Weathering rates and carbon storage along a climosequence of soils developed from contrasting granites in northeast Brazil

Abstract

I- and S-type granites comprise large areas and play a key role in global soil weathering patterns. I-type granites are originated from melting of igneous source rocks, whereas S-type granites result from melting of sedimentary sources. This gives rise to differences in mineralogical and geochemical characteristics of the rocks. The objective of this study was to address the effect of petrology and mineralogy of I- and S-type granites on weathering, pedogenesis and total organic carbon stocks across a climosequence. Significant differences in morphological, physical and chemical properties of soils derived from I- and S-type granites were observed and directly linked to petrological, mineralogical and geochemical signatures of the underlying granites, e.g., presence of more mafic minerals in the I-type granite, and therefore a higher clay and iron content in their derived soils. In addition, this higher iron content favored the hematite pathway and, thus, the red soil development. Despite the influence of the climate on weathering patterns, i.e., higher soil development in humid areas, parent material seems to play a decisive role in determining soils characteristics in the studied area. The type of parent material also governed the rates of carbon accumulation in soils. I-type granites originated soils with higher TOC stocks than soil profiles developed from S-type granites. This carbon accumulation is mainly due to soil chemical and physical characteristics driven by the type of granite, notably soil fertility and clay content.