巴丹吉林沙漠东南缘查格勒布鲁剖面CGS1层段粒度特征及其指示的全新世千年尺度气候变化

 位于巴丹吉林沙漠东南缘的查格勒布鲁剖面CGS1层段记录了全新世以来显示风力强弱的沙丘砂与黄土堆积旋回。以Md（Φ）、Mz（Φ）的5 Φ（31.5 μm）为界,可以划分出10个“C1—C10”明显的和1个“C11”较弱的（<5 Φ）旋回变化。其中,有7个属于沙丘砂与之上覆黄土或古土壤构成的旋回。这些旋回在Md（Φ）、Mz（Φ）上显示出多谷峰波动的形式。不仅如此,粒度的σ、SC/D值和>63 μm含量亦随之响应。研究认为,CGS1层段粗粒和细粒层位Md（Φ）等参数和>63 μm含量的变化分别代表了东亚冬夏季风的作用过程;冬季风时期的C1与北大西洋IRD事件的冷期B0和B1,C2、C3、C4依次与B2、B3、B4,C7、C9、C10依次与B5、B6、B7在时间-气候性质上具有很好的对应;北大西洋B8冷期在CGS1中没有明显表现,但仍然能够在Md（Φ）、Mz（Φ）曲线上看到这是一个<5 Φ的低值时期,而>63 μm的含量相应增高;C5、C6和C8寒冷时段虽未见于北大西洋,但在中国一些地点却有发现。这些由若干粒度指标反映出来的寒冷事件表明,在全新世东亚夏季风活动盛行的总的形势下还存在频繁的千年尺度的冬季风波动。而尤为重要的是这些寒冷事件存在的与北大西洋寒冷事件的遥相关的关系表明,除C5、C6和C8以外的CGS1粒度记录的寒冷事件都隐含了北大西洋的强烈信号。从这个意义上来说,笔者讨论的内容可为全新世北半球的D/O震荡及其形成机制提供一个比较理想的东亚季风变化与中国沙漠区域环境响应的地质证据。

Holocene Climate Variations on Millennium-scale from Grain-size Record of CGS1 Segment in the Badain Jaran Desert, China

The CGS1 segment of the Chagelebulu section in the southeastern Badain Jaran Desert recorded sedimentary cycles during the Holocene,which consists of dune sands alternating with overlying paleosol or loess.Divided by the 5 Φ(equal to 31.5 m) of Md and Mz,ten obvious cycles(C1 to C10) and one weak cycle(C11) are found.Among them,seven sedimentary cycles of dune sands covered by paleosol or loess show considerable fluctuations over the values of Md and Mz.Besides,the grain-size values of σ,SC/D and >63 μm component content also respond to these cycles.The variations of Md and >63 μm component content in the CGS1 segment reflect the alternation between East Asian summer and winter monsoon.The cold period C1 corresponds to B0 and B1 in the North Atlantic;C2,C3 and C4 correspond to B2,B3 and B4;and C7,C9 and C10 correspond to B5,B6 and B7,respectively.Although B8 is not obvious in the CGS1 segment,<5 Φ low values of Md and Mz appear in this period,whereas the content of >63 μm component correspondingly increase.Particularly,the cold events of C5,C6 and C8 are not discovered in the North Atlantic,but they appear in some places of China.This study suggests that the Holocene frequent climate fluctuations on millennium-scale were subject to the East Asian winter monsoon changes within the overall prevalence of East Asian summer monsoon.Except for C5,C6 and C8,the correlations between the cold event records in the CGS1 segment and those in the North Atlantic reveal that the East Asian monsoon variations in China’s deserts may account for the corresponding mechanism for Dansgaard-Oeschger oscillations in the North Hemisphere during the Holocene,which serve as the geologic evidence for the desert regional response to the global climate variations in the Holocene.