Are Mediterranean mountains Entisols weakly developed? The case of Orthents from Sierra Nevada (Southern Spain)

Two Orthents from Sierra Nevada National Park (Spain), classified as loamy-skeletal mesic Typic Xerorthent and loamy-skeletal frigid Lithic Cryorthent were studied. They were situated at 1460 and 2000 m, derived from micaschists and quartzites under Mediterranean mountain climate conditions with mesic and cryic temperature regimes and xeric moisture regime. These Orthents are weakly developed, as shown by their reduced thickness, their lack of diagnostics subsurface horizons, sandy loam textures, skeletal, and lithochromic colors. Quartz is present in significant amounts, particularly in the fine light sand fraction. Analysis of the quartz grains of the fine light sand by scanning electron microscope (SEM) and backscattered electron images (BSE) revealed the presence of significant physical and chemical alteration features such as fractures, corrosion gulfs, fields of etch pits and dissolution of intergranular surfaces. This process is confirmed by electron microprobe analysis (EMPA) since the edges of the quartz grains have a higher proportion of cations other than Si, compared to their centre. Further evidence indicates the authigenic nature of the process. Starting from quartz etching an assessment of soil weathering has been made (W index from Marcelino et al. (1999). The alteration of the quartz, together with the development of a ultramicrofabric with several fabric units (investigated with SEM), and other characteristics (mineralogical, chemical, etc.) are considered indicative of some pedogenic evolution. These facts are especially interesting in the case of weakly developed Mediterranean mountain soils from Sierra Nevada, where processes of chemical weathering have traditionally not been considered very active.