Knowledge Resource Center for Ecological Environment in Arid Area
| 晚新生代塔里木盆地干旱化历史及其对全球变化的响应 | |
| 其他题名 | The History and Response to Global Change of Aridity Recorded by Late Cenozoic Sediments in the Tarim Basin |
| 王宁 | |
| 出版年 | 2009 |
| 学位类型 | 博士 |
| 导师 | 刘卫国 |
| 学位授予单位 | 中国科学院地球环境研究所 |
| 中文摘要 | 本文通过对中国大陆环境钻探获取的罗布泊LS1和LS2钻孔岩芯主要气候代用指标的综合分析，建立了该地区过去7Ma以来的古环境变化序列。结合对西北干旱、半干旱区现代过程的研究，讨论了晚新生代塔里木盆地干旱化的历史。通过 LS2孔古气候记录与海陆风尘记录以及深海氧同位素记录的对比，论证了晚新生代主要气候变化阶段海陆古气候记录的可比性，并初步探讨了亚洲内陆不同干旱阶段主要的气候驱动因素。通过本文初步研究，得出以下主要结论：\n 1.建立并评估了湖相沉积混合矿物中白云石和方解石稳定同位素样品提取实验室方法，该方法对白云石的回收率约为90%，并可以通过XRD衍射峰中矿物特征峰的积分强度比值来表征矿物的相对含量。样品处理过程的溶蚀作用对不同白云石含量的样品中白云石的碳、氧同位素组成没有影响，碳、氧同位素变化均在实验允许的误差范围之内。方解石碳同位素的估算是在误差允许范围内，氧同位素的略偏大，但可以满足定性或半定量研究需要。\n 2.干旱区表土不同粒级样品碳氧同位素的分析结果显示：表土粒径越细，碳酸盐含量越高，氧同位素越偏正，碳同位素越偏负。我们初步认为细颗粒组分中土壤次生碳酸盐相对比例大，而粗颗粒组分中原生碳酸盐相对占优势。而且可能由于受蒸发作用的影响，使得土壤次生碳酸盐比原生碳酸盐的氧同位素更为偏正，而次生碳酸盐受植物等生物作用影响，其碳同位素较原生碳酸盐更为偏负。进而使细颗粒组分较粗颗粒组分碳酸盐的氧同位素更偏正，碳同位素更偏负。这或许暗示干旱区土壤细颗粒组分碳酸盐能更好地反映成壤过程中碳酸盐形成时期的气候环境信息。因此，提取沉积物细颗粒组分可能对我们研究干旱区土壤碳酸盐的气候环境意义更有帮助。另外，颗粒越粗，外源碳酸盐贡献越大，这一特征可能对风沙影响较大的干旱区其他沉积物（如湖泊沉积物）也有一定的适用性。\n 3.根据干旱-半干旱地区14个现代湖泊沉积物碳酸盐矿物的氧同位素与相应气候环境指标的相关分析，探讨了该地区沉积物中的碳酸盐矿物的氧同位素的影响因素，其中方解石δ18O主要受湖水δ18O、温度、海拔和纬度的影响；白云石δ18O受降水量/蒸发量的影响；总碳酸盐δ18O受湖水δ18O组成、温度、降水量/蒸发量、海拔和纬度多种因素影响。总碳酸盐δ18O对湖水δ18O、温度、海拔和纬度的响应是以方解石为载体而体现的；总碳酸盐δ18O对降水量/蒸发量的响应则更多地归因于白云石δ18O对其的响应结果；另外，总碳酸盐、白云石、方解石的氧同位素可以有效地指示湖水盐度的变化，而且用白云石的氧同位素来反映湖水盐度可能优于总碳酸盐和方解石。对湖泊碳酸盐氧同位素组成起决定性作用的还是各种环境因素诱导的湖水氧同位素的变化。该研究初步建立了总碳酸盐、方解石和白云石氧同位素与环境各个指标之间的响应关系，对于揭示过去干旱-半干旱地区环境变化有重要参考意义。\n 4.根据LS1及LS2孔沉积物各项环境代用指标的测试结果，结合LS2孔的古地磁年龄控制点数据，重建了罗布泊地区晚新生代以来气候环境的变化序列。过去7Ma以来，塔里木盆地的古环境整体划分为6个演化阶段：第一阶段（7-6MaBP）湖泊以深湖相还原环境为主，气候温暖偏干，后期略转湿凉，温度相对不稳定，湖泊植被类型相对复杂；第二阶段（6-5.3MaBP）湖泊处于深湖向浅湖转化的时期，气候在相对湿凉的背景下呈现冷湿-暖干-冷湿的次级波动，湿润程度较上一阶段有所增加；第三阶段（5.3-3.7MaBP）湖泊为浅湖相沉积环境，气候干旱，但干燥度较为和缓，植被单一；第四阶段（3.7-2.6MaBP）湖水进一步收缩，由浅湖向滨湖演变，气候冷干，沉积受地表作用影响加剧；第五阶段（2.6-0.24MaBP）湖泊处于水体较浅的滨湖相，气候暖干；第六阶段（0.24-0MaBP）湖泊沉积逐渐被风砂堆积取代，气候趋于极端干旱。\n 5.罗布泊地区乃至塔里木盆地在7-6.4MaBP时段整体气候相对干旱；6.4-5.3MaBP气候开始转为相对湿凉；5.3-3.7MaBP气候又开始干旱，但干燥程度较为和缓，3.7MaBP干燥程度开始明显增加，气候日趋冷干，到2.6MaBP气候转为暖干，随后持续到约0.24MaBP左右，气候发展为极端干旱。LS2孔岩芯记录所反映的罗布泊及塔里木盆地地区气候的干旱化至少可以追溯到最近7MaBP，持续的干旱化则开始于最近5.3MaBP，而现代意义的干旱化则始于3.7MaBP。\n 6.结合罗布泊地区环境演化的特点，我们对罗布泊LS2孔下部沉积物中白云石进行了分析，初步推断其为微生物诱导成因的。而且白云石的相对含量和氧碳同位素对环境的变化均有指示作用：蒸发作用强时白云石相对含量高，氧同位素偏正，碳同位素偏负；蒸发作用减弱时白云石相对含量低，氧同位素偏负，碳同位素偏正。因此该地区白云石的相对含量及其氧碳同位素组成具有重要的环境意义，可以间接的反映环境的变化。\n 7.罗布泊气候指标所揭示的7MaBP以来的气候变化记录与海陆风尘记录以及深海氧同位素记录具有很好的可比性，可以有效地指示7MaBP以来亚洲内陆干旱化的发展过程。\n 本文在对亚洲内陆干旱化过程、全球冰量变化、青藏高原构造隆升的耦合关系初步探讨的基础上，认为7MaBP以来的亚洲内陆的干旱化可能主要受全球冰量的变化尤其是北半球冰盖的形成和发展以及青藏高原阶段性构造隆升所驱动。 |
| 英文摘要 | Based on the integrated analysis of multi-climate proxy indexes of LS1 and LS2 cores obtained in Lop Nur region through the Chinese Continental Drilling Program (CCDP), the palaeoenviroment change process in Lop Nur region since 7 Ma BP was constructed. Combined with the study on the modern environment process in arid and semi-arid regions, the history of aridity in Tarim Basin since Late Cenozoic was discussed. Comparison of the palaeoclimate record in LS2 core with the continental and marine aeolian flux records and the benthic δ18O record indicated that there was a good correlation of main climate change stages between the continental and the marine climate records during Late Cenozoic. The primary controlling factors of palaeoclimate change for different aridity episodes in inner Asian were primarily discussed. The main conclusions of this dissertation are as followed:\n 1.The laboratory analysis method of stable isotopes of dolomite and calcite in poly-minerals in lacustrine sediments was constructed and evaluated. In this method, the extraction rate of dolomite is about 90%. It is feasible that using the ratio of the integral intensity of the main XRD peaks of minerals as their relative content. The solution during the sample treatment has no effect on the carbon and oxygen isotope composition of dolomite. And the variations of the carbon and oxygen isotope of dolomite extracted and the carbon isotope estimation of calcite are all in the experimental error range allowed. The deviation of oxygen isotope estimation of calcite is slightly larger, but it still can be used for qualitative or semi-quantitative research.\n 2.The results of our study on the surface soil in China arid region indicate that the carbonate content and the isotopic composition of different grain size samples vary greatly. As the grain size decreasing, both the carbonate content and the oxygen isotope increase and the carbon isotope gets more negative. Based on the above results, we deduce that pedogenic carbonate is regnant in fine grain samples, while the protogenetic carbonate predominates in coarse grain group. Compared with protogenetic carbonate, the oxygen isotope shows more positive due to evaporation, and the carbon isotope is more negative resulted by the biological effect (eg vegetation). Therefore, the oxygen isotope of fine grain group is more positive and the carbon isotope is more negative when compared with the coarse grain group. It is suggested the carbonate in fine grain group can be regarded as pedogenic carbonate and may better reflect the information about the climate and environment during the formation process of pedogenic carbonate in the arid land. In addition, the character that the contribution of exogenous carbonates to bulk carbonates increases with the larger grain size may be true for other sediments (eg lacustine sediments) in arid land, which strongly affected by wind blown sand.\n 3.Based on the correlation analysis between δ18O of modern lacustrine carbonates of 14 typical lakes in Tibet Plateau and corresponding environmental indicators around each lake, the impact factors of oxygen isotope of the carbonates in lacustrine sediments are elaborated. The δ18O of calcite is mainly controlled by the δ18O of lake water, temperature, altitude and latitude. The δ18O of dolomite was in response to P/E. The δ18O of bulk carbonate was affected by multi-factors such as the δ18O of lake water, temperature, P/E, altitude and latitude. Calcite was responsible for the relationship between δ18O of bulk carbonate and the δ18O of lake water, temperature, altitude and latitude. Via dolomite, the δ18O of bulk carbonate was linked to P/E. The δ18O of bulk carbonate, dolomite and calcite can effectively indicate the change of lake salinity, among which the δ18O of dolomite maybe the most sensitive. The key control factor of the oxygen isotope of lacustrine carbonates is the variation of the δ18O of lake water resulted by the changes of the environmental factors. This study constructed the primary relationship between the δ18O of bulk carbonate, calcite and dolomite and environmental factors. It may have significance to the research of the past environmental change in arid and semi-arid region.\n 4.Based on the multi-proxy analysis results of LS1 and LS2 cores sediments and the age controlling points of magnetic polarity boundary of LS2 core, the late Cenozoic climate change sequence in Lop Nur region was reconstructed. The climate and environment change shows six evolution stages since 7 Ma BP in Lop Nur region. \n7-6 Ma BP: The lake was in the deoxidize environment with deep water. The climate was warm and arid, and the slightly cool and humid during the later period. The temperature fluctuated frequently. The vegetation types in the lake region were complex.\n6-5.3 Ma BP: The depositional environment gradually changed to shallow water state. In the context of aridity, the climate showed the cold-humid, warm-arid and cold-humid fluctuations. The humid extent was reduced when compared with the previous stage.\n5.3-3.7 Ma BP: Lake was in the shallow water depositional environment. The climate turned to arid and the arid extent was mild. The vegetation types in the lake region were simplex.\n3.7-2.6 Ma BP: The water volume further decreased. The lake turned to shore lake depositional environment. The climate was cold and arid. During this period, the alteration of the earth surface process to lake sediments obviously increased.\n2.6-0.24 Ma BP: Lake was in the shore lake depositional environment with very shallow water. The climate was warm and arid.\nAfter 0.24 Ma BP: The site of LS2 core gradually withdrew from the lake basin. The lacustrine sediments had been gradually replaced by the aeolian deposits. The climate turned to extremely arid.\n 5.The climate during 7-6.4 Ma BP period in Lop Nur region and the Tarim Basin was arid. The humid and cool climate began at 6.4 Ma BP. Since 5.3 Ma BP the arid climate prevailed, but the arid extent was mild. After 3.7 Ma BP the climate sharply turned to cold and arid, and continued until 0.24 Ma BP. Then the climate showed extremely arid. The aridity of Tarim Basin indicated by the record of LS2 core can be traced back to at least 7 Ma BP. The persistent aridity began at 5.3 Ma BP. The present- like arid climate began at 3.7 Ma BP.\n 6.According to the environmental evolution characteristics in Lop Nur region, the dolomite in the lower part of LS2 core was analyzed. Here, we inferred that the formation of dolomite was microbial-induced. Both the relative content of dolomite and its carbon and oxygen isotopes can be used as the indicator of environment change. As the strengthening of evaporation, the relative content of dolomite increased, its oxygen isotope got more positive and carbon isotope turned to more negative. In contrast, when the evaporation was weak, its relative content was lower, and the oxygen isotope was more negative and the carbon isotope was heavier. Therefore, the relative content of dolomite and its carbon and oxygen isotopes had important environmental significance, and they would indirectly reflect the change of environment in Lop Nur region.\n 7.There is a good correlation between the climate record indicated by multi-proxy of LS2 core and the continental and marine eolian flux and benthic oxygen isotope records since 7 Ma BP. The climate change record revealed by the Lop Nur sediments can effectively reflect the arid process in inner Asian.\n Based on the primary understanding of the inner Asian aridity and the link of which to global ice volume and the tectonic uplifting of the Tibet Plateau, the author believes that the inner Asian aridity since 7MaBP may be mainly controlled by the change of global ice volume, especially the formation and development of northern hemisphere ice sheet and the stage-by-stage tectonic uplift of the Tibet Plateau. |
| 中文关键词 | 晚新生代 ; 罗布泊 ; 碳酸盐 ; 碳氧同位素 ; 干旱化 |
| 英文关键词 | Late Cenozoic Lop Nur Carbonate Carbon and oxygen isotope Aridity |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 第四纪地质学 |
| 来源机构 | 中国科学院地球环境研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286744 |
| 推荐引用方式 GB/T 7714 | 王宁. 晚新生代塔里木盆地干旱化历史及其对全球变化的响应[D]. 中国科学院地球环境研究所,2009. |
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