فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و پنجم شماره 2 (پیاپی 75، تابستان 1398)

 In this study, petrography and geochemistry of the sandstones and shales of Padeha Formation in Khoshyeilagh section in Eastern Alborz have been used to obtain more information on their provenance. The Padeha Formation in the studied section has a thickness of 341 meters and overlies the Late Ordovician-Silurian Soltan-Meydan basalts and disconformably underlies the Middle to Upper Devonian Khoshyeilagh Formation. After field studies, 20 medium-grained sandstone samples were selected for point-counting and eight sandstone and two shale samples were selected for geochemical analysis. Based on the calculated percentages of point counting data, the composition of these sandstones has been detected as quartzarenites, subarkose and sub litharenites. Based on Q/Q+F in sandstones and geochemical properties of sandstones and shales, such as Al2O3/TiO2 ratio and TiO2 against Zr, the dominant parent rock of these deposits can be considered as felsic igneous rocks. The QmFLt and QtFL diagrams show the tectonic setting of the Padeha sandstones as a stable craton. The geochemistry has also largely confirmed the tectonic setting of passive continental and rifted margins. Considering paleogeography of the region, tectonic uplifts and erosion of the Cadomian granitic basement and also the entrance of clastic materials from granitic rocks of Arabian craton can be considered as other source rocks of the sediments of Padeha Formation.

     Petrography and the composition of siliciclastic sediment and sedimentary rock components provide important information on parent rock, which is one of the main factors in the reconstruction of tectonic evolution and sedimentation. In addition, by using the chemical composition (major, trace and rare earth elements) of siliciclastic sediments and sedimentary rocks, one can also estimate the provenance and other sedimentary processes such as weathering, transport and diagenesis (McLennan et al. 1993; Armstrong-Altrin et al. 2012; Armstrong-Altrin 2015).
In this study, petrography and geochemistry of the sandstones and shales of the Padeha Formation in Khoshyeilagh section in Eastern Alborz have been used to obtain more information on their provenance.
 

     The Padeha Formation in the studied section has a thickness of 341 meters and overlies the Late Ordovician-Silurian Soltan-Meydan basalts and disconformably underlies the Middle to Upper Devonian Khoshyeilagh Formation. In this study, 30 samples of sandstones of the Padeha Formation in Khoshyeilagh section were selected after field sampling and petrographic studies. Twenty medium- to fine-grained sandstone samples were selected for modal analysis, and about 300 points were counted on every thin section using the Gazzi-Dickinson method (Ingersoll et al. 1984). According to the point counting, the main and accessory components of this sandstones are identified and quartz, feldspar and rock fragments modes are utilized for naming the sandstones according to the Folk classification (Folk 1980) as well as different diagrams of the provenance (Dickinson 1985). Based on the calculated percentages of point counting data, the composition of these sandstones has been detected as quartz arenites, sub arkose and sub litharenites. Eight samples of medium-grained sandstone samples with the lowest amount of carbonate cement and two samples of shales in the middle member of the Padeha Formation were selected, crushed and powdered with a mill and sent to the Zarazma Laboratory, Tehran for geochemical analysis (ICP-MS method) to determine the major, trace and rare earth elements.
 

    According to the ratio of quartz to total feldspar and quartz in the sandstones of the Padeha Formation, which is 0.95 and geochemical properties of sandstones and shales, such as Al2O3/TiO2 ratio and TiO2 against Zr, the dominant parent rock of these deposits can be considered as felsic igneous rocks. The QmFLt and QtFL diagrams show the tectonic setting of the Padeha sandstones as a stable craton. Passive continental and rifted margins for Padeha Formation has also largely confirmed by geochemistry of sandstone and shale samples. Considering paleogeography of the region, tectonic uplifts and erosion of the Cadomian granitic basement and also the entrance of clastic materials from granitic rocks of Arabian craton can be considered as the other source rocks of the sediments of Padeha Formation.

In this study, for the first time depositional conditions, sequence stratigraphy and elemental geochemistry of the Taleh Zang Formation with Paleocene to Lower Eocene age in the Kermanshah province (Kaboutar Bala section) have been evaluated. In this section, the Taleh Zang Formation conformably overlies the Amiran Formation and is overlain by the Kashkan Formation with a disconformity surface. Field and microscopic studies led to recognition of six microfacies within the succession. Gradual microfacies change, the absence of calciturbidites and lack of extensive barrier reefs with considerable thickness, confirms a carbonate ramp. Sequence stratigraphic studies led to the identification of one-third order depositional sequence which includes TST and HST facies association. The lower boundary of this sequence, specified as type II and the upper boundary with evidences of subaerial exposure is type I. The maximum flooding surface (MFS) is determined with bioclastic coral corallinacea floatstone/rudstone microfacies of proximal middle ramp. The results of geochemical analysis of major elements (Ca, Mg) and minor elements (Sr, Na, Mn and Fe) indicate that the original carbonate mineralogy is aragonite and diagenetic system is semi-close to open system. Trend of elements changes along this stratigraphic section shows that in the HST sediments, the amount of Sr is decreased, while Fe and Mn are increased due to more meteoric diagenetic effect.

The Taleh Zang Formation is part of Lower Paleogene (Upper Paleocene–Middle Eocene) in the Lorestan zone of Zagros basin (Aghanabati 2010). At the type locality, this formation conformably overlies Cretaceous beds of marl and siltstone belonging to the Amiran Formation and is overlain by the Kashkan Formation with an unconformity (Aghanabati 2010). The thickness of the Taleh Zang Formation is very variable, as in some areas, this formation is absent and the Kashkan Formation directly overlies the Amiran Formation (Rajabi et al. 2011). In this paper the carbonate deposits of the Taleh Zang Formation in the Kermanshah province (Kaboutar Bala section) have been studied for the first time. The previous study of the Taleh Zang Formation in the Kermanshah province are focused on the biostratigraphy and also the components of this current study is different from other sections in the Lorestan zone (such as the absence of larger benthic foraminifera e.g. nummulitidae, alveolinidae and discocyclinidae and presence of corals and algae). So in this research for the first time depositional conditions, sequence stratigraphy and elemental geochemistry of the Taleh Zang Formation in the Kermanshah province (Kaboutar Bala section) have been evaluated.
 

For the present study, one surface section of the Taleh Zang Formation in the south of the Kermanshah region (Kaboutar Bala section) has been studied. The section measured a total thickness of 65 m and consists of limestone, dolomitic limestone, dolostone and minor amount of marl. During the fieldwork studies, 33 rock samples from carbonate deposits (limestone and dolostone) have been taken for petrographic studies. In order to differentiate ferroan and non-ferroan calcite from ferroan and non-ferroan dolomite in thin sections, the staining method of Dickson (1965) was applied. According to the methods of some researchers such as Haq et al. (1987) and Posamentier et al. (1988), depositional sequences were recognized. Elemental geochemistry analysis were performed form 12 samples of carbonates at the geochemistry laboratory of Shahid Beheshti University, Iran.
 

Based on the field and petrographic studies, the microfacies and depositional environment of the Taleh Zang Formation were recognized. This formation in the Kaboutar Bala section have been made of six microfacies which occur in four facies belts. The tidal flat sediment is composed of dolomicrite with ranging in size from 4 to 16 µm and contain silt-size quartz grains. Many researchers believe that dolomicrite forms during very early diagenesis in supratidal to intertidal environments (e.g. Sibley and Gregg 1987; Adabi 2009). From the shoreline towards the seas, the lagoon facies belt consists of two microfacies; bioclastic benthic foraminifera peloidal wackestone, and bioclastic benthic foraminifera dasycladacea wackestone to packstone. The lack of marine biota and abundant components of restricted biota (such as miliolids and dasycladacea), represent a restricted conditions in the lagoon environment (Bachmann and Hirsch 2006; Adabi et al. 2015; Kahsnitz et al. 2018). Barrier facies belt is composed of coral boundstone microfacies with limited lateral extension. The main components of this microfacies are only corals. The dominance of coral colonies indicate a high energy environment in the barrier facies belt (Vescogni et al. 2016; Ghafari et al. 2017). The open marine facies belt includes coral floatstone and bioclastic coral corallinacea floatstone/rudstone microfacies. The common coral debris may have derived from erosion of pre-existing coral colonies (in the barrier facies belt) by currents and/or storms (Roozpeykar and Maghfouri Moghaddam 2015; Shabafrooz et al. 2015). Gradual microfacies change, the absence of calciturbidites and lack of extensive barrier reefs with considerable thickness, confirms a carbonate ramp .
Based on the sequence stratigraphic studies, one depositional sequence was identified in the studied sequence. The lower boundary of this sequence is located at the base of the formation and specified as type II. The upper boundary with evidences of subaerial exposure and the presence of siliciclastic Kashkan Formation specified as type I. The MFS is determined with bioclastic coral corallinacea floatstone/rudstone microfacies belonging to the proximal middle ramp.
Geochemical analysis in limestone parts of the formation including Ca (37.57–39.25%), Mg (0.25–1.3%), Sr (964–1833 ppm), Na (65–160 ppm), Mn (161–421 ppm) and Fe (281–2107 ppm), and their variations indicate that the original carbonate mineralogy is aragonite and diagenetic system is semi-close to open system.
Variation trends of elements along the stratigraphic column shows that the amounts of elements in the TST and HST are different from each other. Generally in the HST sediments, the amount of Sr is decreased, while Fe and Mn are increased due to more meteoric diagenetic effect at this part of the sequence.

The Devonian/Carboniferous (DC) transition is characterized by several transgressive/regressive cycles which led to a widespread ocean anoxia known as the Hangenberg Black Shale Event (HBS), close to the D/C boundary a major sea-level fall (Hangenberg Sandstone, HSS), can be recognized in many sections around the world. Both events known as the Hangenberg Crises. In order to examine the D/C transition, the Mighan section, in Eastern Alborz was selected and studied. The outcrop section is located 25 Kms NE Shahrood city.  Frothy five conodont samples (4-5 kg) were systematically taken from 91 ms of the D/C transition interval. Although the conodonts show low frequency but high diversity exhibit important zonal index taxa of the widely applied conodont standard zonation. Twenty-three conodont species belong to five genera were identified and let to discrimination of six following zonal boundaries: Bispathodus aculeatus aculeatus zone, Bispathodus costatus zone, Bispathodus ultimus zone, praesulcata zone, CKl interregnum, sulcate zone. At the D/C transition in Mighan section a black shale and sandstone units are observable that corresponds to the Hangenberg Crisis, that highly affected trilobite, ammonoid, brachiopod and conodont faunas. Kockeli Zone at the latest Famennian is missing at the studied profile due to the major sea level regression.      

The study of DC boundary, the mechanism and reasons for the reduction of different fauna, has been an important issue for many paleontologists in the world and in Iran as well.   DC boundary is one of the most important boundaries on the Earth, in or shortly before which, an important biological event called Hangenberg event, occurred. The Hangenberg event is one of the major events in the Phanerozoic, and affected more than 20% of marine invertebrate families and 45% of the general population (Simakov 1993; Sepkoski 1996). The Hangenberg event has been identified on epicontinental basins and continental margins in the world.  Black shale and Sandstone deposits are very important in identifying this event in different climatic and oceanographic studies. Kaiser (2005) considered that the Hangenberg event is a polyphase crisis, and different groups of fossils from different climates affect, including various rock-diverse changes, and black shales is the main extinction phase of the Hangenberg crisis. These black shales (HBS) occurred during a vast and short-term marine flooding surface within costatus-kockeli interregnum. Successively, a vast eustatic sea-level fall at the end of the Devonian led to deposition of HSS (Becker 1993a). DC boundary is defined via the first appearance Datum (FAD) of the basal Carboniferous conodont Siphonodella sulcata, from Global Stratotype Section and point (GSSP) located in La Serre Trench E’ section, Montag Norie, France (Paproth et al. 1991). However, the decision to define the DC boundary based on the evolutionary species of Siphonodella has some limitations such as: Detection of morphotype Si. sulcata is very hard because Holottape of Si. Sulcata is the interstitial state of Si. sulcata and Si. duplicate (Huddle 1934) and between the Si. praesulcata and Si. sulcata, there are many morphotypes whose exact diagnosis depends on the long-standing personal taste (Kaiser and Coradini 2008). In order to solve this, Corradini et al. (2011) by revising Siphonodellid in the type section and other global sections, divided Siphonodellids into seven groups based on the Platform's shapes, Basal cavity and features of Pseudokeel. The base of Carboniferous system is also defined by the FAD of Protognathodus kuheni (Corradini et al. 2011) and according to new global zonatin of Corradini et al. (2016) and Spalleta et al. (2017) is defined by the FAD of Protognathodus kockelio. The main purposes of this study are to summarize a detailed stratigraphy below and above the D/C boundary in the Mighan section, on the base of conodonts according to new global zonation.  

During field work, 91m of the Upper Devonian–-Lower Carboniferous succession at Mighan section has been investigate and about 45 conodont samples (3-4kg each) were collected from the Mighan section. The samples were processed with diluted acetic acid (20%). The conodonts were extracted from residues by hand picking and are stored at the University of Isfahan, I.R. Iran and also State Museum of Natural History Stuttgart, Germany. 

The Mighan area is located about 20 km northeast of Shahrud city which is located near the Mighan village. Geographical coordinates of the base and top of this studied section are: N: 36° 38′ 38″, E: 54° 57′ 55″ base and N: 36° 38′ 39″, E: 54° 56′ 55″ top.  This section includes late Devonian uppermost sediments of Khoshyeilagh Formation (74.47 m thick) and lowermost Carboniferous of Mobarak Formation (16.53 m thick), which subdivided into six lithological units (units A to F). The conodont zonation scheme proposed by Corradini et al. (2016) and Spalleta et al. (2017) for the Upper Devonian and Lower Carboniferous strata were utilized for lower part of the Mighan section in this paper. According to these conodont zonations Protognathodus kuheni is considered as the base of the Carbonoferous. However, due to the lack of Protognathodus in the Mighan section, we used conodont zonations of Kaiser et al. (2009) to define DC boundary based on the appearance of Siphonodella praesulcata and Siphonodella sulcata. Totally five bio-intervals have been discriminated in the Mighan section: Bi. aculeatus aculeatus Zone, Bi. costatusZone, Bi. ultimus Zone,The praesulcta Zone, The Costatus-kockeli interregnum (CKI), andthe sulcata Zone. Field works and lab examinations led to identification of a dark and organic-rich shaley horizon at the D/C transition which corresponds to the costatus-kockeli interregnum (CKI) conodont biozone and are indicative of Hangenberg Crisis. Transgression of seawater and expansion of dark shales caused the organisms to wipe out and following regression formed HSS in the Mighan section. These dark shales are representative of the dominance of dysoxic to anoxic conditions accompanied by low rate of deposition and considerable decline of organisms. The migration of anoxic waters during the transgression of sea water, which is evidenced through the occurrence and increase of conodont species such as Bispathodid, gave rise to the losing habitats, invasion and competition to occupy the habitat and extensive decline of benthic organisms. The reduction of brachiopods, trilobites and ammonoids in the dark shales and topmost beds at the Mighan section are potential documents for this event. Despite intensive sampling in this study, no latest Famennian kockeli Zone was recognized at the studied section implying the presence of disconformity and discontinuity of deposition. Therefore, the basal limestone immediately above the sandstones at the Mighan section is comparable to Early Tournaisian Si. sulcata Zone.

The Ruteh Formation is the second sedimentary cycle in Alborz basin. The petrography and laboratory studies of these deposits led to the identification of 15 microfacies which were deposited in seven sub-environments including supratidal, intertidal, lagoon, shoal, open marine, middle ramp, and outer ramp. Since there were no turbidity deposits, the lack of marginal reef belt and the gradual changes of facies, it turned out that these sediments were deposited in a homoclinal carbonate ramp. The study of relative sea level changes was done according to vertical distribution of facies and their stacking patterns. These studies lead to identification of four depositional sequences. The petrography data and geochemical analyzes were used in order to identify the diagenetic processes and geochemical changes. The recognized diagenesis processes include micritization, cementation, compaction, stylolitization, silicification, ferrugenation and neomorphysm. These diagenetic processes took place in three diagenetic environments: marine-phreatic, meteoric-phreatic and burial. Geochemical analyzes confirms that the carbonate sediments of Ruteh Formation were originally composed of aragonite, which was eventually recrystallized to calcite during diagenesis. Plotting Sr/Ca versus Mn diagram approved that sediments was subjected to a meteoric diagenesis in a semi-closed to open diagenetic system. The results of this research can be used to provide a sedimentary model for these deposits which completes the palaeogeographical data for the Tethys Ocean.
 

The geological observations indicating a coherent Iranian-Gondwanaland continental landmass during the Late Precambrian to Permian are consistent with palaeomagnetic data (Berberian and King 1980). Palaeomagnetic evidences from the Upper Precambrian rocks and iron ores of Bafq area in central Iran (Becker et al. 1973), the Lower Paleozoic rocks of kuh-e-Gahkom and Surmeh of the Zagros (Burek and Furst 1975), the Cambrian purple sandstone of the salt range of Pakistan (McElhiny 1970), the Upper Devonian–Lower Carboniferous of the Alborz Mountain in north Iran (Geiroud Formation; Wensink et al. 1978) and from the Upper Precambrian, Ordovician and Permian rocks of central Iran (Soffel et al. 1975; Soffel and Forster 1977) show similar geomagnetic poles with those of Afro-Arabia. These data and the widespread similarity of Paleozoic sedimentary succession indicate that during the Late Precambrian and Paleozoic, Central Iran, the Alborz in northern Iran and the Zagros in south Iran were parts of Gondwana (Berberian and King 1981). In the Late Carboniferous–Early Permian, continental rifting separated these lands from Gondwana due to the expansion of Neo-Tethys Ocean. Due to the glaciers growth and Hercynian orogeny movements in that time (Berberian and King 1981; Lasemi 2000), the Early Permian sedimentary facies in Iran are mainly siliciclastic (Dorud Formation in Alborz–Azarbaijan zone). In the Late Permian, after deposition of the Droud Formation, glaciers regression, tectonic tension activities and increasing volume of mid ocean ridges led to the sea progress and carbonate platforms restoring in the southern margin of Paleo-Tethys (Lasemi 2000). The carbonate rocks of the Upper Permian Ruteh (Asserto 1963) and Nesen (Glaus 1964) formationsin the Alborz–Azarbaijan zone and the Jamal Formation in central Iran, record the development of these carbonate platforms. The Ruteh Formation studied here is exposed about 15 km north of Mahabad city. Since no studies have been carried out on the Ruteh Formation in this area so far, this research aims to identify the sedimentary environment, sequence stratigraphy, diagenesis and geochemistry of this formation.

After literature review and preliminary visits of the study area, for the most complete and appropriate succession in the field was selected. Then, its rock units were delineated by means of horizontal and vertical scrolling. Based on the geometric features of sedimentary units, stratigraphic planes, sedimentary structures and biotic and abiotic components, the existing sedimentary units were divided and separated into diverse facies. In order to determine the microfacies and sedimentary environment of the Ruteh Formation 101 rock samples were collected systematically, and by taking into account the changes in the facies. To analyze the microfacies, textures, depositional environments, the facies components, the ratio between its components and various diagenesis processes, the samples were sent to the laboratories, and a thin microscopic section was made from the collected rock samples. Thin sections were studied under polarizing microscopes. In order to determine the frequency of allochems, the comparison charts (Bacelle and Bosellini 1965) were used. The microfacies naming was done by means of Folk’s (1962) and Danham’s (1962) methods, environmental energy detection based on Flügel's method (2010), texture studies based on Tucker's (2002) method, diagenesis evidences, energy detection and sedimentary environments were done by means of Wilson’s (1975) and Flügel’s (2010) methods. To detect depositinal sequences, the models presented by Hunt and Tucker (1992) were also used. To study the early mineralogy of the Permian carbonate rocks in northern region of Mahabad, after thoroughly studying thin sections petrography, eight limestones samples with the highest micritic matrix and least alternation and lowest fossil contents were selected. Then they were subjected to elemental analysis using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and alkali melting methods in laboratory of Zarazma Company (Tehran), then geochemical values plotted in geochemical diagrams for early mineralogy determination.

With regard to the identified microfacies, the process of the basin deepening from the carbonate platform towards the deep basin, the absence of oncoids, pisoid and aggregate grains, which are specific to carbonate shelf and rarely found in carbonate ramps (Flügel 2010), also, lack of re-deposited carbonate facies, sediments related to gravity flow processes in sediments of the Ruteh Formation indicates sedimentation of these sediments in a low-slope and approximately uniform gradient in the basin floor slope a homoclinal ramp profile can be predicted for the deposits of the Ruteh Formation in this study area (Wilson 1975; Read 1985; Lee et al. 2001; Flugel 2010). Due to the low expansion of the reefs in the carbonate ramp compared to the rimmed carbonate platforms, the lack of widespread barrier reef and the presence of patch reef in the Ruteh Formation is another reason for this fact that the sedimentary environment of this formation is a homoclinal carbonate ramp (Bastami 2016). On the other hand, by reviewing of distributed facies in sub-environments and their constituents it can be concluded that Ruteh Formation depositional environment is a bioclastic carbonate ramp similar to that introduced by Kolodka (2012) for Dalan Formation in Fars province. Based on the vertical distribution of facies, relative sea level changes these studies lead to identification of four depositional sequences. Early marine diagenetic processes like micritization and marginal micrite cements well represente transgression of sea level. During the sea level regression (sequence boundaries), sediments have been affected by meteoric diagenetic processes such as granular calcite cement, blocky calcite cement, syntaxial cement, ferrugination and neomorphism. Also the evidences of deep burial diagenetic process observed by physical compaction, druzy calcite cement, stylolization, poikilotopic calcite cement and silisification processes. Geochemical analyzes confirms that the carbonate sediments of Ruteh Formation were originally composed of aragonite, which was eventually recrystallized to calcite during diagenesis. Plotting Sr/Ca vs. Mn diagram approved that sediments was subjected to a meteoric diagenesis in a semi-closed to open diagenetic system.

The Mishrif Formation (Cenomanian–Turonian) is one of the most important hydrocarbon reservoirs in the Persian Gulf. In this study, 151 microscopic thin sections and the porosity and permeability data on wells SIE-5 and SIE-6 in Esfand Oilfield were studied to identify the microfacies, depositional environment and the diagenetic processes of the Mishrif reservoir, to evaluate the effect of these processes on the reservoir quality. Lucia's petrophysical classification and the reservoir quality descriptive classification were also used in the optimal analysis of the reservoir characteristics. Petrographic analyses revealed 11 microfacies that belonged to the peritaidal zone, lagoon, shoal, middle and outer ramp sub-environments on a homoclinal carbonate ramp. Most of the microfacies of these two wells are belong to the shoal and lagoon facies belts. The succession in both wells show shallowing upward sequences. The most important diagenetic characteristics of the Mishrif Formation include dissolution, cementation, compaction, dolomitization and stylolitization. Porosity type consists of intercrystalline, vuggy, moldic and fracture porosities. Almost all microfacies in both wells are also in classes one and two of Lucia's petrophysical classification. Furthermore, the facies in the peritidal zone and shoal sub-environments in SIE-5 are in a better reservoir condition than SIE-6. On the other hand, the open marine facies in SIE-6 have a higher quality than the facies in SIE-5. In summary, it could be stated that diagenetic processes have had a larger role in the increase or decrease in the reservoir quality than the depositional environment. Thus, the Mishrif reservoir could be considered a diagenetic reservoir.

The Middle-East has the largest oil and gas reserves in the world, with its major portion being stored in the Arabian Plate (Sharland et al. 2001). The thick Cretaceous-aged sediments accumulated in the Arabian platform and Zagros basin contain enormous and economically valuable hydrocarbon reserves (Setudehnia 1978; Alsharhan and Nairn 1986, 1988; Ghabeishavi et al. 2009, 2010; Hollis 2011; Lapponi et al. 2011). The Cretaceous-aged (Cenomanian–Turonian) Mishrif reservoir is one of the most important hydrocarbon reservoirs in the Persian Gulf. Therefore, a better knowledge of its reservoir properties and depicting the sedimentary environment and diagenetic processes is of high importance.

In this study, 151 thin sections at coring spaces of one m were taken from the Mishrif Formation at SIE-5 and SIE-6 wells respectively, in the Esfand Oilfield. Then, they underwent petrographic examinations with a polarizing microscope to evaluate the microfacies and diagenetic processes. In order to determine the reservoir quality, the porosity-permeability data were plotted in petrophysical classification (Lucia 1983). Subsequently, each microfacies was evaluated separately, with its reservoir status being described based on descriptive classification (Ahr 2008).

Based on the conducted studies on the thin sections prepared from the cores of Mishrif Formation in two wells, 11 microfacies were identified belong to five groups of the intertidal zone, lagoon, shoal, middle ramp, and outer ramp.
The Mishrif Formation (Cenomanian–Turonian) in both wells indicate an evident thinning upward, which is consistent with the trend of sedimentation and its simultaneous depositional sequences in the Persian Gulf and Zagros regions. However, small thinning and thickening cycles showing a local performance in these deposits are also observed in both wells.
The most important diagenetic factors in the Mishrif Formation include dissolution, cementation, dolomitization, stylolitization, bioturbation, pyritization, hematitization, neomorphism, fracturing, and filling. Hematitization, dolomitization, and fracturing are the most important factors, which have increased the total porosity. These processes have created large amounts of intercrystalline, vuggy, and fracturing porosities in the oilfield and have improved the reservoir quality. The significant impact of meteoric diagenetic processes on the Mishrif Formation and upper section of Sarvak Formation has been proved and attributed to the mid-Turonian discontinuity (Hajkazemi et al. 2010; Razin et al. 2010, Taghavi et al. 2006; Rahimpour-Bonab et al. 2012; Hahjkazemi et al. 2017).
By comparing the porosity and permeability data of the microfacies from different facies belts on the petrophysical classification diagram of Lucia, it was found that the tidal zone microfacies of the two wells show a remarkable difference in their reservoir quality. It can be said that although they have deposited in similar sedimentary environments, but the differences in the diagenetic processes have caused the tidal zone microfacies of SIE-5 to have better reservoir quality. The dolomitization process and the presence of fracturing were more and wider in the microfacies of Mishrif Formation at SIE-5 and have been highly effective in the improvement of the reservoir quality. The lagoon microfacies of both wells show a similar trend, indicating the similarity of sedimentary environment and relatively similar effect of diagenetic processes in both wells, although the reservoir status of lagoon microfacies is obviously better at SIE-5. Although the microfacies sub-environment of carbonate shoal in both wells have the same environment, they are affected by diagenetic processes in different ways. This facies belt in SIE-5 is a complete reservoir belt, but in SIE-6 well it is divided into two reservoir and non-reservoir units. The petrographic examinations in the microfacies of this belt show that cementation, as a negative parameter in the reservoir quality, has more intensity in SIE-6, while dissolution and formation of various porosities, as positive reservoir parameters, have happened more at SIE-5. The microfacies of the middle ramp show a similar trend in both wells having a relatively good reservoir quality. The microfacies of the outer ramp, which are only observed in the SIE-5, show poor reservoir quality or have no reservoir status.
The Mishrif Formation with the age of Cenomanian–Turonian is one of the most important reservoirs of the Persian Gulf. The petrographic studies conducted on this formation led to the identification of 11 microfacies. These microfacies have been deposited in five sub-environments of the tidal zone (MF1), lagoon (MF2–MF5), shoal (MF6–MF8), middle ramp (MF9–MF10) and outer ramp (MF11) indicating a homoclinal carbonate ramp. Most of the microfacies of this formation at SIE-5 and SIE-6 wells are deposited in the sub-environments of carbonate shoal and lagoon facies belts, respectively. Dissolution, dolomitization, and fracturing are of the main factors affecting the increase of total porosities. These processes have created large amounts of intercrystalline, vuggy, and fracturing porosities in the studied field and have had a positive effect on increasing the reservoir quality. Evaluation of main diagenetic process has resulted in separation of three marine, meteoric, and burial diagenetic environments. The existing evidence shows that although the diagenetic processes have affected these deposits from the beginning of sedimentation to the deep burial phases, but mostly effected by  burial and meteoric diagenesis environments.
The reservoir evaluation showed that most of the sedimentary microfacies of this formation at both studied wells are plotted in classes one and two of the Lucia, which have a better reservoir status. In addition, the diagenetic processes have highly affected the porosity and permeability of these microfacies. Based on the dispersion of microfacies in different classes of Lucia in both wells, it was found that the sedimentary and diagenetic environments have affected the reservoir quality of sedimentary microfacies, both together and sometimes with different proportions. On the other hand, the results show that the microfacies of the tidal zone, lagoon, and shoal in SIE-5 and those of lagoon and middle ramp in SIE-6 have the best reservoir qualities. This is due to the presence of dissolution and dolomitization processes and formation of interconnected porosities.

In order to investigate the concentrations of heavy metals in stream sediments of the Baycheh-Bagh area, northwest of Zanjan province, 131 samples were collected from intended stations. These samples after dissolution by four acid method, were analyzed by ICP-OES. To determine the type of spatial distribution of data, two important spatial statistics, i.e. global Moran’s I and Anselin local Moran’s I were employed. The average concentrations of As, Bi, Cd, Ni, Pb, Sb and Cu in stream sediment samples were 21.83, 0.32, 0.35, 35.57, 68.96, 37.67, 1.96 and 82.71 ppm, respectively which are higher than the average of crust whereas the average concentration of Co is 20.30 ppm. The obtained results indicate that the heavy metals in the study area has a spatial structure and distributed in cluster form.According to the Local Moran’s I results, the most contaminated area in the study area was detected in western part of the Baycheh-Bagh abounded mine and located on the present polymetallic vein-veinlet mineralizations and their related alterations. Analysis of obtained data and investigation of their relationship with the geological rock units of the study area show that concentration of the studied elements have geogenic source and is related to the mineralizations and alterations.

Heavy metals are one of the most important sediment contaminations and are important in low concentrations due to their in solubility and their physiological effects on organisms and human (Zare Khosh Eghbal et al. 2012). In an aqueous environment, sediments are the final destination of heavy metals accumulation and can act as a source of water pollution. On the other hand, mineral resources, especially metal deposits, contain significant amounts of heavy metals and potentially toxic elements. Contact of surface and underground water with the host rocks, ore mineralizations and altered rocks releases various elements, provides a large amount of heavy metals and potentially toxic elements in downstream deposits and surrounded soils. This fact highlights the importance of environmental studies of stream sediments. Spatial statistics is one of the basic concepts of modern sciences in monitoring and analyzing environmental data that focuses on the spatial relationship of data.
Spatial analysis of environmental data is crucial factor in spatial statistics. The first step in spatial analysis is identifying the data dispersal structure. Regarding to the importance of monitoring the spatial changes of environmental data and considering the distribution, arrangement and behavior patterns of variables in environmental topics, this study attempts to investigate the pattern of heavy metals dispersion in the stream sediments of the Baycheh-Bagh area, located in the northwest of Zanjan.

In order to evaluate the environmental contamination of heavy metals in the Baycheh-Bagh area, 131 samples were selected from intended stations. In this step, about 500 gr of stream sediments from a depth of 5-15 cm was selected from each station. After crushing and milling the samples, the obtained powders were dissolved by the four acid solutions and were analyzed by the ICP-OES at Environmental Science Research Laboratory, University of Zanjan. The studied elements in this research include As, Sb, Cd, Pb, Zn, Ni, Co, Bi and Cu. After receiving the analytical results from the laboratory, the data were processed statistically. For this purpose, the statistical parameters such as mean, median, mod, standard deviation, skewness, Kurtosis, range, minimum and maximum were analyzed for the nine mentioned elements using SPSS 22 software. Furthermore, Kolmogorov-Smirnov test was used to examine the distribution of the normal data. In the absence of normal data, the logarithm transformation method was used to normalizing them. To determine the amount of stream sediments contamination to heavy elements in the study area, global Moran’s I and Anselin local Moran’s I were employed. Determination of the degree of dispersion or clustering of features, global Moran’s I was used.
 

  The Global Morans’s I spatial autocorrelation was used to determine the spatial distribution of the data. The results of this analysis indicate that all metals have a strong correlation and cluster distribution. The Moron index for all metals is above 0.9 and among them the strongest and weakest correlation is for Bi and Cd elements, respectively. Accordingly, it can be concluded that the studied heavy metals have a spatial structure and are distributed in cluster form. In other words, the data tend to be concentrated in study area and have been influenced by almost the same factors. The results of the local Moran’s I analysis showed that the Bi and Pb have the highest and lowest high-high points, respectively, and the Co and Pb have the highest and lowest low-low points, respectively. According to the local Moran’s I statistics, the most polluted region of the study area was detected in the western part of the Baycheh-Bagh mine which are located on the polymetallic vein-veinlet mineralizations and related alterations. These metals include As, Bi, Cd, Co, Sb, Zn and Pb which have sheared between high-high points. The analysis of the samples from the stream sediments shows that the source of the concentration of the studied elements is geogenic (resulted from geological processes) and is related to mineralizations and alterations.