Regolith mass balance inferred from combined mineralogical, geochemical and geophysical studies: Mule Hole gneissic watershed, South India

Braun, Jean‐Jacques; Descloîtres, Marc; Riotte, Jean; Fleury, Simon; Barbiéro, Laurent; Boeglin, Jean-Loup; Violette, Aurélie; Lacarce, Eva; Ruiz, Laurent; Sekhar, M.; Kumar, M. S. Mohan; Subramanian, S.; Dupré, Bernard

doi:10.1016/j.gca.2008.11.013

Cited by 118 publications

(106 citation statements)

References 45 publications

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“…To demonstrate how our model (and its parameters) can be constrained by field measurements of regolith thickness and/or used to understand regolith formation at a specific site, we propose here to reanalyze the data set collected by Braun et al [2009] in the Mule Hole watershed in India. We also show how our model can help put constraints on important timescales pertaining to weathering and regolith formation.…”

Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

“…The Mule Hole watershed is located in the Kabini River basin in Karnataka State of southwestern India (see Braun et al [2009] for exact location). It is approximately 4.3 km 2 in area (i.e., 3000 × 1500 m) and covered by a thick regolith.…”

Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

“…The protolith basement is made of the relatively heterogeneous Precambrian Peninsular Gneiss intermingled with a small amount (10-15%) of mafic and ultramafic volcano-sedimentary rocks. Regolith thickness is constrained by 12 electric resistivity tomography profiles [Braun et al, 2009]. Although determining regolith thickness using contrast in electrical resistivity is tainted with relatively large uncertainties, estimates in the Mule Hole watershed range from 13.5 m at the outlet to 23.7 at the top, with a mean of ≈ 17 m [Braun et al, 2009].…”

Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

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A simple model for regolith formation by chemical weathering

et al. 2016

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We present here a new model for the formation of regolith on geological timescales by chemical weathering based on the assumption that the rate of chemical weathering is primarily controlled by the ability of groundwater to transport solute away from the reacting solid‐fluid interface and keep the system from reaching equilibrium (saturation). This allows us to specify the rate of propagation of the weathering front as linearly proportional to the pore fluid velocity which we obtain by computing the water table geometry in the regolith layer. The surface of the regolith layer is affected by mass transport and erosion. The main prediction of the model is that the geometry of the regolith, i.e., whether it is thickest beneath topographic highs or topographic lows, is controlled by the value of a dimensionless number, which depends on the square of the surface slope, the hydraulic conductivity, and local precipitation rate, but is independent of the chemical weathering rate. In orogenic environments, where regolith formation by chemical weathering competes with surface erosion, the model predicts that the existence and thickness of the regolith layer are controlled by the value of another dimensionless number which is the ratio between the timescale for erosion and the timescale for weathering. The model also predicts that in anorogenic areas, regolith thickness increases as the square root of time, whereas in orogenic environments, a steady state regolith thickness can be achieved, when the propagation of the weathering front is equal to erosion rate.

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Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

Section: How To Use This Model: Case Example Of the Mule Hole Gneiss mentioning

confidence: 99%

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A simple model for regolith formation by chemical weathering

et al. 2016

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“…P1 Myr) would have influenced the balance between both weathering and erosion processes, hence denudation processes, but not enough to strip off the landforms as it has occurred in the sub-humid and arid part in South India (i.e. the Kabini River basin, case of Mule Hole SEW) (Gunnell, 1998;Gunnell et al, 2003;Braun et al, 2009).…”

Section: Implication On the Long-term Evolution Of Lateritic Terrainsmentioning

confidence: 99%

“…In order to refine the elemental transfers in lateritic covers developed on silicate basement and to get deeper insight into (i) the contemporary saprolite production rates and (ii) the combined effect of precipitation and evapotranspiration on the aggressiveness of the draining solutions, a first attempt has been carried out both on the studied mature profile of the Nsimi SEW and with the immature ridge top weathering profile from the Mule Hole SEW (South India), developed on a similar granodioritic basement Braun et al, 2009;Marechal et al, 2009;Ruiz et al, 2010;Violette et al, 2010;Soumya et al, 2011;Maré-chal et al, 2011b). Finally, taking into account the results of the present study and the known history of the South Cameroon landscape, we infer the average saprolite production rate on a long term basis.…”

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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Multiscale geophysical imaging of the critical zone

Parsekian

Singha

Minsley

et al. 2015

Reviews of Geophysics

205

171

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Details of Earth's shallow subsurface-a key component of the critical zone (CZ)-are largely obscured because making direct observations with sufficient density to capture natural characteristic spatial variability in physical properties is difficult. Yet this inaccessible region of the CZ is fundamental to processes that support ecosystems, society, and the environment. Geophysical methods provide a means for remotely examining CZ form and function over length scales that span centimeters to kilometers. Here we present a review highlighting the application of geophysical methods to CZ science research questions. In particular, we consider the application of geophysical methods to map the geometry of structural features such as regolith thickness, lithological boundaries, permafrost extent, snow thickness, or shallow root zones. Combined with knowledge of structure, we discuss how geophysical observations are used to understand CZ processes. Fluxes between snow, surface water, and groundwater affect weathering, groundwater resources, and chemical and nutrient exports to rivers. The exchange of gas between soil and the atmosphere have been studied using geophysical methods in wetland areas. Indirect geophysical methods are a natural and necessary complement to direct observations obtained by drilling or field mapping. Direct measurements should be used to calibrate geophysical estimates, which can then be used to extrapolate interpretations over larger areas or to monitor changing processes over time. Advances in geophysical instrumentation and computational approaches for integrating different types of data have great potential to fill gaps in our understanding of the shallow subsurface portion of the CZ and should be integrated where possible in future CZ research.

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Regolith mass balance inferred from combined mineralogical, geochemical and geophysical studies: Mule Hole gneissic watershed, South India

Cited by 118 publications

References 45 publications

A simple model for regolith formation by chemical weathering

A simple model for regolith formation by chemical weathering

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

Multiscale geophysical imaging of the critical zone

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