Intense Weathering Research Articles

Multidimensional Approach for the Assessment of Environmental Pollution and Health Risk Associated With V, Ni, Cr, Cu, and Zn in the Recent Sediments of Kabini Interstate River, Southeastern Western Ghats, India

ABSTRACTThe present work intends to study the variation of heavy metals (HMs) to scrutinize the scenario of pollution index and associated environmental risk, as well as source weathering conditions along the Kabini River. The decreasing order of concentration of HMs along the basin is Cr > V > Ni > Zn > Cu. The paper spotlights the pollution grade in sediments, assessed by the geo‐accumulation index (Igeo), contamination factor (Cf), pollution load index (PLI), and enrichment factor (Ef). The assessment of ecological risk is studied as potential ecological risk index (RI), toxic risk index (TRI), and modified hazard quotients (mHQs). As per the Igeo and Cf, V and Cr concentrations are higher in the region. Further, PLI confirmed that 35% of samples exceeded the limits of sediment quality guidelines. The RI and TRI values show that a higher ecological risk is associated with Ni, V, and Cr and with Cu and Cr, respectively. Additionally, the 23% Ni and 20% Cu samples from mHQ indicate the severity of pollution in the aquatic environment. The inputs from anthropogenic and natural sources change the concentration of these HMs along the region. Moreover, the study of CIA and plagioclase index of alteration plots confirmed the low to intense weathering conditions. The statistical approach shows the linkage between Cr–V, Cu–Zn, and principal component analysis–derived prominent sources: industrial and agricultural runoff, as well as higher silicate weathering, contribute to the HMs concentration in the region. The Kabini River passes through different climatic and land‐use domains of Kerala and Karnataka, which eventually regulate the HM concentration and geo‐environmental processes in the region and affect the health risk to humans in one or the other way. The reference data generated from the present work are absolutely new and would be significant in the future for deriving sustainable development plans for the well‐being of human beings and precious natural resources.

Weathering and pedogenesis of the Holocene aeolian loess-paleosol sections in the Guanzhong Basin on the Chinese Loess Plateau

The aeolian loess-paleosol sections on the Chinese Loess Plateau (CLP) represent invaluable archives for elucidating the dynamics of the East Asian Monsoon (EAM) across Quaternary glacial-interglacial cycles. In this study, a Holocene aeolian loess-paleosol section in the Guanzhong Basin on the CLP was meticulously investigated to assess the intensity of weathering and pedogenesis, and to discern its paleoclimatic implications. Through comprehensive analysis of chemical element composition and micromorphology, it was revealed that the majority of stratigraphic units within the Holocene aeolian loess-paleosol section exhibit indications of weak weathering and pedogenesis, while the mid-Holocene paleosol approaches to moderate weathering and pedogenesis. Hierarchically, the intensity of weathering and pedogenesis among the stratigraphic units can be ranked as follows: paleosol > topsoil > recent loess > transitional loess. Furthermore, the chemical index of alteration (CIA) values of the mid-Holocene paleosol exhibit a gradient decline from southeast to northwest, aligning with present-day temperature and precipitation distributions under the predominant influence of the East Asian summer Monsoon (EASM). Thus, it can be inferred that the robust impact of the EASM on weathering and pedogenesis of paleosol was pronounced during the mid-Holocene Climatic Optimum. These results are of significance in exploring the Holocene weathering and pedogenesis and paleoenvironmental evolution on the CLP.

Provenance, Intensity of Weathering, and Economic Potential of Placer-bearing Sediments on the Shelf off Quilon, Southwestern Coast, India

ABSTRACT In this study, the mineralogy and geochemistry of sediments of the continental shelf off Quilon, southwest coast, India is used as proxies to constrain their provenance, the intensity of weathering at source, and economic potential. The weathering index calculations were carried out on the sediments and the results showed that Chemical Alteration Index (CIA) (Average = 72.88), Chemical Index of Weathering (CIW) (Average = 92.72), and Plagioclase Alteration Index (PIA) (Average = 89.74) are high, indicating moderate to intense source area weathering. High source area weathering is also supported by high Th/U ratio (Average = 5.68) which is above the average crustal Th/U ratio of 3.8. The sediments are first-cycle sediments derived from the nearby source area, as evidenced by the identification of unaltered heavy minerals and rock-forming minerals, along with a high Average Composition Variability Index (ICV) (Average = 1.20). The high K2O/Na2O ratios (Average = 3.88), and LREE/HREE ratios (Average = 20), plotting of samples in the felsic field of various binary plots (SiO2 vs. Al2O3/TiO2, Zr vs. TiO2, Ce vs. La/Yb and La/Th vs. Hf binary plots) and normalized REE patterns with LREE enrichment and negative Eu anomaly indicate the sediments were primarily derived from Khondalites of the Trivandrum block and were transported by the Kallada and Ithikkara rivers. Average Σ REE, Th, and U concentrations are 222 ppm, 15.2 ppm, and 2.58 ppm respectively in the bulk sediments. The heavy mineral separates showed significantly increased concentrations of Σ REE (Average = 3009 ppm), Th (Average = 478 ppm), and U (Average = 30 ppm) due to the presence of monazite. Due to high Σ REE, Th, and U concentrations in the sediments due to monazite, present study recommend for further exploration of these sediments, which could contribute significantly to the resource base of the nation.

Provenance and tectonic setting of sandstones of the Lomas Coloradas Formation, Cabullona Group, Sonora, México: Constraints on petrography and geochemistry

The sedimentary rocks of the Cabullona Group are well exposed in the Cabullona Basin of northeastern Sonora, México, which represent syntectonic sedimentation associated with Laramide-style deformation during the Campanian−early Maastrichtian. The sandstones of the Lomas Coloradas Formation deposited at the upper part of the Cabullona Group. Petrography and geochemical (major, trace, and rare earth elements) studies were carried out on the sandstones to interpret the palaeoweathering, provenance, and tectonic setting of the Lomas Coloradas Formation sandstones. Most of the sandstone modal analysis data plotted in the QFL and QmFLt ternary diagrams fall into the fields of dissected arcs and recycled orogens, respectively. Geochemically the sandstones are classified as litharenites while few samples plot into the arkosic field. The chondrite-normalized REE diagrams for sandstones have LREE-enriched, relatively flat HREE patterns with negative Eu anomalies. CIA values and the A‒CN‒K diagram indicate a low intensity of chemical weathering in the source area. The tectonic setting diagram suggests both arc and rift settings for the studied sandstones. The bivariate and ternary diagrams and elemental ratios suggest a felsic source for the Lomas Coloradas Formation. The average REE patterns of the studied sandstones are comparable with REE patterns of the granite from the Caborca block, the rhyolite and granite of the Tarahumara Formation, and the Mesozoic felsic volcanic rocks. The modeled mixture of 40% Proterozoic granite, 30% Triassic arc, 10% Jurassic arc, and 20% Laramide arc represents the probable source rocks for the Lomas Coloradas Formation.

The Hydrochemistry Characteristics and Chemical Weathering Intensity of an Anthropogenically Involved Catchment, South China

The hydrochemical characteristics of watersheds are influenced by many factors, with chemical weathering and human activities exerting the most substantial influence. Performing a quantitative evaluation of the factors contributing to the chemical weathering of rocks is of significant scientific importance. This research zeroes in on the Qingtang River basin to elaborate on the hydrochemical characteristic, explore the origins of ions, and quantify the influence of anthropogenic discharges amidst cation interferences, thus improving the accuracy of chemical weathering rate estimations. The samples encompassed surface water, groundwater, and water from dripping in karst caves. The findings indicate that human-induced alterations significantly influence hydrogeochemical dynamics, although chemical weathering of rocks in their natural state is the controlling factor. The mean contributions of cations from atmospheric deposition, human inputs, carbonate weathering, and silicate weathering were 17.56%, 21.05%, 51.77%, and 9.54%, respectively. The chemical weathering rate for carbonate rocks was 62.4 t·km−2·a−1, which increased by 27.87% due to the influence of exogenous acids. The anthropogenic impact is predominantly evident in two aspects: (1) the alteration of hydrochemical processes within the watershed through direct input of ions, and (2) the acceleration of rock weathering rates in the watershed due to the exogenous acids.

Solid Earth forcing of Mesozoic oceanic anoxic events

Oceanic anoxic events are geologically abrupt phases of extreme oxygen depletion in the oceans that disrupted marine ecosystems and brought about evolutionary turnover. Typically lasting ~1.5 million years, these events occurred frequently during the Mesozoic era, from about 183 to 85 million years ago, an interval associated with continental breakup and widespread large igneous province volcanism. One hypothesis suggests that anoxic events resulted from enhanced chemical weathering of Earth’s surface in a greenhouse world shaped by high volcanic carbon outgassing. Here we test this hypothesis using a combination of plate reconstructions, tectonic–geochemical analysis and global biogeochemical modelling. We show that enhanced weathering of mafic lithologies during continental breakup and nascent seafloor spreading can plausibly drive a succession of anoxic events. Weathering pulses collectively gave rise to substantial releases of the nutrient phosphorus to the oceans, stimulating biological primary production. This, in turn, enhanced organic carbon burial and caused widespread ocean deoxygenation on a scale sufficient to drive recurrent anoxia. This model complements volcanic outgassing-centred hypotheses for triggering these events by demonstrating well-quantified basaltic sources of phosphorus release during periods of intense weathering related to climate warmth. Our study highlights a close coupling between the solid Earth and biosphere during continental reorganization.

Enhanced erosion and silicate weathering of the West African craton during the late Cretaceous cooling evidenced by mineralogical and Hf[sbnd]Nd isotope proxies

The evolution of oceanic temperatures between the Turonian and the K/T boundary indicates a long-term cooling coincident with a decrease of atmospheric CO2 levels, yet the cause of climate cooling at that time still remains debated. In this study, we evaluated the possible implication of enhanced silicate weathering as a sink for atmospheric CO2 by applying paired NdHf isotope measurements to detrital clay records from the West African margin. The use of this novel proxy for chemical weathering intensity (ΔɛHf(t)clay) was complemented by additional mineralogical and major-trace element analyses in order to investigate the variability of mechanical erosion patterns and further explore potential linkages between tectonics, weathering and climate during the late Cretaceous.Our ΔɛHf(t)clay data suggest more intense silicate weathering on the West African Craton during the Santonian to the middle Campanian period, coincident with enhanced physical erosional inputs as inferred from higher Quartz/Clays and Feldspar/Clays ratios. This observation suggests that the shift towards intensified chemical weathering at that time was driven by enhanced mechanical erosion, possibly related to a moderate tectonic event on the West African craton. Evidence for increasing kaolinite contents and higher ΔɛHf(t)clay values during the Maastrichtian point towards more hydrolysing conditions, inducing either destabilization of older Mesozoic lateritic material or favouring the development of kaolinite-rich soils.Overall, this study was compared with several new data of chemical weathering evolution along the south Atlantic margins, adding new insights on tectonic-weathering-climate interactions during the late Cretaceous, suggesting a possible link between silicate weathering feedbacks and global cooling at that time.

Experimental analysis of dust deposition and physical weathering intensity in the Gobi Desert

Experimental analysis of dust deposition and physical weathering intensity in the Gobi Desert

Application of (U-Th)/He hematite geochronology to the Çaldağ lateritic Ni-Co deposit, Western Anatolia: Implications for multi-stage weathering events during interglacial periods/segments

Lateritic Ni-Co deposits are supergene deposits that develop due to intense weathering of the underlying ultramafic parent rocks and/or their serpentinized equivalents under tropical to sub-tropical climatic conditions. These deposits provide not only important sources of valuable metals such as iron, aluminium, nickel, and cobalt, but they also provide a proxy for paleoclimatic conditions. In this regard, geochronological studies on these deposits are critical to determine the timing of the paleoclimatic conditions, which is important for a better understanding of the paleoclimate at regional scale and for identification of favourable weathering periods that can be targeted in the exploration of undiscovered lateritic deposits in a region. In this contribution, we report hematite (U-Th)/He geochronology results from a well-preserved Çaldağ lateritic Ni-Co deposit in Western Türkiye. We sampled the different parts of the lateritic profile from the different laterite zones at the Çaldağ deposit and carried out analyses of polished thin section to determine and identify the phases of hematite formation and primary hematite formed during primary lateritization. Then, we applied scanning electron microscopy (SEM) analysis and TESCAN Integrated Mineral Analyser (TIMA) mineral mapping to identify the suitable areas on primary hematites for subsequent (U-Th)/He dating.Primary hematites are detected at the base of the lateritic profiles (transition between the limonite zone and altered serpentinite) that are only in-situ parts of the laterites exposed in two different pits in the deposit. The obtained (U-Th)/He dates of ca. 502, 206, 178, and 63 ka correspond to the interglacial periods. The three youngest (U-Th)/He dates (206, 178, and 63 ka) from the weathering front of the hematite pit become younger towards the deeper parts of the profile in the direction of weathering. The ages indicate the weathering processes should have lasted until the Quaternary with some interruptions during interglacial periods/segments, despite the fact that the main intensive lateralization period is thought to be during the Middle Eocene.This study presents the first hematite (U-Th)/He dating of lateritic Ni-Co deposits and demonstrates the reliable use of this method after a careful selection of hematite samples. Our results suggest that, in contrast to the short-living lateritization model for lateritic Ni-Co deposits, they may have a multi-stage weathering history throughout their long-lasting development. In addition, the study showed that it has huge potential for the dating of lateritization and weathering processes that are related to paleoclimatic events. Finally, knowledge of the favourable paleoclimatic periods of chemical weathering in a region may help in determining the potential areas for ultramafic exposures for discovering new lateritic deposits.

Sediment composition and U–Pb ages of detrital zircons in the Salina Cruz and Puerto Ángel beaches along the Gulf of Tehuantepec, Mexican Pacific

The Salina Cruz and Puerto Ángel beach areas in the Gulf of Tehuantepec, Mexican Pacific coast represent an important economic sector of the region. In this study, the mineralogy and geochemistry of bulk sediments, and geochronology of 400 detrital zircons recovered from the beach sediments were analysed to investigate their origin. The sediments are abundant in quartz, feldspar, ilmenite, cordierite, aragonite and anorthite. The chemical index of weathering revealed a moderate to intense weathering in the source area. The chondrite normalized REE patterns of bulk sediments are similar to the found in the Upper Continental Crust, suggesting the derivation of sediments from felsic igneous rocks. The REE patterns of zircons and the trace elemental ratios reveal a continental crust origin. Zircon U–Pb ages in the Salina Cruz beach were represented by Proterozoic (~545.1–1314.1 Ma; n = 170) and Cenozoic (~0.01–66 Ma; n = 20). The Puerto Ángel beach was abundant in Proterozoic zircon grains (~600.9–1171.4 Ma; n = 109) and followed by Mesozoic grains (~73.78–246.9 Ma; n = 40). The comparison of zircon U–Pb ages of this study with probable source rocks reveals that the Oaxaquia Terrane and Chiapas Massif Complex were the major contributors of Proterozoic zircons to the coastal areas. Similarly, the results indicate that the Cenozoic zircons were contributed by the Chiapas Massif Complex, coastal batholith and Cuicateco Terrane. The Mesozoic zircons are very few, derived from the nearby Xolapa Complex and the Chuacús Terrane.

Provenance and Paleoclimate of the Triassic to Middle Jurassic Adigrat Sandstone, Blue Nile Basin, Central Ethiopia

AbstractMineralogical and geochemical studies have been undertaken on the Triassic to Lower Jurassic Adigrat Sandstone of the Blue Nile Basin of central Ethiopia to infer its source rock type, paleoweathering, and paleoclimatic history. The Adigrat Sandstone occurs at the basal section of the Mesozoic sedimentary formation and unconformably overlays the Neoproterozoic–Paleozoic crystalline rocks, or locally, the Karroo sediments in the northern Blue Nile Basin. A mineralogical study reveals that quartz (Q), feldspars (F), and lithic fragments (L) are the framework grains of the sandstone. On the QFL diagram, the plot of the modal composition of the sandstone mainly falls within the feldspathic arenite and quartzose arenite fields. The geochemical data of the lower section of the sandstone mainly falls within the arkose and subarkose fields, whereas the upper section data falls within the quartzose and sublithic arenite fields. Mineralogical and geochemical weathering indices indicate that the provenances of the Adigrat Sandstone were exposed to pronounced weathering intensity, where the lower part of the sandstone was controlled by arid to semi‐arid conditions, whereas the upper section was linked to humid to semi‐humid (tropical to subtropical) climatic conditions. Mineralogical and geochemical data also indicate that mafic to intermediate basement rocks were the primary source rocks of the sediment. Perhaps the sediment was assumed to have been reworked by multi‐cyclic sedimentary processes. The discriminant function diagram, the REE pattern, La/Th vs. La/Yb, and the Th–Hf–Co plot are consistent. A comparison of provenance studies for the Adigrat Sandstone in the Blue Nile Basin and the Mekele outlier of northern Ethiopia indicates that the sediment of the former is highly sorted, experienced higher weathering intensity, and compositionally derived from mafic to intermediate crystalline rocks. On the other hand, the sediment of the latter is essentially a weathering product of felsic rocks.

Redox changes in the Iapetus Ocean during the Late Ordovician extinction crises

The cause of the Late Ordovician mass extinction (LOME) is widely debated, with glaciation, volcanism and oceanic redox fluctuations being proposed as possible drivers. Here, we apply a multi-proxy approach to deep-water Iapetus Ocean samples from Dob's Linn, Scotland, to determine oceanic redox conditions and changes in chemical weathering intensity. We document major redox fluctuations between anoxic ferruginous and oxic conditions during the first, end-Katian extinction pulse, whereas the end-Hirnantian extinction phase witnessed more persistent anoxia. These two episodes were separated by oxic conditions and a major, short-lived decline in chemical weathering during the Hirnantian glaciation, suggesting that although global cooling may have placed stress on certain biota, it was unlikely to be the cause of the extinction crisis. Late Hirnantian anoxia persisted into the Silurian, with widespread euxinia resulting in global drawdown of redox-sensitive trace metals. Recent studies have identified a mid-Katian biotic crisis and recovery prior to the LOME, although the precise stratigraphic position is not yet defined. The mid-Katian record at Dob's Linn shows a major redox change, with dysoxic to anoxic ferruginous deep ocean waters giving way to well-oxygenated conditions at this time. However, links between the mid-Katian biotic crisis and these redox changes remain unclear.

Strontium Isotopic Composition as Tracers for Identifying Groundwater Recharge Sources in the Choushui River Alluvial Plain, Western Taiwan

Groundwater is a vital resource in the Chuoshui River alluvial plain (CSAP), a key agricultural area in Taiwan. Understanding groundwater recharge is crucial for sustainable water management amidst changing climatic conditions and increasing water demand. This study investigates the major ion composition, solute Sr concentrations, and 87Sr/86Sr ratios in groundwater and stream water from the Choushui River (CSR) to trace groundwater recharge sources. The Piper diagram reveals that most groundwater samples are of the freshwater Ca–HCO3 type, aligning with the total dissolved solids (TDS) classification. TDS and major ion compositions indicate that groundwater near Baguashan Terrace (BGT) and Douliu Hill (DLH) primarily derives from stream water and rainwater. Na+ and Cl− enrichment in some aquifers of BGT and DLH is attributed to the dissolution of paleo-sea salt and mixing with paleo-seawater from sedimentary porewater. Elevated dissolved Sr concentrations and lower 87Sr/86Sr ratios in these aquifers further support the intrusion of paleo-seawater. Groundwater in the proximal fan shows high TDS due to intensive weathering, complicating the use of TDS as a tracer. Sr isotopic compositions and solute Sr2+ concentrations effectively distinguish recharge sources, revealing that the CSR mainstream primarily recharges the proximal fan and BGT region, while CSR tributaries and rainwater mainly recharge the DLH region. This study concludes that Sr isotopic compositions and solute Sr2+ concentrations are more reliable than TDS and major ion compositions in identifying groundwater recharge sources, enhancing our understanding of groundwater origins and the processes affecting water quality.

Climatic and Environmental Impacts on the Sedimentation of the SW Taiwan Margin Since the Last Deglaciation: Geochemical and Mineralogical Investigations

AbstractMany scientific studies have been conducted to constrain present and past source‐to‐sink processes and their controlling factors. The role of typhoon and monsoon rainfall on chemical weathering and soils erosion in east Asia is still not well established. Clay minerals and major elements, combined with Nd and Sr isotopic compositions were analyzed on sediments from Core MD18‐3569 located on the Taiwan margin in the northeastern South China Sea. The aim was to reconstruct the weathering history of small river basins of southwest Taiwan and to establish the impact of East Asian summer monsoon and typhoon rainfall on source to sink processes since the last glacial period. 87Sr/86Sr and ɛNd values and predominant illite‐chlorite indicate that the rivers of southwest Taiwan is the sole source of sediments to Core MD18‐3569 since last deglaciation. Variations in clay mineral assemblages and major elements allowed us to evaluate the intensity of past weathering in the rivers of southwest Taiwan. We demonstrated that long‐term changes of chemical weathering intensity record from Taiwan are driven by changes in the summer monsoon rainfall. The deglaciation is characterized by a progressive increase in the intensity of chemical weathering, which peaked at the beginning of the Holocene. The chemical weathering degree of sediments from Taiwan decreases during the Holocene concurrently with a weakening of the summer monsoon, increase in typhoon activity, and changes in the vegetation cover. All these processes induce soil erosion, regressive pedogenesis, due to shorter residence time of minerals in the soils of southwest Taiwan.

Paleoclimate Controls on West African Dust Inferred from Rb/Sr and Si/Al of Sediments in an Eastern Equatorial Atlantic Marine Core

Increased dust emissions from dryland areas and their effects on human health, ecosystem viability, and environmental change are a global concern in the face of the growing climate crisis. Dust plume emissions from the West African landmass, Sahara, and Sahel areas comprise a major fraction of the global aerosol budget. Dust plume intensity is closely related to regional winds (e.g., Harmattan, Sahara Air Layer), the Intertropical Convergence Zone, monsoonal seasonality, marine currents, and physiography. To study terrigenous material emitted from the continent over the last ~260 kyr (late Quaternary), we used X-ray fluorescence spectroscopy (XRF) to analyze a ~755 cm long marine sediment core from the eastern equatorial Atlantic Ocean, resulting in nearly 1400 discrete measurements. Spectral analysis results suggest that concentrations of elements (Rb, Sr, Si, Al) preserved in the sediments are correlated to different types of orbital climate forcing. Chemical weathering intensity indicated by the Rb/Sr ratio was sensitive to seasonal insolation variations controlled by precession cycles (23–18 kyr), which presumably reflects the relationship between monsoonal rainfall and sensible heating of the continent. Spectral analysis of silicate mineral grain size (Si/Al) showed significant 40 kyr cycles that were paced by obliquity. Based on these data, we infer that winter tradewind activity accelerated in response to the intertropical insolation gradient induced by high obliquity. High Rb/Sr ratios during the last glacial maximum and penultimate glacial maximum may have been due to a predominance of mechanical weathering over chemical weathering under dry/cool climates or the dissolution of Sr-bearing carbonates by corrosive glacial bottom waters.

Siliceous deposition in limestone-marl alternations of the Yangtze Carbonate platform during the Permian Chert Event

During the Permian Chert Event (PCE), limestone-marl alternations (LMAs), contemporaneously developing in the Yangtze region with chert-mudstone alternations, differed from typical LMAs by their enrichment in authigenic siliceous components (quartziferous components and Mg-phyllosilicates). However, the factors driving the transition from distal chert deposits to proximal siliceous-rich carbonate deposits remain unclear, and the genesis of authigenic siliceous components is puzzling. Resolving these issues could provide a deeper understanding of the paleoclimate and paleoenvironment during the PCE. Optical and SEM observations and geochemical analyses revealed that Si4+, derived from seawater, silica-secreting organisms, and terrigenous clasts, precipitated as authigenic quartziferous components under relatively acidic conditions, while it precipitated as Mg-phyllosilicates through reverse weathering by combining with the dissolved high-Mg calcites under relatively alkaline conditions. Through the facies division of LMAs, its variations describe relative and short-term sea-level fluctuations in the Yangtze Carbonate Platform (YCP). By integrating tendency comparisons and time series analyses of sea level fluctuations, continental weathering intensity, authigenic siliceous content, and relative proportions of quartz vs. Mg-phyllosilicates, four proxies exhibit covariation and similar astronomical signals, indicating that the high sea level period of the YCP, corresponding to intensified continental weathering, favored the deposition of authigenic siliceous components and reverse weathering. Because the facies variations encompass short eccentricity, obliquity, and precession cycles, sea level fluctuations are considered to have been influenced by Gondwana glaciation P3. The seawater in the continental shelf cooled and became rich in silica and nutrients under the effect of upwelling. Interglacial periods may trigger high sea levels and intensified continental weathering in the YCP, facilitating the influx of Si-rich eutrophic seawater and stimulating biological silica secretion by radiolarians. However, the direct precipitation of activated silica resulted in weakened reverse weathering. Consequently, the lithological transformation from distal to proximal areas during the PCE was attributed to differences in silica-secreting organism abundance, upwelling intensity, biological pump activity, reverse weathering intensity, OM abundance, pH conditions, and seawater temperature between the continental shelf and carbonate platform.

Using the pedogenic oxide ratio in distinguishing volcanic soil weathering intensity in subtropical region

Pedogenic oxide ratio (POR) helps identify and understand pedogenic processes. However, POR is seldom used to study and distinguish the weathering intensity of volcanic soils that are moderately weathered in the subtropical region. The research was conducted by collecting thirty-three subtropical volcanic soils from the northeastern Tatung Volcanic Group (TVG) region in Yangmingshan National Park, near Taipei, located in northern Taiwan. These volcanic soils could be grouped into two groups with different weathering intensities based on three weathering indices, pedogenic Fe-oxides ratios (PORs) - Feo/Fed, ((Fed-Feo)/Fet), and total reserve in bases (TRB): the highly weathered (HW) group and the lower weathered (LW) group. The two PORs show significant differences between the two groups, but not for TRB, which indicates the PORs are a good indicator for providing quantitative measurements of weathering intensity. Except for the soil bulk density (BD) meeting andic soil properties, the soils of the HW group have a lower content of Al plus 1/2 Fe content (by ammonium oxalate) (Alo + 1/2Feo) and phosphorus (P) retention, and soils of the LW group only have a lower P retention. Within those soil physicochemical properties and selective dissolution analysis results and index values, Alo + 1/2Feo, pyrophosphate extractable C (Cp), P retention, and dithionite-citrate-bicarbonate (DCB) extractable aluminum (Ald) are four critical factors for the discrimination of the soils. The soils in the study area still have relict volcanic soil properties after moderately weathered. Our research results indicate that the PO and POR are good indicators of moderately weathered volcanic soils in the subtropical region, allowing for a more precise assessment of the soil weathering process, in addition to quantitative measurements of weathering intensity.

Geochemistry of Neoproterozoic arenites from the Murwara area, Katni District, Madhya Pradesh: Implications for provenance, weathering and Tectonic Setting

Geochemical analysis in terms of major, trace and rare earth elements of the Neo-Proterozoic arenites of Rewa and Bhander Groups of the Vindhyan Supergroup from Murwara, Katni district, M.P., has been carried out to determine the provenance, weathering and tectonic setting. The arenites are rich in SiO2 content but less in Na2O, K2O and CaO contents, suggesting the dominance of quartz and less amount of feldspars and rock fragments. Geochemically, these rocks are classified as quartz arenites to sub litharenite to sub-arkose. The CIA (75-98) and PIA values for these arenites and A-CN-K diagram indicates a high intensity of weathering in the source area. High LREE/HREE ratios, negative Eu anomaly and La/Sc, Th/Sc, Th/Co and Cr/Th ratio values suggest felsic source of these arenites. The discriminant diagram for these arenites indicates a quartzose sedimentary provenance. Ni vs TiO2 and Th/Sc vs Sc bivariate plots indicate that the felsic rocks have been the source rock for these arenites. The discrimination diagrams based on log (K2O+Na2O) vs SiO2 and Fe2O3+MgO vs TiO2 contents show a passive margin setting. Whereas the results of new discriminant function multi-dimensional diagram for the high silica arenites reveals a change from collision to continental rift setting

Geochemistry of Pelites at Chengmen Area: Implications for Sediments Resource and Tectonic Environment.

The pelite samples were collected from drillholes from the Chengmen area of the Fuzhou Basin of Fujian, China to reveal the sediments resource and tectonic environment of these pelites via an analysis of its lithology and geochemistry. The rare earth element distribution pattern of the pelites exhibited a high degree of fractionation between light and heavy rare earth elements, moderate negative Eu anomalies, and positive Ce anomalies, which are consistent with the rare earth element distribution pattern of Minjiang sediments and Fujian soils. Moreover, the variations in trace elements are also generally consistent, indicating a common provenance. The extremely high chemical index of alteration (CIA) and index of chemical variability (ICV) values of the pelites suggest that the source area experienced intense weathering, indicating a subtropical hot and humid climate environment in the source area and the Fuzhou Basin at that time. The source rock attribute discrimination diagrams show that the main source of pelites is felsic igneous rocks. The ratios of REDOX parameters show that during the sedimentary period, the water body in the study area was predominantly in an oxidizing environment. Furthermore, the tectonic background diagrams reveal that the source area underwent geological tectonic evolution processes of active and passive continental margins, marking the transition from the continental margin above the subduction of the ancient Pacific plate to the continental margin extension after subduction cessation.

Quartz arenites as signatures of cratonisation: examples from the Archaean Stratigraphic Record, southern Africa

Abstract Holocene quartz-rich sands such as in the Orinoco River of Venezuela and Columbia, develop under a unique set of conditions including tectonic stability, intense weathering and long-term storage of sediment prior to burial. This review paper proposes that a similar set of conditions existed on the Mesoarchaean Earth by 3.0 Ga. Compositionally and texturally mature quartz arenites are present in the Mesoarchaean Hospital Hill Subgroup and correlative lower Mozaan Group, in the cover rocks of the Beitbridge Complex in the Limpopo Belt and at Buhwa in southern Zimbabwe as well as the Neoarchaean Manjeri Formation of Zimbabwe. These quartz arenites are interpreted as first-cycle and developed following the formation of stable cratons under conditions of slow subsidence (<10 cm/1 000 years), intense weathering in a hostile chemical environment related to the ambient carbon dioxide-rich atmosphere, long-distance intrabasinal transport by tides and/or waves and microbial processes that influenced the local chemical environment. Similar examples of Mesoarchaean quartz arenites are documented from the Yilgarn Block in Western Australia, the Slave and Superior provinces in Canada and the Dharwar and Singhbhum cratons in India. On a global scale, cratonisation was diachronous with the Kaapvaal Craton stabilised on a regional scale by 3.0 Ga whereas microcontinents existed over the remainder of Earth.