فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و نهم شماره 3 (پیاپی 92، پاییز 1402)

In this research, the organic matter present in the Pabdeh Formation is investigated using Rock-Eval pyrolysis and organic petrographic techniques. For this purpose, a total of 22 cutting samples were collected at 50-meter intervals from 3 wells in the Kilur-Karim Oilfield. According to hydrogen index (HI) versus maximum temperature (Tmax) diagrams, the Pabdeh Formation in this oilfield contains type II/III kerogen, with thermal maturity corresponding to the early stages of hydrocarbon generation. In general, according to the Rock-Eval pyrolysis data, the middle parts of the Pabdeh Formation show a higher potential for hydrocarbon generation. On the other hand, organic petrography results show that samples from the middle parts of the Pabdeh Formation contain high amounts of amorphous organic matter along with solid bitumen. In addition, the upper and lower parts of this formation contain lower amounts of organic matter and mainly have abundant fossil content. A combination of results from two analytical techniques reveals that the Pabdeh Formation in the Kilur-Karim Oilfield contains a relatively organic-rich zone in the middle, which is surrounded by organic-poor facies above and below. These results can be helpful for a better understanding of the organic facies and palaeodepositional environments of the Pabdeh Formation in the study area.

Sargelu and Garau formations are significant geological units in the Zagros, which are known for having the most important unconventional hydrocarbon resources in Iran. This study aimed to evaluate the hydrocarbon generation potential of two formations by analyzing 15 oil-shale samples collected from the Gashun-G and Pirbadush sections along the Qolyan River in the Qalikuh area, Lorestan. The analysis method used was Rock-Eval pyrolysis. To determine the scatter pattern of heavy elements, a total of 15 samples of river sediments and water were analyzed using ICP-MS. The average values for total organic carbon (TOC) and most hydrocarbon production indicators in Garau oil shales exceed the values observed in Sargelu oil shales. Based on the findings of the elemental analysis and pollution index calculations conducted on sediments, it can be seen that Sargelu shows a higher presence of heavy elements, a higher contamination factor (CF) and average pollution load index (PLI) compared to Garau samples. This difference can be attributed to the physical and chemical characteristics of the sediments. Conversely, Garau samples show a higher average Contamination Degree (CD) in its water, which may be attributed to environmental factors such as temperature and pH of water. The results of the statistical analysis demonstrate a wide range of heavy element formation factors within the sediments and waterways of the Garau route. As a result, despite the lack of human activity in this area, in addition to the amount of organic matter in the oil-shale, the geo-genic activity causes natural environmental pollution that is influenced by various factors, including oxidation-reduction potential, reactive processes, type of bedrock, clay minerals, sediment texture and environmental conditions.

In order to study the environmental characteristics of Semnan spas, water, sediment, and slime samples were collected. The concentration of Ag, As, Cd, Pb and Zn (0.7, 33, 0.4, 128.5, and 297 mg/kg, respectively) in the sediment samples are much higher than their respective values in mean crust and mean sediment compositions. The sediments are not enriched in Mo, Ni, Th, Co, Cr, Mn, Fe and U, while moderately enriched in Sb and Cu, significantly enriched in Cd, As, Zn and Pb, and highly enriched in Ag. The Bioconcentration Factor (BCF) values of As, Mn, Cu, Ni, Pb and Zn in slime samples are very high (1286, 2863, 2340, 1053, 1236, and 976, respectively). The water samples are classified as neutral-high-metal, and the concentrations of B, Li, Ba, Zn, Pb, Se, Cu, As, Ni and Mn in all samples are higher than their mean concentrations in unpolluted natural waters. The values of Contamination Degree (Cd) and Heavy Metal Pollution Index (HPI) in all samples are higher than 3 and 75, respectively, confirming the high level of pollution in the samples. The Water Hazard Index (WHI) values of the studied samples are lower than 5, indicating the non-toxicity of the target elements. The high concentration of potentially toxic elements in water, sediments and slime samples of Semnan Spa should be taken into account by people who use the Semnan spas for therapeutic purposes.

In this study, one and two-dimensional models of petroleum systems were constructed in the internal part of the Fars region. Based on the results obtained from one-dimensional modeling and the study of thermal maturation history, the Sarchahan Formation is considered the main source rock of the Paleozoic petroleum system, which started hydrocarbon generation about 130 to 140 million years ago. The liquid hydrocarbon content in wells A and B is estimated to be 720 and 5100 (Kg/m2) respectively, and the gas hydrocarbon content is estimated to be 70 and 600 (Kg/m2). Furthermore, based on the results of two-dimensional modeling, the younger petroleum system source rocks such as the Cretaceous and younger source rocks are thermally immature and have not entered into the oil window. According to the migration modeling results, the most important factor in the movement of hydrocarbon fluids prior to the Zagros orogeny is vertical migration in the career layers, but after this orogeny and tectonic compression, the horizontal migration component has also become active.

The Sarvak Formation, the second important oil reservoir in the Zagros Basin, has a complicated diagenetic history. This study focuses on the diagenetic processes of this formation in the Abadan Plain. To achieve this goal, petrographic investigations of core samples, thin sections, X-ray diffraction, and scanning electron microscopy are integrated with the results of elemental geochemical data. Intensive meteoric dissolution (karstification), paleosol formation, dissolution-collapsed brecciation, meteoric cementation, and silicification are major meteoric diagenetic processes. Such intensive meteoric diagenesis along with the dominance of kaolinite and montmorillonite, as predominant clay types within the paleosol, all indicate a warm and humid paleoclimatic condition at the time of exposure. These diagenetic alterations provided special trends of variations in the elemental contents of altered carbonates. They include a clear increase in Na, Mn, Fe, and Rb along with the decrease in Sr contents recorded below the Cenomanian–Turonian and mid-Turonian disconformities. The variations in Mg contents depend on the original mineralogy of carbonates that can result in variable trends in response to the meteoric diagenesis. Below the mid-Turonian disconformity, the development of mud-dominated facies hampered the free fluid circulation and, consequently, diagenetic alterations and their related geochemical trends are limited within the Turonian sequence.

To investigate the Upper Cretaceous deposits in the Central Alborz Basin, a 100-meter thick stratigraphic section was chosen in the southwest of Dareh Zar village in the east of Tehran. In this study, a total of 75 species, belonging to 44 dinocyst genera, and 10 species from seven spore genera were identified. Consequently, two biozones—Dinogymnium acuminatum and Carpatella cornuta—have been determined. The association of the Dinogymnium acuminatum biozone with index planktonic foraminifers such as Contusotruncana contusa, Globotruncana arca, and Globotruncana ventricosa at the base of the studied section confirms the Late Cretaceous age. Furthermore, the presence and abundance of the Carpatella cornuta biozone in sample 44 indicate the beginning of the Paleocene. The presence of this biozone with typical dinocysts such as Damassadinium californicum, Thalassiphora delicate, and Tectatodinium sp. suggests the upper Paleocene age range for the end of the stratigraphic section. The presented biozones based on dinocysts are consistent with those in eastern Europe and northwestern Tethys, indicating a marine connection between these regions in the Late Cretaceous.