【摘要】 始新世—渐新世是古近纪气候变化中最显著的时期.通过对西宁盆地42.5～26.0 Ma沉积物颜色指标的详细分析,发现颜色参数L^*,a^*,b^*曲线明显以32.8 Ma为界分为上下两段.其中:L^*值在下段（42.5～32.8 Ma）波动剧烈并呈缓慢降低趋势,至32.8 Ma左右大幅度降低,此后（32.8～26.0 Ma）波动变小、稍有回升;a^*,b^*值则与L^*值的变化趋势相反,在下段（42.5～32.8 Ma）呈逐渐增大趋势,剧烈波动,在32.8 Ma左右时突然大幅度升高,至上段波动变小.结合西宁盆地孢粉、有机质及CaCO₃质量分数变化的特征分析,该区域在32.8 Ma时可能发生大幅度的降温事件（对应于海洋记录所揭示的Oi-1事件）,此事件之前气候干旱程度相对较弱、氧化作用逐渐增强、气候波动剧烈.在Oi-1事件之后大陆性干旱程度增强、氧化强烈、气候波动幅度较小.这是在该区高分辨率获得Oi-1事件前后气候变化的记录,它对始新世—渐新世全球气候变冷背景下陆地系统响应研究具有重要意义.更多还原

【Abstract】 The climatic changes at the boundary of the eocene-oligocene are most significant during the cenozoic.The records of the colors measured from the lacustrine sediments during 42.5～26.0 Ma in the Xining Basin,northeastern Tibetan Plateau,NW China,show that the color curves can be divided into two phases at 32.8 Ma.The lower phase（42.5～32.8 Ma）of L^* values fluctuated intensively and decreased slowly, and to the younger phase（32.8～26.0 Ma）,they became smaller and the values rebounded.The trends of a^* and b^* were opposite to L^*,but both of them were low and fluctuated intensively at the bottom,then increased gradually with smaller fluctuations since 32.8 Ma.Combined with pollen,organic and CaCO₃,the color proxies might indicate that a great cooling period in this area occurred in 32.8 Ma,corresponding with the Oi-1 event.The drought and oxidation was faint,and fluctuation was intensive before 32.8 Ma.After Oi-1 event,the extent of drought eased up and the oxidation strengthened.But the fluctuation of climate became faint.The high resolution record obtained from this area around the Oi-1 event is very important for the research in that it may indicate that land system responded to global cooling during the Eocene-Oligocene.更多还原