%0 Journal Article
%T Rb/Sr VARIATIONS AND ITS CLIMATIC STRATIGRAPHICAL SIGNIFICANCE OF A LOESS-PALEOSOL PROFILE FROMLUOCHUAN,SHAANXI PROVINCE<br>陕西洛川黄土剖面的Rb/Sr值及其气候地层学意义
%A Chen Jun
%A Wang Yongjin
%A Ji Junfeng
%A Chen Yang
%A Lu Huayu
%A <br>陈骏
%A 汪永进
%A 季峻峰
%A 陈
%A 鹿化煜
%J 第四纪研究
%D 1999
%I 
%X The loess-paleosol sequence in centyal China conshtutes an excellent long-termproxy record of East Asian monsoon climate variations during the Quaremary. Manyinvestigations have indicated that magnetic susceptibility and grain size variations ofthe sequence are good measures of summer and winter monsoon intensity respectively.However, these monsoon records need to be verified by other associated indices thatare independent and vary synchronology. Some trace element ratios have been provedto be of potential impoftance in reconstructing history of the regional. climate. Herewe present the vertical distribution of the Rb/Sr ratio in the Luochuan loess-paleosolsequence and discuss its climatic significance.The concentrations of Rb and Sr, and magnetic susceptibility have beenmeasured in a 140m thick loess-paleosol sequence from the Luochuan profile. Resultsshow that the Rb/ Sr ratio vary from 0.39 in loess to 1.20 in paleosols.The averagevalue of Rb/ Sr ratios is lower than that in paleosols with 0.55 and 0.73 respectively.Similar to magnetic susceptibility signal, the Rb/Sr ratio can be used to distinguishloess and paleosol layers.The difference of Rb/Sr between loess and paleosols is mainly due topostdepositional processes of loess deposits, which may cause the marked fractionationof Rb and Sr in the profile. The significant process was weathering and pedogenesis.Studies show that Rb is stable element and appears to retain in the profile during thestage of weathering and pedogenesis, while Sr is mobile and its concentrationdecreases with the enhancement of weathering and pedogenesis intensities. Therefore,variation of the Rb/Sr ratio essentially reflects strength of leaching of loess depositsduring weathering and pedogenesis. It should be pointed out that extent of leachingduring pedogenesis is related to amount of precipitation which represents the intensityof summer monsoon. During the domination of summer monsoon, the precipitationon the Loess Plateau is heavier, leaching and eluviation are stronger and thedepletion of Sr is greater, resulting in higher Rb/Sr ratios in paleosols. This meansthe Rb/Sr ratio can be served as an indicator for the intensity of summer monsoon inthe Loess Plateau.It can be seen that the distribution curves of Rb/Sr ratios and magneticsusceptibility along the whole profile show much similar pattern in both curve shapeand phase transition, further proving the reliability of the Rb/Sr ratio as an indicatorfor summer monsoon. On the other hand, perhaps owing to various degrees inresponding to climate changes, the two parameters have striking differences inrelative amplitude, as shown in the following:First The Rb/Sr signal confirms that 0.80Ma B. P. was an impotent boundary(within the layer S8) at which monsoon climate have changed sharply, i.e. from high-frequency, low- amplitude fluctuations to low-frequency, high-amplitude variations.This corresponds well with the variation of global ice volume recorded in deep-seaoxyge
%K loess
%K paleoclimate
%K summer monsoon
%K Rb/Sr ratio<br>黄土
%K 古气候
%K 夏季风
%K Rb／Sr值
%K 地层
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=EA07051745CDC8D89D5F01A3A4CFE6A9&aid=423928E8DF1F3372890DA53499760B48&yid=B914830F5B1D1078&vid=2A8D03AD8076A2E3&iid=E158A972A605785F&sid=406BF8ED3BCE1927&eid=35E8A259891FB32F&journal_id=1001-7410&journal_name=第四纪研究&referenced_num=36&reference_num=16