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粒度和磁化率是两个研究黄土古气候最常用的古环境变化指示参数,它们随着黄上占土壤地层变化而出现峰和谷的对应已经被证明是反映了天文轨道要素的周期变化。文章试图忽略这些受控于轨道要素的气候周期变化,而主要侧重考察黄土地层这两个参数的平均值(或背景值)所反映的长期变化趋势。对兰州九州台黄土进行了系统采样和测量,发现兰州九州台黄土剖面粒度和磁化率曲线显示出两个明显的趋势,粒度从剖面底部向上有明显逐渐变粗趋势,指示着冬季风增强,与此同时,磁化率自下而上却逐渐增大,指示着夏季风增强的趋势。与黄土高原其他黄土剖面磁化率和粒度曲线对比发现,这是两个普遍存在的趋势。地理位置靠近青藏高原的剖面,这两个增大的趋势更明显。冬、夏季风同时逐渐增强是海陆热力差异增大所引起,反映了青藏高原第四纪时期的逐渐不断的隆升过程。因此,根据粒度和磁化率曲线变化趋势线的变化特点可以帮助分析和反推第四纪以来青藏高原隆升的过程。兰州九州台以及黄土高原各剖面粒度和磁化率曲线的线性变化趋势则可能指示着第四纪以来青藏高原是逐渐均匀缓慢的变化过程。我们对22Ma以来风积地层记录的变化趋势也做了分析。前人过去普遍认识的第四纪以来跳跃式或间歇式剧烈隆升在我们的数据中没有得到反映。黄土高原西部西宁、兰州、靖远等剖面磁化率显著的增长趋势可能与青藏高原隆升到一定高度后高原季风加强所致。
Particle size and magnetic susceptibility are the two most commonly used indicators of paleoenvironmental changes in paleoclimate. The correspondence of the peaks and valleys with the change of yellow soil layer has been shown to reflect the periodic variation of the orbital elements. The paper tries to ignore these cyclical changes controlled by orbital elements, and mainly focuses on the long-term trends reflected by the average (or background) of these two parameters of the loess formation. The systematic sampling and measurement of loess in Kyushu of Lanzhou showed that the particle size and magnetic susceptibility curves of loess section in Kyushu of Lanzhou showed two obvious trends. The grain size gradually increased from the bottom to the top of the profile, which indicated that the winter monsoon enhanced and At the same time, the magnetic susceptibility increases gradually from bottom to top, indicating a trend of intensification of the summer monsoon. Comparing with the magnetic susceptibility and particle size curves of other loess profiles on the Loess Plateau, it is found that there are two ubiquitous trends. Geographic location close to the profile of the Qinghai-Tibet Plateau, the trend of these two increases more pronounced. The gradual increase of winter and summer monsoons is caused by the increase of the difference of sea-land heat, reflecting the gradual and continuous uplift of the Qinghai-Tibet Plateau during the Quaternary period. Therefore, according to the changing trend of the changing trend line of the grain size and susceptibility curve, it can help to analyze and reverse the process of the Qinghai-Tibet Plateau uplift since Quaternary. The trend of linear variation of grain size and magnetic susceptibility curves in the sections of Kyushu of Lanzhou and the Loess Plateau may indicate that the Qinghai-Tibet Plateau is a gradually uniform and slow change process since Quaternary. We have also analyzed the trend of the records of aeolian strata since 22 Ma. The sudden or intermittent ups and downs since the Quaternary period, which were generally recognized by our predecessors in the past, have not been reflected in our data. The significant increase trend of magnetic susceptibility in the Xining, Lanzhou and Jingyuan sections of the western Loess Plateau may be caused by the intensification of the plateau monsoon after the Qinghai-Tibet Plateau uplift to a certain height.