Weathering Crust Research Articles

The Color Formation of “Lumu Stone” in the Weathering Processes: The Role of Secondary Hematite and Goethite

Rocks and minerals buried in the earth’s surface usually undergo weathering processes and change color in the burying environment. A kind of yellow Chinese stamp stone named “Lumu stone”, which is buried in a yellowish weathering crust (yellowish soil), was selected to investigate its color changes in the weathering processes. In this study, the appearance features, mineral components, micromorphology, spectroscopy characteristics, and color causation of the “Lumu stone” were studied by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), an electron probe microanalyzer (EPMA), a laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), and a UV-Visible (UV-Vis) spectrum. The “Lumu stone” usually exhibits a darker yellow outer layer and a lighter yellow core, suggesting that yellow color permeated into the stone from the surface to the core gradually and the color is secondary forming. The results from XRD and SEM show the studied samples are mainly composed of dickite and illite. The individual particles of the dickite and illite are about 2–5 μm, randomly distributing in the three-dimensional space and constituting voids among the particles. The acid pickling experiments using HCl coupled with KSCN confirmed that the mineral phases that caused the yellow color of the matrix are iron oxide and hydroxide. On the other hand, goethite and hematite were observed gathering in the yellow and brown-red cracks on the “Lumu stone” by SEM study. However, iron oxide and hydroxide in the matrix were difficult to observe and detect among the dickite and illite aggregates by SEM and XRD methods. It indicates that they may be nanoscale in size and very low in content. According to the calculation of the second derivative of Kubelka-Munk (K-M) transformed diffuse reflection spectroscopy (DRS) curves obtained from UV-Vis, the characteristic peaks of goethite and hematite were found in the yellow matrix, and their contributions to the color were confirmed. The concentrations of goethite and hematite were calculated to be 0.32 to 1.87 g/kg and 0.22 to 0.93 g/kg in the studied samples, respectively. In this study, a series of methods were employed to detect very low levels of goethite and hematite in the samples undergoing weathering processes. Additionally, nanoscale goethite and hematite were considered newly formed minerals when buried in the weathering processes and may gradually move into the voids among phyllosilicate particles. Therefore, they turned the “Lumu stone” yellow.

STRUCTURAL AND LITHOLOGICAL MODEL OF THE WESTERN SECTION OF THE GLUKHIVETSKY DEPOSIT OF THE ELUVIAL KAOLIN

The material on the western section of the Glukhivetsky deposit of eluvial kaolins, which is located in the Koziatyn district of the Vinnytsia region, near the village of Glukhiv and is part of the Glukhivetsko-Turbivsky kaolin region.
 The causal relationships of different petrotypes of bedrock with the thickness, material composition and zonation of the weathering crust and, as a consequence, with the structural and lithological structure of the eluvial kaolin deposit and its qualitative indicators are revealed.
 Based on the coordinates and description of wells, the relief of the top and of the bottom surface of the kaolinite-hydromicaceous zone of the weathering crust and of the layer of eluvial kaolins, as well as the lateral change in their average thickness, were studied. Correlations between of the top and of the bottom surface and thickness of the kaolinite-hydromicaceous zone and eluvial kaolins have been studied. Based on the results of well testing and chemical analysis of kaolins, the lateral distribution of the average contents of iron and titanium oxides and the average content of the whiteness index, as well as their correlations, was studied. 

Effects of Ammonium Salts on Rare Earth Leaching Process of Weathered Crust Elution-Deposited Rare Earth Ores

In order to reveal the influence of ammonium salts on the rare earth leaching process of weathered crust elution-deposited rare earth ores, ammonium acetate, ammonium chloride, and ammonium sulfate were used as leaching agents. The effects of the leaching agent on the rare earth leaching efficiency and the expansion, dissolution, and transformation behavior of clay minerals in the rare earth leaching process were studied. The results showed that rare earth leaching efficiency followed the order ammonium acetate > ammonium chloride > ammonium sulfate, with values of 90.60%, 85.96%, and 84.12%, respectively. The swelling ratio of clay mineral followed the order ammonium acetate < ammonium chloride < ammonium sulfate; the clay mineral swelling ratio was 2.09% when ammonium acetate was the leaching agent. Thermogravimetric analysis showed that the interlayer water content was the lowest when ammonium acetate was used as the leaching agent. Under the conditions of different leaching agents, the clay mineral contents changed from illite and halloysite to smectite and kaolinite. When ammonium acetate was used as the leaching agent, the relative conversion of illite was 1.49%, and that of smectite was only 0.17%. SEM analysis showed that the clay minerals expanded and dissolved obviously when ammonium chloride and ammonium sulfate were used as the leaching agents. Meanwhile, the clay mineral layered structure was relatively complete when ammonium acetate was used as the leaching agent. Therefore, when ammonium acetate was used as the leaching agent, it had the least effect on the swelling, dissolution, and transformation of clay minerals. This can provide a theoretical basis for the safe production of weathered crust elution-deposited rare earth ore, and for the screening of green and efficient leaching agents.

Typomorphic features of native gold in the placers of the Tarlau area (Southern Urals)

Typomorphic features of native gold from two placers of the Tarlau area were studied. It was demonstrated that migration of the gold particles had been proceeded both through transition to lower hypsometric levels in the weathering crust and during transportation by water flows. The complex of the studied features allows one to testify for the gold deposition within a single stage of the ore process, to suggest that the primary source was represented by a gold-sulfide-quartz type occurrence, and to assign the Tarlau and Murin placers to the origin section of the scattering zone of a unified placer.

Development characteristics and main controlling factors of Carboniferous volcanic reservoirs in the Shixi area, Junggar Basin

The Carboniferous volcanic reservoirs in the Shixi area of the Junggar Basin are complex and diverse. Identifying the characteristics and main factors controlling high-quality volcanic reservoirs is the key to increasing oil and gas reserves and production in this area. Through core observations, thin section identification, physical property and pore structure analyses, combined with production data, the main controlling factors and development modes of high-quality reservoirs were analysed. The results show that the Carboniferous strata in the Shixi area mainly contain andesite and dacite of overflow facies, followed by volcanic breccia and tuff of explosive facies. Volcanic reservoirs in the study area are high-porosity–low-permeability and medium-porosity–low-permeability reservoirs. Volcanic breccia of explosive facies has the best physical properties, showing the characteristics of high porosity and medium permeability. The reservoir space is mainly composed of gas cavities, corrosion pores and fractures, among which the corrosion pores are the most important reservoir spaces of the Carboniferous volcanic rocks. Lithology and lithofacies, weathering and corrosion, and fractures are the main factors controlling the development of high-quality volcanic reservoirs. Volcanic rocks that had experienced weathering and denudation for a long time developed a large number of secondary corrosion pores due to the corrosion of soluble minerals or volcanic ash. Fractures further improved the physical properties, causing volcanic rocks to eventually develop into weathering crust reservoirs. The physical properties of the volcanic rocks far away from the weathering crust were improved through primary gas cavities and structural fractures, and these volcanic rocks eventually developed into the inner reservoir.

The World’s Largest Bauxite-Bearing Province, Fouta Djallon–Mandingo (West Africa). Part 4: a Zoning Mechanism in Laterite Bauxite-Bearing Weathering Crust

The results of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust, of the very large bauxite-bearing province, Fouta Djallon–Mandingo, thanks to a reliable factual base, made it possible for the first time to draw a number of important conclusions about the conditions and features of zoning formation in the lateritic weathering profile. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: an upper one, consisting of hydroxides and oxides of iron and aluminum, and a lower one, composed of clayey eluvium and products of hydration and decomposition of aluminosilicates—polymineral clays and kaolinite. In both columns, the processes of change begin with the same rainwater, but differ in the hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Features of biological and soil processes and hydrodynamics and hydrochemistry in the weathering profile lead to a threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidation, reduction, gley, adsorption) barriers, which is the main mechanism of zonal distribution of matter in lateritic weathering crusts.

Regional unconformities and their controls on hydrocarbon accumulation in Sichuan Basin, SW China

Based on outcrop, seismic and drilling data, the main regional unconformities in the Sichuan Basin and their controls on hydrocarbon accumulation were systematically studied. Three findings are obtained. First, six regional stratigraphic unconformities are mainly developed in the Sichuan Basin, from the bottom up, which are between pre-Sinian and Sinian, between Sinian and Cambrian, between pre-Permian and Permian, between middle and upper Permian, between middle and upper Triassic, and between Triassic and Jurassic. Especially, 16 of 21 conventional (and tight) gas fields discovered are believed to have formed in relation to regional unconformities. Second, regional unconformity mainly controls hydrocarbon accumulation from five aspects: (1) The porosity and permeability of reservoirs under the unconformity are improved through weathering crust karstification to form large-scale karst reservoirs; (2) Good source-reservoir-caprock assemblage can form near the unconformity, which provides a basis for forming large gas field; (3) Regional unconformity may lead to stratigraphic pinch-out and rugged ancient landform, giving rise to a large area of stratigraphic and lithologic trap groups; (4) Regional unconformity provides a dominant channel for lateral migration of oil and gas; and (5) Regional unconformity is conducive to large-scale accumulation of oil and gas. Third, the areas related to regional unconformities are the exploration focus of large gas fields in the Sichuan Basin. The pre-Sinian is found with source rocks, reservoir rocks and other favorable conditions for the formation of large gas fields, and presents a large exploration potential. Thus, it is expected to be an important strategic replacement.

Typomorphic Features and Source of Native Gold from the Sykhoi Log Area Placer Deposits, Bodaibo Gold-Bearing District, Siberia, Russia

The Bodaibo gold-bearing district in the Lena gold province of Siberia is one of the largest and oldest placer gold-bearing provinces in the world. Approximately 1650 tons of gold has been extracted from the region. Precise studies on the source of these unique placer deposits are lacking and still controversial. Native gold from four different locations was gathered to investigate its morphology, chemical signatures, structure and inclusions. Some data on primary bedrock mineralization were obtained from the published literature. The linear weathering crusts developed along the zones of disjunctive dislocations near the Sukhoi Log gold deposit were researched. If they coincided with zones of low-grade veinlet-disseminated gold–quartz–sulphide mineralization with small gold grain sizes, a supergene replacement of primary mineralization was known to have occurred, accompanied by the formation of gold-rich rims and an increase in the size, content and purity of gold. Such mineralization associated with linear weathering crusts can be a source of local eluvial–proluvial placers, while placers of large valleys are formed due to low-sulphide gold–quartz lodes.

The Dimensional Effect and Crystal Morphological Peculiarities of Gibbsite in a Bauxite-Bearing Weathering Crust

The correlation between the crystal morphological peculiarities of gibbsite and its position in a bauxite-bearing weathering profile is revealed from the example of the Tsentral’noe deposit of the Chadobets Uplift. The free space favorable for the growth of gibbsite increases from bottom to top in various parts of the profile as a result of infiltration metasomatosis and various physicochemical conditions. The higher the position of the rock, the higher its porosity. The size of the gibbsite crystals thus increases, and their morphology becomes more complex upward through the section. The results of thermal analysis showed that the higher the sizes of the gibbsite crystals, the higher the amount of boehmite forms upon its heating. These conclusions will help the technologists to choose the most feasible reworking scheme of bauxites.

Quantitative characterization of vertical zonation of Mesozoic granite weathering reservoirs in the coastal area of eastern Fujian Province, China

Weathering crust reservoirs have obvious vertical zonation, which is the focus of weathering crust reservoir research, but there is a lack of quantitative characterization indexes. To achieve the quantitative characterization of granite weathering crust reservoir and provide the basis for oil exploration of granite weathering crust buried hill reservoir, in this paper, the vertical zonation of granite weathering crust reservoir is quantitatively divided by testing and analyzing the uniaxial compressive strength (UCS), magnetic susceptibility (MS), permeability, and chemical index of alteration (CIA) of the Mesozoic granite weathering crust in the coastal area of eastern Fujian. The results show that the granite weathering crust reservoir can be divided into four zones vertically: a soil zone (SZ), weathered and dissolved zone (WDZ), fracture zone (FZ), and bedrock zone (BZ). A cataclastic area is developed in the FZ and BZ, in which structural fractures are well-developed, the fracture surface density is usually greater than 200 m/m2, and the contribution to the fractures in the rock mass is up to about 50%, making this the sweet spot of the reservoir. In the SZ, the rocks are loose, and the pores are well-developed. The UCS is less than 10 MPa, and the average rate of change of the UCS (Δσ) is 0.90. The average permeability is 2823.00 mD, and the average rate of change of the permeability (Δκ) is 5.13. The average CIA is 74.9%. The average clay mineral content is 7%. The rocks in the WDZ have been significantly weathered by physical and chemical processes, and the weathering fractures and dissolution pores are well-developed. The average UCS is 18.2 MPa, and the average Δσ is 0.70. The average permeability is 143.80 mD, and average Δκ is 4.17. The average CIA is 65.3%. The average clay mineral content is 4%. Under the influence of tectonic movement and physical weathering, the rocks in the FZ have developed structural fractures and a few weathered fractures. The average UCS is 57.9 MPa, and the average Δσ is 0.18. The average permeability is 5.50 mD, and the average Δκ is 2.55. The average CIA is 61.6%. The average clay mineral content is 2%. In the BZ, the rocks are intact and hard. The average UCS is 69.9 MPa, and the average Δσ is 0.13. The average permeability is 1.46 mD, and the average Δκ is 1.43. The average CIA is 57.8%. The average clay mineral content is less than 1%. The multi-parameter combination of the UCS, Δσ, permeability, Δκ, CIA, and clay mineral content achieved good results in the division of the zones of the weathering crust. The UCS increases gradually from top to bottom, while Δσ, permeability, Δκ, CIA, and clay mineral content all decrease gradually. In addition, based on the petrophysical parameters of the rocks, including the density, resistivity, and acoustic velocity, a good division effect was also achieved, which can provide a basis for the vertical zonation of the granite buried-hill weathering crust reservoir.

A model of the weathering crust and microbial activity on an ice-sheet surface

Abstract. Shortwave radiation penetrating beneath an ice-sheet surface can cause internal melting and the formation of a near-surface porous layer known as the weathering crust, a dynamic hydrological system that provides home to impurities and microbial life. We develop a mathematical model, incorporating thermodynamics and population dynamics, for the evolution of such layers. The model accounts for conservation of mass and energy, for internal and surface-absorbed radiation, and for logistic growth of a microbial species mediated by nutrients that are sourced from the melting ice. It also accounts for potential melt–albedo and microbe–albedo feedbacks, through the dependence of the absorption coefficient on the porosity or microbial concentration. We investigate one-dimensional steadily melting solutions of the model, which give rise to predictions for the weathering crust depth, water content, melt rate, and microbial abundance, depending on a number of parameters. In particular, we examine how these quantities depend on the forcing energy fluxes, finding that the relative amounts of shortwave (surface-penetrating) radiation and other heat fluxes are particularly important in determining the structure of the weathering crust. The results explain why weathering crusts form and disappear under different forcing conditions and suggest a range of possible changes in behaviour in response to climate change.

THE WORLD’S LARGEST FOUTA DJALLON–MANDINGO BAUXITE PROVINCE (WEST AFRICA): PART 4. THE MECHANISM OF ZONING FORMATION IN LATERITE BOXITE-BEARING WEATHERING CRUSTS

Obtained as a result of detailed exploration and year-round observations of the hydrogeological regime at large deposits, as well as special hydrochemical studies of various types of water and changes in the gas composition of the underground atmosphere in the lateritic weathering crust of the largest bauxite-bearing province FDM, thanks to a reliable factual base, allowed us to draw a number of important conclusions on the conditions and features of the formation of zoning in the lateritic weathering profile for the first time. The weathering profile consists of two metasomatic columns spatially combined in plan, but vertically separated: the upper, lateritic cover, composed mainly of the products of the final hydrolysis of lateritic weathering, that is, hydroxides and oxides of iron and aluminum; the lower one, composed of clayey eluvium, products of hydration and decomposition of aluminosilicates - polymineral clays and kaolinite. In both columns, the processes of changing begin with the same rainwater, but differ in hydrodynamic parameters in each of the columns. Changes in the weathering profile occur in accordance with the main patterns of low-temperature infiltration metasomatism. The modern hydrogeological and gas regime in the bauxite-bearing lateritic covers controls the mineralogical and geochemical zoning. Peculiarities of biological and soil processes, hydrodynamics and hydrochemistry in the weathering profile lead to the threshold nature of the change in physicochemical and biochemical conditions, providing the action of geochemical (oxidative, reducing, gley, adsorption) barriers - the main mechanism of zonal distribution of matter in lateritic crusts.

DIMENSIONAL EFFECT AND CRYSTALLOMORPHOLOGICAL FEATURES OF GIBBSITE IN THE BAUXITE-BEARING WEATHERING CRUST

Using the example of the Central Chadobets uplift deposit, the relationship of the crystallomorphological features of gibbsite with its position in the bauxite-bearing profile of the weathering crust is revealed. From the down up, in various parts of the profile, as a result of infiltration metasomatosis and various physico-chemical conditions, there is an increase in free space, contributing to the growth of gibbsite crystals. The higher the rock lies, the more porous it is. Thus, in the down-up section, the size of gibbsite crystals increases, its morphology becomes more complicated. By the method of thermal analysis, it was found that the larger the size of the gibbsite crystals, the more boehmite is formed when it is heated. These conclusions will help technologists to choose the most rational scheme for processing bauxite.

Geophysical research of underground hydraulic structures, old Glubochinsky water tunnel case study

Research objective is to study the features of geophysical fields and parameters in the area of the artificial underground water tunnel and estimate the capabilities of geophysical methods of identifying hidden underground industrial facilities. Methods of research. Measurements of self-potential signals (SP) were carried out using nonpolarizing electrodes and an electrical exploration receiver. The magnetic exploration was carried out by a proton magnetometer. Electrotomography was carried out using multielectrode electrical survey equipment with a Schlumberger symmetrical scheme of surveys. The microseismic background was recorded using an autonomous seismic station. The georadar survey was carried out using the SIR-3000 ground penetrating radar and antennas with the frequencies of 100 MHz and 270 MHz. Results. Based on the survey results, graphs of magnetic and self-potential fields, electrotomographic and microseismic sections, and radarogram were built on the research profile. The research has shown different levels of the magnetic field and the SP in the area of volcanic rocks and dikes of gabbro-dolerites occurrence. A significant increase in microseismic noise was observed with an increase in the weathering crust thickness. A local decrease in the SP potential, abnormally high values of specific electrical resistivity and intensive reflections of radio waves from the tunnel top were recorded above the underground water tunnel. Conclusions. Qualitative and quantitative geophysical characteristics were obtained in the area of the old underground water tunnel. The research showed different levels of the magnetic field and spontaneous polarization potentials in the occurrence area of rocks of different composition. A significant increase in microseismic noise was recorded with an increase in the weathering crust thickness. Geophysical signs of the boundaries between geological structures and artificial underground objects are revealed. The exact position and depth of the old underground tunnel of Glubochinsky hydraulic structures was determined.

Review of rare earth element (REE) adsorption on and desorption from clay minerals: Application to formation and mining of ion-adsorption REE deposits

Ion-adsorption rare earth elements (iREE) deposits are the globally predominant source of heavy rare earth elements (HREE), which are mainly discovered and mined in southern China. This paper reviews the genesis and mining mechanisms of iREE deposits. These deposits are mainly formed in the weathering crust of rare earth elements (REE)-rich granites, volcanic rocks and metamorphic rocks. During the weathering and eluviation, REE are released by the dissolution of REE-bearing minerals, depending on the weathering resistance of such minerals. Then, aqueous REE cations migrate downwards and are adsorbed by clay minerals. The adsorption and fractionation of REE are affected by variations in oxygen, pH and ionic species and strength. REE are mainly adsorbed on clay minerals through ion exchange and surface complexation. The former reaction cannot cause evident REE fractionation, whereas the latter induces an enrichment of HREE over LREE. The enrichment and fractionation characteristics of REE are also constrained by their occurrence states. REE with different occurrence states can be distinguished via sequential extraction, and the micro-occurrence states of REE can be probed using high-sensitivity, high-resolution characterisation. Furthermore, the leaching mechanism of iREE deposits is summarized, where REE are exchanged by foreign cations. Ammonium sulphate is the main leaching agent, but its excessive use can cause serious environmental pollution. Thus, leaching agents with little or no ammonium, such as MgSO4 and CaCl2, have been recommended. The controlling factors of REE leaching are the concentration of leaching agents, pH, temperature and solid/liquid ratio. The above summary deepens the understanding of the formation mechanism of iREE deposits and provides beneficial information for the efficient but green mining of iREE deposits.

Rare Earth Occurrence States of Weathered Crust Elution-Deposited Rare Earth Ores in Southern Yunnan

To reveal the regularity of variation in the rare earth occurrence states of weathered crust elution-deposited rare earth ores, ore samples from different weathering crust layers were obtained by performing the sequential extraction procedure. The order of rare earth contents firmly obeyed the following sequence: the weathered layer > humic layer > partly weathered layer. The occurrence states of rare earth elements were mainly the ion exchange state, carbonate bound state, iron–manganese oxide state, organic binding state and residual state. The proportions of rare earth elements found in the rare earth ion exchange state of the weathered layer, humic layer and partly weathered layer were 78.55%, 73.53% and 53.88%, respectively. The light rare earth elements (LREEs) found in the rare earth ion exchange state were enriched in the upper part of the weathering crust, while the heavy rare earth elements (HREEs) were enriched in the lower part. There were also obvious negative anomalies in the content of cerium in the ion exchange state. The content of rare earth elements found in the carbonate bound state was small, and the rare earth partition pattern was basically consistent with that of the ion exchange state, which had little effect on the differentiation of the rare earth elements. The iron–manganese oxide state was mainly enriched with cerium, and the content of cerium increased with the depth of the weathering crust. The iron–manganese oxide state was the main factor causing the phenomenon of the anomaly in the cerium content. Meanwhile, the iron oxides in the iron–manganese oxide state were mainly hematite and goethite. The organic binding state mainly beneficiated yttrium and cerium by complexation and certain adsorption. The content of elements found in the rare earth residual state was related to the degree of weathering and reflected the release sequence of rare earth elements in the mineralization process. Clarifying the rare earth occurrence states is conducive to better revealing the metallogenic regularity of weathered crust elution-deposited rare earth ores. In addition, the results can provide a valuable reference for expanding the available rare earth resources and the efficient comprehensive utilization of rare earth ore.

Reflection of peculiarities of the gold-bearing weathering crust composition in mineralogical halos and geochemical anomalies on the example of some sites of the Eravnensk prospective area, Republic of Buryatia

The composition and gold-bearing potential of linear-areal weathering crusts of the Eravnensk prospective area in the Republic of Buryatia, that are located within complex gold-bearing ore prospects, are considered. Data on the forms of gold occurrence and some of the gold features are provided. The character of gold ore mineralization in deluvium and proluvium is shown. The effectiveness and reliability of various geochemical methods are compared in relation to the landscape conditions of the work area.

Dynamic background on formation, evolution, and later reformation of the Late Paleozoic–Early Mesozoic Basin in Songliao and its significance for hydrocarbon exploration

Located on the Songnen block of the Northeast Asia block group, the Songliao Basin is sandwiched by three major plates in Siberia, North China, and the Pacific Ocean. The recognition of the basin's properties and the dynamic processes of formation, evolution, and late reformation of the Late Paleozoic–Early Mesozoic Basin (LP-EMB), which has suffered from intense multi-stage, and various types of late reformation, are always controversial. On the basis of previous research on the regional tectonic geological background, combined with petrochemical and chronological data from core samples and seismic data, the attributes, evolution process, and late reformation of the LP-EMB and its dynamic environments have been deeply analyzed. Since the Late Paleozoic, it has successively experienced the development of Late Hercynian to Early–Middle Indosinian rifts and subsequent multi-stage superimposed transformation stages, which can be divided into the near-north-trending thrust reformation in the Late Indosinian, the near-west-trending thrust reformation in the Early Yanshanian, the differential extensional reformation in the early Late Yanshanian, the strike-slip shearing and deep burial reformation in the middle Late Yanshanian, and the strike-slip compression fold transformation in the late Late Yanshanian to the early Himalayan. The formation of the LP-EMB was mainly controlled by back-arc extension caused by the subduction and retreat of the paleo-Pacific Plate and partly by the closure of the Paleo-Asian Ocean between the North China Plate and the Northeast Asia micro-block group. The later reformation stages were closely related to the collision extrusion, strike-slip activity, and deep mantle activity caused by either the relative convergence movement between Songnen and other micro-blocks in the Northeast China micro-block group or by the remote collision effect of the Northeast China micro-block group and the surrounding plates. The inner fault zone (body), which was formed by multi-phase fault cutting, and the top weathering and denudation unconformity surface, are potential sites of hydrocarbon accumulation, from which natural gas has been transported along the fault and fracture belt into the weathering crust and the inner fracture zone in the Upper Paleozoic–Lower Mesozoic (UP-LM). This study significantly expands our knowledge of the tectonic evolution and gas exploration of the Songliao Basin.

ОЦЕНКА САДОПРИГОДНОСТИ ДЕРНОВО-ПОДЗОЛИСТЫХ ПОЧВ НА КРЕМНИСТЫХ ПОРОДАХ ЮГО-ЗАПАДА КАЛУЖСКОЙ ОБЛАСТИ

The data of the survey of sod-podzolic soils under industrial gardens on the weathering crust of trepels and flanks and on water-glacial deposits underlain by siliceous rocks are presented. The main reason for the op-pression and death of trees is a sharply acidic reaction deeper than 50 cm (pHKCl < 3.9), the exchange Al content is above the toxicity threshold (>0.9 mmol /100g of soil). Soils on homogeneous sediments are characterized by a density of 0.6-0.8 g / cm3, an active moisture range of 25-30%, an average content of exchangeable Ca and Mg, soils on binomial deposits – a density of 0.9-1.3 g / cm3, an active moisture range of 5-15%, a low content of exchangeable Ca and Mg. Before laying perennial plantings, it is neces-sary to introduce dolomite flour with a high Mg content into planting pits, the approximate dose is 15-25 t / ha. In gardens on homogeneous rocks, moisture–charging irrigation is possible, on binomial deposits, drip irrigation or fertigation is better. Sod-podzolic soils on homogeneous sediments are diagnosed by a power-ful 50-70 cm A2 horizon. In the profile of soils on binomial deposits under the A2 horizon with a thick-ness of 25-30 cm, the Bf horizon of ochre color is formed.

What kind of gully can develop into benggang?

Benggang is a special landform with serious erosion damage, resulting in intensive soil erosion and land degradation. However, few studies have been conducted on prediction and critical conditions of benggang formation. This study analyzed the topography, hydrogeological conditions, number and size of benggang in Yuankengshui watershed (Guangdong, China) by extracting a digital orthophoto map (DOM) and digital surface models (DSMs) based on unmanned air vehicle (UAV) aerial images. The benggang number was found to increase first and then decrease with the increase of elevation, slope gradient and slope length, in contrast to a decrease with the increase of benggang catchment area. The elevation distribution is consistent between the small watershed and regional benggang, with the maximum benggang density in the elevation range of 200–250 m. The maximum benggang number is in the area with a slope gradient and slope length of 25-26° and 61–70 m, respectively, and the average benggang catchment area is 0.3 ha. Benggang formation and development was mainly affected by benggang catchment area and slope drop, whose correlation coefficients with benggang area and collapsing wall height were 0.957, 0.633 and 0.581, 0.568, respectively (P < 0.01, n = 296), enabling the establishment of their relationship with benggang development, which can be used to estimate whether the hydrological condition of the slope meets the conditions for benggang formation. Collapsing wall height is an important indicator of benggang formation, and under the conditions that the predicted value of the developed gully depth is greater than 3 m and the granite weathering crust is more than 10 m, the gully in such an area can develop into benggang. Meanwhile, benggang is shown to differ from gully in catchment area, lithology demand, shape, dominant erosion type, and erosion modulus. Therefore, benggang and gully should be treated differently when adopting control measures. This study may enrich our understanding and prediction of benggang development.