三峡巫山黄土Sr-Nd同位素组成与物源示踪

Sr-Nd Isotopic Composition and Provenance Tracing of Wushan Loess,Three Gorges,Yangtze River

巫山黄土作为中国南方黄土的重要组成部分,弄清该区的物源将为破译这一宝贵沉积记录提供重要的环境信息.对巫山黄土剖面进行了系统取样和Sr-Nd同位素分析,并与黄土高原同期黄土及近源的河流沉积物等进行了比较.结果表明,巫山黄土的87Sr/86Sr值变化范围为0.717411~0.719163,平均值为0.717998,与黄土高原末次冰期黄土的87Sr/86Sr值(变化范围为0.718235~0.719673,平均值为0.718623)几乎一致;巫山黄土εNd(0)值在-10.1^-11.7之间,平均值为-11.4,明显与长江上游现代河漫滩沉积物εNd(0)值(-5.9^-7.2)差别较大,而与黄土高原黄土εNd(0)值(-9.2^-11.3)接近.研究结果表明巫山黄土的粉尘主要为北方输入,与黄土高原黄土同源.据此认为,巫山黄土的形成并不是因为冰期导致三峡地区干旱河滩干涸暴露而引发粉尘近源堆积,这与近年来长江下游下蜀黄土的研究结果有所不同.

As one of the most important elements of the loess in southern China,the provenance of“Wushan Loess”can provide crucial environmental information to deciphering valuable sedimentary record in the area.Based on previous studies,we have collected samples from“Wushan Loess”profile and carried out Sr-Nd isotope analysis,and compared with sediments synchronous to Loess Plateau and fluvial sediments with nearby provenance.The results show that the variation range of 87Sr/86Sr of“Wushan Loess”is 0.717411-0.719163 with an average value of 0.717998,which is almost identical with the 87Sr/86Sr values of Loess Plateau during the last glacial period(variation range is 0.718235 to 0.719673,average is 0.718623).The value ofεNd(0)of“Wushan Loess”loess ranges from-10.1 to-11.7 with an average value of-11.4,which is quite different from the value ofεNd(0)(-5.9 to-7.2)of modern floodplain sediments in the upper reaches of the Yangtze River,is close to that of Loess Plateau(-9.2 to-11.3).Our research shows that the dust of“Wushan Loess”is mainly imported from the north and is homologous to the loess of Loess Plateau.Therefore,we believe that“Wushan Loess”is not formed by stockpiling dust from the drying up tributaries in Three Gorges area due to the glacial period,which is different from the research result of“Xiashu Loess”in the lower reaches of the Yangtze River in recent years.