Illite Content Research Articles

Implications for Provenance since the Last Glaciations in Southeastern Andaman Sea Sediments by Clay Mineralogy

This study presents high-resolution clay mineralogy of Core MASS-III-10, located in the southeastern Andaman Sea. The study aimed to investigate terrigenous sedimentary input from various potential provenances throughout different periods of geological time. The clay mineral assemblages of MASS-III-10 reveal a high amount of smectite at 73% (65-79%), a moderate kaolinite at 12% (10-17%), and a low illite and chlorite content(<15%) over the last 45 ka. Provenance analysis suggests the most fine-grained terrigenous sediments originated from the Irrawaddy Delta Shelf (IDS), with minor sediments deriving from the Andaman Islands, the East Continental Shelf (ECS), and Sumatra provenance. The results show that IDS were predominantly smectite (~44%) while the ECS largely produced kaolinite (47%). The provenance interpretation based on the smectite content revealed that over time there has been no change in the main source of sediment in the Andaman Sea, despite changes in the volume of sedimentary input. Since the last glaciation, the Myanmar provenance (including IDS) has always contributed clay minerals, while other sources made up only minor contributions to the Andaman Sea. The clay minerals from the Myanmar provenance increased when the sea level was at a low stand (MIS 2), potentially due to shoreline retreat which enabled easier transportation of sediment from other sources. During the interglacial period (MIS 1 and 3), the study found a decrease in Myanmar-sourced clay minerals, which may be because the higher sea level made clay mineral deposition more difficult.

Influence of reservoir properties on the adsorption capacity and fractal features of shales from Qinshui coalfield

Abstract To investigate the adsorption capacity and fractal features of coal-measure shales and understand the influence of shale properties on the adsorption capacity and fractal features, a series of experiments were conducted on fifteen shale samples from Shanxi-Taiyuan Formations in the Yushe-Wuxiang Block, South-Central Qinshui Basin. The results indicate that organic and clay minerals are the two adsorption carriers for coal-measure shales, Langmuir volume (VL) of shales increases as the total organic matter (TOC) content or clay minerals content increases. Additionally, there is a negative correlation between VL and quartz content. As vitrinite reflectance (Ro%) increases, VL has an evolutionary path of first increasing and then decreasing, the maximum value is reached at near Ro = 2.1%. Furthermore, VL increases as specific surface area (SSA) increases or average pore diameter (APD) decreases. The coal-measure shales exhibit double fractal features. The fractal dimension of pore surface (D1) and fractal dimension of pore structure (D2) vary from 2.4899 to 2.6272 and 2.7318–2.840, respectively. The fractal dimensions show an increasing trend as SSA increases. As pore volume increases, D1 presents a slight increasing trend while D2 shows a decreasing trend. And fractal dimensions increase as APD decreases. The relationships of TOC with D1 and D2 are opposite. Clay minerals are the determining factor of the fractal dimensions as the fractal dimensions (D1 and D2) show an increasing trend as clay minerals content increases. An increase in quartz content or organic matter maturity will greatly reduce the heterogeneity of shales. As for non-clay minerals, the fractal dimensions (D1 and D2) show an increasing trend as pyrite content increases, while D1 increases and D2 decreases as carbonate mineral content increases. Regarding the composition of clay minerals, D1 increases as the mixed layers of illite/smectite (I/S) and illite contents increase or kaolinite and chlorite contents increase, while D2 is opposite. Shales with higher fractal dimensions develop stronger adsorption capacity while shales with higher D1 and lower D2 develop lower Langmuir pressure (PL).

Origin of Smectite in Salinized Soil of Junggar Basin in Xinjiang of China

In this paper, salinized soils with different degrees of salinity are sampled in Junggar Basin of Xinjiang of China. The X-ray diffraction, transmission electron microscopy, and inductively coupled plasma mass spectrometry are employed to investigate the morphology and distribution characteristics of smectite in salinized soil profiles. In the salinized soil profiles of this region, crystals of smectite are poor where lattice fringes are not parallel. In all soil layers, the content of smectite in the soil increases with the decrease in content of illite, which has demonstrated significant negative correlation (r = 0.79, n = 50, p < 0.01) between illite and smectite. This phenomenon has demonstrated that illite may be transformed into smectite in salinized soils of studied regions. In general, the transformation process of illite to smectite is affected by climate condition. The δ18O values of secondary carbonate in the 0–10 cm soil layers is higher than that in deep soil layers, which indicates that δ18O concentrates in surface soil and reflects temperature rise during soil layer formation. The δ13C values of secondary carbonate and soil organic matter in 0-10cm soil layers are higher than that in deep soil layers. It indicates that C4 plants were the main plants, which reflects that the climate was relatively dry during the formation of the surface soil. Thus, the climate during the surface soil formation is arid, which is not conducive for leaching K+ from illite of the 0–10 cm soil to form smectite. As a result, the content of the smectite becomes lowest in the soil surface. In the relative humid condition of deep soil layers, the K+ of the illite of the soil would be relative easily leached and more smectite may be formed. Furthermore, the presence of salt in the salinized soil would promote the formation of smectite in Junggar Basin of Xinjiang. A lot of Ca2+, Na + and Mg2+ in the soil solution of salinized soils would enter into the illite and occupy K+ positions. The studied result shows that the amount of smectite would increase with the increase of salt below 10cm of the soil layer, where the amount of smectite would be significantly correlated with soil electrical conductivity (r = 0.64, n = 39, p < 0.01). In the Junggar Basin in Xinjiang, therefore, the salinized soil below 10 cm would have the necessary water conditions and chemical components for illite transformation to smectite.

Pore characterization and controlling factors analysis of organic-rich shale from Upper Paleozoic marine-continental transitional facies in western Ordos Basin of China

In China, marine-continental transitional organic-rich shale gas reservoirs are widely distributed. However, studies on pore systems of this kind of gas shales were relatively rare. In this paper, we investigated the problems about characteristics, genesis, structure of pores in upper Paleozoic of western Ordos basin of China.Various types of pores were identified by the images from focus ion beam scanning electron microscopes (FIB-SEM). Meanwhile, in order to have a better understanding of genesis and influencing factors in pore development process and reservoir features, kerogen microscopic examination, content of organic carbon test, X-ray diffraction, nuclear magnetic resonance (NMR), porosity and permeability tests were performed to collect information of organic geochemistry, mineralogy, pore-size distribution, physical properties.Considering the genesis and position of pores, there are six kinds of pore types found in the research area which including organic pores, interparticle pores in minerals, dissolved pores, intercrystal pores in iron-minerals, intrapore in organic-clay complex and micro fractures. The development of organic pores, which are usually in shapes like bubbles or honeycomb, depends on the organic matter maturity, content of illite and illite-smectite(I/S). The growth of interparticle pores, mostly in triangular and irregular shapes, are mainly controlled by buried depth, content of brittle mineral, illite and I/S. Dissolution pores which formed when clay particles dissolved and intercrystal pores exist in iron-minerals grains, have a great relation with the sedimentary environment and the content of clay minerals. The formation of micro fractures is associated with stress and compaction of layers.

Toxicity mitigation and bioaccessibility of the cationic surfactant cetyltrimethylammonium bromide in a sorbent-modified biodegradation study

Biodegradation potential of cationic surfactants may be hampered by inhibition of inoculum at concentrations required to accurately measure inorganic carbon. At >0.3 mg/L cetyltrimethylammonium bromide (CTAB) negatively impacted degradation of the reference compound aniline. We used silicon dioxide (SiO2) and illite as inorganic sorbents to mitigate toxicity of CTAB by lowering freely dissolved concentrations. In an OECD Headspace Test we tested whether 16.8 mg/L CTAB was readily biodegradable in presence of two concentrations of SiO2 and illite. SiO2 adsorbed 85% and 98% CTAB, resulting in concentrations of 2.5 and 0.34 mg/L, mineralized to CO2 >60% within 16 and 23 d, respectively. With 89% and 99% sorbed to illite, 60% mineralization was reached within 9 and 23 d, respectively. However, higher sorbent concentrations increased time needed to reach >60% mineralization. Thus, desorption kinetics likely decreased bioaccessibility. It is therefore essential to determine appropriate concentrations of mitigating sorbents to render a Headspace Test based on carbon analysis suitable to determine ready biodegradability of compounds which might inhibit inoculum. This would avoid use of expensive radiolabeled compounds. However, high sorbent concentrations can reduce bioaccessibility and limit degradation kinetics, particularly for relatively toxic substances that require strong mitigation.

Potassium supplying capacity of a red soil from eastern India after forty-two years of continuous cropping and fertilization

Fertilizer use in Indian agriculture is skewed towards nitrogen (N) and phosphorus (P), and farmers generally neglect potassium (K) input ignoring K requirement of crops. We, therefore, studied the long-term effect of imbalanced fertilization (i.e. without K) on K supplying capacity of a kaolinitic red soil (Typic Haplustalf) after 42 years of intensive cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 42 cropping cycles from an on-going long-term fertilizer experiment located at Birsa Agricultural University, Ranchi, India, from six treatments, viz. control (unfertilized), fertilizer N, NP, NPK, 150% NPK (1.5 times of NPK) and NPK + FYM (NPK + farmyard manure), along with adjacent uncultivated land. Soil K pools, clay minerals, quantity-intensity relationship and K release kinetics along with grain yield and K uptake of soybean and wheat were studied. Among the treatments, NP treated soils showed the lowest amounts of labile (KL) and non-exchangeable K (Knex). Equilibrium activity ratio (AReK) and non-specifically held K (−ΔK0) were also lowest under NP treatment. The gap between equilibrium exchangeable K (EK0) and minimum exchangeable K (EKmin) was minimum under NP. Cropping and fertilization-induced transformation in clay minerals was noticed wherein continuous neglect of K fertilizer led to a decrease in illite content with a concomitant increase in interstratified minerals. On the other hand, noticeably lower alteration in clay minerals and comparatively less depletion in overall K-supplying capacity of soil were recorded under K addition as compared to imbalanced fertilization (i.e. without K). Soybean showed a significant positive response to K application. The study thus underlined the necessity of adequate K input for the sustenance of soil health, inherent K-supplying capacity and crop productivity.

Experimental evidence for abiotic formation of low-temperature proto-dolomite facilitated by clay minerals

Abstract The origin of sedimentary dolomite is a subject of long-standing enigma that still awaits resolution. Previous studies have shown that room temperature synthesis of abiotic dolomite is rarely achieved and primary (proto-)dolomite precipitation is closely associated with microbial activities. In this study, we demonstrate through laboratory carbonation experiments that highly negative-charged clay minerals (as indicated by the values of zetal potential) such as illite and montmorillonite can aid the precipitation of abiotic proto-dolomite under ambient conditions, whereas nearly-neutral charged kaolinite exerts negligible influence on such process. In comparison to montmorillonite, illite has higher surface-charge density, thus is more effective in catalyzing proto-dolomite precipitation. Furthermore, the signal of proto-dolomite in carbonate neoformations is enhanced with increasing concentrations of illite or montmorillonite. On the basis of these results, we suggest that clay minerals catalyze dolomite formation perhaps via electrostatic binding of Mg2+ and Ca2+ ions and simultaneous desolvation of these strongly hydrated cations, a crucial step for dolomite crystallization. The resulting proto-dolomites display the morphologies, textures, and structures similar to those of biogenic dolomite reported before, which are considered precursors of ordered sedimentary dolomite. Therefore, our results offer a possible route to authigenic dolomite found in sedimentary environments.

Clay minerals in the late Quaternary sediment of Tulare Lake, California: Implications for climate change, weathering, and erosion processes

The clay mineralogy of Tulare Lake sediment was examined to investigate hydroclimatic and environmental changes in the southern Sierra Nevada Mountains (SNM) since the most recent glacial maximum. Evolution of clay mineral assemblages elucidates significant changes in weathering, erosion, and hydroclimatic condition in the catchment. During the last glacial period (24.4–15.1 cal ka BP), low illite content implies less physical erosion of the granitic batholith rocks and a cold and arid environment in the southern SNM. Abrupt increases of illite content at 21.8–20.8 and 17.6 cal ka BP resulted from the glacier advances to the ablation zone and illite-rich glacier flour was transported down to the lake. The gradual increase of smectite induced by progressive depletion of illite-rich glacier flour from 17.6 cal ka BP toward the end of this period indicates climate was beginning to get warm and wet. From 11.9 to 5.3 cal ka BP, two warm and wet periods (10.7–9.4 and 8.2–5.2 cal ka BP) were characterized by high smectite/illite content ratios and low illite crystallinity values, suggesting intensive rainfall precipitation and more physical erosion in the highland and lowland catchment as well as more smectite formation in the terrace soils. Since the last glacial period, physical erosion, in comparison to the chemical weathering, was the dominant process responding to the hydroclimatic change in the Tulare Lake catchment. Moderate to weak chemical weathering was signified by the mostly low illite chemical weathering index of the core sediments. Such results suggest that vegetation cover in the southern SNM was low and limited.

Characteristics, classification and genesis of vertisols under seasonally contrasted climate in the Lake Chad Basin, Central Africa

General properties of Vertisols are known world-wide, but these properties vary in different areas due to specific environmental conditions. The mastery of the specific characteristics of each Vertisols in a given area requires detailed site-scale investigation. This work aims to study the properties of the Lake Chad Basin Vertisols, attempt to highlight their genetic processes and classification. These Vertisols are dark, clayey and massive, very compact, with deep wide-opened cracks and gilgaï micro-relief. They show neutral to slightly alkaline pH, low organic matter content (0.7–2.73%) and high C/N ratio values (7.34–39.64). Ca2+ and Mg2+ are the most represented exchangeable cations (5.92–30.72% and 1.28–5.44%, respectively) on the absorption complex. Smectite is the main clay mineral species, but small contents of kaolinite, illite, quartz and feldspars are also present. The most concentrated elements in the profile are silica (61.07–77.78 wt.% SiO2), aluminium (7.08–15.54 wt.% Al2O3) and iron (1.78–6.92 wt.% Fe2O3). The Si/Al ratio (>2) and chemical index of alteration (CIA) are moderate to high (56.76–88.39) and indicate a moderate to intense weathering. Such properties reflect the pedogenic influence of the environmental factors like contrasting climate, low topographic position and the alluvial parent material. The accumulation of basic cations favours the neosynthesis of smectite minerals typical of a dominant bisiallitisation process. The Vertisols profiles, due to the presence of a perched water table, enable to classify these soils as Epiaquerts and Endoaquerts Vertisols (USDA soil taxonomy) and Gleyics and Fulvics Vertisols (WRB). Their physical characteristics and notably their difficult water management constitute a limitation to agricultural activities.

An Experimental Study of Mineral and Microstructure for Undisturbed Loess Polluted by Landfill Leachate

To investigate the shear strength and microstructure of undisturbed loess polluted by landfill leachate, a series of laboratory tests were carried out to determine the shear strength, mineral composition, surface morphology, particle size distribution and pore characteristics of the loess. The stress-strain curve of undisturbed soil polluted by landfill leachate showed typical strain-softening behavior. The deviatoric stress, cohesion and angle of shearing resistance of undisturbed soil decreased at increased landfill leachate concentrations, decreased by 31.03%, 30.01%, respectively. But pore water pressure was positively related to leachate concentrations. The content of primary minerals remained stable, and the content of montmorillonite and illite decreased with increased leachate concentration, reduced by 26.02%, 23.93%, respectively. Soil structure changed into an unstable honeycomb structure when the leachate concentration increased. Moreover, the average particle size decreased by 62.1%, and the specific surface area increased and then stabilized at 500 ~ 650 m2/kg. The soil particles became nonuniform and porous and their sizes gradually decreased. The pore radius of soil mainly ranged from 0.02 μm to 1 μm. The maximum radius and optimal radius of the pore increased when the leachate concentrations increased.

Giant bauxite deposits of South China: Multistage formation linked to Late Paleozoic Ice Age (LPIA) eustatic fluctuations

The Lower Carboniferous Jiujialu Formation bauxite deposits at Zunyi, northern Guizhou are distinguished by their great thickness (to 110 m) and cyclic alternation of bauxite ore and bauxitic claystone layers. These features are typical of the Kazakhstan subtype of karst bauxite deposits, although the genesis of this type of deposit is poorly understood. Here, we undertook a petrological, mineralogical, and geochemical study of the Zunyi deposit in drillcore ZK5600 to gain insights into its formation history. The Zunyi profile contains seven bauxite cycles, as recorded by petrological, mineralogical and geochemical features, indicating a multistage formation history. Each cycle is composed of a lower bauxitic claystone layer and an upper bauxite ore layer. The bauxite ore is characterized by high Al2O3, high Al-mineral (diaspore), and low SiO2 content. Positive Ce anomalies, high CIA values (>90), and strong depletion of major elements indicate that the bauxite ore formed through intense chemical weathering and leaching in a well-drained soil environment. The bauxitic claystone is characterized by relatively lower Al2O3 and higher SiO2 and clay mineral (mostly illite) content. This lithology exhibits both negative and positive Ce anomalies, moderate CIA values (70–80), and enrichment of some elements (e.g., Fe, K), indicating formation through moderate chemical weathering in a poorly drained soil environment. Secular variations in chemical weathering intensity and soil drainage conditions were linked to regional hydrologic changes. During the early Carboniferous, the Zunyi area was located in a karstified coastal upland setting, and its hydrologic system was affected by glacio-eustatic fluctuations. High groundwater table elevations during eustatic highstands led to formation of bauxitic claystone layers, whereas low groundwater table elevations during eustatic lowstands led to formation of bauxite ore layers.

Influences of organic matter and kaolinite on pore structures of transitional organic-rich mudstone with an emphasis on S2 controlling specific surface area

Nanopore networks in organic-rich mudstone play a key role in providing pore space, surface area and channels for gas storage and migration. Controls of nanopore development are still poorly understood, especially for transitional mudstone. Differing from marine and lacustrine mudstone, transitional mudstone is characterized by high kaolinite and low illite contents, and complex organic input. Six transitional mudstones in Linxing Area, eastern Ordos Basin were selected to figure out the influence of kaolinite and organic matter (OM) on pore structures. Sample preparation (OM-removal and kerogen isolation), mineralogical, organic petrographic and geochemical analyses and textural analysis (low-pressure Ar and CO2 adsorption) were performed. Data in other publications were used to test and perfect our conclusion of specific surface area changing with S2 (second peak in Rock-Eval pyrolysis). Our study demonstrates the pores within 5–50 nm are mainly controlled by quartz contents and are negatively correlated with kaolinite or clay mineral contents. Kaolinite content has little influence on specific surface area, but organic pores, most of which are within 0.3 to ∼5 nm, contribute much to specific surface area. Higher proportion of marine OM has larger organic pores. “Quasi-parabolic +” was used to describe the firstly increasing, secondly decreasing and then uncertain relationship between specific surface area and S2 values. The relationship was found in both transitional and marine mudstones. Surface area changing with S2 is because TOC, thermal maturity and organic input affect organic pore development and also control S2 values. Micropore specific area of kerogen has a firstly increasing and secondly decreasing trend with hydrogen index (HI) values while S2 affects micropore surface area of mudstones. Our findings can be used to estimate pore parameters of organic-rich mudstone.

Состав, структура и селективная сорбция ионов цезия алюмосиликатным сорбентом, полученным из отходов калийногопроизводства ОАО «Беларуськалий»

Представлены результаты комплексного исследования алюмосиликатного сорбента, полу-ченного в результате кислотно-водной обработки образца глинисто-солевого шлама – крупнотоннаж-ного отхода калийного производства ОАО «Беларуськалий» Республики Беларусь. Установлен его вещественный состав и коллоидно-химические характеристики. По минералогическому составу алюмосиликатный сорбент относится к гидрослюдистой группе. Выявлена высокая эффективность извле-чения данным сорбентом ионов цезия из водного раствора. Определены коэффициенты распределе-ния цезия и значения сорбционной селективной емкости цезия для двух типов сорбционных центров алюмосиликатного сорбента.

Factors controlling reservoir properties and hydrocarbon accumulation of the Eocene lacustrine beach-bar sandstones in the Dongying Depression, Bohai Bay Basin, China

Abstract Lacustrine beach-bar sandstone reservoirs are economical important exploration targets in the Dongying Depression, Bohai Bay Basin. The factors that controls reservoir quality and hydrocarbon accumulation in lacustrine beach-bar sandstones were systematically investigated through an integrated petrographic, petrophysical, and diagenesis analysis. The reservoir properties of the beach-bar sandstones are mainly affected by compaction, carbonate cementation and dissolution. Significant negative relationships exist between both the porosity and permeability and the volume of carbonate cement. Carbonate cement is mainly distributed along the sandstone-mudstone contacts. Sandstones with thicknesses less than 1 m are generally tightly cemented to form zones with low petrophysical properties. The material source of the carbonate cement in the tightly cemented zone was highly likely from the interbedded mudstone. Content of carbonate cements in the center of the thick sandstones is low, whereas compaction is the dominant diagenetic process, with some dissolution. There is a positive correlation between the petrophysical properties of the beach-bar sandstones and the content of kaolinite. The petrophysical properties have an inverse correlation with the contents of illite and illite-smectite mixed-layer clays. Reservoir petrophysical property largely controls hydrocarbon accumulation in the beach-bar sandstones. Compared with non-oil bearing sandstones, oil-bearing sandstones have higher porosity and a larger pore-throat size. Sandstones with a porosity of less than 8.5% and/or low permeability of less than 1.02 × 10−3 μm2 are mostly incapable of accumulating oil.

Feldspar Dissolution and Its Influence on Reservoirs: A Case Study of the Lower Triassic Baikouquan Formation in the Northwest Margin of the Junggar Basin, China

Feldspar dissolution is a common feature in clastic rock reservoirs of petroliferous basins and has an important influence on reservoir quality. However, the effect of feldspar dissolution on reservoir quality varies under different depositional environments and diagenetic systems. The study area in this paper is located in the Baikouquan Formation in the northwestern margin of the Junggar Basin, which is significantly influenced by feldspar dissolution. Based on the analyses of core and thin section observations, QEMSEM, XRD, SEM, CL, fluorescence, and image analysis software combined with logging and physical property data, this study shows that feldspar dissolution in the subaqueous distributary channel of a fan delta plain, which has good original physical properties and low mud contents, significantly improves the properties of the reservoir. The main reasons for this are as follows: (1) the sedimentary facies with good original properties and low mud content is a relatively open system in the burial stage. The acidic fluids needed for feldspar dissolution are mostly derived from organic acids associated with the source rocks and migrate to the good-permeability area of the reservoir; (2) the by-products of feldspar dissolution, such as authigenic clay minerals and authigenic quartz, are transported by pore water in a relatively open diagenetic system and then precipitated in a relatively closed diagenetic system; and (3) the clay minerals produced by feldspar dissolution in different diagenetic environments and diagenetic stages have different effects on the reservoir. When the kaolinite content is less than 3%, the illite content is less than 4%, and the chlorite content is less than 12%, the clay minerals have a positive effect on the porosity. These clay minerals can reduce porosity and block pore throats when their contents are larger than these values.

Assessment of chemical and mineralogical composition of tertiary shales from the Nigerian sector of Iullemmeden basin: Implication for paleoclimate and provenance

The Sokoto basin of Nigeria is the southeastern sector of the larger Iullemmeden basin. Shales dated Maastrichtian to Late Paleocene were collected from Illela borehole and Tunga village, part of Sokoto basin and were assessed using chemical (xrf) and mineralogical (xrd) analyses. This was aimed at obtaining detailed information on provenance, paleoclimate and degree of weathering. Chemical composition as obtained from Al2O3/TiO2 ratios indicate mafic – intermediate source, the plot of log (K2O/Na2O) against SiO2 also indicates island arc – active continental margin province. Paleoredox parameters such as Cu/Zn, Ni/Co and V/Cr suggest a well oxidizing condition of deposition. In addition, assemblage of clay minerals (high kaolinite with minor concentrations of Illite and chlorite) is an indicative of a warm and humid (seasonal) sub-tropical climate. Moreover, plotting A12O3 against Na2O, most of the samples plot in the field of Amazon mud, while a few plots close to the post-Archean shale and this suggests that the sediments were exposed to increasing effects of weathering or they were derived from moderate to highly weathered terrain.

A red clay layer in soils of the Yellow River Delta: Occurrence, properties and implications for elemental budgets and biogeochemical cycles

Clay-enriched layers occurring in deltas are important as they reveal erosion, transportation and deposition of source materials from the basin to the coast. In the Yellow River Delta a red clay layer (RCL) with a thickness of 5–50 cm at 1 m depth in the soil profile occurs in the floodplain area dominated by fluvo-aquic soil derived from Yellow River sediments. The RCL typically has a median grain size of <20 μm, redness (a⁎) of >7, and relatively high contents of illite, calcite and iron oxides. In the Loess-Yellow River sediment-Yellow River Delta soil continuum a regime of weathering, mechanical sorting and dilution by carbonates and silica have been important factors altering the elemental geochemistry. The abundance of secondary minerals and deficiencies of silica and zircon in the RCL suggest that it was separated from a mixed source and was likely derived from highly weathered sediments (such as paleosol) from the basin. RCL samples show substantial accumulation of inorganic carbon with enhancement of the organic carbon content, indicating that increasing organic carbon in alkaline soils may lead to an increase in inorganic carbon in the subsoil. Large variations in elemental ratios have been found in the RCL characterized by excess nitrogen and trace metals and phosphorus deficiency due to adsorption and weathering effects. Implementation of the water-sediment regulation scheme (WSRS) may have altered the sedimentary environment and may have aggravated an elemental imbalance due to the occurrence of the yellow silt layer (YSL)-RCL sequence and thereby impacted biogeochemical cycling in the river-delta-coast continuum.

Role of dust fluxes in stimulating Ethmodiscus rex giant diatom blooms in the northwestern tropical Pacific during the Last Glacial Maximum

The strontium (Sr) and neodymium (Nd) isotope compositions and clay-mineral assemblages of the lithogenic fraction of sediments in the southern Mariana Trench together with major- and trace-elements concentrations of bulk sediments have been determined to trace the sediment provenance and investigate the relationship between Asian dust input and blooms of the giant diatom Ethmodiscus rex (E. rex). Enrichment of barium (Ba) in relative to upper continental crust (UCC) and low average Rb/K ratios in all study cores point to both hydrothermal and volcaniclastic inputs to the sediments. Both the Sr-Nd isotope compositions and the clay-mineral assemblages of the lithogenic fraction reflect a two-component mixing system consisting of Mariana arc volcaniclastics and Asian eolian dust. Decreases in smectite content and kaolinite/chlorite ratio and increases in illite content and illite/kaolinite ratio just preceding the formation of laminated diatom mats (LDMs) suggest changes in the source of the eolian dust from eastern Asian deserts (EADs) to central Asian deserts (CADs) at the onset of the Last Glacial Maximum (LGM) which stimulated the blooming of E. rex giant diatom. These observations suggest a potential causal linkage among atmospheric circulation patterns, the sources of Asian eolian dust, and marine productivity. We postulate that intensified eolian dust input sourced from CADs may have played a greater role in promoting biological productivity in the oligotrophic northwestern tropical Pacific Ocean during the LGM than previously realized.

Особенности профильного распределения минералов во фракциях разной размерности в солонце светлом корковом сухостепной зоны юга России

Mineralogical composition of different texture fractions of Solonetz (Calcic Gypsic Endosalic Solonetz (Columnic Cutanic differentic) was studied. Inves-tigated object was located on the Borsi key plot in the northern part of the Caspian lowland (absolute height of the territory about 48 m) and developed on Early Khvalynian deposits. The profile of Solonetz is formed on coarsesilty clays and is characterized by depletion of silt in the upper 5cm horizon. The modern pedogenesis causes eluvial-illuvial distribution of silt fraction along the profile and the different ratio of mineral phases: 1) trioctahedral illites prevail in the SEL horizon, which indicates the process of illitization; 2) the upper natric horizon differs from the underlying ones by the predominance of labile minerals with the segregation of smectite packages. This pattern is associated with the process of lessivage, which occurs as the forming of clayey coatings. According to the mineralogical composition, some stratification of the soil-forming material is noted: in the upper part of the profile there was an increased content of illite of tridioctahedral type and mixed-layer minerals in comparison with the lower horizons. Comparing to the accumulative-calcareous horizons BCA and BSN3s the calcareous (Cca,s) horizon has a higher content of chlorite and kaolinite with perfect structure. The distribution of clastogenic minerals along the Solonetz profile in silt fractions and ≥ 10 μm has a weak disordered variation. With the increase of fractions sizes, an increase in the content of quartz, feldspars, plagioclases was marked. Also, the decrease of micas due to their more active disintegration during the pedogenesis was revealed.

Changing sediment sources in the Bay of Bengal: Evidence of summer monsoon intensification and ice-melt over Himalaya during the Late Quaternary

A gravity core retrieved from the southern Bay of Bengal (BoB) was studied to determine the sources of sediments and factors controlling their distributions during the Late Quaternary. The parameters used for this study was sediment grain size, organic carbon, clay mineralogy and environmental magnetic properties. Radiocarbon ages of sediments indicate that the 3.06 m long sediment core covers a period since ~45 cal kyr B.P. The sediments deposited before ~14 cal kyr B.P. were clayey silt with higher magnetic susceptibility (MS) values (av: 26 × 10−8 m3 kg−1) and those deposited after ~14 cal kyr B.P. were sandy silt with lower MS values (avg: 13 × 10−8 m3 kg−1). The latter period (after ~14 cal kyr B.P.) indicated high energy turbidites from the Himalayan Rivers into the BoB due to the strengthening of summer monsoon and ice-melt in the Himalayas. Higher smectite and lower illite contents during the last glacial maximum (LGM) reflected low sediment supply from the Ganges-Brahmaputra River System (GBRS) and higher illite and lower smectite during ~14 cal kyr B.P. indicated increased sediment supply from GBRS during this interglacial period. The magnetic grain size of sediments deposited from ~15 cal kyr B.P. was more fine-grained at the start of the Bølling-Ållerød (B-A) event and coarse-grained during ~13 cal kyr B.P. (Younger Dryas event). Fine-grained magnetic minerals also showed a peak at ~11 cal kyr B.P. along with higher summer solar insolation. The down-core variations in sediment grain size, magnetic properties and clay minerals were interpreted in relation to the significant changes in sources of sediments in the BoB during different climatic events. The changing sediment supply in the BoB was due to the combined influence of ice-melt by increased solar insolation and intensification of summer monsoon over Himalaya. Increase of fine-grained magnetic minerals at ~15 cal kyr B.P. and coarser sediment fraction at ~14 cal kyr B.P. indicated time gap between intensification of summer monsoon and ice-melt over Himalaya, respectively. The trend of the magnetic grain size record seems to be modulated by orbital-scale variations in June insolation, which coincides with the summer monsoon variations also. These observed climatic variations are correlating well with the climate changes of the Northern Hemisphere during the Late Quaternary.