Pedoplasmation, therefore, is best studied by comparing sequential thin sections, from the saprolite upwards. The thickness of the pedoplasmation zone can reach several decimetres or metres on coarse-grained rocks in the tropics, and the zone can be almost absent on fine-grained quartz-free material. The boundary between saprolite and totally pedoplasmated material can be sharp (even represented in a single thin section) or gradual, as already noticed by Harrison (1933) in his classic work on various igneous rocks from Guyana. Fölster (1971) used the word ‘homogenisation’, and Nahon (1991) used the general term ‘pedoturbation’, which is however a more general concept. Romashkevich (1964) described the transformation of ‘weathering crust’ to ‘active soil material’, and she later called this process ‘soil formation’ ( Romashkevich, 1965 Romashkevich et al., 1977). Other terms have been used to refer to this process. Although the term ‘plasma’ as such has been abandoned in micromorphology, the term pedoplasmation is still in use, meaning the in situ development of a structured, loose material in which the original fabric of the saprolite or sediment is no longer visible. In the case of deep tropical soils, it would have been more appropriate to speak more generally of transformation to loose soil parent material rather than to B-horizons. (1968) introduced the term ‘pedoplasmation’, which they defined as ‘the transformation of weathered rock (saprolite) to soil B-horizons’. (2010, this book), and (ii) homogenisation resulting in the transformation of the saprolite into soil material (pedoplasmation), which is the subject of the present chapter.įlach et al. For coherent rocks, two subsequent steps can be distinguished: (i) weathering, giving rise to a saprolite, which is reviewed in the chapter by Zauyah et al. The transformation of loose sediments to soil material is mainly a matter of pedoturbation, especially bioturbation (see also Kooistra & Pulleman, 2010, this book). In the first stage, the situation is different for loose sediments and for coherent rocks. In the general process of soil formation the transformation of rock into soil parent material is followed by the vertical differentiation of the soil material into horizons (pedogenesis). Schaefer, in Interpretation of Micromorphological Features of Soils and Regoliths, 2010 1 Introduction 3.3.4 AquifugesĪquifuges are not capable of absorbing water. Also, it seems that the USGS prefers to use the term ‘confining unit’ for aquicludes, aquitards, and aquifuges. Ĭonfining unit: A hydrogeologic unit of impermeable or distinctly less permeable material bounding one or more aquifers and is a general term that replaces aquitard, aquifuge, aquiclude ( AGI, 1980).Īlthough aquitards do not have much water in store, they can transmit from nearby aquifers.It does not readily yield water to wells or springs, but may serve as a storage unit for ground water ( AGI, 1980). Īquitard: A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer a leaky confining bed.Īquiclude: A hydrogeologic unit, which although porous and capable of storing water, does not transmit it at rates sufficient to furnish an appreciable supply for a well or spring.The following are the definitions given by the US Geological Survey (USGS): Apparently, there is a slight difference between aquicludes and aquitards. But unlike aquicludes, aquitards can transmit water from adjacent aquifers. Aquitards as in the case of aquicludes, can absorb water but would not yield an appreciable quantity of water.
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