Evidence for Paleoclimatic Significance of Grain Size Composite of Loess Deposit in Central Chinese Loess Plateau

摘要

The typical loess profile in central Chinese loess plateau was sequentially sampled at 5-10 cm interval from the bottom of the penultimate interglacial period deposit (S2) to the top of Holocene deposit, total 314 samples were measured for grain size, the results show that grain size distribution ranges from 0 to 200 urn. Therefore. we divided the distribution into 42 grades by equivalent phi value (the step is 0.25), variations of content of every grade was plotted against a new calculated time scale, and 42 curves was obtained. Every curve was attentively compared with the SPECMAP oxygen isotope time series curve which indicate the ice volume changes. We found that >30 ^m coarse-grained fraction of the loess-palaeosol is one sensitive proxy index of East Asia winter monsoon strength, content of grains with diameter of 2-8 urn is inversely proportional to the winter monsoon strength, and it is not as good as >30 um coarse-grained fraction to indicate winter monsoon strength changes.