晚中新世西宁盆地沉积演化及环境变化

发布时间：2018-05-30 15:55

  本文选题：晚中新世 + 古生物化石　； 参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：西宁盆地位于青藏高原东北缘,处于我国东部湿润季风区、西北内陆干旱区和青藏高原高寒区三大自然地理区的交界处。盆地内沉积一套记录始新世-晚中新世青藏高原隆升和环境变化的连续的河湖相地层,是研究青藏高原隆升和气候变化的理想之地。本文采用古地磁学手段建立了班彦剖面和红崖子剖面剖面晚中新世的年代格架,通过分析沉积物粒度、磁化率、碳酸盐含量、(C、O)同位素古气候代用指标,研究探讨了晚中新世西宁盆地沉积演化及环境变化。初步的得到以下认识:1.磁性地层学研究结果显示,古地磁年龄范围为8.22 Ma~6.98Ma,化石年龄为8.1 Ma;红崖子剖面古地磁年龄范围为12.15 Ma~6.92Ma。这在前人咸水河组地层年龄研究基础之上,扩展了西宁盆地晚中新世地层咸水河组的顶部年龄。2.西宁盆地在8.25Ma左右其沉积时速率突然增加到147.03 m/Ma,其粒度、磁化率、(C、O)同位素发生明显变化,古生物化石显示在这一时期气候为温暖的亚热带半干旱。化石对比表明拉脊山在8.1 Ma左右快速隆升。3.红崖子剖面沉积物速率在7.33Ma达到整个剖面的最大值320m/Ma,沉积物为一套砾石;磁化率、碳酸盐含量及C、O同位素发生显著改变。西宁盆地7.33Ma干冷气候很可能是全球变冷和青藏高原加速隆升双重驱动使得沉积环境发生了变化。4.根据沉积环境的指标显示,西宁盆地晚中新世气候环境呈现阶段性变化趋势:四个主要时期共6个沉积阶段。1)晚中新世早期(12.16~8.25Ma):包括Ⅰ阶段(12.16~11.1Ma)、Ⅱ阶段(11.1~9.46Ma)和Ⅲ阶段(9.46~8.25Ma),沉积物速率较为稳定,西宁盆地气候条件相对温暖半湿润—潮湿。2)晚中新世中—中晚期(8.25~7.91Ma):即Ⅳ阶段(8.25~7.91Ma),该时期沉积物粒度、磁化率强烈波动,沉积物速率突然升高到147.03 m/Ma,沉积物为滨湖相的砾石层。构造活动强烈,气候以半干旱为主。3)晚中新世中晚期(7.91~7.16Ma):即Ⅴ阶段(7.91~7.16Ma),其湖泊水位波动较大,总体呈现出间歇式变浅趋势。西宁盆地干冷气候很可能是全球变冷和青藏高原加速隆升双重驱动引起的。4)晚中新世晚期(7.16~6.92Ma):即Ⅵ阶段(7.16~6.92Ma):该时期沉积物粒度呈现出剧烈的波动,C同位素迅速降低,O同位素快速增大,该时期气候温度比晚中新世中晚期高。
[Abstract]:Xining basin is located in the northeast margin of Qinghai-Xizang Plateau, at the junction of three natural geographical regions: the humid monsoon region in the eastern part of China, the inland arid region in the northwest and the high and cold region of the Qinghai-Xizang Plateau. A set of continuous fluvial facies strata recording the uplift and environmental change of the Qinghai-Tibet Plateau during the Eocene to the late Miocene is an ideal place to study the uplift and climate change of the Qinghai-Xizang Plateau. The late Miocene dating framework of Banyan and Hongyazi sections has been established by paleomagnetic means. The paleoclimate substitution indices of sediments, magnetic susceptibility, carbonate content and paleoclimate have been analyzed. The sedimentary evolution and environmental change of Xining basin in the late Miocene were studied. A preliminary understanding of the following: 1. The results of magnetic stratigraphic study show that the paleomagnetic age range is 8.22 Ma ~ 6.98 Ma and the fossil age is 8.1 Ma, and the paleomagnetic age range of Hongyazi section is 12.15 Ma ~ 6.92 Ma. This extends the upper age of Xianshuihe formation of late Miocene in Xining Basin on the basis of the previous study on the stratigraphic age of Xianshuihe formation. The deposition rate of Xining basin suddenly increased to 147.03 m / Ma. the grain size and magnetic susceptibility of Xining basin suddenly increased to 147.03 m / Ma.The paleontological fossils showed a warm subtropical semi-arid climate during this period. The fossil correlation indicates that the Lachi Mountain rapidly uplifted at about 8.1 Ma. The sediment velocity of Hongyazi section reaches the maximum value of 320m / Ma. in 7.33Ma, the sediment is a set of gravel, and the magnetic susceptibility, carbonate content and Con O isotopes are significantly changed. The 7.33Ma dry cold climate in Xining basin is probably driven by global cooling and accelerated uplift of the Qinghai-Xizang Plateau. According to indicators of the sedimentary environment, The late Miocene climatic environment in Xining basin shows a phase change trend: 6 sedimentary stages in four major periods. 1) early late Miocene stage 12. 16 + 8. 25 MaA: including stage I (12. 16 + 11. 1 Ma), stage II (11. 1 + 9. 46 Maa) and stage III (9. 46 ~ 8. 25 Ma-1), and the sediment rate is relatively stable. The climatic conditions of Xining basin are relatively warm, semi-humid and humid. 2) the late Miocene middle to late Miocene is 8.257.91MaA: stage 鈪，

本文编号：1955869