我国黄土高原西北边缘风成沉积及其气候环境意义

发布时间：2018-03-17 12:15

本文选题：晚第四纪　切入点：沙漠-黄土边界带　出处：《兰州大学》2017年硕士论文　论文类型：学位论文

【摘要】：我国黄土高原堆积有巨厚的黄土沉积,为不同尺度的古气候对比研究提供了重要的陆相记录。目前为止,有关黄土沉积空间范围的研究相对较少,然而黄土沉积空间范围的变化可能直接影响到黄土物质的堆积过程与代用指标古气候意义解释。沙漠-黄土边界带风成沉积地层多表现为风成砂、砂质黄土与砂质古土壤的互层沉积,有效地记录了区域风沙活动和粉尘堆积历史,为研究我国黄土沉积范围变化与北方沙漠演化提供了重要的地层资料。选取黄土高原西北边缘的风成沉积为研究对象。风成剖面包括位于腾格里沙漠南部香山北坡香山剖面(XS-A和XS-B)以及共和盆地东南部卡加剖面(KJ)。通过分析风成沉积岩性变化以及粒度组成、元素含量、磁化率和烧失量等代用指标,结合光释光(OSL)测年结果,探讨了中更新世以来我国黄土高原沉积范围的变化及其潜在的区域气候环境意义。主要结论如下:1、沙漠-黄土边界带3个风成剖面中的黄土沉积与黄土高原典型黄土沉积特征一致,而风成砂为含有一定粉砂组分的亚砂土沉积。香山剖面显示该区典型黄土沉积至少出现在240 ka之前,并持续到42.5 ka,甚至25.4 ka前后;共和盆地东南部典型黄土沉积至少在在中更新世已经出现,并阶段性地持续到末次盛冰期之前。2、沙漠-黄土边界带气候由冷干转向暖湿时,研究区发育草原或者干草原植被,风成沉积类型由风成砂逐渐向典型黄土沉积过渡,沉积连续,黄土沉积的范围向北、向西扩张。气候由暖湿转向冷干时,地表风力侵蚀加剧。沉积地层出现沉积间断,形成假整合接触面,表现为由黄土沉积向风成砂沉积的快速过渡,黄土沉积的范围向南收缩。3、至少中更新世以来,黄土高原北部黄土沉积区域远大于现在的范围,可能到达腾格里沙漠南部以及鄂尔多斯盆地大部分地区。黄土高原西部黄土堆积的范围至少到达共和盆地东南部的贵南地区,甚至更西的位置。受风蚀、水蚀作用的影响,黄土地层曾被风力或流水侵蚀,上覆的风成砂沉积指示了典型黄土在研究区存在沉积间断,代表黄土沉积范围收缩。4、尽管中更新世以来腾格里沙漠、木格滩沙地可能存在一定规模的扩张,然而,其扩张范围远没有达到现在的位置。研究区末次盛冰期沙漠/沙地的扩张,奠定了现代沙漠/沙地的基本格局。5、中更新世以来黄土沉积范围变化伴随的风蚀过程,意味着下风向黄土沉积可能有部分粉尘物质源自黄土本身。这种过程或许解释了黄土记录中某些时段粒度组成变化较小时,粉尘通量增加的现象。
[Abstract]:There are very thick loess deposits on the Loess Plateau in China, which provide an important continental record for the comparative study of paleoclimate on different scales. So far, there have been relatively few researches on the spatial range of loess deposits. However, the variation of the spatial range of loess deposition may directly affect the accumulation process of loess material and the interpretation of paleoclimate meaning of the proxy index. The aeolian sedimentary strata in the desert loess boundary zone are mostly represented as aeolian sand. The interbedded deposits of sandy loess and sandy paleosol have effectively recorded the regional aeolian activity and dust accumulation history. It provides important stratigraphic data for studying the variation of loess sedimentary range in China and the evolution of the northern desert. The aeolian deposits on the northwest margin of the Loess Plateau are selected as the objects of study. The aeolian profiles include those located in the northern part of Xiangshan Mountain in the south of Tenggri Desert. The XS-A and XS-B of the Poxiangshan section and the KJJ of the Kaga section of the southeastern Gonghe basin are analyzed by analyzing the lithologic changes and granularity composition of the aeolian sediments. Element content, magnetic susceptibility and burning loss, etc., combined with the results of OSL dating, The variation of sedimentary range of loess plateau in China since the Middle Pleistocene and its potential regional climatic and environmental significance are discussed. The main conclusions are as follows: 1, loess deposits in three eolian sections of desert loess boundary zone and typical loess plateau. The sedimentary characteristics of loess are consistent. The Xiangshan section shows that the typical loess deposits in the area appeared at least before 240 ka and lasted until 42.5 ka or even 25.4 ka. The typical loess deposits in the southeast of Gonghe Basin appeared at least in the Middle Pleistocene and lasted periodically until the last glacial peak. When the climate of the desert loess boundary zone changed from cold to dry to warm and wet, grassland or steppe vegetation was developed in the study area. The type of aeolian deposits is gradually transitioning from aeolian sand to typical loess deposits, with continuous deposition, the range of loess deposits extending northward and westward. When the climate changes from warm and wet to cold and dry, the surface wind erosion intensifies, and sedimentary strata occur sedimentary discontinuity. The formation of pseudo-integrated contact surface is characterized by a rapid transition from loess deposition to aeolian sand deposition, and the extent of loess deposition shrinks to the south. At least since the Middle Pleistocene, the loess sedimentary area in the northern part of the Loess Plateau is much larger than the present one. Possibly reaching the southern part of the Tenggri Desert and most of the Ordos Basin. The loess accumulation in the western part of the Loess Plateau is at least as far as the southern part of the Gonghe Basin, or even further west. Affected by wind and water erosion, Loess layers have been eroded by wind or income, and the overlying aeolian sand deposits indicate that there are sedimentary discontinuities in typical loess in the study area, representing the shrinking of loess sedimentary range, although since the Middle Pleistocene, the Tenggri Desert, Mug beach sandy land may have a certain scale of expansion, however, its expansion scope is far from its present position. The last glacial period desert / sandy land expansion in the study area, The basic pattern of modern desert / sandy land. 5. The process of wind erosion associated with the variation of loess sedimentary range since the Middle Pleistocene. This process may explain the increase of dust flux due to the small change of particle size composition in some periods in loess records.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P512.2;P532

【参考文献】