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| 晚第四纪柴达木盆地东部高湖面石英光释光年代学及其环境意义 | |
| 其他题名 | Quartz Optically Stimulated Luminescence chronology for high lake levels in the eastern Qaidam Basin,northeastern Qinghai-Tibetan Plateau since late Quaternary and its palaeoenvironmental implications |
| 樊启顺 | |
| 出版年 | 2009 |
| 学位类型 | 博士 |
| 导师 | 董治宝 |
| 学位授予单位 | 中国科学院青海盐湖研究所 |
| 中文摘要 | 自上世纪80年代开始，国内外学者通过对青藏高原湖泊的考察，发现众多的湖泊周围保存有多级湖岸堤或高位湖相沉积物；他们认为在氧同位素三阶段晚期青藏高原地区普遍存在“泛湖期”（40~28 ka BP）、“大湖期”（40~25 ka BP）或“暖湿期”（40~30 ka BP）（主要通过14C测年），并且其温度和降水比全新世还高。这些气候事件也存在于青藏高原周边地区，如腾格里沙漠、巴丹吉林沙漠、塔克拉玛干沙漠。高湖面是湖泊演化的鼎盛期，代表着区域温暖湿润的气候。因氧同位素三阶段处于末次冰期的间冰阶，在全球的古气候变化框架中不应出现这种特殊的暖湿现象。近十几年来，随着测年技术（释光、电子自旋共振、铀系法等）的提高和成熟，部分学者选择青藏高原及周边地区一些湖泊（如青海湖、纳木错、甜水海湖、结则茶卡湖、罗布泊、玛纳斯湖等）为研究对象，通过热释光（Thermoluminescence, TL）、光释光（Optically Stimulated Luminescence, OSL）、电子自旋共振（Electron Spin Resonance, ESR）和铀系（U/Th）法对湖泊周围发育的古湖岸阶地或高位湖相沉积物测年则认为，青藏高原及周边地区的高湖面应出现在氧同位素五阶段。柴达木盆地位于青藏高原东北部，是中纬度地区最大的内陆盆地之一。本论文选择柴达木盆地作为研究区域，拟应用光释光测年方法确定该区域高湖面的年代框架。柴达木盆地高湖面的研究不仅对认识该区域湖泊演化提供年代框架，而且也为青藏高原湖泊高湖面研究提供新的年代学证据。\n 柴达木盆地盐湖的成盐期是继高湖面之后，湖泊演化到晚期的产物，代表着区域极端干旱的气候。目前柴达木盆地高湖面年代与盆地内察尔汗盐湖开始成盐年代相矛盾：对于察尔汗盐湖成盐期，一种观点认为整个察尔汗盐湖成盐年代为25 ka，不老于30 ka；另一种观点认为察尔汗盐湖不同区段的成盐年代会有所不同，达布逊区段成盐年代为50 ka，别勒滩区段成盐年代为25 ka。如果第一种观点成立，则与察尔汗盐湖东缘贝壳堤获得的高湖面测年结果（39.7~17.5 ka）相矛盾，尤其是25~17.5 ka连续有高湖面存在是很难理解的；如果第二种观点成立，说明察尔汗盐湖成盐年代东部比西部老，柴达木盆地东部地区至少老于50 ka才能出现高湖面。这个结论则与盆地内贝壳堤（38.6~28.6 ka、50~30 ka或39.7~17.5 ka）、小柴旦湖（51~37 ka）、冷湖（62.7~37.2 ka）和茶卡盐湖（50.5 ka）等获得的高湖面年代记录相矛盾。因此，柴达木盆地高湖面年代的研究是对察尔汗盐湖成盐年代的有利补充。解决上述问题的关键在于建立系统可靠的年代框架。本论文选择柴达木盆地东部的尕海湖和贝壳堤两个地点的湖岸阶地及古湖相沉积物为研究对象，运用OSL（石英）技术测年（共34个年代样品）以及贝壳堤湖相沉积物（共45个样品）X衍射分析，探讨了碳酸盐指标指示的环境意义。通过OSL年代学和环境指标（碳酸盐和碎屑岩含量）的研究，共得到以下几个方面的结论：\n 1. 通过对提取的石英OSL物理性质分析，发现尕海湖GH-03样品6个样片之间以及尕海湖6个样品之间都存有标准生长曲线，且再生剂量达到300 Gy时生长曲线仍然在增长；同样在贝壳堤剖面样品中，也发现BQD-C样品7个样片之间以及贝壳堤剖面6个样品之间都存有标准生长曲线，且再生剂量达到600 Gy时生长曲线仍然在增长。这个生长曲线为测定更老的湖相样品提供了可能性。\n 2. 通过对德令哈盆地托素湖现代湖相样品（离地表15 cm）OSL年代测定，其等效剂量（De）值为1.7±0.3 Gy，年龄为0.72±0.08 ka。说明德令哈盆地湖相沉积物在其搬运的过程中基本上被阳光或日光完全晒褪，为测定该区域古湖相沉积物提供了技术参数。\n 3. 通过对德令哈尕海湖GH-03样品和贝壳堤BQD-H样品预热坪、剂量恢复和离散度实验表明，单片再生剂量法适宜于测定该区域湖相沉积物石英的等效剂量。\n 4. 通过石英OSL测年，尕海湖高湖面年代结果为100~75 ka、82~73 ka和63~55 ka；贝壳堤高湖面年代结果为143~76 ka。说明柴达木盆地东部高湖面出现在MIS 5和MIS 3早期，而不是MIS 3晚期。通过对比青藏高原、周边地区及南半球湖泊高湖面记录，发现晚第四纪以来青藏高原高湖面年代具有多期性，最高湖面出现在MIS 5，之后湖面逐渐下降。亚洲夏季风的加强可能是柴达木盆地东部形成高湖面的主要因素。\n 5. 通过对贝壳堤剖面湖相沉积物X衍射分析，发现剖面中碳酸盐含量由下到上逐渐减少，且与碎屑岩含量呈反相关变化。剖面湖相沉积物自生碳酸盐含量高值代表着温暖气候条件下湖泊相对淡化时期的产物。根据OSL年代和湖相沉积物环境指标（碳酸盐和碎屑岩含量）研究，发现察尔汗湖高湖面出现在134~120 ka、~110 ka和89~78 ka，且湖面有逐渐下降的趋势。 |
| 英文摘要 | High lake levels are the humid period of lake evolution, which indicates warm and humid climatic conditions. Controversy exists regarding the chronology for high lake levels in the QTP. Significant efforts have been invested to define the timing of palaeoshoreline deposits using radiocarbon dating on the QTP, and ‘pan-lake period’ (40~28 ka BP), ‘the great lake period’ (40~25 ka BP) or ‘rather warm and humid period’ (40~30 ka BP) has been proposed in late marine isotpe stage (MIS) 3. Also using 14C dating, similar observations were reported from adjacent regions, such as the Tengger Desert, the Badain Jaran Desert and the Taklamakan Desert in Western China. However, with the development of dating techniques (Optically Stimulated Luminescence, Electron Spinning Resonance and U/Th) in recent years, some researchers investigated lakes (Qinghai Lake, Nam Co Lake, Tianshuihai Lake, Jiezechaka Salt Lake, Lop Nor and Manas Lake and so on) on the QTP and adjacent regions, and found that the highest lake level occurred in MIS 5. \n Conflict exists between the chronology of high lake levels and that of salt deposit formation in the Chaerhan Salt Lakes in the eastern Qaidam Basin. Some proposed that salt forming period in the entire Chaerhan Salt Lakes started at about 25 ka. However, others argued that the age of salt deposits forming is different for different regions in the Chaerhan Salt Lakes. In Dabuxun salt region the age of salt deposits forming is at 50 ka, while in Bieletan salt region it is at 25 ka. The results are in conflict with the chronologies high lake levels of the shell bar (39.7~17.5 ka), Xiao Qaidam lake (51~37 ka), Lenghu (62.7~37.2 ka) and Chaka Salt Lake (50.5 ka). \nThe aim of this study is to establish the quartz OSL chronology, using SAR protocol, for high lake levels in Gahai lake and the shell bar of Chaerhan salt lake, and discuss palaeoenvironmental significance of carbonate content in shell bar, which are located in the Qaidam Basin of the eartern QTP. It is concluded that:\n 1. There exists quartz OSL standardized growth curves of six aliquots and six samples from Gahai Lake. And there are also similar results of seven aliquots and six samples from shell bar in the eastern Chaerhan Lake. The saturation level of the growth curve is more than 400 Gy, which allows the De determination up to at least 300 Gy.\n 2. For a modern sample collected from Toson Lake (close to near Gahai Lake), the De value is only 1.7±0.3 Gy, with a corresponding OSL age of 0.72±0.08 ka. The De may have contribution from both the unbleached singal and the thermal transferred signal. However, in any case, it has negligible effects on the OSL ages of the samples under study (normally older than 50 ka). \n 3. Preheat Plateau, dose recovery test and scatter of De for sample GH-03 and BQD-H indicate that the SAR protocol is appropriate for De determination for lacustrine deposits in the eastern Qaidam Basin.\n 4. OSL dating results show that the high lake levels in Gahai Lake and shell bar of Chaerhan Lake occurred in MIS 5 and early MIS 3, not in the late MIS 3. The possible mechanism for the formation of high lake levels was strong Asian summer monsoon. \n 5. Total carbonate contents (TCC) of lacustrine deposits is gradually decreasing from the bottom to the top in shell bar section. And higher TCC indicates lower salinity and higher lake level of ancient Chaerhan Lake. By analyzing OSL dating and palaeoenvironmental significance of TCC, the results show that high lake levels of Chaerhan Lake occurred in the period of 130~120 ka, ~110 ka and 89~78 ka, respectively. |
| 中文关键词 | 晚第四纪 ; 柴达木盆地 ; 高湖面 ; 石英 ; 光释光年代学 ; 环境意义 |
| 英文关键词 | Late Quaternary Qaidam Basin High lake levels Quartz OSL dating Palaeoenvironmental implications |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地球化学 |
| 来源机构 | 中国科学院青海盐湖研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286778 |
| 推荐引用方式 GB/T 7714 | 樊启顺. 晚第四纪柴达木盆地东部高湖面石英光释光年代学及其环境意义[D]. 中国科学院青海盐湖研究所,2009. |
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