ABSTRACT
The Luochuan loess section (Shaanxi province, Central China) contains an uninterrupted record of Quaternary palaeomonsoon strength. A high resolution proxy record of palaeomonsoon fluctuations is established by detailed sampling and grainsize analysis using a Laser particle sizer. Principal component analysis indicates that grainsize parameters measuring the amounts of coarse silt relative to fine silt (U- ratio) adequately depict the climate-induced grainsize variation. Besides grainsize, sedimentation rate is also influenced by the strength of the winter monsoons, resulting in a positive correlation between grainsize and sedimentation rate. We use this relation to establish a detailed absolute chronology for the section. Since loesses and soils in the section are compacted to a different amount, a correction for compaction is applied to ensure that the duration of the glacial-interglacial cycles is represented correctly in the time scale. Spectral analysis using this time scale yields consistent results for the orbital cycles. Other frequencies are also found, that may be related to nonlinear reactions of the climate system to orbital forcing. Further improvement of the time scale and spectral analysis results may be achieved by application of a more detailed compaction model.
