For this purpose, In this study, 20 thin sections were made from gravelly rock samples as well as 27 surface sediment samples from nine stations has been collected. Routine sedimentologic tests have been done on these samples including quantitative mineralogy by XRD, separation, and identification of heavy minerals using bromoform solution and magnetic property, heavy metals and primary oxides were analyzed by XRF and petrographic study using a polarizing microscope. The results indicate that the sediments are sandy to gravel in terms of grain size. The average amount of calcium carbonate is 32 to 62 percent. The mineralogy of sediments shows that suite of calcite, quartz, feldspar, plagioclase, dolomite, aragonite, clay minerals (Kaolinite and Illite) and heavy minerals (magnetite, hematite, oligiste, epidote, pyroxene, pyrite, goethite, limonite, apatite, barite,) are other components of superficial sediments. The study of thin sections under the polarizing microscope shows that most gravels on the coast have an igneous origin (rhyolitic and trachytic). The findings of this study indicate that the main source of these sediments is the alteration and erosion of the Hormoz Serie (the Late Precambrian–Cambrian) in the center of the island under wet, humid conditions.

This study tries to evaluate the geological properties of a travertine spring and its related deposits. The identification of sedimentary facies of springs could be applied as a method to distinguish the type of travertine springs. Therefore in this study, that method has been used for the determination of the type of the spring. Results obtained from facies analysis reveal 13 sedimentary facies that could be categorized into two groups including organic facies which contain five facies and abiotic facies containing eight facies. These facies show the character of hydrothermal spring and set the spring in the thermogenic group. The chemical composition analysis of the spring water represents the facies of NaCl, Na-Ca-SO4-Cl can be considered to be precise chemical facies. The presence of calcium and sulfate as the second most frequent ions, after sodium and chloride, may initially indicates the existence of gypsum or anhydrite deposits in this area. On the other hand, given the absence of sulfate-bearing sediments in this region, it can be concluded that the interaction of water and magmatic systems was the most important source of sulfate in the spring water. Based on the rock mechanical properties of the travertine, it was revealed that with increasing age of the sediments their consolidation degree increases. The hardness of sediments shows an increasing trend by increasing distance from the spring vent.