فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و دوم شماره 1 (پیاپی 62، بهار 1395)

In this research the sedimentary successions of the Asmari Formation with the age of Oligocene – Miocene in two outcrops of kuh–e Asmari, located in the Dezful embayment with a thickness of 349 m and kuh–e Gurpi (Pabdeh valley), located at the Izeh zone with a thickness of 352m have been studied. The aim of this study is to provide the possibility of comparing Asmari depositional condition in both mentioned area based on lithological studies, determination of microfacies, sedimentary environment and separation of sedimentary sequences. Based on petroghraphic studies, 18 microfacies were identified that were deposited in the three sedimentary environments such as inner ramp, mid ramp and outer ramp. The result of this study showed that Oligo-Miocene carbonates in the kuh–e Asmari section mainly formed in inner ramp environment while in the Pabdeh valley sedimentation occurred in the deeper waters of outer and mid ramp and shallow parts of inner ramp. In the kuh–e Asmari section, sedimentary units shows three third–order depositional sequences, while sequence stratigraphic analysis in the Pabdeh valley shows deposition of the Asmari Formation contains five third–order depositional sequences.

Sedimentological characteristics, sedimentary environment and see-level change of the middle Cretaceous oolitic ironstones of one hydrocarbon field in central Persian Gulf were analyzed in this study. The analyses include petrography, XRD and size analysis using laser particle sizing. Core analysis of the sequence shows that it is composed of shaly limestone, limy shale, carbonate cemented sandstones, shale and oolitic ironstones from bottom to top. The dominant minerals of these deposits at the upper part are goethite, phosphate, calcite, clay minerals and siderite. These analyses showed that the studied ooids were deposited in a shallow marine environment with bidirectional currents and occasional storms. Lack of limestone relics, the presence of marine ooids, change in iron minerals from siderite to goethite in sediment sequence from bottom to top and high roundness and symmetry of grains confirms such environment. Deposition of a shale layer just above this complex has protected them from considerable diagenetic changes with creating two impermeable layers around this unit. The sea-level falls toward the oolitic ironstone layer and rises again after the deposition of this layer. If this sequence be present at the other parts of the Persian Gulf, it could be used as a key bed in stratigraphic studies and correlations in Persian Gulf area.

Marusk Catchment with an area of 131.87 square kilometers is located in the Northwest of Neyshabur. Baghi River as one of the main tributary of this catchment has been studied with a length of about20.1km.For sedimentological studies a total of 32 sediment samples taken from the active mid-channel of the river that after drying, the granulometry has been analyzed by dry sieving method. After the sample sieving, statistical parameters (median, mean, sorting, skewness and kurtosis) were calculated.3 sedimentary discontinuities have been detected in the sediments of the river. First and second discontinuity is due to input of sediments from the alluvial fan and tributary into the main channel, respectively, and third discontinuity is due to changes in lithology. To determine the percentage of erosion in the formations in this region and determine the amount of sediment yield in each of formations, Abrasion Los Angeles Test is done. Based on this method, Dalichai Formation with according to its lithology and also a great expansion in the region is main formation for sediment yield in this area. In the study area, coarse-grained sedimentary facies (Gmg, Gci), medium-grained sedimentary facies (Sm) and fine-grained sedimentary facies (Fl) were identified. According to sedimentary facies, the architectural elements of SG and FF have been identified. Sedimentary models proposed for this river are including braided gravelly river with sediment gravity flow and shallow braided river with gravel-bed load.

During the precipitation of Sarvak formation imprints of climate, tectonic and sea level fluctuation lead to some of the most prolific reservoirs in Zagros and Persian Gulf basins. The reservoir quality of upper Sarvak formation in Abadan plain oil fields are highly influenced by various diagenetic process. Based on core studies, petrographic analysis, well logs and properm data from two key well in a giant field, diagenetic sequence is reconstructed and the main processes effecting the reservoir quality are discussed. Three main diagenetic environments including 1- marine diagenesis (Micritization, Bioturbation, marine cementation) 2- meteoric diagenesis (mineralogy stability, recrystallization, meteoric cementation, mixing zone dolomitization, Dedolomitization, fabric and none fabric selective dissolution) and finally 3- burial diagenesis (physical and chemical compaction, burial dolomitization, fracturing, burial cementation, Silicification and pyritization and some none fabric dissolution) have affected the upper Sarvak formation after deposition. Dissolution of matrix and grain, especially aragonite shells was a main porosity creating process, and took place primarily by meteoric diagenesis. Diagenetic studies indicate meteoric environment products highly modified reservoir quality. Calcite cementation and compaction are the chief factors controlling the reduction properm whilst dissolution and fracturing have enhanced reservoir quality of the studied interval. This study resulted that distribution and intensity of diagenetic process are dominantly controlled pore systems and reservoir quality.

The upper part of Neogene sequence of the Zagros Mountains consists of a clastic succession which is identified as Aghajari and Bakhtyari formations. The sequence is an excellent example of synorogenic sedimentation or molasse deposited in northern portion of the Zagros foreland basin. Sedimentological analysis of an outcrop section representing Miocene-Pliocene sediments in central Dezful Embayment resulted in recognizing 9 lithofacies and 4 architectural elements. These lithofacies include conglometate (Gt, Gh, Gmm), sandstone (Sp, Sh, Sr, St) and mudstone (Fm, Fl) that were deposited in meandering stream, braided river and alluvial fan environments. Paleocurrent analysis of cross-beds, channels and asymmetric ripple marks indicate that these Neogene clastics were mainly drived from Cretaceous to Paleogene highlands in the Zagros Mountains on the north. This stratigraphic record is coarsening-upward and formed by a regressive depositional megacycle under arid climate. Facies and depositional history analysis show that sedimentation of the Zagros molasse was primarily controlled by base-level changes rather than catchment lithology or climate. The sedimentary record of this regressive megacycle reveales the base-level was constantly falling down on one hand and the provenance was uplifting on the other hand. Tectonic activities and Zagros Mountains rising in the Late Miocene resulted in deposition of fining-upward point-bar and floodplain sequences of the Aghajari Formation in low-gradient meandering streams. The Lahbari Member of the Aghajari Formation represents deposition in braided rivers that composed predominantly of flood-plain deposits in the Early Pliocene. Finally, the sedimentary cycle of the Zagros molasse deposits terminated with massive conglomerates of the Bakhtyari Formation deposited in large alluvial fans near the source area.

In this study, the sediments of Qom Formation were investigated in South East of Kashan. This Formation with a thickness of about 339 m consists of marl, limestone and marly limestone that disconformity lie between Lower Red Formation and conglomerate of Pliocene at the top. The study of 113 samples taken from the section led to the identification of 34 species and12 genera of calcareous nannofossils. In this study were used of biozonation introduced by Martini for study of biostratigraphy and determination age of Qom Formation. According to distribution of the index species, created four distinct biostratigraphic marker zones in this section, described as nanno floral zones Triquetrorhabdulus carinatus zone (NN1), Discoaster druggii zone (NN2), Sphenolithus belemnos zone (NN3) and Helicosphaera ampliaperta zone (NN4). As a result of this study and based on the identified zones, the age of Qom Formation in the South East of Kashan is Late Chattian to Burdigalian/Langhian.