Controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay on the Chinese Loess Plateau

The colour of soil is one of its most striking features, and records the palaeoenvironment conditions when the soil is formed; however, the controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay are poorly understood. In this study, the Jiaxian section, on the northern edge of the Chinese Loess Plateau, was selected to explore the aforementioned issue using colour reflectance, diffuse reflectance spectroscopy (DRS), geochemical, and magnetic approaches. In the red clay sequence, (1) the concentration of iron oxides (mainly haematite and goethite) and the intensity of pedogenesis were significantly positively correlated with redness (a*) and yellowness (b*). (2) a*, b*, and a*/b* can be used as proxy indicators of haematite concentration, goethite concentration, and temperature, respectively. (3) The parameters derived from colour reflectance and DRS measurements were proven to be better than magnetic susceptibility (χ) in recording palaeoclimatic evolution, and Ca*b* was better than the chemical weathering index in recording soil development.