Quantitative geochemical approach to pedogenesis: importance of parent material reduction, volumetric expansion, and eolian influx in lateritization

摘要: Abstract Using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock. Through calculation net fluxes through soils Mali, West Africa, show removal mobile elements with a corresponding increase bulk porosity and decrease density, contributes only very minor fraction Al, Fe, Si Au. Instead, demonstrate abundance these due to influx accumulation selective retention chemically mature detritus local foreign origin clearly evident micromorphological infilling features. At same sample depths reaches extreme values, volumetric expansion excess 200% has occurred locally. We infer spatially coincidental zones rock-forming metals Si, also Au dilational hyperstrains result from mutually reinforcing, mechanical interaction between material effects subsurface deformational processes such as shrink-swell cycles root growth decay. propose progressive available connected voids illuvial microsedimentary deposits insoluble resistate neoformed minerals, capacity for combined skeleton plasma remain isovulumetric exceeded. speculate resultant space problem relieved upwards towards overlying free surface. Continued translocation void occur are limited depth where size translocational particles smaller than voids. Consequently, accumulate above this critical long-term influence proposed wedge chemically-resistant minerals against which numerous generations plant roots have exerted stresses. Eclectic surficial contaminants involved continuously derived leaving no indication relict source region within present soil profile they might been extracted. largely existing regolith column itself releases addition, supplemented deposition colluvial shed nearby escarpment retreat