Mineralogy and pore space characteristics of traprocks from Central Siberia, Russia: Prerequisite of weathering trends and soil formation (original) (raw)
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Clays and Clay Minerals, 2016
The study of hard rock conversion into fine earths and clayey materials in the pedosphere is important in understanding the relative proportions of recent soil features to features that were inherited from ancient epochs. Cold environments are widely thought to be areas of physical weathering, but the coexistence of physical and chemical processes have also been shown. To further examine mafic rock (dolerite) weathering in soil environments and the conversion into clayey materials, Entic Podzols formed in the cold continental climate were studied. The key study was located in the central part of the flood basalt complex, or traps (traprocks), of the Central Siberian Plateau (Russia). The qualitative mineralogy was studied using X-ray diffraction and the quantitative mineral composition was determined using X-ray diffraction and subsequent Rietveld analysis. The micromorphological characteristics of the soils were studied in thin sections. Dolerite fragments and fine earths were sampled from soil profiles underlain by dolerite. XRD analyses indicated that pyroxene and especially plagioclase contents in the dolerite fragments and fine earths decreased from the bottom to the top soil horizons mostly in the mature soil profiles that were affected by chemical weathering of dolerite. The dioctahedral and trioctahedral smectites in the soils were inherited from a dolerite previously subjected to chemical weathering. The smectite was conserved in the inherited aggregates and protected against dissolution even in acidic soil horizons. Recent pedogenesis processes fractured individual fragments, converted it into soil micromass, and slightly decreased the total smectite content of the <1 mm soil fraction. However, in soil samples collected from the bottom to the top horizons of a mature soil profile, trioctahedral smectite contents decreased as dioctahedral smectite contents increased. This suggests that dioctahedral smectites formed by pedogenic alteration of inherited trioctahedral smectites.
Applied Clay Science, 2012
The transformation of primary and secondary minerals in a recent shallow soil (Haplic Cryosol (Reductaquic)) from a highly weatherable ultrabasic rock (serpentinous dunite) of the mountainous tundra of the Polar Urals was determined. Primary and secondary mineral associations were analyzed in thin sections, by electron microscopy, X-ray diffraction, IR-spectroscopy, and thermal analysis. The susceptibility of the fresh rock for weathering was characterized by the micromorphology of the connective pores. Disintegration of the rock resulted in relatively high amounts of inherited olivine, serpentine, talc, and chlorite in the fine soil. Element release from fresh mineral surfaces exposed also in internal pore systems of rock fragments is a decisive factor for the appearance of secondary minerals in the fine soil. Secondary minerals are two smectites, saponite and nontronite, and vermiculite. Especially the silicates rich in Mg, olivine and serpentine with lower contents in the b 1 mm fraction of the soil horizons in comparison with the fresh rock, are the most probable sources for saponite. The source of nontronite is not fully understood. It is supposed that olivine and serpentine and/or pyroxenes that are allochthonous for serpentinous dunite and inherited from harzburgite affect their formation in the soil. Most probably vermiculite is the result of chlorite transformation. Content of smectites decreases in the upper horizons of the soil whereas in an opposite trend, vermiculite increases. Supposedly biota, especially moss and lichens, have a strong contribution to silicate weathering which leads to saponite and nontronite decomposition and chlorite transformation despite neutral to alkaline pH-values in the whole soil. Relatively high amounts of dithionite and oxalate soluble Fe indicate a marked release of Fe by silicate weathering. For element release freezing in the permafrost environment seems to have a decisive role by affecting pore systems in the rock and the soil skeleton fraction.
Eurasian Soil Science, 2008
Soil formation on hard rocks-nepheline syenite, amphibolite, metamorphized gabbro diabase, and their derivatives-was studied in the mountainous tundra and in the northern and middle taiga zones of the Kola Peninsula and Karelia (in the Kivach Reserve). It was found that the soils developing from these rocks could be classified into three groups: (1) petrozems with the O-M profile (the most common variant), (2) podzols and podzolized podburs on the substrates with an admixture of morainic derivatives of acid rocks, and shallow (<5-10 cm) pebbly soils on the substrates without an admixture of allochthonous material (the rarest variant). In soils of the third group, the pedogenic alteration of the mineral matrix does not result in the appearance of phyllosilicates in the fine fractions if these phyllosilicates are initially absent in the rock. In these soils, the processes of modern pedogenesis (rock disintegration, migration of Al-Fe-humus compounds, in situ transformation of the organic matter, and binding of iron released from the weathered silicate minerals into iron-organic complexes) are virtually undifferentiated by the separate soil horizons because of the very low thickness of the soil profiles. These soils have the Oao-BHFao-M profile; it is suggested that they can be classified as leptic podburs. An admixture of morainic material containing phyllosilicate minerals favors a more pronounced differentiation of the modern pedogenic processes by separate soil horizons even in the case of shallow soil profiles; the intense transformation of phyllosilicates takes place in the soils.
Clays and Clay Minerals, 1999
Formation of kaolinite-smectite (K-S) mixed layers in a soil toposequence developed from basaltic parent material was examined. The soil formed in a temperate climate with alternating dry and wet seasons in Sardinia (Italy). Chemical composition and charge characteristics of the smectite component in the K-S mixed layers were analyzed to help determine a mechanism for formation. Soils were sampled at the top, intermediate, and base of a steep (35%) slope. As indicated by X-ray diffraction data, the fine clay fraction (<0.1 0-m) in the soils is dominated by K-S with a decreasing proportion of kaolinite from the top (70%) to the base (30%). Rapid internal drainage induced by the slope is probably the major factor responsible for the formation of K-S. Chemical composition and charge characteristics of the smectite component in the K-S were analyzed by X-ray diffraction (intercalation with alkylammonium ions), cation exchanged capacity (CEC) and surface area measurements, and infrared spectroscopy. Results indicate that the smectite component is nearly identical over the soil toposequence. The smectite component is the same with respect to charge magnitude and chemical composition, independent of the proportion of kaolinite and smectite components. This suggests the pedogenic formation of K-S by transformation of smectite through dissolution of some smectite layers and subsequent crystallization of kaolinite between the layers of the remaining smectite crystallites.
CATENA, 2015
Knowledge about the pathways of pedogenic calcite formations and clay transformations on igneous rocks in semiarid regions plays a vital role in the commentary of soil development on these rocks. The present study was conducted to explore the weathering stages and pathways for the formation of pedogenic calcite in soils developed on selected plutonic and volcanic rocks in a semiarid climate in north-western Iran. The soils developed on plutonic rocks were found to be in the primary stage of weathering with very few pedogenic calcites, except for soil developed on alkali granite which contained few calcitic pedofeatures. Calcitic crystallitic b-fabrics and calcitic pedofeatures were found in all soils developed on volcanic rocks. In situ weathering of Ca-bearing minerals such as plagioclases, amphiboles and pyroxenes could be the possible explanation for the accumulation of pedogenic calcite in the absence of calcareous parent rocks in the studied area. Micritic calcite was observed to be the dominant form in most of the soils developed on volcanic rocks, indicating a rapid precipitation of calcium carbonate. Smectite, kaolinite and mica (illite) were present in the soils developed on plutonic rocks and the clay content in these soils was less than that of the volcanic rocks. Feldspars plus mica were supposed to be the most likely source minerals for the formation of pedogenic illite which could be consequently transformed into smectite in these semi-arid environments. Smectite, mica (illite) and kaolinite were the most abundant clay minerals in the soils developed on dacite and andesite rocks, while a minor quantity of vermiculite occurred only in andesite derived soils. Smectite, as the dominant mineral, and some kaolinite with fairly constant variation in content with depth were observed in the soils formed on hornblende andesite and pyroxene andesite. This could indicate that the smectite had the authigenic origin and was formed most likely from the weathering of plagioclase, hornblende and pyroxene. In general, in situ crystallization of pedogenic carbonates and high quantities of smectite in the clay fraction confirmed that the soils formed on volcanic rocks were more developed than those on plutonic rocks in the studied semiarid region. Moreover, our results showed that releasing calcium from Ca-bearing minerals in igneous rocks in conjunction with biological activities resulted in pedogenic calcite formation.
Revealing soil swelling and estimation of swelling rate are of great importance at the initial survey stages as well as the bases for further determination of more accurate factors used for selection of recovery methods and facility design. The paper states briefly the most conventional prediction express-methods and determination of swelling indicators, the results of laboratory research in clay composition and properties, free swell index of Quaternary and Paleogene clays in the southeast of West Siberian iron-ore, gives the estimates of the swelling rate. The results have been statistically analyzed, revealing the relationship of properties, on the basis of which the correlation dependencies are suggested to predict the free swell index as well as to apply it for frost heave prediction. 1. Introduction When changing the temperature-humidity conditions swelling clay poses a serious problem for construction as, when steeping, one observes a transition from solid and semi-solid phases to plastic one, density reduction, several time decrease in strength properties, and increase in maximum swelling pressure up to 2 MPa that can result in partial or complete facility destruction. In accordance with the normative techniques used in geological engineering survey [1], swell index is determined for soils of natural humidity, which depends on the test time and may be significantly different depending on weather conditions at different time of the year. Even slight humidity changes are enough for the same soil to be classified differently in terms of relative swelling ε sw according to [2]. Therefore, revealing of swelling clays is one of the most important tasks of a geological engineer for further detail study. The purpose of the paper is to reveal the distribution of soils prone to swelling in the profile of southeastern part of West Siberian iron ore basin. The objectives include the review of previously conducted research in geological engineering conditions of the area to establish the presence of smectite and hydromica minerals, study the prediction methods of expansive soil behavior and its classifications, selection of express-methods to determine swelling characteristics, sample preparation and laboratory soil tests; statistical data processing and establishment of relationship between the values of their composition and properties.
Geoderma, 2006
This study examined pedogenesis, as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials. The main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy. Palygorskite, chlorite, illite, smectite, quartz and interstratified minerals were observed in both soil and rock samples, using XRD, TEM and EDX analyses. Illite, chlorite, and interstratified minerals are inherited largely from parent rocks. Most of the smectite is inherited from highly smectite marl formations, although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons. Neoformation of palygorskite, as a result of calcite and gypsum precipitation, seems to be a major pathway for the occurrence of this mineral, especially on plateau physiographic units, although inheritance has less importance. Gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils. Three morphological forms of palygorskite, related to degree of weathering, were identified in the studied pedons. New great groups and subgroups of Ustepts (Aridic Gypsiustepts and Aridic-calcic Gypsiustepts) are suggested to be included in Soil Taxonomy based on the properties of some of the studied pedons. Dissolution and transport of anhydrite from outcrops, is considered the main source of pedogenic gypsum in these soils. Micromorphological studies, including thin section observations and SEM analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment.
Journal of Geochemical Exploration, 2010
The MiddleÀUpper MioceneÀPliocene sediments near Polatlı contain commercial sepiolitic clay deposits. The sepiolite-rich Polatlı basin sediments were studied to describe the sepiolitic clay deposits of the area and to assess the environments of formation using X-ray diffraction, optical and scanning electron microscopy, and chemical analysis. The Polatlı basin is an elongated, rift-related graben trending NEÀSW in central Turkey, filled with continental Late Miocene to Early Pliocene sediments. The sediments which comprise claystone, marl and limestone, dolostone, and evaporites are characteristic deposits of low-salinity, playa-lake depositional environments. These sepiolite-rich deposits include sepiolite, dolomite, and calcite, with minor amounts of palygorskite, quartz, moganite, amorphous silica (opal-CT), and feldspar.