Getting a grip on soil reworking – Single-grain feldspar luminescence as a novel tool to quantify soil reworking rates

Soil reworking, e.g. due to bioturbation, is an important aspect of soil and landscape evolution. Yet, rates of soil mixing are poorly constrained, especially on pedological and geomorphological relevant time scales of decades to millennia. This study presents a novel method to reconstruct soil reworking rates on such timescales by utilising luminescence signals from individual sand-sized feldspar grains as soil reworking tracers. We propose a post-IR IRSL procedure to harvest two luminescence signals from individual feldspar grains. We applied this method to four soil samples from a single soil profile in Spain, and compared our results to those derived through a more conventional approach based on single-grain quartz luminescence analysis. We also propose novel ways of deriving effective soil reworking rates from luminescence data, using not only apparent burial ages of mineral grains but also the proportion of mineral grains that never reached the soil surface. Our results confirm the general suitability of feldspar post-IR IRSL as soil reworking tracer in terms of measurement performance, luminescence signal resetting and eventually the determination of soil reworking rate. We furthermore demonstrate that the feldspar based method is more time and labour efficient than quartz based methods, and we expect it to be more widely applicable. Most importantly, the method provides a reliable measures of the soil reworking intensity, which was not possible with quartz based methods. We conclude that feldspar single-grain luminescence analysis has the potential to become the method of choice for investigating soil reworking rates