https://psj.basu.ac.ir/ Applied Sedimentology en daily 1 Wed, 06 May 2026 00:00:00 +0330 Wed, 06 May 2026 00:00:00 +0330 https://psj.basu.ac.ir/article_6603.html In this study, the siliciclastic Amiran Formation (Cretaceous–Paleocene) is investigated from petrographic and geochemical perspectives as evidence of foreland basin development in the Zagros region. For this purpose, three stratigraphic sections within the Lurestan sedimentary basin were selected and sampled. The petrofacies of this formation consist of chertarenite and calclithaite. Detrital materials were mainly supplied by the erosion of metamorphic and volcanic masses of the Sanandaj–Sirjan Zone, resulting from abnormal tectonic uplift and activity during the Late Cretaceous. Some of the clastic materials originated from the reworking of neighboring shallow-water deposits, particularly underlying Cretaceous calcareous and marly units, which were transported to deeper parts of the basin through turbidity currents. Modal analysis of sandstones plotted on QFL and QmFLt diagrams confirms a recycled or transitional recycled orogenic setting. Geochemical studies reveal that the source rocks of the studied samples formed under an arid climate with moderate chemical weathering. Diagrams of trace elements such as Th versus Sc and Co/Th versus La/Sc indicate that the provenance rocks were dominantly intermediate (andesitic) in composition. Triangular plots of La–Sc–Th and Th–Sc–Zr/10 values show that all samples fall within the Continental Island Arc (CIA) field. Major oxide composition analyses of the Amiran Formation suggest that these turbiditic deposits were derived from a relatively young clastic source, consisting of mixed metamorphic and intermediate volcanic materials related to the magmatic arc of the Sanandaj–Sirjan Zone. https://psj.basu.ac.ir/article_6656.html The purpose of this research is to investigate the diagenesis processes of Amiran Formation using petrographic evidence. For this purpose, the Morani and Pirshamseddin stratigraphic sections in southern Lorestan were selected. The lithology of Amiran Formation in the studied areas , The lower boundary of the Amiran Formation in the sections studied Gurpi Formation, and its upper boundary is erosional discontinuous with the Kashkan Formation. Developed diagenetic processes as well as replacement processes have been observed in this formation. In some cases, fossils or fossils with a healthy shell and without any fractures or wear in them are filled with debris in the sandstone facies, so that only traces or ghosts of fossils remain. can be seen In some cases, the replacement by detrital material is selective, so that there is a relationship between the size of the replaced seeds and the size of the shell of the oysters. In the shell of Alokums or fossils that have a larger size, the seeds are easily placed in the shell of these fossils. But in the case of allocames or fossils that have a smaller size, the detrital grains could not enter the space of the fossils, so they are less affected by the replacement process. . Based on petrographic evidence, the paragenetic sequence of Amiran Formation deposits in these sections has been interpreted in four environments: marine, freshwater, burial and uplift. Three stages of diagenesis initial diagenesis , middle diagenesis and final diagenesis have been determined for the studied deposits. https://psj.basu.ac.ir/article_6083.html In this research, a cross-section of the Gachsaran Formation in the Afrineh syncline (south of Lorestan) has been selected and sampled to understand the dolomitization model of this formation. This section, with a thickness of 380 meters, is located in 46 kilometers southwest of Khorram Abad and in the Zagros folded zone. The Gachsaran Formation in the studied area is situated on the Asmari carbonate Formation and is covered by the red clastics of the Aghajari Formation as a discontinuity. In this section, petrographic studies on 100 thin sections and geochemical studies on 17 samples show the significant diagenetic processes in the Gachsaran Formation, such as the extensive dissolution and dolomitization. In this section, four groups of dolomites were identified: microcrystalline dolomites (first type), medium crystal (second type), coarse crystal (third type), and very coarse-crystalline dolomites filling fractures (fourth type, Baroque). The dolomitization mechanism is considered to be the tidal environment for the first-type dolomites, the mixing zone of saline and fresh water for the second- and third-type dolomites, and the burial model for the fourth-type dolomites. The presence of extensive mold porosity, fresh water calcite cement equant, fresh water vadose environment cements, regular and bright sugar grain dolomites, as well as medium crystal dolomites (dolomicrosparites) during shallow burial are evidence of a mixed type dolomitization model in Gachsaran Formation deposits. . https://psj.basu.ac.ir/article_6449.html The sedimentary rock deposits of the studied section are found in the northern subzone of Fars province and within the sedimentary-structural zone of central Iran. This carbonate-clastic sedimentary sequence has a thickness of 222 meters, mostly includes sandy limestone, sandstone and shale units, which are thin, medium and thick layers, and can be considered equal to Shishtu 1 sub-formation based on lithological studies and geological age. In this sub-zone of Fars, the Late Devonian series rocks are widely spread and covered with the Early Carboniferous series limestone units (equal to the Shishtu 2 sub-formation). From the point of view of stratigraphy and based on field research, the Late Devonian deposits in this section have been classified into ten stratigraphic units or lithofacies (Sh.I-X). Based on the presence of Famennian conodonts, the age of the stratigraphic units in the selected section is Late Devonian. By studying, identifying and classifying the microfacies, six packages of microfacies and one type of petrofacies were separated, from the sea to the coast in five sedimentary sub-environments: deep sea from basin to outer ramp (DSB-O.), sub-deep sea in middle ramp (SDSM.), open-restricted marine in inner ramp (O-RMI.), carbonate sand hills/bioclastic shoal in inner ramp (SI.) and lagoon-peritidal zone in inner ramp (L-PI.). Also, by obtaining these data and comparing them with standard patterns, it can be suggested that this sedimentary sequence was deposited on a carbonate platform of the low-slope ramp or homoclinal ramp type. https://psj.basu.ac.ir/article_6522.html The Fahliyan Formation (Neocomian) is a major hydrocarbon reservoir in the southern and southwestern oil-prone regions of Iran, particularly in the Dezful Embayment and Abadan Plain. This study integrates core, thin-section, gamma-ray and sonic log data from two wells in the Rudak and Milatun fields to investigate the depositional setting, sequence stratigraphy and reservoir quality of the formation in the southern Dezful Embayment. The studied subsurface sections are about about 445-460 m thick and they consist of 5 microfacies which deposited in a homoclinal carbonate ramp. Facies and well-log analyses indicate the presence of two third-order depositional sequences corresponding to the lower part of the Mehrdad supersequence and the K30 and K40 maximum flooding surfaces in the Zagros Basin. Based on the stacking pattern of various depositional microfacies and reservoir quality of the studied intervals, the Fahliyan Formation can be divided into two reservoir units. The upper part consists mostly of bioclastic wackestones of the protected lagoon and open marine settings, which has a low reservoir quality. On the other hand, the good reservoir quality of the underlying carbonates is related to high pro-perm values of the peloidal grainstones and algal packstones deposited in a high-energy mid-ramp setting. https://psj.basu.ac.ir/article_6569.html The Asmari Formation, as the principal carbonate reservoir of the Zagros Basin, exhibits significant lateral facies heterogeneity on a regional scale. This study aims to identify the depositional model governing the marginal parts of this basin through microfacies analysis and palaeoenvironmental interpretation of the Tange-Chug surface section in the Eshger Anticline (northeastern Izeh Zone). Based on the study of 280 thin sections prepared from the Pabdeh and Asmari successions, 20 microfacies belonging to outer ramp, middle ramp (distal and proximal), shoal, and inner ramp (open lagoon to intertidal zone) environments were identified. The gradual vertical transition of these facies, coupled with the complete absence of gravity-flow deposits, continuous barrier reefs, and coated grains (ooids), confirms the establishment of a very low-angle homoclinal carbonate ramp in this area during the Oligo-Miocene. This model is fully consistent with findings from adjacent studies in the Izeh Zone, which indicate the dominance of heterozoan assemblages and oligo-mesotrophic conditions. Furthermore, the overall congruence of this pattern with ramp models proposed for more central parts of the basin (e.g., the Dezful Embayment) suggests a shared primary control of eustatic sea-level fluctuations on the basin geometry. However, significant facies differences—such as the development of lower-energy shoal facies and the presence of anhydrite layers in the upper parts of the sequence documented in this study compared to southeastern fields and the Interior Fars—highlight the role of local controlling factors like palaeogeographic position, basement topography, and potential clastic influx in lateral facies variability and heterogeneity. https://psj.basu.ac.ir/article_6581.html The Upper Jurassic Surmeh Formation in the study areas of the southern Dezful Embayment and the Izeh Zone (Zagros sedimentary basin, southwestern Iran) was investigated in three sections: Fahliyan, Khami, and Mongasht. This research interprets data obtained from petroleum fluid inclusions present in double-polished thin sections prepared from the samples. The data include temperature, salinity, and fluorescence reflectance color. Using this information, the characteristics of these sections were evaluated. The burial depth of the host rock of the fluid inclusions was estimated using the trapping temperature and pressure of the fluid inclusions at the time of their formation in these areas. The predicted depths are 2040 meters for the Fahliyan Anticline section, 2140 meters for the Khami Anticline section, and 600 meters for the Mongasht Anticline section in Tang-e Kord. The Fahliyan section, with a GOI value of 12.96%, is introduced as a reservoir rock with weak oil saturation. The Khami section, with a GOI value of 29.4%, represents a reservoir rock with moderate oil saturation. The Mongasht Anticline section, with an average GOI value of 53.5%, is introduced as a reservoir rock with good oil saturation. The API gravity values derived from the fluorescence reflectance spectra of the petroleum fluid inclusions for the studied sections are as follows: the petroleum fluid inclusions in the Fahliyan Anticline section contain trapped ultra-light oil; those in the Khami Anticline section indicate light oil at the time of trapping; and the oil in the fluid inclusions from the Mongasht Anticline section is classified as medium oil. In general, using the above information, it can be inferred for the studied areas that oil density increases from the Fahliyan Anticline towards the Mongasht Anticline. This likely indicates that the degree of oil maturity increases from the Fahliyan Anticline towards the Mongasht Anticline due to the decrease in the depth of fluid inclusion formation. https://psj.basu.ac.ir/article_6605.html The aim of this research is to investigate the diagenetic processes, paragenetic sequences, and the dolomitization model of the Taleh-Zang Formation (Late Thanetian) in the Lorestan Sedimentary Basin, utilizing petrographic and elemental geochemical evidence. For this purpose, three surface sections were selected and sampled. The lower and upper boundaries of the Taleh-Zang Formation in all four studied sections are conformable with the Amiran flysch Formation and the Kashkan clastic Formation, respectively. Petrographic studies led to the identification of several diagenetic processes, including micritization, cementation, neomorphism, compaction, dissolution, porosity, and replacement, which ultimately determined its diagenetic model. Based on petrographic evidence, the paragenetic sequence of the Taleh-Zang Formation deposits in these sections is interpreted across four environments: marine, burial, uplift, and fresh water. These processes have passed through three diagenetic stages: early (eogenesis), middle (mesogenesis), and late (telogenesis). Dolomites in the studied sections formed as both primary and secondary. Elemental analysis of the samples by EDS method (with an accuracy of one-hundredth percent) on the dolomites showed that primary dolomites possess low Fe content and high amounts of Sr and Na, whereas secondary dolomites have a high concentration of Fe and Mn and lower Sr content compared to primary dolomites. This finding suggests a shallow to deep diagenetic burial environment for the secondary dolomites. The dolomitization model of the Taleh-Zang Formation deposits in all three studied sections is attributed to tidal flat, seepage, shallow burial, and deep burial settings. https://psj.basu.ac.ir/article_6613.html Although many studies have examined the general impact of diagenesis on porosity development, the direct relationship between the morphology and size of dolomite crystals and the distribution of different pore types has received less attention. This study systematically investigates this relationship in the Upper Dalan and Kangan formations of the central Persian Gulf. The dataset includes thin-section petrography and core-derived porosity and permeability measurements from a single well. The results reveal that increasing dolomite content significantly alters the pore system. With dolomitization, vuggy porosity shows an increasing trend, while moldic porosity decreases. The highest vuggy porosity occurs in fully dolomitized samples, whereas moldic porosity is most abundant in slightly dolomitized limestones. Dolomitization enhanced reservoir quality by generating intercrystalline pores that progressively evolved into vuggy porosity. Texturally, planar dolomite crystals exhibit higher porosity and, particularly, higher permeability than nonplanar types due to their more regular crystal boundaries and better-connected pore networks. Coarse, sucrosic dolomites also show higher porosity and permeability than fine-grained dolomicrites, as larger crystal size promotes the development of wider throats and more effective flow pathways. Conversely, anhydrite cementation and late calcite precipitation have locally reduced reservoir quality by occluding pores and throats. This study demonstrates that the combined analysis of microfacies and dolomite crystal characteristics provides a powerful approach for interpreting the controls on moldic and vuggy porosity. The findings offer a useful model for evaluating similar carbonate reservoirs worldwide. https://psj.basu.ac.ir/article_6630.html In this research, four stratigraphic sections of the Amiran Flysch Formation in the Lorestan sedimentary basin were studied and examined. The thickness of the Amiran Formation in the Lorestan sedimentary basin reaches over 800 meters, and lithologically, it includes conglomerate, sandstone, shale, and, to a lesser extent, limestone. The Lowe sequence is observed in the coarse-grained facies of this formation, the Bouma sequence in the medium-grained facies, and the Stow sequence in the fine-grained facies, all indicating a submarine fan depositional environment. The Lowe sequence in these deposits includes six parts: R1 (traction bedload), R2 (traction sheet), R3 (traction sheet), S1 (traction bedload), S2 (traction sheet), and S3 (suspended load and water). The Bouma sequence includes five parts: A (sand and gravel with gradual grading), B (sand with parallel lamination), C (rippled sand), D (laminated silt), and E (mud with bioturbation at the top). The Stow sequence in these deposits includes nine parts: T0 (tabular planar lamination), T1 (contorted lamination), T2 (lenticular-wavy lamination), T3 (regular and thin lamination), T4 (indistinct lamination), T5 (grouped silt lamination), T6 (gradually graded silty-muddy lenses), T7 (mud with gradual grading), and T8 (mud with fine bioturbations). In these sequences, the S3 part of the Lowe sequence is equivalent to the A part of the Bouma sequence, and the C part of the Bouma sequence is equivalent to the T0 part of the Stow sequence. https://psj.basu.ac.ir/article_6697.html In this study, the diagenetic processes and paragenetic sequences of Oligocene–Miocene deposits in a subsurface section of the Marun Oil Field were investigated. The lower boundary of the Asmari Formation is in contact with the Pabdeh Formation, and the upper boundary is with the Gachsaran Formation. Petrographic studies led to the identification of several diagenetic processes such as micritization, neomorphism (both aggrading and degrading types), cementation (Equant, fibrous isopachous rim, poikilotopic, blocky, drusy, pervasive, and dolomitic cements), compaction (mechanical and chemical), dissolution and development of porosity (fabric-selective and non-fabric-selective), and replacement (iron-staining, dolomitization, and replacement by terrigenous materials). Based on petrographic evidence, the paragenetic sequence of the Asmari Formation deposits in this oil field was interpreted within four diagenetic environments: marine, meteoric (freshwater), burial, and uplift zones. Three diagenetic stages—early (eogenesis), middle (mesogenesis), and late (telogenesis)—were identified for the studied deposits. Micritization and cementation, particularly in mud-supported facies, have led to the occlusion of intergranular spaces and reduced primary porosity. Overburden-induced compaction further decreased porosity and limited reservoir quality. Dissolution enhanced secondary porosity mainly in grain-supported facies, thereby improving reservoir quality. Dolomitization showed a dual effect: in some intervals, the development of intercrystalline porosity increased reservoir quality, while in others; dolomitic cementation reduced permeability and sealed pore spaces. Consequently, the reservoir quality of the Asmari Formation is heterogeneous and dependent on both the facies type and the intensity of diagenetic processes. The best reservoir potential is observed in grain-supported facies and zones affected by selective dissolution and dolomitization.