Chemical Weathering

Analyses of spatial distribution of clay minerals, sediment texture, and > 63 μm fractions of the grab samples from the S W continental margin of India exhibit: (i) higher contents of illite and chlorite on the lower slope and (ii) a well-defined no-clay zone on the entire shelf. Kaolinite and smectite are also present in significant quantities on the slope with traces of gibbsite and palygorskite in some samples. The high contents of illite and chlorite (clay minerals which are not abundant in the soils and estuarine sediments of this region) in the southern region of the study area are evidence for sediment contribution from the Bay of Bengal waters (BBW), which enter this region after the SW monsoon. Distribution trends of kaolinite, smectite, gibbsite, and laterite granules on the slope are suggestive of contribution from chemically weathered soils of Peninsular India.

A 700 km long soil transect in the southern Russian plain was studied. The difference in the average annual precipitation within the transect was 240 mm/year, and the average annual temperature was 3 • C. The objective of this study was to understand the behaviour of chemical elements and features of chemical weathering in semiarid soils that developed on loesses and loess-like sediments. It was found that the semi-arid soils of the Russian plain are characterized by a low intensity of present chemical weathering. In an alkaline environment with a low amount of precipitation, the rate and direction of silicate weathering are determined not by the climate, but by the geochemical environment of the soil formation, which had already taken shape by the beginning of the Holocene. The alkaline oxidative environment hinders the hydrolysis and prevents the migration of chemical elements in ionic form. As a result, the removal of chemical elements from primary silicate minerals to soil solutions is not a determining process for vertical geochemical migration. The degree of weathering of present soils is mostly inherited from the parent materials of the Quaternary. Conditions for acid hydrolysis occur only in the upper horizons during increased biochemical activity and lower pH values. However, soil processes (carbonatization, salinization, illitization, and loessivage) make the behaviour of alkali (Na 2 O, K 2 O) and alkalineearth (MgO, CaO, Sr) metals more complex, involving them in recycling in the upper soil horizons, and hinder the quantitative characterization of weathering of silicate minerals. Therefore, the use of CIA geochemical indicator as a quantitative measure of chemical weathering for semiarid soils formed in the Holocene becomes problematic. This study will improve the understanding of the geochemical processes that took place in modern soils in semi-arid regions and clarify the possibility of using geochemical weathering ratios in saline sediments.

The petrographic and geochemical composition of the Dharla River sediments has been examined to infer their sediment type, degree of weathering, provenance, and tectonic settings. Petrographically the sediments are characterized by the high quartz content (64.97 to 74.24 wt%), followed by feldspar (7.04 to 15.20 wt%), mica (5.38 to 19.92 wt%), lithic fragment (3.46 to 8.14 wt%), and heavy minerals (1.98 to 6.94 wt%). Geochemical composition shows marked enrichment of SiO 2 (mean ~ 74.16%) and a strong negative correlation with the other major oxides because of quartz dilution. The Chemical index of alteration (CIA, 45.52 to 63.51); Plagioclase index of alteration (PIA, 43.13 to 66.55); W index (20.15 to 32.86) and Rb/Sr ratios (0.35 to 0.98) suggest low to moderate intensity of chemical weathering in the source area. Geochemical classifications of the studied samples show mostly litharenitic immature type of sediments also reflects high index of compositional variability (ICV, 0.96 to 1.72). The ternary diagrams of Al 2 O 3-(CaO + Na 2 O)-K 2 O (or A-CN-K) and of mafic rocks, felsic rocks and degree of weathering of the source rocks (or MFW) and several immobile trace element ratios (e.g. light rare earth element/heavy rare earth element or LREE

Surface water and soil samples were collected from a series of small catchments on granitic gneiss in the Canton of Ticino in southern Switzerland. Elevations of the sampling points ranged from 220 to 2400 m; vegetation varied correspondingly from deciduous forest through coniferous forest to alpine pasture and essentially unvegetated rock and talus. Annual precipitation averaged 1.9 to 2.4 m. The concentrations of the major cations and silica in surface waters decreased more or less exponentially with elevation. The cationic denudation rate decreased from about 500 meq/m 2 · y at the lower elevations to about 20 meq/m 2 · y at the highest. Alkalinity decreased from 250 to about -7 μeq/1. Although total concentrations decreased with elevation, there were no clear systematic trends in the ratios of the concentrations of the major cations and silica. This suggests that the nature of the secondary minerals formed during weathering in the area does not change with elevation, despite great changes in soil type and environmental conditions. The clay mineralogy of the soils is dominated by unweathered and slightly weathered bedrock minerals: mica and chlorite, hydrobiotite, and poorly characterized mixed-layer material. Small amounts of kaolinite and smectite were observed in a few samples, but there do not appear to be any systematic trends in clay mineralogy with elevation. Mass-balance arguments suggest that the major (in terms of solute generation) weathering product is either kaolinite or a mixture of A1(OH) 3 and 2:1 clays. The lack of dependence of weathering stoichiometry on elevation (a surrogate for several environmental variables) or solute concentrations perhaps reflects the importance of local relief, which did not vary systematically with elevation.

Quartz-diorite, diorite and granodiorite of Archaic ages are the most common rock types in the Swaziland Middleveld. The composition of the regolith cover is dominated by soil-saprolite complexes. The genetic and mineralogical gradient within the soil-saprolite complexes ...

It is quite impossible to travel far in India without observing the remarkable ferruginous crust to which F. Buchanan in 1807 gave the name of laterite. In Indian peninsula it is a post-Cretaceous stratigraphic succession with polycyclic nature of evolution which marks the unconformity with Recent Quaternary Alluvium. There are perennial problems and research gaps in the investigation of laterites in India as well as West Bengal – (1) defining, indentifying and classifying lateritic materials, (2) mode of formation of laterite and its other horizons, (3) determining the ages of laterites, (4) reliability of laterites as palaeoclimatic indicators, (5) identifying topographic requirements and pedo-geomorphic processes for laterite formation and (6) reconstructions of former lateritized landscapes. The formation of north – south lateritc cover (i.e. Rarh Bengal) on the Rajmahal Traps, Archaean granite – gneiss, Gondwana sedimentary, Paleogene gravels and Old Deltaic Alluvium is analyzed here to resolve the aforesaid problems and to depict the variable characteristics of laterites with special reference to its tectono – climatic evolution in northwest marginal part of the Bengal Basin. This paper reveals that the low-level secondary laterites (probably Pliocene – Early Pleistocene age) of Rarh Bengal are composed of heterogeneous iron – aluminum rich gravelly materials which were derived from the high-level primary laterites (probably Eocene – Miocene age) of Plateau since Paleogene Period by the peninsular river system, following the underlying structure of the Bengal Basin. Alongside the roles of drifting of Indian Plate, establishment of monsoon climate, neo-tectonic uplifts and re-lateritisation of ferruginous shelf deposits are determined here to unearth the palaeogenesis of primary and secondary laterites in West Bengal.

“Stone runs” is the Falklands vernacular term for openwork boulder accumulations, which include extensive blockstreams like the famous Darwin “stone-river” and associated features such as stone stripes. Since the early 20th century, they have been interpreted as the product of a suite of periglacial processes, including frost-wedging, gelifluction, frost heave, frost-sorting and snowmelt runoff. Following a literature review, the results of recent field investigations of the valley-floor blockstreams of East Falkland are presented. Access to the internal structure of these forms provides evidence for the existence of a three-fold profile, with clear vertical size gradation presenting striking similarities with an inverted weathering profile. Micromorphological analyses, SEM, XRD, thin sections and grain-size analyses lead to the hypothesis of an alternative model of stone run formation. It is suggested that the material forming the stone run profile lato sensu (including the superficial pavement) is not of periglacial origin, but derives directly from the stripping and accumulation downslope of a regolith, possibly Tertiary in age and formed under subtropical or temperate conditions. The valley-floor stone runs should, therefore, be considered as complex polygenetic landforms that may have formed according to a six-stage scenario, including in situ chemical weathering, regolith stripping by mass movements, soil formation, further regolith stripping, downslope accumulation and matrix washing-out (all phases possibly achieved by the Early Quaternary). Periglacial reworking of the stone run material would have operated at a “final” stage, i.e. during Quaternary cold stages, with boulder bioweathering and limonite-staining operating during the temperate intervals including the present one. The suggested antiquity of the Falklands blockstreams is in accordance with Caine's pioneer interpretation of Tasmania blockfields and with recent analyses and cosmogenic datings of blockfields from Scandinavia and North America.

KOROZYON ve YAŞLANDIRMA TESTLERİ nedir? Neden ve Nasıl Gerçekleştirilir? Özellikle,  GÜVENİLİR ve DOĞRU SONUÇLAR vermediği kanıtlanmış* ASTM B117 TUZ-SİSİ PÜSKÜRTME TESTİ alternatifi olan DÖNGÜSEL (CYCLIC) HIZLANDIRILMIŞ KOROZYON ve YAŞLANMANDIRMA TESTLERİ incelenecektir.

* Bu konuda gerçekleştirilmiş çok sayıda uluslararası araştırma programlarına göre...

Sixteen samples of orange-red and yellow Fe-oxide earthy pigments mainly from bole grounds of Baroque paintings were studied by elemental and phase analysis and voltammetry. Fe, K, and Ti content were found to be suitable for further classification of those earthy pigments. According to the chemical and phase composition the yellow grounds were natural yellow ochres formed by intense chemical weathering in a moderate climate. Very similar phase and elemental composition of part of the orange-red boles indicated their similar geological origin or even their formation by calcination of yellow ochres. Part of the orange-red boles differed significantly from the yellow boles, especially in their increased content of Ti, indicating their relation to end products of intense weathering, e.g. laterites formed in a tropical climate. Analogous materials with a correspondingly large Ti content are not currently commercially available and their geological origin (provenance) is not clear. In se...

Rock weathering is controlled by variety of factors. The lithological control on the chemical weathering has been investigated with special reference to the mobility of major elements. The various rock types occurring in the Vasai-Virar area, north of Mumbai (India) have been studied for their chemical weathering under all other controlling factors remaining essentially constant. In order to evaluate the mobility of major elements, the chemical analyses of samples of weathered and fresh rocks were carried out. Binary and ternary plots, by considering the behavior of single element oxide or a group of elemental oxides during progressive weathering, give interesting information. These chemical studies revealed that crystallinity of rocks, intensity of fracturing and jointing in the rocks and their depth of exposure to various weathering processes, to great extent, have controlled the chemical composition of the weathered products. Irrespective of the type of rock, the compositions of weathered products seem to have been governed by the mobility of elements during weathering. The rocks during weathering, despite their different mineral and chemical composition, have shown a general depletion of alkalies (K and Na) and alkaline earths (Ca and Mg), Fe ++ and Si on one hand and enrichment of Al, Fe+++ and H2O+ on other hand. The magnitude of depletion or enrichment of these elements however has been different chiefly due to their chemical composition. Keywords: Chemical weathering, elemental mobility, geochemistry, lithological control.

ABSTRAK Kawasan kajian yang terletak di kawasan pergunungan pantai barat Sabah sering dikaitkan dengan kejadian tanah runtuh dan kegagalan cerun. Secara geologi, kawasan di sepanjang jalan raya Ranau-Tambunan (RTM) terdiri daripada cerun potongan batuan sedimen arenit daripada Formasi Crocker dan metasedimen argilit daripada Formasi Trusmadi yang telah terluluhawa serta beberapa bahagian yang terdiri daripada endapan Aluvium Kuartener. Pencirian sifat kimia ke atas bahan cerun tanah yang gagal di kawasan tropika, terutama sekali di kawasan kajian jarang dilakukan. Pencirian ini adalah penting kerana bukan ciri fizikal bahan cerun sahaja yang mempengaruhi kejadian tanah runtuh. Oleh itu, kajian ini memberi perhatian utama kepada pencirian sifat kimia dan mineralogi lempung telah dilakukan ke atas cerun-cerun yang gagal di kawasan kajian. Bagi mencapai objektif kajian ini, sebanyak 12 sampel tanah cerun gagal yang terdiri daripada luluhawa gred VI diuji. Analisis inventori cerun gagal menunjukkan terdapat 10 kegagalan cerun tanah (T) dan 8 kegagalan jenis khas (TB) dengan 3 kegagalan cerun dikelaskan berisi padu besar (> 500 m 3), 7 cerun berisi padu sederhana (50-500 m 3) dan 2 kegagalan cerun berisi padu kecil (10 – 50 m 3). Analisis kimia menunjukkan kandungan organik tanah (BOT) yang rendah hingga sederhana daripada 3.75%-7.23%, pH tanah dikelaskan sebagai berasid amat tinggi hingga beralkali rendah. Analisis XRD menunjukkan komposisi mineral lempung utama terdiri daripada kaolinit dan ilit dan beberapa mineral lain seperti montmorilonit, haloisit, dickit dan vermikulit. Komposisi mineral bukan lempung utama terdiri daripada kuarza dan muskovit. Hasil kajian menunjukkan wujud perkaitan signifikan antara sifat kimia dan mineralogi tanah daripada segi pertukaran unsur kimia, hubungan air liang dan kekuatan ikatan butiran tanah dalam pembentukan mineral lempung yang menggalakkan berlakunya kegagalan cerun. Oleh itu, pembinaan dan pengurusan kerja-kerja potongan cerun bukan sahaja mengambil kira aspek sifat fizikal dan kejuruteraan tanah malah sifat kimia tanah juga amat penting terutamanya yang melibatkan batuan yang terluluhawa supaya sebarang kegagalan yang melibatkan cerun potongan dapat ditangani sewajarnya. ABSTRACT The study area which is located in the mountainous region of Sabah west coast is often associated with landslide and slope failure. In terms of geology, the area along the Ranau-Tambunan road (RTM) is consist of arenaceous sedimentary rocks in the Crocker Formation and weathered argiliceous meta-sedimentary rocks in the Trusmadi Formation, as well as deposit of quarternary alluvium in some parts of the study area. Characterization of chemical properties of failed materials in the tropical region, especially in the study area is seldom conducted. This characterization is important because it is not only the physical properties that influence landslide occurrences. Therefore, this study focused on the characterization of chemical characteristic and clay mineralogy on failed slope material in the study area. In order to achieve the objectives of this study, 12 soil samples from failed slopes that were categorized as grade VI in the weathering grade were tested. The inventory analysis on failed slopes showed that there were 10 failed soil slopes (T) and 8 distinctive failed slopes (TB) with 3 failed slopes classified as high volume (>500 m 3), 7 moderate volume (50-500 m 3) and 2 small volume (10-50 m 3). The chemical analysis conducted showed low to moderate organic content (BOT) (3.75%-7.23%) and pH from highly acidic to low alkaline for the failed materials. The XRD analysis showed that the clay compositions were kaolinite, illite and several other minerals such as monmorillonite, halosite, dicktite and vermiculite. The non-clay mineral compositions were quartz and muscovite. The result showed that there is a significant association between chemical characteristics and soil mineralogy in terms of chemical changes, porewater relationship and soil bonding in clay forming minerals that induce slope failure. Therefore, construction and management of slope should not only taking into account the physical aspect and soil engineering of the soil slope, but also the chemical characteristics especially that involve weathered rocks so that any failure on slope cut can be managed appropriately.

In a headwater catchment in the Oregon Coast Range, we find that solid-phase mass losses due to chemical weathering are equivalent in the bedrock and the soil. However, the long-term rate of mass loss per unit volume of parent rock is greater in the soil than in the rock. We attribute this finding to the effects of biotic processes in

The Greenbrier Limestone Group (Figure 1), known in West Virginia as the “Big Lime”, is an extensive, calcium-pure limestone unit of Mississippian Age (350-340 million years). Deposited in a shallow ocean basin during the Carboniferous, the Big Lime is over 1000 feet thick in the Greenbrier Valley of West Virginia. The wet climate of central Appalachia provides the hydraulics and corrosive carbonic acid action necessary to form frequent and sizeable karst dissolution features, such as caves, sinkholes, and springs. Some of the world’s largest caves form here as contact caves, where the Big Lime meets the underlying McCrady Shale Formation, including Scott Hollow Cave (47.5 km), Organ Cave (61.9 km), The Hole (37.0 km), and Maxwelton Sink Cave (18.3 km; Figure 2). Likewise, thousands of sinkholes and pits have formed via dissolution of bedrock and collapse into subsurface cave passages. These features create geohazards to infrastructure and provide pathways for aquifer contamination through sediment and pollutant transport, thereby requiring a geographic understanding of karst feature density.

Atmospheric CO 2 and global climate are closely coupled. Since 800 ka CO 2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr–Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to sub-aerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for $9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial–inter-glacial variation of $80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced

Global warming is inferred to have been one of the main causes of the Permian-Triassic (P-Tr) boundary mass extinction. Although a strong temperature rise in tropical sea-surface temperatures during the latest Permian has been documented, coeval climate changes in terrestrial sections are less well-known. Here, we analyzed multiple weathering indexes (including CIA, CIW, and PIA) for two terrestrial sections in North China (Shichuanhe and Yima), all of which show a major excursion toward higher values (greater weathering intensity) around the end-Permian plant extinction (EPPE). At Shichuanhe, the CIA (chemical index of alteration) increases from 70 to 75 over the interval of 11–36 m, which straddles the EPPE at 33 m, and then decreases from 75 to 71 in the overlying strata. At Yima, CIA increases from 63 to 79 over the interval of 57–68 m, extending up to the EPPE at 68 m, and then gradually decreases from 78 to 72 in the overlying strata. These results imply a strong warming event coupled with intense chemical weathering in soil environments leading up to the end-Permian plant extinction. The decline in CIA values following the EPPE may reflect loss of weathered soils through physical erosion rather than climatic cooling. Estimation of atmospheric temperatures from the CIA data indicate rapid rises at Shichuanhe (from ~11.6 °C to 16.5 °C) and Yima (from 9.3 °C to 18.4 °C) during the end-Permian crisis. The findings in this study are consistent with the hypothesis that a sharp temperature rise caused the extinction of terrestrial organisms during the end-Permian crisis.