Abstract The Yulin River in the northern Tibetan Plateau, consists of multiple geomorphological features, including alluvial fans, fluvial terraces, and river profile knickpoints. Collectively, these provide a natural laboratory for exploring the late Quaternary fluvial landform evolution in response to both climatic change and tectonic activities in the region of the Altyn Tagh Fault. In this study, we investigated the distribution, sequences and sediment characteristics of the fluvial landforms along the Yulin River based on high-precision (0.5 m-resolution) Worldview satellite images and field observations. Mid-Pleistocene alluvial fans formed the highest fluvial landform surface into which ten major inset fluvial terraces were developed, distributed along three stream segments. Real-time kinematic global positioning system (RTK-GPS) measurement of terrace surfaces and the modern river longitudinal profiles was conducted across the Dongbatu Shan to show fluvial landform geometry and tectonic deformation. Fluvial terrace surfaces were deformed due to fault uplift as illustrated by spatially variable surface geometries. The chronological sequences of terraces along the Yulin River since 160 ka were reconstructed based on 10Be terrestrial cosmogenic nuclides (TCNs) dating. Results indicated that river incision occurred mainly during periods of climate transition, suggesting that terrace evolution was partly controlled by climate changes. Moreover, terrace exposure ages showed an upstream younging trend along the river, demonstrating a probable response to knickpoint retreat. Combined with terrace deformation and ages, fault uplift rates were constrained, which were lower than the river incision rates during the Late Quaternary, indicating that crustal shortening was mainly absorbed by the growth of the regional anticline. Collectively, our results suggest that the evolution of fluvial landforms along the Yulin River is a function of interplay between regional tectonic activities and climatic changes, which is significant to understand the NW-outward splay of the Altyn Tagh Fault.

中文翻译：

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青藏高原北部榆林河沿岸晚第四纪河流地貌演化及控制因素

摘要 青藏高原北部榆林河具有冲积扇、河流阶地、河流剖面等多种地貌特征。总的来说，这些为探索响应阿尔金断层地区气候变化和构造活动的晚第四纪河流地貌演化提供了一个天然实验室。在这项研究中，我们基于高精度（0.5 m 分辨率）Worldview 卫星图像和现场观测研究了榆林河沿岸河流地貌的分布、序列和沉积特征。中更新世冲积扇形成了最高的河流地貌面，其中发育十个主要的内嵌河流阶地，沿三个河段分布。对整个东巴图山进行梯田表面和现代河流纵向剖面的实时运动学全球定位系统 (RTK-GPS) 测量，以显示河流地貌几何形状和构造变形。如空间变化的表面几何形状所示，河流阶地表面由于断层隆起而变形。基于10Be陆地宇宙核素（TCNs）测年重建了160ka以来榆林河沿岸阶地的年代序列。结果表明河流切口主要发生在气候转变时期，表明阶地演化部分受气候变化控制。此外，阶地暴露年龄显示出沿河上游年轻化的趋势，表明可能对小点后退做出反应。结合台地变形和年龄，断层抬升速率受到限制，低于晚第四纪的河流切入速率，表明地壳缩短主要被区域背斜的增长所吸收。总体而言，我们的研究结果表明，榆林河沿岸河流地貌的演变是区域构造活动与气候变化相互作用的函数，这对于理解阿尔金断裂的 NW 向外扩张具有重要意义。