Sedimentary facies analysis of the fluvial systems in the Siwalik Group, Karnali River section, Nepal Himalaya, and their significance for understanding the paleoclimate and Himalayan tectonics
Sedimentary facies analysis of the fluvial systems in the Siwalik Group, Karnali River section, Nepal Himalaya, and their significance for understanding the paleoclimate and Himalayan tectonics
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尼泊尔喜马拉雅卡纳利河段西瓦利克群河流沉积相分析及其对古气候和喜马拉雅构造的意义
DOI：
10.3126/jngs.v51i0.24084
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
T. Sakai
中科院分区：
文献类型：
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作者：
Ashok Sigdel;T. Sakai
喜马拉雅前陆盆地Siwalik序列的河流沉积是研究喜马拉雅构造和中新世气候变化历史的重要大陆档案之一。这项研究重新分析了沿卡纳利河的Siwalik群的河流相，推测大的古卡纳利河水系就是在那里流过的。重新解释的河流体系由细粒曲流河(FA1)、洪水主导型辫状河(FA2)、深浅砂质辫状河(FA3、FA4)到砾质辫状河(FA5)、泥石流主导型辫状河(FA6)相组合依次递增。前人的研究发现砂质洪水流为主的曲流河和网状河体系，但本次研究将它们分别重新解释为洪水主导的曲流河体系和浅层砂质辫状河体系。卡纳里河段河流沉积体系的出现顺序与其他斯瓦利克段相似，但河流相变化的时间不同。卡纳里河河段早期(3~4 Ma)洪水主导型曲流河水系的出现，可能是由于古卡纳里河较大集水区的早期抬升，改变了降水格局，即印度夏季风的加强。从曲流河系到辫状河系的变化也比尼泊尔其他Siwalik段早1~3 Ma。冲断系统的差异和历时活动可能与集水区的变化以及历时的隆升和气候有关，这两者的结合是这种历时的主要可能原因。
Fluvial sediments of the Siwalik successions in the Himalayan Foreland Basin are one of the most important continental archives for the history of Himalayan tectonics and climate change during the Miocene Period. This study reanalyzes the fluvial facies of the Siwalik Group along the Karnali River, where the large paleo-Karnali River system is presumed to have flowed. The reinterpreted fluvial system comprises fine-grained meandering river (FA1), flood-flow dominated meandering river with intermittent appearance of braided rivers (FA2), deep and shallow sandy braided rivers (FA3, FA4) to gravelly braided river (FA5) and finally debris-flow dominated braided river (FA6) facies associations, in ascending order. Previous work identified sandy flood-flow dominated meandering and anastomosed systems, but this study reinterprets these systems as a flood-flow dominated meandering river system with intermittent appearance of braided rivers, and a shallow sandy braided system, respectively. The order of the appearance of fluvial depositional systems in the Karnali River section is similar to those of other Siwalik sections, but the timing of the fluvial facies changes differs. The earlier appearance (3-4 Ma) of the flood-flow dominated meandering river system in the Karnali River section at about 13.5 Ma may have been due to early uplift of the larger catchment size of the paleo-Karnali River which may have changed the precipitation pattern i.e. intensification of the Indian Summer Monsoon. The change from a meandering river system to a braided river system is also recorded 1 to 3 Ma earlier than in other Siwalik sections in Nepal. Differential and diachronous activities of the thrust systems could be linked to change in catchment area as well as diachronous uplift and climate, the combination of which are major probable causes of this diachronity.