Abstract
Loess provides a valuable terrestrial record of past environmental conditions, including the dynamics and trajectories of air mass circulation responsible for dust transport. Here we explore variations in the luminescence sensitivity characteristics of sedimentary quartz and feldspar as possible tools for identifying changes in source down a loess-palaeosol sequence (LPS). Luminescence sensitivity is a rapidly measurable index which is the product of interplay between source lithology and the history of the quartz or feldspar clasts. Variations in sensitivity of down profile may therefore reflect changes in sediment provenance as well as other factors such as weathering through pedogenesis. We undertake an empirical investigation of the luminescence sensitivity of quartz and feldspar from different grain-size fractions from the Schwalbenberg LPS in the German Rhine valley. We compare samples from a 30 m core spanning the last full glacial cycle with samples of oxygen isotope stage (OIS) 3–2 age exposed within nearby profile. We find an overall inverse relationship between quartz and feldspar sensitivity, as well as variability in sensitivity between different quartz grain sizes. Statistical analyses yield a significant correlation between IR50 sensitivity from unprocessed sediments and clay content, and feldspar sensitivity and Si/Al ratios down the core. Since Si/Al ratios may indicate changes in provenance, the latter correlation suggests that IR50 measurements on unprocessed samples may be used to provide a reliable, rapid scan of source variability over millennial timescales.
Highlights
Whilst the focus of this study is on the luminescence sensitivity of different minerals and grain-size fractions in the Schwalbenberg loess deposit, we provide the approximate equivalent doses as a means of initially assessing the robustness of the age–depth relationships using the different protocols
While signals from the pIR200 IRSL290 and pIR50 IRSL290 protocol measurements were both stable, sensitivity between aliquots and samples was more variable for the higher initial temperature protocol than for lower initial temperatures
Our statistical analyses demonstrate that the key predictors for IR50 sensitivity are clay percentage and Si/Al ratios, which represent proxies for weathering/pedogenesis and source changes, respectively
Summary
Loess—a homogeneous, predominantly silt-sized aeolian sediment [1,2]—has long been recognised as a valuable terrestrial record of past environmental conditions [3,4,5]. Loess deposits drape some 10% of the Earth’s land surface, predominantly in the dry subhumid to semi-arid temperate mid-latitudes [6], accumulating almost continuously for more than one million years (1 My) in some regions [7,8,9]. Most aeolian dust is thought not to travel far, often deriving from fine-grained material transported by rivers from glaciated regions [11,12,13], distal transport is widely acknowledged, e.g., [14,15]. Loess deposits are implicitly linked with the pathways of major air masses thought to transport the dust, e.g., [16,17]
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