Chemical Index Of Weathering Research Articles

"Iron Ion Relative Weathering Index": A New Index for Identifying the Weathering Degree in Red Sandstone.

The red bed region in west central and southern China is affected by hot and humid climate, where sandstone is intensely weathered. The weathered hazardous rocks seriously threaten the road and slope, making it challenging to protect the Danxia red bed. After considering the red sandstone's material composition and the local area's main weathering effects. We noticed that iron ions in red sandstone are susceptible to weathering, which leads to changes in the valence and content of iron ions. This study attempts to establish a new chemical weathering index called the "iron ion relative weathering index" (IRWI) to classify the weathering degree of red sandstone. This paper mainly explores the changes of physical characteristics (mineral composition, physical indicator, microstructure, and pore structure) from the surface to the interior of red sandstone in the actual environment and their correlation with IRWI. The study on the correlation between the physical indicators such as longitudinal wave velocity, resistivity, density, water absorption, and IRWI reveals that they have the same trends and are closely related to the weathering degree. The shallow weathering zone of Chishui red sandstone is divided into strong, medium, and slight weathering zones. Microscopically, the cementation and pore distribution of the red sandstone are consistent with the characteristics of the weathering zone. Therefore, IRWI not only is a reliable chemical quantitative method in indicating the weathering of red sandstone but also takes into account the controlling role of iron in the color development of red beds, which provides a new research idea for the quantitative identification of weathering degree and color mechanism of red sandstone.

Geochemical and mineralogical proxies from the Messinian mudrocks (Catanzaro Basin, southern Italy): Paleoweathering and paleoclimate evolution during the onset of the Messinian salinity Crisis

The bulk mineralogy and geochemistry of mudrock samples from a representative section of the Calcare di Base Formation outcropping in the Catanzaro Basin (Calabria) were studied using X-Ray Diffraction and X-Ray Fluorescence techniques. Phyllosilicates are the main mineralogical constituents followed by quartz, calcite, feldspar, hematite and gypsum in the lower part of the studied succession, whereas calcite is the main mineralogical component in the upper part. The geochemical composition reveals that SiO2, Fe2O3, Al2O3, CaO and MgO are the most abundant oxides on average. The chemical weathering indices, such as the CIA (Chemical Index of Alteration) and its modifications, show low-medium values and thus suggest weak-moderate source area(s) weathering conditions, under a mainly dry/arid paleoclimate environment. The low kaolinite amounts confirm a low-moderate degree of weathering processes. The studied samples originate from an environment in which non-steady-state weathering conditions prevailed and active tectonism allows erosional processes. This trend suggests a paleoclimate characterized by persistent dry (arid) conditions alternating with relatively wet (humid) conditions. The studied mudrocks are characterized by recycling effects as recorded in the Al–Zr–Ti plot. The provenance of the studied samples is mainly related to a felsic source such as the rocks composing the Sila Massif.The composition of the studied samples was compared to that of similar samples from the Calcare di Base formation of the Rossano Basin to reconstruct the paleoclimate scenario of the Mediterranean area during the Messinian Salinity Crisis. The analogies between the mudrocks investigated in this work and the argillaceous marls from the Calcare di Base formation of the Rossano Basin suggest that they formed in the same (i) non-steady-state weathering and (ii) dry/arid paleoclimatic conditions. All the evidences allow to hypothesize that semi-closed basins, even if distant and not necessarily synchronous from each other, may have developed in a comparable way due to similar local climate condition, geochemistry of the body water and river run-off. The geochemical and mineralogical proxies from the mudrocks of the Calcare di Base Formation may open a new scenario for the understanding of paleoclimatic condition during the Messinian Salinity Crisis.

Geochemical characterization of Lokoja-Basange Sandstone at Imiegba and Okpekpe areas, Benin flank of Anambra basin, Nigeria: implications for provenance, tectonic setting and source-rock weathering

This study investigates the geochemical attributes of the Lokoja-Basange Sandstone situated in Okpekpe and Imiegba areas of the Benin Flank of Anambra Basin, Nigeria. The aim of this study is to unveil its provenance, tectonic setting, and source rock weathering extent. Using energy dispersive x-ray fluorescence (EDXRF) "Minipal 4" spectrometer analysis, nine outcrop samples were examined for major oxide concentrations. The results show significant average SiO2 (77.09 wt. %), Al2O3 (12.10 wt. %), Fe2O3 (2.72 wt. %), Na2O (1.64 wt. %), K2O (2.41 wt. %), while TiO2, MnO, MgO, CaO, P2O5, LOI had average concentrations of less than 1.00 wt. %. Bivariate plots of log [Fe2O3/K2O] versus log [SiO2/Al2O3] indicate 77.80% litharenites and 22.20% arkose sediments. The [Al2O3]-[CaO+Na2O]-[K2O] ternary plot, the tectonic discriminant diagrams of [SiO2/20]-[K2O+Na2O]-[TiO2+Fe2O3+MgO], log [K2O/Na2O] versus SiO2, [SiO2/Al2O3] versus log [K2O/Na2O] and bivariate discriminant functions plot indicate that the sediments have felsic igneous provenance and quartzose sedimentary origin, within a passive margin tectonic setting and the source-area underwent moderate to near complete chemical weathering in semi-arid to humid climatic conditions with increasing chemical maturity. Conclusively, the chemical alteration index (CIA) ranges from 65.4% to 74.2%, averaging 70.70%; the chemical index of weathering (CIW) averages 82.37%; the plagioclase index of alteration (PIA) averages 78.88%; and the mineralogical index of alteration (MIA) averages 41.43%. These data signify extensive weathering of felsic igneous source rocks, highlighting mineralogical maturity of Lokoja-Basange Sandstone. In essence, this study enriches insights into the sandstone's origins, sedimentary context, and weathering history.

Provenance of the lower Cretaceous Lumshiwal Formation, Surghar Range, northwestern Indian Plate, Pakistan: Insights from new petrographical and geochemical analysis

This paper documents the provenance and palaeoclimatic conditions of the Cretaceous Lumshiwal Formation near the western margin of the Indian plate in the Surghar Range, northwest Pakistan. The combined techniques of petrography, X-ray diffraction (XRD), and bulk rock geochemistry were utilized to reveal the source and mineral-geochemical composition and sandstone type. The petrographic analysis of the sandstones confirms the dominance of quartz, feldspar, and rock fragments, with subordinate occurrences of muscovite, magnetite, and hematite. Heavy minerals consist of tourmaline, titanite (sphene), rutile, cassiterite, monazite, and zircon. The cementing material includes ferruginous clays, jarosite, glauconite, calcite, minor dolomite, gypsum, and silica. The modal composition plot of the sandstones falls into arkose to sub-arkose, with a few lithic arkose varieties. Lithic fragments mainly include granite, with a minor occurrence of granitic gneiss, chert, phyllite, and quartz mica schist. The discriminatory provenance diagram of the sandstones suggests a transitional continental provenance. The bulk rock geochemistry of the sandstones reveals the presence of SiO2, TiO2, Al2O3, Fe2O3, FeO, MnO, CaO, MgO, Na2O, K2O and P2O5. The petrographical mineral findings were corroborated with XRD, SEM, and bulk rock geochemistry analysis (major element concentrations and their ratios), which collectively all confirm a felsic igneous source. The tectonic discrimination diagram (SiO2-log K2O/Na2O wt %) implies a dominant influx of sediment sourced from the passive continental margin of the uplifted Gondwana Indian plate. Terrigenous sediments found in the Lumshiwal Formation are interpreted to have been derived from granites and granitic gneisses of the Indian Shield. The palaeo-weathering index, including the chemical index of alteration (CIA) and the chemical index of weathering (CIW) of the Lumshiwal Formation confirms a low to moderately weathered source area. The climate discrimination plot (SiO2 versus Al2O3 + Na2O + K2O) shows that humid to semi-humid climatic conditions during the deposition of the Lumshiwal Formation.

Geochemistry and geochronology of Upper Triassic sedimentary rocks from the south of the Dabie Orogen: Implications for the paleoenvironment, provenance and tectonic setting

The formation and evolution of the foreland basin in the south of the Dabie Orogen are both closely related to the uplift of the orogenic belt. However, the Late Triassic paleoenvironment and the provenance of the sediments in the foreland basin remain controversial. Nine samples from the Upper Triassic Puqi Group of the foreland basin were analysed for whole‐rock major and trace elements and three sandstone samples were selected for zircon dating by U–Pb laser ablation inductively coupled plasma mass spectrometry. The concentrations of some major (e.g., CaO and Na2O) and trace (e.g., Rb, Sr and Ba) elements varied over a large range and showed different degrees of depletion. A series of major and trace element indicators, as well as the patterns of the rare earth elements, suggested derivation from felsic igneous rocks. The Late Triassic experienced fluctuations between cold warm climates, as indicated by the chemical weathering index ranging from 51.33 to 88.65. The CaO/(FeO + CaO), Rb/Sr and Ba/K ratios indicated that the paleosalinity changed from high to low. The Fe2O3/FeO, U/Th, V/Cr and Ni/Co ratios indicated an oxidizing sedimentary environment. The cathodoluminescence images, Th/U ratios and rare earth elements patterns of the detrital zircons all indicated a magmatic origin. Three samples showed significant peak ages of 224, 440, 748, 1870 and 2492 Ma, corresponding to the development of the Dabie Orogen. Our comprehensive analyses suggest that the Upper Triassic Puqi Group was formed by deposition during continental–continental collision. The Dabie Orogen was exhumed in the Late Triassic and supplied detrital sediments to the foreland basin.

Significance of organo-mineralogical constituents on pore distribution, fractals and gas sorption mechanism of Permian shale beds in Korba sub-basin of the Son-Mahanadi Valley, India

In this study, shale samples obtained from the Korbasub-basin of Central India have been evaluated for the significance of organo-inorganic constituents in terms of their source potential of gas genesis, pore-matrix setup, and gas adsorption and desorption. The samples were analysed for various properties, such as megascopic features, lithological variations, depositional facies, and sources of organic and inorganic sediments. Also, maceral content, mineralogical constituents, kerogen type, pore distribution, pore structure, fractal characteristics and gas storage capacity were examined. The analysis revealed a trend of alternating bands of carbonaceous matter, silts, intercalations, and fluvial bedding lithofacies patterns indicating that the sediments were deposited under fluvio-terrestrial-lacustrine depositional conditions. Ternary facies analysis of maceral composition and van Krevelen diagram suggested the evolutionary path of type IV kerogen and are thermally matured source material located within the dry hydrocarbon generation window. Evaluation of pore types and pore structures using BET sorption plots (hysteresis H3 and isotherm type IV) revealed the presence of cylindrical, slit and combined cylindrical-slit pores with two distinct fractal characteristics. The discrete macerals underwent partial decomposition during transportation and mixing with inorganic components (clay and minerals), which influenced organic matter preservation, gas genesis, pore fractals and storage mechanism. The chemical index of alteration (CIA – 88.36 to 91.97), weathering (CIW – 96.60 to 98.80) and compositional variation (ICV – 0.31 to 0.70) demonstrated the influence of partial decomposition and strong weathering patterns on the organo-inorganic matter. A significant correlation was observed between pore fractals and elemental composition, particularly related to the resistance of weathering elements such as MgO, Al2O3, Fe2O3, SiO2, P2O5, TiO2, etc., which partially contributed to the formation of pore rugged surfaces. Microscopic and XRD analyses were employed to determine the mineral type, grain shape and size, and their amount leading to the development of the shales brittleness index (MBI). The importance of brittle characteristics, governed by minerals and clays within the shale, is discussed in relation to the hydro-fracturing technique for permeability enhancement. The results of high-pressure methane sorption indicated a moderate gas storage potential. The variation in sorption capacity (VL – 6.65 to 8.25 cc/g) is described through relationships with the ICV, pore diameter, pore volume, liptinite and total maceral content. Fractal dimensions D1 (2.4571–2.5611) and D2 (2.5804–2.7529) exhibited a direct relationship with adsorption properties, indicating the presence of rugged surfaces associated with meso- and macro-scale pores, which primarily control gas storage in shale. This research offers detailed insights into shale gas, providing valuable information for CBM and petroleum operators engaged in methane gas exploration and production. While commercial CBM production has been ongoing in India for over a decade, the exploration and understanding of shale gas reservoir characteristics are still in progress. This investigation adds significant value and highlights the extensive opportunities for research and potentially commercially recovering shale gas in the Korba sub-basin.

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.

Petrography and Geochemistry of Sullavai Sandstones of Kanpa-Tempa, Chandrapur District, Maharashtra, India

Abstract The data on petrography and geochemical behaviour of Neoproterozoic siliciclastic sandstones of Kanpa-Tempa area from Chandrapur District are presented here to determine the provenance, source rock weathering and tectonic setting. The major elemental composition reveals that the Neoproterozoic sandstones are mainly as litharenite. The interrelationship of Zr vs. TiO2, Y/ Ni vs. Cr/V, TiO2 vs. Al2O3, high LREE/HREE ratios (8.97 to 12.46) and negative Eu anomalies (Eu/Eu*= 0.52 to 0.79) suggest that the sandstones were mainly derived from the parent felsic igneous rocks. The higher values of paleo-weathering indices such as Plagioclase Index of Alteration (PIA), grading from 66.42 to 80.82 and Chemical Index of Weathering (CIW), ranging from 70.58 to 82.39 clearly point out that the sediments and their source rocks experienced moderate to intense weathering. The Chemical Index of Alteration (CIA) values (ranging from 62.79 to 76.16) coupled with average content of K2O (1.66) is indicative of K-addition during diagenetic processes. Similarly lower values of K2O/Na2O ratio (0.52) suggest limited chemical maturity and SiO2-K2O/Na2O discrimination plot exhibits the active continental marginal tectonic settings.

Geochemical characterisation of mangrove sediments in Tiko (SW, Cameroon, West Africa): Implication for provenance, paleoweathering and sediment maturity

Geochemistry was performed on clastic core sediments from the Tiko Mangroves estuary, South western region of Cameroon, to categorise the rock source composition, tectonic setting, past weathering intensity of the source area in relation to past climate and sediment maturity in relation to sedimentary cycle. Plots of La/Co, La/Sc, Cr/Th, discriminant function (DF1&2), TiO2vs Al2O3 and TiO2 vs Zr point to an acid (felsic) and mixed (intermediate) rock source composition for the Tiko sediments. The acid composition portrayed by the sediments is also confirmed by their LREE (Light rare earth elements) abundance, and a negative Europium anomaly on chondrite normalisation, while the intermediate (mix) composition reflects the multiple sources of the sediments (Douala Basin and basaltic debris from Mount Cameroon). Binary plots Discriminant function (A-P) M, and Discriminant function (A-P) MT signpost active tectonic domain for the studied sediments, that resulted from the tectonothermal of the Pan African orogenic history and eruptive activity of the mount Cameroon. The weathering indexes denoted as CIX (chemical index of weathering) and PIX (plagioclase index of weathering) for the Tiko sediments advocate an intense source area weathering in a humid hot climate. The PIX advocate a high-level plagioclase lixiviation. The low values of ICV (index compositional variation) less than 1 (<1) couple with correlation plots Zr/Sc vs Th/Sc, and Zr vs (La/Yb)N confirms that Tiko mangrove sediments are matured recycled sediments with compositional variations. This is the first comprehensive provenance study of mangrove ecosystem sediments in Cameroon.

WEATHERING PATTERNS IN ALLUVIAL SOILS UNDER MEDITERRANEAN CLIMATIC CONDITIONS IN ALBANIA AND IMPLICATIONS FOR SOIL FERTILITY

This study comprehensively assesses weathering and soil development in the alluvial plains of Albania's Drin and Mat rivers. By analyzing soil properties, mineralogical compositions, and weathering indices, it provides crucial insights into the intricate link between geological processes and soil fertility in these key agricultural areas. The focus is on weathering indices such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA), which reveal distinct weathering patterns across soil profiles and alluvial plains. Drin River alluvial soils display moderate indices, signaling relatively lower weathering, while Mat River alluvial soils exhibit higher indices, indicating more pronounced weathering. The study emphasizes the role of mineral composition on weathering and soil development, with easily weathered minerals suggesting a more conducive environment for weathering in Mat River soils compared to Drin River soils. Elemental composition differences in these soils significantly impact fertility, potentially affecting agricultural productivity. Correlation analyses highlight the influence of mineralogy and chemical composition on weathering rates. This study's insights into weathering dynamics, mineralogical, and elemental composition in alluvial soils highlight soil fertility implications, crucial for optimizing agriculture and addressing environmental concerns in these vital Albanian regions.

The weathering process of carbonatite: weathering time.

Soil formation by rock weathering is driven by a combination of parent material, climate, organisms, topography, and time. Among these soil-forming factors, time plays a pivotal role in the weathering of carbonatite but it is a challenging factor to study quantitatively. A method for determining the weathering duration of carbonatite based on its weathering characteristics over a century-scale time period has not been clearly established. In this study, we selected abandoned carbonatite tombstones commonly found in the karst region of southwest China for investigation, using the date when the tombstones were erected as the onset of weathering. Chemical weathering indices were used to evaluate the weathering degree of different oxide contents produced by the carbonatite weathering process. In order to explore the weathering characteristics over time, the relationship between weathering duration and weathering degree was established. The results showed the following: (1) magnesium (Mg), aluminum (Al), silicon (Si), iron (Fe), titanium (Ti) are gradually enriched in the carbonatite regolith, and calcium (Ca) is gradually reduced. (2) The chemical indices of alteration (CIA), leaching coefficient (Lc), alumina-to-calcium ratio (AC) and mobiles index (Imob) can be successfully used for evaluation of the weathering degree of the carbonatite in different weathering time periods. (3) During the weathering of carbonatite, the weathering rate is a logarithmic function of time. Our research shows that over a period of more than 100 years of weathering, the carbonatite weathering process is characterized by fast weathering rates and low weathering degree in the early stages, but slow weathering rates in the later stages.

Interactions of soil quality, ages of alluvial fans, and mechanisms controlling total soil organic carbon dynamics

So far, no studies have tested how alluvial fan aging and associated geomorphological differences can affect the mechanisms that control soil organic carbon (SOC) dynamics. In order to understand the SOC dynamics, we quantified the relationship between soil quality (SQ) indicators and alluvial fans aging over area of about 10,000 km2 in north-eastern Iran, using a minimum data set (MDS) and regression analyses. Twenty seven soil attributes and weathering indices were measured at 90 old and young fans. Total SOC and its fractions were found as the key indicators of the MDS. Despite the higher content of SOC in younger fans (6.25 – 7.11 g kg−1), they exhibited a lower value of SQ (0.35 – 0.42). Younger fans had a low content of fine-sized pedogenic oxides, and, thus, a lower sorption potential, giving rise to a lower ability for stabilising SOC. The higher content of SOC in younger fans was due to an accumulation of coarse particulate organic carbon. Long-term exposure of the older surfaces to weathering caused a statistically significant increase in the chemical index of alteration (57.94 – 72.32 %), chemical index of weathering (64.3 – 77.2 %), the carbon size fraction 53 – 250 µm (2.66 – 5.56 g kg−1), the dithionite-extractable Al (48.4 – 59.2 g kg−1) and Fe (21.5 – 25.7 g kg−1) oxalate-extractable Al (25.6 – 32.7 g kg−1) and Fe (9.5 – 13.0 g kg−1). These characteristics promote physical protection of SOC against microbial decomposition. Alluvial fan aging leads to geomorphological differences in terms of the weathering degree, processes of flooding, inundation, and erosion, contributing to high variability of the SOC dynamics. A proper understanding of the relationships between the age evolution of landforms and associated variations in mechanism regulating the preservation and stability of soil C can help to develop new perspectives for geo-conservation and restoration efforts.

Response of Paleogene Fine-Grained Clastic Rock Deposits in the South Qiangtang Basin to Environments and Thermal Events on the Qinghai-Tibet Plateau.

The Chamdo Basin is a secondary basin in the eastern part of Tibet China and is one of the most promising of petroliferous basins for new petroleum exploration. The Qamdo Basin records a complex burial history from the Mesozoic to the Cenozoic; however, the poorly constrained sedimentology of Cenozoic strata in this basin has severely obscured the overall profile and impeded further explorations of oil and gas resources. Here, we conduct whole-rock geochemical analyses of major, trace, and rare earth elements in fine-grained clastic rocks of the Paleocene Gongjue Formation, Qamdo Basin to reveal depositional environments, provenance, and tectonic setting. Petrologically, the Gongjue Formation is dominated by red fine-grained sandy mudstones/siltstones with ripple marks. The high values of the chemical index of alteration (avg. of 78.93), chemical index of weathering (avg. of 90.10), and index of compositional variability (avg. of 2.5) suggest that the basin has undergone heavy weathering. Cross-plots of La vs Th, Th vs Sc vs Zr/10, and Th vs Co vs Zr/10 reveal a continental arc tectonic setting. Paleosalinity (Sr/Ba), paleoclimate (Sr/Cu), and redox proxies (V/Cr, U/Th, and enrichment factors of Mo and U) indicate brackish to saline and oxidizing paleowater masses during deposition of the Gongjue Formation. Provenance analyses via elements and petrology reveal that sediments in the Gongjue Formation are mainly derived from intermediate-acidic rocks of the upper crust. We conclude that the first and third members are more arid climate and heavily chemically weathered than the second member. In combination with previous studies of the structural evolution of the Qamdo Basin since the Paleogene, a model is built to describe the sedimentary environment and evolution of the Qamdo Basin during transition to the Paleocene. The first and third members, i.e., the Eg1 and Eg3 members of the Gongjue Formation, are dominated by an oxidizing environment of seawater-saltwater, and the climate ranges from warm and humid to arid and hot, with relatively stable environmental changes. The Eg2 member of the Gongjue Formation is dominated by an oxidizing environment of seawater-saltwater, and the climate ranges from warm and humid to arid and hot, with more frequent environmental evolution. Our model aids in better understanding of the Paleocene climate evolution of the eastern Tibetan Plateau.

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

Geochemical compositions and provenance of Late Holocene core sediments from Mullipallam Creek, southeast coast of India

Geochemical analyses of major oxides (SiO2, Al2O3, Fe2O3, Na2O, K2O, CaO, MgO, P2O5 and TiO2) were carried out on the Late Holocene core sediments in the Mullipallam Creek, Southeast coast of India to infer their texture, sediment classification and provenance for paleoweathering conditions. Based on their major oxides compositions, the sediments were classified as Fe-Shale. Bivariate plots of grain size parameters (mean against sorting) are distinguished between open and closed-basin conditions. Chemical Index of Alteration (C1-70.21; C2-69.02), Chemical Index of Weathering (C1-75.25; C2-74.68), Plagioclase Index of Alteration (C1-73.32; C2-72.44) indices and A-CN-K plot suggests moderate chemical weathering in the source area, which was favoured and accelerated under the existing humid conditions of the tropical climate. Al2O3 /TiO2 ratio also proposes the intermediate to felsic source rocks and some of the sediments are derived from mafics. The provenance discrimination diagram explains that the plots appeared in mafic provenance fields indicating that they are derived from different environments.

Chemical Weathering Indices and their Use for Paleoclimatic Reconstructions (on the Example of the Vendian‒Lower Cambrian Section of Podolsk Transnistria)

The article provides an overview of various indices/indicators (Vogt, Parker, CIA, CIW, PIA, MIA, etc.) used in the study of weathering profiles/crusts and reconstruction of paleoclimatic environments of sedimentary sequence accumulation. Their possibilities are demonstrated by the example of Vendian-Lower Cambrian terrigenous deposits of Podolsk Transnistria (southwestern slope of the Ukrainian Shield). The distribution of the ba1 index values in this section indicates the presence of the material most transformed by the processes of chemical weathering in the mudstones of the Nagoryany Formation, the lower part of the Danylivka and the middle part of the Studenytsya formations. For mudstones of the Danylivka–Zbruch interval, the HM values are close to the HMPAAS. For rocks of the Yaryshiv–Nagoryany interval, the HM values are slightly higher, and for mudstones in the lower part of the Yaryshiv Formation, they are comparable to those inherent in continental clays of a hot tropical climate. The average SA index for mudstones of the entire section is 5.6 ± ± 0.7. Mudstones of the Hrushka–Nagoryany interval, where SA SAPAAS, are composed of more weathered material. The WIP values in the mudstones of the Mohyliv and Yaryshiv formations, as well as in the upper part of the Zbruch Formation, correspond to the interval of their values between PAAS and the average Archean granite. Clay rocks of other formations have WIP ≤ WIPPAAS values. The average CIA value for mudstones is 71 ± 4, which practically corresponds to the CIA value (70), which separates the sediments of cold/arid and warm/humid climates. Variations in the CIW index along the section are symbate with variations in the CIA. The vast majority of mudstones are characterized by PIA PIAPAAS values. The average CPA value is 91 ± 4, which is also typical for PAAS. The above and other data show that on the basis of a “direct” interpretation of the values of various indices of chemical weathering inherent in fine-grained clastic rocks, the paleoclimate that existed in the Vendian‒Early Cambrian on the territory of Podolsk Transnistria was rather moderate or warm humid. Comparison of the CIA values of mudstones with the values of this indicator for the particulate suspended matter of modern rivers suggests that the climate in the Vendian‒Early Cambrian resembled dry and humid subtropical or dry tropical with elements of humid.

Soil chronosequence derived from landslides on the upper reach of Minjiang River, western China

Soil chronosequences derived from landslides with certain time series are the great avenue to elevate our understanding on the processes of pedogenesis, nutrient dynamics, and ecosystem evolution. However, the construction of reliable soil chronosequence from historical landslides remains intricate. Here, we presented a 22,000-year soil chronosequence from multiple landslides on the upper reach of Minjiang River, western China. The variation in a variety of pedogenesis indices and soil nutrients verified the reliability of the chronosequence. The silica-alumina ratio and silica sesquioxide ratio decreased significantly with soil age. This reflected the enrichment of Al/Fe/Ti oxides but the depletion of Si oxides with the soil development. Meanwhile, the values of the Chemical Index of Weathering and the Chemical Index of Alteration increased significantly with soil age, especially from 5 to 89 years. These variations were attributed to the soil weathering, which led to the destruction of soil minerals with the rapid loss of most of cations (e.g., K, Na, Ca, and Mg) during the soil development. The concentrations of carbon and nitrogen in topsoil increased with soil age, and the carbon accumulation rate slowed significantly from 5,500 to 22,000 years. The total phosphorus concentrations decreased with soil age, suggesting the gradual loss of soil phosphorus with soil development. The results indicate that the landslide chronosequence established on the upper reach of Minjiang River is reliable and delineates a long-term soil development process, which will provide a great platform for further improvement of biogeochemical theories and understanding sustainable vegetation restoration.

A 200-year snapshot of soil development in pyroclastic deposits derived from the 1815 super explosive eruption of Mount Tambora in Indonesia

Early-stage pedogenic processes and formation rates on completely obliterated volcanic landscapes, such as the super explosive 1815 Mount Tambora eruption, have not previously been robustly explored. The objectives of this study were to determine (i) the mineralogical composition of the sand fraction, selected physical and chemical soil properties and potential nutrient reserves after 200 years of pedogenesis, and (ii) chemical weathering indices, rate of soil formation, and rates of C and N accretion. Soil formation was examined for five soil profiles on stable plain/foot slope positions representing the diversity of soils in these landscape positions, which are important for agricultural production. Results showed that the soil mineralogical composition of the sand fraction was dominated by easily weatherable minerals (e.g., labradorite and augite volcanic glass) indicating high potential nutrient reserves (e.g., Ca2+, Mg2+, K+, P) as confirmed by X-ray fluorescence (XRF) analyses. Allophanic material formation was minimal (<2.3%) owing to the preferential accumulation of Al3+ into Al-humic complexes. The low contents of allophanic materials and metal-humus complexes resulted in low P-retention (17.5–43.4%) within the soil solum, with the highest value in surface horizons (33–43%). Morphological features showed rapid solum (A + B horizons) development of 22 to 107 cm. Shallow soils occurred on shallow eruption deposits (consisting of pyroclastic flow underlain by pumice), whereas the deepest soils were found on thick deposit consisting of either trachyandesite pyroclastic or basaltic andesite materials. The chemical index of alteration (CIA) followed the order of A horizons (48.4 ± 4.6) > B horizons (45.4 ± 2.4) > C horizons (43.8 ± 4.2) ≈ tephra/lava (43.1), indicating accumulation of Al oxides and depletion of base cations in the upper horizons. Similarly, the base depletion index (BDI) showed a trend of A horizons (1.13 ± 0.18) < B horizons (1.25 ± 0.09) < C horizons (1.34 ± 0.20) ≈ tephra/lava (1.35), indicating depletion of base cations (Ca2+, Mg2+, K+, Na+) from the soil surface to C horizons. Based on solum depths (A + B horizons) and 200 years of post-eruption soil development, the solum formation rate ranged from 1.2 to 5.3 mm yr−1. Appreciable stocks of SOC (2.3–12.8 kg C m−2) and SON (0.21–0.77 kg m−2) accumulated over the 200 year period. Eruption materials from the Mt. Tambora eruption with a precisely known timescale contributed new pedological insights documenting rapid soil formation rates from pyroclastic materials leading to a rapid recovery of soil functions to support agricultural production.

Comparison of the Late Miocene Sediments and Early Quaternary Red Paleosols in the Penghu Islands, Taiwan and Zhangpu, Fujian

This study aims to compare the clay mineralogy and whole-soil major chemistry of elements in late Miocene soil sediments and early Quaternary red paleosols in the Penghu Islands, (Pescadores), Taiwan, and Zhangpu Volcanic Park, Fujian. There were the late Miocene Chu Wan (CWI and CWII), Shiao Men Yu (SMY) and two intergrade red soils, Chu Wan (CW(irs)) and Shiao Men Yu (SMY(irs)), with three distinctive zones of different dominating kaolins in the profiles of the Penghu Islands. A Tong Wei (TW) paleosol of early Quaternary basaltic eruptions in the Penghu Islands was collected. The Anzei (AZ), Si Yu (HY) and Chianmei (CM) paleosols were sampled from the Penghu Islands and Yulinshi (YLS) paleosols near the Zhangpu Volcanic Park for this study. The CW and SMY paleosols erupted in the late Miocene, and the other paleosols erupted on the Penghu Islands. These paleosols were fractionated into clay fractions and subjected to soil physical and chemical analyses. Kaolin minerals were dominant in the CW(irs) and SMY(irs) paleosols. The top layer (layer one) in the CW(irs) was 7 Å-halloysite, and order/disordered kaolinites were present in layers two and three. The CW(irs) and SMY(irs) hexagonal-like, platy kaolinites (0.1–0.2 µm in diameter), spheroidal and hollow 7 Å-halloysite (layer 1) was determined with transmission electron microscopic (TEM) investigations. The early Quaternary red soil of TW consisted of kaolinite, illite, vermiculite and smectite clay assemblages. Late Miocene paleosols were classified as fine, kaolinite, hyperthermic and Typic Rhodic Paleudults, and the early Quaternary red paleosols were classified as fine, mixed, hyperthermic and Typic Rodistalf, respectively. Late Miocene paleosols contained more clays, lower SiO2/Al2O3 and higher chemical index of weathering (CIW) than early Quaternary paleosols. The kaolin, illite, smectite and vermiculite mineralogy, physical and chemical properties of paleosols and landscapes in the Zhangpu YLS, Fujian, were similar to those of late Miocene sediments and early Quaternary red paleosols in the Penghu Islands.

Paleo-weathering of different basement rocks along a first-order nonconformity - case study at the post-Variscan nonconformity (Germany)

Intracratonic sedimentary basins develop on first-order nonconformities. Although the evolution of such basins has been the focus of many studies, the formation of the basement surfaces has rarely been considered. In this paper, we investigated the physical and chemical paleoweathering of different basement rocks at the post-Variscan nonconformity in Central Europe. We used a comprehensive approach by accounting for different scales and integrating physical and chemical weathering. Physical weathering was qualitatively classified at the macro/mesoscale and quantitatively classified at the microscale using thin sections and through measuring fracture areas by image analysis. Chemical weathering was quantified by distinguishing the mineralogical and geochemical characteristics measured by X-ray diffractometry (XRD), X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Compared to previous studies, common physical and chemical weathering indices were normalized to the rock types to improve the weathering intensity comparison. Clay transformation and carbonate/dolomite precipitation in the paleoweathering sections indicate a temperature interval of 100 to 300 °C for the circulating fluids during burial. The maximum chemical weathering intensity was found at the top surface of the basaltic andesite with a CIAN (normalized chemical index of alteration) value of 83, whereas the IPWN (normalized index of physical weathering) was less than 0.1. The gabbroic diorite and granite had a CIAN value of 78, whereas the physical weathering intensity was approximately 0.6. The lowest chemical weathering intensity was observed at the top of the granodiorite and tonalite at 71, and both rock types showed the highest physical weathering intensity of approximately 4. Because of the normalization procedure, the differences in the ratio of chemical versus physical weathering can be directly linked to aridity-humidity changes in the lower Permian paleoclimate. The concept and results of this work can be used for future studies on continental paleoclimate as well as for reservoir modeling.