فصلنامه پژوهش های چینه نگاری و رسوب شناسی
سال سی و پنجم شماره 4 (پیاپی 77، زمستان 1398)

This study led to identify 30 species and 16 genera of eight different plant macrofossils orders including Equisetales, Cycadales, Bennettitales, Coniferales, Peltaspermales, Ginkgoales, Corystospermales, and Filicales at the Deh-Shiykh section, north of Kerman. According to stratigraphic ranges of the index taxa such as Otozamites furoni, Nilssoniopteris mosafolia, Nilssonia tenuicaulis, Anomozamites major, Coniopteris hymenophylloides, Nilssonia bozorga and Elatides thomasii the age of early Middle Jurassic (Bajocian–Bathonian) is assigned to the Deh-Shiykh section. Middle Jurassic ichno fossils of the Hojedk Formation in the Deh-Sheikh section have been studied for the first time. The study also led to the determination of terrestrial ichno fossils including eight ichno species, belonging to four ichnogenera such as Planolithes, Rhizoliths, Taenidium and Thalassinoides. They have been found alongside the stems of Equisetals. Combination of the results of ichno fossil studies with plant fossils help us to identify the palaeoenvironment. These plant fossils are generally indicator of humid conditions. Moreover, the identified ichnofossils in accordance with the sedimentological studies, represent deltaic environments influenced by the river systems and channels. This is the first study of the combination of three studies of paleontology (Plant macrofossils), sedimentology and ichnology in east central Iran. The results have contributed to the accurate understanding of the paleoenvironment of fossiliferous horizons of the Hojedk Formation.

Abstract Well preserved and diverse organic-walled marine microphytoplankton cysts (acritarchs sensu lato) occur in Member 4 (comprising mostly of fine-grained clastics with thin carbonate intercalations) of the Mila Formation at the type section, southwestern Damghan. Based on the association of such index acritarch taxa as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. in the material studied, an local biozone, namely Ooidium rossicum -Vulcanisphaera africana assemblage biozone dated as Late Cambrian (Furongian), and a barren interval are introduced in the upper and lower parts, respectively, of the rock unit investigated. Occurrence in the examined assemblages of such middle latitude acritarchs as Ninadiacrodium indicates that the Alborz Ranges was located in southern mid-latitudes (30º–60º) during the Late Cambrian. Retrieved marine microphytoplankton cysts from Member 4 of the Mila Formation is comparable with the Late Cambrian assemblages recorded from elsewhere, this allows for the pertinent assemblages to be associated with peri-Gondwanan palynofloras. Keywords: Biostratigraphy, Palaeoecology, Acritarchs, Late Cambrian, Mila Formation.   Introduction Biostratigraphic zonation of the Middle and Upper Cambrian strata is based mainly on trilobites, particularly planktonic agnostids and olenids. For example, in South China base of the Furongian Series is defined by Glyptagnostus reticulatus Zone (Peng et al. 2004). In the last decades, organic-walled microfossils (acritarchs) have been widely used for Palaeozoic stratigraphic subdivisions (Molyneux et al. 1996). The Acritarch group is defined as organic-walled microfossils of unknown biological affinities by Evitt (1963). They are a heterogeneous group of various microfossils and may include the remains of a wide range of different kinds of organisms, such as egg of small metazoans, spores of different algal classes, and resting cysts (Servais 1996). Recently, some of the acritarchs have been attributed to different groups of algae e.g. Prasinophytes or Chlorophytes (Colbath and Grenfell 1995). In the last decades, organic-walled microphytoplankton have been widely used for stratigraphic correlation both regionally and globally and their utility in dating Proterozoic and Palaeozoic marine sedimentary rocks is widely recognized (Playford 2003). Acritarchs feature a relatively rapid development of morphological innovations and a large number of new morphotypes appeared. Several palynological investigations have been undertaken on the Upper Cambrian strata across the world; e.g., Canada (Martin and Dean 1988; Palacios 2012), Russia (Raevskaya and Golubkova 2006), Germany (Montenari and Servais 2000), Iran (Ghavidel-Syooki 2006; Ghavidel-Syooki and Vecoli, 2008), North Africa (Vecoli 1999), England (Potter et al. 2012) and Spain (Albani et al. 2006). The Mila Formation is the first lithostratigraphic unit representing the Middle–Upper Cambrian strata in the Alborz Ranges and the other parts of Iran (Aghanabati 2004). Palaeontological and structural geological studies in the Alborz indicate that northern Iran, along with central Iran and Zagros located on the divergent margin of protopaleotethys and north of the Gondwana palaeocontinents. The Mila Formation at its type section measured 585 m (Stöcklin et al. 1964) and subdivided into five members: Member 1, dolostone–marl; Member 2, terrigenous – carbonate; Member 3 fossiliferous limestone; and mainly terrigenous members 4 and 5. According to palaeontological and stratigraphical studies the first 2 units attributed to the Middle Cambrian and members 3 and 4 to the Late Cambrian. The former Member 5 of this unit was later considered to be equivalent of the Lashkarak Formation (Early Ordovician). The Mila Formation at the its type section is underlain and overlain by the Lalun and Jeirud formations, respectively. The Mila Formation generally consists of dolostone, thin-bedded, crystalline, glauconitic limestone, marl, coloured shales and sandstones. Several palaeontological investigations have been conducted such as on trilobites (Kushan 1973; Peng et al. 1999), brachiopods (Popov et al. 2009, 2013), conodonts (Müller 1973; Fazli and Hamdi 2008; Jahangir et al. 2016) and palynomorphs (Ghavidel-Syooki 2006). Considering the stratigraphic significance of organic-walled marine microphytoplankton in the Lower Palaeozoic biostratigraphy, the aim of this study is to determine relative age and to derive palaeogeographic implications for the Member 4 at its type section.   Material & To retrieve palynological content of the Member 4 of Mila Formation at the type section, 21 surface samples collected from this rock unit. All samples prepared in palynological laboratories at Kharazmi University, Tehran and University of Lille, France using standard palynological processing procedures, encompassing initial treatment with HCl 10-50% and HF 40% for dissolution of carbonates and silicates, respectively. Then the residues saturated with ZnCl2 solution (2.0 gr/cm3) for mineral separation. All residues are sieved with 15 and 20 µm mesh and three slides of each sample are made.   Discussion of Results & Well-preserved and diverse palynomorphs occur in Member 4 of the Mila Formation at the Mila Kuh section. The assemblage contains 14 species assigned to 13 genera of acritarchs and one species of prasinophytes. Based on the occurrence and stratigraphic distribution of index acritarch taxa such as Timofeevia phosphoritica, Cristallinium cambriense, Ninadiacrodium dumontii, Vulcanisphaera africana, Ooidium rossicum, Cymatiogalea cuvillieri, Caldariola glabra, and Dasydiacrodium sp. one local assemblage biozone namely Ooidium rossicum-Vulcanisphaera africana assemblage biozone is introduced in 41 m of the Member 4 and assigned to the Late Cambrian (Furongian). Additionally, one barren interval zone at the base (45 m) of the rock unit is also identifiable. The biozone (Ooidium rossicum-Vulcanisphaera africana) introduced herein is comparable to microflora A2 (partial) – A6 of Martin and Dean (1981, 1988) and RA3–RA10 microflora of Parsons and Anderson (2000) as well as the upper part of VK2 to VK5 of Volkova (1990) at the East European Platform. Furthermore, it is equivalent with the Zone II to IV of Ghavidel-Syooki and Vecoli (2008) in the High Zagros Mountains, southern Iran. Occurrence of such mid-latitude taxa as Ninadiacrodium and comparison of the acritarch assemblages with those from elsewhere in the world indicates the peri-Gondawanan affinity; thus supporting a 30°-60°S palaeolatitude for the eastern Alborz in the Late Cambrian

Travertine deposits cover a vast area in the southwest of Azarshahr (East Azarbaijan province) and in some parts there are active springs which currently deposit these types of sediments. Regarding the field observations in the Azarshahr area, the typical morphology of Azarshahr travertine deposits is in situ and consists of the mounds, fissure-ridge and cascades. Geochemical studies on the travertine deposits of the Taptapan and Qizildagh springs revealed that the amount of iron in travertine deposits clearly emphasizes their thermogenic nature. The amounts of strontium, barium and beryllium also indicate the thermogenesis and calcareous, evaporative or dolomite origin. The depleted oxygen isotope (δ18O) and enriched carbon isotope (δ13C) is also indicator of thermogenic source, and carbonate source rocks for these deposits. Based on geochemical studies, it can be concluded that hydrothermal fluids may have initially taken the CO2-derived from magma, and during the upward movement with carbonate rocks, decarbonization has been occurred. These fluids transport CO2 from carbonates, and then they appear as spring’s water at the surface and precipitate travertine due to the rapid release of CO2.

 

In this study, the Late Cretaceous Ilam Formation of the Bangestan group in the northwest of Abdanan in the Kabir-Kuh anticline has been investigated for sedimentological and geochemical properties, and diagenetic processes. Field studies indicate that this formation in studied section reach a thickness of 281 m and composed of medium to thin-bedded limestones with shales and argillaceous limestones intercalations. The upper and lower boundaries of the Ilam Formation in the studied section are disconfirmable with the Gurpi and Sarvak formations, respectively. Based on the petrographic studies, nine microfacies and one petrofacies have been identified for the Ilam Formation which mainly deposited in the outer ramp-basin setting. The main diagenetic features affecting the Ilam Formation in the studied section include micritization, cementation, mechanical and chemical compactions, dissolution, pyritization, phosphatization, and glauconitization. Geochemical characteristic (major and trace elements) of the Ilam carbonate deposits indicate closed diagenetic system. Variations of V/Cr, V/(V+Ni) and Ni/Co indicate that the carbonate samples of the Ilam Formation are subjected to suboxic and mostly anoxic conditions. Separating the Sarvak and Ilam boundary can be aided by some geochemical data variations such as Sr/Ca, Sr/Na, Sr/Mn, Ag, V, Ni, Zn, Sr, Fe, Co and P at the Kabir-Kuh anticline in the Abdanan section.

The Badavar River is an important surface water resource in Lorestan province. The purpose of this study is to assess the quality of the Badavar water and sediments. For these purpose, 19 water and five surface sediment samples were collected. The physicochemical properties of the water (i.e. pH, electrical conductivity, the major ion concentrations, microbial analysis, and potentially toxic element concentrations) and sediment samples (i.e. pH, organic matter, carbonate calcium, cation exchange capacity, major and trace element concentrations) were determined using standard methods. The obtained results indicate that the concentration of major ions influenced by natural processes (i.e. halite and gypsum dissolution, calcite, aragonite and dolomite precipitation, and ion exchange) and anthropogenic factors (i.e. discharge of domestic wastewater and agricultural runoff into the river). The concentration of the potentially toxic elements, especially Pb, is influenced by anthropogenic activity. The results of the microbial analysis confirm the pollution of the water samples with pathogenic agents. On the basis of pH values, the sediment samples are placed in neutral to alkaline class. Sediment samples are rich in organic matter and CaCO3, and their cation exchange capacity is high. The total concentration of elements in sediments shows that there is a risk of pollution with Cd, Cr, and Ni. The contamination degree values show that the studied sediments are highly polluted, which is due to the discharge of urban and agricultural wastewaters into the Badavar River.

Abstract The late Tithonian Manifa carbonate is one of the important oil producing intervals in some oil fields of the Northwestern Persian Gulf. The combination of geological and petrophysical data in three key wells in one of oilfield, enabled us to clarify the effects of depositional facies and diagenesis on reservoir quality in a sequence stratigraphic framework. Nine microfacies were recognized that deposited in three facies belts: tidal flat, lagoon and leeward shoal in a homoclinal carbonate ramp. The carbonate interval of the Manifa has been subjected to a variety of diagenetic processes, including micritization, bioturbation, recrystallization, dissolution, cementation, dolomitization, dedolomitization and compaction in three realm of marine, meteoric and burial diagenesis. From the identification of sequence boundaries and maximum flooding surfaces, one third-order sequence was recognized and interpreted. The sequence boundaries are important local and regional disconformity surfaces. Investigation of reservoir quality of different facies demonstrates that diagenetic features have considerable effects on the reservoir characteristics and regulated pore system characteristics. After deposition of the shallow marine Manifa carbonate was drastically subjected to the fresh-water diagenesis in the meteoric realm. The main important meteoric diagenesis alterations including karstification, dissolution, cementation and recrystallization are mainly concentrated below disconformity surfaces of the Manifa carbonate. The poroperm properties are very good related to dissolution phenomena creating interconnected pore space. Vuggy and solution enlarged interparticle porosities are the two dominant interconnected pore types within the reservoir. Considering the reservoir significance of the Manifa carbonate in the northwest Persian Gulf, the conclusion drawn from this investigation can be utilized for a better reservoir characterization. Keywords: Manifa, Persian Gulf, Facies, Diagenesis, Sequence Stratigraphy, Reservoir Quality   Introduction Reservoir quality of carbonate reservoirs is controlled by many interrelated factors such as depositional facies, diagenetic processes and tectonic setting (Lucia 2007; Ahr 2008; Moore & Wade 2013). In fact, by controlling the pore system properties, these parameters affect the fluid flow and saturation within the reservoirs (Ahr 2008). Although, the original sedimentary properties substantially control the reservoir quality, but diagenesis may exert considerable influence on pore characteristics (Lucia 2007; Ahr 2008; Moore & Wade 2013). The reservoir quality may be enhanced or deteriorated depending on the type of dominant diagenetic processes (Ahr 2008). The Late Tithonian sequences of the Manifa carbonate is notable carbonate reservoir in some part of the Arabian Platform. Despite of this importance, a little is known about various geological and petrophysical characteristics in Iranian northwestern part of the Persian Gulf. This study is the first report of sedimentological and reservoir geological aspects of this carbonate sequences in subsurface sections of the northwestern Persian Gulf. In this study, by using a complete dataset of drilled cores, thin sections, petrophysical well log and porosity-permeability data, interpretation of reservoir quality evaluation has been carried out on the Manifa carbonate. The aims of this study are to investigate the facies characteristics, depositional environments, diagenetic alterations and evaluate pore system and reservoir properties in relation to the disconformity surface of the Manifa Formation in the northwestern part of the Persian Gulf   Material & Methods A continuous, 52-m-thick core through the Manifa Formation was logged in one of oilfield in the northwestern Persian Gulf. To differentiate the calcite from dolomite, all thin sections were stained with Alizarin Red-S (Dickson 1966). Also, in order to determine pores types and their properties, epoxy resin was injected to the samples (130 thin section), and all samples were scanned by a high-resolution (Up to 10000 DPI) scanner (CREO-IQSMART3) at the Petroleum Industry of Research Institute. Petrographic studies were carried out to identify different types of depositional facies, and based on the allochems type and their frequency, different sub-environments were distinguished. Also, the important diagenetic processes affecting the pores system were identified. Based on the combination of the results of facies/diagenesis studies the framework of sequence stratigraphy was introduced and one third-order sequences interpreted. Due to the interpreted distribution of depositional and diagenetic characteristics, petrophysical well logs were used for their correlation between the three studied wells in the studied field.   Discussion of Results & Conclusion The core description and petrographic studies resulted in the identification of nine microfacies. These microfacies were attributed to three facies belts including tidal flat, lagoon, and leeward shoal. The carbonate ramp model proposed for the Manifa Formation is comparable with the model and facies distribution presented for this interval in the neighboring area. The Manifa carbonate has been subjected to a variety of diagenetic processes including micritization, bioturbation, recrystallization, compaction, cementation, dissolution, dolomitization, dedolomitization and fracturing. Dissolution, cementation, dolomitization, compaction, along with fracturing have had the greatest impact on the pore system and reservoir properties of the Manifa carbonate. In order to establish a sequence stratigraphic framework and specify the sequence boundaries and maximum flooding surfaces for the studied formation, the results from depositional and diagenetic studies were integrated. Hence, sequence stratigraphic analysis of the studied interval has resulted in the recognition of one third-order depositional sequences with aggradational-progradational stacking pattern. At the Late Tithonian, a eustatic sea-level fall caused platform emersion and subaerial exposure at top of the Manifa carbonate. This sequences are bounded with two local and regional disconformities. From reservoir quality point of view, intense meteoric dissolution of grain-to mud-dominated facies exert a main improving effect and development of intervals with high porosity and permeability. Core poroperm data interpretation clearly demonstrate that most grain- and mud-dominated facies related to different sub-environments have a good reservoir quality due to the high impact of dissolution related to meteoric diagenesis. With respect to the effect of diagenesis on the reservoir properties, the defined diagenetic facies display a distinct trend on poroperm distribution. Porosity-permeability distribution indicating the high heterogeneity is strongly related to the effects of both depositional and diagenetic characteristics. Vuggy and solution interparticle pore spaces are two dominant pore types and show high pore connectivity. Thus, an integrated sedimentological and petrophysical reservoir evaluation of the Manifa carbonate in one of oilfield in the northwestern Persian Gulf indicate that diagenetic alterations had main role in pore system characteristics and reservoir evolution.