【作者】 于永涛；

【导师】 杨太保； 周尚哲；

【作者基本信息】 兰州大学 ， 第四纪地质学， 2006， 博士

【摘要】 地球气候系统在中更新世发生了巨大的变化，由早更新世时期高频、低幅的41-kyr地轴倾角周期逐渐进入晚更新世低频、高幅的准100-kyr冰期—间冰期旋回。由于轨道驱动配置在中更新世并未发生明显的变化，因此100-kyr周期的起源和中更新世气候转型的起因就成了整个第四纪气候演变中的一个根本性的谜团。青藏高原的阶段性构造隆升作为晚新生代最显著的地质事件之一，对高原本身及其周边地区乃至全球的气候都有强烈的影响。柴达木盆地作为高原内部的一个巨型山间盆地，发育了连续、完整、巨厚的第四纪沉积，高分辨率的湖泊沉积物古气候变化研究对于加深高原内部气候变化历史的认识，探讨高原隆升在中更新世转型过程中的作用具有十分重要的意义。柴达木盆地西北缘长222米的尕斯库勒湖GSK0305钻孔就提供了这样的一个难得的机会。 本文根据磁性地层学基础建立了GSK0305钻孔的天文轨道调谐时间标尺，钻孔的底界年龄约为1320kyr，这为区域和全球气候对比提供了坚实的年代学基础。钻孔的磁化率记录与深海氧同位素记录在冰期—间冰期旋回尺度上具有高度一致性。磁化率的高值对应于全球冰量较少的间冰期而低值则对应于冰期，并且表现出一定的不对称结构（尤其在晚更新世），即冰期向间冰期的过渡迅速而间冰期向冰期的过渡缓慢。磁化率记录的这种形式可能反映了入湖径流搬运能力的变化。在冰期时，河流流量减少，无法将流域范围内因强烈物理风化形成的大量碎屑磁性矿物搬运到尕斯库勒湖西岸的冲积平原，沉积物粒径变细，磁化率信号也较弱。与此相反，间冰期增强的河流搬运能力可以将粗颗粒的磁性矿物带入湖盆，沉积物粒径变粗，磁化率值增高。 在时间域与大洋环流指标δ¹³C对比的基础上，我们认为中更新世转型是一个始于～1250kyr，结束于～530kyr，时间跨度达720kyr的渐变过程，并将其划分为四个阶段：预变期（～1250—1060kyr，相当于MIS 38—31／30）；转折期A（～1060—900kyr，对应于MIS 31／30—23／22）；中间过渡期（～900—650kyr，对应于MIS 23／22—17／16），以及转折期B（～650—530kyr，对应于MIS 16—14）。其中中间过渡期是中更新世转型的主体阶段。这四个阶段由五个短事件来定义：～1260—1240kyr，～1060—1040kyr，～920—900kyr，～660—645kyr以及～545—530kyr，分别命名为Event1—Event5。 演化谱分析显示，在～1.2—1.1Ma左右曾经出现过一次～100-kyr周期，同更多还原

【Abstract】 In the middle Pleistocene, Earth’s climate gradually descends from high-frequency, low-amplitude 41-kyr obliquity band into the low-frequency, high-amplitude quasi-periodic （～100-kyr） glacial-interglacial cycles in the late Pleistocene. Because this prominent transition occurs in the absence of any significant changes in orbital forcing configuration, the origin of the ～100-kyr cycles and the associated mid-Pleistocene climatic transition （MPT） remains a fundamental mystery in climatic evolutions during the Quaternary period. Episodic tectonic uplifts of Qinghai-Tibetan Plateau represent one of the most significant geologic events in the late Cenozoic, strongly imprinted on regional climate changes in and around the Plateau, and even on a global scale. As a huge intermountane basin in the Plateau, Qaidam Basin develops nearly continuous, integrative and ultra-thick Quaternary sediment sequences in response to the rapid uplifts, of the Plateau. High-resolution paleoclimatic researches on lake sediments from the Basin are of great importance to the understanding of climatic change history in the interior of the Plateau, and also to the comprehension of the role played by Tibetan uplifts in the progress of the MPT. Toward this end, a 222-meter-long sediment core （labeled GSK0305） was retrieved from Lake Gas Hure in the northwestern margin of Qaidam Basin, providing such a unique opportunity.On the basis of tie points derived by matching the observed magnetostratigraphy to the geomagnetic polarity timescale （GPTS）, an orbitally tuned timescale for core GSK0305 was developed, which assigns an age of 1320 kyr for the base of the core. This provides a robust chronological basis for subsequent regional and global climate correlations. The magnetic susceptibility （MS） record is highly consistent with deep-sea δ¹⁸O record on glacial-interglacial timescale. In general, high peaks of MS correspond to interglacial periods with less ice volume and low peaks to glacials with more ice volume. Moreover, the MS record displays certain asymmetric sawtoothed patterns, especially during the late Pleistocene, comparable to δ¹⁸O record, i.e. rather rapid transitions from glacials to interglacials and much slower changes from interglacials to glacial periods. We interpret the pattern of changes in the MS record as a reflection of changes in stream carrying capacity. In glacials, dropped river discharges are simply unable to transport a large amount of clastic更多还原