藏南吉隆新近纪盆地古高程的时空二维定量重建

At the base of the subsidence center in the southeastern Gyirong Basin, South Tibet, a series of alluvial sequences are new reported, associated to tectonic onset of deposition. Based on thermochronological and magnetostratigraphic research, we brack the complete time scale of the basin firstly, and reveal the main factor of environmental changes on the basis of sedimentary research. Through paleontology analyses of the selected section, a large number of pollen, ostracod and gastropoda fossils were found during 7.0-3.2 Ma. Over this period, five key layers were picked out on the basis of major climatic and tectonic significance, then to do paleontological research, including palynological assemblages analyses, element and stable carbon & oxygen isotope analysis of the ostracod and gastropoda shells. Citing oxygen isotope paleoaltimetry in Nepal Himalaya and modern pollen transfer function on the basis of Locally Weighted Weighted Averaging (LWWA) model in the Qinghai- Tibetan Plateau, which can be used to constrain the highest elevation and average elevation respectively, we can obtain the highest and average paleoelevation of the five key time slices in the Gyirong area. Based on the two quantitative estimation, details of spatio-temporal altitude change can be two-dimensionally reconstructed in the Neogene Gyirong Basin, South Tibet.

在藏南吉隆盆地东南缘的沉降中心新发现一套地层，通过控盆断裂的锆石裂变径迹年代学研究，结合已有的古脊椎动物化石和古地磁年代学成果，建立了该盆地完整的年代格架，并通过沉积物源分析初步恢复环境变化的主因。通过研究剖面的古生物化石分析处理，在7.0-3.2 Ma发现了大量的孢粉、介形虫和腹足化石；选择该时间段内具有重大气候和构造意义的5个关键点位进行古生物研究，建立其孢粉组合，并对介形虫和腹足壳体进行元素成分分析和稳定碳氧同位素分析，确认灰质成分的形成历史及气候变化的影响。此外，引用适用于研究区的氧同位素古高程法和现代表土孢粉转换函数法，结合古生物化石分析对误差的校正，进行古高程的定量估算，分别获得5个关键点位的最高海拔和平均海拔。基于以上两种古高程计的模拟，从时空二维角度定量重塑藏南吉隆地区新近纪的海拔变化。

青藏高原新生代地表隆升的定量过程重建是近十多年以来的研究热点。当前古高程数据资料分析多集中于氧同位素、古植物、氢同位素和△47古温度-古高程计等方法上，并采用单一手段为主，与研究区的岩相古地理、生物组合和古气候等数据的综合分析较弱。大量资料的收集整理划分出中国新生代沉积盆地的3个演化阶段，晚始新世和中新世以来作为关键时间段，选择冈底斯、藏南和滇西作为对比区域。基于古生物学和碳氧同位素分析，冈底斯措勤盆地在39.4-35.7Ma获得接近海平面的古高程，推测34Ma以来青藏高原发生了剧烈的构造隆升，并驱动了全球的降温事件。