新疆孔雀河北岸72～51 ka BP湖相沉积物元素地球化学特征分析

Element geochemistry characteristic from the 72-51 ka BP lake sediments in northern margin of Kongqi River,Xinjiang

通过对新疆孔雀河北岸LX02剖面湖相沉积物开展光释光和地球化学测试分析,重建了研究区72~51 ka BP的气候变化过程。72.4~66.8 ka BP期间,Al、K、Ti、Fe、Ca、Mg元素含量和烧失量低,Fe/Mn、Rb/Sr、(Fe+A1+Mn)/(K^+Ca+Mg)、CIA、C值低,而Sa、Saf值高,指示该时段为冷干气候环境;66.8~56.1 ka BP期间,Al、K、Ti、Fe、Ca、Mg元素含量和烧失量均增加,Fe/Mn、Rb/Sr、(Fe+A1+Mn)/(K^+Ca+Mg)、CIA、C值明显增加,而Sa、Saf值明显降低,指示该时段为暖湿气候环境;56.1~51.0 ka BP期间,Al、K、Ti、Fe、Mg元素含量和烧失量均减少,Fe/Mn、Rb/Sr、(Fe+A1+Mn)/(K^+Ca+Mg)、CIA、C值略有降低,而Sa、Saf值明显增加,指示该时段为较冷干气候环境。这与粘土矿物特征所反映的古气候特征及其变化一致,亦与柴达木盆地东部介形类丰度特征研究、柴达木盆地东部古湖泊高湖面光释光年代学研究、北京平原区有机碳同位素研究等结果吻合较好。研究表明塔里木盆地东部晚更新世气候仍以暖湿-冷干气候变化模式为主,但这一气候变化规律的内部驱动机制还有待进一步深入研究。

In this paper, a 5.4-m-thick section of lake sediments （89°55＇, 40°40＇） was discovered in the northern margin of the Kongqi River at Tarim Town, Yuli County, southern Xinjiang, Northwestern China. From up to bottom, six Optically Stimulated Luminescence （OSL） ages were achieved, i.e., 53.1±4.4 ka BP at 0.18 m, 56.1±3.2 ka BP at 1.19 m, 57.9±3.3 ka BP at 2.21 m, 60.5±4.0 ka BP at 3.10 m, 67.0±6.0 ka BP at 3.71 m and 71.0±3.6 ka BP at 4.69 m, indicating that this section spanned Late-Pleistocene interval of 72-51 ka BP, and establishing a reliable chronological framework for the LX02 section. In the meanwhile, 57 Geochemistry samples collected in the section were tested. Based on the analysis of geochemical element contents and geochemical elements ratio, three palaeoclimatic stages have been identified：（1） during 72.4-67.8 ka BP, the contents of Al, K, Ti, Fe, Ca, Mg and loss on ignition were low, the Fe/Mn, Rb/Sr, （Fe＋A1＋Mn）/（K＋Ca＋Mg）, CIA and C presented low value, however the value of Sa and Saf were high, indicating that the climate was dry-cold during 72.4-67.8 ka BP. （2） During 67.8-56.1 ka BP, the contents of Al, K, Ti, Fe, Ca, Mg and loss on ignition increased, the value of Fe/Mn, Rb/Sr, （Fe＋A1＋Mn）/（K＋Ca＋Mg）, CIA and C also significantly increased, Whereas the value of Sa and Saf decreased obviously, indicating that the climate was humid-warm during 67.8-56.1 ka BP.（3） During 56.1-51.0 ka BP, the contents of Al, K, Ti, Fe, Ca, Mg and loss on ignition decreased, the value of Fe/Mn, Rb/Sr, （Fe＋A1＋ Mn）/（K＋Ca＋Mg）, CIA and C decreased slightly, however the value of Sa and Saf increased slightly, indicating that the climate was dry-cold during 56.1-51.0 ka BP. This mode of climate change in the study area was well correlated with the changes of weathering intensity revealed by the character of clay mineral, also the Ostracoda abundance in upper well Dacan1 located at the sourtheast Qaidam Basin, Luminescence Chronology of High Lake levels of Paleolakes in the Late Quaternary eastern Qaidam Basin, and Organic Carbon Isotopic characteristics of Beijing Plain. These suggest that climate in the study area was characterized generally by dry-cold and humid-warm patterns during the Late-Pleistocene period. Nevertheless, the internal forcing mechanism for this mode of climate changes in the study area remains unclear up to now and deserves further investigation.