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A Quaternary fluvial chronosequence (Guadalquivir River, southern Spain), consisting of five soil profiles with estimated ages of 300 years (Haplic Fluvisol), 7000 years (Haplic Calcisol), 70 000 years (Cutanic Luvisol), 300 000 years (Lixic Calcisol) and 600 000 years (Cutanic Luvisol), was studied. Increasing soil age was associated with increases in: reddening, development of structure, clay content, dithionite-extractable iron (Fe d ) and aluminium (Al d ) and strengthening of X-ray diffraction (XRD) peaks for phyllosilicates and iron oxides; there were also decreases in pH and percentage of carbonates in the fine earth and lower XRD peaks for calcite and dolomite. These changes indicate that the principal pedogenic processes were weathering, clay illuviation, rubefaction and the weathering and leaching of carbonates. We have further characterized the pedogenetic chronosequence by quantification of ultramicrofabrics of ped interiors using image analysis (IA) techniques on images obtained with scanning electron microscopy (SEM). We have estimated morphometric ultramicrofabric parameters for particle clusters, skeleton grains and pore space. These are closely related to analytical, mineralogical and macromorphological properties. In the principal component analysis, the first two principal components of the combined morphological, analytical and mineralogical data accounted for 78% of the total variance. The first component (48%) is loaded by variables associated with clay illuviation, relative accumulation of iron and aluminium sesquioxides and the weathering and leaching of carbonates. The components are related to ultramicrofabric development trends. We tested several chronofunctions derived from analytical and morphometric attributes. The logarithmic model fitted best, and we interpret this as indicating pedogenetic processes that are converging towards a steady state.

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Gully erosion is one of the main processes of soil degradation, representing 50%–90% of total erosion at basin scales. Thus, its precise characterization has received growing attention in recent years. Geomatics techniques, mainly photogrammetry and LiDAR, can support the quantitative analysis of gully development. This paper deals with the application of these techniques using aerial photographs and airborne LiDAR data available from public database servers to identify and quantify gully erosion through a long period (1980–2016) in an area of 7.5 km2 in olive groves. Several historical flights (1980, 1996, 2001, 2005, 2009, 2011, 2013 and 2016) were aligned in a common coordinate reference system with the LiDAR point cloud, and then, digital surface models (DSMs) and orthophotographs were obtained. Next, the analysis of the DSM of differences (DoDs) allowed the identification of gullies, the calculation of the affected areas as well as the estimation of height differences and volumes between models. These analyses result in an average depletion of 0.50 m and volume loss of 85000 m3 in the gully area, with some periods (2009–2011 and 2011–2013) showing rates of 10,000–20,000 m3/year (20–40 t/ha*year). The manual edition of DSMs in order to obtain digital elevation models (DTMs) in a detailed sector has facilitated an analysis of the influence of this operation on the erosion calculations, finding that it is not significant except in gully areas with a very steep shape.

Summary A soil chronosequence from the River Guadalquivir (Spain) was studied at a nanometre scale (10−9 m), this being a poorly investigated aspect of soil genesis. The fine mineral fractions (< 50 µm) were studied by X‐ray diffraction (XRD) and analytical electron microscopy (TEM‐AEM). At a nano‐scale, the dominant materials in the chronosequence were dioctahedral 2:1 phyllosilicates, such as potassium mica (mainly muscovites and illites), mixed‐layer smectite/illite and smectite (beidellite). Sodium mica brammallite was described for the first time in soils. These dioctahedral phases are related genetically to illite by inheritance of muscovite and posterior transformation of illite into beidellite. These processes involve (i) loss of regularity in the layer stacking sequence in high‐resolution TEM images, even to the point of losing the contrast between layers; (ii) loss of three‐dimensional order in selected area (electron) diffraction (SAED) patterns, with increased diffusivity and weak spots on hkl levels; (iii) smaller layer packets producing superimposed SAED patterns (high‐angle boundaries in 00l); (iv) changing from two‐layer ordered polytypes (2M1) to one‐layer random polytypes (1Md); and (v) chemically, loss of charge and ions in the interlayer. The final result is beidellites with almost tactoid morphologies. As these processes are related to the soil‐forming factor of time it was possible to establish logarithmic chrono‐functions tending to steady state for nano‐scale properties such as the percentage of 2M1 polytypes, the layer charge, interlayer charge and the interlayer ion content in 2:1 phyllosilicates (more smectite‐like micas). This shows that time affects soil‐forming processes at the nano‐scale to the same extent as described for other scales such as ultra‐microfabric (10−6 m), horizon (10−1 m) or pedon (100 m).