Magnetostratigraphic study on post-Miocene transitions in the uplift-erosion processes, climate and biota in Nepal Himalaya

本项目获得的尼泊尔亚喜马拉雅和加德满都谷地沉积物的新磁学和沉积学数据提供了以下宝贵的地球科学/环境信息：对包括Tinau Khola North在内的8至5公里厚的Siwalik沉积物剖面的磁极数据进行了重新研究，超过600公里长的亚喜马拉雅山脉牢固地支撑了沉积物沉积年龄从bbbb16到1万年前。沉积速率为25 ~ 65 cm/kyr，在10.9 ~ 9.7和5.2 ~ 3.6 myr前有两个峰值；前者可能是高喜马拉雅结晶隆起、高山侵蚀/剥蚀加剧、夏季风到来引发的前陆盆地以洪水为主导的曲流体系的形成、盆地沉降等多种因果现象的综合反应。细粒沉积物中一致的W-E ~ NW-SE磁性线理记录了轻微的N-S或NNE-SSW方向压缩引起的弱变形，可作为古应力的代用物。在加德满都谷地，Lukundol剖面的反演地层揭示了1.1-0.7 myr前的沉积，并提供了约0.96 myr前大量砾石沉积的证据，与现在形成南部谷壁的Mahabharat山脉的隆起相吻合。盆地北侧的新数据支持了达帕西剖面底部附近的Laschamp反转事件对约45-34 kyr前的Gokarna组年龄的支持。2 .细粒三角洲前沉积物的激光粒度测定——平静水下沉积的标志——表明粉砂-粉砂沉积物呈双峰至三峰分布，表明物源混合或沉积后沉积物混合。磁化率作为一种实用的工具，可用于绘制小喜马拉雅地层，对邻近剖面进行快速岩性对比，破译加德满都盆地的旋回沉积，也可用于量化古和现代的环境污染（例如，由于车辆交通）。少

New magnetic and sedimentological data from Nepalese Subhimalayan and Kathmandu Valley sediments obtained in this project provide following valuable geoscientific/environmental information:1. Magnetic polarity data for 8 up to 5km thick Siwalik sediment sections, including Tinau Khola North studied anew, over 600 km length of the Sub Himalaya firmly bracket the sediment deposition age from >16 to 1 myr ago. Sediment accumulation rate ranged from 25 to 65 cm/kyr with two peaks during 10.9-9.7 and 5.2-3.6 myr ago; the former likey to be a combined response of multiple causal phenomena such as uplift of Higher Himalayan Crystallines, elevated mountain erosion/denudation, and effects marked by initiation of flood-flow dominated meandering system in the foreland basin, basin subsidence, etc. triggered by advent of summer monsoon. A consistent W-E to NW-SE magnetic lineation in fine-grained sediments records weak deformation induced by mild N-S or NNE-SSW directed compression and serves as a … More paleostress proxy.2. In Kathmandu Valley, reversal stratigraphy in Lukundol section reveals sediment deposition during 1.1-0.7 myr ago and gives evidence for massive deposition of gravel at ca. 0.96 myr ago coinciding with uplift of Mahabharat range that now forms the southern valley wall. New data from the basin's north bracket the age of Gokarna Formation at Dhapasi to ca. 45-34 kyr ago supported by Laschamp reversal event near the base of Dhapasi section. Laser granulometry of fine-grained prodelta deposits-indicators of calm subaqueous deposition suggests bi- to trimodal distribution for the silt to silty sand deposits indicative of a mixed sediment provenance or post-depositional sediment mixing.3. Magnetic susceptibility serves as a practical tool for mapping the Lesser Himalayan formations, rapid lithological correlation of the adjacent sections and deciphering the cyclic deposition in Kathmandu basin, and also quantification of paleo- and present- day environmental pollution (e.g. due to vehicular traffic). Less