Soils and Sediments

Paquet, Hélène; Clauer, Norbert

doi:10.1007/978-3-642-60525-3

Cited by 29 publications

(7 citation statements)

References 98 publications

(127 reference statements)

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“…In the tropical dry savannah of the Extreme North of Cameroon, the weathering of granite leads to the exclusive neoformation of beidellite, suggesting that the chemical process acting at the bottom of the profile in this area is a bisiallitisation [18]. This process is favoured by the following morphoclimatic and hydrological conditions in this bioclimatic zone [14]: low rainfall, followed by dry periods that include evaporation, induce soil solutions concentrated in silica and basic cations; thus smectite clays are formed [12,17,18,23]. In the upper horizons, beidellite evolves and transforms into montmorillonite and kaolinite [1,10].…”

Section: Discussionmentioning

confidence: 99%

Altération différentielle du granite en zone tropicale. Exemple de deux séquences étudiées au Cameroun (Afrique centrale)

Nguetnkam

Kamga

Villièras³

et al. 2008

Comptes Rendus. Géoscience

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Deux séquences d'altération du granite, développées dans deux zones bioclimatiques du Cameroun, ont été étudiées au moyen de l'analyse macroscopique et microscopique, de la diffraction des rayons X (DRX), des analyses chimiques, ainsi que des observations au MEB et au MET. Dans le Sud du Cameroun, en zone forestière tropicale humide, à collines en demi-orange, à pentes moyennes à fortes et à drainage excellent, l'altération du granite conduit à la néoformation de la kaolinite et à la formation d'un sol ferrallitique, constitué de quatre horizons à pH acide et à rapport SiO 2 /Al 2 O 3 < 3. À l'extrême-nord, en zone tropicale sèche, à végétation de savane, à pentes faibles et à drainage limité, l'altération du granite conduit à la néoformation de la beidellite et à la formation d'un vertisol chromique, constitué de trois horizons à pH basique et à rapport SiO 2 /Al 2 O 3 > 3. Ces résultats soulignent l'influence du climat et des facteurs de station dans la néoformation des minéraux argileux et dans la différenciation des sols en régions intertropicales. Pour citer cet article :

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Section: Discussionmentioning

confidence: 99%

Altération différentielle du granite en zone tropicale. Exemple de deux séquences étudiées au Cameroun (Afrique centrale)

Nguetnkam

Kamga

Villièras³

et al. 2008

Comptes Rendus. Géoscience

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“…As suggested by Mongelli, [29], the formation of autochthonous bauxites includes three stages, in which clayey material deposition at the bottom of karst cavities, bauxitization (i.e., intense weathering), and late formation of ooidal concretions in a pedogenic environment occur. In such a natural environment, where dry and wet conditions alternate frequently, Fe-and Al-rich ooids may form and coexist [39]. Dry climate conditions promote the formation of boehmite, whereas wetter conditions favor the stability of Al-hematite [29,34].…”

Section: Discussionmentioning

confidence: 99%

Mineralogical and Geochemical Features of Cretaceous Bauxite from San Giovanni Rotondo (Apulia, Southern Italy): A Provenance Tool

Sinisi

2018

Minerals

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In this study, the mineralogical and chemical compositions of bauxite from San Giovanni Rotondo (SGR) on the Gargano Promontory (northern Apulia, Italy) are presented and discussed with the aim of assessing the nature of its source material. Bauxite from the SGR, which is known as the “Montecatini mine”, was exploited intensively until the 1970s to recover alumina. As with most of the autochthonous peri-Mediterranean bauxites, the studied deposit is a karst bauxite with a massive, matrix-supported texture and an oolitic structure. Boehmite and hematite are the main mineral phases, and anatase, rutile, and kaolinite are present in lesser amounts along with detrital zircons and monazite grains. Calcite is abundant only in the deposit’s lower portion, triggering a significant dilution effect on trace element concentrations. However, with respect to the average crust and chondrite compositions, strong enrichments of trace metals (up to 10X Upper Continental Crust’s (UCC)) and rare earth elements (REEs, up to 800X chondrite) exist throughout the studied deposit. The distribution of REEs, the (La/Yb)N and Eu/Eu* ratios, and an Eu/Eu* versus Sm/Nd diagram have been used for determining the bauxite’s provenance. These geochemical proxies point to a parental material consisting of a mixture of distant magmatic and siliciclastic components.

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“…They conclude that 15 m of bauxite require 45 m of granite in the first case. In the second case, Paquet and Clauer (1997) describe a rate of beauxitisation of 3 m.M yr −1 with data from Fritz and Tardy (1973). Boulangé et al (1997) report landscape lowering rates from bauxite formation on granite in the Ivory Coast of 30 m to form 15 m of bauxite and up to a 70~% volume reduction to form the pisolitic bauxite overlying the main bauxite.…”

Section: Constraining New Model Parametersmentioning

confidence: 91%

“…Most studies have been carried out during the last century, by authors e.g. Leneuf (1959); Gac (1980); Boulangé (1984); Tardy and Roquin (1992); Boulangé et al (1997); Paquet and Clauer (1997) who have tried to describe duricrust formation rates in the African, South-American and Australian regions. Note that in citing them, we have included estimates of laterisation rates and ages for duricrusts assumed to form through laterisation too, as too few data are available for ferricrete formation under the hydrological hypothesis alone, which would lead to a bias.…”

Section: Constraining New Model Parametersmentioning

confidence: 99%

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A numerical model for duricrust formation by water table fluctuations

Fenske,

Braun,

Guillocheau

et al. 2024

Preprint

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Abstract. Duricrusts are hard elemental layers forming in climatically contrasted environments. Ferricretes (or iron duricrusts) are a type of duricrust, made of indurated iron layers. They form in tropical to semi-arid environments, but can be currently observed all around the world, in areas such as Africa, South America, India, and Australia. In most cases, they cap hills and appear to protect softer layers beneath. Two hypotheses have been proposed for the formation of duricrusts, i.e., the hydrological or horizontal model where the enrichment in the hardening element (iron for ferricretes) is the product of leaching and precipitation through the beating of the water table during contrasted seasonal cycles, and the laterisation or vertical model, where the formation of iron duricrusts is the final stage of laterisation. In this article, we present the first numerical model for the formation of iron duricrusts based on the hydrological hypothesis. The model is an extension to an existing regolith formation model where the position of the water table is used to predict the formation of a hardened layer at a rate set by a characteristic time scale τ and over a depth set by the beating range of the water table, λ. Hardening causes a decrease in surface erodibility, which we introduce in the model as a dimensionless factor κ that multiplies the surface transport coefficient of the model. Using the model we show under which circumstances duricrusts form by introducing two dimensionless numbers that combine the model parameters (λ and τ) as well as parameters representing external forcing like precipitation rate and uplift rate. We demonstrate that by using model parameter values obtained by independent constraints from field observations, hydrology and geochronology, the model predictions reproduce the observed conditions for duricrust formation. We also show that there exists a strong feedback from duricrust formation on the shape of the regolith and the position of the water table. Finally we demonstrate that the commonly accepted view that, because they are commonly found at the top of hills, duricrusts protect elements of the landscape is most likely an over-interpretation and that caution must be taken before using duricrusts as markers of uplift and/or base level falls.

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Soils and Sediments

Cited by 29 publications

References 98 publications

Altération différentielle du granite en zone tropicale. Exemple de deux séquences étudiées au Cameroun (Afrique centrale)

Altération différentielle du granite en zone tropicale. Exemple de deux séquences étudiées au Cameroun (Afrique centrale)

Mineralogical and Geochemical Features of Cretaceous Bauxite from San Giovanni Rotondo (Apulia, Southern Italy): A Provenance Tool

A numerical model for duricrust formation by water table fluctuations

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