Eastern Margin Research Articles

Assessment of anthropogenic pollution in Guanabara Bay (SE Brazil) through biogeochemical data and stable isotope mixing models.

This work intends to identify pollution sources along the margins of Guanabara Bay (GB; SE Brazil) through a multiproxy approach and Bayesian stable isotopic mixture model (BSIMM). For this purpose, 33 surface sediment samples were collected and analyzed for granulometry, geochemistry (heavy metals, total organic carbon-TOC, stable isotopes of carbon and nitrogen-δ13C and δ15N, Rock-Eval pyrolysis parameters-REPP), and physicochemical parameters. Metal concentrations (E) dissolved in water (EW), adsorbed by organic matter (EOM) and by Mn hydroxides (EMn), and total extracted concentrations (ET) were analyzed. Sampling was conducted in 2018 after an oil spill from Reduc Oil Refinery. Potential Ecological risk index (PERI), based on metals, classified 85% of the analyzed stations as having moderate to considerable ecological risk. The metals with the potential to cause the highest ecological risk were CdW, CdOM, PbOM, and HgOM. The combination of BSIMM and REPP data was an effective proxy for oil spill detection by indicating the presence of polycyclic aromatic hydrocarbons (PAHs). Relatively high TOC contents suggested that the analyzed stations are eutrophicated environments. BSIMM discriminated three groups of stations with different sources of organic matter (OM), endorsing the result previously shown by the cluster analysis: (A) Niterói region, Botafogo marina, Glória marina, Fiscal and Fundão islands with diffuse sources of OM, including marine phytoplankton and material of continental origin from highly polluted rivers and domestic sewage; (B) region near Fundão and Governador islands and Mangue Channel outlet with OM (≃70%) supplied by highly polluted streams and a small contribution of PAHs; (C) Duque de Caxias and Botafogo-Urca inlet with significant contributions of PAHs, materials from C-3 plants and rivers polluted by urban sewage. Results of linear regressions in conjunction with BSIMM indicate that HgMn and PbOM mainly affect Group A's stations. Although the eastern margin of GB (Niterói; Group A) showed greater oceanic interaction than the other groups, it presented substantial concentrations of metals, potentially harmful (i.e., Hg and Pb) to marine biota and human health.

Petrology and Geochemistry of Lamprophyres from Tirthal Area, in Eastern Margin of the Eastern Dharwar Craton, Khammam, Telangana, India

The presence of lamprophyre dykes is very common in the Eastern Dharwar Craton (EDC), southern India. The present paper reports five new lamprophyre bodies from the Tirthal area near the bank of the Muneru River (80°08ʹ 13.00ʹʹ:17°19ʹ 9.0ʹʹ), north of Khammam, Telangana.Petrography and geochemistry of the lamprophyre dykes are also discussed in this paper. The study area mainly consists of granitoids of Peninsular Gneissic Complex-II (PGC-II) of the EDC. The lamprophyre intrudes the granitoids of the EDC.Petrographic studies revealed the presence of panidiomorphic texture. Euhedral crystals of clinopyroxene, biotite and amphibole are present as phenocryst in the lamprophyre,while k-feldspar, plagioclase feldspar, biotite and apatite are present in the groundmass.The lamprophyre is characterized by SiO2 (40.03%-45.23%), Fe2O3(9.09%-13.45%), MgO (9.78%-11.96%), CaO (8.25%-14.78%), K2O (0.69%-2.37%), TiO2 (1.3%-1.53%) and Al2O3 (9.76%-12.02%) contents. Similarly trace elements analysis gavehigher amounts of Ba (2030-10498ppm), Sr (438-925 ppm), Ni (156-225 ppm), Zr (417-590 ppm), V (141-169 ppm) and Cr(388-482 ppm). All the samples gave higher LREE values as compared to HREE with a total REE content within the range of 1108.50-2004.49 ppm. The lamprophyre is classified as minette belonging to Calc Alkaline Group based on geochemical and petrological studies.

Lithostratigraphy and Microfacies of the Upper Cretaceous Muti Formation of the Oman Foreland Basin, Nakhal Area, Oman

The Upper Cretaceous Muti Formation was deposited in the Oman Foreland Basin during the obduction of the allochthonous units on the eastern margin of the Arabian Platform. The formation is exposed in various isolated outcrops around Jabal Akhdar Mountain and is located between the Mesozoic platform carbonates below and the allochthonous nappe above. The current study is the first to describe the outcrops of the Muti Formation in the Nakhal area. It focuses on the lithofacies, microfacies distribution, and the characterization of the depositional environment of the formation. The lithofacies and microfacies of the formation are described from two measured sections in the study area. The Nakhal section is about 50 m thick and consists of four lithofacies: marl, bedded limestone, nodular limestone, and clay. A total of four microfacies are identified, including echinoderm-spine wackestone, bioclastic packestone, arenaceous wackestone, and mudstone. Diagenetic features such as fractures, cementations, and dissolutions, and their products, for instance, porosities, were also identified, and their paragenetic history was reconstructed. Additionally, microfossils, such as bryozoan fragments, calcispheres, bivalves, fragments of echinoids, and brachiopod fragments, benthic and planktonic foraminifera were recognized. Based on lithological and biotic variations, it is suggested that the Muti Formation in the Nakhal area was deposited in a shallow marine environment on the outer to the mid-carbonate shelves. This formation is subjected to diagenetic changes starting with eogenesis in marine settings followed by burial diagenesis, and subsequently, the formation is exposed to the telogenetic diagenesis phase. Keywords: Muti Formation, Nakhal Area, Oman Foreland Basin, Upper Cretaceous, Jabal Akhdar.

A 3D glacier dynamics–line plume model to estimate the frontal ablation of Hansbreen, Svalbard

Abstract. Frontal ablation is responsible for a large fraction of the mass loss from tidewater glaciers. The main contributors to frontal ablation are iceberg calving and submarine melting, with calving often being the largest. However, submarine melting, in addition to its direct contribution to mass loss, also promotes calving through the changes induced in the stress field at the glacier terminus, so both processes should be jointly analysed. Among the factors influencing submarine melting, the formation of a buoyant plume due to the emergence of fresh subglacial water at the glacier grounding line plays a key role. In this study we used Elmer/Ice to develop a 3D glacier dynamics model including calving and subglacial hydrology coupled with a line plume model to calculate the calving front position at every time step. We applied this model to the Hansbreen–Hansbukta glacier–fjord system in southern Spitsbergen, Svalbard, where a large set of data are available for both the glacier and the fjord from September 2008 to March 2011. We found that our 3D model reproduced the expected seasonal cycle of advance–retreat. Besides, the modelled front positions were in good agreement with the observed front positions at the central part of the calving front, with longitudinal differences, on average, below 15 m for the period from December 2009 to March 2011. But there were regions of the front, especially the eastern margin, that presented major differences.

Full-Scale Pore and Microfracture Characterization of Deep Coal Reservoirs: A Case Study of the Benxi Formation Coal in the Daning–Jixian Block, China

The pore-fracture structure of deep coal reservoirs is highly important for evaluating, exploring, and developing coalbed methane (CBM) resources. This study considers three coal samples from the DJ57 well in the Benxi Formation in the Daning–Jixian block on the eastern margin of the Ordos Basin as the research object. Based on the coal quality parameters of the coal samples, field emission scanning electron microscopy (FE-SEM), gas adsorption experiments, high-pressure mercury intrusion porosimetry (MIP), and microcomputed tomography (micro-CT) scanning were used to quantitatively characterize the nanoscale pores and microscale fractures in deep coal reservoirs and to evaluate the pore-fracture structure at different scales. The results reveal that the pore types in the Benxi Formation coal samples are diverse and include mainly organic matter (OM) pores, inorganic pores (intraparticle and interparticle pores), and microfractures. The organic pores are diverse in shape and mainly exhibit round, oval, and wedge shapes, while the microfractures exhibit slender stripes or serrated curves. The multiscale quantitative characterization of deep coal reservoir pores and fractures is based on a variety of pore characterization methods, and the pore and fracture volume distributions are mainly U-shaped, revealing the coexistence of micropores and microfractures. The volumes of micropores (0.3–2 nm), mesopores (2–50 nm), macropores (50 nm to 10 μm), and microfractures (>10 μm) account for 78.00%, 6.78%, 2.08%, and 13.14%, respectively, of the total pore volume (PV). Based on a full-scale pore-fracture splicing calculation, the total permeability of the Benxi Formation coal samples ranges from 5.77 to 28.22 mD. The observation results indicate that the microfractures are connected to each other, forming a network structure with strong connectivity. The microfractures are mainly associated with pore diameters>100 μm, accounting for approximately 95% of the total permeability. Moreover, micropores in deep coal reservoirs provide a large space for CBM adsorption, and microfractures enhance the seepage capacity of CBM.

Evaluation of recoverable potential of deep coalbed methane in the Linxing Block, Eastern Margin of the Ordos Basin

The deep coalbed methane (CBM) resources are widely developed in the Linxing Block. However, the evaluation of CBM geological areas suitable for CBM exploitation remains unexplored, hindering further development. This research optimizes the key geological parameters that influence the development of deep CBM from the perspectives of resource and development conditions. The evaluation system for deep CBM recoverability has been established, and the multi-fuzzy evaluation method has been used to perform the quantitative evaluation of recoverability. The results indicate that the resource conditions of No.8 + 9 coal seam are superior to those of No.4 + 5 coal seam. Favorable resource conditions are predominantly concentrated in the northeast and specific southern portions of the research area. Favorable development conditions for both coal seams are mostly concentrated in the northeastern area. Based on the classification standard of recoverable favorable areas, the Level II area is crucial for the development of No.4 + 5 coal seam. This area is primarily distributed in the northeast of the research area., Both Level I and Level II areas for the No. 8 + 9 coal seam are situated in the northeast. The Level III area is earmarked for deep CBM production and shows potential for exploration. Further analysis reveals that the resource conditions in the favorable area are generally superior to the development conditions. These areas are classified as Class A, including categories such as I-A, II-A, and III-A, indicating relatively complex reservoir transformation.

Geochronological (36Cl and OSL) and geomorphic insights into the formation of Terkhiin Tsagaan Lake and Khorgo Volcano in Central Mongolia: Unravelling a pre-Holocene paleolake

Multiple lava flows have profoundly shaped the landscape of Terkhiin Tsagaan Lake (TTL) in central Mongolia, influencing its level and extent over the Quaternary. Optically Stimulated Luminescence (OSL) dating of terraces unveils ages ranging from 65 to 59 ka at 2073 m, 54–51 ka at 2069 m, and approximately 46 ka at 2065 m. Additionally, cosmogenic 36Cl dating of a lava flow provides insights into the timing of the most recent volcanic eruption, dating it to 7.2 ka ago. The integration of geomorphic and geochronological evidence, along with observations of Lava-Water-Interaction features, suggests the presence of a paleolake preceding the last Holocene eruption of Khorgo Volcano. The geomorphic evolution unfolds in three stages: (i) A Pleistocene lava flow formed multiple dams across the Tariat Basin, creating temporally successive lava-dammed lakes. (ii) The paleolakes underwent fluctuations, leaving lacustrine terraces, and experiencing lower levels. (iii) Holocene eruption of Khorgo, which is one of the youngest in Central Asia, shaped the current TTL by releasing lavas over the eastern margin of the paleolake. The study contributes valuable insights into the paleoenvironmental dynamics, shedding light on the interplay between volcanic activity, climate, and landscape evolution.

Evaluation of Deep Coalbed Methane Potential and Prediction of Favorable Areas within the Yulin Area, Ordos Basin, Based on a Multi-Level Fuzzy Comprehensive Evaluation Method

The research on the deep coalbed methane (CBM) in the Ordos Basin is mostly concentrated on the eastern margin of the basin. The geological resources of the Benxi Formation in the Yulin area, located in the central-eastern part, cover 15,000 × 108 m3, indicating enormous resource potential. However, the characteristics of the reservoir distribution and the favorable areas are not yet clear. This research comprehensively performed data logging, coal rock experiments, and core observations to identify the geological characteristics of the #8 coal seam, using a multi-level fuzzy mathematics method to evaluate the favorable area. The results indicate the following: (1) The thickness of the #8 coal in the Yulin Block ranges from 2.20 m to 11.37 m, with depths of between 2285.72 m and 3282.98 m, and it is mainly underlain by mudstone; the gas content ranges from 9.74 m3/t to 23.38 m3/t, showing a northwest–low and southeast–high trend. The overall area contains low-permeability reservoirs, with a prevalence of primary structural coal. (2) A multi-level evaluation system for deep CBM was established, dividing the Yulin Block into three types of favorable areas. This block features a wide range of Type I favorable areas, concentrated in the central-eastern, northern, and southwestern parts; Type II areas are closely distributed around the edges of Type I areas. The subsequent development process should prioritize the central-eastern part of the study area. The evaluation system established provides a reference for selecting favorable areas for deep CBM and offers theoretical guidance for targeted exploration and development in the Yulin area.

Formation mechanical mechanism of low-angle fractures in pre-salt carbonate reservoirs: a case study from Carboniferous KT-I formation of the NT oilfield in the eastern margin of the Precaspian Basin, Kazakhstan

Fracture is an important factor that affects the oil and gas productivity of carbonate reservoirs. Much researches have been done on the origin of high-angle fractures in carbonate reservoirs, but few efforts have been made on the genetic mechanical mechanism of low-angle fractures. Based on the seismic data, core data, conventional logging data and rock mechanics experimental data, combined with three-dimensional in situ stress field simulation methods, the features, formation geological conditions and genetic mechanical mechanism of low-angle fractures (LAFs) were analyzed by applying Coulomb–Moore criterion, Griffith criterion and non-coordination criterion. The proportion of the number of shear fractures is as high as 90.2%, while that of tensile fractures is only 9.8% in the study area. Shear fractures are mainly unfilled fractures, and tensile fractures are mainly partially filled fractures. The LAFs were formed in the second tectonic movement, in which the knee-fold structure with high in the west and low in the east developed in the study area. The buried depth of most parts of the KT-I formation is 800 m when the study area develops the knee-fold structure, with a maximum depth of 1800 m and a minimum buried depth of 70 m, and the dip angle of the steepest part of the stratum is about 20°. A large number of LAFs were formed in the study area under the joint influence of tectonics and abnormally high pressure of water, including near-horizontal LAFs in the non-weak fabrics section (type I low-angle shear fractures), the LAFs having a certain angle with bedding in the non-weak fabrics section (type II low-angle shear fractures) and near-horizontal LAFs in the weak fabrics section (type III low-angle shear fractures). The formation of type I and type II low-angle shear fractures follows the Coulomb–Moore criterion. Type I low-angle shear fractures are formed in strata with a certain dip angle, while type II low-angle shear fractures are formed in near-horizontal strata. Type III low-angle shear fractures are formed under the comprehensive influence of pre-existing weak fabrics and strong horizontal extrusion, which follows the non-coordination criterion. Low-angle tensile fractures are mainly caused by abnormally high pressure and reverse faults in the study area, following Griffith’s criterion. The research in this paper not only reveals the formation mechanical mechanism of LAFs in pre-salt carbonate reservoirs but also provides guidance for the prediction of LAFs and solving the problem of water channeling caused by LAFs in oil fields.

Facies architecture, geochemistry and petrogenesis of Middle Triassic volcaniclastic deposits of Mt. Ivanščica (NW Croatia): evidence of bimodal volcanism in the Alpine-Dinaridic transitional zone

During the Middle Triassic, intensive volcanic activity took place along the eastern margin of Pangea, including the Greater Adria promontory, due to the Neotethyan oceanization. This resulted in the formation of various volcanic and volcaniclastic rock types. The region of NW Croatia, acting as a transition zone between the Southern Alps and the Dinarides, showcases the outcrops of these rocks. The present study investigates the facies of volcaniclastic rocks, the distribution of those facies, formation processes, as well as the genesis of the primary magma to gain a better understanding of the complex geodynamics of this region during the Middle Triassic. Six profiles across the Vudelja quarry front were surveyed using drone imaging and samples were collected for detailed petrographic and geochemical analyses. Two groups of volcaniclastic rocks were identified—mafic and intermediate/felsic. The former is represented by (I) autoclastic effusive facies and (II) resedimented autoclastic facies, while the latter is represented by (III) secondary pyroclastic facies. Mafic volcaniclastics were generated through basaltic effusions in marine environments, fragmentation in contact with seawater, mixing with shallow marine carbonate clasts, and subsequent redeposition in deeper marine areas. The secondary pyroclastic facies (III) consists of a regionally distributed felsic Pietra Verde tuff whose deposits may be related to pyroclastic density currents and syn-eruptive resedimentation by turbidite-like currents. Geochemical data indicate that parental magmas responsible for generating the mafic volcaniclastics had a calc-alkaline composition and originated in ensialic and mature arc settings of an active continental margin. The observed chemical composition is likely inherited from older, arc-related lithologies, associated with the subduction of the Paleotethys Ocean. Parental magmas are thought to have formed during continental rifting of the passive Middle Triassic margins of the Greater Adria through (i) partial melting of the heterogeneous lithospheric mantle, which had been metasomatized during an earlier Hercynian subduction, and (ii) subordinate processes related to the melting of the upper continental crust and subsequent fractionation. Ar/Ar dating on plagioclase separates yielded an age of 244.5 ± 2.8 Ma for mafic volcaniclastics. This aligns well with biostratigraphic ages of felsic tuffs which crop out on a broader regional scale of the Dinarides, the Southern Alps, and the Transdanubian Range. The overlapping ages obtained from radiometric dating of mafic volcaniclastics and biostratigraphic ages of the felsic Pietra Verde tuffs strongly suggest that the Greater Adria region experienced concurrent bimodal volcanism during the Middle Triassic.

Origin of fluids in the Lancangjiang tin belt, southwestern Yunnan Province, China: Evidence from trace element and boron isotopic compositions of tourmaline

The Lancangjiang tin belt is located on the eastern margin of the Tibetan Plateau, which is in the northern part of the Southeast Asian tin belt that contains Sn, W, and base metal ore deposits. Tourmaline alteration and high B contents are typical features of the magmatic–hydrothermal systems in the Lancangjiang tin belt. Our new data for tourmaline intergrown with cassiterite reveal complex geochemical features that provide important insights into the origins of ore-forming fluids in this B-rich tin belt. Most of the tourmaline in the Sn deposits and metamorphic rocks belongs to the alkali-group dravite series, except for some that is part of the X-vacant group. The tourmaline compositions differ among the ore districts, but all exhibit Fe-poor (0.61–1.08 apfu) and Mg-rich (1.43–2.06 apfu) compositions, with Fe/(Fe + Mg) = 0.18–0.46. Most trace elements in the tourmaline occur at low contents (<50 ppm), including the large-ion lithophile elements (e.g., Cs and Ba) and high-field-strength elements (e.g., Nb, Ta, Hf, and Th). However, some trace elements (e.g., Zn, Sr, and V) and Sn have high contents (up to several hundreds or thousands of ppm). The δ11B values of tourmaline from the Sn deposits range from −14.7 ‰ to −11.3 ‰, except for those in the Man Makhsan Sn deposit, which range from −12.0 ‰ to −8.1 ‰. The δ11B values (−14.7 ‰ to −8.1 ‰) and the positive correlation between Sn contents and Nb/Ta, Al/Ga, and K/Cs ratios in the ore-related tourmaline indicate that the exsolved ore-forming fluids were derived from highly fractionated S − type granitic magmas. The fluids were mainly B-, Sn-, and Al-enriched. The low Fe/(Mg + Fe) ratios, high oxygen fugacity, and Al saturation were favorable for cassiterite precipitation, and are proxies for the ore-forming potential of large-scale Sn deposits.

Altitudinal variation in soil nematode communities in an alpine mountain region of the eastern Tibetan plateau

Distribution patterns of species diversity in high mountains have received considerable attention in scientific research and conservation efforts. However, our understanding of the corresponding altitudinal patterns of soil fauna across spatial scales, particularly on high-altitude plateaus, remains limited. To address this gap, we conducted a case study on Balang Mountain, located at the eastern margin of the Tibetan Plateau. Our focus was on soil nematodes within an altitudinal range of approximately 3000 to 4000 m. We collected climate, soil, and vegetation data to test multiple hypotheses, including the effects of energy, water availability, productivity, soil resource availability, and pH constraints on nematode communities. Dominance analysis and commonality analysis were employed to determine the relative support of these hypotheses in explaining nematode abundance, diversity, and composition. Beta-diversity, which links local alpha-diversity and regional gamma-diversity, was decomposed into distinct components to elucidate ecological processes along altitude and across diversity facets. Our findings revealed distinct yet significant altitudinal patterns in nematode abundance (concave-down), richness (monotonous decrease), and evenness (concave-up). Water and soil resource availability emerged as dominant factors influencing nematode abundance, while energy and pH played pivotal roles in determining nematode richness. Additionally, water and productivity were identified as the most significant drivers shaping nematode community composition. Furthermore, a significant influence of pH on gamma- and beta-diversities was observed, surpassing the impact of other predictors at a coarse level. Upon decomposing beta-diversities into different components, we discovered that taxa substitution (turnover) and individual substitution (balance-variation) were the primary contributors to community dissimilarity among altitudes, indicating strong effects of environmental sorting or spatial and historical constraints on soil nematode communities. These findings contribute to our understanding of the distribution patterns and processes of soil nematode communities along altitude in alpine ecosystems. Moreover, they offer valuable insights into soil biodiversity distribution and conservation in high-mountain environments.

Geochemical characteristics of rare earth elements in late Palaeozoic coals from North China

Introduction: China is a large country of REE resources and production, supplying more than 90% of the world’s rare earth consumption market, China’s traditional REE resources, although rich, but reserves are also declining, in recent years, scholars have shown that the REEs in the specific geological conditions in the coals can be enriched, and even reach the industrial grade, the search for more REE mineral resources will be of great strategic significance.Methods: The article has selected the Zibo, Taozao, Huainan, Datong, Huozhou, Jungar, and Weibei coalfields in North China as the research objects. Based on inductively coupled plasma mass spectrometry (ICP-MS) analyses, the study provides a detailed analysis of the enrichment rules and distribution patterns of rare earth elements (REEs) in coal under different geological conditions.Results: The REE distribution patterns in Late Palaeozoic coals in North China are characterized by enrichment of LREEs, deficit of HREEs with gentle changes, and obvious negative anomalies of Eu, the enrichment of REE in coal is controlled by provenance and volcanism, and is related to distance of transport terrigenous material and the sedimentary environment. The REEs concentrations in North China indicates that Late Palaeozoic coals in the mining areas of the north, northwest, and western parts of North China are significantly enriched in REEs. In addition, REEs in Late Palaeozoic coals in the southeastern mining areas are relatively enriched, and the central and eastern regions are significantly depleted.Discussion: Large coal-type rare earth deposits are expected to be developed in North China, particularly the Datong coalfield, Jungar coal mine and the Weibei coal mine in the eastern margin of the Ordos Basin, and the Zibo coalfield.

Upper Permian paleoclimate of the Sino-Korean block: an example from the Gohan Formation (Korea) in the eastern margin and a synthesis

Upper Permian paleoclimate of the Sino-Korean block: an example from the Gohan Formation (Korea) in the eastern margin and a synthesis

Thermal Modeling of the Sanbagawa and Ryoke Belts

The Sanbagawa and Ryoke belts were formed in a convergent plate boundary along the eastern margin of Eurasia. Thermal modeling using the geological records of these belts as constraints allows quantitative estimates of both shear heating along the Wadati-Benioff zone and magma fluxes beneath the volcanic arc. In contrast to real-time observations of crustal movement and heat flow, rocks record changes in pressures and temperatures that occur over periods of several million years and can be used to examine conditions from the surface to the mantle. Thermal modeling combined with such geological records helps to bridge the gap in our knowledge between real-time observations of ongoing geological processes and the development of orogenies in convergent plate margins over geological time.

Extreme massive hydraulic fracturing in deep coalbed methane horizontal wells: A case study of the Linxing Block, eastern Ordos Basin, NW China

Deep coal seams show low permeability, low elastic modulus, high Poisson’s ratio, strong plasticity, high fracture initiation pressure, difficulty in fracture extension, and difficulty in proppants addition. We proposed the concept of large-scale stimulation by fracture network, balanced propagation and effective support of fracture network in fracturing design and developed the extreme massive hydraulic fracturing technique for deep coalbed methane (CBM) horizontal wells. This technique involves massive injection with high pumping rate + high-intensity proppant injection + perforation with equal apertures and limited flow + temporary plugging and diverting fractures + slick water with integrated variable viscosity + graded proppants with multiple sizes. The technique was applied in the pioneering test of a multi-stage fracturing horizontal well in deep CBM of Linxing Block, eastern margin of the Ordos Basin. The injection flow rate is 18 m3/min, proppant intensity is 2.1 m3/m, and fracturing fluid intensity is 16.5 m3/m. After fracturing, a complex fracture network was formed, with an average fracture length of 205 m. The stimulated reservoir volume was 1 987×104 m3, and the peak gas production rate reached 6.0×104 m3/d, which achieved efficient development of deep CBM.

Lithological and geochemical characteristics and sedimentary environments of the Cambrian high-carbon deposits in the east of the Siberian platform (Kyulenke river basin)

Relevance. The need to study high-carbon deposits as potential sources of hydrocarbons and ore minerals that can significantly increase the mineral resource of Russia. In addition, the analysis of lithological and geochemical features and the reconstruction of the sedimentation conditions of the Kuonamka Formation make it possible to more accurately judge the nature of the Lower and Middle Cambrian paleobasin in the east of the Siberian Platform. Aim. To identify lithological and geochemical features of the composition and determine the sedimentation environment of the Kuonamka Formation. Object. High-carbon deposits of the Kuonamka Formation uncovered by exploration wells on the eastern margin of the Mun arch of the Siberian platform in the Kulenke river basin. Methods. Lithological description of core material; mineralogical and petrographic analysis; X-ray diffraction, X-ray fluorescence and microelement analysis; determination of the content of sulfur and iron forms by wet chemistry; scanning electron microscopy using X-ray spectral microprobe; analysis of petrochemical modules. Results. It was established that the Kuonamka Formation in the studied sections has a consistent structure of four well-defined lithological-stratigraphic horizons. The composition of the deposits is predominantly mixed and is determined by variations in three main mineral groups: clay, carbonate and siliceous, in addition organic matter. The paper demonstrates different forms of organic matter confirming the mixed algal-bacterial genesis of the biocenosis of the Kuonamka basin. The revealed lithological features and lithochemical data indicate the accumulation of high-carbon deposits at a considerable distance from the drift sources in the depression zone of the open sea basin with weak circulation of bottom waters in anoxic conditions. The geochemical euxinic environment was dominant in carbonate-siliceous muds. Sedimentation occurred during one major transgressive-regressive sedimentation cycle being a typical sequence of filling a uncompensated deep depression.

Magmatic Intrusion during the Yanshanian Period and Multi-Mineral Enrichment Mechanisms in the Eastern Margin of the North China Craton

The mineralization within the North China Craton (NCC) is intricately linked to Mesozoic large-scale extension in eastern China and is a consequence of a unified geodynamic tectonic background. Despite previous attempts to elucidate the relationship between large-scale mineralization and magmatic activity in the NCC, a lack of systematic research has hindered the identification of connections among deposits with inconsistent metallogenic ages. This study focuses on the coal measures of the Huanghebei Coalfield (HHBC) in western Shandong, presenting a regional magmatic–hydrothermal metallogenic system with a genetic connection. It delves into the intricate interplay between the multi-mineral enrichment mechanism, metallogenic regularity, and the NCC’s destruction. The findings reveal that: (1) Various stages of magmatic intrusion during the Yanshanian period significantly influenced the Late Paleozoic coal measures in the HHBC. The coal measures exhibit distinct ranks, ranging from medium-rank bituminous C to A and high-rank anthracite C, resulting in noticeable differences in gas generation among different coal ranks. The shale between the coal seams C5 and C7 emerges as excellent with a good hydrocarbon-generating capacity during the middle-maturity stage. (2) The “Intrusion along the rock layer type” proves most conducive to shale gas enrichment, while the “laccolith type” is more favorable for shale gas enrichment compared to “dike type” intrusions, which have a limited impact on shale gas enrichment. (3) The mineralization process of CBM, shale gas, and iron ore is influenced by Yanshanian-period magma. The enrichment degree of CBM and shale gas exhibits an inverse correlation with the distance from the magmatic intrusion. Iron deposits demonstrate a close association with the magmatic intrusion, with enhanced enrichment along the rock layer. The results indicate that the destruction of the NCC triggered intense metasomatism in the deep cratonic fluids, serving as the primary driving mechanism for large-scale mineralization during the Yanshanian period. Magmatic intrusions bring hydrothermal fluids conducive to mineralization, and the heat release from these intrusions promotes thermal evolution, hydrocarbon generation, and the enrichment of organic-rich strata.

Interannual variability of coastal upwelling features along the eastern and western margins of the Arabian Sea

ABSTRACT The Arabian Sea (AS), a basin in the North Indian Ocean (NIO), possesses strong coastal upwelling in its eastern and western margins. The spatio-temporal variability of upwelling over Somalia, Oman and the southwest coast of India is analysed using observed datasets. The spectral analysis of upwelling indices highlights that the semi-annual and annual frequencies were dominant by two orders of magnitude compared with the inter-annual variability over these upwelling zones. The inter-annual variability of coastal upwelling was demarcated with variations in the causative forcing of upwelling associated with the positive modes of Indian Ocean Dipole (pIOD), El-Niño Southern Oscillation (El-Niño) and combined pIOD and El-Niño events over the southwest coast of India (SWCI) and Somalia. Along SWCI, the sea surface temperature and meridional wind stress weakened leading to warming associated with the suppression of upwelling during El-Niño, pIOD and combined events. Along Somalia, the upwelling favourable wind stress showed slight weakening due to pIOD and strong decline due to El-Niño and combined modes. Along Oman, the upwelling favourable wind stress indicated negligible changes due to pIOD, an increase due to El-Niño and a slight decline due to combined modes.

Russian war, Estonian exceptions: Sovereignty, governmentality, biopolitics

The author analyzes Estonia as a case study to explore two interrelated research questions – how exceptions are produced and reversed through the mechanisms of sovereignty and governmentality projected onto geo- and biopolitical domains, and how the new practices of exceptionalization and de-exceptionalization contribute to the emergence of a new spatial order at Europe’s eastern margins? Three types of policies unfolded in Estonia as reactions to the Russian war against Ukraine are identified. First, the Estonian government introduced extraordinary measures based on the logic of national interests, which left much space for discretionary power to define risks, threats, and dangers. Secondly, some policy domains were intentionally de-exceptionalized for the sake of their better integration into Estonian normative space and as a reaction to the effects of the war. Third, in some cases there were exceptions from exceptions, which meant certain steps back toward normalization of the previously taken exceptional measures. The theoretical frame of the article consists of two nodal concepts – sovereignty and governmentality to be projected onto geo- and biopolitics treated as spheres in which sovereign and governmental powers operate and expose their political qualities.