柴达木盆地西部晚中新世以来干旱气候与古湖水演化研究

The Qaidam Basin has been a closed inland basin since the Paleogene and is filled with a maximum thickness of 12 000 m of Cenozoic sediments derived from the surrounding mountains. These thick sediments detailedly record the Asian inland aridity history and salt lake evolution history. Previous studies revealed that the depocenter of the Qaidam Basin has experienced a marked shift from the western part of the basin toward the southeast to its present position in the Sanhu depression with uplift of the Tibetan Plateau and compression of the western Qaidam Basin since about the Oligocene. As a result, two important salt-forming stages formed during Pliocene and late Pleiostocene. However, recent studies based on two deep drilling cores from the western Qaidam Basin indicated that salt forming stages and arid climate were existed and prevailed since the late Pliocene and the basin experienced a stepwised aridity process since that time. The relation between aridity climate and salt resources formation were also believed more complicated than previous understanding.. Based on a deep drilling core (SG-1b)（7.3-1.6 Ma）from the western Qaidam Basin, high resolution multi-proxy study including ion contents, carbonate content, Sr/Ca and Mg/Ca as well as carbon and oxygen isotope analysis of carbonate will be presented. Then, the arid climate and salt lake evolution history of the western Qaidam Basin since late Miocene will be explored. In addition, we will compare our geochemical records with regional and global climate records as well as regional tectonic activity history to discuss the impact of global climate and Tibentan Plateau uplift on the evolution of the arid climate of the western Qaidam basin. The above studies are critical in understanding the main controlling factor on arid climate evolution of the western Qaidam basin and helpful in revealling the relation between aridity climate and salt resources formation.

柴达木盆地新生代以来的巨厚沉积物详细地记录了亚洲内陆干旱化过程及青藏高原东北部的构造活动历史。过去的研究认为，随着青藏高原隆升,盆地沉积中心经历了由西向东的迁移过程，并形成了上新世和晚更新世以来两个重要的成盐期。然而我们在盆地西部的深钻研究揭示，干旱气候条件和成盐期自晚上新世以来一直存在，是一个明显波动并逐步阶段性干旱的过程，干旱气候演化与盆地盐类资源形成的关系也比早期认识的复杂。本项目将基于岩芯SG-1b（7.3-1.6 Ma），高分辨率地分析岩芯沉积物的离子组成和含量、碳酸盐含量及其微量元素和碳氧同位素组成，重建晚中新世以来盆地气候环境变化历史与古湖水演化过程，捕获重大干旱气候事件。通过与区域及全球气候记录的对比，揭示晚中新世以来盆地西部气候环境变化如何响应全球气候变化与区域构造隆升，探讨盆地气候变化的主控因素及其对盐类资源形成的指示，为认识气候变化和盐类资源发生之间的关系提供科学依据

亚洲内陆干旱化的演化过程及控制机制不仅关乎深入理解和预测未来气候环境，也对与之息息相关的盐类等表生矿床的迁移聚集具有重要影响。为此，本项目基于中德联合在柴达木盆地西部（柴西）获取的具有精确古地磁年代的SG-1b深钻细粒湖相沉积物的高分辨率离子组成与含量、Sr/Ca和Mg/Ca 比值、碳酸盐含量以及碳氧同位素的分析，并结合该孔岩相、岩石磁学、矿物学、孢粉以及中德一期钻孔相关资料的综合集成分析，获得如下原创性成果：（1）完整建立了柴西地区晚中新世以来的古湖水文特征和气候环境变化记录，发现该区7.3Ma以来的持续干旱化，和在3.6-3.3、2.2、1.2、0.6和0.3Ma期间干旱化的显著加剧。（2）通过与我国黄土高原、中亚高纬度贝加尔湖地区气候环境记录的时间和频率域及高维动力学演化过程的精细对比，发现亚洲内陆不同系统在4.2-3.0Ma同步经历了气候环境转型。并提出7.3-4.2Ma亚洲内陆地区气候环境演化受控于天体轨道参数控制的太阳辐射变化，4.2Ma和3.0Ma的转型与南极冰盖和北半球冰盖的演化相关，这一成果也得到了数值模拟的证实。（3）通过对两个钻孔盐层发生规律的研究，发现天体倾角低幅期与偏心率低值的同步时期，会通过季节性的降低影响柴达木盆地的水文循环，从而促进盆地盐层的发育。这为亚洲内陆干旱化的深入研究以及查明柴达木盆地盐类资源形成、演化及其与气候变化间的关系提供了新的视角和证据。