库姆塔格沙漠第四纪地层沉积特征记录的沙漠演化过程

How to set up the high-resolution spatiotemporal sequence of desert evolution is an imperative issue in Quaternary researches in China. Kumtagh Desert is located at the fringe of northern Qinghai-Tibetan plateau, and in the east of Taklamakan Desert. It is the only one desert of China that is unknown for us today, and few studies about it, especially about its evolutionary study, have been carried out until today. The desert provide an ideal place for studying the dry environment changes and desert evolution of norhwestern China due to lots of Quaternary natural stratum within it. In this study we will make a field observation and characterization on the typical Quaternary stratum sections with palaeo-aeolian sand, and also sample these sections systematically. The high-resolution information concerning the stratum depositional environment will be extracted through the chronological analysis such as 14C, ESR, OSL and paleomagnetic dating, and the analysis of conventional paleoenvironment substitutive indexes such as particle size, magnetic susceptibility, indicator chemical elements and micro-morphology of quartz sand. We attempts to set up the depostional timing sequence of Quaternary stratum and to re-construct the ancient geological environment of this region. The evolutionary histroy of the desert will be disscussed based on the characteristics of spatiotemporal distribution and deposition of palaeo-aeolian sand in the stratum, subsequently, providing some valuable information for studying the formation and changes of the arid environent in northwestern China as well as lifting process of Qinghai-Tibetan Plateau. The results of this study will provide some more geologically historical references for investigating aeolian sand landform development and combating desertificaiton, and also enrich the Quaternary desert researches of China.

如何建立高分辨率的沙漠环境演变时空序列是我国沙漠第四纪研究中亟待解决的关键问题。库姆塔格沙漠位于青藏高原北缘、塔克拉玛干沙漠东部，是目前我国研究最晚、认识最少的一个沙漠，其形成演化方面的研究尤其少。该沙漠广布第四纪天然露头地层，是研究干旱区气候环境演变和沙漠形成演化的理想场地。本项目拟对含古风成砂的第四纪典型地层剖面进行野外观测描述和系统采样，经年代学（古地磁、14C、ESR、OSL）和常规古环境代用指标分析（粒度、磁化率、特征化学元素、石英砂表面微形态），高分辨率提取地层沉积环境信息记录，研究建立沙漠第四纪地层沉积时间序列，重建古地理环境；并依据古风成砂在地层中的时空分布及沉积结构构造特征，探讨沙漠的演化过程，并为我国西北干旱区环境形成演变及青藏高原隆升过程提供证据。本研究是对我国沙漠第四纪研究的进一步补充和完善，同时为风沙地貌发育研究与沙漠化防治提供地质历史参考。

通过对库姆塔格沙漠地区第四纪露头地层剖面调查与分析，选择库姆塔格沙漠腹地不同沉积相的典型剖面如梭梭沟剖面、小泉沟剖面、干湖盆剖面和砾石体剖面以及沙漠东南缘的BL砂黄土剖面进行沉积相观测和描述，特别是对典型剖面梭梭沟ZH剖面和BL剖面进行翔实的沉积相野外观察、描述、量测和系统采样，并对地层样品进行室内相分析包括地层年代学分析与沉积物粒度、矿物组成、特征化学元素、磁化率等环境代用指标进行测试分析，高分辨率提取了剖面沉积的环境信息记录，重建了研究区古地理环境和古气候过程，并依据古风成砂在地层剖面中的时空分布及沉积结构特征，探讨了库姆塔格沙漠的古气候与演化过程。.BL剖面是考察发现的位于库姆塔格沙漠东南约25 km阿尔金山北部山麓地带的一处极具研究价值的典型风成砂黄土剖面，厚度350cm，经物源分析， BL剖面的沉积物来源于库姆塔格沙漠。经剖面沉积物粒度特征与环境分析发现，粒径＞110 μm的粗颗粒组分与＞60 μm的颗粒组分可作为极端干旱区冬季风气候的良好替代性指标，对干冷气候事件响应较为敏感，在BL剖面中的变化很好地记录了8次变冷或变干的气候突变事件，对应的地层年代分别为8.18ka、7.5 ka、6.6 ka、5.7ka、3.8～4.23ka、2.86～2.49ka 、1.12～1.37ka和0.37～0.50ka，对公认的全球性的全新世8.2 ka、5.5 ka、4.2 ka、2.8 ka、1.4 ka和0.4 ka的6次冷事件都有不同程度的记录。说明BL砂黄土剖面很好地记录了全新世早期8.29±0.70ka以来的古气候过程，可划分为不同的三个阶段：全新世早期冷暖变化剧烈期（8.3～5.5ka）、中期温暖平稳期（5.5～2.8ka）和晚期温暖变动期（2.8ka以来），总的变化趋势是风力变缓，气候逐渐变暖。.库姆塔格沙漠地表风成砂与下伏地层风成砂和冲洪积物的粒度特征和重矿物组成具有极强的一致性，说明库姆塔格沙漠属就地起沙。并依据沙漠腹地梭梭沟露头剖面沉积物粒度和特征化学元素记录的环境信息，将库姆塔格沙漠一定历史时期的古气候过程划分为四个发展阶段。