JOURNAL OF STRATIGRAPHY AND SEDIMENTOLOGY RESEARCHES
Year:2018 | Volume:34 | Issue:1 (70) |Papers Count:7

Introduction: The Sarvak Formation is mainly composed of limestone and is one of the most important rock reservoirs in the Zagros sedimentary basin. This formation has been studied extensively in many parts of the Zagros; however the information about various aspects of this formation in northern Lorestan is limited. Due to the discovery of a pycnodont fish tooth plate from Aleshtar area, and because of scarce data on Cretaceous deposits in this region, we conducted this research. Material &Methods: In order to study the age, sedimentary environment and sequence stratigraphy of the Sarvak Formation, field and microscopic studies of 100 thin sections from an outcrop near Aleshtar (north of Lorestan) has been carried out. Discussion of Results &Conclusions: The Sarvak Formation in the studied section is Cenomanian in age and is 835 meters thick. It is bounded by Garu and Surgah formations at the base and top respectively. It is mainly composed of thick, medium, and thin bedded limestone rich in chert nodules, bioturbation and rudists. The studied outcrops can be subdivided into four units litho-stratigraphically. The first unit is 200 meters of thick, grey limestone with benthic foraminifera and echinoids. Second unit is 320 meters of mainly grey, medium bedded limestone with reddish intercalation of shale, containing benthic foraminifera, rudist debris and bioturbation. 180 meters of thick bedded, grey limestone with rudist and other bivalve debris forms the third unit. The last litho-stratigraphic unit consists of 135 meters of medium to thin bedded, grey limestone with interlayers of dolomitic limestone and rudist/bivalve debris and bioturbation. Benthic foraminifera are less abundant here. Our study led to the identification of 12 microfacies and 3 facies-belts, which belong to tidal flat, lagoon, and open marine environments. These microfacies are differentiated based on abundance and diversity of skeletal and non skeletal remains and rock texture. These facies, ordered from shallower to deeper environments, include: bioclastic stromatolite wackestone to bindstone, and pisoid rudstone in tidal-flat facies belt; bioclast peloid intraclast grainstone, bioclast green algae wackestone to packstone, peloid ooid grainstone to packstone, bioclast echinoderm benthic foraminifera wackestone, rudist benthic foraminifera wackestone, orbitolina miliolid wackestone to packstone, bioclast miliolid wackestone, and benthic foraminifera rudist floatstone to rudstone in lagoon facies belt; and rudist floatstone to rudstone, and bioclast oligosteginid wackestone within open marine facies belt. According to type and gradual changes of microfacies in lower parts of the Sarvak Formation, and compared to abrupt changes of microfacies and presence of extensive rudists in the upper parts of this formation, lower and upper parts of the Sarvak Formation are deposited in two different sedimentary environments. Presence of micrite in most of microfacies, formation of sedimentary textures such as wackestone to packstone and absence of traceable reefs on the ground, shows that the carbonate sediments of the Sarvak Formation in the lower parts in the studied section were deposited in a ramp carbonate platform. Widespread distribution of rudists in the field, abundance of oligosteginids, and abrupt changes of microfacies along the section; like alteration of pisoid and stromatolite facies to oligosteginids in a short interval, indicates that the upper parts of the studied section were deposited in a carbonate shelf. Three third-order depositional sequences were determined based on the deepening and shallowing trend of facies. The transgressive systems tract consists mainly of microfacies belonging to the lagoon and open marine sedimentary environments, which contain the benthic foraminifera, echinoids and oligosteginids. The highstand systems tract consists mainly of microfacies belonging to the lagoon with green algae and the benthic foraminifera, and also to the microfacies belonging to the tidal flat, which contain stromatolite and pisoid. The maximum progression level in sediment sequences 1 and 2 was determined by microfacies rich in echinoid and rudist debris. In sedimentary sequence 3 it is identified with oligosteginid rich microfacies.

Introduction: One of the most extensive Tertiary deposits is the marine strata of Pabdeh and Asmari Formations in Zagros, which was studied based on paleontology studies. Type section of Pabdeh Formation is located in Tang-e Pabdeh, North of Lali oilfield and type section of Asmari Formation is located in Tang-e Gel-Torsh in Asmari Mountains (James & Wynd, 1965). One of the most important achievement obtained from Pabdeh and Asmari Formations is the evaluationof boundaryand biostratigraphy of it. In the north eastern limb of Gurpi anticline, boundarybetweenof Pabdeh and Asmari Formations consists of 290 m thick which mainly consists of marl, marly limestone and shale.Material & Methods: In this study 64 samples from Pabdeh and Asmari interval have been studied. Samples were prepared following standard smear slide method (Bown and Young 1998). All slides were studied under polarized light microscope at ×1000 magnification. The nomenclature of calcareous nannofossil follows the taxonomic schemes of Perch-Nielsen (1985) and Fornaciari et al. (2010).Discussion of Results & Conclusion: In order to study biostratigraphy based on calcareous nannofossils, boundary of the Pabdeh/Asmari in north eastern limb of Gurpi anticline, Emamzadeh Baba section was selected. In this section, Pabdeh Formation with 235m thickness is mainly consists of shale, marly limestones, marl and Asmari Formation with 55m thickness is consists of limestones. For introducing index species, calcareous nannofossil assemblages and biozones, slides have been studied at the Pabdeh/Asmari Formations interval which led to the recognition of 39 species and 18 genera of calcareous nannofossils. In this study four biozones were detected in Pabdeh/Asmari boundary. Biozones Sphenolithus pseudoradians Zone(NP20), Ericsonia subdisticha zone (NP21), Helicosphaera reticulata Zone (NP22) and Sphenolithus predistintus Zone (NP23) in Pabdeh Formation with Priabonian-Rupelian in age and Sphenolithus distentus Zone (NP24) in Asmari Formation with Rupelian- Chattian of Martini (1971) zonation, equivalent to biozones (CNE19 - CNO5) of Agnini et al. (2014) zonation and (CP15b- CP19a) of Okada and Bukry (1980) zonation. According to the first and last occurrence of index species the following bio zones are identified:Sphenolithus pseudoradians zone (NP20/CP15b)This biozone is recorded from the FOSphenolithus pseudoradians to the LO of Discoaster saipanensis. The age of this zone is Late Eocene (Priabonian). The thickness of this zone has been measured approximately 71.4 m.Ericsonia subdisticha zone (NP21)The second zone is recorded from the LO of Discoaster saipanensis to the LO of Ericsonia formosa. The age of this zone is Late Eocene- Early Oligocene (Priabonian/ Rupelian). The thickness of this zone is 73 m.Helicosphaera reticulata zone (NP22/ CP16c) This zone spans the interval from the LO of Ericsonia formosa to the last occurrence of Reticulofenestra umbilica. The age of this zone is Early Oligocene (Rupelian). The thickness of this zone is 25 m.Sphenolithus predistentus zone (NP23/ CP17-18)The next nannofossil unit recorded in this study is theNP23. This zone spans the interval from the LO of Reticulofenestra umbilica to the FO of Sphenolithus ciperoensis. The age of this zone is Early Oligocene (Rupelian). The thickness of this zone was measured about 85 m.Sphenolithus distentus zone (NP24 / CP19a)The last biozone recorded is NP24. This zone is from the lower part of Asmari Formation. This zone spans the interval from the FO of Sphenolithus ciperoensisto the LO of Sphenolithus distentus. The age of this zone is Late Oligocene (Chattian). The thickness of this zone was measured about 34 m.So, as result of this study and according to the identified biozones, the age of Pabdeh/Asmari boundary is Late Eocene (Priabonian) to Late Oligocene (Chattian).

Introduction: The abundances of minor-elements in carbonate rocks depend on the noncarbonate materials, including detrital minerals, accessory authigenic precipitates, noncarbonate skeletal material, organic matter, phases formed during diagenesis and the elements adsorbed upon all of these materials (Graf, 1960; Lian et al. 2008). Mo, V, Cu and Ni abundancey in carbonate rocks depend on CaCO3, organic carbon (Le-Riche, 1959; Snow et al., 2005; Lian et al., 2008). The carbonate materials rich in organic matter should be enriched in Ag, As, Mo, V, Ni, Pb, Cu, Ge, Br and I whereas carbonate rocks and sediments containing manganese oxides have high amounts of Co, Mo and Ba trace elements (Krauskopf, 1955; Madhavaraju et al., 2015). Due to the economic importance of the Qom Formation as a hydrocarbon reservoir and presence of celectite and chalk deposits, this formation studied mostly on petrology, stratigraphy and paleoenvironment view (e.g. Seyrafian et al. 2007; Mohammadi et al. 2009; Reuter et al. 2009; Safari et al. 2014; Daneshian et al. 2017; Nasiri Ghareh Shiran 2017). However, minor geochemical studies were done on the Qom Formation deposits. In this research, the Qom Formation was studied by geochemical data in Khani Abad stratigraphic section from southeast of Kashan. The aim was to investigate the trace and major elements to reconstruction of paleoredox conditions and find their relationship with sedimentary environment. Material and Methods: To determine sedimentary characteristic of the Qom Formation, 70 thin sections have been studied. Thin sections were stained with potassium ferricyanide and alizarin-red S solution (Dickson, 1965). The petrographic classification for carbonates is based on the Dunham limestone classification (1962) and Embry and Klovan (1971). Wilson (1975) and Flugel (2010) facies belts and sedimentary models were also used. After petrographic studies, twenty powdered micrite samples were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) by 4-Acid Digestion method for trace, major and rare earth element contents at the Met-Solve Analytical Services Inc., BC, Canada. Discussion of Results & Conclusions: The Qom Formation has 70 m thickness in Khani Abad stratigraphic section and consists of thin to thick bedded and massive limestone, argillaceous limestone and marl. This formation stay among non-marine rocks of lower and upper Red Formations. The petrographic study shows that the main grains in Qom Formation are foraminifers, red algae, echinoderm, bryozoan, pelecypods, gastropods, corals and peloids that have precipitated in lagoon and shoal facies belts. Geochemical data indicates that amounts of Al, Ti, Th and Zr are low in studied samples and might show the low terrigenous input during the precipitation of the Qom Formation carbonates. The amount As in selected samples are lower than 5 ppm. In two samples with argillaceous limestone and marl, the As content are increased in compare to others. There are a positive correlation between Sr contents with bivalve frequency and Na contents with foraminifera frequency as skeletal allochems in stratigraphic section. Sr/Ca versus Man and Mg show that the carbonate deposits of the Qom Formation are situated in mostly semi-closed to open diagenetic system. Also, variations in amounts of Mn, V/Cr, V/(V+Ni) and Mo/Zr ratios in studied carbonate rocks are indicative of mainly dysoxic conditions of precipitation in Qom Formation carbonates. Correlation of V/Cr ratio and amounts of Mn, Na and Ba versus skeletal allochems and facies belts shows that the frequency of these elements are different in depth of lagoon toward the land and shoal and in mid parts of lagoon. In middle parts of the lagoon with low level of energy, amounts of Ba, Mn and V/Cr are higher than other parts which indicates more dysoxic condition in comparison to other parts. In lagoonal parts toward the shoal, the V/Cr, Mn and Ba amounts are lower comparing to other parts that indicates oxic to dysoxic conditions.

Introduction: Today, Soil erosion has become one of the biggest problems in the country, especially in arid and semi-arid including Semnan. Effective and long term water and soil conservation programs require the concentration of resources on limited areas. For that purpose, regional-scale assessments of erosion risk are required. There are various methods to studying, evaluating, calculate and prevention with soil erosion. In addition, a number of parameters such as lithology, slope, aspect, land cover, elevation, and distance to stream, drainage density, vegetable cover, land use, river banks, and human activities are recommended to analyze the mechanism of soil erosion. So a rapid and cost effective methodological erosion assessment for these regions is required to describe and monitor the processes that control erosion. This study uses one of the remote sensing analyses to describe the contribution of several factors that control erosion in Semnan drainage basin where erosion is the major environmental problem. Remote sensing monitoring has been carried out by using aero photos, or multispectral images, DTM (Digital Terrain Model) or ALS (Airborne LASER Scanning) data. Semnan basin, study area, is located in north of Kavir plain and south of Alborz mountain range.Methodology: This study was conducted to evaluate the potential of analyzing regional erosion risk Topography, land use; vegetation density, soil properties and climatic proxies are used to determine erosion risk and to provide basic maps of water and soil conservation practices. A hierarchical decision tree is used to sum and combine the weight of parameters controlling the erosion. The assigned weights of each spatial unit express the susceptibility to erosion. The most important attributes in the definition of erosion landforms like gullies were selected using decision tree induction algorithms, being these attributes spectral, altimetry and texture. Classifications hierarchical and by decision trees were carried out. Using decision tree the classification is performed only by a factor of scale, not allowing the identification of all the constituent features of the erosion landforms system. One of the advantages of this method is that it can be used if there are insufficient experimental data. The lack of experimental data can be compensated for through the use of expert evaluations.Results and discussion: Three different combinations of the three dominant controlling factors are yielded in this study. In order to optimize the qualitative erosion risk assessment, each combination is discussed and evaluated depending on the contribution of parameters involved in the erosion process. As different erosion landforms erosion is similar when presents the same evolution stage and soil type, it is not possible to select attributes to classify all erosion landform systems, being necessary to investigate attributes for each erosion landform erosion, based on available data and existing land use classes in the area. The erosion landforms are the biggest erosive processes and, consequently, responsible for ambient, social and financial damages. Corrective and preventive measures need mapping and monitoring, which can be made by local measurements or by remote sensing. In relation to the remote sensing, the erosion landform erosion presents spectral heterogeneity (soil, vegetation, shade and water mix), spatial heterogeneity (existence of features as head, canals and digits with irregular forms and variable dimensions) and altimetry variation (with high declivity on the edges). Due to spectral heterogeneity, it is not enough use only spectral data, being necessary auxiliary data, as altimetry and texture data. This clearly shows that the study area is generally exposed to a high hazard of soil erosion. Nevertheless, there is a probability that the rate of erosion will increase in the future, as hazard is the probability of occurrence of a potential damaging phenomenon, within a period of time and a given area. As known, there is always an interest to depend on latest developments when making subjective judgments. In spite of the results obtained in this study, the development of a susceptibility map is usually determined by the needs and available resources, and AHP method can be equally important for all sorts of susceptibility zoning practices.Conclusion: The purpose of this study was to assess the soil erosion hazard in the Semnan province for planning appropriate conservation measures. The integrated GIS-AHP model was used to define spatial distribution of soil erosion hazard. In this area, erosion risk mainly was related with vegetation and also, it anticipated that the southern and south-eastern region due to the poverty of vegetation associated with increased levels of erosion. In each of the three mapped models, the area of the class with high erosion sensitivity was more than 75% and for observational data, the area in all three maps is above 71%. Also, the results of the assessment show that in all three maps there are over 99% correlation between the data obtained from the modeling and the test data. The erosion landforms present spectral and spatial heterogeneity and altimetry variation. This research demonstrates that the model developed was an effective tool for fast assessment of soil erosion hazard by the integration of remote sensed data, AHP, and GIS techniques. Nevertheless, the results obtained in this study are valid only for generalized planning and assessment purposes. They may be less useful at the site-specific scale, where local geological and geographic heterogeneities may prevail. Finally, any proposed decision-making tool in erosion control studies should also include local experimentation data to better simulate the erosion hazard, resulting thereby in the most appropriate and efficient choice of soil conservation works.

Introduction: In this study, successions including red beds siliciclastic and the carbonate rocks of Lower Cretaceous sequence is studied at Kuh-e-Bejareh in the south western margin of Central East Iranian Microcontinent. The Lower Cretaceous red beds represents the first deposits after the Late Cimmerian phase and unconformably overlies the dark green sandstones and shales of Nayband Formation and overlain conformably by cliff-forming carbonate deposits of the Aptian Orbitolina Limestone. The Jurassic is gap in between and sediments are missing in the study area. Mazroei-Sebdani (2016) and Mazroei-Sebdani et al. (2018) studied in detail the provenance and diagenetic events of similar succession. In this research, recognition of clastic lithofacies and carbonate microfacies would result to the interpretation of depositional environments and to reconstruction of palaeoenvironment and palaeogeography of the south western margin of Central East Iranian Microcontinent during Early Cretaceous (Barremian?-Aptian). Material & Methods: The studied outcrop section at Kuh-e-Bejareh represent the Lower Cretaceous siliciclastic red beds (base coordinate: N 33o 05′ 33.7″, E 51o 57′ 34.9″) in western margin of Central East Iranian Microcontinent, 47 km northeast of Isfahan, central Iran. The interval were logged bed-by-bed using Jacob Staff. The succession have 138 m thickness in that nine lithostratigraphic sub-units were defined. Lithofacies types were determined using the modified lithofacies classifications of Miall (2006). Palaeocurrent indicators were measured at 74 locations. Stereonet version 9.8.3 were used to construct rose diagrams. Total of 75 samples were collected from the outcrop section in the field. The petrographic classification for sandstone were based on Folk (1974) and carbonates rocks is based on Dunham limestone classification (Dunham, 1962). Wilson (1975) and Flügel (2010) facies belts and sedimentary models were used to interpret the carbonate microfacies. Discussion of Results & Conclusions: Lithostratigraphic sub-units 1-6 are grouped into the K1 unit (92 meters) and 7-9 (46 meters) into lower part of the K2 unit. The K1 unit composed of red clast-supported conglomerate, fine-grained cross-bedded sandstone and siltstones. The K2 unit composed of sandy limestone and fossiliferous (Orbitolina) limestone with verity of rocks textures. Lithofacies analysis led to identification of four coarse-grained (Gcm, Gp, Gh, Gt), five medium-grained (St, Sm, Sh, Sp, Sr), two fine-grained (Fl, Fm) and an intermediate facies (Sh and Fl). Sandstones of the Lower Cretaceous siliciclastic red beds plot into quartz-rich sublitharenite field of a QFL ternary plot of Folk (1974). Recalculating the rock fragments to 100% and plotting them on rock fragment triangles indicates that these sandstones are sub-chert arenites and sub-phyllarenites. Identified lithofacies, geometry of beds, horizontal and vertical stacking patterns, stratal surfaces, palaeocurrents as well as the fossil and trace fossil contents of the strata led to identification of three siliciclastic and one mixed siliciclastic-carbonate facies associations represents a terrestrial to shallow-marine succession from braided and meandring fluvial, supratidal to tidal flat environments. The Lower Cretaceous clastic sequence represents palaeocurrent direction from the south to the north. Based on the measured palaeocurrent, the Sanandaj–Sirjan Zone have been considered as a main source for the siliciclastic rocks. The investigation of carbonate thin sections led to the identification of five microfacies with a verity of mudstone to garinstone texture. The identified microfacies comprises sandy mudstone, peloid grainstone, bio-/peloid wack-, pack-, and grainstone, and intraclastic, echinoid, Orbitolina garinstone. The identified carbonate microfacies were deposited in the mixed siliciclastic-carbonate tidal flat, restricted and open lagoons toward bioclastic shoal of the inner part of likely an epiric carbonate platform. This carbonate sequence has been deposited in the near shore area of such a shallow-water carbonate platform that covered some parts of central Iranian Block, as northern margin of Neotethys Ocean, during Early Cretaceous.