Parent Lithology Research Articles

Mineralogy and Geochemical Characteristics of Lateritic Nickel Deposit in Wiwirano District, North Konawe, SE Sulawesi, Indonesia

This research aims to understand the mineralogical and geochemical characteristics of the nickel laterite deposit in the East Sulawesi Ophiolite Belt in Wiwirano District, North Konawe, Southeast Sulawesi, Indonesia. The deposit is analyzed and described to determine the laterization process and supergene enrichment. The geochemical data was obtained from X-ray fluorescence analysis, and mineralogical data from petrography and X-ray diffraction analysis. The minerals in the limonite zone are dominated by goethite and hematite. Minerals found in the saprolite zone include quartz, orthopyroxene, and lizardite, whereas the bedrock is made up of olivine, orthopyroxene, serpentine, and chromite. Fe2O3, Al2O3, and Co contents are high in the limonite zone, SiO2 and MgO have high content in the saprolite zone, and Ni is enriched in the saprolite zone. The distribution of enriched Ni is controlled by bedrock or parent lithology with an average content of 1.3% - 2.4% in saprolite, while in the limonite zone, Ni content is lower with an average content of 0.8% - 1.2%.

Mineralogical Characterization and Geochemical Signatures of Supergene Kaolinitic Clay Deposits: Insight of Ropp Complex Kaolins, Northcentral Nigeria

This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM).

An investigation into the physical factors that control slow mass movements

The behavior of slow mass movements like soil creep is well known to be governed by soil composition, slope, and cycles in temperature and rainfall. However, their magnitude and importance vary dramatically in often unpredictable ways, with important consequences for creep rate and infrastructure damage prediction. Here, we present long-term (2015–2022) creep measurements for four regions of the UK characterized by intense mass movement activity but different bedrock lithologies. We also obtained co-located temperature and precipitation time series over this period, as well as local measurements of slope and soil thickness and composition. Our goal was to deconvolve the relative importance of each observable on creep behavior. Our results imply that parent lithology governs first-order creep rates indirectly via hillslope repose angles and soil thickness and composition. Rates of ground movement on peat and sandstone soils are dictated by annual fluctuations in precipitation and temperature, respectively. By employing a simple error-minimizing regression routine, we demonstrate how creep rates can be predicted in these settings as a function of climatological observables. Over thinner limestone and thicker clay soils, however, our model fails: in these settings, we suggest that creep behavior is instead dominated by variations in regolith thickness, and slope and clay mineral content, respectively.

A comparison of PCA and ICA in geochemical pattern recognition of soil data: The case of Cyprus

Multivariate analysis of soil geochemistry is a powerful tool for differentiating lithological units and detecting geochemical dispersion halos related to mineralization or contamination. While univariate analysis can effectively identify lithological units with pronounced variations, it may fail to differentiate between subtler variations in lithologies. Traditional multivariate techniques such as principal component analysis (PCA) have limitations, including difficulties in understanding the individual contributions of each variable and an inability to work with non-Gaussian data. Independent component analysis (ICA) has emerged as a potential alternative, as it can effectively identify independent components of non-Gaussian data. In this study, we compared the effectiveness of PCA and ICA in relating multivariate soil geochemistry to parent lithology using the Soil Geochemical Atlas of Cyprus and associated digital geological maps. Both PCA and ICA were able to differentiate between the ultramafic units within the Troodos Ophiolite (TO) and the Circum-Troodos Sedimentary Succession (CTSS). However, ICA was more effective than PCA in identifying pillow lavas, providing a clear separation in the scores for IC4 and IC5. Furthermore, both PCA and ICA were able to separate the sheeted dykes from the cumulate mafic units within the TO. The gabbro unit is closely defined by IC2 scores. In contrast, PCA failed to provide factors that effectively delineated the Mamonia Terrane from other units, especially the TO, while ICA was able to provide a distinct separation in IC4 and IC5 scores. Separation between the CTSS and Quaternary units was weakly observed in IC2 scores. These findings demonstrate that there is a difference in the effectiveness of PCA and ICA in identifying different lithological units and emphasize the need for a careful selection of multivariate methods to differentiate between subtle differences in soil geochemistry relating to variations in parent lithology.

The role of parent lithology in nanoscale clay-mineral transformations in a subtropical monsoonal climate

Abstract Clay minerals are among the most important reactive components of soil systems, acting as a bridge linking organic and inorganic components. Lithology is a key factor in clay-mineral genesis and transformation, yet it has received scant attention to date at the nanoscale. Inferences regarding pedogenic clay-mineral transformations based on X-ray diffraction (XRD) are sometimes speculative, whereas mineralogic relationships documented by high-resolution transmission electron microscopy (HRTEM) are more robust due to direct evidence from lattice-fringe observations. In this contribution, the mineralogical and geochemical characteristics of four soils derived from different parent rock types (a gneiss, an Fe-rich siltstone, a sandstone, and a dolostone) from subtropical China were determined using HRTEM, XRD, and geochemical elemental data. The predominance of 2:1 clay minerals and kaolinite in the investigated soils is typical of subtropical climatic settings. Lattice-fringe images suggest the prevalence of topotactic transformations during clay-mineral alteration. Two distinct alteration pathways were observed in the investigated soils, one starting with chlorite and the other with illite, with convergence of mineralogic compositions toward kaolinite and crystalline iron and aluminum (oxyhydr)oxides. In the early stages of weathering, chlorite transformed into expandable clays through a continuous, solid-state mechanism with corrensite and/or randomly interstratified chlorite-vermiculite/chlorite-smectite as intermediate products. Unlike chlorite, which tends to form a 1:1 regularly interstratified phase, the weathering of illite commonly starts at layer edges. Under subtropical monsoonal climates, the precursor minerals in host rocks and aeolian materials determine the starting composition and, to a certain extent, the trajectory of clay-mineral transformation over time. With advanced weathering, mineralogic convergence toward kaolinite and Fe/Al-(oxyhydr)oxides tends to obscure the initial substrate composition. This study advances our understanding of the role of parent lithology in clay-mineral evolution at the nanoscale.

The effect of rock lithology on the background concentrations of trace elements in alluvial soils: Implications for environmental regulation

To assess the extent of soil contamination with a potentially toxic element, it is important to determine the background concentration of that element in the soil. In this study we decided to investigate the relationship between trace element concentrations in soils and the lithology of their parent rocks. We collected 85 topsoils (0–20 cm) samples from the Petorca, La Ligua, Aconcagua, and Casablanca River basins (Valparaiso region, central Chile). For soil sampling, we chose 11 tributary watersheds free of anthropogenic influence. The areas that contributed to the formation of each alluvial soil were delineated and the parent lithologies were acquired from 1:250,000 geological maps. The results show that the total concentrations of arsenic (As), copper (Cu), lead (Pb), and zinc (Zn) in soil vary considerably among the four river basins studied. Soil concentrations of all elements under study are positively correlated with the presence of andesitic volcanic rocks. Furthermore, soils formed from marine sediments and felsic volcanic rocks had the highest concentrations of Pb and As. The carbonate-bearing marine sediments may have adsorbed As and Pb released by weathering of felsic volcanic rocks found upstream of the study area. In contrast, lithologies dominated by continental sedimentary and plutonic rocks showed negative correlations with the concentrations of As, Cu, Pb, and Zn in the soil. Thus, the differences in soil element concentrations in the watersheds under study were due to the different rock types present in the area. We argue that absolute “one-limit-fits-all” background trace element values may be inadequate to assess the extent of soil contamination. Therefore, it is important to determine background concentrations of soil elements in each river basin in the anthropogenically impacted areas. In contrast, erroneous conclusions can be drawn when background concentrations are determined in one region and then applied in another region that is lithologically different.

Sources Identification, Ecological Risk Assessment, and Controlling Factors of Potentially Toxic Elements in Typical Lead-Zinc Mine Area, Guizhou Province, Southwest China

Carbonatite and basalt are widely distributed in southwest China, and potentially toxic elements (PTEs) are associated with the naturally high background properties. It is important to carry out ecological risk assessments and identify potential sources of PTEs. A total of 3180 soil samples (0-20 cm) were collected in Hezhang county, a typical high background area of PTEs with the parent lithology of carbonatite and basalt. Samples were obtained from 18 large lead-zinc mines, which belong to a multi-ecological risk superimposed area with high ecological risk. The concentration of PTEs (Cd, Cr, As, Hg, Pb, Cu, Zn, and Ni) in the topsoil were analyzed, and statistical analysis (SA), geographic information system (GIS), enrichment factor (EF), potential ecological risk index (RI), and positive matrix factorization (PMF) methods were used to assess the ecological risk and quantify sources of PTEs. The mean values of PTEs concentrations in topsoil were 24.55, 2.25, 176.40, 89.60, 0.19, 64.20, 102.00, and 257.00 mg·kg-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than the average background value (ABV) of soils in Guizhou Province. The average concentrations of Cd, Cr, Cu, Ni, Pb, and Zn exceeded the screening values specified for the soil contamination risk in agricultural land (GB 15618-2018) by 7.50, 1.18, 1.79, 1.07, 1.40, and 1.29 times, respectively. The EF showed that Cd had a large area of moderate pollution; Pb, Zn, and Cu had a small area of slight pollution; the EFs values of Hg, Cr, Ni, and As were near the baseline value (EF≈1), and contaminations were slight or nonexistent. The PMF indicated that there were five sources, namely pyrite mines, lead-zinc mines, natural sources of basalt and carbonatite, and agricultural activities; the risk contribution ratios were 5.25%, 27.37%, 28.94%, 17.91%, and 20.53%, respectively. The most toxic coefficients of Hg and Cd were mainly natural sources, with contribution ratios of 86.3% and 72.7%, respectively. The soil samples in the mining areas expectedly contained high ratios of Zn/Cd and Pb/Cd, which confirmed that PTEs in the soil were mainly derived from the smelting wastes. The contents of metal oxides such as Fe, Mn, and Si were the influencing factors of PTEs enrichment. On the contrary, soil samples exhibited much lower Zn/Cd and Pb/Cd ratios in non-mining areas, indicating that the main origin of these metals in soil was the smelting flue gas dusts and geological background.

Depth profiles of soil organic carbon isotopes across a lithosequence: implications for drivers of soil δ 13C vertical changes

ABSTRACT To addresshow parent materials are affecting organic carbon dynamics in a soil profile, soils from a lithosequence comprising six parent lithologies under a rangeland ecosystem have been explored at three depth intervals for soil organic carbon (SOC) content and its 13C depth trends. Studied parent materials ranged from metamorphic (foliated: FM and non-foliated: NFM) to sedimentary (clastic carbonate: CCS) to plutonic (intermediate: IP, felsic: FP and intermediate felsic: IFP) geological contexts. The relationship between SOC concentration and its isotopic signatures to a depth of 50 cm in FM, NFM, FP and IFP profiles was well described by the kinetic fractionation of SOC during biodegradation. For CCS and IP lithologies, strong divergence from the Rayleigh equation was observed suggesting that the 13C enrichments in these soils resulted from both mixing different SOC pools and isotope fractionation related to the C mineralization. Results suggest that SOC across the lithosequence goes through different isotopic evolutions resulting from different 13C-enriched inputs and pedogenic properties as described by the extended Rayleigh equation (0 ≤ β C ≤ 0.80). These are presumably caused by the bedrock lithology implying that parent material affects C storage and dynamics.

Trends and Composition—A Sedimentological-Chemical-Mineralogical Approach to Constrain the Origin of Quaternary Deposits and Landforms—From a Review to a Manual

In this study, six basic Quaternary landform series (LFS) and their sedimentary deposits (LFS1 aeolian, LFS 2.1 to 2.2 mass wasting, LFS 3 cryogenic-glacial, LFS 4.1 to 4.6 fluvial, LFS 5.1 to 5.2 coastal-marine, LFS 6.1 to 6.3 lacustrine) are subdivided into subtypes and examined with regard to their sedimentological parameters and their mineralogical and chemical compositions. Emphasis is placed on the textural (related to transport and deposition), compositional (sediment load/weight, Eh and pH) and geodynamic maturity of the sedimentary deposits which are influenced by the parent lithology and bedrock tectonic and by the climate during the last 2 Ma. To constrain the development of the LFS and their sediments, composite trend-line diagrams are designed combining sedimentological (x-axis) and chemical/mineralogical dataset (y-axis): (1) sorting vs. heavy mineral content; (2) sphericity of grains vs. silica/carbonate contents; and (3) median vs. Ti/Fe ratios. In addition, the x-y plots showing the log SiO2/Al2O3 vs. log Na2O/K2O are amended by a dataset of the three most common clay minerals, i.e., kaolinite-, mica-, and smectite-group clay minerals. Such joint sedimentological-chemical-mineralogical investigations focused on the depositional environment of unconsolidated clastic sediments of Quaternary age can be used to describe the economic geology and environmental geology of mineral deposits in the pre-Quaternary sedimentary series according to the phrase: “The Present is the key to the Past”. Both trend diagrams and compositional x-y plots can contribute to constraining the development of the full transect of landform series from the fluvial incision and slope retreat to reef islands fringing the coastal zone towards the open sea as far as they are built up of clastic sedimentary deposits enriched in siliceous and/or carbonate minerals. Climate zonation and crustal maturity are the exogenous and endogenous “drivers”, as can be deduced from the compositional (mineralogy and chemistry) and physical (transport and deposition) variations observed in the Quaternary sediments. The current study bridges the gap between a review only based on literature and a hybrid manual generated by practical field studies devoted to applied geosciences in economic and environmental geology (“E & E issue”).

Influence of parent lithology on field appearances and engineering properties of indurated laterites under same geographical conditions

Laterites derived from different parent lithologies in the same tropical area and under the same climatic condition are likely to have different engineering properties. In this study, two nearby abandoned laterite quarries at Haripur and Tengara in Dhenkanal district (in the state of Odisha, India) were investigated. The first objective of this study was to evaluate the strength and physical properties of the indurated laterites with reference to the characterization of the selected profiles. The other drive of this work was to demonstrate how different parent lithologies of these two lateritic profiles that share same geographical conditions can be related to the variation of engineering properties of the indurated laterites. In order to address these two objectives, the lateritic profiles were characterized which was followed by the determination of strength and physical properties of the indurated laterites; petrographic study; and XRD analysis.Although the variation patterns of engineering properties (i.e. uniaxial compressive, point load and Brazilian tensile strengths; effective porosity; dry density; vug volumetric percentage; and slake durability indices) of the indurated laterites with profile depths at Haripur and Tengara show prominent differences, such variations depict a good compliance with the characterized horizons of the respective profiles. Based on the analysis of the engineering properties in relation to characterized profiles, it was shown that for construction purposes, the indurated laterites of both areas can be classified based on the point load strength. From the geological investigation, it was ascertained that the difference in engineering properties between the indurated laterites of Haripur and Tengara is very much dependent on the mineralogy such as sesquioxides, clay content and other minerals altered from the parent lithologies.

Category-based fractal modelling: A novel model to integrate the geology into the data for more effective processing and interpretation

Parent lithology exerts a major influence on the associated regolith geochemistry and affects the setting of population or domain boundaries. In regional geochemical mapping and anomaly detection, a lack of samples pertaining to one or more key lithologies may results in interpolation errors. Such errors can be addressed via category-based fractal modelling to characterise different background and anomalous populations by taking both error propagation and geochemical data values into account. Such geochemical anomaly classification models have been developed using Monte Carlo simulation (MCSIM) within a given lithological domain to provide estimates of population breaks. Two types of category-based fractal models used are (i) related lithological groups representative samples where there is an adequate number of samples derived from a given lithological or geological domain, and (ii) related lithological groups whole samples and a group of Gaussian simulated samples regenerated based on the mean and standard deviation of the available samples per lithological group. Both models were applied to VMS-related element concentrations in the low-density till geochemical mapping of Sweden following centred log-ratio (clr) transformation. Compared with the concentration-area fractal model the category-based fractal models provided more reliable estimates for population thresholds and identification of anomalous classes.

Concentration-concentration fractal modelling: A novel insight for correlation between variables in response to changes in the underlying controlling geological-geochemical processes

Fractal/multifractal classification models applied to regional geochemical data are typically based on relationships between geochemical concentrations and mathematical, statistical or geometrical properties such as sample numbers, surface areas, perimeter and distance. There is, however, another component of geochemical datasets that is implicitly addressed using multi-variate methods such as factor analysis or various forms of clustering. This is the degree of correlation and changes in the nature of the correlation between elements as the processes affecting sample geochemistry change. In regional datasets, much of the change is related to differences in parent lithology or regolith type, but also relates to the effects of mineralisation or contamination. Where two elements display systematic changes in their mutual correlation in response to different ‘forcings’, joint modelling of such bivariate relationships can provide new ‘dimensions’ to data interpretation. Bivariate probability plots indicate distinct population breaks representing the intersections between different sub-populations within the two variables. This concept is extended in this study to fractal analysis and a proposed concentration-concentration (C–C) fractal model. A soil dataset from Cyprus was studied in this research to demonstrate and interpret the C–C results associated with copper (Cu)-related VMS mineralisation considering the geological-geochemical evidence. The C–C models generated based on the relation between Cu and indium (In) were compared to the established number-size (N-S), concentration-area (C-A), spectrum-area (S-A) and singularity models. All the models were applied to the same datasets, but in different formats, i.e., raw data, and multi-variate approaches of Box-Cox transformed data, factor analysis (FA) and centred log-ratio (clr) transformed data scores. This is to visualise and evaluate the robustness of the C–C model comparing to uni- and multi-variate studies. Therefore, based on the maps classified by the C–C model and the geology in Cyprus comparing to the mentioned models, the robustness of the C–C fractal model was demonstrated. In addition, applying Monte Carlo simulation on each class characterised by all the models applied, demonstrated a remarkably high certainty of the thresholds obtained by the C–C fractal model.

Controls on soil geochemistry fractal characteristics in Lemesos (Limassol), Cyprus

This study extends the program of urban soil geochemical mapping in Cyprus to Lemesos, the country's second largest and fastest developing urban centre. Data from 411 soil samples are combined with samples previously analysed as part of the detailed soil geochemical atlas of Cyprus (GAC). Parent lithology is the dominant control on the distribution of most elements with soils derived from carbonate units contrasting with those developed on alluvium-colluvium that contains input from both the carbonates and mafic-ultramafic units of the nearby Troodos Ophiolite. Anthropogenic contamination is best indicated by the Pb-Sn-Ag-Bi suite with elevated values in a belt crossing the southern and older section of the city that is unrelated to parent lithology or current land use classification. As in Lefkosia, children's playgrounds display much higher As contents than at other sites due to application of a natural secondary carbonate (‘pouri’) as the surface layer, and elevated concentrations of Cu, Fe, Ti, Al, S and Mn associated with basaltic soils used in most school grounds. Multivariate patterns in the Lemesos data largely reflect those of similar parent lithologies within the national soil atlas, but there is closer clustering of the contamination-related elements and an ultramafic suite involving Ni-Cr-Pt-Pd-V-Co in Lemesos. Whereas most elements display multifractal populations using number-size fractal modelling, in urban and contaminated areas some higher concentration element populations do not display fractal behaviour, thus providing a means of identifying anthropogenic influences.

Regional-scale mapping for determining geochemical background values in soils of the Itacaiúnas River Basin, Brazil: The use of compositional data analysis (CoDA)

This study aims at providing high quality soil geochemical data at a regional scale (1 sample per 25 km2) to understand the source and distribution of potentially toxic elements (PTEs: Al, As, Ba, Cd, Cu, Co, Cr, Fe, Hg, Mo, Mn, Ni, Pb, Se, U, V, and Zn) and to define their geochemical background threshold values (GBTVs) in the Itacaiúnas River Basin (IRB), Brazilian Amazon. A total of 2958 soil samples were collected at two depths (surface: 0–10 cm; bottom: 30–50 cm) and the fine fractions (<0.117 mm) were analyzed by ICP-MS and ICP-AES after aqua-regia digestion. The compositional nature of geochemical data was evaluated using the log-ratio approach and compared with traditional methods. Results show that compared to raw/log-transformation, centred log-ratio (clr) transformation improves spatial mapping and also better separated variables in Principal Component Analysis (PCA). Correlation analysis based on the isometric log-ratio (ilr) transformation in heat-maps provides reliable and better structure of the results. The spatial maps (clr) indicate that most of the elements in surface and bottom soils are mainly governed by underlying bedrock geology (parent lithologies and mineralization), while anthropogenic factors are insignificant. The resulting clr-based PCA and cluster analyses associated with geological information indicate that geochemical patterns of Fe-Ti-V-Cr-Sc can be linked to mafic to intermediate metavolcanic rocks and banded-iron formations, which are dominant in the Carajás basin, while Ni and Cr distribution pattern is attributed to mafic and ultramafic lithologies, and Cu anomalous values are mainly related to hydrothermal mineralized copper belts. Among the statistical methods applied for estimation of GBTVs, TIF produced the highest BTVs, followed by 98th and mMAD, with few exceptions, while mMAD was considered the more suitable for defining GBTVs. The number of potential anomalies of PTEs identified by these methods follow the order of MAD > 98th > TIF or MAD > TIF > 98th, and overall the anomalies are mostly related to the local lithology/mineralization with no indication of anthropogenic contamination. Compared with Brazilian guidelines (CONAMA Resolution No. 420/2009), the GBTVs determined for Cr, Co, Ni, and Cu by TIF, MAD, and 98th percentile mostly exceeded both IV and PV limits. However, these high values are due to the influence of local lithology. This reveals that the Brazilian CONAMA guidelines of these elements for the IRB are unrealistic because that suggests a large number of sites requiring investigation, which is not consistent with the geochemical evidence. Therefore, site-specific GBTVs must be considered for the accurate evaluation of anthropogenic contamination, as well as the ecological and human health risks of PTEs in this region.

Cu and Zn isotope fractionation during extreme chemical weathering

Copper and Zn are trace metal micronutrients whose stable isotope systematics are receiving increasing attention as possible paleoenvironmental tracers. However, to realise this potential, their behaviour during chemical weathering must be better constrained. We present coupled Cu and Zn isotope data for a well-characterised Indian laterite weathering profile, which includes a full suite of samples from unaltered greywacke bedrock to indurated lateritic duricrust. This sample set provides an exceptional opportunity to interrogate Cu and Zn isotope compositions during an extreme example of chemical weathering. Despite their occurrence in different host phases within the parent greywacke, Cu and Zn isotopes behave coherently during weathering. We observe preferential loss of heavy isotopes at increasing degrees of alteration, with 0.6‰ total variability in δ66Zn and 0.9‰ in δ65Cu. Given the absence of evidence for CuS or ZnS phases in the parent lithology, we attribute the liberation of heavy isotopes to organic complexation in the aqueous phase and/or incorporation of light isotopes in secondary aluminous Fe-oxides. Strong enrichment of both metals is also associated with a peak in Mn at a previously identified paleo-water table horizon. This dataset confirms that weathering under oxygenated conditions releases isotopically heavy Cu, regardless of the host phase. Meanwhile, Zn isotopes are only fractionated to any significant extent at the most extreme degrees of chemical weathering reached during lateritization. We conclude that the isotopic composition of the weathering-derived input of Zn to rivers should be largely insensitive to climate change on geological timescales.

Soil CO2 and O2 Concentrations Illuminate the Relative Importance of Weathering and Respiration to Seasonal Soil Gas Fluctuations

Soil CO2 and O2 cycles are coupled in some processes (e.g., respiration) but uncoupled in others (e.g., silicate weathering). One benchmark for interpreting soil biogeochemical processes affected by soil pCO2 and pO2 is to calculate the apparent respiratory quotient (ARQ). When aerobic respiration and diffusion are the dominant controls on gas concentrations, ARQ equals 1; ARQ deviates from 1 when other processes dominate soil CO2 and O2 chemistry. Here, we used ARQ to understand lithologic, hillslope, and seasonal controls on soil gases at the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. We measured soil pCO2 and pO2 at three depths from the soil surface to bedrock across catenas in one shale and one sandstone watershed over three growing seasons. We found that both parent lithology and hillslope position significantly affect soil gas concentrations and ARQ. Soil pCO2 was highest (&gt;5%) and pO2 was lowest (&lt;16%) in the valley floors. Controlling for depth, pCO2 was higher and pO2 was lower across all sites in the sandstone watershed. We attribute this pattern to higher macroporosity in sandstone lithologies, which results in greater root respiration at depth. We recorded seasonal variation in ARQ at all sites, with ARQ rising above 1 during July through September, and dipping below 1 in the early spring. We hypothesize that this seasonal fluctuation arises from anaerobic respiration in reducing microsites July through September when the soils are wet and demand for O2 is high, followed by oxidation of reduced species when the soils drain and re‐oxygenate. We estimate that this anaerobic respiration in microsites contributes 36 g C m−2 yr−1 to the soil C flux. Our results provide evidence for a conceptual model of metal cycling in temperate watersheds and point to the importance of anaerobic respiration to the carbon flux from forest soils.Core Ideas Hillslope position and lithology affect soil CO2 and O2 in humid temperate forests. The ratio of CO2 and O2 (ARQ) fluctuates over the growing season. The ARQ fluctuations indicate seasonal metal redox cycling at all hillslope positions. Anaerobic respiration is important to soil CO2 flux during the late growing season.

A joint study in geomorphology, pedology and sedimentology of a Mesoeuropean landscape in the Meseta and Atlas Foreland (NW Morocco). A function of parent lithology, geodynamics and climate

The origin of the landscape spreading across NW Morocco (Meseta, Atlas Mts. Foreland) is geodynamically controlled by two collisional and one extensional regime, while climate changes had only a minor impact on the shaping the landscape. The existing landscape pertains to the series characterized by highly to partially eroded mountain blocks of Paleozoic and Early Mesozoic age which is represented at its best by the relics of the Variscan orogeny resultant in what is called “Mesoeurope”. The Mesoeuropean landscape in Morocco is described by four morphodynamic units.MD 1 (0.4–1.8 Ma/generation 3) has brought about landforms in a fluvial (-alluvial) depositional environment with a strong aeolian influence at its margins. Its drainage patterns feature a moderate to gentle dip of the palaeo-current with a predominantly meandering depositional regime. The major minerals are quartz, calcite, smectite, and smectite-illite mixed-layers (submature landscape).MD 2 (2.0–3.0 Ma/generation 2) involves coastal-marine processes of a microtidal environment. Only quartz warrants mentioning as major constituent (supermature landscape).MD 3 (Neogene/generation 1) is the core zone with extensive planation and chemical weathering which gave rise to amorphous silica and smectite-group minerals (mature landscape).MD 4 (Quaternary/generation 4) encompasses landforms typical of alluvial-fluvial environments evolving under a moderate to strong palaeo-current in the foothills of the Atlas Mts. Aside of quartz, calcite, chlorite, muscovite, illite, and feldspar, labile heavy minerals are as widespread as the calcitic carbocretes. Modern structural disturbances are accountable for the immature landforms and high preservation potential of labile mineral constituents.A morphodynamic comparison between the reference type of “Mesoeurope” and the current morphodynamic type under study in Morocco results into a binary classification scheme encompassing two phases, an older one called phase of planation and a younger one called phase of dissection, a sequence which reflects quiescence and relative stable geodynamic conditions succeeded by a period of tectonic mobility. There is one striking difference between the Moroccan landscape and the reference type in Mid-Europe; the reference type has no equivalent morphodynamic unit which was triggered by the opening of the Atlantic Ocean denoted by the lack of U/Pb data of supergene alteration minerals in the reference log. The most widespread soil types encountered in the Moroccan study sites are vertisols (MD 1, MD3), luvisols (MD 1, MD 2, MD 4) and cambisols. Second in abundance are planosols, which are confined to MD 2 and, locally, arenosol associated with plinthite (MD 1); kastanozem and chernozem (MD 3) are rare members of the topsoil. While the log activity of SiO2 varies in a narrow range, the pH of the meteoric water is considerable wide, from 4.2 to 9.4. The physical-chemical regime suggests a binary subdivision into a more acidic regime (MD1, MD2) in the N and an alkaline one (MD 3, MD4) in the S which goes along with the change in the redox ratios of organic matter (LER/HER) and the climate-zonation.

Engineering characteristics of soils prone to rainfall-induced slope failure in Viti Levu, Fiji

Fiji's infrastructure is regularly affected by rainfall-induced slope failures, but the engineering properties of failed soils are rarely described. We report mineralogical, geotechnical and index properties of soils from headscarp exposures of 18 slope failures from tropical residual soils of differing parent rocks in Viti Levu, Fiji. Scanning electron microscopy and X-ray diffraction revealed that kaolinite and smectite are the dominant clay minerals in the soils. Index properties included in situ moisture content (28–114%), dry bulk density (0.7–1.5 g cm −3 ), Atterberg limits (25–56% plastic limit; 38–79% liquid limit), effective particle size (0.4–12.6 μm) and clay fraction (0.6–19%). Geotechnical measurements included field compressive strength (127–461 kPa), hydraulic conductivity ( c. 10 −7 m s −1 ), shear vane (16–128 kPa), ring shear (9.3–17.4°) and Emerson dispersion. Collectively, results indicated that most of the soils were cohesive, stiff, sensitive and in a plastic state in the field. Soils plotted below the A-line on the plasticity chart as fine silts of intermediate to high plasticity, and can theoretically sustain &gt;50° slopes. Failure of these soils following high rainfall events is influenced by low permeability and the presence of expanding clays (e.g. smectite), causing temporary porewater pressure increases. No explicit relationships between soil properties and parent lithology were evident.

Storage and drivers of soil organic carbon and nitrogen in a rangeland ecosystem across a lithosequence in western Iran

Identifying the drivers of soil organic carbon (SOC) and nitrogen (N) dynamics is profoundly needed to get insight into the nutrient cycling in the terrestrial ecosystems. Soil parent material is one of the important factors affecting SOC and N dynamics. The aim of this research was to explore C and N dynamics of a soil lithosequence with parent materials ranging from sedimentary to metamorphic and plutonic bedrock in the eastern Kurdistan province, in western Iran.We examined the hypothesis that SOC and N accumulation potential and turnover vary significantly with soil bedrock lithology. To test our hypothesis, we collected soil samples at three depth intervals (0–5, 5–25 and 25–50 cm) as well as aboveground plant materials in six geological contexts: clastic carbonate sedimentary (CCS), foliated metamorphic (FM), non-foliated metamorphic (NFM), intermediate plutonic (IP), felsic plutonic (FP) and intermediate felsic plutonic (IFP). Soil characteristics (SOC, total N, δ13C, δ15N, soil texture, pH, EC, carbonates, available P) and plant material properties (C and N contents and their stable isotopic signatures) were determined in 45 soil samples and 18 plant materials, respectively.Results showed that both geology and soil depth strongly influenced the SOC and total N concentrations as well as their stable C and N isotopic composition. Both SOC and total N were highest per site/lithology in the soils over FM geology (5.42 and 0.51 g kg−1 soil for SOC and total N, respectively) and least in the soils forming on FP parent material (0.97 and 0.12 g kg−1 soil for SOC and total N, respectively). In the case of stable C and N isotopic composition, the highest mean value per lithology was found in the NFM soils (−23.68‰ for δ13C) and FP soils (13.74‰ for δ15N), while the lowest mean signature was observed in the soils developed over FM geology (−25.41‰ and 7.88‰ for δ13C and δ15N, respectively). Vertical distribution of both δ13C and δ15N signatures in the studied soils showed an increasing trend by depth. The main controlling factors for organic C and N concentrations across the lithosequence were explored using PLSR and PCA analyses.Results indicated that different soil properties controlled the SOC and total N contents at the different depths. Soil stable C and N isotopic compositions and pH were the factors that influenced negatively the organic C and N contents across the studied lithosequence. Differently, soil C/N ratio was strongly positively associated with SOC and TN contents. Clay- and silt-size fractions had no substantial influence on the organic C and N concentrations, although importance of silt particles for SOC and TN storage increased with increasing soil depth. These findings provide evidence that geology, as soil parent material, can control both SOC and N accumulation and turnover. However, a more in-depth study is required to understand the mechanisms by which parent lithology affects the organic C and N dynamics.

Geochemical pattern recognition through matrix decomposition

This study compares the use of joint singular value decomposition and semi-discrete decomposition (JSS) and non-negative matrix factorisation with univariate analysis of raw data, to detect multi-element patterns in soils related to geochemical dispersion from Mississippi Valley-Type Pb-Zn deposits in the Irankuh area of central Iran. Joint singular value decomposition and semi-discrete decomposition clustering of the data identified a suite of mineralisation-related variables and corresponding sample clusters that are spatially associated with mineralisation or variations in parent lithology. Non-negative matrix factorisation generated three main factors and sample clusters that relate to the main zones of sulphide mineralisation, variations in clay mineralogy and the composition of unaltered host rocks. These two matrix decomposition techniques deliver similar results, though JSS delivers a significantly higher sample classification accuracy. Both methods result in delineation of a contiguous cluster of samples above an extensive zone of blind mineralisation at the Tappe Sorkh Pb-Zn deposit and define new potentially mineralised targets between this deposit and the Gushfil Pb-Zn deposit. More conventional univariate methods to detect anomalous populations of Pb and Zn in the soil geochemical data, such as number-size fractal analysis, were less effective at defining these targets. Joint application of practical matrix decomposition techniques, utilising noise removal and modelling of the underlying geochemical patterns associated with ore-forming processes, has led to more reliable prospectivity mapping of the Pb-Zn deposits in Irankuh.