Physical and chemical characteristics of soil and weathering profiles in Longnan, Jiangxi province, south China

Bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11-meter profile weathering on a granite ridgeline under subtropical climate conditions in south China. The weathering sequence is delineated by mineralogy and major element variations. Apatite, biotite, hornblende and plagioclase dissolve early during weathering, resulting in nearly 100% Ca and Na loss and significant Mg, Fe and P depletion at depth. The K-feldspar reaction front begins at the depth of depletion of plagioclase, leading to a loss of ~ 80% of the K at the land surface near the bottom of the ridgeline and almost 100% at the top. Dissolution of quartz and other silicates releases about 60% of Si in the profiles. Kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer. The soil horizon (upper 100 cm) is the zone dominated by pedogenic processes, including active biological activity, physical erosion and influx of high concentrations of atmospheric components (especially CO2 and O2). The pedogenic processes are characterized by low pH (~ 4.54 to 5.85), high clay content (kaolinite: 6-16 wt.%; gibbsite: 2-8 wt.%) and total organic carbon content (0.13-3.93%) and intensive fracturing and dissolution of quartz and K-feldspar compared with the lower horizons. […]