Experiencing new perspectives in the application of reflectance spectroscopy in loess research

Diffuse reflectance spectroscopy (DRS) parameters, such as the redness index and hematite/goethite ratios are popular in the study of loess-paleosol sequences. The suggested parameters, however, have their limitations: only some parts of the whole reflectance spectrum are being used, and the spectra of some important components may be excluded from the analysis. A mathematical statistical method, hierarchical cluster analysis, was applied to the loess-paleosol succession at Mala nad Hronom (Slovak Republic) in order to characterize the entire reflectance spectrum and to classify sediment groups. The sedimentary units were classified into seven different cluster groups such as sediments, weak and well-developed paleosols. The distribution of the spectral features in the reflectance spectra was located by using the key-wavelength, provided by the Wilk's lambda analysis. The key-minerals, which play an important role in the classification, were determined by characteristic extrema in the second derivative of reflectance spectra of the seven reference minerals (hematite, goethite, muscovite, illite, montmorillonite, kaolinite and calcite). Mineral groups influence certain wavelengths within the measured range, therefore curve sections modified by individual minerals only in a few cases. The mentioned mineral groups refer to characteristics of the formation environment and to climate change during the Pleistocene.