Integrating magnetic susceptibility and colorimetric parameters for palaeoenvironmental reconstructions from loess-palaeosol sequences: A case study from northern Serbia for the last 430 ka

Abstract:

Loess palaeosol sequences (LPSs) are terrestrial climatic archives capable of recording past climatic change. In particular, the alternation of interglacial and glacial periods is recognized in LPSs as intercalated buried soils (palaeosols) within loess units. For LPSs of the Eurasian loess belt, correlating low-frequency magnetic susceptibility (χlf) to global palaeoclimate variations, such as benthic foraminifera oxygen isotope ratios (e.g. LR04 stack) and global ice volume models, is a widespread approach to generate age models for the LPS of interest. The underlying assumption to this approach is that χlf variations result from changes in pedogenic alteration intensity. Physically, χlf values are biased towards changes in concentration of soft ferrimagnetic minerals (e.g. maghemite and magnetite) inclusive of all grain sizes. Variations in mineralogical assemblage and/or concentration due to changes in loess provenance or in grain size due to varying wind strengths could also lead to significant variations of χlf. In this context, the absolute frequency dependence of magnetic susceptibility (Δχ) is favored to isolate uniquely the pedogenic signal. Δχ increases when magnetic minerals of a distinct grain size (20-50 nm), assumed to be exclusively neo-formed during pedogenesis, are present. In addition, colorimetric measurements (CMs) provide indicators for the hard magnetic minerals hematite and goethite through definite characteristics in the first derivatives of color spectra. However, discriminating goethite and hematite from room-temperature χlf and Δχ alone is beyond challenging. Nevertheless, CM parameters of luminance (L*) and redness (a*) are routinely used in paleoclimate studies as proxies for pedogenesis. In this study we investigate magnetic susceptibility parameters (Δχ, χlf) and colorimetric L*, a* and b* (blueness) of a LPS located in northern Serbia spanning the last 430 ka. The study demonstrates that integrating colorimetric parameters to magnetic susceptibility parameters provides (1) a more comprehensive view of the contribution of palaeoclimatic relevant minerals to the LPS and enables (2) detecting millennial scale climatic variations over the last 4 interglacial/glacial cycles in the middle Danubian Basin.