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Orbitally Tuned Time Scale Based on Climate Proxy Indicator of Grain Size Distribution in Nihewan Basin

HAN Zhi-yong~ 1,2 , LI Xu-sheng~1 1.Department of Urban and Resources Sciences, Nanjing University, Nanjing 210093, China 2.State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China  
The Donggou Section located in the east of Nihewan basin contains a suite of strata consisted mainly of lacustrine sediments approximate to 100m thick. Both grain size distribution and magnetic susceptibility are measured in successive samples collected from this section. A preliminary time scale can be derived, based on the comparison between records of magnetic susceptibility, from the geomagnetic polarity reversals determined by previous studies. In this study, the grain (20-50μm) content record of Donggou Section can be correlated to the ETP curve. The low value of the former is compared with the high value of the latter. This negative correlation implies that the dust inputs into sediments in the Nihewan basin decreases while the solar radiation on the north hemisphere increases. This scenario is compatible with the known evolution of the aeolian activity in North China. Therefore, the grain (20-50μm) content is a reliable proxy indicator of the paleoclimate change. Orbital tuning method is performed and a time scale of high resolution is obtained for the strata older than 780ka since the sedimentation rate here is relatively high. The 20ka and 41ka periodic components filtered from the obtained grain (20-50μm) content time series are consistent with the theoretic cycles of the precession and the tilt, respectively, indicating that the grain (20-50μm) content record of Donggou Section can be used as the climatic curve for orbital tuning.
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