Chemical mobilizations in laterites: evidence from trace elements and 238 U- 234 U- 230 Th disequilibria

Dequincey, O.; Chabaux, François; Clauer, Norbert; Sigmarsson, Olgeir; Liewig, Nicole; Leprun, Jean-Claude

doi:10.1016/s0016-7037(01)00845-6

Cited by 137 publications

(109 citation statements)

References 32 publications

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“…Studies of U/Th disequilibrium (Dequincey et al, 2002;Chabaux et al, 2003) and radiation-induced defects in kaolinite (Balan et al, 2005) suggest that each horizon of the lateritic profile behaves independently, reflecting the superimposition of further remobilization effects upon older formation steps. Although the petrology, mineralogy and geochemistry of lateritic profiles developed on silicate rocks have been extensively studied, the quantification of the chemical fluxes within the regolith and, hence, the saprolite and soil production rates remain poorly constrained.…”

Section: Introductionmentioning

confidence: 99%

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

Braun

Maréchal

Riotte

et al. 2012

Geochimica et Cosmochimica Acta

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International audienceThe comparison between contemporary and long-term weathering has been carried out in the Small Experimental Watershed (SEW) of Nsimi, South Cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover. We focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer. This study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements. The mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates (i) strong depletion profiles for alkalis (Na, K, Rb) and alkaline earths (Mg, Ca, Sr, Ba), (ii) moderate depletion profiles for Si, P, Cd, Cu, Zn, Ni and Co, (iii) depletion/enrichment profiles for Al, Ga, Ge, Sn, Pb, LREE, HREE, Y, U, Fe, V, Cr, Mn. It is noteworthy that (i) Mn and Ce are not significantly redistributed according to oxidative processes as it is the case for Fe, V and Cr, and (ii) Ge is fractionated compared to silica with enrichment in Fe-rich horizons. The calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements, among which are those specifically accumulated as the redox sensitive elements (Fe, V, Cr) and iron oxide related elements like Th. The overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy. 94% of the whole Na flux generated from the hillside corrected from atmospheric deposits (77 mol/ha/yr) represents the current weathering rates of plagioclase (oligoclase) in the system, the other remaining 6% may be attributed to the dissolution of hornblende. The silica hillside flux is 300 mol/ha/yr and can be mostly attributed to the plagioclase and kaolinite dissolution. Al and Ga are exported from the lateritic regolith and maybe due to the dissolution of kaolinite crystals. Compared to the other immobile elements (Zr, Hf, Nb and Th), Ti is significantly exported. Among redox-sensitive elements (Fe, V, Cr, Mn, Ce), only Ce and Mn are exported out of the hillside system. The other elements (Fe, V, Cr) are likely able to be mobilized but over a short distance only. Rb , Sr, Ba, Ni, Cu, Zn are affected by export processes. LREE and Y are exported but in very low amounts (in the range from µmol/ha/yr to mmol/ha/yr) while HREE and U are exported in negligible quantities. A first attempt is carried out to compare the mature ridge top profile from Nsimi SEW with the immature ridge top weathering profile from the Mule Hole SEW (South India), developed on similar granodioritic basement, in order to get deeper insight into (i) the contemporary saprolite production rates and (ii) the combined effect of precipitation (in terms of Mean Annual Rainfall, MAR) and evapotranspiration on the aggressiveness of the draining solutions. Consider...

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Section: Introductionmentioning

confidence: 99%

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

Braun

Maréchal

Riotte

et al. 2012

Geochimica et Cosmochimica Acta

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“…For same climatic conditions (compare with granodiorite lithology in Puerto Rico), soil is produced 3 times faster over andesite than over granodiorite. Data are from this study and (Dequincey et al, 2002;Dosseto et al, 2007;Dosseto et al, 2008;Ma et al, 2010;Mathieu et al, 1995). Figure 4.…”

Section: Discussionmentioning

confidence: 77%

“…This can be used in turn to estimate rates of soil production. Previous works have shown that in granitic terrains, soil production rates vary between about 20 to 80 mm/kyr (Dequincey et al, 2002;Dosseto et al, 2007;Dosseto et al, 2008;Mathieu et al, 1995). These studies focused on lateritic profiles in tropical lowlands (Dequincey et al, 2002;Mathieu et al, 1995), actively eroding tropical island (Dosseto et al, 2007) and retreating escarpment under temperate climate (Dosseto et al, 2008).…”

Section: Introductionmentioning

confidence: 96%

“…Previous works have shown that in granitic terrains, soil production rates vary between about 20 to 80 mm/kyr (Dequincey et al, 2002;Dosseto et al, 2007;Dosseto et al, 2008;Mathieu et al, 1995). These studies focused on lateritic profiles in tropical lowlands (Dequincey et al, 2002;Mathieu et al, 1995), actively eroding tropical island (Dosseto et al, 2007) and retreating escarpment under temperate climate (Dosseto et al, 2008). In a recent study, U-series isotopes were used to infer soil production rates over shales in temperate eastern US and yielded values similar to granitic profiles between 17 and 45 mm/kyr (Ma et al, 2007).…”

Section: Introductionmentioning

confidence: 96%

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The delicate balance between soil production and erosion, and its role on landscape evolution

Dosseto

Buss

Suresh

2011

Applied Geochemistry

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“…The uranium-series (U-series) isotopes are a valuable tool for deriving the timescales of weathering and erosion processes (e.g., Plater et al, 1992;Scott et al, 1992;Vigier et al, 2001;Dequincey et al, 2002;Chabaux et al, 2003;Granet et al, 2007;Dosseto et al, 2008a;Dosseto et al, 2008b;Chabaux et al, 2008;Vigier and Bourdon, 2011). Recently, developed a method for dating the formation age of finegrained sediments, in other words, the time elapsed to present day since physical weathering of source rock to a threshold grain size (≤ ~50 µm), termed the 'comminution age' Lee et al, 2010;Handley et al, in press).…”

Section: Introductionmentioning

confidence: 99%

Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

Handley¹,

Turner²,

Dosseto³

et al. 2013

Chemical Geology

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Uranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The (234U/238U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1Ma, i.e. the timeframe for 234U and 238U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock (234U/238U) ratio instead of an assumed (234U/238U) activity ratio of unity for the source would significantly reduce calculated residence times. This result warrants concern for future studies using the comminution approach for which a secular equilibrium source (234U/238U) activity ratio is assumed. Significant input of aeolian material may modify the measured (234U/238U) activity ratios. Such input may be more tightly constrained in future studies using rare earth element and radiogenic isotopic data. Future comminution studies would benefit from further consideration of the importance of 1) leaching lost 234U from source rock and bulk sediment samples, 2) wind deposition of fine-grained material and 3) the appropriateness and robustness of sample pre-treatment procedures. AbstractUranium isotope ratios have been determined for the fine-grained detrital fraction of Pleistocene Wilkawillina valley-fill sediments, four local Proterozoic bedrock samples and fine-grained aeolian material from a sand dune deposit of the Flinders Ranges, South Australia. The aim was to quantify the comminution age, i.e. the time elapsed since physical weathering of the bedrock, and residence time of the valley-fill sediments and to place tighter constraints on input parameters for the comminution age calculation. Despite using two independent approaches for determination of the recoil lost fraction of 234 U from the sediment (weighted geometric and surface area estimates), samples fail to produce realistic comminution ages and hence, residence times. The issues involved in the ability to determine sediment comminution ages are discussed. The ( 234 U/ 238 U) activity ratio of the local bedrock is not in secular equilibrium, despite the bedrock being much older than 1 Ma, i.e. the timeframe for 234 U and 238 U to reach secular equilibrium in a closed system. Using the average Flinders Ranges bedrock ( 234 U/ 238 U) ratio instead of an ass...

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Chemical mobilizations in laterites: evidence from trace elements and 238 U- 234 U- 230 Th disequilibria

Cited by 137 publications

References 32 publications

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

Elemental weathering fluxes and saprolite production rate in a Central African lateritic terrain (Nsimi, South Cameroon)

The delicate balance between soil production and erosion, and its role on landscape evolution

Considerations for U-series dating of sediments: Insights from the Flinders Ranges, South Australia

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