Knowledge Resource Center for Ecological Environment in Arid Area
| 青海湖近岸滩坝沉积特征及其水动力机制 | |
| 其他题名 | Sedimentary characteristics and hydrodynamic mechanism of coastal sand body of Qinghai Lake |
| 韩元红 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 王琪 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 青海湖盆地是我国西北内陆干旱区典型的山间断陷湖盆，与我国一些陆相含油气盆地沉积特征十分相似，发育有三角洲、滩坝和泻湖等有利于油气储集的沉积体系。对于青海湖这些沉积体系的研究，可以为陆相含油气盆地相同沉积体系的研究提供借鉴。湖泊水动力是湖泊中最基本的物理过程，是湖泊物质输运和能量传输的动力，控制着湖泊沉积物、水质环境和水生生物等要素的发展。对于青海湖水动力特征的研究可以为湖泊近岸沉积砂体的形成演变机制的分析提供重要信息。 本文采用了野外实地分析技术（包括露头和探槽分析）、样品室内分析技术（沉积物矿物组成和水样化学组成分析）以及先进的遥感技术和计算机数值模拟技术等相结合的研究手段。研究的主要内容包括：通过对青海湖近岸滩坝砂体的实地考察、典型滩坝剖面的精细解剖及滩坝沉积物的组成与分布特征的分析，系统研究青海湖近岸现代沉积体系的岩性岩相组合、沉积层序、剖面结构、沉积构造及沉积物粒度、矿物分布等沉积特征；在对比分析前人研究成果的基础上，通过对湖区近 40 年（1972~2010 年）来多张遥感图像的判读，分析青海湖近岸沉积砂体的时空演变特征；通过对青海湖水动力特征及其驱动下的沉积物输运模拟，结合湖区内各个滩坝的实际沉积演变特征，推测滩坝的形成机制，并预测未来一段时间内青海湖滨湖区域沉积砂体演变趋势。本文取得以下结论和认识： （1）青海湖近岸发育的现代沉积滩坝具有特定的沉积特征，具体表现为沉积物粒度较粗，分选性较差，结构和成分成熟度均较低，沉积构造多见平行层理、交错层理和冲洗交错层理的发育。青海湖近岸发育的滩坝大多为进积型滩坝，垂向上均为上粗下细的反旋回，常见上部砾石层-中间砂砾或泥砾混合层-下部砂层或泥层的沉积组合模式。滩坝砂体层内非均质性强，可以较好的区分滩坝亚相及微相类型，并分析各亚相和微相的沉积特征。 （2）青海湖近岸发育的滩坝砂体类型丰富多样，按照沉积物物源和滩坝发育的地理位置可以划分为 5 种，分别为废弃三角洲前缘改造区滩坝，三角洲侧缘区滩坝，湖岸拐弯区滩坝，开阔滨浅湖区滩坝和冲积扇/基岩改造区滩坝。根据滩坝形成的水动力机制可以分为为浪控型滩坝、湖流控型滩坝和波浪-湖流共控型滩坝 3 种。青海湖近岸浪控型滩坝主要分布在东岸和南岸，湖流控制型滩坝主要分布在湖岸拐弯明显的沙咀砂体发育区域，波浪-湖流共控型滩坝主要分布在三角洲侧缘区域。浪流共控型和湖流控制型滩坝一般比浪控型滩坝发育规模大，浪控型滩坝物性特征最好，其次是浪流共控型，湖流控制型滩坝物性特征相对最差。 （3）影响青海湖近岸滩坝发育的因素很多，主要包括物质来源、水动力条件和构造地貌等，这些因素控制着滩坝砂体的形成、发育规模及沉积特征。滩坝形成之后是否能够保存下来，主要由湖泊基准面升降特征及速率控制， 湖泊基准面以较快速度上升，有利于滩坝沉积的保存。而湖泊基准面的变化又取决于一定时期内湖泊气候特征。 （4）青海湖水动力特征复杂，在平面上，滨浅湖区水动力最强，向湖中心逐渐减弱，垂向上2米水深处水动力最强，自上而下可分为动力区、过渡区和静水区。青海湖水动力主要包括湖流和湖浪，湖流表现出三个大的顺时针环流和一些次级小环流。青海湖浪作用表现出湖泊东岸和南岸比西岸和北岸强，迎风侧强而背风侧弱的特征。盛行风和入湖河流径流特征是青海湖水动力特征的主要控制因素，气候条件决定了湖区风场和入湖河流径流特征，为控制青海湖水动力特征的最终因素。 （5）青海湖沉积物在特定的水动力作用下表现出一定的输运规律，沉积物整体表现出自西北向东南输运的趋势，湖东岸和南岸受浪力侵蚀作用明显。湖岸线和近岸滩坝砂体也表现出一定的演变趋势，湖岸线整体正在萎缩，湖西岸和北岸湖岸线比湖东岸和南岸湖岸线萎缩速度更快，河流三角洲前缘区域和湖岸线拐弯较大区域，沉积演变最明显。根据沉积砂体演变特征和沉积物输运规律，结合整个湖区气候和水动力特征，反推了滩坝砂体形成过程，建立了典型滩坝砂体成因模式，推测了今后一段时期内青海湖近岸砂体沉积演变趋势。 （6）青海湖水动力驱动下的沉积物输运规律和青海湖近岸沉积砂体演变趋势十分对应，水动力与沉积充填响应良好。青海湖水动力特征是青海湖近岸滩坝砂体形成、展布和演变的主要决定因素。对湖泊近岸滩坝沉积体系的研究应重视水动力特征的研究。 |
| 英文摘要 | Qinghai Lake Basin, situated in the arid region of northwest China, is a typical intermontane downfaulted Basin. Its sedimentary systems are very similar to some petroliferous basins in China. There developed typical sedimentary facies (e.g. deltas, shoal-bars and lagoons) which were good for hydrocarbon accumulation. Thus, researching the sedimentary systems of Qinghai Lake could provide us a good example of paleogeographic recovery in the similar lacustrine basin. The hydrodynamic force is the basic physical processes in lakes, and the driving force to make matter transport and energy diffusion. The sediments, water environments and aquatic organisms of the lake are all controlled by hydrodynamic force. Thus, the researching of hydrodynamic characteristics could provide important information for accurately analyzing the mechanism of beach bar in Qinghai Lake. To achieve the research purposes, the field analysis techniques (contains outcrops and trenches analysis technology), laboratory analysis techniques (contains mineral composition analysis of sediments and chemical characteristics test of water), remote sensing techniques and computer numerical simulation techniques were used in this paper. The main content of the thesis included: the sedimentary characteristics (e.g. facies association, lithologic composition, deposition sequence, sectional structure, sedimentary structure and mineralogical compositions of the sediments) of the beach bar were investigated in both field and laboratory. Meanwhile, evolution and development characteristics of beach bar around Qinghai Lake were analyzed by interpretation of remote sensing images of Qinghai Lake in nearly 40 years (1972~2010). Moreover, computer numerical simulation method was used in this study to show hydrodynamic and sediment transport patterns of Qinghai Lake. In the end, the formation mechanisms and sedimentary evolution tendency in a period of time of beach bars around the Qinghai Lake were discussed. The main conclusions and results of this paper are as follows: (1) A number of sedimentary characteristics of beach bars were found in Qinghai Lake. It was shown that sediments of beach bars were coarse, poorly sorted. Both the compositional and textural maturities of the sediments were low. The main bedding structures of the beach bar were parallel bedding, cross bedding and flushing cross-bedding in Qinghai Lake. Beach bars developed in Qinghai Lake were mainly progradational beach bars which had reverse grain size orders in ascending order. They had a pattern of sedimentary sequences which manifested gravel layer - sand-gravel or mud-gravel layer - sand or mud layer from the top down. Beach bars in Qinghai Lake were of strong heterogeneity, for which the types of subfacies and microfacies of beach bars were distinguished and the sedimentary characteristics of subfacies and microfacies of beach bars were analyzed. (2)The sedimentary types of beach bars in Qinghai Lake were diverse. According to provenances and geographic positions of beach bars they were divided into five categories: beach bars in transformation zone of the abandoned delta front, beach bars in delta flanks, beach bars in Bays of the lake, beach bars in open shallow strand area, and beach bars in transformation zone of alluvial fans or bedrocks. And according to hydrodynamic mechanisms of beach bars they were divided into three categories: beach bars controlled by waves, beach bars controlled by currents, and beach bars controlled by both waves and lake currents. Different types of beach bar showed different sedimentary characteristics, scales and distribution rules. Beach bars controlled by waves were mainly distributed in east and south coast area, beach bars controlled by currents mainly developed in Bays of the lake (e.g. in Spit), and the beach bars controlled by both waves and lake currents mainly developed in delta flanks. The beach bars controlled by waves were relatively small, but the physical properties of them were relatively more suitable for stockpiling oil and gas. (3)There were a lot of factors that affect the development of beach bars in Qinghai Lake. These factors, mainly including material sources, hydrodynamic conditions, tectonic setting and terrain features, controlled the formation mechanism, the scale and sedimentary characteristics of the beach bar. Whether beach bars could be preserved was determined by the changing features of the lake datum and its speed. It was concluded that beach bars were more easily to preserve in the ascending period of the datum. The changing features of the lake datum and its speed were determined by the climatic features in a period. (4)Hydrodynamics characteristics of Qinghai Lake were very complicated. In the horizontal direction, the hydrodynamic forces were strongest in the coastal waters and it weakened gradually from the shore shallow area to the middle deep area of Qinghai Lake. Moreover, in the vertical direction, the hydrodynamic forces were strongest in the upper water zones (2 meters deep), and it weakened gradually from the top to the bottom of the Qinghai Lake. Hydrodynamics of Qinghai Lake included water currents and waves. There were three clockwise main water circulations and some secondary water circulations in the Qinghai Lake. The water waves developed in the eastern and southern coastal waters were stronger than those developed in the eastern and southern coastal waters of the Qinghai Lake. In addition, the water waves developed in windward waters were stronger than those developed in leeward waters. The prevailing wind of Qinghai lake basin and the runoff of the rivers were the most important factors controlling the hydrodynamics characteristics of Qinghai Lake. Furthermore, the climate of Qinghai Lake basin, controlling the prevailing wind and the runoff of the rivers, was the ultimate determinant of hydrodynamics characteristics of Qinghai Lake. (5) The sediment transport patterns in the coastal waters of Qinghai Lake were found in this study. It showed that sediments transported from northwest waters to southeast waters. The eastern and southern lakeshores were clearly eroded by water waves. We also found the evolution trend of the shoreline and coastal beach bars of Qinghai Lake. Qinghai Lake was shrinking and its shoreline was moving lakeward. However there are significant differences for the degree of shrinkage. It was suggesting that the move speed of west and north shoreline higher than the south and east shoreline. And the most obvious evolution of the shoreline and coastal beach bars developed in the river estuary areas and the spit areas. The formation processes of coastal beach bars were deduced, the hydrogenetic models of coastal beach bars were established, and the evolution trendency of coastal beach bars in a future period of time were speculated in this study, according to the evolution characteristics of coastal beach bars, and the sediment transport patterns, climate and hydrodynamics characteristics of Qinghai Lake. (6)The sediment transport patterns in the coastal waters were well agreed with the evolution trend of the shoreline and coastal beach bars of Qinghai Lake. Meanwhile, the responses of hydrodynamics characteristics and sedimentation VIII characteristics were very good in coastal area of Qinghai Lake. Thus it can be seen that hydrodynamic condition was the most important determinant in the formation mechanism, distribution features and evolution patterns of the coastal beach bars in Qinghai Lake. The studies of hydrodynamic waves and currents should be strengthened when analyzing beach bars in coastal area of lake. |
| 中文关键词 | 青海湖 ; 近岸沉积 ; 滩坝 ; 沉积模式 ; 水动力 ; 遥感技术 ; 数值模拟 |
| 英文关键词 | Qinghai Lake littoral sediment beach bar hydrodynamic characteristics remote sensing computer numerical simulation sedimentary model |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 矿物学、岩石学、矿床学 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287504 |
| 推荐引用方式 GB/T 7714 | 韩元红. 青海湖近岸滩坝沉积特征及其水动力机制[D]. 中国科学院大学,2015. |
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