构造与气候对中国中部渭河盆地沉积动力学的影响

发布时间：2018-09-01 18:45

【摘要】：新生代地球岩石圈发生强烈构造变动,导致全球海陆格局、地貌形态、大气环流和气候系统发生了剧烈变化。亚洲最为显著的构造事件是印度板块向欧亚板块的俯冲,导致了青藏高原的隆升。青藏高原隆升过程中,印度板块挤压的应力不断向NE方向传递,导致扬子地块向东南推出,在秦岭山前形成大型左旋走滑断层。同时太平洋板块自东而西向亚洲板块下俯冲,华北板块受到NW-SE向拉张作用,也加剧了渭河盆地的拉张断陷。断陷盆地内堆积了较为连续的湖相-河流相-粉尘堆积,这些堆积记录了青藏高原隆升远程的构造效应、东亚季风系统演化过程、黄河及其支流的形成及演化过程。本论文通过分析汾渭盆地东北部卤阳湖钻孔LYH-1上部221m (约1Ma)沉积地层,结合临近洛河下游的地貌及沉积学分析,重建1Ma以来卤阳湖的演化过程及其对区域构造、水系演变及气候变化的响应。论文第一章结合区域地质、水文与气候背景,介绍了研究选题、思路及技术路线。第二章详细介绍了研究方法。第三章首先建立了年代框架,结合岩性及沉积特征、古生物学及其它沉积学指标如粒度分布等手段描述了卤阳湖地区的沉积环境演变过程。第四章通过使用地球化学和矿物学手段进一步分析了卤阳湖地区沉积环境演变特征。第五章结合洛河下游地貌及沉积学分析,研究洛河演化对卤阳湖地区沉积历史的贡献和影响。第六章中通过对比钻孔沉积物的沉积特征与黄土高原黄土-古土壤序列,进一步精确第三章中建立的年龄框架。最终,利用频谱分析提取沉积物中的频谱数据并探讨其可能指示的气候信息。研究主要结论如下:(1)卤阳湖沉积岩相变化较大,主要沉积环境为冲积扇、浅水湖泊、干盐湖以及风尘堆积,部分沉积相上部曾经历微弱的成壤过程。重建的沉积环境及构造特征表明,卤阳湖位于断陷洼地内河流冲积扇末端,其北部的河流源自疏松易蚀的黄土高原,其搬运携带的大量碎屑物不仅堆积了出山口的冲积扇,也为卤阳湖的沉积发育提供了物源。(2)冲积扇的生长发生于气候较冷时期,该时期黄土高原缺乏足够的植被保护。相反,冲积扇的后退则发生于气候温暖时期,该时期土壤的发育使得流域侵蚀减弱。当流域降雨和蒸发加强时,浅水湖泊及干盐湖发育。(3)岩心沉积物磁化率、碳酸盐以及粒度组分的频谱分析显示,沉积序列中存在着米兰科维奇旋回。这表明,气候对渭河盆地北部沉积具有驱动作用。然而,沉积物中的旋回并不连续并且依赖于钻孔点位置的构造沉降速率。当钻孔位置没有足够空间容纳沉积物时,气候信息将难以保留。除了米兰科维奇旋回外,同时存在着由冲积扇自旋回产生的更高频率的旋回。通过对沉积物地球化学分析得到区域长尺度的气候变化信息:0.7-0.6Ma前,盆地中粘土含量开始增高。这与夏季风开始增加的时间相吻合,夏季风的加强也有利于黄土高原土壤发育及自生粘土的形成。(4)根据岩相分布特征,将研究部分钻孔分为3段:1-0.69Ma; 0.69-0.33 Ma;0.33-0 Ma。首尾两个阶段湖面扩大,而中间阶段湖面萎缩。末期湖面扩大可能是盆地逐渐减弱的沉降速率导致。对洛河流域的地貌及沉积学分析也证实了这一观点,现今洛河沿钻孔附近河谷流动,但早期洛河却通过自身冲积扇向卤阳湖区提供沉积物。在200-240 ka左右,断层活动加强,洛河下切改道并停止对钻孔位置沉积物的物质输送,此后卤阳湖沉积物主要源自其北部的河流。由于断层引发的褶皱作用,卤阳湖区相对沉降速率增加,导致洪水沉积增多,浅水湖面扩大,同时伴随水生生物多样性的增加。(5)本次研究揭示了构造活动、水系演变及气候变化对渭河盆地北部沉积作用的复杂影响,研究并未发现1Ma来该地区有大湖存在的证据,表明三门古湖仅存在于1Ma前。
[Abstract]:Strong tectonic changes in the Cenozoic lithosphere led to drastic changes in the global land-sea pattern, geomorphology, atmospheric circulation and climate system. The most notable tectonic event in Asia was the subduction of the Indian plate to the Eurasian plate, which led to the uplift of the Qinghai-Tibet Plateau. The NE-trending faulting resulted in the southeastward extension of the Yangtze block and the formation of large-scale sinistral strike-slip faults in the piedmont of the Qinling Mountains. At the same time, the Pacific plate subducted from the east to the West under the Asian plate, and the North China plate was extensionally affected by NW-SE trending, which aggravated the extensional fault depression of the Weihe basin. Dust accumulation, which records the long-range tectonic effect of the uplift of the Qinghai-Tibet Plateau, the evolution of the East Asian monsoon system, the formation and evolution of the Yellow River and its tributaries. The evolution process of the lake and its response to regional tectonics, river system evolution and climate change since the beginning of the year are introduced in the first chapter of this paper. Combining regional geology, hydrology and climate background, the research topics, ideas and technical routes are introduced. The second chapter introduces the research methods in detail. Physical and other sedimentological indices such as grain size distribution are used to describe the evolution of sedimentary environment in the area. Chapter 4 further analyzes the evolution characteristics of sedimentary environment in the area by using geochemical and mineralogical methods. In Chapter 6, by comparing the sedimentary characteristics of borehole sediments with the loess-paleosol sequence of the Loess Plateau, the age framework established in Chapter 3 is further refined. The following: (1) The sedimentary facies of the lake changed greatly. The main sedimentary environments were alluvial fans, shallow lakes, dry salt lakes and aeolian dust deposits. The upper part of some sedimentary facies had undergone a weak process of soil formation. In the Loess Plateau, a large amount of debris not only accumulated in the alluvial fans at the entrance of the mountain, but also provided a source of material for the sedimentary development of the lake. As rainfall and evaporation intensify, shallow lakes and dry salt lakes develop. (3) Spectral analysis of magnetic susceptibility, carbonate and grain size components of core sediments shows that Milankovitch cycles exist in sedimentary sequences. This indicates that climate drives sedimentation in the northern Weihe basin. The cycles in the sediments are discontinuous and depend on the rate of tectonic subsidence at the point of the borehole. Climate information is difficult to retain when the borehole location does not have enough space to accommodate sediments. In addition to the Milankovitch cycle, there are also cycles of higher frequency generated by the alluvial fan spin. Sediment geochemical analyses have yielded results. Regional long-scale climate change information: before 0.7-0.6 Ma, the clay content in the basin began to increase. This coincides with the time when the summer monsoon began to increase. The strengthening of the summer monsoon is also conducive to the development of soil and the formation of authigenic clay in the Loess Plateau. (4) According to the lithofacies distribution characteristics, some boreholes were divided into three sections: 1-0.69 Ma; 0.69-0.33 Ma; 0.33-0. Ma. The lake surface enlarged in the first and last two stages and shrank in the middle stage. The lake surface enlarged in the last stage may be caused by the subsidence rate of the basin gradually weakening. Geomorphological and sedimentological analysis of the Luohe River Valley confirms this view. Today the Luohe River flows along the valley near the borehole, but in the early stage the Luohe River provides subsidence to the Hanyang Lake area through its own alluvial fan. The deposits were mainly from the rivers in the north of the lake. Due to the folding caused by faults, the relative subsidence rate of the lake area increased, resulting in the increase of flood deposits and the enlargement of the shallow lake surface accompanied by water. (5) This study reveals the complex effects of tectonic activities, river system evolution and climate change on sedimentation in the northern Weihe Basin. No evidence of the existence of a large lake in this area has been found in the past 1 Ma, indicating that Sanmen ancient lake existed only 1 Ma ago.
【学位授予单位】：南京师范大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P512.2

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