Elika Formation Research Articles

The yengejeh diasporic karst bauxite deposit, NW Iran: Constraints on distribution and fractionation of major and rare earth elements

The Yengejeh diasporic karst bauxite deposit (NW Iran) was developed as discontinuous layers and lenses along the contact of dolomitic limestone of the Ruteh Formation (middle-upper Permian) and dolomite of the Elika Formation (Triassic). This deposit is constituted by two conspicuous subset layers, (1) green bauxite (GB) and (2) red bauxite (RB). The XRD analytic data revealed that diaspore is accompanied by chlorite and anatase in the GB subset and by hematite in the RB subset. Minerals such as pyrophyllite, kaolinite, illite, and rutile are present within the both subsets. The antithetical distributions of Al with Fe and Al with Ti in the deposit are indicative of the controlling role of climatic changes of the depositional environment and the function of post-formation diagenetic processes. The increment in certain geochemical ratios like La/Y, (La/Yb)N, and (LREE/HREE)N from the top toward the bottom of the horizon is designative of pH increase in depositional milieu by buffering of the percolating solutions, and of preferential scavenging of LREE by hematite. The positive Ce anomaly in the GB subset took place as the result of change in the oxidation state of this element from Ce3+ to Ce4+. However, the positive Ce anomalies in the RB subset implicates preferential scavenging of Ce onto hematite. The marked variation range in anomaly values of Eu/Eu* (0.38–1.01) at Yengejeh reveals that this index acted as non-conservative during the evolution of this deposit, and this behavior is related most likely to influences of post-formation diagenetic processes.

Geochemical constraints on the Gano karst bauxite deposit, eastern Alborz Mountains, northern Iran: Implications for provenance, elemental mobility, and distribution of critical metals

The Gano karst bauxite deposit is located in the eastern Alborz Mountains, 90 km NE of Semnan city, northern Iran. The layers and lenticular patches of bauxite are hosted in the Triassic karstified carbonate rocks interbedded with calcareous shale of the Elika Formation, unconformably overlain by siliciclastics of the early Jurassic Shemshak Formation. The bauxite ores have a mineral assemblage dominated by diaspore and hematite, with lesser kaolinite, illite, chlorite, goethite, anatase, dolomite, and quartz. In the Gano area, intrusions range from monzonite to quartz monzonite in composition with an alkaline composition that generated in an extensional regime within a plate tectonic setting. Geochemical signatures of the Gano bauxite ores suggest a derivation from the monzonite intrusions at the base of the Elika Formation, although a contribution of interbedded calcareous shale of the Elika Formation cannot be excluded. Based on the variation of Ce anomaly across the studied profile and the integration of petrographic evidence and mineralogical and geochemical data, the Gano deposit formed in an oxidized environment under warm-humid climates, significantly linked to rainfall seasonality and groundwater-level fluctuations. Gallium, Nb, and V median values of the Gano bauxite ores are a bit above the maximum value of these critical metals in the northwestern Iranian and Alborz bauxite data set, making diaspore-, anatase-, and hematite-rich layers and lenses valuable for further exploration of these critical metals.

REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran

The Huri bauxite deposit is located 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran. Bauxite horizons at Huri develop within karstic depressions and sinkholes of carbonate footwalls of the Ruteh Formation, overlain by carbonate of the Elika Formation. Powder X-ray diffraction (PXRD) and scanning electron microscope, coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses show that the Huri bauxite ores consist of hematite, diaspore, kaolinite, and lesser amounts of halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, rutile, zircon, and monazite. Based on geochemical studies (Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams), basalt rocks interbedded in limestone of the Ruteh Formation are the possible precursor rocks of the Huri bauxite deposit. The pH variations of weathering solutions, fluctuations in the groundwater table level, the function of carbonate bedrock as a geochemical barrier, simultaneous precipitation of Fe-bearing minerals, and preferential scavenging of light rare earth elements (LREE) by hematite played an important role in the fractionation of LREE from heavy rare earth elements (HREE) in the Huri bauxite ores. Fluctuations in groundwater table level, increasing pH of acidic solutions percolating downward, preferential adsorption of Ce onto hematite at the base of the profile, and the possible presence of Ce-bearing fluorocarbonates played an important role in increasing Ce anomaly from the top of the profile downward.

Geochemical constraints on the middle Triassic Kani Zarrineh karst bauxite deposit, Irano–Himalayan belt, NW Iran: Implications for elemental fractionation and parental affinity

The middle Triassic Kani Zarrineh bauxite deposit, in the Irano–Himalayan belt, located 20 km northwest of Saqqez city in northwestern Iran, occurs in depressions of the early Triassic bedrock carbonates of the Elika Formation. The ores formed during the Carnian Pluvial Event under high atmospheric pCO2 conditions and humid episodes. Powder-XRD analyses revealed that the Kani Zarrineh bauxite is mainly composed of diaspore, hematite, and kaolinite. There is a broad inverse relationship between hematite abundance and diaspore abundance in the profile with a downward increase of hematite and an upward increase of diaspore. Among minor constituents, single crystals rich in high field strength elements, such as florencite, monazite-(Ce), xenotime-(Y), and zircon were detected by SEM-EDS analyses. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor accounting for the competition between the Al2O3–TiO2–Ga–HFSE pool and the SiO2–Fe2O3–U–first row transition metals pool, and related to the coupled effect of a change of redox conditions and climatic regime. The other two factors are related to the importance of phosphate minerals (e.g., florencite and monazite) in hosting LREE, and to the influence that the chemistry of the soil solutions, especially pH, exerted in promoting the preferential mobility of HREE. Both these factors contribute to explaining LREE/HREE fractionation in the Kani Zarrineh bauxite ores. A negative correlation between the Ce/Ce* and the TOC (r = –0.91) corroborates the fact that bauxitization occurred in an environment characterized by a progressive increase in Eh upward. The coupled Ce/Ce* increase and TOC decrease upward are likely related to soil aeration, a progressive increase in soil temperature, and a reduction in soil moisture. An upward decrease of soil moisture is also consistent with an increase in the abundance of Al hydroxides that require drier conditions than those necessary for the formation of Fe oxyhydroxides. Finally, the evaluation of elemental mobility and results of the R-mode factor analysis indicate that, in addition to Al, high field strength elements Nb and Ta can be used confidently for assessing parental affinity of the Kani Zarrineh bauxite ores. The Al/Ta and Nb/Ta ratios and the Sm/Nd and Eu/Eu* provenance proxies reveal that mafic rocks interbedded in the early Triassic bedrock carbonates of the Elika Formation are likely protoliths of the Kani Zarrineh bauxite ores. This finding is consistent with what is observed for some bauxite deposits from the Mediterranean-type karst bauxite belt, especially from northwestern Iran of different ages that basalt rocks were the parent rock of these deposits.

The Occurrence of Corundum-Rich Metabauxite in the Qaradash District, NW Iran

The corundum-rich metabauxites were, very rare worldwide, reported in the Attic-Cycladic metamorphic complex in Greece and the southern and western margins of the Menderes Massif in southwestern Turkey. The Qaradash bauxite deposit is located in the Iran-Himalayan karst bauxite belt, 25km northwest of Shahindezh city, northwestern Iran (Figure 1a). The rock units in the Qaradash district mainly occur in an asymmetric fold and in the core of an anticline (Figure 1b). They, from the oldest to youngest, include the Permian carbonates of the Ruteh Formation, the Triassic sandstone and carbonate of the Elika Formation, and the Plio-Quaternary sandy conglomerate. Carbonates of the Ruteh Formation are dark grey in color that were intruded by the Oligocene monzonite and quartz monzonite intrusions. The marbles occur at the contact of these intrusions with carbonates of the Ruteh Formation. The bauxite horizons occur as 7-15-m-thick layers along the contact of carbonates of the Ruteh Formation (Permian) and sandstone and carbonate of the Elika Formation (Triassic) that were also affected by these intrusive masses and were partially converted to metabauxite.

Diagenetic Processes and Geochemical Propertiesof the Elika Formation in Gadamgah Anticline in South of Central Alborz

Diagenetic Processes and Geochemical Propertiesof the Elika Formation in Gadamgah Anticline in South of Central Alborz

Geochemical and mineralogical features of karst bauxite deposits from the Alborz zone (Northern Iran): Implications for conditions of formation, behavior of trace and rare earth elements and parental affinity

The present study focuses on three outcrops of Upper Permian to Lower Jurassic karst bauxite deposits in the Alborz zone, north of Iran. The deposits occur as sharp semi-continuous lenses within the Upper Permian Ruteh Formation (Gheshlagh) and the Upper Triassic Elika Formation (Siahrudbar and Separdeh) carbonate rocks. Textural characteristics such as pelitomorphic matrix, local ooidic-pisoidic, fluidal, and clastic textures indicate authigenic-allothigenic origins. Mineralogically, kaolinite, boehmite, goethite, and hematite in the Gheshlagh, diaspore, hematite, and kaolinite in the Siahrudbar, and kaolinite, hematite, goethite, diaspore, siderite, and chamosite in the Separdeh deposits are the main phases. The distribution patterns of major elements normalized to the upper continental crust (UCC) depict enrichments of Al, Fe, and Ti in all three deposits. The three deposits are variably enriched in transition trace elements (Cr, Ni, Co, V), U, Th, and high field strength elements (Ga, Hf, Zr, Nb, Y) relative to UCC. The studied bauxites have average concentrations of rare earth elements (ΣREE, La-Lu) between 305.97 and 373.69 ppm. Geochemical data reveal progressive enrichment of REE and an intense (LREE/HREE)N fractionation toward the lower parts of the profile in the Separdeh deposit due to the alkaline conditions of the carbonate bedrock, and irregular distribution patterns at the Gheshlagh and Siahrudbar deposits due to water level and pH fluctuations. The positive Ce anomalies at Separdeh and Siahrudbar suggest oxidizing conditions in the upper parts of the profiles. At Gheshlagh, the negative to nil Ce anomalies reflect low intensity of oxidation. Based on previous geochemical analysis data, the Upper Permian basalts in the Gheshlagh, and the Upper Triassic basalts in the Separdeh and Siahrudbar areas were the most likely source materials. The local uplift of the Permian-Upper Triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate. The initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of Al, Fe, and Ti. Then, they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade. The overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments. In the eastern part of the Alborz zone (at Siahrudbar and Gheshlagh), better drainage conditions have enhanced the quality of ores.

Comparison of stratigraphic rock and sedimentary environment of Shemshak formation in Central Alborz: sections Glendrood - Lavij – Vaz, Iran

The study area lockated in the central Allborz whch is in accordance with U shape Caspian Sea. In this Research Shemshak Formtion in the Glandrud region has been Studid and compared in three Section A, B, C in therm Litology Effective Tectonice prossesing in the Formation,Sedementary Environment and Squence of Calasses. These Sections are consisting of sedementry Layer of shemshak Formation, the layer bandray (Elika Formtion & older Formtion) and upper bandray(Lar-Dalichai) in the type section desegnation of shemshak 4 litozone the litilogy of this intity is much more diverse. Sedementry rocks in the studied area are based on desert traps including sandeston types such as quartzit conglomerent, laterite, sub liticarenait, shaillean thin layers and Coal which are Generally Paraconformity or angular unconformity with dolomitic – calcrus cross. on the due to the earlier Cimmerian orogeny phse, carbonate sedimentary environment changed to coal depasetis formation.the UPPER Triassic carbonat rocks in the study area are somtime contain oroganic matte and iron oxide hidroxid of shemshak which formed in the sedementry Environment tidal flats or lagoon. In addition the lateritic section at the base of shemshak formation shows the sedementry discontinuity of the earlier cimmirian land tenure phase.In the section A at the base of shemshak formation is on the part of Laterit Hoeizon but at the upper part bordered Dalichai formation. At th section of B on the in the hillside of Sordar the Lower boundray of Shemshak Formation contain Laterit Hoeizon the form of Paraconformity and is located on Elika Formation but the upper boundary in the form of angular unconformity bordered Dalichai formation. At th section of C lower boundary of shemshak formation does not contain bauxite- laterit and is located on the Elika formation and the upper bandray ends in direction of Dalichai Formation. in term sedimentary environment Dolomit–Limeston formed in the Tidal Flats, Sandeston in the shallow coastal or condition open River and Coal has been depasited castal marsh and sowamp. The bauxite – Laterit horizon are of peneplain type.

Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran

The Amir-Abad karst-type bauxite deposit is located in the Irano–Himalayan bauxite belt, 8 km of south of Maragheh city in northwestern Iran. The bauxite ores occur as layers and lens-shaped pockets in the contact of the Triassic dolomitic limestone of the Elika Formation and the Lower Jurassic sandstone, siltstone, shale, and coal of the Shemshak Formation. Based on the PXRD and SEM-EDS analyses, the bauxite ores mainly consist of diaspore, hematite, and kaolinite group minerals (e.g., kaolinite and montmorillonite), with lesser amounts of goethite, anatase/rutile, and zircon. Nickel, Cr, Co, and V show a pattern similar to Fe; they were leached from the uppermost parts of the profile by acidic percolating solutions, and concentrated toward the carbonate bedrock under alkaline conditions. Aluminum, Nb, Ga, Ta, Th, Hf, and Zr can be regarded as less mobile elements. Variations of the La/Y, (ΣLREE/ΣHREE)N, and (La/Yb)N ratios across the weathering profile, together with leaching of alkali and alkaline earth metals indicate an acidic environment in the uppermost parts, and a basic environment in the basal parts of the profile. Mineral control and physico-chemical conditions (e.g., Eh and pH) probably had effective roles in the behavior of elements during weathering. Based on the concentration of trace elements, such as Zr, Cr, and Ga, and the conservative elemental indices (e.g., Sm/Nd, Ti/Zr, and Nb/Ta), the basaltic rocks were a plausible source rock for the Amir-Abad karst-type bauxite deposit.

Assessment of risks of tunneling project in Iran using artificial bee colony algorithm

The soft computing techniques have been widely applied to model and analyze the complex and uncertain problems. This paper aims to develop a novel model for the risk assessment of tunneling projects using artificial bee colony algorithm. To this end, the risk of the second part of the Emamzade Hashem tunnel was assessed and analyzed in seven sections after testing geotechnical characteristics. Five geotechnical and hydrological properties of study zone are considered for the clustering of geological units in front of tunneling project including length of tunnel, uniaxial compressive strength, rock mass rating, tunneling index Q, density and underground water condition. These sections were classified in two low-risk and high-risk groups based on their geotechnical characteristics and using clustering technique. It was resulted that three sections with lithologies Durood Formation, Mobarak Formation, and Ruteh Formation are placed in the high risk group and the other sections with lithologies Baroot Formation, Elika Formation, Dacite tuff of Eocene, and Shear Tuff, and Lava Eocene are placed in the low risk group. In addition, the underground water condition and density with 0.722 and 1 Euclidean distances have the highest and lowest impacts in the high risk group, respectively. Therefore, comparing the obtained results of modelling and actual excavation data demonstrated that this technique can be applied as a powerful tool for modeling risks of tunnel and underground constructions.

GEOCHEMISTRY AND MICROFACIES OF THE RUTEH FORMATION IN THE RUTEH AREA, CENTRAL ALBORZ, IRAN

To understand microfacies, depositional environment and geochemistry of Upper Permian rocks in Alborz region, the type sections of Ruteh Formation were studied. During the Permian, the Alborz region was a part of the east-west trending Paleotethys sea. Stratigraphic studies indicate that the Ruteh Formation in Ruteh section is composed of thin to massive limestone, argillaceous limestone interbedded with shale, is overlain by distinct laterite horizon of the Elika Formation and is underlain by the disconformity by the Dorud Formation. Facies analysis and petrographic studies led to the recognition of 11 microfacies in Ruteh section. These facies were deposited in 4 facies belts such as tidal flat, lagoon, shoal and open marine sub-environment. The Permian calcareous algae in the Ruteh Formation are widespread and well documented to determine the environment and microfacies of Permian deposits. Cementation and dolomitization are the main diagenetic processes in Ruteh Formation. Based on petrographic (size and fabric) studies, 4 dolomite types such as dolomicrite, dolomicrospar, dolospar, and dolomite cement were recognized. Seawater was the main source of Mg for early diagenetic dolomite (type 1), while Mg for late diagenetic dolomite (types 2,3,4) probably were sourced by shale pressing processes and pressure solution. Major and minor element studies led to there cognition of aragonite mineralogy. The geochemical study illustrates that these carbonates were affected mostly by meteoric diagenesis, which is occurred in a semi-close to open diagenetic system.

Anachronistic facies and carbon isotopes during the end-Permian biocrisis: Evidence from the mid-Tethys (Kisejin, Iran)

Late Permian mass extinction (LPME) research has focused primarily on Tethyan sections because it is believed that these successions are more complete than those from other localities, and provide a more comprehensive record of the largest, most devastating extinction event in Earth history. The Kisejin section, a previously undocumented mid-Tethyan, Upper Permian-Lower Triassic succession located in the Central-Iran Plate. The Kisejin section contains a continuous Permian-Triassic sequence with only small breaks in sedimentation and was examined in order to determine sedimentologic, biostratigraphic, and carbon isotopic trends across the Permian-Triassic transition. Abnormal (anachronistic) carbonates developed in the study area following the LPME, and include microbialites, edgewise conglomerates, sparitic microspheres, and microbially-coated grains; microbialites occur as thrombolites, stromatolites, and as agglutinated forms. Renalcis-type calcimicrobes are documented for the first time from Permian-Triassic boundary microbialites (PTBMs) of Iran. Coated grains fall into two groups, and include pre-PTBM ooids, which are dense and cloudy, and possibly microbial in origin, and post-PTBM cortoids with destructive and constructive micrite envelopes. Latest Permian conodonts (H. praeparvus, M. ultima), coupled with carbon isotopic values, place the Permian-Triassic boundary within the lowermost thrombolite unit, about 2.1 m above the boundary between the Nessen Formation and the Elika Formation, and indicate that microbialite growth began during the latest Permian. Our study of this previously unknown section shows that, unlike other well-known PTB sections from Iran, the microbialite pattern is complicated, and is more similar to PTBM successions from Turkey. In addition, we note a similarity between the unusual facies of the Kisejin section and those of eastern Tethyan sections from China (i.e. sparry microspheres and Renalcis-type calcimicrobes); these unusual facies have not been previously reported from other well-known Iranian sections, including Julfa and Abadeh, which are thick and have been extensively studied.

Geochemical characteristics of the Arbanos karst-type bauxite deposit, NW Iran: Implications for parental affinity and factors controlling the distribution of elements

The Arbanos bauxite deposit is located in the Iran-Himalayan karst-type bauxite belt and about 25 km northeast of Bukan city, northwestern Iran. The bauxite ores occur as layers and lenses along the contact of the carbonate (limestone and dolomite with intercalations of shale) of the Ruteh Formation (Upper Permian) and dolomite of the Elika Formation (Triassic). Hematite, kaolinite, and diaspore are the major rock-forming minerals in the ores, accompanied by lesser amounts of chlorite, montmorillonite, chamosite, siderite, goethite, boehmite, calcite, rutile, anatase, zircon, and quartz. Mass balance calculations indicate that the distribution of Ni, V, and Cr is controlled by the iron oxyhydroxides, whereas the distribution of Ba and Sr is controlled by kaolinite. The bivariate diagrams of the Sm/Nd versus the conservative elemental indices such as TiO2/Al2O3, Al2O3/Hf, Al2O3/Nb, and Nb/Ta reveal that the shale of the Ruteh Formation is the most plausible parent rock for the bauxite ores. The factor analysis method indicates that the paleo-environmental changes, soil redox state, and water activity in the pedogenic environments played a fundamental role in distribution of the major, minor, and trace elements.

Geoeconomics of fluorspar as strategic and critical mineral in Iran

Supply of strategic materials during the Cold War was under the influence of military competition between East and West. But after the cold war and turning of geopolitics and geostrategy to geoeconomics, the assessment method of criticality matrix with dimension of economic importance and supply risk has been commenced by the US National Research Council. It has spread based on conflict between north and south and security or economic power of the developed countries. In this paper it is attempt to study a mineral using various critical minerals assessment methods to verify its effectiveness in economic development and its geoeconomics importance of Iran. One of such materials is the fluorite strategic mineral with trade mark of fluorspar that its deposits are found in the carbonate rocks of Triassic and Elika formation in Central Alborz and Shotori formation in central Iran. It was shown that the assessment methods used by the US Geological Survey, the US Department of Defense, EU and German Industries, depicted the fluorspar as a critical and strategic mineral in the world. Fluorspar economic value is because of its use in steel, aluminum, hydro-fluorocarbons, Teflon, renewable and clean energy production. The results of this study show the rank of Iran is seven in the world in terms of production, but this country is one of the main importers for intermediate goods made from these mineral among its neighboring countries. So as a first step, investment on systematic exploration of fluorspar resources is necessary to increase the supply of raw materials for the country's aluminum industry. Exploration of new reserves can also reduce concerns relevant to supply risk at the international level for developed countries. It can also be concluded that the joint investment, cooperation and concurrently researches in relation to raw materials and minerals, may lead to a reduction in competition between North and South countries. Hence, the review and monitoring of evaluation methods of critical raw materials in the developed countries is very important and valuable for choosing the appropriate policies for those developing countries that own these resources.

Paleoecology of Permo-Triassic Boundary According to Palynoflora in Shourjestan, Iran

Using palynoflora findings, the present study was conducted to determine paleoecology of Permo-Triassic boundary in Shourjestan Region in north of Fars Province. Permo-Triassic boundary in this region is gradational (transitional) and continuous. Four stratigraphic sections were selected and 7 spore and pollen instances were identified after sampling and performing needed experiments for separation of palynomorph samples. Based on the achieved palynomorphs on pyroclastic deposits in the studied sections, it can be concluded that Coniferophyta, Equisetopsids, Filicopsids, Progymnosperms and Cordaitales had probably higher relative frequency in plant tissue around the basin environment. According to relatively high frequency of land palynomorphs in the studied deposits and on the basis of association of land and marine palynomorphs in the studied palynoflora, it can be concluded that pyroclastic deposits of upper Permian are formed in shallow marine setting. Regarding studies on the identified palynomorphs of Elika Formation equivalent deposits, one might infer that probably in plant tissue around these deposits, Triassic seed ferns and Coniferophyta had higher frequency and distribution and also the aforementioned deposits are settled in shallow marine settings.

Geochemical characteristics of the Qahr-Abad fluorite deposit, southeast of Saqqez, western Iran

Fluorite vein mineralization has mainly occurred in carbonate rocks of the Triassic Elika Formation in the Qahr-Abad district, situated southeast of the city of Saqqez in western Iran. It consists mainly of three colored fluorite types (violet, blue, and colorless), calcite, dolomite, and quartz. The subordinate components are iron oxides and clay minerals. Local wall-rock alterations include argillization and silicification. Geochemical studies of the deposit show that violet fluorites were formed at an early stage of mineralization and colorless and blue fluorites at a late stage. Violet fluorites are more enriched in major and trace elements than other fluorite types. The Tb/Ca and Y/Ho ratios suggest a hydrothermal origin for the Qahr-Abad fluorites. The Ce/Yb ratios and chondrite-normalized patterns revealed that the early fluorites are enriched in light rare earth elements, whereas the late fluorites are enriched in heavy rare earth elements. The Yb/Ca ratio versus the Yb/La ratio shows that early fluorites are the result of assimilation and replacement of wall rock, and late fluorites are the result of recrystallization and remobilization. Considering the negative Ce anomalies in late-stage fluorites, it can be assumed that the mineralization of violet fluorites in this deposit occurred in relatively oxidizing basic conditions and that of colorless to light yellow and blue to greenish blue fluorites in relatively reducing acidic conditions.

Petrography and Geochemistry of the Jajarm Bauxite ore Deposit, Northeast Iran: Implications for Source Rock Material and Ore Genesis

The Jajarm bauxite deposit, northeast Iran, is the largest such deposit in Iran. The deposit is sandwiched between the Triassic Elika formation and the Jurassic Shemshak formation, housed within karstic features developed within the former unit. The deposit generally shows an internal layering defined by the following four distinct horizons (from bottom to top): (a) a lower argillaceous horizon, approximately 50-80 cm thick, is mainly composed of clay minerals that directly overlies the carbonate footwall (Elika formation); (b) a bauxitic clay layer approximately 2-3 m thick that consists mainly of hematite, kaolinite, anatase, and diaspore; (c) a red bauxite layer (the main high-grade ore), about 5 m thick and composed of diaspore, kaolinite, anatase, and hematite; and (d) an upper kaolinitic layer that is 20-50 cm thick, composed mainly of kaolinite, and overlain by the Shemshak formation. Detailed petrographic studies reveal diagenetic alteration of the bauxitic protolith. The main observed bauxite textures are microgranular, oolitic, pisolitic, fluidal-collomorphic, and microclastic. Microgranular and microclastic textures associated with the residual fractured and corroded quartz grains, as well as feldspar grains are almost completely replaced by platy diaspore. Geochemical analyses of the red bauxite reveal enrichment of less mobile elements (Nb, Th, Zr, Mo, Ga, and Cr) and depletion of mobile elements (Rb, K, Na, Sr, La, Mg, and Pb); the opposite result is obtained for the bauxitic clay. Chondrite-normalized REE (Rare Earth Element) patterns for the upper kaolinite layer are similar to those for the underlying red bauxite, and the patterns obtained for the lower argillaceous layer are similar to those for the overlying argillaceous bauxite horizon. Ce shows a positive anomaly in the red bauxite and a negative anomaly in the bauxitic clay. The correlation coefficients calculated between REE and other elements demonstrate that the likely REE-bearing minerals are oxides of Ti and Nb, clay minerals, and zircon. In contrast to the present diasporic mineralogical composition of the Jajarm bauxite, the geochemical and mineralogical data indicate an original gibbsitic composition. Finally, the observed mineralogical and textural evidence, combined with the evidence provided by variation diagrams and REE patterns, indicates a mixed origin for the Jajarm bauxite from both basic igneous and sedimentary rocks. In fact, bauxitization was initiated on basic source rocks and continued during reworking and replacement within the karstic features.

The Lower Triassic Sorkh Shale Formation of the Tabas block, east central Iran: Succession of a failed-rift basin at the paleotethys margin

The Lower Triassic Sorkh Shale Formation is a dominantly red colored marginal marine succession deposited in the north-south trending Tabas Basin of east central Iran. It is correlated with the unconformity-bounded lower limestone member of the Elika Formation of the Alborz Mountains of northern Iran. The Sorkh Shale is bounded by the pre-Triassic and post-Lower Triassic interregional unconformities and consists mainly of carbonates, sandstones, and evaporites with shale being a minor constituent. Detailed facies analysis of the Sorkh Shale Formation resulted in recognition of several genetically linked peritidal facies that are grouped into restricted subtidal, carbonate tidal flat, siliciclastic tidal flat, coastal plain and continental evaporite facies associations. These were deposited in a low energy, storm-dominated inner-ramp setting with a very gentle slope that fringed the Tabas Block of east central Iran and passed northward (present-day coordinates) into deeper water facies of the Paleotethys passive margin of northern Cimmerian Continent. Numerous carbonate storm beds containing well-rounded intraclasts, ooids and bioclasts of mixed fauna are present in the Sorkh Shale Formation of the northern Tabas Basin. The constituents of the storm beds are absent in the fair weather peritidal facies of the Sorkh Shale Formation, but are present throughout the lower limestone member of the Elika Formation.

Carbonate Ramp Deposits of the Lower-Middle-Triassic Elika Formation in the Bibi Shahrbanou Area, Northern Iran, Facies, Paleoenvironments, and Sequences

Carbonate Ramp Deposits of the Lower-Middle-Triassic Elika Formation in the Bibi Shahrbanou Area, Northern Iran, Facies, Paleoenvironments, and Sequences

Sur la présence deMeandrospira pusilla (Ho) (Foraminifère), dans le Trias inférieur de Kuh-e-Ali Bashi, Julf a, NW Iran

In the course of preliminary micropaleontologic and sedimentologic investigations of several sections in the Lower Trias of Julfa, NW Iran, the stratigraphically significantMeandrospira pusilla (Ho) (=Citaella iulia Premoli Silva) was shown to be present in the uppermost beds of the platy limestones of the Elika formation.