A closed Quaternary saline paleolake, currently still a lake and named Dalangtan after one of its largest sub-basins, has widely distributed sediments in the western Qaidam Basin, NE Tibetan Plateau. Lacustrine salt minerals and fine sediments from this paleolake provide an environmental record for investigating paleoclimatic evolution in the Asian interior. However, detailed continuous Pliocene–Quaternary paleoclimatic records are broadly lacking from the NE Tibetan Plateau owing to poor exposure of the outcrops in section. For this study, we performed a detailed magnetostratigraphic dating and rock magnetic analysis on a 590-m-long core from the SG-5 borehole in the western Qaidam Basin. The results demonstrate that the lacustrine sediments in the SG-5 borehole were deposited more than ~3.0 Ma. Saline minerals began to increase at 1.2 Ma, and the magnetic susceptibility (χ) also changed at that time; the percentage frequency-dependent magnetic susceptibility was relatively low and uniform throughout the whole core. These observations, combined with the χ, pollen, salt ion, and grain-size records from other boreholes, indicate that the western Qaidam Basin and the greater Asian interior had a significant climate transition at 1.2 Ma during an extreme drought.

中文翻译：

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青藏高原东北部柴达木盆地西部第四纪古气候变迁的年代学和岩磁约束

在青藏高原东北部柴达木盆地西部，一个封闭的第四纪含盐古湖，目前仍然是一个湖泊，以其最大的亚盆地之一命名为大浪潭。来自该古湖的湖相盐矿物和精细沉积物为研究亚洲内陆的古气候演化提供了环境记录。然而，由于断面露头暴露不足，青藏高原东北部普遍缺乏详细的上新世-第四纪古气候连续记录。在这项研究中，我们对柴达木盆地西部 SG-5 钻孔的 590 米长岩心进行了详细的磁地层测年和岩石磁力分析。结果表明，SG-5 钻孔中的湖相沉积物沉积超过~3.0 Ma。盐分矿物在 1.2 Ma 开始增加，并且磁化率（χ）也在那个时候发生了变化；与频率相关的百分比磁化率在整个核心中相对较低且均匀。这些观测结果，结合其他钻孔的χ、花粉、盐离子和粒度记录，表明柴达木盆地西部和大亚洲内陆在极端干旱期间发生了1.2 Ma的显着气候转变。