Parent Rock Research Articles

Method of choosing soils as CEB or pavement layers based on geological and environmental information and mode of treatment

During research on the geological, mineralogical, mechanical and geotechnical nature of thick layers of soils developed on the rocks of the lower zone of the southern slopes of Mount Bambouto (West Cameroon), a couple of observations were made. The mechanical behavior of soils as construction materials is linked to the nature of the parent rock and its environment of formation. Four different types of rock have been noted: trachybasalt, orthogneiss, anatexite, and biotite-hornblende granitoid. These rocks in a hot and humid mountain climate, exposed to the monsoon wind, have weathered to give soils with exploitable characteristics in compressed earth bricks (CEB) and pavement layers. This article proposes a method of choosing a soil for pavement layers and for the production of fired earth bricks / earth bricks treated or not with hydraulic binders, based on the nature of the bedrock and the climatic environment. Several formulation models have been defined. The performance, fairness, accuracy and adequacy of these models with real values were made by metric evaluation. So, it is:•Preliminary method for quickly and easily formulating masonry units in clay soil.•Preliminary method for quickly and easily formulating pavement layers in clay soil.•Simple and reliable method for choosing clay soils as construction materials from elementary geological information.

Raw Materials Used in Traditional Pottery from Northern Morocco: Possible Alternative Material for a Sustainable Future in the Fran Ali Area

AbstractThe colluvium and saprolite deposits in the Fran Ali area (Oued Laou, northern Morocco) constitute the main source of raw materials used in traditional pottery. These materials are becoming scarce, however, so alternative materials with the same characteristics are needed; this would ensure the sustainability of pottery activities in the area. The objective of the present study was to examine ten representative samples of clayey materials extracted from the Fran Ali area, i.e. the Ikhadimene, Dar Haddoune, Ihadounene, Aqqbat Ajjoua, and Isalahene sites. The geological materials consist mainly of grayish to brownish phyllites, thin layers of yellowish clay, thicker intervals of reddish-yellow soils ranging in depth from 1 to 4 m, and reddish colluvium soils. The physical properties of these materials were determined using semi-wet sieving and Atterberg limit tests, while chemical, mineralogical, and thermal properties were obtained from the methylene blue test (MBT), the calcimetry test, X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), and thermogravimetric and differential thermal (TGA/DTGA) analysis. The results suggest that the soils contain 21–35% clay, 28–34% silt, and 37–52% sand. They are moderately plastic, with methylene blue adsorption capacities ranging from 3 to 7% and minimal CaCO3 carbonate contents (1–4%). Samples are dominated by SiO2 (51–57%), Al2O3 (17–21%), and Fe2O3 (8–10%). Mineralogically, they are composed of illite (19–27%), chlorite (0–22%), kaolinite (5–9%), and quartz (29–32%). Thermal analysis showed a relatively large mass loss of ~10%. The samples are deemed to be moderately plastic. The results indicate that this raw material is acceptable for pottery fabrication, given the small proportion of irregular interlayer content and its average geotechnical properties. In addition, extraction of the colluvium material is not sustainable because of the relative scarcity of the material. Given the mineralogical similarity between the weathered layers (colluvium) and their parent rock (shales), the present results suggest that the latter is a suitable alternative to the former.

Assessment of groundwater potential zones using an integration of Remote Sensing, GIS and 2D Electrical Resistivity imaging in the Echway watershed, Baro River Basin, Southwest Ethiopia

The objective of this study is to delineate and identify the groundwater potential zone of degraded land in the Echway watershed, southwest Ethiopia, employing a combined approach that includes 2D electrical resistivity, the analytical hierarchy process (AHP), geographic information systems (GIS) and remote sensing (RS). Using a geographic information system (GIS) and remote sensing data, groundwater potential zones were identified by taking into account the soil types, drainage density, geology, lineament density, Land use and land cover, rainfall and slope. Using the AHP method, calculate the weight of thematic layers and rank of subclasses based on the effects of various thematic layers on groundwater potential. A significant weight was provided on the geology of the research region, total annual rainfall, and lineament density. Due to significant effects on groundwater potential zones, only three of the seven theme levels were assigned significant weight in this analysis. The weighted overlay analysis was used to construct the diagram of the zones with groundwater potential. 2D electrical resistivity was utilized to find the groundwater aquifer, and four major electrical layers were discovered: clayey silt, sand, moderately weathered/fractured rock, and basement parent rock. The groundwater potential zones in the study area have been classified into five categories: very low (22.97%), low (13.43%), moderate (32.50%), high (25.12%), and very high (5.98%) covered, respectively. The groundwater potential zone image was created by combining GIS, remote sensing, AHP, and an electrical survey

Genetic Features of Soils on Dense Parent Rocks of the Donetsk Ridge

The present study investigates morphological, physical and chemical properties of Chernozems at dense parent rocks. The research was carried out on the protected areas native soils of the north-west of the Rostov region. This territory is representing eastern slopes of the Donetsk Ridge, which predetermines the dense rocks release to the surface. It has been found that morphological, physical and chemical properties of Chernozems on dense rocks have emphasized their originality and uniqueness, and at the same time clearly have indicate their classification as Chernozem order. In comparison with the zonal soil – Calcic Chernozem – Chernozems on dense rocks are characterized by a reduced thickness of humus-accumulative layers, an increased of humus content, the presence of gravel in profile bottom half, a weak expression of calcareous accumulations, features of the particle-size distribution of soil components, even if it belongs to the same soil texture class. Chernozems on dense carbonate rocks either do not have accumulation or are characterized by a weak manifestation of secondary carbonates (pseudomycelia and nodules). This fact has differed such soil from the same order Chrernozems on fine-grained rocks (Calcic Chernozems) for which it is diagnostic criteria. Therefore, the mention of the suborder of these soils is incorrect in the designation. In the soil covering of the spurs of the Donetsk Ridge, dark humus soils are also occure, previously classified as incomplete developed chernozems, differing from chernozems by the absence of medium part of soil profiles.

Geochemical and mineralogical analysis of the Upper Cretaceous dolomitic phosphates at Queih Mine, Quseir, Central Eastern Desert, Egypt: depositional environment implications and pollution indices

Soon for the security of phosphorus world supply, which comes primarily from non-renewable sources, the moderate carbonate phosphates will need further geochemical multidiscipline investigations to participate in the phosphorous supply chains necessary to increase human productivity. Dolomitic phosphates represented the main carbonate phosphate rocks of the Upper Member of Duwi Formation, at Um Queih Mine, South-Western Quseir, that phosphate can be classified as intermediate grade phosphate ore. It was enriched in V, Ni, Mo, U, Cu, Cr, Cd, Co as well as Zn and their ratios indicated that the deposition occurred in anoxic environment (reducing conditions). Mineralogical investigations indicated that the studied phosphorites are composed of two main mineral phases; fluorapatite and non-phosphatic minerals (dolomite, calcite, pyrite, gypsum, and quartz). The petrographic examination revealed that these phosphorites are composed of phosphatic lithoclasts, phosphatic bioclasts, opaques, and quartz grains embedded in a cryptocrystalline phosphatic matrix. The parent rocks of the studied phosphorites represented by basaltic mafic provenance were affected by low chemical weathering and deposited under marine anoxic environment. The mineralogical and geochemical characteristics indicated that the studied phosphorites deposited in marine anoxic condition. The weathering of these rocks can be harmful to the surrounding environment owing to its content of pyrite and potentially toxic elements (PTEs), the EF (enrichment factor) gives extremely high enriched with Mo, Cd, and Se.

Source-to-sink controls on modern fluvial sands in the Pantanal back-bulge basin (Brazil)

Sedimentological processes are underexplored in retro-arc basin segments of source-to-sink systems, particularly in the distal back-bulge depozone. The extant Pantanal Basin of Latin America is a large sub-tropical continental back-bulge for which the boundary conditions on riverine sedimentation (tectonics, climate, phytogeography) are reasonably understood. Here, we use a new database of riverbed sand samples (n = 97) to investigate the modern provenance of the Pantanal Basin. Petrographic analysis of grain-mounted thin sections and Gazzi-Dickinson point counting were used to assess the framework composition of the sands, and a pour point analysis based on geographic information systems (GIS) defined the hinterland geological environment for each sample. Six provenance domains were defined: (a) lowlands, (b) Amazon craton, (c) Rio Apa craton, (d) plateau, (e) South Paraguay Belt, and (f) North Paraguay Belt. Most Pantanal samples are quartzose non-orogenic detritus (Qt88\F5\L7). Rivers draining the Paraguay Belt highlands carry more lithic grains derived from carbonate parent rocks. The occurrence of plagioclase grains is rare. However, river sands where >30% of the total assemblage was K-feldspar were present downstream of foliated metamorphic outcrops of the Rio Apa craton. Sand relatively rich in fine K-feldspar grains in the medial Taquari River megafan were attributed to channel avulsion, incision, and reworking of floodplain deposits. Statistical analysis suggests that bedrock lithology and average annual rainfall are important controls on fluvial sands in the Pantanal Basin, with watershed slope, temperature, and dilution playing secondary roles in the spatial distribution of dominant grain types. This study provides new actualistic data that aim to improve interpretations of the geological record.

Source apportionment and migration characteristics of heavy metal(loid)s in soil and groundwater of contaminated site

The rapid industrial growth has generated heavy metal(loid)s contamination in the soil, which poses a serious threat to the ecology and human health. In this study, 580 samples were collected in Henan Province, China, for source apportionment, migration characterization and health risk evaluation using self-organizing map, positive matrix factorization and multivariate risk assessment methods. The results showed that samples were classified into four groups and pollution sources included chromium slag dump, soil parent rock and abandoned factory. The contents of Cr, Pb, As and Hg were low in Group 1. Group 2 was characterized by total Cr, Cr(Ⅵ) and pH. The enrichment of total Cr and Cr(Ⅵ) in soil was mainly attributed to chromium slag dump, accounting for more than 84.0%. Group 3 was dominated by Hg and Pb. Hg and Pb were primarily attributed to abandoned factory, accounting for 84.7% and 70.0%, respectively. Group 4 was characterized by As. The occurrence of As was not limited to one individual region. The contribution of soil parent rock reached 83.0%. Furthermore, the vertical migration of As, Hg, Pb and Cr(Ⅵ) in soil was mainly influenced by medium permeability, pH and organic matter content. The trends of As, Pb, and Hg with depth were basically consistent with the trends of organic matter with depth, and were negatively correlated with the change in pH with depth. The trends of Cr(Ⅵ) with depth were basically consistent with the changes in pH with the depth. The content of Cr(Ⅵ) in the deep soil did not exceed the detection limits and Cr(Ⅵ) contamination occurred in the deep aquifer, suggesting that Cr(Ⅵ) in the deep groundwater originated from the leakage of shallow groundwater. The assessment indicated that the non-carcinogenic and carcinogenic risks for children and adults could not be neglected. Moreover, children were more susceptible than adults.

Influence of the parent rock nature on the mineralogical and geochemical composition of ferralsols used for sedentary agriculture in the Paleoproterozoic Franceville sub-basin (Gabon)

The aim of this study was to assess the influence of parent rock nature on the mineralogical and geochemical properties of ferralsols used by sedentary subsistence farmers in the Proterozoic Franceville subbasin of Gabon. Thus, soils developed from cherts, black shales and sandstones were investigated for their mineralogical composition and their heavy metal contamination of topsoil using the X-ray diffraction (XRD), and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). Results show that the dominant mineralogical assemblage is made of quartz, illite, kaolinite and smectite, and this is reflected in the major-element chemistry which include essentially SiO2 (46.4 - 89.2%), Al2O3 (4.3 - 19.8%) followed by Fe2O3 (0.7 - 15.3%), with highest amounts of SiO2 and lowest amounts of Al2O3 and Fe2O3 found in soils developed from sandstone. The geochemical data revealed some doleritic intrusions through the chert formations with highest values of Fe2O3 and TiO2 in the overlying soils. Results indicated serious health concern associated with a geogenic source of As, Ba, Cd, Cu, La, Pb, Rb, Th and U in soils developed from cherts and black shales. Consequently, only the uncontaminated soils developed from sandstone could be appropriate for smallholder farming communities.

Analysing of palaeoenvironment and organic matter enrichment: A case study from the Triassic Yanchang Formation in the southern Ordos Basin, China

The organic‐rich shale of the seventh Oil Member (Chang 7 Member for short) of the Middle‐Late Triassic Yanchang Formation is extensively distributed in the southern margin of the Ordos Basin. Understanding the palaeoenvironmental conditions during the sedimentary period of the Chang 7 Member is crucial to exploring the main factors that control the enrichment of organic matter in high‐quality source rocks. In this study, lithofacies analysis was conducted, and samples were collected from the N36 well located in the southern part of the Ordos Basin. Subsequently, element geochemical analysis was performed to reconstruct the palaeoenvironment, and total organic carbon (TOC) tests were conducted to analyse the characteristics of organic matter enrichment. The findings indicate that the sedimentary period of the Chang 7 Member was characterized by a relatively warm and humid palaeo‐climate and a brackish water environment with oxygen‐poor or sub‐oxygen‐rich conditions, and a gradual decrease in palaeo‐water depth. The parent rock types were mainly felsic igneous rock and intermediate igneous rock, which provide limited nutritional elements for primary producers. The enrichment of organic matter in the Chang 7 Member is influenced by several factors, mainly including palaeo‐salinity, palaeo‐water depth, palaeo‐redox conditions, terrestrial inputs, and palaeo‐climate. The warm and humid palaeo‐climate, higher palaeo‐productivity, relatively higher palaeo‐salinity, lower terrigenous input, deeper palaeo‐water depth, and better preservation conditions are conducive to the development of high‐quality source rock in the Chang 7 Member.

GEMAS: Chemical weathering of silicate parent materials revealed by agricultural soil of Europe

The chemical composition of soil represents to a large extent the primary mineralogy and geochemistry of the source bedrock, the effects of pre- and post-depositional weathering and element mobility, either by leaching or mineral sorting with the addition of secondary products such as clays. Agricultural soil in Europe (0–20 cm, 33 countries, 5.6 million km2) was sampled during the continental-scale soil mapping project (GEochemical Mapping of Agricultural and grazing land Soil - GEMAS). Total element concentrations were determined by wavelength dispersive X-ray fluorescence spectrometry. Bulk content of major elements (SiO2, TiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, P2O5) in soil has been used to calculate weathering indices such as chemical index of alteration (CIA), reductive and oxidative mafic indices of alteration (MIA), the change in mass balance (τ calculation relative to immobile Nb) for soil derived from silicate bedrocks (granite, gneiss and schist) at the European continental-scale, which are useful tools for evaluating chemical weathering trends.The greatest variation of CIA values is exhibited by soil derived from granite, followed by soil derived from schist. The CIA results show clearly that Ca and Na are removed from agricultural soil (0–20 cm) during soil development. Geographical distribution of weathering indices shows that weak chemical weathering of agricultural soil samples, sourced from gneissic and granitic bedrock, occurs in the Fennoscandian Shield; intermediate chemical weathering in granite, schist and gneiss occurring in the Iberian Peninsula and France, and intense chemical weathering in schist sourced agricultural soil occurring in areas with intense rainfall and moderate temperature (Wales, England, Ireland and western Iberia). In addition, values of CIA and MIA, higher than those for standard rock compositions, suggest more active enrichment/depletion processes during soil formation and subsequent soil weathering/maturation.The range of the elemental mass transfer coefficient τ is wide for agricultural soil derived from gneiss and granite, and narrow for agricultural soil sourced from schist parent rocks. The weathering behaviour of chemical elements, assessed by using the τ mass transport model, suggests an order of susceptibility of K ≈ Na > Al > Fe > Ca > Mg > Ti.Weathering indices and gain-loss mass transfer coefficients, tested on agricultural soil samples, provide an insight to the weathering processes affecting the silicate parent rocks and their impact on soil development at the European scale. This can have further implications for evaluation of soil nutritional conditions and mitigating of soil erosion and deprivation.

Germanium: distribution, migration and accumulation in the natural environment

In this paper we attempt to generalize information published in the scientific literature about the distribution, migration and accumulation of chemical forms of germanium in the natural environment, with the main attention paid to the content of this trace element in various components of the environment. Despite the fact that germanium is found in the lithosphere, hydrosphere and atmosphere it is one of the least studied elements in mineral and geochemical terms. It belongs to rare scattered elements with a relatively high migration capacity in the earth's crust and on its surface. Depending on the physical and chemical conditions, the mineral and lithogenesis of germanium can exhibit different properties, which determines the variety of ways of its migration. The nature and form of migration of germanium in the natural environment is not determined only by its chemical properties but also by a complex set of reactions of interaction with various underground water addendums, the granulometric and chemical-mineralogical composition of soil-forming rocks and soils, biogenic and technogenic processes. Studies have shown that the content of germanium in natural waters, soils and plants can vary widely and depends on many factors. In particular, its concentration in groundwater and surface water depends on the natural geological environment, pressure, temperature, meteorological and anthropogenic factors; soil by their type, region, features of soil-forming processes, chemical composition of the parent rocks, climatic conditions and amounts of organic substances; in plants by their species and varietal facilities, the growth stage of the plants, the availability of soils by this element, the forms of germanium compounds in the soil (inorganic or organic), the ability of soil to retain labile form of germanium and climatic conditions. Analysis of the actual content of germanium in diets indicates an insufficient level of provision of the human body with this trace element, due to its low concentrations in food and water. However, it has been suggested that any products with a high content of germanium may pose a risk to human health through its toxic effects.

Geochemical and Sedimentological Signatures of Ariyankuppam and Chunnambar Estuarine Sediments, Pondicherry, India: Implications on Weathering and Provenance

Abstract Thirty surface sediment samples collected from Ariyankuppam (N = 12) and Chunnambar estuaries (N = 18) located along the coast of Pondicherry, India, are analyzed to understand the nature of weathering and provenance. The granulometric study reveals that sediments are poorly sorted, positively skewed and platykurtic to leptokurtic in nature. The abundance and inverse relationship of SiO2 with other major oxides signify the detention of silica within quartz. The Index of Chemical Variability (ICV) suggests that sediments are compositionally immature and are derived from less weathered source rock. The weathering indices such as the Chemical Index of Alteration (CIA); Chemical Index of Weathering (CIW); Plagioclase Index of Alteration (PIA), and A-CN-K diagram also suggest less intense weathering of parent rocks. The major and trace element ratios viz. Al2O3/TiO2, TiO2/Zr, Cr/V and Y/Ni and discrimination diagrams indicate that estuarine sediment is derived from felsic and intermediate provenance.

Variations in trophic niches of soil microarthropods with elevation in two distant mountain regions in Eurasia as indicated by stable isotopes (15N, 13C)

Knowledge on the trophic niche of animal species is important for understanding their coexistence and hence animal diversity. Trophic niches have been shown to vary with environmental conditions, but consequences of trophic niche shifts for food-web structure and functioning are little studied and this applies in particular for belowground communities. Here, using stable isotopes (15N, 13C), we investigated shifts in trophic niches of oribatid mites as model soil animal taxon along elevational gradients of two mountain ranges in Eurasia, the Alps in Austria and Changbai Mountain in China. The results showed pronounced differences in the use of basal resources (Δ13C values) and trophic positions (Δ15N values) between the two mountains due to the different parent rock with calcareous soils in the Alps and basalt bedrock on Changbai Mountain. Further, trophic positions changed with altitude, primarily related to changes in litter quality. Differences in trophic niches of oribatid mites between the two mountains were related to differences in functional traits such as body mass and reproductive mode. Generally, stable isotope values closely correlated with body mass underlining the importance of morphological characteristics as well as the parent rock for variations in trophic niches. Moreover, stable isotope values differed between parthenogenetic and sexual species, but this depended on mountain and parent rock, with higher trophic plasticity in parthenogenetic species on Changbai Mountain than in the Alps. Overall, our findings highlight the decisive role of parent rock in structuring montane soil food webs and provide novel insight into factors responsible for shifts in trophic niches in soil invertebrates.

Are South China granites special in forming ion-adsorption REE deposits?

Ion-adsorption REE deposits associated with clay minerals are the main global HREE producer. The majority of these deposits are formed by the weathering of granites in South China, but whether there is any fundamental difference between the granites in and outside South China is still unclear. Besides, an effective evaluation system of granite mineralization potential is urgently needed for HREE exploration.To answer this question, we compiled a global granite geochemical dataset from within (n = 1932) and outside (n = 6109) South China, together with a dataset of representative REE deposits in South China (n = 128). The geochemical comparation shows that the South China granites share similar REE contents with those of many granites from places outside South China. Such similarity has also been found between REE ore-related and ore-barren granites in South China. This shows that granites from outside South China could also have ore-forming potential. Warm humid climate and quasi-equalized crustal state promote chemical weathering to continuously leach REEs and store them in the weathering crust. The enrichment ratio (Rx) can be used to quantify the climatic effect between orebodies and parent rocks. The calculated average Enrichment Ratios (Rx) of LREE- and HREE-rich deposits are 2.41 and 2.68, respectively. Sufficient REE content in granite is the prerequisite for mineralization, and we propose that the combination of the minimum REE + Y (172 and 108 ppm in LREE- and HREE-rich parent rocks, respectively) and REE oxide ratio (1.32) can reveal the granite metallogenic potential. Together with the suitable tropical and temperate climate area with ion-adsorption REE deposits, we further identified certain regions with high REE mineralization potential outside South China to assist future exploration.

Phillipsite in pelagic REY-rich sediments and ferromanganese nodules from the Western Pacific: Geochemical characteristics and implications for REY enrichments

Recent studies have shown that the rare earth elements and yttrium (REY)-rich deep-sea sediments often contain abundant phillipsite, which is considered as an indicator mineral for REY-rich sediments. However, the phillipsite contains very low REY content, and the coexistence of abundant phillipsite and REY enrichment is generally explained by the low sedimentation rate in deep sea environment. Whether the phillipsite has the capacity to enrich REY and why it is REY-poor is still unclear. Phillipsite is also present in ferromanganese nodules in the surface of the deep-sea sediments, yet whether there is any compositional/genetic difference between the sediment-hosted and nodule-hosted phillipsite is unclear. Here, we study the phillipsite in pelagic REY-rich sediments and ferromanganese nodules from the Western Pacific Marcus‐Wake seamount chain. Mineralogical, morphologic, and geochemical analyses of the sediment-/nodule-hosted phillipsite were carried out. Our results show that the XRD patterns and Si/Al ratios of the sediment-/nodule-hosted phillipsite are the same, and they are both K-phillipsite. However, the consistent Fe/Ti, Zr/Hf and Nb/Ta ratios as well as similar Zr/Nb and Zr/Ta ratios of sediment-hosted phillipsite indicate that the sediment-hosted phillipsite has a homogeneous parent rock and has undergone the same degree of low-temperature alteration. In contrast, the nodule-hosted phillipsite may have inhomogeneous parent rock and have undergone different degree alteration because of the varying Fe/Ti, Zr/Hf and Nb/Ta ratios, as well as the wide range of Zr/Nb and Zr/Ta ratios in the nodule-hosted phillipsite. Both sediment-/nodule-hosted phillipsite have similar REY patterns to those of the pore water and have low total REY contents, indicating that they do obtain REYs from the pore water. In deep-sea REY-rich sediments, the phillipsite does not enrich REY, although the REY can enter the phillipsite lattice. This may be caused by the low cation exchange selectivity for REYs in phillipsite, which can be attributed to high hydration energy. Our study indicates that phillipsite does not participate in REY-enrichment. The implication of phillipsite for REY enrichment may be attributed to the consistency of the environmental conditions between the phillipsite formation and REY enrichment.

Hydrological characteristics and available water storage of typical karst soil in SW China under different soil–rock structures

Soil hydrological characteristics are influenced by factors such as parent rock weathering, human activities, and soil texture. However, the influence of the complex soil–rock structures and heterogeneous soil types on soil hydrological characteristics resulting from the weathering of carbonate rocks into soils on slopes in the karst region of SW China is not fully understood. The relationships between zonal and nonzonal soil hydrological characteristic differences, land uses, and soil–rock structures were analyzed using a typical watershed in the SW China karst region. In this study, (1) the difference between zonal and nonzonal soil hydrological characteristics is significant. For infiltration capacity (Ks), yellow soil (19.50 ∼ 1058.00 cm·d-1) < limestone soil (34.50 ∼ 2364.00 cm·d-1), while for soil available water storage, limestone soil on the dolomitic slope (43.26 mm) > yellow soil (20.16 ∼ 35.25 mm) > limestone soil on the limestone slope (17.73 ∼ 34.72 mm). (2) Land-use practices and soil–rock structures have long affected the hydrological characteristics of soil in karst. (3) The bare bedrock on carbonate slopes leads to a reduction in the total amount of soil per unit area on the slope, which compresses the space for vegetation growth and reduces the total amount of water provided by the soil for vegetation growth per unit area, which confirms one of the reasons for the low plant biomass in karst. These results suggest that the utilization of soil water in karst areas should consider the weights of soil type, lithology, and soil–rock structures.

Investigating the Formation of Hot-Dry Rock in Gonghe Basin, Qinghai, China

The Gonghe Basin, Qinghai Province, China, has rich geothermal and hot-dry rock resources. Through a magnetotelluric survey line with 400 points, combined with regional geology data, the deep geoelectrical structural background and thermal source mechanisms of the Gonghe Basin were explored. The results showed that (1) a deep structure with high conductivity may exist at a depth of 15 km in the basin, and could be compared to the layer-shaped, low-velocity, high-conductivity structure in the eastern part of the Qinghai–Tibet Plateau; (2) the rushing reverse fault played a crucial role in heat control and conduction from the hot field; and (3) high-temperature heat storage existed, including four layers of geothermal resources. This study proposed a triple-polymorphism model of hot-dry rock in the area; that is, the high-conductivity layer in the Middle–Late Cenozoic crust was the principal heat source; the Middle–Late Triassic granite was the essential heat-storing body, as well as a parent rock to the hot-dry rock; and the Cenozoic sedimentary rock was the effective caprock. This model is critical to understanding geothermal causes, predicting geothermal resources, and planning, on the Qinghai–Tibet Plateau.

The formation and evolution of Al‐rich protoliths in the southern Ribeira belt, Brazil: Insights from remnants of a Precambrian paleoweathering surface

AbstractBauxitic clays, clayey bauxites and bauxites are residual products formed from the weathering of aluminosilicate‐rich parent rocks under wet and warm conditions. These deposits show a complex interplay between remobilisation of pre‐existing kaolinitic soils and depositional micro‐environments.In the southern Ribeira belt, Brazil, a paleoweathering surface developed on the continental shelf of the Capiru Group passive margin strata and on its basement/source rocks. This weathering cycle gave rise to a paleosol profile on the continental domain and a karstic paleotopography on the emerged carbonate shelf. The surface and karstic nets were later caped and filled with Al‐rich materials, typical of remobilised soils, bauxitic clays, clayey bauxites and pods of karst‐type bauxites.The age of the disconformity is Pre‐Brazilian/Pan‐African, implying a Neoproterozoic age for the weathering surface. In this study, we investigate the relationship among disconformities, paleosols and karst topography to better understand the stratigraphic control, chemical composition and mineralogy of the Al‐rich materials. We interpret this horizon as the remnants of a (meta‐)paleoweathering surface that can serve as a valuable key bed for stratigraphic correlation and paleogeographic reconstructions.We propose that the triggering process for the genesis of the paleosol profiles, bauxitic material and bauxite pods was a coupled mechanism between favourable climate and uplift along the northern margin of the Curitiba–Angola craton, creating a karstic topography that allowed the down‐plain transport of Al‐rich materials. In a later stage, these deposits were metamorphosed, developing a series of Al silicates in unusual paragenesis, typical of Al‐rich protoliths.The presence of these paragenesis, along with the recognition of the disconformity–paleoweathering surface pair, could be a useful tool to understand the paleoenvironmental and paleogeographic evolution of highly deformed terrains.

Geochemistry of Weathering Cover and the Main Influencing Factors in Karst Area of Guilin, Southwest China

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. We present the chemical composition of weathering covers in karst area of Guilin, Guangxi province, analyze their weathering process and strength, and compare them with the other weathering covers in other karst area in China, including Yunnan, Guizhou, Hunan, and Qinghai Tibet Plateau. The results showed: (1) the chemical composition of Guilin weathering covers were similar to that of carbonate weathering covers in other areas of China, and had the common characteristics of uniform distribution of chemical composition in the profile and obvious enrichment of Fe, Al and trace elements. During the formation of carbonate weathering cover and the residua, the rapid dissolution of Ca and Mg had an important impact on the migration and enrichment of other elements. (2) The chemical index of alteration (CIA) of carbonate weathering covers in Guilin and other karst areas of China was much larger than that in the upper crust (UCC) (60.13), which showed strong chemical weathering characteristics of the humid and hot climate. (3) The weathering process of carbonate rock was different from that of silicate and loess. In the early stage of carbonate rock weathering, soluble components (calcite and dolomite) had been rapidly dissolved and leached. All the carbonate weathering residua was measured to be in the stage of K2O weathering and Al2O3 increasing. Therefore, the weathering degree of carbonate weathering cover was mainly determined by the leaching of K2O and the increase of Al2O3. As a result, there was no correlation between CIA and Na/K (molar ratio), but was a significant negative correlation between CIA and K/Al (molar ratio) in the carbonate weathering cover. (4) The CIA values of weathering residua and carbonate weathering cover in southern China were negatively correlated with latitude, reflecting the influence of climate factors. From the influence of lithology, the chemical compositions of parent rock can affect the CIA of weathering cover, and the content of insoluble matter in carbonate rock was negatively correlated with CIA. From the influence of topography, the CIA value of weathering residua decreased from the high to the low position and from the shallow to the deep part of the profile.

An appraisal of trace element concentration and environmental risk of sediments: a baseline study of sediments from Arasalar River Estuary, Tamil Nadu, India.

A total of 21 surface sediment samples collected from Arasalar River are subjected to sediment texture (sand-silt-clay ratio), trace elements, organic matter, and CaCO3 studies to understand the accumulation dynamics of sediments. To assess the impact of metal pollution in estuarine sediments, the essential parameters should be done by checking the sediment characteristics, spatial distribution of heavy metal sources, sediment dynamics, and geochemical analysis. To evaluate the contamination level of metal pollution, a basic standard reference is required to decipher the values ranging from natural to anthropogenic contribution. From this research analysis, it is observed that the study area predominantly comprises silty sand and sand silty nature. The calcium carbonate content in the sediment is found to be proportional to the presence of shell fragments, whereas the organic matter (OM) is derived from riverine and coastal input which acts as a primary source. The obtained results confessed the average contents (mg/g) for the following selected eight elements in the order of Fe (35249-49068) > Mn (286-519) > Ni (107-279) > Cu (78.30-155.70) > Cr (50-99) > Zn (38.70-91.90) > Pb (39.90-62.40), and Co (12.6-29.1) by using an atomic absorption spectrophotometer (AAS) are utilized for this analysis. Multivariate analysis of heavy metals affirms geogenic sources (weathering of parent rocks) for Fe, Mn, Cr, Co, and Zn, whereas Cu, Ni, and Pb originated from anthropogenic activities (urban and industrial activities). The pollution load index, sediment pollution index, Igeo index, and PERI are categorized as under polluted, low to moderate polluted, and low potential environmental risk variety. Constant inspection and guidance are needed to prevent effluences from various agriculture and industrial activities in the nearby regions. The findings from this research may support and help the government to follow the suitable remediation on the better management of river and coastal areas.