Potential of VNIR spectroscopy for prediction of clay mineralogy and magnetic properties, and its paleoclimatic application to two contrasting Quaternary soil deposits

Abstract The properties of phyllosilicates, iron oxides (oxyhydroxides), and magnetic minerals in soils can respond to changes in pedogenic weathering intensity and past climate. Numerous paleoclimate reconstructions using soil mineralogy have made use of only one or two of these mineral types, generally in order to limit analytical effort or expense, thereby foregoing comparisons between different mineralogic proxies. Quaternary soil deposits in China afford a unique opportunity for assessing the potential of visible and near-infrared reflectance (VNIR) spectroscopy for analysis of soil minerals, chemical weathering, and paleoclimate reconstruction. Here, we investigated two typical Quaternary soil types exhibiting different weathering degrees, i.e., a loess-paleosol sequence in northern China and a red earth deposit in southern China. Clay and iron mineralogy from the soils was compared with VNIR data using partial least squares regression (PLSR) and continuum-removal-based multiple linear regression (MLRCR) approaches. VNIR spectra show potential for analysis of pedogenic weathering and paleoclimate reconstruction in weakly to highly weathered soils in that spectral behavior is strongly related to both clay-mineral composition and magnetic properties. Both higher concentrations of minerals and their wider variability can improve model predictive ability. Phyllosilicates and non-magnetic Fe-oxides are predicted more accurately for highly weathered red earth deposits, whereas soil magnetic properties are predicted more accurately for loess-paleosols. The predictors identified by the MLRCR method (D2200, D680, and D900) and the ranges constrained by the PLSR method (650–700 and 2150–2250 nm) deserve more attention in future studies of spectral pedology and chemical weathering. We suggest that VNIR spectroscopy has the potential to be an alternative and broadly applicable tool for reconstructing paleoclimate using soil-mineral properties, substituting for a series of common mineralogic analyses. This would significantly reduce the workload and expense of experiments and improve the resolution of paleoclimate studies.