Environmental Change Inferred from Distribution of Rb and Sr in Different Grain Size Fractions from Lacustrine Sediments in Huangqihai Lake, Inner Mongolia
内蒙古黄旗海不同粒级湖泊沉积物Rb、Sr组成与环境变化

The Huangqihai Lake, a small enclosed lake in Inner Mongolia of China, lies at the northern boundary of Eastern Asian Summer Monsoon and in the central part of Asian Winter Monsoon. Thus, its lacustrine sediment sensitively recorded the climate change of the above two monsoon systems. Based on the geochemical elements Rb and Sr of three different grain size fractions sediment from profile H3 on the northern lacustrine bottomland 13 m above the Huangqihai Lake surface in 1986, this paper investigates the record of palaeolake stand state, sedimentary environment evolution, and winter monsoon change. First, these samples are divided into three different grain size fractions, i.e., total sediments, 77-20m and < 20 m. Second, the chemical elements, Rb and Sr of the grain size separation, are tested and analyzed systematically in this paper. Then these elements compositions of these samples are measured using VP-320 mode fluorescence spectrum instrument, respectively. The magnetic susceptibilities of these samples are measured using Kappabridge KLY-3 mode instrument made in Czech AGICO Company. The results showed the elements of Rb and Sr and the ratios of Rb/Sr vary regularly with the grain size. But the ratios of Rb/Sr in the sediments with < 20 m correlate positively with the magnetic susceptibility of these samples. Therefore, the ratios of Rb/Sr in the fraction < 20m from the lake sediments reflect the weathering intensity in the deposition sites. It is a good indicator of the summer monsoon-induced weathering and pedogentic fluctuations and can be used to reconstruct the conditions of the paleoclimate and paleoenvironment.