若尔盖黄河唐克段河岸沉积序列测年及地表过程变化

通过对若尔盖盆地进行野外考察，在盆地中部黄河唐克段右岸发现了包含深湖相的河岸沉积物，进行了细致的地层观测和系统年代学样品采集。在实验室利用光释光和AMS¹⁴C测年技术建立了年代框架，并结合各个层次的地层沉积相宏观特征和理化性质，分析探讨了若尔盖盆地内部从末次冰期古湖消亡以来的环境和地表过程变化规律。研究结果表明：古黄河在37 ka沿着玛曲断陷谷地溯源侵蚀，沟通了若尔盖古湖水系，盆地内部在30.9 ka之前为深湖环境，稳定地沉积了蓝灰色湖相淤泥层。30.9 ka之后，黄河贯穿若尔盖湖盆内部，古湖水外泄消失，原有的古湖水系转变成为黄河源水系。黄河从湖盆上游远距离搬运携带来的浊黄橙色泥沙大量沉积，覆盖了古湖相沉积层，湖盆内部风沙作用盛行。在末次冰盛期（Last Glacial Maximum， LGM），盆地内部松散沉积物普遍地受到冰缘冻融作用的改造，形成了冻融褶皱现象。到了14.6~12.5 ka，响应B/A（B?lling-Aller?d）时期的温暖气候，盆地周边山地冰川消融，冰融水汇入盆地，古湖盆底部各种浅洼地形成了大小不等的浅湖，沉积了滨浅湖相的沙层。在12.5~11.7 ka，对应于全球性新仙女木（Younger Dryas，YD）事件，盆地气候再次变冷，转变为冰缘冻土环境，盆地内部滨浅湖相的沙层受到冻融作用和古地震扰动，形成复式褶皱现象。进入全新世，在11.7~4.8 ka气候逐渐变得温暖湿润，古湖盆底部浅洼地积水成为淤泥质沼泽环境，在全新世中后期4.8~1.8 ka则转变成为沼泽草甸环境，在1.8 ka之后，盆地内沼泽面积收缩，风沙活动盛行，河岸台地的近源沙尘暴沉积物经过成壤改造形成亚高山草甸黑土类现代土壤。

Chronology of the sedimentary sequence and the changes in surface processes along the Tangke reach of the Yellow River in the Zoige Basin

The research in this paper mainly focuses on the banks of the Tangke section of the Yellow River in the Zoige Basin， and studies the natural sedimentary profiles directly exposed by the lower cut of the Yellow River. The purpose is to establish the stratigraphic sequence and age frame of soil sediments， and to deeply explore the upstream erosion of the Yellow River into the interior of the Zoige Basin. The characteristics of regional surface process changes during the process provide chronological and stratigraphic evidence for the Yellow River running through the Zoige Basin. Through field investigation of the Zoige Basin， a sequence of riparian soil sediments containing deep lacustrine sediments was found on the right bank of the Tangke section of the Yellow River in the middle of the basin， and in-depth observations and systematic sampling were carried out. In the laboratory， the chronological framework was established by using the optical luminescence and AMS¹⁴C dating techniques. Combined with the macroscopic characteristics and physicochemical properties of soil sedimentary facies at various levels， the environment and surface processes were thoroughly analyzed and discussed in the Zoige Basin since the demise of the last glacial paleolake. The research results show that the ancient Yellow River eroded headward along the Maqu rift valley at 37 ka， which connected the Zoige ancient lake water system， while the interior of the basin was a deep lake environment before 30.9 ka， and a blue-gray lacustrine silt layer was deposited stably. After 30.9 ka， the Yellow River penetrated through the interior of the Zoige Lake Basin， the ancient lake water leaked out and disappeared， and the original ancient lake water system was completely transformed into the Yellow River source water system. A large amount of turbid yellow-orange sediment carried by the Yellow River from the upper reaches of the lake basin was deposited in large quantities， covering the paleolacustrine sediment， and aeolian sand action prevailed in the lake basin. During the Last Glacial Maximum （LGM）， the loose sediments in the basin were generally transformed by the freezing and thawing of the periglacial environment， forming freeze-thaw folds. From 14.6 to 12.5 ka， in response to the warm climate in the B?lling-Aller?d （B/A） period， the mountain glaciers around the basin melted and melted water flowed into the basin. Various shallow depressions at the bottom of the ancient lake basin formed shallow lakes of different sizes. Sand layers of littoral-shallow lacustrine facies were deposited. From 12.5 to 11.7 ka， corresponding to the global Younger Dryas （YD） event， the climate became cold again and transformed into a permafrost environment in the basin. Paleo-earthquake disturbances have formed complex double-fold folds. In the Holocene， the climate gradually became warm and humid from 11.7 to 4.8 ka， and the shallow depression at the bottom of the ancient lake basin became a silty swamp environment， and a muddy soil layer was developed. In the middle and late Holocene 4.8~1.8 ka， it transformed into a swamp meadow environment and developed swamp meadow black soil paleosols. After 1.8 ka， the marshes in the basin shrank， aeolian sand activities prevailed， the floodplain sand was transformed into sand dunes by wind， and the near-source sandstorm sediments in the riparian highlands were transformed into subalpine meadow black soil modern soils by pedogenesis.