Products Of Chemical Weathering Research Articles

Geochemical evidence for changes in provenance and paleoclimate during the Holocene obtained from a fluvial–eolian sequence in the southern Mu Us Desert, north-central China

Identifying the sources and weathering degree of sediments in the northern deserts of China is crucial to understand the evolution of the Asian monsoon system and corresponding induced changes in surface processes. Great progress has been made in the reconstruction of paleoclimate and paleoenvironment from the Early Holocene onwards based on chronostratigraphy and proxies of aeolian sedimentary sequences in the Mu Us Desert (MUD). However, previous studies have given rise to some controversial over the timing of the Holocene optimum period, and there is a scarcity of studies on the sediment provenance evolution of the desert during the Holocene and its internal relationship with the East Asian summer (EASM) and winter (EAWM) monsoons. Here, we provide new elemental geochemical data from a fluvial–aeolian sedimentary sequence in the southern MUD; we then combine these data with other available elemental data and hydroclimatology information to investigate the characteristics of sediment source evolution and their possible connection with the EASM and EAWM on the southern margin of the MUD-desert/loess transition zone since the latter part of the Early-Holocene. The elemental composition and geochemical characteristics of the studied sedimentary sequence differed markedly in the periods before and after 6.4 ka BP, suggesting a change in the source of the sediments across this boundary. From the late Early-Holocene (10.6 cal. ka BP), sediments were dominated by the chemical weathering products of local source material, with a gradual increase in chemical weathering over time, indicating a gradual strengthening of the EASM; the EASM reached its peak Holocene strength at 8.4–6.4 ka BP, accompanied by a moderate level of chemical weathering. After 6.4 ka BP, with the weakening of monsoon precipitation, the EAWM began to strengthen, and long-distance transport of source material from the west and northwest increased; however, chemical weathering of local source material driven by the EASM remained dominant until 4.0 ka BP. After 4.0 ka BP, the EAWM became dominant, and sediments showed strong sedimentary cycles, mainly transported from long-distance sources by aeolian activity, and the MUD became an important sedimentary sink for the northern-central deserts. After 0.7 ka BP, the sediments in the MUD became a mixture of different-age sediments due to river scouring and the transport of pre-existing sediments along the shoreline. Collectively, the elemental geochemical and other proxy data from Holocene sediments on the southern margin of the MUD record an inverse relationship between the EASM and EAWM; these two monsoonal circulations have alternated in their control of the sedimentary source characteristics and geomorphological environmental evolution processes across the southern margin of the MUD during the Holocene.

The collapsible nature of reworked residual granites in the Stellenbosch Municipality, South Africa

In South Africa, residual granite is associated with the collapse phenomenon, a geotechnical hazard that was first identified in the 1950s. Residual granite is a product of chemical weathering (in-situ decomposition) or physical weathering of the parent rock (granite) whilst reworked residual granites is defined as residual granite reworked in-situ by termites. Residual granite usually consists of bulky-sized quartz particles, with silts, and bridged by colloidal matter. Extreme leaching of the colloidal matter creates a structure like a honeycomb. It, however, leaves voids within the structure, which affects the mechanical behaviour of the soil. The soil collapses upon wetting under additional loading. Construction on soils with a collapsible fabric has led to many documented problems. This paper, therefore, reports on the examination of mineral composition and particle shape examination and its effect on behavioural changes of potentially collapsible soil. The soil used for this study includes reworked residual granite obtained from the Stellenbosch area in the Western Cape of South Africa. A multi-element analysis and morphological studies were performed on mounts using the ZEISS EVO MA15 scanning electron microscope at the Centre for Analytical Facility at Stellenbosch University. Shape analysis confirmed that the severity of collapse increased with increasing angularity. In addition, the type and amount of clay present at particle contacts influenced the swell and collapse behaviour of reworked residual granite.

Red clays indicate sub-aerial exposure of the Rio Grande Rise during the Eocene volcanic episode

Autonomous underwater vehicle (AUV) mapping of the western Rio Grande Rise (RGR), South Atlantic, and subsequent exploration and photography of horizontal lava flows exposed in near vertical, faulted escarpments, showed occurrences of red clays/weathered volcanic tops trapped between successive alkaline lava flows. These red clays indicate a hiatus in successive volcanic eruptions. Here, we report detailed mineralogical, geochemical, and rock magnetic characteristics of one such distinct red clay dredged from ~ 650 m water depth in the western RGR. The mineral constituents of the red clay are kaolinite, magnetite, oxidized magnetite (/maghemite), hematite, and goethite, with biogenic calcite and halite occupying voids or precipitated on the surface of the red clay. The chemical index of alteration (CIA) has a value of 93, showing that red clay is a product of extreme chemical weathering of the lava flows. The alkaline volcanic rocks recovered from nearby show an age of ~ 44 Ma, indicating an Eocene age for the volcanism. We show that the red clays are a product of sub-aerial chemical weathering of these Eocene volcanic rocks, in a warm-wet climate, before the thermal subsidence of the RGR to its modern-day bathymetric depth.

Investigating weathering signatures in terrestrial muds: Can climatic signatures be separated from provenance?

Siliciclastic muds (clay- and silt-sized sediment) concentrate physical and chemical weathering products. However, both rock composition and climate can affect the mineralogy and geochemistry of these sediments. We quantitatively assessed the influence of provenance and climate on muds collected from end-member climates to test, which, if any, of these potential weathering signatures are indicative of climate in fine-grained, fluvial sediments. Granulometry, mineralogy, and geochemistry of the studied muds indicated that provenance and mineral sorting hinder interpretation of (paleo)climate signals. These issues also affect chemical index of alteration (CIA) values, as well as mafic-felsic-weathering (MFW), Al2O3−(CaO* + Na2O)−K2O (A-CN-K), and Al2O3−(CaO* + Na2O + K2O)−(FeOT + MgO) (A-CNK-FM) ternary plots, decreasing their utility as paleoclimate proxies. CaO content is heavily weighted within the calculations, resulting in even felsic-sourced sediment commonly plotting as mafic owing to the relative enrichment in CaO from preferential sorting of Ca-rich minerals into the mud-sized fraction during transport. These results cast doubt on the indiscriminate use of CIA values and ternary plots for interpreting chemical weathering and paleoclimate within muds, particularly from glacial systems. Most notably, the positive correlations between CIA and climatic parameters (mean annual temperature and mean annual precipitation) diminished when sediments that had formed in nonglacial settings were filtered out from the data sets. This implies that CIA may only be applicable when used in nonglacial systems in which the composition of the primary source material is well constrained—such as soil/paleosol profiles. Within this end-member climate data set, CIA was only useful in discriminating hot-humid climates.

Chemical weathering signatures at Mt. Achernar, Central Transantarctic Mountains II: Surface exposed sediments

Mt Achernar Moraine is a high altitude, high latitude blue ice moraine where typical conditions preclude the presence of liquid water. Cosmogenic and salt accumulation dating indicate that the moraine’s surface is progressively older away from the active ice margin, with surface exposure ages up to 1 Ma. We analyze the chemical and mineralogical transformations in the <63 µm fraction along transects across the moraine. Data include bulk chemical composition, crystalline mineralogy by X-ray diffraction (XRD), and the composition of amorphous or low abundance products of chemical weathering by sequential extraction. These data are analyzed by multiple regression as a function of exposure age and as a function of composition of the moraine’s cobble and pebble-sized clasts. Change with exposure age is defined by the development of salts and carbonate minerals along with the input of detrital material, principally from sedimentary rocks. Clay minerals and amorphous cements breakdown as detrital material in proportions far above their abundance in the rock clasts, whereas framework silicates (i.e. feldspars and quartz) break down in relatively small proportions. Both the carbonate minerals and some of the salts form from atmospheric acids (i.e. H2CO3) that in turn react with other minerals. Mass balance shows that the input of these atmospheric acids balances with gains in authigenic smectites, zeolites, and amorphous material. Many of these minerals also form in the subglacial environment, but are poorly represented in the underlying rock, suggesting a similar chemical weathering regime in both the subglacial and surface environments of this hyper cold and arid setting. The rate of CO2 drawdown into carbonate minerals increases as the moraine progressively thickens, from 3 mg·m2·a−1 in freshly emerging sediments to ∼50 mg·m2·a−1 after 500 ka of exposure. Weathering from acidic aerosols is proportional to atmospheric flux documented in ice cores and does not vary with moraine thickness. The carbonate mineral formation rates are more than an order of magnitude below those of the subglacial environment and as much as two orders of magnitude below those found in warm desert soils. Nevertheless, the drawdown of atmospheric CO2 into carbonate minerals occurs in a terrestrial setting where water exists only in vapor form.

The role of organic matter diversity on the Re-Os systematics of organic-rich sedimentary units: Insights into the controls of isochron age determinations from the lacustrine Green River Formation

The range of 187Re/188Os values measured from samples of five organic-rich lacustrine mudstones units in the Eocene Green River Formation in the easternmost Uinta Basin covaries with organic matter diversity driven by changing water column conditions. A set of samples from the Douglas Creek Member has the highest pristane/phytane ratio and lowest β-carotane/n-C30 ratio compared to overlying units, indicating deposition in an oxic-anoxic environment with low salinity that would have allowed for the accumulation of a diverse assemblage of aquatic organisms. These samples define the broadest 187Re/188Os range of 1504. In contrast, samples from the R6 and Mahogany zones possess lower pristane/phytane ratios and higher β-carotane/n-C30 ratios indicating deposition in a more restricted lacustrine environment with elevated salinities and alkalinities that would have limited aquatic organic matter diversity. The R6 and Mahogany zones have the narrowest range of 187Re/188Os values measured in this study of 254.9 and 154.6, respectively. As noted by previous workers, these results suggest that organic matter diversity plays a primary role in determining the range of 187Re/188Os ratios in a sample set, and in turn the uncertainty of Re-Os age determinations from organic-rich sedimentary rocks.The Re-Os data from the R3 zone and R6 zone yield ages of 49.7 ± 3.4 Ma and 42.0 ± 18 Ma, respectively, which are statistically indistinguishable based on 2σ uncertainty from three previously reported Re-Os age determinations and those provided by 40Ar/39Ar geochronology of interbedded volcanic ash beds. Although the age uncertainty is high, these findings further highlight the importance of Re-Os geochronology in lacustrine basins, particularly those with thick mudstone successions that lack volcanic ash layers, reliable biostratigraphy, or magnetostratigraphic control. In these cases, even ages with large uncertainties can be useful to constrain burial history and thermal history models.Together, the initial 187Os/188Os ratios of five sets of samples analyzed from the Uinta Basin define the largest Os isotope stratigraphic record from any lacustrine basin compiled to date and record a shift from a value of 1.40 to 1.48 between the R3 and R4 zones in the lower part of the Parachute Creek Member. This small shift may signify a change in the chemical weathering products that entered the lake preserved 20 to 50 m above the contact between the Douglas Creek and the lower Parachute Creek members during a period when the basin transitioned from a shallow lake with mostly open hydrology to an alkaline lake with more frequent basin restrictions.

Ultraviolet Photooxidation of Smectite‐Bound Fe(II) and Implications for the Origin of Martian Nontronites

AbstractClay minerals detected with orbital and in situ instruments in ancient Martian terrains constrain Mars' climate and aqueous alteration history. Early in its history, Mars experienced an atmospheric redox change and iron‐bearing clay minerals may preserve the effects of that transition. Ferrous smectites, the thermodynamically predicted product of chemical weathering of basalts under anoxic conditions, may have undergone oxidation by exposure to chemical oxidants in the atmosphere or regolith, or by direct photooxidation at the surface. To assess these potential oxidation pathways, ferrous trioctahedral smectites of varying initial iron content were synthesized and subjected to oxidation by ultraviolet (UV) irradiation. Experimental UV irradiation under an anoxic atmosphere equivalent to approximately 7 years of flux on the Martian surface caused partial oxidation of smectite‐bound Fe (Fe3+/ΣFe = 16–18%) and octahedral sheet contraction. Metal‐OH vibrational bands in visible/near infrared (VNIR) reflectance spectra of oxidized smectites changed in band depth and asymmetry with higher iron content. X‐ray diffraction patterns of UV irradiated samples indicate the formation of a mixed di‐ and trioctahedral smectite or a secondary nontronite phase, possibly on the surfaces of higher iron content smectites. These experiments suggest that UV irradiation is able to oxidize structurally bound iron in smectites without the presence of other chemical oxidants. Photooxidation may have influenced the mineralogy, both syndepositionally and postdepositionally, of Martian alteration assemblages formed near the surface and this process needs not be limited to one part of their formation history.

Study of technological properties of the sample ethiopian iron ore of the arabian-nubian shield. Part 1. Study of the substance composition of the ore sample

A literary analysis of the presented studies of the Arabian-Nubian shield, its history of formation and geological features was performed. It was found that the iron ores of Ethiopia have a certain technological value, but the technological expediency of their enrichment should be confirmed by relevant studies. A sample of iron ore from an Ethiopian deposit was received and prepared for research. Preparation and work with the samples took place in accordance with the state standards of Ukraine. A sieve analysis of the material of the original sample of iron ore from the Arabian-Nubian shield, which was received for research, was performed. It was found that the genetically studied raw material is a product of chemical weathering of the original volcanic-sedimentary rock. The structure of the rock is fine-grained, oolitic, sometimes hornblende, porphyry, rarely psammitic and psephytic. The texture is powdery, mottled, in some places conglomerate-like, breccia-like, hollow, interspersed, almond-like. The chemical analysis of various samples for the content of total iron and silicon showed an even distribution of components by class. An initial examination of +5 mm fragments was performed, which showed that they consist mainly of two components - the separation of quartz and the cement that binds them. Based on the results of the analysis, four types of fragments were distinguished by the content of cement, which is represented by suric-ochre-clay cement: low-clay with a content of 5-10% cement, medium-clay with a content of 10-50% cement, clay with a content of more than 50% of cement and poor clay. The ore separation of the material was carried out, with the selection of five mineralogy-petrological varieties. The mineral composition is mainly represented by dispersed hematite, hydrohematite and quartz. There is also goethite, hydrogoethite, kaolinite and calcite. A single phenocryst of chalcopyrite was noted. The conclusions reached regarding the mineralogical and petrographic composition of the presented ore provide a basis for further electron-microscopic studies and analysis of the ore for the possibility of its enrichment

Rubidium isotope fractionation during chemical weathering of granite

Rubidium is an active element on Earth, but whether and how its isotopes fractionate during geological processes are not known yet. In this study, we present data showing large variations in δ87Rb in bulk samples and individual mineral species from a granite weathering profile in South China as well as in surrounding stream water. The bulk samples show that the mobility of Rb (τRbTiO2) fluctuates dramatically from −42.0% to 259%, and δ87Rb values vary from −0.30 ± 0.13‰ in the unaltered bedrock to 0.04 ± 0.08‰ in the weathered saprolites. Significant isotopic variations exist among individual mineral species. In the parent rock, biotite, chlorite, K-feldspar and plagioclase have the δ87Rb values of −0.42‰, −0.30‰, −0.23‰ and +0.01‰, respectively. In weathered products, major Rb-bearing minerals are K-feldspar, illite and kaolinite. The δ87Rb values of K-feldspar range from −0.23‰ to 0.14‰, which are likely influenced by the secondary clay minerals adhered on the surface. Illite is the intermediate secondary mineral during biotite and K-feldspar decomposition into kaolinite. The δ87Rb values of illite vary from −0.28‰ to −0.10‰. As the final product of chemical weathering in this profile, kaolinite has the heaviest isotopic composition, with calculated δ87Rb values ranging from −0.07‰ to 0.20‰. Chemical weathering drives the δ87Rb values of saprolites to become heavier. Nearby stream water has the average δ87Rb value of −0.22‰, which is slightly heavier than the value of parent rock but lighter than the saprolites at the upper part of the profile. Our results demonstrate significant Rb isotope fractionation at the Earth’s surface and that adsorption and desorption of clay minerals play a crucial role in triggering Rb isotope fractionation.

Formation of plinthite mediated by redox fluctuations and chemical weathering intensity in a Quaternary red soil, southern China

Widely distributed Quaternary red soils (QRSs) in southern China represent the product of intense chemical weathering under a warm and humid climate. Soil containing plinthite is an important part of China’s QRSs, yet the soil environment and mechanism of formation of QRS with plinthite have been insufficiently studied. By comparing iron and clay mineralogy, magnetic properties, visible- and near-infrared (VNIR) spectral behavior, and chemical weathering and redox conditions between the plinthic soil and the overlying homogeneous soil, we determined the environmental conditions and mechanism by which plinthic soil forms. Weathering intensity scale (WIS)-related plots, as well as vertical profiles and ANOVA plots of several mineralogical parameters related to chemical weathering, indicate generally more intense weathering in the plinthic horizon (PH) compared to the homogeneous horizon (HH). Soil VNIR spectral parameters differed for the PH and HH mainly due to differences in mineralogical composition related to horizon-specific pedogenic processes. Horizon-specific pedogenic dynamics also resulted in differences in rare earth element + yttrium (REY) distributions. Based on our integrated geochemical and mineralogic dataset, we infer that the PH formed in a relatively warmer and periodically water-saturated environment with seasonal redox fluctuations, whereas the HH formed in a cooler/drier environment with less rainfall and a lower water table, reflecting transient aridification of local climate during glacial stages. Based on environmental analysis, we propose a model for the formation/development mechanism of plinthic QRS, in which soil pedogenic environment plays a key role in pedogenesis in particular iron mineral transformation. Our findings are of importance for understanding pedogenesis in tropical/subtropical regions and iron cycling and mineral transformation in the Earth’s critical zones.

Chemical weathering signatures from Mt. Achernar Moraine, Central Transantarctic Mountains I: Subglacial sediments compared with underlying rock

In order to determine chemical weathering rates on the subglacial land surface of Antarctica, we compare the composition and mineralogy of freshly emerging fine sediments to that of the underlying bedrock, as represented by glacially derived cobble-sized clasts. Samples were collected from Mt. Achernar Moraine, a large blue ice moraine, where subglacial material naturally emerges through sublimation of the surrounding ice. Both rocks and sediments were analyzed for total elemental composition, mineral abundance by X-ray diffraction, and by sequential extractions targeting chemical weathering products. The fine sediment fraction is significantly enriched in chemical weathering products and depleted in primary minerals compared with the cobble clasts. The alteration pathways consist primarily of the development of smectite, kaolinite, carbonate minerals, and amorphous material. Extensive Fe oxidation is evidenced by a decline in magnetic susceptibility and by increases in extractable Fe. If we assume the only input into the subglacial system is the water and ice-trapped gas supplied by basal melt, the net chemical alteration is explained through oxidation of organic matter equal to ∼0.7% of the bedrock mass and subsequent carbonation weathering. The underlying sedimentary rock is sufficiently rich in organic matter for this pathway to be plausible. For the O2 that is oxidizing organic matter to be supplied by basal meltwater, water fluxes would need to be three orders of magnitude larger than sediment fluxes. Independent models of basal melt and sediment transport at our field site confirm that such a difference between water and sediment flux is likely at the study site. The rate of subglacial carbonation weathering inferred from the Mt. Achernar Moraine site may be comparable to that found in high latitude subaerial environments. If Mt. Achernar Moraine is typical of other Antarctic sites, the subglacial land surface of Antarctica does play a role in global geochemical cycling.

Tracking drainage basin evolution, continental tectonics, and climate change: Implications from osmium isotopes of lacustrine systems

Organic matter in the lacustrine Eocene Green River Formation in two cores separated by 16 km in the Uinta Basin record similar centimeter-scale initial 187Os/188Os (denoted as Osi) stratigraphic profiles. This demonstrates that the Os isotopic composition of lacustrine organic matter is spatially homogeneous and in this case documents variation on the time scale of thousands of years. The Osi stratigraphy developed here indicates temporal change in the Os isotopic composition of lake water which is regulated by the Os isotopic composition of inflowing chemical weathering products from the surrounding drainage basin. Although observed Osi variability is just above the level of analytical uncertainty, it can be modeled with less than a 6% change in water input from radiogenic to nonradiogenic sources. This highlights the sensitivity of this isotopic tracer. Changes in Os isotope composition may reflect changes in relative discharge of rivers with different Os isotope composition, changes in the footprint of the drainage area to include or exclude different rock types, or unroofing. Thus, this study suggests that Os isotope stratigraphy in lacustrine settings can be used to link basin stratigraphy to changes in the drainage basin which are driven by climatic, tectonic, and geomorphic processes.The similarity in Os isotope stratigraphy between the two cores documented here highlights its utility for detailed chronostratigraphic correlation within and between lacustrine basins. A conservative sedimentation rate suggests that Osi in these lacustrine deposits changed at a rate of ~0.01 per kiloyear, two orders of magnitude faster than has been reported in marine organic-rich sedimentary rocks (Ravizza, 2007). Furthermore, linear regression of 187Re/188Os and 187Os/188Os ratios of all samples yields a Model 3 depositional age determination of 48.3 ± 2.8 Ma (2σ, MSWD = 8.2) which statistically indistinguishable from a weighted mean laser fusion 40Ar/39Ar sanidine age of 49.58 ± 0.32 Ma (Smith and Carroll, 2015) of a temporally adjacent volcanic ash.

Geochemistry and sediment in the main stream of the Ca River basin, Vietnam: weathering process, solute-discharge relationships, and reservoir impact

In this study, we investigated the chemical composition of dissolved solids in the Ca River basin, North-Central Vietnam. Water samples were collected from August 2017 to July 2018 at three hydrological stations located in the main stream of the Ca River. Carbonate weathering was found as the dominant process controlling the water chemistry in that area. The average concentrations of dissolved solids generally decreased from upstream to downstream, resulting in low concentrations of the major ions in the downstream basin. Variations in the concentrations of major chemical ions and suspended solids at discharge were also investigated. Major chemical weathering products were found to behave chemostatically with increasing discharges upstream. However, dilution behaviors of solutes were shown in both midstream and downstream. Primary evidence shows that water storage in reservoirs impacts a variety of suspended solids and dissolved solids in the Ca River.

High-CO2, acidic and oxygen-starved weathering at the Fennoscandian Shield at the Archean-Proterozoic transition

Chemical weathering of continental crust plays an important role in Earth‘s surface evolution and also controls the nutrient flow to the ocean. Major changes in the development of Earth’s geochemical system were taking place at a critical time coinciding with the Archean-Proterozoic transition when Earth’s atmosphere became oxygenated, thus triggering a whole new set of chemical weathering reactions. A paleoweathering crust on basalts of the Kuksha Volcanic Formation in the Paleoproterozoic Imandra-Varzuga Greenstone Belt, northwestern Russia developed between 2.5 and 2.44 Ga, just before the Great Oxidation Event and can potentially shed light on the paleoatmosphere composition and weathering modes of this time. The 3 m-thick Kuksha paleoweathering profile is characterized by Al-phyllosilicate clay minerals that are typical products of strong chemical weathering of igneous rocks. The mineralogy of the uppermost part of Kuksha weathering crust confirms formation under high CO2 partial pressures, consistent with previous estimates of pCO2 exceeding 0.1 atm during that time interval. That is in agreement with the geochemical and mineralogical proxies thereby also suggesting an intense acidic weathering under low-oxygen conditions.

The Geochemistry of Englacial Brine From Taylor Glacier, Antarctica

AbstractBlood Falls is a hypersaline, iron‐rich discharge at the terminus of the Taylor Glacier in the McMurdo Dry Valleys, Antarctica. In November 2014, brine in a conduit within the glacier was penetrated and sampled using clean‐entry techniques and a thermoelectric melting probe called the IceMole. We analyzed the englacial brine sample for filterable iron (fFe), total Fe, major cations and anions, nutrients, organic carbon, and perchlorate. In addition, aliquots were analyzed for minor and trace elements and isotopes including δD and δ18O of water, δ34S and δ18O of sulfate, 234U, 238U, δ11B, 87Sr/86Sr, and δ81Br. These measurements were made in order to (1) determine the source and geochemical evolution of the brine and (2) compare the chemistry of the brine to that of nearby hypersaline lake waters and previous supraglacially sampled collections of Blood Falls outflow that were interpreted as end‐member brines. The englacial brine had higher Cl− concentrations than the Blood Falls end‐member outflow; however, other constituents were similar. The isotope data indicate that the water in the brine is derived from glacier melt. The H4SiO4 concentrations and U and Sr isotope suggest a high degree of chemical weathering products. The brine has a low N:P ratio of ~7.2 with most of the dissolved inorganic nitrogen in the form of NH4+. Dissolved organic carbon concentrations are similar to end‐member outflow values. Our results provide strong evidence that the original source of solutes in the brine was ancient seawater, which has been modified with the addition of chemical weathering products.

Chemical weathering across the western foreland of the Greenland Ice Sheet

Proglacial streams deliver melt water and chemical weathering products, including nutrients and radiogenic isotopes, from continental ice sheets to the ocean. Weathering products are also delivered to the ocean in non-glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides. If weathering reactions differ in non-glacial and proglacial stream catchments, the streams could deliver different types and magnitudes of solutes to the ocean, depending on relative discharge volumes. Unlike proglacial streams, however, little is known of non-glacial stream solute compositions or discharge. Here we show specific discharges are similar from a proglacial stream draining the Greenland Ice Sheet (GrIS) with several streams disconnected from the ice sheet. We also evaluate weathering reactions across a 170-km transect in western Greenland that contains one proglacial stream draining the GrIS, and two coastal (ice distal) and three inland (ice proximal) areas with non-glacial streams. Non-glacial streams exhibit solute compositions and offsets between dissolved and bedload Sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation. Major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast. Strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in-stream weathering that consumes CO2. About 5 times less CO2 is consumed per liter in the proglacial than inland non-glacial streams; however, arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total CO2 weathering than proglacial stream. One coastal area consumes less CO2 per liter than the proglacial stream and another coastal area exhibits net CO2 production. These results indicate estimates for glacial foreland solute fluxes and CO2 weathering consumption and production should include estimates from both non-glacial and proglacial streams. Understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and CO2 fluxes associated with continued ice sheet retreat.

Spatial variability of saprolitic soil properties and relationship with joint set orientation of parent rock: Insights from cases in Hong Kong

Geomaterials are known to be associated with significant heterogeneity, and the natural variations in properties can affect the occurrence of landslides and failure of engineering structures. While these variations are often observed to be spatially correlated, the correlation patterns and their relationships with the geological origins of the materials are not well understood. This study utilizes a three-dimensional spatial variability model to investigate the correlation features in mechanical properties of saprolitic soils, which are products of chemical weathering of granite. Rigorous geostatistical analyses are performed for soil test data at four locations in Hong Kong, each also consisting of extensive rock joint survey information. The analyses show that the principal directions of spatial variability in saprolitic soils correlate well with joint set orientations in the parent rock, providing quantitative evidence that soil heterogeneity partly arises from the different rates of weathering along various directions relative to the rock discontinuities.

Tropical Residual Soil Properties on Slopes

Tropical residual soil is a product of chemical weathering, thus its characteristics are dependent upon environmental factors such as parent rocks, climate, topography and age. This type of soil can be found in many countries all over the world, especially in the tropical region. Since there are many accident happens due to slope failure, a comprehensive laboratory study need to be conducted in order to determine the properties of soil located at Pahang Matriculation College. Several experiments involving physical index and engineering properties of soil are conducted. The typical tropical residual properties are showed and can be considered as sandy SILT of high plasticity.

Impacts of hydrologic variations on chemical weathering and solute sources in the Min River basin, Himalayan–Tibetan region

Feedback between hydrologic variations and chemical weathering is thought to play a crucial role in modulating global carbon cycling. The mechanisms associated with the impacts of hydrologic variations on solute sources and chemical weathering were evaluated by examining the relationships between river discharge and hydrochemistry based on high-frequency sampling of the Min River, which originates in the Himalayan-Tibetan region. Fluid transit times and flow pathways vary with changes in discharge, thereby affecting various biogeochemical processes. Although shorter transit times occur during the high-flow season than during the low-flow season, concentrations of chemical weathering products exhibit chemostatic behaviour (less variation than changes in discharge) in response to increasing discharge due to hydrologic flushing of minerals, which increases the amount of reactive mineral surface area. The contributions of various sources to dissolved loads in the Min River were estimated using a forward model. The calculated annual carbonate and silicate weathering fluxes are 24.1 and 9.6t/km2year, respectively. Atmospheric contributions increase with increasing discharge, whereas the contributions of silicate weathering decrease with increasing discharge. Both the carbonate weathering flux (FCarb) and silicate weathering flux (FSil) are positively correlated with the discharge, indicating that temporal variations in chemical weathering fluxes in the Min River are highly affected by hydrologic variations. The slope of the relationship between FCarb and discharge is much greater than that between FSil and discharge due to the rapid dissolution of carbonate minerals, suggesting that carbonate weathering is more sensitive than silicate weathering to hydrologic variations. This study demonstrates that high-frequency sampling is necessary when investigating solute sources and chemical weathering processes in river basins influenced by a monsoon climate.

Late Pleistocene–Holocene clay mineral record from the Great Rann of Kachchh basin, Western India: Implications for palaeoenvironments and sediment sources

The present study uses clay mineralogy to delineate a ∼17 ka record of palaeoenvironmental/palaeoclimatic changes in the recently uplifted palaeogulf of Arabian Sea i.e. Great Rann of Kachchh (GRK). Situated on continental margin of Indian subcontinent and flanked by Indus delta, the GRK basin has preserved continuous record of post glacial sedimentation. Clay mineral studies on two long cores (∼60 m and 50 m long) show more abundance of physical weathering products (illite and chlorite) over the chemical weathering products (smectite and kaolinite). We show that the GRK sediments depict multiple sources of sediment input. Dominance of illite-chlorite suggests GRK received sediments dominantly from the Himalayan terrain with minor contribution from adjacent regions. We present the oldest clay mineralogical signature of an interval of intensified monsoon conditions during the late Pleistocene (∼17.7–16.3 cal ka B.P.). Monsoon became stronger before ∼8.4 cal ka B.P., and whereas the mid Holocene weakening of monsoon occurred after ∼7 cal ka B.P. Despite the differences in source region and composition of clay mineral records from the GRK with northeastern and southeastern Arabian Sea, the sedimentation responded to major climatic shifts that have occurred since the LGM.