Évolution géochimique superficielle naissante des anorthosites. Cas du profil de Château-Richer (Québec), Canada

1982 ◽  
Vol 19 (8) ◽  
pp. 1697-1706 ◽  
Author(s):  
J. Dejou ◽  
C. R. De Kimpe ◽  
P. Lasalle
Keyword(s):  
Chemical Weathering ◽  
Crystalline Rocks ◽  
Parent Rock ◽  
Internal Drainage ◽  
Strong Decrease ◽  
Weathering Index ◽  
Weathering Zone

The initial stages of the superficial geochemical weathering of anorthosites have been investigated in a deposit at Château-Richer, Québec. The parent rock consists almost exclusively of andesine and is weathered to a thickness of about 120 cm. A till overburden indicates that the profile was truncated by the Wisconsinian ice. The rock is not extensively disintegrated, but the chemical weathering is rather intense. The Parker diagram shows a strong decrease of the weathering index from the parent rock to the weathering zone. While this is not the case for other crystalline rocks in the area, it may be accounted for by the fragility of the plagioclase.The < 2 μm fraction, which amounts to 2% of the soil, presents an evolution that is influenced by the site, especially the drainage conditions. At the base of the profile, drainage is poor and 2:1 minerals, smectite and vermiculite, are present in addition to 40% kaolinite. The 1:1 mineral increases to 60% near the contact with the till, while the amount of 2:1 minerals decreases because of the better internal drainage conditions.

scholarly journals Provenance and weathering index of the Upper Cretaceous São Carlos Formation and its tectonic significance in the eastern Bauru Basin, SE Brazil

2019 ◽  
Vol 19 (3) ◽  
pp. 77-94
Author(s):  
Lara Ferreira Neves ◽  
Alessandro Batezelli
Keyword(s):  
Trace Elements ◽  
Chemical Weathering ◽  
Upper Cretaceous ◽  
Source Area ◽  
Sedimentary Basins ◽  
Major And Trace Elements ◽  
Published Data ◽  
Weathering Index ◽  
Se Brazil ◽  
Eastern Border

Geochemistry of major and trace elements has been used as an important tool for the study of provenance and tectonic and climatic evolution of sedimentary basins. The São Carlos Formation is an Upper Cretaceous unit that lies on the eastern border of the Bauru Basin. Despite the paleontological and paleodepositional studies performed in this unit in the last years, little is known about the correspondence between tectonic and climatic conditions acting during the first stages of sedimentation. The hypothesis of this paper is to evaluate São Carlos and Araçatuba formations and understand the evolution of the eastern border of the basin. Thus, were conducted geochemical studies using X-ray fluorescence on sandstones, siltstones, and shales from the São Carlos Formation. According to the chemical weathering index, which presented values ranging from 57.12 to 71.58%, the oxides of major elements indicate that moderate weathering processes affected the source area, possibly associated with the arid-semiarid climate. Alkaline rocks, granites, gneisses, and metasediments were the main lithotypes of the source area. Ternary diagrams show that the tectonic environment was equivalent to the passive continental margin, coinciding with the Serra do Mar and, secondarily, Alto Paranaíba Uplift regions. Based on major and trace elements, their ratios, and published data on the basin, was elaborated a paleogeographic model of the eastern border of the Bauru Basin, concluding that the source area of the sediments was constituted by intermediate and felsic rocks, sometimes recycled by sedimentary processes.

scholarly journals Estimation of Pressuremeter Modulus and Limit Pressure in Weathered Granite Based on the SPT-N Value and Chemical Weathering Index: A Case Study in South Korea

2021 ◽  
Vol 11 (8) ◽  
pp. 3411
Author(s):  
Seung-Hwan Lee ◽  
Tae-Young Kwak ◽  
Ka-Hyun Park
Keyword(s):  
South Korea ◽  
Chemical Weathering ◽  
Regression Analyses ◽  
Weathering Index ◽  
N Value ◽  
Weathered Granite ◽  
Limit Pressure ◽  
Simple Regression ◽  
Pressuremeter Modulus ◽  
Spt N Value

A pressuremeter test (PMT) is a representative and highly reliable in situ test for assessing the stress–strain behavior of weathered granite. Its application, however, is restricted by its cost and time requirements. Many researchers have also investigated the correlations between the SPT-N value and the pressuremeter modulus (Em) and limit pressure (PL) of soils, but they have mostly focused on sand, silt, and clay and have employed simple regression analysis. In this study, equations for Em and PL were derived for weathered granite through multiple nonlinear regression analyses using a chemical weathering index that quantitatively represents the degree of weathering. Nonlinear multiple regression analyses were conducted by combining the allometric models that produced the optimal correlations between Em, PL, energy corrected SPT-N (SPT-N60), and normalized VR (Vogt’ ratio) with vertical effective stress. The obtained equations for Em and PL had higher R2 values (0.76 and 0.46, respectively) compared with the simple regression equations reported in previous studies. Because local characteristics are important determinants of the engineering properties of geo-materials, the Em and PL equations proposed in this paper are intended for use in geotechnical surveys of weathered granite in South Korea.

scholarly journals Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland

2021 ◽  
Vol 9 ◽  
Author(s):  
J. Jotautas Baronas ◽  
Douglas E. Hammond ◽  
Mia M. Bennett ◽  
Olivier Rouxel ◽  
Lincoln H. Pitcher ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Isotope Fractionation ◽  
Batch Reactor ◽  
Parent Rock ◽  
Secondary Phases ◽  
Fractionation Factor ◽  
Rock Composition ◽  
West Greenland ◽  
Water Interaction ◽  
Glacial Environments

Glacial environments offer the opportunity to study the incipient stages of chemical weathering due to the high availability of finely ground sediments, low water temperatures, and typically short rock-water interaction times. In this study we focused on the geochemical behavior of germanium (Ge) in west Greenland, both during subglacial weathering by investigating glacier-fed streams, as well as during a batch reactor experiment by allowing water-sediment interaction for up to 2 years in the laboratory. Sampled in late August 2014, glacial stream Ge and Si concentrations were low, ranging between 12–55 pmol/L and 7–33 µmol/L, respectively (Ge/Si = 0.9–2.2 µmol/mol, similar to parent rock). As reported previously, the dissolved stable Ge isotope ratio (δ74Ge) of the Watson River was 0.86 ± 0.24‰, the lowest among global rivers and streams measured to date. This value was only slightly heavier than the suspended load (0.48 ± 0.23‰), which is likely representative of the bulk parent rock composition. Despite limited Ge/Si and δ74GeGe fractionation, both Ge and Si appear depleted relative to Na during subglacial weathering, which we interpret as the relatively congruent uptake of both phases by amorphous silica (aSi). Continued sediment-water interaction over 470–785 days in the lab produced a large increase in dissolved Si concentrations (up to 130–230 µmol/L), a much smaller increase in dissolved Ge (up to ∼70 pmol/L), resulting in a Ge/Si decrease (to 0.4–0.5 µmol/mol) and a significant increase in δ74Ge (to 1.9–2.2‰). We argue that during the experiment, both Si and Ge are released by the dissolution of previously subglacially formed aSi, and Ge is then incorporated into secondary phases (likely adsorbed to Fe oxyhydroxides), with an associated Δ74Gesecondary−dissolved fractionation factor of −2.15 ± 0.46‰. In summary, we directly demonstrate Ge isotope fractionation during the dissolution-precipitation weathering reactions of natural sediments in the absence of biological Ge and Si uptake, and highlight the significant differences in Ge behavior during subglacial and non-glacial weathering.

Provenance Control on Chemical Weathering Index of Fluvio‐Lacustrine Sediments: Evidence From the Qaidam Basin, NE Tibetan Plateau

2019 ◽  
Vol 20 (7) ◽  
pp. 3216-3224 ◽  
Author(s):  
Xueping Ren ◽  
Junsheng Nie ◽  
Joel E. Saylor ◽  
Hua Li ◽  
Meredith A. Bush ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Chemical Weathering ◽  
Qaidam Basin ◽  
Lacustrine Sediments ◽  
Weathering Index ◽  
Ne Tibetan Plateau

scholarly journals Geochemical and Petrographical Evolution of the Weathering Mantle Derived from Basalt in Bangam Locality (West-Cameroon): Implication in the Bauxitisation Process

2019 ◽  
pp. 1-20
Author(s):  
Taylor Moise Sojien ◽  
Estelle Lionelle Tamto Mamdem ◽  
Armand Sylvain Ludovic Wouatong ◽  
Dieudonne Lucien Bitom Oyono
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Iron Oxides ◽  
Major Elements ◽  
Redox Condition ◽  
Parent Rock ◽  
Negative Anomaly ◽  
Weathering Index ◽  
Chemical Index ◽  
Chemical Index Of Alteration

A petrographical and geochemistry study of weathering mantle derived from the basaltic parent rock (plagioclase, olivine, pyroxene, zircon) has been conducted in the locality of Bangam (West-Cameroon). The weathered profile shows a vertical lithology succession of weathered parent rock, isalteritic clayed domain and superficial duricrust (alloterite). The weathering of basalt started by the formation of “pain d’epices” structure rich in gibbsite, metahalloysite, kaolinite. The geochemistry analysis of major elements indicate that SiO2 (46% -1.33%), K2O (0.84% - 0.01%), Na2O (3.6% -0.01%), MnO (0.3% - 0.04%), P2O5 (1.9% - 0.38%) and CaO (5% -0.02%) decrease from the bottom to the surface, however TiO2 (2.3% - 4.08%) remain constant, Fe2O3 (24.2% - 24,6%) and Al2O3 (14.5% - 45.2%) increase. The different weathering index such as, chemical index of alteration (55% - 99%), index of lateritization (41% - 103.5%) and Ruxton Ratio (0.12 - 3.21) just indicate an evolution of parent rock dominated by an alumina and iron phases under a control of hydrolysis phenomenon as bisialitisation, monosiallitisation and allitisation with the formation of minerals smectites group, kaolinite group gibbsite and iron oxides group. The fractionation patterns of rare earth elements (REE) show a positive and negative anomaly in Cerium and other rare earth elements, one more, the correlation between major, trace and REE prove a link of different pedological horizons developed on the basalt in redox condition.

scholarly journals Soils of amazonia with particular reference to the rainfor sites

2009 ◽  
Vol 6 (2) ◽  
pp. 3851-3921 ◽  
Author(s):  
C. A. Quesada ◽  
J. Lloyd ◽  
L. O. Anderson ◽  
N. M. Fyllas ◽  
M. Schwarz ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Size Fraction ◽  
Original Data ◽  
Soil Types ◽  
Soil Evolution ◽  
Weathering Index ◽  
Geographical Patterns ◽  
Rich Diversity ◽  
Morphologic Characteristics ◽  
Soil Groups

Abstract. The tropical forests of Amazonia occur on a wide variety of different soil types reflecting a rich diversity of geologic and geomorphologic conditions. We here review the existing literature about the main soil groups of Amazonia, describing their genesis, geographical patterns and principal chemical, physical and morphologic characteristics. Original data is also presented with profiles of exchangeable cations, carbon and particle size fraction illustrated for the principal soil types, also emphasizing the high diversity existing within the main soil groups when possible. Maps of geographic distribution of soils occurring under forest vegetation are also introduced, and to contextualize soils into an evolutionary framework, a scheme of soil development is proposed having as its basis a chemical weathering index. We identify a continuum of soil evolution in Amazonia with soil properties varying predictably along this pedogenetic gradient.

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