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| 第四纪中晚期以来长江三角洲CJ1孔古地磁及古环境研究 | |
| 其他题名 | Paleomagnetism and Paleoenvironment of core CJ1 in Changjiang delta during the middle-late Quaternary |
| 段宗奇 | |
| 出版年 | 2014 |
| 学位类型 | 博士 |
| 导师 | 刘青松 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 长江三角洲地区位于我国东部沿海，是联接青藏高原、中亚干旱区和西太平洋边缘海的重要枢纽。第四纪以来该区接受了巨厚沉积物，其中蕴含着丰富的气候和环境信息，是探讨长江物质源汇过程、海陆相互作用、三角洲发育史、海平面变化、以及亚洲宏观环境变迁的重要靶区之一。此外，作为青藏高原侵蚀物质的汇聚地之一，长江三角洲在探索长江形成、流域化学风化方面的作用业已引起广泛重视。近年来，磁极性地层学在长江三角洲的应用取得进展，加深了我们对一系列重大问题的认识，如该区B/M（松山期/布容期）的埋藏深度从南东的220 m减小到西北山前的50 m（图2），并且在布容正向期内观测到诸多小的负极性事件。然而前人对该区古地磁数据的可靠性还未进行过深入探讨。为此，本论文研究选取了位于上海市浦东新区机场镇的一个深达173米的CJ1钻孔。通过结合古地磁学、岩石磁学及环境替代性指标探讨该区第四纪中晚期沉积物中的剩磁记录的可靠性机制，为建立更为可靠的磁性地层提供理论基础。在此基础上，进一步探讨该区的气候和环境演化模式。 岩石磁学结果显示沉积物的载磁矿物主要为低矫顽力的磁铁矿和高矫顽力的赤铁矿，样品的粒径以假单畴为主，少量样品落在单畴和超顺磁混合区域或趋近多畴区域。对于磁化率各向异性，大多数样品的磁化率最小轴（K3）近似于垂直于最大轴（K1） 和中间轴（K2）位于的层面，为正常的沉积组构；部分样品的K3的偏角和倾角（K3inc）偏离正常值，指示原始沉积状态遭到扰动或者是非正常的沉积过程。我们提出用K3inc≧60°这一标准进行识别，揭示出该区钻孔内诸多古地磁方向记录异常是由非正常沉积（沉积过快或沉积后发生扰动）造成的。 排除这些干扰后，CJ1孔记录了布容正极性时和松山负极性时期，其转换界线在埋深约152.46 m。布容正极性期内记录了至少5个负极性漂移事件。根据地层的岩性特征、环境参数和前人在该区的研究结果，我们将埋深29.2~29.35 m、64.72~64.81 m和 102.49~102.63 m的三次事件确立为着Mono Lake事件、Laschamp事件和Blake事件，布容期内的其余两个负极性漂移事件尚不能具体确定其对应的事件。松山负极性期内记录了两次可靠的正极性漂移事件，其可能对应着Pre M-B、Kamikatsura和Pre M-B中的两个。结合前人研究，我们获得了该区第四纪中晚期以来可靠的磁性地层。 在磁性地层的年代框架基础上，我们对CJ1孔的沉积地层进行划分，从下往上分为早更新统（底部起至150.29 m），中更新统（150.29~102.63 m），晚更新统（102.63~26.16 m），全新统（自26.16 m深度至钻孔顶部）。并对不同层位的环境参数进行了初步分析。总体而言，粒度反映沉积物的岩性变化，与搬运沉积物的水动力的变化有关。Fe，Ti等元素变化同岩性具有一定的关系，粗颗粒砂中的含量低于细颗粒的粉砂及粘土，表明这些元素在细颗粒中比较富集。色度参数与岩性相关性不大，主要反映沉积环境（氧化还原条件）的多变性。环境磁学参数的变化较为复杂，受物源、沉积后的环境及气候演化共同影响。这些环境替代性指标在不同层位间具有不同的相互关系，表明该区存在明显的气候变化及复杂多变沉积环境。 |
| 英文摘要 | The Changjiang (Yangtze) delta is located on the east coast of China, closely linking the Tibetan Plateau, the arid central Asia and the west pacific marginal sea. It accepted the very thick clastic sediments during the Quaternary age, and thus provides great information to better understand and solve the stratigraphy of coastal zones, marine transgression events on the coastal plains and palaeoenvironmental problems involving the evolution of East Asian monsoon and the sediment-to-source process during the Quaternary. The recent years have witnessed a considerable progress in the palaeomagnetic dating of its stratigraphy, which has notably increased our understanding of a series of important issues such as the depth of the boundary between Matuyama and Brunhes (B/M). From the southeast to northwest, the depth of M/B boundary from ~220 m to ~50 m within too many tiny polarity events during the Brunhes Chrons. However, there lacks the estimate of the magnetostratigraphy from the paleomagnetic and rock magnetic analysis, and the numerous tiny polarity events have been still poorly understood. In this study, a combined paleomagnetism, rock magnetism, and some other proxy records was carried out on the CJ1 core from the eastern of the Yangtze delta in order to discuss the reliability of remanent magnetization and establish a more reliable magnetostratigraphy in this region. Moreover, we devote a simple discussion about the sedimentary environments, sources and palaeoclimatology significance since the middle-late Quaternary. The major research results of core CJ1 sediments are as follows: Detailed rock magnetic investigation, such as hysteresis loop and the high-temperature magnetic analyses, suggest that the main magnetic carriers of these samples are stable magnetite and haematite with contrasting coercivities. Cross-plots of Mrs/Ms vs Bcr/Bc indicate that the main magnetic grain sizes are PSD, some tend to MD and the mixture zone of SD and SP. The anisotropy of magnetic susceptibility show that the magnetic fabrics of the most studied sediments represent a normal primary sedimentary fabric and some others displays apparent disorder and disturbance. We propose the K3inc≧60° as a standard for identifying the normal primary sedimentary fabric, and the results show that the numerous tiny polarity events are abnormal sedimentary fabric, which may deposit too fast or suffered disturbing after deposition. Besides, the particle size analyses suggest that the finer particle is dominant in most samples, which is fit for the record of depositional remanent magnetization. Palaeomagnetic results indicate that CJ1 core has recorded the Brunhes Chron and the late Matuyama Chron, and the depth of the B/M is in 152.46m. There are five negative excursions recorded during the Brunhes Chron in CJ1 core. Based on the lithologic character, environmental proxies and other former research, we consider that the upper three negative excursions are Monolake event (29.2~29.35 m), Laschamp event (64.72~64.81 m) and Blake event (102.49~102.63 m), and we can not confirm the identification of the other two. The two reliable positive excursions are two of the three excursions including Pre M-B, Kamikatsura and Pre M-B. Our findings, coupled with previously published results, have established that the reliable magnetostratigraphy in the eastern of Yangtze delta since the middle-late Quaternary. In the framework of the magnetostratigraphy, the strata of the middle-late Quaternary in CJ1 core is divided as Early Pleistocene (from the bottom to the depth of 150.29 m), Middle Pleistocene (150.29 m~102.63 m), Late Pleistocene (102.63~26.16 m), and Holocene (from the depth of 150.29 m to the top). There is complex mechanism effect on the different environmental proxies. In summary, the particle size indicate the change of water dynamic which transport the sediment. The elements such as Ti and Fe are enrichment on the finer particles, which reflect the difference o |
| 中文关键词 | 长江三角洲 ; 磁性地层 ; 岩石磁学 ; 环境磁学 ; 沉积地层 |
| 英文关键词 | Changjiang (Yangtze) delta Paleomagnetism Rock magnetism Environmental magnetism sedimentary sequence |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 海洋地质 |
| 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/2XILL650/287371 |
| 推荐引用方式 GB/T 7714 | 段宗奇. 第四纪中晚期以来长江三角洲CJ1孔古地磁及古环境研究[D]. 中国科学院大学,2014. |
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