A Quaternary climate record based on grain size analysis from the Luochuan loess section on the Central Loess Plateau, China

Abstract

Important climatic information is stored in the Luochuan sediment record on the Central Loess Plateau in China. Large quantities of dust have registered the activity of the summer and winter monsoon. In this paper, the process that caused the loess deposition is explained and the influence of (palaeo)climate on this sedimentation process is discussed. The concept of establishing a time scale is based on the fact that grain size and sedimentation rate (SR) appear to correlate very well with the strength of the winter monsoon in northern China. Grain-size analysis does not only offer the opportunity to construct an independent numerical Quaternary time scale, but also to reconstruct temporal palaeoclimatic changes. In a reference curve, the correlation between grain size and SR is determined, afterwards the SR of all layers could be calculated based on their grain size. In this work, the climatic results of the Luochuan loess section are determined by making two important adjustment steps. Firstly, a general grain-size trend has been removed since the layers tend to coarsen upwards in the section. Secondly, the real quantity of sediment deposited is calculated by multiplying the SR with the bulk density of the layer, which results in dust flux values. The bulk density of the loess layers appears to fluctuate both in depth as well as with palaeoclimate during dust deposition. Finally, climatic results derived from this improved time scale are discussed.