Chemical Weathering Processes Research Articles

Middle Jurassic - Early Cretaceous drastic paleoenvironmental changes in the Ordos Basin: Constraints on sandstone-type uranium mineralization

Middle Jurassic - Early Cretaceous paleoenvironmental evolution is fundamental to U (Uranium) migration and U-enrichment in the Ordos Basin. However, the detailed long-term terrestrial climate evolution across the Jurassic/Cretaceous (J/K) transition is still lacking. This study presents a comprehensive geochemical element analysis of 88 fine-grained sediments from Well Pengyang-SDI to verify the major paleoenvironmental changes including the changes in paleoclimate, paleoweathering, paleosalinity, and paleo-redox conditions. Various paleoweathering proxies (e.g., CIA) suggest that the sediments in the source area experienced a stronger chemical weathering process during the Jurassic than during the Early Cretaceous. The paleoclimate proxies (e.g., C–value, Rb/Sr, and Sr/Cu ratios) and the sharp increase in the salinity of the Luohandong Formation (LHDF) in the Ordos Basin may provide strong evidence for the continuous aridification since the Early Cretaceous. In the Lower Cretaceous non-uranium mineralization section in the basin, large U primary enrichments (high U/Th ratio) may be related to the rise in atmospheric oxygen levels during the Cretaceous. This remarkable paleoenvironmental transition controls the spatial–temporal collocation of the coal and oil in deep strata and the uranium in upper host rocks. The large-scale hydrocarbon migration from the deep strata transformed the Cretaceous aeolian sandstones into favorable uranium reservoirs. Core alteration observation and iron content testing shows that the large-scale oxygen-containing uranium surface fluid came from the western margin of the Tianhuan Depression. Finally, based on the analysis of the genetic relationships among uranium, coal, hydrocarbons, and alteration this study proposes that regions adjacent to the western margin of the Changqing oilfield with large faded alteration in the Lower Cretaceous strata are new ideal target areas for further uranium exploration.

On the significance of periglacial conditions in active mountain belts for chemical weathering processes: Insights from the Chayu area, SE Tibet

Chemical weathering is a key player of the long-term (Ma) timescale carbon cycle. Weathering processes under alpine periglacial environment could be important during the Quaternary glacial-interglacial cycles, but such timescale is difficult to fully apprehend for the weathering impact on C cycles. The Chayu river catchment in SE Tibet spans a geographical gradient from a periglacial environment in the north to a monsoonal environment in the south and we have investigated the various chemical weathering along this climatological gradient. The lithology of the catchment is dominated by granitoid rocks. Due to the active tectonic activity and the periglacial environment, mass wasting deposits including landslide deposits, talus and rock glaciers are found in the catchment. In order to figure out the influence of mass wasting process on water chemistry, we sampled seepage water from the mass wasting deposits and nearby stream water for comparison. Cyclic input contributes 5.7 to 8.2% to the dissolved load of the water samples, suggesting the dominance of weathering contribution within this granitoid catchment. The contributions from sulfuric acid and carbonate to chemical weathering are estimated based on the elemental data and the oxidation of sulfide as the source of dissolved sulfate. In the monsoonal South Chayu, the K*/Si, Ca*/Si ratios of the bedrock landslide seepages are higher than the streams by 265% and 117%, respectively. Together with the high contribution of carbonate (~80%) and sulfuric acid (20 to 40%), the results indicates that landslide deposits have strong influences on local water chemistry by processes identical to bedrock landslides of greywacke and carbonate lithology in active mountain belts, suggesting that the enhanced weathering by landslide process can apply to granitoid regions as well. In the North Chayu with periglacial environment, the chemistry of the seepages and streams are nearly identical, and are similar to the landslide seepage water in the south. Such result highlights the role of the periglacial critical zone without the influence of mass wasting deposits that possibly enhances chemical weathering. The high porosity created by repeat freeze-thaw cycles provides more fresh mineral surfaces for water-rock interaction. But, the low temperature and the partial availability of water, restricted to thaw periods, provide strong kinetic limitations that inhibit the silicate weathering. Such features of the alpine periglacial critical zone led to the preferential weathering of the most reactive mineral phases including calcite, sulfide, and the interlayer K+ of sheet silicates (biotite, chlorite), resulting in the characteristic periglacial water chemistry. The influence of periglacial environment on local water chemistry may apply beyond the North Chayu and may play an important role in modulating the chemical weathering within the transition between Quaternary glacial and interglacial period.

Have land use and land cover change affected soil thickness and weathering degree in a subtropical region in Southern Brazil? Insights from applied mid-infrared spectroscopy

Land use and land cover changes (LUCC) can drastically alter various components of the critical zone, including soil thickness and soil chemical weathering processes. Often these studies, however, tend to focus on extreme cases, not representing what actually happens on average at larger, regional scales. Here, we evaluate the impact of LUCC on soil thickness and soil weathering degree at the regional scale, where we use soil spectroscopy to derive weathering indices. In a subtropical region in Southern Brazil, we collected calibration/validation soil samples (n = 49) from 4 different locations for which we measured the mid-infrared (MIR) spectral reflectance and 3 soil chemical weathering indices: chemical index of alteration (CIA), the total reserve in bases (TRB), and the iron ratio (Fed/Fet). We used partial least square regressions on this calibration/validation dataset to relate the MIR spectra of the soil samples to these weathering indices, resulting in good calibration relationships with R2 values of 0.97, 0.91 and 0.84 for CIA, TRB and Fed/Fet, respectively. Applying these relations to MIR spectra of regionally collected soil samples allowed us to calculate soil weathering degrees for a large number of soil samples (n = 229), without requiring costly and time-consuming chemical analyses. We collected these soil samples at 100 mid-slope positions: 50 under forest and 50 under agricultural land use. Land use explained only a minor part of the variation in soil thickness and weathering degree. Thus, while local water and tillage erosion rates might be considerable after deforestation, this has not led to significant reductions in average soil thickness and has not affected soil weathering degree. Slope gradient is the main factor influencing the spatial variability in soil thickness and weathering degree on mid-slope sections in our study area. Human activities over the last century did not fundamentally alter these patterns.

Sedimentological and geochemical characteristics of Lower Jurassic Sandstones from Gümüşhane, NE Turkey: implications for source to sink processes, paleoenvironmental conditions, provenance and tectonic settings

ABSTRACT The eastern Sakarya Zone (SZ), one of the Alpine Himalayan Belt’s main components, has complex Mesozoic–Cenozoic geodynamic evolution, which remains controversial. Early-Middle Jurassic volcano-sedimentary successions (Şenköy Formation) extensively outcrops in Gümüşhane region, NE Turkey. It is regarded as a critical unit to understand the Mesozoic tectonic evolution of the eastern Sakarya Zone. One of the Şenköy Formation’s predominant units is sandstone succession, preserving implications for paleoenvironmental conditions and tectono-sedimentary development of Neotethys Ocean. Thus, a combined analysis of comprehensive petrography, whole-rock major, trace and rare earth element data is carried out on the sandstones, which are well constrained as late Sinemurian- Pliensbachian. The sandstones are mainly arkosic to lithic arenites in lithology showing poor textural maturities. They are mostly represented by relatively high ICV, low CIA, high K2O/Al2O3, Fe2O3+ MgO, TiO2, Th/U, pronounced negative Eu anomaly, enriched LREEs, elevated GdN/YbN, low Ce/Ce*, Ni/Co, La/V and Zr/Ti. The petrographic and geochemical characteristics imply that the sediments may have experienced relatively low chemical weathering processes and slight reworking and recycling processes with a short transport distance before deposition in the basin. Early Jurassic sandstone successions were interpreted as a transgressive series, showing a predominantly open sea environment with oxidizing paleoenvironmental conditions. The sandstone samples’ paleoenvironment is likely to be located along the southern margin of the arc and the Neotethyan basin to the south. The extensional and trans-extensional tectonic regime might have played an essential role in controlling the basin’s isolated-half graben and/or asymmetric geometry, leading to changes in the provenance of studied sandstone samples. Thus, the geochemical signature differences are probably associated with basement-related proximal origins and minor effects of the multi-phases petrogenesis that experienced different source to sink processes. Early Jurassic sandstones were probably derived from multi-genetic source rocks, including (i) granite and (ii) metamorphic rocks. Our new data has also indicated that other source rocks can include mafic to felsic volcanic succession. The possible provenance for granitic pluton and metamorphic rocks can be provided by the Hercynian heterogenetic crystalline basement widespread throughout the SZ. However, mafic to felsic volcanic rock source is likely to be associated with the pre-Early Jurassic nearby volcanic-arc, which is rarely recorded in the eastern SZ. The source rock signatures may imply a close genetic link with ancient magmatic-arc generation due to the southward subduction of Palaeotethys.

Global Biogeochemical Cycle of Lithium

AbstractThe total human mobilization of Li from the Earth's crust, >1,000 × 109 g/year, is much larger than Li mobilized by the natural processes of chemical and mechanical weathering (94 and 132 × 109 g/year, respectively), representing a ∼500% perturbation of the global cycle of Li by human activities. The anthropogenic perturbation of the global Li cycle shows enhanced releases to freshwaters from oil‐produced water (46 × 109 g/year), leaching of coal ash (7–20 × 109 g/year), and extraction of groundwaters (29 × 109 g/year). The sum of these anthropogenic sources more than doubles the natural transport of dissolved Li to the sea in rivers (69 × 109 g/year). Currently, releases from the excretion of therapeutic drugs and disposal of lithium‐ion batteries are a small component of the transport of Li in rivers, although the latter may increase markedly as lithium‐ion batteries dominant global energy storage. Human emissions of Li particles to the atmosphere—55 × 109 g/year from coal combustion—comprise about 38% of the emission of Li to the atmosphere from various sources. The inputs to the atmosphere are more than the estimated deposition of Li from the atmosphere, which is poorly constrained by available data.

Denudation rates of granitic regolith along climatic gradient in Eastern China

In order to assess the impact of the monsoonal climate on denudation, physical erosion, and chemical weathering processes, we measured cosmogenic nuclides 10Be, 26Al and immobile element Zr in five granitic regolith profiles across Northeast to South China. The 10Be and 26Al concentrations are 2.98 × 104–25.20 × 104 atoms g−1 and 2.18 × 105–16.62 × 105 atoms g−1, respectively. Compiling previous depth profile data from Leymon and Beacon Heights, we find that the 26Al/10Be ratios systematically increase or decrease with the depth. Our numerical model shows that muons contributions can produce higher 26Al/10Be ratios (greater than 6.75) in both steady-state and non-steady state scenarios, which can result in underestimated burial age (initial 26Al/10Be ratio) and exaggerated denudation rates (due to non-negligible production from muons) for the application of dual-nuclide in Earth Science. The denudation rates, chemical weathering rates and physical erosion rates derived from cosmogenic nuclides and Zr are 28–45, 9–31 and 6–22 m Ma−1, respectively. Chemical weathering rates, excluding the JLN profile, comprise a large proportion of the denudation rates (greater than 50%). Despite the wide range of mean annual precipitation (MAP) and mean annual temperature (MAT), the denudation rates vary without an apparent gradient from northeast to south. However, the physical erosion and chemical weathering results show good relationships with climate, suggesting the limitation type changed from kinetic-limited in the north, to supply-limited in the south. Chemical weathering indices (chemical index of alteration, CIA and weathering intensity factor, WIF) also indicate that the extent of chemical weathering strengthens from northeast to south and increases with chemical weathering rates, but decreases with physical erosion rates.

Paleoproductivity evolution in the northeastern Indian Ocean since the last glacial maximum: Evidence from biogenic silica variations

Changes of marine paleoproductivity could reflect the history of marine biogenic cycle process, and exploring the evolution and mechanism of marine productivity are important for understanding the global biogenic factor cycle and its roles in past, present and future climate change. Based on the analysis of biogenic silica (BSi) in core ADM-159 and core BoB-56 from the northeastern Indian Ocean, high-resolution curves of paleoproductivity evolution were obtained. The results show that the BSi contents in these two core sediments are less than 1.8%, mainly affected by the low supply of silica skeleton and the high dissolution and dilution of terrigenous materials. Distinct fluctuations in BSi contents could still be reflected, and their relative values were controlled by chemical weathering processes and terrigenous material supply. The power spectrum analysis of BSi content shows reliable periodicities of 5.86 kyr, 1.95 kyr, 1.35 kyr and 1.09 kyr, suggesting that millennial-scale BSi value might be affected by solar activity. Based on the BSi mass accumulation rates (MAR), lower paleoproductivity during the glacial period and higher level during the Holocene were revealed in our records, which matched well with the global climate changes. Temperatures controlled by low latitude insolation changes could influence the nutrient substance supply, further promote productivity variations at the glacial–interglacial scale. Some millennial events, such as the Heinrich stadial 1 (HS1) and Younger Dryas (YD) periods, showed relatively low paleoproductivity, while the Bølling/Allerød (B/A) period and the middle Holocene showed higher paleoproductivity. These millennial paleoproductivity fluctuations may be due to the changes of nutrient supply caused by Indian summer monsoon (ISM). In addition, the BSi MAR of core ADM-159 and core BoB-56 are well correlated with the isotopic compositions of Greenland ice core and Chinese speleothem, providing robust evidence for the link between northeastern Indian Ocean paleoproductivity and global climate change.

Ca and Sr isotope constraints on chemical weathering processes: A view through the Ebro river basin, Spain

The Ebro River (928 km long, 85,530 km2 drainage basin) in north-eastern Spain flows into the western Mediterranean Sea through several large cities, and agricultural, mining and industrial areas. The river is one of the largest contributors of freshwater to the Mediterranean and ends in the Ebro delta, one of the most important wetlands in Europe. Bedrock of the Ebro River basin mainly consists of carbonate rocks and evaporites of Paleozoic and Mesozoic age. The Ebro river mainstream was sampled monthly for a year (2006) near the outlet at Amposta, and a field campaign in April of the same year sampled the Ebro along its main course as well as its main tributaries. The behaviour of Ca and its isotopes—combined with that of Sr-isotopes—during water/rock interactions was investigated at the basin scale, with the objective of elucidating the processes controlling the isotope signatures of a large river draining mostly sedimentary bedrock. The δ44Casw values (normalized to seawater) ranged from −0.87 to −1.09‰ along the Ebro mainstream, decreasing toward the delta as the Ca content increased. At Amposta, the δ44Casw ratio ranged between −0.66 and − 1.04‰, with a tendency to decrease with increasing discharge. These variations were similar to those given by the 87Sr/86Sr values and Sr contents. For the main tributaries, the δ44Casw ratio in river waters ranged between −0.43 and − 1.04‰, whereas anhydrite-gypsum bedrock values ranged from −0.94 to −1.22‰ and carbonate bedrock from −1.04 to −1.39‰. Comparing Sr-isotope values and Ca/Na ratios showed the role of anhydrite/halide bedrock weathering for some tributaries (Guadalope, Matarrana, Aragon, Ega), that of carbonate/halide bedrock weathering dominating the others (Gallego, Cinca, Segre), the Ebro mainstream being a mix of both. Bedrock weathering masks the sea-salt signal, if any. As halides contain no Ca, a comparison of δ44Casw and 87Sr/86Sr values further demonstrated the role of anhydrite and limestone for the Ebro and its tributaries, highlighting geochemical processes like carbonate supersaturation in the Guadalope and Matarrana tributaries.

Evidence for extreme Sm[sbnd]Nd fractionation during chemical weathering

During subaerial chemical weathering, submarine weathering and other intracrustal processes, SmNd chemical fractionation remains uncertain, while a little is known about the conditions, scale and magnitude, specific processes and actual mechanism for possible SmNd fractionation. Here, an in situ terra rossa weathering profile developed on dolostone is chosen for the study. Based on sequential extraction experiments and measurements of the mineral and geochemical compositions including SrNd isotopic compositions, we suggest that subaerial chemical weathering not only leads to considerable SmNd mobilization, redistribution and secondary enrichment, but also gives rise to extreme SmNd fractionation, apparent 143Nd isotope homogenization, nearly complete resetting of the 147Sm143Nd isotope system, anomalous initial 143Nd/144Nd ratios, and meaningless 143Nd model age (TDM) for weathering products. We found that the lanthanide tetrad effect, rather than mineralogical control, is responsible for the observed substantial SmNd fractionation and for the other rare earth element fractionation. Under domination of the lanthanide tetrad effect, the mobility of Sm is preferential to that of Nd during their migration in the form of dissolved organic complexes. Our results also illustrate that resetting of the 147Sm143Nd isotope system in weathering products is controlled by the combined effect of the extraneous dissolved SmNd input and additional SmNd fractionation. Finally, we argue that similar scenarios may occur in submarine weathering, diagenesis and other geological processes.

Hydrological and biogeochemical controls on temporal variations of dissolved carbon and solutes in a karst river, South China

BackgroundUnderstanding the responses of riverine dissolved carbon dynamics and chemical weathering processes to short-term climatic variabilities is important to understand the Surface-Earth processes under ongoing climate change. Temporal variations of solutes and stable carbon isotope of dissolved inorganic carbon (δ13CDIC) were analysed during a hydrological year in the Guijiang River, South China. We aimed to unravel the chemical weathering processes and carbon dynamics in karst areas under ongoing climate changes.ResultsSignificant positive relationships were found between weathering rates and climatic factors (i.e. temperature and discharge) over the hydrological year. The total flux of CO2 consumption (760.4 × 103 mol/km2/year) in the Guijiang River was much higher than the global mean flux, with a higher CO2 consumption capacity in the Guijiang River relative to most other global rivers. Chemical weathering fluxes in this karst area showed high sensitivity to global climate change. CO2 evasion during the warm–wet seasons was much lower than those during cold–dry seasons. Light δ13CDIC values occurred under high-flow conditions, corresponding with the high temperatures in high-flow seasons. IsoSource modelling revealed that biological carbon could account for 53% of all dissolved inorganic carbon (DIC), controlling the temporal carbon variabilities.ConclusionThis study quantitatively evaluated the temporal variations in CO2 fluxes and carbon cycling of karstic river systems and demonstrated that riverine carbon cycling will have a higher sensibility to ongoing global climate change. High discharges accelerate solutes transport, with relatively large quantities of 13C-depleted carbon being flushed into rivers. Meanwhile, high temperatures also accelerate organic carbon mineralisation, producing high content of soil CO2, whose influx can shift the 13C-depleted values in the high-flow seasons. Taken together, biological carbon influx should be responsible for the temporal carbon dynamics.

A new type of polygonal terrain formed by sulfate weathering in arid regions

Polygonal terrain (or simply, polygons) is a common geomorphological feature in arid regions. Polygons with diverse shapes and different sizes ranging from several meters to more than one hundred meters are widespread in playas. Here, we report a new geometric type of polygons in the playas in the western Qaidam Basin on the northern Tibetan Plateau. These polygons are characterized by raised rims that are interlocked with each other, forming irregular boundaries resembling jigsaw puzzle piece-shapes. The average size of these polygons is around 80 m, which is larger than most of the reported polygons in playas elsewhere. While most polygonal terrain in playa environments is bounded by cracks generated by desiccation or thermal contraction, these unusual features are delimited by raised rims likely caused by a chemical weathering process. Thenardite, a dense anhydrous sodium sulfate mineral originally formed in a saline playa, has been weathered and hydrated to form widespread gypsum. As gypsum leads to a larger volume than thenardite during precipitation, we propose that the volume expansion develops the raised rims of polygons as pressure ridges.

Glaciation enhanced chemical weathering in a cold glacial catchment, western Nyaingêntanglha Mountains, central Tibetan Plateau

The uplift of the Tibetan Plateau (TP) not only may enhance physical denudation and chemical weathering but also makes this area contain the largest glacier storage outside the polar regions. There is an argument on whether glaciation favours chemical weathering and carbon sequestration. To explore chemical weathering processes and intensities in the cold glacial region of the central TP, hydrochemistry of the river water in two catchments, i.e. the Qugaqiong and Qugaqie, was monitored from April to September 2018 with high-frequency sampling. These two catchments share similar geographical features except there are some cold glaciers in the upper reaches of the Qugaqie. The results of chemical composition show that the river water of the Qugaqie has a lower proportion of Ca2+ and HCO3− but higher SO42− and K++Na+ compared with the Qugaqiong. The seasonal variation of ionic concentration in the Qugaqie is significant but minor in the Qugaqiong. Those differences highlight the glacial impact in the Qugaqie compared with the non-glacierized Qugaqiong. Solutes in the glacial runoff of the Qugaqie mainly derive from sulfide oxidation. Its contribution to cations in the runoff of the Zhadang glacier and the Hanging glacier reaches 39% and 36%. The second most important contribution is carbonate dissolution (32% for both glacial runoffs). Silicate weathering provides fewer solutes and its contribution is only 20% and 11% in the two glacial runoffs, respectively. River water of the Qugaqiong shares similar hydrochemical characteristics with the non-glacial tributaries draining granodiorite/biotite adamellite in the Qugaqie. The contribution of sulfide oxidation to solutes in those rivers decreases to 10% while carbonate dissolution increases to 50%. Glacial comminution exposed trace sulfide minerals, thus made sulfide oxidation became pretty active due to this reaction is much faster than other mineral dissolution. The carbonate weathering rate (CWR) and silicate weathering rate (SWR) in the Qugaqie catchment are 9.7 t/km2/y and 6.7 t/km2/y. In comparison, values in the Qugaqiong catchment are 6.9 t/km2/y and 3.8 t/km2/y, respectively, which means CWR and SWR is 1.4 and 1.8 times higher in the Qugaqie catchment, respectively. Higher runoff and physical erosion rates are considered as the main reasons for higher chemical denudation rates in the Qugaqie catchment. The drainage system of the glaciers is dominated by the distributed pattern, which caused longer residences time of water, thus further promoted chemical weathering in the glacierized region. Our observation supports the idea that glaciation in the glacierized catchment of the central TP enhances chemical weathering, especially for SWR. Chemical denudation rates in the Qugaqie catchment remain at a moderate level compared with other glacierized catchments in the world and lithology and runoff are important factors to cause this spatial heterogeneity.

Source of selenium in Handan geochemical anomaly belt: Evidences from petrology and geochemistry of Upper Paleozoic in western Handan, China

Handan lies in a geochemical anomaly belt characterized by enrichment of selenium (Se) in rock, soil, and water, contrasted with deficiency of Se in the North China Plain. In this study, 27 environmental soil samples and 96 rock samples in the Upper Paleozoic were analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) for major and trace element concentrations to determine the source of Se in the environment.Se concentrations in soil vary from 0.054 μg/g to 2.869 μg/g, with an average of 0.598 μg/g. Ignoring the anthropogenic contamination, Se concentrations in soils elevate with the decrease of distance from outcrops in Mountain Zishan (Mt. Zishan). There is a strong positive correlation between Se and Al2O3 (r = 0.679, P < 0.01, n = 27), and between Se and TiO2 (r = 0.638, P < 0.05, n = 27). Furthermore, Se is significantly negatively correlated with MgO, Na2O, K2O, and Sr (r = −0.674, −0.755, −0.716, −0.739, respectively, P < 0.01 for all, n = 27). It indicates that Se in the soil is derived from weathering products.Se is the most highly enriched trace element within Upper Paleozoic, which is composed of Benxi Formation (BX Fm.), Taiyuan Formation (TY Fm.), Shanxi Formation (SX Fm.), and Shihezi Formation (SHZ Fm.), in outcrops in Mt. Zishan area, western Handan. Se concentrations of rock samples vary from 0.021 μg/g to 4.971 μg/g, with an average of 0.401 μg/g. The maximum of Se concentration is 99.41 times higher than the Upper Continental Crust (UCC). The order of the rest trace elements enrichment degrees is S > Pb > As > Ga > Li > Bi > Th > Sc > In > U > Cd > Y > Rb > Ba > Cr > V > Be > Cs > Ni > Zn > Tl > Sr > Co > Mo > Cu. Se enrichment appears in two types of rocks, which are gray clay rocks and black mudstones and shales (including coal and gangue). Stratigraphically, Se is more highly enriched in TY Fm. and SX Fm., with average enrichment factor (EF) values of 14.64 and 5.59, respectively.Chemical index of alteration (CIA) and several environmentally sensitive elements, such as Th, U, Sr, Ba, V, Cr, and Ce, were employed for sedimentary environment analysis. The results revealed that Se-enriched rocks were deposited mainly in a weak, reducing freshwater environment, and their sediments were subject to an intermediate chemical weathering process. The discrimination diagrams of SiO2-TiO2, F1-F2, ∑REE-La/Yb, and La/Sc-Co/Th indicate that the terrestrial clastic sediments were dominated by multiple types of original rocks. Se-laden clastic materials derived from mafic and ultramafic rocks in Yinshan ancient land provided main source of Se in Upper Paleozoic in western Handan, and adsorption of clayey and organic materials and biological accumulation induced Se enrichment ultimately.

Major Elements in the Upstream of Three Gorges Reservoir: An Investigation of Chemical Weathering and Water Quality during Flood Events

Rivers transport terrestrial matter into the ocean, constituting a fundamental channel between inland and oceanic ecosystem and affect global climate change. To reveal chemical weathering processes and environmental health risks during flood periods, water samples were collected in the upper reaches of Three Gorges Reservoir (TGR) in 2020. HCO3− and Ca2+ were the most abundant anions and cations of the river water, respectively. The range of HCO3− concentration was between 1.81 and 3.02 mmol/L, while the mean content of Ca2+ was 1.03 mmol/L. The results of the Piper diagram and element ratios revealed that the river solutes were mainly contributed by carbonate weathering and gypsum-rich evaporite dissolution. A mass balance model indicated that the contribution order of sources to cations in the main channel (Yibin-Luzhou) was evaporites &gt; carbonates &gt; atmospheric input &gt; silicates. The order in the Chongqing—Three Gorges Dam was carbonates &gt; atmospheric input &gt; evaporites &gt; silicates. These results showed a lithologic control on hydrochemical characteristics. Most sampling sites were suitable for agricultural irrigation according to the water quality assessment. However, indexes sodium adsorption ratio (SAR) and soluble sodium percentage (Na%) were higher than 1.0 in Yibin-Luzhou and 30% in Yibin–Chongqing, respectively, suggesting a potential sodium hazard. In addition, except Tuojiang River and Shennong River, the risk of sodium hazard in tributaries was relatively low. High Na+ concentration in irrigation water can damage soil structure and function and ultimately affect agricultural production. Water quality in the upstream of a Piper diagram should attract enough attention.

Geochemistry of heavy metal-contaminated sediments from the Four River inlets of Dongting lake, China.

The concentrations of major and trace elements in the sediments from the Four River inlets of Dongting Lake were analysed. The results show that the element compositions of the Four River inlet sediments are different, among which higher amounts of Al2O3, Fe2O3, MnO, Cs, Rb, Th, U, Y, and REE are found, while MgO, CaO, Na2O, and Sr are more depleted in the sediments from the Xiangjiang and Zijiang inlets than in the sediments from the Yuanjiang and Lishui inlets. The Xiangjiang inlet sediments are distinctly higher enriched (EF > 5.0) in heavy metals Bi, Cd, Mn, Cu, Pb, and Zn, while the other river sediments are moderately enriched (EF > 2.0) in these heavy metals. These geochemical differences are resulted from the source lithology, chemical weathering, hydrological sorting, and anthropogenic processes taking place in the watersheds. The principal component analysis and the geochemical vertical profiles suggest that the trace metals Ba, Mo, V, Cr, Co, Ni, Cs, Rb, Sc, Th, U, Ga, Ge, Zr, Hf, Ta, Nb, and REE are of terrigenous sources. The heavy metals including Bi, Cd, Mn, Cu, Pb, and Zn in the sediments can include those contributed by anthropogenic processes, such as mining and smelting of Pb-Zn ores. Therefore, presenting a scheme for the geochemical backgrounds of the watershed is recommended here for future assessment of the heavy metal contamination in sediments of the watershed.

Lithogenic hydrogen supports microbial primary production in subglacial and proglacial environments

Life in environments devoid of photosynthesis, such as on early Earth or in contemporary dark subsurface ecosystems, is supported by chemical energy. How, when, and where chemical nutrients released from the geosphere fuel chemosynthetic biospheres is fundamental to understanding the distribution and diversity of life, both today and in the geologic past. Hydrogen (H2) is a potent reductant that can be generated when water interacts with reactive components of mineral surfaces such as silicate radicals and ferrous iron. Such reactive mineral surfaces are continually generated by physical comminution of bedrock by glaciers. Here, we show that dissolved H2 concentrations in meltwaters from an iron and silicate mineral-rich basaltic glacial catchment were an order of magnitude higher than those from a carbonate-dominated catchment. Consistent with higher H2 abundance, sediment microbial communities from the basaltic catchment exhibited significantly shorter lag times and faster rates of net H2 oxidation and dark carbon dioxide (CO2) fixation than those from the carbonate catchment, indicating adaptation to use H2 as a reductant in basaltic catchments. An enrichment culture of basaltic sediments provided with H2, CO2, and ferric iron produced a chemolithoautotrophic population related to Rhodoferax ferrireducens with a metabolism previously thought to be restricted to (hyper)thermophiles and acidophiles. These findings point to the importance of physical and chemical weathering processes in generating nutrients that support chemosynthetic primary production. Furthermore, they show that differences in bedrock mineral composition can influence the supplies of nutrients like H2 and, in turn, the diversity, abundance, and activity of microbial inhabitants.

Middle to late Eocene chemical weathering history in the southeastern Tibetan Plateau and its response to global cooling

Continental weathering is a crucial factor to maintain the balance of the carbon cycle and thus the livability of the Earth. The Tibetan Plateau (TP), known as the Third Pole of the Earth, has undergone strong uplift since the Cenozoic, thus making it an ideal area to study continental weathering processes and associated driving factors. However, early Cenozoic weathering records are rare in this region. Here, we report high quality mineralogical and geochemical records of clay fraction (< 2 μm) of a middle to late Eocene sequence retrieved from the Qujing Basin, southeastern TP, to track the early Cenozoic chemical weathering history in this area. The results show that the main clay mineral assemblages contain illite-smectite mixed layers, illite and palygorskite. The chemical weathering intensity indicators (e.g., clay mineral assemblages and the chemical index of alteration (CIA)) collectively indicate a clear long-term modulation of global cooling on regional chemical weathering processes during middle to late Eocene, as indicated by high correlation between global temperatures and chemical weathering indicators and the similarity in their periodicity characteristics. Moreover, a sudden decrease of the chemical weathering intensity with large fluctuations was identified at 42–39.9 Ma, which may be linked to rapid transport of clay minerals caused by tectonic activity and/or an increased precipitation in the southeastern TP. This study indicates a control of global cooling on chemical weathering of the southeastern TP area during middle to late Eocene, while tectonic activity or other factors might exert catalytic influences at some certain periods.

The distribution of lithium in nature and the application of lithium isotope tracing

In recent years, with the advancement of isotope analysis methods, lithium isotopes have been widely used in tracing geological processes. This article introduces the unique geochemical properties of lithium and the lithium content and isotope characteristics in all kinds of natural geological reservoirs, and analyzes the fractionation mechanism of lithium isotope in the geological process which happened on the surface and the inner part of the earth. Further, this article summarizes and analyzes the application of lithium isotopes in tracing continental chemical weathering and slab subduction process, and discusses the distribution of lithium among various reservoirs in the light of the material circulation process on the surface and underground.

Characteristics of uranium mineralization in the Tin-Seririne sedimentary basin (Algeria)

This article presents the results of studying the uranium mineralization of various parts of the Tin-Seririne sedimentary basin located in the southern part of the Hoggar massif in south-eastern Algeria. Mineralization of uranium is localized at different stratigraphic levels: in altered rocks of the Archean basement and unconformity overlying basal conglomerates (Tahaggart region), and in Devonian sandstones (uranium ore occurrences Tamart-N-Iblis, Timouzaline, etc.). For laboratory studies, 07 samples were taken: As and A1 granites, Tedjart, Timouzaline and Tamart-N-Iblis sandstones, gneisses and conglomerates of the Tahaggart deposit. The samples were examined using gamma spectrometric, chemical and microprobe analyzes. Mineralization is represented by minerals of hexavalent uranium: autunite, torbernite, carnotite, vanuralite and uranophane. The hypergenesis zone of the deposit, it is noted that the geochemical features of the formation of uranium mineralization are typical for regions of arid climate. The arid climate corresponds to oxidative processes of chemical weathering, with weakly alkaline or neutral uranium-bearing solutions. When studying samples taken from different stratigraphic levels, a difference in mineral composition was noted, which indicates some differences in the conditions of formation of uranium mineralization.

Solute Production and Transport Processes in Chinese Monsoonal Rivers: Implications for Global Climate Change

AbstractThe negative feedback between chemical weathering and climate is hypothesized to act as an important control on modulating atmospheric CO2 over geologic timescales, affecting the evolution of Earth's climate over the history of Earth. Here, we investigated solute production processes by analyzing concentration‐discharge, denoted here as concentration‐runoff (C‐q), relationships of Chinese monsoonal rivers, through both the empirical power law relationship and a recently developed Solute Production Model. We found that solute concentrations were highly modulated by hydrologic conditions which shifted the Damköhler number, Da, the ratio of fluid transit time versus the time required to reach equilibrium. Additionally, the among‐catchment behavior of HCO3− responding to changing runoff was correlated with the average Da of each catchment. Rivers with high average Da induced high maximum weathering fluxes, while the maximum weathering potential was primarily controlled by the Damköhler coefficient (Dw, m/yr), the reactivity of the material in the weathering zone over a given length scale, among the catchments in this study. Globally, HCO3− behaviors and weathering characteristics are highly influenced by carbonate bedrock distributions and abundance. In addition, Chinese monsoonal rivers have higher weathering fluxes, weathering potential, and climate‐weathering feedback sensitivity (4.4%/°C) than most other global rivers. Our work disclosed the mechanisms that link runoff, lithology, and weathering fluxes in monsoonal rivers and analyzed the controlling factors on solute dynamics on global scale, which can be implemented in exploring the chemical weathering processes under ongoing global climate change.