Saprolithology applied to pedology: Integrated study of soil and saprolite derived from crystalline rocks to better understand properties of whole regoliths along a climate gradient (NE Brazil)

Saprolite is the weathered rock below the soil and constitutes the least researched region of the regolith. The association between saprolithology and pedology can contribute to a better understanding of the whole regolith. The Triunfo massif in the state of Pernambuco (NE Brazil) is a natural laboratory suitable for the study of regoliths derived from crystalline rocks under a climate gradient, from the semiarid climate at the base to a humid climate at the top, due to an orographic effect of climate. In this work, we integrated pedology with saprolithology for a taxonomic description of three regolith profiles along the climate gradient in Triunfo massif to better understand the regolith properties. We evaluated the climate effect on the physical, chemical, and morphological properties in horizons and layers of regolith profiles (depth: 2.0 m). The results indicated that a) the integration of taxonomic systems and morphological description protocols of the soil and saprolites in field studies is possible and can contribute to studies on the properties of the whole regoliths, b) the most developed soils were described under wetter climates. However, the climatic gradient did not significantly influence the weathering degree of the saprolite layers below these soils, c) the greater depth and the Bt horizon in the soil under humid climate attenuated the weathering intensity in the underlying saprolite, resulting in saprolite layers with weathering degrees similar to those described in the regolith profile under the semi-arid climate, d) the weathering degree did not advance only from top to bottom, it also moved to zones of greater biological activity, resulting in preferential weathering of the saprolite structure in pedoplasmation zones, e) there is a need to correct the values of physical and chemical properties of the saprolite layers determined in fractions < 2 mm to mitigate the dilution effect, which overestimated by 317% the values of chemical and physical properties in the saprolite layers.