Based on sedimentary and tectonic geomorphological analysis, this study found that the paleogeographic environment of the Qaidam and Suganhu basins underwent significant changes during the middle Pleistocene. In the early Pleistocene (2.54–0.78 Ma), the Qaidam and Suganhu basins shared a widespread lacustrine environment. Paleo-currents indicate a drainage connection between the two basins. However, since the mid-Pleistocene (0.78 Ma to present), continuous tectonic activities, evidenced by soft sediment deformation structures, in the North Qaidam structural belt resulted in the uplift of Xiaosaishiteng range, which separated the Qaidam and Suganhu basins. The lacustrine environment became alluvial fans and braided river environments near the ranges, while isolated small saline lakes dominated the distal areas. We attribute the rapid evolution of paleogeographic environment and drainage system in the Qaidam and Suganhu basins to the mid-Pleistocene uplift of the North Qaidam structural belt. The uplifted North Qaidam structural belt blocked the runoff from the South Qilian Shan into the Qaidam Basin, causing the lakes within the Qaidam Basin to shrink and dry out since the middle Pleistocene.

Qaidam Basin, Suganhu Basin, mid-Pleistocene, tectonic uplift, sedimentary environment, paleogeographic evolution

通过对野外观察点沉积特征和构造地貌的分析, 发现中更新世柴达木盆地和苏干湖盆地的古地理环境发生快速的变化。柴达木盆地和苏干湖盆地早更新世(2.54~0.78 Ma)发育广泛的湖泊, 古水流的流向显示此时二者存在水系沟通。中更新世以来(0.78Ma至今), 软沉积变形构造指示的柴北缘构造带持续构造活动事件导致小赛什腾山逐渐隆升, 成为完全分隔柴达木盆地与苏干湖盆地的地形屏障, 原有的湖泊环境在山前地区转变为冲积扇–洪积扇及辫状河环境, 在远端地区转变为孤立的小型咸水湖环境。因此, 柴北缘构造带中更新世的构造隆升事件导致柴达木盆地和苏干湖盆地古地理环境和流域体系的剧烈变迁。隆升形成的柴北缘构造带阻断发源自南祁连地区的河流, 最终减少柴达木盆地的入湖径流量, 促进中更新世以来柴达木盆地内湖泊的萎缩和干涸。

柴达木盆地, 苏干湖盆地, 中更新世, 构造隆升, 沉积环境, 古地理演化