جستجوی مقالات مرتبط با کلیدواژه « sedimentary sequence » در نشریات گروه « زمین شناسی »

In this research, the process of lithological changes and diagenetic processes of Asmari formation with Oligo-Miocene age has been investigated. For this purpose, 400 samples were selected and collected from a section of the Masjid Suleiman oil field and the surface section of the Asmari anticline in the Dezful depression and the Gurpi anticline in the Izeh zone. Petrographic studies revealed 18 sedimentary microfacies that were deposited on a ramp-type carbonate platform. Among the significant diagenetic processes in the region are the process of micritization, bioturbation and the influence of burrowing organisms, cementation (types of cement related to marine, meteoric and burial diagenesis environments), dissolution (meteoric and burial dissolution), dolomitization (in different phases), silicification, pyritization, phosphatization, mechanical compaction, chemical compaction, fracture and porosity. Based on the identification of the sequence boundaries and following the facies depth changes, the carbonate sequence of the Asmari formation in the subsurface section and the Asmari anticline section are introduced in the form of 3 sedimentary sequences of the third order shallowing upwards, which are the former Aquitanian, the late Aquitanian and Bordigalin belong. Among the dominant porosities in the Asmari Formation, we can mention the hole, mold and fracture porosities.

The carbonate deposits of the Taleh Zang Formation are exposed extensively in the southeastern to northern Lorestan zone, SW Iran. The thickness of the shallow water carbonate Taleh Zang Formation in Ritt Anticline is 84.5 meters. It overlies on top of the turbidity Amiran Formation and it is overlain by the clastic-dominated Kashkan Formation. Petrographic examinations revealed seven facies deposited in tidal flat, lagoon, shoal and open marine. Detailed analysis of sedimentary facies indicates that in the Late Paleocene interval, the depositional system of the Taleh Zangi Formation was a ramp carbonate platform. Changes in the depositional facies and cycle stacking patterns indicate one transgressive-regressive sea-level cycle from the bottom to the top of the section, which is equivalent to the last eustatic sea level rise in the Late Paleocene (Thanetian).  This depositional sequence is separated by type 2 and 1 sequence boundaries at its lower and upper boundaries, respectively. Elemental geochemical evidence indicates a closed to weakly open digenetic system, with low water-rock interaction for carbonates of the Taleh Zang Formation. The relatively open digenesis system in this formation could be due to the influence of meteoric fluids in the erosional discontinuity at the border between the two formations, the Taleh Zang and Kashkan formations.

The Oligo-Miocene Asmari Formation is one of the most important hydrocarbon reservoirs in the Zagros sedimentary basin, especially in the Dezful depression. The Formation in most of the oil fields of the Dezful depression consists of a mixed carbonate-siliciclastic sequence. In this study, the relationship between sedimentary sequences and diagenetic processes with reservoir zones is considered. For this purpose, sedimentological data and petrophysical logs of a key well were used. Based on microscopic studies on the core thin sections, four detrital petrofacies and eight carbonate microfacies were identified that were deposited in four facies belts, including open marine, shoal, lagoon, and tidal flat environments, related to a homoclinal ramp. In addition, six depositional sequences (third order) were identified by facies analysis and well logs. Reservoir properties have been increased by dissolution and dolomitization with pore space expansion, while being decreased by cementation and compaction. The Asmari Formation in the investigated well is subdivided into eight reservoir zones based on sedimentary characteristics and petrophysical properties. The coincidence of the facies boundaries with the reservoir zone boundaries in most cases shows that the changes in the reservoir properties are mainly related to the changes in the sea level. This is well-known in the lower zones

To developing and explore hydrocarbon fields, it is necessary to know geological models and reservoir quality changes. Therefore, the Ilam Formation with approximate 145m thickness was examined in the Susangerd oilfield. The sedimentary model was considered carbonate ramp type due to the lack of slump and reef structures. Two complete and one incomplete third-order sedimentary sequences were identified. Close to the sequence boundary in the middle part of the Ilam Formation, reservoir conditions improve with the development of vug and mold dissolutions, especially in green algae by corrosive fluids passing through stylolites and fractures. But near the sequence boundary in the upper part of the Ilam Formation, however intergranular porosity develops between peloids and ooids but almost destroyed with cementation. The southeastern domain of the oilfield contains shallower microfacies in the lower sedimentary sequence and most part of transgressive system tract of the middle sequence in comparison with the northwestern domain. It seems that the southeastern part of the oilfield is located on paleo high and the lower values ​​of porosity log in the northwestern part are probably due to the distance from this paleo high. Therefore, the southeast of the oilfield is suggested for the development of the Susangerd oilfield and future explorations.

Tungsten (Cu-Au-Zn) deposits and occurrences in Iran can be divided into two separate categories based on their genesis, tectonic setting, mineral paragenesis and related processes inherent in their formation. The first category contains deposits, which are located in metamorphosed Late Triassic-Middle Jurassic volcano-sedimentary sequences, and their distribution is indicated by layering. These deposits are located in a specific stratigraphic position and are concentrated in contact of volcanic units with carbonate rocks. The geodynamic setting of this category probably is intracontinental rifting. The second category contains deposits located in metamorphosed sedimentary rocks of the Shemshak group and Jurassic granitoids. These deposits have vein-veinlet geometry and their formation is controlled by faults, fractures and shear zones. The geodynamic setting of this category probably is active continental margins. The mineral paragenesis of the first group generally contains scheelite and Cu-Fe-Zn sulfides, whereas the paragenesis of the second group is wolframite, scheelite, chalcopyrite, arsenopyrite, with gold and specifically bismuth.

The Mn mineralization occurs in the northeastern segment of the Sabzevar zone (SZ)، north of the Central Iranian Microcontinent (CIM). This Zone (SZ) is located between the CIM fragmentation in the south and the Kopeh dagh sedimentary sequence in the north. The ore deposits of the northeastern segment of the Sabzevar zone can be divided into three groups، each with different metal association and spatial distribution and each related to a major geodynamic event. The first mineralization with associated Ordovician host rock is characterized by Taknar polymetallic (Fe-rich) massive sulfide deposit. The Cretaceous mineralization consists of Cr deposits associated with serpentinized peridotites، Cyprus type VMS، Mn deposit in pillow lava، volcano-sedimentary hosted Besshi type VMS and Mn deposit. Paleogene mineralization in eastern segment of the Sabzevar zone began with porphyry deposits، Cu Red Bed mineralization occurs in the Paleogene sandy red marl.

A field study and sampling was performed during the autumn of 2012. To assess the geochemical characteristics of 48 systematic samples (least fractured and altered) of ore-bearing layers and host rocks were collected from the deposit for polished thin section examination. In order to correctly characterize their chemical compositions، 15 least-altered and fractured samples were chosen for major elements analysis.

The Late Cretaceous volcano-sedimentary sequence in south-southwest of Sabzevar hosts numerous manganese mineralization. The sequence based on the stratigraphic position، age and composition of the rocks، can be divided into two lower and upper parts. The lower part or K2tv unit mainly formed from marine sediments interbedded with volcanic rocks. The sedimentary rocks of this part include silicified tuff، chert، shale and sandstone، and the volcanic rocks involve pyroclastic rocks of various composition، rhyolite، dacite and andesitic lava. The upper part or LMV unit comprised of limestone، marl and volcanic rocks، overlies concordantly on the lower part (K2tv). The manganese mineralization within the host volcano-sedimentary sequence، based on stratigraphic position، relative age and type of host rocks involved the two horizons: the first horizon (Mn Ia، Ib) consisting of Benesbourd (Masoudi، 2008)، Nudeh (Nasrolahi et al.، 2012)، Homaie (Nasiri et al.، 2010)، Goft and Manganese Gostar Khavar Zamin deposits، occurred in the lower part of the sequence (K2tv unit) and is hosted by red tuffs. The second horizon (Mn II) comprising of Zakeri (Taghizadeh et al.، 2012)، Cheshmeh Safeid، Mohammad Abad Oryan and Chah Setareh deposits، is hosted by marly-carbonate tuffs and locates within the upper part of the sequence (LMV unit) (Maghfouri، 2012). Geometry and shape of the ore bodies in various deposits are as stratiform، layered، parallel and concordant with layering of the host rocks. Textures of the ores include massive، lenticular، banded، laminated and disseminated. Mineralogy of the ores in the two ore horizons is simple and similar and is dominated by pyrolusite، psilomelane and braunite. Gangue minerals are predominantly the host rock-forming minerals including quartz، chlorite and feldspar.

Geochemical data، structures and textures، stratigraphic position and lithologic characteristics of the host rocks represent that manganese reserves in south-southwest Sabzevar were formed as sedimentary-exhalative.