柴达木盆地一里坪石膏~(230)Th定年及成盐期与第四纪冰期和构造运动的关系

本文采用多接收电感耦合等离子体质谱法(MC-ICP-MS),对柴达木盆地一里坪15YZK01钻孔中前336.2 m含石盐地层中的7个石膏样品进行230Th定年。依据年代-深度公式,获得S1-S4盐层的成盐年代分别为733.8~716.0 ka、581.9~573.8 ka、181.6~179.3 ka和158.0~154.2 ka;含芒硝粉砂地层的年代为171.6 ka。结合前人对一里坪表面盐壳的14C测年数据,证实一里坪表面盐层S5开始形成于末次冰期。15YZK01钻孔记录的成盐期与青藏高原第四纪冰期及构造运动存在一定的对应关系:石盐层S1对应于"昆黄运动"之后的望昆冰期,以及深海氧同位素第18阶段(MIS18);S2对应于大间冰期,但是该年代比较接近望昆冰期;S3和S4石盐层及含芒硝粉砂层对应于共和运动和倒数第二次冰期MIS6;S5石盐层开始形成的时代对应于末次冰期MIS2。同时,通过对柴达木盆地多个钻孔含盐地层的测年数据进行总结,证实中更新世以来青藏高原冰川活动与柴达木盆地盐类沉积存在着一定的对应关系。柴达木盆地西北部的成盐盆地中通常发于有倒数第二次冰期和末次冰期的石盐层;而盆地东南部的察尔汗盐湖区仅发现有末次冰期以来的石盐层。柴达木盆地成盐期受到青藏高原第四纪冰期和构造运动的影响,第四纪冰期中盐湖水源补给量的减少,是导致柴达木盆地成盐的重要驱动因素。

Gypsum 230Th Dating of the 15YZK01 Drilling Core in the Qaidam Basin: Salt Deposits and Their Link to Quaternary Glaciation andTectonic Movement

The authors applied 230Th dating to 7 samples of the salt-bearing strata from the 15YZK01 drilling core in the Yiliping playa, northwestern Qaidam Basin. The isotope ratios of U and Th contained in gypsum crystals were measured by Neptune Plus multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). On the basis of the depth-age plot, calculations show that the 5 salt-bearing deposits should be formed at 733.8~716.0 ka, 581.9~573.8 ka, 181.6~179.3 ka, 158.0~154.2 ka and 32.5~2 ka. The salt deposits recorded in the Yiliping playa can be correlated with Quaternary glaciation and tectonic movement on the Tibetan Plateau: the S1 salt deposit was correlated with the marine isotope stage 18 (MIS18) during the Wangkun Glaciation after the Kunlun-Huanghe Movement; the S2 salt deposit corresponded to MIS15 in the Great Interglaciation; the S3 and S4 salt deposits corresponded to the Gonghe Movement and MIS6 in the Penultimate Glaciation; and S5 began to form during MIS2 in the Last Glacial Maximum (LGM). Based on the summary of the dating ages of salt-forming strata in the Qaidam Basin, the authors confirmed that there existed a certain link between the salt-forming period in the Qaidam Basin and the Quaternary glaciation and tectonic movement on the Tibetan Plateau. In the salt lakes or playas of the western Qaidam Basin salt deposits formed in the Penultimate Glaciation and Last Glaciation have been usually preserved; in contrast, in the Qarhan Salt Lake in the southeast Qaidam Basin there are only salt deposits formed since the Last Glaciation. A reduction in the water supply of the salt lakes during the Quaternary glaciations was an important driving factor for the formation of salt deposits in the Qaidam Basin, whereas the Quaternary glaciations were closely related to the tectonic activities of the Tibetan Plateau.