LOESSFEST'09 | Aug. 31st – Sept. 3rd, 2009 |Novi Sad-Serbia
Loess Spectroscopy and its Use as a Proxy for Past Climate Change
Smith, M. J.1, Stevens, T.1
1Kingston University, London, UK, Royal Holloway, University of London, Egham Hill, EGHAM, TW20 0EX, UK
The loess record in China constitutes one of the most important archives of past environmental change. However, the relative importance of both regional climate patterns (i.e. the monsoon) and local site-specific influences on proxy records such as magnetic susceptibility is unclear and may be modulated through site-specific sedimentation rate. At present regional versus local influences are poorly constrained and significantly increases the degree of uncertainty over the wider-scale applicability of climate reconstructions from individual sites. To resolve this issue on sub-orbital timescales, a rapidly deployable technique is needed that can be used to test multiple sites and differentiate between local and regional signals. This research develops the use of full spectrum reflectance spectroscopy in studying loess in the field for the first time at one site on the south of the Loess Plateau, and utilises statistical analyses to compare such data with magnetic susceptibility records. The technique potentially allows the compilation of large data sets in order to investigate lateral facies variations in loess profiles, and hence extract a broad scale climate record.
Field spectra were obtained from 350-1100 nm, with red edge reflectance spectra indicating the presence of iron-oxides, previously demonstrated to be indicators of pedogenesis through laboratory measurements. In order to further test the potential of higher wavelength field measurements, reflectance spectra between 400-2400 nm were analysed on laboratory samples. Absorption features indicative of montmorillonite and illite/muscovite were noted and stepwise regression modelling utilising absolute reflectance, first derivative spectra and continuum removed spectra indicate strong predictive relationships with magnetic susceptibility, particularly against the presence of montmorillonite. The abundance of such clay minerals can be used to infer weathering rates and hence be used as a proxy for pedogensis. Reconstructions for the studied site are presented and demonstrate the power of this technique in environmental reconstruction.